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Sample records for ah receptor ligands

  1. Modeling of the Aryl Hydrocarbon Receptor (AhR) ligand binding domain and its utility in virtual ligand screening to predict new AhR ligands

    PubMed Central

    Bisson, William; Koch, Daniel; O’Donnell, Edmond; Khalil, Sammy M.; Kerkvliet, Nancy; Tanguay, Robert; Abagyan, Ruben; Kolluri, Siva Kumar

    2012-01-01

    The Aryl Hydrocarbon Receptor (AhR) is a ligand-activated transcription factor; the AhR Per-AhR/Arnt-Sim (PAS) domain binds ligands. We developed homology models of the AhR PAS domain to characterize previously observed intra- and inter-species differences in ligand binding using Molecular Docking. In silico structure-based virtual ligand screening using our model resulted in the identification of pinocembrin and 5-hydroxy-7-methoxyflavone, which promoted nuclear translocation and transcriptional activation of AhR and AhR-dependent induction of endogenous target genes. PMID:19719119

  2. Detection of the TCDD Binding-Fingerprint within the Ah Receptor Ligand Binding Domain by Structurally Driven Mutagenesis and Functional Analysis†

    PubMed Central

    Pandini, Alessandro; Soshilov, Anatoly A.; Song, Yujuan; Zhao, Jing; Bonati, Laura; Denison, Michael S.

    2010-01-01

    The aryl hydrocarbon receptor (AhR) is a ligand-dependent, basic helix–loop–helix Per-Arnt-Sim (PAS)-containing transcription factor that can bind and be activated by structurally diverse chemicals, including the toxic environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Our previous three-dimensional homology model of the mouse AhR (mAhR) PAS B ligand binding domain allowed identification of the binding site and its experimental validation. We have extended this analysis by conducting comparative structural modeling studies of the ligand binding domains of six additional high-affinity mammalian AhRs. These results, coupled with site-directed mutagenesis and AhR functional analysis, have allowed detection of the “TCDD binding-fingerprint” of conserved residues within the ligand binding cavity necessary for high-affinity TCDD binding and TCDD-dependent AhR transformation DNA binding. The essential role of selected residues was further evaluated using molecular docking simulations of TCDD with both wild-type and mutant mAhRs. Taken together, our results dramatically improve our understanding of the molecular determinants of TCDD binding and provide a basis for future studies directed toward rationalizing the observed species differences in AhR sensitivity to TCDD and understanding the mechanistic basis for the dramatic diversity in AhR ligand structure. PMID:19456125

  3. Ligand-dependent interactions of the Ah receptor with coactivators in a mammalian two-hybrid assay

    SciTech Connect

    Zhang Shu; Rowlands, Craig; Safe, Stephen

    2008-03-01

    2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a high affinity ligand for the aryl hydrocarbon receptor (AhR). In this study, we investigated structure-dependent differences in activation of the AhR by a series of halogenated aromatic hydrocarbons. TCDD, 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), and 3,3',4,4',5-pentachlorobiphenyl (PCB126) induced CYP1A1-dependent activities in HEK293 human embryonic kidney, Panc1 pancreatic cancer, and Hepa1c1c7 mouse hepatoma cell lines. There was a structure-dependent difference in the efficacy of TCDF and PCB126 in HEK293 and Panc1 cells since induced CYP1A1 mRNA levels were lower than observed for the other congeners. A mammalian two-hybrid assay in cells transfected with GAL4-coactivator and AhR-VP16 chimeras was used to investigate structure-dependent interactions of these chimeras in Panc1, HEK293, and Hepa1c1c7 cells. The reporter construct pGAL4-luc contains five tandem GAL4 response elements linked to the luciferase gene and the GAL4-coactivator chimeras express several coactivators including steroid receptor coactivator 1 (SRC-1), SRC-2 and SRC-3, the mediator coactivator TRAP220, coactivator associated arginine methyl transferase 1 (CARM-1), and peroxisome proliferator-activated receptor {gamma} coactivator 1 (PGC-1). Results of the mammalian two-hybrid studies clearly demonstrate that activation of pGAL4-luc in cells transfected with VP-AhR and GAL4-coactivator chimeras is dependent on the structure of the HAH congener, cell context, and coactivator, suggesting that the prototypical HAH congeners used in this study exhibit selective AhR modulator activity.

  4. Benzimidazoisoquinolines: A New Class of Rapidly Metabolized Aryl Hydrocarbon Receptor (AhR) Ligands that Induce AhR-Dependent Tregs and Prevent Murine Graft-Versus-Host Disease

    PubMed Central

    Punj, Sumit; Kopparapu, Prasad; Jang, Hyo Sang; Phillips, Jessica L.; Pennington, Jamie; Rohlman, Diana; O’Donnell, Edmond; Iversen, Patrick L.; Kolluri, Siva Kumar; Kerkvliet, Nancy I.

    2014-01-01

    The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that plays multiple roles in regulation of immune and inflammatory responses. The ability of certain AhR ligands to induce regulatory T cells (Tregs) has generated interest in developing AhR ligands for therapeutic treatment of immune-mediated diseases. To this end, we designed a screen for novel Treg-inducing compounds based on our understanding of the mechanisms of Treg induction by the well-characterized immunosuppressive AhR ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). We screened a ChemBridge small molecule library and identified 10-chloro-7H-benzimidazo[2,1-a]benzo[de]Iso-quinolin-7-one (10-Cl-BBQ) as a potent AhR ligand that was rapidly metabolized and not cytotoxic to proliferating T cells. Like TCDD,10-Cl-BBQ altered donor CD4+ T cell differentiation during the early stages of a graft versus host (GVH) response resulting in expression of high levels of CD25, CTLA-4 and ICOS, as well as several genes associated with Treg function. The Treg phenotype required AhR expression in the donor CD4+ T cells. Foxp3 was not expressed in the AhR-induced Tregs implicating AhR as an independent transcription factor for Treg induction. Structure-activity studies showed that unsubstituted BBQ as well as 4, 11-dichloro-BBQ were capable of inducing AhR-Tregs. Other substitutions reduced activation of AhR. Daily treatment with 10-Cl-BBQ during the GVH response prevented development of GVH disease in an AhR-dependent manner with no overt toxicity. Together, our data provide strong support for development of select BBQs that activate the AhR to induce Tregs for treatment of immune-mediated diseases. PMID:24586378

  5. Identification of the Ah-Receptor Structural Determinants for Ligand Preferences

    PubMed Central

    Xing, Yongna

    2012-01-01

    The aryl hydrocarbon receptor (AHR) is a transcription factor that responds to diverse ligands and plays a critical role in toxicology, immune function, and cardiovascular physiology. The structural basis of the AHR for ligand promiscuity and preferences is critical for understanding AHR function. Based on the structure of a closely related protein HIF2α, we modeled the AHR ligand binding domain (LBD) bound to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and benzo(a)pyrene (BaP) and identified residues that control ligand preferences by shape and H-bond potential. Mutations to these residues, particularly Q377 and G298, resulted in robust and opposite changes in the potency of TCDD and BaP and up to a 20-fold change in the ratio of TCDD/BaP efficacy. The model also revealed a flexible “belt” structure; molecular dynamic (MD) simulation suggested that the “belt” and several other structural elements in the AHR-LBD are more flexible than HIF2α and likely contribute to ligand promiscuity. Molecular docking of TCDD congeners to a model of human AHR-LBD ranks their binding affinity similar to experimental ranking of their toxicity. Our study reveals key structural basis for prediction of toxicity and understanding the AHR signaling through diverse ligands. PMID:22659362

  6. Mixed-ligand copper(II) complexes activate aryl hydrocarbon receptor AhR and induce CYP1A genes expression in human hepatocytes and human cell lines.

    PubMed

    Kubešová, Kateřina; Dořičáková, Aneta; Trávníček, Zdeněk; Dvořák, Zdeněk

    2016-07-25

    The effects of four copper(II) mixed-ligand complexes [Cu(qui1)(L)]NO3·H2O (1-3) and [Cu(qui2)(phen)]NO3 (4), where qui1=2-phenyl-3-hydroxy-4(1H)-quinolinone, Hqui2=2-(4-amino-3,5-dichlorophenyl)-N-propyl-3-hydroxy-4(1H)-quinolinone-7-carboxamide, L=1,10-phenanthroline (phen) (1), 5-methyl-1,10-phenanthroline (mphen) (2), bathophenanthroline (bphen) (3), on transcriptional activities of steroid receptors, nuclear receptors and xenoreceptors have been studied. The complexes (1-4) did not influence basal or ligand-inducible activities of glucocorticoid receptor, androgen receptor, thyroid receptor, pregnane X receptor and vitamin D receptor, as revealed by gene reporter assays. The complexes 1 and 2 dose-dependently induced luciferase activity in stable gene reporter AZ-AhR cell line, and this induction was reverted by resveratrol, indicating involvement of aryl hydrocarbon receptor (AhR) in the process. The complexes 1, 2 and 3 induced CYP1A1 mRNA in LS180 cells and CYP1A1/CYP1A2 in human hepatocytes through AhR. Electrophoretic mobility shift assay EMSA showed that the complexes 1 and 2 transformed AhR in its DNA-binding form. Collectively, we demonstrate that the complexes 1 and 2 activate AhR and induce AhR-dependent genes in human hepatocytes and cancer cell lines. In conclusion, the data presented here might be of toxicological importance, regarding the multiple roles of AhR in human physiology and pathophysiology.

  7. Predicting the sensitivity of fishes to dioxin-like compounds: possible role of the aryl hydrocarbon receptor (AhR) ligand binding domain.

    PubMed

    Doering, Jon A; Giesy, John P; Wiseman, Steve; Hecker, Markus

    2013-03-01

    Dioxin-like compounds are chronically toxic to most vertebrates. However, dramatic differences in sensitivity to these chemicals exist both within and among vertebrate classes. A recent study found that in birds, critical amino acid residues in the aryl hydrocarbon receptor (AhR) ligand binding domain are predictive of sensitivity to dioxin-like compounds in a range of species. It is currently unclear whether similar predictive relationships exist for fishes, a group of animals at risk of exposure to dioxin-like compounds. Effects of dioxin-like compounds are mediated through the AhR in fishes and birds. However, AhR dynamics are more complex among fishes. Fishes possess AhRs that can be grouped within at least three distinct clades (AhR1, AhR2, AhR3) with each clade possibly containing multiple isoforms. AhR2 has been shown to be the active form in most teleosts, with AhR1 not binding dioxin-like compounds. The role of AhR3 in dioxin-like toxicity has not been established to date and this clade is only known to be expressed in some cartilaginous fishes. Furthermore, multiple mechanisms of sensitivity to dioxin-like compounds that are not relevant in birds could exist among fishes. Although, at this time, deficiencies exist for the development of such a predictive relationship for application to fishes, successfully establishing such relationships would offer a substantial improvement in assessment of risks of dioxin-like compounds for this class of vertebrates. Elucidation of such relationships would provide a mechanistic foundation for extrapolation among species to allow the identification of the most sensitive fishes, with the ultimate goal of the prediction of risk posed to endangered species that are not easily studied.

  8. The AhR Ligand, TCDD, Regulates Androgen Receptor Activity Differently in Androgen-Sensitive versus Castration-Resistant Human Prostate Cancer Cells

    PubMed Central

    Ghotbaddini, Maryam; Powell, Joann B.

    2015-01-01

    The reported biological effects of TCDD include induction of drug metabolizing enzymes, wasting syndrome and tumor promotion. TCDD elicits most of its effects through binding the aryl hydrocarbon receptor (AhR). TCDD induced degradation of AhR has been widely reported and requires ubiquitination of the protein. The rapid depletion of AhR following TCDD activation serves as a mechanism to modulate AhR mediated gene induction. In addition to inducing AhR degradation, TCDD has been reported to induce degradation of hormone receptors. The studies reported here, evaluate the effect of TCDD exposure on androgen receptor (AR) expression and activity in androgen-sensitive LNCaP and castration-resistant C4-2 prostate cancer cells. Our results show that TCDD exposure does not induce AhR or AR degradation in C4-2 cells. However, both AhR and AR are degraded in LNCaP cells following TCDD exposure. In addition, TCDD enhances AR phosphorylation and induces expression of AR responsive genes in LNCaP cells. Our data reveals that TCDD effect on AR expression and activity differs in androgen-sensitive and castration-resistant prostate cancer cell models. PMID:26154658

  9. Newspapers and newspaper ink contain agonists for the ah receptor.

    PubMed

    Bohonowych, Jessica E S; Zhao, Bin; Timme-Laragy, Alicia; Jung, Dawoon; Di Giulio, Richard T; Denison, Michael S

    2008-04-01

    Ligand-dependent activation of the aryl hydrocarbon receptor (AhR) pathway leads to a diverse array of biological and toxicological effects. The best-studied ligands for the AhR include polycyclic and halogenated aromatic hydrocarbons, the most potent of which is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, as new AhR ligands are identified and characterized, their structural and physiochemical diversity continues to expand. Our identification of AhR agonists in crude extracts from diverse materials raises questions as to the magnitude and extent of human exposure to AhR ligands through normal daily activities. We have found that solvent extracts of newspapers from countries around the world stimulate the AhR signaling pathway. AhR agonist activity was observed for dimethyl sulfoxide (DMSO), ethanol, and water extracts of printed newspaper, unprinted virgin paper, and black printing ink, where activation of luciferase reporter gene expression was transient, suggesting that the AhR active chemical(s) was metabolically labile. DMSO and ethanol extracts also stimulated AhR transformation and DNA binding, and also competed with [(3)H]TCDD for binding to the AhR. In addition, DMSO extracts of printed newspaper induced cytochrome P450 1A associated 7-ethoxyresorufin-O-deethylase activity in zebrafish embryos in vivo. Although the responsible bioactive chemical(s) remain to be identified, our results demonstrate that newspapers and printing ink contain relatively potent metabolically labile agonists of the AhR. Given the large amount of recycling and reprocessing of newspapers throughout the world, release of these easily extractable AhR agonists into the environment should be examined and their potential effects on aquatic organisms assessed.

  10. Newspapers and Newspaper Ink Contain Agonists for the Ah Receptor

    PubMed Central

    Bohonowych, Jessica E. S.; Zhao, Bin; Timme-Laragy, Alicia; Jung, Dawoon; Di Giulio, Richard T.; Denison, Michael S.

