Transcriptional activation of human mu-opioid receptor gene by insulin-like growth factor-I in neuronal cells is modulated by the transcription factor REST.

PubMed

Bedini, Andrea; Baiula, Monica; Spampinato, Santi

2008-06-01

The human mu-opioid receptor gene (OPRM1) promoter contains a DNA sequence binding the repressor element 1 silencing transcription factor (REST) that is implicated in transcriptional repression. We investigated whether insulin-like growth factor I (IGF-I), which affects various aspects of neuronal induction and maturation, regulates OPRM1 transcription in neuronal cells in the context of the potential influence of REST. A series of OPRM1-luciferase promoter/reporter constructs were transfected into two neuronal cell models, neuroblastoma-derived SH-SY5Y cells and PC12 cells. In the former, endogenous levels of human mu-opioid receptor (hMOPr) mRNA were evaluated by real-time PCR. IGF-I up-regulated OPRM1 transcription in: PC12 cells lacking REST, in SH-SY5Y cells transfected with constructs deficient in the REST DNA binding element, or when REST was down-regulated in retinoic acid-differentiated cells. IGF-I activates the signal transducer and activator of transcription-3 signaling pathway and this transcription factor, binding to the signal transducer and activator of transcription-1/3 DNA element located in the promoter, increases OPRM1 transcription. We propose that a reduction in REST is a critical switch enabling IGF-I to up-regulate hMOPr. These findings help clarify how hMOPr expression is regulated in neuronal cells.

A human-specific, truncated α7 nicotinic receptor subunit assembles with full-length α7 and forms functional receptors with different stoichiometries.

PubMed

Lasala, Matías; Corradi, Jeremías; Bruzzone, Ariana; Esandi, María Del Carmen; Bouzat, Cecilia

2018-05-21

The cholinergic α7 nicotinic receptor gene, CHRNA7, encodes a subunit that forms the homopentameric α7 receptor, involved in learning and memory. In humans, exons 5-10 in CHRNA7 are duplicated and fused to the FAM7A genetic element, giving rise to the hybrid gene CHRFAM7A. Its product, dupα7, is a truncated subunit lacking part of the N-terminal extracellular ligand-binding domain and is associated with neurological disorders, including schizophrenia, and immunomodulation.We combined dupα7 expression on mammalian cells with patch clamp recordings to understand its functional role. Transfected cells expressed dupα7 protein, but they exhibited neither surface binding of the α7 antagonist α-bungarotoxin nor responses to acetylcholine (ACh) or to an allosteric agonist that binds to the conserved transmembrane region. To determine if dupα7 assembles with α7, we generated receptors comprising α7 and dupα7 subunits, one of which was tagged with conductance substitutions that report subunit stoichiometry and monitored ACh-elicited channel openings elicited by ACh in the presence of a positive allosteric α7 modulator. We found that α7 and dupα7 subunits co-assemble into functional heteromeric receptors, that at least two α7 subunits are required for channel opening, and that dupα7's presence in the pentameric arrangement does not affect the duration of the potentiated events compare with that of α7. Using an α7 subunit mutant, we found that activation of (α7)2(dupα7)3 receptors occurs through ACh binding at the α7/α7 interfacial binding site. Our study contributes to the understanding of the modulation of α7 function by the human specific, duplicated subunit, associated with human disorders. Published under license by The American Society for Biochemistry and Molecular Biology, Inc.

Allosteric Modulation of Chemoattractant Receptors

PubMed Central

Allegretti, Marcello; Cesta, Maria Candida; Locati, Massimo

2016-01-01

Chemoattractants control selective leukocyte homing via interactions with a dedicated family of related G protein-coupled receptor (GPCR). Emerging evidence indicates that the signaling activity of these receptors, as for other GPCR, is influenced by allosteric modulators, which interact with the receptor in a binding site distinct from the binding site of the agonist and modulate the receptor signaling activity in response to the orthosteric ligand. Allosteric modulators have a number of potential advantages over orthosteric agonists/antagonists as therapeutic agents and offer unprecedented opportunities to identify extremely selective drug leads. Here, we resume evidence of allosterism in the context of chemoattractant receptors, discussing in particular its functional impact on functional selectivity and probe/concentration dependence of orthosteric ligands activities. PMID:27199992

Negative modulation of the chicken infectious anemia virus promoter by COUP-TF1 and an E box-like element at the transcription start site binding deltaEF1.

PubMed

Miller, Myrna M; Jarosinski, Keith W; Schat, Karel A

2008-12-01

Expression of enhanced green fluorescent protein (EGFP) under control of the promoter-enhancer of chicken infectious anemia virus (CAV) is increased in an oestrogen receptor-enhanced cell line when treated with oestrogen and the promoter-enhancer binds unidentified proteins that recognize a consensus oestrogen response element (ERE). Co-transfection assays with the CAV promoter and the nuclear receptor chicken ovalbumin upstream promoter transcription factor 1 (COUP-TF1) showed that expression of EGFP was decreased by 50 to 60 % in DF-1 and LMH cells. The CAV promoter that included sequences at and downstream of the transcription start point had less expression than a short promoter construct. Mutation of a putative E box at this site restored expression levels. Electromobility shift assays showed that the transcription regulator delta-EF1 (deltaEF1) binds to this E box region. These findings indicate that the CAV promoter activity can be affected directly or indirectly by COUP-TF1 and deltaEF1.

Thyroid hormones upregulate apolipoprotein E gene expression in astrocytes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roman, Corina; Fuior, Elena V.; Trusca, Violeta G.

Apolipoprotein E (apoE), a protein mainly involved in lipid metabolism, is associated with several neurodegenerative disorders including Alzheimer's disease. Despite numerous attempts to elucidate apoE gene regulation in the brain, the exact mechanism is still uncovered. The mechanism of apoE gene regulation in the brain involves the proximal promoter and multienhancers ME.1 and ME.2, which evolved by gene duplication. Herein we questioned whether thyroid hormones and their nuclear receptors have a role in apoE gene regulation in astrocytes. Our data showed that thyroid hormones increase apoE gene expression in HTB14 astrocytes in a dose-dependent manner. This effect can be intermediatedmore » by the thyroid receptor β (TRβ) which is expressed in these cells. In the presence of triiodothyronine (T3) and 9-cis retinoic acid, in astrocytes transfected to overexpress TRβ and retinoid X receptor α (RXRα), apoE promoter was indirectly activated through the interaction with ME.2. To determine the location of TRβ/RXRα binding site on ME.2, we performed DNA pull down assays and found that TRβ/RXRα complex bound to the region 341–488 of ME.2. This result was confirmed by transient transfection experiments in which a series of 5′- and 3′-deletion mutants of ME.2 were used. These data support the existence of a biologically active TRβ binding site starting at 409 in ME.2. In conclusion, our data revealed that ligand-activated TRβ/RXRα heterodimers bind with high efficiency on tissue-specific distal regulatory element ME.2 and thus modulate apoE gene expression in the brain. - Highlights: • T3 induce a dose-dependent increase of apoE expression in astrocytes. • Thyroid hormones activate apoE promoter in a cell specific manner. • Ligand activated TRβ/RXRα bind on the distal regulatory element ME.2 to modulate apoE. • The binding site of TRβ/RXRα heterodimer is located at 409 bp on ME.2.« less

Recent Progress in the Design and Discovery of RXR Modulators Targeting Alternate Binding Sites of the Receptor.

PubMed

Su, Ying; Zeng, Zhiping; Chen, Ziwen; Xu, Dan; Zhang, Weidong; Zhang, Xiao-Kun

2017-01-01

Retinoid X receptors (RXRs) occupy a central position within the nuclear receptor superfamily. They not only function as important transcriptional factors but also exhibit diverse nongenomic biological activities. The pleiotropic actions of RXRs under both physiological and pathophysiological conditions confer RXRs important drug targets for the treatment of cancer, and metabolic and neurodegenerative diseases. RXR modulators have been studied for the purpose of developing both drug molecules and chemical tools for biological investigation of RXR. Development of RXR modulators has focused on small molecules targeting the canonical ligand-binding pocket. However, accumulating results have demonstrated that there are other binding mechanisms by which small molecules interact with RXR to act as RXR modulators. This review discusses the recent development in the design and discovery of RXR modulators with a focus on those targeting novel binding sites on RXR.

An IFNG SNP with an estrogen-like response element selectively enhances promoter expression in peripheral but not lamina propria T cells.

PubMed

Gonsky, R; Deem, R L; Bream, J H; Young, H A; Targan, S R

2006-07-01

This study examines mucosa-specific regulatory pathways involved in modulation of interferon-gamma (IFN-gamma) in lamina propria T cells. Previous studies identified mucosa-specific CD2 cis-elements within the -204 to -108 bp IFNG promoter. Within this region, a single-site nucleotide polymorphism, -179G/T, imparts tumor necrosis factor-alpha stimulation of IFNG in peripheral blood lymphocytes, and is linked with accelerated AIDS progression. We discovered a putative estrogen response element (ERE) introduced by the -179T, which displays selective activation in peripheral blood mononuclear cells (PBMC) vs lamina propria mononuclear cells (LPMC). Transfection of PBMC with constructs containing the -179G or -179T site revealed CD2-mediated enhancement of the -179T compared to -179G allele, although, in LPMC, a similar level of expression was detected. Electrophoretic mobility shift assay (EMSA) analysis demonstrated CD2-mediated nucleoprotein binding to the -179T but not the -179G in PBMC. In LPMC, binding is constitutive to both -179G and -179T regions. Sequence and EMSA analysis suggests that the -179T allele creates an ERE-like binding site capable of binding recombinant estrogen receptor. Estrogen response element transactivation is enhanced by CD2 signaling, but inhibited by estrogen in PBMC but not in LPMC, although expression of estrogen receptor was similar. This is the first report to describe a potential molecular mechanism responsible for selectively controlling IFN-gamma production in LPMC.

FUNCTIONAL ANALYSIS OF A NOVEL POSITIVE ALLOSTERIC MODULATOR OF AMPA RECEPTORS DERIVED FROM A STRUCTURE-BASED DRUG DESIGN STRATEGY

PubMed Central

Harms, Jonathan E.; Benveniste, Morris; Maclean, John K. F.; Partin, Kathryn M.; Jamieson, Craig

2012-01-01

Positive allosteric modulators of α-amino-3-hydroxy-5-methyl-isoxazole-propionic acid (AMPA) receptors facilitate synaptic plasticity and can improve various forms of learning and memory. These modulators show promise as therapeutic agents for the treatment of neurological disorders such as schizophrenia, ADHD, and mental depression. Three classes of positive modulator, the benzamides, the thiadiazides, and the biarylsulfonamides differentially occupy a solvent accessible binding pocket at the interface between the two subunits that form the AMPA receptor ligand-binding pocket. Here, we describe the electrophysiological properties of a new chemotype derived from a structure-based drug design strategy (SBDD), which makes similar receptor interactions compared to previously reported classes of modulator. This pyrazole amide derivative, JAMI1001A, with a promising developability profile, efficaciously modulates AMPA receptor deactivation and desensitization of both flip and flop receptor isoforms. PMID:22735771

The human apolipoprotein AV gene is regulated by peroxisome proliferator-activated receptor-alpha and contains a novel farnesoid X-activated receptor response element.

PubMed

Prieur, Xavier; Coste, Herve; Rodriguez, Joan C

2003-07-11

The newly identified apolipoprotein AV (apoAV) gene is a key player in determining plasma triglyceride concentrations. Because hypertriglyceridemia is a major independent risk factor in coronary artery disease, the understanding of the regulation of the expression of this gene is of considerable importance. We presently characterize the structure, the transcription start site, and the promoter of the human apoAV gene. Since the peroxisome proliferator-activated receptor-alpha (PPARalpha) and the farnesoid X-activated receptor (FXR) have been shown to modulate the expression of genes involved in triglyceride metabolism, we evaluated the potential role of these nuclear receptors in the regulation of apoAV transcription. Bile acids and FXR induced the apoAV gene promoter activity. 5'-Deletion, mutagenesis, and gel shift analysis identified a heretofore unknown element at positions -103/-84 consisting of an inverted repeat of two consensus receptor-binding hexads separated by 8 nucleotides (IR8), which was required for the response to bile acid-activated FXR. The isolated IR8 element conferred FXR responsiveness on a heterologous promoter. On the other hand, in apoAV-expressing human hepatic Hep3B cells, transfection of PPARalpha specifically enhanced apoAV promoter activity. By deletion, site-directed mutagenesis, and binding analysis, a PPARalpha response element located 271 bp upstream of the transcription start site was identified. Finally, treatment with a specific PPARalpha activator led to a significant induction of apoAV mRNA expression in hepatocytes. The identification of apoAV as a PPARalpha target gene has major implications with respect to mechanisms whereby pharmacological PPARalpha agonists may exert their beneficial hypotriglyceridemic actions.

Ligand and receptor dynamics contribute to the mechanism of graded PPARγ agonism

PubMed Central

Hughes, Travis S.; Chalmers, Michael J.; Novick, Scott; Kuruvilla, Dana S.; Chang, Mi Ra; Kamenecka, Theodore M.; Rance, Mark; Johnson, Bruce A.; Burris, Thomas P.; Griffin, Patrick R.; Kojetin, Douglas J.

2011-01-01

SUMMARY Ligand binding to proteins is not a static process, but rather involves a number of complex dynamic transitions. A flexible ligand can change conformation upon binding its target. The conformation and dynamics of a protein can change to facilitate ligand binding. The conformation of the ligand, however, is generally presumed to have one primary binding mode, shifting the protein conformational ensemble from one state to another. We report solution NMR studies that reveal peroxisome proliferator-activated receptor γ (PPARγ) modulators can sample multiple binding modes manifesting in multiple receptor conformations in slow conformational exchange. Our NMR, hydrogen/deuterium exchange and docking studies reveal that ligand-induced receptor stabilization and binding mode occupancy correlate with the graded agonist response of the ligand. Our results suggest that ligand and receptor dynamics affect the graded transcriptional output of PPARγ modulators. PMID:22244763

Few residues within an extensive binding interface drive receptor interaction and determine the specificity of arrestin proteins.

PubMed

Vishnivetskiy, Sergey A; Gimenez, Luis E; Francis, Derek J; Hanson, Susan M; Hubbell, Wayne L; Klug, Candice S; Gurevich, Vsevolod V

2011-07-08

Arrestins bind active phosphorylated forms of G protein-coupled receptors, terminating G protein activation, orchestrating receptor trafficking, and redirecting signaling to alternative pathways. Visual arrestin-1 preferentially binds rhodopsin, whereas the two non-visual arrestins interact with hundreds of G protein-coupled receptor subtypes. Here we show that an extensive surface on the concave side of both arrestin-2 domains is involved in receptor binding. We also identified a small number of residues on the receptor binding surface of the N- and C-domains that largely determine the receptor specificity of arrestins. We show that alanine substitution of these residues blocks the binding of arrestin-1 to rhodopsin in vitro and of arrestin-2 and -3 to β2-adrenergic, M2 muscarinic cholinergic, and D2 dopamine receptors in intact cells, suggesting that these elements critically contribute to the energy of the interaction. Thus, in contrast to arrestin-1, where direct phosphate binding is crucial, the interaction of non-visual arrestins with their cognate receptors depends to a lesser extent on phosphate binding and more on the binding to non-phosphorylated receptor elements.

Few Residues within an Extensive Binding Interface Drive Receptor Interaction and Determine the Specificity of Arrestin Proteins*

PubMed Central

Vishnivetskiy, Sergey A.; Gimenez, Luis E.; Francis, Derek J.; Hanson, Susan M.; Hubbell, Wayne L.; Klug, Candice S.; Gurevich, Vsevolod V.

2011-01-01

Arrestins bind active phosphorylated forms of G protein-coupled receptors, terminating G protein activation, orchestrating receptor trafficking, and redirecting signaling to alternative pathways. Visual arrestin-1 preferentially binds rhodopsin, whereas the two non-visual arrestins interact with hundreds of G protein-coupled receptor subtypes. Here we show that an extensive surface on the concave side of both arrestin-2 domains is involved in receptor binding. We also identified a small number of residues on the receptor binding surface of the N- and C-domains that largely determine the receptor specificity of arrestins. We show that alanine substitution of these residues blocks the binding of arrestin-1 to rhodopsin in vitro and of arrestin-2 and -3 to β2-adrenergic, M2 muscarinic cholinergic, and D2 dopamine receptors in intact cells, suggesting that these elements critically contribute to the energy of the interaction. Thus, in contrast to arrestin-1, where direct phosphate binding is crucial, the interaction of non-visual arrestins with their cognate receptors depends to a lesser extent on phosphate binding and more on the binding to non-phosphorylated receptor elements. PMID:21471193

The nuclear orphan receptors COUP-TF and ARP-1 positively regulate the trout estrogen receptor gene through enhancing autoregulation.

PubMed Central

Lazennec, G; Kern, L; Valotaire, Y; Salbert, G

1997-01-01

The rainbow trout estrogen receptor (rtER) is a positively autoregulated gene in liver cells. In a previous report, we showed that upregulation is mediated by an estrogen response element (ERE) located in the proximal promoter of the gene and that a half binding site for nuclear receptors (5'-TGACCT-3') located 15 bp upstream of the ERE is involved in the magnitude of the estrogen response. We now report that the human orphan receptor COUP-TF and a COUP-TF-like protein from trout liver are able to bind to the consensus half-site. When cotransfected with the rtER gene proximal promoter, COUP-TF had no regulatory functions on its own. Interestingly, COUP-TF enhanced rtER transactivation properties in the presence of estradiol in a dose-dependent manner when cotransfected with the rtER gene promoter. Unliganded retinoid receptor heterodimers had the same helper function as COUP-TF in the presence of estradiol but were switched to repressors when the ligand all-trans-retinoic acid was added. Mutation of the consensus half-site only slightly reduced COUP-TF helper function, suggesting that it actually results from a complex mechanism that probably involves both DNA binding of COUP-TF to the promoter and protein-protein interaction with another transcription factor bound to the promoter. Nevertheless, a DNA-binding-defective mutant of COUP-TF was also defective in ER helper function. Competition footprinting analysis suggested that COUP-TF actually establishes contacts with the consensus upstream half-site and the downstream ERE half-site that would form a DR-24-like response element. Interaction of COUP-TF with the DR-24 element was confirmed in footprinting assays by using nuclear extracts from Saccharomyces cerevisiae expressing COUP-TF. Finally, interaction of COUP-TF with mutants of the rtER gene promoter showed that COUP-TF recognizes the ERE when the upstream half-site is mutated. These data show that COUP-TF may activate transcription through interaction with other nuclear receptors. This cross-talk between liganded nuclear receptors and orphan receptors is likely to modulate the spectrum of action of a particular ligand-receptor complex and may participate in the cell-type specificity of the ligand effect. PMID:9271383

Modulation of GABAergic receptor binding by activation of calcium and calmodulin-dependent kinase II membrane phosphorylation.

PubMed

Churn, S B; DeLorenzo, R J

1998-10-26

gamma-Aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system (CNS). Because of the important role that GABA plays in the CNS, alteration of GABAA receptor function would significantly affect neuronal excitability. Protein phosphorylation is a major mechanism for regulating receptor function in the brain and has been implicated in modulating GABAA receptor function. Therefore, this study was initiated to determine the role of calmodulin-dependent kinase II (CaM kinase II) membrane phosphorylation on GABAA receptor binding. Synaptosomal membrane fractions were tested for CaM kinase II activity towards endogenous substrates. In addition, muscimol binding was evaluated under equilibrium conditions in synaptosomal membrane fractions subjected to either basal (Mg2+ alone) or maximal CaM kinase II-dependent phosphorylation. Activation of endogenous CaM kinase II-dependent phosphorylation resulted in a significant enhancement of the apparent Bmax for muscimol binding without significantly altering the apparent binding affinity. The enhanced muscimol binding could be increased further by the addition of exogenous CaM kinase II to synaptosomal membrane fractions. Co-incubation with inhibitors of kinase activity during the phosphorylation reactions blocked the CaM kinase II-dependent increase in muscimol binding. The data support the hypothesis that activation of CaM kinase II-dependent phosphorylation caused an increased GABAA receptor binding and may play an important role in modulating the function of this inhibitory receptor/chloride ion channel complex. Copyright 1998 Elsevier Science B.V.

Prediction of consensus binding mode geometries for related chemical series of positive allosteric modulators of adenosine and muscarinic acetylcholine receptors.

PubMed

Sakkal, Leon A; Rajkowski, Kyle Z; Armen, Roger S

2017-06-05

Following insights from recent crystal structures of the muscarinic acetylcholine receptor, binding modes of Positive Allosteric Modulators (PAMs) were predicted under the assumption that PAMs should bind to the extracellular surface of the active state. A series of well-characterized PAMs for adenosine (A 1 R, A 2A R, A 3 R) and muscarinic acetylcholine (M 1 R, M 5 R) receptors were modeled using both rigid and flexible receptor CHARMM-based molecular docking. Studies of adenosine receptors investigated the molecular basis of the probe-dependence of PAM activity by modeling in complex with specific agonist radioligands. Consensus binding modes map common pharmacophore features of several chemical series to specific binding interactions. These models provide a rationalization of how PAM binding slows agonist radioligand dissociation kinetics. M 1 R PAMs were predicted to bind in the analogous M 2 R PAM LY2119620 binding site. The M 5 R NAM (ML-375) was predicted to bind in the PAM (ML-380) binding site with a unique induced-fit receptor conformation. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Allosteric modulation of ATP-gated P2X receptor channels

PubMed Central

Coddou, Claudio; Stojilkovic, Stanko S.; Huidobro-Toro, J. Pablo

2013-01-01

Seven mammalian purinergic receptor subunits, denoted P2X1 to P2X7, and several spliced forms of these subunits have been cloned. When heterologously expressed, these cDNAs encode ATP-gated non-selective cation channels organized as trimers. All activated receptors produce cell depolarization and promote Ca2+ influx through their pores and indirectly by activating voltage-gated calcium channels. However, the biophysical and pharmacological properties of these receptors differ considerably, and the majority of these subunits are also capable of forming heterotrimers with other members of the P2X receptor family, which confers further different properties. These channels have three ATP binding domains, presumably located between neighboring subunits, and occupancy of at least two binding sites is needed for their activation. In addition to the orthosteric binding sites for ATP, these receptors have additional allosteric sites that modulate the agonist action at receptors, including sites for trace metals, protons, neurosteroids, reactive oxygen species and phosphoinositides. The allosteric regulation of P2X receptors is frequently receptor-specific and could be a useful tool to identify P2X members in native tissues and their roles in signaling. The focus of this review is on common and receptor-specific allosteric modulation of P2X receptors and the molecular base accounting for allosteric binding sites. PMID:21639805

Transcription factor assisted loading and enhancer dynamics dictate the hepatic fasting response

PubMed Central

Goldstein, Ido; Baek, Songjoon; Presman, Diego M.; Paakinaho, Ville; Swinstead, Erin E.; Hager, Gordon L.

2017-01-01

Fasting elicits transcriptional programs in hepatocytes leading to glucose and ketone production. This transcriptional program is regulated by many transcription factors (TFs). To understand how this complex network regulates the metabolic response to fasting, we aimed at isolating the enhancers and TFs dictating it. Measuring chromatin accessibility revealed that fasting massively reorganizes liver chromatin, exposing numerous fasting-induced enhancers. By utilizing computational methods in combination with dissecting enhancer features and TF cistromes, we implicated four key TFs regulating the fasting response: glucocorticoid receptor (GR), cAMP responsive element binding protein 1 (CREB1), peroxisome proliferator activated receptor alpha (PPARA), and CCAAT/enhancer binding protein beta (CEBPB). These TFs regulate fuel production by two distinctly operating modules, each controlling a separate metabolic pathway. The gluconeogenic module operates through assisted loading, whereby GR doubles the number of sites occupied by CREB1 as well as enhances CREB1 binding intensity and increases accessibility of CREB1 binding sites. Importantly, this GR-assisted CREB1 binding was enhancer-selective and did not affect all CREB1-bound enhancers. Single-molecule tracking revealed that GR increases the number and DNA residence time of a portion of chromatin-bound CREB1 molecules. These events collectively result in rapid synergistic gene expression and higher hepatic glucose production. Conversely, the ketogenic module operates via a GR-induced TF cascade, whereby PPARA levels are increased following GR activation, facilitating gradual enhancer maturation next to PPARA target genes and delayed ketogenic gene expression. Our findings reveal a complex network of enhancers and TFs that dynamically cooperate to restore homeostasis upon fasting. PMID:28031249

Estrogen Receptor Folding Modulates cSrc Kinase SH2 Interaction via a Helical Binding Mode.

PubMed

Nieto, Lidia; Tharun, Inga M; Balk, Mark; Wienk, Hans; Boelens, Rolf; Ottmann, Christian; Milroy, Lech-Gustav; Brunsveld, Luc

2015-11-20

The estrogen receptors (ERs) feature, next to their transcriptional role, important nongenomic signaling actions, with emerging clinical relevance. The Src Homology 2 (SH2) domain mediated interaction between cSrc kinase and ER plays a key role in this; however the molecular determinants of this interaction have not been elucidated. Here, we used phosphorylated ER peptide and semisynthetic protein constructs in a combined biochemical and structural study to, for the first time, provide a quantitative and structural characterization of the cSrc SH2-ER interaction. Fluorescence polarization experiments delineated the SH2 binding motif in the ER sequence. Chemical shift perturbation analysis by nuclear magnetic resonance (NMR) together with molecular dynamics (MD) simulations allowed us to put forward a 3D model of the ER-SH2 interaction. The structural basis of this protein-protein interaction has been compared with that of the high affinity SH2 binding sequence GpYEEI. The ER features a different binding mode from that of the "two-pronged plug two-hole socket" model in the so-called specificity determining region. This alternative binding mode is modulated via the folding of ER helix 12, a structural element directly C-terminal of the key phosphorylated tyrosine. The present findings provide novel molecular entries for understanding nongenomic ER signaling and targeting the corresponding disease states.

Liver X receptor regulates hepatic nuclear O-GlcNAc signaling and carbohydrate responsive element-binding protein activity[S

PubMed Central

Bindesbøll, Christian; Fan, Qiong; Nørgaard, Rikke C.; MacPherson, Laura; Ruan, Hai-Bin; Wu, Jing; Pedersen, Thomas Å.; Steffensen, Knut R.; Yang, Xiaoyong; Matthews, Jason; Mandrup, Susanne; Nebb, Hilde I.; Grønning-Wang, Line M.

2015-01-01

Liver X receptor (LXR)α and LXRβ play key roles in hepatic de novo lipogenesis through their regulation of lipogenic genes, including sterol regulatory element-binding protein (SREBP)-1c and carbohydrate responsive element-binding protein (ChREBP). LXRs activate lipogenic gene transcription in response to feeding, which is believed to be mediated by insulin. We have previously shown that LXRs are targets for glucose-hexosamine-derived O-linked β-N-acetylglucosamine (O-GlcNAc) modification enhancing their ability to regulate SREBP-1c promoter activity in vitro. To elucidate insulin-independent effects of feeding on LXR-mediated lipogenic gene expression in vivo, we subjected control and streptozotocin-treated LXRα/β+/+ and LXRα/β−/− mice to a fasting-refeeding regime. We show that under hyperglycemic and hypoinsulinemic conditions, LXRs maintain their ability to upregulate the expression of glycolytic and lipogenic enzymes, including glucokinase (GK), SREBP-1c, ChREBPα, and the newly identified shorter isoform ChREBPβ. Furthermore, glucose-dependent increases in LXR/retinoid X receptor-regulated luciferase activity driven by the ChREBPα promoter was mediated, at least in part, by O-GlcNAc transferase (OGT) signaling in Huh7 cells. Moreover, we show that LXR and OGT interact and colocalize in the nucleus and that loss of LXRs profoundly reduced nuclear O-GlcNAc signaling and ChREBPα promoter binding activity in vivo. In summary, our study provides evidence that LXRs act as nutrient and glucose metabolic sensors upstream of ChREBP by modulating GK expression, nuclear O-GlcNAc signaling, and ChREBP expression and activity. PMID:25724563

Molecular blueprint of allosteric binding sites in a homologue of the agonist-binding domain of the α7 nicotinic acetylcholine receptor

PubMed Central

Spurny, Radovan; Debaveye, Sarah; Farinha, Ana; Veys, Ken; Vos, Ann M.; Gossas, Thomas; Atack, John; Bertrand, Sonia; Bertrand, Daniel; Danielson, U. Helena; Tresadern, Gary; Ulens, Chris

2015-01-01

The α7 nicotinic acetylcholine receptor (nAChR) belongs to the family of pentameric ligand-gated ion channels and is involved in fast synaptic signaling. In this study, we take advantage of a recently identified chimera of the extracellular domain of the native α7 nicotinic acetylcholine receptor and acetylcholine binding protein, termed α7-AChBP. This chimeric receptor was used to conduct an innovative fragment-library screening in combination with X-ray crystallography to identify allosteric binding sites. One allosteric site is surface-exposed and is located near the N-terminal α-helix of the extracellular domain. Ligand binding at this site causes a conformational change of the α-helix as the fragment wedges between the α-helix and a loop homologous to the main immunogenic region of the muscle α1 subunit. A second site is located in the vestibule of the receptor, in a preexisting intrasubunit pocket opposite the agonist binding site and corresponds to a previously identified site involved in positive allosteric modulation of the bacterial homolog ELIC. A third site is located at a pocket right below the agonist binding site. Using electrophysiological recordings on the human α7 nAChR we demonstrate that the identified fragments, which bind at these sites, can modulate receptor activation. This work presents a structural framework for different allosteric binding sites in the α7 nAChR and paves the way for future development of novel allosteric modulators with therapeutic potential. PMID:25918415

N-3 polyunsaturated fatty acid regulation of hepatic gene transcription

PubMed Central

Jump, Donald B.

2009-01-01

Purpose of review The liver plays a central role in whole body lipid metabolism and adapts rapidly to changes in dietary fat composition. This adaption involves changes in the expression of genes involved in glycolysis, de-novo lipogenesis, fatty acid elongation, desaturation and oxidation. This review brings together metabolic and molecular studies that help explain n-3 (omega-3) polyunsaturated fatty acid regulation of hepatic gene transcription. Recent findings Dietary n-3 polyunsaturated fatty acid regulates hepatic gene expression by targeting three major transcriptional regulatory networks: peroxisome proliferator-activated receptor α, sterol regulatory element binding protein-1 and the carbohydrate regulatory element binding protein/Max-like factor X heterodimer. 22 : 6,n-3, the most prominent n-3 polyunsaturated fatty acid in tissues, is a weak activator of peroxisome proliferator-activated receptor α. Hepatic metabolism of 22 : 6,n-3, however, generates 20 : 5,n-3, a strong peroxisome proliferator-activated receptor α activator. In contrast to peroxisome proliferator-activated receptor α, 22 : 6,n-3 is the most potent fatty acid regulator of hepatic sterol regulatory element binding protein-1. 22 : 6,n-3 suppresses sterol regulatory element binding protein-1 gene expression while enhancing degradation of nuclear sterol regulatory element binding protein-1 through 26S proteasome and Erk1/2-dependent mechanisms. Both n-3 and n-6 polyunsaturated fatty acid suppress carbohydrate regulatory element binding protein and Max-like factor X nuclear abundance and interfere with glucose-regulated hepatic metabolism. Summary These studies have revealed unique mechanisms by which specific polyunsaturated fatty acids control peroxisome proliferator activated receptor α, sterol regulatory element binding protein-1 and carbohydrate regulatory element binding protein/Max-like factor X function. As such, specific metabolic and signal transduction pathways contribute significantly to the fatty acid regulation of these transcription factors and their corresponding regulatory networks. PMID:18460914

Signaling cross-talk between peroxisome proliferator-activated receptor/retinoid X receptor and estrogen receptor through estrogen response elements.

PubMed

Keller, H; Givel, F; Perroud, M; Wahli, W

1995-07-01

Peroxisome proliferator-activated receptors (PPARs) and retinoid X receptors (RXRs) are nuclear hormone receptors that are activated by fatty acids and 9-cis-retinoic acid, respectively. PPARs and RXRs form heterodimers that activate transcription by binding to PPAR response elements (PPREs) in the promoter of target genes. The PPREs described thus far consist of a direct tandem repeat of the AGGTCA core element with one intervening nucleotide. We show here that the vitellogenin A2 estrogen response element (ERE) can also function as a PPRE and is bound by a PPAR/RXR heterodimer. Although this heterodimer can bind to several other ERE-related palindromic response elements containing AGGTCA half-sites, only the ERE is able to confer transactivation of test reporter plasmids, when the ERE is placed either close to or at a distance from the transcription initiation site. Examination of natural ERE-containing promoters, including the pS2, very-low-density apolipoprotein II and vitellogenin A2 genes, revealed considerable differences in the binding of PPAR/RXR heterodimers to these EREs. In their natural promoter context, these EREs did not allow transcriptional activation by PPARs/RXRs. Analysis of this lack of stimulation of the vitellogenin A2 promoter demonstrated that PPARs/RXRs bind to the ERE but cannot transactivate due to a nonpermissive promoter structure. As a consequence, PPARs/RXRs inhibit transactivation by the estrogen receptor through competition for ERE binding. This is the first example of signaling cross-talk between PPAR/RXR and estrogen receptor.

Quantification of transcription factor-DNA binding affinity in a living cell

PubMed Central

Belikov, Sergey; Berg, Otto G.; Wrange, Örjan

2016-01-01

The apparent dissociation constant (Kd) for specific binding of glucocorticoid receptor (GR) and androgen receptor (AR) to DNA was determined in vivo in Xenopus oocytes. The total nuclear receptor concentration was quantified as specifically retained [3H]-hormone in manually isolated oocyte nuclei. DNA was introduced by nuclear microinjection of single stranded phagemid DNA, chromatin is then formed during second strand synthesis. The fraction of DNA sites occupied by the expressed receptor was determined by dimethylsulphate in vivo footprinting and used for calculation of the receptor-DNA binding affinity. The forkhead transcription factor FoxA1 enhanced the DNA binding by GR with an apparent Kd of ∼1 μM and dramatically stimulated DNA binding by AR with an apparent Kd of ∼0.13 μM at a composite androgen responsive DNA element containing one FoxA1 binding site and one palindromic hormone receptor binding site known to bind one receptor homodimer. FoxA1 exerted a weak constitutive- and strongly cooperative DNA binding together with AR but had a less prominent effect with GR, the difference reflecting the licensing function of FoxA1 at this androgen responsive DNA element. PMID:26657626

Substitution of synthetic chimpanzee androgen receptor for human androgen receptor in competitive binding and transcriptional activation assays for EDC screening

EPA Science Inventory

The potential effect of receptor-mediated endocrine modulators across species is of increasing concern. In attempts to address these concerns we are developing androgen and estrogen receptor binding assays using recombinant hormone receptors from a number of species across differ...

Structural Overview of the Nuclear Receptor Superfamily: Insights into Physiology and Therapeutics

PubMed Central

Huang, Pengxiang; Chandra, Vikas; Rastinejad, Fraydoon

2013-01-01

As ligand-regulated transcription factors, the nuclear hormone receptors are nearly ideal drug targets, with internal pockets that bind to hydrophobic, drug-like molecules and well-characterized ligand-induced conformational changes that recruit transcriptional coregulators to promoter elements. Yet, due to the multitude of genes under the control of a single receptor, the major challenge has been the identification of ligands with gene-selective actions, impacting disease outcomes through a narrow subset of target genes and not across their entire gene-regulatory repertoire. Here, we summarize the concepts and work to date underlying the development of steroidal and nonsteroidal receptor ligands, including the use of crystal structures, high-throughput screens, and rational design approaches for finding useful therapeutic molecules. Difficulties in finding selective receptor modulators require a more complete understanding of receptor interdomain communications, posttranslational modifications, and receptor-protein interactions that could be exploited for target gene selectivity. PMID:20148675

A dihydropyridine receptor alpha1s loop region critical for skeletal muscle contraction is intrinsically unstructured and binds to a SPRY domain of the type 1 ryanodine receptor.

PubMed

Cui, Yanfang; Tae, Han-Shen; Norris, Nicole C; Karunasekara, Yamuna; Pouliquin, Pierre; Board, Philip G; Dulhunty, Angela F; Casarotto, Marco G

2009-03-01

The II-III loop of the dihydropyridine receptor (DHPR) alpha(1s) subunit is a modulator of the ryanodine receptor (RyR1) Ca(2+) release channel in vitro and is essential for skeletal muscle contraction in vivo. Despite its importance, the structure of this loop has not been reported. We have investigated its structure using a suite of NMR techniques which revealed that the DHPR II-III loop is an intrinsically unstructured protein (IUP) and as such belongs to a burgeoning structural class of functionally important proteins. The loop does not possess a stable tertiary fold: it is highly flexible, with a strong N-terminal helix followed by nascent helical/turn elements and unstructured segments. Its residual structure is loosely globular with the N and C termini in close proximity. The unstructured nature of the II-III loop may allow it to easily modify its interaction with RyR1 following a surface action potential and thus initiate rapid Ca(2+) release and contraction. The in vitro binding partner for the II-III was investigated. The II-III loop interacts with the second of three structurally distinct SPRY domains in RyR1, whose function is unknown. This interaction occurs through two preformed N-terminal alpha-helical regions and a C-terminal hydrophobic element. The A peptide corresponding to the helical N-terminal region is a common probe of RyR function and binds to the same SPRY domain as the full II-III loop. Thus the second SPRY domain is an in vitro binding site for the II-III loop. The possible in vivo role of this region is discussed.

Structural and Functional Analysis of Two New Positive Allosteric Modulators of GluA2 Desensitization and Deactivation

PubMed Central

Timm, David E.; Benveniste, Morris; Weeks, Autumn M.; Nisenbaum, Eric S.

2011-01-01

At the dimer interface of the extracellular ligand-binding domain of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors a hydrophilic pocket is formed that is known to interact with two classes of positive allosteric modulators, represented by cyclothiazide and the ampakine 2H,3H,6aH-pyrrolidino(2,1–3′,2′)1,3-oxazino(6′,5′-5,4)benzo(e)1,4-dioxan-10-one (CX614). Here, we present structural and functional data on two new positive allosteric modulators of AMPA receptors, phenyl-1,4-bis-alkylsulfonamide (CMPDA) and phenyl-1,4-bis-carboxythiophene (CMPDB). Crystallographic data show that these compounds bind within the modulator-binding pocket and that substituents of each compound overlap with distinct moieties of cyclothiazide and CX614. The goals of the present study were to determine 1) the degree of modulation by CMPDA and CMPDB of AMPA receptor deactivation and desensitization; 2) whether these compounds are splice isoform-selective; and 3) whether predictions of mechanism of action could be inferred by comparing molecular interactions between the ligand-binding domain and each compound with those of cyclothiazide and CX614. CMPDB was found to be more isoform-selective than would be predicted from initial binding assays. It is noteworthy that these new compounds are both more potent and more effective and may be more clinically relevant than the AMPA receptor modulators described previously. PMID:21543522

Distinct effects of loss of classical estrogen receptor signaling versus complete deletion of estrogen receptor alpha on bone

PubMed Central

Syed, Farhan A.; Fraser, Daniel G.; Monroe, David G.; Khosla, Sundeep

2011-01-01

Estrogen receptor (ER)α is a major regulator of bone metabolism which can modulate gene expression via a “classical” pathway involving direct DNA binding to estrogen-response elements (EREs) or via “non-classical” pathways involving protein-protein interactions. While the skeletal consequences of loss of ERE binding by ERα have been described, a significant unresolved question is how loss of ERE binding differs from complete loss of ERα. Thus, we compared the skeletal phenotype of wild-type (ERα+/+) and ERα knock out (ERα−/−) mice with that of mice in which the only ERα present had a knock-in mutation abolishing ERE binding (non-classical ERα knock-in [NERKI], ERα−/NERKI). All three groups were in the same genetic background (C57BL/6). As compared to both ERα+/+ and ERα−/− mice, ERα−/NERKI mice had significantly reduced cortical volumetric bone mineral density and thickness at the tibial diaphysis; this was accompanied by significant decreases in periosteal and endocortical mineral apposition rates. Colony forming unit (CFU)-fibroblast, CFU-alkaline phosphatase, and CFU-osteoblast numbers were all increased in ERα−/− compared to ERα+/+ mice, but reduced in ERα−/NERKI mice compared to the two other groups. Thus, using mice in identical genetic backgrounds, our data indicate that the presence of an ERα that cannot bind DNA but can function through protein-protein interactions may have more deleterious skeletal effects than complete loss of ERα. These findings suggest that shifting the balance of classical versus non-classical ERα signaling triggers pathways that impair bone formation. Further studies defining these pathways may lead to novel approaches to selectively modulate ER signaling for beneficial skeletal effects. PMID:21458604

DAMGO binding to mouse brain membranes: influence of salts, guanine nucleotides, substance P, and substance P fragments.

PubMed

Krumins, S A; Kim, D C; Igwe, O J; Larson, A A

1993-01-01

Substance P (SP) appears to mediate many processes of the central nervous system, including pain. This report deals with modulation of opioid binding in the mouse brain by SP and SP fragments, as well as by salts and guanine nucleotides. Binding studies of the selective mu opioid receptor agonist [D-Ala2, MePhe4,Gly(ol)5]enkephalin (DAMGO) to mouse brain membrane preparations demonstrated that guanine nucleotide modulation of DAMGO binding affinity was modified by SP. However, SP had little or no influence on inhibition of DAMGO binding induced by salts, such as MgCl2, CaCl2, or NaCl. By replacing GTP with GppNHp, SP (0.1 nM) produced multiple affinity forms of the DAMGO receptor, while at a higher concentration (10 nM), SP lost its influence on DAMGO binding. Furthermore, 0.1 nM SP changed DAMGO binding parameters in a medium containing NaCl, CaCl2, and GppNHp such that the high- and low-affinity conformations of the receptor converted to a single site following the addition of SP to the incubation medium. While the C-terminal SP fragment SP(5-11) was without effect, the N-terminal SP fragments SP(1-9) and SP(1-7) appeared to imitate SP in modifying GppNHp-modulated DAMGO binding. These results suggest that SP functions as a modulator of opioid binding at the mu receptor and it appears that the N-terminus of SP plays a role in the modulatory process.

Diarylureas as allosteric modulators of the cannabinoid CB1 receptor: structure-activity relationship studies on 1-(4-chlorophenyl)-3-{3-[6-(pyrrolidin-1-yl)pyridin-2-yl]phenyl}urea (PSNCBAM-1).

PubMed

German, Nadezhda; Decker, Ann M; Gilmour, Brian P; Gay, Elaine A; Wiley, Jenny L; Thomas, Brian F; Zhang, Yanan

2014-09-25

The recent discovery of allosteric modulators of the CB1 receptor including PSNCBAM-1 (4) has generated significant interest in CB1 receptor allosteric modulation. Here in the first SAR study on 4, we have designed and synthesized a series of analogs focusing on modifications at two positions. Pharmacological evaluation in calcium mobilization and binding assays revealed the importance of alkyl substitution at the 2-aminopyridine moiety and electron deficient aromatic groups at the 4-chlorophenyl position for activity at the CB1 receptor, resulting in several analogs with comparable potency to 4. These compounds increased the specific binding of [(3)H]CP55,940, in agreement with previous reports. Importantly, 4 and two analogs dose-dependently reduced the Emax of the agonist curve in the CB1 calcium mobilization assays, confirming their negative allosteric modulator characteristics. Given the side effects associated with CB1 receptor orthosteric antagonists, negative allosteric modulators provide an alternative approach to modulate the pharmacologically important CB1 receptor.

A fractal analysis of protein to DNA binding kinetics using biosensors.

PubMed

Sadana, Ajit

2003-08-01

A fractal analysis of a confirmative nature only is presented for the binding of estrogen receptor (ER) in solution to its corresponding DNA (estrogen response element, ERE) immobilized on a sensor chip surface [J. Biol. Chem. 272 (1997) 11384], and for the cooperative binding of human 1,25-dihydroxyvitamin D(3) receptor (VDR) to DNA with the 9-cis-retinoic acid receptor (RXR) [Biochemistry 35 (1996) 3309]. Ligands were also used to modulate the first reaction. Data taken from the literature may be modeled by using a single- or a dual-fractal analysis. Relationships are presented for the binding rate coefficient as a function of either the analyte concentration in solution or the fractal dimension that exists on the biosensor surface. The binding rate expressions developed exhibit a wide range of dependence on the degree of heterogeneity that exists on the surface, ranging from sensitive (order of dependence equal to 1.202) to very sensitive (order of dependence equal to 12.239). In general, the binding rate coefficient increases as the degree of heterogeneity or the fractal dimension of the surface increases. The predictive relationships presented provide further physical insights into the reactions occurring on the biosensor surface. Even though these reactions are occurring on the biosensor surface, the relationships presented should assist in understanding and in possibly manipulating the reactions occurring on cellular surfaces.

Mechanism of Positive Allosteric Modulators Acting on AMPA Receptors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin,R.; Clark, S.; Weeks, A.

2005-01-01

Ligand-gated ion channels involved in the modulation of synaptic strength are the AMPA, kainate, and NMDA glutamate receptors. Small molecules that potentiate AMPA receptor currents relieve cognitive deficits caused by neurodegenerative diseases such as Alzheimer's disease and show promise in the treatment of depression. Previously, there has been limited understanding of the molecular mechanism of action for AMPA receptor potentiators. Here we present cocrystal structures of the glutamate receptor GluR2 S1S2 ligand-binding domain in complex with aniracetam [1-(4-methoxybenzoyl)-2-pyrrolidinone] or CX614 (pyrrolidino-1, 3-oxazino benzo-1, 4-dioxan-10-one), two AMPA receptor potentiators that preferentially slow AMPA receptor deactivation. Both potentiators bind within the dimermore » interface of the nondesensitized receptor at a common site located on the twofold axis of molecular symmetry. Importantly, the potentiator binding site is adjacent to the 'hinge' in the ligand-binding core 'clamshell' that undergoes conformational rearrangement after glutamate binding. Using rapid solution exchange, patch-clamp electrophysiology experiments, we show that point mutations of residues that interact with potentiators in the cocrystal disrupt potentiator function. We suggest that the potentiators slow deactivation by stabilizing the clamshell in its closed-cleft, glutamate-bound conformation.« less

Transcription factor assisted loading and enhancer dynamics dictate the hepatic fasting response.

PubMed

Goldstein, Ido; Baek, Songjoon; Presman, Diego M; Paakinaho, Ville; Swinstead, Erin E; Hager, Gordon L

2017-03-01

Fasting elicits transcriptional programs in hepatocytes leading to glucose and ketone production. This transcriptional program is regulated by many transcription factors (TFs). To understand how this complex network regulates the metabolic response to fasting, we aimed at isolating the enhancers and TFs dictating it. Measuring chromatin accessibility revealed that fasting massively reorganizes liver chromatin, exposing numerous fasting-induced enhancers. By utilizing computational methods in combination with dissecting enhancer features and TF cistromes, we implicated four key TFs regulating the fasting response: glucocorticoid receptor (GR), cAMP responsive element binding protein 1 (CREB1), peroxisome proliferator activated receptor alpha (PPARA), and CCAAT/enhancer binding protein beta (CEBPB). These TFs regulate fuel production by two distinctly operating modules, each controlling a separate metabolic pathway. The gluconeogenic module operates through assisted loading, whereby GR doubles the number of sites occupied by CREB1 as well as enhances CREB1 binding intensity and increases accessibility of CREB1 binding sites. Importantly, this GR-assisted CREB1 binding was enhancer-selective and did not affect all CREB1-bound enhancers. Single-molecule tracking revealed that GR increases the number and DNA residence time of a portion of chromatin-bound CREB1 molecules. These events collectively result in rapid synergistic gene expression and higher hepatic glucose production. Conversely, the ketogenic module operates via a GR-induced TF cascade, whereby PPARA levels are increased following GR activation, facilitating gradual enhancer maturation next to PPARA target genes and delayed ketogenic gene expression. Our findings reveal a complex network of enhancers and TFs that dynamically cooperate to restore homeostasis upon fasting. Published by Cold Spring Harbor Laboratory Press.

Transcriptional switches in the control of macronutrient metabolism.

PubMed

Wise, Alan

2008-06-01

This review shows how some transcription factors respond to alterations in macronutrients. Carbohydrates induce enzymes for their metabolism and fatty acid synthesis. Fatty acids reduce carbohydrate processing, induce enzymes for their metabolism, and increase both gluconeogenesis and storage of fat. Fat stores help control carbohydrate uptake by other cells. The following main transcription factors are discussed: carbohydrate response element-binding protein; sterol regulatory element-binding protein-1c, cyclic AMP response element-binding protein, peroxisome proliferator-activated receptor-alpha, and peroxisome proliferator-activated receptor-gamma.

The high mobility group protein 1 enhances binding of the estrogen receptor DNA binding domain to the estrogen response element.

PubMed

Romine, L E; Wood, J R; Lamia, L A; Prendergast, P; Edwards, D P; Nardulli, A M

1998-05-01

We have examined the ability of the high-mobility group protein 1 (HMG1) to alter binding of the estrogen receptor DNA-binding domain (DBD) to the estrogen response element (ERE). HMG1 dramatically enhanced binding of purified, bacterially expressed DBD to the consensus vitellogenin A2 ERE in a dose-dependent manner. The ability of HMG1 to stabilize the DBD-ERE complex resulted in part from a decrease in the dissociation rate of the DBD from the ERE. Antibody supershift experiments demonstrated that HMG1 was also capable of forming a ternary complex with the ERE-bound DBD in the presence of HMG1-specific antibody. HMG1 did not substantially affect DBD-ERE contacts as assessed by methylation interference assays, nor did it alter the ability of the DBD to induce distortion in ERE-containing DNA fragments. Because HMG1 dramatically enhanced estrogen receptor DBD binding to the ERE, and the DBD is the most highly conserved region among the nuclear receptor superfamily members, HMG1 may function to enhance binding of other nuclear receptors to their respective response elements and act in concert with coactivator proteins to regulate expression of hormone-responsive genes.

Molecular Basis for Modulation of Metabotropic Glutamate Receptors and Their Drug Actions by Extracellular Ca2+

PubMed Central

Zou, Juan; Jiang, Jason Y.; Yang, Jenny J.

2017-01-01

Metabotropic glutamate receptors (mGluRs) associated with the slow phase of the glutamatergic signaling pathway in neurons of the central nervous system have gained importance as drug targets for chronic neurodegenerative diseases. While extracellular Ca2+ was reported to exhibit direct activation and modulation via an allosteric site, the identification of those binding sites was challenged by weak binding. Herein, we review the discovery of extracellular Ca2+ in regulation of mGluRs, summarize the recent developments in probing Ca2+ binding and its co-regulation of the receptor based on structural and biochemical analysis, and discuss the molecular basis for Ca2+ to regulate various classes of drug action as well as its importance as an allosteric modulator in mGluRs. PMID:28335551

The aryl hydrocarbon receptor and glucocorticoid receptor interact to activate human metallothionein 2A

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sato, Shoko, E-mail: satosho@rs.tus.ac.jp; Shirakawa, Hitoshi, E-mail: shirakah@m.tohoku.ac.jp; Tomita, Shuhei, E-mail: tomita@med.tottori-u.ac.jp

2013-11-15

Although the aryl hydrocarbon receptor (AHR) and glucocorticoid receptor (GR) play essential roles in mammalian development, stress responses, and other physiological events, crosstalk between these receptors has been the subject of much debate. Metallothioneins are classic glucocorticoid-inducible genes that were reported to increase upon treatment with AHR agonists in rodent tissues and cultured human cells. In this study, the mechanism of human metallothionein 2A (MT2A) gene transcription activation by AHR was investigated. Cotreatment with 3-methylcholanthrene and dexamethasone, agonists of AHR and GR respectively, synergistically increased MT2A mRNA levels in HepG2 cells. MT2A induction was suppressed by RNA interference against AHRmore » or GR. Coimmunoprecipitation experiments revealed a physical interaction between AHR and GR proteins. Moreover, chromatin immunoprecipitation assays indicated that AHR was recruited to the glucocorticoid response element in the MT2A promoter. Thus, we provide a novel mechanism whereby AHR modulates expression of human MT2A via the glucocorticoid response element and protein–protein interactions with GR. - Highlights: • Aryl hydrocarbon receptor forms a complex with glucocorticoid receptor in cells. • Human metallothionein gene is regulated by the AHR and GR interaction. • AHR–GR complex binds to glucocorticoid response element in metallothionein gene. • We demonstrated a novel transcriptional mechanism via AHR and GR interaction.« less

AP1 Keeps Chromatin Poised for Action | Center for Cancer Research

Cancer.gov

The human genome harbors gene-encoding DNA, the blueprint for building proteins that regulate cellular function. Embedded across the genome, in non-coding regions, are DNA elements to which regulatory factors bind. The interaction of regulatory factors with DNA at these sites modifies gene expression to modulate cell activity. In cells, DNA exists in a complex with proteins called chromatin that compacts the DNA in the nucleus, strongly restricting access to DNA sequences. As a result, regulatory factors only interact with a small subset of their potential binding elements in a given cell to regulate genes. How factors recognize and select sites in chromatin across the genome is not well understood -- but several discoveries in CCR’s Laboratory of Receptor Biology and Gene Expression (LRBGE) have shed light on the mechanisms that direct factors to DNA.

ERalpha and AP-1 interact in vivo with a specific sequence of the F promoter of the human ERalpha gene in osteoblasts.

PubMed

Lambertini, Elisabetta; Tavanti, Elisa; Torreggiani, Elena; Penolazzi, Letizia; Gambari, Roberto; Piva, Roberta

2008-07-01

Estrogen-responsive genes often have an estrogen response element (ERE) positioned next to activator protein-1 (AP-1) binding sites. Considering that the interaction between ERE and AP-1 elements has been described for the modulation of bone-specific genes, we investigated the 17-beta-estradiol responsiveness and the role of these cis-elements present in the F promoter of the human estrogen receptor alpha (ERalpha) gene. The F promoter, containing the sequence analyzed here, is one of the multiple promoters of the human ERalpha gene and is the only active promoter in bone tissue. Through electrophoretic mobility shift (EMSA), chromatin immunoprecipitation (ChIP), and re-ChIP assays, we investigated the binding of ERalpha and four members of the AP-1 family (c-Jun, c-fos, Fra-2, and ATF2) to a region located approximately 800 bp upstream of the transcriptional start site of exon F of the human ERalpha gene in SaOS-2 osteoblast-like cells. Reporter gene assay experiments in combination with DNA binding assays demonstrated that F promoter activity is under the control of upstream cis-acting elements which are recognized by specific combinations of ERalpha, c-Jun, c-fos, and ATF2 homo- and heterodimers. Moreover, ChIP and re-ChIP experiments showed that these nuclear factors bind the F promoter in vivo with a simultaneous occupancy stimulated by 17-beta-estradiol. Taken together, our findings support a model in which ERalpha/AP-1 complexes modulate F promoter activity under conditions of 17-beta-estradiol stimulation. (c) 2008 Wiley-Liss, Inc.

Asymmetric binding of histone H1 stabilizes MMTV nucleosomes and the interaction of progesterone receptor with the exposed HRE.

PubMed

Vicent, Guillermo P; Meliá, María J; Beato, Miguel

2002-11-29

Packaging of mouse mammary tumor virus (MMTV) promoter sequences in nucleosomes modulates access of DNA binding proteins and influences the interaction among DNA bound transcription factors. Here we analyze the binding of histone H1 to MMTV mononucleosomes assembled with recombinant histones and study its influence on nucleosome structure and stability as well as on progesterone receptor (PR) binding to the hormone responsive elements (HREs). The MMTV nucleosomes can be separated into three main populations, two of which exhibited precise translational positioning. Histone H1 bound preferentially to the 5' distal nucleosomal DNA protecting additional 27-28 nt from digestion by micrococcal nuclease. Binding of histone H1 was unaffected by prior crosslinking of protein and DNA in nucleosomes with formaldehyde. Neither the translational nor the rotational nucleosome positioning was altered by histone H1 binding, but the nucleosomes were stabilized as judged by the kinetics of nuclease cleavage. Unexpectedly, binding of recombinant PR to the exposed distal HRE-I in nucleosomes was enhanced in the presence of histone H1, as demonstrated by band shift and footprinting experiments. This enhanced PR affinity may contribute to the reported positive effect of histone H1 on the hormonal activation of MMTV reporter genes.

Evaluation of 11C-Me-NB1 as a Potential PET Radioligand for Measuring GluN2B-Containing NMDA Receptors, Drug Occupancy, and Receptor Cross Talk.

PubMed

Krämer, Stefanie D; Betzel, Thomas; Mu, Linjing; Haider, Ahmed; Herde, Adrienne Müller; Boninsegni, Anna K; Keller, Claudia; Szermerski, Marina; Schibli, Roger; Wünsch, Bernhard; Ametamey, Simon M

2018-04-01

Clinical and preclinical research with modulators at the N -methyl-d-aspartate (NMDA) receptor GluN2B N-terminal domain (NTD) aims for the treatment of various neurologic diseases. The interpretation of the results is hampered by the lack of a suitable NMDA PET tracer for assessing the receptor occupancy of potential drugs. We have developed 11 C-Me-NB1 as a PET tracer for imaging GluN1/GluN2B-containing NMDA receptors and used it to investigate in rats the dose-dependent receptor occupancy of eliprodil, a GluN2B NTD modulator. Methods: 11 C-Me-NB1 was synthesized and characterized by in vitro displacement binding experiments with rat brain membranes, in vitro autoradiography, and blocking and displacement experiments by PET and PET kinetic modeling. Receptor occupancy by eliprodil was studied by PET with 11 C-Me-NB1. Results: 11 C-Me-NB1 was synthesized at 290 ± 90 GBq/μmol molar activity, 7.4 ± 1.9 GBq total activity at the end of synthesis ( n = 17), and more than 99% radiochemical purity. 11 C-Me-NB1 binding in rat brain was blocked in vitro and in vivo by the NTD modulators Ro-25-6981 and eliprodil. Half-maximal receptor occupancy by eliprodil occurred at 1.5 μg/kg. At 1 mg/kg of eliprodil, a dose with reported neuroprotective effects, more than 99.5% of binding sites were occupied. In vitro, 11 C-Me-NB1 binding was independent of the σ-1 receptor (Sigma1R), and the Sigma1R agonist (+)-pentazocine did not compete for high-affinity binding. In vivo, a 2.5 mg/kg dose of (+)-pentazocine abolished 11 C-Me-NB1-specific binding, indicating an indirect effect of Sigma1R on 11 C-Me-NB1 binding. Conclusion: 11 C-Me-NB1 is suitable for the in vivo imaging of NMDA GluN1/GluN2B receptors and the assessment of receptor occupancy by NTD modulators. GluN1/GluN2B NMDA receptors are fully occupied at neuroprotective doses of eliprodil. Furthermore, 11 C-Me-NB1 enables imaging of GluN1/GluN2B NMDA receptor cross talk. © 2018 by the Society of Nuclear Medicine and Molecular Imaging.

Receptor binding of somatostatin-14 and somatostatin-28 in rat brain: differential modulation by nucleotides and ions.

PubMed

Srikant, C B; Dahan, A; Craig, C

1990-02-04

The tissue-selective binding of the two principal bioactive forms of somatostatin, somatostatin-14 (SS-14) and somatostatin-28 (SS-28), their ability to modulate cAMP-dependent and -independent regulation of post-receptor events to different degrees and the documentation of specific labelling of SS receptor subtypes with SS-28 but not SS-14 in discrete regions of rat brain suggest the existence of distinct SS-14 and SS-28 binding sites. Receptor binding of SS-14 ligands has been shown to be modulated by nucleotides and ions, but the effect of these agents on SS-28 binding has not been studied. In the present study we investigated the effects of adenine and guanine nucleotides as well as monovalent and divalent cations on rat brain SS receptors quantitated with radioiodinated analogs of SS-14 ([125I-Tyr11]SS14, referred to in this paper as SS-14) and SS-28 ([Leu8, D-Trp22, 125I-Tyr25] SS-28, referred to as LTT* SS-28) in order to determine if distinct receptor sites for SS-14 and SS-28 could be distinguished on the basis of their modulation by nucleotides and ions. GTP as well as ATP exerted a dose-dependent inhibition (over a concentration range of 10(-7)-10(-3) M) of the binding of the two radioligands. The nucleotide inhibition of binding resulted in a decrease the Bmax of the SS receptors, the binding affinity remaining unaltered. GTP (10(-4) M) decreased the Bmax of LTT* SS-28 binding sites to a greater extent than ATP (145 +/- 10 and 228 +/- 16 respectively, compared to control value of 320 +/- 20 pmol mg-1). Under identical conditions GTP was less effective than ATP in reducing the number of T* SS-14 binding sites (Bmax = 227 +/- 8 and 182 +/- 15, respectively, compared to 340 +/- 15 pmol mg-1 in the absence of nucleotides). Monovalent cations inhibited the binding of both radioligands, Li+ and Na+ inhibited the binding of T* SS-14 to a greater extent than K+. The effect of divalent cations on the other hand was varied. At low concentration (2 mM) Mg2+, Ba2+, Mn2+, Ca2+ and Co2+ augmented the binding of both T* SS-14 and LTT* SS-28, while higher than 4 mM Co2+ inhibited binding of both ligands. LTT* SS-28 binding was reduced in the presence of high concentrations of Ba2+ and Mn2+ also. Interestingly Ca2+ at higher than 10 mM preferentially inhibited LTT* SS-28 binding and increased the affinity of SS-14 but not SS-28 for LTT* SS-28 binding sites.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of strychnine-sensitive glycine receptor in the intact frog retina: modulation by protein kinases.

PubMed

Salceda, Rocío; Aguirre-Ramirez, Marisela

2005-03-01

We studied 3H-glycine and 3H-strychnine specific binding to glycine receptor (GlyR) in intact isolated frog retinas. To avoid glycine binding to glycine uptake sites, experiments were performed at low ligand concentrations in a sodium-free medium. The binding of both radiolabeled ligands was saturated. Scatchard analysis of bound glycine and strychnine revealed a KD of 2.5 and 2.0 microM, respectively. Specific binding of glycine was displaced by beta-alanine, sarcosine, and strychnine. Strychnine binding was displaced 50% by glycine, and sarcosine. Properties of the strychnine-binding site in the GlyR were modified by sarcosine. Binding of both radioligands was considerably reduced by compounds that inhibit or activate adenylate cyclase and increased cAMP levels. A phorbol ester activator of PKC remarkably decreased glycine and strychnine binding. These results suggest modulation of GlyR in response to endogenous activation of protein kinases A and C, as well as protein phosphorylation modulating GlyR function in retina.

Structure-Based Rational Design of a Toll-like Receptor 4 (TLR4) Decoy Receptor with High Binding Affinity for a Target Protein

PubMed Central

Lee, Sang-Chul; Hong, Seungpyo; Park, Keunwan; Jeon, Young Ho; Kim, Dongsup; Cheong, Hae-Kap; Kim, Hak-Sung

2012-01-01

Repeat proteins are increasingly attracting much attention as alternative scaffolds to immunoglobulin antibodies due to their unique structural features. Nonetheless, engineering interaction interface and understanding molecular basis for affinity maturation of repeat proteins still remain a challenge. Here, we present a structure-based rational design of a repeat protein with high binding affinity for a target protein. As a model repeat protein, a Toll-like receptor4 (TLR4) decoy receptor composed of leucine-rich repeat (LRR) modules was used, and its interaction interface was rationally engineered to increase the binding affinity for myeloid differentiation protein 2 (MD2). Based on the complex crystal structure of the decoy receptor with MD2, we first designed single amino acid substitutions in the decoy receptor, and obtained three variants showing a binding affinity (KD) one-order of magnitude higher than the wild-type decoy receptor. The interacting modes and contributions of individual residues were elucidated by analyzing the crystal structures of the single variants. To further increase the binding affinity, single positive mutations were combined, and two double mutants were shown to have about 3000- and 565-fold higher binding affinities than the wild-type decoy receptor. Molecular dynamics simulations and energetic analysis indicate that an additive effect by two mutations occurring at nearby modules was the major contributor to the remarkable increase in the binding affinities. PMID:22363519

A2A adenosine receptor ligand binding and signalling is allosterically modulated by adenosine deaminase.

PubMed

Gracia, Eduard; Pérez-Capote, Kamil; Moreno, Estefanía; Barkešová, Jana; Mallol, Josefa; Lluís, Carme; Franco, Rafael; Cortés, Antoni; Casadó, Vicent; Canela, Enric I

2011-05-01

A2ARs (adenosine A2A receptors) are highly enriched in the striatum, which is the main motor control CNS (central nervous system) area. BRET (bioluminescence resonance energy transfer) assays showed that A2AR homomers may act as cell-surface ADA (adenosine deaminase; EC 3.5.4.4)-binding proteins. ADA binding affected the quaternary structure of A2ARs present on the cell surface. ADA binding to adenosine A2ARs increased both agonist and antagonist affinity on ligand binding to striatal membranes where these proteins are co-expressed. ADA also increased receptor-mediated ERK1/2 (extracellular-signal-regulated kinase 1/2) phosphorylation. Collectively, the results of the present study show that ADA, apart from regulating the concentration of extracellular adenosine, may behave as an allosteric modulator that markedly enhances ligand affinity and receptor function. This powerful regulation may have implications for the physiology and pharmacology of neuronal A2ARs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Xin; Chen, Hao; Shaffer, Paul L.

Ivermectin acts as a positive allosteric modulator of several Cys-loop receptors including the glutamate-gated chloride channels (GluCls), γ-aminobutyric acid receptors (GABA ARs), glycine receptors (GlyRs), and neuronal α7-nicotinic receptors (α7 nAChRs). The crystal structure of Caenorhabditis elegans GluCl complexed with ivermectin revealed the details of its ivermectin binding site. Although the electron microscopy structure of zebrafish GlyRα1 complexed with ivermectin demonstrated a similar binding orientation, detailed structural information on the ivermectin binding and pore opening for Cys-loop receptors in vertebrates has been elusive. Here we present the crystal structures of human GlyRα3 in complex with ivermectin at 2.85 and 3.08more » Å resolution. Our structures allow us to explore in detail the molecular recognition of ivermectin by GlyRs, GABA ARs, and α7 nAChRs. Comparisons with previous structures reveal how the ivermectin binding expands the ion channel pore. Our results hold promise in structure-based design of GlyR modulators for the treatment of neuropathic pain.« less

Effects of neuronal nicotinic acetylcholine receptor allosteric modulators in animal behavior studies

PubMed Central

Pandya, Anshul. A.; Yakel, Jerrel L.

2013-01-01

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated cation-conducting transmembrane channels from the cys-loop receptor superfamily. The neuronal subtypes of these receptors (e.g. the α7 and α4β2 subtypes) are involved in neurobehavioral processes such as anxiety, the central processing of pain, food intake, nicotine seeking behavior, and a number of cognitive functions like learning and memory. Neuronal nAChR dysfunction is involved in the pathophysiology of many neurological disorders, and behavioral studies in animals are useful models to assess the effects of compounds that act on these receptors. Allosteric modulators are ligands that bind to the receptors at sites other than the orthosteric site where acetylcholine, the endogenous agonist for the nAChRs, binds. While conventional ligands for the neuronal nAChRs have been studied for their behavioral effects in animals, allosteric modulators for these receptors have only recently gained attention, and research on their behavioral effects is growing rapidly. Here we will discuss the behavioral effects of allosteric modulators of the neuronal nAChRs. PMID:23732296

Zinc as Allosteric Ion Channel Modulator: Ionotropic Receptors as Metalloproteins.

PubMed

Peralta, Francisco Andrés; Huidobro-Toro, Juan Pablo

2016-07-02

Zinc is an essential metal to life. This transition metal is a structural component of many proteins and is actively involved in the catalytic activity of cell enzymes. In either case, these zinc-containing proteins are metalloproteins. However, the amino acid residues that serve as ligands for metal coordination are not necessarily the same in structural proteins compared to enzymes. While crystals of structural proteins that bind zinc reveal a higher preference for cysteine sulfhydryls rather than histidine imidazole rings, catalytic enzymes reveal the opposite, i.e., a greater preference for the histidines over cysteines for catalysis, plus the influence of carboxylic acids. Based on this paradigm, we reviewed the putative ligands of zinc in ionotropic receptors, where zinc has been described as an allosteric modulator of channel receptors. Although these receptors do not strictly qualify as metalloproteins since they do not normally bind zinc in structural domains, they do transitorily bind zinc at allosteric sites, modifying transiently the receptor channel's ion permeability. The present contribution summarizes current information showing that zinc allosteric modulation of receptor channels occurs by the preferential metal coordination to imidazole rings as well as to the sulfhydryl groups of cysteine in addition to the carboxyl group of acid residues, as with enzymes and catalysis. It is remarkable that most channels, either voltage-sensitive or transmitter-gated receptor channels, are susceptible to zinc modulation either as positive or negative regulators.

Zinc as Allosteric Ion Channel Modulator: Ionotropic Receptors as Metalloproteins

PubMed Central

Peralta, Francisco Andrés; Huidobro-Toro, Juan Pablo

2016-01-01

Zinc is an essential metal to life. This transition metal is a structural component of many proteins and is actively involved in the catalytic activity of cell enzymes. In either case, these zinc-containing proteins are metalloproteins. However, the amino acid residues that serve as ligands for metal coordination are not necessarily the same in structural proteins compared to enzymes. While crystals of structural proteins that bind zinc reveal a higher preference for cysteine sulfhydryls rather than histidine imidazole rings, catalytic enzymes reveal the opposite, i.e., a greater preference for the histidines over cysteines for catalysis, plus the influence of carboxylic acids. Based on this paradigm, we reviewed the putative ligands of zinc in ionotropic receptors, where zinc has been described as an allosteric modulator of channel receptors. Although these receptors do not strictly qualify as metalloproteins since they do not normally bind zinc in structural domains, they do transitorily bind zinc at allosteric sites, modifying transiently the receptor channel’s ion permeability. The present contribution summarizes current information showing that zinc allosteric modulation of receptor channels occurs by the preferential metal coordination to imidazole rings as well as to the sulfhydryl groups of cysteine in addition to the carboxyl group of acid residues, as with enzymes and catalysis. It is remarkable that most channels, either voltage-sensitive or transmitter-gated receptor channels, are susceptible to zinc modulation either as positive or negative regulators. PMID:27384555

Molecular Mechanism of Action for Allosteric Modulators and Agonists in CC-chemokine Receptor 5 (CCR5).

PubMed

Karlshøj, Stefanie; Amarandi, Roxana Maria; Larsen, Olav; Daugvilaite, Viktorija; Steen, Anne; Brvar, Matjaž; Pui, Aurel; Frimurer, Thomas Michael; Ulven, Trond; Rosenkilde, Mette Marie

2016-12-23

The small molecule metal ion chelators bipyridine and terpyridine complexed with Zn 2+ (ZnBip and ZnTerp) act as CCR5 agonists and strong positive allosteric modulators of CCL3 binding to CCR5, weak modulators of CCL4 binding, and competitors for CCL5 binding. Here we describe their binding site using computational modeling, binding, and functional studies on WT and mutated CCR5. The metal ion Zn 2+ is anchored to the chemokine receptor-conserved Glu-283 VII:06/7.39 Both chelators interact with aromatic residues in the transmembrane receptor domain. The additional pyridine ring of ZnTerp binds deeply in the major binding pocket and, in contrast to ZnBip, interacts directly with the Trp-248 VI:13/6.48 microswitch, contributing to its 8-fold higher potency. The impact of Trp-248 was further confirmed by ZnClTerp, a chloro-substituted version of ZnTerp that showed no inherent agonism but maintained positive allosteric modulation of CCL3 binding. Despite a similar overall binding mode of all three metal ion chelator complexes, the pyridine ring of ZnClTerp blocks the conformational switch of Trp-248 required for receptor activation, thereby explaining its lack of activity. Importantly, ZnClTerp becomes agonist to the same extent as ZnTerp upon Ala mutation of Ile-116 III:16/3.40 , a residue that constrains the Trp-248 microswitch in its inactive conformation. Binding studies with 125 I-CCL3 revealed an allosteric interface between the chemokine and the small molecule binding site, including residues Tyr-37 I:07/1.39 , Trp-86 II:20/2.60 , and Phe-109 III:09/3.33 The small molecules and CCL3 approach this interface from opposite directions, with some residues being mutually exploited. This study provides new insight into the molecular mechanism of CCR5 activation and paves the way for future allosteric drugs for chemokine receptors. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Effect of B-ring substitution pattern on binding mode of propionamide selective androgen receptor modulators.

PubMed

Bohl, Casey E; Wu, Zengru; Chen, Jiyun; Mohler, Michael L; Yang, Jun; Hwang, Dong Jin; Mustafa, Suni; Miller, Duane D; Bell, Charles E; Dalton, James T

2008-10-15

Selective androgen receptor modulators (SARMs) are essentially prostate sparing androgens, which provide therapeutic potential in osteoporosis, male hormone replacement, and muscle wasting. Herein we report crystal structures of the androgen receptor (AR) ligand-binding domain (LBD) complexed to a series of potent synthetic nonsteroidal SARMs with a substituted pendant arene referred to as the B-ring. We found that hydrophilic B-ring para-substituted analogs exhibit an additional region of hydrogen bonding not seen with steroidal compounds and that multiple halogen substitutions affect the B-ring conformation and aromatic interactions with Trp741. This information elucidates interactions important for high AR binding affinity and provides new insight for structure-based drug design.

The Structure–Function Relationships of Classical Cannabinoids: CB1/CB2 Modulation

PubMed Central

Bow, Eric W.; Rimoldi, John M.

2016-01-01

The cannabinoids are members of a deceptively simple class of terpenophenolic secondary metabolites isolated from Cannabis sativa highlighted by (−)-Δ9-tetrahydrocannabinol (THC), eliciting distinct pharmacological effects mediated largely by cannabinoid receptor (CB1 or CB2) signaling. Since the initial discovery of THC and related cannabinoids, synthetic and semisynthetic classical cannabinoid analogs have been evaluated to help define receptor binding modes and structure–CB1/CB2 functional activity relationships. This perspective will examine the classical cannabinoids, with particular emphasis on the structure–activity relationship of five regions: C3 side chain, phenolic hydroxyl, aromatic A-ring, pyran B-ring, and cyclohexenyl C-ring. Cumulative structure–activity relationship studies to date have helped define the critical structural elements required for potency and selectivity toward CB1 and CB2 and, more importantly, ushered the discovery and development of contemporary nonclassical cannabinoid modulators with enhanced physicochemical and pharmacological profiles. PMID:27398024

Intercalation of XR5944 with the estrogen response element is modulated by the tri-nucleotide spacer sequence between half-sites

PubMed Central

Sidell, Neil; Mathad, Raveendra I.; Shu, Feng-jue; Zhang, Zhenjiang; Kallen, Caleb B.; Yang, Danzhou

2011-01-01

DNA-intercalating molecules can impair DNA replication, DNA repair, and gene transcription. We previously demonstrated that XR5944, a DNA bis-intercalator, specifically blocks binding of estrogen receptor-α (ERα) to the consensus estrogen response element (ERE). The consensus ERE sequence is AGGTCAnnnTGACCT, where nnn is known as the tri-nucleotide spacer. Recent work has shown that the tri-nucleotide spacer can modulate ERα-ERE binding affinity and ligand-mediated transcriptional responses. To further understand the mechanism by which XR5944 inhibits ERα-ERE binding, we tested its ability to interact with consensus EREs with variable tri-nucleotide spacer sequences and with natural but non-consensus ERE sequences using one dimensional nuclear magnetic resonance (1D 1H NMR) titration studies. We found that the tri-nucleotide spacer sequence significantly modulates the binding of XR5944 to EREs. Of the sequences that were tested, EREs with CGG and AGG spacers showed the best binding specificity with XR5944, while those spaced with TTT demonstrated the least specific binding. The binding stoichiometry of XR5944 with EREs was 2:1, which can explain why the spacer influences the drug-DNA interaction; each XR5944 spans four nucleotides (including portions of the spacer) when intercalating with DNA. To validate our NMR results, we conducted functional studies using reporter constructs containing consensus EREs with tri-nucleotide spacers CGG, CTG, and TTT. Results of reporter assays in MCF-7 cells indicated that XR5944 was significantly more potent in inhibiting the activity of CGG- than TTT-spaced EREs, consistent with our NMR results. Taken together, these findings predict that the anti-estrogenic effects of XR5944 will depend not only on ERE half-site composition but also on the tri-nucleotide spacer sequence of EREs located in the promoters of estrogen-responsive genes. PMID:21333738

Application of GPCR Structures for Modelling of Free Fatty Acid Receptors.

PubMed

Tikhonova, Irina G

2017-01-01

Five G protein-coupled receptors (GPCRs) have been identified to be activated by free fatty acids (FFA). Among them, FFA1 (GPR40) and FFA4 (GPR120) bind long-chain fatty acids, FFA2 (GPR43) and FFA3 (GPR41) bind short-chain fatty acids and GPR84 binds medium-chain fatty acids. Free fatty acid receptors have now emerged as potential targets for the treatment of diabetes, obesity and immune diseases. The recent progress in crystallography of GPCRs has now enabled the elucidation of the structure of FFA1 and provided reliable templates for homology modelling of other FFA receptors. Analysis of the crystal structure and improved homology models, along with mutagenesis data and structure activity, highlighted an unusual arginine charge-pairing interaction in FFA1-3 for receptor modulation, distinct structural features for ligand binding to FFA1 and FFA4 and an arginine of the second extracellular loop as a possible anchoring point for FFA at GPR84. Structural data will be helpful for searching novel small-molecule modulators at the FFA receptors.

Pregnane and Xenobiotic Receptor gene expression in liver cells is modulated by Ets-1 in synchrony with transcription factors Pax5, LEF-1 and c-jun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumari, Sangeeta; Saradhi, Mallampati; Rana, Manjul

2015-01-15

Nuclear receptor PXR is predominantly expressed in liver and intestine. Expression of PXR is observed to be dysregulated in various metabolic disorders indicating its involvement in disease development. However, information available on mechanisms of PXR self-regulation is fragmentary. The present investigation identifies some of the regulatory elements responsible for its tight regulation and low cellular expression. Here, we report that the PXR-promoter is a target for some key transcription factors like PU.1/Ets-1, Pax5, LEF-1 and c-Jun. Interestingly, we observed that PXR-promoter responsiveness to Pax5, LEF-1 and c-Jun, is considerably enhanced by Ets transcription factors (PU.1 and Ets-1). Co-transfection of cellsmore » with Ets-1, LEF-1 and c-Jun increased PXR-promoter activity by 5-fold and also induced expression of endogenous human PXR. Site-directed mutagenesis and transfection studies revealed that two Ets binding sites and two of the three LEF binding sites in the PXR-promoter are functional and have a positive effect on PXR transcription. Results suggest that expression of Ets family members, in conjunction with Pax5, LEF-1 and c-Jun, lead to coordinated up-regulation of PXR gene transcription. Insights obtained on the regulation of PXR gene have relevance in offering important cues towards normal functioning as well as development of several metabolic disorders via PXR signaling. - Highlights: • The study identified cis-regulatory elements in the nuclear receptor PXR promoter. • Several trans-acting factors modulating the PXR-promoter have been identified. • PU.1/Ets-1, Pax5, LEF-1, c-Jun, LyF-VI and NF-1 act as modulators of the PXR-promoter. • Ets-1 in conjunction with LEF-1 and c-Jun exhibit 5-fold activation of the PXR-promoter. • Insights into PXR-regulation have relevance in normal and pathological conditions.« less

The pure estrogen receptor antagonist ICI 182,780 promotes a novel interaction of estrogen receptor-alpha with the 3',5'-cyclic adenosine monophosphate response element-binding protein-binding protein/p300 coactivators.

PubMed

Jaber, Basem M; Gao, Tong; Huang, Luping; Karmakar, Sudipan; Smith, Carolyn L

2006-11-01

Estrogen receptor-alpha (ERalpha) is a member of the nuclear receptor superfamily of ligand-activated transcription factors. Abundant evidence demonstrates that ERalpha agonists promote, whereas antagonists inhibit, receptor binding to coactivators. In this report we demonstrate that binding of the ICI 182,780 (ICI) pure antiestrogen to ERalpha promotes its interaction with the cAMP response element-binding protein-binding protein (CBP)/p300 but not the p160 family of coactivators, demonstrating the specificity of this interaction. Amino acid mutations within the coactivator binding surface of the ERalpha ligand-binding domain revealed that CBP binds to this region of the ICI-liganded receptor. The carboxy-terminal cysteine-histidine rich domain 3 of CBP, rather than its amino-terminal nuclear interacting domain, shown previously to mediate agonist-dependent interactions of CBP with nuclear receptors, is required for binding to ICI-liganded ERalpha. Chromatin immunoprecipitation assays revealed that ICI but not the partial agonist/antagonist 4-hydroxytamoxifen is able to recruit CBP to the pS2 promoter, and this distinguishes ICI from this class of antiestrogens. Chromatin immunoprecipitation assays for pS2 and cytochrome P450 1B1 promoter regions revealed that ICI-dependent recruitment of CBP, but not receptor, to ERalpha targets is gene specific. ICI treatment did not recruit the steroid receptor coactivator 1 to the pS2 promoter, and it failed to induce the expression of this gene. Taken together, these data indicate that recruitment of the CBP coactivator/cointegrator without steroid receptor coactivator 1 to ERalpha is insufficient to promote transcription of ERalpha target genes.

GABAB Receptor Positive Modulation Decreases Selective Molecular and Behavioral Effects of Cocaine

PubMed Central

Lhuillier, Loic; Mombereau, Cedric; Cryan, John F.; Kaupmann, Klemens

2006-01-01

Exposure to cocaine induces selective behavioral and molecular adaptations. In rodents, acute cocaine induces increased locomotor activity whereas prolonged drug exposure results in behavioral locomotor sensitization, which is thought to be a consequence of drug–induced neuroadaptive changes. Recent attention has been given to compounds activating GABAB receptors as potential anti-addictive therapies. In particular the principle of allosteric positive GABAB receptor modulators is very promising in this respect, as positive modulators lack the sedative and muscle relaxant properties of full GABAB receptor agonists such as baclofen. Here we investigated the effects of systemic application of the GABAB receptor positive modulator GS39783 in animals treated with acute and chronic cocaine administration. Both GS39783 and baclofen dose-dependently attenuated acute cocaine-induced hyperlocomotion. Furthermore, both compounds also efficiently blocked cocaine-induced Fos induction in the striatal complex. In chronic studies GS39783 induced a modest attenuation of cocaine-induced locomotor sensitization. Chronic cocaine induces the accumulation of the transcription factor ΔFosB and up regulates cAMP-response-element-binding-protein (CREB) and dopamine-and-cAMP-regulated-phosphoprotein of 32 kd (DARPP-32). GS39783 blocked the induction/activation of DARPP-32 and CREB in the nucleus accumbens and dorsal striatum and partially inhibited ΔFosB accumulation in the dorsal striatum. In summary our data provide evidence that GS39783 attenuates the acute behavioral effects of cocaine exposure in rodents and in addition prevents the induction of selective long-term adaptive changes in dopaminergic signaling pathways. Further investigation of GABAB receptor positive modulation as a novel therapeutic strategy for the treatment of cocaine dependence and possibly other drugs of abuse is therefore warranted. PMID:16710312

Sex Differences in Serotonin 1 Receptor Binding in Rat Brain

NASA Astrophysics Data System (ADS)

Fischette, Christine T.; Biegon, Anat; McEwen, Bruce S.

1983-10-01

Male and female rats exhibit sex differences in binding by serotonin 1 receptors in discrete areas of the brain, some of which have been implicated in the control of ovulation and of gonadotropin release. The sex-specific changes in binding, which occur in response to the same hormonal (estrogenic) stimulus, are due to changes in the number of binding sites. Castration alone also affects the number of binding sites in certain areas. The results lead to the conclusion that peripheral hormones modulate binding by serotonin 1 receptors. The status of the serotonin receptor system may affect the reproductive capacity of an organism and may be related to sex-linked emotional disturbances in humans.

Synthesis of (nor)tropeine (di)esters and allosteric modulation of glycine receptor binding.

PubMed

Maksay, Gábor; Nemes, Péter; Vincze, Zoltán; Bíró, Timea

2008-02-15

(Hetero)aromatic mono- and diesters of tropine and nortropine were prepared. Modulation of [3H]strychnine binding to glycine receptors of rat spinal cord was examined with a ternary allosteric model. The esters displaced [3H]strychnine binding with nano- or micromolar potencies and strong negative cooperativity. Coplanarity and distance of the ester moieties of diesters affected the binding affinity being nanomolar for isophthaloyl-bistropane and nortropeines. Nortropisetron had the highest affinity (K(A) approximately 10 nM). Two esters displayed negative cooperativity with glycine in displacement, while three esters of low-affinity and nortropisetron exerted positive cooperativity with glycine.

Crystal Structure of a Histidine Kinase Sensor Domain with Similarity to Periplasmic Binding Proteins

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheung, J.; Le-Khac, M; Hendrickson, W

2009-01-01

Histidine kinase receptors are elements of the two-component signal transduction systems commonly found in bacteria and lower eukaryotes, where they are crucial for environmental adaption through the coupling of extracellular changes to intracellular responses. The typical two-component system consists of a membrane-spanning histidine kinase sensor and a cytoplasmic response regulator. In the calssic system, extracellular signals such as small molecule ligands and ions are detected by the periplasmic sensor domain of the histidine kinase receptor, which modulates the catalytic activity of the cytoplasmic histidine kinase domain and promotes ATP-dependent autophosphorylation of a conserved histidine residue. G. sulfurreducens genomic DNA wasmore » used.« less

Probing the Allosteric Modulator Binding Site of GluR2 with Thiazide Derivatives

PubMed Central

Ptak, Christopher P.; Ahmed, Ahmed H.; Oswald, Robert E.

2009-01-01

Ionotropic glutamate receptors mediate the majority of vertebrate excitatory synaptic transmission and are therapeutic targets for cognitive enhancement and treatment of schizophrenia. The binding domains of these tetrameric receptors consist of two dimers, and the dissociation of the dimer interface of the ligand-binding domain leads to desensitization in the continued presence of agonist. Positive allosteric modulators act by strengthening the dimer interface and reducing desensitization, thereby increasing steady-state activation. Removing the desensitized state for simplified analysis of receptor activation is commonly achieved using cyclothiazide (CTZ), the most potent modulator of the benzothiadiazide class, with the flip form of the AMPA receptor subtype. IDRA-21, the first benzothiadiazide to have an effect in behavioral tests, is an important lead compound in clinical trials for cognitive enhancement as it can cross the blood-brain barrier. Intermediate structures between CTZ and IDRA-21 show reduced potency suggesting that these two compounds have different contact points associated with binding. To understand how benzothiadiazides bind to the pocket bridging the dimer interface, we generated a series of crystal structures of the GluR2 ligand-binding domain complexed with benzothiadiazide derivatives (IDRA-21, hydroflumethiazide, hydrochlorothiazide, chlorothiazide, trichlormethiazide, and althiazide) for comparison with an existing structure for cyclothiazide. The structures detail how changes in the substituents in the 3- and 7-positions of the hydrobenzothiadiazide ring shift the orientation of the drug in the binding site and, in some cases, change the stoichiometry of binding. All derivatives maintain a hydrogen bond with the Ser754 hydroxyl, affirming the partial selectivity of the benzothiadiazides for the flip form of AMPA receptors. PMID:19673491

Ligand-Dependent Activation and Deactivation of the Human Adenosine A2A Receptor

PubMed Central

Li, Jianing; Jonsson, Amanda L.; Beuming, Thijs; Shelley, John C.; Voth, Gregory A.