    2010-01-01

    Ligand-dependent activation of the aryl hydrocarbon receptor (AhR) pathway leads to a diverse array of biological and toxicological effects. The best-studied ligands for the AhR include polycyclic and halogenated aromatic hydrocarbons, the most potent of which is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, as new AhR ligands are identified and characterized, their structural and physiochemical diversity continues to expand. Our identification of AhR agonists in crude extracts from diverse materials raises questions as to the magnitude and extent of human exposure to AhR ligands through normal daily activities. We have found that solvent extracts of newspapers from countries around the world stimulate the AhR signaling pathway. AhR agonist activity was observed for dimethyl sulfoxide (DMSO), ethanol, and water extracts of printed newspaper, unprinted virgin paper, and black printing ink, where activation of luciferase reporter gene expression was transient, suggesting that the AhR active chemical(s) was metabolically labile. DMSO and ethanol extracts also stimulated AhR transformation and DNA binding, and also competed with [3H]TCDD for binding to the AhR. In addition, DMSO extracts of printed newspaper induced cytochrome P450 1A associated 7-ethoxyresorufin-O-deethylase activity in zebrafish embryos in vivo. Although the responsible bioactive chemical(s) remain to be identified, our results demonstrate that newspapers and printing ink contain relatively potent metabolically labile agonists of the AhR. Given the large amount of recycling and reprocessing of newspapers throughout the world, release of these easily extractable AhR agonists into the environment should be examined and their potential effects on aquatic organisms assessed. PMID:18203687

  11. Identification of a novel mechanism of regulation of Ah (dioxin) receptor function

    PubMed Central

    Mimura, Junsei; Ema, Masatsugu; Sogawa, Kazuhiro; Fujii-Kuriyama, Yoshiaki

    1999-01-01

    Ah receptor (AhR) is a ligand-activated transcription factor that mediates pleiotropic effects of environmental pollutants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin on host animals. In addition to induction of drug-metabolizing enzymes, the liganded AhR complex was found to activate gene expression of a factor designated AhR repressor (AhRR), which inhibits AhR function by competing with AhR for dimerizing with Arnt and binding to the XRE sequence. Thus, AhR and AhRR form a regulatory circuit in the xenobiotic signal transduction pathway and provide a novel mechanism of regulation of AhR function that may determine tissue-specific sensitivity to environmental pollutants. PMID:9887096

  12. The activation mechanism of the aryl hydrocarbon receptor (AhR) by molecular chaperone HSP90

    PubMed Central

    Tsuji, Noriko; Fukuda, Kana; Nagata, Yuhtaroh; Okada, Hirotaka; Haga, Asami; Hatakeyama, Shiori; Yoshida, Shiho; Okamoto, Tomoya; Hosaka, Miki; Sekine, Kazuhiro; Ohtaka, Kei; Yamamoto, Soh; Otaka, Michiro; Grave, Ewa; Itoh, Hideaki

    2014-01-01

    The aryl hydrocarbon receptor is a member of the nuclear receptor superfamily that associates with the molecular chaperone HSP90 in the cytoplasm. The activation mechanism of the AhR is not yet fully understood. It has been proposed that after binding of ligands such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 3methylcholanthrene (3-MC), or β-naphthoflavone (β-NF), the AhR dissociates from HSP90 and translocates to the nucleus. It has also been hypothesized that the AhR translocates to the nucleus and forms a complex with HSP90 and other co-chaperones. There are a few reports about the direct association or dissociation of AhR and HSP90 due to difficulties in purifying AhR. We constructed and purified the PAS domain from AhR. Binding of the AhR-PAS domain to β-NF affinity resin suggested that it possesses ligand-binding affinity. We demonstrated that the AhR-PAS domain binds to HSP90 and the association is not affected by ligand binding. The ligand 17-DMAG inhibited binding of HSP90 to GST-PAS. In an immunoprecipitation assay, HSP90 was co-immunoprecipitated with AhR both in the presence or absence of ligand. Endogenous AhR decreased in the cytoplasm and increased in the nucleus of HeLa cells 15 min after treatment with ligand. These results suggested that the ligand-bound AhR is translocated to nucleus while in complex with HSP90. We used an in situ proximity ligation assay to confirm whether AhR was translocated to the nucleus alone or together with HSP90. HSP90 was co-localized with AhR after the nuclear translocation. It has been suggested that the ligand-bound AhR was translocated to the nucleus with HSP90. Activated AhR acts as a transcription factor, as shown by the transcription induction of the gene CYP1A1 8 h after treatment with β-NF. PMID:25349783

  13. Ligand Promiscuity of Aryl Hydrocarbon Receptor Agonists and Antagonists Revealed by Site-Directed Mutagenesis

    PubMed Central

    Soshilov, Anatoly A.

    2014-01-01

    The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that can be activated by structurally diverse chemicals. To examine the mechanisms responsible for the promiscuity in AhR ligand binding, we determined the effects of mutations within the AhR ligand-binding domain (LBD) on the activity of diverse AhR ligands. Site-directed mutagenesis identified Ile319 of the mouse AhR and, to a lesser extent, Phe318 as residues involved in ligand-selective modulation of AhR transformation using a panel of 12 AhR ligands. These ligands could be categorized into four distinct structurally related groups based on their ability to activate AhR mutants at position 319 in vitro. The mutation I319K was selectively activated by FICZ and not by other examined ligands in vitro and in cell culture. F318L and F318A mutations resulted in the conversion of AhR agonists β-naphthoflavone and 3-methylcholanthrene, respectively, into partial agonists/antagonists. Hsp90 binding to the AhR was decreased with several mutations and was inversely correlated with AhR ligand-binding promiscuity. Together, these data define overlapping amino acid residues within the AhR LBD involved in the selectivity of ligand binding, the agonist or antagonist mode of ligand binding, and hsp90 binding and provide insights into the ligand diversity of AhR activators. PMID:24591650

  14. Transgenic Overexpression of Aryl Hydrocarbon Receptor Repressor (AhRR) and AhR-Mediated Induction of CYP1A1, Cytokines, and Acute Toxicity

    PubMed Central

    Vogel, Christoph F.A.; Chang, W.L. William; Kado, Sarah; McCulloh, Kelly; Vogel, Helena; Wu, Dalei; Haarmann-Stemmann, Thomas; Yang, GuoXiang; Leung, Patrick S.C.; Matsumura, Fumio; Gershwin, M. Eric

    2016-01-01

    Background: The aryl hydrocarbon receptor repressor (AhRR) is known to repress aryl hydrocarbon receptor (AhR) signaling, but very little is known regarding the role of the AhRR in vivo. Objective: This study tested the role of AhRR in vivo in AhRR overexpressing mice on molecular and toxic end points mediated through a prototypical AhR ligand. Methods: We generated AhRR-transgenic mice (AhRR Tg) based on the genetic background of C57BL/6J wild type (wt) mice. We tested the effect of the prototypical AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the expression of cytochrome P450 (CYP)1A1 and cytokines in various tissues of mice. We next analyzed the infiltration of immune cells in adipose tissue of mice after treatment with TCDD using flow cytometry. Results: AhRR Tg mice express significantly higher levels of AhRR compared to wt mice. Activation of AhR by TCDD caused a significant increase of the inflammatory cytokines Interleukin (IL)-1β, IL-6 and IL-10, and CXCL chemokines in white epididymal adipose tissue from both wt and AhRR Tg mice. However, the expression of IL-1β, CXCL2 and CXCL3 were significantly lower in AhRR Tg versus wt mice following TCDD treatment. Exposure to TCDD caused a rapid accumulation of neutrophils and macrophages in white adipose tissue of wt and AhRR Tg mice. Furthermore we found that male AhRR Tg mice were protected from high-dose TCDD-induced lethality associated with a reduced inflammatory response and liver damage as indicated by lower levels of TCDD-induced alanine aminotransferase and hepatic triglycerides. Females from both wt and AhRR Tg mice were less sensitive than male mice to acute toxicity induced by TCDD. Conclusion: In conclusion, the current study identifies AhRR as a previously uncharacterized regulator of specific inflammatory cytokines, which may protect from acute toxicity induced by TCDD. Citation: Vogel CF, Chang WL, Kado S, McCulloh K, Vogel H, Wu D, Haarmann-Stemmann T, Yang GX, Leung PS, Matsumura F

  15. Altered adrenergic response and specificity of the receptors in rat ascites hepatoma AH130.

    PubMed

    Sanae, F; Miyamoto, K; Koshiura, R

    1989-11-15

    Adenylate cyclase activation through adrenergic receptors in rat ascites hepatoma (AH) 130 cells in response to adrenergic drugs was studied, and receptor binding and displacement were compared with those of normal rat hepatocytes. Epinephrine (Epi) and norepinephrine (NE) activated AH130 adenylate cyclase about half as much as isoproterenol (IPN) but equaled IPN after treatment with the alpha-antagonist phentolamine or islet-activating protein (IAP). The three catecholamines in hepatocytes were similar regardless of phentolamine or IAP. These catecholamines activated adenylate cyclase in order of IPN greater than NE greater than Epi in AH130 cells but IPN greater than Epi greater than NE in hepatocytes. We then used the alpha 1-selective ligand [3H]prazosin, the alpha 2-selective ligand [3H]clonidine, and the beta-ligand [125I]iodocyanopindolol [( 125I]ICYP), and found that AH130 cells had few prazosin-binding sites, about eight times as many clonidine-binding sites with high affinity, and many more ICYP-binding sites than in hepatocytes. The dissociation constant (Ki) of the beta 1-selective drug metoprolol by Hofstee plots for AH130 cells was lower than that for hepatocytes. The inhibition of specific ICYP binding by the beta 2-selective agonist salbutamol for AH130 cells gave only one Ki value which was much higher than both high and low Ki values of the drug for hepatocytes. These findings indicate that the alpha- and beta-adrenergic receptors in hepatocytes are predominantly alpha 1-type and beta 2-type, but that those in AH130 cells are predominantly alpha 2-type and beta 1-type, and the low adrenergic response of AH130 cells is due to the dominant appearance of alpha 2-adrenergic receptors, linked with the inhibitory guanine-nucleotide binding regulatory protein, instead of alpha 1-adrenergic receptors, and beta 1-adrenergic receptors with low affinity for the hormone.

  16. Access Path to the Ligand Binding Pocket May Play a Role in Xenobiotics Selection by AhR

    PubMed Central

    Szöllősi, Dániel; Erdei, Áron; Gyimesi, Gergely; Magyar, Csaba; Hegedűs, Tamás

    2016-01-01

    Understanding of multidrug binding at the atomic level would facilitate drug design and strategies to modulate drug metabolism, including drug transport, oxidation, and conjugation. Therefore we explored the mechanism of promiscuous binding of small molecules by studying the ligand binding domain, the PAS-B domain of the aryl hydrocarbon receptor (AhR). Because of the low sequence identities of PAS domains to be used for homology modeling, structural features of the widely employed HIF-2α and a more recent suitable template, CLOCK were compared. These structures were used to build AhR PAS-B homology models. We performed molecular dynamics simulations to characterize dynamic properties of the PAS-B domain and the generated conformational ensembles were employed in in silico docking. In order to understand structural and ligand binding features we compared the stability and dynamics of the promiscuous AhR PAS-B to other PAS domains exhibiting specific interactions or no ligand binding function. Our exhaustive in silico binding studies, in which we dock a wide spectrum of ligand molecules to the conformational ensembles, suggest that ligand specificity and selection may be determined not only by the PAS-B domain itself, but also by other parts of AhR and its protein interacting partners. We propose that ligand binding pocket and access channels leading to the pocket play equally important roles in discrimination of endogenous molecules and xenobiotics. PMID:26727491

  17. A novel AhR ligand, 2AI, protects the retina from environmental stress

    PubMed Central

    Gutierrez, Mark A.; Davis, Sonnet S.; Rosko, Andrew; Nguyen, Steven M.; Mitchell, Kylie P.; Mateen, Samiha; Neves, Joana; Garcia, Thelma Y.; Mooney, Shaun; Perdew, Gary H.; Hubbard, Troy D.; Lamba, Deepak A.; Ramanathan, Arvind

    2016-01-01

    Various retinal degenerative diseases including dry and neovascular age-related macular degeneration (AMD), retinitis pigmentosa, and diabetic retinopathy are associated with the degeneration of the retinal pigmented epithelial (RPE) layer of the retina. This consequently results in the death of rod and cone photoreceptors that they support, structurally and functionally leading to legal or complete blindness. Therefore, developing therapeutic strategies to preserve cellular homeostasis in the RPE would be a favorable asset in the clinic. The aryl hydrocarbon receptor (AhR) is a conserved, environmental ligand-dependent, per ARNT-sim (PAS) domain containing bHLH transcription factor that mediates adaptive response to stress via its downstream transcriptional targets. Using in silico, in vitro and in vivo assays, we identified 2,2′-aminophenyl indole (2AI) as a potent synthetic ligand of AhR that protects RPE cells in vitro from lipid peroxidation cytotoxicity mediated by 4-hydroxynonenal (4HNE) as well as the retina in vivo from light-damage. Additionally, metabolic characterization of this molecule by LC-MS suggests that 2AI alters the lipid metabolism of RPE cells, enhancing the intracellular levels of palmitoleic acid. Finally, we show that, as a downstream effector of 2AI-mediated AhR activation, palmitoleic acid protects RPE cells from 4HNE-mediated stress, and light mediated retinal degeneration in mice. PMID:27364765

  18. Retinoids repress Ah receptor CYP1A1 induction pathway through the SMRT corepressor.

    PubMed

    Fallone, Frédérique; Villard, Pierre-Henri; Sérée, Eric; Rimet, Odile; Nguyen, Quock Binh; Bourgarel-Rey, Véronique; Fouchier, Francis; Barra, Yves; Durand, Alain; Lacarelle, Bruno

    2004-09-17

    CYP1A1 isoform is mainly regulated by the transcription factor AhR and to a lesser extent by the nuclear receptor RAR. The effect of a coexposure with 3MC, a AhR ligand, and RA, a RAR ligand, which are, respectively, strong and weak CYP1A1 inducers, is poorly known. We showed in Caco-2 cells that addition of RA significantly decreased 3MC-induced CYP1A1 expression by -55% for mRNA level and -30% for promoter and enzymatic activities. We further showed that RA decreased AhR protein level. Moreover, a physical interaction between AhR and the RAR-corepressor SMRT has been described in vitro. Using the corepressor inhibitor TSA, transfected-cells with SMRT cDNA, and coimmunoprecipitation experiments, we demonstrated that RA addition repressed AhR function through a marked AhR/SMRT physical interaction. This interaction explains the decrease of 3MC-induced CYP1A1 expression. This new mechanism involving the repression of AhR-induced CYP1A1 expression by retinoids allows better knowledge of the CYP1A1 regulation.

  19. A comparison of adrenergic receptors of rat ascites hepatoma AH130 cells with those of normal rat hepatocytes.

    PubMed

    Sanae, F; Miyamoto, K; Koshiura, R

    1988-04-01

    The pharmacological specificity of adrenergic receptors in the plasma membrane of rat ascites hepatoma AH130 cells was compared with that in normal rat hepatocytes. The number of [125I]iodocyanopindolol-binding sites was much greater in AH130 cells than in the hepatocytes. We characterized the alpha-adrenergic receptor subtypes using the alpha 1-selective ligand [3H]prazosin and the alpha 2-selective ligand [3H]clonidine. AH130 cells had fewer prazosin-binding sites than the hepatocytes and about 8 times as many clonidine-binding sites of high affinity. The results showed that the adrenergic receptors in AH130 cells have pharmacological properties that are very different from those of the receptors in normal rat hepatocytes.

  20. The Nuclear Receptor AhR Controls Bone Homeostasis by Regulating Osteoclast Differentiation via the RANK/c-Fos Signaling Axis

    PubMed Central

    Izawa, Takashi; Arakaki, Rieko; Mori, Hiroki; Tsunematsu, Takaaki; Kudo, Yasusei; Tanaka, Eiji

    2016-01-01

    The aryl hydrocarbon receptor (AhR) pathway plays a key role in receptor activator of NF-κB ligand (RANKL)–mediated osteoclastogenesis. However, the mechanism underlying the regulation of AhR expression in osteoclasts and the signaling pathway through which AhR controls osteoclastogenesis remain unclear. We found that the expression of AhR in bone marrow–derived osteoclasts was upregulated by RANKL at an earlier stage than was the expression of signature osteoclast genes such as those encoding cathepsin K and NFAT, cytoplasmic, calcineurin-dependent 1. In response to RANKL, bone marrow macrophages isolated from AhR−/− mice exhibited impaired phosphorylation of Akt and MAPK as well as NF-κB, whereas their response to M-CSF remained unchanged. Osteoclast differentiation mediated by the AhR signaling pathway was also regulated in an RANKL/c-Fos–dependent manner. Furthermore, ligand activation of AhR by the smoke toxin benzo[a]pyrene accelerated osteoclast differentiation in a receptor-dependent manner, and AhR-dependent regulation of mitochondrial biogenesis in osteoclasts was observed. Moreover, AhR−/− mice exhibited impaired bone healing with delayed endochondral ossification. Taken together, the present results suggest that the RANKL/AhR/c-Fos signaling axis plays a critical role in osteoclastogenesis, thereby identifying the potential of AhR in treating pathological, inflammatory, or metabolic disorders of the bone. PMID:27849171

  1. The constitutively active Ah receptor (CA-AhR) mouse as a model for dioxin exposure - effects in reproductive organs.

    PubMed

    Brunnberg, Sara; Andersson, Patrik; Poellinger, Lorenz; Hanberg, Annika

    2011-12-01

    The dioxin/aryl hydrocarbon receptor (AhR) mediates most toxic effects of dioxins. In utero/lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) impairs fetal/neonatal development and the developing male reproductive tract are among the most sensitive tissues. TCDD causes antiestrogenic responses in rodent mammary gland and uterus and in human breast cancer cell lines in the presence of estrogen. Also, more recently an estrogen-like effect of TCDD/AhR has been suggested in the absence of estrogen. A transgenic mouse expressing a constitutively active AhR (CA-AhR) was developed as a model mimicking a situation of constant exposure to AhR agonists. Male and female reproductive tissues of CA-AhR mice were characterized for some of the effects commonly seen after dioxin exposure. Sexually mature CA-AhR female mice showed decreased uterus weight, while an uterotrophic assay in immature CA-AhR mice resulted in increased uterus weight. In immature mice, both TCDD-exposure and CA-AhR increased the expression of the estrogen receptor target gene Cathepsin D. When co-treated with 17β-estradiol no increase in Cathepsin D levels occurred in either TCDD-exposed or CA-AhR mice. In sexually mature male CA-AhR mice the weights of testis and ventral prostate were decreased and the epididymal sperm reserve was reduced. The results of the present study are in accordance with previous studies on dioxin-exposed rodents in that an activated AhR (here CA-AhR) leads to antiestrogenic effects in the presence of estrogen, but to estrogenic effects in the absence of estrogen. These results suggest the CA-AhR mouse model as a useful tool for studies of continuous low activity of the AhR from early development, resembling the human exposure situation.

  2. EGF receptor ligands: recent advances

    PubMed Central

    Singh, Bhuminder; Carpenter, Graham; Coffey, Robert J.

    2016-01-01

    Seven ligands bind to and activate the mammalian epidermal growth factor (EGF) receptor (EGFR/ERBB1/HER1): EGF, transforming growth factor-alpha (TGFA), heparin-binding EGF-like growth factor (HBEGF), betacellulin (BTC), amphiregulin (AREG), epiregulin (EREG), and epigen (EPGN). Of these, EGF, TGFA, HBEGF, and BTC are thought to be high-affinity ligands, whereas AREG, EREG, and EPGN constitute low-affinity ligands. This focused review is meant to highlight recent studies related to actions of the individual EGFR ligands, the interesting biology that has been uncovered, and relevant advances related to ligand interactions with the EGFR. PMID:27635238

  3. Cancer-promoting and Inhibiting Effects of Dietary Compounds: Role of the Aryl Hydrocarbon Receptor (AhR)

    PubMed Central

    Powell, Joann B.; Ghotbaddini, Maryam

    2014-01-01

    Polyaromatic hydrocarbons, heterocyclic aromatic amines and dioxin-like compounds are environmental carcinogens shown to initiate cancer in a number of tissue types including prostate and breast. These environmental carcinogens elicit their effects through interacting with the aryl hydrocarbon receptor (AhR), a ligand activated transcription factor. Naturally occurring compounds found in fruits and vegetables shown to have anti-carcinogenic effects also interact with the AhR. This review explores dietary and environmental exposure to chemical carcinogens and beneficial natural compounds whose effects are elicited by the AhR. PMID:25258701

  4. Aryl hydrocarbon receptor (AhR)-dependent regulation of pulmonary miRNA by chronic cigarette smoke exposure.

    PubMed

    Rogers, Sarah; de Souza, Angela Rico; Zago, Michela; Iu, Matthew; Guerrina, Necola; Gomez, Alvin; Matthews, Jason; Baglole, Carolyn J

    2017-01-12

    The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor historically known for its toxic responses to man-made pollutants such as dioxin. More recently, the AhR has emerged as a suppressor of inflammation, oxidative stress and apoptosis from cigarette smoke by mechanisms that may involve the regulation of microRNA. However, little is known about the AhR regulation of miRNA expression in the lung in response to inhaled toxicants. Therefore, we exposed Ahr(-/-) and Ahr(+/-) mice to cigarette smoke for 4 weeks and evaluated lung miRNA expression by PCR array. There was a dramatic regulation of lung miRNA by the AhR in the absence of exogenous ligand. In response to cigarette smoke, there were more up-regulated miRNA in Ahr(-/-) mice compared to Ahr(+/-) mice, including the cancer-associated miRNA miR-96. There was no significant change in the expression of the AhR regulated proteins HuR and cyclooxygenase-2 (COX-2). There were significant increases in the anti-oxidant gene sulfiredoxin 1 (Srxn1) and FOXO3a- predicted targets of miR-96. Collectively, these data support a prominent role for the AhR in regulating lung miRNA expression. Further studies to elucidate a role for these miRNA may further uncover novel biological function for the AhR in respiratory health and disease.

  5. Pityriazepin and other potent AhR ligands isolated from Malassezia furfur yeast.

    PubMed

    Mexia, Nikitia; Gaitanis, Georgios; Velegraki, Aristea; Soshilov, Anatoly; Denison, Michael S; Magiatis, Prokopios

    2015-04-01

    Malassezia furfur yeast strains isolated from diseased human skin preferentially biosynthesize indole alkaloids which can be detected in the human skin and are highly potent activators of the aryl hydrocarbon receptor (AhR) and AhR-dependent gene expression. Chemical analysis of an EtOAc extract of a M. furfur strain obtained from diseased human skin and grown on l-tryptophan agar revealed several known AhR active tryptophan metabolites along with a previously unidentified compound, pityriazepin. While its structure resembled that of the known alkaloid pityriacitrin, the comprised pyridine ring had been transformed into an azepinone. The indoloazepinone scaffold of pityriazepin is extremely rare in nature and has only been reported once previously. Pityriazepin, like the other isolated compounds, was found to be a potent activator of the AhR-dependent reporter gene assay in recombinant cell lines derived from four different species, although significant species differences in relative potency were observed. The ability of pityriazepin to competitively bind to the AhR and directly stimulate AhR DNA binding classified it as a new naturally-occurring potent AhR agonist. M. furfur produces an expanded collection of extremely potent naturally occurring AhR agonists, which produce their biological effects in a species-specific manner.

  6. The constitutively active Ah receptor (CA-Ahr) mouse as a potential model for dioxin exposure--effects in vital organs.

    PubMed

    Brunnberg, Sara; Andersson, Patrik; Lindstam, Maria; Paulson, Ivar; Poellinger, Lorenz; Hanberg, Annika

    2006-07-25

    The dioxin/aryl hydrocarbon receptor (AhR) mediates most, if not all, toxic effects of dioxins and functions as a ligand-activated transcription factor regulating transcription of a battery of genes. In order to study the mechanisms behind the toxicity of ligands of the Ah receptor we have created a transgenic mouse model expressing a constitutively active Ah receptor (CA-AhR). The mutant Ah receptor is expressed and functionally active in all organs studied. The purpose of the present study was to characterize histopathologically, the phenotype of the CA-AhR with regard to the liver, kidney, lung, heart, spleen and thymus of male and female transgenic CA-AhR mice. Moreover, cell-specific activity of the CA-AhR using up-regulation of the AhR target gene CYP1A1 as a marker, was also examined. The relative weight of liver, kidney and heart were increased while relative thymus weight was decreased. Furthermore, slight morphological lesions of the liver, kidney and spleen was seen. Expression of CYP1A1 was found in cells corresponding to endothelial cells in all of the organs studied. In some tissues additional cell types, such as hepatocytes, renal tubuli cell and Clara cells expressed CYP1A1. Both the effects on organ weights and the cellular expression of CYP1A1 in CA-AhR mice correspond well to observations in TCDD-exposed mice. In conclusion, this characterization further support that the CA-AhR mouse is a useful model for life-long continuous low-level activity of the AhR, i.e. the dioxin exposure situation of humans of the general population.

  7. What are Nuclear Receptor Ligands?

    PubMed Central

    Sladek, Frances M.

    2010-01-01

    Nuclear receptors (NRs) are a family of highly conserved transcription factors that regulate transcription in response to small lipophilic compounds. They play a role in every aspect of development, physiology and disease in humans. They are also ubiquitous in and unique to the animal kingdom suggesting that they may have played an important role in their evolution. In contrast to the classical endocrine receptors that originally defined the family, recent studies suggest that the first NRs might have been sensors of their environment, binding ligands that were external to the host organism. The purpose of this review is to provide a broad perspective on NR ligands and address the issue of exactly what constitutes a NR ligand from historical, biological and evolutionary perspectives. This discussion will lay the foundation for subsequent reviews in this issue as well as pose new questions for future investigation. PMID:20615454

  8. Ligand independent aryl hydrocarbon receptor inhibits lung cancer cell invasion by degradation of Smad4.

    PubMed

    Lee, Chen-Chen; Yang, Wen-Hao; Li, Ching-Hao; Cheng, Yu-Wen; Tsai, Chi-Hao; Kang, Jaw-Jou

    2016-07-01

    The aryl hydrocarbon receptor (AhR) is a ligand-dependent-activated transcriptional factor that regulates the metabolism of xenobiotic and endogenous compounds. Although AhR plays a crucial role in air toxicant-induced carcinogenesis, AhR expression was shown to negatively regulate tumorigenesis. Therefore, in the present study, we investigated the effect of AhR without ligand treatment on cancer invasion in lung cancer cell lines. Lung cancer cells expressing lower levels of AhR showed higher invasion ability (H1299 cells) compared with cells expressing higher levels of AhR (A549 cells). Overexpression of AhR in H1299 cells inhibited the invasion ability. We found that vimentin expression was inhibited in AhR-overexpressing H1299 cells. Additionally, the expression of EMT-related transcriptional factors Snail and ID-1 decreased. Interestingly, we found that Smad4 degradation was induced in AhR-overexpressing H1299 cells. Our data showed that AhR could interact with Jun-activation domain binding protein (Jab1) and Smad4, which may cause degradation of Smad4 by the proteasome. Our data suggest that AhR affects the transforming growth factor-β signaling pathway by inducing Smad4 degradation by the proteasome and suppressing tumor metastasis via epithelial to mesenchymal transition reduction in lung cancer cells.

  9. Ablating the aryl hydrocarbon receptor (AhR) in CD11c+ cells perturbs intestinal epithelium development and intestinal immunity

    PubMed Central

    Chng, Song Hui; Kundu, Parag; Dominguez-Brauer, Carmen; Teo, Wei Ling; Kawajiri, Kaname; Fujii-Kuriyama, Yoshiaki; Mak, Tak Wah; Pettersson, Sven

    2016-01-01

    Diet and microbiome derived indole derivatives are known to activate the ligand induced transcription factor, the Aryl hydrocarbon Receptor (AhR). While the current understanding of AhR biology has confirmed its role in mucosal lymphocytes, its function in intestinal antigen presenting cells (APCs) is poorly understood. Here, we report that Cre-mediated deletion of AhR in CD11c-expressing cells in C57/BL6 mice is associated with altered intestinal epithelial morphogenesis in vivo. Moreover, when co-cultured with AhR-deficient DCs ex vivo, intestinal organoids showed reduced SRY (sex determining region Y)-box 9 and increased Mucin 2 expression, which correlates with reduced Paneth cells and increased goblet cell differentiation, similar to the data obtained in vivo. Further, characterization of intestinal APC subsets, devoid of AhR, revealed an expression pattern associated with aberrant intrinsic Wnt pathway regulation. At a functional level, the loss of AhR in APCs resulted in a dysfunctional epithelial barrier, associated with a more aggressive chemically induced colitis compared to wild type animals. Our results are consistent with a model whereby the AhR signalling pathway may participate in the regulation of innate immunity through intestinal epithelium development and mucosal immunity. PMID:27068235

  10. Ablating the aryl hydrocarbon receptor (AhR) in CD11c+ cells perturbs intestinal epithelium development and intestinal immunity.