2013-01-01

G protein-coupled receptors (GPCRs) are membrane proteins with critical functions in cellular signal transduction, representing a primary class of drug targets. Acting by direct binding, many drugs modulate GPCR activity and influence the signaling pathways associated with numerous diseases. However, complete details of ligand-dependent GPCR activation/deactivation are difficult to obtain from experiments. Therefore, it remains unclear how ligands modulate a GPCR’s activity. To elucidate the ligand-dependent activation/deactivation mechanism of the human adenosine A2A receptor (AA2AR), a member of the class A GPCRs, we performed large-scale unbiased molecular dynamics and metadynamics simulations of the receptor embedded in a membrane. At the atomic level, we have observed distinct structural states that resemble the active and inactive states. In particular we noted key structural elements changing in a highly concerted fashion during the conformational transitions, including six conformational states of a tryptophan (Trp2466.48). Our findings agree with a previously proposed view, that during activation, this tryptophan residue undergoes a rotameric transition that may be coupled to a series of coherent conformational changes, resulting in the opening of the G protein-binding site. Further, metadynamics simulations provide quantitative evidence for this mechanism, suggesting how ligand binding shifts the equilibrium between the active and inactive states. Our analysis also proposes that a few specific residues are associated with agonism/antagonism, affinity and selectivity, and suggests that the ligand-binding pocket can be thought of as having three distinct regions, providing dynamic features for structure-based design. Additional simulations with AA2AR bound to a novel ligand are consistent with our proposed mechanism. Generally, our study provides insights into the ligand-dependent AA2AR activation/deactivation in addition to what has been found in crystal structures. These results should aid in the discovery of more effective and selective GPCR ligands. PMID:23678995

Ligand-dependent activation and deactivation of the human adenosine A(2A) receptor.

PubMed

Li, Jianing; Jonsson, Amanda L; Beuming, Thijs; Shelley, John C; Voth, Gregory A

2013-06-12

G-protein-coupled receptors (GPCRs) are membrane proteins with critical functions in cellular signal transduction, representing a primary class of drug targets. Acting by direct binding, many drugs modulate GPCR activity and influence the signaling pathways associated with numerous diseases. However, complete details of ligand-dependent GPCR activation/deactivation are difficult to obtain from experiments. Therefore, it remains unclear how ligands modulate a GPCR's activity. To elucidate the ligand-dependent activation/deactivation mechanism of the human adenosine A2A receptor (AA2AR), a member of the class A GPCRs, we performed large-scale unbiased molecular dynamics and metadynamics simulations of the receptor embedded in a membrane. At the atomic level, we have observed distinct structural states that resemble the active and inactive states. In particular, we noted key structural elements changing in a highly concerted fashion during the conformational transitions, including six conformational states of a tryptophan (Trp246(6.48)). Our findings agree with a previously proposed view that, during activation, this tryptophan residue undergoes a rotameric transition that may be coupled to a series of coherent conformational changes, resulting in the opening of the G-protein binding site. Further, metadynamics simulations provide quantitative evidence for this mechanism, suggesting how ligand binding shifts the equilibrium between the active and inactive states. Our analysis also proposes that a few specific residues are associated with agonism/antagonism, affinity, and selectivity, and suggests that the ligand-binding pocket can be thought of as having three distinct regions, providing dynamic features for structure-based design. Additional simulations with AA2AR bound to a novel ligand are consistent with our proposed mechanism. Generally, our study provides insights into the ligand-dependent AA2AR activation/deactivation in addition to what has been found in crystal structures. These results should aid in the discovery of more effective and selective GPCR ligands.

The Endocrine Disrupting Chemical Tolylfluanid Alters Adipocyte Metabolism via Glucocorticoid Receptor Activation

PubMed Central

Neel, Brian A.; Brady, Matthew J.

2013-01-01

Glucocorticoid signaling plays a critical role in regulating energy metabolism. Emerging data implicate environmental endocrine-disrupting chemicals as contributors to the obesity and diabetes epidemics. Previous studies have shown that the phenylsulfamide fungicide tolylfluanid (TF) augments glucocorticoid receptor (GR)-dependent luciferase expression in 3T3-L1 preadipocytes while modulating insulin action in primary murine and human adipocytes. Studies were performed to interrogate glucocorticoid signaling in primary adipocytes exposed to TF. TF mimicked the gene transcription profile of the murine glucocorticoid corticosterone (Cort). Cellular fractionation assays demonstrated that TF treatment promoted the activating serine phosphorylation of GR, augmenting its cytoplasmic-to-nuclear translocation as well as its enrichment at glucocorticoid response elements on the glucocorticoid-induced leucine zipper gene promoter. After acute treatment, Cort or TF promoted insulin receptor substrate-1 (IRS-1) gene and protein expression. Either treatment also enriched GR binding at an identified glucocorticoid response element in the IRS-1 gene. TF or Cort each increased insulin-stimulated lipogenesis, an effect resulting from increased lipogenic gene expression and enhanced insulin-stimulated dephosphorylation of acetyl-coenzyme A carboxylase. The augmentation of insulin-stimulated lipogenesis was mediated through a specific enhancement of Akt phosphorylation at T308. These findings support modulation of IRS-1 levels as a mechanism for glucocorticoid-mediated changes in insulin action in primary adipocytes. Albeit with less affinity than Cort, in silico analysis suggests that TF can interact with the ligand binding pocket of GR. Collectively, these studies identify TF as a structurally unique environmental glucocorticoid. Glucocorticoid signaling may thus represent a novel pathway by which environmental toxicants promote the development of metabolic diseases. PMID:23340252

Regulatory elements involved in tax-mediated transactivation of the HTLV-I LTR.

PubMed

Seeler, J S; Muchardt, C; Podar, M; Gaynor, R B

1993-10-01

HTLV-I is the etiologic agent of adult T-cell leukemia. In this study, we investigated the regulatory elements and cellular transcription factors which function in modulating HTLV-I gene expression in response to the viral transactivator protein, tax. Transfection experiments into Jurkat cells of a variety of site-directed mutants in the HTLV-1 LTR indicated that each of the three motifs A, B, and C within the 21-bp repeats, the binding sites for the Ets family of proteins, and the TATA box all influenced the degree of tax-mediated activation. Tax is also able to activate gene expression of other viral and cellular promoters. Tax activation of the IL-2 receptor and the HIV-1 LTR is mediated through NF-kappa B motifs. Interestingly, sequences in the 21-bp repeat B and C motifs contain significant homology with NF-kappa B regulatory elements. We demonstrated that an NF-kappa B binding protein, PRDII-BF1, but not the rel protein, bound to the B and C motifs in the 21-bp repeat. PRDII-BF1 was also able to stimulate activation of HTLV-I gene expression by tax. The role of the Ets proteins on modulating tax activation was also studied. Ets 1 but not Ets 2 was capable of increasing the degree of tax activation of the HTLV-I LTR. These results suggest that tax activates gene expression by either direct or indirect interaction with several cellular transcription factors that bind to the HTLV-I LTR.

The allosteric site regulates the voltage sensitivity of muscarinic receptors.

PubMed

Hoppe, Anika; Marti-Solano, Maria; Drabek, Matthäus; Bünemann, Moritz; Kolb, Peter; Rinne, Andreas

2018-01-01

Muscarinic receptors (M-Rs) for acetylcholine (ACh) belong to the class A of G protein-coupled receptors. M-Rs are activated by orthosteric agonists that bind to a specific site buried in the M-R transmembrane helix bundle. In the active conformation, receptor function can be modulated either by allosteric modulators, which bind to the extracellular receptor surface or by the membrane potential via an unknown mechanism. Here, we compared the modulation of M 1 -Rs and M 3 -Rs induced by changes in voltage to their allosteric modulation by chemical compounds. We quantified changes in receptor signaling in single HEK 293 cells with a FRET biosensor for the G q protein cycle. In the presence of ACh, M 1 -R signaling was potentiated by voltage, similarly to positive allosteric modulation by benzyl quinolone carboxylic acid. Conversely, signaling of M 3 -R was attenuated by voltage or the negative allosteric modulator gallamine. Because the orthosteric site is highly conserved among M-Rs, but allosteric sites vary, we constructed "allosteric site" M 3 /M 1 -R chimeras and analyzed their voltage dependencies. Exchanging the entire allosteric sites eliminated the voltage sensitivity of ACh responses for both receptors, but did not affect their modulation by allosteric compounds. Furthermore, a point mutation in M 3 -Rs caused functional uncoupling of the allosteric and orthosteric sites and abolished voltage dependence. Molecular dynamics simulations of the receptor variants indicated a subtype-specific crosstalk between both sites, involving the conserved tyrosine lid structure of the orthosteric site. This molecular crosstalk leads to receptor subtype-specific voltage effects. Copyright © 2017 Elsevier Inc. All rights reserved.

The Molecular Determinants of Small-Molecule Ligand Binding at P2X Receptors

PubMed Central

Pasqualetto, Gaia; Brancale, Andrea; Young, Mark T.

2018-01-01

P2X receptors are trimeric eukaryotic ATP-gated cation channels. Extracellular ATP—their physiological ligand—is released as a neurotransmitter and in conditions of cell damage such as inflammation, and substantial evidence implicates P2X receptors in diseases including neuropathic pain, cancer, and arthritis. In 2009, the first P2X crystal structure, Danio rerio P2X4 in the apo- state, was published, and this was followed in 2012 by the ATP-bound structure. These structures transformed our understanding of the conformational changes induced by ATP binding and the mechanism of ligand specificity, and enabled homology modeling of mammalian P2X receptors for ligand docking and rational design of receptor modulators. P2X receptors are attractive drug targets, and a wide array of potent, subtype-selective modulators (mostly antagonists) have been developed. In 2016, crystal structures of human P2X3 in complex with the competitive antagonists TNP-ATP and A-317491, and Ailuropoda melanoleuca P2X7 in complex with a series of allosteric antagonists were published, giving fascinating insights into the mechanism of channel antagonism. In this article we not only summarize current understanding of small-molecule modulator binding at P2X receptors, but also use this information in combination with previously published structure-function data and molecular docking experiments, to hypothesize a role for the dorsal fin loop region in differential ATP potency, and describe novel, testable binding conformations for both the semi-selective synthetic P2X7 agonist 2′-(3′)-O-(4-benzoyl)benzoyl ATP (BzATP), and the P2X4-selective positive allosteric modulator ivermectin. We find that the distal benzoyl group of BzATP lies in close proximity to Lys-127, a residue previously implicated in BzATP binding to P2X7, potentially explaining the increased potency of BzATP at rat P2X7 receptors. We also present molecular docking of ivermectin to rat P2X4 receptors, illustrating a plausible binding conformation between the first and second transmembrane domains which not only tallies with previous mutagenesis studies, but would also likely have the effect of stabilizing the open channel structure, consistent with the mode of action of this positive allosteric modulator. From our docking simulations and analysis of sequence homology we propose a series of mutations likely to confer ivermectin sensitivity to human P2X1. PMID:29456508

Selective Modulators of PPAR-γ Activity: Molecular Aspects Related to Obesity and Side-Effects

PubMed Central

Zhang, Fang; Lavan, Brian E.; Gregoire, Francine M.

2007-01-01

Peroxisome proliferator-activated receptor γ (PPAR-γ) is a key regulator of lipid metabolism and energy balance implicated in the development of insulin resistance and obesity. The identification of putative natural and synthetic ligands and activators of PPAR-γ has helped to unravel the molecular basis of its function, including molecular details regarding ligand binding, conformational changes of the receptor, and cofactor binding, leading to the emergence of the concept of selective PPAR-γ modulators (SPPARγMs). SPPARγMs bind in distinct manners to the ligand-binding pocket of PPAR-γ, leading to alternative receptor conformations, differential cofactor recruitment/displacement, differential gene expression, and ultimately differential biological responses. Based on this concept, new and improved antidiabetic agents for the treatment of diabetes are in development. This review summarizes the current knowledge on the mechanism of action and biological effects of recently characterized SPPARγMs, including metaglidasen/halofenate, PA-082, and the angiotensin receptor antagonists, recently characterized as a new class of SPPARγMs. PMID:17389769

Radioligand Recognition of Insecticide Targets.

PubMed

Casida, John E

2018-04-04

Insecticide radioligands allow the direct recognition and analysis of the targets and mechanisms of toxic action critical to effective and safe pest control. These radioligands are either the insecticides themselves or analogs that bind at the same or coupled sites. Preferred radioligands and their targets, often in both insects and mammals, are trioxabicyclooctanes for the γ-aminobutyric acid (GABA) receptor, avermectin for the glutamate receptor, imidacloprid for the nicotinic receptor, ryanodine and chlorantraniliprole for the ryanodine receptor, and rotenone or pyridaben for NADH + ubiquinone oxidoreductase. Pyrethroids and other Na + channel modulator insecticides are generally poor radioligands due to lipophilicity and high nonspecific binding. For target site validation, the structure-activity relationships competing with the radioligand in the binding assays should be the same as that for insecticidal activity or toxicity except for rapidly detoxified or proinsecticide analogs. Once the radioligand assay is validated for relevance, it will often help define target site modifications on selection of resistant pest strains, selectivity between insects and mammals, and interaction with antidotes and other chemicals at modulator sites. Binding assays also serve for receptor isolation and photoaffinity labeling to characterize the interactions involved.

Antagonism of human CC-chemokine receptor 4 can be achieved through three distinct binding sites on the receptor

PubMed Central

Slack, Robert J; Russell, Linda J; Barton, Nick P; Weston, Cathryn; Nalesso, Giovanna; Thompson, Sally-Anne; Allen, Morven; Chen, Yu Hua; Barnes, Ashley; Hodgson, Simon T; Hall, David A

2013-01-01

Chemokine receptor antagonists appear to access two distinct binding sites on different members of this receptor family. One class of CCR4 antagonists has been suggested to bind to a site accessible from the cytoplasm while a second class did not bind to this site. In this report, we demonstrate that antagonists representing a variety of structural classes bind to two distinct allosteric sites on CCR4. The effects of pairs of low-molecular weight and/or chemokine CCR4 antagonists were evaluated on CCL17- and CCL22-induced responses of human CCR4+ T cells. This provided an initial grouping of the antagonists into sets which appeared to bind to distinct binding sites. Binding studies were then performed with radioligands from each set to confirm these groupings. Some novel receptor theory was developed to allow the interpretation of the effects of the antagonist combinations. The theory indicates that, generally, the concentration-ratio of a pair of competing allosteric modulators is maximally the sum of their individual effects while that of two modulators acting at different sites is likely to be greater than their sum. The low-molecular weight antagonists could be grouped into two sets on the basis of the functional and binding experiments. The antagonistic chemokines formed a third set whose behaviour was consistent with that of simple competitive antagonists. These studies indicate that there are two allosteric regulatory sites on CCR4. PMID:25505571

Thermodynamics and structural analysis of positive allosteric modulation of the ionotropic glutamate receptor GluA2.

PubMed

Krintel, Christian; Frydenvang, Karla; Olsen, Lars; Kristensen, Maria T; de Barrios, Oriol; Naur, Peter; Francotte, Pierre; Pirotte, Bernard; Gajhede, Michael; Kastrup, Jette S

2012-01-01

Positive allosteric modulators of the ionotropic glutamate receptor-2 (GluA2) are promising compounds for the treatment of cognitive disorders, e.g. Alzheimer's disease. These modulators bind within the dimer interface of the LBD (ligand-binding domain) and stabilize the agonist-bound conformation slowing receptor desensitization and/or deactivation. In the present study, we employ isothermal titration calorimetry to determine binding affinities and thermodynamic details of binding of modulators of GluA2. A mutant of the LBD of GluA2 (LBD-L483Y-N754S) that forms a stable dimer in solution was used. The potent GluA2 modulator BPAM-97 was used as a reference compound. Evidence that BPAM-97 binds in the same pocket as the well-known GluA2 modulator cyclothiazide was obtained from X-ray structures. The LBD-L483Y-N754S:BPAM-97 complex has a Kd of 5.6 μM (ΔH=-4.9 kcal/mol, -TΔS=-2.3 kcal/mol; where 1 kcal≈4.187 kJ). BPAM-97 was used in a displacement assay to determine a Kd of 0.46 mM (ΔH=-1.2 kcal/mol, -TΔS=-3.3 kcal/mol) for the LBD-L483Y-N754S:IDRA-21 complex. The major structural factors increasing the potency of BPAM-97 over IDRA-21 are the increased van der Waals contacts to, primarily, Met496 in GluA2 imposed by the ethyl substituent of BPAM-97. These results add important information on binding affinities and thermodynamic details, and provide a new tool in the development of drugs against cognitive disorders.

Deciphering the Regulatory Logic of an Ancient, Ultraconserved Nuclear Receptor Enhancer Module

PubMed Central

Bagamasbad, Pia D.; Bonett, Ronald M.; Sachs, Laurent; Buisine, Nicolas; Raj, Samhitha; Knoedler, Joseph R.; Kyono, Yasuhiro; Ruan, Yijun; Ruan, Xiaoan

2015-01-01

Cooperative, synergistic gene regulation by nuclear hormone receptors can increase sensitivity and amplify cellular responses to hormones. We investigated thyroid hormone (TH) and glucocorticoid (GC) synergy on the Krüppel-like factor 9 (Klf9) gene, which codes for a zinc finger transcription factor involved in development and homeostasis of diverse tissues. We identified regions of the Xenopus and mouse Klf9 genes 5–6 kb upstream of the transcription start sites that supported synergistic transactivation by TH plus GC. Within these regions, we found an orthologous sequence of approximately 180 bp that is highly conserved among tetrapods, but absent in other chordates, and possesses chromatin marks characteristic of an enhancer element. The Xenopus and mouse approximately 180-bp DNA element conferred synergistic transactivation by hormones in transient transfection assays, so we designate this the Klf9 synergy module (KSM). We identified binding sites within the mouse KSM for TH receptor, GC receptor, and nuclear factor κB. TH strongly increased recruitment of liganded GC receptor and serine 5 phosphorylated (initiating) RNA polymerase II to chromatin at the KSM, suggesting a mechanism for transcriptional synergy. The KSM is transcribed to generate long noncoding RNAs, which are also synergistically induced by combined hormone treatment, and the KSM interacts with the Klf9 promoter and a far upstream region through chromosomal looping. Our findings support that the KSM plays a central role in hormone regulation of vertebrate Klf9 genes, it evolved in the tetrapod lineage, and has been maintained by strong stabilizing selection. PMID:25866873

Characterization of the novel positive allosteric modulator, LY2119620, at the muscarinic M(2) and M(4) receptors.

PubMed

Croy, Carrie H; Schober, Douglas A; Xiao, Hongling; Quets, Anne; Christopoulos, Arthur; Felder, Christian C

2014-07-01

The M(4) receptor is a compelling therapeutic target, as this receptor modulates neural circuits dysregulated in schizophrenia, and there is clinical evidence that muscarinic agonists possess both antipsychotic and procognitive efficacy. Recent efforts have shifted toward allosteric ligands to maximize receptor selectivity and manipulate endogenous cholinergic and dopaminergic signaling. In this study, we present the pharmacological characterization of LY2119620 (3-amino-5-chloro-N-cyclopropyl-4-methyl-6-[2-(4-methylpiperazin-1-yl)-2-oxoethoxy] thieno[2,3-b]pyridine-2-carboxamide), a M(2)/M(4) receptor-selective positive allosteric modulator (PAM), chemically evolved from hits identified through a M4 allosteric functional screen. Although unsuitable as a therapeutic due to M(2) receptor cross-reactivity and, thus, potential cardiovascular liability, LY2119620 surpassed previous congeners in potency and PAM activity and broadens research capabilities through its development into a radiotracer. Characterization of LY2119620 revealed evidence of probe dependence in both binding and functional assays. Guanosine 5'-[γ-(35)S]-triphosphate assays displayed differential potentiation depending on the orthosteric-allosteric pairing, with the largest cooperativity observed for oxotremorine M (Oxo-M) LY2119620. Further [(3)H]Oxo-M saturation binding, including studies with guanosine-5'-[(β,γ)-imido]triphosphate, suggests that both the orthosteric and allosteric ligands can alter the population of receptors in the active G protein-coupled state. Additionally, this work expands the characterization of the orthosteric agonist, iperoxo, at the M(4) receptor, and demonstrates that an allosteric ligand can positively modulate the binding and functional efficacy of this high efficacy ligand. Ultimately, it was the M(2) receptor pharmacology and PAM activity with iperoxo that made LY2119620 the most suitable allosteric partner for the M(2) active-state structure recently solved (Kruse et al., 2013), a structure that provides crucial insights into the mechanisms of orthosteric activation and allosteric modulation of muscarinic receptors. Copyright © 2014 by The American Society for Pharmacology and Experimental Therapeutics.

Identification of novel modulators for ionotropic glutamate receptor, iGluA2 by in-silico screening

PubMed Central

2013-01-01

Background Ionotropic glutamate receptors (iGluAs, IUPHAR nomenclature) are the major excitatory amino acid neurotransmitter receptors in the mammalian central nervous system (CNS). iGluAs are potential therapeutic drug targets for various neurological disorders including ischemia, epilepsy, Parkinson’s and Alzheimer’s diseases. The known iGluA modulators, cyclothiazide (CTZ), IDRA-21, and other benzothiadiazide derivatives (ALTZ, HCTZ, and CLTZ) bind to the ligand-binding domain of flip-form of iGluA2 at the dimer interface, thereby increasing steady-state activation by reducing desensitization. Methods To discover new modulator compounds, we performed virtual screening for the ligand binding domain (LBD) of iGluA2 against NCI Diversity Set III library containing 1597 compounds, and subsequently performed binding-energy analysis for selected compounds. The crystal structure of rat iGluA2 S1S2J (PDB ID: 3IJO) was used for docking studies. Results and conclusion From this study, we obtained four compounds: (1) 10-2(methoxyethyl)-3-phenylbenzo[g]pteridine-2,4-dione, (2) 2-benzo[e]benzotriazol-2-yl-aniline, (3) 9-nitro-6H-indolo-(2,3,-b)quinoxaline, and (4) 1-hydroxy-n-(3-nitrophenyl)-2-napthamide. The binding mode of these four compounds is very similar to that of abovementioned established modulators: two molecules of each compound independently bind to the protein symmetrically at the dimer interface; occupy the subsites B, C, B’ and C’; potentially interact with Ser518 and Ser775. Binding energy analysis shows that all the four hits are comparable to the drug molecule, CTZ, and hence, we propose that the discovered hits may be potential molecules to develop new chemical libraries for modulating the flip form of iGluA2 function. PMID:23855825

Identification of novel modulators for ionotropic glutamate receptor, iGluA2 by in-silico screening.

PubMed

Padmanabhan, Balasundaram

2013-07-15

Ionotropic glutamate receptors (iGluAs, IUPHAR nomenclature) are the major excitatory amino acid neurotransmitter receptors in the mammalian central nervous system (CNS). iGluAs are potential therapeutic drug targets for various neurological disorders including ischemia, epilepsy, Parkinson's and Alzheimer's diseases. The known iGluA modulators, cyclothiazide (CTZ), IDRA-21, and other benzothiadiazide derivatives (ALTZ, HCTZ, and CLTZ) bind to the ligand-binding domain of flip-form of iGluA2 at the dimer interface, thereby increasing steady-state activation by reducing desensitization. To discover new modulator compounds, we performed virtual screening for the ligand binding domain (LBD) of iGluA2 against NCI Diversity Set III library containing 1597 compounds, and subsequently performed binding-energy analysis for selected compounds. The crystal structure of rat iGluA2 S1S2J (PDB ID: 3IJO) was used for docking studies. From this study, we obtained four compounds: (1) 10-2(methoxyethyl)-3-phenylbenzo[g]pteridine-2,4-dione, (2) 2-benzo[e]benzotriazol-2-yl-aniline, (3) 9-nitro-6H-indolo-(2,3,-b)quinoxaline, and (4) 1-hydroxy-n-(3-nitrophenyl)-2-napthamide. The binding mode of these four compounds is very similar to that of abovementioned established modulators: two molecules of each compound independently bind to the protein symmetrically at the dimer interface; occupy the subsites B, C, B' and C'; potentially interact with Ser518 and Ser775. Binding energy analysis shows that all the four hits are comparable to the drug molecule, CTZ, and hence, we propose that the discovered hits may be potential molecules to develop new chemical libraries for modulating the flip form of iGluA2 function.

Modulation of the NMDA receptor by polyamines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, K.; Romano, C.; Dichter, M.A.

1991-01-01

Results of recent biochemical and electrophysiological studies have suggested that a recognition site for polyamines exists as part of the NMDA receptor complex. The endogenous polyamines spermine and spermidine increase the binding of open-channel blockers and increase NMDA-elicited currents in cultured neutrons. These polyamines have been termed agonists at the polyamine recognition site. Studies of the effects of natural and synthetic polyamines on the binding of ({sup 3}H)MK-801 and on NMDA-elicited currents in cultured neurons have led to the identification of compounds classified as partial agonists, antagonists, and inverse agonists at the polyamine recognition site. Polyamines have also been foundmore » to affect the binding of ligands to the recognition sites for glutamate and glycine. However, these effects may be mediated at a site distinct from that at which polyamines act to modulate the binding of open-channel blockers. Endogenous polyamines may modulate excitatory synaptic transmission by acting at the polyamine recognition site of the NMDA receptor. This site could represent a novel therapeutic target for the treatment of ischemia-induced neurotoxicity, epilepsy, and neurodegenerative diseases.« less

Method for detecting binding events using micro-X-ray fluorescence spectrometry

DOEpatents

Warner, Benjamin P.; Havrilla, George J.; Mann, Grace

2010-12-28

Method for detecting binding events using micro-X-ray fluorescence spectrometry. Receptors are exposed to at least one potential binder and arrayed on a substrate support. Each member of the array is exposed to X-ray radiation. The magnitude of a detectable X-ray fluorescence signal for at least one element can be used to determine whether a binding event between a binder and a receptor has occurred, and can provide information related to the extent of binding between the binder and receptor.

Involvement of neuron-derived orphan receptor-1 (NOR-1) in LDL-induced mitogenic stimulus in vascular smooth muscle cells: role of CREB.

PubMed

Rius, Jordi; Martínez-González, José; Crespo, Javier; Badimon, Lina

2004-04-01

Low density lipoproteins (LDLs) modulate the expression of key genes involved in atherogenesis. Recently, we have shown that the transcription factor neuron-derived orphan receptor-1 (NOR-1) is involved in vascular smooth muscle cell (VSMC) proliferation. Our aim was to analyze whether NOR-1 is involved in LDL-induced mitogenic effects in VSMC. LDL induced NOR-1 expression in a time- and dose-dependent manner. Antisense oligonucleotides against NOR-1 inhibit DNA synthesis induced by LDL in VSMCs as efficiently as antisense against the protooncogene c-fos. The upregulation of NOR-1 mRNA levels by LDL involves pertusis-sensitive G protein-coupled receptors, Ca2+ mobilization, protein kinases A (PKA) and C (PKC) activation, and mitogen-activated protein kinase pathways (MAPK) (p44/p42 and p38). LDL promotes cAMP response element binding protein (CREB) activation (phosphorylation in Ser133). In transfection assays a dominant-negative of CREB inhibits NOR-1 promoter activity, while mutation of specific (cAMP response element) CRE sites in the NOR-1 promoter abolishes LDL-induced NOR-1 promoter activity. In VSMCs, LDL-induced mitogenesis involves NOR-1 upregulation through a CREB-dependent mechanism. CREB could play a role in the modulation by LDL of key genes (containing CRE sites) involved in atherogenesis.

Melatonin membrane receptors in peripheral tissues: Distribution and functions

PubMed Central

Slominski, Radomir M.; Reiter, Russel J.; Schlabritz-Loutsevitch, Natalia; Ostrom, Rennolds S.; Slominski, Andrzej T.

2012-01-01

Many of melatonin’s actions are mediated through interaction with the G-protein coupled membrane bound melatonin receptors type 1 and type 2 (MT1 and MT2, respectively) or, indirectly with nuclear orphan receptors from the RORα/RZR family. Melatonin also binds to the quinone reductase II enzyme, previously defined the MT3 receptor. Melatonin receptors are widely distributed in the body; herein we summarize their expression and actions in non-neural tissues. Several controversies still exist regarding, for example, whether melatonin binds the RORα/RZR family. Studies of the peripheral distribution of melatonin receptors are important since they are attractive targets for immunomodulation, regulation of endocrine, reproductive and cardiovascular functions, modulation of skin pigmentation, hair growth, cancerogenesis, and aging. Melatonin receptor agonists and antagonists have an exciting future since they could define multiple mechanisms by which melatonin modulates the complexity of such a wide variety of physiological and pathological processes. PMID:22245784

Evaluation of transcriptional activity of the oestrogen receptor with sodium iodide symporter as an imaging reporter gene.

PubMed

Kang, Joo Hyun; Chung, June-Key; Lee, Yong Jin; Kim, Kwang Il; Jeong, Jae Min; Lee, Dong Soo; Lee, Myung Chul

2006-10-01

Oestrogen receptors are ligand-dependent transcription factors whose activity is modulated either by oestrogens or by an alternative signalling pathway. Oestrogen receptors interact via a specific DNA-binding domain, the oestrogen responsive element (ERE), in the promoter region of sensitive genes. This binding leads to an initiation of gene expression and hormonal effects. To determine the transcriptional activity of the oestrogen receptor, we developed a molecular imaging system using sodium iodide symporter (NIS) as a reporter gene. The NIS reporter gene was placed under the control of an artificial ERE derived from pERE-TA-SEAP and named as pERE-NIS. pERE-NIS was transferred to MCF-7, human breast cancer cells, which highly expressed oestrogen receptor-alpha with lipofectamine. Stably expressing cells were generated by selection with G418 for 14 days. After treatment of 17beta-oestradiol and tamoxifen with serial doses, the (125)I uptake was measured for the determination of NIS expression. The inhibition of NIS activity was performed with 50 micromol x l(-1) potassium perchlorate. The MCF7/pERE-NIS treated with 17beta-oestradiol accumulated (125)I up to 70-80% higher than did non-treated cells. NIS expression was increased according to increasing doses of 17beta-oestradiol. MCF7/pERE-NIS treated with tamoxifen also accumulated (125)I up to 50% higher than did non-treated cells. Potassium perchlorate completely inhibited (125)I uptake. When MDA-MB231 cells, the oestrogen receptor-negative breast cancer cells, were transfected with pERE-NIS, (125)I uptake of MDA-MB-231/pERE-NIS did not increase. This pERE-NIS reporter system is sufficiently sensitive for monitoring transcriptional activity of the oestrogen receptor. Therefore, cis-enhancer reporter systems with ERE will be applicable to the development of a novel selective oestrogen receptor modulator with low toxicity and high efficacy.

Structural and Thermodynamic Consequences of the Replacement of Zinc with Environmental Metals on ERα-DNA Interactions

PubMed Central

Deegan, Brian J.; Bona, Anna M.; Bhat, Vikas; Mikles, David C.; McDonald, Caleb B.; Seldeen, Kenneth L.; Farooq, Amjad

2011-01-01

Estrogen receptor α (ERα) acts as a transcription factor by virtue of the ability of its DNA-binding (DB) domain, comprised of a tandem pair of zinc fingers, to recognize the estrogen response element (ERE) within the promoters of target genes. Herein, using an array of biophysical methods, we probe structural consequences of the replacement of zinc within the DB domain of ERα with various environmental metals and their effects on the thermodynamics of binding to DNA. Our data reveal that while the DB domain reconstituted with divalent ions of zinc, cadmium, mercury and cobalt binds to DNA with affinities in the nanomolar range, divalent ions of barium, copper, iron, lead, manganese, nickel and tin are unable to regenerate DB domain with DNA-binding potential though they can compete with zinc for coordinating the cysteine ligands within the zinc fingers. We also show that the metal-free DB domain is a homodimer in solution and that the binding of various metals only results in subtle secondary and tertiary structural changes, implying that metal-coordination may only be essential for DNA-binding. Collectively, our findings provide mechanistic insights into how environmental metals may modulate the physiological function of a key nuclear receptor involved in mediating a plethora of cellular functions central to human health and disease. PMID:22038807

Calcitonin and Amylin Receptor Peptide Interaction Mechanisms: INSIGHTS INTO PEPTIDE-BINDING MODES AND ALLOSTERIC MODULATION OF THE CALCITONIN RECEPTOR BY RECEPTOR ACTIVITY-MODIFYING PROTEINS.

PubMed

Lee, Sang-Min; Hay, Debbie L; Pioszak, Augen A

2016-04-15

Receptor activity-modifying proteins (RAMP1-3) determine the selectivity of the class B G protein-coupled calcitonin receptor (CTR) and the CTR-like receptor (CLR) for calcitonin (CT), amylin (Amy), calcitonin gene-related peptide (CGRP), and adrenomedullin (AM) peptides. RAMP1/2 alter CLR selectivity for CGRP/AM in part by RAMP1 Trp-84 or RAMP2 Glu-101 contacting the distinct CGRP/AM C-terminal residues. It is unclear whether RAMPs use a similar mechanism to modulate CTR affinity for CT and Amy, analogs of which are therapeutics for bone disorders and diabetes, respectively. Here, we reproduced the peptide selectivity of intact CTR, AMY1 (CTR·RAMP1), and AMY2 (CTR·RAMP2) receptors using purified CTR extracellular domain (ECD) and tethered RAMP1- and RAMP2-CTR ECD fusion proteins and antagonist peptides. All three proteins bound salmon calcitonin (sCT). Tethering RAMPs to CTR enhanced binding of rAmy, CGRP, and the AMY antagonist AC413. Peptide alanine-scanning mutagenesis and modeling of receptor-bound sCT and AC413 supported a shared non-helical CGRP-like conformation for their TN(T/V)G motif prior to the C terminus. After this motif, the peptides diverged; the sCT C-terminal Pro was crucial for receptor binding, whereas the AC413/rAmy C-terminal Tyr had little or no influence on binding. Accordingly, mutant RAMP1 W84A- and RAMP2 E101A-CTR ECD retained AC413/rAmy binding. ECD binding and cell-based signaling assays with antagonist sCT/AC413/rAmy variants with C-terminal residue swaps indicated that the C-terminal sCT/rAmy residue identity affects affinity more than selectivity. rAmy(8-37) Y37P exhibited enhanced antagonism of AMY1 while retaining selectivity. These results reveal unexpected differences in how RAMPs determine CTR and CLR peptide selectivity and support the hypothesis that RAMPs allosterically modulate CTR peptide affinity. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Allosteric Modulation of Metabotropic Glutamate Receptors

PubMed Central

Sheffler, Douglas J.; Gregory, Karen J.; Rook, Jerri M.; Conn, P. Jeffrey

2013-01-01

The development of receptor subtype-selective ligands by targeting allosteric sites of G protein-coupled receptors (GPCRs) has proven highly successful in recent years. One GPCR family that has greatly benefited from this approach is the metabotropic glutamate receptors (mGlus). These family C GPCRs participate in the neuromodulatory actions of glutamate throughout the CNS, where they play a number of key roles in regulating synaptic transmission and neuronal excitability. A large number of mGlu subtype-selective allosteric modulators have been identified, the majority of which are thought to bind within the transmembrane regions of the receptor. These modulators can either enhance or inhibit mGlu functional responses and, together with mGlu knockout mice, have furthered the establishment of the physiologic roles of many mGlu subtypes. Numerous pharmacological and receptor mutagenesis studies have been aimed at providing a greater mechanistic understanding of the interaction of mGlu allosteric modulators with the receptor, which have revealed evidence for common allosteric binding sites across multiple mGlu subtypes and the presence for multiple allosteric sites within a single mGlu subtype. Recent data have also revealed that mGlu allosteric modulators can display functional selectivity toward particular signal transduction cascades downstream of an individual mGlu subtype. Studies continue to validate the therapeutic utility of mGlu allosteric modulators as a potential therapeutic approach for a number of disorders including anxiety, schizophrenia, Parkinson’s disease, and Fragile X syndrome. PMID:21907906

[On the role of selective silencer Freud-1 in the regulation of the brain 5-HT(1A) receptor gene expression].

PubMed

Naumenko, V S; Osipova, D V; Tsybko, A S

2010-01-01

Selective 5-HT(1A) receptor silencer (Freud-1) is known to be one of the main factors for transcriptional regulation of brain serotonin 5-HT(1A) receptor. However, there is a lack of data on implication of Freud-1 in the mechanisms underlying genetically determined and experimentally altered 5-HT(1A) receptor system state in vivo. In the present study we have found a difference in the 5-HT(1A) gene expression in the midbrain of AKR and CBA inbred mouse strains. At the same time no distinction in Freud-1 expression was observed. We have revealed 90.3% of homology between mouse and rat 5-HT(1A) receptor DRE-element, whereas there was no difference in DRE-element sequence between AKR and CBA mice. This indicates the absence of differences in Freud-1 binding site in these mouse strains. In the model of 5-HT(1A) receptor desensitization produced by chronic 5-HT(1A) receptor agonist administration, a significant reduction of 5-HT(1A) receptor gene expression together with considerable increase of Freud-1 expression were found. These data allow us to conclude that the selective silencer of 5-HT(1A) receptor, Freud-1, is involved in the compensatory mechanisms that modulate the functional state of brain serotonin system, although it is not the only factor for 5-HT(1A) receptor transcriptional regulation.

β1-adrenergic receptors activate two distinct signaling pathways in striatal neurons

PubMed Central

Meitzen, John; Luoma, Jessie I.; Stern, Christopher M.; Mermelstein, Paul G.

2010-01-01

Monoamine action in the dorsal striatum and nucleus accumbens plays essential roles in striatal physiology. Although research often focuses on dopamine and its receptors, norepinephrine and adrenergic receptors are also crucial in regulating striatal function. While noradrenergic neurotransmission has been identified in the striatum, little is known regarding the signaling pathways activated by β-adrenergic receptors in this brain region. Using cultured striatal neurons, we characterized a novel signaling pathway by which activation of β1-adrenergic receptors leads to the rapid phosphorylation of cAMP Response Element Binding Protein (CREB), a transcription-factor implicated as a molecular switch underlying long-term changes in brain function. Norepinephrine-mediated CREB phosphorylation requires β1-adrenergic receptor stimulation of a receptor tyrosine kinase, ultimately leading to the activation of a Ras/Raf/MEK/MAPK/MSK signaling pathway. Activation of β1-adrenergic receptors also induces CRE-dependent transcription and increased c-fos expression. In addition, stimulation of β1-adrenergic receptors produces cAMP production, but surprisingly, β1-adrenergic receptor activation of adenylyl cyclase was not functionally linked to rapid CREB phosphorylation. These findings demonstrate that activation of β1-adrenergic receptors on striatal neurons can stimulate two distinct signaling pathways. These adrenergic actions can produce long-term changes in gene expression, as well as rapidly modulate cellular physiology. By elucidating the mechanisms by which norepinephrine and β1-adrenergic receptor activation affects striatal physiology, we provide the means to more fully understand the role of monoamines in modulating striatal function, specifically how norepinephrine and β1-adrenergic receptors may affect striatal physiology. PMID:21143600

Small-Molecule “BRCA1-Mimetics” Are Antagonists of Estrogen Receptor-α

PubMed Central

Ma, Yongxian; Tomita, York; Preet, Anju; Clarke, Robert; Englund, Erikah; Grindrod, Scott; Nathan, Shyam; De Oliveira, Eliseu; Brown, Milton L.

2014-01-01

Context: Resistance to conventional antiestrogens is a major cause of treatment failure and, ultimately, death in breast cancer. Objective: The objective of the study was to identify small-molecule estrogen receptor (ER)-α antagonists that work differently from tamoxifen and other selective estrogen receptor modulators. Design: Based on in silico screening of a pharmacophore database using a computed model of the BRCA1-ER-α complex (with ER-α liganded to 17β-estradiol), we identified a candidate group of small-molecule compounds predicted to bind to a BRCA1-binding interface separate from the ligand-binding pocket and the coactivator binding site of ER-α. Among 40 candidate compounds, six inhibited estradiol-stimulated ER-α activity by at least 50% in breast carcinoma cells, with IC50 values ranging between 3 and 50 μM. These ER-α inhibitory compounds were further studied by molecular and cell biological techniques. Results: The compounds strongly inhibited ER-α activity at concentrations that yielded little or no nonspecific toxicity, but they produced only a modest inhibition of progesterone receptor activity. Importantly, the compounds blocked proliferation and inhibited ER-α activity about equally well in antiestrogen-sensitive and antiestrogen-resistant breast cancer cells. Representative compounds disrupted the interaction of BRCA1 and ER-α in the cultured cells and blocked the interaction of ER-α with the estrogen response element. However, the compounds had no effect on the total cellular ER-α levels. Conclusions: These findings suggest that we have identified a new class of ER-α antagonists that work differently from conventional antiestrogens (eg, tamoxifen and fulvestrant). PMID:25264941

Modulation of the cytosolic androgen receptor in striated muscle by sex steroids

NASA Technical Reports Server (NTRS)

Rance, N. E.; Max, S. E.

1982-01-01

The influence of orchiectomy (GDX) and steroid administration on the level of the cytosolic androgen receptor in the rat levator ani muscle and in rat skeletal muscles (tibialis anterior and extensor digitorum longus) was studied. Androgen receptor binding to muscle cytosol was measured using H-3 methyltrienolone (R1881) as ligand, 100 fold molar excess unlabeled R1881 to assess nonspecific binding, and 500 fold molar excess of triamcinolone acetonide to prevent binding to glucocorticoid and progestin receptors. Results demonstrate that modification of the levels of sex steroids can alter the content of androgen receptors of rat striated muscle. Data suggest that: (1) cytosolic androgen receptor levels increase after orchiectomy in both levator ani muscle and skeletal muscle; (2) the acute increase in receptor levels is blocked by an inhibitor of protein synthesis; and (3) administration of estradiol-17 beta to castrated animals increases receptor binding in levator ani muscle but not in skeletal muscle.

Molecular mechanism of the sweet taste enhancers.

PubMed

Zhang, Feng; Klebansky, Boris; Fine, Richard M; Liu, Haitian; Xu, Hong; Servant, Guy; Zoller, Mark; Tachdjian, Catherine; Li, Xiaodong

2010-03-09

Positive allosteric modulators of the human sweet taste receptor have been developed as a new way of reducing dietary sugar intake. Besides their potential health benefit, the sweet taste enhancers are also valuable tool molecules to study the general mechanism of positive allosteric modulations of T1R taste receptors. Using chimeric receptors, mutagenesis, and molecular modeling, we reveal how these sweet enhancers work at the molecular level. Our data argue that the sweet enhancers follow a similar mechanism as the natural umami taste enhancer molecules. Whereas the sweeteners bind to the hinge region and induce the closure of the Venus flytrap domain of T1R2, the enhancers bind close to the opening and further stabilize the closed and active conformation of the receptor.

Structure and dynamics of AMPA receptor GluA2 in resting, pre-open and desensitized states

PubMed Central

Dürr, Katharina L.; Chen, Lei; Stein, Richard A.; De Zorzi, Rita; MihaelaFolea, I.; Walz, Thomas; Mchaourab, Hassane S.; Gouaux, Eric

2014-01-01

Summary Ionotropic glutamate receptors (iGluRs) mediate the majority of fast excitatory signaling in the nervous system. Despite the profound importance of iGluRs in the nervous system, little is known about the structures and dynamics of intact receptors in distinct functional states. Here we elucidate the structures of the intact GluA2 AMPA receptor in an apo resting/closed state, in an activated/pre-open state bound with the partial agonists and a positive allosteric modulator and in a desensitized/closed state in complex with FW alone. To probe the conformational properties of these states, we carried out double electron-electron resonance experiments on cysteine mutants and cryo-electron microscopy studies. We show how agonist binding modulates the conformation of the ligand binding domain 'layer' of the intact receptors and how, upon desensitization, the receptor undergoes large conformational rearrangements of amino-terminal and ligand-binding domains. We define mechanistic principles by which to understand antagonism, activation and desensitization in AMPA iGluRs. PMID:25109876

Modulation of ionotropic glutamate receptor function by vertebrate galectins.

PubMed

Copits, Bryan A; Vernon, Claire G; Sakai, Ryuichi; Swanson, Geoffrey T

2014-05-15

AMPA and kainate receptors are glutamate-gated ion channels whose function is known to be altered by a variety of plant oligosaccharide-binding proteins, or lectins, but the physiological relevance of this activity has been uncertain because no lectins with analogous allosteric modulatory effects have been identified in animals. We report here that members of the prototype galectin family, which are β-galactoside-binding lectins, exhibit subunit-specific allosteric modulation of desensitization of recombinant homomeric and heteromeric AMPA and kainate receptors. Galectin modulation of GluK2 kainate receptors was dependent upon complex oligosaccharide processing of N-glycosylation sites in the amino-terminal domain and downstream linker region. The sensitivity of GluA4 AMPA receptors to human galectin-1 could be enhanced by supplementation of culture media with uridine and N-acetylglucosamine (GlcNAc), precursors for the hexosamine pathway that supplies UDP-GlcNAc for synthesis of complex oligosaccharides. Neuronal kainate receptors in dorsal root ganglia were sensitive to galectin modulation, whereas AMPA receptors in cultured hippocampal neurons were insensitive, which could be a reflection of differential N-glycan processing or receptor subunit selectivity. Because glycan content of integral proteins can be modified dynamically, we postulate that physiological or pathological conditions in the CNS could arise in which galectins alter excitatory neurotransmission or neuronal excitability through their actions on AMPA or kainate receptors. © 2014 The Authors. The Journal of Physiology © 2014 The Physiological Society.

Modulation of ionotropic glutamate receptor function by vertebrate galectins

PubMed Central

Copits, Bryan A; Vernon, Claire G; Sakai, Ryuichi; Swanson, Geoffrey T

2014-01-01

AMPA and kainate receptors are glutamate-gated ion channels whose function is known to be altered by a variety of plant oligosaccharide-binding proteins, or lectins, but the physiological relevance of this activity has been uncertain because no lectins with analogous allosteric modulatory effects have been identified in animals. We report here that members of the prototype galectin family, which are β-galactoside-binding lectins, exhibit subunit-specific allosteric modulation of desensitization of recombinant homomeric and heteromeric AMPA and kainate receptors. Galectin modulation of GluK2 kainate receptors was dependent upon complex oligosaccharide processing of N-glycosylation sites in the amino-terminal domain and downstream linker region. The sensitivity of GluA4 AMPA receptors to human galectin-1 could be enhanced by supplementation of culture media with uridine and N-acetylglucosamine (GlcNAc), precursors for the hexosamine pathway that supplies UDP-GlcNAc for synthesis of complex oligosaccharides. Neuronal kainate receptors in dorsal root ganglia were sensitive to galectin modulation, whereas AMPA receptors in cultured hippocampal neurons were insensitive, which could be a reflection of differential N-glycan processing or receptor subunit selectivity. Because glycan content of integral proteins can be modified dynamically, we postulate that physiological or pathological conditions in the CNS could arise in which galectins alter excitatory neurotransmission or neuronal excitability through their actions on AMPA or kainate receptors. PMID:24614744

The first three domains of the insulin receptor differ structurally from the insulin-like growth factor 1 receptor in the regions governing ligand specificity

PubMed Central

Lou, Meizhen; Garrett, Thomas P. J.; McKern, Neil M.; Hoyne, Peter A.; Epa, V. Chandana; Bentley, John D.; Lovrecz, George O.; Cosgrove, Leah J.; Frenkel, Maurice J.; Ward, Colin W.

2006-01-01

The insulin receptor (IR) and the type-1 insulin-like growth factor receptor (IGF1R) are homologous multidomain proteins that bind insulin and IGF with differing specificity. Here we report the crystal structure of the first three domains (L1–CR–L2) of human IR at 2.3 Å resolution and compare it with the previously determined structure of the corresponding fragment of IGF1R. The most important differences seen between the two receptors are in the two regions governing ligand specificity. The first is at the corner of the ligand-binding surface of the L1 domain, where the side chain of F39 in IR forms part of the ligand binding surface involving the second (central) β-sheet. This is very different to the location of its counterpart in IGF1R, S35, which is not involved in ligand binding. The second major difference is in the sixth module of the CR domain, where IR contains a larger loop that protrudes further into the ligand-binding pocket. This module, which governs IGF1-binding specificity, shows negligible sequence identity, significantly more α-helix, an additional disulfide bond, and opposite electrostatic potential compared to that of the IGF1R. PMID:16894147

Detailed Analysis of the Binding Mode of Vanilloids to Transient Receptor Potential Vanilloid Type I (TRPV1) by a Mutational and Computational Study

PubMed Central

Mori, Yoshikazu; Ogawa, Kazuo; Warabi, Eiji; Yamamoto, Masahiro; Hirokawa, Takatsugu

2016-01-01

Transient receptor potential vanilloid type 1 (TRPV1) is a non-selective cation channel and a multimodal sensor protein. Since the precise structure of TRPV1 was obtained by electron cryo-microscopy, the binding mode of representative agonists such as capsaicin and resiniferatoxin (RTX) has been extensively characterized; however, detailed information on the binding mode of other vanilloids remains lacking. In this study, mutational analysis of human TRPV1 was performed, and four agonists (capsaicin, RTX, [6]-shogaol and [6]-gingerol) were used to identify amino acid residues involved in ligand binding and/or modulation of proton sensitivity. The detailed binding mode of each ligand was then simulated by computational analysis. As a result, three amino acids (L518, F591 and L670) were newly identified as being involved in ligand binding and/or modulation of proton sensitivity. In addition, in silico docking simulation and a subsequent mutational study suggested that [6]-gingerol might bind to and activate TRPV1 in a unique manner. These results provide novel insights into the binding mode of various vanilloids to the channel and will be helpful in developing a TRPV1 modulator. PMID:27606946

Differential Potency of 2,6-Dimethylcyclohexanol Isomers for Positive Modulation of GABAA Receptor Currents.

PubMed

Chowdhury, Luvana; Croft, Celine J; Goel, Shikha; Zaman, Naina; Tai, Angela C-S; Walch, Erin M; Smith, Kelly; Page, Alexandra; Shea, Kevin M; Hall, C Dennis; Jishkariani, D; Pillai, Girinath G; Hall, Adam C

2016-06-01

GABAA receptors meet all of the pharmacological requirements necessary to be considered important targets for the action of general anesthetic agents in the mammalian brain. In the following patch-clamp study, the relative modulatory effects of 2,6-dimethylcyclohexanol diastereomers were investigated on human GABAA (α1β3γ2s) receptor currents stably expressed in human embryonic kidney cells. Cis,cis-, trans,trans-, and cis,trans-isomers were isolated from commercially available 2,6-dimethylcyclohexanol and were tested for positive modulation of submaximal GABA responses. For example, the addition of 30 μM cis,cis-isomer resulted in an approximately 2- to 3-fold enhancement of the EC20 GABA current. Coapplications of 30 μM 2,6-dimethylcyclohexanol isomers produced a range of positive enhancements of control GABA responses with a rank order for positive modulation: cis,cis > trans,trans ≥ mixture of isomers > > cis,trans-isomer. In molecular modeling studies, the three cyclohexanol isomers bound with the highest binding energies to a pocket within transmembrane helices M1 and M2 of the β3 subunit through hydrogen-bonding interactions with a glutamine at the 224 position and a tyrosine at the 220 position. The energies for binding to and hydrogen-bond lengths within this pocket corresponded with the relative potencies of the agents for positive modulation of GABAA receptor currents (cis,cis > trans,trans > cis,trans-2,6-dimethylcyclohexanol). In conclusion, the stereochemical configuration within the dimethylcyclohexanols is an important molecular feature in conferring positive modulation of GABAA receptor activity and for binding to the receptor, a consideration that needs to be taken into account when designing novel anesthetics with enhanced therapeutic indices. Copyright © 2016 by The American Society for Pharmacology and Experimental Therapeutics.

Benzodiazepines modulate the A2 adenosine binding sites on 108CC15 neuroblastoma X glioma hybrid cells.

PubMed Central

Snell, C. R.; Snell, P. H.

1984-01-01

We have demonstrated high affinity diazepam binding sites of the Ro5-4864 benzodiazepine receptor subtype on 108CC15 neuroblastoma X glioma hybrid cells. These cells were previously shown to have purinoceptors of the A2 adenosine subtype and we have now found that [3H]-adenosine can be displaced from this binding site by the benzodiazepines and related compounds that can also bind to the Ro5-4864 site. Diazepam was found to have no intrinsic activity at the A2-receptor as measured by the stimulation of adenosine 3':5'-cyclic monophosphate (cyclic AMP) production in this cell line. At concentrations sufficient to compete for the A2-receptor, diazepam was shown to facilitate, by approximately 2 fold, the stimulation of cyclic AMP by adenosine. These effects are not due to inhibition of adenosine uptake or phosphodiesterase activity, but are probably a consequence of modulation of the coupling of the A2-receptor to cyclic AMP production in this hybrid cell line. PMID:6150742

Synergistic Interactions between Chemokine Receptor Elements in Recognition of Interleukin-8 by Soluble Receptor Mimics†

PubMed Central

Barter, Emily F.; Stone, Martin J.

2012-01-01

Interleukin-8 (IL-8 or CXCL8), the archetypal member of the CXC chemokine subfamily, stimulates neutrophil chemotaxis by activation of the receptors CXCR1/IL8RA and CXCR2/IL8RB. Previous mutational studies have implicated both the N-terminal and third extracellular loop (E3) regions of these receptors in binding to IL-8. To investigate the interactions of these receptor elements with IL-8, we have constructed soluble proteins in which the N-terminal and E3 elements of either CXCR1 or CXCR2 are juxtaposed on a soluble scaffold protein; these are referred to as CROSS-NX1E3X1 and CROSS-NX2E3X2, respectively. Isothermal titration calorimetry (ITC) and NMR spectroscopy were used to compare the IL-8 binding properties of the receptor mimics to those of control proteins containing only the N-terminal or the E3 receptor element. CROSS-NX2E3X2 bound to monomeric IL-8 with the same affinity and induced the same chemical shift changes as the control protein containing only the N-terminal element of CXCR2, indicating that the E3 element of CXCR2 did not contribute to IL-8 binding. In contrast, CROSS-NX1E3X1 bound to IL-8 with ~10-fold increased affinity and induced different chemical shift changes compared to the control protein containing only the N-terminal element of CXCR1, suggesting that the E3 region of CXCR1 was interacting with IL-8. However, a chimeric protein containing the N-terminal region of CXCR1 and the E3 region of CXCR2 (CROSS-NX1E3X2) bound to IL-8 with thermodynamic properties and induced chemical shift changes indistinguishable from those of CROSS-NX1E3X1 and substantially different from those of CROSS-NX2E3X2. These results indicate that the N-terminal and E3 regions of CXCR1 interact synergistically to achieve optimal binding interactions with IL-8. PMID:22242662

Gamma-aminobutyric acid-modulated benzodiazepine binding sites in bacteria

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lummis, S.C.R.; Johnston, G.A.R.; Nicoletti, G.

1991-01-01

Benzodiazepine binding sites, which were once considered to exist only in higher vertebrates, are here demonstrated in the bacteria E. coli. The bacterial ({sup 3}H)diazepam binding sites are modulated by GABA; the modulation is dose dependent and is reduced at high concentrations. The most potent competitors of E.Coli ({sup 3}H)diazepam binding are those that are active in displacing ({sup 3}H)benzodiazepines from vertebrate peripheral benzodiazepine binding sites. These vertebrate sites are not modulated by GABA, in contrast to vertebrate neuronal benzodiazepine binding sites. The E.coli benzodiazepine binding sites therefore differ from both classes of vertebrate benzodiazepine binding sites; however the ligandmore » spectrum and GABA-modulatory properties of the E.coli sites are similar to those found in insects. This intermediate type of receptor in lower species suggests a precursor for at least one class of vertebrate benzodiazepine binding sites may have existed.« less

Ligand affinity of the 67-kD elastin/laminin binding protein is modulated by the protein's lectin domain: visualization of elastin/laminin-receptor complexes with gold-tagged ligands

PubMed Central

1991-01-01

Video-enhanced microscopy was used to examine the interaction of elastin- or laminin-coated gold particles with elastin binding proteins on the surface of live cells. By visualizing the binding events in real time, it was possible to determine the specificity and avidity of ligand binding as well as to analyze the motion of the receptor-ligand complex in the plane of the plasma membrane. Although it was difficult to interpret the rates of binding and release rigorously because of the possibility for multiple interactions between particles and the cell surface, relative changes in binding have revealed important aspects of the regulation of affinity of ligand-receptor interaction in situ. Both elastin and laminin were found to compete for binding to the cell surface and lactose dramatically decreased the affinity of the receptor(s) for both elastin and laminin. These findings were supported by in vitro studies of the detergent-solubilized receptor. Further, immobilization of the ligand-receptor complexes through binding to the cytoskeleton dramatically decreased the ability of bound particles to leave the receptor. The changes in the kinetics of ligand-coated gold binding to living cells suggest that both laminin and elastin binding is inhibited by lactose and that attachment of receptor to the cytoskeleton increases its affinity for the ligand. PMID:1848864

Structure of the Zinc-Bound Amino-Terminal Domain of the NMDA Receptor NR2B Subunit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karakas, E.; Simorowski, N; Furukawa, H

2009-01-01

N-methyl-D-aspartate (NMDA) receptors belong to the family of ionotropic glutamate receptors (iGluRs) that mediate the majority of fast excitatory synaptic transmission in the mammalian brain. One of the hallmarks for the function of NMDA receptors is that their ion channel activity is allosterically regulated by binding of modulator compounds to the extracellular amino-terminal domain (ATD) distinct from the L-glutamate-binding domain. The molecular basis for the ATD-mediated allosteric regulation has been enigmatic because of a complete lack of structural information on NMDA receptor ATDs. Here, we report the crystal structures of ATD from the NR2B NMDA receptor subunit in the zinc-freemore » and zinc-bound states. The structures reveal the overall clamshell-like architecture distinct from the non-NMDA receptor ATDs and molecular determinants for the zinc-binding site, ion-binding sites, and the architecture of the putative phenylethanolamine-binding site.« less

The metabotropic glutamate receptors: structure, activation mechanism and pharmacology.

PubMed

Pin, Jean-Philippe; Acher, Francine

2002-06-01

The metabotropic glutamate receptors are G-protein coupled receptors (GPCR) involved in the regulation of many synapses, including most glutamatergic fast excitatory synapses. Eight subtypes have been identified that can be classified into three groups. The molecular characterization of these receptors revealed proteins much more complex than any other GPCRs. They are composed of a Venus Flytrap (VFT) module where glutamate binds, connected to a heptahelical domain responsible for G-protein coupling. Recent data including the structure of the VFT module determined with and without glutamate, indicate that these receptors function as dimers. Moreover a number of intracellular proteins can regulate their targeting and transduction mechanism. Such structural features of mGlu receptors offer multiple possibilities for synthetic compounds to modulate their activity. In addition to agonists and competitive antagonists acting at the glutamate binding site, a number of non-competitive antagonists with inverse agonist activity, and positive allosteric modulators have been discovered. These later compounds share specific properties that make them good candidates for therapeutic applications. First, their non-amino acid structure makes them pass more easily the blood brain barrier. Second, they are much more selective than any other compound identified so far, being the first subtype selective molecules. Third, for the negative modulators, their non competitive mechanism of action makes them relatively unaffected by high concentrations of glutamate that may be present in disease states (e.g. stroke, epilepsy, neuropathic pain, etc.). Fourth, like the benzodiazepines acting at the GABA(A) receptors, the positive modulators offer a new way to increase the activity of these receptors in vivo, with a low risk of inducing their desensitization. The present review article focuses on the specific structural features of these receptors and highlights the various possibilities these offer for drug development.

A comparison of progestin and androgen receptor binding using the CoMFA technique

NASA Astrophysics Data System (ADS)

Loughney, Deborah A.; Schwender, Charles F.

1992-12-01

A series of 48 steroids has been studied with the SYBYL QSAR module using Relative Binding Affinities (RBAs) to progesterone and androgen receptors obtained from the literature. Models for the progesterone and androgen data were developed. Both models show regions where sterics and electrostatics correlate to binding affinity but are different for androgen and progesterone which suggests differences possibly important for receptor selectivity. The progesterone model is more predictive than the androgen (predictive r2 of 0.725 vs. 0.545 for progesterone and androgen, respectively).

A retinoic acid response element that overlaps an estrogen response element mediates multihormonal sensitivity in transcriptional activation of the lactoferrin gene.

PubMed

Lee, M O; Liu, Y; Zhang, X K

1995-08-01

The lactoferrin gene is highly expressed in many different tissues, and its expression is controlled by different regulators. In this report, we have defined a retinoic acid response element (RARE) in the 5'-flanking region of the lactoferrin gene promoter. The lactoferrin-RARE is composed of two AGGTCA-like motifs arranged as a direct repeat with 1-bp spacing (DR-1). A gel retardation assay demonstrated that it bound strongly with retinoid X receptor (RXR) homodimers and RXR-retinoic acid receptor (RAR) heterodimers as well as chicken ovalbumin upstream promoter transcription factor (COUP-TF) orphan receptor. In CV-1 cells, the lactoferrin-RARE linked with a heterologous thymidine kinase promoter was strongly activated by RXR homodimers in response to 9-cis-retinoic acid (9-cis-RA) but not to all-trans-RA. When the COUP-TF orphan receptor was cotransfected, the 9-cis-RA-induced RXR homodimer activity was strongly repressed. A unique feature of the lactoferrin-RARE is that it has an AGGTCA-like motif in common with an estrogen-responsive element (ERE). The composite RARE/ERE contributes to the functional interaction between retinoid receptors and the estrogen receptor (ER) and their ligands. In CV-1 cells, cotransfection of the retinoid and estrogen receptors led to mutual inhibition of the other's activity, while an RA-dependent inhibition of ER activity was observed in breast cancer cells. Furthermore, the lactoferrin-RARE/ERE showed differential transactivation activity in different cell types. RAs could activate the lactoferrin-RARE/ERE in human leukemia HL-60 cells and U937 cells but not in human breast cancer cells. By gel retardation analyses, we demonstrated that strong binding of the endogenous COUP-TF in breast cancer cells to the composite element contributed to diminished RA response in these cells. Thus, the lactoferrin-RARE/ERE functions as a signaling switch module that mediates multihormonal responsiveness in the regulation of lactoferrin gene expression.

Kinetic Contributions to Gating by Interactions Unique to N-methyl-d-aspartate (NMDA) Receptors*

PubMed Central

Borschel, William F.; Cummings, Kirstie A.; Tindell, LeeAnn K.; Popescu, Gabriela K.

2015-01-01

Among glutamate-gated channels, NMDA receptors produce currents that subside with unusually slow kinetics, and this feature is essential to the physiology of central excitatory synapses. Relative to the homologous AMPA and kainate receptors, NMDA receptors have additional intersubunit contacts in the ligand binding domain that occur at both conserved and non-conserved sites. We examined GluN1/GluN2A single-channel currents with kinetic analyses and modeling to probe these class-specific intersubunit interactions for their role in glutamate binding and receptor gating. We found that substitutions that eliminate such interactions at non-conserved sites reduced stationary gating, accelerated deactivation, and imparted sensitivity to aniracetam, an AMPA receptor-selective positive modulator. Abolishing unique contacts at conserved sites also reduced stationary gating and accelerated deactivation. These results show that contacts specific to NMDA receptors, which brace the heterodimer interface within the ligand binding domain, stabilize actively gating receptor conformations and result in longer bursts and slower deactivations. They support the view that the strength of the heterodimer interface modulates gating in both NMDA and non-NMDA receptors and that unique interactions at this interface are responsible in part for basic differences between the kinetics of NMDA and non-NMDA currents at glutamatergic synapses. PMID:26370091

Real-time characterization of cannabinoid receptor 1 (CB1 ) allosteric modulators reveals novel mechanism of action.

PubMed

Cawston, Erin E; Redmond, William J; Breen, Courtney M; Grimsey, Natasha L; Connor, Mark; Glass, Michelle

2013-10-01

The cannabinoid receptor type 1 (CB1 ) has an allosteric binding site. The drugs ORG27569 {5-chloro-3-ethyl-N-[2-[4-(1-piperidinyl)phenyl]ethyl]-1H-indole-2-carboxamide} and PSNCBAM-1 {1-(4-chlorophenyl)-3-[3-(6-pyrrolidin-1-ylpyridin-2-yl)phenyl]urea} have been extensively characterized with regard to their effects on signalling of the orthosteric ligand CP55,940 {(-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-trans-4-(3-hydroxypropyl)cyclohexanol}, and studies have suggested that these allosteric modulators increase binding affinity but act as non-competitive antagonists in functional assays. To gain a deeper understanding of allosteric modulation of CB1 , we examined real-time signalling and trafficking responses of the receptor in the presence of allosteric modulators. Studies of CB1 signalling were carried out in HEK 293 and AtT20 cells expressing haemagglutinin-tagged human and rat CB1 . We measured real-time accumulation of cAMP, activation and desensitization of potassium channel-mediated cellular hyperpolarization and CB1 internalization. ORG27569 and PSNCBAM-1 produce a complex, concentration and time-dependent modulation of agonist-mediated regulation of cAMP levels, as well as an increased rate of desensitization of CB1 -mediated cellular hyperpolarization and a decrease in agonist-induced receptor internalization. Contrary to previous studies characterizing allosteric modulators at CB1, this study suggests that the mechanism of action is not non-competitive antagonism of signalling, but rather that enhanced binding results in an increased rate of receptor desensitization and reduced internalization, which results in time-dependent modulation of cAMP signalling. The observed effect of the allosteric modulators is therefore dependent on the time frame over which the signalling response occurs. This finding may have important consequences for the potential therapeutic application of these compounds. © 2013 The British Pharmacological Society.

RACK1 binds to Smad3 to modulate transforming growth factor-beta1-stimulated alpha2(I) collagen transcription in renal tubular epithelial cells.

PubMed

Okano, Kazuhiro; Schnaper, H William; Bomsztyk, Karol; Hayashida, Tomoko

2006-09-08

Although it is clear that transforming growth factor-beta1 (TGF-beta1) is critical for renal fibrogenesis, the complexity of the involved mechanisms is increasingly apparent. TGF-beta1 stimulates phosphorylation of Smad2/3 and activates other signaling molecules as well. The molecular link between these other kinases and Smads is not known. We sought new binding partners for Smad3 in renal cells and identified receptor for activated protein kinase C 1 (RACK1) as a novel binding partner of Smad3. The linker region of Smad3 and the tryptophan-aspartic acid repeat 6 and 7 of RACK1 are sufficient for the association. RACK1 also interacts with Smad3 in the human kidney epithelial cell line, HKC. Silencing RACK1 increases transcriptional activity of TGF-beta1-responsive promoter sequences of the Smad binding element (SBE), p3TP-Lux, and alpha2(I) collagen. Conversely, overexpressed RACK1 negatively modulates alpha2(I) collagen transcriptional activity in TGF-beta1-stimulated cells. RACK1 did not affect phosphorylation of Smad3 at the C terminus or in the linker region. However, RACK1 reduced direct binding of Smad3 to the SBE motif. Mutating a RACK1 tyrosine at residue 246, but not at 228, decreased the inhibitory effect of RACK1 on both alpha2(I) collagen promoter activity and Smad binding to SBE induced by TGF-beta1. These results suggest that RACK1 modulates transcription of alpha2(I) collagen by TGF-beta1 through interference with Smad3 binding to the gene promoter.

Cryptic glucocorticoid receptor-binding sites pervade genomic NF-κB response elements.

PubMed

Hudson, William H; Vera, Ian Mitchelle S de; Nwachukwu, Jerome C; Weikum, Emily R; Herbst, Austin G; Yang, Qin; Bain, David L; Nettles, Kendall W; Kojetin, Douglas J; Ortlund, Eric A

2018-04-06

Glucocorticoids (GCs) are potent repressors of NF-κB activity, making them a preferred choice for treatment of inflammation-driven conditions. Despite the widespread use of GCs in the clinic, current models are inadequate to explain the role of the glucocorticoid receptor (GR) within this critical signaling pathway. GR binding directly to NF-κB itself-tethering in a DNA binding-independent manner-represents the standing model of how GCs inhibit NF-κB-driven transcription. We demonstrate that direct binding of GR to genomic NF-κB response elements (κBREs) mediates GR-driven repression of inflammatory gene expression. We report five crystal structures and solution NMR data of GR DBD-κBRE complexes, which reveal that GR recognizes a cryptic response element between the binding footprints of NF-κB subunits within κBREs. These cryptic sequences exhibit high sequence and functional conservation, suggesting that GR binding to κBREs is an evolutionarily conserved mechanism of controlling the inflammatory response.

Medicinal chemistry of P2X receptors: allosteric modulators.

PubMed

Müller, Christa E

2015-01-01

P2X receptors are trimeric ligand-gated ion channels whose potential as novel drug targets for a number of diseases has been recognized. They are mainly involved in inflammatory processes, including neuroinflammation, and pain sensation. The orthosteric binding site is lined by basic amino acid residues that bind the negatively charged agonist ATP. Therefore it is not easy to develop orthosteric ligands that possess drug-like properties for such a highly polar binding site. However, ligand-gated ion channels offer multiple additional binding sites for allosteric ligands, positive or negative allosteric modulators enhancing or blocking receptor function. So far, the P2X3 (and P2X2/3), as well as the P2X7 receptor subtype have been the main focus of drug development efforts. A number of potent and selective allosteric antagonists have been developed to block these receptors. We start to see the development of novel allosteric ligands also for the other P2X receptor subtypes, P2X1, P2X2 and especially P2X4. The times when only poor, non-selective, non-drug-like tools for studying P2X receptor function were available have been overcome. The first clinical studies with allosteric P2X3 and P2X7 antagonists suggest that P2X therapeutics may soon become a reality.

Functional Validation of Virtual Screening for Novel Agents with General Anesthetic Action at Ligand-Gated Ion Channels

PubMed Central

Heusser, Stephanie A.; Howard, Rebecca J.; Borghese, Cecilia M.; Cullins, Madeline A.; Broemstrup, Torben; Lee, Ui S.; Lindahl, Erik; Carlsson, Jens

2013-01-01

GABAA receptors play a crucial role in the actions of general anesthetics. The recently published crystal structure of the general anesthetic propofol bound to Gloeobacter violaceus ligand-gated ion channel (GLIC), a bacterial homolog of GABAA receptors, provided an opportunity to explore structure-based ligand discovery for pentameric ligand-gated ion channels (pLGICs). We used molecular docking of 153,000 commercially available compounds to identify molecules that interact with the propofol binding site in GLIC. In total, 29 compounds were selected for functional testing on recombinant GLIC, and 16 of these compounds modulated GLIC function. Active compounds were also tested on recombinant GABAA receptors, and point mutations around the presumed binding pocket were introduced into GLIC and GABAA receptors to test for binding specificity. The potency of active compounds was only weakly correlated with properties such as lipophilicity or molecular weight. One compound was found to mimic the actions of propofol on GLIC and GABAA, and to be sensitive to mutations that reduce the action of propofol in both receptors. Mutant receptors also provided insight about the position of the binding sites and the relevance of the receptor’s conformation for anesthetic actions. Overall, the findings support the feasibility of the use of virtual screening to discover allosteric modulators of pLGICs, and suggest that GLIC is a valid model system to identify novel GABAA receptor ligands. PMID:23950219

Tumor microenvironment: Modulation by decorin and related molecules harboring leucine-rich tandem motifs.

PubMed

Goldoni, Silvia; Iozzo, Renato V

2008-12-01

Decorin, the prototype member of the small leucine-rich proteoglycans, resides in the tumor microenvironment and affects the biology of various types of cancer by downregulating the activity of several receptors involved in cell growth and survival. Decorin binds to and modulates the signaling of the epidermal growth factor receptor and other members of the ErbB family of receptor tyrosine kinases. It exerts its antitumor activity by a dual mechanism: via inhibition of these key receptors through their physical downregulation coupled with attenuation of their signaling, and by binding to and sequestering TGFbeta. Decorin also modulates the insulin-like growth factor receptor and the low-density lipoprotein receptor-related protein 1, which indirectly affects the TGFbeta receptor pathway. When expressed in tumor xenograft-bearing mice or injected systemically, decorin inhibits both primary tumor growth and metastatic spreading. In this review, we summarize the latest reports on decorin and related molecules that are relevant to cancer and bring forward the idea of decorin as an anticancer therapeutic and possible prognostic marker for patients affected by various types of tumors. We also discuss the role of lumican and LRIG1, a novel cell growth inhibitor homologous to decorin. (c) 2008 Wiley-Liss, Inc.

Dietary fiber prevents obesity-related liver lipotoxicity by modulating sterol-regulatory element binding protein pathway in C57BL/6J mice fed a high-fat/cholesterol diet.

PubMed

Han, Shufen; Jiao, Jun; Zhang, Wei; Xu, Jiaying; Wan, Zhongxiao; Zhang, Weiguo; Gao, Xiaoran; Qin, Liqiang

2015-10-29

Adequate intake of dietary fibers has proven metabolic and cardiovascular benefits, molecular mechanisms remain still limited. This study was aimed to investigate the effects of cereal dietary fiber on obesity-related liver lipotoxicity in C57BL/6J mice fed a high-fat/cholesterol (HFC) diet and underlying mechanism. Forty-eight adult male C57BL/6J mice were randomly given a reference chow diet, or a high fat/cholesterol (HFC) diet supplemented with or without oat fiber or wheat bran fiber for 24 weeks. Our results showed mice fed oat or wheat bran fiber exhibited lower weight gain, lipid profiles and insulin resistance, compared with HFC diet. The two cereal dietary fibers potently decreased protein expressions of sterol regulatory element binding protein-1 and key factors involved in lipogenesis, including fatty acid synthase and acetyl-CoA carboxylase in target tissues. At molecular level, the two cereal dietary fibers augmented protein expressions of peroxisome proliferator-activated receptor alpha and gamma, liver X receptor alpha, and ATP-binding cassette transporter A1 in target tissues. Our findings indicated that cereal dietary fiber supplementation abrogated obesity-related liver lipotoxicity and dyslipidemia in C57BL/6J mice fed a HFC diet. In addition, the efficacy of oat fiber is greater than wheat bran fiber in normalizing these metabolic disorders and pathological profiles.

Dietary fiber prevents obesity-related liver lipotoxicity by modulating sterol-regulatory element binding protein pathway in C57BL/6J mice fed a high-fat/cholesterol diet

PubMed Central

Han, Shufen; Jiao, Jun; Zhang, Wei; Xu, Jiaying; Wan, Zhongxiao; Zhang, Weiguo; Gao, Xiaoran; Qin, Liqiang

2015-01-01

Adequate intake of dietary fibers has proven metabolic and cardiovascular benefits, molecular mechanisms remain still limited. This study was aimed to investigate the effects of cereal dietary fiber on obesity-related liver lipotoxicity in C57BL/6J mice fed a high-fat/cholesterol (HFC) diet and underlying mechanism. Forty-eight adult male C57BL/6J mice were randomly given a reference chow diet, or a high fat/choleserol (HFC) diet supplemented with or without oat fiber or wheat bran fiber for 24 weeks. Our results showed mice fed oat or wheat bran fiber exhibtied lower weight gain, lipid profiles and insulin resistance, compared with HFC diet. The two cereal dietary fibers potently decreased protein expressions of sterol regulatory element binding protein-1 and key factors involved in lipogenesis, including fatty acid synthase and acetyl-CoA carboxylase in target tissues. At molecular level, the two cereal dietary fibers augmented protein expressions of peroxisome proliferator-activated receptor alpha and gamma, liver X receptor alpha, and ATP-binding cassette transporter A1 in target tissues. Our findings indicated that cereal dietary fiber supplementation abrogated obesity-related liver lipotoxicity and dyslipidemia in C57BL/6J mice fed a HFC diet. In addition, the efficacy of oat fiber is greater than wheat bran fiber in normalizing these metabolic disorders and pathological profiles. PMID:26510459

How glucocorticoid receptors modulate the activity of other transcription factors: a scope beyond tethering.

PubMed

Ratman, Dariusz; Vanden Berghe, Wim; Dejager, Lien; Libert, Claude; Tavernier, Jan; Beck, Ilse M; De Bosscher, Karolien

2013-11-05

The activity of the glucocorticoid receptor (GR), a nuclear receptor transcription factor belonging to subclass 3C of the steroid/thyroid hormone receptor superfamily, is typically triggered by glucocorticoid hormones. Apart from driving gene transcription via binding onto glucocorticoid response elements in regulatory regions of particular target genes, GR can also inhibit gene expression via transrepression, a mechanism largely based on protein:protein interactions. Hereby GR can influence the activity of other transcription factors, without contacting DNA itself. GR is known to inhibit the activity of a growing list of immune-regulating transcription factors. Hence, GCs still rule the clinic for treatments of inflammatory disorders, notwithstanding concomitant deleterious side effects. Although patience is a virtue when it comes to deciphering the many mechanisms GR uses to influence various signaling pathways, the current review is testimony of the fact that groundbreaking mechanistic work has been accumulating over the past years and steadily continues to grow. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

Mechanism of allosteric regulation of β2-adrenergic receptor by cholesterol

PubMed Central

Manna, Moutusi; Niemelä, Miia; Tynkkynen, Joona; Javanainen, Matti; Kulig, Waldemar; Müller, Daniel J; Rog, Tomasz; Vattulainen, Ilpo

2016-01-01

There is evidence that lipids can be allosteric regulators of membrane protein structure and activation. However, there are no data showing how exactly the regulation emerges from specific lipid-protein interactions. Here we show in atomistic detail how the human β2-adrenergic receptor (β2AR) – a prototypical G protein-coupled receptor – is modulated by cholesterol in an allosteric fashion. Extensive atomistic simulations show that cholesterol regulates β2AR by limiting its conformational variability. The mechanism of action is based on the binding of cholesterol at specific high-affinity sites located near the transmembrane helices 5–7 of the receptor. The alternative mechanism, where the β2AR conformation would be modulated by membrane-mediated interactions, plays only a minor role. Cholesterol analogues also bind to cholesterol binding sites and impede the structural flexibility of β2AR, however cholesterol generates the strongest effect. The results highlight the capacity of lipids to regulate the conformation of membrane receptors through specific interactions. DOI: http://dx.doi.org/10.7554/eLife.18432.001 PMID:27897972

Interferon Lambda: Modulating Immunity in Infectious Diseases.

PubMed

Syedbasha, Mohammedyaseen; Egli, Adrian

2017-01-01

Interferon lambdas (IFN-λs; IFNL1-4) modulate immunity in the context of infections and autoimmune diseases, through a network of induced genes. IFN-λs act by binding to the heterodimeric IFN-λ receptor (IFNLR), activating a STAT phosphorylation-dependent signaling cascade. Thereby hundreds of IFN-stimulated genes are induced, which modulate various immune functions via complex forward and feedback loops. When compared to the well-characterized IFN-α signaling cascade, three important differences have been discovered. First, the IFNLR is not ubiquitously expressed: in particular, immune cells show significant variation in the expression levels of and susceptibilities to IFN-λs. Second, the binding affinities of individual IFN-λs to the IFNLR varies greatly and are generally lower compared to the binding affinities of IFN-α to its receptor. Finally, genetic variation in the form of a series of single-nucleotide polymorphisms (SNPs) linked to genes involved in the IFN-λ signaling cascade has been described and associated with the clinical course and treatment outcomes of hepatitis B and C virus infection. The clinical impact of IFN-λ signaling and the SNP variations may, however, reach far beyond viral hepatitis. Recent publications show important roles for IFN-λs in a broad range of viral infections such as human T-cell leukemia type-1 virus, rotaviruses, and influenza virus. IFN-λ also potentially modulates the course of bacterial colonization and infections as shown for Staphylococcus aureus and Mycobacterium tuberculosis . Although the immunological processes involved in controlling viral and bacterial infections are distinct, IFN-λs may interfere at various levels: as an innate immune cytokine with direct antiviral effects; or as a modulator of IFN-α-induced signaling via the suppressor of cytokine signaling 1 and the ubiquitin-specific peptidase 18 inhibitory feedback loops. In addition, the modulation of adaptive immune functions via macrophage and dendritic cell polarization, and subsequent priming, activation, and proliferation of pathogen-specific T- and B-cells may also be important elements associated with infectious disease outcomes. This review summarizes the emerging details of the IFN-λ immunobiology in the context of the host immune response and viral and bacterial infections.

A Novel Bifunctional Alkylphenol Anesthetic Allows Characterization of γ-Aminobutyric Acid, Type A (GABAA), Receptor Subunit Binding Selectivity in Synaptosomes.

PubMed

Woll, Kellie A; Murlidaran, Sruthi; Pinch, Benika J; Hénin, Jérôme; Wang, Xiaoshi; Salari, Reza; Covarrubias, Manuel; Dailey, William P; Brannigan, Grace; Garcia, Benjamin A; Eckenhoff, Roderic G

2016-09-23

Propofol, an intravenous anesthetic, is a positive modulator of the GABAA receptor, but the mechanistic details, including the relevant binding sites and alternative targets, remain disputed. Here we undertook an in-depth study of alkylphenol-based anesthetic binding to synaptic membranes. We designed, synthesized, and characterized a chemically active alkylphenol anesthetic (2-((prop-2-yn-1-yloxy)methyl)-5-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenol, AziPm-click (1)), for affinity-based protein profiling (ABPP) of propofol-binding proteins in their native state within mouse synaptosomes. The ABPP strategy captured ∼4% of the synaptosomal proteome, including the unbiased capture of five α or β GABAA receptor subunits. Lack of γ2 subunit capture was not due to low abundance. Consistent with this, independent molecular dynamics simulations with alchemical free energy perturbation calculations predicted selective propofol binding to interfacial sites, with higher affinities for α/β than γ-containing interfaces. The simulations indicated hydrogen bonding is a key component leading to propofol-selective binding within GABAA receptor subunit interfaces, with stable hydrogen bonds observed between propofol and α/β cavity residues but not γ cavity residues. We confirmed this by introducing a hydrogen bond-null propofol analogue as a protecting ligand for targeted-ABPP and observed a lack of GABAA receptor subunit protection. This investigation demonstrates striking interfacial GABAA receptor subunit selectivity in the native milieu, suggesting that asymmetric occupancy of heteropentameric ion channels by alkylphenol-based anesthetics is sufficient to induce modulation of activity. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

A Novel Bifunctional Alkylphenol Anesthetic Allows Characterization of γ-Aminobutyric Acid, Type A (GABAA), Receptor Subunit Binding Selectivity in Synaptosomes*

PubMed Central

Woll, Kellie A.; Murlidaran, Sruthi; Pinch, Benika J.; Hénin, Jérôme; Wang, Xiaoshi; Salari, Reza; Covarrubias, Manuel; Dailey, William P.; Brannigan, Grace; Garcia, Benjamin A.; Eckenhoff, Roderic G.

2016-01-01

Propofol, an intravenous anesthetic, is a positive modulator of the GABAA receptor, but the mechanistic details, including the relevant binding sites and alternative targets, remain disputed. Here we undertook an in-depth study of alkylphenol-based anesthetic binding to synaptic membranes. We designed, synthesized, and characterized a chemically active alkylphenol anesthetic (2-((prop-2-yn-1-yloxy)methyl)-5-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenol, AziPm-click (1)), for affinity-based protein profiling (ABPP) of propofol-binding proteins in their native state within mouse synaptosomes. The ABPP strategy captured ∼4% of the synaptosomal proteome, including the unbiased capture of five α or β GABAA receptor subunits. Lack of γ2 subunit capture was not due to low abundance. Consistent with this, independent molecular dynamics simulations with alchemical free energy perturbation calculations predicted selective propofol binding to interfacial sites, with higher affinities for α/β than γ-containing interfaces. The simulations indicated hydrogen bonding is a key component leading to propofol-selective binding within GABAA receptor subunit interfaces, with stable hydrogen bonds observed between propofol and α/β cavity residues but not γ cavity residues. We confirmed this by introducing a hydrogen bond-null propofol analogue as a protecting ligand for targeted-ABPP and observed a lack of GABAA receptor subunit protection. This investigation demonstrates striking interfacial GABAA receptor subunit selectivity in the native milieu, suggesting that asymmetric occupancy of heteropentameric ion channels by alkylphenol-based anesthetics is sufficient to induce modulation of activity. PMID:27462076

Soy protein supports cardiovascular health by downregulating hydroxymethylglutaryl-coenzyme A reductase and sterol regulatory element-binding protein-2 and increasing antioxidant enzyme activity in rats with dextran sodium sulfate-induced mild systemic inflammation.

PubMed

Marsh, Tanya G; Straub, Rachel K; Villalobos, Fatima; Hong, Mee Young

2011-12-01

Animal and human studies have indicated that the presence of soy in the diet improves cardiovascular health. Inflammation plays a pivotal role in the progression of cardiovascular disease (CVD). However, little is known about how dextran sodium sulfate (DSS)-induced systemic inflammation impacts overall heart health and, correspondingly, how soy protein modulates risk of CVD development in DSS-induced systemic inflammation. We hypothesized that soy protein-fed rats would have a lower risk of CVD by beneficial alteration of gene expression involving lipid metabolism and antioxidant capacity in DSS-induced systemic inflammation. Forty Sprague-Dawley rats were divided into 4 groups: casein, casein + DSS, soy protein, and soy protein + DSS. After 26 days, inflammation was induced in one group from each diet by incorporating 3% DSS in drinking water for 48 hours. Soy protein-fed rats had lower final body weights (P = .010), epididymal fat weights (P = .049), total cholesterol (P < .001), and low-density lipoprotein cholesterol (P < .001). In regard to gene expression, soy protein-fed rats had lower sterol regulatory element-binding protein-2 (P = .032) and hydroxymethylglutaryl-coenzyme A reductase (P = .028) levels and higher low-density lipoprotein receptor levels (P = .036). Antioxidant enzyme activity of superoxide dismutase and catalase was higher among the soy protein groups (P = .037 and P = .002, respectively). These results suggest that soy protein positively influences cardiovascular health by regulating serum lipids through modified expression of sterol regulatory element-binding protein-2 and its downstream genes (ie, hydroxymethylglutaryl-coenzyme A reductase and low-density lipoprotein receptor) and by promoting the antioxidant enzyme activity of superoxide dismutase and catalase. Copyright © 2011 Elsevier Inc. All rights reserved.

Tumour necrosis factors modulate the affinity state of the leukotriene B4 receptor on human neutrophils.

PubMed Central

Brom, J; Knöller, J; Köller, M; König, W

1988-01-01

Pre-incubation of human polymorphonuclear granulocytes with recombinant human tumour necrosis factors (TNF) revealed a time- and dose-dependent reduction of the expression of leukotriene B4-receptor sites. Analysis of the binding data by Scatchard plots showed a shift from a heterologous receptor population (indicating high- and low-affinity subsets) to a homologous population. From the results it is considered that TNF can influence host defence through the modulation of leukotriene B4 receptor affinity. PMID:2851543

Vitamin D receptor displays DNA binding and transactivation as a heterodimer with the retinoid X receptor, but not with the thyroid hormone receptor.

PubMed

Thompson, P D; Hsieh, J C; Whitfield, G K; Haussler, C A; Jurutka, P W; Galligan, M A; Tillman, J B; Spindler, S R; Haussler, M R

1999-12-01

The vitamin D receptor (VDR) is a transcription factor believed to function as a heterodimer with the retinoid X receptor (RXR). However, it was reported [Schräder et al., 1994] that, on putative vitamin D response elements (VDREs) within the rat 9k and mouse 28k calcium binding protein genes (rCaBP 9k and mCaBP 28k), VDR and thyroid hormone receptor (TR) form heterodimers that transactivate in response to both 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) and triiodothyronine (T(3)). We, therefore, examined associations of these receptors on the putative rCaBP 9k and mCaBP 28k VDREs, as well as on established VDREs from the rat osteocalcin (rOC) and mouse osteopontin (mOP) genes, plus the thyroid hormone response element (TRE) from the rat myosin heavy chain (rMHC) gene. In gel mobility shift assays, we found no evidence for VDR-TR heterodimer interaction with any tested element. Further, employing these hormone response elements linked to reporter genes in transfected cells, VDR and TR mediated responses to their cognate ligands only from the rOC/mOP and rMHC elements, respectively, while the CaBP elements were unresponsive to any combination of ligand(s). Utilizing the rOC and mOP VDREs, two distinct repressive actions of TR on VDR-mediated signaling were demonstrated: a T(3)-independent action, presumably via direct TR-RXR competition for DNA binding, and a T(3)-dependent repression, likely by diversion of limiting RXR from VDR-RXR toward the formation of TR-RXR heterodimers. The relative importance of these two mechanisms differed in a response element-specific manner. These results may provide a partial explanation for the observed association between hyperthyroidism and bone demineralization/osteoporosis. Copyright 1999 Wiley-Liss, Inc.