    PubMed

    Chng, Song Hui; Kundu, Parag; Dominguez-Brauer, Carmen; Teo, Wei Ling; Kawajiri, Kaname; Fujii-Kuriyama, Yoshiaki; Mak, Tak Wah; Pettersson, Sven

    2016-04-12

    Diet and microbiome derived indole derivatives are known to activate the ligand induced transcription factor, the Aryl hydrocarbon Receptor (AhR). While the current understanding of AhR biology has confirmed its role in mucosal lymphocytes, its function in intestinal antigen presenting cells (APCs) is poorly understood. Here, we report that Cre-mediated deletion of AhR in CD11c-expressing cells in C57/BL6 mice is associated with altered intestinal epithelial morphogenesis in vivo. Moreover, when co-cultured with AhR-deficient DCs ex vivo, intestinal organoids showed reduced SRY (sex determining region Y)-box 9 and increased Mucin 2 expression, which correlates with reduced Paneth cells and increased goblet cell differentiation, similar to the data obtained in vivo. Further, characterization of intestinal APC subsets, devoid of AhR, revealed an expression pattern associated with aberrant intrinsic Wnt pathway regulation. At a functional level, the loss of AhR in APCs resulted in a dysfunctional epithelial barrier, associated with a more aggressive chemically induced colitis compared to wild type animals. Our results are consistent with a model whereby the AhR signalling pathway may participate in the regulation of innate immunity through intestinal epithelium development and mucosal immunity.

  11. Analysis of Ah receptor pathway activation by brominated flame retardants.

    PubMed

    Brown, David J; Van Overmeire, Ilse; Goeyens, Leo; Denison, Michael S; De Vito, Michael J; Clark, George C

    2004-06-01

    Brominated flame-retardants (BFRs) are used as additives in plastics to decrease the rate of combustion of these materials, leading to greater consumer safety. As the use of plastics has increased, the production and use of flame-retardants has also grown. Many BFRs are persistent and have been detected in environmental samples, raising concerns about the biological/toxicological risk associated with their use. Most BFRs appear to be non-toxic, however there is still some concern that these compounds, or possible contaminants in BFRs mixtures could interact with cellular receptors. In this study we have examined the interaction of decabromodiphenyl ether, Firemaster BP4A (tetrabromobisphenol A), Firemaster PHT4 (tetrabromophthalic anhydride), hexabromobenzene, pentabromotoluene, decabromobiphenyl, Firemaster BP-6 (2,2',4,4',5,5'-hexabromobiphenyl) and possible contaminants of BFR mixtures with the Ah receptor. Receptor binding and activation was examined using the Gel Retardation Assay and increased expression of dioxin responsive genes was detected using the reporter gene based CALUX assay. The results demonstrate the ability of BFRs to activate the AhR signal transduction pathway at moderate to high concentrations as assessed using both assays. AhR-dependent activation by BFRs may be due in part to contaminants present in commercial/technical mixtures. This was suggested by our comparative analysis of Firemaster BP-6 versus its primary component 2,2',4,4',5,5'-hexabromobiphenyl. Some technical mixtures of brominated flame-retardants contain brominated biphenyls, dioxins or dibenzofurans as contaminants. When tested in the CALUX assay these compounds were found to be equivalent to, or more active than their chlorinated analogues. Relative effective potency values were determined from dose response curves for these brominated HAHs.

  12. Lack of Ligand-Selective Binding of the Aryl Hydrocarbon Receptor to Putative DNA Binding Sites Regulating Expression of Bax and Paraoxonase 1 Genes

    PubMed Central

    DeGroot, Danica E.; Hayashi, Ai; Denison, Michael S.

    2013-01-01

    The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that mediates the biological and toxicological effects of structurally diverse chemicals through its ability to bind specific DNA recognition sites (dioxin responsive elements (DREs)), and activate transcription of adjacent genes. While the DRE has a highly conserved consensus sequence, it has been suggested that the nucleotide specificity of AhR DNA binding may be ligand-dependent. The upstream regulatory regions of the murine Bax and human paraoxonase 1 (PON1) genes reportedly contain unique DRE-like sequences that respond to AhRs activated by some ligands but not others. Given the significant implications of this observation to understanding the diversity in AhR responses and that of other ligand-dependent nuclear receptors, a combination of DNA binding, nuclear translocation and gene expression analysis was used to investigate the molecular mechanisms underlying these ligand-selective responses. Although known AhR agonists stimulated AhR nuclear translocation, DRE binding and gene expression, the ligand-selective DRE-like DNA elements identified in the Bax and PON1 upstream regulatory regions failed to bind ligand-activated AhR or confer AhR-responsiveness upon a reporter gene. These results argue against the reported ligand-selectivity of AhR DNA binding and suggest DNA binding by ligand activated AhR involves DRE-containing DNA. PMID:24200861

  13. Inhibitory Ah Receptor-Androgen Receptor Crosstalk in Prostate Cancer

    DTIC Science & Technology

    2005-02-01

    induced luciferase ac- cleft palate, immunotoxicity and porphyria in mice and tivity in the latter cell line. This suggests that inhibitory CYP1A1 in...Williamson, H. Asou, J.W. Said, porphyria in genetically inbred mice: partial antagonism and S. Holden, I. Miyoshi, H.P. Koeffler, Ligand for peroxisome

  14. Identification and expression of aryl hydrocarbon receptors (AhR1 and AhR2) provide insight in an evolutionary context regarding sensitivity of white sturgeon (Acipenser transmontanus) to dioxin-like compounds.

    PubMed

    Doering, Jon A; Wiseman, Steve; Beitel, Shawn C; Giesy, John P; Hecker, Markus

    2014-05-01

    Sturgeons are ancient fishes, which are endangered in many parts of the world. Due to their benthic nature and longevity, sturgeon are at great risk of exposure to bioaccumulative contaminants such as dioxin-like compounds (DLCs). Despite their endangered status, little research has been conducted to characterize the relative sensitivity of sturgeons to DLCs. Proper assessment of risk of DLCs posed to these fishes therefore, requires a better understanding of this sensitivity and the factors that are driving it. Adverse effects associated with exposure to DLCs are mediated by the aryl hydrocarbon receptor (AhR). This study identified and characterized two distinct AhRs, AhR1 and AhR2, in white sturgeon (Acipenser transmontanus) for the first time as a first step in studying the relative sensitivities of sturgeons to DLCs. Furthermore, tissue-specific expression of both AhRs under basal conditions and in response to exposure to the model DLC, β-naphthoflavone (βNF), was determined. The sequence of amino acids of AhR1 of white sturgeon had greater similarity to AhRs of tetrapods, including amphibians, birds, and mammals, than to AhR1s of other fishes. The sequence of amino acids in the ligand binding domain of the AhR1 had greater than 80% similarity to AhRs known to bind DLCs and was less similar to AhRs not known to bind DLCs. AhR2 of white sturgeon had greatest similarity to AhR2 of other fishes. Profiles of expression of AhR1 and AhR2 in white sturgeon were distinct from those known in other fishes and appear more similar to profiles observed in birds. Expressions of both AhR1 and AhR2 of white sturgeon were greatest in liver and heart, which are target organs for DLCs. Furthermore, abundances of transcripts of AhR1 and AhR2 in all tissues from white sturgeon were greater than controls (up to 35-fold) following exposure to βNF. Based upon both AhRs having similar abundances of transcript in target organs of DLC toxicity, both AhRs being up-regulated following

  15. Green fluorescent protein (GFP) as a marker of aryl hydrocarbon receptor (AhR) function in developing zebrafish (Danio rerio).

    PubMed

    Mattingly, C J; McLachlan, J A; Toscano, W A

    2001-08-01

    We developed an inducible in vivo reporter system to examine expression of the aryl hydrocarbon receptor (AhR) during development in zebrafish (Danio rerio). AhR is a ligand-activated transcription factor that mediates the toxic actions of environmental contaminants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Induction of cytochrome P4501A1 (CYP1A1) is an early biomarker of AhR activation. A 1905 base pair region of the human CYP1A1 promoter/enhancer region was regulated by AhR in zebrafish liver cells after exposure to TCDD (10 nM) in a transient transfection assay. This regulatory region was fused to the cDNA sequence encoding green fluorescent protein (GFP) of jellyfish (Aequorea victoria). Transgenic zebrafish were generated to express this AhR-regulated GFP construct. Injected fish exposed to TCDD exhibited induction of GFP in the eye, nose, and vertebrae of zebrafish embryos (48 and 72 hr after fertilization) compared to vehicle controls (DMSO), which did not express GFP. To investigate whether AhR-regulated GFP expression correlated with sites of TCDD toxicity, we exposed wild-type zebrafish to DMSO or TCDD and examined them for morphologic abnormalities. By 5 days after fertilization, TCDD-exposed fish exhibited gross dysmorphogenesis in cranio-facial and vertebral development.

  16. Aryl hydrocarbon receptor (AhR)-dependent regulation of pulmonary miRNA by chronic cigarette smoke exposure

    PubMed Central

    Rogers, Sarah; de Souza, Angela Rico; Zago, Michela; Iu, Matthew; Guerrina, Necola; Gomez, Alvin; Matthews, Jason; Baglole, Carolyn J.

    2017-01-01

    The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor historically known for its toxic responses to man-made pollutants such as dioxin. More recently, the AhR has emerged as a suppressor of inflammation, oxidative stress and apoptosis from cigarette smoke by mechanisms that may involve the regulation of microRNA. However, little is known about the AhR regulation of miRNA expression in the lung in response to inhaled toxicants. Therefore, we exposed Ahr−/− and Ahr+/− mice to cigarette smoke for 4 weeks and evaluated lung miRNA expression by PCR array. There was a dramatic regulation of lung miRNA by the AhR in the absence of exogenous ligand. In response to cigarette smoke, there were more up-regulated miRNA in Ahr−/− mice compared to Ahr+/− mice, including the cancer-associated miRNA miR-96. There was no significant change in the expression of the AhR regulated proteins HuR and cyclooxygenase-2 (COX-2). There were significant increases in the anti-oxidant gene sulfiredoxin 1 (Srxn1) and FOXO3a- predicted targets of miR-96. Collectively, these data support a prominent role for the AhR in regulating lung miRNA expression. Further studies to elucidate a role for these miRNA may further uncover novel biological function for the AhR in respiratory health and disease. PMID:28079158

  17. CB receptor ligands from plants.

    PubMed

    Woelkart, Karin; Salo-Ahen, Outi M H; Bauer, Rudolf

    2008-01-01

    Advances in understanding the physiology and pharmacology of the endogenous cannabinoid system have potentiated the interest of cannabinoid receptors as potential therapeutic targets. Cannabinoids have been shown to modulate a variety of immune cell functions and have therapeutic implications on central nervous system (CNS) inflammation, chronic inflammatory conditions such as arthritis, and may be therapeutically useful in treating autoimmune conditions such as multiple sclerosis. Many of these drug effects occur through cannabinoid receptor signalling mechanisms and the modulation of cytokines and other gene products. Further, endocannabinoids have been found to have many physiological and patho-physiological functions, including mood alteration and analgesia, control of energy balance, gut motility, motor and co-ordination activities, as well as alleviation of neurological, psychiatric and eating disorders. Plants offer a wide range of chemical diversity and have been a growing domain in the search for effective cannabinoid ligands. Cannabis sativa L. with the known plant cannabinoid, Delta(9-)tetrahydrocannabinol (THC) and Echinacea species with the cannabinoid (CB) receptor-binding lipophilic alkamides are the best known herbal cannabimimetics. This review focuses on the state of the art in CB ligands from plants, as well their possible therapeutic and immunomodulatory effects.

  18. Aryl hydrocarbon receptor suppresses intestinal carcinogenesis in ApcMin/+ mice with natural ligands

    PubMed Central

    Kawajiri, Kaname; Kobayashi, Yasuhito; Ohtake, Fumiaki; Ikuta, Togo; Matsushima, Yoshibumi; Mimura, Junsei; Pettersson, Sven; Pollenz, Richard S.; Sakaki, Toshiyuki; Hirokawa, Takatsugu; Akiyama, Tetsu; Kurosumi, Masafumi; Poellinger, Lorenz; Kato, Shigeaki; Fujii-Kuriyama, Yoshiaki

    2009-01-01

    Intestinal cancer is one of the most common human cancers. Aberrant activation of the canonical Wnt signaling cascade, for example, caused by adenomatous polyposis coli (APC) gene mutations, leads to increased stabilization and accumulation of β-catenin, resulting in initiation of intestinal carcinogenesis. The aryl hydrocarbon receptor (AhR) has dual roles in regulating intracellular protein levels both as a ligand-activated transcription factor and as a ligand-dependent E3 ubiquitin ligase. Here, we show that the AhR E3 ubiquitin ligase has a role in suppression of intestinal carcinogenesis by a previously undescribed ligand-dependent β-catenin degradation pathway that is independent of and parallel to the APC system. This function of AhR is activated by both xenobiotics and natural AhR ligands, such as indole derivatives that are converted from dietary tryptophan and glucosinolates by intestinal microbes, and suppresses intestinal tumor development in ApcMin/+ mice. These findings suggest that chemoprevention with naturally-occurring and chemically-designed AhR ligands can be used to successfully prevent intestinal cancers. PMID:19651607

  19. Naturally-Occurring Marine Brominated Indoles are Aryl Hydrocarbon Receptor Ligands/Agonists

    PubMed Central

    DeGroot, Danica E.; Franks, Diana G.; Higa, Tatsuo; Tanaka, Junichi; Hahn, Mark E.; Denison, Michael S.

    2015-01-01

    The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that mediates the toxic and biological effects of structurally diverse chemicals, including the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). As part of a larger effort to identify the full spectrum of chemicals that can bind to and activate the AhR, we have examined the ability of several naturally-occurring marine-derived brominated indoles and brominated (methylthio)indoles (collectively referred to as “brominated indoles”) to bind to the AhR and stimulate AhR-dependent gene expression. Incubation of mouse, rat and guinea pig recombinant cell lines containing a stably transfected AhR-responsive luciferase reporter gene with eight brominated indoles revealed that all compounds stimulated luciferase reporter gene activity, although some species-specific differences were observed. All compounds induced significantly more luciferase activity when incubated with cells for 4 h as compared to 24 h, demonstrating that these compounds are transient activators of the AhR signaling pathway. Three of the brominated indoles induced CYP1A1 mRNA in human HepG2 cells in vitro and Cyp1a mRNA in zebrafish embryos in vivo. The identification of the brominated indoles as direct ligands and activators/agonists of the AhR was confirmed by their ability to compete with [3H]TCDD for binding to the AhR and to stimulate AhR transformation and DNA binding in vitro. Taken together, these marine-derived brominated indoles are members of a new class of naturally-occurring AhR agonists. PMID:26001051

  20. Characterizing the role of endothelin-1 in the progression of cardiac hypertrophy in aryl hydrocarbon receptor (AhR) null mice

    SciTech Connect

    Lund, Amie K.; Goens, M. Beth; Nunez, Bethany A.; Walker, Mary K. . E-mail: mkwalker@unm.edu

    2006-04-15

    The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor characterized to play a role in detection and adaptation to environmental stimuli. Genetic deletion of AhR results in hypertension, and cardiac hypertrophy and fibrosis, associated with elevated plasma angiotensin II (Ang II) and endothelin-1 (ET-1), thus AhR appears to contribute to cardiovascular homeostasis. In these studies, we tested the hypothesis that ET-1 mediates cardiovascular pathology in AhR null mice via ET{sub A} receptor activation. First, we determine the time courses of cardiac hypertrophy, and of plasma and tissue ET-1 expression in AhR wildtype and null mice. AhR null mice exhibited increases in heart-to-body weight ratio and age-related expression of cardiac hypertrophy markers, {beta}-myosin heavy chain ({beta}-MHC), and atrial natriuretic factor (ANF), which were significant at 2 months. Similarly, plasma and tissue ET-1 expression was significantly elevated at 2 months and increased further with age. Second, AhR null mice were treated with ET{sub A} receptor antagonist, BQ-123 (100 nmol/kg/day), for 7, 28, or 58 days and blood pressure, cardiac fibrosis, and cardiac hypertrophy assessed, respectively. BQ-123 for 7 days significantly reduced mean arterial pressure in conscious, catheterized mice. BQ-123 for 28 days significantly reduced the histological appearance of cardiac fibrosis. Treatment for 58 days significantly reduced cardiac mass, assessed by heart weight, echocardiography, and {beta}-MHC and ANF expression; and reduced cardiac fibrosis as determined by osteopontin and collagen I mRNA expression. These findings establish ET-1 and the ET{sub A} receptor as primary determinants of hypertension and cardiac pathology in AhR null mice.

  1. Role of AhR/ARNT system in skin homeostasis.

    PubMed

    Furue, Masutaka; Takahara, Masakazu; Nakahara, Takeshi; Uchi, Hiroshi

    2014-11-01

    Aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that binds to structurally diverse synthetic and naturally occurring chemicals including dioxins, flavonoids, tryptophan photoproducts, and Malassezia metabolites. Upon binding to its ligands, cytoplasmic AhR translocates to the nucleus, heterodimerizes with aryl hydrocarbon receptor nuclear translocator (ARNT), and mediates numerous biological and toxicological effects by inducing the transcription of various AhR-responsive genes. AhR ligation controls oxidation/antioxidation, epidermal barrier function, photo-induced response, melanogenesis, and innate immunity. This review summarizes recent advances in the understanding of the regulatory mechanisms of skin homeostasis mediated by the AhR/ARNT system.

  2. Interrupting autocrine ligand-receptor binding: comparison between receptor blockers and ligand decoys.

    PubMed Central

    Forsten, K E; Lauffenburger, D A

    1992-01-01

    Stimulation of cell behavioral functions by ligand/receptor binding can be accomplished in autocrine fashion, where cells secrete ligand capable of binding to receptors on their own surfaces. This proximal secretion of autocrine ligands near the surface receptors on the secreting cell suggests that control of these systems by inhibitors of receptor/ligand binding may be more difficult than for systems involving exogenous ligands. Hence, it is of interest to predict the conditions under which successful inhibition of cell receptor binding by the autocrine ligand can be expected. Previous theoretical work using a compartmentalized model for autocrine cells has elucidated the conditions under which addition of solution decoys for the autocrine ligand can interrupt cell receptor/ligand binding via competitive binding of the secreted molecules (Forsten, K. E., and D. A. Lauffenburger. 1992. Biophys. J. 61:1-12.) We now apply a similar modeling approach to examine the addition of solution blockers targeted against the cell receptor. Comparison of the two alternative inhibition strategies reveals that a significantly lower concentration of receptor blockers, compared to ligand decoys, will obtain a high degree of inhibition. The more direct interruption scheme characteristic of the receptor blockers may make them a preferred strategy when feasible. PMID:1330038

  3. ANALYSIS OF AH RECEPTOR-ARNT AND AH RECEPTOR-ARNT2 COMPLEXES IN VITRO AND IN CELL CULTURE

    PubMed Central

    Dougherty, Edward J.; Pollenz, Richard S.

    2008-01-01

    ARNT and ARNT2 proteins are expressed in mammalian and aquatic species and exhibit a high level of amino acid identity in the bHLH/PAS domains involved in protein interactions and DNA binding. Since the analysis of ARNT2 function at the protein level has been limited, ARNT2 function in aryl hydrocarbon receptor (AHR) mediated signaling was evaluated and compared to ARNT. In vitro, ARNT and ARNT2 dimerized equally with the AHR in the presence of TCDD and ARNT2 out-competed ARNT for binding to the AHR when expressed in excess. In contrast, activation of the AHR with 3-methylcholanthrene or benzo[a]pyrene resulted in predominant formation of AHR•ARNT complexes. ARNT2 expressed in Hepa-1 cell culture lines with reduced ARNT protein resulted in minimal induction of endogenous CYP1A1 protein compared to cells expressing ARNT and mutation of the putative proline residue at amino acid 352 to histidine failed to produce an ARNT2 that could function in AHR-mediated signaling. However, the expression of ARNT2 in wild type Hepa-1 cells reduced TCDD-mediated induction of endogenous CYP1A1 protein by 30%, even though AHR•ARNT2 complexes could not be detected in nuclear extracts. Western blot analysis of numerous mouse tissues and various cell culture line showed that both endogenous ARNT and ARNT2 could be detected in cells derived from kidney, CNS and retinal epithelium. Thus, ARNT2 has the ability to dimerize with the liganded AHR in vitro.and is influenced by the activating ligand yet appears to be limited in its ability to influence AHR mediated signaling in cell culture. PMID:18096572

  4. [Central effects of ORL1 receptor ligands].

    PubMed

    Maslov, L N; Lishmanov, Iu B; Calo, G; Ma, L

    2003-01-01

    It has been discussed literature data on molecular structure of ORL1 receptor and its interaction with intracellular signal systems and neurotransmitters. Data on chemical structure of ORL1 receptor ligands and their central effects (nociception, locomotion, feeding, cognition) are presented.

  5. Engineering death receptor ligands for cancer therapy.

    PubMed

    Wajant, Harald; Gerspach, Jeannette; Pfizenmaier, Klaus

    2013-05-28

    CD95, TNFR1, TRAILR1 and TRAILR2 belong to a subgroup of TNF receptors which is characterized by a conserved cell death-inducing protein domain that connects these receptors to the apoptotic machinery of the cell. Activation of death receptors in malignant cells attracts increasing attention as a principle to fight cancer. Besides agonistic antibodies the major way to stimulate death receptors is the use of their naturally occurring "death ligands" CD95L, TNF and TRAIL. However, dependent from the concept followed to develop a death ligand-based therapy various limiting aspects have to be taken into consideration on the way to a "bedside" usable drug. Problems arise in particular from the cell associated transmembrane nature of the death ligands, the poor serum half life of the soluble fragments derived from the transmembrane ligands, the ubiquitous expression of the death receptors and the existence of additional non-death receptors of the death ligands. Here, we summarize strategies how these limitations can be overcome by genetic engineering.

  6. AH6809, a prostaglandin DP-receptor blocking drug on human platelets.

    PubMed Central

    Keery, R. J.; Lumley, P.

    1988-01-01

    1. The effect of AH6809 (6-isopropoxy-9-oxoxanthene-2-carboxylic acid) has been studied upon the anti-aggregatory and aggregatory actions of various agents on human platelets in whole blood. 2. Prostaglandin D2 (PGD2), BW245C, 9 alpha, 11 beta-PGF2, PGI2 and 5'-N-ethylcarboxamide adenosine (NECA) all inhibited ADP-induced platelet aggregation in whole blood. The anti-aggregatory activity of PGD2, BW245C and 9 alpha, 11 beta-PGF2 but not PGI2 or NECA was antagonized by AH6809. NECA was antagonized by AH6809. 3. The antagonism of the anti-aggregatory activity of PGD2 by AH6809 was concentration-related and could be overcome by increasing the concentration of PGD2. Analysis of the data yielded an apparent pA2 for AH6809 of 5.35. 4. At approximately 10 fold higher concentrations than those required to antagonize the action of PGD2, AH6809 also antagonized the aggregatory effect of U-46619 in whole blood (pA2 = 4.45). However, concentrations of AH6809 up to 300 microM were without effect upon either ADP- or platelet activating factor (Paf)-induced aggregation (pA2 less than 3.5). 5. The potency of AH6809 against PGD2 and U-46619 was increased in a resuspended platelet preparation suggesting that the drug is extensively bound to plasma proteins. However, in resuspended platelets the specificity of AH6809 relative to that seen in whole blood was reduced since aggregation by ADP and Paf was also slightly antagonized. 6. In conclusion, AH6809 appears to be a weak but specific DP-receptor blocking drug on human platelets and should prove to be a useful drug tool for defining the involvement of endogenous PGD2 in platelet aggregation and classifying the mode of action of anti-aggregatory prostanoids. PMID:2460179

  7. Studies on the role of the Ah receptor in hexachloro-benzene-induced porphyria

    SciTech Connect

    Hahn, M.E.

    1987-01-01

    Many of the effects of hexachlorobenzene (HCB) resemble those of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), whose effects are initiated by its binding to the AH receptor, the regulatory gene product of the Ah locus. I investigated the ability of HCB to interact with the AH receptor and the involvement of this protein in HCB-induced porphyria. The induction of two cytochrome P450 isozymes regulated by the Ah locus was also examined in light of their possible role in the pathogenesis of HCB- and TCDD-induced porphyria. HCB competitively inhibited the in vitro specific binding of ({sup 3}H)-TCDD to the rat hepatic Ah receptor (K{sub I} = 2.1 {mu}M) without affecting the solubility of ({sup 3}H)TCDD. Following the administration of HCB to rats, the number of ({sup 3}H)TCDD specific binding sites was reduced by up to 40%. HCB induced cytochromes P450b, P450e, P450c, and P450d, confirming that it is a mixed-type P450 inducer. The presence of porphyria in mice was assessed by measuring urinary and hepatic porphyrins and hepatic uroporphyrinogen decarboxylase activity.

  8. The aryl hydrocarbon receptor AhR links atopic dermatitis and air pollution via induction of the neurotrophic factor artemin.

    PubMed

    Hidaka, Takanori; Ogawa, Eisaku; Kobayashi, Eri H; Suzuki, Takafumi; Funayama, Ryo; Nagashima, Takeshi; Fujimura, Taku; Aiba, Setsuya; Nakayama, Keiko; Okuyama, Ryuhei; Yamamoto, Masayuki

    2017-01-01

    Atopic dermatitis is increasing worldwide in correlation with air pollution. Various organic components of pollutants activate the transcription factor AhR (aryl hydrocarbon receptor). Through the use of AhR-CA mice, whose keratinocytes express constitutively active AhR and that develop atopic-dermatitis-like phenotypes, we identified Artn as a keratinocyte-specific AhR target gene whose product (the neurotrophic factor artemin) was responsible for epidermal hyper-innervation that led to hypersensitivity to pruritus. The activation of AhR via air pollutants induced expression of artemin, alloknesis, epidermal hyper-innervation and inflammation. AhR activation and ARTN expression were positively correlated in the epidermis of patients with atopic dermatitis. Thus, AhR in keratinocytes senses environmental stimuli and elicits an atopic-dermatitis pathology. We propose a mechanism of air-pollution-induced atopic dermatitis via activation of AhR.

  9. Indole and Tryptophan Metabolism: Endogenous and Dietary Routes to Ah Receptor Activation

    PubMed Central

    Hubbard, Troy D.; Murray, Iain A.

    2015-01-01

    The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor recognized for its role in xenobiotic metabolism. The physiologic function of AHR has expanded to include roles in immune regulation, organogenesis, mucosal barrier function, and the cell cycle. These functions are likely dependent upon ligand-mediated activation of the receptor. High-affinity ligands of AHR have been classically defined as xenobiotics, such as polychlorinated biphenyls and dioxins. Identification of endogenous AHR ligands is key to understanding the physiologic functions of this enigmatic receptor. Metabolic pathways targeting the amino acid tryptophan and indole can lead to a myriad of metabolites, some of which are AHR ligands. Many of these ligands exhibit species selective preferential binding to AHR. The discovery of specific tryptophan metabolites as AHR ligands may provide insight concerning where AHR is activated in an organism, such as at the site of inflammation and within the intestinal tract. PMID:26041783

  10. [Functional selectivity of opioid receptors ligands].

    PubMed

    Audet, Nicolas; Archer-Lahlou, Elodie; Richard-Lalonde, Mélissa; Piñeyro-Filpo, Graciela

    2010-01-01

    Opiates are the most effective analgesics available for the treatment of severe pain. However, their clinical use is restricted by unwanted side effects such as tolerance, physical dependence and respiratory depression. The strategy to develop new opiates with reduced side effects has mainly focused on the study and production of ligands that specifically bind to different opiate receptors subtypes. However, this strategy has not allowed the production of novel therapeutic ligands with a better side effects profile. Thus, other research strategies need to be explored. One which is receiving increasing attention is the possibility of exploiting ligand ability to stabilize different receptor conformations with distinct signalling profiles. This newly described property, termed functional selectivity, provides a potential means of directing the stimulus generated by an activated receptor towards a specific cellular response. Here we summarize evidence supporting the existence of ligand-specific active conformations for two opioid receptors subtypes (delta and mu), and analyze how functional selectivity may contribute in the production of longer lasting, better tolerated opiate analgesics. double dagger.