Design and Synthesis of Cannabinoid 1 Receptor (CB1R) Allosteric Modulators: Drug Discovery Applications.

PubMed

Kulkarni, Abhijit R; Garai, Sumanta; Janero, David R; Thakur, Ganesh A

2017-01-01

Also expressed in various peripheral tissues, the type-1 cannabinoid receptor (CB1R) is the predominant G protein-coupled receptor (GPCR) in brain, where it is responsible for retrograde control of neurotransmitter release. Cellular signaling mediated by CB1R is involved in numerous physiological processes, and pharmacological CB1R modulation is considered a tenable therapeutic approach for diseases ranging from substance-use disorders and glaucoma to metabolic syndrome. Despite the design and synthesis of a variety of bioactive small molecules targeted to the CB1R orthosteric ligand-binding site, the potential of CB1R as a therapeutic GPCR has been largely unrealized due to adverse events associated with typical orthosteric CB1R agonists and antagonists/inverse agonists. Modulation of CB1R-mediated signal transmission by targeting alternative allosteric ligand-binding site(s) on the receptor has garnered interest as a potentially safer and more effective therapeutic modality. This chapter highlights the design and synthesis of novel, pharmacologically active CB1R allosteric modulators and emphasizes how their molecular properties and the positive and negative allosteric control they exert can lead to improved CB1R-targeted pharmacotherapeutics, as well as designer covalent probes that can be used to map CB1R allosteric binding domains and inform structure-based drug design. © 2017 Elsevier Inc. All rights reserved.

The insect repellent N,N-diethyl-m-toluamide (DEET) induces angiogenesis via allosteric modulation of the M3 muscarinic receptor in endothelial cells.

PubMed

Legeay, Samuel; Clere, Nicolas; Hilairet, Grégory; Do, Quoc-Tuan; Bernard, Philippe; Quignard, Jean-François; Apaire-Marchais, Véronique; Lapied, Bruno; Faure, Sébastien

2016-06-27

The insect repellent N,N-diethyl-m-toluamide (DEET) has been reported to inhibit AChE (acetylcholinesterase) and to possess potential carcinogenic properties with excessive vascularization. In the present paper, we demonstrate that DEET specifically stimulates endothelial cells that promote angiogenesis which increases tumor growth. DEET activates cellular processes that lead to angiogenesis including proliferation, migration and adhesion. This is associated with an enhancement of NO production and VEGF expression in endothelial cells. M3 silencing or the use of a pharmacological M3 inhibitor abrogates all of these effects which reveals that DEET-induced angiogenesis is M3 sensitive. The experiments involving calcium signals in both endothelial and HEK cells overexpressing M3 receptors, as well as binding and docking studies demonstrate that DEET acts as an allosteric modulator of the M3 receptor. In addition, DEET inhibited AChE which increased acetylcholine bioavailability and binding to M3 receptors and also strengthened proangiogenic effects by an allosteric modulation.

ApoA-II modulates the association of HDL with class B scavenger receptors SR-BI and CD36.

PubMed

de Beer, Maria C; Castellani, Lawrence W; Cai, Lei; Stromberg, Arnold J; de Beer, Frederick C; van der Westhuyzen, Deneys R

2004-04-01

The class B scavenger receptors SR-BI and CD36 exhibit a broad ligand binding specificity. SR-BI is well characterized as a HDL receptor that mediates selective cholesteryl ester uptake from HDL. CD36, a receptor for oxidized LDL, also binds HDL and mediates selective cholesteryl ester uptake, although much less efficiently than SR-BI. Apolipoprotein A-II (apoA-II), the second most abundant HDL protein, is considered to be proatherogenic, but the underlying mechanisms are unclear. We previously showed that apoA-II modulates SR-BI-dependent binding and selective uptake of cholesteryl ester from reconstituted HDL. To investigate the effect of apoA-II in naturally occurring HDL on these processes, we compared HDL without apoA-II (from apoA-II null mice) with HDLs containing differing amounts of apoA-II (from C57BL/6 mice and transgenic mice expressing a mouse apoA-II transgene). The level of apoA-II in HDL was inversely correlated with HDL binding and selective cholesteryl ester uptake by both scavenger receptors, particularly CD36. Interestingly, for HDL lacking apoA-II, the efficiency with which CD36 mediated selective uptake reached a level similar to that of SR-BI. These results demonstrate that apoA-II exerts a marked effect on HDL binding and selective lipid uptake by the class B scavenger receptors and establishes a potentially important relationship between apoA-II and CD36.

Time course of the estradiol-dependent induction of oxytocin receptor binding in the ventromedial hypothalamic nucleus of the rat

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, A.E.; Ball, G.F.; Coirini, H.

1989-09-01

Oxytocin (OT) transmission is involved in the steroid-dependent display of sexual receptivity in rats. One of the biochemical processes stimulated by the ovarian steroid 17 beta-estradiol (E2) that is relevant to reproduction is the induction of OT receptor binding in the ventromedial hypothalamic nucleus (VMN). The purpose of these experiments was to determine if E2-induced changes in OT receptor binding in the VMN occur within a time frame relevant to cyclic changes in ovarian steroid secretion. OT receptor binding was measured in the VMN of ovariectomized rats implanted for 0-96 h with E2-containing Silastic capsules. The rate of decay ofmore » OT receptor binding was measured in another group of animals 6-48 h after capsule removal. Receptors were labeled with the specific OT receptor antagonist ({sup 125}I)d(CH2)5(Tyr(Me)2,Thr4,Tyr-NH2(9))OVT, and binding was measured with quantitative autoradiographic methods. In addition, plasma E2 levels and uterine weights were assessed in animals from each treatment condition. Significant increases in E2-dependent OT receptor binding and uterine weight occurred within 24 h of steroid treatment. After E2 withdrawal, OT receptor binding and uterine weight decreased significantly within 24 h. These results are consistent with the hypothesis that steroid modulation of OT receptor binding is necessary for the induction of sexual receptivity.« less

Leptin rapidly activates PPARs in C2C12 muscle cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bendinelli, Paola; Piccoletti, Roberta; Maroni, Paola

2005-07-08

Experimental evidence suggests that leptin operates on the tissues, including skeletal muscle, also by modulating gene expression. Using electrophoretic mobility shift assays, we have shown that physiological doses of leptin promptly increase the binding of C2C12 cell nuclear extracts to peroxisome proliferator-activated receptor (PPAR) response elements in oligonucleotide probes and that all three PPAR isoforms participate in DNA-binding complexes. We pre-treated C2C12 cells with AACOCF{sub 3}, a specific inhibitor of cytosolic phospholipase A{sub 2} (cPLA{sub 2}), an enzyme that supplies ligands to PPARs, and found that it abrogates leptin-induced PPAR DNA-binding activity. Leptin treatment significantly increased cPLA{sub 2} activity, evaluatedmore » as the release of [{sup 3}H]arachidonic acid from pre-labelled C2C12 cells, as well as phosphorylation. Further, using MEK1 inhibitor PD-98059 we showed that leptin activates cPLA{sub 2} through ERK induction. These results support a direct effect of leptin on skeletal muscle cells, and suggest that the hormone may modulate muscle transcription also by precocious activation of PPARs through ERK-cPLA{sub 2} pathway.« less

The neuronal Ca(2+) -binding protein 2 (NECAB2) interacts with the adenosine A(2A) receptor and modulates the cell surface expression and function of the receptor.

PubMed

Canela, Laia; Luján, Rafael; Lluís, Carme; Burgueño, Javier; Mallol, Josefa; Canela, Enric I; Franco, Rafael; Ciruela, Francisco

2007-09-01

Heptaspanning membrane also known as G protein-coupled receptors (GPCR) do interact with a variety of intracellular proteins whose function is regulate receptor traffic and/or signaling. Using a yeast two-hybrid screen, NECAB2, a neuronal calcium binding protein, was identified as a binding partner for the adenosine A(2A) receptor (A(2A)R) interacting with its C-terminal domain. Co-localization, co-immunoprecipitation and pull-down experiments showed a close and specific interaction between A(2A)R and NECAB2 in both transfected HEK-293 cells and also in rat striatum. Immunoelectron microscopy detection of NECAB2 and A(2A)R in the rat striatopallidal structures indicated that both proteins are co-distributed in the same glutamatergic nerve terminals. The interaction of NECAB2 with A(2A)R modulated the cell surface expression, the ligand-dependent internalization and the receptor-mediated activation of the MAPK pathway. Overall, these results show that A(2A)R interacts with NECAB2 in striatal neurones co-expressing the two proteins and that the interaction is relevant for A(2A)R function.

Estrogen receptor accessory proteins augment receptor-DNA interaction and DNA bending.

PubMed

Landel, C C; Potthoff, S J; Nardulli, A M; Kushner, P J; Greene, G L

1997-01-01

Increasing evidence suggests that accessory proteins play an important role in the ability of the estrogen receptor (ER) and other nuclear hormone receptors to modulate transcription when bound to cis-acting hormone response elements in target genes. We have previously shown that four proteins, hsp70, protein disulfide isomerase (PDI) and two unknown proteins (p48 and p45), copurify with ER that has been isolated by site-specific DNA chromatography (BERE) and influence the interaction of ER with DNA in vitro. To better define the nature of these effects, we used filter binding and electrophoretic mobility shift assays to study the ability of these proteins to alter the kinetics of ER-DNA interaction and to influence the ability of ER to bend DNA when bound to an estrogen response element (ERE). The results of both assays indicate that ERE-purified ER, with its four associated proteins (hsp70, PDI, p48, p45), has a greater ability to bind to the vitellogenin A2 ERE than ER purified by estradiol-Sepharose chromatography in the absence (ESeph) or presence (EATP) of ATP, in which p48, p45 (ESeph) and hsp70 (EATP) are removed. Surprisingly, the rates of association and dissociation of ER and ERE were essentially the same for all three mixtures, suggesting that one or more ER-associated proteins, especially p45 and p48, may be required for ER to attain maximum DNA binding activity. In addition, circular permutation and phasing analyses demonstrated that the same ER-associated proteins produced higher order ER-DNA complexes that significantly increased the magnitude of DNA distortion, but did not alter the direction of the ER-induced bend of ERE-containing DNA fragments, which was toward the major groove of the DNA helix. These results suggest that p45 and/or p48 and possibly hsp70, play an important role both in the specific DNA binding and bending activities of ER and thus contribute to the overall stimulation of transcription in target genes that contain cis-acting EREs.

Differential manipulation of arrestin-3 binding to basal and agonist-activated G protein-coupled receptors.

PubMed

Prokop, Susanne; Perry, Nicole A; Vishnivetskiy, Sergey A; Toth, Andras D; Inoue, Asuka; Milligan, Graeme; Iverson, Tina M; Hunyady, Laszlo; Gurevich, Vsevolod V

2017-08-01

Non-visual arrestins interact with hundreds of different G protein-coupled receptors (GPCRs). Here we show that by introducing mutations into elements that directly bind receptors, the specificity of arrestin-3 can be altered. Several mutations in the two parts of the central "crest" of the arrestin molecule, middle-loop and C-loop, enhanced or reduced arrestin-3 interactions with several GPCRs in receptor subtype and functional state-specific manner. For example, the Lys139Ile substitution in the middle-loop dramatically enhanced the binding to inactive M 2 muscarinic receptor, so that agonist activation of the M 2 did not further increase arrestin-3 binding. Thus, the Lys139Ile mutation made arrestin-3 essentially an activation-independent binding partner of M 2 , whereas its interactions with other receptors, including the β 2 -adrenergic receptor and the D 1 and D 2 dopamine receptors, retained normal activation dependence. In contrast, the Ala248Val mutation enhanced agonist-induced arrestin-3 binding to the β 2 -adrenergic and D 2 dopamine receptors, while reducing its interaction with the D 1 dopamine receptor. These mutations represent the first example of altering arrestin specificity via enhancement of the arrestin-receptor interactions rather than selective reduction of the binding to certain subtypes. Copyright © 2017. Published by Elsevier Inc.

Transcriptional targets shared by estrogen receptor- related receptors (ERRs) and estrogen receptor (ER) alpha, but not by ERbeta.

PubMed Central

Vanacker, J M; Pettersson, K; Gustafsson, J A; Laudet, V

1999-01-01

The physiological activities of estrogens are thought to be mediated by specific nuclear receptors, ERalpha and ERbeta. However, certain tissues, such as the bone, that are highly responsive to estrogens only express a low level of these receptors. Starting from this apparent contradiction, we have evaluated the potentials of two related receptors ERRalpha and ERRbeta to intervene in estrogen signaling. ERalpha, ERRalpha and ERRbeta bind to and activate transcription through both the classical estrogen response element (ERE) and the SF-1 response element (SFRE). In contrast, ERbeta DNA-binding and transcriptional activity is restricted to the ERE. Accordingly, the osteopontin gene promoter is stimulated through SFRE sequences, by ERRalpha as well as by ERalpha, but not by ERbeta. Analysis of the cross-talk within the ER/ERR subgroup of nuclear receptors thus revealed common targets but also functional differences between the two ERs. PMID:10428965

Significance of the lipid phase in the dynamics and functions of the xanthophyll cycle as revealed by PsbS overexpression in tobacco and in-vitro de-epoxidation in monogalactosyldiacylglycerol micelles.

PubMed

Hieber, A David; Kawabata, Osamu; Yamamoto, Harry Y

2004-01-01

The dynamics of the xanthophyll cycle relative to non-photochemical quenching (NPQ) were examined in tobacco plants overexpressing violaxanthin de-epoxidase (VDE), PsbS and PsbS+VDE for effects on NPQ and violaxanthin (V) de-epoxidation over a range of light intensities. Induction of de-epoxidation and NPQ increased in overexpressed VDE and PsbS plants, respectively. Surprisingly, under low light, overexpressing PsbS enhanced de-epoxidation in addition to NPQ. The effect was hypothesized as due to PsbS binding zeaxanthin (Z) or inducing the binding of Z within the quenching complex, thus shifting the equilibrium toward higher de-epoxidation states. Studies in model systems show that Z can stereospecifically inhibit VDE activity against violaxanthin. This effect, observed under conditions of limiting lipid concentration, was interpreted as product feedback inhibition. These results support the hypothesis that the capacity of the thylakoid lipid phase for xanthophylls is limited and modulates xanthophyll-cycle activity, in conjunction with the release of V and binding of Z by pigment-binding proteins. These modulating factors are incorporated into a lipid-matrix model that has elements of a signal transduction system wherein the light-generated protons are the signal, VDE the signal receptor, Z the secondary messenger, the lipid phase the transduction network, and Z-binding proteins the targets.

Participation of Water in the Binding of Estrogen Receptor with Estrogen Responsive Element in vitro.

PubMed

Zhu, Guo-Zhang; Tang, Guo-Qing; Ruan, Kang-Cheng; Gong, Yue-Ting; Zhang, Yong-Lian

1998-01-01

Many reports have showed that bound water was involved in the interaction between/among the macromolecules. However, it has not been reported whether bound water is also involved in the binding of trans-factors and cis-elements in the regulation of the eukaryotic gene trans-cription or not. Preliminary studies have been made on the effect of bound water on the binding of estrogen receptor with estrogen responsive element in vitro. In the gel retardation assay using the cytosol extract of rat uterus as the supplier of estrogen receptor and 32 bp oligonucleotide containing a concensus vitellogenin A(2) ERE as the probe, various cosolvents, such as glycerol, sucrose, N-dimethylformamide and dimethylsulfoxide, were added respectively to the reaction mixture in varying concentrations to regulate the osmotic pressure. The results indicated that the binding of ER-ERE was enhanced with the increase in the final concentration of these individual cosolvents. On the other hand, when the reaction was carried out under an increasing hydrostatic pressure, the ER-ERE binding was decreased sharply. After decompression the binding of ER-ERE was gradually restored to the normal level with the lapse of time. These results suggested that bound water was directly involved in the binding of ER-ERE and may play an important role in the regulation of the eukaryotic gene transcription.

Crystal structures of a GABAA-receptor chimera reveal new endogenous neurosteroid-binding sites.

PubMed

Laverty, Duncan; Thomas, Philip; Field, Martin; Andersen, Ole J; Gold, Matthew G; Biggin, Philip C; Gielen, Marc; Smart, Trevor G

2017-11-01

γ-Aminobutyric acid receptors (GABA A Rs) are vital for controlling excitability in the brain. This is emphasized by the numerous neuropsychiatric disorders that result from receptor dysfunction. A critical component of most native GABA A Rs is the α subunit. Its transmembrane domain is the target for many modulators, including endogenous brain neurosteroids that impact anxiety, stress and depression, and for therapeutic drugs, such as general anesthetics. Understanding the basis for the modulation of GABA A R function requires high-resolution structures. Here we present the first atomic structures of a GABA A R chimera at 2.8-Å resolution, including those bound with potentiating and inhibitory neurosteroids. These structures define new allosteric binding sites for these modulators that are associated with the α-subunit transmembrane domain. Our findings will enable the exploitation of neurosteroids for therapeutic drug design to regulate GABA A Rs in neurological disorders.

Endogenous vs Exogenous Allosteric Modulators in GPCRs: A dispute for shuttling CB1 among different membrane microenvironments

NASA Astrophysics Data System (ADS)

Stornaiuolo, Mariano; Bruno, Agostino; Botta, Lorenzo; Regina, Giuseppe La; Cosconati, Sandro; Silvestri, Romano; Marinelli, Luciana; Novellino, Ettore

2015-10-01

A Cannabinoid Receptor 1 (CB1) binding site for the selective allosteric modulator ORG27569 is here identified through an integrate approach of consensus pocket prediction, mutagenesis studies and Mass Spectrometry. This unprecedented ORG27569 pocket presents the structural features of a Cholesterol Consensus Motif, a cholesterol interacting region already found in other GPCRs. ORG27569 and cholesterol affects oppositely CB1 affinity for orthosteric ligands. Moreover, the rise in cholesterol intracellular level results in CB1 trafficking to the axonal region of neuronal cells, while, on the contrary, ORG27568 binding induces CB1 enrichment at the soma. This control of receptor migration among functionally different membrane regions of the cell further contributes to downstream signalling and adds a previously unknown mechanism underpinning CB1 modulation by ORG27569 , that goes beyond a mere control of receptor affinity for orthosteric ligands.

Inhibition of estrogen-responsive gene activation by the retinoid X receptor beta: evidence for multiple inhibitory pathways.

PubMed

Segars, J H; Marks, M S; Hirschfeld, S; Driggers, P H; Martinez, E; Grippo, J F; Brown, M; Wahli, W; Ozato, K

1993-04-01

The retinoid X receptor beta (RXR beta; H-2RIIBP) forms heterodimers with various nuclear hormone receptors and binds multiple hormone response elements, including the estrogen response element (ERE). In this report, we show that endogenous RXR beta contributes to ERE binding activity in nuclear extracts of the human breast cancer cell line MCF-7. To define a possible regulatory role of RXR beta regarding estrogen-responsive transcription in breast cancer cells, RXR beta and a reporter gene driven by the vitellogenin A2 ERE were transfected into estrogen-treated MCF-7 cells. RXR beta inhibited ERE-driven reporter activity in a dose-dependent and element-specific fashion. This inhibition occurred in the absence of the RXR ligand 9-cis retinoic acid. The RXR beta-induced inhibition was specific for estrogen receptor (ER)-mediated ERE activation because inhibition was observed in ER-negative MDA-MB-231 cells only following transfection of the estrogen-activated ER. No inhibition of the basal reporter activity was observed. The inhibition was not caused by simple competition of RXR beta with the ER for ERE binding, since deletion mutants retaining DNA binding activity but lacking the N-terminal or C-terminal domain failed to inhibit reporter activity. In addition, cross-linking studies indicated the presence of an auxiliary nuclear factor present in MCF-7 cells that contributed to RXR beta binding of the ERE. Studies using known heterodimerization partners of RXR beta confirmed that RXR beta/triiodothyronine receptor alpha heterodimers avidly bind the ERE but revealed the existence of another triiodothyronine-independent pathway of ERE inhibition. These results indicate that estrogen-responsive genes may be negatively regulated by RXR beta through two distinct pathways.

Metabotropic glutamate receptors as therapeutic targets in Parkinson's disease: An update from the last 5 years of research.

PubMed

Litim, Nadhir; Morissette, Marc; Di Paolo, Thérèse

2017-03-15

Disturbance of glutamate neurotransmission in Parkinson's disease (PD) and l-DOPA induced dyskinesia (LID) is well documented. This review focuses on advances during the past five years on pharmacological modulation of metabotropic glutamate (mGlu) receptors in relation to anti-parkinsonian activity, LID attenuation, and neuroprotection. Drug design and characterization have led to the development of orthosteric agonists binding the same site as glutamate and Positive and Negative Allosteric modulators (PAMs and NAMs) binding sites different from the orthosteric site and offering subtype selectivity. Inhibition of group I (mGlu1 and mGlu5) receptors with NAMs and activation of group II (mGlu2 and 3 receptors) and group III (mGlu 4, 7 and 8 receptors) with PAMs and orthosteric agonists have shown their potential to inhibit glutamate release and attenuate excitotoxicity. Earlier and recent studies have led to the development of mGlu5 receptors NAMs to reduce LID and for neuroprotection, mGlu3 receptor agonists for neuroprotection while mGlu4 receptor PAMs and agonists for antiparkinsonian effects and neuroprotection. Furthermore, homo- and heterodimers of mGlu receptors are documented and highlight the complexity of the functioning of these receptors. Research on partial allosteric modulators and biased mGlu receptor allosteric modulators offer new glutamatergic drugs with better therapeutic effects and less off target adverse activity. Thus these various mGlu receptor targets will enable the development of novel drugs with improved clinical effects for normalization of glutamate transmission, treat PD and LID relief. This article is part of the Special Issue entitled 'Metabotropic Glutamate Receptors, 5 years on'. Copyright © 2016 Elsevier Ltd. All rights reserved.

Sympathetic control of bone mass regulated by osteopontin

PubMed Central

Nagao, Masashi; Feinstein, Timothy N.; Ezura, Yoichi; Hayata, Tadayoshi; Notomi, Takuya; Saita, Yoshitomo; Hanyu, Ryo; Hemmi, Hiroaki; Izu, Yayoi; Takeda, Shu; Wang, Kathryn; Rittling, Susan; Nakamoto, Tetsuya; Kaneko, Kazuo; Kurosawa, Hisashi; Karsenty, Gerard; Denhardt, David T.; Vilardaga, Jean-Pierre; Noda, Masaki

2011-01-01

The sympathetic nervous system suppresses bone mass by mechanisms that remain incompletely elucidated. Using cell-based and murine genetics approaches, we show that this activity of the sympathetic nervous system requires osteopontin (OPN), a cytokine and one of the major members of the noncollagenous extracellular matrix proteins of bone. In this work, we found that the stimulation of the sympathetic tone by isoproterenol increased the level of OPN expression in the plasma and bone and that mice lacking OPN (OPN-KO) suppressed the isoproterenol-induced bone loss by preventing reduced osteoblastic and enhanced osteoclastic activities. In addition, we found that OPN is necessary for changes in the expression of genes related to bone resorption and bone formation that are induced by activation of the sympathetic tone. At the cellular level, we showed that intracellular OPN modulated the capacity of the β2-adrenergic receptor to generate cAMP with a corresponding modulation of cAMP-response element binding (CREB) phosphorylation and associated transcriptional events inside the cell. Our results indicate that OPN plays a critical role in sympathetic tone regulation of bone mass and that this OPN regulation is taking place through modulation of the β2-adrenergic receptor/cAMP signaling system. PMID:21990347

TRPV1 recapitulates native capsaicin receptor in sensory neurons in association with Fas-associated factor 1.

PubMed

Kim, Sangsung; Kang, Changjoong; Shin, Chan Young; Hwang, Sun Wook; Yang, Young Duk; Shim, Won Sik; Park, Min-Young; Kim, Eunhee; Kim, Misook; Kim, Byung-Moon; Cho, Hawon; Shin, Youngki; Oh, Uhtaek

2006-03-01

TRPV1, a cloned capsaicin receptor, is a molecular sensor for detecting adverse stimuli and a key element for inflammatory nociception and represents biophysical properties of native channel. However, there seems to be a marked difference between TRPV1 and native capsaicin receptors in the pharmacological response profiles to vanilloids or acid. One plausible explanation for this overt discrepancy is the presence of regulatory proteins associated with TRPV1. Here, we identify Fas-associated factor 1 (FAF1) as a regulatory factor, which is coexpressed with and binds to TRPV1 in sensory neurons. When expressed heterologously, FAF1 reduces the responses of TRPV1 to capsaicin, acid, and heat, to the pharmacological level of native capsaicin receptor in sensory neurons. Furthermore, silencing FAF1 by RNA interference augments capsaicin-sensitive current in native sensory neurons. We therefore conclude that FAF1 forms an integral component of the vanilloid receptor complex and that it constitutively modulates the sensitivity of TRPV1 to various noxious stimuli in sensory neurons.

Glutaraldehyde pretreatment blocks phospholipase A2 modulation of adrenergic receptors.

PubMed

Cohen, R M; McLellan, C; Dauphin, M; Hirata, F

1985-01-07

Treatment of rat cerebral cortical membranes with phospholipase A2 affects, in a parallel fashion, beta-, alpha 1- and alpha 2-adrenergic receptor binding, but not the affinity of these receptors for their respective ligands. Pretreatment of membranes with 0.1 percent glutaraldehyde blocks the effects of phospholipase A2 on adrenergic receptor binding. The results support the hypothesis that desensitization or "masking" of adrenergic receptors may involve changes in membrane lipid composition. Furthermore, glutaraldehyde may prove a useful tool in the investigation of the dynamic roles of lipids in receptor function and more specifically, their regulation and coupling to physiological events.

Location analysis for the estrogen receptor-α reveals binding to diverse ERE sequences and widespread binding within repetitive DNA elements

PubMed Central

Mason, Christopher E.; Shu, Feng-Jue; Wang, Cheng; Session, Ryan M.; Kallen, Roland G.; Sidell, Neil; Yu, Tianwei; Liu, Mei Hui; Cheung, Edwin; Kallen, Caleb B.

2010-01-01

Location analysis for estrogen receptor-α (ERα)-bound cis-regulatory elements was determined in MCF7 cells using chromatin immunoprecipitation (ChIP)-on-chip. Here, we present the estrogen response element (ERE) sequences that were identified at ERα-bound loci and quantify the incidence of ERE sequences under two stringencies of detection: <10% and 10–20% nucleotide deviation from the canonical ERE sequence. We demonstrate that ∼50% of all ERα-bound loci do not have a discernable ERE and show that most ERα-bound EREs are not perfect consensus EREs. Approximately one-third of all ERα-bound ERE sequences reside within repetitive DNA sequences, most commonly of the AluS family. In addition, the 3-bp spacer between the inverted ERE half-sites, rather than being random nucleotides, is C(A/T)G-enriched at bona fide receptor targets. Diverse ERα-bound loci were validated using electrophoretic mobility shift assay and ChIP-polymerase chain reaction (PCR). The functional significance of receptor-bound loci was demonstrated using luciferase reporter assays which proved that repetitive element ERE sequences contribute to enhancer function. ChIP-PCR demonstrated estrogen-dependent recruitment of the coactivator SRC3 to these loci in vivo. Our data demonstrate that ERα binds to widely variant EREs with less sequence specificity than had previously been suspected and that binding at repetitive and nonrepetitive genomic targets is favored by specific trinucleotide spacers. PMID:20047966

Location analysis for the estrogen receptor-alpha reveals binding to diverse ERE sequences and widespread binding within repetitive DNA elements.

PubMed

Mason, Christopher E; Shu, Feng-Jue; Wang, Cheng; Session, Ryan M; Kallen, Roland G; Sidell, Neil; Yu, Tianwei; Liu, Mei Hui; Cheung, Edwin; Kallen, Caleb B

2010-04-01

Location analysis for estrogen receptor-alpha (ERalpha)-bound cis-regulatory elements was determined in MCF7 cells using chromatin immunoprecipitation (ChIP)-on-chip. Here, we present the estrogen response element (ERE) sequences that were identified at ERalpha-bound loci and quantify the incidence of ERE sequences under two stringencies of detection: <10% and 10-20% nucleotide deviation from the canonical ERE sequence. We demonstrate that approximately 50% of all ERalpha-bound loci do not have a discernable ERE and show that most ERalpha-bound EREs are not perfect consensus EREs. Approximately one-third of all ERalpha-bound ERE sequences reside within repetitive DNA sequences, most commonly of the AluS family. In addition, the 3-bp spacer between the inverted ERE half-sites, rather than being random nucleotides, is C(A/T)G-enriched at bona fide receptor targets. Diverse ERalpha-bound loci were validated using electrophoretic mobility shift assay and ChIP-polymerase chain reaction (PCR). The functional significance of receptor-bound loci was demonstrated using luciferase reporter assays which proved that repetitive element ERE sequences contribute to enhancer function. ChIP-PCR demonstrated estrogen-dependent recruitment of the coactivator SRC3 to these loci in vivo. Our data demonstrate that ERalpha binds to widely variant EREs with less sequence specificity than had previously been suspected and that binding at repetitive and nonrepetitive genomic targets is favored by specific trinucleotide spacers.

Structure of the bacteriophage T4 long tail fiber receptor-binding tip

PubMed Central

Bartual, Sergio G.; Otero, José M.; Garcia-Doval, Carmela; Llamas-Saiz, Antonio L.; Kahn, Richard; Fox, Gavin C.; van Raaij, Mark J.

2010-01-01

Bacteriophages are the most numerous organisms in the biosphere. In spite of their biological significance and the spectrum of potential applications, little high-resolution structural detail is available on their receptor-binding fibers. Here we present the crystal structure of the receptor-binding tip of the bacteriophage T4 long tail fiber, which is highly homologous to the tip of the bacteriophage lambda side tail fibers. This structure reveals an unusual elongated six-stranded antiparallel beta-strand needle domain containing seven iron ions coordinated by histidine residues arranged colinearly along the core of the biological unit. At the end of the tip, the three chains intertwine forming a broader head domain, which contains the putative receptor interaction site. The structure reveals a previously unknown beta-structured fibrous fold, provides insights into the remarkable stability of the fiber, and suggests a framework for mutations to expand or modulate receptor-binding specificity. PMID:21041684

H-2RIIBP, a member of the nuclear hormone receptor superfamily that binds to both the regulatory element of major histocompatibility class I genes and the estrogen response element.

PubMed

Hamada, K; Gleason, S L; Levi, B Z; Hirschfeld, S; Appella, E; Ozato, K

1989-11-01

Transcription of major histocompatibility complex (MHC) class I genes is regulated by the conserved MHC class I regulatory element (CRE). The CRE has two factor-binding sites, region I and region II, both of which elicit enhancer function. By screening a mouse lambda gt 11 library with the CRE as a probe, we isolated a cDNA clone that encodes a protein capable of binding to region II of the CRE. This protein, H-2RIIBP (H-2 region II binding protein), bound to the native region II sequence, but not to other MHC cis-acting sequences or to mutant region II sequences, similar to the naturally occurring region II factor in mouse cells. The deduced amino acid sequence of H-2RIIBP revealed two putative zinc fingers homologous to the DNA-binding domain of steroid/thyroid hormone receptors. Although sequence similarity in other regions was minimal, H-2RIIBP has apparent modular domains characteristic of the nuclear hormone receptors. Further analyses showed that both H-2RIIBP and the natural region II factor bind to the estrogen response element (ERE) of the vitellogenin A2 gene. The ERE is composed of a palindrome, and half of this palindrome resembles the region II binding site of the MHC CRE. These results indicate that H-2RIIBP (i) is a member of the superfamily of nuclear hormone receptors and (ii) may regulate not only MHC class I genes but also genes containing the ERE and related sequences. Sequences homologous to the H-2RIIBP gene are widely conserved in the animal kingdom. H-2RIIBP mRNA is expressed in many mouse tissues, in agreement with the distribution of the natural region II factor.

The association of metabotropic glutamate receptor type 5 with the neuronal Ca2+-binding protein 2 modulates receptor function.

PubMed

Canela, Laia; Fernández-Dueñas, Víctor; Albergaria, Catarina; Watanabe, Masahiko; Lluís, Carme; Mallol, Josefa; Canela, Enric I; Franco, Rafael; Luján, Rafael; Ciruela, Francisco

2009-10-01

Metabotropic glutamate (mGlu) receptors mediate in part the CNS effects of glutamate. These receptors interact with a large array of intracellular proteins in which the final role is to regulate receptor function. Here, using co-immunoprecipitation and pull-down experiments we showed a close and specific interaction between mGlu(5) receptor and NECAB2 in both transfected human embryonic kidney cells and rat hippocampus. Interestingly, in pull-down experiments increasing concentrations of calcium drastically reduced the ability of these two proteins to interact, suggesting that NECAB2 binds to mGlu(5) receptor in a calcium-regulated manner. Immunoelectron microscopy detection of NECAB2 and mGlu(5) receptor in the rat hippocampal formation indicated that both proteins are codistributed in the same subcellular compartment of pyramidal cells. In addition, the NECAB2/mGlu(5) receptor interaction regulated mGlu(5b)-mediated activation of both inositol phosphate accumulation and the extracellular signal-regulated kinase/mitogen-activated protein kinase pathway. Overall, these findings indicate that NECAB2 by its physical interaction with mGlu(5b) receptor modulates receptor function.

Direct labelling of the human P2X7 receptor and identification of positive and negative cooperativity of binding.

PubMed

Michel, A D; Chambers, L J; Clay, W C; Condreay, J P; Walter, D S; Chessell, I P

2007-05-01

The P2X(7) receptor exhibits complex pharmacological properties. In this study, binding of a [(3)H]-labelled P2X(7) receptor antagonist to human P2X(7) receptors has been examined to further understand ligand interactions with this receptor. The P2X(7) receptor antagonist, N-[2-({2-[(2-hydroxyethyl)amino]ethyl}amino)-5-quinolinyl]-2-tricyclo[3.3.1.1(3,7)]dec-1-ylacetamide (compound-17), was radiolabelled with tritium and binding studies were performed using membranes prepared from U-2 OS or HEK293 cells expressing human recombinant P2X(7) receptors. Binding of [(3)H]-compound-17 was higher in membranes prepared from cells expressing P2X(7) receptors than from control cells and was inhibited by ATP suggesting labelled sites represented human P2X(7) receptors. Binding was reversible, saturable and modulated by P2X(7) receptor ligands (Brilliant Blue G, KN62, ATP, decavanadate). Furthermore, ATP potency was reduced in the presence of divalent cations or NaCl. Radioligand binding exhibited both positive and negative cooperativity. Positive cooperativity was evident from bell shaped Scatchard plots, reduction in radioligand dissociation rate by unlabelled compound-17 and enhancement of radioligand binding by KN62 and unlabelled compound-17. ATP and decavanadate inhibited binding in a negative cooperative manner as they enhanced radioligand dissociation. These data demonstrate that human P2X(7) receptors can be directly labelled and provide novel insights into receptor function. The positive cooperativity observed suggests that binding of compound-17 to one subunit in the P2X(7) receptor complex enhances subsequent binding to other P2X(7) subunits in the same complex. The negative cooperative effects of ATP suggest that ATP and compound-17 bind at separate, interacting, sites on the P2X(7) receptor.

Direct labelling of the human P2X7 receptor and identification of positive and negative cooperativity of binding

PubMed Central

Michel, A D; Chambers, L J; Clay, W C; Condreay, J P; Walter, D S; Chessell, I P

2007-01-01

Background and Purpose: The P2X7 receptor exhibits complex pharmacological properties. In this study, binding of a [3H]-labelled P2X7 receptor antagonist to human P2X7 receptors has been examined to further understand ligand interactions with this receptor. Experimental Approach: The P2X7 receptor antagonist, N-[2-({2-[(2-hydroxyethyl)amino]ethyl}amino)-5-quinolinyl]-2-tricyclo[3.3.1.13,7]dec-1-ylacetamide (compound-17), was radiolabelled with tritium and binding studies were performed using membranes prepared from U-2 OS or HEK293 cells expressing human recombinant P2X7 receptors. Key Results: Binding of [3H]-compound-17 was higher in membranes prepared from cells expressing P2X7 receptors than from control cells and was inhibited by ATP suggesting labelled sites represented human P2X7 receptors. Binding was reversible, saturable and modulated by P2X7 receptor ligands (Brilliant Blue G, KN62, ATP, decavanadate). Furthermore, ATP potency was reduced in the presence of divalent cations or NaCl. Radioligand binding exhibited both positive and negative cooperativity. Positive cooperativity was evident from bell shaped Scatchard plots, reduction in radioligand dissociation rate by unlabelled compound-17 and enhancement of radioligand binding by KN62 and unlabelled compound-17. ATP and decavanadate inhibited binding in a negative cooperative manner as they enhanced radioligand dissociation. Conclusions: These data demonstrate that human P2X7 receptors can be directly labelled and provide novel insights into receptor function. The positive cooperativity observed suggests that binding of compound-17 to one subunit in the P2X7 receptor complex enhances subsequent binding to other P2X7 subunits in the same complex. The negative cooperative effects of ATP suggest that ATP and compound-17 bind at separate, interacting, sites on the P2X7 receptor. PMID:17339830

A New Regulator of Osteoclastogenesis: Estrogen Response Element–Binding Protein in Bone

PubMed Central

Chen, Hong; Gilbert, Linda C; Lu, X; Liu, Zhaofan; You, Shaojin; Weitzmann, M Neale; Nanes, Mark S; Adams, John

2012-01-01

The heterogeneous nuclear ribonucleoprotein (hnRNP)–like estrogen response element–binding protein (ERE-BP) competes with estrogen receptor α (ERα) for occupancy of estrogen response elements (EREs). Here we report that ERE-BP potently stimulates osteoclastogenesis. ERE-BP mRNA and protein were found to be expressed ubiquitously in bone. Overexpression of ERE-BP in cultured osteoblasts stimulated expression of the receptor activator of NF-κB ligand (RANKL) and decreased osteoprotegerin (OPG). The effect of ERE-BP on RANKL was shown to be transcriptional in transient transfection assay and competed with via the ER. Constitutive expression of ERE-BP increased the sensitivity of cells toward 1,25-dihydroxyvitamin D3 stimulation of RANKL expression. In contrast, knockdown of ERE-BP in stromal ST-2 cells decreased basal RANKL promoter activity. Cocultures of ERE-BP lentivirus–transduced ST-2 cells with spleen monocytes induced formation of multinucleated osteoclasts (OCs) characterized by tartrate-resistant acid phosphatase, calcitonin receptors, and functional calcium resorption from bone slices. Although ERα competed with ERE-BP for an ERE in a dose-dependent manner, ERE-BP was an independent and potent regulator of RANKL and osteoclastogenesis. In preosteoclastic RAW cells, overexpression of ERE-BP increased RANK, upregulated NF-κB signaling, and enhanced differentiation toward a mature OC phenotype independent of RANKL. These results identify ERE-BP as a potent modulator of osteoclastogenesis. We hypothesize that ERE-BP may play a critical role in the regulation of bone homeostasis as a modulator of estrogen sensitivity as well as by direct action on the transcription of critical osteoclastogenic genes. PMID:21773989

Innate immune interactions within the central nervous system modulate pathogenesis of viral infections

PubMed Central

Nair, Sharmila; Diamond, Michael S.

2015-01-01

The innate immune system mediates protection against neurotropic viruses that replicate in the central nervous system (CNS). Virus infection within specific cells of the CNS triggers activation of several families of pattern recognition receptors including Toll-like receptors, retinoic acid-inducible gene 1 like receptors, nucleotide-binding oligomerization domain-like receptors, and cytosolic DNA sensors. In this review, we highlight recent advances in our understanding of how cell-intrinsic host defenses within the CNS modulate infection of different DNA and RNA viruses. PMID:26163762

Heterodimers of Retinoic Acid Receptors and Thyroid Hormone Receptors Display Unique Combinatorial Regulatory Properties

PubMed Central

Lee, Sangho; Privalsky, Martin L.

2009-01-01

Nuclear receptors are ligand-regulated transcription factors that regulate key aspects of metazoan development, differentiation, and homeostasis. Nuclear receptors recognize target genes by binding to specific DNA recognition sequences, denoted hormone response elements (HREs). Many nuclear receptors can recognize HREs as either homodimers or heterodimers. Retinoid X receptors (RXRs), in particular, serve as important heterodimer partners for many other nuclear receptors, including thyroid hormone receptors (TRs), and RXR/TR heterodimers have been proposed to be the primary mediators of target gene regulation by T3 hormone. Here, we report that the retinoic acid receptors (RARs), a distinct class of nuclear receptors, are also efficient heterodimer partners for TRs. These RAR/TR heterodimers form with similar affinities as RXR/TR heterodimers on an assortment of consensus and natural HREs, and preferentially assemble with the RAR partner 5′ of the TR moiety. The corepressor and coactivator recruitment properties of these RAR/TR heterodimers and their transcriptional activities in vivo are distinct from those observed with the corresponding RXR heterodimers. Our studies indicate that RXRs are not unique in their ability to partner with TRs, and that RARs can also serve as robust heterodimer partners and combinatorial regulators of T3-modulated gene expression. PMID:15650024

Cellular level models as tools for cytokine design.

PubMed

Radhakrishnan, Mala L; Tidor, Bruce

2010-01-01

Cytokines and growth factors are critical regulators that connect intracellular and extracellular environments through binding to specific cell-surface receptors. They regulate a wide variety of immunological, growth, and inflammatory response processes. The overall signal initiated by a population of cytokine molecules over long time periods is controlled by the subtle interplay of binding, signaling, and trafficking kinetics. Building on the work of others, we abstract a simple kinetic model that captures relevant features from cytokine systems as well as related growth factor systems. We explore a large range of potential biochemical behaviors, through systematic examination of the model's parameter space. Different rates for the same reaction topology lead to a dramatic range of biochemical network properties and outcomes. Evolution might productively explore varied and different portions of parameter space to create beneficial behaviors, and effective human therapeutic intervention might be achieved through altering network kinetic properties. Quantitative analysis of the results reveals the basis for tensions among a number of different network characteristics. For example, strong binding of cytokine to receptor can increase short-term receptor activation and signal initiation but decrease long-term signaling due to internalization and degradation. Further analysis reveals the role of specific biochemical processes in modulating such tensions. For instance, the kinetics of cytokine binding and receptor activation modulate whether ligand-receptor dissociation can generally occur before signal initiation or receptor internalization. Beyond analysis, the same models and model behaviors provide an important basis for the design of more potent cytokine therapeutics by providing insight into how binding kinetics affect ligand potency. (c) 2010 American Institute of Chemical Engineers

α-Helical element at the hormone-binding surface of the insulin receptor functions as a signaling element to activate its tyrosine kinase

PubMed Central

Whittaker, Jonathan; Whittaker, Linda J.; Roberts, Charles T.; Phillips, Nelson B.; Ismail-Beigi, Faramarz; Lawrence, Michael C.; Weiss, Michael A.

2012-01-01

The primary hormone-binding surface of the insulin receptor spans one face of the N-terminal β-helix of the α-subunit (the L1 domain) and an α-helix in its C-terminal segment (αCT). Crystallographic analysis of the free ectodomain has defined a contiguous dimer-related motif in which the αCT α-helix packs against L1 β-strands 2 and 3. To relate structure to function, we exploited expanded genetic-code technology to insert photo-activatable probes at key sites in L1 and αCT. The pattern of αCT-mediated photo–cross-linking within the free and bound receptor is in accord with the crystal structure and prior mutagenesis. Surprisingly, L1 photo-probes in β-strands 2 and 3, predicted to be shielded by αCT, efficiently cross-link to insulin. Furthermore, anomalous mutations were identified on neighboring surfaces of αCT and insulin that impair hormone-dependent activation of the intracellular receptor tyrosine kinase (contained within the transmembrane β-subunit) disproportionately to their effects on insulin binding. Taken together, these results suggest that αCT, in addition to its hormone-recognition role, provides a signaling element in the mechanism of receptor activation. PMID:22736795

α-Helical element at the hormone-binding surface of the insulin receptor functions as a signaling element to activate its tyrosine kinase.

PubMed

Whittaker, Jonathan; Whittaker, Linda J; Roberts, Charles T; Phillips, Nelson B; Ismail-Beigi, Faramarz; Lawrence, Michael C; Weiss, Michael A

2012-07-10

The primary hormone-binding surface of the insulin receptor spans one face of the N-terminal β-helix of the α-subunit (the L1 domain) and an α-helix in its C-terminal segment (αCT). Crystallographic analysis of the free ectodomain has defined a contiguous dimer-related motif in which the αCT α-helix packs against L1 β-strands 2 and 3. To relate structure to function, we exploited expanded genetic-code technology to insert photo-activatable probes at key sites in L1 and αCT. The pattern of αCT-mediated photo-cross-linking within the free and bound receptor is in accord with the crystal structure and prior mutagenesis. Surprisingly, L1 photo-probes in β-strands 2 and 3, predicted to be shielded by αCT, efficiently cross-link to insulin. Furthermore, anomalous mutations were identified on neighboring surfaces of αCT and insulin that impair hormone-dependent activation of the intracellular receptor tyrosine kinase (contained within the transmembrane β-subunit) disproportionately to their effects on insulin binding. Taken together, these results suggest that αCT, in addition to its hormone-recognition role, provides a signaling element in the mechanism of receptor activation.

Conformational changes in the M2 muscarinic receptor induced by membrane voltage and agonist binding

PubMed Central

Navarro-Polanco, Ricardo A; Galindo, Eloy G Moreno; Ferrer-Villada, Tania; Arias, Marcelo; Rigby, J Ryan; Sánchez-Chapula, José A; Tristani-Firouzi, Martin

2011-01-01

Abstract The ability to sense transmembrane voltage is a central feature of many membrane proteins, most notably voltage-gated ion channels. Gating current measurements provide valuable information on protein conformational changes induced by voltage. The recent observation that muscarinic G-protein-coupled receptors (GPCRs) generate gating currents confirms their intrinsic capacity to sense the membrane electrical field. Here, we studied the effect of voltage on agonist activation of M2 muscarinic receptors (M2R) in atrial myocytes and how agonist binding alters M2R gating currents. Membrane depolarization decreased the potency of acetylcholine (ACh), but increased the potency and efficacy of pilocarpine (Pilo), as measured by ACh-activated K+ current, IKACh. Voltage-induced conformational changes in M2R were modified in a ligand-selective manner: ACh reduced gating charge displacement while Pilo increased the amount of charge displaced. Thus, these ligands manifest opposite voltage-dependent IKACh modulation and exert opposite effects on M2R gating charge displacement. Finally, mutations in the putative ligand binding site perturbed the movement of the M2R voltage sensor. Our data suggest that changes in voltage induce conformational changes in the ligand binding site that alter the agonist–receptor interaction in a ligand-dependent manner. Voltage-dependent GPCR modulation has important implications for cellular signalling in excitable tissues. Gating current measurement allows for the tracking of subtle conformational changes in the receptor that accompany agonist binding and changes in membrane voltage. PMID:21282291

Crystal Structure of the FERM-SH2 Module of Human Jak2.

PubMed

McNally, Randall; Toms, Angela V; Eck, Michael J

2016-01-01

Jak-family tyrosine kinases mediate signaling from diverse cytokine receptors. Binding of Jaks to their cognate receptors is mediated by their N-terminal region, which contains FERM and SH2 domains. Here we describe the crystal structure of the FERM-SH2 region of Jak2 at 3.0Å resolution. The structure reveals that these domains and their flanking linker segments interact intimately to form an integrated structural module. The Jak2 FERM-SH2 structure closely resembles that recently described for Tyk2, another member of the Jak family. While the overall architecture and interdomain orientations are preserved between Jak2 and Tyk2, we identify residues in the putative receptor-binding groove that differ between the two and may contribute to the specificity of receptor recognition. Analysis of Jak mutations that are reported to disrupt receptor binding reveals that they lie in the hydrophobic core of the FERM domain, and are thus expected to compromise the structural integrity of the FERM-SH2 unit. Similarly, analysis of mutations in Jak3 that are associated with severe combined immunodeficiency suggests that they compromise Jak3 function by destabilizing the FERM-SH2 structure.

Molecular, pharmacological, and signaling properties of octopamine receptors from honeybee (Apis mellifera) brain.

PubMed

Balfanz, Sabine; Jordan, Nadine; Langenstück, Teresa; Breuer, Johanna; Bergmeier, Vera; Baumann, Arnd

2014-04-01

G protein-coupled receptors are important regulators of cellular signaling processes. Within the large family of rhodopsin-like receptors, those binding to biogenic amines form a discrete subgroup. Activation of biogenic amine receptors leads to transient changes of intracellular Ca²⁺-([Ca²⁺](i)) or 3',5'-cyclic adenosine monophosphate ([cAMP](i)) concentrations. Both second messengers modulate cellular signaling processes and thereby contribute to long-lasting behavioral effects in an organism. In vivo pharmacology has helped to reveal the functional effects of different biogenic amines in honeybees. The phenolamine octopamine is an important modulator of behavior. Binding of octopamine to its receptors causes elevation of [Ca²⁺](i) or [cAMP](i). To date, only one honeybee octopamine receptor that induces Ca²⁺ signals has been molecularly and pharmacologically characterized. Here, we examined the pharmacological properties of four additional honeybee octopamine receptors. When heterologously expressed, all receptors induced cAMP production after binding to octopamine with EC₅₀(s) in the nanomolar range. Receptor activity was most efficiently blocked by mianserin, a substance with antidepressant activity in vertebrates. The rank order of inhibitory potency for potential receptor antagonists was very similar on all four honeybee receptors with mianserin > cyproheptadine > metoclopramide > chlorpromazine > phentolamine. The subroot of octopamine receptors activating adenylyl cyclases is the largest that has so far been characterized in arthropods, and it should now be possible to unravel the contribution of individual receptors to the physiology and behavior of honeybees. © 2013 International Society for Neurochemistry.

Structural basis for receptor activity-modifying protein-dependent selective peptide recognition by a G protein-coupled receptor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Booe, Jason M.; Walker, Christopher S.; Barwell, James

Association of receptor activity-modifying proteins (RAMP1-3) with the G protein-coupled receptor (GPCR) calcitonin receptor-like receptor (CLR) enables selective recognition of the peptides calcitonin gene-related peptide (CGRP) and adrenomedullin (AM) that have diverse functions in the cardiovascular and lymphatic systems. How peptides selectively bind GPCR:RAMP complexes is unknown. We report crystal structures of CGRP analog-bound CLR:RAMP1 and AM-bound CLR:RAMP2 extracellular domain heterodimers at 2.5 and 1.8 Å resolutions, respectively. The peptides similarly occupy a shared binding site on CLR with conformations characterized by a β-turn structure near their C termini rather than the α-helical structure common to peptides that bind relatedmore » GPCRs. The RAMPs augment the binding site with distinct contacts to the variable C-terminal peptide residues and elicit subtly different CLR conformations. Lastly, the structures and accompanying pharmacology data reveal how a class of accessory membrane proteins modulate ligand binding of a GPCR and may inform drug development targeting CLR:RAMP complexes.« less

Structural basis for receptor activity-modifying protein-dependent selective peptide recognition by a G protein-coupled receptor

DOE PAGES

Booe, Jason M.; Walker, Christopher S.; Barwell, James; ...

2015-05-14

Association of receptor activity-modifying proteins (RAMP1-3) with the G protein-coupled receptor (GPCR) calcitonin receptor-like receptor (CLR) enables selective recognition of the peptides calcitonin gene-related peptide (CGRP) and adrenomedullin (AM) that have diverse functions in the cardiovascular and lymphatic systems. How peptides selectively bind GPCR:RAMP complexes is unknown. We report crystal structures of CGRP analog-bound CLR:RAMP1 and AM-bound CLR:RAMP2 extracellular domain heterodimers at 2.5 and 1.8 Å resolutions, respectively. The peptides similarly occupy a shared binding site on CLR with conformations characterized by a β-turn structure near their C termini rather than the α-helical structure common to peptides that bind relatedmore » GPCRs. The RAMPs augment the binding site with distinct contacts to the variable C-terminal peptide residues and elicit subtly different CLR conformations. Lastly, the structures and accompanying pharmacology data reveal how a class of accessory membrane proteins modulate ligand binding of a GPCR and may inform drug development targeting CLR:RAMP complexes.« less

The epidermal growth factor receptor (EGFR) promotes uptake of influenza A viruses (IAV) into host cells.

PubMed

Eierhoff, Thorsten; Hrincius, Eike R; Rescher, Ursula; Ludwig, Stephan; Ehrhardt, Christina

2010-09-09

Influenza A viruses (IAV) bind to sialic-acids at cellular surfaces and enter cells by using endocytotic routes. There is evidence that this process does not occur constitutively but requires induction of specific cellular signals, including activation of PI3K that promotes virus internalization. This implies engagement of cellular signaling receptors during viral entry. Here, we present first indications for an interplay of IAV with receptor tyrosine kinases (RTKs). As representative RTK family-members the epidermal growth factor receptor (EGFR) and the c-Met receptor were studied. Modulation of expression or activity of both RTKs resulted in altered uptake of IAV, showing that these receptors transmit entry relevant signals upon virus binding. More detailed studies on EGFR function revealed that virus binding lead to clustering of lipid-rafts, suggesting that multivalent binding of IAV to cells induces a signaling platform leading to activation of EGFR and other RTKs that in turn facilitates IAV uptake.

The Epidermal Growth Factor Receptor (EGFR) Promotes Uptake of Influenza A Viruses (IAV) into Host Cells

PubMed Central

Eierhoff, Thorsten; Hrincius, Eike R.; Rescher, Ursula; Ludwig, Stephan; Ehrhardt, Christina

2010-01-01

Influenza A viruses (IAV) bind to sialic-acids at cellular surfaces and enter cells by using endocytotic routes. There is evidence that this process does not occur constitutively but requires induction of specific cellular signals, including activation of PI3K that promotes virus internalization. This implies engagement of cellular signaling receptors during viral entry. Here, we present first indications for an interplay of IAV with receptor tyrosine kinases (RTKs). As representative RTK family-members the epidermal growth factor receptor (EGFR) and the c-Met receptor were studied. Modulation of expression or activity of both RTKs resulted in altered uptake of IAV, showing that these receptors transmit entry relevant signals upon virus binding. More detailed studies on EGFR function revealed that virus binding lead to clustering of lipid-rafts, suggesting that multivalent binding of IAV to cells induces a signaling platform leading to activation of EGFR and other RTKs that in turn facilitates IAV uptake. PMID:20844577

The human oxytocin gene promoter is regulated by estrogens.

PubMed

Richard, S; Zingg, H H

1990-04-15

Gonadal steroids affect brain function primarily by altering the expression of specific genes, yet the specific mechanisms by which neuronal target genes undergo such regulation are unknown. Recent evidence suggests that the expression of the neuropeptide gene for oxytocin (OT) is modulated by estrogens. We therefore examined the possibility that this regulation occurred via a direct interaction of the estrogen-receptor complex with cis-acting elements flanking the OT gene. DNA-mediated gene transfer experiments were performed using Neuro-2a neuroblastoma cells and chimeric plasmids containing portions of the human OT gene 5'-glanking region linked to the chloramphenicol acetyltransferase gene. We identified a 19-base pair region located at -164 to -146 upstream of the transcription start site which is capable of conferring estrogen responsiveness to the homologous as well as to a heterologous promoter. The hormonal response is strictly dependent on the presence of intracellular estrogen receptors, since estrogen induced stimulation occurred only in Neuro-2a cells co-transfected with an expression vector for the human estrogen receptor. The identified region contains a novel imperfect palindrome (GGTGACCTTGACC) with sequence similarity to other estrogen response elements (EREs). To define cis-acting elements that function in synergism with the ERE, sequences 3' to the ERE were deleted, including the CCAAT box, two additional motifs corresponding to the right half of the ERE palindrome (TGACC), as well as a CTGCTAA heptamer similar to the "elegans box" found in Caenorhabditis elegans. Interestingly, optimal function of the identified ERE was fully independent of these elements and only required a short promoter region (-49 to +36). Our studies define a molecular mechanism by which estrogens can directly modulate OT gene expression. However, only a subset of OT neurons are capable of binding estrogens, therefore, direct action of estrogens on the OT gene may be restricted to a subpopulation of OT neurons.

Inhibition Of Call-Cell Binding By Kipid Assemblies

DOEpatents

Nagy, Jon O. , Bargatze, Robert F.

2003-12-16

This invention relates generally to the field of therapeutic compounds designed to interfere between the binding of ligands and their receptors on cell surface. More specifically, it provides products and methods for inhibiting cell migration and activation using lipid assemblies with surface recognition elements that are specific for the receptors involved in cell migration and activation.

Inhibition of cell-cell binding by lipid assemblies

DOEpatents

Nagy, Jon O.; Bargatze, Robert F.

2001-05-22

This invention relates generally to the field of therapeutic compounds designed to interfere between the binding of ligands and their receptors on cell surface. More specifically, it provides products and methods for inhibiting cell migration and activation using lipid assemblies with surface recognition elements that are specific for the receptors involved in cell migration and activation.

Neuroexcitatory Drug Receptors in Mammals and Invertebrates.

DTIC Science & Technology

1986-11-30

1082 . 9. Lawrence, J.J. and Casida, J.E. (1983) Stereospecific action of pyrethroid insecticides on the y-aminobutyric acid receptor-ionophore...1984). Olsen, R.W. and A.M. Snowman. Avermectin B Modulation of GABA Receptor Binding in Rat Brain, J. Neurochem. 44, 1074- 1082 (1985). Lunt, G.G., T

Lithospermum erythrorhizon Root and its Naphthoquinones Repress SREBP1c and Activate PGC1α Through AMPKα.

PubMed

Velliquette, Rodney A; Rajgopal, Arun; Rebhun, John; Glynn, Kelly

2018-01-01

To examine specific molecular mechanisms involved in modulating hepatic lipogenesis and mitochondria biogenesis signals by Lithospermum erythrorhizon (gromwell) root extract. Stable cell lines with luciferase reporter constructs were generated to examine sterol regulatory element binding protein 1c (SREBP1c) and peroxisome proliferator-activated receptor gamma, coactivator 1 (PGC1) α promoter activity and estrogen-related receptor (ERR) α response element activity. Gene expression of SREBP1c, stearoyl coenzyme A desaturase 1, and PGC1α was measured by using reverse transcription polymerase chain reaction. Lipogenesis was measured in human hepatoma cells with Nile red staining and flow cytometry. Phosphorylation of AMP-activated protein kinase (AMPK) α was determined by using ELISA and Western blot. Gromwell root extract and its naphthoquinones dose-dependently repressed high glucose and liver X receptor α induction of SREBP1c promoter activity and gene expression. Hepatic lipogenesis was repressed, and PGC1α promoter and gene expression and ERRα response element activity were increased by gromwell root extract. Gromwell root extract, shikonin, and α-methyl-n-butyrylshikonin increased AMPKα phosphorylation, and inhibition of AMPK blunted the repression in SREBP1c promoter activity by gromwell root extract and its naphthoquinones. Data suggest that gromwell root extract and its naphthoquinones repress lipogenesis by increasing the phosphorylated state of AMPKα and stimulating mitochondrial biogenesis signals. © 2017 The Obesity Society.

Coco is a dual activity modulator of TGFβ signaling

PubMed Central

Deglincerti, Alessia; Haremaki, Tomomi; Warmflash, Aryeh; Sorre, Benoit; Brivanlou, Ali H.

2015-01-01

The TGFβ signaling pathway is a crucial regulator of developmental processes and disease. The activity of TGFβ ligands is modulated by various families of soluble inhibitors that interfere with the interactions between ligands and receptors. In an unbiased, genome-wide RNAi screen to identify genes involved in ligand-dependent signaling, we unexpectedly identified the BMP/Activin/Nodal inhibitor Coco as an enhancer of TGFβ1 signaling. Coco synergizes with TGFβ1 in both cell culture and Xenopus explants. Molecularly, Coco binds to TGFβ1 and enhances TGFβ1 binding to its receptor Alk5. Thus, Coco acts as both an inhibitor and an enhancer of signaling depending on the ligand it binds. This finding raises the need for a global reconsideration of the molecular mechanisms regulating TGFβ signaling. PMID:26116664

Corticotropin-releasing hormone-binding protein and stress: from invertebrates to humans.

PubMed

Ketchesin, Kyle D; Stinnett, Gwen S; Seasholtz, Audrey F

2017-09-01

Corticotropin-releasing hormone (CRH) is a key regulator of the stress response. This peptide controls the hypothalamic-pituitary-adrenal (HPA) axis as well as a variety of behavioral and autonomic stress responses via the two CRH receptors, CRH-R1 and CRH-R2. The CRH system also includes an evolutionarily conserved CRH-binding protein (CRH-BP), a secreted glycoprotein that binds CRH with subnanomolar affinity to modulate CRH receptor activity. In this review, we discuss the current literature on CRH-BP and stress across multiple species, from insects to humans. We describe the regulation of CRH-BP in response to stress, as well as genetic mouse models that have been utilized to elucidate the in vivo role(s) of CRH-BP in modulating the stress response. Finally, the role of CRH-BP in the human stress response is examined, including single nucleotide polymorphisms in the human CRHBP gene that are associated with stress-related affective disorders and addiction. Lay summary The stress response is controlled by corticotropin-releasing hormone (CRH), acting via CRH receptors. However, the CRH system also includes a unique CRH-binding protein (CRH-BP) that binds CRH with an affinity greater than the CRH receptors. In this review, we discuss the role of this highly conserved CRH-BP in regulation of the CRH-mediated stress response from invertebrates to humans.

LAR-RPTP Clustering Is Modulated by Competitive Binding between Synaptic Adhesion Partners and Heparan Sulfate

PubMed Central

Won, Seoung Youn; Kim, Cha Yeon; Kim, Doyoun; Ko, Jaewon; Um, Ji Won; Lee, Sung Bae; Buck, Matthias; Kim, Eunjoon; Heo, Won Do; Lee, Jie-Oh; Kim, Ho Min

2017-01-01

The leukocyte common antigen-related receptor protein tyrosine phosphatases (LAR-RPTPs) are cellular receptors of heparan sulfate (HS) and chondroitin sulfate (CS) proteoglycans that direct axonal growth and neuronal regeneration. LAR-RPTPs are also synaptic adhesion molecules that form trans-synaptic adhesion complexes by binding to various postsynaptic adhesion ligands, such as Slit- and Trk-like family of proteins (Slitrks), IL-1 receptor accessory protein-like 1 (IL1RAPL1), interleukin-1 receptor accessory protein (IL-1RAcP) and neurotrophin receptor tyrosine kinase C (TrkC), to regulate synaptogenesis. Here, we determined the crystal structure of the human LAR-RPTP/IL1RAPL1 complex and found that lateral interactions between neighboring LAR-RPTP/IL1RAPL1 complexes in crystal lattices are critical for the higher-order assembly and synaptogenic activity of these complexes. Moreover, we found that LAR-RPTP binding to the postsynaptic adhesion ligands, Slitrk3, IL1RAPL1 and IL-1RAcP, but not TrkC, induces reciprocal higher-order clustering of trans-synaptic adhesion complexes. Although LAR-RPTP clustering was induced by either HS or postsynaptic adhesion ligands, the dominant binding of HS to the LAR-RPTP was capable of dismantling pre-established LAR-RPTP-mediated trans-synaptic adhesion complexes. These findings collectively suggest that LAR-RPTP clustering for synaptogenesis is modulated by a complex synapse-organizing protein network. PMID:29081732

[Receptor elements for biosensors in two ways of methylotrophic yeast immobilization].

PubMed

Zaĭtsev, M G; Arliapov, V A; Alferov, V A; Reshetilov, A N

2012-01-01

Receptor elements for biosensors based on Hansenula polymorpha NCYC 495 In yeast cells for ethanol assay were developed using two ways of cell immobilization, i.e., physical adsorption on a glass fiber membrane and covalent binding on a modified nitrocellulose membrane. The linear diapason of ethanol assays for a biosensor based on yeast cells adsorbed on glass fiber was 0.05-1.18; for a biosensor based on yeasts immobilized on a nitrocellulose membrane, 0.2-1.53 mM. Receptor elements based on sorbed cells possessed 2.5 times higher long-term stability. The time response was 1.5 times less for cells immobilized using DEAE-dextran and benzochinone. The results of ethyl alcohol assays using biosensors based on cells immobilized via adsorption and covalent binding, as well as using the standard areometric method, had high correlation coefficients (0.998 and 0.997, respectively, for the two ways of immobilization). The results indicate the possibility to consider the described models of receptor elements for biosensors as prototypes for experimental samples for practical use.

A dopamine D2 receptor mutant capable of G protein-mediated signaling but deficient in arrestin binding.

PubMed

Lan, Hongxiang; Liu, Yong; Bell, Michal I; Gurevich, Vsevolod V; Neve, Kim A

2009-01-01

Arrestins mediate G protein-coupled receptor desensitization, internalization, and signaling. Dopamine D(2) and D(3) receptors have similar structures but distinct characteristics of interaction with arrestins. The goals of this study were to compare arrestin-binding determinants in D(2) and D(3) receptors other than phosphorylation sites and to create a D(2) receptor that is deficient in arrestin binding. We first assessed the ability of purified arrestins to bind to glutathione transferase (GST) fusion proteins containing the receptor third intracellular loops (IC3). Arrestin3 bound to IC3 of both D(2) and D(3) receptors, with the affinity and localization of the binding site indistinguishable between the receptor subtypes. Mutagenesis of the GST-IC3 fusion proteins identified an important determinant of the binding of arrestin3 in the N-terminal region of IC3. Alanine mutations of this determinant (IYIV212-215) in the full-length D(2) receptor generated a signaling-biased receptor with intact ligand binding and G-protein coupling and activation, but deficient in receptor-mediated arrestin3 translocation to the membrane, agonist-induced receptor internalization, and agonist-induced desensitization in human embryonic kidney 293 cells. This mutation also decreased arrestin-dependent activation of extracellular signal-regulated kinases. The finding that nonphosphorylated D(2)-IC3 and D(3)-IC3 have similar affinity for arrestin is consistent with previous suggestions that the differential effects of D(2) and D(3) receptor activation on membrane translocation of arrestin and receptor internalization are due, at least in part, to differential phosphorylation of the receptors. In addition, these results imply that the sequence IYIV212-215 at the N terminus of IC3 of the D(2) receptor is a key element of the arrestin binding site.

High-throughput screening and mechanism-based evaluation of estrogenic botanical extracts

PubMed Central

Overk, Cassia R.; Yao, Ping; Chen, Shaonong; Deng, Shixing; Imai, Ayano; Main, Matthew; Schinkovitz, Andreas; Farnsworth, Norman R.; Pauli, Guido F.; Bolton, Judy L.

2009-01-01

Symptoms associated with menopause can greatly affect the quality of life for women. Botanical dietary supplements have been viewed by the public as safe and effective despite a lack of evidence indicating a urgent necessity to standardize these supplements chemically and biologically. Seventeen plants were evaluated for estrogenic biological activity using standard assays: competitive estrogen receptor (ER) binding assay for both alpha and beta subtypes, transient transfection of the estrogen response element luciferase plasmid into MCF-7 cells expressing either ER alpha or ER beta, and the Ishikawa alkaline phosphatase induction assay for both estrogenic and antiestrogenic activities. Based on the combination of data pooled from these assays, the following was determined: a) a high rate of false positive activity for the competitive binding assays, b) some extracts had estrogenic activity despite a lack of ability to bind the ER, c) one extract exhibited selective estrogen receptor modulator (SERM) activity, and d) several extracts show additive/synergistic activity. Taken together, these data indicate a need to reprioritize the order in which the bioassays are performed for maximal efficiency of programs involving bioassay-guided fractionation. In addition, possible explanations for the conflicts in the literature over the estrogenicity of Cimicifuga racemosa (black cohosh) are suggested. PMID:18473738

Conservative nature of oestradiol signalling pathways in the brain lobes of octopus vulgaris involved in reproduction, learning and motor coordination.

PubMed

De Lisa, E; Paolucci, M; Di Cosmo, A

2012-02-01

Oestradiol plays crucial roles in the mammalian brain by modulating reproductive behaviour, neural plasticity and pain perception. The cephalopod Octopus vulgaris is considered, along with its relatives, to be the most behaviourally advanced invertebrate, although the neurophysiological basis of its behaviours, including pain perception, remain largely unknown. In the present study, using a combination of molecular and imaging techniques, we found that oestradiol up-regulated O. vulgaris gonadotrophin-releasing hormone (Oct-GnRH) and O. vulgaris oestrogen receptor (Oct-ER) mRNA levels in the olfactory lobes; in turn, Oct-ER mRNA was regulated by NMDA in lobes involved in learning and motor coordination. Fluorescence resonance energy transfer analysis revealed that oestradiol binds Oct-ER causing conformational modifications and nuclear translocation consistent with the classical genomic mechanism of the oestrogen receptor. Moreover, oestradiol triggered a calcium influx and cyclic AMP response element binding protein phosphorylation via membrane receptors, providing evidence for a rapid nongenomic action of oestradiol in O. vulgaris. In the present study, we demonstrate, for the first time, the physiological role of oestradiol in the brain lobes of O. vulgaris involved in reproduction, learning and motor coordination. © 2011 The Authors. Journal of Neuroendocrinology © 2011 Blackwell Publishing Ltd.

Enthalpy-Entropy Compensation in the Binding of Modulators at Ionotropic Glutamate Receptor GluA2.

PubMed

Krintel, Christian; Francotte, Pierre; Pickering, Darryl S; Juknaitė, Lina; Pøhlsgaard, Jacob; Olsen, Lars; Frydenvang, Karla; Goffin, Eric; Pirotte, Bernard; Kastrup, Jette S

2016-06-07

The 1,2,4-benzothiadiazine 1,1-dioxide type of positive allosteric modulators of the ionotropic glutamate receptor A2 (GluA2) are promising lead compounds for the treatment of cognitive disorders, e.g., Alzheimer's disease. The modulators bind in a cleft formed by the interface of two neighboring ligand binding domains and act by stabilizing the agonist-bound open-channel conformation. The driving forces behind the binding of these modulators can be significantly altered with only minor substitutions to the parent molecules. In this study, we show that changing the 7-fluorine substituent of modulators BPAM97 (2) and BPAM344 (3) into a hydroxyl group (BPAM557 (4) and BPAM521 (5), respectively), leads to a more favorable binding enthalpy (ΔH, kcal/mol) from -4.9 (2) and -7.5 (3) to -6.2 (4) and -14.5 (5), but also a less favorable binding entropy (-TΔS, kcal/mol) from -2.3 (2) and -1.3 (3) to -0.5 (4) and 4.8 (5). Thus, the dissociation constants (Kd, μM) of 4 (11.2) and 5 (0.16) are similar to those of 2 (5.6) and 3 (0.35). Functionally, 4 and 5 potentiated responses of 10 μM L-glutamate at homomeric rat GluA2(Q)i receptors with EC50 values of 67.3 and 2.45 μM, respectively. The binding mode of 5 was examined with x-ray crystallography, showing that the only change compared to that of earlier compounds was the orientation of Ser-497 pointing toward the hydroxyl group of 5. The favorable enthalpy can be explained by the formation of a hydrogen bond from the side-chain hydroxyl group of Ser-497 to the hydroxyl group of 5, whereas the unfavorable entropy might be due to desolvation effects combined with a conformational restriction of Ser-497 and 5. In summary, this study shows a remarkable example of enthalpy-entropy compensation in drug development accompanied with a likely explanation of the underlying structural mechanism. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.

A phenylalanine rotameric switch for signal-state control in bacterial chemoreceptors

NASA Astrophysics Data System (ADS)

Ortega, Davi R.; Yang, Chen; Ames, Peter; Baudry, Jerome; Parkinson, John S.; Zhulin, Igor B.

2013-12-01

Bacterial chemoreceptors are widely used as a model system for elucidating the molecular mechanisms of transmembrane signalling and have provided a detailed understanding of how ligand binding by the receptor modulates the activity of its associated kinase CheA. However, the mechanisms by which conformational signals move between signalling elements within a receptor dimer and how they control kinase activity remain unknown. Here, using long molecular dynamics simulations, we show that the kinase-activating cytoplasmic tip of the chemoreceptor fluctuates between two stable conformations in a signal-dependent manner. A highly conserved residue, Phe396, appears to serve as the conformational switch, because flipping of the stacked aromatic rings of an interacting F396-F396‧ pair in the receptor homodimer takes place concomitantly with the signal-related conformational changes. We suggest that interacting aromatic residues, which are common stabilizers of protein tertiary structure, might serve as rotameric molecular switches in other biological processes as well.

FK506 binding proteins: cellular regulators of intracellular Ca2+ signalling.

PubMed

MacMillan, Debbi

2013-01-30

In many cell types the intracellular Ca(2+) store performs a central role in the regulation of the cytosolic Ca(2+) concentration ([Ca(2+)](c)), the elevation of which triggers diverse and fundamental activities from reproduction to apoptosis, as well as being the major trigger for contraction. Two distinct classes of Ca(2+) release channels, which mobilize Ca(2+) from the store, exist; the inositol 1,4,5-trisphosphate (IP(3)) receptor and the ryanodine receptor. Considerable attention has been directed towards the importance of modulatory proteins that interact with these channels including, FK506 binding proteins (FKBPs), FKBP12 and its isoform, FKBP12.6. Although FKBP12 was first identified as the principal intracellular target for the immunosuppressive drugs, FK506 and rapamycin, new insights into the role of FKBPs have since emerged. These regulatory proteins are reportedly important modulators of intracellular Ca(2+) release. FKBPs may regulate ryanodine and IP(3) receptors either directly, by binding to the cytoplasmic aspect of the channel, or indirectly via modulation of two targets, the phosphatase, calcineurin or the kinase, mammalian target of rapamycin (mTOR). Dissociation of FKBP12 or FKBP12.6 from either Ca(2+) release channel may increase, decrease or have no effect on ryanodine receptor- or IP(3) receptor-mediated Ca(2+) release. These important controversies may be attributed to FKBPs' ability to regulate the receptor indirectly via the kinase and phosphatase pathways modulated by the accessory proteins. This brief review discusses the regulation of intracellular ryanodine and IP(3) receptor Ca(2+) release channels by accessory FKBPs, with important implications for the role of FKBPs in the pathophysiology of a number of diseases. Copyright © 2012 Elsevier B.V. All rights reserved.

Glycine Hinges with Opposing Actions at the Acetylcholine Receptor-Channel Transmitter Binding SiteS⃞

PubMed Central

Purohit, Prasad

2011-01-01

The extent to which agonists activate synaptic receptor-channels depends on both the intrinsic tendency of the unliganded receptor to open and the amount of agonist binding energy realized in the channel-opening process. We examined mutations of the nicotinic acetylcholine receptor transmitter binding site (α subunit loop B) with regard to both of these parameters. αGly147 is an “activation” hinge where backbone flexibility maintains high values for intrinsic gating, the affinity of the resting conformation for agonists and net ligand binding energy. αGly153 is a “deactivation” hinge that maintains low values for these parameters. αTrp149 (between these two glycines) serves mainly to provide ligand binding energy for gating. We propose that a concerted motion of the two glycine hinges (plus other structural elements at the binding site) positions αTrp149 so that it provides physiologically optimal binding and gating function at the nerve-muscle synapse. PMID:21115636

SH2 and SH3 domains: elements that control interactions of cytoplasmic signaling proteins.

PubMed

Koch, C A; Anderson, D; Moran, M F; Ellis, C; Pawson, T

1991-05-03

Src homology (SH) regions 2 and 3 are noncatalytic domains that are conserved among a series of cytoplasmic signaling proteins regulated by receptor protein-tyrosine kinases, including phospholipase C-gamma, Ras GTPase (guanosine triphosphatase)-activating protein, and Src-like tyrosine kinases. The SH2 domains of these signaling proteins bind tyrosine phosphorylated polypeptides, implicated in normal signaling and cellular transformation. Tyrosine phosphorylation acts as a switch to induce the binding of SH2 domains, thereby mediating the formation of heteromeric protein complexes at or near the plasma membrane. The formation of these complexes is likely to control the activation of signal transduction pathways by tyrosine kinases. The SH3 domain is a distinct motif that, together with SH2, may modulate interactions with the cytoskeleton and membrane. Some signaling and transforming proteins contain SH2 and SH3 domains unattached to any known catalytic element. These noncatalytic proteins may serve as adaptors to link tyrosine kinases to specific target proteins. These observations suggest that SH2 and SH3 domains participate in the control of intracellular responses to growth factor stimulation.

A new genetic variant in the Sp1 binding cis-element of cholecystokinin gene promoter region and relationship to alcoholism.

PubMed

Harada, S; Okubo, T; Tsutsumi, M; Takase, S; Muramatsu, T

1998-05-01

Neuropeptide cholecystokinin (CCK) and the CCK receptors in the central nervous system mediate actions on increasing firings, anxiety, and nociceptions. Furthermore, CCK modulates the release of dopamine and dopamine-related behaviors in the mesolimbic pathway. In our study, genetic variation in the promoter and coding regions of the prepro-CCK gene were analyzed among 66 Japanese, 66 American Whites, 54 Chinese, and 41 Colombian natives. Two nucleotide sequence variants were found: a frequent mutation at nucleotide position -45 C to T involved in core sequence of Sp1 binding cis-element of the promoter region, and a C to T substitution at the 1662 position in intron 2. Analysis for the segregation study in 10 families of twins confirmed codominant heredity of two alleles. Distribution of genotypes and gene frequencies of 66 controls and 108 alcoholics in Japan presented that allelic variant T type in alcoholics was found in higher frequencies than that of controls, and distribution of these genotypes was significantly different between the both groups.

Transforming Growth Factor β Suppresses Peroxisome Proliferator–Activated Receptor γ Expression via Both SMAD Binding and Novel TGF-β Inhibitory Elements

PubMed Central

Lakshmi, Sowmya P.; Reddy, Aravind T.; Reddy, Raju C.

2017-01-01

Transforming growth factor β (TGF-β) contributes to wound healing and, when dysregulated, to pathological fibrosis. TGF-β and the anti-fibrotic nuclear hormone receptor peroxisome proliferator-activated receptor γ (PPARγ) repress each other’s expression, and such PPARγ downregulation is prominent in fibrosis and mediated, via previously unknown SMAD-signaling mechanisms. Here we show that TGF-β induces association of SMAD3 with both SMAD4, needed for translocation of the complex into the nucleus, and the essential context-sensitive corepressors E2F4 and p107. The complex mediates TGF-β-induced repression by binding to regulatory elements in the target promoter. In the PPARG promoter, we found that the SMAD3-SMAD4 complex binds both to a previously unknown consensus TGF-β inhibitory element (TIE) and also to canonical SMAD-binding elements (SBEs). Furthermore, the TIE and SBEs independently mediated partial repression of PPARG transcription, the first demonstration of a TIE and SBEs functioning within the same promoter. Also, TGF-β-treated fibroblasts contained SMAD complexes that activated a SMAD target gene in addition to those repressing PPARG transcription, the first finding of such dual activity within the same cell. These findings describe in detail novel mechanisms by which TGF-β represses PPARG transcription, thereby facilitating its own pro-fibrotic activity. PMID:28100650

Studies on the mechanism of functional cooperativity between progesterone and estrogen receptors.

PubMed

Bradshaw, M S; Tsai, S Y; Leng, X H; Dobson, A D; Conneely, O M; O'Malley, B W; Tsai, M J

1991-09-05

Steroid response elements (SREs) cooperate with many different cis-acting elements including NF-1 sites, CACCC boxes, and other SREs to induce target gene expression (Schule, R., Muller, M., Otsuka-Murakami, H., and Renkawitz, R. (1988) Nature 332, 87-90; Strahle, U., Schmid, W., and Schutz, G. (1988) EMBO J. 7, 3389-3395). Induction of gene expression can be additive or synergistic with respect to the level of activation by either transactivators. Two mechanisms have been proposed for how synergism occurs: 1) cooperative binding of transcriptional activators to DNA or 2) simultaneous interaction of individually bound activators with a common target protein. We have shown previously that cooperative binding of receptors is important for synergism between two progesterone response elements (PREs). Here we showed that an estrogen response element (ERE) and a PRE can also functionally cooperate and this synergism between an ERE and a PRE is not contributed by cooperative DNA binding. Furthermore, we have demonstrated that the activation domains of the progesterone receptor (PR) (C1Act) are required for synergism between two PREs and sufficient for confirming cooperative binding. However these two activation domains of PR are not sufficient for synergism between an ERE and a PRE. Additional regions within the NH2-terminal and COOH-terminal domains are also required for synergistic interaction between two heterologous SREs.

Vitamin C modulates glutamate transport and NMDA receptor function in the retina.

PubMed

Domith, Ivan; Socodato, Renato; Portugal, Camila C; Munis, Andressa F; Duarte-Silva, Aline T; Paes-de-Carvalho, Roberto

2018-02-01

Vitamin C (in the reduced form ascorbate or in the oxidized form dehydroascorbate) is implicated in signaling events throughout the central nervous system (CNS). In the retina, a high-affinity transport system for ascorbate has been described and glutamatergic signaling has been reported to control ascorbate release. Here, we investigated the modulatory role played by vitamin C upon glutamate uptake and N-methyl-d-aspartate (NMDA) receptor activation in cultured retinal cells or in intact retinal tissue using biochemical and imaging techniques. We show that both forms of vitamin C, ascorbate or dehydroascorbate, promote an accumulation of extracellular glutamate by a mechanism involving the inhibition of glutamate uptake. This inhibition correlates with the finding that ascorbate promotes a decrease in cell surface levels of the neuronal glutamate transporter excitatory amino acid transporter 3 in retinal neuronal cultures. Interestingly, vitamin C is prone to increase the activity of NMDA receptors but also promotes a decrease in glutamate-stimulated [ 3 H] MK801 binding and decreases cell membrane content of NMDA receptor glutamate ionotropic receptor subunit 1 (GluN1) subunits. Both compounds were also able to increase cAMP response element-binding protein phosphorylation in neuronal nuclei in a glutamate receptor and calcium/calmodulin kinase-dependent manner. Moreover, the effect of ascorbate is not blocked by sulfinpyrazone and then does not depend on its uptake by retinal cells. Overall, these data indicate a novel molecular and functional target for vitamin C impacting on glutamate signaling in retinal neurons. © 2017 International Society for Neurochemistry.

Nanomechanical mapping of first binding steps of a virus to animal cells

NASA Astrophysics Data System (ADS)

Alsteens, David; Newton, Richard; Schubert, Rajib; Martinez-Martin, David; Delguste, Martin; Roska, Botond; Müller, Daniel J.

2017-02-01

Viral infection is initiated when a virus binds to cell surface receptors. Because the cell membrane is dynamic and heterogeneous, imaging living cells and simultaneously quantifying the first viral binding events is difficult. Here, we show an atomic force and confocal microscopy set-up that allows the surface receptor landscape of cells to be imaged and the virus binding events within the first millisecond of contact with the cell to be mapped at high resolution (<50 nm). We present theoretical approaches to contour the free-energy landscape of early binding events between an engineered virus and cell surface receptors. We find that the first bond formed between the viral glycoprotein and its cognate cell surface receptor has relatively low lifetime and free energy, but this increases as additional bonds form rapidly (≤1 ms). The formation of additional bonds occurs with positive allosteric modulation and the three binding sites of the viral glycoprotein are quickly occupied. Our quantitative approach can be readily applied to study the binding of other viruses to animal cells.

Endogenous Positive Allosteric Modulation of GABAA Receptors by Diazepam binding inhibitor

PubMed Central

Christian, Catherine A.; Herbert, Anne G.; Holt, Rebecca L.; Peng, Kathy; Sherwood, Kyla D.; Pangratz-Fuehrer, Susanne; Rudolph, Uwe; Huguenard, John R.

2014-01-01

Summary Benzodiazepines (BZs) allosterically modulate γ-aminobutyric acid type-A receptors (GABAARs) to increase inhibitory synaptic strength. Diazepam binding inhibitor (DBI) protein is a BZ site ligand expressed endogenously in the brain, but functional evidence for BZ-mimicking positive modulatory actions has been elusive. We demonstrate an endogenous potentiation of GABAergic synaptic transmission and responses to GABA uncaging in the thalamic reticular nucleus (nRT) that is absent in both nm1054 mice, in which the Dbi gene is deleted, and mice in which BZ binding to α3 subunit-containing GABAARs is disrupted. Viral transduction of DBI into nRT is sufficient to rescue the endogenous potentiation of GABAergic transmission in nm1054 mice. Both mutations enhance thalamocortical spike-and-wave discharges characteristic of absence epilepsy. Together these results indicate that DBI mediates endogenous nucleus-specific BZ-mimicking (“endozepine”) roles to modulate nRT function and suppress thalamocortical oscillations. Enhanced DBI signaling might serve as a novel therapy for epilepsy and other neurological disorders. PMID:23727119

Estrogen receptor β (ERβ1) transactivation is differentially modulated by the transcriptional coregulator Tip60 in a cis-acting element-dependent manner.

PubMed

Lee, Ming-Tsung; Leung, Yuet-Kin; Chung, Irving; Tarapore, Pheruza; Ho, Shuk-Mei

2013-08-30

Estrogen receptor (ER) β1 and ERα have overlapping and distinct functions despite their common use of estradiol as the physiological ligand. These attributes are explained in part by their differential utilization of coregulators and ligands. Although Tip60 has been shown to interact with both receptors, its regulatory role in ERβ1 transactivation has not been defined. In this study, we found that Tip60 enhances transactivation of ERβ1 at the AP-1 site but suppresses its transcriptional activity at the estrogen-response element (ERE) site in an estradiol-independent manner. However, different estrogenic compounds can modify the Tip60 action. The corepressor activity of Tip60 at the ERE site is abolished by diarylpropionitrile, genistein, equol, and bisphenol A, whereas its coactivation at the AP-1 site is augmented by fulvestrant (ICI 182,780). GRIP1 is an important tethering mediator for ERs at the AP-1 site. We found that coexpression of GRIP1 synergizes the action of Tip60. Although Tip60 is a known acetyltransferase, it is unable to acetylate ERβ1, and its coregulatory functions are independent of its acetylation activity. In addition, we showed the co-occupancy of ERβ1 and Tip60 at ERE and AP-1 sites of ERβ1 target genes. Tip60 differentially regulates the endogenous expression of the target genes by modulating the binding of ERβ1 to the cis-regulatory regions. Thus, we have identified Tip60 as the first dual-function coregulator of ERβ1.

Estrogen Receptor β (ERβ1) Transactivation Is Differentially Modulated by the Transcriptional Coregulator Tip60 in a cis-Acting Element-dependent Manner*

PubMed Central

Lee, Ming-Tsung; Leung, Yuet-Kin; Chung, Irving; Tarapore, Pheruza; Ho, Shuk-Mei

2013-01-01

Estrogen receptor (ER) β1 and ERα have overlapping and distinct functions despite their common use of estradiol as the physiological ligand. These attributes are explained in part by their differential utilization of coregulators and ligands. Although Tip60 has been shown to interact with both receptors, its regulatory role in ERβ1 transactivation has not been defined. In this study, we found that Tip60 enhances transactivation of ERβ1 at the AP-1 site but suppresses its transcriptional activity at the estrogen-response element (ERE) site in an estradiol-independent manner. However, different estrogenic compounds can modify the Tip60 action. The corepressor activity of Tip60 at the ERE site is abolished by diarylpropionitrile, genistein, equol, and bisphenol A, whereas its coactivation at the AP-1 site is augmented by fulvestrant (ICI 182,780). GRIP1 is an important tethering mediator for ERs at the AP-1 site. We found that coexpression of GRIP1 synergizes the action of Tip60. Although Tip60 is a known acetyltransferase, it is unable to acetylate ERβ1, and its coregulatory functions are independent of its acetylation activity. In addition, we showed the co-occupancy of ERβ1 and Tip60 at ERE and AP-1 sites of ERβ1 target genes. Tip60 differentially regulates the endogenous expression of the target genes by modulating the binding of ERβ1 to the cis-regulatory regions. Thus, we have identified Tip60 as the first dual-function coregulator of ERβ1. PMID:23857583

Intracellular calcium levels determine differential modulation of allosteric interactions within G protein-coupled receptor heteromers.