  11. The Retinoid X Receptors and Their Ligands

    PubMed Central

    Dawson, Marcia I.; Xia, Zebin

    2014-01-01

    This chapter presents an overview of the current status of studies on the structural and molecular biology of the retinoid X receptor subtypes α, β, and γ (RXRs, NR2B1–3), their nuclear and cytoplasmic functions, post-transcriptional processing, and recently reported ligands. Points of interest are the different changes in the ligand-binding pocket induced by variously shaped agonists, the communication of the ligand–bound pocket with the coactivator binding surface and the heterodimerization interface, and recently identified ligands that are natural products, those that function as environmental toxins or drugs that had been originally designed to interact with other targets, as well as those that were deliberately designed as RXR-selective transcriptional agonists, synergists, or antagonists. Of these synthetic ligands, the general trend in design appears to be away from fully aromatic rigid structures to those containing partial elements of the flexible tetraene side chain of 9-cis-retinoic acid. PMID:22020178

  12. Early development of sigma-receptor ligands.

    PubMed

    Narayanan, Sanju; Bhat, Rohit; Mesangeau, Christophe; Poupaert, Jacques H; McCurdy, Christopher R

    2011-01-01

    Sigma receptors (σ-1 and σ-2) are non-opioid proteins implicated in the pathophysiology of various neurological disorders and cancer. The σ-1 subtype is a chaperon protein widely distributed in the CNS and peripheral tissues. These receptors are involved in the modulation of K(+)- and Ca(2+)-dependent signaling cascades at the endoplasmic reticulum and modulation of neurotransmitter release. σ-1 receptors are emerging targets for the treatment of neurophychiatric diseases (schizophrenia and depression) and cocaine addiction. σ-2 receptors are lipid raft proteins. They are highly expressed on many tumor cells and hence considered potential targets for anticancer drugs. σ receptors bind to a diverse class of pharmacological compounds like cocaine, methamphetamine, benzomorphans like (±)-pentazocine, (±)-SKF-10,047 and endogenous neurosteroids and sphingolipids. In this review we focus on the early development of σ receptor-specific ligands and radiolabeling agents.

  13. Ligands for Ionotropic Glutamate Receptors

    PubMed Central

    Swanson, Geoffrey T.; Sakai, Ryuichi

    2010-01-01

    Marine-derived small molecules and peptides have played a central role in elaborating pharmacological specificities and neuronal functions of mammalian ionotropic glutamate receptors (iGluRs), the primary mediators of excitatory synaptic transmission in the central nervous system (CNS). As well, the pathological sequelae elicited by one class of compounds (the kainoids) constitute a widely-used animal model for human mesial temporal lobe epilepsy (mTLE). New and existing molecules could prove useful as lead compounds for the development of therapeutics for neuropathologies that have aberrant glutamatergic signaling as a central component. In this chapter we discuss natural source origins and pharmacological activities of those marine compounds that target ionotropic glutamate receptors. PMID:19184587

  14. Nucleotide Specificity of DNA Binding of the Aryl Hydrocarbon Receptor:ARNT Complex Is Unaffected by Ligand Structure

    PubMed Central

    Denison, Michael S.

    2014-01-01

    The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates the toxic and biological effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) and a wide variety of structurally diverse ligands through its ability to translocate into the nucleus and bind to a specific DNA recognition site (the dioxin-responsive element [DRE]) adjacent to responsive genes. Although the sequence of the DRE is well defined, several reports suggested that the nucleotide specificity of AhR DNA binding may vary depending on the structure of its bound ligand. Given the potential toxicological significance of this hypothesis, an unbiased DNA-selection-and-PCR-amplification approach was utilized to directly determine whether binding and activation of the AhR by structurally diverse agonists alter its nucleotide specificity of DNA binding. Guinea pig hepatic cytosolic AhR activated in vitro by equipotent concentrations of TCDD, 3-methylcholanthrene, β-naphthoflavone, indirubin, L-kynurenine, or YH439 was incubated with a pool of DNA oligonucleotides containing a 15-base pair variable region consisting of all possible nucleotides. The AhR-bound oligonucleotides isolated by immunoprecipitation were PCR amplified and used in subsequent rounds of selection. Sequence analysis of a total of 196 isolated oligonucleotides revealed that each ligand-activated AhR:ARNT complex only bound to DRE-containing DNA oligonucleotides; no non-DRE-containing DNA oligonucleotides were identified. These results demonstrate that the binding and activation of the AhR by structurally diverse agonists do not appear to alter its nucleotide specificity of DNA binding and suggest that stimulation of gene expression mediated by direct DNA binding of ligand-activated AhR:ARNT complexes is DRE dependent. PMID:24136190

  15. Structural and Functional Characterization of the Aryl Hydrocarbon Receptor Ligand Binding Domain by Homology Modeling and Mutational Analysis†

    PubMed Central

    Pandini, Alessandro; Denison, Michael S.; Song, Yujuan; Soshilov, Anatoly A.; Bonati, Laura

    2010-01-01

    The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that is activated by a structurally diverse array of synthetic and natural chemicals, including toxic halogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Analysis of the molecular events occurring in the AhR ligand binding and activation processes requires structural information on the AhR Per-Arnt-Sim (PAS) B-containing ligand binding domain, for which no experimentally determined structure has been reported. With the availability of extensive structural information on homologous PAS-containing proteins, a reliable model of the mouse AhR PAS B domain was developed by comparative modeling techniques. The PAS domain structures of the functionally related hypoxia-inducible factor 2α (HIF-2α) and AhR nuclear translocator (ARNT) proteins, which exhibit the highest degree of sequence identity and similarity with AhR, were chosen to develop a two-template model. To confirm the features of the modeled domain, the effects of point mutations in selected residue positions on both TCDD binding to the AhR and TCDD-dependent transformation and DNA binding were analyzed. Mutagenesis and functional analysis results are consistent with the proposed model and confirm that the cavity modeled in the interior of the domain is indeed involved in ligand binding. Moreover, the physicochemical characteristics of some residues and of their mutants, along with the effects of mutagenesis on TCDD and DNA binding, also suggest some key features that are required for ligand binding and activation of mAhR at a molecular level, thus providing a framework for further studies. PMID:17223691

  16. Nitrosamines as nicotinic receptor ligands

    PubMed Central

    Schuller, Hildegard M.

    2007-01-01

    Nitrosamines are carcinogens formed in the mammalian organism from amine precursors contained in food, beverages, cosmetics and drugs. The potent carcinogen, NNK, and the weaker carcinogen, NNN, are nitrosamines formed from nicotine. Metabolites of the nitrosamines react with DNA to form adducts responsible for genotoxic effects. We have identified NNK as a high affinity agonist for the alpha7 nicotinic acetylcholine receptor (α7nAChR) whereas NNN bound with high affinity to epibatidine-sensitive nAChRs. Diethylnitrosamine (DEN) bound to both receptors but with lower affinity. High levels of the α7nAChR were expressed in human small cell lung cancer (SCLC) cell lines and in hamster pulmonary neuroendocrine cells (PNECs), which serve as a model for the cell of origin of human SCLC. Exposure of SCLC or PNECs to NNK or nicotine increased expression of the a7nAChR and caused influx of Ca2+, activation of PKC, Raf-1, ERK1/2, and c-myc, resulting in the stimulation of cell proliferation. Signaling via the α7nAChR was enhanced when cells were maintained in an environment of 10–15% CO2 similar to that in the diseased lung. Hamsters with hyperoxia-induced pulmonary fibrosis developed neuroendocrine lung carcinomas similar to human SCLC when treated with NNK, DEN, or nicotine. The development of the NNK-induced tumors was prevented by green tea or theophylline. The beta-adrenergic receptor agonist, isoproterenol or theophylline blocked NNK-induced cell proliferation in vitro. NNK and nicotine-induced hyperactivity of the α7nAChR/RAF/ERK1/2 pathway thus appears to play a crucial role in the development of SCLC in smokers and could be targeted for cancer prevention. PMID:17459420

  17. Nitrosamines as nicotinic receptor ligands.

    PubMed

    Schuller, Hildegard M

    2007-05-30

    Nitrosamines are carcinogens formed in the mammalian organism from amine precursors contained in food, beverages, cosmetics and drugs. The potent carcinogen, NNK, and the weaker carcinogen, NNN, are nitrosamines formed from nicotine. Metabolites of the nitrosamines react with DNA to form adducts responsible for genotoxic effects. We have identified NNK as a high affinity agonist for the alpha7 nicotinic acetylcholine receptor (alpha7nAChR) whereas NNN bound with high affinity to epibatidine-sensitive nAChRs. Diethylnitrosamine (DEN) bound to both receptors but with lower affinity. High levels of the alpha7nAChR were expressed in human small cell lung cancer (SCLC) cell lines and in hamster pulmonary neuroendocrine cells (PNECs), which serve as a model for the cell of origin of human SCLC. Exposure of SCLC or PNECs to NNK or nicotine increased expression of the alpha7nAChR and caused influx of Ca(2+), activation of PKC, Raf-1, ERK1/2, and c-myc, resulting in the stimulation of cell proliferation. Signaling via the alpha7nAChR was enhanced when cells were maintained in an environment of 10-15% CO(2) similar to that in the diseased lung. Hamsters with hyperoxia-induced pulmonary fibrosis developed neuroendocrine lung carcinomas similar to human SCLC when treated with NNK, DEN, or nicotine. The development of the NNK-induced tumors was prevented by green tea or theophylline. The beta-adrenergic receptor agonist, isoproterenol or theophylline blocked NNK-induced cell proliferation in vitro. NNK and nicotine-induced hyperactivity of the alpha7nAChR/RAF/ERK1/2 pathway thus appears to play a crucial role in the development of SCLC in smokers and could be targeted for cancer prevention.

  18. Molecular modulators of benzodiazepine receptor ligand binding

    SciTech Connect

    Villar, H.O.; Loew, G.H. )

    1989-01-01

    Ten derivatives of {beta}-carbolines with known affinities to the GABA{sub A}/BDZ (benzodiazepine) receptor were studied using the Am 1 and MNDO/H Semiempirical techniques to identify and characterize molecular modulators of receptor recognition. Steric, lipophilic, and electrostatic properties of these compounds were calculated and examined for their possible role in recognition. Particular attention was paid to the regions around the two most favorable proton-accepting sites, the ON and the substituent at the C{sub 3} position, already implicated in recognition, as well as to the acidic N9H group that could be a proton donating center. To probe further the role of these three ligand sites in receptor interactions, a model of the receptor using three methanol molecules was made and optimum interactions of these three sites with them characterized. The results indicate some similarity in the shape of these ligands, which could reflect a steric requirement. The receptor affinity appears to be modulated to some extent by the ratio of lipophilic to hydrophilic surface, the negative potential at the {beta}N, provided there is also one at the C{sub 3} substituent confirming the importance of two accepting sites in recognition. The acidic N9H does not appear to be a modulator of affinity or does it form a stable H-bond with methanol as acceptor. The two proton donating molecules do form such a stable complex, and both are needed for high affinity.

  19. Chemistry and pharmacology of GABAB receptor ligands.

    PubMed

    Froestl, Wolfgang

    2010-01-01

    This chapter presents new clinical applications of the prototypic GABA(B) receptor agonist baclofen for the treatment of addiction by drugs of abuse, such as alcohol, cocaine, nicotine, morphine, and heroin, a novel baclofen prodrug Arbaclofen placarbil, the GABA(B) receptor agonist AZD3355 (Lesogabaran) currently in Phase 2 clinical trials for the treatment of gastroesophageal reflux disease, and four positive allosteric modulators of GABA(B) receptors (CGP7930, GS39783, NVP-BHF177, and BHFF), which have less propensity for the development of tolerance due to receptor desensitization than classical GABA(B) receptor agonists. All four compounds showed anxiolytic affects. In the presence of positive allosteric modulators the "classical" GABA(B) receptor antagonists CGP35348 and 2-hydroxy-saclofen showed properties of partial GABA(B) receptor agonists. Seven micromolar affinity GABA(B) receptor antagonists, phaclofen; 2-hydroxy-saclofen; CGP's 35348, 36742, 46381, 51176; and SCH50911, are discussed. CGP36742 (SGS742) showed statistically significant improvements of working memory and attention in a Phase 2 clinical trial in mild, but not in moderate Alzheimer patients. Eight nanomolar affinity GABA(B) receptor antagonists are presented (CGP's 52432, 54626, 55845, 56433, 56999, 61334, 62349, and 63360) that were used by pharmacologists for numerous in vitro and in vivo investigations. CGP's 36742, 51176, 55845, and 56433 showed antidepressant effects. Several compounds are also available as radioligands, such as [(3)H]CGP27492, [(3)H]CGP54626, [(3)H]CGP5699, and [(3)H]CGP62349. Three novel fluorescent and three GABA(B) receptor antagonists with very high specific radioactivity (>2,000 Ci/mmol) are presented. [(125)I]CGP64213 and the photoaffinity ligand [(125)I]CGP71872 allowed the identification of GABA(B1a) and GABA(B1b) receptors in the expression cloning work.

  20. Affinity Regulates Spatial Range of EGF Receptor Autocrine Ligand Binding

    SciTech Connect

    Dewitt, Ann; Iida, Tomoko; Lam, Ho-Yan; Hill, Virginia; Wiley, H S.; Lauffenburger, Douglas A.

    2002-08-08

    Proper spatial localization of EGFR signaling activated by autocrine ligands represents a critical factor in embryonic development as well as tissue organization and function, and ligand/receptor binding affinity is among the molecular and cellular properties suggested to play a role in governing this localization. The authors employ a computational model to predict how receptor-binding affinity affects local capture of autocrine ligand vis-a-vis escape to distal regions, and provide experimental test by constructing cell lines expressing EGFR along with either wild-type EGF or a low-affinity mutant, EGF{sup L47M}. The model predicts local capture of a lower affinity autocrine ligand to be less efficient when the ligand production rate is small relative to receptor appearance rate. The experimental data confirm this prediction, demonstrating that cells can use ligand/receptor binding affinity to regulate ligand spatial distribution when autocrine ligand production is limiting for receptor signaling.

  1. AhR ligands, malassezin, and indolo[3,2-b]carbazole are selectively produced by Malassezia furfur strains isolated from seborrheic dermatitis.