PubMed

Navarro, Gemma; Aguinaga, David; Moreno, Estefania; Hradsky, Johannes; Reddy, Pasham P; Cortés, Antoni; Mallol, Josefa; Casadó, Vicent; Mikhaylova, Marina; Kreutz, Michael R; Lluís, Carme; Canela, Enric I; McCormick, Peter J; Ferré, Sergi

2014-11-20

The pharmacological significance of the adenosine A2A receptor (A2AR)-dopamine D2 receptor (D2R) heteromer is well established and it is being considered as an important target for the treatment of Parkinson’s disease and other neuropsychiatric disorders. However, the physiological factors that control its distinctive biochemical properties are still unknown. We demonstrate that different intracellular Ca2+ levels exert a differential modulation of A2AR-D2R heteromer-mediated adenylyl-cyclase and MAPK signaling in striatal cells. This depends on the ability of low and high Ca2+ levels to promote a selective interaction of the heteromer with the neuronal Ca2+-binding proteins NCS-1 and calneuron-1, respectively. These Ca2+-binding proteins differentially modulate allosteric interactions within the A2AR-D2R heteromer, which constitutes a unique cellular device that integrates extracellular (adenosine and dopamine) and intracellular (Ca+2) signals to produce a specific functional response.

Transcriptional Regulation of T-Cell Lipid Metabolism: Implications for Plasma Membrane Lipid Rafts and T-Cell Function.

PubMed

Robinson, George A; Waddington, Kirsty E; Pineda-Torra, Ines; Jury, Elizabeth C

2017-01-01

It is well established that cholesterol and glycosphingolipids are enriched in the plasma membrane (PM) and form signaling platforms called lipid rafts, essential for T-cell activation and function. Moreover, changes in PM lipid composition affect the biophysical properties of lipid rafts and have a role in defining functional T-cell phenotypes. Here, we review the role of transcriptional regulators of lipid metabolism including liver X receptors α/β, peroxisome proliferator-activated receptor γ, estrogen receptors α/β (ERα/β), and sterol regulatory element-binding proteins in T-cells. These receptors lie at the interface between lipid metabolism and immune cell function and are endogenously activated by lipids and/or hormones. Importantly, they regulate cellular cholesterol, fatty acid, glycosphingolipid, and phospholipid levels but are also known to modulate a broad spectrum of immune responses. The current evidence supporting a role for lipid metabolism pathways in controlling immune cell activation by influencing PM lipid raft composition in health and disease, and the potential for targeting lipid biosynthesis pathways to control unwanted T-cell activation in autoimmunity is reviewed.

Transcriptional Regulation of T-Cell Lipid Metabolism: Implications for Plasma Membrane Lipid Rafts and T-Cell Function

PubMed Central

Robinson, George A.; Waddington, Kirsty E.; Pineda-Torra, Ines; Jury, Elizabeth C.

2017-01-01

It is well established that cholesterol and glycosphingolipids are enriched in the plasma membrane (PM) and form signaling platforms called lipid rafts, essential for T-cell activation and function. Moreover, changes in PM lipid composition affect the biophysical properties of lipid rafts and have a role in defining functional T-cell phenotypes. Here, we review the role of transcriptional regulators of lipid metabolism including liver X receptors α/β, peroxisome proliferator-activated receptor γ, estrogen receptors α/β (ERα/β), and sterol regulatory element-binding proteins in T-cells. These receptors lie at the interface between lipid metabolism and immune cell function and are endogenously activated by lipids and/or hormones. Importantly, they regulate cellular cholesterol, fatty acid, glycosphingolipid, and phospholipid levels but are also known to modulate a broad spectrum of immune responses. The current evidence supporting a role for lipid metabolism pathways in controlling immune cell activation by influencing PM lipid raft composition in health and disease, and the potential for targeting lipid biosynthesis pathways to control unwanted T-cell activation in autoimmunity is reviewed. PMID:29225604

Allosteric nature of P2X receptor activation probed by photoaffinity labelling

PubMed Central

Bhargava, Y; Rettinger, J; Mourot, A

2012-01-01

BACKGROUND AND PURPOSE In P2X receptors, agonist binding at the interface between neighbouring subunits is efficiently transduced to ion channel gating. However, the relationship between binding and gating is difficult to study because agonists continuously bind and unbind. Here, we covalently incorporated agonists in the binding pocket of P2X receptors and examined how binding site occupancy affects the ability of the channel to gate. EXPERIMENTAL APPROACH We used a strategy for tethering agonists to their ATP-binding pocket, while simultaneously probing ion channel gating using electrophysiology. The agonist 2′,3′-O-(4-benzoylbenzoyl)-ATP (BzATP), a photoaffinity analogue of ATP, enabled us to trap rat homomeric P2X2 receptor and a P2X2/1 receptor chimera in different agonist-bound states. UV light was used to control the degree of covalent occupancy of the receptors. KEY RESULTS Irradiation of the P2X2/1 receptor chimera – BzATP complex resulted in a persistent current that lasted even after extensive washout, consistent with photochemical tethering of the agonist BzATP and trapping of the receptors in an open state. Partial labelling with BzATP primed subsequent agonist binding and modulated gating efficiency for both full and partial agonists. CONCLUSIONS AND IMPLICATIONS Our photolabelling strategy provides new molecular insights into the activation mechanism of the P2X receptor. We show here that priming with full agonist molecules leads to an increase in gating efficiency after subsequent agonist binding. PMID:22725669

CCL2 binding is CCR2 independent in primary adult human astrocytes.

PubMed

Fouillet, A; Mawson, J; Suliman, O; Sharrack, B; Romero, I A; Woodroofe, M N

2012-02-09

Chemokines are low relative molecular mass proteins, which have chemoattractant actions on many cell types. The chemokine, CCL2, has been shown to play a major role in the recruitment of monocytes in central nervous system (CNS) lesions in multiple sclerosis (MS). Since resident astrocytes constitute a major source of chemokine synthesis including CCL2, we were interested to assess the regulation of CCL2 by astrocytes. We showed that CCL2 bound to the cell surface of astrocytes and binding was not modulated by inflammatory conditions. However, CCR2 protein was not detected nor was activation of the classical CCR2 downstream signaling pathways. Recent studies have shown that non-signaling decoy chemokine receptors bind and modulate the expression of chemokines at site of inflammation. Here, we show that the D6 chemokine decoy receptor is constitutively expressed by primary human adult astrocytes at both mRNA and protein level. In addition, CCL3, which binds to D6, but not CCL19, which does not bind to D6, displaced CCL2 binding to astrocytes; indicating that CCL2 may bind to this cell type via the D6 receptor. Our results suggest that CCL2 binding to primary adult human astrocytes is CCR2-independent and is likely to be mediated via the D6 decoy chemokine receptor. Therefore we propose that astrocytes are implicated in both the establishment of chemokine gradients for the migration of leukocytes into and within the CNS and in the regulation of CCL2 levels at inflammatory sites in the CNS. Copyright © 2011 Elsevier B.V. All rights reserved.

A Structural Model for Binding of the Serine-Rich Repeat Adhesin GspB to Host Carbohydrate Receptors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pyburn, Tasia M.; Bensing, Barbara A.; Xiong, Yan Q.

2014-10-02

GspB is a serine-rich repeat (SRR) adhesin of Streptococcus gordonii that mediates binding of this organism to human platelets via its interaction with sialyl-T antigen on the receptor GPIb{alpha}. This interaction appears to be a major virulence determinant in the pathogenesis of infective endocarditis. To address the mechanism by which GspB recognizes its carbohydrate ligand, we determined the high-resolution x-ray crystal structure of the GspB binding region (GspB{sub BR}), both alone and in complex with a disaccharide precursor to sialyl-T antigen. Analysis of the GspB{sub BR} structure revealed that it is comprised of three independently folded subdomains or modules: (1)more » an Ig-fold resembling a CnaA domain from prokaryotic pathogens; (2) a second Ig-fold resembling the binding region of mammalian Siglecs; (3) a subdomain of unique fold. The disaccharide was found to bind in a pocket within the Siglec subdomain, but at a site distinct from that observed in mammalian Siglecs. Confirming the biological relevance of this binding pocket, we produced three isogenic variants of S. gordonii, each containing a single point mutation of a residue lining this binding pocket. These variants have reduced binding to carbohydrates of GPIb{alpha}. Further examination of purified GspB{sub BR}-R484E showed reduced binding to sialyl-T antigen while S. gordonii harboring this mutation did not efficiently bind platelets and showed a significant reduction in virulence, as measured by an animal model of endocarditis. Analysis of other SRR proteins revealed that the predicted binding regions of these adhesins also had a modular organization, with those known to bind carbohydrate receptors having modules homologous to the Siglec and Unique subdomains of GspBBR. This suggests that the binding specificity of the SRR family of adhesins is determined by the type and organization of discrete modules within the binding domains, which may affect the tropism of organisms for different tissues.« less

Functional characterization of c-Mpl ectodomain mutations that underlie congenital amegakaryocytic thrombocytopenia.

PubMed

Varghese, Leila N; Zhang, Jian-Guo; Young, Samuel N; Willson, Tracy A; Alexander, Warren S; Nicola, Nicos A; Babon, Jeffrey J; Murphy, James M

2014-02-01

Activation of the cell surface receptor, c-Mpl, by the cytokine, thrombopoietin (TPO), underpins megakaryocyte and platelet production in mammals. In humans, mutations in c-Mpl have been identified as the molecular basis of Congenital Amegakaryocytic Thrombocytopenia (CAMT). Here, we show that CAMT-associated mutations in c-Mpl principally lead to defective receptor presentation on the cell surface. In contrast, one CAMT mutant c-Mpl, F104S, was expressed on the cell surface, but showed defective TPO binding and receptor activation. Using mutational analyses, we examined which residues adjacent to F104 within the membrane-distal cytokine receptor homology module (CRM) of c-Mpl comprise the TPO-binding epitope, revealing residues within the predicted Domain 1 E-F and A-B loops and Domain 2 F'-G' loop as key TPO-binding determinants. These studies underscore the importance of the c-Mpl membrane-distal CRM to TPO-binding and suggest that mutations within this CRM that perturb TPO binding could give rise to CAMT.

Intrasteric inhibition mediates the interaction of the I/LWEQ module proteins Talin1, Talin2, Hip1, and Hip12 with actin.

PubMed

Senetar, Melissa A; Foster, Stanley J; McCann, Richard O

2004-12-14

The I/LWEQ module superfamily is a class of actin-binding proteins that contains a conserved C-terminal actin-binding element known as the I/LWEQ module. I/LWEQ module proteins include the metazoan talins, the cellular slime mold talin homologues TalA and TalB, fungal Sla2p, and the metazoan Sla2 homologues Hip1 and Hip12 (Hip1R). These proteins possess a similar modular organization that includes an I/LWEQ module at their C-termini and either a FERM domain or an ENTH domain at their N-termini. As a result of this modular organization, I/LWEQ module proteins may serve as linkers between cellular compartments, such as the plasma membrane and the endocytic machinery, and the actin cytoskeleton. Previous studies have shown that I/LWEQ module proteins bind to F-actin. In this report, we have determined the affinity of the I/LWEQ module proteins Talin1, Talin2, huntingtin interacting protein-1 (Hip1), and the Hip1-related protein (Hip1R/Hip12) for F-actin and identified a conserved structural element that interferes with the actin binding capacity of these proteins. Our data support the hypothesis that the actin-binding determinants in native talin and other I/LWEQ module proteins are cryptic and indicate that the actin binding capacities of Talin1, Talin2, Hip1, and Hip12 are regulated by intrasteric occlusion of primary actin-binding determinants within the I/LWEQ module. We have also found that the I/LWEQ module contains a dimerization motif and stabilizes actin filaments against depolymerization. This activity may contribute to the function of talin in cell adhesion and the roles of Hip1, Hip12 (Hip1R), and Sla2p in endocytosis.

Phosphorylation of poly(rC) binding protein 1 (PCBP1) contributes to stabilization of mu opioid receptor (MOR) mRNA via interaction with AU-rich element RNA-binding protein 1 (AUF1) and poly A binding protein (PABP)

PubMed Central

Hwang, Cheol Kyu; Wagley, Yadav; Law, Ping-Yee; Wei, Li-Na; Loh, Horace H.

2016-01-01

Gene regulation at the post-transcriptional level is frequently based on cis- and trans-acting factors on target mRNAs. We found a C-rich element (CRE) in mu-opioid receptor (MOR) 3′-untranslated region (UTR) to which poly (rC) binding protein 1 (PCBP1) binds, resulting in MOR mRNA stabilization. RNA immunoprecipitation and RNA EMSA revealed the formation of PCBP1-RNA complexes at the element. Knockdown of PCBP1 decreased MOR mRNA half-life and protein expression. Stimulation by forskolin increased cytoplasmic localization of PCBP1 and PCBP1/MOR 3′-UTR interactions via increased serine phosphorylation that was blocked by protein kinase A (PKA) or (phosphatidyl inositol-3) PI3-kinase inhibitors. The forskolin treatment also enhanced serine- and tyrosine-phosphorylation of AU-rich element binding protein (AUF1), concurrent with its increased binding to the CRE, and led to an increased interaction of poly A binding protein (PABP) with the CRE and poly(A) sites. AUF1 phosphorylation also led to an increased interaction with PCBP1. These findings suggest that a single co-regulator, PCBP1, plays a crucial role in stabilizing MOR mRNA, and is induced by PKA signaling by conforming to AUF1 and PABP. PMID:27836661

High-Mobility Group Chromatin Proteins 1 and 2 Functionally Interact with Steroid Hormone Receptors To Enhance Their DNA Binding In Vitro and Transcriptional Activity in Mammalian Cells

PubMed Central

Boonyaratanakornkit, Viroj; Melvin, Vida; Prendergast, Paul; Altmann, Magda; Ronfani, Lorenza; Bianchi, Marco E.; Taraseviciene, Laima; Nordeen, Steven K.; Allegretto, Elizabeth A.; Edwards, Dean P.

1998-01-01

We previously reported that the chromatin high-mobility group protein 1 (HMG-1) enhances the sequence-specific DNA binding activity of progesterone receptor (PR) in vitro, thus providing the first evidence that HMG-1 may have a coregulatory role in steroid receptor-mediated gene transcription. Here we show that HMG-1 and the highly related HMG-2 stimulate DNA binding by other steroid receptors, including estrogen, androgen, and glucocorticoid receptors, but have no effect on DNA binding by several nonsteroid nuclear receptors, including retinoid acid receptor (RAR), retinoic X receptor (RXR), and vitamin D receptor (VDR). As highly purified recombinant full-length proteins, all steroid receptors tested exhibited weak binding affinity for their optimal palindromic hormone response elements (HREs), and the addition of purified HMG-1 or -2 substantially increased their affinity for HREs. Purified RAR, RXR, and VDR also exhibited little to no detectable binding to their cognate direct repeat HREs but, in contrast to results with steroid receptors, the addition of HMG-1 or HMG-2 had no stimulatory effect. Instead, the addition of purified RXR enhanced RAR and VDR DNA binding through a heterodimerization mechanism and HMG-1 or HMG-2 had no further effect on DNA binding by RXR-RAR or RXR-VDR heterodimers. HMG-1 and HMG-2 (HMG-1/-2) themselves do not bind to progesterone response elements, but in the presence of PR they were detected as part of an HMG-PR-DNA ternary complex. HMG-1/-2 can also interact transiently in vitro with PR in the absence of DNA; however, no direct protein interaction was detected with VDR. These results, taken together with the fact that PR can bend its target DNA and that HMG-1/-2 are non-sequence-specific DNA binding proteins that recognize DNA structure, suggest that HMG-1/-2 are recruited to the PR-DNA complex by the combined effect of transient protein interaction and DNA bending. In transient-transfection assays, coexpression of HMG-1 or HMG-2 increased PR-mediated transcription in mammalian cells by as much as 7- to 10-fold without altering the basal promoter activity of target reporter genes. This increase in PR-mediated gene activation by coexpression of HMG-1/-2 was observed in different cell types and with different target promoters, suggesting a generality to the functional interaction between HMG-1/-2 and PR in vivo. Cotransfection of HMG-1 also increased reporter gene activation mediated by other steroid receptors, including glucocorticoid and androgen receptors, but it had a minimal influence on VDR-dependent transcription in vivo. These results support the conclusion that HMG-1/-2 are coregulatory proteins that increase the DNA binding and transcriptional activity of the steroid hormone class of receptors but that do not functionally interact with certain nonsteroid classes of nuclear receptors. PMID:9671457

Estrogen-dependent downregulation of hairy and enhancer of split homolog-1 gene expression in breast cancer cells is mediated via a 3' distal element.

PubMed

Müller, Patrick; Merrell, Kenneth W; Crofts, Justin D; Rönnlund, Caroline; Lin, Chin-Yo; Gustafsson, Jan-Ake; Ström, Anders

2009-03-01

Regulation of hairy and enhancer of split homologue-1 (HES-1) by estradiol and all-trans retinoic acid affects proliferation of human breast cancer cells. Here, we identify and characterize cis-regulatory elements involved in HES-1 regulation. In the distal 5' promoter of the HES-1 gene, we found a retinoic acid response element and in the distal 3' region, an estrogen receptor alpha(ER)alpha binding site. The ERalpha binding site, composed of an estrogen response element (ERE) and an ERE half-site, is important for both ERalpha binding and transcriptional regulation. Chromatin immunoprecipitation assays revealed that ERalpha is recruited to the ERE and associates with the HES-1 promoter. We also show recruitment of nuclear receptor co-regulators to the ERE in response to estradiol, followed by a decrease in histone acetylation and RNA polymerase II docking in the HES-1 promoter region. Our findings are consistent with a novel type of repressive estrogen response element in the distal 3' region of the HES-1 gene.

Efavirenz directly modulates the oestrogen receptor and induces breast cancer cell growth.

PubMed

Sikora, M J; Rae, J M; Johnson, M D; Desta, Z

2010-10-01

Efavirenz-based HIV therapy is associated with breast hypertrophy and gynaecomastia. Here, we tested the hypothesis that efavirenz induces gynaecomastia through direct binding and modulation of the oestrogen receptor (ER). To determine the effect of efavirenz on growth, the oestrogen-dependent, ER-positive breast cancer cell lines MCF-7, T47D and ZR-75-1 were treated with efavirenz under oestrogen-free conditions in the presence or absence of the anti-oestrogen ICI 182,780. Cells treated with 17β-oestradiol in the absence or presence of ICI 182,780 served as positive and negative controls, respectively. Cellular growth was assayed using the crystal violet staining method and an in vitro receptor binding assay was used to measure the ER binding affinity of efavirenz. Efavirenz induced growth in MCF-7 cells with an estimated effective concentration for half-maximal growth (EC(50)) of 15.7 μM. This growth was reversed by ICI 182,780. Further, efavirenz binds directly to the ER [inhibitory concentration for half maximal binding (IC(50)) of ∼52 μM] at a roughly 1000-fold higher concentration than observed with 17β-oestradiol. Our data suggest that efavirenz-induced gynaecomastia may be caused, at least in part, by drug-induced ER activation in breast tissues.

GABAA receptor activity modulating piperine analogs: In vitro metabolic stability, metabolite identification, CYP450 reaction phenotyping, and protein binding.

PubMed

Zabela, Volha; Hettich, Timm; Schlotterbeck, Götz; Wimmer, Laurin; Mihovilovic, Marko D; Guillet, Fabrice; Bouaita, Belkacem; Shevchenko, Bénédicte; Hamburger, Matthias; Oufir, Mouhssin

2018-01-01

In a screening of natural products for allosteric modulators of GABA A receptors (γ-aminobutyric acid type A receptor), piperine was identified as a compound targeting a benzodiazepine-independent binding site. Given that piperine is also an activator of TRPV1 (transient receptor potential vanilloid type 1) receptors involved in pain signaling and thermoregulation, a series of piperine analogs were prepared in several cycles of structural optimization, with the aim of separating GABA A and TRPV1 activating properties. We here investigated the metabolism of piperine and selected analogs in view of further cycles of lead optimization. Metabolic stability of the compounds was evaluated by incubation with pooled human liver microsomes, and metabolites were analyzed by UHPLC-Q-TOF-MS. CYP450 isoenzymes involved in metabolism of compounds were identified by reaction phenotyping with Silensomes™. Unbound fraction in whole blood was determined by rapid equilibrium dialysis. Piperine was the metabolically most stable compound. Aliphatic hydroxylation, and N- and O-dealkylation were the major routes of oxidative metabolism. Piperine was exclusively metabolized by CYP1A2, whereas CYP2C9 contributed significantly in the oxidative metabolism of all analogs. Extensive binding to blood constituents was observed for all compounds. Copyright © 2017 Elsevier B.V. All rights reserved.

A role for neuronal cAMP responsive-element binding (CREB)-1 in brain responses to calorie restriction

PubMed Central

Fusco, Salvatore; Ripoli, Cristian; Podda, Maria Vittoria; Ranieri, Sofia Chiatamone; Leone, Lucia; Toietta, Gabriele; McBurney, Michael W.; Schütz, Günther; Riccio, Antonella; Grassi, Claudio; Galeotti, Tommaso; Pani, Giovambattista

2012-01-01

Calorie restriction delays brain senescence and prevents neurodegeneration, but critical regulators of these beneficial responses other than the NAD+-dependent histone deacetylase Sirtuin-1 (Sirt-1) are unknown. We report that effects of calorie restriction on neuronal plasticity, memory and social behavior are abolished in mice lacking cAMP responsive-element binding (CREB)-1 in the forebrain. Moreover, CREB deficiency drastically reduces the expression of Sirt-1 and the induction of genes relevant to neuronal metabolism and survival in the cortex and hippocampus of dietary-restricted animals. Biochemical studies reveal a complex interplay between CREB and Sirt-1: CREB directly regulates the transcription of the sirtuin in neuronal cells by binding to Sirt-1 chromatin; Sirt-1, in turn, is recruited by CREB to DNA and promotes CREB-dependent expression of target gene peroxisome proliferator-activated receptor-γ coactivator-1α and neuronal NO Synthase. Accordingly, expression of these CREB targets is markedly reduced in the brain of Sirt KO mice that are, like CREB-deficient mice, poorly responsive to calorie restriction. Thus, the above circuitry, modulated by nutrient availability, links energy metabolism with neurotrophin signaling, participates in brain adaptation to nutrient restriction, and is potentially relevant to accelerated brain aging by overnutrition and diabetes. PMID:22190495

Hepatitis B virus X protein modulates peroxisome proliferator-activated receptor gamma through protein-protein interaction.

PubMed

Choi, Youn-Hee; Kim, Ha-il; Seong, Je Kyung; Yu, Dae-Yeul; Cho, Hyeseong; Lee, Mi-Ock; Lee, Jae Myun; Ahn, Yong-ho; Kim, Se Jong; Park, Jeon Han

2004-01-16

Ligand activation of peroxisome proliferator-activated receptor gamma (PPARgamma) has been reported to induce growth inhibition and apoptosis in various cancers including hepatocellular carcinoma (HCC). However, the effect of hepatitis B virus X protein (HBx) on PPARgamma activation has not been characterized in hepatitis B virus (HBV)-associated HCC. Herein, we demonstrated that HBx counteracted growth inhibition caused by PPARgamma ligand in HBx-associated HCC cells. We found that HBx bound to DNA binding domain of PPARgamma and HBx/PPARgamma interaction blocked nuclear localization and binding to recognition site of PPARgamma. HBx significantly suppressed a PPARgamma-mediated transactivation. These results suggest that HBx modulates PPARgamma function through protein-protein interaction.

Capacity for cooperative binding of thyroid hormone (T3) receptor dimers defines wild type T3 response elements.

PubMed

Brent, G A; Williams, G R; Harney, J W; Forman, B M; Samuels, H H; Moore, D D; Larsen, P R

1992-04-01

Thyroid hormone response elements (T3REs) have been identified in a variety of promoters including those directing expression of rat GH (rGH), alpha-myosin heavy chain (rMHC), and malic enzyme (rME). A detailed biochemical and genetic analysis of the rGH element has shown that it consists of three hexamers related to the consensus [(A/G)GGT(C/A)A]. We have extended this analysis to the rMHC and rME elements. Binding of highly purified thyroid hormone receptor (T3R) to T3REs was determined using the gel shift assay, and thyroid hormone (T3) induction was measured in transient tranfections. We show that the wild type version of each of the three elements binds T3R dimers cooperatively. Mutational analysis of the rMHC and rME elements identified domains important for binding T3R dimers and allowed a direct determination of the relationship between T3R binding and function. In each element two hexamers are required for dimer binding, and mutations that interfere with dimer formation significantly reduce T3 induction. Similar to the rGH element, the rMHC T3RE contains three hexameric domains arranged as a direct repeat followed by an inverted copy, although the third domain is weaker than in rGH. All three are required for full function and T3R binding. The rME T3RE is a two-hexamer direct repeat T3RE, which also binds T3R monomer and dimer. Across a series of mutant elements, there was a strong correlation between dimer binding in vitro and function in vivo for rMHC (r = 0.99, P less than 0.01) and rME (r = 0.67, P less than 0.05) T3REs. Our results demonstrate a similar pattern of T3R dimer binding to a diverse array of hexameric sequences and arrangements in three wild type T3REs. Addition of nuclear protein enhanced T3R binding but did not alter the specificity of binding to wild type or mutant elements. Binding of purified T3R to T3REs was highly correlated with function, both with and without the addition of nuclear protein. T3R dimer formation is the common feature which defines the capacity of these elements to confer T3 induction.

Efavirenz directly modulates estrogen receptor and induces breast cancer cell growth

PubMed Central

Sikora, Matthew J.; Rae, James M.; Johnson, Michael D.; Desta, Zeruesenay

2010-01-01

Objectives Efavirenz-based HIV therapy is associated with breast hypertrophy and gynecomastia. Here, we tested the hypothesis that efavirenz induces gynecomastia through direct binding and modulation of estrogen receptor (ER). Methods To determine the effect of efavirenz on growth, the estrogen-dependent, ER-positive breast cancer cell lines MCF-7, T47D and ZR-75-1 were treated with efavirenz under estrogen-free conditions in the presence or absence of the anti-estrogen ICI 182,780. Cells treated with 17β-estradiol in the absence or presence of ICI 182,780 served as positive and negative controls, respectively. Cellular growth was assayed using the crystal violet staining method and an in vitro receptor binding assay was used to measure efavirenz’s ER binding affinity. Results Efavirenz induced growth in MCF-7 cells with an estimated EC50 of 15.7µM. This growth was reversed by ICI 182,780. Further, efavirenz binds directly to ER (IC50 of ~52µM) at roughly 1000-fold higher concentration than observed with E2. Conclusions Our data suggest that efavirenz-induced gynecomastia may be due, at least in part, to drug-induced ER activation in breast tissues. PMID:20408889

Considerations on pharmacodynamics and pharmacokinetics: can everything be explained by the extent of drug binding to its receptor?

PubMed

Castañeda-Hernández, G; Granados-Soto, V

2000-03-01

It is frequently assumed that pharmacological responses depend solely on the extent of drug binding to its receptor according to the occupational theory. It is therefore presumed that the intensity of the effect is determined by drug concentration at its receptor site, yielding a unique concentration-effect relationship. However, when dependence, abstinence, and tolerance phenomena occur, as well as for pharmacological responses in vivo that are modulated by homeostatic mechanisms, the rate of drug input shifts the concentration-effect relationship. Hence, such responses cannot be explained on the sole basis of the extent of drug binding to its receptor. Information on the cellular and molecular processes involved in the generation of abstinence, dependence, and tolerance will undoubtedly result in the development of pharmacodynamic models allowing a satisfactory explanation of drug effects modulated by these phenomena. Notwithstanding, integrative physiology concepts are required to develop pharmacokinetic-pharmacodynamic models allowing the description of drug effects in an intact organism. It is therefore important to emphasize that integrative physiology cannot be neglected in pharmacology teaching and research, but should be considered as an equally valuable tool as molecular biology and other biomedical disciplines for the understanding of pharmacological effects.

Structural basis for ligand recognition at the benzodiazepine binding site of GABAA alpha 3 receptor, and pharmacophore-based virtual screening approach.

PubMed

Vijayan, R S K; Ghoshal, Nanda

2008-10-01

Given the heterogeneity of GABA(A) receptor, the pharmacological significance of identifying subtype selective modulators is increasingly being recognized. Thus, drugs selective for GABA(A) alpha(3) receptors are expected to display fewer side effects than the drugs presently in clinical use. Hence we carried out 3D QSAR (three-dimensional quantitative structure-activity relationship) studies on a series of novel GABA(A) alpha(3) subtype selective modulators to gain more insight into subtype affinity. To identify the 3D functional attributes required for subtype selectivity, a chemical feature-based pharmacophore, primarily based on selective ligands representing diverse structural classes was generated. The obtained pseudo receptor model of the benzodiazepine binding site revealed a binding mode akin to "Message-Address" concept. Scaffold hopping was carried out across multi-conformational May Bridge database for the identification of novel chemotypes. Further a focused data reduction approach was employed to choose a subset of enriched compounds based on "Drug likeness" and "Similarity-based" methods. These results taken together could provide impetus for rational design and optimization of more selective and high affinity leads with a potential to have decreased adverse effects.

Molecular modeling on structure-function analysis of human progesterone receptor modulators.

PubMed

Pal, Ria; Islam, Md Ataul; Hossain, Tabassum; Saha, Achintya

2011-01-01

Considering the significance of progesterone receptor (PR) modulators, the present study is explored to envisage the biophoric signals for binding to selective PR subtype-A using ligand-based quantitative structure activity relationship (QSAR) and pharmacophore space modeling studies on nonsteroidal substituted quinoline and cyclocymopol monomethyl ether derivatives. Consensus QSAR models (Training set (Tr): n(Tr)=100, R(2) (pred)=0.702; test set (Ts): n(Ts)=30, R(2) (pred)=0.705, R(2) (m)=0.635; validation set (Vs): n(Vs)=40, R(2) (pred)=0.715, R(2) (m)=0.680) suggest that molecular topology, atomic polarizability and electronegativity, atomic mass and van der Waals volume of the ligands have influence on the presence of functional atoms (F, Cl, N and O) and consequently contribute significant relations on ligand binding affinity. Receptor independent space modeling study (Tr: n(Tr)=26, Q(2)=0.927; Ts: n(Ts)=60, R(2) (pred)=0.613, R(2) (m)=0.545; Vs: n(Vs)=84, R(2) (pred)=0.611, R(2) (m)=0.507) indicates the importance of aromatic ring, hydrogen bond donor, molecular hydrophobicity and steric influence for receptor binding. The structure-function characterization is adjudged with the receptor-based docking study, explaining the significance of the mapped molecular attributes for ligand-receptor interaction in the catalytic cleft of PR-A.

The C-module-binding factor supports amplification of TRE5-A retrotransposons in the Dictyostelium discoideum genome.

PubMed

Bilzer, Annika; Dölz, Heike; Reinhardt, Alexander; Schmith, Anika; Siol, Oliver; Winckler, Thomas

2011-01-01

Retrotransposable elements are molecular parasites that have invaded the genomes of virtually all organisms. Although retrotransposons encode essential proteins to mediate their amplification, they also require assistance by host cell-encoded machineries that perform functions such as DNA transcription and repair. The retrotransposon TRE5-A of the social amoeba Dictyostelium discoideum generates a notable amount of both sense and antisense RNAs, which are generated from element-internal promoters, located in the A module and the C module, respectively. We observed that TRE5-A retrotransposons depend on the C-module-binding factor (CbfA) to maintain high steady-state levels of TRE5-A transcripts and that CbfA supports the retrotransposition activity of TRE5-A elements. The carboxy-terminal domain of CbfA was found to be required and sufficient to mediate the accumulation of TRE5-A transcripts, but it did not support productive retrotransposition of TRE5-A. This result suggests different roles for CbfA protein domains in the regulation of TRE5-A retrotransposition frequency in D. discoideum cells. Although CbfA binds to the C module in vitro, the factor regulates neither C-module nor A-module promoter activity in vivo. We speculate that CbfA supports the amplification of TRE5-A retrotransposons by suppressing the expression of an as yet unidentified component of the cellular posttranscriptional gene silencing machinery.

Non-canonical modulators of nuclear receptors.

PubMed

Tice, Colin M; Zheng, Ya-Jun

2016-09-01

Like G protein-coupled receptors (GPCRs) and protein kinases, nuclear receptors (NRs) are a rich source of pharmaceutical targets. Over 80 NR-targeting drugs have been approved for 18 NRs. The focus of drug discovery in NRs has hitherto been on identifying ligands that bind to the canonical ligand binding pockets of the C-terminal ligand binding domains (LBDs). Due to the development of drug resistance and selectivity concerns, there has been considerable interest in exploring other, non-canonical ligand binding sites. Unfortunately, the potencies of compounds binding at other sites have generally not been sufficient for clinical development. However, the situation has changed dramatically over the last 3years, as compounds with sufficient potency have been reported for several NR targets. Here we review recent developments in this area from a medicinal chemistry point of view in the hope of stimulating further interest in this area of research. Copyright © 2016 Elsevier Ltd. All rights reserved.

CCN2/CTGF binds to fibroblast growth factor receptor 2 and modulates its signaling.

PubMed

Aoyama, Eriko; Kubota, Satoshi; Takigawa, Masaharu

2012-12-14

CCN2 plays a critical role in the development of mesenchymal tissues such as cartilage and bone, and the binding of CCN2 to various cytokines and receptors regulates their signaling.By screening a protein array, we found that CCN2 could bind to fibroblast growth factor receptors (FGFRs) 2 and 3, with a higher affinity toward FGFR2.We ascertained that FGFR2 bound to CCN2 and that the binding of FGFR2 to FGF2 and FGF4 was enhanced by CCN2.CCN2 and FGF2 had a collaborative effect on the phosphorylation of ERK and the differentiation of osteoblastic cells.The present results indicate the biological significance of the binding of CCN2 to FGFR2 in bone metabolism. Copyright © 2012 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

Identifying a Mechanism for Crosstalk Between the Estrogen and Glucocorticoid Receptors | Center for Cancer Research

Cancer.gov

Estrogen has long been known to play important roles in the development and progression of breast cancer. Its receptor (ER), a member of the steroid receptor family, binds to estrogen response elements (EREs) in DNA and regulates gene transcription. More recently, another steroid receptor family member, the glucocorticoid receptor (GR), has been implicated in breast cancer

Positive modulator of bone morphogenic protein-2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zamora, Paul O.; Pena, Louis A.; Lin, Xinhua

Compounds of the present invention of formula I and formula II are disclosed in the specification and wherein the compounds are modulators of Bone Morphogenic Protein activity. Compounds are synthetic peptides having a non-growth factor heparin binding region, a linker, and sequences that bind specifically to a receptor for Bone Morphogenic Protein. Uses of compounds of the present invention in the treatment of bone lesions, degenerative joint disease and to enhance bone formation are disclosed.

Positive modulator of bone morphogenic protein-2

DOEpatents

Zamora, Paul O [Gaithersburg, MD; Pena, Louis A [Poquott, NY; Lin, Xinhua [Plainview, NY; Takahashi, Kazuyuki [Germantown, MD

2009-01-27

Compounds of the present invention of formula I and formula II are disclosed in the specification and wherein the compounds are modulators of Bone Morphogenic Protein activity. Compounds are synthetic peptides having a non-growth factor heparin binding region, a linker, and sequences that bind specifically to a receptor for Bone Morphogenic Protein. Uses of compounds of the present invention in the treatment of bone lesions, degenerative joint disease and to enhance bone formation are disclosed.

HPLC-Based Activity Profiling: Discovery of Piperine as a Positive GABAA Receptor Modulator Targeting a Benzodiazepine-Independent Binding Site

PubMed Central

Zaugg, Janine; Baburin, Igor; Strommer, Barbara; Kim, Hyun-Jung; Hering, Steffen; Hamburger, Matthias

2011-01-01

A plant extract library was screened for GABAA receptor activity making use of a two-microelectrode voltage clamp assay on Xenopus laevis oocytes. An ethyl acetate extract of black pepper fruits [Piper nigrum L. (Piperaceae) 100 μg/mL] potentiated GABA-induced chloride currents through GABAA receptors (composed of α1, β2, and γ2S subunits) by 169.1 ± 2.4%. With the aid of an HPLC-based activity profiling approach, piperine (5) was identified as the main active compound, together with 12 structurally related less active or inactive piperamides (1–4, 6–13). Identification was achieved by on-line high-resolution mass spectrometry and off-line microprobe 1D and 2D NMR spectroscopy, using only milligram amounts of extract. Compound 5 induced a maximum potentiation of the chloride currents by 301.9 ± 26.5% with an EC50 of 52.4 ± 9.4 μM. A comparison of the modulatory activity of 5 and other naturally occurring piperamides enabled insights into structural features critical for GABAA receptor modulation. The stimulation of chloride currents through GABAA receptors by compound 5 was not antagonized by flumazenil (10 μM). These data show that piperine (5) represents a new scaffold of positive allosteric GABAA receptor modulators targeting a benzodiazepine-independent binding site. PMID:20085307

Reversibly bound chloride in the atrial natriuretic peptide receptor hormone-binding domain: possible allosteric regulation and a conserved structural motif for the chloride-binding site.

PubMed

Ogawa, Haruo; Qiu, Yue; Philo, John S; Arakawa, Tsutomu; Ogata, Craig M; Misono, Kunio S

2010-03-01

The binding of atrial natriuretic peptide (ANP) to its receptor requires chloride, and it is chloride concentration dependent. The extracellular domain (ECD) of the ANP receptor (ANPR) contains a chloride near the ANP-binding site, suggesting a possible regulatory role. The bound chloride, however, is completely buried in the polypeptide fold, and its functional role has remained unclear. Here, we have confirmed that chloride is necessary for ANP binding to the recombinant ECD or the full-length ANPR expressed in CHO cells. ECD without chloride (ECD(-)) did not bind ANP. Its binding activity was fully restored by bromide or chloride addition. A new X-ray structure of the bromide-bound ECD is essentially identical to that of the chloride-bound ECD. Furthermore, bromide atoms are localized at the same positions as chloride atoms both in the apo and in the ANP-bound structures, indicating exchangeable and reversible halide binding. Far-UV CD and thermal unfolding data show that ECD(-) largely retains the native structure. Sedimentation equilibrium in the absence of chloride shows that ECD(-) forms a strongly associated dimer, possibly preventing the structural rearrangement of the two monomers that is necessary for ANP binding. The primary and tertiary structures of the chloride-binding site in ANPR are highly conserved among receptor-guanylate cyclases and metabotropic glutamate receptors. The chloride-dependent ANP binding, reversible chloride binding, and the highly conserved chloride-binding site motif suggest a regulatory role for the receptor bound chloride. Chloride-dependent regulation of ANPR may operate in the kidney, modulating ANP-induced natriuresis.

Reversibly Bound Chloride in the Atrial Natriuretic Peptide Receptor Hormone Binding Domain: Possible Allosteric Regulation and a Conserved Structural Motif for the Chloride-binding Site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ogawa, H.; Qiu, Y; Philo, J

2010-01-01

The binding of atrial natriuretic peptide (ANP) to its receptor requires chloride, and it is chloride concentration dependent. The extracellular domain (ECD) of the ANP receptor (ANPR) contains a chloride near the ANP-binding site, suggesting a possible regulatory role. The bound chloride, however, is completely buried in the polypeptide fold, and its functional role has remained unclear. Here, we have confirmed that chloride is necessary for ANP binding to the recombinant ECD or the full-length ANPR expressed in CHO cells. ECD without chloride (ECD(-)) did not bind ANP. Its binding activity was fully restored by bromide or chloride addition. Amore » new X-ray structure of the bromide-bound ECD is essentially identical to that of the chloride-bound ECD. Furthermore, bromide atoms are localized at the same positions as chloride atoms both in the apo and in the ANP-bound structures, indicating exchangeable and reversible halide binding. Far-UV CD and thermal unfolding data show that ECD(-) largely retains the native structure. Sedimentation equilibrium in the absence of chloride shows that ECD(-) forms a strongly associated dimer, possibly preventing the structural rearrangement of the two monomers that is necessary for ANP binding. The primary and tertiary structures of the chloride-binding site in ANPR are highly conserved among receptor-guanylate cyclases and metabotropic glutamate receptors. The chloride-dependent ANP binding, reversible chloride binding, and the highly conserved chloride-binding site motif suggest a regulatory role for the receptor bound chloride. Chloride-dependent regulation of ANPR may operate in the kidney, modulating ANP-induced natriuresis.« less

Reversibly bound chloride in the atrial natriuretic peptide receptor hormone-binding domain: Possible allosteric regulation and a conserved structural motif for the chloride-binding site

PubMed Central

Ogawa, Haruo; Qiu, Yue; Philo, John S; Arakawa, Tsutomu; Ogata, Craig M; Misono, Kunio S

2010-01-01

The binding of atrial natriuretic peptide (ANP) to its receptor requires chloride, and it is chloride concentration dependent. The extracellular domain (ECD) of the ANP receptor (ANPR) contains a chloride near the ANP-binding site, suggesting a possible regulatory role. The bound chloride, however, is completely buried in the polypeptide fold, and its functional role has remained unclear. Here, we have confirmed that chloride is necessary for ANP binding to the recombinant ECD or the full-length ANPR expressed in CHO cells. ECD without chloride (ECD(−)) did not bind ANP. Its binding activity was fully restored by bromide or chloride addition. A new X-ray structure of the bromide-bound ECD is essentially identical to that of the chloride-bound ECD. Furthermore, bromide atoms are localized at the same positions as chloride atoms both in the apo and in the ANP-bound structures, indicating exchangeable and reversible halide binding. Far-UV CD and thermal unfolding data show that ECD(−) largely retains the native structure. Sedimentation equilibrium in the absence of chloride shows that ECD(−) forms a strongly associated dimer, possibly preventing the structural rearrangement of the two monomers that is necessary for ANP binding. The primary and tertiary structures of the chloride-binding site in ANPR are highly conserved among receptor-guanylate cyclases and metabotropic glutamate receptors. The chloride-dependent ANP binding, reversible chloride binding, and the highly conserved chloride-binding site motif suggest a regulatory role for the receptor bound chloride. Chloride-dependent regulation of ANPR may operate in the kidney, modulating ANP-induced natriuresis. PMID:20066666

Structure-activity relationship study of tetrapeptide inhibitors of the Vascular Endothelial Growth Factor A binding to Neuropilin-1.

PubMed

Tymecka, Dagmara; Lipiński, Piotr F J; Fedorczyk, Bartłomiej; Puszko, Anna; Wileńska, Beata; Perret, Gerard Y; Misicka, Aleksandra

2017-08-01

Neuropilin-1 is considered as one of the key receptors responsible for signaling pathways involved in pathological angiogenesis necessary for tumor progression, therefore targeting of VEGF 165 binding to NRP-1 could be a relevant strategy for antiangiogenic treatment. It was shown before that the VEGF 165 /NRP-1 interaction can be inhibited by short tetrapeptides with K/RXXR sequence. Here, we present a structure-activity relationship study of the systematic optimization of amino acid residues in positions 1-3 in the above tetrapeptides. All the 13 synthesized analogs possessed C-terminal arginine that is a necessary element for interaction with NRP-1. The obtained results of the inhibitory activity and modeling by molecular dynamics indicate that simultaneous interactions of the basic amino acid residues in position 1 and 4 (Arg) with Neuropilin-1 are crucial and their cooperation strongly affects the inhibitory activity. In addition, the binding strength is modulated by the flexibility of the peptide backbone (in the central part of the peptide), and the nature of the side chain of the amino acids at the second or third position. A dramatic decrease in the activity to the receptor is observed in flexible derivatives that are missing proline residues. The results described in this paper should prove useful for future studies aimed at establishing the best pharmacophore for inhibitors of VEGF 165 binding to NRP-1. Copyright © 2017 Elsevier Inc. All rights reserved.

Progesterone receptor modulates estrogen receptor-α action in breast cancer

PubMed Central

Mohammed, Hisham; Russell, I. Alasdair; Stark, Rory; Rueda, Oscar M.; Hickey, Theresa E.; Tarulli, Gerard A.; Serandour, Aurelien A. A.; Birrell, Stephen N.; Bruna, Alejandra; Saadi, Amel; Menon, Suraj; Hadfield, James; Pugh, Michelle; Raj, Ganesh V.; Brown, Gordon D.; D’Santos, Clive; Robinson, Jessica L. L.; Silva, Grace; Launchbury, Rosalind; Perou, Charles M.; Stingl, John; Caldas, Carlos; Tilley, Wayne D.; Carroll, Jason S.

2015-01-01

Summary Progesterone receptor (PR) expression is employed as a biomarker of estrogen receptor-α (ERα) function and breast cancer prognosis. We now show that PR is not merely an ERα-induced gene target, but is also an ERα-associated protein that modulates its behaviour. In the presence of agonist ligands, PR associates with ERα to direct ERα chromatin binding events within breast cancer cells, resulting in a unique gene expression programme that is associated with good clinical outcome. Progesterone inhibited estrogen-mediated growth of ERα+ cell line xenografts and primary ERα+ breast tumour explants and had increased anti-proliferative effects when coupled with an ERα antagonist. Copy number loss of PgR is a common feature in ERα+ breast cancers, explaining lower PR levels in a subset of cases. Our findings indicate that PR functions as a molecular rheostat to control ERα chromatin binding and transcriptional activity, which has important implications for prognosis and therapeutic interventions. PMID:26153859

α Actinin 4 (ACTN4) Regulates Glucocorticoid Receptor-mediated Transactivation and Transrepression in Podocytes*

PubMed Central

Zhao, Xuan; Khurana, Simran; Charkraborty, Sharmistha; Tian, Yuqian; Sedor, John R.; Bruggman, Leslie A.; Kao, Hung-Ying

2017-01-01

Glucocorticoids are a general class of steroids that possess renoprotective activity in glomeruli through their interaction with the glucocorticoid receptor. However, the mechanisms by which glucocorticoids ameliorate proteinuria and glomerular disease are not well understood. In this study, we demonstrated that α actinin 4 (ACTN4), an actin-cross-linking protein known to coordinate cytoskeletal organization, interacts with the glucocorticoid receptor (GR) in the nucleus of human podocytes (HPCs), a key cell type in the glomerulus critical for kidney filtration function. The GR-ACTN4 complex enhances glucocorticoid response element (GRE)-driven reporter activity. Stable knockdown of ACTN4 by shRNA in HPCs significantly reduces dexamethasone-mediated induction of GR target genes and GRE-driven reporter activity without disrupting dexamethasone-induced nuclear translocation of GR. Synonymous mutations or protein expression losses in ACTN4 are associated with kidney diseases, including focal segmental glomerulosclerosis, characterized by proteinuria and podocyte injury. We found that focal segmental glomerulosclerosis-linked ACTN4 mutants lose their ability to bind liganded GR and support GRE-mediated transcriptional activity. Mechanistically, GR and ACTN4 interact in the nucleus of HPCs. Furthermore, disruption of the LXXLL nuclear receptor-interacting motif present in ACTN4 results in reduced GR interaction and dexamethasone-mediated transactivation of a GRE reporter while still maintaining its actin-binding activity. In contrast, an ACTN4 isoform, ACTN4 (Iso), that loses its actin-binding domain is still capable of potentiating a GRE reporter. Dexamethasone induces the recruitment of ACTN4 and GR to putative GREs in dexamethasone-transactivated promoters, SERPINE1, ANGPLT4, CCL20, and SAA1 as well as the NF-κB (p65) binding sites on GR-transrepressed promoters such as IL-1β, IL-6, and IL-8. Taken together, our data establish ACTN4 as a transcriptional co-regulator that modulates both dexamethasone-transactivated and -transrepressed genes in podocytes. PMID:27998979

Transforming growth factor β suppresses peroxisome proliferator-activated receptor γ expression via both SMAD binding and novel TGF-β inhibitory elements.

PubMed

Lakshmi, Sowmya P; Reddy, Aravind T; Reddy, Raju C

2017-04-24

Transforming growth factor β (TGF-β) contributes to wound healing and, when dysregulated, to pathological fibrosis. TGF-β and the anti-fibrotic nuclear hormone receptor peroxisome proliferator-activated receptor γ (PPARγ) repress each other's expression, and such PPARγ down-regulation is prominent in fibrosis and mediated, via previously unknown SMAD-signaling mechanisms. Here, we show that TGF-β induces the association of SMAD3 with both SMAD4, needed for translocation of the complex into the nucleus, and the essential context-sensitive co-repressors E2F4 and p107. The complex mediates TGF-β-induced repression by binding to regulatory elements in the target promoter. In the PPARG promoter, we found that the SMAD3-SMAD4 complex binds both to a previously unknown consensus TGF-β inhibitory element (TIE) and also to canonical SMAD-binding elements (SBEs). Furthermore, the TIE and SBEs independently mediated the partial repression of PPARG transcription, the first demonstration of a TIE and SBEs functioning within the same promoter. Also, TGF-β-treated fibroblasts contained SMAD complexes that activated a SMAD target gene in addition to those repressing PPARG transcription, the first finding of such dual activity within the same cell. These findings describe in detail novel mechanisms by which TGF-β represses PPARG transcription, thereby facilitating its own pro-fibrotic activity. © 2017 The Author(s); published by Portland Press Limited on behalf of the Biochemical Society.

Regulation of DREAM Expression by Group I mGluR

PubMed Central

Lee, Jinu; Kim, Insook; Oh, So Ra; Ko, Suk Jin; Lim, Mi Kyung; Kim, Dong Goo

2011-01-01

DREAM (downstream regulatory element antagonistic modulator) is a calcium-binding protein that regulates dynorphin expression, promotes potassium channel surface expression, and enhances presenilin processing in an expression level-dependent manner. However, no molecular mechanism has yet explained how protein levels of DREAM are regulated. Here we identified group I mGluR (mGluR1/5) as a positive regulator of DREAM protein expression. Overexpression of mGluR1/5 increased the cellular level of DREAM. Up-regulation of DREAM resulted in increased DREAM protein in both the nucleus and cytoplasm, where the protein acts as a transcriptional repressor and a modulator of its interacting proteins, respectively. DHPG (3,5-dihydroxyphenylglycine), a group I mGluR agonist, also up-regulated DREAM expression in cortical neurons. These results suggest that group I mGluR is the first identified receptor that may regulate DREAM activity in neurons. PMID:21660149

Molecular Determinants of Magnolol Targeting Both RXRα and PPARγ

PubMed Central

Chen, Lili; Chen, Jing; Hu, Lihong; Jiang, Hualiang; Shen, Xu

2011-01-01

Nuclear receptors retinoic X receptor α (RXRα) and peroxisome proliferator activated receptor γ (PPARγ) function potently in metabolic diseases, and are both important targets for anti-diabetic drugs. Coactivation of RXRα and PPARγ is believed to synergize their effects on glucose and lipid metabolism. Here we identify the natural product magnolol as a dual agonist targeting both RXRα and PPARγ. Magnolol was previously reported to enhance adipocyte differentiation and glucose uptake, ameliorate blood glucose level and prevent development of diabetic nephropathy. Although magnolol can bind and activate both of these two nuclear receptors, the transactivation assays indicate that magnolol exhibits biased agonism on the transcription of PPAR-response element (PPRE) mediated by RXRα:PPARγ heterodimer, instead of RXR-response element (RXRE) mediated by RXRα:RXRα homodimer. To further elucidate the molecular basis for magnolol agonism, we determine both the co-crystal structures of RXRα and PPARγ ligand-binding domains (LBDs) with magnolol. Structural analyses reveal that magnolol adopts its two 5-allyl-2-hydroxyphenyl moieties occupying the acidic and hydrophobic cavities of RXRα L-shaped ligand-binding pocket, respectively. While, two magnolol molecules cooperatively accommodate into PPARγ Y-shaped ligand-binding pocket. Based on these two complex structures, the key interactions for magnolol activating RXRα and PPARγ are determined. As the first report on the dual agonist targeting RXRα and PPARγ with receptor-ligand complex structures, our results are thus expected to help inspect the potential pharmacological mechanism for magnolol functions, and supply useful hits for nuclear receptor multi-target ligand design. PMID:22140563

Insights into structure–activity relationship of GABAA receptor modulating coumarins and furanocoumarins

PubMed Central

Singhuber, Judith; Baburin, Igor; Ecker, Gerhard F.; Kopp, Brigitte; Hering, Steffen

2011-01-01

The coumarins imperatorin and osthole are known to exert anticonvulsant activity. We have therefore analyzed the modulation of GABA-induced chloride currents (IGABA) by a selection of 18 coumarin derivatives on recombinant α1β2γ2S GABAA receptors expressed in Xenopus laevis oocytes by means of the two-microelectrode voltage clamp technique. Osthole (EC50=14±1 μM) and oxypeucedanin (EC50=25±8 μM) displayed the highest efficiency with IGABA potentiation of 116±4% and 547±56%, respectively. IGABA enhancement by osthole and oxypeucedanin was not inhibited by flumazenil (1 μM) indicating an interaction with a binding site distinct from the benzodiazepine binding site. In general, prenyl residues are essential for the positive modulatory activity, while longer side chains or bulkier residues (e.g. geranyl residues) diminish IGABA modulation. Generation of a binary classification tree revealed the importance of polarisability, which is sufficient to distinguish actives from inactives. A 4-point pharmacophore model based on oxypeucedanin – comprising three hydrophobic and one aromatic feature – identified 6 out of 7 actives as hits. In summary, (oxy-)prenylated coumarin derivatives from natural origin represent new GABAA receptor modulators. PMID:21749864

Elucidating the Functional Roles of Spatial Organization in Cross-Membrane Signal Transduction by a Hybrid Simulation Method.

PubMed

Chen, Jiawen; Xie, Zhong-Ru; Wu, Yinghao

2016-07-01

The ligand-binding of membrane receptors on cell surfaces initiates the dynamic process of cross-membrane signal transduction. It is an indispensable part of the signaling network for cells to communicate with external environments. Recent experiments revealed that molecular components in signal transduction are not randomly mixed, but spatially organized into distinctive patterns. These patterns, such as receptor clustering and ligand oligomerization, lead to very different gene expression profiles. However, little is understood about the molecular mechanisms and functional impacts of this spatial-temporal regulation in cross-membrane signal transduction. In order to tackle this problem, we developed a hybrid computational method that decomposes a model of signaling network into two simulation modules. The physical process of binding between receptors and ligands on cell surfaces are simulated by a diffusion-reaction algorithm, while the downstream biochemical reactions are modeled by stochastic simulation of Gillespie algorithm. These two processes are coupled together by a synchronization framework. Using this method, we tested the dynamics of a simple signaling network in which the ligand binding of cell surface receptors triggers the phosphorylation of protein kinases, and in turn regulates the expression of target genes. We found that spatial aggregation of membrane receptors at cellular interfaces is able to either amplify or inhibit downstream signaling outputs, depending on the details of clustering mechanism. Moreover, by providing higher binding avidity, the co-localization of ligands into multi-valence complex modulates signaling in very different ways that are closely related to the binding affinity between ligand and receptor. We also found that the temporal oscillation of the signaling pathway that is derived from genetic feedback loops can be modified by the spatial clustering of membrane receptors. In summary, our method demonstrates the functional importance of spatial organization in cross-membrane signal transduction. The method can be applied to any specific signaling pathway in cells.

Calcitonin and Amylin Receptor Peptide Interaction Mechanisms

PubMed Central

Lee, Sang-Min; Hay, Debbie L.; Pioszak, Augen A.

2016-01-01

Receptor activity-modifying proteins (RAMP1–3) determine the selectivity of the class B G protein-coupled calcitonin receptor (CTR) and the CTR-like receptor (CLR) for calcitonin (CT), amylin (Amy), calcitonin gene-related peptide (CGRP), and adrenomedullin (AM) peptides. RAMP1/2 alter CLR selectivity for CGRP/AM in part by RAMP1 Trp-84 or RAMP2 Glu-101 contacting the distinct CGRP/AM C-terminal residues. It is unclear whether RAMPs use a similar mechanism to modulate CTR affinity for CT and Amy, analogs of which are therapeutics for bone disorders and diabetes, respectively. Here, we reproduced the peptide selectivity of intact CTR, AMY1 (CTR·RAMP1), and AMY2 (CTR·RAMP2) receptors using purified CTR extracellular domain (ECD) and tethered RAMP1- and RAMP2-CTR ECD fusion proteins and antagonist peptides. All three proteins bound salmon calcitonin (sCT). Tethering RAMPs to CTR enhanced binding of rAmy, CGRP, and the AMY antagonist AC413. Peptide alanine-scanning mutagenesis and modeling of receptor-bound sCT and AC413 supported a shared non-helical CGRP-like conformation for their TN(T/V)G motif prior to the C terminus. After this motif, the peptides diverged; the sCT C-terminal Pro was crucial for receptor binding, whereas the AC413/rAmy C-terminal Tyr had little or no influence on binding. Accordingly, mutant RAMP1 W84A- and RAMP2 E101A-CTR ECD retained AC413/rAmy binding. ECD binding and cell-based signaling assays with antagonist sCT/AC413/rAmy variants with C-terminal residue swaps indicated that the C-terminal sCT/rAmy residue identity affects affinity more than selectivity. rAmy(8–37) Y37P exhibited enhanced antagonism of AMY1 while retaining selectivity. These results reveal unexpected differences in how RAMPs determine CTR and CLR peptide selectivity and support the hypothesis that RAMPs allosterically modulate CTR peptide affinity. PMID:26895962

Effect of novel negative allosteric modulators of neuronal nicotinic receptors on cells expressing native and recombinant nicotinic receptors: implications for drug discovery.

PubMed

González-Cestari, Tatiana F; Henderson, Brandon J; Pavlovicz, Ryan E; McKay, Susan B; El-Hajj, Raed A; Pulipaka, Aravinda B; Orac, Crina M; Reed, Damon D; Boyd, R Thomas; Zhu, Michael X; Li, Chenglong; Bergmeier, Stephen C; McKay, Dennis B

2009-02-01

Allosteric modulation of nAChRs is considered to be one of the most promising approaches for drug design targeting nicotinic acetylcholine receptors (nAChRs). We have reported previously on the pharmacological activity of several compounds that seem to act noncompetitively to inhibit the activation of alpha3beta4(*) nAChRs. In this study, the effects of 51 structurally similar molecules on native and recombinant alpha3beta4 nAChRs are characterized. These 51 molecules inhibited adrenal neurosecretion activated via stimulation of native alpha3beta4(*) nAChR, with IC(50) values ranging from 0.4 to 13.0 microM. Using cells expressing recombinant alpha3beta4 nAChRs, these molecules inhibited calcium accumulation (a more direct assay to establish nAChR activity), with IC(50) values ranging from 0.7 to 38.2 microM. Radiolabeled nAChR binding studies to orthosteric sites showed no inhibitory activity on either native or recombinant nAChRs. Correlation analyses of the data from both functional assays suggested additional, non-nAChR activity of the molecules. To test this hypothesis, the effects of the drugs on neurosecretion stimulated through non-nAChR mechanisms were investigated; inhibitory effects ranged from no inhibition to 95% inhibition at concentrations of 10 microM. Correlation analyses of the functional data confirmed this hypothesis. Several of the molecules (24/51) increased agonist binding to native nAChRs, supporting allosteric interactions with nAChRs. Computational modeling and blind docking identified a binding site for our negative allosteric modulators near the orthosteric binding site of the receptor. In summary, this study identified several molecules for potential development as negative allosteric modulators and documented the importance of multiple screening assays for nAChR drug discovery.

Effect of Novel Negative Allosteric Modulators of Neuronal Nicotinic Receptors on Cells Expressing Native and Recombinant Nicotinic Receptors: Implications for Drug Discovery

PubMed Central

González-Cestari, Tatiana F.; Henderson, Brandon J.; Pavlovicz, Ryan E.; McKay, Susan B.; El-Hajj, Raed A.; Pulipaka, Aravinda B.; Orac, Crina M.; Reed, Damon D.; Boyd, R. Thomas; Zhu, Michael X.; Li, Chenglong; Bergmeier, Stephen C.; McKay, Dennis B.

2009-01-01

Allosteric modulation of nAChRs is considered to be one of the most promising approaches for drug design targeting nicotinic acetylcholine receptors (nAChRs). We have reported previously on the pharmacological activity of several compounds that seem to act noncompetitively to inhibit the activation of α3β4* nAChRs. In this study, the effects of 51 structurally similar molecules on native and recombinant α3β4 nAChRs are characterized. These 51 molecules inhibited adrenal neurosecretion activated via stimulation of native α3β4* nAChR, with IC50 values ranging from 0.4 to 13.0 μM. Using cells expressing recombinant α3β4 nAChRs, these molecules inhibited calcium accumulation (a more direct assay to establish nAChR activity), with IC50 values ranging from 0.7 to 38.2 μM. Radiolabeled nAChR binding studies to orthosteric sites showed no inhibitory activity on either native or recombinant nAChRs. Correlation analyses of the data from both functional assays suggested additional, non-nAChR activity of the molecules. To test this hypothesis, the effects of the drugs on neurosecretion stimulated through non-nAChR mechanisms were investigated; inhibitory effects ranged from no inhibition to 95% inhibition at concentrations of 10 μM. Correlation analyses of the functional data confirmed this hypothesis. Several of the molecules (24/51) increased agonist binding to native nAChRs, supporting allosteric interactions with nAChRs. Computational modeling and blind docking identified a binding site for our negative allosteric modulators near the orthosteric binding site of the receptor. In summary, this study identified several molecules for potential development as negative allosteric modulators and documented the importance of multiple screening assays for nAChR drug discovery. PMID:18984653

Binding, Thermodynamics, and Selectivity of a Non-peptide Antagonist to the Melanocortin-4 Receptor

PubMed Central

Saleh, Noureldin; Kleinau, Gunnar; Heyder, Nicolas; Clark, Timothy; Hildebrand, Peter W.; Scheerer, Patrick

2018-01-01

The melanocortin-4 receptor (MC4R) is a potential drug target for treatment of obesity, anxiety, depression, and sexual dysfunction. Crystal structures for MC4R are not yet available, which has hindered successful structure-based drug design. Using microsecond-scale molecular-dynamics simulations, we have investigated selective binding of the non-peptide antagonist MCL0129 to a homology model of human MC4R (hMC4R). This approach revealed that, at the end of a multi-step binding process, MCL0129 spontaneously adopts a binding mode in which it blocks the agonistic-binding site. This binding mode was confirmed in subsequent metadynamics simulations, which gave an affinity for human hMC4R that matches the experimentally determined value. Extending our simulations of MCL0129 binding to hMC1R and hMC3R, we find that receptor subtype selectivity for hMC4R depends on few amino acids located in various structural elements of the receptor. These insights may support rational drug design targeting the melanocortin systems.

Spacing requirements for interactions between the C-terminal domain of the alpha subunit of Escherichia coli RNA polymerase and the cAMP receptor protein.

PubMed Central

Lloyd, G S; Busby, S J; Savery, N J

1998-01-01

During transcription initiation at bacterial promoters, the C-terminal domain of the RNA polymerase alpha subunit (alphaCTD) can interact with DNA-sequence elements (known as UP elements) and with activator proteins. We have constructed a series of semi-synthetic promoters carrying both an UP element and a consensus DNA-binding site for the Escherichia coli cAMP receptor protein (CRP; a factor that activates transcription by making direct contacts with alphaCTD). At these promoters, the UP element was located at a variety of distances upstream of the CRP-binding site, which was fixed at position -41.5 bp upstream of the transcript start. At some positions, the UP element caused enhanced promoter activity whereas, at other positions, it had very little effect. In no case was the CRP-dependence of the promoter relieved. DNase I and hydroxyl-radical footprinting were used to study ternary RNA polymerase-CRP-promoter complexes formed at two of the most active of these promoters, and co-operativity between the binding of CRP and purified alpha subunits was studied. The footprints show that alphaCTD binds to the UP element as it is displaced upstream but that this displacement does not prevent alphaCTD from being contacted by CRP. Models to account for this are discussed. PMID:9461538

Hydrogen-Deuterium Exchange Mass Spectrometry Reveals Calcium Binding Properties and Allosteric Regulation of Downstream Regulatory Element Antagonist Modulator (DREAM).

PubMed

Zhang, Jun; Li, Jing; Craig, Theodore A; Kumar, Rajiv; Gross, Michael L

2017-07-18

Downstream regulatory element antagonist modulator (DREAM) is an EF-hand Ca 2+ -binding protein that also binds to a specific DNA sequence, downstream regulatory elements (DRE), and thereby regulates transcription in a calcium-dependent fashion. DREAM binds to DRE in the absence of Ca 2+ but detaches from DRE under Ca 2+ stimulation, allowing gene expression. The Ca 2+ binding properties of DREAM and the consequences of the binding on protein structure are key to understanding the function of DREAM. Here we describe the application of hydrogen-deuterium exchange mass spectrometry (HDX-MS) and site-directed mutagenesis to investigate the Ca 2+ binding properties and the subsequent conformational changes of full-length DREAM. We demonstrate that all EF-hands undergo large conformation changes upon calcium binding even though the EF-1 hand is not capable of binding to Ca 2+ . Moreover, EF-2 is a lower-affinity site compared to EF-3 and -4 hands. Comparison of HDX profiles between wild-type DREAM and two EF-1 mutated constructs illustrates that the conformational changes in the EF-1 hand are induced by long-range structural interactions. HDX analyses also reveal a conformational change in an N-terminal leucine-charged residue-rich domain (LCD) remote from Ca 2+ -binding EF-hands. This LCD domain is responsible for the direct interaction between DREAM and cAMP response element-binding protein (CREB) and regulates the recruitment of the co-activator, CREB-binding protein. These long-range interactions strongly suggest how conformational changes transmit the Ca 2+ signal to CREB-mediated gene transcription.

The evolutionary origin of the need to sleep: an inevitable consequence of synaptic neurotransmission?

PubMed

Cantor, Robert S

2015-01-01

It is proposed that the evolutionary origin of the need to sleep is the removal of neurotransmitters (NTs) that escape reuptake and accumulate in brain interstitial fluid (ISF). Recent work suggests that the activity of ionotropic postsynaptic receptors, rapidly initiated by binding of NTs to extracellular sites, is modulated over longer times by adsorption of these NTs to the lipid bilayers in which the receptors are embedded. This bilayer-mediated mechanism is far less molecularly specific than binding, so bilayer adsorption of NTs that have diffused into synapses for other receptors would modulate their activity as well. Although NTs are recycled by membrane protein reuptake, the process is less than 100% efficient; a fraction escapes the region in which these specific reuptake proteins are localized and eventually diffuses throughout the ISF. It is estimated that even if only 0.1% of NTs escape reuptake, they would accumulate and adsorb to bilayers in synapses of other receptors sufficiently to affect receptor activity, the harmful consequences of which are avoided by sleep: a period of efficient convective clearance of solutes together with greatly reduced synaptic activity.

Estrogen regulation of chicken riboflavin carrier protein gene is mediated by ERE half sites without direct binding of estrogen receptor.

PubMed

Bahadur, Urvashi; Ganjam, Goutham K; Vasudevan, Nandini; Kondaiah, Paturu

2005-02-28

Estrogen is an important steroid hormone that mediates most of its effects on regulation of gene expression by binding to intracellular receptors. The consensus estrogen response element (ERE) is a 13bp palindromic inverted repeat with a three nucleotide spacer. However, several reports suggest that many estrogen target genes are regulated by diverse elements, such as imperfect EREs and ERE half sites (ERE 1/2), which are either the proximal or the distal half of the palindrome. To gain more insight into ERE half site-mediated gene regulation, we used a region from the estrogen-regulated chicken riboflavin carrier protein (RCP) gene promoter that contains ERE half sites. Using moxestrol, an analogue of estrogen and transient transfection of deletion and mutation containing RCP promoter/reporter constructs in chicken hepatoma (LMH2A) cells, we identified an estrogen response unit (ERU) composed of two consensus ERE 1/2 sites and one non-consensus ERE 1/2 site. Mutation of any of these sites within this ERU abolishes moxestrol response. Further, the ERU is able to confer moxestrol responsiveness to a heterologous promoter. Interestingly, RCP promoter is regulated by moxestrol in estrogen responsive human MCF-7 cells, but not in other cell lines such as NIH3T3 and HepG2 despite estrogen receptor-alpha (ER-alpha) co transfection. Electrophoretic mobility shift assays (EMSAs) with promoter regions encompassing the half sites and nuclear extracts from LMH2A cells show the presence of a moxestrol-induced complex that is abolished by a polyclonal anti-ERalpha antibody. Surprisingly, estrogen receptor cannot bind to these promoter elements in isolation. Thus, there appears to be a definite requirement for some other factor(s) in addition to estrogen receptor, for the generation of a suitable response of this promoter to estrogen. Our studies therefore suggest a novel mechanism of gene regulation by estrogen, involving ERE half sites without direct binding of ER to the cognate elements.

The effect of extracts of the roots of the stinging nettle (Urtica dioica) on the interaction of SHBG with its receptor on human prostatic membranes.

PubMed

Hryb, D J; Khan, M S; Romas, N A; Rosner, W

1995-02-01

Extracts from the roots of the stinging nettle (Urtica dioica) are used in the treatment of benign prostatic hyperplasia. The mechanisms underlying this treatment have not been elucidated. We set out to determine whether specific extracts from U. dioica had the ability to modulate the binding of sex hormone-binding globulin to its receptor on human prostatic membranes. Four substances contained in U. dioica were examined: an aqueous extract; an alcoholic extract; U. dioica agglutinin, and stigmasta-4-en-3-one. Of these, only the aqueous extract was active. It inhibited the binding of 125I-SHBG to its receptor. The inhibition was dose related, starting at about 0.6 mg/ml and completely inhibited binding at 10 mg/ml.

Differential CLE peptide perception by plant receptors implicated from structural and functional analyses of TDIF-TDR interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zhijie; Chakraborty, Sayan; Xu, Guozhou

Tracheary Element Differentiation Inhibitory Factor (TDIF) belongs to the family of post-translationally modified CLE (CLAVATA3/embryo surrounding region (ESR)-related) peptide hormones that control root growth and define the delicate balance between stem cell proliferation and differentiation in SAM (shoot apical meristem) or RAM (root apical meristem). In Arabidopsis, Tracheary Element Differentiation Inhibitory Factor Receptor (TDR) and its ligand TDIF signaling pathway is involved in the regulation of procambial cell proliferation and inhibiting its differentiation into xylem cells. Here we present the crystal structures of the extracellular domains (ECD) of TDR alone and in complex with its ligand TDIF resolved at 2.65more » Åand 2.75 Å respectively. These structures provide insights about the ligand perception and specific interactions between the CLE peptides and their cognate receptors. Our in vitro biochemical studies indicate that the interactions between the ligands and the receptors at the C-terminal anchoring site provide conserved binding. While the binding interactions occurring at the N-terminal anchoring site dictate differential binding specificities between different ligands and receptors. Our studies will open different unknown avenues of TDR-TDIF signaling pathways that will enhance our knowledge in this field highlighting the receptor ligand interaction, receptor activation, signaling network, modes of action and will serve as a structure function relationship model between the ligand and the receptor for various similar leucine-rich repeat receptor-like kinases (LRR-RLKs).« less

A key agonist-induced conformational change in the cannabinoid receptor CB1 is blocked by the allosteric ligand Org 27569.

PubMed

Fay, Jonathan F; Farrens, David L

2012-09-28

Allosteric ligands that modulate how G protein-coupled receptors respond to traditional orthosteric drugs are an exciting and rapidly expanding field of pharmacology. An allosteric ligand for the cannabinoid receptor CB1, Org 27569, exhibits an intriguing effect; it increases agonist binding, yet blocks agonist-induced CB1 signaling. Here we explored the mechanism behind this behavior, using a site-directed fluorescence labeling approach. Our results show that Org 27569 blocks conformational changes in CB1 that accompany G protein binding and/or activation, and thus inhibit formation of a fully active CB1 structure. The underlying mechanism behind this behavior is that simultaneous binding of Org 27569 produces a unique agonist-bound conformation, one that may resemble an intermediate structure formed on the pathway to full receptor activation.

The signaling helix: a common functional theme in diverse signaling proteins

PubMed Central

Anantharaman, Vivek; Balaji, S; Aravind, L

2006-01-01

Background The mechanism by which the signals are transmitted between receptor and effector domains in multi-domain signaling proteins is poorly understood. Results Using sensitive sequence analysis methods we identify a conserved helical segment of around 40 residues in a wide range of signaling proteins, including numerous sensor histidine kinases such as Sln1p, and receptor guanylyl cyclases such as the atrial natriuretic peptide receptor and nitric oxide receptors. We term this helical segment the signaling (S)-helix and present evidence that it forms a novel parallel coiled-coil element, distinct from previously known helical segments in signaling proteins, such as the Dimerization-Histidine phosphotransfer module of histidine kinases, the intra-cellular domains of the chemotaxis receptors, inter-GAF domain helical linkers and the α-helical HAMP module. Analysis of domain architectures allowed us to reconstruct the domain-neighborhood graph for the S-helix, which showed that the S-helix almost always occurs between two signaling domains. Several striking patterns in the domain neighborhood of the S-helix also became evident from the graph. It most often separates diverse N-terminal sensory domains from various C-terminal catalytic signaling domains such as histidine kinases, cNMP cyclase, PP2C phosphatases, NtrC-like AAA+ ATPases and diguanylate cyclases. It might also occur between two sensory domains such as PAS domains and occasionally between a DNA-binding HTH domain and a sensory domain. The sequence conservation pattern of the S-helix revealed the presence of a unique constellation of polar residues in the dimer-interface positions within the central heptad of the coiled-coil formed by the S-helix. Conclusion Combining these observations with previously reported mutagenesis studies on different S-helix-containing proteins we suggest that it functions as a switch that prevents constitutive activation of linked downstream signaling domains. However, upon occurrence of specific conformational changes due to binding of ligand or other sensory inputs in a linked upstream domain it transmits the signal to the downstream domain. Thus, the S-helix represents one of the most prevalent functional themes involved in the flow of signals between modules in diverse prokaryote-type multi-domain signaling proteins. Reviewers This article was reviewed by Frank Eisenhaber, Arcady Mushegian and Sandor Pongor. PMID:16953892

A New Family of Nuclear Receptor Coregulators That Integrate Nuclear Receptor Signaling through CREB-Binding Protein

PubMed Central

Mahajan, Muktar A.; Samuels, Herbert H.

2000-01-01

We describe the cloning and characterization of a new family of nuclear receptor coregulators (NRCs) which modulate the function of nuclear hormone receptors in a ligand-dependent manner. NRCs are expressed as alternatively spliced isoforms which may exhibit different intrinsic activities and receptor specificities. The NRCs are organized into several modular structures and contain a single functional LXXLL motif which associates with members of the steroid hormone and thyroid hormone/retinoid receptor subfamilies with high affinity. Human NRC (hNRC) harbors a potent N-terminal activation domain (AD1), which is as active as the herpesvirus VP16 activation domain, and a second activation domain (AD2) which overlaps with the receptor-interacting LXXLL region. The C-terminal region of hNRC appears to function as an inhibitory domain which influences the overall transcriptional activity of the protein. Our results suggest that NRC binds to liganded receptors as a dimer and this association leads to a structural change in NRC resulting in activation. hNRC binds CREB-binding protein (CBP) with high affinity in vivo, suggesting that hNRC may be an important functional component of a CBP complex involved in mediating the transcriptional effects of nuclear hormone receptors. PMID:10866662

Synthesis and biological evaluation of cyclopropyl analogues of 2-amino-5-phosphonopentanoic acid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dappen, M.S.; Pellicciari, R.; Natalini, B.

1991-01-01

A series of cyclopropyl analogues related to 2-amino-5-phosphonopentanoic acid (AP5) were synthesized and their biological activity was assessed as competitive antagonists for the N-methyl-D-aspartate (NMDA) receptor. In vitro receptor binding using (3H)-L-glutamate as the radioligand provided affinity data, while modulation of (3H)MK-801 binding was used as a functional assay. The analogues were also evaluated in (3H)kainate binding to assess selectivity over non-NMDA glutamate receptors. Of the compounds tested, 4,5-methano-AP5 analogue 26 was the most potent selective NMDA antagonist; however, potency was lower than that for (((+/-)-2-carboxypiperidin-4-yl)methyl)phosphonic acid (CGS 19755, 5).

A new series of estrogen receptor modulators that display selectivity for estrogen receptor beta.

PubMed

Henke, Brad R; Consler, Thomas G; Go, Ning; Hale, Ron L; Hohman, Dana R; Jones, Stacey A; Lu, Amy T; Moore, Linda B; Moore, John T; Orband-Miller, Lisa A; Robinett, R Graham; Shearin, Jean; Spearing, Paul K; Stewart, Eugene L; Turnbull, Philip S; Weaver, Susan L; Williams, Shawn P; Wisely, G Bruce; Lambert, Millard H

2002-12-05

A series of 1,3,5-triazine-based estrogen receptor (ER) modulators that are modestly selective for the ERbeta subtype are reported. Compound 1, which displayed modest potency and selectivity for ERbeta vs ERalpha, was identified via high-throughput screening utilizing an ERbeta SPA-based binding assay. Subsequent analogue preparation resulted in the identification of compounds such as 21 and 43 that display 25- to 30-fold selectivity for ERbeta with potencies in the 10-30 nM range. These compounds profile as full antagonists at ERbeta and weak partial agonists at ERalpha in a cell-based reporter gene assay. In addition, the X-ray crystal structure of compound 15 complexed with the ligand binding domain of ERbeta has been solved and was utilized in the design of more conformationally restrained analogues such as 31 in an attempt to increase selectivity for the ERbeta subtype.

Inhibition of cholesterol absorption associated with a PPAR alpha-dependent increase in ABC binding cassette transporter A1 in mice.

PubMed

Knight, Brian L; Patel, Dilip D; Humphreys, Sandy M; Wiggins, David; Gibbons, Geoffrey F

2003-11-01

Dietary supplementation with the peroxisome proliferator-activated receptor alpha (PPAR alpha) ligand WY 14,643 gave rise to a 4- to 5-fold increase in the expression of mRNA for the ATP binding cassette transporter A1 (ABCA1) in the intestine of normal mice. There was no effect in the intestine of PPAR alpha-null mice. Consumption of a high-cholesterol diet also increased intestinal ABCA1 expression. The effects of WY 14,643 and the high-cholesterol diet were not additive. WY 14,643 feeding reduced intestinal absorption of cholesterol in the normal mice, irrespective of the dietary cholesterol concentration, and this resulted in lower diet-derived cholesterol and cholesteryl ester concentrations in plasma and liver. At each concentration of dietary cholesterol, there was a similar significant inverse correlation between intestinal ABCA1 mRNA content and the amount of cholesterol absorbed. The fibrate-induced changes in the intestines of the normal mice were accompanied by an increased concentration of the mRNA encoding the sterol-regulatory element binding protein-1c gene (SREBP-1c), a known target gene for the oxysterol receptor liver X receptor alpha (LXR alpha). There was a correlation between intestinal ABCA1 mRNA and SREBP-1c mRNA contents, but not between SREBP-1c mRNA content and cholesterol absorption. These results suggest that PPAR alpha influences cholesterol absorption through modulating ABCA1 activity in the intestine by a mechanism involving LXR alpha.

Differential Regulation of Native Estrogen Receptor-Regulatory Elements by Estradiol, Tamoxifen, and Raloxifene

PubMed Central

Levy, Nitzan; Tatomer, Dierdre; Herber, Candice B.; Zhao, Xiaoyue; Tang, Hui; Sargeant, Toby; Ball, Lonnele J.; Summers, Jonathan; Speed, Terence P.; Leitman, Dale C.

2008-01-01

Estrogen receptors (ERs) regulate gene transcription by interacting with regulatory elements. Most information regarding how ER activates genes has come from studies using a small set of target genes or simple consensus sequences such as estrogen response element, activator protein 1, and Sp1 elements. However, these elements cannot explain the differences in gene regulation patterns and clinical effects observed with estradiol (E2) and selective estrogen receptor modulators. To obtain a greater understanding of how E2 and selective estrogen receptor modulators differentially regulate genes, it is necessary to investigate their action on a more comprehensive set of native regulatory elements derived from ER target genes. Here we used chromatin immunoprecipitation-cloning and sequencing to isolate 173 regulatory elements associated with ERα. Most elements were found in the introns (38%) and regions greater than 10 kb upstream of the transcription initiation site (38%); 24% of the elements were found in the proximal promoter region (<10 kb). Only 11% of the elements contained a classical estrogen response element; 23% of the elements did not have any known response elements, including one derived from the naked cuticle homolog gene, which was associated with the recruitment of p160 coactivators. Transfection studies found that 80% of the 173 elements were regulated by E2, raloxifene, or tamoxifen with ERα or ERβ. Tamoxifen was more effective than raloxifene at activating the elements with ERα, whereas raloxifene was superior with ERβ. Our findings demonstrate that E2, tamoxifen, and raloxifene differentially regulate native ER-regulatory elements isolated by chromatin immunoprecipitation with ERα and ERβ. PMID:17962382

Development of allosteric modulators of GPCRs for treatment of CNS disorders.

PubMed

Nickols, Hilary Highfield; Conn, P Jeffrey

2014-01-01

The discovery of allosteric modulators of G protein-coupled receptors (GPCRs) provides a promising new strategy with potential for developing novel treatments for a variety of central nervous system (CNS) disorders. Traditional drug discovery efforts targeting GPCRs have focused on developing ligands for orthosteric sites which bind endogenous ligands. Allosteric modulators target a site separate from the orthosteric site to modulate receptor function. These allosteric agents can either potentiate (positive allosteric modulator, PAM) or inhibit (negative allosteric modulator, NAM) the receptor response and often provide much greater subtype selectivity than orthosteric ligands for the same receptors. Experimental evidence has revealed more nuanced pharmacological modes of action of allosteric modulators, with some PAMs showing allosteric agonism in combination with positive allosteric modulation in response to endogenous ligand (ago-potentiators) as well as "bitopic" ligands that interact with both the allosteric and orthosteric sites. Drugs targeting the allosteric site allow for increased drug selectivity and potentially decreased adverse side effects. Promising evidence has demonstrated potential utility of a number of allosteric modulators of GPCRs in multiple CNS disorders, including neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Huntington's disease, as well as psychiatric or neurobehavioral diseases such as anxiety, schizophrenia, and addiction. © 2013.

Membrane and Integrative Nuclear Fibroblastic Growth Factor Receptor (FGFR) Regulation of FGF-23*

PubMed Central

Han, Xiaobin; Xiao, Zhousheng; Quarles, L. Darryl

2015-01-01

Fibroblastic growth factor receptor 1 (FGFR1) signaling pathways are implicated in the regulation of FGF-23 gene transcription, but the molecular pathways remain poorly defined. We used low molecular weight (LMW, 18 kDa) FGF-2 and high molecular weight (HMW) FGF-2 isoforms, which, respectively, activate cell surface FGF receptors and intranuclear FGFR1, to determine the roles of membrane FGFRs and integrative nuclear FGFR1 signaling (INFS) in the regulation of FGF-23 gene transcription in osteoblasts. We found that LMW-FGF-2 induced NFAT and Ets1 binding to conserved cis-elements in the proximal FGF-23 promoter and stimulated FGF-23 promoter activity through PLCγ/calcineurin/NFAT and MAPK pathways in SaOS-2 and MC3T3-E1 osteoblasts. In contrast, HMW-FGF-2 stimulated FGF-23 promoter activity in osteoblasts through a cAMP-dependent binding of FGFR1 and cAMP-response element-binding protein (CREB) to a conserved cAMP response element (CRE) contiguous with the NFAT binding site in the FGF-23 promoter. Mutagenesis of the NFAT and CRE binding sites, respectively, inhibited the effects of LMW-FGF-2 and HMW-FGF-23 to stimulate FGF-23 promoter activity. FGF-2 activation of both membrane FGFRs and INFS-dependent FGFR1 pathways may provide a means to integrate systemic and local regulation of FGF-23 transcription under diverse physiological and pathological conditions. PMID:25752607

FMRP acts as a key messenger for dopamine modulation in the forebrain.

PubMed

Wang, Hansen; Wu, Long-Jun; Kim, Susan S; Lee, Frank J S; Gong, Bo; Toyoda, Hiroki; Ren, Ming; Shang, Yu-Ze; Xu, Hui; Liu, Fang; Zhao, Ming-Gao; Zhuo, Min

2008-08-28

The fragile X mental retardation protein (FMRP) is an RNA-binding protein that controls translational efficiency and regulates synaptic plasticity. Here, we report that FMRP is involved in dopamine (DA) modulation of synaptic potentiation. AMPA glutamate receptor subtype 1 (GluR1) surface expression and phosphorylation in response to D1 receptor stimulation were reduced in cultured Fmr1(-/-) prefrontal cortex (PFC) neurons. Furthermore, D1 receptor signaling was impaired, accompanied by D1 receptor hyperphosphorylation at serine sites and subcellular redistribution of G protein-coupled receptor kinase 2 (GRK2) in both PFC and striatum of Fmr1(-/-) mice. FMRP interacted with GRK2, and pharmacological inhibition of GRK2 rescued D1 receptor signaling in Fmr1(-/-) neurons. Finally, D1 receptor agonist partially rescued hyperactivity and enhanced the motor function of Fmr1(-/-) mice. Our study has identified FMRP as a key messenger for DA modulation in the forebrain and may provide insights into the cellular and molecular mechanisms underlying fragile X syndrome.

Memory Effects of Benzodiazepines: Memory Stages and Types Versus Binding-Site Subtypes

PubMed Central

Savić, Miroslav M.; Obradović, Dragan I.; Ugrešić, Nenad D.; Bokonjić, Dubravko R.

2005-01-01

Benzodiazepines are well established as inhibitory modulators of memory processing. This effect is especially prominent when applied before the acquisition phase of a memory task. This minireview concentrates on the putative subtype selectivity of the acquisition-impairing action of benzodiazepines. Namely, recent genetic studies and standard behavioral tests employing subtype-selective ligands pointed to the predominant involvement of two subtypes of benzodiazepine binding sites in memory modulation. Explicit memory learning seems to be affected through the GABAA receptors containing the α1 and α1 subunits, whereas the effects on procedural memory can be mainly mediated by the α1 subunit. The pervading involvement of the α1 subunit in memory modulation is not at all unexpected because this subunit is the major subtype, present in 60% of all GABAA receptors. On the other hand, the role of α5 subunits, mainly expressed in the hippocampus, in modulating distinct forms of memory gives promise of selective pharmacological coping with certain memory deficit states. PMID:16444900

Allosteric regulation by oleamide of the binding properties of 5-hydroxytryptamine7 receptors.