    PubMed

    Gaitanis, George; Magiatis, Prokopios; Stathopoulou, Konstantina; Bassukas, Ioannis D; Alexopoulos, Evangelos C; Velegraki, Aristea; Skaltsounis, Alexios-Leandros

    2008-07-01

    Malassezia yeasts are connected with seborrheic dermatitis (SD) whereas M. furfur pathogenicity is associated with the production of bioactive indoles. In this study, the production of indoles by M. furfur isolates from healthy and diseased skin was compared, the respective HPLC patterns were analyzed, and substances that are preferentially synthesized by strains isolated from SD lesions were isolated and characterized. Malassezin, pityriacitrin, indole-3-carbaldehyde, and indolo[3,2-b]carbazole (ICZ) were isolated by HPLC from extracts of M. furfur grown in L-tryptophan agar, and identified by nuclear magnetic resonance and mass spectroscopy. Of these, ICZ, a potent ligand of the aryl hydrocarbon receptor (AhR), is described for the first time to our knowledge as a M. furfur metabolite. HPLC-photodiode array detection analysis of strain extracts from 7 healthy subjects and 10 SD patients showed that M. furfur isolates from only SD patients consistently produce malassezin and ICZ. This discriminatory production of AhR agonists provides initial evidence for a previously unreported mechanism triggering development of SD and indicates that the variable pathogenicity patterns recorded for M. furfur-associated SD conditions may be attributed to selective production (P<0.001) of measurable bioactive indoles.

  2. The aryl hydrocarbon receptor (AhR) pathway as a regulatory pathway for cell adhesion and matrix metabolism

    PubMed Central

    Kung, Tiffany; Murphy, K.A.; White, L.A.

    2009-01-01

    The aryl hydrocarbon receptor (AhR) is an orphan receptor in the basic-helix-loop-helix PAS family of transcriptional regulators. Although the endogenous regulator of this pathway has not been identified, the AhR is known to bind and be activated by a variety of compounds ranging from environmental contaminants to flavanoids. The function of this receptor is still unclear; however, animal models indicate that the AhR is important for normal development. One hypothesis is that the AhR senses cellular stress and initiates the cellular response by altering gene expression and inhibiting cell cycle progression and that activation of the AhR by exogenous environmental chemicals results in the dysregulation of this normal function. In this review we will examine the role of the AhR in the regulation of genes and proteins involved in cell adhesion and matrix remodeling, and discuss the implications of these changes in development and disease. In addition, we will discuss evidence suggesting that the AhR pathway is responsive to changes in matrix composition as well as cell-cell and cell-matrix interactions. PMID:18940186

  3. [Peripheral effects of ligands of ORL1 receptors].

    PubMed

    Maslov, L N; Lishmanov, Iu B; Calo, G; Ma, L; Lambert, D G

    2003-01-01

    It has been discussed literature data on the role for ORL1 (NOR) receptors in the regulation of function of gastrointestinal, respiratory, cardiovascular, immune, endocrine systems. In addition, it has been discussed a possibility of penetration of blood brain barrier for ORL1 receptor ligands and species dependence of NOR-ligands' effects.

  4. Structural Analysis of Chemokine Receptor-Ligand Interactions.

    PubMed

    Arimont, Marta; Sun, Shan-Liang; Leurs, Rob; Smit, Martine; de Esch, Iwan J P; de Graaf, Chris

    2017-03-10

    This review focuses on the construction and application of structural chemokine receptor models for the elucidation of molecular determinants of chemokine receptor modulation and the structure-based discovery and design of chemokine receptor ligands. A comparative analysis of ligand binding pockets in chemokine receptors is presented, including a detailed description of the CXCR4, CCR2, CCR5, CCR9, and US28 X-ray structures, and their implication for modeling molecular interactions of chemokine receptors with small-molecule ligands, peptide ligands, and large antibodies and chemokines. These studies demonstrate how the integration of new structural information on chemokine receptors with extensive structure-activity relationship and site-directed mutagenesis data facilitates the prediction of the structure of chemokine receptor-ligand complexes that have not been crystallized. Finally, a review of structure-based ligand discovery and design studies based on chemokine receptor crystal structures and homology models illustrates the possibilities and challenges to find novel ligands for chemokine receptors.

  5. Environmental Ligands of the Aryl Hydrocarbon Receptor and Their Effects in Models of Adult Liver Progenitor Cells

    PubMed Central

    Vondráček, Jan; Machala, Miroslav

    2016-01-01

    The toxicity of environmental and dietary ligands of the aryl hydrocarbon receptor (AhR) in mature liver parenchymal cells is well appreciated, while considerably less attention has been paid to their impact on cell populations exhibiting phenotypic features of liver progenitor cells. Here, we discuss the results suggesting that the consequences of the AhR activation in the cellular models derived from bipotent liver progenitors could markedly differ from those in hepatocytes. In contact-inhibited liver progenitor cells, the AhR agonists induce a range of effects potentially linked with tumor promotion. They can stimulate cell cycle progression/proliferation and deregulate cell-to-cell communication, which is associated with downregulation of proteins forming gap junctions, adherens junctions, and desmosomes (such as connexin 43, E-cadherin, β-catenin, and plakoglobin), as well as with reduced cell adhesion and inhibition of intercellular communication. At the same time, toxic AhR ligands may affect the activity of the signaling pathways contributing to regulation of liver progenitor cell activation and/or differentiation, such as downregulation of Wnt/β-catenin and TGF-β signaling, or upregulation of transcriptional targets of YAP/TAZ, the effectors of Hippo signaling pathway. These data illustrate the need to better understand the potential role of liver progenitors in the AhR-mediated liver carcinogenesis and tumor promotion. PMID:27274734

  6. Bivalent Ligands for the Serotonin 5-HT3 Receptor

    PubMed Central

    2011-01-01

    The serotonin 5-HT3 receptor is a ligand-gated ion channel, which by virtue of its pentameric architecture, can be considered to be an intriguing example of intrinsically multivalent biological receptors. This paper describes a general design approach to the study of multivalency in this multimeric ion channel. Bivalent ligands for 5-HT3 receptor have been designed by linking an arylpiperazine moiety to probes showing different functional features. Both homobivalent and heterobivalent ligands have shown 5-HT3 receptor affinity in the nanomolar range, providing evidence for the viability of our design approach. Moreover, the high affinity shown by homobivalent ligands suggests that bivalency is a promising approach in 5-HT3 receptor modulation and provides the rational basis for applying the concepts of multivalency to the study of 5-HT3 receptor function. PMID:24900351

  7. Ligand binding was acquired during evolution of nuclear receptors

    PubMed Central

    Escriva, Hector; Safi, Rachid; Hänni, Catherine; Langlois, Marie-Claire; Saumitou-Laprade, Pierre; Stehelin, Dominique; Capron, André; Pierce, Raymond; Laudet, Vincent

    1997-01-01

    The nuclear receptor (NR) superfamily comprises, in addition to ligand-activated transcription factors, members for which no ligand has been identified to date. We demonstrate that orphan receptors are randomly distributed in the evolutionary tree and that there is no relationship between the position of a given liganded receptor in the tree and the chemical nature of its ligand. NRs are specific to metazoans, as revealed by a screen of NR-related sequences in early- and non-metazoan organisms. The analysis of the NR gene duplication pattern during the evolution of metazoans shows that the present NR diversity arose from two waves of gene duplications. Strikingly, our results suggest that the ancestral NR was an orphan receptor that acquired ligand-binding ability during subsequent evolution. PMID:9192646

  8. Limited proteolysis for assaying ligand binding affinities of nuclear receptors.

    PubMed

    Benkoussa, M; Nominé, B; Mouchon, A; Lefebvre, B; Bernardon, J M; Formstecher, P; Lefebvre, P

    1997-01-01

    The binding of natural or synthetic ligands to nuclear receptors is the triggering event leading to gene transcription activation or repression. Ligand binding to the ligand binding domain of these receptors induces conformational changes that are evidenced by an increased resistance of this domain to proteases. In vitro labeled receptors were incubated with various synthetic or natural agonists or antagonists and submitted to trypsin digestion. Proteolysis products were separated by SDS-PAGE and quantified. The amount of trypsin-resistant fragments was proportional to receptor occupancy by the ligand, and allowed the determination of dissociation constants (kDa). Using the wild-type or mutated human retinoic acid receptor alpha as a model, kDa values determined by classical competition binding assays using tritiated ligands are in agreement with those measured by the proteolytic assay. This method was successfully extended to human retinoic X receptor alpha, glucocorticoid receptor, and progesterone receptor, thus providing a basis for a new, faster assay to determine simultaneously the affinity and conformation of receptors when bound to a given ligand.

  9. Tissue specificity of aryl hydrocarbon receptor (AhR) mediated responses and relative sensitivity of white sturgeon (Acipenser transmontanus) to an AhR agonist.

    PubMed

    Doering, Jon A; Wiseman, Steve; Beitel, Shawn C; Tendler, Brett J; Giesy, John P; Hecker, Markus

    2012-06-15

    Sturgeons are endangered in some parts of the world. Due to their benthic nature and longevity sturgeon are at greater risk of exposure to bioaccumulative contaminants such as dioxin-like compounds that are associated with sediments. Despite their endangered status, little research has been conducted to characterize the relative responsiveness of sturgeon to dioxin-like compounds. In an attempt to study the biological effects and possible associated risks of exposure to dioxin-like compounds in sturgeon, the molecular and biochemical responses of white sturgeon (Acipenser transmontanus) to a model aryl hydrocarbon receptor (AhR) agonist, β-naphthoflavone (βNF) were investigated. White sturgeon were injected intraperitoneally with one of three doses of βNF (0, 50, or 500mg/kg, bw). Rainbow trout (Oncorhynchus mykiss) were used as a reference species since their responses have been well characterized in the past. Three days following injection with βNF, fish were euthanized and livers, gills, and intestines collected for biochemical and molecular analyses. White sturgeon exposed to βNF had significantly greater ethoxyresorufin O-deethylase (EROD) activity in liver (up to 37-fold), gill (up to 41-fold), and intestine (up to 36-fold) than did unexposed controls. Rainbow trout injected with βNF exhibited EROD activity that was significantly greater in liver (88-fold), than that of controls, but was undetectable in gills or intestine. Abundance of CYP1A transcript displayed a comparable pattern of tissue-specific induction with intestine (up to 189-fold), gills (up to 53-fold), and liver (up to 21-fold). Methoxyresorufin O-deethylase (MROD) and pentoxyresorufin O-deethylase (PROD) activities were undetectable in unexposed white sturgeon tissues while exposed tissues displayed MROD activity that was only moderately greater than the activity that could be detected. Differential inducibility among liver, gill, and intestine following exposure to an AhR agonist is

  10. Imidazolines stimulate release of insulin from RIN-5AH cells independently from imidazoline I1 and I2 receptors.

    PubMed

    Olmos, G; Kulkarni, R N; Haque, M; MacDermot, J

    1994-09-01

    The effect on insulin release of efaroxan, an alpha 2-adrenoceptor antagonist and a highly potent drug at imidazoline I1 receptors, and the effects of seven other imidazoline compounds selective for the imidazoline I1 or I2 receptors, were studied in the rat insulinoma cell line RIN-5AH. The cells released insulin in response to glucose (0.3-10 mM), and efaroxan (100 microM) potentiated glucose-induced insulin release. (-)-Adrenaline completely displaced the binding of [125I]p-iodoclonidine to membranes of RIN-5AH cells, indicating that these cells do not express imidazoline I1 receptors. Cirazoline and idazoxan (100 microM), both highly potent drugs at imidazoline I2 receptors, and the guanidines guanoxan and amiloride (200 microM), also promoted insulin release from RIN-5AH cells. Irreversible blockade of imidazoline I2 receptors with 10 microM clorgyline did not prevent the stimulatory effects of cirazoline or idazoxan; however, these compounds completely reversed the inhibition by diazoxide (250 microM), an opener of ATP-dependent K+ channels (K+ATP channels), of glucose-induced insulin release. These data indicate that the imidazoline/guanidine compounds promote insulin release from RIN-5AH cells, by interacting with a novel binding site related to K+ATP channels that does not represent any of the known imidazoline I1 or I2 receptors.

  11. Development of Species-Specific Ah Receptor-Responsive Third Generation CALUX Cell Lines with Increased Sensitivity and Responsiveness

    PubMed Central

    Brennan, Jennifer C.; He, Guochun; Tsutsumi, Tomoaki; Zhao, Jing; Wirth, Ed; Fulton, Michael H.; Denison, Michael S.

    2016-01-01

    The Ah receptor (AhR)-responsive CALUX (chemically-activated luciferase expression) cell bioassay is commonly used for rapid screening of samples for the presence of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin), dioxin-like compounds, and AhR agonists/antagonists. By increasing the number of AhR DNA recognition sites (dioxin responsive elements), we previously generated a novel third generation (G3) recombinant AhR-responsive mouse CALUX cell line (H1L7.5c3) with significantly enhanced sensitivity and response to DLCs compared to existing AhR-CALUX cell bioassays. However, the elevated background luciferase activity of these cells and the absence of comparable G3 cell lines derived from other species have limited their utility for screening purposes. Here, we describe the development and characterization of species-specific G3 recombinant AhR-responsive CALUX cell lines (rat, human, and guinea pig) that exhibit significantly improved sensitivity and dramatically increased TCDD induction response. The low background luciferase activity, low minimal detection limit (0.1 pM TCDD) and enhanced induction response of the rat G3 cell line (H4L7.5c2) over the H1L7.5c3 mouse G3 cells, identifies them as a more optimal cell line for screening purposes. The utility of the new G3 CALUX cell lines were demonstrated by screening sediment extracts and a small chemical compound library for the presence of AhR agonists. The increased sensitivity and response of these new G3 CALUX cell lines will facilitate species-specific analysis of DLCs and AhR agonists in samples with low levels of contamination and/or in small sample volumes. PMID:26366531

  12. Sliding tethered ligands add topological interactions to the toolbox of ligand-receptor design.

    PubMed

    Bauer, Martin; Kékicheff, Patrick; Iss, Jean; Fajolles, Christophe; Charitat, Thierry; Daillant, Jean; Marques, Carlos M

    2015-09-09

    Adhesion in the biological realm is mediated by specific lock-and-key interactions between ligand-receptor pairs. These complementary moieties are ubiquitously anchored to substrates by tethers that control the interaction range and the mobility of the ligands and receptors, thus tuning the kinetics and strength of the binding events. Here we add sliding anchoring to the toolbox of ligand-receptor design by developing a family of tethered ligands for which the spacer can slide at the anchoring point. Our results show that this additional sliding degree of freedom changes the nature of the adhesive contact by extending the spatial range over which binding may sustain a significant force. By introducing sliding tethered ligands with self-regulating length, this work paves the way for the development of versatile and reusable bio-adhesive substrates with potential applications for drug delivery and tissue engineering.