PubMed

Hedlund, P B; Carson, M J; Sutcliffe, J G; Thomas, E A

1999-12-01

Oleamide belongs to a family of amidated lipids with diverse biological activities, including sleep induction and signaling modulation of several 5-hydroxytryptamine (5-HT) receptor subtypes, including 5-HT1A, 5-HT2A/2C, and 5-HT7. The 5-HT7 receptor, predominantly localized in the hypothalamus, hippocampus, and frontal cortex, stimulates cyclic AMP formation and is thought to be involved in the regulation of sleep-wake cycles. Recently, it was proposed that oleamide acts at an allosteric site on the 5-HT7 receptor to regulate cyclic AMP formation. We have further investigated the interaction between oleamide and 5-HT7 receptors by performing radioligand binding assays with HeLa cells transfected with the 5-HT7 receptor. Methiothepin, clozapine, and 5-HT all displaced specific [3H]5-HT (100 nM) binding, with pK(D) values of 7.55, 7.85, and 8.39, respectively. Oleamide also displaced [3H]5-HT binding, but the maximum inhibition was only 40% of the binding. Taking allosteric (see below) cooperativity into account, a K(D) of 2.69 nM was calculated for oleamide. In saturation binding experiments, oleamide caused a 3-fold decrease in the affinity of [3H]5-HT for the 5-HT7 receptor, without affecting the number of binding sites. A Schild analysis showed that the induced shift in affinity of [3H]5-HT reached a plateau, unlike that of a competitive inhibitor, illustrating the allosteric nature of the interaction between oleamide and the 5-HT7 receptor. Oleic acid, the product of oleamide hydrolysis, had a similar effect on [3H]5-HT binding, whereas structural analogs of oleamide, trans-9,10-octadecenamide, cis-8,9-octadecenamide, and erucamide, did not alter [3H]5-HT binding significantly. The findings support the hypothesis that oleamide acts via an allosteric site on the 5-HT7 receptor regulating receptor affinity.

The effect of the sigma-1 receptor selective compound LS-1-137 on the DOI-induced head twitch response in mice.

PubMed

Malik, Maninder; Rangel-Barajas, Claudia; Mach, Robert H; Luedtke, Robert R

2016-09-01

Several receptor mediated pathways have been shown to modulate the murine head twitch response (HTR). However, the role of sigma receptors in the murine (±)-2,5-dimethoxy-4-iodoamphetamine (DOI)-induced HTR has not been previously investigated. We examined the ability of LS-1-137, a novel sigma-1 vs. sigma-2 receptor selective phenylacetamide, to modulate the DOI-induced HTR in DBA/2J mice. We also assessed the in vivo efficacy of reference sigma-1 receptor antagonists and agonists PRE-084 and PPCC. The effect of the sigma-2 receptor selective antagonist RHM-1-86 was also examined. Rotarod analysis was performed to monitor motor coordination after LS-1-137 administration. Radioligand binding techniques were used to determine the affinity of LS-1-137 at 5-HT2A and 5-HT2C receptors. LS-1-137 and the sigma-1 receptor antagonists haloperidol and BD 1047 were able to attenuate a DOI-induced HTR, indicating that LS-1-137 was acting in vivo as a sigma-1 receptor antagonist. LS-1-137 did not compromise rotarod performance within a dose range capable of attenuating the effects of DOI. Radioligand binding studies indicate that LS-1-137 exhibits low affinity binding at both 5-HT2A and 5-HT2C receptors. Based upon the results from these and our previous studies, LS-1-137 is a neuroprotective agent that attenuates the murine DOI-induced HTR independent of activity at 5-HT2 receptor subtypes, D2-like dopamine receptors, sigma-2 receptors and NMDA receptors. LS-1-137 appears to act as a sigma-1 receptor antagonist to inhibit the DOI-induced HTR. Therefore, the DOI-induced HTR can be used to assess the in vivo efficacy of sigma-1 receptor selective compounds. Copyright © 2016. Published by Elsevier Inc.

Selective progesterone receptor modulators 2: use in reproductive medicine.

PubMed

Benagiano, Giuseppe; Bastianelli, Carlo; Farris, Manuela

2008-10-01

Synthetic compounds can bind to progesterone receptors and these progesterone receptor ligands exhibit a spectrum of activities ranging from pure antagonism to a mixture of agonism and antagonism. These substances have been classified as antiprogestins or as selective progesterone receptor modulators. There are several hundred selective progesterone receptor modulators available, although only a dozen or so have been evaluated to any significant extent. The best-known selective progesterone receptor modulators are mifepristone (RU 486), asoprisnil (J 867), onapristone (ZK 98299), ulipristal (CDB 2914), Proellex() (CDB 4124), ORG 33628 and ORG 31710. A careful evaluation of existing major review papers and of recently published articles was carried out for the indications under review, focusing not only on mifepristone, but also on those other selective progesterone receptor modulators for which data are available. Outside pregnancy, selective progesterone receptor modulators are used or have been tested clinically for a number of indications in reproductive medicine: as oral contraceptives, alone or in combination with a progestin, to improve cycle control in users of progestin-only contraceptives, as emergency contraceptives, for the medical treatment of uterine fibroids, in cases of endometriosis and premenstrual syndrome and to improve ovarian stimulation prior to in vitro fertilisation. In the authors' opinion, as of today, few applications outside pregnancy seem worthy of large-scale use: emergency contraception and long-term medical management of uterine fibroids and possibly of endometriosis.

Cargo binding promotes KDEL receptor clustering at the mammalian cell surface

PubMed Central

Becker, Björn; Shaebani, M. Reza; Rammo, Domenik; Bubel, Tobias; Santen, Ludger; Schmitt, Manfred J.

2016-01-01

Transmembrane receptor clustering is a ubiquitous phenomenon in pro- and eukaryotic cells to physically sense receptor/ligand interactions and subsequently translate an exogenous signal into a cellular response. Despite that receptor cluster formation has been described for a wide variety of receptors, ranging from chemotactic receptors in bacteria to growth factor and neurotransmitter receptors in mammalian cells, a mechanistic understanding of the underlying molecular processes is still puzzling. In an attempt to fill this gap we followed a combined experimental and theoretical approach by dissecting and modulating cargo binding, internalization and cellular response mediated by KDEL receptors (KDELRs) at the mammalian cell surface after interaction with a model cargo/ligand. Using a fluorescent variant of ricin toxin A chain as KDELR-ligand (eGFP-RTAH/KDEL), we demonstrate that cargo binding induces dose-dependent receptor cluster formation at and subsequent internalization from the membrane which is associated and counteracted by anterograde and microtubule-assisted receptor transport to preferred docking sites at the plasma membrane. By means of analytical arguments and extensive numerical simulations we show that cargo-synchronized receptor transport from and to the membrane is causative for KDELR/cargo cluster formation at the mammalian cell surface. PMID:27353000

Cargo binding promotes KDEL receptor clustering at the mammalian cell surface

NASA Astrophysics Data System (ADS)

Becker, Björn; Shaebani, M. Reza; Rammo, Domenik; Bubel, Tobias; Santen, Ludger; Schmitt, Manfred J.

2016-06-01

Transmembrane receptor clustering is a ubiquitous phenomenon in pro- and eukaryotic cells to physically sense receptor/ligand interactions and subsequently translate an exogenous signal into a cellular response. Despite that receptor cluster formation has been described for a wide variety of receptors, ranging from chemotactic receptors in bacteria to growth factor and neurotransmitter receptors in mammalian cells, a mechanistic understanding of the underlying molecular processes is still puzzling. In an attempt to fill this gap we followed a combined experimental and theoretical approach by dissecting and modulating cargo binding, internalization and cellular response mediated by KDEL receptors (KDELRs) at the mammalian cell surface after interaction with a model cargo/ligand. Using a fluorescent variant of ricin toxin A chain as KDELR-ligand (eGFP-RTAH/KDEL), we demonstrate that cargo binding induces dose-dependent receptor cluster formation at and subsequent internalization from the membrane which is associated and counteracted by anterograde and microtubule-assisted receptor transport to preferred docking sites at the plasma membrane. By means of analytical arguments and extensive numerical simulations we show that cargo-synchronized receptor transport from and to the membrane is causative for KDELR/cargo cluster formation at the mammalian cell surface.

Botulinum neurotoxin: a marvel of protein design.

PubMed

Montal, Mauricio

2010-01-01

Botulinum neurotoxin (BoNT), the causative agent of botulism, is acknowledged to be the most poisonous protein known. BoNT proteases disable synaptic vesicle exocytosis by cleaving their cytosolic SNARE (soluble NSF attachment protein receptor) substrates. BoNT is a modular nanomachine: an N-terminal Zn(2+)-metalloprotease, which cleaves the SNAREs; a central helical protein-conducting channel, which chaperones the protease across endosomes; and a C-terminal receptor-binding module, consisting of two subdomains that determine target specificity by binding to a ganglioside and a protein receptor on the cell surface and triggering endocytosis. For BoNT, functional complexity emerges from its modular design and the tight interplay between its component modules--a partnership with consequences that surpass the simple sum of the individual component's action. BoNTs exploit this design at each step of the intoxication process, thereby achieving an exquisite toxicity. This review summarizes current knowledge on the structure of individual modules and presents mechanistic insights into how this protein machine evolved to this level of sophistication. Understanding the design principles underpinning the function of such a dynamic modular protein remains a challenging task.

GIV/Girdin activates Gαi and inhibits Gαs via the same motif

PubMed Central

Gupta, Vijay; Bhandari, Deepali; Leyme, Anthony; Aznar, Nicolas; Midde, Krishna K.; Lo, I-Chung; Ear, Jason; Niesman, Ingrid; López-Sánchez, Inmaculada; Blanco-Canosa, Juan Bautista; von Zastrow, Mark; Garcia-Marcos, Mikel; Farquhar, Marilyn G.; Ghosh, Pradipta

2016-01-01

We previously showed that guanine nucleotide-binding (G) protein α subunit (Gα)-interacting vesicle-associated protein (GIV), a guanine-nucleotide exchange factor (GEF), transactivates Gα activity-inhibiting polypeptide 1 (Gαi) proteins in response to growth factors, such as EGF, using a short C-terminal motif. Subsequent work demonstrated that GIV also binds Gαs and that inactive Gαs promotes maturation of endosomes and shuts down mitogenic MAPK–ERK1/2 signals from endosomes. However, the mechanism and consequences of dual coupling of GIV to two G proteins, Gαi and Gαs, remained unknown. Here we report that GIV is a bifunctional modulator of G proteins; it serves as a guanine nucleotide dissociation inhibitor (GDI) for Gαs using the same motif that allows it to serve as a GEF for Gαi. Upon EGF stimulation, GIV modulates Gαi and Gαs sequentially: first, a key phosphomodification favors the assembly of GIV–Gαi complexes and activates GIV’s GEF function; then a second phosphomodification terminates GIV’s GEF function, triggers the assembly of GIV–Gαs complexes, and activates GIV’s GDI function. By comparing WT and GIV mutants, we demonstrate that GIV inhibits Gαs activity in cells responding to EGF. Consequently, the cAMP→PKA→cAMP response element-binding protein signaling axis is inhibited, the transit time of EGF receptor through early endosomes are accelerated, mitogenic MAPK–ERK1/2 signals are rapidly terminated, and proliferation is suppressed. These insights define a paradigm in G-protein signaling in which a pleiotropically acting modulator uses the same motif both to activate and to inhibit G proteins. Our findings also illuminate how such modulation of two opposing Gα proteins integrates downstream signals and cellular responses. PMID:27621449

Resveratrol modulates the inflammatory response via an estrogen receptor-signal integration network

PubMed Central

Nwachukwu, Jerome C; Srinivasan, Sathish; Bruno, Nelson E; Parent, Alexander A; Hughes, Travis S; Pollock, Julie A; Gjyshi, Olsi; Cavett, Valerie; Nowak, Jason; Garcia-Ordonez, Ruben D; Houtman, René; Griffin, Patrick R; Kojetin, Douglas J; Katzenellenbogen, John A; Conkright, Michael D; Nettles, Kendall W

2014-01-01

Resveratrol has beneficial effects on aging, inflammation and metabolism, which are thought to result from activation of the lysine deacetylase, sirtuin 1 (SIRT1), the cAMP pathway, or AMP-activated protein kinase. In this study, we report that resveratrol acts as a pathway-selective estrogen receptor-α (ERα) ligand to modulate the inflammatory response but not cell proliferation. A crystal structure of the ERα ligand-binding domain (LBD) as a complex with resveratrol revealed a unique perturbation of the coactivator-binding surface, consistent with an altered coregulator recruitment profile. Gene expression analyses revealed significant overlap of TNFα genes modulated by resveratrol and estradiol. Furthermore, the ability of resveratrol to suppress interleukin-6 transcription was shown to require ERα and several ERα coregulators, suggesting that ERα functions as a primary conduit for resveratrol activity. DOI: http://dx.doi.org/10.7554/eLife.02057.001 PMID:24771768

SH2/SH3 signaling proteins.

PubMed

Schlessinger, J

1994-02-01

SH2 and SH3 domains are small protein modules that mediate protein-protein interactions in signal transduction pathways that are activated by protein tyrosine kinases. SH2 domains bind to short phosphotyrosine-containing sequences in growth factor receptors and other phosphoproteins. SH3 domains bind to target proteins through sequences containing proline and hydrophobic amino acids. SH2 and SH3 domain containing proteins, such as Grb2 and phospholipase C gamma, utilize these modules in order to link receptor and cytoplasmic protein tyrosine kinases to the Ras signaling pathway and to phosphatidylinositol hydrolysis, respectively. The three-dimensional structures of several SH2 and SH3 domains have been determined by NMR and X-ray crystallography, and the molecular basis of their specificity is beginning to be unveiled.

Nutrigenomics and Beef Quality: A Review about Lipogenesis.

PubMed

Ladeira, Marcio M; Schoonmaker, Jon P; Gionbelli, Mateus P; Dias, Júlio C O; Gionbelli, Tathyane R S; Carvalho, José Rodolfo R; Teixeira, Priscilla D

2016-06-10

The objective of the present review is to discuss the results of published studies that show how nutrition affects the expression of genes involved in lipid metabolism and how diet manipulation might change marbling and composition of fat in beef. Several key points in the synthesis of fat in cattle take place at the molecular level, and the association of nutritional factors with the modulation of this metabolism is one of the recent targets of nutrigenomic research. Within this context, special attention has been paid to the study of nuclear receptors associated with fatty acid metabolism. Among the transcription factors involved in lipid metabolism, the peroxisome proliferator-activated receptors (PPARs) and sterol regulatory element-binding proteins (SREBPs) stand out. The mRNA synthesis of these transcription factors is regulated by nutrients, and their metabolic action might be potentiated by diet components and change lipogenesis in muscle. Among the options for dietary manipulation with the objective to modulate lipogenesis, the use of different sources of polyunsaturated fatty acids, starch concentrations, forage ratios and vitamins stand out. Therefore, special care must be exercised in feedlot feed management, mainly when the goal is to produce high marbling beef.

RNA-induced silencing complex (RISC) Proteins PACT, TRBP, and Dicer are SRA binding nuclear receptor coregulators

PubMed Central

Redfern, Andrew D.; Colley, Shane M.; Beveridge, Dianne J.; Ikeda, Naoya; Epis, Michael R.; Li, Xia; Foulds, Charles E.; Stuart, Lisa M.; Barker, Andrew; Russell, Victoria J.; Ramsay, Kerry; Kobelke, Simon J.; Li, Xiaotao; Hatchell, Esme C.; Payne, Christine; Giles, Keith M.; Messineo, Adriana; Gatignol, Anne; Lanz, Rainer B.; O’Malley, Bert W.; Leedman, Peter J.

2013-01-01

The cytoplasmic RNA-induced silencing complex (RISC) contains dsRNA binding proteins, including protein kinase RNA activator (PACT), transactivation response RNA binding protein (TRBP), and Dicer, that process pre-microRNAs into mature microRNAs (miRNAs) that target specific mRNA species for regulation. There is increasing evidence for important functional interactions between the miRNA and nuclear receptor (NR) signaling networks, with recent data showing that estrogen, acting through the estrogen receptor, can modulate initial aspects of nuclear miRNA processing. Here, we show that the cytoplasmic RISC proteins PACT, TRBP, and Dicer are steroid receptor RNA activator (SRA) binding NR coregulators that target steroid-responsive promoters and regulate NR activity and downstream gene expression. Furthermore, each of the RISC proteins, together with Argonaute 2, associates with SRA and specific pre-microRNAs in both the nucleus and cytoplasm, providing evidence for links between NR-mediated transcription and some of the factors involved in miRNA processing. PMID:23550157

RNA-induced silencing complex (RISC) Proteins PACT, TRBP, and Dicer are SRA binding nuclear receptor coregulators.

PubMed

Redfern, Andrew D; Colley, Shane M; Beveridge, Dianne J; Ikeda, Naoya; Epis, Michael R; Li, Xia; Foulds, Charles E; Stuart, Lisa M; Barker, Andrew; Russell, Victoria J; Ramsay, Kerry; Kobelke, Simon J; Li, Xiaotao; Hatchell, Esme C; Payne, Christine; Giles, Keith M; Messineo, Adriana; Gatignol, Anne; Lanz, Rainer B; O'Malley, Bert W; Leedman, Peter J

2013-04-16

The cytoplasmic RNA-induced silencing complex (RISC) contains dsRNA binding proteins, including protein kinase RNA activator (PACT), transactivation response RNA binding protein (TRBP), and Dicer, that process pre-microRNAs into mature microRNAs (miRNAs) that target specific mRNA species for regulation. There is increasing evidence for important functional interactions between the miRNA and nuclear receptor (NR) signaling networks, with recent data showing that estrogen, acting through the estrogen receptor, can modulate initial aspects of nuclear miRNA processing. Here, we show that the cytoplasmic RISC proteins PACT, TRBP, and Dicer are steroid receptor RNA activator (SRA) binding NR coregulators that target steroid-responsive promoters and regulate NR activity and downstream gene expression. Furthermore, each of the RISC proteins, together with Argonaute 2, associates with SRA and specific pre-microRNAs in both the nucleus and cytoplasm, providing evidence for links between NR-mediated transcription and some of the factors involved in miRNA processing.

Carboxypeptidase M Is a Positive Allosteric Modulator of the Kinin B1 Receptor*

PubMed Central

Zhang, Xianming; Tan, Fulong; Skidgel, Randal A.

2013-01-01

Ligand binding to extracellular domains of G protein-coupled receptors can result in novel and nuanced allosteric effects on receptor signaling. We previously showed that the protein-protein interaction of carboxypeptidase M (CPM) and kinin B1 receptor (B1R) enhances B1R signaling in two ways; 1) kinin binding to CPM causes a conformational activation of the B1R, and 2) CPM-generated des-Arg-kinin agonist is efficiently delivered to the B1R. Here, we show CPM is also a positive allosteric modulator of B1R signaling to its agonist, des-Arg10-kallidin (DAKD). In HEK cells stably transfected with B1R, co-expression of CPM enhanced DAKD-stimulated increases in intracellular Ca2+ or phosphoinositide turnover by a leftward shift of the dose-response curve without changing the maximum. CPM increased B1R affinity for DAKD by ∼5-fold but had no effect on basal B1R-dependent phosphoinositide turnover. Soluble, recombinant CPM bound to HEK cells expressing B1Rs without stimulating receptor signaling. CPM positive allosteric action was independent of enzyme activity but depended on interaction of its C-terminal domain with the B1R extracellular loop 2. Disruption of the CPM/B1R interaction or knockdown of CPM in cytokine-treated primary human endothelial cells inhibited the allosteric enhancement of CPM on B1R DAKD binding or ERK1/2 activation. CPM also enhanced the DAKD-induced B1R conformational change as detected by increased intramolecular fluorescence or bioluminescence resonance energy transfer. Thus, CPM binding to extracellular loop 2 of the B1R results in positive allosteric modulation of B1R signaling, and disruption of this interaction could provide a novel therapeutic approach to reduce pathological B1R signaling. PMID:24108126

An Allosteric Coagonist Model for Propofol Effects on α1β2γ2L γ-Aminobutyric Acid Type A Receptors

PubMed Central

Ruesch, Dirk; Neumann, Elena; Wulf, Hinnerk; Forman, Stuart A.

2011-01-01

Background Propofol produces its major actions via γ-aminobutyric acid type A (GABAA) receptors. At low concentrations, propofol enhances agonist-stimulated GABAA receptor activity, and high propofol concentrations directly activate receptors. Etomidate produces similar effects, and there is convincing evidence that a single class of etomidate sites mediate both agonist modulation and direct GABAA receptor activation. It is unknown if the propofol binding site(s) on GABAA receptors that modulate agonist-induced activity also mediate direct activation. Methods GABAA α1β2γ2L receptors were heterologously expressed in Xenopus oocytes and activity was quantified using voltage clamp electrophysiology. We tested whether propofol and etomidate display the same linkage between agonist modulation and direct activation of GABAA receptors by identifying equi-efficacious drug solutions for direct activation. We then determined whether these drug solutions produce equal modulation of GABA-induced receptor activity. We also measured propofol-dependent direct activation and modulation of low GABA responses. Allosteric coagonist models similar to that established for etomidate, but with variable numbers of propofol sites, were fitted to combined data. Results Solutions of 19 μM propofol and 10 μM etomidate were found to equally activate GABAA receptors. These two drug solutions also produced indistinguishable modulation of GABA-induced receptor activity. Combined electrophysiological data behaved in a manner consistent with allosteric co-agonist models with more than one propofol site. The best fit was observed when the model assumed three equivalent propofol sites. Conclusions Our results support the hypothesis that propofol, like etomidate, acts at GABAA receptor sites mediating both GABA modulation and direct activation. PMID:22104494

Allosteric modulation model of the mu opioid receptor by herkinorin, a potent not alkaloidal agonist

NASA Astrophysics Data System (ADS)

Marmolejo-Valencia, A. F.; Martínez-Mayorga, K.

2017-05-01

Modulation of opioid receptors is the primary choice for pain management and structural information studies have gained new horizons with the recently available X-ray crystal structures. Herkinorin is one of the most remarkable salvinorin A derivative with high affinity for the mu opioid receptor, moderate selectivity and lack of nitrogen atoms on its structure. Surprisingly, binding models for herkinorin are lacking. In this work, we explore binding models of herkinorin using automated docking, molecular dynamics simulations, free energy calculations and available experimental information. Our herkinorin D-ICM-1 binding model predicted a binding free energy of -11.52 ± 1.14 kcal mol-1 by alchemical free energy estimations, which is close to the experimental values -10.91 ± 0.2 and -10.80 ± 0.05 kcal mol-1 and is in agreement with experimental structural information. Specifically, D-ICM-1 molecular dynamics simulations showed a water-mediated interaction between D-ICM-1 and the amino acid H2976.52, this interaction coincides with the co-crystallized ligands. Another relevant interaction, with N1272.63, allowed to rationalize herkinorin's selectivity to mu over delta opioid receptors. Our suggested binding model for herkinorin is in agreement with this and additional experimental data. The most remarkable observation derived from our D-ICM-1 model is that herkinorin reaches an allosteric sodium ion binding site near N1503.35. Key interactions in that region appear relevant for the lack of β-arrestin recruitment by herkinorin. This interaction is key for downstream signaling pathways involved in the development of side effects, such as tolerance. Future SAR studies and medicinal chemistry efforts will benefit from the structural information presented in this work.

The arrestin-1 finger loop interacts with two distinct conformations of active rhodopsin.

PubMed

Elgeti, Matthias; Kazmin, Roman; Rose, Alexander S; Szczepek, Michal; Hildebrand, Peter W; Bartl, Franz J; Scheerer, Patrick; Hofmann, Klaus Peter

2018-03-23

Signaling of the prototypical G protein-coupled receptor (GPCR) rhodopsin through its cognate G protein transducin (G t ) is quenched when arrestin binds to the activated receptor. Although the overall architecture of the rhodopsin/arrestin complex is known, many questions regarding its specificity remain unresolved. Here, using FTIR difference spectroscopy and a dual pH/peptide titration assay, we show that rhodopsin maintains certain flexibility upon binding the "finger loop" of visual arrestin (prepared as synthetic peptide ArrFL-1). We found that two distinct complexes can be stabilized depending on the protonation state of E3.49 in the conserved (D)ERY motif. Both complexes exhibit different interaction modes and affinities of ArrFL-1 binding. The plasticity of the receptor within the rhodopsin/ArrFL-1 complex stands in contrast to the complex with the C terminus of the G t α-subunit (GαCT), which stabilizes only one specific substate out of the conformational ensemble. However, G t α-subunit binding and both ArrFL-1-binding modes involve a direct interaction to conserved R3.50, as determined by site-directed mutagenesis. Our findings highlight the importance of receptor conformational flexibility and cytoplasmic proton uptake for modulation of rhodopsin signaling and thereby extend the picture provided by crystal structures of the rhodopsin/arrestin and rhodopsin/ArrFL-1 complexes. Furthermore, the two binding modes of ArrFL-1 identified here involve motifs of conserved amino acids, which indicates that our results may have elucidated a common modulation mechanism of class A GPCR-G protein/-arrestin signaling. © 2018 by The American Society for Biochemistry and Molecular Biology, Inc.

BA321, a novel carborane analog that binds to androgen and estrogen receptors, acts as a new selective androgen receptor modulator of bone in male mice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watanabe, Kenta; Cooperative Major in Advanced Health Science, Tokyo University of Agriculture and Technology, 2-24-16 Nakamachi, Koganei, Tokyo 184-8588; Hirata, Michiko

Carboranes are a class of carbon-containing polyhedral boron cluster compounds with globular geometry and hydrophobic surface that interact with hormone receptors such as estrogen receptor (ER) and androgen receptor (AR). We have synthesized BA321, a novel carborane compound, which binds to AR. We found here that it also binds to ERs, ERα and ERβ. In orchidectomized (ORX) mice, femoral bone mass was markedly reduced due to androgen deficiency and BA321 restored bone loss in the male, whilst the decreased weight of seminal vesicle in ORX mice was not recovered by administration of BA321. In female mice, BA321 acts as amore » pure estrogen agonist, and restored both the loss of bone mass and uterine atrophy due to estrogen deficiency in ovariectomized (OVX) mice. In bone tissues, the trabecular bone loss occurred in both ORX and OVX mice, and BA321 completely restored the trabecular bone loss in both sexes. Cortical bone loss occurred in ORX mice but not in OVX mice, and BA321 clearly restored cortical bone loss due to androgen deficiency in ORX mice. Therefore, BA321 is a novel selective androgen receptor modulator (SARM) that may offer a new therapy option for osteoporosis in the male. - Highlights: • A novel carborane compound BA321 binds to both AR and ERs, ERα and ERβ. • BA321 restores bone loss in orchidectomized mice without effects on sex organ. • BA321 acts as an estrogen agonist in bone and uterus in ovariectomized mice. • BA321 may be a new SARM to prevent the loss of musculoskeletal mass in elder men.« less

Molecular mechanism of ATP binding and ion channel activation in P2X receptors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hattori, Motoyuki; Gouaux, Eric

P2X receptors are trimeric ATP-activated ion channels permeable to Na{sup +}, K{sup +} and Ca{sup 2+}. The seven P2X receptor subtypes are implicated in physiological processes that include modulation of synaptic transmission, contraction of smooth muscle, secretion of chemical transmitters and regulation of immune responses. Despite the importance of P2X receptors in cellular physiology, the three-dimensional composition of the ATP-binding site, the structural mechanism of ATP-dependent ion channel gating and the architecture of the open ion channel pore are unknown. Here we report the crystal structure of the zebrafish P2X4 receptor in complex with ATP and a new structure ofmore » the apo receptor. The agonist-bound structure reveals a previously unseen ATP-binding motif and an open ion channel pore. ATP binding induces cleft closure of the nucleotide-binding pocket, flexing of the lower body {beta}-sheet and a radial expansion of the extracellular vestibule. The structural widening of the extracellular vestibule is directly coupled to the opening of the ion channel pore by way of an iris-like expansion of the transmembrane helices. The structural delineation of the ATP-binding site and the ion channel pore, together with the conformational changes associated with ion channel gating, will stimulate development of new pharmacological agents.« less

How Oliceridine (TRV-130) Binds and Stabilizes a μ-Opioid Receptor Conformational State That Selectively Triggers G Protein Signaling Pathways.

PubMed

Schneider, Sebastian; Provasi, Davide; Filizola, Marta

2016-11-22

Substantial attention has recently been devoted to G protein-biased agonism of the μ-opioid receptor (MOR) as an ideal new mechanism for the design of analgesics devoid of serious side effects. However, designing opioids with appropriate efficacy and bias is challenging because it requires an understanding of the ligand binding process and of the allosteric modulation of the receptor. Here, we investigated these phenomena for TRV-130, a G protein-biased MOR small-molecule agonist that has been shown to exert analgesia with less respiratory depression and constipation than morphine and that is currently being evaluated in human clinical trials for acute pain management. Specifically, we carried out multimicrosecond, all-atom molecular dynamics (MD) simulations of the binding of this ligand to the activated MOR crystal structure. Analysis of >50 μs of these MD simulations provides insights into the energetically preferred binding pathway of TRV-130 and its stable pose at the orthosteric binding site of MOR. Information transfer from the TRV-130 binding pocket to the intracellular region of the receptor was also analyzed, and was compared to a similar analysis carried out on the receptor bound to the classical unbiased agonist morphine. Taken together, these studies lead to a series of testable hypotheses of ligand-receptor interactions that are expected to inform the structure-based design of improved opioid analgesics.

The C-Module-Binding Factor Supports Amplification of TRE5-A Retrotransposons in the Dictyostelium discoideum Genome ▿

PubMed Central

Bilzer, Annika; Dölz, Heike; Reinhardt, Alexander; Schmith, Anika; Siol, Oliver; Winckler, Thomas

2011-01-01

Retrotransposable elements are molecular parasites that have invaded the genomes of virtually all organisms. Although retrotransposons encode essential proteins to mediate their amplification, they also require assistance by host cell-encoded machineries that perform functions such as DNA transcription and repair. The retrotransposon TRE5-A of the social amoeba Dictyostelium discoideum generates a notable amount of both sense and antisense RNAs, which are generated from element-internal promoters, located in the A module and the C module, respectively. We observed that TRE5-A retrotransposons depend on the C-module-binding factor (CbfA) to maintain high steady-state levels of TRE5-A transcripts and that CbfA supports the retrotransposition activity of TRE5-A elements. The carboxy-terminal domain of CbfA was found to be required and sufficient to mediate the accumulation of TRE5-A transcripts, but it did not support productive retrotransposition of TRE5-A. This result suggests different roles for CbfA protein domains in the regulation of TRE5-A retrotransposition frequency in D. discoideum cells. Although CbfA binds to the C module in vitro, the factor regulates neither C-module nor A-module promoter activity in vivo. We speculate that CbfA supports the amplification of TRE5-A retrotransposons by suppressing the expression of an as yet unidentified component of the cellular posttranscriptional gene silencing machinery. PMID:21076008

DEVELOPMENT OF TWO ANDROGEN RECEPTOR ASSAYS USING ADENOVIRAL TRANSDUCTION OF MMTV-LUC REPORTER AND/OR HAR FOR ENDOCRINE SCREENING

EPA Science Inventory

Abstract
The discovery of xenobiotics which interfere with androgen activity has highlighted the need to assess chemicals for their ability to modulate dihydrotestosterone (DHT)-receptor binding. Previous test systems have used cells transfected with plasmid containing a rep...

Determinants of Ligand Subtype-Selectivity at α1A-Adrenoceptor Revealed Using Saturation Transfer Difference (STD) NMR.

PubMed

Yong, Kelvin J; Vaid, Tasneem M; Shilling, Patrick J; Wu, Feng-Jie; Williams, Lisa M; Deluigi, Mattia; Plückthun, Andreas; Bathgate, Ross A D; Gooley, Paul R; Scott, Daniel J

2018-04-20

α 1A - and α 1B -adrenoceptors (α 1A -AR and α 1B -AR) are closely related G protein-coupled receptors (GPCRs) that modulate the cardiovascular and nervous systems in response to binding epinephrine and norepinephrine. The GPCR gene superfamily is made up of numerous subfamilies that, like α 1A -AR and α 1B -AR, are activated by the same endogenous agonists but may modulate different physiological processes. A major challenge in GPCR research and drug discovery is determining how compounds interact with receptors at the molecular level, especially to assist in the optimization of drug leads. Nuclear magnetic resonance spectroscopy (NMR) can provide great insight into ligand-binding epitopes, modes, and kinetics. Ideally, ligand-based NMR methods require purified, well-behaved protein samples. The instability of GPCRs upon purification in detergents, however, makes the application of NMR to study ligand binding challenging. Here, stabilized α 1A -AR and α 1B -AR variants were engineered using Cellular High-throughput Encapsulation, Solubilization, and Screening (CHESS), allowing the analysis of ligand binding with Saturation Transfer Difference NMR (STD NMR). STD NMR was used to map the binding epitopes of epinephrine and A-61603 to both receptors, revealing the molecular determinants for the selectivity of A-61603 for α 1A -AR over α 1B -AR. The use of stabilized GPCRs for ligand-observed NMR experiments will lead to a deeper understanding of binding processes and assist structure-based drug design.

Selective androgen receptor modulators: in pursuit of tissue-selective androgens.

PubMed

Omwancha, Josephat; Brown, Terry R

2006-10-01

The androgen receptor mediates the androgenic and anabolic activity of the endogenous steroids testosterone and 5alpha-dihydrotestosterone. Current knowledge of the androgen receptor protein structure, and the molecular mechanisms surrounding the binding properties and activities of agonists and antagonists has led to the design and development of novel nonsteroidal ligands with selected tissue-specific androgen receptor agonist and antagonist activities. The activity of these compounds, termed selective androgen receptor modulators (SARMs), is directed toward the maintenance or enhancement of anabolic effects on bone and muscle with minimal androgenic effects on prostate growth. SARMs are of potential therapeutic value in the treatment of male hypogonadism, osteoporosis, frailty and muscle wasting, burn injury and would healing, anemia, mood and depression, benign prostatic hyperplasia and prostate cancer.

Modulation of Estrogen Response Element-Driven Gene Expressions and Cellular Proliferation with Polar Directions by Designer Transcription Regulators

PubMed Central

Muyan, Mesut; Güpür, Gizem; Yaşar, Pelin; Ayaz, Gamze; User, Sırma Damla; Kazan, Hasan Hüseyin; Huang, Yanfang

2015-01-01

Estrogen receptor α (ERα), as a ligand-dependent transcription factor, mediates 17β-estradiol (E2) effects. ERα is a modular protein containing a DNA binding domain (DBD) and transcription activation domains (AD) located at the amino- and carboxyl-termini. The interaction of the E2-activated ERα dimer with estrogen response elements (EREs) of genes constitutes the initial step in the ERE-dependent signaling pathway necessary for alterations of cellular features. We previously constructed monomeric transcription activators, or monotransactivators, assembled from an engineered ERE-binding module (EBM) using the ERα-DBD and constitutively active ADs from other transcription factors. Monotransactivators modulated cell proliferation by activating and repressing ERE-driven gene expressions that simulate responses observed with E2-ERα. We reasoned here that integration of potent heterologous repression domains (RDs) into EBM could generate monotransrepressors that alter ERE-bearing gene expressions and cellular proliferation in directions opposite to those observed with E2-ERα or monotransactivators. Consistent with this, monotransrepressors suppressed reporter gene expressions that emulate the ERE-dependent signaling pathway. Moreover, a model monotransrepressor regulated DNA synthesis, cell cycle progression and proliferation of recombinant adenovirus infected ER-negative cells through decreasing as well as increasing gene expressions with polar directions compared with E2-ERα or monotransactivator. Our results indicate that an ‘activator’ or a ‘repressor’ possesses both transcription activating/enhancing and repressing/decreasing abilities within a chromatin context. Offering a protein engineering platform to alter signal pathway-specific gene expressions and cell growth, our approach could also be used for the development of tools for epigenetic modifications and for clinical interventions wherein multigenic de-regulations are an issue. PMID:26295471

Structural determinants of arrestin functions.

PubMed

Gurevich, Vsevolod V; Gurevich, Eugenia V

2013-01-01

Arrestins are a small protein family with only four members in mammals. Arrestins demonstrate an amazing versatility, interacting with hundreds of different G protein-coupled receptor (GPCR) subtypes, numerous nonreceptor signaling proteins, and components of the internalization machinery, as well as cytoskeletal elements, including regular microtubules and centrosomes. Here, we focus on the structural determinants that mediate various arrestin functions. The receptor-binding elements in arrestins were mapped fairly comprehensively, which set the stage for the construction of mutants targeting particular GPCRs. The elements engaged by other binding partners are only now being elucidated and in most cases we have more questions than answers. Interestingly, even very limited and imprecise identification of structural requirements for the interaction with very few other proteins has enabled the development of signaling-biased arrestin mutants. More comprehensive understanding of the structural underpinning of different arrestin functions will pave the way for the construction of arrestins that can link the receptor we want to the signaling pathway of our choosing. Copyright © 2013 Elsevier Inc. All rights reserved.

Structural Determinants of Arrestin Functions

PubMed Central

Gurevich, Vsevolod V.; Gurevich, Eugenia V.

2015-01-01

Arrestins are a small protein family with only four members in mammals. Arrestins demonstrate an amazing versatility, interacting with hundreds of different G protein-coupled receptor (GPCR) subtypes, numerous nonreceptor signaling proteins, and components of the internalization machinery, as well as cytoskeletal elements, including regular microtubules and centrosomes. Here, we focus on the structural determinants that mediate various arrestin functions. The receptor-binding elements in arrestins were mapped fairly comprehensively, which set the stage for the construction of mutants targeting particular GPCRs. The elements engaged by other binding partners are only now being elucidated and in most cases we have more questions than answers. Interestingly, even very limited and imprecise identification of structural requirements for the interaction with very few other proteins has enabled the development of signaling-biased arrestin mutants. More comprehensive understanding of the structural underpinning of different arrestin functions will pave the way for the construction of arrestins that can link the receptor we want to the signaling pathway of our choosing. PMID:23764050

Positive allosteric modulators as an approach to nicotinic acetylcholine receptor- targeted therapeutics: advantages and limitations

PubMed Central

Williams, Dustin K.; Wang, Jingyi; Papke, Roger L.

2011-01-01

Neuronal nicotinic acetylcholine receptors (nAChR), recognized targets for drug development in cognitive and neuro-degenerative disorders, are allosteric proteins with dynamic interconversions between multiple functional states. Activation of the nAChR ion channel is primarily controlled by the binding of ligands (agonists, partial agonists, competitive antagonists) at conventional agonist binding sites, but is also regulated in either negative or positive ways by the binding of ligands to other modulatory sites. In this review, we discuss models for the activation and desensitization of nAChR, and the discovery of multiple types of ligands that influence those processes in both heteromeric nAChR, such as the high affinity nicotine receptors of the brain, and homomeric α7-type receptors. In recent years, α7 nAChRs have been identified as a potential target for therapeutic indications leading to the development of α7-selective agonists and partial agonists. However, unique properties of α7 nAChR, including low probability of channel opening and rapid desensitization, may limit the therapeutic usefulness of ligands binding exclusively to conventional agonist binding sites. New enthusiasm for the therapeutic targeting of α7 has come from the identification of α7-selective positive allosteric modulators (PAMs) that work effectively on the intrinsic factors that limit α7 ion channel activation. While these new drugs appear promising for therapeutic development, we also consider potential caveats and possible limitations for their use, including PAM-insensitive forms of desensitization and cytotoxicity issues. PMID:21575610

Positive allosteric modulators as an approach to nicotinic acetylcholine receptor-targeted therapeutics: advantages and limitations.

PubMed

Williams, Dustin K; Wang, Jingyi; Papke, Roger L

2011-10-15

Neuronal nicotinic acetylcholine receptors (nAChR), recognized targets for drug development in cognitive and neuro-degenerative disorders, are allosteric proteins with dynamic interconversions between multiple functional states. Activation of the nAChR ion channel is primarily controlled by the binding of ligands (agonists, partial agonists, competitive antagonists) at conventional agonist binding sites, but is also regulated in either negative or positive ways by the binding of ligands to other modulatory sites. In this review, we discuss models for the activation and desensitization of nAChR, and the discovery of multiple types of ligands that influence those processes in both heteromeric nAChR, such as the high-affinity nicotine receptors of the brain, and homomeric α7-type receptors. In recent years, α7 nAChRs have been identified as a potential target for therapeutic indications leading to the development of α7-selective agonists and partial agonists. However, unique properties of α7 nAChR, including low probability of channel opening and rapid desensitization, may limit the therapeutic usefulness of ligands binding exclusively to conventional agonist binding sites. New enthusiasm for the therapeutic targeting of α7 has come from the identification of α7-selective positive allosteric modulators (PAMs) that work effectively on the intrinsic factors that limit α7 ion channel activation. While these new drugs appear promising for therapeutic development, we also consider potential caveats and possible limitations for their use, including PAM-insensitive forms of desensitization and cytotoxicity issues. Copyright © 2011 Elsevier Inc. All rights reserved.

Crystal structure of arrestin-3 reveals the basis of the difference in receptor binding between two non-visual subtypes

PubMed Central

Zhan, Xuanzhi; Gimenez, Luis E.; Gurevich, Vsevolod V.; Spiller, Benjamin W.

2011-01-01

Arrestins are multi-functional proteins that regulate signaling and trafficking of the majority of G protein-coupled receptors (GPCRs), as well as sub-cellular localization and activity of many other signaling proteins. Here we report the first crystal structure of arrestin-3, solved at 3.0Å. Arrestin-3 is an elongated two-domain molecule with the overall fold and key inter-domain interactions that hold free protein in the basal conformation similar to the other subtypes. Arrestin-3 is the least selective member of the family, binding wide variety of GPCRs with high affinity and demonstrating lower preference for active phosphorylated forms of the receptors. In contrast to the other three arrestins, part of the receptor-binding surface in the arrestin-3 C-domain does not form a contiguous β-sheet, consistent with increased flexibility. By swapping the corresponding elements between arrestin-2 and -3 we show that the presence of this loose structure correlates with reduced arrestin selectivity for activated receptor, consistent with a conformational change in this β-sheet upon receptor binding. PMID:21215759

Synthesis, biological evaluation and molecular modelling of diversely functionalized heterocyclic derivatives as inhibitors of acetylcholinesterase/butyrylcholinesterase and modulators of Ca2+ channels and nicotinic receptors.

PubMed

Marco, José L; de los Ríos, Cristóbal; García, Antonio G; Villarroya, Mercedes; Carreiras, M Carmo; Martins, Carla; Eleutério, Ana; Morreale, Antonio; Orozco, M; Luque, F Javier

2004-05-01

The synthesis and the biological activity of compounds 5-40 as inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), as well as modulators of voltage-dependent Ca(2+) channels and nicotinic receptors, are described. These molecules are tacrine analogues, which have been prepared from polyfunctionalized 6-amino-5-cyano-4H-pyrans, 6-amino-5-cyano-pyridines and 5-amino-2-aryl-3-cyano-1,3-oxazoles via Friedländer reaction with selected cycloalkanones. These compounds are moderate acetylcholinesterase and butyrylcholinesterase inhibitors, the BuChE/AChE selectivity of the most active molecules ranges from 10.0 (compound 29) to 76.9 (compound 16). Interestingly, the 'oxazolo-tacrine' derivatives are devoid of any activity. All compounds showed an important inhibitory effect on the nicotinic acetylcholine receptor. Most of them also blocked L-type Ca(2+) channels, and three of them, 64, 19 and 67, the non-L type of Ca(2+) channels. Molecular modelling studies suggest that these compounds might bind at the peripheral binding site of AChE, which opens the possibility to design inhibitors able to bind at both, the catalytic and peripheral binding sites of the enzyme.

Erythroblast transferrin receptors and transferrin kinetics in iron deficiency and various anemias

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muta, K.; Nishimura, J.; Ideguchi, H.

1987-06-01

To clarify the role of transferrin receptors in cases of altered iron metabolism in clinical pathological conditions, we studied: number of binding sites; affinity; and recycling kinetics of transferrin receptors on human erythroblasts. Since transferrin receptors are mainly present on erythroblasts, the number of surface transferrin receptors was determined by assay of binding of /sup 125/I-transferrin and the percentage of erythroblasts in bone marrow mononuclear cells. The number of binding sites on erythroblasts from patients with an iron deficiency anemia was significantly greater than in normal subjects. Among those with an aplastic anemia, hemolytic anemia, myelodysplastic syndrome, and polycythemia veramore » compared to normal subjects, there were no considerable differences in the numbers of binding sites. The dissociation constants (Kd) were measured using Scatchard analysis. The apparent Kd was unchanged (about 10 nmol/L) in patients and normal subjects. The kinetics of endocytosis and exocytosis of /sup 125/I-transferrin, examined by acid treatment, revealed no variations in recycling kinetics among the patients and normal subjects. These data suggest that iron uptake is regulated by modulation of the number of surface transferrin receptors, thereby reflecting the iron demand of the erythroblast.« less

Characterization of the Igf-II Binding Site of the IGF-II/MAN-6-P Receptor Extracellular Domain.

NASA Astrophysics Data System (ADS)

Garmroudi, Farideh

1995-01-01

In mammals, insulin-like growth factor II (IGF -II) and glycoproteins bearing the mannose 6-phosphate (Man -6-P) recognition marker bind with high affinity to the same receptor. The functional consequences of IGF-II binding to the receptor at the cell surface are not clear. In these studies, we sought to broaden our understanding of the functional regions of the receptor regarding its IGF -II binding site. The IGF-II binding/cross-linking domain of the IGF-II/Man-6-P receptor was mapped by sequencing receptor fragments covalently attached to IGF-II. Purified rat placental or bovine liver receptors were affinity-labeled, with ^{125}I-IGF-II and digested with endoproteinase Glu-C. Analysis of digests by gel electrophoresis revealed a major radiolabeled band of 18 kDa, which was purified by gel filtration chromatography followed by reverse-phase HPLC and electroblotting. Sequence analysis revealed that, the peptide S(H)VNSXPMF, located within extracellular repeat 10 and beginning with serine 1488 of the bovine receptor, was the best candidate for the IGF-II cross-linked peptide. These data indicated that residues within repeats 10-11 were important for IGF -II binding. To define the location of the IGF-II binding site further, a nested set of six human receptor cDNA constructs was designed to produce epitope-tagged fusion proteins encompassing the region between repeats 8 and 11 of the human IGF-II/Man-6-P receptor extracellular domain. These truncated receptors were transiently expressed in COS-7 cells, immunoprecipitated and analyzed for their abilities to bind and cross-link to IGF-II. All of the constructs were capable of binding/cross-linking to IGF-II, except for the 9.0-11 construct. Displacement curve analysis indicated that the truncated receptors were approximately equivalent in IGF-II binding affinity, but were of 5- to 10-fold lower affinity than full-length receptors. Sequencing of the 9.0-11 construct indicated the presence of a point mutation substituting threonine for isoleucine at position 1621, which is located in the N-terminal half of repeat 11, and was found to abrogate IGF-II binding. Collectively, our work indicates that repeat 11 of the IGF-II/Man-6-P receptor's extracellular domain encompasses the elements both for binding and cross-linking to IGF-II.

Structure of the measles virus hemagglutinin bound to its cellular receptor SLAM.

PubMed

Hashiguchi, Takao; Ose, Toyoyuki; Kubota, Marie; Maita, Nobuo; Kamishikiryo, Jun; Maenaka, Katsumi; Yanagi, Yusuke

2011-02-01

Measles virus, a major cause of childhood morbidity and mortality worldwide, predominantly infects immune cells using signaling lymphocyte activation molecule (SLAM) as a cellular receptor. Here we present crystal structures of measles virus hemagglutinin (MV-H), the receptor-binding glycoprotein, in complex with SLAM. The MV-H head domain binds to a β-sheet of the membrane-distal ectodomain of SLAM using the side of its β-propeller fold. This is distinct from attachment proteins of other paramyxoviruses that bind receptors using the top of their β-propeller. The structure provides templates for antiviral drug design, an explanation for the effectiveness of the measles virus vaccine, and a model of the homophilic SLAM-SLAM interaction involved in immune modulations. Notably, the crystal structures obtained show two forms of the MV-H-SLAM tetrameric assembly (dimer of dimers), which may have implications for the mechanism of fusion triggering.

Molecular interactions between general anesthetics and the 5HT2B receptor.

PubMed

Matsunaga, Felipe; Gao, Lu; Huang, Xi-Ping; Saven, Jeffery G; Roth, Bryan L; Liu, Renyu

2015-01-01

Serotonin modulates many processes through a family of seven serotonin receptors. However, no studies have screened for interactions between general anesthetics currently in clinical use and serotonergic G-protein-coupled receptors (GPCRs). Given that both intravenous and inhalational anesthetics have been shown to target other classes of GPCRs, we hypothesized that general anesthetics might interact directly with some serotonin receptors and thus modify their function. Radioligand binding assays were performed to screen serotonin receptors for interactions with propofol and isoflurane as well as for affinity determinations. Docking calculations using the crystal structure of 5-HT2B were performed to computationally confirm the binding assay results and locate anesthetic binding sites. The 5-HT2B class of receptors interacted significantly with both propofol and isoflurane in the primary screen. The affinities for isoflurane and propofol were determined to be 7.78 and .95 μM, respectively, which were at or below the clinical concentrations for both anesthetics. The estimated free energy derived from docking calculations for propofol (-6.70 kcal/mol) and isoflurane (-5.10 kcal/mol) correlated with affinities from the binding assay. The anesthetics were predicted to dock at a pharmacologically relevant binding site of 5HT2B. The molecular interactions between propofol and isoflurane with the 5-HT2B class of receptors were discovered and characterized. This finding implicates the serotonergic GPCRs as potential anesthetic targets.

Selective progesterone receptor modulators 1: use during pregnancy.

PubMed

Benagiano, Giuseppe; Bastianelli, Carlo; Farris, Manuela

2008-10-01

A large number of synthetic compounds known as selective progesterone receptor modulators can bind to progesterone receptors: the ligands exhibit a spectrum of activities ranging from pure antagonism to a mixture of agonism and antagonism. Only a dozen or so selective progesterone receptor modulators have been tested to any significant extent: among them are mifepristone (RU 486), asoprisnil (J867), onapristone (ZK 98 299), ulipristal (CDB 2914), Proellex() (CDB 4124), ORG 33628 and ORG 31710. Their clinical applications during pregnancy are discussed. A careful evaluation of existing major review papers and recently published articles was carried out focusing on mifepristone, the most widely studied selective progesterone receptor modulator, which was first used for the voluntary interruption of an early gestation. Other selective progesterone receptor modulators, especially those with partial agonist action, have shown little activity during pregnancy in animal models. Besides early and late voluntary interruption of gestation, selective progesterone receptor modulators have been tested in a variety of obstetrical situations: to obtain a ripening of the cervix, for the medical management of early embryonic loss and foetal death, for the induction of labour at term and for the medical treatment of extra-uterine pregnancies. The only applications that seem worthy of large-scale utilisation during pregnancy are voluntary interruption of early and late gestation, medical management of early delayed miscarriage and late foetal demise.

Endogenous dopamine (DA) modulates (3H)spiperone binding in vivo in rat brain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bischoff, S.; Krauss, J.; Grunenwald, C.

1991-01-01

(3H)spiperone (SPI) binding in vivo, biochemical parameters and behavior were measured after modulating DA levels by various drug treatments. DA releasers and uptake inhibitors increased SPI binding in rat striatum. In other brain areas, the effects were variable, but only the pituitary remained unaffected. Surprisingly, nomifensine decreased SPI binding in frontal cortex. The effects of these drugs were monitored by measuring DA, serotonin (5-HT) and their metabolites in the same rats. The increased SPI binding in striatum was parallel to the locomotor stimulation with the following rank order: amfonelic acid greater than nomifensine greater than D-amphetamine greater than or equalmore » to methylphenidate greater than amineptine greater than bupropion. Decreasing DA levels with reserpine or alpha-methyl-para-tyrosine reduced SPI binding by 45% in striatum only when both drugs were combined. In contrast, reserpine enhanced SPI binding in pituitary. Thus, the amount of releasable DA seems to modulate SPI binding characteristics. It is suggested that in vivo, DA receptors are submitted to dynamic regulation in response to changes in intrasynaptic concentrations of DA.« less

High Throughput Techniques for Discovering New Glycine Receptor Modulators and their Binding Sites

PubMed Central

Gilbert, Daniel F.; Islam, Robiul; Lynagh, Timothy; Lynch, Joseph W.; Webb, Timothy I.

2009-01-01

The inhibitory glycine receptor (GlyR) is a member of the Cys-loop receptor family that mediates inhibitory neurotransmission in the central nervous system. These receptors are emerging as potential drug targets for inflammatory pain, immunomodulation, spasticity and epilepsy. Antagonists that specifically inhibit particular GlyR isoforms are also required as pharmacological probes for elucidating the roles of particular GlyR isoforms in health and disease. Although a substantial number of both positive and negative GlyR modulators have been identified, very few of these are specific for the GlyR over other receptor types. Thus, the potential of known compounds as either therapeutic leads or pharmacological probes is limited. It is therefore surprising that there have been few published studies describing attempts to discover novel GlyR isoform-specific modulators. The first aim of this review is to consider various methods for efficiently screening compounds against these receptors. We conclude that an anion sensitive yellow fluorescent protein is optimal for primary screening and that automated electrophysiology of cells stably expressing GlyRs is useful for confirming hits and quantitating the actions of identified compounds. The second aim of this review is to demonstrate how these techniques are used in our laboratory for the purpose of both discovering novel GlyR-active compounds and characterizing their binding sites. We also describe a reliable, cost effective method for transfecting HEK293 cells in single wells of a 384-well plate using nanogram quantities of plasmid DNA. PMID:19949449

Nuclear receptor coactivators function in estrogen receptor- and progestin receptor-dependent aspects of sexual behavior in female rats

PubMed Central

Molenda-Figueira, Heather A.; Williams, Casey A.; Griffin, Andreana L.; Rutledge, Eric M.; Blaustein, Jeffrey D.; Tetel, Marc J.

2008-01-01

The ovarian hormones, estradiol (E) and progesterone (P) facilitate the expression of sexual behavior in female rats. E and P mediate many of these behavioral effects by binding to their respective intracellular receptors in specific brain regions. Nuclear receptor coactivators, including Steroid Receptor Coactivator-1 (SRC-1) and CREB Binding Protein (CBP), dramatically enhance ligand-dependent steroid receptor transcriptional activity in vitro. Previously, our lab has shown that SRC-1 and CBP modulate estrogen receptor (ER)-mediated induction of progestin receptor (PR) gene expression in the ventromedial nucleus of the hypothalamus (VMN) and hormone-dependent sexual receptivity in female rats. Female sexual behaviors can be activated by high doses of E alone in ovariectomized rats, and thus are believed to be ER-dependent. However, the full repertoire of female sexual behavior, in particular, proceptive behaviors such as hopping, darting and ear wiggling, are considered to be PR-dependent. In the present experiments, the function of SRC-1 and CBP in distinct ER- (Exp. 1) and PR- (Exp. 2) dependent aspects of female sexual behavior was investigated. In Exp. 1, infusion of antisense oligodeoxynucleotides to SRC-1 and CBP mRNA into the VMN decreased lordosis intensity in rats treated with E alone, suggesting that these coactivators modulate ER-mediated female sexual behavior. In Exp. 2, antisense to SRC-1 and CBP mRNA around the time of P administration reduced PR-dependent ear wiggling and hopping and darting. Taken together, these data suggest that SRC-1 and CBP modulate ER and PR action in brain and influence distinct aspects of hormone-dependent sexual behaviors. These findings support our previous studies and provide further evidence that SRC-1 and CBP function together to regulate ovarian hormone action in behaviorally-relevant brain regions. PMID:16769066

Sterols regulate 3β-hydroxysterol Δ24-reductase (DHCR24) via dual sterol regulatory elements: cooperative induction of key enzymes in lipid synthesis by Sterol Regulatory Element Binding Proteins.

PubMed

Zerenturk, Eser J; Sharpe, Laura J; Brown, Andrew J

2012-10-01

3β-Hydroxysterol Δ24-reductase (DHCR24) catalyzes a final step in cholesterol synthesis, and has been ascribed diverse functions, such as being anti-apoptotic and anti-inflammatory. How this enzyme is regulated transcriptionally by sterols is currently unclear. Some studies have suggested that its expression is regulated by Sterol Regulatory Element Binding Proteins (SREBPs) while another suggests it is through the Liver X Receptor (LXR). However, these transcription factors have opposing effects on cellular sterol levels, so it is likely that one predominates. Here we establish that sterol regulation of DHCR24 occurs predominantly through SREBP-2, and identify the particular region of the DHCR24 promoter to which SREBP-2 binds. We demonstrate that sterol regulation is mediated by two sterol regulatory elements (SREs) in the promoter of the gene, assisted by two nearby NF-Y binding sites. Moreover, we present evidence that the dual SREs work cooperatively to regulate DHCR24 expression by comparison to two known SREBP target genes, the LDL receptor with one SRE, and farnesyl-diphosphate farnesyltransferase 1, with two SREs. Copyright © 2012 Elsevier B.V. All rights reserved.

The SAM domains of Anks family proteins are critically involved in modulating the degradation of EphA receptors.

PubMed

Kim, Jieun; Lee, Haeryung; Kim, Yujin; Yoo, Sooyeon; Park, Eunjeong; Park, Soochul

2010-04-01

We recently reported that the phosphotyrosine-binding (PTB) domain of Anks family proteins binds to EphA8, thereby positively regulating EphA8-mediated signaling pathways. In the current study, we identified a potential role for the SAM domains of Anks family proteins in EphA signaling. We found that SAM domains of Anks family proteins directly bind to ubiquitin, suggesting that Anks proteins regulate the degradation of ubiquitinated EphA receptors. Consistent with the role of Cbl ubiquitin ligases in the degradation of Eph receptors, our results revealed that the ubiquitin ligase c-Cbl induced the ubiquitination and degradation of EphA8 upon ligand binding. Ubiquitinated EphA8 also bound to the SAM domains of Odin, a member of the Anks family proteins. More importantly, the overexpression of wild-type Odin protected EphA8 and EphA2 from undergoing degradation following ligand stimulation and promoted EphA-mediated inhibition of cell migration. In contrast, a SAM domain deletion mutant of Odin strongly impaired the function of endogenous Odin, suggesting that the mutant functions in a dominant-negative manner. An analysis of Odin-deficient primary embryonic fibroblasts indicated that Odin levels play a critical role in regulating the stability of EphA2 in response to ligand stimulation. Taken together, our studies suggest that the SAM domains of Anks family proteins play a pivotal role in enhancing the stability of EphA receptors by modulating the ubiquitination process.

Sweet Taste Receptor Signaling Network: Possible Implication for Cognitive Functioning

PubMed Central

Welcome, Menizibeya O.; Mastorakis, Nikos E.; Pereverzev, Vladimir A.

2015-01-01

Sweet taste receptors are transmembrane protein network specialized in the transmission of information from special “sweet” molecules into the intracellular domain. These receptors can sense the taste of a range of molecules and transmit the information downstream to several acceptors, modulate cell specific functions and metabolism, and mediate cell-to-cell coupling through paracrine mechanism. Recent reports indicate that sweet taste receptors are widely distributed in the body and serves specific function relative to their localization. Due to their pleiotropic signaling properties and multisubstrate ligand affinity, sweet taste receptors are able to cooperatively bind multiple substances and mediate signaling by other receptors. Based on increasing evidence about the role of these receptors in the initiation and control of absorption and metabolism, and the pivotal role of metabolic (glucose) regulation in the central nervous system functioning, we propose a possible implication of sweet taste receptor signaling in modulating cognitive functioning. PMID:25653876

Functional cis-regulatory modules encoded by mouse-specific endogenous retrovirus

PubMed Central

Sundaram, Vasavi; Choudhary, Mayank N. K.; Pehrsson, Erica; Xing, Xiaoyun; Fiore, Christopher; Pandey, Manishi; Maricque, Brett; Udawatta, Methma; Ngo, Duc; Chen, Yujie; Paguntalan, Asia; Ray, Tammy; Hughes, Ava; Cohen, Barak A.; Wang, Ting

2017-01-01

Cis-regulatory modules contain multiple transcription factor (TF)-binding sites and integrate the effects of each TF to control gene expression in specific cellular contexts. Transposable elements (TEs) are uniquely equipped to deposit their regulatory sequences across a genome, which could also contain cis-regulatory modules that coordinate the control of multiple genes with the same regulatory logic. We provide the first evidence of mouse-specific TEs that encode a module of TF-binding sites in mouse embryonic stem cells (ESCs). The majority (77%) of the individual TEs tested exhibited enhancer activity in mouse ESCs. By mutating individual TF-binding sites within the TE, we identified a module of TF-binding motifs that cooperatively enhanced gene expression. Interestingly, we also observed the same motif module in the in silico constructed ancestral TE that also acted cooperatively to enhance gene expression. Our results suggest that ancestral TE insertions might have brought in cis-regulatory modules into the mouse genome. PMID:28348391

Positive allosteric modulators of the μ-opioid receptor: a novel approach for future pain medications

PubMed Central

Burford, N T; Traynor, J R; Alt, A

2015-01-01

Morphine and other agonists of the μ-opioid receptor are used clinically for acute and chronic pain relief and are considered to be the gold standard for pain medication. However, these opioids also have significant side effects, which are also mediated via activation of the μ-opioid receptor. Since the latter half of the twentieth century, researchers have sought to tease apart the mechanisms underlying analgesia, tolerance and dependence, with the hope of designing drugs with fewer side effects. These efforts have revolved around the design of orthosteric agonists with differing pharmacokinetic properties and/or selectivity profiles for the different opioid receptor types. Recently, μ-opioid receptor-positive allosteric modulators (μ-PAMs) were identified, which bind to a (allosteric) site on the μ-opioid receptor separate from the orthosteric site that binds an endogenous agonist. These allosteric modulators have little or no detectable functional activity when bound to the receptor in the absence of orthosteric agonist, but can potentiate the activity of bound orthosteric agonist, seen as an increase in apparent potency and/or efficacy of the orthosteric agonist. In this review, we describe the potential advantages that a μ-PAM approach might bring to the design of novel therapeutics for pain that may lack the side effects currently associated with opioid therapy. LINKED ARTICLES This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2 PMID:24460691

Quantitative analysis of rat brain alpha 2-receptors discriminated by [3H]clonidine and [3H]rauwolscine.

PubMed

Asakura, M; Tsukamoto, T; Imafuku, J; Matsui, H; Ino, M; Hasegawa, K

1984-10-30

Quantitative analysis of direct ligand binding of both [3H]clonidine and [3H]rauwolscine to the rat cerebral cortex alpha 2-receptors indicates the existence of two affinity states of the same receptor populations. In the presence of Mn2+, the high affinity state of [3H]clonidine binding was increased, whereas the high affinity state of [3H]rauwolscine binding was reduced. By contrast, GTP in micromolar ranges caused a decrease of the agonist high affinity state and an increase of the antagonist high affinity state. The total receptor sites and the respective separate affinities for both radioligands were approximately equal to their control values under all conditions, indicating that Mn2+ and GTP modulate the proportion of the two affinity states of the receptor. These results can be incorporated into a two-step, ternary complex model involving a guanine nucleotide binding protein (N protein) for the agonist and antagonist interaction with the alpha 2-receptor. Furthermore, the effects of GTP on the interaction of both ligands with the two affinity states can be mimicked by EDTA. It is suggested that divalent cations induce the formation of the receptor-N protein binary complex showing high affinity for agonists and low affinity for antagonists.

Crystal Structure of the Botulinum Neurotoxin Type G Binding Domain: Insight into Cell Surface Binding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stenmark, Pål; Dong, Min; Dupuy, Jérôme

2011-11-02

Botulinum neurotoxins (BoNTs) typically bind the neuronal cell surface via dual interactions with both protein receptors and gangliosides. We present here the 1.9-{angstrom} X-ray structure of the BoNT serotype G (BoNT/G) receptor binding domain (residues 868-1297) and a detailed view of protein receptor and ganglioside binding regions. The ganglioside binding motif (SxWY) has a conserved structure compared to the corresponding regions in BoNT serotype A and BoNT serotype B (BoNT/B), but several features of interactions with the hydrophilic face of the ganglioside are absent at the opposite side of the motif in the BoNT/G ganglioside binding cleft. This may significantlymore » reduce the affinity between BoNT/G and gangliosides. BoNT/G and BoNT/B share the protein receptor synaptotagmin (Syt) I/II. The Syt binding site has a conserved hydrophobic plateau located centrally in the proposed protein receptor binding interface (Tyr1189, Phe1202, Ala1204, Pro1205, and Phe1212). Interestingly, only 5 of 14 residues that are important for binding between Syt-II and BoNT/B are conserved in BoNT/G, suggesting that the means by which BoNT/G and BoNT/B bind Syt diverges more than previously appreciated. Indeed, substitution of Syt-II Phe47 and Phe55 with alanine residues had little effect on the binding of BoNT/G, but strongly reduced the binding of BoNT/B. Furthermore, an extended solvent-exposed hydrophobic loop, located between the Syt binding site and the ganglioside binding cleft, may serve as a third membrane association and binding element to contribute to high-affinity binding to the neuronal membrane. While BoNT/G and BoNT/B are homologous to each other and both utilize Syt-I/Syt-II as their protein receptor, the precise means by which these two toxin serotypes bind to Syt appears surprisingly divergent.« less

Crystal structure of the botulinum neurotoxin type G binding domain: insight into cell surface binding.

PubMed

Stenmark, Pål; Dong, Min; Dupuy, Jérôme; Chapman, Edwin R; Stevens, Raymond C

2010-04-16

Botulinum neurotoxins (BoNTs) typically bind the neuronal cell surface via dual interactions with both protein receptors and gangliosides. We present here the 1.9-A X-ray structure of the BoNT serotype G (BoNT/G) receptor binding domain (residues 868-1297) and a detailed view of protein receptor and ganglioside binding regions. The ganglioside binding motif (SxWY) has a conserved structure compared to the corresponding regions in BoNT serotype A and BoNT serotype B (BoNT/B), but several features of interactions with the hydrophilic face of the ganglioside are absent at the opposite side of the motif in the BoNT/G ganglioside binding cleft. This may significantly reduce the affinity between BoNT/G and gangliosides. BoNT/G and BoNT/B share the protein receptor synaptotagmin (Syt) I/II. The Syt binding site has a conserved hydrophobic plateau located centrally in the proposed protein receptor binding interface (Tyr1189, Phe1202, Ala1204, Pro1205, and Phe1212). Interestingly, only 5 of 14 residues that are important for binding between Syt-II and BoNT/B are conserved in BoNT/G, suggesting that the means by which BoNT/G and BoNT/B bind Syt diverges more than previously appreciated. Indeed, substitution of Syt-II Phe47 and Phe55 with alanine residues had little effect on the binding of BoNT/G, but strongly reduced the binding of BoNT/B. Furthermore, an extended solvent-exposed hydrophobic loop, located between the Syt binding site and the ganglioside binding cleft, may serve as a third membrane association and binding element to contribute to high-affinity binding to the neuronal membrane. While BoNT/G and BoNT/B are homologous to each other and both utilize Syt-I/Syt-II as their protein receptor, the precise means by which these two toxin serotypes bind to Syt appears surprisingly divergent. Copyright (c) 2010. Published by Elsevier Ltd.

Probing ligand recognition of the opioid pan antagonist AT-076 at nociceptin, kappa, mu, and delta opioid receptors through structure-activity relationships.

PubMed

Journigan, V Blair; Polgar, Willma E; Tuan, Edward W; Lu, James; Daga, Pankaj R; Zaveri, Nurulain T

2017-10-16

Few opioid ligands binding to the three classic opioid receptor subtypes, mu, kappa and delta, have high affinity at the fourth opioid receptor, the nociceptin/orphanin FQ receptor (NOP). We recently reported the discovery of AT-076 (1), (R)-7-hydroxy-N-((S)-1-(4-(3-hydroxyphenyl)piperidin-1-yl)-3-methylbutan-2-yl)-1,2,3,4-tetrahydroisoquinoline-3-carboxamide, a pan antagonist with nanomolar affinity for all four subtypes. Since AT-076 binds with high affinity at all four subtypes, we conducted a structure-activity relationship (SAR) study to probe ligand recognition features important for pan opioid receptor activity, using chemical modifications of key pharmacophoric groups. SAR analysis of the resulting analogs suggests that for the NOP receptor, the entire AT-076 scaffold is crucial for high binding affinity, but the binding mode is likely different from that of NOP antagonists C-24 and SB-612111 bound in the NOP crystal structure. On the other hand, modifications of the 3-hydroxyphenyl pharmacophore, but not the 7-hydroxy Tic pharmacophore, are better tolerated at kappa and mu receptors and yield very high affinity multifunctional (e.g. 12) or highly selective (e.g. 16) kappa ligands. With the availability of the opioid receptor crystal structures, our SAR analysis of the common chemotype of AT-076 suggests rational approaches to modulate binding selectivity, enabling the design of multifunctional or selective opioid ligands from such scaffolds.

The structure of cytomegalovirus immune modulator UL141 highlights structural Ig-fold versatility for receptor binding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nemčovičová, Ivana; Slovak Academy of Sciences, Dúbravská cesta 9, SK 84505 Bratislava; Zajonc, Dirk M., E-mail: dzajonc@liai.org

2014-03-01

The crystal structure of Human cytomegalovirus immune modulator UL141 was solved at 3.25 Å resolution. Here, a detailed analysis of its intimate dimerization interface and the biophysical properties of its receptor (TRAIL-R2 and CD155) binding interactions are presented. Natural killer (NK) cells are critical components of the innate immune system as they rapidly detect and destroy infected cells. To avoid immune recognition and to allow long-term persistence in the host, Human cytomegalovirus (HCMV) has evolved a number of genes to evade or inhibit immune effector pathways. In particular, UL141 can inhibit cell-surface expression of both the NK cell-activating ligand CD155more » as well as the TRAIL death receptors (TRAIL-R1 and TRAIL-R2). The crystal structure of unliganded HCMV UL141 refined to 3.25 Å resolution allowed analysis of its head-to-tail dimerization interface. A ‘dimerization-deficient’ mutant of UL141 (ddUL141) was further designed, which retained the ability to bind to TRAIL-R2 or CD155 while losing the ability to cross-link two receptor monomers. Structural comparison of unliganded UL141 with UL141 bound to TRAIL-R2 further identified a mobile loop that makes intimate contacts with TRAIL-R2 upon receptor engagement. Superposition of the Ig-like domain of UL141 on the CD155 ligand T-cell immunoreceptor with Ig and ITIM domains (TIGIT) revealed that UL141 can potentially engage CD155 similar to TIGIT by using the C′C′′ and GF loops. Further mutations in the TIGIT binding site of CD155 (Q63R and F128R) abrogated UL141 binding, suggesting that the Ig-like domain of UL141 is a viral mimic of TIGIT, as it targets the same binding site on CD155 using similar ‘lock-and-key’ interactions. Sequence alignment of the UL141 gene and its orthologues also showed conservation in this highly hydrophobic (L/A)X{sub 6}G ‘lock’ motif for CD155 binding as well as conservation of the TRAIL-R2 binding patches, suggesting that these host–receptor interactions are evolutionary conserved.« less

The neuroanatomical distribution of oxytocin receptor binding and mRNA in the male rhesus macaque (Macaca mulatta).

PubMed

Freeman, Sara M; Inoue, Kiyoshi; Smith, Aaron L; Goodman, Mark M; Young, Larry J

2014-07-01

The rhesus macaque (Macaca mulatta) is an important primate model for social cognition, and recent studies have begun to explore the impact of oxytocin on social cognition and behavior. Macaques have great potential for elucidating the neural mechanisms by which oxytocin modulates social cognition, which has implications for oxytocin-based pharmacotherapies for psychiatric disorders such as autism and schizophrenia. Previous attempts to localize oxytocin receptors (OXTR) in the rhesus macaque brain have failed due to reduced selectivity of radioligands, which in primates bind to both OXTR and the structurally similar vasopressin 1a receptor (AVPR1A). We have developed a pharmacologically-informed competitive binding autoradiography protocol that selectively reveals OXTR and AVPR1A binding sites in primate brain sections. Using this protocol, we describe the neuroanatomical distribution of OXTR in the macaque. Finally, we use in situ hybridization to localize OXTR mRNA. Our results demonstrate that OXTR expression in the macaque brain is much more restricted than AVPR1A. OXTR is largely limited to the nucleus basalis of Meynert, pedunculopontine tegmental nucleus, the superficial gray layer of the superior colliculus, the trapezoid body, and the ventromedial hypothalamus. These regions are involved in a variety of functions relevant to social cognition, including modulating visual attention, processing auditory and multimodal sensory stimuli, and controlling orienting responses to visual stimuli. These results provide insights into the neural mechanisms by which oxytocin modulates social cognition and behavior in this species, which, like humans, uses vision and audition as the primary modalities for social communication. Copyright © 2014 Elsevier Ltd. All rights reserved.

The neuroanatomical distribution of oxytocin receptor binding and mRNA in the male rhesus macaque (Macaca mulatta)

PubMed Central

Freeman, Sara M.; Inoue, Kiyoshi; Smith, Aaron L.; Goodman, Mark M.; Young, Larry J.

2014-01-01

The rhesus macaque (Macaca mulatta) is an important primate model for social cognition, and recent studies have begun to explore the impact of oxytocin on social cognition and behavior. Macaques have great potential for elucidating the neural mechanisms by which oxytocin modulates social cognition, which has implications for oxytocin-based pharmacotherapies for psychiatric disorders such as autism and schizophrenia. Previous attempts to localize oxytocin receptors (OXTR) in the rhesus macaque brain have failed due to reduced selectivity of radioligands, which in primates bind to both OXTR and the structurally similar vasopressin 1a receptor (AVPR1A). We have developed a pharmacologically-informed competitive binding autoradiography protocol that selectively reveals OXTR and AVPR1A binding sites in primate brain sections. Using this protocol, we describe the neuroanatomical distribution of OXTR in the macaque. Finally, we use in situ hybridization to localize OXTR mRNA. Our results demonstrate that OXTR expression in the macaque brain is much more restricted than AVPR1A. OXTR is largely limited to the nucleus basalis of Meynert, pedunculopontine tegmental nucleus, the superficial gray layer of the superior colliculus, the trapezoid body, and the ventromedial hypothalamus. These regions are involved in a variety of functions relevant to social cognition, including modulating visual attention, processing auditory and multimodal sensory stimuli, and controlling orienting responses to visual stimuli. These results provide insights into the neural mechanisms by which oxytocin modulates social cognition and behavior in this species, which, like humans, uses vision and audition as the primary modalities for social communication. PMID:24845184

Aripiprazole Increases the PKA Signalling and Expression of the GABAA Receptor and CREB1 in the Nucleus Accumbens of Rats.

PubMed

Pan, Bo; Lian, Jiamei; Huang, Xu-Feng; Deng, Chao

2016-05-01

The GABAA receptor is implicated in the pathophysiology of schizophrenia and regulated by PKA signalling. Current antipsychotics bind with D2-like receptors, but not the GABAA receptor. The cAMP-responsive element-binding protein 1 (CREB1) is also associated with PKA signalling and may be related to the positive symptoms of schizophrenia. This study investigated the effects of antipsychotics in modulating D2-mediated PKA signalling and its downstream GABAA receptors and CREB1. Rats were treated orally with aripiprazole (0.75 mg/kg, ter in die (t.i.d.)), bifeprunox (0.8 mg/kg, t.i.d.), haloperidol (0.1 mg/kg, t.i.d.) or vehicle for 1 week. The levels of PKA-Cα and p-PKA in the prefrontal cortex (PFC), nucleus accumbens (NAc) and caudate putamen (CPu) were detected by Western blots. The mRNA levels of Gabrb1, Gabrb2, Gabrb3 and Creb1, and their protein expression were measured by qRT-PCR and Western blots, respectively. Aripiprazole elevated the levels of p-PKA and the ratio of p-PKA/PKA in the NAc, but not the PFC and CPu. Correlated with this elevated PKA signalling, aripiprazole elevated the mRNA and protein expression of the GABAA (β-1) receptor and CREB1 in the NAc. While haloperidol elevated the levels of p-PKA and the ratio of p-PKA/PKA in both NAc and CPu, it only tended to increase the expression of the GABAA (β-1) receptor and CREB1 in the NAc, but not the CPu. Bifeprunox had no effects on PKA signalling in these brain regions. These results suggest that aripiprazole has selective effects on upregulating the GABAA (β-1) receptor and CREB1 in the NAc, probably via activating PKA signalling.

Signalling properties and pharmacological analysis of two sulfakinin receptors from the red flour beetle, Tribolium castaneum

USDA-ARS?s Scientific Manuscript database

Sulfakinin is an insect neuropeptide that constitutes an important component of the complex network of hormonal and neural factors that regulate feeding and digestion. The key modulating functions of sulfakinin are mediated by binding and signaling via G-protein coupled receptors. Although a subst...

α2-containing GABAA receptors expressed in hippocampal region CA3 control fast network oscillations

PubMed Central

Heistek, Tim S; Ruiperez-Alonso, Marta; Timmerman, A Jaap; Brussaard, Arjen B; Mansvelder, Huibert D

2013-01-01

GABAA receptors are critically involved in hippocampal oscillations. GABAA receptor α1 and α2 subunits are differentially expressed throughout the hippocampal circuitry and thereby may have distinct contributions to oscillations. It is unknown which GABAA receptor α subunit controls hippocampal oscillations and where these receptors are expressed. To address these questions we used transgenic mice expressing GABAA receptor α1 and/or α2 subunits with point mutations (H101R) that render these receptors insensitive to allosteric modulation at the benzodiazepine binding site, and tested how increased or decreased function of α subunits affects hippocampal oscillations. Positive allosteric modulation by zolpidem prolonged decay kinetics of hippocampal GABAergic synaptic transmission and reduced the frequency of cholinergically induced oscillations. Allosteric modulation of GABAergic receptors in CA3 altered oscillation frequency in CA1, while modulation of GABA receptors in CA1 did not affect oscillations. In mice having a point mutation (H101R) at the GABAA receptor α2 subunit, zolpidem effects on cholinergically induced oscillations were strongly reduced compared to wild-type animals, while zolpidem modulation was still present in mice with the H101R mutation at the α1 subunit. Furthermore, genetic knockout of α2 subunits strongly reduced oscillations, whereas knockout of α1 subunits had no effect. Allosteric modulation of GABAergic receptors was strongly reduced in unitary connections between fast spiking interneurons and pyramidal neurons in CA3 of α2H101R mice, but not of α1H101R mice, suggesting that fast spiking interneuron to pyramidal neuron synapses in CA3 contain α2 subunits. These findings suggest that α2-containing GABAA receptors expressed in the CA3 region provide the inhibition that controls hippocampal rhythm during cholinergically induced oscillations. PMID:23109109

Genetic Polymorphism in Extracellular Regulators of Wnt Signaling Pathway

PubMed Central

Sharma, Ashish Ranjan; Seo, Eun-Min; Nam, Ju-Suk

2015-01-01

The Wnt signaling pathway is mediated by a family of secreted glycoproteins through canonical and noncanonical mechanism. The signaling pathways are regulated by various modulators, which are classified into two classes on the basis of their interaction with either Wnt or its receptors. Secreted frizzled-related proteins (sFRPs) are the member of class that binds to Wnt protein and antagonizes Wnt signaling pathway. The other class consists of Dickkopf (DKK) proteins family that binds to Wnt receptor complex. The present review discusses the disease related association of various polymorphisms in Wnt signaling modulators. Furthermore, this review also highlights that some of the sFRPs and DKKs are unable to act as an antagonist for Wnt signaling pathway and thus their function needs to be explored more extensively. PMID:25945348

Development of allosteric modulators of GPCRs for treatment of CNS disorders

PubMed Central

Nickols, Hilary Highfield; Conn, P. Jeffrey

2013-01-01

The discovery of allosteric modulators of G protein-coupled receptors (GPCRs) provides a promising new strategy with potential for developing novel treatments for a variety of central nervous system (CNS) disorders. Traditional drug discovery efforts targeting GPCRs have focused on developing ligands for orthosteric sites which bind endogenous ligands. Allosteric modulators target a site separate from the orthosteric site to modulate receptor function. These allosteric agents can either potentiate (positive allosteric modulator, PAM) or inhibit (negative allosteric modulator, NAM) the receptor response and often provide much greater subtype selectivity than do orthosteric ligands for the same receptors. Experimental evidence has revealed more nuanced pharmacological modes of action of allosteric modulators, with some PAMs showing allosteric agonism in combination with positive allosteric modulation in response to endogenous ligand (ago-potentiators) as well as “bitopic” ligands that interact with both the allosteric and orthosteric sites. Drugs targeting the allosteric site allow for increased drug selectivity and potentially decreased adverse side effects. Promising evidence has demonstrated potential utility of a number of allosteric modulators of GPCRs in multiple CNS disorders, including neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease, as well as psychiatric or neurobehavioral diseases such as anxiety, schizophrenia, and addiction. PMID:24076101

Free Energy Landscape of Lipid Interactions with Regulatory Binding Sites on the Transmembrane Domain of the EGF Receptor.

PubMed

Hedger, George; Shorthouse, David; Koldsø, Heidi; Sansom, Mark S P

2016-08-25

Lipid molecules can bind to specific sites on integral membrane proteins, modulating their structure and function. We have undertaken coarse-grained simulations to calculate free energy profiles for glycolipids and phospholipids interacting with modulatory sites on the transmembrane helix dimer of the EGF receptor within a lipid bilayer environment. We identify lipid interaction sites at each end of the transmembrane domain and compute interaction free energy profiles for lipids with these sites. Interaction free energies ranged from ca. -40 to -4 kJ/mol for different lipid species. Those lipids (glycolipid GM3 and phosphoinositide PIP2) known to modulate EGFR function exhibit the strongest binding to interaction sites on the EGFR, and we are able to reproduce the preference for interaction with GM3 over other glycolipids suggested by experiment. Mutation of amino acid residues essential for EGFR function reduce the binding free energy of these key lipid species. The residues interacting with the lipids in the simulations are in agreement with those suggested by experimental (mutational) studies. This approach provides a generalizable tool for characterizing the interactions of lipids that bind to specific sites on integral membrane proteins.

Free Energy Landscape of Lipid Interactions with Regulatory Binding Sites on the Transmembrane Domain of the EGF Receptor

PubMed Central

2016-01-01

Lipid molecules can bind to specific sites on integral membrane proteins, modulating their structure and function. We have undertaken coarse-grained simulations to calculate free energy profiles for glycolipids and phospholipids interacting with modulatory sites on the transmembrane helix dimer of the EGF receptor within a lipid bilayer environment. We identify lipid interaction sites at each end of the transmembrane domain and compute interaction free energy profiles for lipids with these sites. Interaction free energies ranged from ca. −40 to −4 kJ/mol for different lipid species. Those lipids (glycolipid GM3 and phosphoinositide PIP2) known to modulate EGFR function exhibit the strongest binding to interaction sites on the EGFR, and we are able to reproduce the preference for interaction with GM3 over other glycolipids suggested by experiment. Mutation of amino acid residues essential for EGFR function reduce the binding free energy of these key lipid species. The residues interacting with the lipids in the simulations are in agreement with those suggested by experimental (mutational) studies. This approach provides a generalizable tool for characterizing the interactions of lipids that bind to specific sites on integral membrane proteins. PMID:27109430

GLUCOCORTICOID RECEPTOR EXPRESSION DURING THE DEVELOPMENT OF THE EMBRYONIC MOUSE SECONDARY PALATE

EPA Science Inventory

Glucocorticoids are important regulators of embryonic growth and development. hese effects are mediated through glucocorticoid receptors (GR) which bind to glucocorticoid response elements upstream of regulated genes. his study examines the expression of GR and GR mRNA in embryon...

Prostanoids and their receptors that modulate dendritic cell-mediated immunity.

PubMed

Gualde, Norbert; Harizi, Hedi

2004-08-01

Dendritic cells (DC) are essential for the initiation of immune responses by capturing, processing and presenting antigens to T cells. In addition to their important role as professional APC, they are able to produce immunosuppressive and pro-inflammatory prostanoids from arachidonic acid (AA) by the action of cyclooxygenase (COX) enzymes. In an autocrine and paracrine fashion, the secreted lipid mediators subsequently modulate the maturation, cytokine production, Th-cell polarizing ability, chemokine receptor expression, migration, and apoptosis of these extremely versatile APC. The biological actions of prostanoids, including their effects on APC-mediated immunity and acute inflammatory responses, are exerted by G protein-coupled receptors on plasma membrane. Some COX metabolites act as anti-inflammatory lipid mediators by binding to nuclear receptors and modulating DC functions. Although the role of cytokines in DC function has been studied extensively, the effects of prostanoids on DC biology have only recently become the focus of investigation. This review summarizes the current knowledge about the role of prostanoids and their receptors in modulating DC function and the subsequent immune responses.

Molecular basis for repression of liver X receptor-mediated gene transcription by receptor-interacting protein 140

PubMed Central

Jakobsson, Tomas; Osman, Waffa; Gustafsson, Jan-Åke; Zilliacus, Johanna; Wärnmark, Anette

2007-01-01

Similarities in physiological roles of LXR (liver X receptors) and co-repressor RIP140 (receptor-interacting protein 140) in regulating energy homoeostasis and lipid and glucose metabolism suggest that the effects of LXR could at least partly be mediated by recruitment of the co-repressor RIP140. In the present study, we have elucidated the molecular basis for regulation of LXR transcriptional activity by RIP140. LXR is evenly localized in the nucleus and neither the N-terminal domain nor the LBD (ligand-binding domain) is necessary for nuclear localization. Both LXR subtypes, LXRα and LXRβ, interact with RIP140 and co-localize in diffuse large nuclear domains. Interaction and co-localization are dependent on the LBD of the receptor. The C-terminal domain of RIP140 is sufficient for full repressive effect. None of the C-terminal NR (nuclear receptor)-boxes is required for the co-repressor activity, whereas the NR-box-like motif as well as additional elements in the C-terminal region are required for full repressive function. The C-terminal NR-box-like motif is necessary for interaction with LXRβ, whereas additional elements are needed for strong interaction with LXRα. In conclusion, our results suggest that co-repression of LXR activity by RIP140 involves an atypical binding mode of RIP140 and a repression element in the RIP140 C-terminus. PMID:17391100

Regulation of Androgen Receptor-Mediated Transcription by RPB5 Binding Protein URI/RMP ▿

PubMed Central

Mita, Paolo; Savas, Jeffrey N.; Djouder, Nabil; Yates, John R.; Ha, Susan; Ruoff, Rachel; Schafler, Eric D.; Nwachukwu, Jerome C.; Tanese, Naoko; Cowan, Nicholas J.; Zavadil, Jiri; Garabedian, Michael J.; Logan, Susan K.

2011-01-01

Androgen receptor (AR)-mediated transcription is modulated by interaction with coregulatory proteins. We demonstrate that the unconventional prefoldin RPB5 interactor (URI) is a new regulator of AR transcription and is critical for antagonist (bicalutamide) action. URI is phosphorylated upon androgen treatment, suggesting communication between the URI and AR signaling pathways. Whereas depletion of URI enhances AR-mediated gene transcription, overexpression of URI suppresses AR transcriptional activation and anchorage-independent prostate cancer cell growth. Repression of AR-mediated transcription is achieved, in part, by URI binding and regulation of androgen receptor trapped clone 27 (Art-27), a previously characterized AR corepressor. Consistent with this idea, genome-wide expression profiling in prostate cancer cells upon depletion of URI or Art-27 reveals substantially overlapping patterns of gene expression. Further, depletion of URI increases the expression of the AR target gene NKX-3.1, decreases the recruitment of Art-27, and increases AR occupancy at the NKX-3.1 promoter. While Art-27 can bind AR directly, URI is bound to chromatin prior to hormone-dependent recruitment of AR, suggesting a role for URI in modulating AR recruitment to target genes. PMID:21730289

Nicotinic modulation of hippocampal cell signaling and associated effects on learning and memory.

PubMed

Kutlu, Munir Gunes; Gould, Thomas J

2016-03-01

The hippocampus is a key brain structure involved in synaptic plasticity associated with long-term declarative memory formation. Importantly, nicotine and activation of nicotinic acetylcholine receptors (nAChRs) can alter hippocampal plasticity and these changes may occur through modulation of hippocampal kinases and transcription factors. Hippocampal kinases such as cAMP-dependent protein kinase (PKA), calcium/calmodulin-dependent protein kinases (CAMKs), extracellular signal-regulated kinases 1 and 2 (ERK1/2), and c-jun N-terminal kinase 1 (JNK1), and the transcription factor cAMP-response element-binding protein (CREB) that are activated either directly or indirectly by nicotine may modulate hippocampal plasticity and in parallel hippocampus-dependent learning and memory. Evidence suggests that nicotine may alter hippocampus-dependent learning by changing the time and magnitude of activation of kinases and transcription factors normally involved in learning and by recruiting additional cell signaling molecules. Understanding how nicotine alters learning and memory will advance basic understanding of the neural substrates of learning and aid in understanding mental disorders that involve cognitive and learning deficits. Copyright © 2015 Elsevier Inc. All rights reserved.

GHSR-D2R heteromerization modulates dopamine signaling through an effect on G protein conformation.

PubMed

Damian, Marjorie; Pons, Véronique; Renault, Pedro; M'Kadmi, Céline; Delort, Bartholomé; Hartmann, Lucie; Kaya, Ali I; Louet, Maxime; Gagne, Didier; Ben Haj Salah, Khoubaib; Denoyelle, Séverine; Ferry, Gilles; Boutin, Jean A; Wagner, Renaud; Fehrentz, Jean-Alain; Martinez, Jean; Marie, Jacky; Floquet, Nicolas; Galès, Céline; Mary, Sophie; Hamm, Heidi E; Banères, Jean-Louis

2018-04-24

The growth hormone secretagogue receptor (GHSR) and dopamine receptor (D2R) have been shown to oligomerize in hypothalamic neurons with a significant effect on dopamine signaling, but the molecular processes underlying this effect are still obscure. We used here the purified GHSR and D2R to establish that these two receptors assemble in a lipid environment as a tetrameric complex composed of two each of the receptors. This complex further recruits G proteins to give rise to an assembly with only two G protein trimers bound to a receptor tetramer. We further demonstrate that receptor heteromerization directly impacts on dopamine-mediated Gi protein activation by modulating the conformation of its α-subunit. Indeed, association to the purified GHSR:D2R heteromer triggers a different active conformation of Gαi that is linked to a higher rate of GTP binding and a faster dissociation from the heteromeric receptor. This is an additional mechanism to expand the repertoire of GPCR signaling modulation that could have implications for the control of dopamine signaling in normal and physiopathological conditions.

Binding Mode and Structure-Activity Relationships of ITE as an Aryl Hydrocarbon Receptor (AhR) Agonist.

PubMed

Dolciami, Daniela; Gargaro, Marco; Cerra, Bruno; Scalisi, Giulia; Bagnoli, Luana; Servillo, Giuseppe; Fazia, Maria Agnese Della; Puccetti, Paolo; Quintana, Francisco J; Fallarino, Francesca; Macchiarulo, Antonio

2018-02-06

Discovered as a modulator of the toxic response to environmental pollutants, aryl hydrocarbon receptor (AhR) has recently gained attention for its involvement in various physiological and pathological pathways. AhR is a ligand-dependent transcription factor activated by a large array of chemical compounds, which include metabolites of l-tryptophan (l-Trp) catabolism as endogenous ligands of the receptor. Among these, 2-(1'H-indole-3'-carbonyl)thiazole-4-carboxylic acid methyl ester (ITE) has attracted interest in the scientific community, being endowed with nontoxic, immunomodulatory, and anticancer AhR-mediated functions. So far, no information about the binding mode and interactions of ITE with AhR is available. In this study, we used docking and molecular dynamics to propose a putative binding mode of ITE into the ligand binding pocket of AhR. Mutagenesis studies were then instrumental in validating the proposed binding mode, identifying His 285 and Tyr 316 as important key residues for ligand-dependent receptor activation. Finally, a set of ITE analogues was synthesized and tested to further probe molecular interactions of ITE to AhR and characterize the relevance of specific functional groups in the chemical structure for receptor activity. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

In Vitro and In Vivo Identification of Novel Positive Allosteric Modulators of the Human Dopamine D2 and D3 Receptor.

PubMed

Wood, Martyn; Ates, Ali; Andre, Veronique Marie; Michel, Anne; Barnaby, Robert; Gillard, Michel

2016-02-01

Agonists at dopamine D2 and D3 receptors are important therapeutic agents in the treatment of Parkinson's disease. Compared with the use of agonists, allosteric potentiators offer potential advantages such as temporal, regional, and phasic potentiation of natural signaling, and that of receptor subtype selectivity. We report the identification of a stereoselective interaction of a benzothiazol racemic compound that acts as a positive allosteric modulator (PAM) of the rat and human dopamine D2 and D3 receptors. The R isomer did not directly stimulate the dopamine D2 receptor but potentiated the effects of dopamine. In contrast the S isomer attenuated the effects of the PAM and the effects of dopamine. In radioligand binding studies, these compounds do not compete for binding of orthosteric ligands, but indeed the R isomer increased the number of high-affinity sites for [(3)H]-dopamine without affecting K(d). We went on to identify a more potent PAM for use in native receptor systems. This compound potentiated the effects of D2/D3 signaling in vitro in electrophysiologic studies on dissociated striatal neurons and in vivo on the effects of L-dopa in the 6OHDA (6-hydroxydopamine) contralateral turning model. These PAMs lacked activity at a wide variety of receptors, lacked PAM activity at related Gi-coupled G protein-coupled receptors, and lacked activity at D1 receptors. However, the PAMs did potentiate [(3)H]-dopamine binding at both D2 and D3 receptors. Together, these studies show that we have identified PAMs of the D2 and D3 receptors both in vitro and in vivo. Such compounds may have utility in the treatment of hypodopaminergic function. Copyright © 2016 by The American Society for Pharmacology and Experimental Therapeutics.

Characterization of the Binding Site of Aspartame in the Human Sweet Taste Receptor

PubMed Central

Maillet, Emeline L.; Cui, Meng; Jiang, Peihua; Mezei, Mihaly; Hecht, Elizabeth; Quijada, Jeniffer; Osman, Roman; Max, Marianna

2015-01-01

The sweet taste receptor, a heterodimeric G protein-coupled receptor comprised of T1R2 and T1R3, binds sugars, small molecule sweeteners, and sweet proteins to multiple binding sites. The dipeptide sweetener, aspartame binds in the Venus Flytrap Module (VFTM) of T1R2. We developed homology models of the open and closed forms of human T1R2 and human T1R3 VFTMs and their dimers and then docked aspartame into the closed form of T1R2’s VFTM. To test and refine the predictions of our model, we mutated various T1R2 VFTM residues, assayed activity of the mutants and identified 11 critical residues (S40, Y103, D142, S144, S165, S168, Y215, D278, E302, D307, and R383) in and proximal to the binding pocket of the sweet taste receptor that are important for ligand recognition and activity of aspartame. Furthermore, we propose that binding is dependent on 2 water molecules situated in the ligand pocket that bridge 2 carbonyl groups of aspartame to residues D142 and L279. These results shed light on the activation mechanism and how signal transmission arising from the extracellular domain of the T1R2 monomer of the sweet receptor leads to the perception of sweet taste. PMID:26377607

Mycophenolate mofetil increases adhesion capacity of tumor cells in vitro.

PubMed

Blaheta, Roman A; Bogossian, Harilaos; Beecken, Wolf-Dietrich; Jonas, Dietger; Hasenberg, Christoph; Makarevic, Jasmina; Ogbomo, Henry; Bechstein, Wolf O; Oppermann, Elsie; Leckel, Kerstin; Cinatl, Jindrich

2003-12-27

The immunosuppressive drug mycophenolate mofetil (MMF) reduces expression of the heterophilic binding elements intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 and thereby prevents attachment of alloactivated leukocytes to donor endothelium. The authors speculated that MMF might further diminish receptors of the immunoglobulin superfamily which, however, act as homophilic binding elements. Because decrease of homophilic adhesion receptors correlates with tumor dissemination and metastasis, MMF could trigger development or recurrence of neoplastic tumors. The authors analyzed the influence of MMF on homotypic adhesion receptors and its consequence for tumor cell attachment to an endothelial cell monolayer. Neuroblastoma (NB) cells, which self-aggregate by means of the homophilic-binding element neural cell adhesion molecule (NCAM), were used. Effects of MMF on the 140- and 180-kDa NCAM isoforms were investigated quantitatively by flow cytometry, Western blot, and reverse-transcriptase (RT) polymerase chain reaction (PCR). The relevance of NCAM for tumor cell binding was proven by treating NB with NCAM antisense oligonucleotides. MMF profoundly increased the number of adherent NB cells, with a maximum effect at 0.1 microM, compared with controls. Decrease of NCAM on the cell surface was detected by flow cytometry. Western blot and RT-PCR demonstrated reduced protein and RNA levels of the 140- and 180-kDa isoforms. Treatment of NB cells with NCAM antisense oligonucleotides showed that reduced NCAM expression leads to enhanced tumor cell adhesion. MMF decreases NCAM receptors, which is associated with enhanced tumor cell invasiveness. The authors conclude that an MMF-based immunosuppressive regimen might increase the risk of tumor metastasis if this process is predominantly conveyed by means of homophilic adhesion proteins.

Discovery of estrogen receptor α modulators from natural compounds in Si-Wu-Tang series decoctions using estrogen-responsive MCF-7 breast cancer cells.

PubMed

Liu, Li; Ma, Hongyue; Tang, Yuping; Chen, Wenxing; Lu, Yin; Guo, Jianming; Duan, Jin-Ao

2012-01-01

The binding between the estrogen receptor α (ER-α) and a variety of compounds in traditional Chinese formulae, Si-Wu-Tang (SWT) series decoctions, was studied using a stably-transfected human breast cancer cell line (MVLN). In 38 compounds tested from SWT series decoctions, the estrogen-like activity of 22 compounds was above 60% in 20 μg mL(-1). Furthermore, theoretical affinity of these compounds was certificated using the functional virtual screen of ER-α modulators by FlexX-Pharm. The accuracy of functional virtual screening of ER-α modulators could reach to 77.27%. The results showed that some compounds, such as organic acids and flavones in SWT series decoctions could be used as selective estrogen receptor modulators (SERMs) and could be selected for further development as potential agents for estrogen related diseases. Copyright © 2011 Elsevier Ltd. All rights reserved.

Heterodimerization of mu and delta opioid receptors: A role in opiate synergy.

PubMed

Gomes, I; Jordan, B A; Gupta, A; Trapaidze, N; Nagy, V; Devi, L A

2000-11-15

Opiate analgesics are widely used in the treatment of severe pain. Because of their importance in therapy, different strategies have been considered for making opiates more effective while curbing their liability to be abused. Although most opiates exert their analgesic effects primarily via mu opioid receptors, a number of studies have shown that delta receptor-selective drugs can enhance their potency. The molecular basis for these findings has not been elucidated previously. In the present study, we examined whether heterodimerization of mu and delta receptors could account for the cross-modulation previously observed between these two receptors. We find that co-expression of mu and delta receptors in heterologous cells followed by selective immunoprecipitation results in the isolation of mu-delta heterodimers. Treatment of these cells with extremely low doses of certain delta-selective ligands results in a significant increase in the binding of a mu receptor agonist. Similarly, treatment with mu-selective ligands results in a significant increase in the binding of a delta receptor agonist. This robust increase is also seen in SKNSH cells that endogenously express both mu and delta receptors. Furthermore, we find that a delta receptor antagonist enhances both the potency and efficacy of the mu receptor signaling; likewise a mu antagonist enhances the potency and efficacy of the delta receptor signaling. A combination of agonists (mu and delta receptor selective) also synergistically binds and potentiates signaling by activating the mu-delta heterodimer. Taken together, these studies show that heterodimers exhibit distinct ligand binding and signaling characteristics. These findings have important clinical ramifications and may provide new foundations for more effective therapies.

Curcumin modulation of high fat diet-induced atherosclerosis and steatohepatosis in LDL receptor deficient mice

USDA-ARS?s Scientific Manuscript database

Consuming curcumin may benefit health by modulating lipid metabolism and suppressing atherogenesis. Fatty acid binding proteins (FABP-4/aP2) and CD36 expression are key factors in lipid accumulation in macrophages and foam cell formation in atherogenesis. Our earlier observations suggest that curcum...

Rational steering of insulin binding specificity by intra-chain chemical crosslinking

NASA Astrophysics Data System (ADS)

Viková, Jitka; Collinsová, Michaela; Kletvíková, Emília; Buděšínský, Miloš; Kaplan, Vojtěch; Žáková, Lenka; Veverka, Václav; Hexnerová, Rozálie; Aviñó, Roberto J. Tarazona; Straková, Jana; Selicharová, Irena; Vaněk, Václav; Wright, Daniel W.; Watson, Christopher J.; Turkenburg, Johan P.; Brzozowski, Andrzej M.; Jiráček, Jiří

2016-01-01

Insulin is a key hormone of human metabolism with major therapeutic importance for both types of diabetes. New insulin analogues with more physiological profiles and better glycemic control are needed, especially analogues that preferentially bind to the metabolic B-isoform of insulin receptor (IR-B). Here, we aimed to stabilize and modulate the receptor-compatible conformation of insulin by covalent intra-chain crosslinking within its B22-B30 segment, using the CuI-catalyzed Huisgen 1,3-dipolar cycloaddition reaction of azides and alkynes. This approach resulted in 14 new, systematically crosslinked insulin analogues whose structures and functions were extensively characterized and correlated. One of the analogues, containing a B26-B29 triazole bridge, was highly active in binding to both IR isoforms, with a significant preference for IR-B. Our results demonstrate the potential of chemistry-driven modulation of insulin function, also shedding new light on the functional importance of hormone’s B-chain C-terminus for its IR-B specificity.

Structural basis for Smoothened receptor modulation and chemoresistance to anti-cancer drugs

PubMed Central

Wang, Chong; Wu, Huixian; Evron, Tama; Vardy, Eyal; Han, Gye Won; Huang, Xi-Ping; Hufeisen, Sandy J.; Mangano, Thomas J.; Urban, Dan J.; Katritch, Vsevolod; Cherezov, Vadim; Caron, Marc G.; Roth, Bryan L.; Stevens, Raymond C.

2014-01-01

The Smoothened receptor (SMO) mediates signal transduction in the hedgehog pathway, which is implicated in normal development and carcinogenesis. SMO antagonists can suppress the growth of some tumors; however, mutations at SMO have been found to abolish their anti-tumor effects, a phenomenon known as chemoresistance. Here we report three crystal structures of human SMO bound to the antagonists SANT1 and Anta XV, and the agonist, SAG1.5, at 2.6–2.8Å resolution. The long and narrow cavity in the transmembrane domain of SMO harbors multiple ligand binding sites, where SANT1 binds at a deeper site as compared with other ligands. Distinct interactions at D4736.55 elucidated the structural basis for the differential effects of chemoresistance mutations on SMO antagonists. The agonist SAG1.5 induces a conformational rearrangement of the binding pocket residues, which could contribute to SMO activation. Collectively, these studies reveal the structural basis for the modulation of SMO by small molecules. PMID:25008467

The cis decoy against the estrogen response element suppresses breast cancer cells via target disrupting c-fos not mitogen-activated protein kinase activity.

PubMed

Wang, Li Hua; Yang, Xiao Yi; Zhang, Xiaohu; Mihalic, Kelly; Xiao, Weihua; Farrar, William L

2003-05-01

Breast cancer, the most common malignancy in women, has been demonstrated to be associated with the steroid hormone estrogen and its receptor (ER), a ligand-activated transcription factor. Therefore, we developed a phosphorothiolate cis-element decoy against the estrogen response element (ERE decoy) to target disruption of ER DNA binding and transcriptional activity. Here, we showed that the ERE decoy potently ablated the 17beta-estrogen-inducible cell proliferation and induced apoptosis of human breast carcinoma cells by functionally affecting expression of c-fos gene and AP-1 luciferase gene reporter activity. Specificity of the decoy was demonstrated by its ability to directly block ER binding to a cis-element probe and transactivation. Moreover, the decoy failed to inhibit ER-mediated mitogen-activated protein kinase signaling pathways and cell growth of ER-negative breast cancer cells. Taken together, these data suggest that estrogen-mediated cell growth of breast cancer cells can be preferentially restricted via targeted disruption of ER at the level of DNA binding by a novel and specific decoy strategy applied to steroid nuclear receptors.

Chronic hypoxia up-regulates expression of adenosine A1 receptors in DDT1-MF2 cells.

PubMed

Hammond, Lucy C; Bonnet, Claire; Kemp, Paul J; Yates, Michael S; Bowmer, Christopher J

2004-02-01

As the first step to understand how chronic hypoxia might regulate smooth muscle function in health and disease, we have employed an established immortalised cell model of smooth muscle, DDT1-MF2 cells, to address the hypothesis that adenosine A1 receptor density is modulated by O2 availability. Maximal specific binding (Bmax) of the selective adenosine A1 receptor antagonist, [3H]-DPCPX, to cell membranes increased 3.5-fold from 0.48 +/- 0.02 pmol/mg to 1.7 +/- 0.5 pmol/mg protein after 16 hr of hypoxia and this effect was not accompanied by any statistically significant changes in either binding affinity (0.84 +/- 0.2 nM vs. 1.2 +/- 0.3 nM) or Hill coefficient (1.1 +/- 0.1 vs. 0.99 +/- 0.03). Hypoxia-evoked increases in membrane receptor density were paralleled in intact DDT1-MF2 cells. In addition, the increase in [3H]-DPCPX binding to intact cells was inhibited by co-incubation during hypoxia with the translational inhibitor cycloheximide, the transcriptional blocker actinomycin D and the NFkappaB inhibitor sulphasalazine. Together, these data show that adenosine A1 receptor density is modulated, at least in part, by O2-dependent activation of the transcription factor NFkappaB and adds to the list of processes dynamically regulated by ambient oxygen availability. Since hypoxia is an initiating factor in acute renal failure, similar changes in transcription may account for up-regulation of adenosine A1 receptors noted previously in the renal vasculature of rats with acute renal failure.

Basic Aspects of Tumor Cell Fatty Acid-Regulated Signaling and Transcription Factors

PubMed Central

Comba, Andrea; Lin, Yi-Hui; Eynard, Aldo Renato; Valentich, Mirta Ana; Fernandez-Zapico, Martin Ernesto; Pasqualini, Marìa Eugenia

2012-01-01

This article reviews the current knowledge and experimental research about the mechanisms by which fatty acids and their derivatives control specific gene expression involved during carcinogenesis. Changes in dietary fatty acids, specifically the polyunsaturated fatty acids (PUFAs) of the ω-3 and ω-6 families and some derived eicosanoids from lipoxygenases (LOXs), cyclooxygenases (COXs), and cytochrome P-450 (CYP-450), seem to control the activity of transcription factor families involved in cancer cell proliferation or cell death. Their regulation may be carried out either through direct binding to DNA as peroxisome proliferator–activated receptors (PPARs) or via modulation in an indirect manner of signaling pathway molecules (e.g., protein kinase C [PKC]) and other transcription factors (nuclear factor kappa B [NFκB] and sterol regulatory element binding protein [SREBP]). Knowledge of the mechanisms by which fatty acids control specific gene expression may identify important risk factors for cancer, and provide insight into the development of new therapeutic strategies for a better management of whole-body lipid metabolism. PMID:22048864

Basic aspects of tumor cell fatty acid-regulated signaling and transcription factors.

PubMed

Comba, Andrea; Lin, Yi-Hui; Eynard, Aldo Renato; Valentich, Mirta Ana; Fernandez-Zapico, Martín Ernesto; Pasqualini, Marìa Eugenia

2011-12-01

This article reviews the current knowledge and experimental research about the mechanisms by which fatty acids and their derivatives control specific gene expression involved during carcinogenesis. Changes in dietary fatty acids, specifically the polyunsaturated fatty acids of the ω-3 and ω-6 families and some derived eicosanoids from lipoxygenases, cyclooxygenases, and cytochrome P-450, seem to control the activity of transcription factor families involved in cancer cell proliferation or cell death. Their regulation may be carried out either through direct binding to DNA as peroxisome proliferator-activated receptors or via modulation in an indirect manner of signaling pathway molecules (e.g., protein kinase C) and other transcription factors (nuclear factor kappa B and sterol regulatory element binding protein). Knowledge of the mechanisms by which fatty acids control specific gene expression may identify important risk factors for cancer and provide insight into the development of new therapeutic strategies for a better management of whole body lipid metabolism.

Modeling the Interaction between Quinolinate and the Receptor for Advanced Glycation End Products (RAGE): Relevance for Early Neuropathological Processes

PubMed Central

Serratos, Iris N.; Castellanos, Pilar; Pastor, Nina; Millán-Pacheco, César; Rembao, Daniel; Pérez-Montfort, Ruy; Cabrera, Nallely; Reyes-Espinosa, Francisco; Díaz-Garrido, Paulina; López-Macay, Ambar; Martínez-Flores, Karina; López-Reyes, Alberto; Sánchez-García, Aurora; Cuevas, Elvis; Santamaria, Abel

2015-01-01

The receptor for advanced glycation end products (RAGE) is a pattern-recognition receptor involved in neurodegenerative and inflammatory disorders. RAGE induces cellular signaling upon binding to a variety of ligands. Evidence suggests that RAGE up-regulation is involved in quinolinate (QUIN)-induced toxicity. We investigated the QUIN-induced toxic events associated with early noxious responses, which might be linked to signaling cascades leading to cell death. The extent of early cellular damage caused by this receptor in the rat striatum was characterized by image processing methods. To document the direct interaction between QUIN and RAGE, we determined the binding constant (Kb) of RAGE (VC1 domain) with QUIN through a fluorescence assay. We modeled possible binding sites of QUIN to the VC1 domain for both rat and human RAGE. QUIN was found to bind at multiple sites to the VC1 dimer, each leading to particular mechanistic scenarios for the signaling evoked by QUIN binding, some of which directly alter RAGE oligomerization. This work contributes to the understanding of the phenomenon of RAGE-QUIN recognition, leading to the modulation of RAGE function. PMID:25757085

Co-Requirement of PICK1 Binding and PKC Phosphorylation for Stable Surface Expression of the Metabotropic Glutamate Receptor mGluR7

PubMed Central

Suh, Young Ho; Pelkey, Kenneth A.; Lavezzari, Gabriela; Roche, Paul A.; Huganir, Richard L.; McBain, Chris J.; Roche, Katherine W.

2008-01-01

SUMMARY The presynaptic metabotropic glutamate receptor (mGluR) mGluR7 modulates excitatory neurotransmission by regulating neurotransmitter release, and plays a critical role in certain forms of synaptic plasticity. Although the dynamic regulation of mGluR7 surface expression governs a novel form of metaplasticity in the hippocampus, little is known about the molecular mechanisms regulating mGluR7 trafficking. We now show that mGluR7 surface expression is stabilized by both PKC phosphorylation and by receptor binding to the PDZ domain-containing protein PICK1. Phosphorylation of mGluR7 on serine 862 (S862) inhibits CaM binding thereby increasing mGluR7 surface expression and receptor binding to PICK1. Furthermore, in mice lacking PICK1, PKC-dependent increases in mGluR7 phosphorylation and surface expression are diminished, and mGluR7-dependent plasticity at mossy fiber-interneuron hippocampal synapses is impaired. These data support a model in which PICK1 binding and PKC phosphorylation act together to stabilize mGluR7 on the cell surface in vivo. PMID:18549785

Unconventional binding sites and receptors for VIP and related peptides PACAP and PHI/PHM: an update.

PubMed

Muller, Jean-Marc; Debaigt, Colin; Goursaud, Stéphanie; Montoni, Alicia; Pineau, Nicolas; Meunier, Annie-Claire; Janet, Thierry

2007-09-01

The 28-amino-acid neuropeptide VIP and related peptides PACAP and PHI/PHM modulate virtually all of the vital functions in the body. These peptides are also commonly recognized as major regulators of cell growth and differentiation. Through their trophic and cytoprotective functions, they appear to play major roles in embryonic development, neurogenesis and the progression of a number of cancer types. These peptides bind to three well-characterized subtypes of G-protein coupled receptors: VPAC1 and VPAC2 share a common high affinity in the nanomolar range for VIP and PACAP; a third receptor type, PAC1, has been characterized for its high affinity for PACAP but its low affinity for VIP. Complex effects and pharmacological behaviors of these peptides suggest that multiple subtypes of binding sites may cooperate to mediate their function in target cells and tissues. In this complex response, some of these binding sites correspond to the definition of the conventional receptors cited above, while others display unexpected pharmacological and functional properties. Here we present potential clues that may lead investigators to further characterize the molecular nature and functions of these atypical binding species.

Computer-aided structure-affinity relationships in a set of piperazine and 3,8-diazabicyclo[3.2.1]octane derivatives binding to the μ-opioid receptor

NASA Astrophysics Data System (ADS)

Barlocco, Daniela; Cignarella, Giorgio; Greco, Giovanni; Novellino, Ettore

1993-10-01

Molecular modeling studies were carried out on a set of piperazine and 3,8-diazabicyclo[3.2.1]octane derivatives with the aim to highlight the main factors modulating their affinity for the μ-opioid receptor. Structure-affinity relationships were developed with the aid of molecular mechanics and semiempirical quantum-mechanics methods. According to our proposed pharmacodynamic model, the binding to the μ-receptor is promoted by the following physico-chemical features: the presence of hydrocarbon fragments on the nitrogen ring frame capable of interacting with one of two hypothesized hydrophobic receptor pockets; a `correct' orientation of an N-propionyl side chain so as to avoid a sterically hindered region of the receptor; the possibility of accepting a hydrogen bond from a receptor site complementary to the morphine phenol oxygen.

PXR-dependent induction of human CYP3A4 gene expression by organochlorine pesticides.

PubMed

Coumoul, Xavier; Diry, Monique; Barouki, Robert

2002-11-15

OCP are xenobiotics which display various toxic effects on animal and human health. One of their effects is to bind and activate estrogen receptor alpha (ERalpha). We have previously studied the down-regulation of induced CYP1A1 (cytochrome P450) expression by this class of molecules in mammary carcinoma cells and shown the importance of ERalpha in this process. However, an alternative mechanism was suggested by those experiments in hepatoma cells. In this study, we have performed Northern blot and transient transfection assays in various cell lines and shown that OCP activate human pregnane X receptor (PXR) and subsequent CYP3A4 mRNA expression. This effect is mediated by the distal xenobiotic responsive element modulator of the promoter. The induction of CYP3A4 by OCP was dose-dependent within the 1-10 microM range. The data suggest that chronic exposure to OCP could alter a major metabolite pathway in human liver and putatively modify the pharmacokinetics of drugs and pollutants.

FOXO3 Modulates Endothelial Gene Expression and Function by Classical and Alternative Mechanisms*

PubMed Central

Czymai, Tobias; Viemann, Dorothee; Sticht, Carsten; Molema, Grietje; Goebeler, Matthias; Schmidt, Marc

2010-01-01

FOXO transcription factors represent targets of the phosphatidylinositol 3-kinase/protein kinase B survival pathway controlling important biological processes, such as cell cycle progression, apoptosis, vascular remodeling, stress responses, and metabolism. Recent studies suggested the existence of alternative mechanisms of FOXO-dependent gene expression beyond classical binding to a FOXO-responsive DNA-binding element (FRE). Here we analyzed the relative contribution of those mechanisms to vascular function by comparing the transcriptional and cellular responses to conditional activation of FOXO3 and a corresponding FRE-binding mutant in human primary endothelial cells. We demonstrate that FOXO3 controls expression of vascular remodeling genes in an FRE-dependent manner. In contrast, FOXO3-induced cell cycle arrest and apoptosis occurs independently of FRE binding, albeit FRE-dependent gene expression augments the proapoptotic response. These findings are supported by bioinformatical analysis, which revealed a statistical overrepresentation of cell cycle regulators and apoptosis-related genes in the group of co-regulated genes. Molecular analysis of FOXO3-induced endothelial apoptosis excluded modulators of the extrinsic death receptor pathway and demonstrated important roles for the BCL-2 family members BIM and NOXA in this process. Although NOXA essentially contributed to FRE-dependent apoptosis, BIM was effectively induced in the absence of FRE-binding, and small interfering RNA-mediated BIM depletion could rescue apoptosis induced by both FOXO3 mutants. These data suggest BIM as a critical cell type-specific mediator of FOXO3-induced endothelial apoptosis, whereas NOXA functions as an amplifying factor. Our study provides the first comprehensive analysis of alternatively regulated FOXO3 targets in relevant primary cells and underscores the importance of such genes for endothelial function and integrity. PMID:20123982

B cell recognition of the conserved HIV-1 co-receptor binding site is altered by endogenous primate CD4.

PubMed

Forsell, Mattias N E; Dey, Barna; Mörner, Andreas; Svehla, Krisha; O'dell, Sijy; Högerkorp, Carl-Magnus; Voss, Gerald; Thorstensson, Rigmor; Shaw, George M; Mascola, John R; Karlsson Hedestam, Gunilla B; Wyatt, Richard T

2008-10-03

The surface HIV-1 exterior envelope glycoprotein, gp120, binds to CD4 on the target cell surface to induce the co-receptor binding site on gp120 as the initial step in the entry process. The binding site is comprised of a highly conserved region on the gp120 core, as well as elements of the third variable region (V3). Antibodies against the co-receptor binding site are abundantly elicited during natural infection of humans, but the mechanism of elicitation has remained undefined. In this study, we investigate the requirements for elicitation of co-receptor binding site antibodies by inoculating rabbits, monkeys and human-CD4 transgenic (huCD4) rabbits with envelope glycoprotein (Env) trimers possessing high affinity for primate CD4. A cross-species comparison of the antibody responses showed that similar HIV-1 neutralization breadth was elicited by Env trimers in monkeys relative to wild-type (WT) rabbits. In contrast, antibodies against the co-receptor site on gp120 were elicited only in monkeys and huCD4 rabbits, but not in the WT rabbits. This was supported by the detection of high-titer co-receptor antibodies in all sera from a set derived from human volunteers inoculated with recombinant gp120. These findings strongly suggest that complexes between Env and (high-affinity) primate CD4 formed in vivo are responsible for the elicitation of the co-receptor-site-directed antibodies. They also imply that the naïve B cell receptor repertoire does not recognize the gp120 co-receptor site in the absence of CD4 and illustrate that conformational stabilization, imparted by primary receptor interaction, can alter the immunogenicity of a type 1 viral membrane protein.

Mapping of the Lassa virus LAMP1 binding site reveals unique determinants not shared by other old world arenaviruses.

PubMed

Israeli, Hadar; Cohen-Dvashi, Hadas; Shulman, Anastasiya; Shimon, Amir; Diskin, Ron

2017-04-01

Cell entry of many enveloped viruses occurs by engagement with cellular receptors, followed by internalization into endocytic compartments and pH-induced membrane fusion. A previously unnoticed step of receptor switching was found to be critical during cell entry of two devastating human pathogens: Ebola and Lassa viruses. Our recent studies revealed the functional role of receptor switching to LAMP1 for triggering membrane fusion by Lassa virus and showed the involvement of conserved histidines in this switching, suggesting that other viruses from this family may also switch to LAMP1. However, when we investigated viruses that are genetically close to Lassa virus, we discovered that they cannot bind LAMP1. A crystal structure of the receptor-binding module from Morogoro virus revealed structural differences that allowed mapping of the LAMP1 binding site to a unique set of Lassa residues not shared by other viruses in its family, illustrating a key difference in the cell-entry mechanism of Lassa virus that may contribute to its pathogenicity.

Steroid signaling: ligand-binding promiscuity, molecular symmetry, and the need for gating.

PubMed

Lathe, Richard; Kotelevtsev, Yuri

2014-04-01

Steroid/sterol-binding receptors and enzymes are remarkably promiscuous in the range of ligands they can bind to and, in the case of enzymes, modify - raising the question of how specific receptor activation is achieved in vivo. Estrogen receptors (ER) are modulated by 27-hydroxycholesterol and 5α-androstane-3β,17β-diol (Adiol), in addition to estradiol (E2), and respond to diverse small molecules such as bisphenol A. Steroid-modifying enzymes are also highly promiscuous in ligand binding and metabolism. The specificity problem is compounded by the fact that the steroid core (hydrogenated cyclopentophenanthrene ring system) has several planes of symmetry. Ligand binding can be in symmetrical East-West (rotation) and North-South (inversion) orientations. Hydroxysteroid dehydrogenases (HSDs) can modify symmetrical 7 and 11, also 3 and 17/20, positions, exemplified here by yeast 3α,20β-HSD and mammalian 11β-HSD and 17β-HSD enzymes. Faced with promiscuity and symmetry, other strategies are clearly necessary to promote signaling selectivity in vivo. Gating regulates hormone access via enzymes that preferentially inactivate (or activate) a subclass of ligands, thereby governing which ligands gain receptor access - exemplified by 11β-HSD gating cortisol access to the mineralocorticoid receptor, and P450 CYP7B1 gating Adiol access to ER. Counter-intuitively, the specificity of steroid/sterol action is achieved not by intrinsic binding selectivity but by the combination of local metabolism and binding affinity. Copyright © 2014 Elsevier Inc. All rights reserved.

DNA binding triggers tetramerization of the glucocorticoid receptor in live cells

PubMed Central

Presman, Diego M.; Ganguly, Sourav; Schiltz, R. Louis; Johnson, Thomas A.; Karpova, Tatiana S.; Hager, Gordon L.

2016-01-01

Transcription factors dynamically bind to chromatin and are essential for the regulation of genes. Although a large percentage of these proteins appear to self-associate to form dimers or higher order oligomers, the stoichiometry of DNA-bound transcription factors has been poorly characterized in vivo. The glucocorticoid receptor (GR) is a ligand-regulated transcription factor widely believed to act as a dimer or a monomer. Using a unique set of imaging techniques coupled with a cell line containing an array of DNA binding elements, we show that GR is predominantly a tetramer when bound to its target DNA. We find that DNA binding triggers an interdomain allosteric regulation within the GR, leading to tetramerization. We therefore propose that dynamic changes in GR stoichiometry represent a previously unidentified level of regulation in steroid receptor activation. Quaternary structure analysis of other members of the steroid receptor family (estrogen, androgen, and progesterone receptors) reveals variation in oligomerization states among this family of transcription factors. Because GR’s oligomerization state has been implicated in therapy outcome, our findings open new doors to the rational design of novel GR ligands and redefine the quaternary structure of steroid receptors. PMID:27382178

Estrogen receptor 1 modulates circadian rhythms in adult female mice.

PubMed

Blattner, Margaret S; Mahoney, Megan M

2014-06-01

Estradiol influences the level and distribution of daily activity, the duration of the free-running period, and the behavioral phase response to light pulses. However, the mechanisms by which estradiol regulates daily and circadian rhythms are not fully understood. We tested the hypothesis that estrogens modulate daily activity patterns via both classical and "non-classical" actions at the estrogen receptor subtype 1 (ESR1). We used female transgenic mice with mutations in their estrogen response pathways; ESR1 knock-out (ERKO) mice and "non-classical" estrogen receptor knock-in (NERKI) mice. NERKI mice have an ESR1 receptor with a mutation in the estrogen-response-element binding domain, allowing only actions via "non-classical" genomic and second messenger pathways. Ovariectomized female NERKI, ERKO, and wildtype (WT) mice were given a subcutaneous capsule with low- or high-dose estradiol and compared with counterparts with no hormone replacement. We measured wheel-running activity in a light:dark cycle and constant darkness, and the behavioral phase response to light pulses given at different points during the subjective day and night. Estradiol increased average daily wheel-running, consolidated activity to the dark phase, and shortened the endogenous period in WT, but not NERKI and ERKO mice. The timing of activity onset during entrainment was advanced in all estradiol-treated animals regardless of genotype suggesting an ESR1-independent mechanism. We propose that estradiol modifies period, activity level, and distribution of activity via classical actions of ESR1 whereas an ESR1 independent mechanism regulates the phase of rhythms.

Identifying a Mechanism for Crosstalk Between the Estrogen and Glucocorticoid Receptors | Center for Cancer Research

Cancer.gov

Estrogen has long been known to play important roles in the development and progression of breast cancer. Its receptor (ER), a member of the steroid receptor family, binds to estrogen response elements (EREs) in DNA and regulates gene transcription. More recently, another steroid receptor family member, the glucocorticoid receptor (GR), has been implicated in breast cancer progression, and ER/GR status is an important predictor of breast cancer outcome.

Interaction of human, rat, and mouse immunoglobulin A (IgA) with Staphylococcal superantigen-like 7 (SSL7) decoy protein and leukocyte IgA receptor.

PubMed

Wines, Bruce D; Ramsland, Paul A; Trist, Halina M; Gardam, Sandra; Brink, Robert; Fraser, John D; Hogarth, P Mark

2011-09-23

Host survival depends on an effective immune system and pathogen survival on the effectiveness of immune evasion mechanisms. Staphylococcus aureus utilizes a number of molecules to modulate host immunity, including the SSL family of which SSL7 binds IgA and inhibits Fcα receptor I (FcαRI)-mediated function. Other Gram-positive bacterial pathogens produce IgA binding proteins, which, similar to SSL7, also bind the Fc at the CH2/CH3 interface (the junction between constant domains 2 and 3 of the heavy chain). The opposing activities of the host FcαRI-IgA receptor ligand pair and the pathogen decoy proteins select for host and pathogen variants, which exert stronger protection or evasion, respectively. Curiously, mouse but not rat IgA contains a putative N-linked glycosylation site in the center of this host receptor and pathogen-binding site. Here, we demonstrate that this site is glycosylated and that the effect of amino acid changes and glycosylation of the CH2/CH3 interface inhibits interaction with the pathogen IgA binding protein SSL7, while maintaining binding of pIgR, essential to the biosynthesis and transport of SIgA.

Influences of Histidine-1 and Azaphenylalanine-4 on the Affinity, Anti-inflammatory, and Antiangiogenic Activities of Azapeptide Cluster of Differentiation 36 Receptor Modulators.

PubMed

Chignen Possi, Kelvine; Mulumba, Mukandila; Omri, Samy; Garcia-Ramos, Yesica; Tahiri, Houda; Chemtob, Sylvain; Ong, Huy; Lubell, William D

2017-11-22

Azapeptide analogues of growth hormone releasing peptide-6 (GHRP-6) exhibit promising affinity, selectivity, and modulator activity on the cluster of differentiation 36 receptor (CD36). For example, [A 1 , azaF 4 ]- and [azaY 4 ]-GHRP-6 (1a and 2b) were previously shown to bind selectively to CD36 and exhibited respectively significant antiangiogenic and slight angiogenic activities in a microvascular sprouting assay using choroid explants. The influences of the 1- and 4-position residues on the affinity, anti-inflammatory, and antiangiogenic activity of these azapeptides have now been studied in detail by the synthesis and analysis of a set of 25 analogues featuring Ala 1 or His 1 and a variety of aromatic side chains at the aza-amino acid residue in the 4-position. Although their binding affinities differed only by a factor of 17, the analogues exhibited significant differences in ability to modulate production of nitric oxide (NO) in macrophages and choroidal neovascularization.

BAF57 Modulation of Androgen Receptor Action and Prostate Cancer Progression

DTIC Science & Technology

2007-12-01

mapped the AR binding site on BAF57 to the N-terminus (proline-rich region). Furthermore, the DBD and hinge region of AR also appear to play a...Accomplishments of Task 1: BAF57 binds to DNA binding domain ( DBD ) and hinge region of AR As outlined in the initial proposal, the first task...the above construct are the well-characterized zinc finger DNA binding domain ( DBD ) and the hinge region. Given the significant role of these two

BAF57 Modulation of Androgen Receptor Action and Prostate Cancer Progression

DTIC Science & Technology

2006-12-01

has fine mapped the AR binding site on BAF57 to the N-terminus (proline-rich region). Furthermore, the DBD and hinge region of AR also appear to...Accomplishments of Task 1: BAF57 binds to DNA binding domain ( DBD ) and hinge region of AR As outlined in the initial proposal, the first task was to...construct are the well-characterized zinc finger DNA binding domain ( DBD ) and the hinge region. Given the significant role of these two domains in AR

Novel DNA Motif Binding Activity Observed In Vivo With an Estrogen Receptor α Mutant Mouse

PubMed Central

Li, Leping; Grimm, Sara A.; Winuthayanon, Wipawee; Hamilton, Katherine J.; Pockette, Brianna; Rubel, Cory A.; Pedersen, Lars C.; Fargo, David; Lanz, Rainer B.; DeMayo, Francesco J.; Schütz, Günther; Korach, Kenneth S.

2014-01-01

Estrogen receptor α (ERα) interacts with DNA directly or indirectly via other transcription factors, referred to as “tethering.” Evidence for tethering is based on in vitro studies and a widely used “KIKO” mouse model containing mutations that prevent direct estrogen response element DNA- binding. KIKO mice are infertile, due in part to the inability of estradiol (E2) to induce uterine epithelial proliferation. To elucidate the molecular events that prevent KIKO uterine growth, regulation of the pro-proliferative E2 target gene Klf4 and of Klf15, a progesterone (P4) target gene that opposes the pro-proliferative activity of KLF4, was evaluated. Klf4 induction was impaired in KIKO uteri; however, Klf15 was induced by E2 rather than by P4. Whole uterine chromatin immunoprecipitation-sequencing revealed enrichment of KIKO ERα binding to hormone response elements (HREs) motifs. KIKO binding to HRE motifs was verified using reporter gene and DNA-binding assays. Because the KIKO ERα has HRE DNA-binding activity, we evaluated the “EAAE” ERα, which has more severe DNA-binding domain mutations, and demonstrated a lack of estrogen response element or HRE reporter gene induction or DNA-binding. The EAAE mouse has an ERα null–like phenotype, with impaired uterine growth and transcriptional activity. Our findings demonstrate that the KIKO mouse model, which has been used by numerous investigators, cannot be used to establish biological functions for ERα tethering, because KIKO ERα effectively stimulates transcription using HRE motifs. The EAAE-ERα DNA-binding domain mutant mouse demonstrates that ERα DNA-binding is crucial for biological and transcriptional processes in reproductive tissues and that ERα tethering may not contribute to estrogen responsiveness in vivo. PMID:24713037

The A2 Adenosine Receptor: Guanine Nucleotide Modulation of Agonist Binding Is Enhanced by Proteolysis

PubMed Central

NANOFF, CHRISTIAN; JACOBSON, KENNETH A.; STILES, GARY L.

2012-01-01

SUMMARY Agonist binding to the A2 adenosine receptor (A2AR) and its regulation by guanine nucleotides was studied using the newly developed radioligand 125l-2-[4-(2-{2-[(4-ammnophenyl)methylcarbonylamino]ethylaminnocarbonyl}ethyl)phenyl]ethylamino-5′-N-ethylcarboxamidoadenosine (1251-PAPA-APEC) and its photoaffinity analog 125l-azido-PAPA-APEC. A single protein of Mr 45,000, displaying the appropriate A2AR pharmacology, is Iabeled in membranes from bovine striatum, PC12 cells, and frog erythrocytes. In DDT1 MF2 cells the labeled protein has a slightly lower molecular weight. Incorporation of 125l-azido-PAPA-APEC into membranes from rabbit striatum, however, reveals two specifically labeled peptides (Mr ~47,O00 and 38,000), both of which display A2AR pharmacology. Inhibition of protease activity leads to a decrease in the amount of the Mr 38,000 protein, with only the Mr 47,000 protein remaining. This suggests that the Mr 38,000 peptide is a proteolytic product of the Mr 47,000 A2AR protein. In membranes containing the intact undigested A2AR protein, guanine nucleotides induce a small to insignificant decrease in agonist binding, which is atypical of stimulatory Gs-coupled receptors. This minimal effect is observed in rabbit striatal membranes prepared in the presence of protease inhibitors, as well as in the other tissues studied. Binding to rabbit stnatal membranes that possess the partially digested receptor protein, however, reveals a 50% reduction in maximal specific agonist binding upon addition of guanine nucleotides. Inhibition of proteolysis in rabbit striatum, on the other hand, results in a diminished ability of guanine nucleotides to regulate agonist binding. Thus, the enhanced effectiveness of guanine nucleotides in rabbit striatal membranes is associated with the generation of the Mr 38,000 peptide fragment. Guanosine 5′-(β,γ-imido)triphosphate reduces photoaffinity labeling by 55% in the Mr 38,000 protein, whereas the labeling is decreased by only 28% in the Mr 47,000 receptor protein. Our data, therefore, suggest that, unless proteolysis occurs, the A2AR in all tissues studied is tightly associated with the Gs protein and displays minimal guanine nucleotide modulation of agonist binding, which makes the A2AR an atypical stimulatory receptor. PMID:1899902

Leptin Increases Striatal Dopamine D2 Receptor Binding in Leptin-Deficient Obese (ob/ob) Mice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pfaffly, J.; Michaelides, M.; Wang, G-J.

2010-06-01

Peripheral and central leptin administration have been shown to mediate central dopamine (DA) signaling. Leptin-receptor deficient rodents show decreased DA D2 receptor (D2R) binding in striatum and unique DA profiles compared to controls. Leptin-deficient mice show increased DA activity in reward-related brain regions. The objective of this study was to examine whether basal D2R-binding differences contribute to the phenotypic behaviors of leptin-deficient ob/ob mice, and whether D2R binding is altered in response to peripheral leptin treatment in these mice. Leptin decreased body weight, food intake, and plasma insulin concentration in ob/ob mice but not in wild-type mice. Basal striatal D2Rmore » binding (measured with autoradiography [{sup 3}H] spiperone) did not differ between ob/ob and wild-type mice but the response to leptin did. In wild-type mice, leptin decreased striatal D2R binding, whereas, in ob/ob mice, leptin increased D2R binding. Our findings provide further evidence that leptin modulates D2R expression in striatum and that these effects are genotype/phenotype dependent.« less

Statins Increase Plasminogen Activator Inhibitor Type 1 Gene Transcription through a Pregnane X Receptor Regulated Element

PubMed Central

Stanley, Frederick M.; Linder, Kathryn M.; Cardozo, Timothy J.

2015-01-01

Plasminogen activator inhibitor type 1 (PAI-1) is a multifunctional protein that has important roles in inflammation and wound healing. Its aberrant regulation may contribute to many disease processes such as heart disease. The PAI-1 promoter is responsive to multiple inputs including cytokines, growth factors, steroids and oxidative stress. The statin drugs, atorvastatin, mevastatin and rosuvastatin, increased basal and stimulated expression of the PAI-1 promoter 3-fold. A statin-responsive, nuclear hormone response element was previously identified in the PAI-1 promoter, but it was incompletely characterized. We characterized this direct repeat (DR) of AGGTCA with a 3-nucleotide spacer at -269/-255 using deletion and directed mutagenesis. Deletion or mutation of this element increased basal transcription from the promoter suggesting that it repressed PAI-1 transcription in the unliganded state. The half-site spacing and the ligand specificity suggested that this might be a pregnane X receptor (PXR) responsive element. Computational molecular docking showed that atorvastatin, mevastatin and rosuvastatin were structurally compatible with the PXR ligand-binding pocket in its agonist conformation. Experiments with Gal4 DNA binding domain fusion proteins showed that Gal4-PXR was activated by statins while other DR + 3 binding nuclear receptor fusions were not. Overexpression of PXR further enhanced PAI-1 transcription in response to statins. Finally, ChIP experiments using Halo-tagged PXR and RXR demonstrated that both components of the PXR-RXR heterodimer bound to this region of the PAI-1 promoter. PMID:26379245

Sodium modulates opioid receptors through a membrane component different from G-proteins. Demonstration by target size analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ott, S.; Costa, T.; Herz, A.

1988-07-25

The target size for opioid receptor binding was studied after manipulations known to affect the interactions between receptor and GTP-binding regulatory proteins (G-proteins). Addition of GTP or its analogs to the binding reaction, exposure of intact cells to pertussis toxin prior to irradiation, or treatment of irradiated membranes with N-ethylmaleimide did not change the target size (approximately equal to 100 kDa) for opioid receptors in NG 108-15 cells and rat brain. These data suggest that the 100-kDa species does not include an active subunit of a G-protein or alternatively that GTP does not promote the dissociation of the receptor-G-protein complex.more » The presence of Na+ (100 mM) in the radioligand binding assay induced a biphasic decay curve for agonist binding and a flattening of the monoexponential decay curve for a partial agonist. In both cases the effect was explained by an irradiation-induced loss of the low affinity state of the opioid receptor produced by the addition of Na+. This suggests that an allosteric inhibitor that mediates the effect of sodium on the receptor is destroyed at low doses of irradiation, leaving receptors which are no longer regulated by sodium. The effect of Na+ on target size was slightly increased by the simultaneous addition of GTP but was not altered by pertussis toxin treatment. Thus, the sodium unit is distinct from G-proteins and may represent a new component of the opioid receptor complex. Assuming a simple bimolecular model of one Na+ unit/receptor, the size of this inhibitor can be measured as 168 kDa.« less

Analysis of Nuclear Factor-κB (NF-κB) Essential Modulator (NEMO) Binding to Linear and Lysine-linked Ubiquitin Chains and Its Role in the Activation of NF-κB*

PubMed Central

Kensche, Tobias; Tokunaga, Fuminori; Ikeda, Fumiyo; Goto, Eiji; Iwai, Kazuhiro; Dikic, Ivan

2012-01-01

Nuclear factor-κB (NF-κB) essential modulator (NEMO), a component of the inhibitor of κB kinase (IKK) complex, controls NF-κB signaling by binding to ubiquitin chains. Structural studies of NEMO provided a rationale for the specific binding between the UBAN (ubiquitin binding in ABIN and NEMO) domain of NEMO and linear (Met-1-linked) di-ubiquitin chains. Full-length NEMO can also interact with Lys-11-, Lys-48-, and Lys-63-linked ubiquitin chains of varying length in cells. Here, we show that purified full-length NEMO binds preferentially to linear ubiquitin chains in competition with lysine-linked ubiquitin chains of defined length, including long Lys-63-linked deca-ubiquitins. Linear di-ubiquitins were sufficient to activate both the IKK complex in vitro and to trigger maximal NF-κB activation in cells. In TNFα-stimulated cells, NEMO chimeras engineered to bind exclusively to Lys-63-linked ubiquitin chains mediated partial NF-κB activation compared with cells expressing NEMO that binds to linear ubiquitin chains. We propose that NEMO functions as a high affinity receptor for linear ubiquitin chains and a low affinity receptor for long lysine-linked ubiquitin chains. This phenomenon could explain quantitatively distinct NF-κB activation patterns in response to numerous cell stimuli. PMID:22605335

Peroxisome Proliferators-Activated Receptor (PPAR) Modulators and Metabolic Disorders

PubMed Central

Cho, Min-Chul; Lee, Kyoung; Paik, Sang-Gi; Yoon, Do-Young

2008-01-01

Overweight and obesity lead to an increased risk for metabolic disorders such as impaired glucose regulation/insulin resistance, dyslipidemia, and hypertension. Several molecular drug targets with potential to prevent or treat metabolic disorders have been revealed. Interestingly, the activation of peroxisome proliferator-activated receptor (PPAR), which belongs to the nuclear receptor superfamily, has many beneficial clinical effects. PPAR directly modulates gene expression by binding to a specific ligand. All PPAR subtypes (α, γ, and σ) are involved in glucose metabolism, lipid metabolism, and energy balance. PPAR agonists play an important role in therapeutic aspects of metabolic disorders. However, undesired effects of the existing PPAR agonists have been reported. A great deal of recent research has focused on the discovery of new PPAR modulators with more beneficial effects and more safety without producing undesired side effects. Herein, we briefly review the roles of PPAR in metabolic disorders, the effects of PPAR modulators in metabolic disorders, and the technologies with which to discover new PPAR modulators. PMID:18566691

Post-translational regulation of P2X receptor channels: modulation by phospholipids

PubMed Central

Bernier, Louis-Philippe; Ase, Ariel R.; Séguéla, Philippe

2013-01-01

P2X receptor channels mediate fast excitatory signaling by ATP and play major roles in sensory transduction, neuro-immune communication and inflammatory response. P2X receptors constitute a gene family of calcium-permeable ATP-gated cation channels therefore the regulation of P2X signaling is critical for both membrane potential and intracellular calcium homeostasis. Phosphoinositides (PIPn) are anionic signaling phospholipids that act as functional regulators of many types of ion channels. Direct PIPn binding was demonstrated for several ligand- or voltage-gated ion channels, however no generic motif emerged to accurately predict lipid-protein binding sites. This review presents what is currently known about the modulation of the different P2X subtypes by phospholipids and about critical determinants underlying their sensitivity to PIPn levels in the plasma membrane. All functional mammalian P2X subtypes tested, with the notable exception of P2X5, have been shown to be positively modulated by PIPn, i.e., homomeric P2X1, P2X2, P2X3, P2X4, and P2X7, as well as heteromeric P2X1/5 and P2X2/3 receptors. Based on various results reported on the aforementioned subtypes including mutagenesis of the prototypical PIPn-sensitive P2X4 and PIPn-insensitive P2X5 receptor subtypes, an increasing amount of functional, biochemical and structural evidence converges on the modulatory role of a short polybasic domain located in the proximal C-terminus of P2X subunits. This linear motif, semi-conserved in the P2X family, seems necessary and sufficient for encoding direct modulation of ATP-gated channels by PIPn. Furthermore, the physiological impact of the regulation of ionotropic purinergic responses by phospholipids on pain pathways was recently revealed in the context of native crosstalks between phospholipase C (PLC)-linked metabotropic receptors and P2X receptor channels in dorsal root ganglion sensory neurons and microglia. PMID:24324400

A selective estrogen receptor modulator for the treatment of hot flushes.

PubMed

Wallace, Owen B; Lauwers, Kenneth S; Dodge, Jeffrey A; May, Scott A; Calvin, Joel R; Hinklin, Ronald; Bryant, Henry U; Shetler, Pamela K; Adrian, Mary D; Geiser, Andrew G; Sato, Masahiko; Burris, Thomas P

2006-02-09

A selective estrogen receptor modulator (SERM) for the potential treatment of hot flushes is described. (R)-(+)-7,9-difluoro-5-[4-(2-piperidin-1-ylethoxy)phenyl]-5H-6-oxachrysen-2-ol, LSN2120310, potently binds ERalpha and ERbeta and is an antagonist in MCF-7 breast adenocarcinoma and Ishikawa uterine cancer cell lines. The compound is a potent estrogen antagonist in the rat uterus. In ovariectomized rats, the compound lowers cholesterol, maintains bone mineral density, and is efficacious in a morphine dependent rat model of hot flush efficacy.

MmTX1 and MmTX2 from coral snake venom potently modulate GABAA receptor activity.

PubMed

Rosso, Jean-Pierre; Schwarz, Jürgen R; Diaz-Bustamante, Marcelo; Céard, Brigitte; Gutiérrez, José M; Kneussel, Matthias; Pongs, Olaf; Bosmans, Frank; Bougis, Pierre E

2015-02-24

GABAA receptors shape synaptic transmission by modulating Cl(-) conductance across the cell membrane. Remarkably, animal toxins that specifically target GABAA receptors have not been identified. Here, we report the discovery of micrurotoxin1 (MmTX1) and MmTX2, two toxins present in Costa Rican coral snake venom that tightly bind to GABAA receptors at subnanomolar concentrations. Studies with recombinant and synthetic toxin variants on hippocampal neurons and cells expressing common receptor compositions suggest that MmTX1 and MmTX2 allosterically increase GABAA receptor susceptibility to agonist, thereby potentiating receptor opening as well as desensitization, possibly by interacting with the α(+)/β(-) interface. Moreover, hippocampal neuron excitability measurements reveal toxin-induced transitory network inhibition, followed by an increase in spontaneous activity. In concert, toxin injections into mouse brain result in reduced basal activity between intense seizures. Altogether, we characterized two animal toxins that enhance GABAA receptor sensitivity to agonist, thereby establishing a previously unidentified class of tools to study this receptor family.

An automated system for the analysis of G protein-coupled receptor transmembrane binding pockets: alignment, receptor-based pharmacophores, and their application.

PubMed

Kratochwil, Nicole A; Malherbe, Pari; Lindemann, Lothar; Ebeling, Martin; Hoener, Marius C; Mühlemann, Andreas; Porter, Richard H P; Stahl, Martin; Gerber, Paul R

2005-01-01

G protein-coupled receptors (GPCRs) share a common architecture consisting of seven transmembrane (TM) domains. Various lines of evidence suggest that this fold provides a generic binding pocket within the TM region for hosting agonists, antagonists, and allosteric modulators. Here, a comprehensive and automated method allowing fast analysis and comparison of these putative binding pockets across the entire GPCR family is presented. The method relies on a robust alignment algorithm based on conservation indices, focusing on pharmacophore-like relationships between amino acids. Analysis of conservation patterns across the GPCR family and alignment to the rhodopsin X-ray structure allows the extraction of the amino acids lining the TM binding pocket in a so-called ligand binding pocket vector (LPV). In a second step, LPVs are translated to simple 3D receptor pharmacophore models, where each amino acid is represented by a single spherical pharmacophore feature and all atomic detail is omitted. Applications of the method include the assessment of selectivity issues, support of mutagenesis studies, and the derivation of rules for focused screening to identify chemical starting points in early drug discovery projects. Because of the coarseness of this 3D receptor pharmacophore model, however, meaningful scoring and ranking procedures of large sets of molecules are not justified. The LPV analysis of the trace amine-associated receptor family and its experimental validation is discussed as an example. The value of the 3D receptor model is demonstrated for a class C GPCR family, the metabotropic glutamate receptors.

Ionotropic GABA receptor antagonism-induced adverse outcome pathways for potential neurotoxicity biomarkers.

PubMed

Gong, Ping; Hong, Huixiao; Perkins, Edward J

2015-01-01

Antagonism of ionotropic GABA receptors (iGABARs) can occur at three distinct types of receptor binding sites causing chemically induced epileptic seizures. Here we review three adverse outcome pathways, each characterized by a specific molecular initiating event where an antagonist competitively binds to active sites, negatively modulates allosteric sites or noncompetitively blocks ion channel on the iGABAR. This leads to decreased chloride conductance, followed by depolarization of affected neurons, epilepsy-related death and ultimately decreased population. Supporting evidence for causal linkages from the molecular to population levels is presented and differential sensitivity to iGABAR antagonists in different GABA receptors and organisms discussed. Adverse outcome pathways are poised to become important tools for linking mechanism-based biomarkers to regulated outcomes in next-generation risk assessment.

Dibutyltin disrupts glucocorticoid receptor function and impairs glucocorticoid-induced suppression of cytokine production.

PubMed

Gumy, Christel; Chandsawangbhuwana, Charlie; Dzyakanchuk, Anna A; Kratschmar, Denise V; Baker, Michael E; Odermatt, Alex

2008-01-01

Organotins are highly toxic and widely distributed environmental chemicals. Dibutyltin (DBT) is used as stabilizer in the production of polyvinyl chloride plastics, and it is also the major metabolite formed from tributyltin (TBT) in vivo. DBT is immunotoxic, however, the responsible targets remain to be defined. Due to the importance of glucocorticoids in immune-modulation, we investigated whether DBT could interfere with glucocorticoid receptor (GR) function. We used HEK-293 cells transiently transfected with human GR as well as rat H4IIE hepatoma cells and native human macrophages and human THP-1 macrophages expressing endogenous receptor to study organotin effects on GR function. Docking of organotins was used to investigate the binding mechanism. We found that nanomolar concentrations of DBT, but not other organotins tested, inhibit ligand binding to GR and its transcriptional activity. Docking analysis indicated that DBT inhibits GR activation allosterically by inserting into a site close to the steroid-binding pocket, which disrupts a key interaction between the A-ring of the glucocorticoid and the GR. DBT inhibited glucocorticoid-induced expression of phosphoenolpyruvate carboxykinase (PEPCK) and tyrosine-aminotransferase (TAT) and abolished the glucocorticoid-mediated transrepression of TNF-alpha-induced NF-kappaB activity. Moreover, DBT abrogated the glucocorticoid-mediated suppression of interleukin-6 (IL-6) and TNF-alpha production in lipopolysaccharide (LPS)-stimulated native human macrophages and human THP-1 macrophages. DBT inhibits ligand binding to GR and subsequent activation of the receptor. By blocking GR activation, DBT may disturb metabolic functions and modulation of the immune system, providing an explanation for some of the toxic effects of this organotin.

A role for the PDZ-binding domain of the coxsackie B virus and adenovirus receptor (CAR) in cell adhesion and growth.

PubMed

Excoffon, Katherine J D Ashbourne; Hruska-Hageman, Alesia; Klotz, Michael; Traver, Geri L; Zabner, Joseph

2004-09-01

The coxsackie and adenovirus receptor (CAR) plays a role in viral infection, maintenance of the junction adhesion complex in polarized epithelia, and modulation of cellular growth properties. As a viral receptor, the C-terminus appears to play no role indicating that the major function of CAR is to tether the virus to the cell. By contrast, the C-terminus is known to play a role in cellular localization and probably has a significant function in CAR-mediated adhesion and cell growth properties. We hypothesized that the CAR PDZ (PSD-95/Disc-large/ZO-1) binding motif interacts with PDZ-domain-containing proteins to modulate the cellular phenotype. CAR was modified by deleting the last four amino acids (CARDeltaGSIV) and evaluated for cell-cell adhesion in polarized primary human airway epithelia and growth characteristics in stably transfected L-cells. Although ablation of the CAR PDZ-binding motif did not affect adenoviral infection, it did have a significant effect both on cell-cell adhesion and on cell growth. Expression of CARDeltaGSIV failed to increase the transepithelial resistance in polarized epithelia to the same degree as wild-type CAR and failed to act as a growth modulator in L-cells. Furthermore, we provide evidence for three new CAR interacting partners, including MAGI-1b, PICK1 and PSD-95. CAR appears to interact with several distinct PDZ-domain-containing proteins and may exert its biological function through these interactions.

Regulation of PCSK9 by nutraceuticals.

PubMed

Momtazi, Amir Abbas; Banach, Maciej; Pirro, Matteo; Katsiki, Niki; Sahebkar, Amirhossein

2017-06-01

PCSK9 (proprotein convertase subtilisin kexin type 9) is a liver secretory enzyme that regulates plasma low-density lipoprotein (LDL) cholesterol (LDL-C) levels through modulation of LDL receptor (LDLR) density on the surface of hepatocytes. Inhibition of PCSK9 using monoclonal antibodies can efficiently lower plasma LDL-C, non-high-density lipoprotein cholesterol and lipoprotein (a). PCSK9 inhibition is also an effective adjunct to statin therapy; however, the cost-effectiveness of currently available PCSK9 inhibitors is under question. Nutraceuticals offer a safe and cost-effective option for PCSK9 inhibition. Several nutraceuticals have been reported to modulate PCSK9 levels and exert LDL-lowering activity. Mechanistically, those nutraceuticals that inhibit PCSK9 through a SREBP (sterol-responsive element binding protein)-independent pathway can be more effective in lowering plasma LDL-C levels compared with those inhibiting PCSK9 through the SREBP pathway. The present review aims to collect available data on the nutraceuticals with PCSK9-inhibitory effect and the underlying mechanisms. Copyright © 2017 Elsevier Ltd. All rights reserved.

General Anesthetics Have Additive Actions on Three Ligand-Gated Ion Channels

PubMed Central

Jenkins, Andrew; Lobo, Ingrid A.; Gong, Diane; Trudell, James R.; Solt, Ken; Harris, R. Adron; Eger, Edmond I

2008-01-01

Background The purpose of this study was to determine whether pairs of compounds, including general anesthetics, could simultaneously modulate receptor function in a synergistic manner, thus demonstrating the existence of multiple intra-protein anesthetic binding sites. Methods Using standard electrophysiologic methods, we measured the effects of at least one combination of benzene, isoflurane, halothane, chloroform, flunitrazepam, zinc and pentobarbital on at least one of the following ligand gated ion channels: N-methyl-D-aspartate receptors (NMDARs), glycine receptors (GlyRs) and γ-aminobutyric acid type A receptors (GABAARs). Results All drug-drug-receptor combinations were found to exhibit additive, not synergistic modulation. Isoflurane with benzene additively depressed NMDAR function. Isoflurane with halothane additively enhanced GlyR function, as did isoflurane with zinc. Isoflurane with halothane additively enhanced GABAAR function as did all of the following: halothane with chloroform, pentobarbital with isoflurane, and flunitrazepam with isoflurane. Conclusions The simultaneous allosteric modulation of ligand gated ion channels by general anesthetics is entirely additive. Where pairs of general anesthetic drugs interact synergistically to produce general anesthesia, they must do so on systems more complex than a single receptor. PMID:18633027

Structure of an Arrestin2-clathrin Complex Reveals a Novel Clathrin Binding Domain that Modulates Receptor Trafficking

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, D.; Kern, R; Puthenveedu, M

2009-01-01

Non-visual arrestins play a pivotal role as adaptor proteins in regulating the signaling and trafficking of multiple classes of receptors. Although arrestin interaction with clathrin, AP-2, and phosphoinositides contributes to receptor trafficking, little is known about the configuration and dynamics of these interactions. Here, we identify a novel interface between arrestin2 and clathrin through x-ray diffraction analysis. The intrinsically disordered clathrin binding box of arrestin2 interacts with a groove between blades 1 and 2 in the clathrin {beta}-propeller domain, whereas an 8-amino acid splice loop found solely in the long isoform of arrestin2 (arrestin2L) interacts with a binding pocket formedmore » by blades 4 and 5 in clathrin. The apposition of the two binding sites in arrestin2L suggests that they are exclusive and may function in higher order macromolecular structures. Biochemical analysis demonstrates direct binding of clathrin to the splice loop in arrestin2L, whereas functional analysis reveals that both binding domains contribute to the receptor-dependent redistribution of arrestin2L to clathrin-coated pits. Mutagenesis studies reveal that the clathrin binding motif in the splice loop is (L/I){sub 2}GXL. Taken together, these data provide a framework for understanding the dynamic interactions between arrestin2 and clathrin and reveal an essential role for this interaction in arrestin-mediated endocytosis.« less

Identification of Global and Ligand-Specific Calcium Sensing Receptor Activation Mechanisms.

PubMed

Keller, Andrew N; Kufareva, Irina; Josephs, Tracy M; Diao, Jiayin; Mai, Vyvyan T; Conigrave, Arthur D; Christopoulos, Arthur; Gregory, Karen J; Leach, Katie

2018-06-01

Calcium sensing receptor (CaSR) positive allosteric modulators (PAMs) are therapeutically important. However, few are approved for clinical use, in part due to complexities in assessing allostery at a receptor where the endogenous agonist (extracellular calcium) is present in all biologic fluids. Such complexity impedes efforts to quantify and optimize allosteric drug parameters (affinity, cooperativity, and efficacy) that dictate PAM structure-activity relationships (SARs). Furthermore, an underappreciation of the structural mechanisms underlying CaSR activation hinders predictions of how PAM SAR relates to in vitro and in vivo activity. Herein, we combined site-directed mutagenesis and calcium mobilization assays with analytical pharmacology to compare modes of PAM binding, positive modulation, and agonism. We demonstrate that 3-(2-chlorophenyl)- N -((1 R )-1-(3-methoxyphenyl)ethyl)-1-propanamine (NPS R568) binds to a 7 transmembrane domain (7TM) cavity common to class C G protein-coupled receptors and used by ( αR )-(-)- α -methyl- N -[3-[3-[trifluoromethylphenyl]propyl]-1-napthalenemethanamine (cinacalcet) and 1-benzothiazol-2-yl-1-(2,4-dimethylphenyl)-ethanol (AC265347); however, there are subtle distinctions in the contribution of select residues to the binding and transmission of cooperativity by PAMs. Furthermore, we reveal some common activation mechanisms used by different CaSR activators, but also demonstrate some differential contributions of residues within the 7TM bundle and extracellular loops to the efficacy of the PAM-agonist, AC265347, versus cooperativity. Finally, we show that PAMS potentiate the affinity of divalent cations. Our results support the existence of both global and ligand-specific CaSR activation mechanisms and reveal that allosteric agonism is mediated in part via distinct mechanisms to positive modulation. Copyright © 2018 by The American Society for Pharmacology and Experimental Therapeutics.

A trans-acting enhancer modulates estrogen-mediated transcription of reporter genes in osteoblasts.

PubMed

Sasaki-Iwaoka, H; Maruyama, K; Endoh, H; Komori, T; Kato, S; Kawashima, H

1999-02-01

The presence of bone-specific estrogen agonists and discovery of the osteoblast-specific transcription factor (TF), Cbfa1, together with the discovery of synergism between a TF Pit-1 and estrogen receptor alpha (ERalpha) on rat prolactin gene, led to investigation of Cbfa1 in the modulation of osteoblast-specific actions of estrogen. Reverse transcribed-polymerase chain reaction demonstrated expression of Cbfa1 in the osteoblastic cell lines, MG63, ROS17/2.8, and MC3T3E1, but not in nonosteoblastic cell lines, MCF7, C3H10T1/2, and HeLa. An ER expression vector and a series of luciferase (Luc) reporter plasmids harboring the Cbfa1 binding site OSE2 (the osteoblast-specific cis element in the osteocalcin promoter) and palindromic estrogen response elements (EREs) were cotransfected into both osteoblastic and nonosteoblastic cells. OSE2 worked as a cis- acting element in osteoblastic cells but not nonosteoblastic cells, whereas EREs were cis- acting in all cell lines. Synergistic transactivation was observed in osteoblastic cells only when both ERE and OSE2 were placed in juxtaposition to the promoter. Forced expression of Cbfa1 in C3H10T1/2 cells also induced synergism. Tamoxifen, a partial agonist/antagonist of estrogen, acted as an osteoblast-specific agonist in cells transfected with a promoter containing ERE and acted synergistically with a promoter containing the ERE-OSE2 enhancer combination. These results support the idea that bone-specific TFs modulate the actions of estrogen in a tissue-specific manner.

Periplakin interferes with G protein activation by the melanin-concentrating hormone receptor-1 by binding to the proximal segment of the receptor C-terminal tail.

PubMed

Murdoch, Hannah; Feng, Gui-Jie; Bächner, Dietmar; Ormiston, Laura; White, Julia H; Richter, Dietmar; Milligan, Graeme

2005-03-04

In mice genetic ablation of expression of either melanin-concentrating hormone or the melanin-concentrating hormone-1 receptor results in alterations in energy metabolism and a lean phenotype. There is thus great interest in the function and regulation of this receptor. Using the yeast two-hybrid system we identified an interaction of the actin- and intermediate filament-binding protein periplakin with the intracellular C-terminal tail of the melanin-concentrating hormone-1 receptor. Direct association of these proteins was verified in pull-down and coimmunoprecipitation experiments. Truncations and internal deletions delineated the site of interaction to a group of 11 amino acids proximal to transmembrane helix VII, which was distinct from the binding site for the melanin-concentrating hormone-1 receptor-interacting zinc finger protein. Immunohistochemistry demonstrated coexpression of periplakin with melanin-concentrating hormone-1 receptor in specific cells of the piriform cortex, amygdala, and other structures of the adult mouse brain. Coexpression of the melanin-concentrating hormone-1 receptor with periplakin in human embryonic kidney 293 cells did not prevent agonist-mediated internalization of the receptor but did interfere with binding of (35)S-labeled guanosine 5'-3-O-(thio)triphosphate ([(35)S]GTPgammaS) to the G protein Galpha(o1) and the elevation of [Ca(2+)](i). Coexpression of the receptor with the interacting zinc finger protein did not modulate receptor internalization or G protein activation. The interaction of periplakin with receptors was selective. Coexpression of periplakin with the IP prostanoid receptor did not result in coimmunoprecipitation nor interfere with agonist-mediated binding of [(35)S]GTPgammaS to the G protein Galpha(s). Periplakin is the first protein described to modify the capacity of the melanin-concentrating hormone-1 receptor to initiate signal transduction.

17Beta-estradiol signaling and regulation of proliferation and apoptosis of rat Sertoli cells.

PubMed

Royer, Carine; Lucas, Thaís F G; Lazari, Maria F M; Porto, Catarina S

2012-04-01

The aim of the present study was to investigate the intracellular signaling events downstream of the classical estrogen receptors (ESRs) and G protein-coupled estrogen receptor 1 (GPER) involved in regulation of proliferation and apoptosis of rat Sertoli cells, in which we have previously described ESR1, ESR2, and GPER. ESRs play a role in Sertoli cell proliferation, and GPER, but not ESRs, plays a role modulating gene expression involved with apoptosis. The present study shows that 17beta-estradiol (E2) and the GPER-selective agonist G-1 rapidly activate phosphatidylinositol 3-kinase (PIK3)/serine threonine protein kinase (AKT) and cyclic AMP response element-binding (CREB) phosphorylation. E2 and the ESR1-selective agonist 4,4',4″-(4-propyl-(1H)-pyrazole-1,3,5-triyl)trisphenol (PPT) increase the expression of cyclin D1 (CCND1), whereas the ESR2-selective agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN) and G-1 do not change the expression of this protein, suggesting that ESR1 is the upstream receptor regulating Sertoli cell proliferation. E2- or PPT-ESR1, through activation of epidermal growth factor receptor (EGFR)/mitogen-activated protein kinase 3/1 (MAPK3/1) and PIK3 pathways, induces upregulation of CCND1. KG-501, the compound that disrupts the phospho-CREB/CREB binding protein (CBP) complex, does not change E2- or PPT-ESR1-mediated CCND1 expression, suggesting that phospho-CREB/cyclic AMP response element/CBP is not involved in the expression of this protein. E2- or G-1-GPER, through activation of EGFR/MAPK3/1 and PIK3 pathways, may be involved in the upregulation of antiapoptotic proteins BCL2 and BCL2L2. E2- or G-1-GPER/EGFR/MAPK3/1/phospho-CREB decreases BAX expression. Taken together, these results show a differential effect of E2-GPER on the CREB-mediated transcription of proapoptotic and antiapoptotic genes of the same BCL2 gene family. ESR1 and GPER can mediate the rapid E2 actions in the Sertoli cells, which in turn can modulate nuclear transcriptional events important for Sertoli cell function and maintenance of normal testis development and homeostasis. Our findings are important to clarify the role of estrogen in a critical period of testicular development, and to direct further studies, which may contribute to better understanding of the causes of male infertility.

Characterization of the intrinsic activity for a novel class of cannabinoid receptor ligands: Indole Quinuclidine analogues

PubMed Central

Franks, Lirit N.; Ford, Benjamin M.; Madadi, Nikhil R.; Penthala, Narsimha R.; Crooks, Peter A.; Prather, Paul L.

2014-01-01

Our laboratory recently reported that a group of novel indole quinuclidine analogues bind with nanomolar affinity to cannabinoid type-1 and type-2 receptors. This study characterized the intrinsic activity of these compounds by determining whether they exhibit agonist, antagonist, or inverse agonist activity at cannabinoid type-1 and/or type-2 receptors. Cannabinoid receptors activate Gi/Go-proteins that then proceed to inhibit activity of the downstream intracellular effector adenylyl cyclase. Therefore, intrinsic activity was quantified by measuring the ability of compounds to modulate levels of intracellular cAMP in intact cells. Concerning cannabinoid type-1 receptors endogenously expressed in Neuro2A cells, a single analogue exhibited agonist activity, while eight acted as neutral antagonists and two possessed inverse agonist activity. For cannabinoid type-2 receptors stably expressed in CHO cells, all but two analogues acted as agonists; these two exceptions exhibited inverse agonist activity. Confirming specificity at cannabinoid type-1 receptors, modulation of adenylyl cyclase activity by all proposed agonists and inverse agonists was blocked by co-incubation with the neutral cannabinoid type-1 antagonist O-2050. All proposed cannabinoid type-1 receptor antagonists attenuated adenylyl cyclase modulation by cannabinoid agonist CP-55,940. Specificity at cannabinoid type-2 receptors was confirmed by failure of all compounds to modulate adenylyl cyclase activity in CHO cells devoid of cannabinoid type-2 receptors. Further characterization of select analogues demonstrated concentration-dependent modulation of adenylyl cyclase activity with potencies similar to their respective affinities for cannabinoid receptors. Therefore, indole quinuclidines are a novel structural class of compounds exhibiting high affinity and a range of intrinsic activity at cannabinoid type-1 and type-2 receptors. PMID:24858620

Secbase: database module to retrieve secondary structure elements with ligand binding motifs.

PubMed

Koch, Oliver; Cole, Jason; Block, Peter; Klebe, Gerhard

2009-10-01

Secbase is presented as a novel extension module of Relibase. It integrates the information about secondary structure elements into the retrieval facilities of Relibase. The data are accessible via the extended Relibase user interface, and integrated retrieval queries can be addressed using an extended version of Reliscript. The primary information about alpha-helices and beta-sheets is used as provided by the PDB. Furthermore, a uniform classification of all turn families, based on recent clustering methods, and a new helix assignment that is based on this turn classification has been included. Algorithms to analyze the geometric features of helices and beta-strands were also implemented. To demonstrate the performance of the Secbase implementation, some application examples are given. They provide new insights into the involvement of secondary structure elements in ligand binding. A survey of water molecules detected next to the N-terminus of helices is analyzed to show their involvement in ligand binding. Additionally, the parallel oriented NH groups at the alpha-helix N-termini provide special binding motifs to bind particular ligand functional groups with two adjacent oxygen atoms, e.g., as found in negatively charged carboxylate or phosphate groups, respectively. The present study also shows that the specific structure of the first turn of alpha-helices provides a suitable explanation for stabilizing charged structures. The magnitude of the overall helix macrodipole seems to have no or only a minor influence on binding. Furthermore, an overview of the involvement of secondary structure elements with the recognition of some important endogenous ligands such as cofactors shows some distinct preference for particular binding motifs and amino acids.

Macrophage Integrins Modulate Response to Ultra-High Molecular Weight Polyethylene Particles and Direct Particle-Induced Osteolysis

PubMed Central

Zaveri, Toral D.; Dolgova, Natalia V.; Lewis, Jamal S.; Hamaker, Kiri; Clare-Salzler, Michael J.; Keselowsky, Benjamin G.

2016-01-01

Aseptic loosening due to peri-prosthetic osteolysis is one of the primary causes for failure of artificial joint replacements. Implant-derived wear particles, often ultra-high molecular weight polyethylene (UHMWPE) microparticles, initiate an inflammatory cascade upon phagocytosis by macrophages, which leads to osteoclast recruitment and activation, ultimately resulting in osteolysis. Investigation into integrin receptors, involved in cellular interactions with biomaterial-adsorbed adhesive proteins, is of interest to understand and modulate inflammatory processes. In this work, we investigate the role of macrophage integrins Mac-1 and RGD-binding integrins in response to UHMWPE wear particles. Using integrin knockout mice as well as integrin blocking techniques, reduction in macrophage phagocytosis and inflammatory cytokine secretion is demonstrated when these receptors are either absent or blocked. Along this line, various opsonizing proteins are shown to differentially modulate microparticle uptake and macrophage secretion of inflammatory cytokines. Furthermore, using a calvarial osteolysis model it is demonstrated that both Mac-1 integrin and RGD-binding integrins modulate the particle induced osteolysis response to UHMWPE microparticles, with a 40% decrease in the area of osteolysis by the absence or blocking of these integrins, in vivo. Altogether, these findings indicate Mac-1 and RGD-binding integrins are involved in macrophage-directed inflammatory responses to UHMWPE and may serve as therapeutic targets to mitigate wear particle induced peri-prosthetic osteolysis for improved performance of implanted joints. PMID:27889664

Human glutathione S-transferase P1-1 functions as an estrogen receptor α signaling modulator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Xiyuan; An, Byoung Ha; Kim, Min Jung

2014-09-26

Highlights: • GSTP induces the classical ERα signaling event. • The functional GSTP is a prerequisite for GSTP-induced ERα transcription activity. • The expression of RIP140, a transcription cofactor, was inhibited by GSTP protein. • We propose the novel non-enzymatic role of GSTP. - Abstract: Estrogen receptor α (ERα) plays a crucial role in estrogen-mediated signaling pathways and exerts its action as a nuclear transcription factor. Binding of the ligand-activated ERα to the estrogen response element (ERE) is a central part of ERα-associated signal transduction pathways and its aberrant modulation is associated with many disease conditions. Human glutathione S-transferase P1-1more » (GSTP) functions as an enzyme in conjugation reactions in drug metabolism and as a regulator of kinase signaling pathways. It is overexpressed in tumors following chemotherapy and has been associated with a poor prognosis in breast cancer. In this study, a novel regulatory function of GSTP has been proposed in which GSTP modulates ERE-mediated ERα signaling events. Ectopic expression of GSTP was able to induce the ERα and ERE-mediated transcriptional activities in ERα-positive but GSTP-negative MCF7 human breast cancer cells. This inductive effect of GSTP on the ERE-transcription activity was diminished when the cells express a mutated form of the enzyme or are treated with a GSTP-specific chemical inhibitor. It was found that GSTP inhibited the expression of the receptor interacting protein 140 (RIP140), a negative regulator of ERα transcription, at both mRNA and protein levels. Our study suggests a novel non-enzymatic role of GSTP which plays a significant role in regulating the classical ERα signaling pathways via modification of transcription cofactors such as RIP140.« less

ATP hydrolysis is essential for Bag-1M-mediated inhibition of the DNA binding by the glucocorticoid receptor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Wei, E-mail: hongwei@tijmu.edu.cn; Chen, Linfeng; Liu, Yunde

2009-12-04

The 70-kDa heat shock protein (Hsp70) is involved in providing the appropriate conformation of various nuclear hormone receptors, including the glucocorticoid receptor (GR). The Bcl-2 associated athanogene 1M (Bag-1M) is known to downregulate the DNA binding by the GR. Also, Bag-1M interacts with the ATPase domain of Hsp70 to modulate the release of the substrate from Hsp70. In this study, we demonstrate that ATP hydrolysis enhances Bag-1M-mediated inhibition of the DNA binding by the GR. However, the inhibitory effect of Bag-1M was abolished when the intracellular ATP was depleted. In addition, a Bag-1M mutant lacking the interaction with Hsp70 didmore » not influence the GR to bind DNA, suggesting the interaction of Bag-1M with Hsp70 in needed for its negative effect. These results indicate that ATP hydrolysis is essential for Bag-1M-mediated inhibition of the DNA binding by the GR and Hsp70 is a mediator for this process.« less

A novel substance P binding site in rat brain regions modulates TRH receptor binding.

PubMed

Sharif, N A

1990-10-01

Binding sites for thyrotropin-releasing hormone (TRH) were labelled with [3H](2-Me-His3)TRH ([3H]MeTRH) on membranes from rat brain regions at 0 degrees C for 5 h. Amygdaloid membranes bound [3H]MeTRH with high-affinity (Kd = 3.1 +/- 0.5 nM (n = 4)). Five TRH analogs competed for this binding with the same rank order and with affinities that matched the pharmacological specificity of pituitary TRH receptors. Substance P (SP) and its C-terminal fragments reduced amygdaloid TRH receptor binding in a concentration dependent manner (IC50 for SP = 65 microM). The rank order of potency of SP analogs at inhibiting TRH receptor binding was: SP greater than nonapeptide (3-11) greater than hexapeptide (6-11) greater than heptapeptide (5-11) greater than pentapeptide (7-11). However, other tachykinins were inactive in this system. SP was a potent inhibitor of [3H]MeTRH binding in hippocampus greater than spinal cord greater than retina greater than n. accumbens greater than hypothalamus greater than amygdaloid greater than olfactory bulb greater than or equal to pituitary greater than pons/medulla in parallel assays. In amygdaloid membranes SP (50 microM) reduced the apparent maximum receptor density by 39% (p less than 0.01) without altering the binding affinity, and 100 microM SP induced a biphasic dissociation of [3H]MeTRH with kinetics faster than those induced by both TRH (10 microM) and serotonin (100 microM). In contrast, other neuropeptides such as neurotensin, proctolin, angiotensin II, bombesin and luteinizing hormone releasing hormone did not significantly inhibit [3H]MeTRH binding to amygdaloid membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Agonist and antagonist modulation of [35S]-GTPγS binding in transfected CHO cells expressing the neurotensin receptor

PubMed Central

Hermans, Emmanuel; Geurts, Muriel; Maloteaux, Jean-Marie

1997-01-01

The functional interaction of the cloned rat neurotensin receptor with intracellular G-proteins was investigated by studying the binding of the radiolabelled guanylyl nucleotide analogue [35S]-GTPγS induced by neurotensin to membranes prepared from transfected Chinese hamster ovary (CHO) cells. The agonist-induced binding of [35S]-GTPγS was only detected in the presence of NaCl in the incubation buffer. However, it was also demonstrated that the binding of [3H]-neurotensin to its receptor was inhibited by NaCl. In the presence of 50 mM NaCl, the binding of the labelled nucleotide was about 2 fold increased by stimulation with saturating concentrations of neurotensin (EC50 value of 2.3±0.9 nM). The stimulation of [35S]-GTPγS binding by neurotensin was mimicked by the stable analogue of neurotensin, JMV-449 (EC50 value of 1.7±0.4 nM) and the neurotensin related peptide neuromedin N (EC50 value of 21±6 nM). The NT-induced [35S]-GTPγS binding was competitively inhibited by SR48692 (pA2 value of 9.55±0.28), a non-peptide neurotensin receptor antagonist. SR48692 alone had no effect on the specific binding of [35S]-GTPγS. The response to neurotensin was found to be inhibited by the aminosteroid U-73122, a putative inhibitor of phospholipase C-dependent processes, indicating that this drug may act at the G-protein level. Taken together, these results constitute the first characterization of the exchange of guanylyl nucleotides at the G-protein level that is induced by the neuropeptide neurotensin after binding to its receptor. PMID:9283723

Structural insights into the interaction of IL-33 with its receptors.

PubMed

Liu, Xi; Hammel, Michal; He, Yanfeng; Tainer, John A; Jeng, U-Ser; Zhang, Linqi; Wang, Shuying; Wang, Xinquan

2013-09-10

Interleukin (IL)-33 is an important member of the IL-1 family that has pleiotropic activities in innate and adaptive immune responses in host defense and disease. It signals through its ligand-binding primary receptor ST2 and IL-1 receptor accessory protein (IL-1RAcP), both of which are members of the IL-1 receptor family. To clarify the interaction of IL-33 with its receptors, we determined the crystal structure of IL-33 in complex with the ectodomain of ST2 at a resolution of 3.27 Å. Coupled with structure-based mutagenesis and binding assay, the structural results define the molecular mechanism by which ST2 specifically recognizes IL-33. Structural comparison with other ligand-receptor complexes in the IL-1 family indicates that surface-charge complementarity is critical in determining ligand-binding specificity of IL-1 primary receptors. Combined crystallography and small-angle X-ray-scattering studies reveal that ST2 possesses hinge flexibility between the D3 domain and D1D2 module, whereas IL-1RAcP exhibits a rigid conformation in the unbound state in solution. The molecular flexibility of ST2 provides structural insights into domain-level conformational change of IL-1 primary receptors upon ligand binding, and the rigidity of IL-1RAcP explains its inability to bind ligands directly. The solution architecture of IL-33-ST2-IL-1RAcP complex from small-angle X-ray-scattering analysis resembles IL-1β-IL-1RII-IL-1RAcP and IL-1β-IL-1RI-IL-1RAcP crystal structures. The collective results confer IL-33 structure-function relationships, supporting and extending a general model for ligand-receptor assembly and activation in the IL-1 family.

G protein-coupled receptor transmembrane binding pockets and their applications in GPCR research and drug discovery: a survey.

PubMed

Kratochwil, Nicole A; Gatti-McArthur, Silvia; Hoener, Marius C; Lindemann, Lothar; Christ, Andreas D; Green, Luke G; Guba, Wolfgang; Martin, Rainer E; Malherbe, Pari; Porter, Richard H P; Slack, Jay P; Winnig, Marcel; Dehmlow, Henrietta; Grether, Uwe; Hertel, Cornelia; Narquizian, Robert; Panousis, Constantinos G; Kolczewski, Sabine; Steward, Lucinda

2011-01-01

G protein-coupled receptors (GPCRs) share a common architecture consisting of seven transmembrane (TM) domains. Various lines of evidence suggest that this fold provides a generic binding pocket within the TM region for hosting agonists, antagonists, and allosteric modulators. Hence, an automated method was developed that allows a fast analysis and comparison of these generic ligand binding pockets across the entire GPCR family by providing the relevant information for all GPCRs in the same format. This methodology compiles amino acids lining the TM binding pocket including parts of the ECL2 loop in a so-called 1D ligand binding pocket vector and translates these 1D vectors in a second step into 3D receptor pharmacophore models. It aims to support various aspects of GPCR drug discovery in the pharmaceutical industry. Applications of pharmacophore similarity analysis of these 1D LPVs include definition of receptor subfamilies, prediction of species differences within subfamilies in regard to in vitro pharmacology and identification of nearest neighbors for GPCRs of interest to generate starting points for GPCR lead identification programs. These aspects of GPCR research are exemplified in the field of melanopsins, trace amine-associated receptors and somatostatin receptor subtype 5. In addition, it is demonstrated how 3D pharmacophore models of the LPVs can support the prediction of amino acids involved in ligand recognition, the understanding of mutational data in a 3D context and the elucidation of binding modes for GPCR ligands and their evaluation. Furthermore, guidance through 3D receptor pharmacophore modeling for the synthesis of subtype-specific GPCR ligands will be reported. Illustrative examples are taken from the GPCR family class C, metabotropic glutamate receptors 1 and 5 and sweet taste receptors, and from the GPCR class A, e.g. nicotinic acid and 5-hydroxytryptamine 5A receptor. © 2011 Bentham Science Publishers

High-mobility group (HMG) protein HMG-1 and TATA-binding protein-associated factor TAF(II)30 affect estrogen receptor-mediated transcriptional activation.

PubMed

Verrier, C S; Roodi, N; Yee, C J; Bailey, L R; Jensen, R A; Bustin, M; Parl, F F

1997-07-01

The estrogen receptor (ER) belongs to a family of ligand-inducible nuclear receptors that exert their effects by binding to cis-acting DNA elements in the regulatory region of target genes. The detailed mechanisms by which ER interacts with the estrogen response element (ERE) and affects transcription still remain to be elucidated. To study the ER-ERE interaction and transcription initiation, we employed purified recombinant ER expressed in both the baculovirus-Sf9 and his-tagged bacterial systems. The effect of high-mobility group (HMG) protein HMG-1 and purified recombinant TATA-binding protein-associated factor TAF(II)30 on ER-ERE binding and transcription initiation were assessed by electrophoretic mobility shift assay and in vitro transcription from an ERE-containing template (pERE2LovTATA), respectively. We find that purified, recombinant ER fails to bind to ERE in spite of high ligand-binding activity and electrophoretic and immunological properties identical to ER in MCF-7 breast cancer cells. HMG-1 interacts with ER and promotes ER-ERE binding in a concentration- and time-dependent manner. The effectiveness of HMG-1 to stimulate ER-ERE binding in the electrophoretic mobility shift assay depends on the sequence flanking the ERE consensus as well as the position of the latter in the oligonucleotide. We find that TAF(II)30 has no effect on ER-ERE binding either alone or in combination with ER and HMG-1. Although HMG-1 promotes ER-ERE binding, it fails to stimulate transcription initiation either in the presence or absence of hormone. In contrast, TAF(II)30, while not affecting ER-ERE binding, stimulates transcription initiation 20-fold in the presence of HMG-1. These results indicate that HMG-1 and TAF(II)30 act in sequence, the former acting to promote ER-ERE binding followed by the latter to stimulate transcription initiation.

Selective binding of the fluorescent dye 1-anilinonaphthalene-8-sulfonic acid to peroxisome proliferator-activated receptor gamma allows ligand identification and characterization.

PubMed

Zorrilla, Silvia; Garzón, Beatriz; Pérez-Sala, Dolores

2010-04-01

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the nuclear receptor superfamily involved in insulin sensitization, atherosclerosis, inflammation, and carcinogenesis. PPARgamma transcriptional activity is modulated by specific ligands that promote conformational changes allowing interaction with coactivators. Here we show that the fluorophore 1-anilinonaphthalene-8-sulfonic acid (ANS) binds to PPARgamma-LBD (ligand binding domain), displaying negligible interaction with other nuclear receptors such as PPARalpha and retinoid X receptor alpha (RXRalpha). ANS binding is competed by PPARgamma agonists such as rosiglitazone, 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), and 9,10-dihydro-15-deoxy-Delta(12,14)-prostaglandin J(2) (CAY10410). Moreover, the affinity of PPARgamma for these ligands, determined through ANS competition titrations, is within the range of that reported previously, thereby suggesting that ANS competition could be useful in the screening and characterization of novel PPARgamma agonists. In contrast, gel-based competition assays showed limited performance with noncovalently bound ligands. We applied the ANS binding assay to characterize a biotinylated analog of 15d-PGJ(2) that does not activate PPAR in cells. We found that although this compound bound to PPARgamma with low affinity, it failed to promote PPARgamma interaction with a fluorescent SRC-1 peptide, indicating a lack of receptor activation. Therefore, combined approaches using ANS and fluorescent coactivator peptides to monitor PPARgamma binding and interactions may provide valuable strategies to fully understand the role of PPARgamma ligands. Copyright 2009 Elsevier Inc. All rights reserved.

Heterodimerization of μ and δ Opioid Receptors: A Role in Opiate Synergy

PubMed Central

Gomes, I.; Jordan, B. A.; Gupta, A.; Trapaidze, N.; Nagy, V.; Devi, L. A.

2011-01-01

Opiate analgesics are widely used in the treatment of severe pain. Because of their importance in therapy, different strategies have been considered for making opiates more effective while curbing their liability to be abused. Although most opiates exert their analgesic effects primarily via μ opioid receptors, a number of studies have shown that δ receptor-selective drugs can enhance their potency. The molecular basis for these findings has not been elucidated previously. In the present study, we examined whether heterodimerization of μ and δ receptors could account for the cross-modulation previously observed between these two receptors. We find that co-expression of μ and δ receptors in heterologous cells followed by selective immunoprecipitation results in the isolation of μ–δ heterodimers. Treatment of these cells with extremely low doses of certain δ-selective ligands results in a significant increase in the binding of a μ receptor agonist. Similarly, treatment with μ-selective ligands results in a significant increase in the binding of a δ receptor agonist. This robust increase is also seen in SKNSH cells that endogenously express both μ and δ receptors. Furthermore, we find that a δ receptor antagonist enhances both the potency and efficacy of the μ receptor signaling; likewise a μ antagonist enhances the potency and efficacy of the δ receptor signaling. A combination of agonists (μ and δ receptor selective) also synergistically binds and potentiates signaling by activating the μ–δ heterodimer. Taken together, these studies show that heterodimers exhibit distinct ligand binding and signaling characteristics. These findings have important clinical ramifications and may provide new foundations for more effective therapies. PMID:11069979

Amino Acid Change in the Carbohydrate Response Element Binding Protein is associated with lower triglycerides and myocardial infarction incidence depending on level of adherence to the Mediterranean diet in the PREDIMED trial

USDA-ARS?s Scientific Manuscript database

A variant (rs3812316, C771G, and Gln241His) in the MLXIPL (Max-like protein X interacting protein-like) gene encoding the carbohydrate response element binding protein has been associated with lower triglycerides. However, its association with cardiovascular diseases and gene-diet interactions modul...

Microsomal receptor for steroid hormones: functional implications for nuclear activity.

PubMed

Muldoon, T G; Watson, G H; Evans, A C; Steinsapir, J

1988-01-01

Target tissues for steroid hormones are responsive by virtue of and to the extent of their content of functional intracellular receptors. Recent years have seen a shift in considerations of the cellular dynamics and distribution of these receptors, with current views favoring predominant intranuclear localization in the intact cell. This paper summarizes our analyses of the microsomal estrogen and androgen binding capability of rat uterine and ventral prostate tissue, respectively; these studies have revealed a set of high affinity sites that may act as a conduit for estrogen traversing the cell en route to the nucleus. These sites have many properties in common with cytosolic receptors, with the salient difference of a failure to activate to a more avid DNA-binding form under conditions which permit such activation of cytosolic receptors. The microsomal estrogen-binding proteins also have appreciable affinity for progesterone, another distinction from other known cellular estrogen receptor species. Various experimental approaches were employed to demonstrate that the microsomal receptors were not simply cytosol contaminants; the most convincing evidence is the recent successful separation of the cytosolic and microsomal forms by differential ammonium sulfate precipitation. Discrete subfractionation of subcellular components on successive sucrose gradients, with simultaneous assessments of binding capability and marker enzyme concentrations, indicates that the major portion of the binding is localized within the vesicles of the endoplasmic reticulum free of significant plasma membrane contamination. The microsomal receptors are readily solubilized by extraction with high- or low-salt-containing buffers or with steroid. The residual microsomes following such extraction have the characteristics of saturable acceptor sites for cytosolic estrogen-receptor complexes. The extent to which these sites will accept the cytosolic complexes is equal to the concentration of microsomal binding sites extracted. These observations suggest three possible roles for the microsomal receptor-like proteins: (a) modulation of estrogen access to nuclear binding sites; (b) formation of functional complexes which diffuse to other extranuclear sites to alter non-genomic cellular processes; (c) regulation of nuclear concentration of estrogen-receptor complexes by virtue of producing microsomal acceptor sites for uptake of free or loosely associated nuclear complexes, previously thought to exist in the cytoplasm.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chien, Ellen Y.T.; Liu, Wei; Zhao, Qiang

Dopamine modulates movement, cognition, and emotion through activation of dopamine G protein-coupled receptors in the brain. The crystal structure of the human dopamine D3 receptor (D3R) in complex with the small molecule D2R/D3R-specific antagonist eticlopride reveals important features of the ligand binding pocket and extracellular loops. On the intracellular side of the receptor, a locked conformation of the ionic lock and two distinctly different conformations of intracellular loop 2 are observed. Docking of R-22, a D3R-selective antagonist, reveals an extracellular extension of the eticlopride binding site that comprises a second binding pocket for the aryl amide of R-22, which differsmore » between the highly homologous D2R and D3R. This difference provides direction to the design of D3R-selective agents for treating drug abuse and other neuropsychiatric indications.« less

Immunomodulatory effects of endogenous and synthetic peptides activating opioid receptors.

PubMed

Pomorska, Dorota K; Gach, Katarzyna; Janecka, Anna

2014-01-01

The main role of endogenous opioid peptides is the modulation of pain. Opioid peptides exert their analgesic activity by binding to the opioid receptors distributed widely in the central nervous system (CNS). However, opioid receptors are also found on tissues and organs outside the CNS, including the cells of the immune system, indicating that opioids are capable of exerting additional effects in periphery. Morphine, which is a gold standard in the treatment of chronic pain, is well-known for its immunosuppressive effects. Much less is known about the immunomodulatory effects exerted by endogenous (enkephalins, endorphins, dynorphins and endomorphins) and synthetic peptides activating opioid receptors. In this review we tried to summarize opioid peptide-mediated modulation of immune cell functions which can be stimulatory as well as inhibitory.

Design and synthesis of tricyclic tetrahydroquinolines as a new series of nonsteroidal selective androgen receptor modulators (SARMs).

PubMed

Nagata, Naoya; Miyakawa, Motonori; Amano, Seiji; Furuya, Kazuyuki; Yamamoto, Noriko; Inoguchi, Kiyoshi

2011-03-15

Some tricyclic tetrahydroquinolines (THQs) were found to have the potential of a new series of nonsteroidal selective androgen receptor modulators (SARMs). Compound 5b was first designed and synthesized under our hypothesis based on a four-point pharmacophoric requirement of the 3-carbonyl, 18-methyl, 17-hydroxyl, and 13-quaternary carbon groups of dihydrotestosterone (DHT). It was revealed that this compound exhibits not only a strong androgen receptor (AR) agonistic activity (EC(50)=9.2 nM) but also the highest selectivity in binding affinity to AR among the steroid hormone receptors. Furthermore, this compound showed a weak virilizing effect with retention of the desired anabolic effect as compared with DHT in vivo. Copyright © 2011 Elsevier Ltd. All rights reserved.

Azadirachtin interacts with retinoic acid receptors and inhibits retinoic acid-mediated biological responses.

PubMed

Thoh, Maikho; Babajan, Banaganapalli; Raghavendra, Pongali B; Sureshkumar, Chitta; Manna, Sunil K

2011-02-11

Considering the role of retinoids in regulation of more than 500 genes involved in cell cycle and growth arrest, a detailed understanding of the mechanism and its regulation is useful for therapy. The extract of the medicinal plant Neem (Azadirachta indica) is used against several ailments especially for anti-inflammatory, anti-itching, spermicidal, anticancer, and insecticidal activities. In this report we prove the detailed mechanism on the regulation of retinoic acid-mediated cell signaling by azadirachtin, active components of neem extract. Azadirachtin repressed all trans-retinoic acid (ATRA)-mediated nuclear transcription factor κB (NF-κB) activation, not the DNA binding but the NF-κB-dependent gene expression. It did not inhibit IκBα degradation, IκBα kinase activity, or p65 phosphorylation and its nuclear translocation but inhibited NF-κB-dependent reporter gene expression. Azadirachtin inhibited TRAF6-mediated, but not TRAF2-mediated NF-κB activation. It inhibited ATRA-induced Sp1 and CREB (cAMP-response element-binding protein) DNA binding. Azadirachtin inhibited ATRA binding with retinoid receptors, which is supported by biochemical and in silico evidences. Azadirachtin showed strong interaction with retinoid receptors. It suppressed ATRA-mediated removal of retinoid receptors, bound with DNA by inhibiting ATRA binding to its receptors. Overall, our data suggest that azadirachtin interacts with retinoic acid receptors and suppresses ATRA binding, inhibits falling off the receptors, and activates transcription factors like CREB, Sp1, NF-κB, etc. Thus, azadirachtin exerts anti-inflammatory and anti-metastatic responses by a novel pathway that would be beneficial for further anti-inflammatory and anti-cancer therapies.

Noncoding somatic and inherited single-nucleotide variants converge to promote ESR1 expression in breast cancer.

PubMed

Bailey, Swneke D; Desai, Kinjal; Kron, Ken J; Mazrooei, Parisa; Sinnott-Armstrong, Nicholas A; Treloar, Aislinn E; Dowar, Mark; Thu, Kelsie L; Cescon, David W; Silvester, Jennifer; Yang, S Y Cindy; Wu, Xue; Pezo, Rossanna C; Haibe-Kains, Benjamin; Mak, Tak W; Bedard, Philippe L; Pugh, Trevor J; Sallari, Richard C; Lupien, Mathieu

2016-10-01

Sustained expression of the estrogen receptor-α (ESR1) drives two-thirds of breast cancer and defines the ESR1-positive subtype. ESR1 engages enhancers upon estrogen stimulation to establish an oncogenic expression program. Somatic copy number alterations involving the ESR1 gene occur in approximately 1% of ESR1-positive breast cancers, suggesting that other mechanisms underlie the persistent expression of ESR1. We report significant enrichment of somatic mutations within the set of regulatory elements (SRE) regulating ESR1 in 7% of ESR1-positive breast cancers. These mutations regulate ESR1 expression by modulating transcription factor binding to the DNA. The SRE includes a recurrently mutated enhancer whose activity is also affected by rs9383590, a functional inherited single-nucleotide variant (SNV) that accounts for several breast cancer risk-associated loci. Our work highlights the importance of considering the combinatorial activity of regulatory elements as a single unit to delineate the impact of noncoding genetic alterations on single genes in cancer.

Pharmacogenetics of Antidepressants

PubMed Central

Crisafulli, Concetta; Fabbri, Chiara; Porcelli, Stefano; Drago, Antonio; Spina, Edoardo; De Ronchi, Diana; Serretti, Alessandro

2010-01-01

Up to 60% of depressed patients do not respond completely to antidepressants (ADs) and up to 30% do not respond at all. Genetic factors contribute for about 50% of the AD response. During the recent years the possible influence of a set of candidate genes as genetic predictors of AD response efficacy was investigated by us and others. They include the cytochrome P450 superfamily, the P-glycoprotein (ABCB1), the tryptophan hydroxylase, the catechol-O-methyltransferase, the monoamine oxidase A, the serotonin transporter (5-HTTLPR), the norepinephrine transporter, the dopamine transporter, variants in the 5-hydroxytryptamine receptors (5-HT1A, 5-HT2A, 5-HT3A, 5-HT3B, and 5-HT6), adrenoreceptor beta-1 and alpha-2, the dopamine receptors (D2), the G protein beta 3 subunit, the corticotropin releasing hormone receptors (CRHR1 and CRHR2), the glucocorticoid receptors, the c-AMP response-element binding, and the brain-derived neurotrophic factor. Marginal associations were reported for angiotensin I converting enzyme, circadian locomotor output cycles kaput protein, glutamatergic system, nitric oxide synthase, and interleukin 1-beta gene. In conclusion, gene variants seem to influence human behavior, liability to disorders and treatment response. Nonetheless, gene × environment interactions have been hypothesized to modulate several of these effects. PMID:21687501

Characterization of the Binding Site of Aspartame in the Human Sweet Taste Receptor.

PubMed

Maillet, Emeline L; Cui, Meng; Jiang, Peihua; Mezei, Mihaly; Hecht, Elizabeth; Quijada, Jeniffer; Margolskee, Robert F; Osman, Roman; Max, Marianna

2015-10-01

The sweet taste receptor, a heterodimeric G protein-coupled receptor comprised of T1R2 and T1R3, binds sugars, small molecule sweeteners, and sweet proteins to multiple binding sites. The dipeptide sweetener, aspartame binds in the Venus Flytrap Module (VFTM) of T1R2. We developed homology models of the open and closed forms of human T1R2 and human T1R3 VFTMs and their dimers and then docked aspartame into the closed form of T1R2's VFTM. To test and refine the predictions of our model, we mutated various T1R2 VFTM residues, assayed activity of the mutants and identified 11 critical residues (S40, Y103, D142, S144, S165, S168, Y215, D278, E302, D307, and R383) in and proximal to the binding pocket of the sweet taste receptor that are important for ligand recognition and activity of aspartame. Furthermore, we propose that binding is dependent on 2 water molecules situated in the ligand pocket that bridge 2 carbonyl groups of aspartame to residues D142 and L279. These results shed light on the activation mechanism and how signal transmission arising from the extracellular domain of the T1R2 monomer of the sweet receptor leads to the perception of sweet taste. © The Author 2015. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Modulating the Intrinsic Disorder in the Cytoplasmic Domain Alters the Biological Activity of the N-Methyl-d-aspartate-sensitive Glutamate Receptor*

PubMed Central

Choi, Ucheor B.; Kazi, Rashek; Stenzoski, Natalie; Wollmuth, Lonnie P.; Uversky, Vladimir N.; Bowen, Mark E.

2013-01-01

The NMDA-sensitive glutamate receptor is a ligand-gated ion channel that mediates excitatory synaptic transmission in the nervous system. Extracellular zinc allosterically regulates the NMDA receptor by binding to the extracellular N-terminal domain, which inhibits channel gating. Phosphorylation of the intrinsically disordered intracellular C-terminal domain alleviates inhibition by extracellular zinc. The mechanism for this functional effect is largely unknown. Proline is a hallmark of intrinsic disorder, so we used proline mutagenesis to modulate disorder in the cytoplasmic domain. Proline depletion selectively uncoupled zinc inhibition with little effect on receptor biogenesis, surface trafficking, or ligand-activated gating. Proline depletion also reduced the affinity for a PDZ domain involved in synaptic trafficking and affected small molecule binding. To understand the origin of these phenomena, we used single molecule fluorescence and ensemble biophysical methods to characterize the structural effects of proline mutagenesis. Proline depletion did not eliminate intrinsic disorder, but the underlying conformational dynamics were changed. Thus, we altered the form of intrinsic disorder, which appears sufficient to affect the biological activity. These findings suggest that conformational dynamics within the intrinsically disordered cytoplasmic domain are important for the allosteric regulation of NMDA receptor gating. PMID:23782697

Functional role of the extracellular N-terminal domain of neuropeptide Y subfamily receptors in membrane integration and agonist-stimulated internalization.

PubMed

Lindner, Diana; Walther, Cornelia; Tennemann, Anja; Beck-Sickinger, Annette G

2009-01-01

The N terminus is the most variable element in G protein-coupled receptors (GPCRs), ranging from seven residues up to approximately 5900 residues. For family B and C GPCRs it is described that at least part of the ligand binding site is located within the N terminus. Here we investigated the role of the N terminus in the neuropeptide Y receptor family, which belongs to the class A of GPCRs. We cloned differentially truncated Y receptor mutants, in which the N terminus was partially or completely deleted. We found, that eight amino acids are sufficient for full ligand binding and signal transduction activity. Interestingly, we could show that no specific amino acids but rather the extension of the first transmembrane helix by any residues is sufficient for receptor activity but also for membrane integration in case of the hY(1) and the hY(4) receptors. In contrast, the complete deletion of the N terminus in the hY(2) receptors resulted in a mutant that is fully integrated in the membrane but does not bind the ligand very well and internalizes much slower compared to the wild type receptor. Interestingly, also these effects could be reverted by any N-terminal extension. Accordingly, the most important function of the N termini seems to be the stabilization of the first transmembrane helix to ensure the correct receptor structure, which obviously is essential for ligand binding, integration into the cell membrane and receptor internalization.

A Chemocentric Informatics Approach to Drug Discovery: Identification and Experimental Validation of Selective Estrogen Receptor Modulators as ligands of 5-Hydroxytryptamine-6 Receptors and as Potential Cognition Enhancers

PubMed Central

Hajjo, Rima; Setola, Vincent; Roth, Bryan L.; Tropsha, Alexander

2012-01-01

We have devised a chemocentric informatics methodology for drug discovery integrating independent approaches to mining biomolecular databases. As a proof of concept, we have searched for novel putative cognition enhancers. First, we generated Quantitative Structure- Activity Relationship (QSAR) models of compounds binding to 5-hydroxytryptamine-6 receptor (5HT6R), a known target for cognition enhancers, and employed these models for virtual screening to identify putative 5-HT6R actives. Second, we queried chemogenomics data from the Connectivity Map (http://www.broad.mit.edu/cmap/) with the gene expression profile signatures of Alzheimer’s disease patients to identify compounds putatively linked to the disease. Thirteen common hits were tested in 5-HT6R radioligand binding assays and ten were confirmed as actives. Four of them were known selective estrogen receptor modulators that were never reported as 5-HT6R ligands. Furthermore, nine of the confirmed actives were reported elsewhere to have memory-enhancing effects. The approaches discussed herein can be used broadly to identify novel drug-target-disease associations. PMID:22537153

Ligand-Receptor Interaction Modulates the Energy Landscape of Enzyme-Instructed Self-Assembly of Small Molecules.

PubMed

Haburcak, Richard; Shi, Junfeng; Du, Xuewen; Yuan, Dan; Xu, Bing

2016-11-30

The concurrence of enzymatic reaction and ligand-receptor interactions is common for proteins, but rare for small molecules and has yet to be explored. Here we show that ligand-receptor interaction modulates the morphology of molecular assemblies formed by enzyme-instructed assembly of small molecules. While the absence of ligand-receptor interaction allows enzymatic dephosphorylation of a precursor to generate the hydrogelator that self-assembles to form long nanofibers, the presence of the ligand-receptor interaction biases the pathway to form precipitous aggregates containing short nanofibers. While the hydrogelators self-assemble to form nanofibers or nanoribbons that are unable to bind with the ligand (i.e., vancomycin), the addition of surfactant breaks up the assemblies to restore the ligand-receptor interaction. In addition, an excess amount of the ligands can disrupt the nanofibers and result in the precipitates. As the first example of the use of ligand-receptor interaction to modulate the kinetics of enzymatic self-assembly, this work not only provides a solution to evaluate the interaction between aggregates and target molecules but also offers new insight for understanding the emergent behavior of sophisticated molecular systems having multiple and parallel processes.

Development of Selective Androgen Receptor Modulators (SARMs)

PubMed Central

Narayanan, Ramesh; Coss, Christopher C.; Dalton, James T.

2018-01-01

The Androgen Receptor (AR), a member of the steroid hormone receptor family, plays important roles in the physiology and pathology of diverse tissues. AR ligands, which include circulating testosterone and locally synthesized dihydrotestosterone, bind to and activate the AR to elicit their effects. Ubiquitous expression of the AR, metabolism and cross reactivity with other receptors limit broad therapeutic utilization of steroidal androgens. However, the discovery of selective androgen receptor modulators (SARMs) and other tissue-selective nuclear hormone receptor modulators that activate their cognate receptors in a tissue-selective manner provides an opportunity to promote the beneficial effects of androgens and other hormones in target tissues with greatly reduced unwanted side-effects. In the last two decades, significant resources have been dedicated to the discovery and biological characterization of SARMs in an effort to harness the untapped potential of the AR. SARMs have been proposed as treatments of choice for various diseases, including muscle-wasting, breast cancer, and osteoporosis. This review provides insight into the evolution of SARMs from proof-of-concept agents to the cusp of therapeutic use in less than two decades, while covering contemporary views of their mechanisms of action and therapeutic benefits. PMID:28624515

Mapping allosteric connections from the receptor to the nucleotide-binding pocket of heterotrimeric G proteins

PubMed Central

Oldham, William M.; Van Eps, Ned; Preininger, Anita M.; Hubbell, Wayne L.; Hamm, Heidi E.

2007-01-01

Heterotrimeric G proteins function as molecular relays that mediate signal transduction from heptahelical receptors in the cell membrane to intracellular effector proteins. Crystallographic studies have demonstrated that guanine nucleotide exchange on the Gα subunit causes specific conformational changes in three key “switch” regions of the protein, which regulate binding to Gβγ subunits, receptors, and effector proteins. In the present study, nitroxide side chains were introduced at sites within the switch I region of Gαi to explore the structure and dynamics of this region throughout the G protein cycle. EPR spectra obtained for each of the Gα(GDP), Gα(GDP)βγ heterotrimer and Gα(GTPγS) conformations are consistent with the local environment observed in the corresponding crystal structures. Binding of the heterotrimer to activated rhodopsin to form the nucleotide-free (empty) complex, for which there is no crystal structure, causes prominent changes relative to the heterotrimer in the structure of switch I and contiguous sequences. The data identify a putative pathway of allosteric changes triggered by receptor binding and, together with previously published data, suggest elements of a mechanism for receptor-catalyzed nucleotide exchange. PMID:17463080

Structure of a Potential Therapeutic Antibody Bound to Interleukin-16 (IL-16)

PubMed Central

Hall, Gareth; Cullen, Eilish; Sawmynaden, Kovilen; Arnold, Joanne; Fox, Simon; Cowan, Richard; Muskett, Frederick W.; Matthews, David; Merritt, Andrew; Kettleborough, Catherine; Cruikshank, William; Taylor, Debra; Bayliss, Richard; Carr, Mark D.

2016-01-01

Interleukin-16 (IL-16) is reported to be a chemoattractant cytokine and modulator of T-cell activation, and has been proposed as a ligand for the co-receptor CD4. The secreted active form of IL-16 has been detected at sites of TH1-mediated inflammation, such as those seen in autoimmune diseases, ischemic reperfusion injury (IRI), and tissue transplant rejection. Neutralization of IL-16 recruitment to its receptor, using an anti-IL16 antibody, has been shown to significantly attenuate inflammation and disease pathology in IRI, as well as in some autoimmune diseases. The 14.1 antibody is a monoclonal anti-IL-16 antibody, which when incubated with CD4+ cells is reported to cause a reduction in the TH1-type inflammatory response. Secreted IL-16 contains a characteristic PDZ domain. PDZ domains are typically characterized by a defined globular structure, along with a peptide-binding site located in a groove between the αB and βB structural elements and a highly conserved carboxylate-binding loop. In contrast to other reported PDZ domains, the solution structure previously reported for IL-16 reveals a tryptophan residue obscuring the recognition groove. We have solved the structure of the 14.1Fab fragment in complex with IL-16, revealing that binding of the antibody requires a conformational change in the IL-16 PDZ domain. This involves the rotation of the αB-helix, accompanied movement of the peptide groove obscuring tryptophan residue, and consequent opening up of the binding site for interaction. Our study reveals a surprising mechanism of action for the antibody and identifies new opportunities for the development of IL-16-targeted therapeutics, including small molecules that mimic the interaction of the antibody. PMID:27231345

Betaglycan expression is transcriptionally up-regulated during skeletal muscle differentiation. Cloning of murine betaglycan gene promoter and its modulation by MyoD, retinoic acid, and transforming growth factor-beta.

PubMed

Lopez-Casillas, Fernando; Riquelme, Cecilia; Perez-Kato, Yoshiaki; Ponce-Castaneda, M Veronica; Osses, Nelson; Esparza-Lopez, Jose; Gonzalez-Nunez, Gerardo; Cabello-Verrugio, Claudio; Mendoza, Valentin; Troncoso, Victor; Brandan, Enrique

2003-01-03

Betaglycan is a membrane-anchored proteoglycan co-receptor that binds transforming growth factor beta (TGF-beta) via its core protein and basic fibroblast growth factor through its glycosaminoglycan chains. In this study we evaluated the expression of betaglycan during the C(2)C(12) skeletal muscle differentiation. Betaglycan expression, as determined by Northern and Western blot, was up-regulated during the conversion of myoblasts to myotubes. The mouse betaglycan gene promoter was cloned, and its sequence showed putative binding sites for SP1, Smad3, Smad4, muscle regulatory factor elements such as MyoD and MEF2, and retinoic acid receptor. Transcriptional activity of the mouse betaglycan promoter reporter was also up-regulated in differentiating C(2)C(12) cells. We found that MyoD, but not myogenin, stimulated this transcriptional activity even in the presence of high serum. Betaglycan promoter activity was increased by RA and inhibited by the three isoforms of TGF-beta. On the other hand, basic fibroblast growth factor, BMP-2, and hepatocyte growth factor/scatter factor, which are inhibitors of myogenesis, had little effect. In myotubes, up-regulated betaglycan was also detectable by TGF-beta affinity labeling and immunofluorescence microscopy studies. The latter indicated that betaglycan was localized both on the cell surface and in the ECM. Forced expression of betaglycan in C(2)C(12) myoblasts increases their responsiveness to TGF-beta2, suggesting that it performs a TGF-beta presentation function in this cell lineage. These results indicate that betaglycan expression is up-regulated during myogenesis and that MyoD and RA modulate its expression by a mechanism that is independent of myogenin.

Crystal structures of the M 1 and M 4 muscarinic acetylcholine receptors

DOE PAGES

Thal, David M.; Sun, Bingfa; Feng, Dan; ...

2016-03-09

Muscarinic M1–M5 acetylcholine receptors are G-protein-coupled receptors that regulate many vital functions of the central and peripheral nervous systems. In particular, the M1 and M4 receptor subtypes have emerged as attractive drug targets for treatments of neurological disorders, such as Alzheimer’s disease and schizophrenia, but the high conservation of the acetylcholine-binding pocket has spurred current research into targeting allosteric sites on these receptors. In this paper, we report the crystal structures of the M1 and M4 muscarinic receptors bound to the inverse agonist, tiotropium. Comparison of these structures with each other, as well as with the previously reported M2 andmore » M3 receptor structures, reveals differences in the orthosteric and allosteric binding sites that contribute to a role in drug selectivity at this important receptor family. Finally, we also report identification of a cluster of residues that form a network linking the orthosteric and allosteric sites of the M4 receptor, which provides new insight into how allosteric modulation may be transmitted between the two spatially distinct domains.« less

Crystal structures of the M 1 and M 4 muscarinic acetylcholine receptors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thal, David M.; Sun, Bingfa; Feng, Dan

Muscarinic M1–M5 acetylcholine receptors are G-protein-coupled receptors that regulate many vital functions of the central and peripheral nervous systems. In particular, the M1 and M4 receptor subtypes have emerged as attractive drug targets for treatments of neurological disorders, such as Alzheimer’s disease and schizophrenia, but the high conservation of the acetylcholine-binding pocket has spurred current research into targeting allosteric sites on these receptors. In this paper, we report the crystal structures of the M1 and M4 muscarinic receptors bound to the inverse agonist, tiotropium. Comparison of these structures with each other, as well as with the previously reported M2 andmore » M3 receptor structures, reveals differences in the orthosteric and allosteric binding sites that contribute to a role in drug selectivity at this important receptor family. Finally, we also report identification of a cluster of residues that form a network linking the orthosteric and allosteric sites of the M4 receptor, which provides new insight into how allosteric modulation may be transmitted between the two spatially distinct domains.« less

Anion-induced reconstitution of a self-assembling system to express a chloride-binding Co10L15 pentagonal prism.

PubMed

Riddell, Imogen A; Smulders, Maarten M J; Clegg, Jack K; Hristova, Yana R; Breiner, Boris; Thoburn, John D; Nitschke, Jonathan R

2012-09-01

Biochemical systems are adaptable, capable of reconstitution at all levels to achieve the functions associated with life. Synthetic chemical systems are more limited in their ability to reorganize to achieve new functions; they can reconfigure to bind an added substrate (template effect) or one binding event may modulate a receptor's affinity for a second substrate (allosteric effect). Here we describe a synthetic chemical system that is capable of structural reconstitution on receipt of one anionic signal (perchlorate) to create a tight binding pocket for another anion (chloride). The complex, barrel-like structure of the chloride receptor is templated by five perchlorate anions. This second-order templation phenomenon allows chemical networks to be envisaged that express more complex responses to chemical signals than is currently feasible.

Characterization of opiates, neuroleptics, and synthetic analogs at ORL1 and opioid receptors

PubMed Central

Zaveri, Nurulain; Polgar, Willma E.; Olsen, Cris M.; Kelson, Andrew B.; Grundt, Peter; Lewis, John W.; Toll, Lawrence

2013-01-01

Nociceptin/orphanin FQ (N/OFQ) was recently identified as the endogenous ligand for the opioid-receptor like (ORL1) receptor. Although the ORL1 receptor shows sequence homology with the opioid receptors, the nociceptin/ORL1 ligand–receptor system has very distinct pharmacological actions compared to the opioid receptor system. Recently, several small-molecule ORL1 receptor ligands were reported by pharmaceutical companies. Most of these ligands had close structural similarities with known neuroleptics and opiates. In this study, we screened several available neuroleptics and opiates for their binding affinity and functional activity at ORL1 and the opioid receptors. We also synthesized several analogs of known opiates with modified piperidine N-substituents in order to characterize the ORL1 receptor ligand binding pocket. Substitution with the large, lipophilic cyclooctylmethyl moiety increased ORL1 receptor affinity and decreased μ receptor affinity and efficacy in the fentanyl series of ligands but had a different effect in the oripavine class of opiate ligands. Our results indicate that opiates and neuroleptics may be good starting points for ORL1 receptor ligand design, and the selectivity may be modulated by appropriate structural modifications. PMID:11779034

Novel series of potent, nonsteroidal, selective androgen receptor modulators based on 7H-[1,4]oxazino[3,2-g]quinolin-7-ones.

PubMed

Higuchi, Robert I; Arienti, Kristen L; López, Francisco J; Mani, Neelakhanda S; Mais, Dale E; Caferro, Thomas R; Long, Yun Oliver; Jones, Todd K; Edwards, James P; Zhi, Lin; Schrader, William T; Negro-Vilar, Andrés; Marschke, Keith B

2007-05-17

Recent interest in orally available androgens has fueled the search for new androgens for use in hormone replacement therapy and as anabolic agents. In pursuit of this, we have discovered a series of novel androgen receptor modulators derived from 7H-[1,4]oxazino[3,2-g]quinolin-7-ones. These compounds were synthesized and evaluated in competitive binding assays and an androgen receptor transcriptional activation assay. A number of compounds from the series demonstrated single-digit nanomolar agonist activity in vitro. In addition, lead compound (R)-16e was orally active in established rodent models that measure androgenic and anabolic properties of these agents. In this assay, (R)-16e demonstrated full efficacy in muscle and only partially stimulated the prostate at 100 mg/kg. These data suggest that these compounds may be utilized as selective androgen receptor modulators or SARMs. This series represents a novel class of compounds for use in androgen replacement therapy.

Hormone induces binding of receptors and transcription factors to a rearranged nucleosome on the MMTV promoter in vivo.

PubMed Central

Truss, M; Bartsch, J; Schelbert, A; Haché, R J; Beato, M

1995-01-01

Hormonal induction of the mouse mammary tumour virus (MMTV) promoter is mediated by interactions between hormone receptors and other transcription factors bound to a complex array of sites. Previous results suggested that access to these sites is modulated by their precise organization into a positioned regulatory nucleosome. Using genomic footprinting, we show that MMTV promoter DNA is rotationally phased in intact cells containing either episomal or chromosomally integrated proviral fragments. Prior to induction there is no evidence for factors bound to the promoter. Following progesterone induction of cells with high levels of receptor, genomic footprinting detects simultaneous protection over the binding sites for hormone receptors, NF-I and the octamer binding proteins. Glucocorticoid or progestin induction leads to a characteristic chromatin remodelling that is independent of ongoing transcription. The centre of the regulatory nucleosome becomes more accessible to DNase I and restriction enzymes, but the limits of the nucleosome are unchanged and the 145 bp core region remains protected against micrococcal nuclease digestion. Thus, the nucleosome covering the MMTV promoter is neither removed nor shifted upon hormone induction, and all relevant transcription factors bind to the surface of the rearranged nucleosome. Since these factors cannot bind simultaneously to free DNA, maintainance of the nucleosome may be required for binding of factors to contiguous sites. Images PMID:7737125

Selective androgen receptor modulators as function promoting therapies.

PubMed

Bhasin, Shalender; Jasuja, Ravi

2009-05-01

The past decade has witnessed an unprecedented discovery effort to develop selective androgen receptor modulators (SARMs) that improve physical function and bone health without adversely affecting the prostate and cardiovascular outcomes. This review describes the historical evolution, the rationale for SARM development, and the mechanisms of testosterone action and SARM selectivity. Although steroidal SARMs have been around since the 1940s, a number of nonsteroidal SARMs that do not serve as substrates for CYP19 aromatase or 5alpha-reductase, act as full agonists in muscle and bone and as partial agonists in prostate are in development. The differing interactions of steroidal and nonsteroidal compounds with androgen receptor (AR) contribute to their unique pharmacologic actions. Ligand binding induces specific conformational changes in the ligand-binding domain, which could modulate surface topology and protein-protein interactions between AR and coregulators, resulting in tissue-specific gene regulation. Preclinical studies have demonstrated the ability of SARMs to increase muscle and bone mass in preclinical rodent models with varying degree of prostate sparing. Phase I trials of SARMs in humans have reported modest increments in fat-free mass. SARMs hold promise as a new class of function promoting anabolic therapies for a number of clinical indications, including functional limitations associated with aging and chronic disease, frailty, cancer cachexia, and osteoporosis.

Modulation of basal and stress-induced amygdaloid substance P release by the potent and selective NK1 receptor antagonist L-822429.

PubMed

Singewald, Nicolas; Chicchi, Gary G; Thurner, Clemens C; Tsao, Kwei-Lan; Spetea, Mariana; Schmidhammer, Helmut; Sreepathi, Hari Kishore; Ferraguti, Francesco; Singewald, Georg M; Ebner, Karl

2008-09-01

It has been shown that anxiety and stress responses are modulated by substance P (SP) released within the amygdala. However, there is an important gap in our knowledge concerning the mechanisms regulating extracellular SP in this brain region. To study a possible self-regulating role of SP, we used a selective neurokinin-1 (NK1) receptor antagonist to investigate whether blockade of NK1 receptors results in altered basal and/or stress-evoked SP release in the medial amygdala (MeA), a critical brain area for a functional involvement of SP transmission in enhanced anxiety responses induced by stressor exposure. In vitro binding and functional receptor assays revealed that L-822429 represents a potent and selective rat NK1 receptor antagonist. Intra-amygdaloid administration of L-822429 via inverse microdialysis enhanced basal, but attenuated swim stress-induced SP release, while the low-affinity enantiomer of L-822429 had no effect. Using light and electron microscopy, synaptic contacts between SP-containing fibres and dendrites expressing NK1 receptors was demonstrated in the medial amygdala. Our findings suggest self-regulatory capacity of SP-mediated neurotransmission that differs in the effect on basal and stress-induced release of SP. Under basal conditions endogenous SP can serve as a signal that tonically inhibits its own release via a NK1 receptor-mediated negative feedback action, while under stress conditions SP release is further facilitated by activation of NK1 receptors, likely leading to high local levels of SP and activation of receptors to which SP binds with lower affinity.

Allosteric modulation of sigma-1 receptors elicits anti-seizure activities.

PubMed

Guo, Lin; Chen, Yanke; Zhao, Rui; Wang, Guanghui; Friedman, Eitan; Zhang, Ao; Zhen, Xuechu

2015-08-01

Application of orthosteric sigma-1 receptor agonists as anti-seizure drugs has been hindered by questionable efficacy and potential adverse effects. Here, we have investigated the anti-seizure effects of the novel and potent allosteric modulator of sigma-1 receptors, SKF83959 and its derivative SOMCL-668 (3-methyl-phenyl-2,3,4,5-tetrahydro-1H-benzo[d]azepin-7-ol). The anti-seizure effects of SKF83959 were investigated in three mouse models, maximal electroshock seizures, pentylenetetrazole-induced convulsions and kainic acid-induced 'status epilepticus'. Also, in rats, the cortical epileptiform activity induced by topical application of picrotoxin was recorded in electrocorticograms. In rat hippocampal brain slices, effects of the drugs on the high potassium-evoked epileptiform local field potentials were studied. Anti-seizure activities of SOMCL-668, a newly developed sigma-1 receptor selective allosteric modulator, were also investigated. SKF83959 (20, 40 mg·kg(-1) ) exhibited anti -seizure actitity in the three mouse models and reduced the cortical epileptiform activity without alteration of spontaneous motor activity and motor coordination. These effects were blocked by the sigma-1 receptor antagonist BD1047, but not the dopamine D1 receptor antagonist SCH23390. SKF83959 alone did not directly inhibit the epileptiform firing of CA3 neurons induced by high potassium in hippocampal slices, but did potentiate inhibition by the orthosteric sigma-1 receptor agonist SKF10047. Lastly, a selective sigma-1 receptor allosteric modulator SOMCL-668, which does not bind to dopamine receptors, exerted similar anti-seizure activities. SKF83959 and SOMCL-668 displayed anti-seizure activities, indicating that allosteric modulation of sigma-1 receptors may provide a novel approach for discovering new anti-seizure drugs. © 2015 The British Pharmacological Society.

Spatial biomarker of disease and detection of spatial organization of cellular receptors

DOEpatents

Salaita, Khalid S.; Nair, Pradeep M.; Das, Debopriya; Gray, Joe W.; Groves, John T.

2017-07-18

A signature of a condition of a live cell is established in an assay that allows distribution of the receptors on the cell surface in response to binding a ligand. The receptors can be optically detected and quantified to provide a value for the condition, Test drugs can be screened for therapeutic potential in the assay: a potentially efficacious drug is identified by an ability to modulate an established signature. The receptor distribution signature can be corroborated with an mRNA expression profile of several genes, indicating, for example, metastasis.

Adenosine A2B receptor: from cell biology to human diseases

NASA Astrophysics Data System (ADS)

Sun, Ying; Huang, Pingbo

2016-08-01

Extracellular adenosine is a ubiquitous signaling molecule that modulates a wide array of biological processes. Recently, significant advances have been made in our understanding of A2B adenosine receptor (A2BAR). In this review, we first summarize some of the general characteristics of A2BAR, and then we describe the multiple binding partners of the receptor, such as newly identified α-actinin-1 and p105, and discuss how these associated proteins could modulate A2BAR’s functions, including certain seemingly paradoxical functions of the receptor. Growing evidence indicates a critical role of A2BAR in cancer, renal disease, and diabetes, in addition to its importance in the regulation of vascular diseases and lung disease. Here, we also discuss the role of A2BAR in cancer, renal disease, and diabetes and the potential of the receptor as a target for treating these three diseases.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zweifel,M.; Leahy, D.; Barrick, D.

Deltex is a cytosolic effector of Notch signaling thought to bind through its N-terminal domain to the Notch receptor. Here we report the structure of the Drosophila Deltex N-terminal domain, which contains two tandem WWE sequence repeats. The WWE repeats, which adopt a novel fold, are related by an approximate two-fold axis of rotation. Although the WWE repeats are structurally distinct, they interact extensively and form a deep cleft at their junction that appears well suited for ligand binding. The two repeats are thermodynamically coupled; this coupling is mediated in part by a conserved segment that is immediately C-terminal tomore » the second WWE domain. We demonstrate that although the Deltex WWE tandem is monomeric in solution, it forms a heterodimer with the ankyrin domain of the Notch receptor. These results provide structural and functional insight into how Deltex modulates Notch signaling, and how WWE modules recognize targets for ubiquitination.« less

Mapping General Anesthetic Sites in Heteromeric γ-Aminobutyric Acid Type A Receptors Reveals a Potential For Targeting Receptor Subtypes.

PubMed

Forman, Stuart A; Miller, Keith W

2016-11-01

IV general anesthetics, including propofol, etomidate, alphaxalone, and barbiturates, produce important actions by enhancing γ-aminobutyric acid type A (GABAA) receptor activation. In this article, we review scientific studies that have located and mapped IV anesthetic sites using photoaffinity labeling and substituted cysteine modification protection. These anesthetics bind in transmembrane pockets between subunits of typical synaptic GABAA receptors, and drugs that display stereoselectivity also show remarkably selective interactions with distinct interfacial sites. These results suggest strategies for developing new drugs that selectively modulate distinct GABAA receptor subtypes.

Identification of an estrogen response element in the 3'-flanking region of the murine c-fos protooncogene.

PubMed

Hyder, S M; Stancel, G M; Nawaz, Z; McDonnell, D P; Loose-Mitchell, D S

1992-09-05

We have used transient transfection assays with reporter plasmids expressing chloramphenicol acetyltransferase, linked to regions of mouse c-fos, to identify a specific estrogen response element (ERE) in this protooncogene. This element is located in the untranslated 3'-flanking region of the c-fos gene, 5 kilobases (kb) downstream from the c-fos promoter and 1.5 kb downstream of the poly(A) signal. This element confers estrogen responsiveness to chloramphenicol acetyltransferase reporters linked to both the herpes simplex virus thymidine kinase promoter and the homologous c-fos promoter. Deletion analysis localized the response element to a 200-base pair fragment which contains the element GGTCACCACAGCC that resembles the consensus ERE sequence GGTCACAGTGACC originally identified in Xenopus vitellogenin A2 gene. A synthetic 36-base pair oligodeoxynucleotide containing this c-fos sequence conferred estrogen inducibility to the thymidine kinase promoter. The corresponding sequence also induced reporter activity when present in the c-fos gene fragment 3 kb from the thymidine kinase promoter. Gel-shift experiments demonstrated that synthetic oligonucleotides containing either the consensus ERE or the c-fos element bind human estrogen receptor obtained from a yeast expression system. However, the mobility of the shifted band is faster for the fos-ERE-complex than the consensus ERE complex suggesting that the three-dimensional structure of the protein-DNA complexes is different or that other factors are differentially involved in the two reactions. When the 5'-GGTCA sequence present in the c-fos ERE is mutated to 5'-TTTCA, transcriptional activation and receptor binding activities are both lost. Mutation of the CAGCC-3' element corresponding to the second half-site of the c-fos sequence also led to the loss of receptor binding activity, suggesting that both half-sites of this element are involved in this function. The estrogen induction mediated by either the c-fos or the consensus ERE was blunted by the antiestrogen tamoxifen. Based on these studies, we believe the 3'-fos ERE sequence we have identified may be a major cis-acting element involved in the physiological regulation of the gene by estrogens in vivo.

Intramolecular co-action of two independent photosensory modules in the fern phytochrome 3.

PubMed

Kanegae, Takeshi

2015-01-01

Fern phytochrome3/neochrome1 (phy3/neo1) is a chimeric photoreceptor composed of a phytochrome-chromophore binding domain and an almost full-length phototropin. phy3 thus contains two different light-sensing modules; a red/far-red light receptor phytochrome and a blue light receptor phototropin. phy3 induces both red light- and blue light-dependent phototropism in phototropin-deficient Arabidopsis thaliana (phot1 phot2) seedlings. The red-light response is dependent on the phytochrome module of phy3, and the blue-light response is dependent on the phototropin module. We recently showed that both the phototropin-sensing module and the phytochrome-sensing module mediate the blue light-dependent phototropic response. Particularly under low-light conditions, these two light-sensing modules cooperate to induce the blue light-dependent phototropic response. This intramolecular co-action of two independent light-sensing modules in phy3 enhances light sensitivity, and perhaps allowed ferns to adapt to the low-light canopy conditions present in angiosperm forests.

Two classes of cholesterol binding sites for the β2AR revealed by thermostability and NMR.

PubMed

Gater, Deborah L; Saurel, Olivier; Iordanov, Iordan; Liu, Wei; Cherezov, Vadim; Milon, Alain

2014-11-18

Cholesterol binding to G protein-coupled receptors (GPCRs) and modulation of their activities in membranes is a fundamental issue for understanding their function. Despite the identification of cholesterol binding sites in high-resolution x-ray structures of the ?2 adrenergic receptor (β2AR) and other GPCRs, the binding affinity of cholesterol for this receptor and exchange rates between the free and bound cholesterol remain unknown. In this study we report the existence of two classes of cholesterol binding sites in β2AR. By analyzing the β2AR unfolding temperature in lipidic cubic phase (LCP) as a function of cholesterol concentration we observed high-affinity cooperative binding of cholesterol with sub-nM affinity constant. In contrast, saturation transfer difference (STD) NMR experiments revealed the existence of a second class of cholesterol binding sites, in fast exchange on the STD NMR timescale. Titration of the STD signal as a function of cholesterol concentration provided a lower limit of 100 mM for their dissociation constant. However, these binding sites are specific for both cholesterol and β2AR, as shown with control experiments using ergosterol and a control membrane protein (KpOmpA). We postulate that this specificity is mediated by the high-affinity bound cholesterol molecules and propose the formation of transient cholesterol clusters around the high-affinity binding sites.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Sungsoo, E-mail: sungsoo.lee@utsouthwestern.edu; Wang, Ping-Yuan; Jeong, Yangsik

Oxysterol binding protein related protein 1S (ORP1S) is a member of a family of sterol transport proteins. Here we present evidence that ORP1S translocates from the cytoplasm to the nucleus in response to sterol binding. The sterols that best promote nuclear import of ORP1S also activate the liver X receptor (LXR) transcription factors and we show that ORP1S binds to LXRs, promotes binding of LXRs to LXR response elements (LXREs) and specifically enhances LXR-dependent transcription via the ME.1 and ME.2 enhancer elements of the apoE gene. We propose that ORP1S is a cytoplasmic sterol sensor, which transports sterols to themore » nucleus and promotes LXR-dependent gene transcription through select enhancer elements. -- Highlights: Black-Right-Pointing-Pointer ORP1S translocates to the nucleus in response to sterol binding. Black-Right-Pointing-Pointer The sterols that best promote nuclear import of ORP1S are LXR agonists. Black-Right-Pointing-Pointer ORP1S binds to LXRs, enhances binding of LXRs to LXREs and promotes LXR-dependent transcription of apoE.« less

Sensitivity of immune response quality to influenza helix 190 antigen structure displayed on a modular virus-like particle.

PubMed

Anggraeni, Melisa R; Connors, Natalie K; Wu, Yang; Chuan, Yap P; Lua, Linda H L; Middelberg, Anton P J

2013-09-13

Biomolecular engineering enables synthesis of improved proteins through synergistic fusion of modules from unrelated biomolecules. Modularization of peptide antigen from an unrelated pathogen for presentation on a modular virus-like particle (VLP) represents a new and promising approach to synthesize safe and efficacious vaccines. Addressing a key knowledge gap in modular VLP engineering, this study investigates the underlying fundamentals affecting the ability of induced antibodies to recognize the native pathogen. Specifically, this quality of immune response is correlated to the peptide antigen module structure. We modularized a helical peptide antigen element, helix 190 (H190) from the influenza hemagglutinin (HA) receptor binding region, for presentation on murine polyomavirus VLP, using two strategies aimed to promote H190 helicity on the VLP. In the first strategy, H190 was flanked by GCN4 structure-promoting elements within the antigen module; in the second, dual H190 copies were arrayed as tandem repeats in the module. Molecular dynamics simulation predicted that tandem repeat arraying would minimize secondary structural deviation of modularized H190 from its native conformation. In vivo testing supported this finding, showing that although both modularization strategies conferred high H190-specific immunogenicity, tandem repeat arraying of H190 led to a strikingly higher immune response quality, as measured by ability to generate antibodies recognizing a recombinant HA domain and split influenza virion. These findings provide new insights into the rational engineering of VLP vaccines, and could ultimately enable safe and efficacious vaccine design as an alternative to conventional approaches necessitating pathogen cultivation. Copyright © 2013 Elsevier Ltd. All rights reserved.

Identification of an allosteric binding site for RORγt inhibition

PubMed Central

Scheepstra, Marcel; Leysen, Seppe; van Almen, Geert C.; Miller, J. Richard; Piesvaux, Jennifer; Kutilek, Victoria; van Eenennaam, Hans; Zhang, Hongjun; Barr, Kenneth; Nagpal, Sunil; Soisson, Stephen M.; Kornienko, Maria; Wiley, Kristen; Elsen, Nathaniel; Sharma, Sujata; Correll, Craig C.; Trotter, B. Wesley; van der Stelt, Mario; Oubrie, Arthur; Ottmann, Christian; Parthasarathy, Gopal; Brunsveld, Luc

2015-01-01

RORγt is critical for the differentiation and proliferation of Th17 cells associated with several chronic autoimmune diseases. We report the discovery of a novel allosteric binding site on the nuclear receptor RORγt. Co-crystallization of the ligand binding domain (LBD) of RORγt with a series of small-molecule antagonists demonstrates occupancy of a previously unreported allosteric binding pocket. Binding at this non-canonical site induces an unprecedented conformational reorientation of helix 12 in the RORγt LBD, which blocks cofactor binding. The functional consequence of this allosteric ligand-mediated conformation is inhibition of function as evidenced by both biochemical and cellular studies. RORγt function is thus antagonized in a manner molecularly distinct from that of previously described orthosteric RORγt ligands. This brings forward an approach to target RORγt for the treatment of Th17-mediated autoimmune diseases. The elucidation of an unprecedented modality of pharmacological antagonism establishes a mechanism for modulation of nuclear receptors. PMID:26640126

Insights into distinct modulation of α7 and α7β2 nicotinic acetylcholine receptors by the volatile anesthetic isoflurane.

PubMed

Mowrey, David D; Liu, Qiang; Bondarenko, Vasyl; Chen, Qiang; Seyoum, Edom; Xu, Yan; Wu, Jie; Tang, Pei

2013-12-13

Nicotinic acetylcholine receptors (nAChRs) are targets of general anesthetics, but functional sensitivity to anesthetic inhibition varies dramatically among different subtypes of nAChRs. Potential causes underlying different functional responses to anesthetics remain elusive. Here we show that in contrast to the α7 nAChR, the α7β2 nAChR is highly susceptible to inhibition by the volatile anesthetic isoflurane in electrophysiology measurements. Isoflurane-binding sites in β2 and α7 were found at the extracellular and intracellular end of their respective transmembrane domains using NMR. Functional relevance of the identified β2 site was validated via point mutations and subsequent functional measurements. Consistent with their functional responses to isoflurane, β2 but not α7 showed pronounced dynamics changes, particularly for the channel gate residue Leu-249(9'). These results suggest that anesthetic binding alone is not sufficient to generate functional impact; only those sites that can modulate channel dynamics upon anesthetic binding will produce functional effects.

Estrogen receptor coregulator binding modulators (ERXs) effectively target estrogen receptor positive human breast cancers

PubMed Central

Raj, Ganesh V; Sareddy, Gangadhara Reddy; Ma, Shihong; Lee, Tae-Kyung; Viswanadhapalli, Suryavathi; Li, Rui; Liu, Xihui; Murakami, Shino; Chen, Chien-Cheng; Lee, Wan-Ru; Mann, Monica; Krishnan, Samaya Rajeshwari; Manandhar, Bikash; Gonugunta, Vijay K; Strand, Douglas; Tekmal, Rajeshwar Rao; Ahn, Jung-Mo; Vadlamudi, Ratna K

2017-01-01

The majority of human breast cancer is estrogen receptor alpha (ER) positive. While anti-estrogens/aromatase inhibitors are initially effective, resistance to these drugs commonly develops. Therapy-resistant tumors often retain ER signaling, via interaction with critical oncogenic coregulator proteins. To address these mechanisms of resistance, we have developed a novel ER coregulator binding modulator, ERX-11. ERX-11 interacts directly with ER and blocks the interaction between a subset of coregulators with both native and mutant forms of ER. ERX-11 effectively blocks ER-mediated oncogenic signaling and has potent anti-proliferative activity against therapy-sensitive and therapy-resistant human breast cancer cells. ERX-11 is orally bioavailable, with no overt signs of toxicity and potent activity in both murine xenograft and patient-derived breast tumor explant models. This first-in-class agent, with its novel mechanism of action of disrupting critical protein-protein interactions, overcomes the limitations of current therapies and may be clinically translatable for patients with therapy-sensitive and therapy-resistant breast cancers. DOI: http://dx.doi.org/10.7554/eLife.26857.001 PMID:28786813

Dynamics and allostery of the ionotropic glutamate receptors and the ligand binding domain.

PubMed

Tobi, Dror

2016-02-01

The dynamics of the ligand-binding domain (LBD) and the intact ionotropic glutamate receptor (iGluR) were studied using Gaussian Network Model (GNM) analysis. The dynamics of LBDs with various allosteric modulators is compared using a novel method of multiple alignment of GNM modes of motion. The analysis reveals that allosteric effectors change the dynamics of amino acids at the upper lobe interface of the LBD dimer as well as at the hinge region between the upper- and lower- lobes. For the intact glutamate receptor the analysis show that the clamshell-like movement of the LBD upper and lower lobes is coupled to the bending of the trans-membrane domain (TMD) helices which may open the channel pore. The results offer a new insight on the mechanism of action of allosteric modulators on the iGluR and support the notion of TMD helices bending as a possible mechanism for channel opening. In addition, the study validates the methodology of multiple GNM modes alignment as a useful tool to study allosteric effect and its relation to proteins dynamics. © 2015 Wiley Periodicals, Inc.

Dibutyltin Disrupts Glucocorticoid Receptor Function and Impairs Glucocorticoid-Induced Suppression of Cytokine Production

PubMed Central

Gumy, Christel; Chandsawangbhuwana, Charlie; Dzyakanchuk, Anna A.; Kratschmar, Denise V.; Baker, Michael E.; Odermatt, Alex

2008-01-01

Background Organotins are highly toxic and widely distributed environmental chemicals. Dibutyltin (DBT) is used as stabilizer in the production of polyvinyl chloride plastics, and it is also the major metabolite formed from tributyltin (TBT) in vivo. DBT is immunotoxic, however, the responsible targets remain to be defined. Due to the importance of glucocorticoids in immune-modulation, we investigated whether DBT could interfere with glucocorticoid receptor (GR) function. Methodology We used HEK-293 cells transiently transfected with human GR as well as rat H4IIE hepatoma cells and native human macrophages and human THP-1 macrophages expressing endogenous receptor to study organotin effects on GR function. Docking of organotins was used to investigate the binding mechanism. Principal Findings We found that nanomolar concentrations of DBT, but not other organotins tested, inhibit ligand binding to GR and its transcriptional activity. Docking analysis indicated that DBT inhibits GR activation allosterically by inserting into a site close to the steroid-binding pocket, which disrupts a key interaction between the A-ring of the glucocorticoid and the GR. DBT inhibited glucocorticoid-induced expression of phosphoenolpyruvate carboxykinase (PEPCK) and tyrosine-aminotransferase (TAT) and abolished the glucocorticoid-mediated transrepression of TNF-α-induced NF-κB activity. Moreover, DBT abrogated the glucocorticoid-mediated suppression of interleukin-6 (IL-6) and TNF-α production in lipopolysaccharide (LPS)-stimulated native human macrophages and human THP-1 macrophages. Conclusions DBT inhibits ligand binding to GR and subsequent activation of the receptor. By blocking GR activation, DBT may disturb metabolic functions and modulation of the immune system, providing an explanation for some of the toxic effects of this organotin. PMID:18958157

Does anesthetic additivity imply a similar molecular mechanism of anesthetic action at N-methyl-D-aspartate receptors?

PubMed

Brosnan, Robert J; Pham, Trung L

2011-03-01

Isoflurane and carbon dioxide (CO(2)) negatively modulate N-methyl-d-aspartate (NMDA) receptors, but via different mechanisms. Isoflurane is a competitive antagonist at the NMDA receptor glycine binding site, whereas CO(2) inhibits NMDA receptor current through extracellular acidification. Isoflurane and CO(2) exhibit additive minimum alveolar concentration effects in rats, but we hypothesized that they would not additively inhibit NMDA receptor currents in vitro because they act at different molecular sites. NMDA receptors were expressed in frog oocytes and studied using 2-electrode voltage clamp techniques. A glycine concentration response for NMDA was measured in the presence and absence of CO(2). Concentration-response curves for isoflurane, H(+), CO(2), and ketamine as a function of NMDA inhibition were measured, and a Hill equation was used to calculate the EC(50) for each compound. Binary drug combinations containing ½ EC(50) were additive if NMDA current inhibition was not statistically different from 50%. The ½ EC(50) binary drug combinations decreased the percentage baseline NMDA receptor current as follows (mean ± SD, n = 5 to 6 oocytes each): CO(2)+ H(+) (51% ± 5%), CO(2 )+ isoflurane (54% ± 5%), H(+) + isoflurane (51% ± 3%), CO(2)+ ketamine (67% ± 8%), and H(+) + ketamine (64% ± 2%). In contrast to our hypothesis, NMDA receptor inhibition by CO(2) and isoflurane is additive. Possibly, CO(2) acidification modulates a pH-sensitive loop on the NMDA receptor that in turn alters glycine binding affinity on the GluN1 subunit. However, ketamine plus either CO(2) or H(+) synergistically inhibits NMDA receptor currents. Drugs acting via different mechanisms can thus exhibit additive or synergistic receptor effects. Additivity may not robustly indicate commonality between molecular anesthetic mechanisms.

Ligand-activated PPARδ upregulates α-smooth muscle actin expression in human dermal fibroblasts: A potential role for PPARδ in wound healing.

PubMed

Ham, Sun Ah; Hwang, Jung Seok; Yoo, Taesik; Lee, Won Jin; Paek, Kyung Shin; Oh, Jae-Wook; Park, Chan-Kyu; Kim, Jin-Hoi; Do, Jung Tae; Kim, Jae-Hwan; Seo, Han Geuk

2015-12-01

The phenotypic changes that accompany differentiation of resident fibroblasts into myofibroblasts are important aspects of the wound healing process. Recent studies showed that peroxisome proliferator-activated receptor (PPAR) δ plays a critical role in wound healing. To determine whether the nuclear receptor PPARδ can modulate the differentiation of human dermal fibroblasts (HDFs) into myofibroblasts. These studies were undertaken in primary HDFs using Western blot analyses, small interfering (si)RNA-mediated gene silencing, reporter gene assays, chromatin immunoprecipitation (ChIP), migration assays, collagen gel contraction assays, and real-time PCR. Activation of PPARδ by GW501516, a specific ligand of PPARδ, specifically upregulated the myofibroblast marker α-smooth muscle actin (α-SMA) in a time- and concentration-dependent manner. This induction was significantly inhibited by the presence of siRNA against PPARδ, indicating that PPARδ is involved in myofibroblast transdifferentiation of HDFs. Ligand-activated PPARδ increased α-SMA promoter activity in a dual mode by directly binding a direct repeat-1 (DR1) site in the α-SMA promoter, and by inducing expression of transforming growth factor (TGF)-β, whose downstream effector Smad3 interacts with a Smad-binding element (SBE) in another region of the promoter. Mutations in these cis-elements totally abrogated transcriptional activation of the α-SMA gene by the PPARδ ligand; thus both sites represent novel types of PPARδ response elements. GW501516-activated PPARδ also increased the migration and contractile properties of HDFs, as demonstrated by Transwell and collagen lattice contraction assays, respectively. In addition, PPARδ-mediated upregulation of α-SMA was correlated with elevated expression of myofibroblast markers such as collagen I and fibronectin, with a concomitant reduction in expression of the epithelial marker E-cadherin. PPARδ plays pivotal roles in wound healing by promoting fibroblast-to-myofibroblast differentiation via TGF-β/Smad3 signaling. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

The PROGINS polymorphism of the human progesterone receptor diminishes the response to progesterone.

PubMed

Romano, Andrea; Delvoux, Bert; Fischer, Dagmar-Christiane; Groothuis, Patrick

2007-02-01

The human progesterone receptor (PR) is a ligand-dependent transcription factor and two isoforms, (PRA and PRB), can be distinguished. PROGINS, a PR polymorphic variant, affects PRA and PRB and acts as a risk-modulating factor in several gynaecological disorders. Little is known about the functional consequences of this variant. Here, we characterise the properties of PROGINS with respect to transcription, mRNA maturation, protein activity and proliferation. PROGINS is characterised by a 320 bp PV/HS-1 Alu insertion in intron G and two point mutations, V660L in exon 4 and H770H (silent substitution) in exon 5. The Alu element contains a half oestrogen-response element/Sp1-binding site (Alu-ERE/Sp1), which acts as an in-cis intronic enhancer leading to increased transcription of the PROGINS allele in response to 17beta-oestradiol. Moreover, Alu insertions in the human genome are frequently methylated. Our data indicate that the PROGINS-Alu does not affect gene transcription due to DNA methylation. However, the Alu element reduced the stability of the PROGINS transcript compared with the CP allele and does not generate splice variants. The amino acid substitution (V600L) in exon 4 leads to differences in PR phosphorylation and degradation in the two PR variants upon ligand binding, most likely as a result of differences in the three-dimensional structures of the two PR variants. As a consequence, the PR-L660 (PROGINS) variant (1) displays decreased transactivation activity in a luciferase reporter system and (2) is less efficient in opposing cell proliferation in hamster ovarian cells expressing human PRA, when compared with the PR-V660 (most common variant). Taken together, our results indicate that the PROGINS variant of PR is less responsive to progestin compared with the most common PR because of (i) reduced amounts of gene transcript and (ii) decreased protein activity.

The AhR and NF-κB/Rel Proteins Mediate the Inhibitory Effect of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin on the 3′ Immunoglobulin Heavy Chain Regulatory Region

PubMed Central

Salisbury, Richard L.; Sulentic, Courtney E. W.

2015-01-01

Transcriptional regulation of the murine immunoglobulin (Ig) heavy chain gene (Igh) involves several regulatory elements including the 3′Igh regulatory region (3′IghRR), which is composed of at least 4 enhancers (hs3A, hs1.2, hs3B, and hs4). The hs1.2 and hs4 enhancers exhibit the greatest transcriptional activity and contain binding sites for several transcription factors including nuclear factor kappaB/Rel (NF-κB/Rel) proteins and the aryl hydrocarbon receptor (AhR). Interestingly, the environmental immunosuppressant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which potently inhibits antibody secretion, also profoundly inhibits 3′IghRR and hs1.2 enhancer activation induced by the B-lymphocyte activator lipopolysaccharide (LPS), but enhances LPS-induced activation of the hs4 enhancer. Within the hs1.2 and hs4 enhancers, the AhR binding site is in close proximity or overlaps an NF-κB/Rel binding site suggesting a potential reciprocal modulation of the 3′IghRR by AhR and NF-κB/Rel. The objective of the current study was to evaluate the role of NF-κB/Rel and the AhR on the 3′IghRR and its enhancers using the AhR ligand TCDD, the AhR antagonist CH223191, and toll-like receptor agonists LPS, Resiquimod (R848), or cytosine-phosphate-guanine-oligodeoxynucleotides (CpG). Utilizing the CH12.LX B-lymphocyte cell line and variants expressing either a 3′IghRR-regulated transgene reporter or an inducible IκBα (inhibitor kappa B-alpha protein) superrepressor (IκBαAA), we demonstrate an AhR- and NF-κB/Rel-dependent modulation of 3′IghRR and hs4 activity. Additionally, in mouse splenocytes or CH12.LX cells, binding within the hs1.2 and hs4 enhancer of the AhR and the NF-κB/Rel proteins RelA and RelB was differentially altered by the cotreatment of LPS and TCDD. These results suggest that the AhR and NF-κB/Rel protein binding profile within the 3′IghRR mediates the inhibitory effects of TCDD on Ig expression and therefore antibody levels. PMID:26377645

Genome-Wide Analysis of Androgen Receptor Targets Reveals COUP-TF1 as a Novel Player in Human Prostate Cancer

PubMed Central

Perets, Ruth; Kaplan, Tommy; Stein, Ilan; Hidas, Guy; Tayeb, Shay; Avraham, Eti; Ben-Neriah, Yinon; Simon, Itamar; Pikarsky, Eli

2012-01-01

Androgen activity plays a key role in prostate cancer progression. Androgen receptor (AR) is the main mediator of androgen activity in the prostate, through its ability to act as a transcription mediator. Here we performed a genome-wide analysis of human AR binding to promoters in the presence of an agonist or antagonist in an androgen dependent prostate cancer cell line. Many of the AR bound promoters are bound in all examined conditions while others are bound only in the presence of an agonist or antagonist. Several motifs are enriched in AR bound promoters, including the AR Response Element (ARE) half-site and recognition elements for the transcription factors OCT1 and SOX9. This suggests that these 3 factors could define a module of co-operating transcription factors in the prostate. Interestingly, AR bound promoters are preferentially located in AT rich genomic regions. Analysis of mRNA expression identified chicken ovalbumin upstream promoter-transcription factor 1 (COUP-TF1) as a direct AR target gene that is downregulated upon binding by the agonist liganded AR. COUP-TF1 immunostaining revealed nucleolar localization of COUP-TF1 in epithelium of human androgen dependent prostate cancer, but not in adjacent benign prostate epithelium. Stromal cells both in human and mouse prostate show nuclear COUP-TF1 staining. We further show that there is an inverse correlation between COUP-TF1 expression in prostate stromal cells and the rising levels of androgen with advancing puberty. This study extends the pool of recognized putative AR targets and identifies a negatively regulated target of AR – COUP-TF1 – which could possibly play a role in human prostate cancer. PMID:23056316

Genome-wide analysis of androgen receptor targets reveals COUP-TF1 as a novel player in human prostate cancer.

PubMed

Perets, Ruth; Kaplan, Tommy; Stein, Ilan; Hidas, Guy; Tayeb, Shay; Avraham, Eti; Ben-Neriah, Yinon; Simon, Itamar; Pikarsky, Eli

2012-01-01

Androgen activity plays a key role in prostate cancer progression. Androgen receptor (AR) is the main mediator of androgen activity in the prostate, through its ability to act as a transcription mediator. Here we performed a genome-wide analysis of human AR binding to promoters in the presence of an agonist or antagonist in an androgen dependent prostate cancer cell line. Many of the AR bound promoters are bound in all examined conditions while others are bound only in the presence of an agonist or antagonist. Several motifs are enriched in AR bound promoters, including the AR Response Element (ARE) half-site and recognition elements for the transcription factors OCT1 and SOX9. This suggests that these 3 factors could define a module of co-operating transcription factors in the prostate. Interestingly, AR bound promoters are preferentially located in AT rich genomic regions. Analysis of mRNA expression identified chicken ovalbumin upstream promoter-transcription factor 1 (COUP-TF1) as a direct AR target gene that is downregulated upon binding by the agonist liganded AR. COUP-TF1 immunostaining revealed nucleolar localization of COUP-TF1 in epithelium of human androgen dependent prostate cancer, but not in adjacent benign prostate epithelium. Stromal cells both in human and mouse prostate show nuclear COUP-TF1 staining. We further show that there is an inverse correlation between COUP-TF1 expression in prostate stromal cells and the rising levels of androgen with advancing puberty. This study extends the pool of recognized putative AR targets and identifies a negatively regulated target of AR - COUP-TF1 - which could possibly play a role in human prostate cancer.

Changes in estrogen receptor signaling alters the timekeeping system in male mice.

PubMed

Blattner, Margaret S; Mahoney, Megan M

2015-11-01

Circadian rhythms are modulated by steroid hormones; however, the mechanisms of this action are not fully understood, particularly in males. In females estradiol regulates activity level, pattern of expression, and free running period (tau). We tested the hypothesis that activity level and distribution in male mice includes both classical and "non-classical" actions of estrogens at the estrogen receptor subtype 1 (ESR1). We used transgenic mice with mutations in their estrogen response pathways: ESR1 knock-out (ERKO) mice lack the ability to respond to estrogens via ESR1. "Non-classical" estrogen receptor knock-in (NERKI) mice have an inserted ESR1 receptor with a mutation in the estrogen-response-element binding domain, allowing activation via non-genomic and second messenger pathways. Gonadectomized male NERKI, ERKO, and wildtype (WT) littermates were given oil, or low or high dose estradiol and daily activity parameters were quantified. Estradiol shortened the ratio of activity in the light relative to dark (LD ratio), shortened tau, advanced the time of activity onset, and altered responsiveness to light cues administered in the late subjective night, suggesting modulation by an ESR1-independent mechanism. Estradiol treatment in NERKI but not WT males altered the timing of activity onset, LD ratio, and the behavioral response to light cues. These results may represent disruptions in the balance of genomic/nongenomic or ESR1/ESR2 signaling pathways. We also found a significant genotype effect on total activity, LD ratio, tau, and activity duration. These data provide new information about the role of ESR1-dependent and independent signaling pathways on the timekeeping system in male mice. Copyright © 2015 Elsevier B.V. All rights reserved.

Adipochemokines induced by ultraviolet irradiation contribute to impaired fat metabolism in subcutaneous fat cells.

PubMed

Kim, E J; Kim, Y K; Kim, S; Kim, J E; Tian, Y D; Doh, E J; Lee, D H; Chung, J H

2018-02-01

Adipose tissue is now appreciated as the pivotal regulator of metabolic and endocrine functions. Subcutaneous (SC) fat, in contrast to visceral fat, may protect against metabolic syndrome and systemic inflammation. We demonstrated that chronic as well as acute ultraviolet (UV) irradiation to the skin induces loss of underlying SC fat. UV-irradiated SC fat may produce chemokines or cytokines that modulate lipid homeostasis and secretion of adipokines. To elucidate UV-induced specific adipochemokines implicated in UV-induced modulation of SC fat. Primary cultured adipocytes were treated with conditioned medium from UV- or sham-irradiated skin cells. Young and older healthy participants provided SC fat from sun-exposed and sun-protected skin. Sun-protected skin from other participants was irradiated with UV. Differentially expressed adipochemokines were screened by cytokine array, and confirmed in vitro and in vivo. The functions of select adipochemokines involved in lipid metabolism were examined via short interfering RNA-mediated knockdown of cognate receptors. Specific adipochemokines, including C-X-C motif chemokine (CXCL) family members such as CXCL5/ENA-78, and C-C motif chemokine (CCL) family members such as CCL20/MIP-3α and CCL5/RANTES, were greatly induced in SC fat by UV exposure. They could impair triglyceride synthesis via downregulation of lipogenic enzymes and sterol regulatory element-binding protein-1 through their respective cognate receptors, CXC chemokine receptor type (CXC-R)2, C-C chemokine receptor type (CCR)-6, and CCR-5. In addition, UV irradiation induced infiltration of adipose tissue macrophages responsible for the secretion of several chemokines into SC fat. These UV-induced adipochemokines may be implicated in the reduction of lipogenesis in SC fat, leading to impairment of fat homeostasis and associated comorbidities such as obesity. © 2017 British Association of Dermatologists.

Selective androgen receptor modulators in preclinical and clinical development.

PubMed

Narayanan, Ramesh; Mohler, Michael L; Bohl, Casey E; Miller, Duane D; Dalton, James T

2008-01-01

Androgen receptor (AR) plays a critical role in the function of several organs including primary and accessory sexual organs, skeletal muscle, and bone, making it a desirable therapeutic target. Selective androgen receptor modulators (SARMs) bind to the AR and demonstrate osteo- and myo-anabolic activity; however, unlike testosterone and other anabolic steroids, these nonsteroidal agents produce less of a growth effect on prostate and other secondary sexual organs. SARMs provide therapeutic opportunities in a variety of diseases, including muscle wasting associated with burns, cancer, or end-stage renal disease, osteoporosis, frailty, and hypogonadism. This review summarizes the current standing of research and development of SARMs, crystallography of AR with SARMs, plausible mechanisms for their action and the potential therapeutic indications for this emerging class of drugs.

Secreted and Transmembrane Wnt Inhibitors and Activators

PubMed Central

Cruciat, Cristina-Maria; Niehrs, Christof

2013-01-01

Signaling by the Wnt family of secreted glycoproteins plays important roles in embryonic development and adult homeostasis. Wnt signaling is modulated by a number of evolutionarily conserved inhibitors and activators. Wnt inhibitors belong to small protein families, including sFRP, Dkk, WIF, Wise/SOST, Cerberus, IGFBP, Shisa, Waif1, APCDD1, and Tiki1. Their common feature is to antagonize Wnt signaling by preventing ligand–receptor interactions or Wnt receptor maturation. Conversely, the Wnt activators, R-spondin and Norrin, promote Wnt signaling by binding to Wnt receptors or releasing a Wnt-inhibitory step. With few exceptions, these antagonists and agonists are not pure Wnt modulators, but also affect additional signaling pathways, such as TGF-β and FGF signaling. Here we discuss their interactions with Wnt ligands and Wnt receptors, their role in developmental processes, as well as their implication in disease. PMID:23085770

Modulation of [3H]DAGO binding by substance P (SP) and SP fragments in the mouse brain and spinal cord via MU1 interactions.

PubMed

Krumins, S A; Kim, D C; Seybold, V S; Larson, A A

1989-01-01

Binding of [3H]DAGO to fresh, frozen or beta-funaltrexamine (beta-FNA) pretreated membranes of mouse brain and spinal cord was extensively studied using substance P (SP) or SP fragments as potential competitors and/or modulators. The objective was to determine whether SP exerts its analgesic effect by interacting with mu opioid receptors. The affinity of DAGO was reduced and binding capacity was increased in the presence of SP or the N-terminal SP fragments SP(1-9) and SP(1-4) but not the C-terminal SP fragment SP(5-11). Because sub-nanomolar concentrations of SP or N-terminal SP fragments displaced [3H] DAGO binding to a minor but detectable degree, it is suggested that SP interacts with mu 1 sites through its N-terminus portion. The effect of SP on DAGO binding was less in the spinal cord compared to the rest of the brain. Modulation of DAGO binding by SP was enhanced in the brain after pretreatment of membranes with the narcotic antagonist beta-FNA. These results suggest a novel mechanism for the analgesic action of SP.

How Native and Alien Metal Cations Bind ATP: Implications for Lithium as a Therapeutic Agent

NASA Astrophysics Data System (ADS)

Dudev, Todor; Grauffel, Cédric; Lim, Carmay

2017-02-01

Adenosine triphosphate (ATP), the major energy currency of the cell, exists in solution mostly as ATP-Mg. Recent experiments suggest that Mg2+ interacts with the highly charged ATP triphosphate group and Li+ can co-bind with the native Mg2+ to form ATP-Mg-Li and modulate the neuronal purine receptor response. However, it is unclear how the negatively charged ATP triphosphate group binds Mg2+ and Li+ (i.e. which phosphate group(s) bind Mg2+/Li+) and how the ATP solution conformation depends on the type of metal cation and the metal-binding mode. Here, we reveal the preferred ATP-binding mode of Mg2+/Li+ alone and combined: Mg2+ prefers to bind ATP tridentately to each of the three phosphate groups, but Li+ prefers to bind bidentately to the terminal two phosphates. We show that the solution ATP conformation depends on the cation and its binding site/mode, but it does not change significantly when Li+ binds to Mg2+-loaded ATP. Hence, ATP-Mg-Li, like Mg2+-ATP, can fit in the ATP-binding site of the host enzyme/receptor, activating specific signaling pathways.

Discovery and SAR of muscarinic receptor subtype 1 (M1) allosteric activators from a molecular libraries high throughput screen. Part 1: 2,5-dibenzyl-2H-pyrazolo[4,3-c]quinolin-3(5H)-ones as positive allosteric modulators.

PubMed

Han, Changho; Chatterjee, Arindam; Noetzel, Meredith J; Panarese, Joseph D; Smith, Emery; Chase, Peter; Hodder, Peter; Niswender, Colleen; Conn, P Jeffrey; Lindsley, Craig W; Stauffer, Shaun R

2015-01-15

Results from a 2012 high-throughput screen of the NIH Molecular Libraries Small Molecule Repository (MLSMR) against the human muscarinic receptor subtype 1 (M1) for positive allosteric modulators is reported. A content-rich screen utilizing an intracellular calcium mobilization triple-addition protocol allowed for assessment of all three modes of pharmacology at M1, including agonist, positive allosteric modulator, and antagonist activities in a single screening platform. We disclose a dibenzyl-2H-pyrazolo[4,3-c]quinolin-3(5H)-one hit (DBPQ, CID 915409) and examine N-benzyl pharmacophore/SAR relationships versus previously reported quinolin-3(5H)-ones and isatins, including ML137. SAR and consideration of recently reported crystal structures, homology modeling, and structure-function relationships using point mutations suggests a shared binding mode orientation at the putative common allosteric binding site directed by the pendant N-benzyl substructure. Copyright © 2014 Elsevier Ltd. All rights reserved.

Azadirachtin Interacts with Retinoic Acid Receptors and Inhibits Retinoic Acid-mediated Biological Responses*

PubMed Central

Thoh, Maikho; Babajan, Banaganapalli; Raghavendra, Pongali B.; Sureshkumar, Chitta; Manna, Sunil K.

2011-01-01

Considering the role of retinoids in regulation of more than 500 genes involved in cell cycle and growth arrest, a detailed understanding of the mechanism and its regulation is useful for therapy. The extract of the medicinal plant Neem (Azadirachta indica) is used against several ailments especially for anti-inflammatory, anti-itching, spermicidal, anticancer, and insecticidal activities. In this report we prove the detailed mechanism on the regulation of retinoic acid-mediated cell signaling by azadirachtin, active components of neem extract. Azadirachtin repressed all trans-retinoic acid (ATRA)-mediated nuclear transcription factor κB (NF-κB) activation, not the DNA binding but the NF-κB-dependent gene expression. It did not inhibit IκBα degradation, IκBα kinase activity, or p65 phosphorylation and its nuclear translocation but inhibited NF-κB-dependent reporter gene expression. Azadirachtin inhibited TRAF6-mediated, but not TRAF2-mediated NF-κB activation. It inhibited ATRA-induced Sp1 and CREB (cAMP-response element-binding protein) DNA binding. Azadirachtin inhibited ATRA binding with retinoid receptors, which is supported by biochemical and in silico evidences. Azadirachtin showed strong interaction with retinoid receptors. It suppressed ATRA-mediated removal of retinoid receptors, bound with DNA by inhibiting ATRA binding to its receptors. Overall, our data suggest that azadirachtin interacts with retinoic acid receptors and suppresses ATRA binding, inhibits falling off the receptors, and activates transcription factors like CREB, Sp1, NF-κB, etc. Thus, azadirachtin exerts anti-inflammatory and anti-metastatic responses by a novel pathway that would be beneficial for further anti-inflammatory and anti-cancer therapies. PMID:21127062

Functional effects of polymorphisms on glucocorticoid receptor modulation of human anxiogenic substance-P gene promoter activity in primary amygdala neurones.

PubMed

Hay, Colin W; Shanley, Lynne; Davidson, Scott; Cowie, Philip; Lear, Marissa; McGuffin, Peter; Riedel, Gernot; McEwan, Iain J; MacKenzie, Alasdair

2014-09-01

Expression or introduction of the neuropeptide substance-P (SP; encoded by the TAC1 gene in humans and Tac1 in rodents) in the amygdala induces anxiety related behaviour in rodents. In addition, pharmacological antagonism of the main receptor of SP in humans; NK1, is anxiolytic. In the current study, we show that the Tac1 locus is up-regulated in primary rat amygdala neurones in response to activation of the glucocorticoid receptor (GR); a classic component of the stress response. Using a combination of bioinformatics, electrophoretic mobility shift assays (EMSA) and reporter plasmid magnetofection into rat primary amygdala neurones we identified a highly conserved GR response sequence (2GR) in the human TAC1 promoter that binds GR in response to dexamethasone (Dex) or forskolin. We also identified a second GR binding site in the human promoter that was polymorphic and whose T-allele is only found in Japanese and Chinese populations. We present evidence that the T-allele of SNPGR increases the activity of the TAC1 promoter through de-sequestration or de-repression of 2GR. The identification of Dex/forskolin response elements in the TAC1 promoter in amygdala neurones suggests a possible link in the chain of molecular events connecting GR activation and anxiety. In addition, the discovery of a SNP which can alter this response may have implications for our understanding of the role of regulatory variation in susceptibility to stress in specific populations. Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved.

Functional effects of polymorphisms on glucocorticoid receptor modulation of human anxiogenic substance-P gene promoter activity in primary amygdala neurones

PubMed Central

Hay, Colin W.; Shanley, Lynne; Davidson, Scott; Cowie, Philip; Lear, Marissa; McGuffin, Peter; Riedel, Gernot; McEwan, Iain J.; MacKenzie, Alasdair

2014-01-01

Summary Expression or introduction of the neuropeptide substance-P (SP; encoded by the TAC1 gene in humans and Tac1 in rodents) in the amygdala induces anxiety related behaviour in rodents. In addition, pharmacological antagonism of the main receptor of SP in humans; NK1, is anxiolytic. In the current study, we show that the Tac1 locus is up-regulated in primary rat amygdala neurones in response to activation of the glucocorticoid receptor (GR); a classic component of the stress response. Using a combination of bioinformatics, electrophoretic mobility shift assays (EMSA) and reporter plasmid magnetofection into rat primary amygdala neurones we identified a highly conserved GR response sequence (2GR) in the human TAC1 promoter that binds GR in response to dexamethasone (Dex) or forskolin. We also identified a second GR binding site in the human promoter that was polymorphic and whose T-allele is only found in Japanese and Chinese populations. We present evidence that the T-allele of SNPGR increases the activity of the TAC1 promoter through de-sequestration or de-repression of 2GR. The identification of Dex/forskolin response elements in the TAC1 promoter in amygdala neurones suggests a possible link in the chain of molecular events connecting GR activation and anxiety. In addition, the discovery of a SNP which can alter this response may have implications for our understanding of the role of regulatory variation in susceptibility to stress in specific populations. PMID:25001955

Ionotropic and Metabotropic Mechanisms of Allosteric Modulation of α7 Nicotinic Receptor Intracellular Calcium.

PubMed

King, Justin R; Ullah, Aman; Bak, Ellen; Jafri, M Saleet; Kabbani, Nadine

2018-06-01

The pharmacological targeting of the α 7 nicotinic acetylcholine receptor ( α 7) is a promising strategy in the development of new drugs for neurologic diseases. Because α 7 receptors regulate cellular calcium, we investigated how the prototypical type II-positive allosteric modulator PNU120596 affects α 7-mediated calcium signaling. Live imaging experiments show that PNU120596 augments ryanodine receptor-driven calcium-induced calcium release (CICR), inositol-induced calcium release (IICR), and phospholipase C activation by the α 7 receptor. Both influx of calcium through the α 7 nicotinic acetylcholine receptor (nAChR) channel as well as the binding of intracellular G proteins were involved in the effect of PNU120596 on intracellular calcium. This is evidenced by the findings that chelation of extracellular calcium, expression of α 7 D44A or α 7 345-348A mutant subunits, or blockade of calcium store release compromised the ability of PNU120596 to increase intracellular calcium transients generated by α 7 ligand activation. Spatiotemporal stochastic modeling of calcium transient responses corroborates these results and indicates that α 7 receptor activation enables calcium microdomains locally and to lesser extent in the distant cytosol. From the model, allosteric modulation of the receptor activates CICR locally via ryanodine receptors and augments IICR through enhanced calcium influx due to prolonged α 7 nAChR opening. These findings provide a new mechanistic framework for understanding the effect of α 7 receptor allosteric modulation on both local and global calcium dynamics. Copyright © 2018 by The American Society for Pharmacology and Experimental Therapeutics.

A synthetic peptide derived from A1 module in CRD4 of human TNF receptor-1 inhibits binding and proinflammatory effect of human TNF-alpha.

PubMed

Cao, Yingnan; Wang, Zhaohe; Bu, Xianzhang; Tang, Shu; Mei, Zhengrong; Liu, Peiqing

2009-06-01

Tumour necrosis factor alpha (TNF-alpha) is a proinflammatory cytokine, which has been shown to be a causative factor in rheumatoid arthritis, inflammatory bowel disease and septic shock. Proinflammatory effect of TNF-alpha is activated mainly through human TNF receptor-1 (TNF-R1). However, the role of the fourth cystein-rich domain (CRD4) of TNF-R1 extracellular portion in the interaction of TNF-alpha with TNF-R1 is still unclear. In the present study, binding activity of TNF-alpha to TNF-R1 and protein levels of IkappaB-alpha and nuclear transcription factor kappa B (NF-kappaB) p65 subunit in HeLa cells were measured using enzyme-linked immunosorbent assay (ELISA) and western-blot analysis. Pep 3 (LRENECVS) which was derived from the hydrophilic region of A1 module in CRD4 remarkably inhibited the binding of TNF-alpha to TNF-R1, and also reversed TNF-alpha-induced degradation of IkappaB-alpha and nuclear translocation of NF-kappaB p65 subunit in HeLa cells. Our results confirmed that the hydrophilic region of A1 module in CRD4 participated in the interaction of TNF-alpha with TNF-R1, and demonstrated the potential of small-molecule TNF-alpha extracellular inhibitors targeting at A1 module in CRD4 of TNF-R1 in suppressing proinflammatory effect of TNF-alpha.

Rigid-body Ligand Recognition Drives Cytotoxic T-lymphocyte Antigen 4 (CTLA-4) Receptor Triggering

PubMed Central

Yu, Chao; Sonnen, Andreas F.-P.; George, Roger; Dessailly, Benoit H.; Stagg, Loren J.; Evans, Edward J.; Orengo, Christine A.; Stuart, David I.; Ladbury, John E.; Ikemizu, Shinji; Gilbert, Robert J. C.; Davis, Simon J.

2011-01-01

The inhibitory T-cell surface-expressed receptor, cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), which belongs to the class of cell surface proteins phosphorylated by extrinsic tyrosine kinases that also includes antigen receptors, binds the related ligands, B7-1 and B7-2, expressed on antigen-presenting cells. Conformational changes are commonly invoked to explain ligand-induced “triggering” of this class of receptors. Crystal structures of ligand-bound CTLA-4 have been reported, but not the apo form, precluding analysis of the structural changes accompanying ligand binding. The 1.8-Å resolution structure of an apo human CTLA-4 homodimer emphasizes the shared evolutionary history of the CTLA-4/CD28 subgroup of the immunoglobulin superfamily and the antigen receptors. The ligand-bound and unbound forms of both CTLA-4 and B7-1 are remarkably similar, in marked contrast to B7-2, whose binding to CTLA-4 has elements of induced fit. Isothermal titration calorimetry reveals that ligand binding by CTLA-4 is enthalpically driven and accompanied by unfavorable entropic changes. The similarity of the thermodynamic parameters determined for the interactions of CTLA-4 with B7-1 and B7-2 suggests that the binding is not highly specific, but the conformational changes observed for B7-2 binding suggest some level of selectivity. The new structure establishes that rigid-body ligand interactions are capable of triggering CTLA-4 phosphorylation by extrinsic kinase(s). PMID:21156796

Structural Basis of Chemokine Sequestration by CrmD, a Poxvirus-Encoded Tumor Necrosis Factor Receptor

PubMed Central

Wang, Dongli; Chen, Dongwei; He, Guangjun; Huang, Li; Wang, Hanzhong; Wang, Xinquan

2011-01-01

Pathogens have evolved sophisticated mechanisms to evade detection and destruction by the host immune system. Large DNA viruses encode homologues of chemokines and their receptors, as well as chemokine-binding proteins (CKBPs) to modulate the chemokine network in host response. The SECRET domain (smallpox virus-encoded chemokine receptor) represents a new family of viral CKBPs that binds a subset of chemokines from different classes to inhibit their activities, either independently or fused with viral tumor necrosis factor receptors (vTNFRs). Here we present the crystal structures of the SECRET domain of vTNFR CrmD encoded by ectromelia virus and its complex with chemokine CX3CL1. The SECRET domain adopts a β-sandwich fold and utilizes its β-sheet I surface to interact with CX3CL1, representing a new chemokine-binding manner of viral CKBPs. Structure-based mutagenesis and biochemical analysis identified important basic residues in the 40s loop of CX3CL1 for the interaction. Mutation of corresponding acidic residues in the SECRET domain also affected the binding for other chemokines, indicating that the SECRET domain binds different chemokines in a similar manner. We further showed that heparin inhibited the binding of CX3CL1 by the SECRET domain and the SECRET domain inhibited RAW264.7 cell migration induced by CX3CL1. These results together shed light on the structural basis for the SECRET domain to inhibit chemokine activities by interfering with both chemokine-GAG and chemokine-receptor interactions. PMID:21829356

A Transmembrane Amino Acid in the GABAA Receptor β2 Subunit Critical for the Actions of Alcohols and Anesthetics

PubMed Central

McCracken, Mandy L.; Borghese, Cecilia M.; Trudell, James R.

2010-01-01

Alcohols and inhaled anesthetics enhance the function of GABAA receptors containing α, β, and γ subunits. Molecular analysis has focused on the role of the α subunits; however, there is evidence that the β subunits may also be important. The goal of our study was to determine whether Asn265, which is homologous to the site implicated in the α subunit (Ser270), contributes to an alcohol and volatile anesthetic binding site in the GABAA receptor β2 subunit. We substituted cysteine for Asn265 and exposed the mutant to the sulfhydryl-specific reagent octyl methanethiosulfonate (OMTS). We used two-electrode voltage-clamp electrophysiology in Xenopus laevis oocytes and found that, after OMTS application, GABA-induced currents were irreversibly potentiated in mutant α1β2(N265C)γ2S receptors [but not α1β2(I264C)γ2S], presumably because of the covalent linking of octanethiol to the thiol group in the substituted cysteine. It is noteworthy that this effect was blocked when OMTS was applied in the presence of octanol. We found that potentiation by butanol, octanol, or isoflurane in the N265C mutant was nearly abolished after the application of OMTS, suggesting that an alcohol and volatile anesthetic binding site at position 265 of the β2 subunit was irreversibly occupied by octanethiol and consequently prevented butanol or isoflurane from binding and producing their effects. OMTS did not affect modulation or direct activation by pentobarbital, but there was a partial reduction of allosteric modulation by flunitrazepam and alphaxalone in mutant α1β2(N265C)γ2S receptors after OMTS was applied. Our findings provide evidence that Asn265 may contribute to an alcohol and anesthetic binding site. PMID:20826568

Mechanisms of protein kinase C signaling in the modulation of 3',5'-cyclic adenosine monophosphate-mediated steroidogenesis in mouse gonadal cells.

PubMed

Manna, Pulak R; Huhtaniemi, Ilpo T; Stocco, Douglas M

2009-07-01

The protein kinase C (PKC) signaling pathway plays integral roles in the expression of the steroidogenic acute regulatory (StAR) protein that regulates steroid biosynthesis in steroidogenic cells. PKC can modulate the activity of cAMP/protein kinase A signaling involved in steroidogenesis; however, its mechanism remains obscure. In the present study, we demonstrate that activation of the PKC pathway, by phorbol 12-myristate 13-acetate (PMA), was capable of potentiating dibutyryl cAMP [(Bu)(2)cAMP]-stimulated StAR expression, StAR phosphorylation, and progesterone synthesis in both mouse Leydig (MA-10) and granulosa (KK-1) tumor cells. The steroidogenic potential of PMA and (Bu)(2)cAMP was linked with phosphorylation of ERK 1/2; however, inhibition of the latter demonstrated varying effects on steroidogenesis. Transcriptional activation of the StAR gene by PMA and (Bu)(2)cAMP was influenced by several factors, its up-regulation being dependent on phosphorylation of the cAMP response element binding protein (CREB). An oligonucleotide probe containing a CREB/activating transcription factor binding region in the StAR promoter was found to bind nuclear proteins in PMA and (Bu)(2)cAMP-treated MA-10 and KK-1 cells. Chromatin immunoprecipitation studies revealed that the induction of phosphorylated CREB was tightly correlated with in vivo protein-DNA interactions and recruitment of CREB binding protein to the StAR promoter. Ectopic expression of CREB binding protein enhanced CREB-mediated transcription of the StAR gene, an event that was markedly repressed by the adenovirus E1A oncoprotein. Further studies demonstrated that the activation of StAR expression and steroid synthesis by PMA and (Bu)(2)cAMP was associated with expression of the nuclear receptor Nur77, indicating its essential role in hormone-regulated steroidogenesis. Collectively, these findings provide insight into the mechanisms by which PKC modulates cAMP/protein kinase A responsiveness involved in regulating the steroidogenic response in mouse gonadal cells.

Towards functional selectivity for α6β3γ2 GABAA receptors: a series of novel pyrazoloquinolinones

PubMed Central

Treven, Marco; Siebert, David C B; Holzinger, Raphael; Bampali, Konstantina; Fabjan, Jure; Varagic, Zdravko; Wimmer, Laurin; Steudle, Friederike; Scholze, Petra; Schnürch, Michael; Mihovilovic, Marko D

2017-01-01

Background and Purpose The GABAA receptors are ligand‐gated ion channels, which play an important role in neurotransmission. Their variety of binding sites serves as an appealing target for many clinically relevant drugs. Here, we explored the functional selectivity of modulatory effects at specific extracellular α+/β− interfaces, using a systematically varied series of pyrazoloquinolinones. Experimental Approach Recombinant GABAA receptors were expressed in Xenopus laevis oocytes and modulatory effects on GABA‐elicited currents by the newly synthesized and reference compounds were investigated by the two‐electrode voltage clamp method. Key Results We identified a new compound which, to the best of our knowledge, shows the highest functional selectivity for positive modulation at α6β3γ2 GABAA receptors with nearly no residual activity at the other αxβ3γ2 (x = 1–5) subtypes. This modulation was independent of affinity for α+/γ− interfaces. Furthermore, we demonstrated for the first time a compound that elicits a negative modulation at specific extracellular α+/β− interfaces. Conclusion and Implications These results constitute a major step towards a potential selective positive modulation of certain α6‐containing GABAA receptors, which might be useful to elicit their physiological role. Furthermore, these studies pave the way towards insights into molecular principles that drive positive versus negative allosteric modulation of specific GABAA receptor isoforms. PMID:29127702

Differential effect of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) on (/sup 3/H)SCH23390 and (/sup numberH/)forskolin binding in rat striatum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Norman, A.B.; Wachendorf, T.J.; Sanberg, P.R.

1989-01-01

The binding of (/sup 3/H)forskolin to a homogeneous population of binding sites in rat striatum was enhanced by NaF, guanine nucleotides and MgCl/sub 2/. These effects of NaF and guanylylimidodiphosphate (Gpp(NH)p) were synergistic with MgCl/sub 2/, but NaF and Gpp(NH)p together elicited no greater enhancement of (/sup 3/H)forskolin binding. These data suggest that (/sup 3/H)forskolin may label a site which is modulated by the guanine nucleotide regulatory subunit which mediates the stimulation of adenylate cyclase (N/sub S/). The D/sub 1/ dopamine receptor is known to stimulate adenylate cyclase via N/sub S/. In rat striatum, the B/sub max/ of (/sup 3/H)forskolinmore » binding sites in the presence of MgCl/sub 2/ and NaF was approximately two fold greater than the B/sub max/ of (/sup 3/H)SCH23390-labeled D/sub 1/ dopamine receptors. Incubation of striatal homogenates with the protein modifying reagent EEDQ elicited a concentration-dependent decrease in the binding of both (/sup 3/H)SCH23390 and (/sup 3/H)forskolin, although EEDQ was approximately 14 fold more potent at inactivating the D/sub 1/ dopamine receptor. Following in vivo administration of EEDQ there was no significant effect on (/sup 3/H)forskolin binding sites using a dose of EEDQ that irreversibly inactivated greater than 90% of D/sub 1/ dopamine receptors. These data suggest that EEDQ is a suitable tool for investigating changes in the stoichiometry of receptors and their second messenger systems.« less

Effects of chronic delta-9-tetrahydrocannabinol (THC) administration on neurotransmitter concentrations and receptor binding in the rat brain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ali, S.F.; Newport, G.D.; Scallet, A.C.

THC is the major psychoactive constituent of marijuana and is also known as an hallucinogenic compound. Numerous reports have shown that large doses of THC produce significant alterations in various neurotransmitter systems. The present study was designed to determine whether chronic exposure to THC produces significant alterations in selected neurotransmitter systems (dopamine, serotonin, acetylcholine, GABAergic, benzodiazepine, and opiate) in the rat brain. In Experiment 1, male Sprague-Dawley rats were gavaged with vehicle, 10 or 20 mg THC/kg body weight daily, 5 days/week for 90 days. Animals were killed either 24 hours or two months after the last dose. Brains weremore » dissected into different regions for neurochemical analyses. Two months after the cessation of chronic administration, there was a significant decrease in GABA receptor binding in the hippocampus of animals in the high dose group. However, no other significant changes were found in neurotransmitter receptor binding characteristics in the hippocampus or in neurotransmitter concentrations in the caudate nucleus, hypothalamus or septum after chronic THC administration. In an attempt to replicate the GABA receptor binding changes and also to determine the (35S)TBPS binding in hippocampus, we designed Experiment 2. In this experiment, we dosed the animals by gavage with 0, 5, 10 or 20 mg THC/kg daily, 5 days/week or with 20 mg THC/kg Monday through Thursday and 60 mg/kg on Friday for 90 days. Results from this experiment failed to replicate the dose-dependent effect of THC on GABA receptor binding in hippocampus. Modulation of (35S)TBPS binding by GABA or 3 alpha-OH-DHP or inhibition by cold TBPS in frontal cortex did not show any significant dose-related effects.« less

Cellular Retinoic Acid Binding Proteins: Genomic and Non-genomic Functions and their Regulation.

PubMed

Wei, Li-Na

Cellular retinoic acid binding proteins (CRABPs) are high-affinity retinoic acid (RA) binding proteins that mainly reside in the cytoplasm. In mammals, this family has two members, CRABPI and II, both highly conserved during evolution. The two proteins share a very similar structure that is characteristic of a "β-clam" motif built up from10-strands. The proteins are encoded by two different genes that share a very similar genomic structure. CRABPI is widely distributed and CRABPII has restricted expression in only certain tissues. The CrabpI gene is driven by a housekeeping promoter, but can be regulated by numerous factors, including thyroid hormones and RA, which engage a specific chromatin-remodeling complex containing either TRAP220 or RIP140 as coactivator and corepressor, respectively. The chromatin-remodeling complex binds the DR4 element in the CrabpI gene promoter to activate or repress this gene in different cellular backgrounds. The CrabpII gene promoter contains a TATA-box and is rapidly activated by RA through an RA response element. Biochemical and cell culture studies carried out in vitro show the two proteins have distinct biological functions. CRABPII mainly functions to deliver RA to the nuclear RA receptors for gene regulation, although recent studies suggest that CRABPII may also be involved in other cellular events, such as RNA stability. In contrast, biochemical and cell culture studies suggest that CRABPI functions mainly in the cytoplasm to modulate intracellular RA availability/concentration and to engage other signaling components such as ERK activity. However, these functional studies remain inconclusive because knocking out one or both genes in mice does not produce definitive phenotypes. Further studies are needed to unambiguously decipher the exact physiological activities of these two proteins.

Regulation of platelet activating factor receptor coupled phosphoinositide-specific phospholipase C activity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morrison, W.J.

1988-01-01

The major objectives of this study were two-fold. The first was to establish whether binding of platelet activating factor (PAF) to its receptor was integral to the stimulation of polyphosphoinositide-specific phospholipase C (PLC) in rabbit platelets. The second was to determine regulatory features of this receptor-coupled mechanism. ({sup 3}H)PAF binding demonstrated two binding sites, a high affinity site with a inhibitory constant (Ki) of 2.65 nM and a low affinity site with a Ki of 0.80 {mu}M. PAF receptor coupled activation of phosphoinositide-specific PLC was studied in platelets which were made refractory, by short term pretreatments, to either PAF ormore » thrombin. Saponin-permeabilized rabbit platelets continue to regulate the mechanism(s) coupling PAF receptors to PLC stimulation. However, TRP{gamma}S and GDP{beta}S, which affect guanine nucleotide regulatory protein functions, were unable to modulate the PLC activity to any appreciable extent as compared to PAF. The possible involvement of protein kinase C (PKC) activation in regulating PAF-stimulated PLC activity was studied in rabbit platelets pretreated with staurosporine followed by pretreatments with PAF or phorbol 12-myristate 13-acetate (PMA).« less

Interactions of L-3,5,3'-Triiodothyronine, Allopregnanolone, and Ivermectin with the GABAA Receptor: Evidence for Overlapping Intersubunit Binding Modes

PubMed Central

Westergard, Thomas; Salari, Reza; Martin, Joseph V.; Brannigan, Grace

2015-01-01

Structural mechanisms of modulation of γ-aminobutyric acid (GABA) type A receptors by neurosteroids and hormones remain unclear. The thyroid hormone L-3,5,3’-triiodothyronine (T3) inhibits GABAA receptors at micromolar concentrations and has common features with neurosteroids such as allopregnanolone (ALLOP). Here we use functional experiments on α2β1γ2 GABAA receptors expressed in Xenopus oocytes to detect competitive interactions between T3 and an agonist (ivermectin, IVM) with a crystallographically determined binding site at subunit interfaces in the transmembrane domain of a homologous receptor (glutamate-gated chloride channel, GluCl). T3 and ALLOP also show competitive effects, supporting the presence of both a T3 and ALLOP binding site at one or more subunit interfaces. Molecular dynamics (MD) simulations over 200 ns are used to investigate the dynamics and energetics of T3 in the identified intersubunit sites. In these simulations, T3 molecules occupying all intersubunit sites (with the exception of the α-β interface) display numerous energetically favorable conformations with multiple hydrogen bonding partners, including previously implicated polar/acidic sidechains and a structurally conserved deformation in the M1 backbone. PMID:26421724

Interactions of L-3,5,3'-Triiodothyronine [corrected], Allopregnanolone, and Ivermectin with the GABAA Receptor: Evidence for Overlapping Intersubunit Binding Modes.

PubMed

Westergard, Thomas; Salari, Reza; Martin, Joseph V; Brannigan, Grace

2015-01-01

Structural mechanisms of modulation of γ-aminobutyric acid (GABA) type A receptors by neurosteroids and hormones remain unclear. The thyroid hormone L-3,5,3'-triiodothyronine (T3) inhibits GABAA receptors at micromolar concentrations and has common features with neurosteroids such as allopregnanolone (ALLOP). Here we use functional experiments on α2β1γ2 GABAA receptors expressed in Xenopus oocytes to detect competitive interactions between T3 and an agonist (ivermectin, IVM) with a crystallographically determined binding site at subunit interfaces in the transmembrane domain of a homologous receptor (glutamate-gated chloride channel, GluCl). T3 and ALLOP also show competitive effects, supporting the presence of both a T3 and ALLOP binding site at one or more subunit interfaces. Molecular dynamics (MD) simulations over 200 ns are used to investigate the dynamics and energetics of T3 in the identified intersubunit sites. In these simulations, T3 molecules occupying all intersubunit sites (with the exception of the α-β interface) display numerous energetically favorable conformations with multiple hydrogen bonding partners, including previously implicated polar/acidic sidechains and a structurally conserved deformation in the M1 backbone.

Indole-3-carbinol and 3’, 3’-diindolylmethane modulate androgen effect up-regulation on C-C chemokine ligand 2 and monocyte attraction to prostate cancer cells

USDA-ARS?s Scientific Manuscript database

Inflammation has a role in prostate tumorigenesis. Recruitment of inflammatory monocytes to the tumor site is mediated by C-C chemokine ligand 2 (CCL2) through binding to its receptor CCR2. We hypothesized that androgen could modulate CCL2 expression in hormone-responsive prostate cancer cells, and ...

Revealing a steroid receptor ligand as a unique PPAR[gamma] agonist

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Shengchen; Han, Ying; Shi, Yuzhe

2012-06-28

Peroxisome proliferator-activated receptor gamma (PPAR{gamma}) regulates metabolic homeostasis and is a molecular target for anti-diabetic drugs. We report here the identification of a steroid receptor ligand, RU-486, as an unexpected PPAR{gamma} agonist, thereby uncovering a novel signaling route for this steroid drug. Similar to rosiglitazone, RU-486 modulates the expression of key PPAR{gamma} target genes and promotes adipocyte differentiation, but with a lower adipogenic activity. Structural and functional studies of receptor-ligand interactions reveal the molecular basis for a unique binding mode for RU-486 in the PPAR{gamma} ligand-binding pocket with distinctive properties and epitopes, providing the molecular mechanisms for the discrimination ofmore » RU-486 from thiazolidinediones (TZDs) drugs. Our findings together indicate that steroid compounds may represent an alternative approach for designing non-TZD PPAR{gamma} ligands in the treatment of insulin resistance.« less

Thyroid Hormone Receptor β (TRβ) and Liver X Receptor (LXR) Regulate Carbohydrate-response Element-binding Protein (ChREBP) Expression in a Tissue-selective Manner*

PubMed Central

Gauthier, Karine; Billon, Cyrielle; Bissler, Marie; Beylot, Michel; Lobaccaro, Jean-Marc; Vanacker, Jean-Marc; Samarut, Jacques

2010-01-01

Thyroid hormone (TR) and liver X (LXR) receptors are transcription factors involved in lipogenesis. Both receptors recognize the same consensus DNA-response element in vitro. It was previously shown that their signaling pathways interact in the control of cholesterol elimination in the liver. In the present study, carbohydrate-response element-binding protein (ChREBP), a major transcription factor controlling the activation of glucose-induced lipogenesis in liver, is characterized as a direct target of thyroid hormones (TH) in liver and white adipose tissue (WAT), the two main lipogenic tissues in mice. Using genetic and molecular approaches, ChREBP is shown to be specifically regulated by TRβ but not by TRα in vivo, even in WAT where both TR isoforms are expressed. However, this isotype specificity is not found in vitro. This TRβ specific regulation correlates with the loss of TH-induced lipogenesis in TRβ−/− mice. Fasting/refeeding experiments show that TRβ is not required for the activation of ChREBP expression particularly marked in WAT following refeeding. However, TH can stimulate ChREBP expression in WAT even under fasting conditions, suggesting completely independent pathways. Because ChREBP has been described as an LXR target, the interaction of LXR and TRβ in ChREBP regulation was assayed both in vitro and in vivo. Each receptor recognizes a different response element on the ChREBP promoter, located only 8 bp apart. There is a cross-talk between LXR and TRβ signaling on the ChREBP promoter in liver but not in WAT where LXR does not regulate ChREBP expression. The molecular basis for this cross-talk has been determined in in vitro systems. PMID:20615868

Identification of spinal 5-HT sub 3 receptors and their role in the modulation of nociceptive responses in the rat

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glaum, S.R.

1988-01-01

The project consisted of two related studies: (1) the characterization of serotonin binding sites in crude and purified synaptic membranes prepared from the rat spinal cord, and (2) the association of serotonin binding sites with functional 5-HT receptor responses in the modulation of nociceptive information at the level of the spinal cord. The first series of experiments involved the preparation of membranes from the dorsal and ventral halves of the rat spinal cord and the demonstration of specific ({sup 3}H)serotonin binding to these membranes. High affinity binding sites which conformed to the 5-HT{sub 3} subtype were identified in dorsal, butmore » not ventral spinal cord synaptic membranes. These experiments also confirmed the presence of high affinity ({sup 3}H)5-HT binding sites in dorsal spinal cord synaptic membranes of the 5-HT{sub 1} subtype. The second group of studies demonstrated the ability of selective 5-HT{sub 3} antagonists to inhibit the antinociceptive response to intrathecally administered 5-HT, as measured by a change in tail flick and hot plate latencies. Intrathecal pretreatment with the selective 5-HT{sub 3} antagonists ICS 205-930 or MDL 72222 abolished the antinociceptive effects of 5-HT. Furthermore, the selective 5-HT{sub 3} agonist 2-methyl-5-HT mimicked the antinociceptive effects of 5-HT.« less

Three classes of ligands each bind to distinct sites on the orphan G protein-coupled receptor GPR84.

PubMed

Mahmud, Zobaer Al; Jenkins, Laura; Ulven, Trond; Labéguère, Frédéric; Gosmini, Romain; De Vos, Steve; Hudson, Brian D; Tikhonova, Irina G; Milligan, Graeme

2017-12-20

Medium chain fatty acids can activate the pro-inflammatory receptor GPR84 but so also can molecules related to 3,3'-diindolylmethane. 3,3'-Diindolylmethane and decanoic acid acted as strong positive allosteric modulators of the function of each other and analysis showed the affinity of 3,3'-diindolylmethane to be at least 100 fold higher. Methyl decanoate was not an agonist at GPR84. This implies a key role in binding for the carboxylic acid of the fatty acid. Via homology modelling we predicted and confirmed an integral role of arginine 172 , located in the 2nd extracellular loop, in the action of decanoic acid but not of 3,3'-diindolylmethane. Exemplars from a patented series of GPR84 antagonists were able to block agonist actions of both decanoic acid and 3,3'-diindolylmethane at GPR84. However, although a radiolabelled form of a related antagonist, [ 3 H]G9543, was able to bind with high affinity to GPR84, this was not competed for by increasing concentrations of either decanoic acid or 3,3'-diindolylmethane and was not affected adversely by mutation of arginine 172 . These studies identify three separable ligand binding sites within GPR84 and suggest that if medium chain fatty acids are true endogenous regulators then co-binding with a positive allosteric modulator would greatly enhance their function in physiological settings.

Probing a 2-aminobenzimidazole library for binding to RNA internal loops via two-dimensional combinatorial screening.

PubMed

Velagapudi, Sai Pradeep; Pushechnikov, Alexei; Labuda, Lucas P; French, Jonathan M; Disney, Matthew D

2012-11-16

There are many potential RNA drug targets in bacterial, viral, and human transcriptomes. However, there are few small molecules that modulate RNA function. This is due, in part, to a lack of fundamental understanding about RNA-ligand interactions including the types of small molecules that bind to RNA structural elements and the RNA structural elements that bind to small molecules. In an effort to better understand RNA-ligand interactions, we diversified the 2-aminobenzimidazole core (2AB) and probed the resulting library for binding to a library of RNA internal loops. We chose the 2AB core for these studies because it is a privileged scaffold for binding RNA based on previous reports. These studies identified that N-methyl pyrrolidine, imidazole, and propylamine diversity elements at the R1 position increase binding to internal loops; variability at the R2 position is well tolerated. The preferred RNA loop space was also determined for five ligands using a statistical approach and identified trends that lead to selective recognition.

Assessment of Homology Templates and an Anesthetic Binding Site within the γ-Aminobutyric Acid Receptor

PubMed Central

Bertaccini, Edward J.; Yoluk, Ozge; Lindahl, Erik R.; Trudell, James R.

2013-01-01

Background Anesthetics mediate portions of their activity via modulation of the γ-aminobutyric acid receptor (GABAaR). While its molecular structure remains unknown, significant progress has been made towards understanding its interactions with anesthetics via molecular modeling. Methods The structure of the torpedo acetylcholine receptor (nAChRα), the structures of the α4 and β2 subunits of the human nAChR, the structures of the eukaryotic glutamate-gated chloride channel (GluCl), and the prokaryotic pH sensing channels, from Gloeobacter violaceus and Erwinia chrysanthemi, were aligned with the SAlign and 3DMA algorithms. A multiple sequence alignment from these structures and those of the GABAaR was performed with ClustalW. The Modeler and Rosetta algorithms independently created three-dimensional constructs of the GABAaR from the GluCl template. The CDocker algorithm docked a congeneric series of propofol derivatives into the binding pocket and scored calculated binding affinities for correlation with known GABAaR potentiation EC50’s. Results Multiple structure alignments of templates revealed a clear consensus of residue locations relevant to anesthetic effects except for torpedo nAChR. Within the GABAaR models generated from GluCl, the residues notable for modulating anesthetic action within transmembrane segments 1, 2, and 3 converged on the intersubunit interface between alpha and beta subunits. Docking scores of a propofol derivative series into this binding site showed strong linear correlation with GABAaR potentiation EC50. Conclusion Consensus structural alignment based on homologous templates revealed an intersubunit anesthetic binding cavity within the transmembrane domain of the GABAaR, which showed correlation of ligand docking scores with experimentally measured GABAaR potentiation. PMID:23770602

Assessment of homology templates and an anesthetic binding site within the γ-aminobutyric acid receptor.

PubMed

Bertaccini, Edward J; Yoluk, Ozge; Lindahl, Erik R; Trudell, James R

2013-11-01

Anesthetics mediate portions of their activity via modulation of the γ-aminobutyric acid receptor (GABAaR). Although its molecular structure remains unknown, significant progress has been made toward understanding its interactions with anesthetics via molecular modeling. The structure of the torpedo acetylcholine receptor (nAChRα), the structures of the α4 and β2 subunits of the human nAChR, the structures of the eukaryotic glutamate-gated chloride channel (GluCl), and the prokaryotic pH-sensing channels, from Gloeobacter violaceus and Erwinia chrysanthemi, were aligned with the SAlign and 3DMA algorithms. A multiple sequence alignment from these structures and those of the GABAaR was performed with ClustalW. The Modeler and Rosetta algorithms independently created three-dimensional constructs of the GABAaR from the GluCl template. The CDocker algorithm docked a congeneric series of propofol derivatives into the binding pocket and scored calculated binding affinities for correlation with known GABAaR potentiation EC50s. Multiple structure alignments of templates revealed a clear consensus of residue locations relevant to anesthetic effects except for torpedo nAChR. Within the GABAaR models generated from GluCl, the residues notable for modulating anesthetic action within transmembrane segments 1, 2, and 3 converged on the intersubunit interface between α and β subunits. Docking scores of a propofol derivative series into this binding site showed strong linear correlation with GABAaR potentiation EC50. Consensus structural alignment based on homologous templates revealed an intersubunit anesthetic binding cavity within the transmembrane domain of the GABAaR, which showed a correlation of ligand docking scores with experimentally measured GABAaR potentiation.

Structural insights into selective agonist actions of tamoxifen on human estrogen receptor alpha.

PubMed

Chakraborty, Sandipan; Biswas, Pradip Kumar

2014-08-01

Tamoxifen-an anti-estrogenic ligand in breast tissues used as a first-line treatment in estrogen receptor (ER)-positive breast cancers-is associated with the development of resistance followed by resumption of tumor growth in about 30 % of cases. Whether tamoxifen assists in proliferation in such cases or whether any ligand-independent pathway to transcription exists is not fully understood; also, no ERα mutants have been detected so far that could lead to tamoxifen resistance. Using in silico conformational analysis of the ERα ligand binding domain (LBD), in the absence and presence of selective agonist (diethylstilbestrol; DES), antagonist (Faslodex; ICI), and selective estrogen receptor modulator (SERM; 4-hydroxy tamoxifen; 4-OHT) ligands, we have elucidated ligand-responsive structural modulations of the ERα-LBD dimer in its agonist and antagonist complexes to address the issue of "tamoxifen resistance". DES and ICI were found to stabilize the dimer in their agonist and antagonist conformations, respectively. The ERα-LBD dimer without the presence of any bound ligand also led to a stable structure in agonist conformation. However, binding of 4-OHT to the antagonist structure led to a flexible conformation allowing the protein to visit conformations populated by agonists as was evident from principal component analysis and radius of gyration plots. Further, the relaxed conformations of the 4-OHT bound protein exhibited a diminished size of the co-repressor binding pocket in the LBD, thus signaling a partial blockage of the co-repressor binding motif. Thus, the ability of 4-OHT-bound ERα-LBD to assume flexible conformations visited by agonists and reduced co-repressor binding surface at the LBD provide crucial structural insights into tamoxifen-resistance that complement our existing understanding.

Extra-epitopic hepatitis C virus polymorphisms confer resistance to broadly neutralizing antibodies by modulating binding to scavenger receptor B1.

PubMed

El-Diwany, Ramy; Cohen, Valerie J; Mankowski, Madeleine C; Wasilewski, Lisa N; Brady, Jillian K; Snider, Anna E; Osburn, William O; Murrell, Ben; Ray, Stuart C; Bailey, Justin R

2017-02-01

Broadly-neutralizing monoclonal antibodies (bNAbs) may guide vaccine development for highly variable viruses including hepatitis C virus (HCV), since they target conserved viral epitopes that could serve as vaccine antigens. However, HCV resistance to bNAbs could reduce the efficacy of a vaccine. HC33.4 and AR4A are two of the most potent anti-HCV human bNAbs characterized to date, binding to highly conserved epitopes near the amino- and carboxy-terminus of HCV envelope (E2) protein, respectively. Given their distinct epitopes, it was surprising that these bNAbs showed similar neutralization profiles across a panel of natural HCV isolates, suggesting that some viral polymorphisms may confer resistance to both bNAbs. To investigate this resistance, we developed a large, diverse panel of natural HCV envelope variants and a novel computational method to identify bNAb resistance polymorphisms in envelope proteins (E1 and E2). By measuring neutralization of a panel of HCV pseudoparticles by 10 μg/mL of each bNAb, we identified E1E2 variants with resistance to one or both bNAbs, despite 100% conservation of the AR4A binding epitope across the panel. We discovered polymorphisms outside of either binding epitope that modulate resistance to both bNAbs by altering E2 binding to the HCV co-receptor, scavenger receptor B1 (SR-B1). This study is focused on a mode of neutralization escape not addressed by conventional analysis of epitope conservation, highlighting the contribution of extra-epitopic polymorphisms to bNAb resistance and presenting a novel mechanism by which HCV might persist even in the face of an antibody response targeting multiple conserved epitopes.

Homology Modeling, Validation and Dynamics of the G Protein-coupled Estrogen Receptor 1 (GPER-1).

PubMed

Bruno, Agostino; Aiello, Francesca; Costantino, Gabriele; Radi, Marco

2016-09-01

Estrogens exert their action mainly by binding three receptors, namely estrogen receptors α and β (ERα and ERβ) and GPER-1 (G-protein coupled estrogen receptor 1). While the patho-physiological role of both ERα and ERβ has been deeply investigated, the role of GPER-1 in estrogens' signaling has not been clearly defined yet. Unfortunately, only few GPER-1 selective ligands were discovered so far, and the real efficiency of such compounds is still matter of debate. To better understand the physiological relevance of GPER-1, new selective chemical probes are higly needed. In this scenario, we report herein the generation and validation of a three-dimensional (3-D) GPER-1 homology model by means of docking studies and molecular dynamics simulations. The model thus generated was employed to (i) decipher the structural basis underlying the ability of estrogens and some Selective Estrogen Receptor Modulators (SERMs) to bind GPER-1 and classical ERα and ERβ, and (ii) generate a reliable G1/GPER-1 complex useful in rationalizing the pharmacological profile of G1 reported in the literature. The G1/GPER-1 complex herein reported could be further exploited in drug design approaches aimed at improving the pharmacological profile of G1 or at identifying new chemical entities (NCEs) as potential modulators of GPER-1. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In Silico Identification and Pharmacological Evaluation of Novel Endocrine Disrupting Chemicals That Act via the Ligand-Binding Domain of the Estrogen Receptor α

PubMed Central

Kufareva, Irina; Abagyan, Ruben

2014-01-01

Endocrine disrupting chemicals (EDCs) pose a significant threat to human health, society, and the environment. Many EDCs elicit their toxic effects through nuclear hormone receptors, like the estrogen receptor α (ERα). In silico models can be used to prioritize chemicals for toxicological evaluation to reduce the amount of costly pharmacological testing and enable early alerts for newly designed compounds. However, many of the current computational models are overly dependent on the chemistry of known modulators and perform poorly for novel chemical scaffolds. Herein we describe the development of computational, three-dimensional multi-conformational pocket-field docking, and chemical-field docking models for the identification of novel EDCs that act via the ligand-binding domain of ERα. These models were highly accurate in the retrospective task of distinguishing known high-affinity ERα modulators from inactive or decoy molecules, with minimal training. To illustrate the utility of the models in prospective in silico compound screening, we screened a database of over 6000 environmental chemicals and evaluated the 24 top-ranked hits in an ERα transcriptional activation assay and a differential scanning fluorimetry-based ERα binding assay. Promisingly, six chemicals displayed ERα agonist activity (32nM–3.98μM) and two chemicals had moderately stabilizing effects on ERα. Two newly identified active compounds were chemically related β-adrenergic receptor (βAR) agonists, dobutamine, and ractopamine (a feed additive that promotes leanness in cattle and poultry), which are the first βAR agonists identified as activators of ERα-mediated gene transcription. This approach can be applied to other receptors implicated in endocrine disruption. PMID:24928891

In silico identification and pharmacological evaluation of novel endocrine disrupting chemicals that act via the ligand-binding domain of the estrogen receptor α.

PubMed

McRobb, Fiona M; Kufareva, Irina; Abagyan, Ruben

2014-09-01

Endocrine disrupting chemicals (EDCs) pose a significant threat to human health, society, and the environment. Many EDCs elicit their toxic effects through nuclear hormone receptors, like the estrogen receptor α (ERα). In silico models can be used to prioritize chemicals for toxicological evaluation to reduce the amount of costly pharmacological testing and enable early alerts for newly designed compounds. However, many of the current computational models are overly dependent on the chemistry of known modulators and perform poorly for novel chemical scaffolds. Herein we describe the development of computational, three-dimensional multi-conformational pocket-field docking, and chemical-field docking models for the identification of novel EDCs that act via the ligand-binding domain of ERα. These models were highly accurate in the retrospective task of distinguishing known high-affinity ERα modulators from inactive or decoy molecules, with minimal training. To illustrate the utility of the models in prospective in silico compound screening, we screened a database of over 6000 environmental chemicals and evaluated the 24 top-ranked hits in an ERα transcriptional activation assay and a differential scanning fluorimetry-based ERα binding assay. Promisingly, six chemicals displayed ERα agonist activity (32nM-3.98μM) and two chemicals had moderately stabilizing effects on ERα. Two newly identified active compounds were chemically related β-adrenergic receptor (βAR) agonists, dobutamine, and ractopamine (a feed additive that promotes leanness in cattle and poultry), which are the first βAR agonists identified as activators of ERα-mediated gene transcription. This approach can be applied to other receptors implicated in endocrine disruption. © The Author 2014. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For permissions, please email: journals.permissions@oup.com.

Nitric oxide/cGMP pathway signaling actively down-regulates α4β1-integrin affinity: an unexpected mechanism for inducing cell de-adhesion.

PubMed

Chigaev, Alexandre; Smagley, Yelena; Sklar, Larry A

2011-05-17

Integrin activation in response to inside-out signaling serves as the basis for rapid leukocyte arrest on endothelium, migration, and mobilization of immune cells. Integrin-dependent adhesion is controlled by the conformational state of the molecule, which is regulated by seven-transmembrane Guanine nucleotide binding Protein-Coupled Receptors (GPCRs). α4β1-integrin (CD49d/CD29, Very Late Antigen-4, VLA-4) is expressed on leukocytes, hematopoietic progenitors, stem cells, hematopoietic cancer cells, and others. VLA-4 conformation is rapidly up-regulated by inside-out signaling through Gαi-coupled GPCRs and down-regulated by Gαs-coupled GPCRs. However, other signaling pathways, which include nitric oxide-dependent signaling, have been implicated in the regulation of cell adhesion. The goal of the current report was to study the effect of nitric oxide/cGMP signaling pathway on VLA-4 conformational regulation. Using fluorescent ligand binding to evaluate the integrin activation state on live cells in real-time, we show that several small molecules, which specifically modulate nitric oxide/cGMP signaling pathway, as well as a cell permeable cGMP analog, can rapidly down-modulate binding of a VLA-4 specific ligand on cells pre-activated through three Gαi-coupled receptors: wild type CXCR4, CXCR2 (IL-8RB), and a non-desensitizing mutant of formyl peptide receptor (FPR ΔST). Upon signaling, we detected rapid changes in the ligand dissociation rate. The dissociation rate after inside-out integrin de-activation was similar to the rate for resting cells. In a VLA-4/VCAM-1-specific myeloid cell adhesion system, inhibition of the VLA-4 affinity change by nitric oxide had a statistically significant effect on real-time cell aggregation. We conclude that nitric oxide/cGMP signaling pathway can rapidly down-modulate the affinity state of the VLA-4 binding pocket, especially under the condition of sustained Gαi-coupled GPCR signaling, generated by a non-desensitizing receptor mutant. This suggests a fundamental role of this pathway in de-activation of integrin-dependent cell adhesion.

Gut Microbiota-Derived Tryptophan Metabolites Modulate Inflammatory Response in Hepatocytes and Macrophages.

PubMed

Krishnan, Smitha; Ding, Yufang; Saedi, Nima; Choi, Maria; Sridharan, Gautham V; Sherr, David H; Yarmush, Martin L; Alaniz, Robert C; Jayaraman, Arul; Lee, Kyongbum

2018-04-24

The gut microbiota plays a significant role in the progression of fatty liver disease; however, the mediators and their mechanisms remain to be elucidated. Comparing metabolite profile differences between germ-free and conventionally raised mice against differences between mice fed a low- and high-fat diet (HFD), we identified tryptamine and indole-3-acetate (I3A) as metabolites that depend on the microbiota and are depleted under a HFD. Both metabolites reduced fatty-acid- and LPS-stimulated production of pro-inflammatory cytokines in macrophages and inhibited the migration of cells toward a chemokine, with I3A exhibiting greater potency. In hepatocytes, I3A attenuated inflammatory responses under lipid loading and reduced the expression of fatty acid synthase and sterol regulatory element-binding protein-1c. These effects were abrogated in the presence of an aryl-hydrocarbon receptor (AhR) antagonist, indicating that the effects are AhR dependent. Our results suggest that gut microbiota could influence inflammatory responses in the liver through metabolites engaging host receptors. Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

Nitric oxide-mediated modulation of iron regulatory proteins: implication for cellular iron homeostasis.

PubMed

Kim, Sangwon; Ponka, Prem

2002-01-01

Iron regulatory proteins (IRP1 and IRP2) control the synthesis of transferrin receptors (TfR) and ferritin by binding to iron-responsive elements (IREs) that are located in the 3' untranslated region (UTR) and the 5' UTR of their respective mRNAs. Cellular iron levels affect binding of IRPs to IREs and consequently expression of TfR and ferritin. Moreover, NO(.), a redox species of nitric oxide that interacts primarily with iron, can activate IRP1 RNA-binding activity resulting in an increase in TfR mRNA levels and a decrease in ferritin synthesis. We have shown that treatment of RAW 264.7 cells (a murine macrophage cell line) with NO(+) (nitrosonium ion, which causes S-nitrosylation of thiol groups) resulted in a rapid decrease in RNA-binding of IRP2, followed by IRP2 degradation, and these changes were associated with a decrease in TfR mRNA levels and a dramatic increase in ferritin synthesis. Moreover, we demonstrated that stimulation of RAW 264.7 cells with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) increased IRP1 binding activity, whereas RNA-binding of IRP2 decreased and was followed by a degradation of this protein. Furthermore, the decrease of IRP2 binding/protein levels was associated with a decrease in TfR mRNA levels and an increase in ferritin synthesis in LPS/IFN-gamma-treated cells, and these changes were prevented by inhibitors of inducible nitric oxide synthase. These results suggest that NO(+)-mediated degradation of IRP2 plays a major role in iron metabolism during inflammation.

Understanding allosteric interactions in G protein-coupled receptors using Supervised Molecular Dynamics: A prototype study analysing the human A3 adenosine receptor positive allosteric modulator LUF6000.

PubMed

Deganutti, Giuseppe; Cuzzolin, Alberto; Ciancetta, Antonella; Moro, Stefano

2015-07-15

The search for G protein-coupled receptors (GPCRs) allosteric modulators represents an active research field in medicinal chemistry. Allosteric modulators usually exert their activity only in the presence of the orthosteric ligand by binding to protein sites topographically different from the orthosteric cleft. They therefore offer potentially therapeutic advantages by selectively influencing tissue responses only when the endogenous agonist is present. The prediction of putative allosteric site location, however, is a challenging task. In facts, they are usually located in regions showing more structural variation among the family members. In the present work, we applied the recently developed Supervised Molecular Dynamics (SuMD) methodology to interpret at the molecular level the positive allosteric modulation mediated by LUF6000 toward the human adenosine A3 receptor (hA3 AR). Our data suggest at least two possible mechanisms to explain the experimental data available. This study represent, to the best of our knowledge, the first case reported of an allosteric recognition mechanism depicted by means of molecular dynamics simulations. Copyright © 2015 Elsevier Ltd. All rights reserved.

Allosteric analysis of glucocorticoid receptor-DNA interface induced by cyclic Py-Im polyamide: a molecular dynamics simulation study.

PubMed

Wang, Yaru; Ma, Na; Wang, Yan; Chen, Guangju

2012-01-01

It has been extensively developed in recent years that cell-permeable small molecules, such as polyamide, can be programmed to disrupt transcription factor-DNA interfaces and can silence aberrant gene expression. For example, cyclic pyrrole-imidazole polyamide that competes with glucocorticoid receptor (GR) for binding to glucocorticoid response elements could be expected to affect the DNA dependent binding by interfering with the protein-DNA interface. However, how such small molecules affect the transcription factor-DNA interfaces and gene regulatory pathways through DNA structure distortion is not fully understood so far. In the present work, we have constructed some models, especially the ternary model of polyamides+DNA+GR DNA-binding domain (GRDBD) dimer, and carried out molecular dynamics simulations and free energy calculations for them to address how polyamide molecules disrupt the GRDBD and DNA interface when polyamide and protein bind at the same sites on opposite grooves of DNA. We found that the cyclic polyamide binding in minor groove of DNA can induce a large structural perturbation of DNA, i.e. a >4 Å widening of the DNA minor groove and a compression of the major groove by more than 4 Å as compared with the DNA molecule in the GRDBD dimer+DNA complex. Further investigations for the ternary system of polyamides+DNA+GRDBD dimer and the binary system of allosteric DNA+GRDBD dimer revealed that the compression of DNA major groove surface causes GRDBD to move away from the DNA major groove with the initial average distance of ∼4 Å to the final average distance of ∼10 Å during 40 ns simulation course. Therefore, this study straightforward explores how small molecule targeting specific sites in the DNA minor groove disrupts the transcription factor-DNA interface in DNA major groove, and consequently modulates gene expression.

Chlorophyll-Derivative Modulation of Rhodopsin Signaling Properties through Evolutionarily Conserved Interaction Pathways

PubMed Central

Woods, Kristina N.; Pfeffer, Jürgen; Klein-Seetharaman, Judith

2017-01-01

Retinal is the light-absorbing chromophore that is responsible for the activation of visual pigments and light-driven ion pumps. Evolutionary changes in the intermolecular interactions of the retinal with specific amino acids allow for adaptation of the spectral characteristics, referred to as spectral tuning. However, it has been proposed that a specific species of dragon fish has bypassed the adaptive evolutionary process of spectral tuning and replaced it with a single evolutionary event: photosensitization of rhodopsin by chlorophyll derivatives. Here, by using a combination of experimental measurements and computational modeling to probe retinal-receptor interactions in rhodopsin, we show how the binding of the chlorophyll derivative, chlorin-e6 (Ce6) in the intracellular domain (ICD) of the receptor allosterically excites G-protein coupled receptor class A (GPCR-A) conserved long-range correlated fluctuations that connect distant parts of the receptor. These long-range correlated motions are associated with regulating the dynamics and intermolecular interactions of specific amino acids in the retinal ligand-binding pocket that have been associated with shifts in the absorbance peak maximum (λmax) and hence, spectral sensitivity of the visual system. Moreover, the binding of Ce6 affects the overall global properties of the receptor. Specifically, we find that Ce6-induced dynamics alter the thermal stability of rhodopsin by adjusting hydrogen-bonding interactions near the receptor active-site that consequently also influences the intrinsic conformational equilibrium of the receptor. Due to the conservation of the ICD residues amongst different receptors in this class and the fact that all GPCR-A receptors share a common mechanism of activation, it is possible that the allosteric associations excited in rhodopsin with Ce6 binding are a common feature in all class A GPCRs. PMID:29312953

Increased cyclic guanosine monophosphate production and overexpression of atrial natriuretic peptide A-receptor mRNA in spontaneously hypertensive rats.

PubMed

Tremblay, J; Huot, C; Willenbrock, R C; Bayard, F; Gossard, F; Fujio, N; Koch, C; Kuchel, O; Debinski, W; Hamet, P

1993-11-01

Atrial natriuretic peptide (ANP) specifically stimulates particulate guanylate cyclase, and cyclic guanosine monophosphate (cGMP) has been recognized as its second messenger. Spontaneously hypertensive rats (SHR) have elevated plasma ANP levels, but manifest an exaggerated natriuretic and diuretic response to exogenous ANP when compared to normotensive strains. In isolated glomeruli, the maximal cGMP response to ANP corresponds to a 12- to 14-fold increase over basal levels in normotensive strains (Wistar 13 +/- 2; Wistar-Kyoto 12 +/- 2; Sprague-Dawley 14 +/- 2) while a maximal 33 +/- 3-fold elevation occurs in SHR (P < 0.001). This hyperresponsiveness of cGMP is reproducible in intact glomeruli from SHR from various commercial sources. Furthermore, this abnormality develops early in life, even before hypertension is clearly established, and persists despite pharmacological modulation of blood pressure, indicating that it is a primary event in hypertension. In vitro studies have revealed a higher particulate guanylate cyclase activity in membranes from glomeruli and other tissues from SHR. This increase is not accounted for by different patterns of ANP binding to its receptor subtypes between normotensive and hypertensive strains, as assessed by competitive displacement with C-ANP102-121, an analog which selectively binds to one ANP receptor subtype. The hyperactivity of particulate guanylate cyclase in SHR and its behavior under basal, ligand (ANP), and detergent-enhanced conditions could be attributed either to increased expression or augmented sensitivity of the enzyme. Radiation-inactivation analysis does not evoke a disturbance in the size of regulatory elements normally repressing enzymatic activity, while the expression of particulate guanylate cyclase gene using mutated standard of A- and B-receptors partial cDNAs, quantified by polymerase chain reaction (PCR) transcript titration assay, manifests a selective increase of one guanylate cyclase subtype. Our data suggest that in hypertension, genetic overexpression of the ANP A-receptor subtype is related to the exaggerated biological response to ANP in this disease.

SRC-like adaptor protein 2 (SLAP2) is a negative regulator of KIT-D816V-mediated oncogenic transformation.

PubMed

Rupar, Kaja; Moharram, Sausan A; Kazi, Julhash U; Rönnstrand, Lars

2018-04-23

KIT is a receptor tyrosine kinase (RTK) involved in several cellular processes such as regulation of proliferation, survival and differentiation of early hematopoietic cells, germ cells and melanocytes. Activation of KIT results in phosphorylation of tyrosine residues in the receptor, and recruitment of proteins that mediate downstream signaling and also modulate receptor signaling. Here we show that the SRC-like adaptor protein 2 (SLAP2) binds to wild-type KIT in a ligand-dependent manner and is furthermore found constitutively associated with the oncogenic mutant KIT-D816V. Peptide fishing analysis mapped pY568 and pY570 as potential SLAP2 association sites in KIT, which overlaps with the SRC binding sites in KIT. Expression of SLAP2 in cells expressing the transforming mutant KIT-D816V led to reduced cell viability and reduced colony formation. SLAP2 also partially blocked phosphorylation of several signal transduction molecules downstream of KIT such as AKT, ERK, p38 and STAT3. Finally, SLAP2 expression enhanced ubiquitination of KIT and its subsequent degradation. Taken together, our data demonstrate that SLAP2 negatively modulates KIT-D816V-mediated transformation by enhancing degradation of the receptor.

Agonistic aptamer to the insulin receptor leads to biased signaling and functional selectivity through allosteric modulation

PubMed Central

Yunn, Na-Oh; Koh, Ara; Han, Seungmin; Lim, Jong Hun; Park, Sehoon; Lee, Jiyoun; Kim, Eui; Jang, Sung Key; Berggren, Per-Olof; Ryu, Sung Ho

2015-01-01

Due to their high affinity and specificity, aptamers have been widely used as effective inhibitors in clinical applications. However, the ability to activate protein function through aptamer-protein interaction has not been well-elucidated. To investigate their potential as target-specific agonists, we used SELEX to generate aptamers to the insulin receptor (IR) and identified an agonistic aptamer named IR-A48 that specifically binds to IR, but not to IGF-1 receptor. Despite its capacity to stimulate IR autophosphorylation, similar to insulin, we found that IR-A48 not only binds to an allosteric site distinct from the insulin binding site, but also preferentially induces Y1150 phosphorylation in the IR kinase domain. Moreover, Y1150-biased phosphorylation induced by IR-A48 selectively activates specific signaling pathways downstream of IR. In contrast to insulin-mediated activation of IR, IR-A48 binding has little effect on the MAPK pathway and proliferation of cancer cells. Instead, AKT S473 phosphorylation is highly stimulated by IR-A48, resulting in increased glucose uptake both in vitro and in vivo. Here, we present IR-A48 as a biased agonist able to selectively induce the metabolic activity of IR through allosteric binding. Furthermore, our study also suggests that aptamers can be a promising tool for developing artificial biased agonists to targeted receptors. PMID:26245346

Azadirachtin interacts with the tumor necrosis factor (TNF) binding domain of its receptors and inhibits TNF-induced biological responses.

PubMed

Thoh, Maikho; Kumar, Pankaj; Nagarajaram, Hampathalu A; Manna, Sunil K

2010-02-19

The role of azadirachtin, an active component of a medicinal plant Neem (Azadirachta indica), on TNF-induced cell signaling in human cell lines was investigated. Azadirachtin blocks TNF-induced activation of nuclear factor kappaB (NF-kappaB) and also expression of NF-kappaB-dependent genes such as adhesion molecules and cyclooxygenase 2. Azadirachtin inhibits the inhibitory subunit of NF-kappaB (IkappaB alpha) phosphorylation and thereby its degradation and RelA (p65) nuclear translocation. It blocks IkappaB alpha kinase (IKK) activity ex vivo, but not in vitro. Surprisingly, azadirachtin blocks NF-kappaB DNA binding activity in transfected cells with TNF receptor-associated factor (TRAF)2, TNF receptor-associated death domain (TRADD), IKK, or p65, but not with TNFR, suggesting its effect is at the TNFR level. Azadirachtin blocks binding of TNF, but not IL-1, IL-4, IL-8, or TNF-related apoptosis-inducing ligand (TRAIL) with its respective receptors. Anti-TNFR antibody or TNF protects azadirachtin-mediated down-regulation of TNFRs. Further, in silico data suggest that azadirachtin strongly binds in the TNF binding site of TNFR. Overall, our data suggest that azadirachtin modulates cell surface TNFRs thereby decreasing TNF-induced biological responses. Thus, azadirachtin exerts an anti-inflammatory response by a novel pathway, which may be beneficial for anti-inflammatory therapy.

Azadirachtin Interacts with the Tumor Necrosis Factor (TNF) Binding Domain of Its Receptors and Inhibits TNF-induced Biological Responses*

PubMed Central

Thoh, Maikho; Kumar, Pankaj; Nagarajaram, Hampathalu A.; Manna, Sunil K.

2010-01-01

The role of azadirachtin, an active component of a medicinal plant Neem (Azadirachta indica), on TNF-induced cell signaling in human cell lines was investigated. Azadirachtin blocks TNF-induced activation of nuclear factor κB (NF-κB) and also expression of NF-κB-dependent genes such as adhesion molecules and cyclooxygenase 2. Azadirachtin inhibits the inhibitory subunit of NF-κB (IκBα) phosphorylation and thereby its degradation and RelA (p65) nuclear translocation. It blocks IκBα kinase (IKK) activity ex vivo, but not in vitro. Surprisingly, azadirachtin blocks NF-κB DNA binding activity in transfected cells with TNF receptor-associated factor (TRAF)2, TNF receptor-associated death domain (TRADD), IKK, or p65, but not with TNFR, suggesting its effect is at the TNFR level. Azadirachtin blocks binding of TNF, but not IL-1, IL-4, IL-8, or TNF-related apoptosis-inducing ligand (TRAIL) with its respective receptors. Anti-TNFR antibody or TNF protects azadirachtin-mediated down-regulation of TNFRs. Further, in silico data suggest that azadirachtin strongly binds in the TNF binding site of TNFR. Overall, our data suggest that azadirachtin modulates cell surface TNFRs thereby decreasing TNF-induced biological responses. Thus, azadirachtin exerts an anti-inflammatory response by a novel pathway, which may be beneficial for anti-inflammatory therapy. PMID:20018848

Differential Modulation of Beta-Adrenergic Receptor Signaling by Trace Amine-Associated Receptor 1 Agonists

PubMed Central

Nürnberg, Daniela; Grüters, Annette; Führer-Sakel, Dagmar; Krude, Heiko; Köhrle, Josef; Schöneberg, Torsten; Biebermann, Heike

2011-01-01

Trace amine-associated receptors (TAAR) are rhodopsin-like G-protein-coupled receptors (GPCR). TAAR are involved in modulation of neuronal, cardiac and vascular functions and they are potentially linked with neurological disorders like schizophrenia and Parkinson's disease. Subtype TAAR1, the best characterized TAAR so far, is promiscuous for a wide set of ligands and is activated by trace amines tyramine (TYR), phenylethylamine (PEA), octopamine (OA), but also by thyronamines, dopamine, and psycho-active drugs. Unfortunately, effects of trace amines on signaling of the two homologous β-adrenergic receptors 1 (ADRB1) and 2 (ADRB2) have not been clarified yet in detail. We, therefore, tested TAAR1 agonists TYR, PEA and OA regarding their effects on ADRB1/2 signaling by co-stimulation studies. Surprisingly, trace amines TYR and PEA are partial allosteric antagonists at ADRB1/2, whereas OA is a partial orthosteric ADRB2-antagonist and ADRB1-agonist. To specify molecular reasons for TAAR1 ligand promiscuity and for observed differences in signaling effects on particular aminergic receptors we compared TAAR, tyramine (TAR) octopamine (OAR), ADRB1/2 and dopamine receptors at the structural level. We found especially for TAAR1 that the remarkable ligand promiscuity is likely based on high amino acid similarity in the ligand-binding region compared with further aminergic receptors. On the other hand few TAAR specific properties in the ligand-binding site might determine differences in ligand-induced effects compared to ADRB1/2. Taken together, this study points to molecular details of TAAR1-ligand promiscuity and identified specific trace amines as allosteric or orthosteric ligands of particular β-adrenergic receptor subtypes. PMID:22073124

Potent and efficacious inhibition of CXCR2 signaling by biparatopic nanobodies combining two distinct modes of action.

PubMed

Bradley, M E; Dombrecht, B; Manini, J; Willis, J; Vlerick, D; De Taeye, S; Van den Heede, K; Roobrouck, A; Grot, E; Kent, T C; Laeremans, T; Steffensen, S; Van Heeke, G; Brown, Z; Charlton, S J; Cromie, K D

2015-02-01

Chemokines and chemokine receptors are key modulators in inflammatory diseases and malignancies. Here, we describe the identification and pharmacologic characterization of nanobodies selectively blocking CXCR2, the most promiscuous of all chemokine receptors. Two classes of selective monovalent nanobodies were identified, and detailed epitope mapping showed that these bind to distinct, nonoverlapping epitopes on the CXCR2 receptor. The N-terminal-binding or class 1 monovalent nanobodies possessed potencies in the single-digit nanomolar range but lacked complete efficacy at high agonist concentrations. In contrast, the extracellular loop-binding or class 2 monovalent nanobodies were of lower potency but were more efficacious and competitively inhibited the CXCR2-mediated functional response in both recombinant and neutrophil in vitro assays. In addition to blocking CXCR2 signaling mediated by CXCL1 (growth-related oncogene α) and CXCL8 (interleukin-8), both classes of nanobodies displayed inverse agonist behavior. Bivalent and biparatopic nanobodies were generated, respectively combining nanobodies from the same or different classes via glycine/serine linkers. Interestingly, receptor mutation and competition studies demonstrated that the biparatopic nanobodies were able to avidly bind epitopes within one or across two CXCR2 receptor molecules. Most importantly, the biparatopic nanobodies were superior over their monovalent and bivalent counterparts in terms of potency and efficacy. Copyright © 2015 by The American Society for Pharmacology and Experimental Therapeutics.

Structural Insights into SraP-Mediated Staphylococcus aureus Adhesion to Host Cells

PubMed Central

Zhang, Juan; Wang, Lei; Bai, Xiao-Hui; Zhang, Shi-Jie; Ren, Yan-Min; Li, Na; Zhang, Yong-Hui; Zhang, Zhiyong; Gong, Qingguo; Mei, Yide; Xue, Ting; Zhang, Jing-Ren; Chen, Yuxing; Zhou, Cong-Zhao

2014-01-01

Staphylococcus aureus, a Gram-positive bacterium causes a number of devastating human diseases, such as infective endocarditis, osteomyelitis, septic arthritis and sepsis. S. aureus SraP, a surface-exposed serine-rich repeat glycoprotein (SRRP), is required for the pathogenesis of human infective endocarditis via its ligand-binding region (BR) adhering to human platelets. It remains unclear how SraP interacts with human host. Here we report the 2.05 Å crystal structure of the BR of SraP, revealing an extended rod-like architecture of four discrete modules. The N-terminal legume lectin-like module specifically binds to N-acetylneuraminic acid. The second module adopts a β-grasp fold similar to Ig-binding proteins, whereas the last two tandem repetitive modules resemble eukaryotic cadherins but differ in calcium coordination pattern. Under the conditions tested, small-angle X-ray scattering and molecular dynamic simulation indicated that the three C-terminal modules function as a relatively rigid stem to extend the N-terminal lectin module outwards. Structure-guided mutagenesis analyses, in addition to a recently identified trisaccharide ligand of SraP, enabled us to elucidate that SraP binding to sialylated receptors promotes S. aureus adhesion to and invasion into host epithelial cells. Our findings have thus provided novel structural and functional insights into the SraP-mediated host-pathogen interaction of S. aureus. PMID:24901708

Mutagenesis of Paramyxovirus Hemagglutinin-Neuraminidase Membrane-Proximal Stalk Region Influences Stability, Receptor Binding, and Neuraminidase Activity.

PubMed

Adu-Gyamfi, Emmanuel; Kim, Lori S; Jardetzky, Theodore S; Lamb, Robert A

2016-09-01

Paramyxoviridae consist of a large family of enveloped, negative-sense, nonsegmented single-stranded RNA viruses that account for a significant number of human and animal diseases. The fusion process for nearly all paramyxoviruses involves the mixing of the host cell plasma membrane and the virus envelope in a pH-independent fashion. Fusion is orchestrated via the concerted action of two surface glycoproteins: an attachment protein called hemagglutinin-neuraminidase (HN [also called H or G depending on virus type and substrate]), which acts as a receptor binding protein, and a fusion (F) protein, which undergoes a major irreversible refolding process to merge the two membranes. Recent biochemical evidence suggests that receptor binding by HN is dispensable for cell-cell fusion. However, factors that influence the stability and/or conformation of the HN 4-helix bundle (4HB) stalk have not been studied. Here, we used oxidative cross-linking as well as functional assays to investigate the role of the structurally unresolved membrane-proximal stalk region (MPSR) (residues 37 to 58) of HN in the context of headless and full-length HN membrane fusion promotion. Our data suggest that the receptor binding head serves to stabilize the stalk to regulate fusion. Moreover, we found that the MPSR of HN modulates receptor binding and neuraminidase activity without a corresponding regulation of F triggering. Paramyxoviruses require two viral membrane glycoproteins, the attachment protein variously called HN, H, or G and the fusion protein (F), to couple host receptor recognition to virus-cell fusion. The HN protein has a globular head that is attached to a membrane-anchored flexible stalk of ∼80 residues and has three activities: receptor binding, neuraminidase, and fusion activation. In this report, we have identified the functional significance of the membrane-proximal stalk region (MPSR) (HN, residues 37 to 56) of the paramyxovirus parainfluenza virus (PIV5), a region of the HN stalk that has not had its structure determined by X-ray crystallography. Our data suggest that the MPSR influences receptor binding and neuraminidase activity via an indirect mechanism. Moreover, the receptor binding head group stabilizes the 4HB stalk as part of the general mechanism to fine-tune F-activation. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

Energetics of Endotoxin Recognition in the Toll-Like Receptor 4 Innate Immune Response.

PubMed

Paramo, Teresa; Tomasio, Susana M; Irvine, Kate L; Bryant, Clare E; Bond, Peter J

2015-12-09

Bacterial outer membrane lipopolysaccharide (LPS) potently stimulates the mammalian innate immune system, and can lead to sepsis, the primary cause of death from infections. LPS is sensed by Toll-like receptor 4 (TLR4) in complex with its lipid-binding coreceptor MD-2, but subtle structural variations in LPS can profoundly modulate the response. To better understand the mechanism of LPS-induced stimulation and bacterial evasion, we have calculated the binding affinity to MD-2 of agonistic and antagonistic LPS variants including lipid A, lipid IVa, and synthetic antagonist Eritoran, and provide evidence that the coreceptor is a molecular switch that undergoes ligand-induced conformational changes to appropriately activate or inhibit the receptor complex. The plasticity of the coreceptor binding cavity is shown to be essential for distinguishing between ligands, whilst similar calculations for a model bacterial LPS bilayer reveal the "membrane-like" nature of the protein cavity. The ability to predict the activity of LPS variants should facilitate the rational design of TLR4 therapeutics.

Energetics of Endotoxin Recognition in the Toll-Like Receptor 4 Innate Immune Response

PubMed Central

Paramo, Teresa; Tomasio, Susana M.; Irvine, Kate L.; Bryant, Clare E.; Bond, Peter J.

2015-01-01

Bacterial outer membrane lipopolysaccharide (LPS) potently stimulates the mammalian innate immune system, and can lead to sepsis, the primary cause of death from infections. LPS is sensed by Toll-like receptor 4 (TLR4) in complex with its lipid-binding coreceptor MD-2, but subtle structural variations in LPS can profoundly modulate the response. To better understand the mechanism of LPS-induced stimulation and bacterial evasion, we have calculated the binding affinity to MD-2 of agonistic and antagonistic LPS variants including lipid A, lipid IVa, and synthetic antagonist Eritoran, and provide evidence that the coreceptor is a molecular switch that undergoes ligand-induced conformational changes to appropriately activate or inhibit the receptor complex. The plasticity of the coreceptor binding cavity is shown to be essential for distinguishing between ligands, whilst similar calculations for a model bacterial LPS bilayer reveal the “membrane-like” nature of the protein cavity. The ability to predict the activity of LPS variants should facilitate the rational design of TLR4 therapeutics. PMID:26647780

Glycan-independent binding and internalization of human IgM to FCMR, its cognate cellular receptor

NASA Astrophysics Data System (ADS)

Lloyd, Katy A.; Wang, Jiabin; Urban, Britta C.; Czajkowsky, Daniel M.; Pleass, Richard J.

2017-02-01

IgM is the first antibody to be produced in immune responses and plays an important role in the neutralization of bacteria and viruses. Human IgM is heavily glycosylated, featuring five N-linked glycan sites on the μ chain and one on the J-chain. Glycosylation of IgG is known to modulate the effector functions of Fcγ receptors. In contrast, little is known about the effect of glycosylation on IgM binding to the human Fcμ receptor (hFCMR). In this study, we identify the Cμ4 domain of IgM as the target of hFCMR, and show that binding and internalization of IgM by hFCMR is glycan-independent. We generated a homology-based structure for hFCMR and used molecular dynamic simulations to show how this interaction with IgM may occur. Finally, we reveal an inhibitory function for IgM in the proliferation of T cells.

Quantitative analysis reveals how EGFR activation and downregulation are coupled in normal but not in cancer cells

PubMed Central

Capuani, Fabrizio; Conte, Alexia; Argenzio, Elisabetta; Marchetti, Luca; Priami, Corrado; Polo, Simona; Di Fiore, Pier Paolo; Sigismund, Sara; Ciliberto, Andrea

2015-01-01

Ubiquitination of the epidermal growth factor receptor (EGFR) that occurs when Cbl and Grb2 bind to three phosphotyrosine residues (pY1045, pY1068 and pY1086) on the receptor displays a sharp threshold effect as a function of EGF concentration. Here we use a simple modelling approach together with experiments to show that the establishment of the threshold requires both the multiplicity of binding sites and cooperative binding of Cbl and Grb2 to the EGFR. While the threshold is remarkably robust, a more sophisticated model predicted that it could be modulated as a function of EGFR levels on the cell surface. We confirmed experimentally that the system has evolved to perform optimally at physiological levels of EGFR. As a consequence, this system displays an intrinsic weakness that causes—at the supraphysiological levels of receptor and/or ligand associated with cancer—uncoupling of the mechanisms leading to signalling through phosphorylation and attenuation through ubiquitination. PMID:26264748

Metabotropic glutamate receptor subtype 5: molecular pharmacology, allosteric modulation and stimulus bias

PubMed Central

Sengmany, K

2015-01-01

The metabotropic glutamate receptor subtype 5 (mGlu5) is a family C GPCR that has been implicated in various neuronal processes and, consequently, in several CNS disorders. Over the past few decades, GPCR‐based drug discovery, including that for mGlu5 receptors, has turned considerable attention to targeting allosteric binding sites. Modulation of endogenous agonists by allosteric ligands offers the advantages of spatial and temporal fine‐tuning of receptor activity, increased selectivity and reduced adverse effects with the potential to elicit improved clinical outcomes. Further, with greater appreciation of the multifaceted nature of the transduction of mGlu5 receptor signalling, it is increasingly apparent that drug discovery must take into consideration unique receptor conformations and the potential for stimulus‐bias. This novel paradigm proposes that different ligands may differentially modulate distinct signalling pathways arising from the same receptor. We review our current understanding of the complexities of mGlu5 receptor signalling and regulation, and how these relate to allosteric ligands. Ultimately, a deeper appreciation of these relationships will provide the foundation for targeted drug design of compounds with increased selectivity, not only for the desired receptor but also for the desired signalling outcome from the receptor. Linked Articles This article is part of a themed section on Molecular Pharmacology of G Protein‐Coupled Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v173.20/issuetoc PMID:26276909

Key structural features of nonsteroidal ligands for binding and activation of the androgen receptor.

PubMed

Yin, Donghua; He, Yali; Perera, Minoli A; Hong, Seoung Soo; Marhefka, Craig; Stourman, Nina; Kirkovsky, Leonid; Miller, Duane D; Dalton, James T

2003-01-01

The purposes of the present studies were to examine the androgen receptor (AR) binding ability and in vitro functional activity of multiple series of nonsteroidal compounds derived from known antiandrogen pharmacophores and to investigate the structure-activity relationships (SARs) of these nonsteroidal compounds. The AR binding properties of sixty-five nonsteroidal compounds were assessed by a radioligand competitive binding assay with the use of cytosolic AR prepared from rat prostates. The AR agonist and antagonist activities of high-affinity ligands were determined by the ability of the ligand to regulate AR-mediated transcriptional activation in cultured CV-1 cells, using a cotransfection assay. Nonsteroidal compounds with diverse structural features demonstrated a wide range of binding affinity for the AR. Ten compounds, mainly from the bicalutamide-related series, showed a binding affinity superior to the structural pharmacophore from which they were derived. Several SARs regarding nonsteroidal AR binding were revealed from the binding data, including stereoisomeric conformation, steric effect, and electronic effect. The functional activity of high-affinity ligands ranged from antagonist to full agonist for the AR. Several structural features were found to be determinative of agonist and antagonist activities. The nonsteroidal AR agonists identified from the present studies provided a pool of candidates for further development of selective androgen receptor modulators (SARMs) for androgen therapy. Also, these studies uncovered or confirmed numerous important SARs governing AR binding and functional properties by nonsteroidal molecules, which would be valuable in the future structural optimization of SARMs.

Quantitative High-throughput Luciferase Screening in Identifying CAR Modulators

PubMed Central

Lynch, Caitlin; Zhao, Jinghua; Wang, Hongbing; Xia, Menghang

2017-01-01

Summary The constitutive androstane receptor (CAR, NR1I3) is responsible for the transcription of multiple drug metabolizing enzymes and transporters. There are two possible methods of activation for CAR, direct ligand binding and a ligand-independent method, which makes this a unique nuclear receptor. Both of these mechanisms require translocation of CAR from the cytoplasm into the nucleus. Interestingly, CAR is constitutively active in immortalized cell lines due to the basal nuclear location of this receptor. This creates an important challenge in most in vitro assay models because immortalized cells cannot be used without inhibiting the basal activity. In this book chapter, we go into detail of how to perform quantitative high-throughput screens to identify hCAR1 modulators through the employment of a double stable cell line. Using this line, we are able to identify activators, as well as deactivators, of the challenging nuclear receptor, CAR. PMID:27518621

Quantitative High-Throughput Luciferase Screening in Identifying CAR Modulators.

PubMed

Lynch, Caitlin; Zhao, Jinghua; Wang, Hongbing; Xia, Menghang

2016-01-01

The constitutive androstane receptor (CAR, NR1I3) is responsible for the transcription of multiple drug metabolizing enzymes and transporters. There are two possible methods of activation for CAR, direct ligand binding and a ligand-independent method, which makes this a unique nuclear receptor. Both of these mechanisms require translocation of CAR from the cytoplasm into the nucleus. Interestingly, CAR is constitutively active in immortalized cell lines due to the basal nuclear location of this receptor. This creates an important challenge in most in vitro assay models because immortalized cells cannot be used without inhibiting the high basal activity. In this book chapter, we go into detail of how to perform quantitative high-throughput screens to identify hCAR1 modulators through the employment of a double stable cell line. Using this line, we are able to identify activators, as well as deactivators, of the challenging nuclear receptor, CAR.

Drug Management of Visceral Pain: Concepts from Basic Research

PubMed Central

Davis, Mellar P.

2012-01-01

Visceral pain is experienced by 40% of the population, and 28% of cancer patients suffer from pain arising from intra- abdominal metastasis or from treatment. Neuroanatomy of visceral nociception and neurotransmitters, receptors, and ion channels that modulate visceral pain are qualitatively or quantitatively different from those that modulate somatic and neuropathic pain. Visceral pain should be recognized as distinct pain phenotype. TRPV1, Na 1.8, and ASIC3 ion channels and peripheral kappa opioid receptors are important mediators of visceral pain. Mu agonists, gabapentinoids, and GABAB agonists reduce pain by binding to central receptors and channels. Combinations of analgesics and adjuvants in animal models have supra-additive antinociception and should be considered in clinical trials. This paper will discuss the neuroanatomy, receptors, ion channels, and neurotransmitters important to visceral pain and provide a basic science rationale for analgesic trials and management. PMID:22619712

Induced Genome-Wide Binding of Three Arabidopsis WRKY Transcription Factors during Early MAMP-Triggered Immunity

PubMed Central

Birkenbihl, Rainer P.; Kracher, Barbara; Roccaro, Mario

2017-01-01

During microbial-associated molecular pattern-triggered immunity (MTI), molecules derived from microbes are perceived by cell surface receptors and upon signaling to the nucleus initiate a massive transcriptional reprogramming critical to mount an appropriate host defense response. WRKY transcription factors play an important role in regulating these transcriptional processes. Here, we determined on a genome-wide scale the flg22-induced in vivo DNA binding dynamics of three of the most prominent WRKY factors, WRKY18, WRKY40, and WRKY33. The three WRKY factors each bound to more than 1000 gene loci predominantly at W-box elements, the known WRKY binding motif. Binding occurred mainly in the 500-bp promoter regions of these genes. Many of the targeted genes are involved in signal perception and transduction not only during MTI but also upon damage-associated molecular pattern-triggered immunity, providing a mechanistic link between these functionally interconnected basal defense pathways. Among the additional targets were genes involved in the production of indolic secondary metabolites and in modulating distinct plant hormone pathways. Importantly, among the targeted genes were numerous transcription factors, encoding predominantly ethylene response factors, active during early MTI, and WRKY factors, supporting the previously hypothesized existence of a WRKY subregulatory network. Transcriptional analysis revealed that WRKY18 and WRKY40 function redundantly as negative regulators of flg22-induced genes often to prevent exaggerated defense responses. PMID:28011690

Non-canonical dynamic mechanisms of interaction between the p66Shc protein and Met receptor

PubMed Central

Landry, Mélissa; Pomerleau, Véronique; Saucier, Caroline

2016-01-01

Met receptor tyrosine kinase (RTK) is known to bind to the three distinct protein isoforms encoded by the ShcA (Shc) gene. Structure–function studies have unveiled critical roles for p52Shc-dependent signalling pathways in Met-regulated biological functions. The molecular basis of the interaction between the Met and p52Shc proteins is well-defined, but not for the longest protein isoform, p66Shc. In the present study, co-immunoprecipitation assays were performed in human embryonic kidney 293 (HEK293) cells, transiently co-transfected with Met and p66Shc mutants, in order to define the molecular determinants involved in mediating Met–p66Shc interaction. Our results show that p66Shc interacts constitutively with the receptor Met, and the Grb2 (growth factor receptor-bound protein-2) and Gab1 (Grb2-associated binder-1) adaptor proteins. Although its phosphotyrosine-binding domain (PTB) and Src homology 2 (SH2) domains co-ordinate p66Shc binding to non-activated Met receptor, these phosphotyrosine-binding modules, and its collagen homology domain 2 (CH2) region, exert negative constraints. In contrast, p66Shc interaction with the activated Met depends mainly on the integrity of its PTB domain, and to a lesser extent of its SH2 domain. Even though not required for the recruitment of p66Shc, tyrosine phosphorylation of p66Shc by activated Met enhances these interactions by mechanisms not reliant on the integrity of the Met multisubstrate-binding site. In turn, this increases phosphotyrosine-dependent p66Shc–Grb2–Gab1 complex formation away from the receptor, while blocking Grb2 and Gab1 recruitment to activated Met. In conclusion, we identify, for the first time, a novel non-canonical dynamic mode of interaction between Met and the p66 protein isoform of Shc and its effects on rewiring binding effector complexes according to the activation state of the receptor. PMID:27048591

Selective androgen receptor modulators in preclinical and clinical development

PubMed Central

Narayanan, Ramesh; Mohler, Michael L.; Bohl, Casey E.; Miller, Duane D.; Dalton, James T.

2008-01-01

Androgen receptor (AR) plays a critical role in the function of several organs including primary and accessory sexual organs, skeletal muscle, and bone, making it a desirable therapeutic target. Selective androgen receptor modulators (SARMs) bind to the AR and demonstrate osteo- and myo-anabolic activity; however, unlike testosterone and other anabolic steroids, these nonsteroidal agents produce less of a growth effect on prostate and other secondary sexual organs. SARMs provide therapeutic opportunities in a variety of diseases, including muscle wasting associated with burns, cancer, or end-stage renal disease, osteoporosis, frailty, and hypogonadism. This review summarizes the current standing of research and development of SARMs, crystallography of AR with SARMs, plausible mechanisms for their action and the potential therapeutic indications for this emerging class of drugs. PMID:19079612

Structural Biology and Evolution of the TGF-β Family

PubMed Central

Hinck, Andrew P.; Mueller, Thomas D.; Springer, Timothy A.

2017-01-01

We review the evolution and structure of members of the transforming growth factor β (TGF-β) family, antagonistic or agonistic modulators, and receptors that regulate TGF-β signaling in extracellular environments. The growth factor (GF) domain common to all family members and many of their antagonists evolved from a common cystine knot growth factor (CKGF) domain. The CKGF superfamily comprises six distinct families in primitive metazoans, including the TGF-β and Dan families. Compared with Wnt/Frizzled and Notch/Delta families that also specify body axes, cell fate, tissues, and other families that contain CKGF domains that evolved in parallel, the TGF-β family was the most fruitful in evolution. Complexes between the prodomains and GFs of the TGF-β family suggest a new paradigm for regulating GF release by conversion from closed- to open-arm procomplex conformations. Ternary complexes of the final step in extracellular signaling show how TGF-β GF dimers bind type I and type II receptors on the cell surface, and enable understanding of much of the specificity and promiscuity in extracellular signaling. However, structures suggest that when GFs bind repulsive guidance molecule (RGM) family coreceptors, type I receptors do not bind until reaching an intracellular, membrane-enveloped compartment, blurring the line between extra- and intracellular signaling. Modulator protein structures show how structurally diverse antagonists including follistatins, noggin, and members of the chordin family bind GFs to regulate signaling; complexes with the Dan family remain elusive. Much work is needed to understand how these molecular components assemble to form signaling hubs in extracellular environments in vivo. PMID:27638177

Distinct effects of Broncho-Vaxom (OM-85 BV) on gp130 binding cytokines

PubMed Central

Roth, M; Block, L

2000-01-01

BACKGROUND—Broncho-Vaxom (OM-85 BV) is known to support respiratory tract resistance to bacterial infections. In vivo and in vitro studies in animals and humans have shown that the action of the drug is based on the modulation of the host immune response, and it has been found to upregulate interferon γ (IFN-γ) and interleukin (IL)-2, IL-6, and IL-8. These immunomodulatory effects of the compound may explain its stimulation on T helper cells and natural killer cells. Following earlier findings that OM-85 BV induces the synthesis of IL-6, a study was undertaken to investigate its possible effect on other gp130 binding cytokines including IL-11, IL-12, leukaemia inhibitory factor (LIF), oncostatin M (OSM), and ciliary neutrophil factor (CNTF). Its modulation of the corresponding receptors of the above mentioned cytokines and of the signal transducer gp130 in human pulmonary fibroblasts and peripheral blood lymphocytes was also studied.
METHODS—Transcription of cytokines was assessed by Northern blot analysis. Secretion of cytokines was analysed using commercially available enzyme linked immunosorbent assay kits. Cytokine receptors and gp130 proteins were determined by Western blot analysis.
RESULTS—OM-85 BV increased the expression of IL-11 in human lung fibroblasts, but not in lymphocytes, in a dose and time dependent manner by maximal fivefold within 20 hours. The compound inhibited serum induced IL-12 expression in peripheral blood lymphocytes but did not induce OSM, LIF, or CNTF at any concentration. In lung fibroblasts the expression of the IL-6 receptor was enhanced fourfold at a concentration of 10 µg/ml OM-85 BV while that of the IL-11 receptor was not altered. In peripheral blood lymphocytes LIF receptor α expression was downregulated in the presence of 10 µg/ml OM-85 BV. At a concentration of 10 µg/ml OM-85 BV enhanced gp130 gene transcription fivefold and increased gp130 protein accumulation in cell membranes by 2.5times.
CONCLUSION—In vitro OM-85 BV exerts immunomodulatory action via modulation of the signal transducer gp130 and gp130 binding cytokines. The increase of IL-6 and IL-11 may explain enhanced T and B cell activity, immunoglobulin synthesis, and IgM to IgG switch. Suppression of IL-12 and LIF receptor-α further contributes to organ protection. With regard to gp130 mediated signalling of the investigated cytokines, OM-85 BV modifies the host immune response towards an increased sensitisation of cells to gp130 binding proteins.

 PMID:10899245

A chemokine-binding domain in the tumor necrosis factor receptor from variola (smallpox) virus

PubMed Central

Alejo, Alí; Ruiz-Argüello, M. Begoña; Ho, Yin; Smith, Vincent P.; Saraiva, Margarida; Alcami, Antonio

2006-01-01

Variola virus (VaV) is the causative agent of smallpox, one of the most devastating diseases encountered by man, that was eradicated in 1980. The deliberate release of VaV would have catastrophic consequences on global public health. However, the mechanisms that contribute to smallpox pathogenesis are poorly understood at the molecular level. The ability of viruses to evade the host defense mechanisms is an important determinant of viral pathogenesis. Here we show that the tumor necrosis factor receptor (TNFR) homologue CrmB encoded by VaV functions not only as a soluble decoy TNFR but also as a highly specific binding protein for several chemokines that mediate recruitment of immune cells to mucosal surfaces and the skin, sites of virus entry and viral replication at late stages of smallpox. CrmB binds chemokines through its C-terminal domain, which is unrelated to TNFRs, was named smallpox virus-encoded chemokine receptor (SECRET) domain and uncovers a family of poxvirus chemokine inhibitors. An active SECRET domain was found in another viral TNFR (CrmD) and three secreted proteins encoded by orthopoxviruses. These findings identify a previously undescribed chemokine-binding and inhibitory domain unrelated to host chemokine receptors and a mechanism of immune modulation in VaV that may influence smallpox pathogenesis. PMID:16581912

Allosteric regulation in NMDA receptors revealed by the genetically encoded photo-cross-linkers

PubMed Central

Tian, Meilin; Ye, Shixin

2016-01-01

Allostery is essential to neuronal receptor function, but its transient nature poses a challenge for characterization. The N-terminal domains (NTDs) distinct from ligand binding domains are a major locus for allosteric regulation of NMDA receptors (NMDARs), where different modulatory binding sites have been observed. The inhibitor ifenprodil, and related phenylethanoamine compounds specifically targeting GluN1/GluN2B NMDARs have neuroprotective activity. However, whether they use differential structural pathways than the endogenous inhibitor Zn2+ for regulation is unknown. We applied genetically encoded unnatural amino acids (Uaas) and monitored the functional changes in living cells with photo-cross-linkers specifically incorporated at the ifenprodil binding interface between GluN1 and GluN2B subunits. We report constraining the NTD domain movement, by a light induced crosslinking bond that introduces minimal perturbation to the ligand binding, specifically impedes the transduction of ifenprodil but not Zn2+ inhibition. Subtle distance changes reveal interfacial flexibility and NTD rearrangements in the presence of modulators. Our results present a much richer dynamic picture of allostery than conventional approaches targeting the same interface, and highlight key residues that determine functional and subtype specificity of NMDARs. The light-sensitive mutant neuronal receptors provide complementary tools to the photo-switchable ligands for opto-neuropharmacology. PMID:27713495

A chemokine-binding domain in the tumor necrosis factor receptor from variola (smallpox) virus.

PubMed

Alejo, Alí; Ruiz-Argüello, M Begoña; Ho, Yin; Smith, Vincent P; Saraiva, Margarida; Alcami, Antonio

2006-04-11

Variola virus (VaV) is the causative agent of smallpox, one of the most devastating diseases encountered by man, that was eradicated in 1980. The deliberate release of VaV would have catastrophic consequences on global public health. However, the mechanisms that contribute to smallpox pathogenesis are poorly understood at the molecular level. The ability of viruses to evade the host defense mechanisms is an important determinant of viral pathogenesis. Here we show that the tumor necrosis factor receptor (TNFR) homologue CrmB encoded by VaV functions not only as a soluble decoy TNFR but also as a highly specific binding protein for several chemokines that mediate recruitment of immune cells to mucosal surfaces and the skin, sites of virus entry and viral replication at late stages of smallpox. CrmB binds chemokines through its C-terminal domain, which is unrelated to TNFRs, was named smallpox virus-encoded chemokine receptor (SECRET) domain and uncovers a family of poxvirus chemokine inhibitors. An active SECRET domain was found in another viral TNFR (CrmD) and three secreted proteins encoded by orthopoxviruses. These findings identify a previously undescribed chemokine-binding and inhibitory domain unrelated to host chemokine receptors and a mechanism of immune modulation in VaV that may influence smallpox pathogenesis.