  13. Formyl peptide receptor chimeras define domains involved in ligand binding.

    PubMed

    Perez, H D; Holmes, R; Vilander, L R; Adams, R R; Manzana, W; Jolley, D; Andrews, W H

    1993-02-05

    We have begun to study the structural requirements for the binding of formyl peptides to their specific receptors. As an initial approach, we constructed C5a-formyl peptide receptor chimeras. Unique (and identical) restriction sites were introduced within the transmembrane domains of these receptors that allowed for the exchange of specific areas. Four types of chimeric receptors were generated. 1) The C5a receptor was progressively substituted by the formyl peptide receptor. 2) The formyl peptide receptor was progressively substituted by the C5a receptor. 3) Specific domains of the C5a receptor were substituted by the corresponding domain of the formyl peptide receptor. 4) Specific domains of the formyl peptide receptor were replaced by the same corresponding domain of the C5a receptor. Wild type and chimeric receptors were transfected into COS 7 cells and their ability to bind formyl peptide determined, taking into account efficiency of transfection and expression of chimeric protein. Based on these results, a ligand binding model is presented in which the second, third, and fourth extracellular (and/or their transmembrane) domains together with the first transmembrane domain form a ligand binding pocket for formyl peptides. It is proposed that the amino-terminal domain plays a role by presumably providing a "lid" to the pocket. The carboxyl-terminal cytoplasmic tail appears to modulate ligand binding by regulating receptor affinity.

  14. In Vivo Dioxin Favors Interleukin-22 Production by Human CD4+ T Cells in an Aryl Hydrocarbon Receptor (AhR)-Dependent Manner

    PubMed Central

    Brembilla, Nicolò Costantino; Ramirez, Jean-Marie; Chicheportiche, Rachel; Sorg, Olivier; Saurat, Jean-Hilaire; Chizzolini, Carlo

    2011-01-01

    Background The transcription factor aryl hydrocarbon receptor (AhR) mediates the effects of a group of chemicals known as dioxins, ubiquitously present in our environment. However, it is poorly known how the in vivo exposure to these chemicals affects in humans the adaptive immune response. We therefore assessed the functional phenotype of T cells from an individual who developed a severe cutaneous and systemic syndrome after having been exposed to an extremely high dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Methodology/Principal Findings T cells of the TCDD-exposed individual were studied for their capacity to produce cytokines in response to polyclonal and superantigenic stimulation, and for the expression of chemokine receptors involved in skin homing. The supernatants from T cells of the exposed individual contained a substantially increased amount of interleukin (IL)-22 but not of IL-17A, interferon (IFN)-γ or IL-10 when compared to nine healthy controls. In vitro experiments confirmed a direct, AhR-dependent, enhancing effect of TCDD on IL-22 production by CD4+ T cells. The increased production of IL-22 was not dependent on AhR occupancy by residual TCDD molecules, as demonstrated in competition experiments with the specific AhR antagonist CH-223191. In contrast, it was due to an increased frequency of IL-22 single producing cells accompanied by an increased percentage of cells expressing the skin-homing chemokine receptors CCR6 and CCR4, identified through a multiparameter flow cytometry approach. Of interest, the frequency of CD4+CD25hiFoxP3+ T regulatory cells was similar in the TCDD-exposed and healthy individuals. Conclusions/Significance This case strongly supports the contention that human exposure to persistent AhR ligands in vivo induce a long-lasting effect on the human adaptive immune system and specifically polarizes CD4+ T cells to produce IL-22 and not other T cell cytokines with no effect on T regulatory cells. PMID:21525997

  15. CLiBE: a database of computed ligand binding energy for ligand-receptor complexes.

    PubMed

    Chen, X; Ji, Z L; Zhi, D G; Chen, Y Z

    2002-11-01

    Consideration of binding competitiveness of a drug candidate against natural ligands and other drugs that bind to the same receptor site may facilitate the rational development of a candidate into a potent drug. A strategy that can be applied to computer-aided drug design is to evaluate ligand-receptor interaction energy or other scoring functions of a designed drug with that of the relevant ligands known to bind to the same binding site. As a tool to facilitate such a strategy, a database of ligand-receptor interaction energy is developed from known ligand-receptor 3D structural entries in the Protein Databank (PDB). The Energy is computed based on a molecular mechanics force field that has been used in the prediction of therapeutic and toxicity targets of drugs. This database also contains information about ligand function and other properties and it can be accessed at http://xin.cz3.nus.edu.sg/group/CLiBE.asp. The computed energy components may facilitate the probing of the mode of action and other profiles of binding. A number of computed energies of some PDB ligand-receptor complexes in this database are studied and compared to experimental binding affinity. A certain degree of correlation between the computed energy and experimental binding affinity is found, which suggests that the computed energy may be useful in facilitating a qualitative analysis of drug binding competitiveness.

  16. Database of Ligand-Receptor Partners, a DIP subset

    DOE Data Explorer

    Graeber, Thomas G.; Eisenberg, David

    The Database of Ligand-Receptor Partners (DLRP) is a subset of DIP (Database of Interacting Proteins). The DLRP is a database of protein ligand and protein receptor pairs that are known to interact with each other. By interact we mean that the ligand and receptor are members of a ligand-receptor complex and, unless otherwise noted, transduce a signal. In some instances the ligand and/or receptor may form a heterocomplex with other ligands/receptors in order to be functional. We have entered the majority of interactions in DLRP as full DIP entries, with links to references and additional information (see the DIP User's Guide). DLRP is a web supplement for: Thomas G. Graeber and David Eisenberg. Bioinformatic identification of potential autocrine signaling loops in cancers from gene expression profiles. Nature Genetics, 29(3):295-300 (November 2001). [Quoted from the DLRP homepage at http://dip.doe-mbi.ucla.edu/dip/DLRP.cgi] Also available from this page is the DLRP chemokine subset.

  17. Differences in activation of aryl hydrocarbon receptors of white sturgeon relative to lake sturgeon are predicted by identities of key amino acids in the ligand binding domain.

    PubMed

    Doering, Jon A; Farmahin, Reza; Wiseman, Steve; Beitel, Shawn C; Kennedy, Sean W; Giesy, John P; Hecker, Markus

    2015-04-07

    Dioxin-like compounds (DLCs) are pollutants of global environmental concern. DLCs elicit their adverse outcomes through activation of the aryl hydrocarbon receptor (AhR). However, there is limited understanding of the mechanisms that result in differences in sensitivity to DLCs among different species of fishes. Understanding these mechanisms is critical for protection of the diversity of fishes exposed to DLCs, including endangered species. This study investigated specific mechanisms that drive responses of two endangered fishes, white sturgeon (Acipenser transmontanus) and lake sturgeon (Acipenser fulvescens) to DLCs. It determined whether differences in sensitivity to activation of AhRs (AhR1 and AhR2) can be predicted based on identities of key amino acids in the ligand binding domain (LBD). White sturgeon were 3- to 30-fold more sensitive than lake sturgeon to exposure to 5 different DLCs based on activation of AhR2. There were no differences in sensitivity between white sturgeon and lake sturgeon based on activation of AhR1. Adverse outcomes as a result of exposure to DLCs have been shown to be mediated through activation of AhR2, but not AhR1, in all fishes studied to date. This indicates that white sturgeon are likely to have greater sensitivity in vivo relative to lake sturgeon. Homology modeling and in silico mutagenesis suggests that differences in sensitivity to activation of AhR2 result from differences in key amino acids at position 388 in the LBD of AhR2 of white sturgeon (Ala-388) and lake sturgeon (Thr-388). This indicates that identities of key amino acids in the LBD of AhR2 could be predictive of both in vitro activation by DLCs and in vivo sensitivity to DLCs in these, and potentially other, fishes.

  18. Novel biosensors for the detection of estrogen receptor ligands.

    PubMed

    De, Siddhartha; Macara, Ian G; Lannigan, Deborah A

    2005-08-01

    There exists a significant need for the detection of novel estrogen receptor (ER) ligands for pharmaceutical uses, especially for treating complications associated with menopause. We have developed fluorescence resonance energy transfer (FRET)-based biosensors that permit the direct in vitro detection of ER ligands. These biosensors contain an ER ligand-binding domain (LBD) flanked by the FRET donor fluorophore, cyan fluorescent protein (CFP), and the acceptor fluorophore, yellow fluorescent protein (YFP). The ER-LBD has been modified so that Ala 430 has been changed to Asp, which increases the magnitude of the FRET signal in response to ligand-binding by more than four-fold compared to the wild-type LBD. The binding of agonists can be distinguished from that of antagonists on the basis of the distinct ligand-induced conformations in the ER-LBD. The approach to binding equilibrium occurs within 30min, and the FRET signal is stable over 24h. The biosensor demonstrates a high signal-to-noise, with a Z' value (a statistical determinant of assay quality) of 0.72. The affinity of the ER for different ligands can be determined using a modified version of the biosensor in which a truncated YFP and an enhanced CFP are used. Thus, we have developed platforms for high-throughput screens for the identification of novel estrogen receptor ligands. Moreover, we have demonstrated that this FRET technology can be applied to other nuclear receptors, such as the androgen receptor.

  19. Regulation of ligands for the NKG2D activating receptor

    PubMed Central

    Raulet, David H.; Gasser, Stephan; Gowen, Benjamin G.; Deng, Weiwen; Jung, Heiyoun

    2014-01-01

    NKG2D is an activating receptor expressed by all NK cells and subsets of T cells. It serves as a major recognition receptor for detection and elimination of transformed and infected cells and participates in the genesis of several inflammatory diseases. The ligands for NKG2D are self-proteins that are induced by pathways that are active in certain pathophysiological states. NKG2D ligands are regulated transcriptionally, at the level of mRNA and protein stability, and by cleavage from the cell surface. In some cases, ligand induction can be attributed to pathways that are activated specifically in cancer cells or infected cells. We review the numerous pathways that have been implicated in the regulation of NKG2D ligands, discuss the pathologic states in which those pathways are likely to act, and attempt to synthesize the findings into general schemes of NKG2D ligand regulation in NK cell responses to cancer and infection. PMID:23298206

  20. Orphan receptor ligand discovery by pickpocketing pharmacological neighbors.

    PubMed

    Ngo, Tony; Ilatovskiy, Andrey V; Stewart, Alastair G; Coleman, James L J; McRobb, Fiona M; Riek, R Peter; Graham, Robert M; Abagyan, Ruben; Kufareva, Irina; Smith, Nicola J

    2017-02-01

    Understanding the pharmacological similarity of G protein-coupled receptors (GPCRs) is paramount for predicting ligand off-target effects, drug repurposing, and ligand discovery for orphan receptors. Phylogenetic relationships do not always correctly capture pharmacological similarity. Previous family-wide attempts to define pharmacological relationships were based on three-dimensional structures and/or known receptor-ligand pairings, both unavailable for orphan GPCRs. Here, we present GPCR-CoINPocket, a novel contact-informed neighboring pocket metric of GPCR binding-site similarity that is informed by patterns of ligand-residue interactions observed in crystallographically characterized GPCRs. GPCR-CoINPocket is applicable to receptors with unknown structure or ligands and accurately captures known pharmacological relationships between GPCRs, even those undetected by phylogeny. When applied to orphan receptor GPR37L1, GPCR-CoINPocket identified its pharmacological neighbors, and transfer of their pharmacology aided in discovery of the first surrogate ligands for this orphan with a 30% success rate. Although primarily designed for GPCRs, the method is easily transferable to other protein families.

  1. The imidazoline receptors and ligands in pain modulation

    PubMed Central

    Bektas, Nurcan; Nemutlu, Dilara; Arslan, Rana

    2015-01-01

    Pain is an unpleasant experience and effects daily routine negatively. Although there are various drugs, many of them are not entirely successful in relieving pain, since pain modulation is a complex process involving numerous mediators and receptors. Therefore, it is a rational approach to identify the factors involved in the complex process and develop new agents that act on these pain producing mechanisms. In this respect, the involvement of the imidazoline receptors in pain modulation has drawn attention in recent years. In this review, it is aimed to focus on the imidazoline receptors and their ligands which contribute to the pain modulation. It is demonstrated that imidazoline-2 (I2) receptors are steady new drug targets for analgesics. Even if the mechanism of I2 receptor is not well known in the modulation of pain, it is known that it plays a role in tonic and chronic pain but not in acute phasic pain. Moreover, the I2 receptor ligands increase the analgesic effects of opioids in both acute and chronic pain and prevent the development of opioid tolerance. So, they are valuable for the chronic pain treatment and also therapeutic coadjuvants in the management of chronic pain with opiate drugs due to the attenuation of opioid tolerance and addiction. Thus, the use of the ligands which bind to the imidazoline receptors is an effective strategy for relieving pain. This educational forum exhibits the role of imidazoline receptors and ligands in pain process by utilizing experimental studies. PMID:26600633

  2. Ligand-Receptor Binding Measured by Laser-Scanning Imaging

    NASA Astrophysics Data System (ADS)

    Zuck, Paul; Lao, Zhege; Skwish, Stephen; Fraser Glickman, J.; Yang, Ke; Burbaum, Jonathan; Inglese, James

    1999-09-01

    This report describes the integration of laser-scanning fluorometric cytometry and nonseparation ligand-binding techniques to provide new assay methods adaptable to miniaturization and high-throughput screening. Receptor-bound, cyanine dye-labeled ligands, [Cy]ligands, were discriminated from those free in solution by measuring the accumulated fluorescence associated with a receptor-containing particle. To illustrate the various binding formats accommodated by this technique, saturation- and competition-binding analyses were performed with [Cy]ligands and their cognate receptors expressed in CHO cells or as fusion proteins coated on polystyrene microspheres. We have successfully applied this technique to the analysis of G protein-coupled receptors, cytokine receptors, and SH2 domains. Multiparameter readouts from ligands labeled separately with Cy5 and Cy5.5 demonstrate the simultaneous analysis of two target receptors in a single well. In addition, laser-scanning cytometry has been used to assay enzymes such as phosphatases and in the development of single-step fluorescent immunoassays.

  3. Pharmacology and therapeutic potential of sigma(1) receptor ligands.

    PubMed

    Cobos, E J; Entrena, J M; Nieto, F R; Cendán, C M; Del Pozo, E

    2008-12-01

    Sigma (sigma) receptors, initially described as a subtype of opioid receptors, are now considered unique receptors. Pharmacological studies have distinguished two types of sigma receptors, termed sigma(1) and sigma(2). Of these two subtypes, the sigma(1) receptor has been cloned in humans and rodents, and its amino acid sequence shows no homology with other mammalian proteins. Several psychoactive drugs show high to moderate affinity for sigma(1) receptors, including the antipsychotic haloperidol, the antidepressant drugs fluvoxamine and sertraline, and the psychostimulants cocaine and methamphetamine; in addition, the anticonvulsant drug phenytoin allosterically modulates sigma(1) receptors. Certain neurosteroids are known to interact with sigma(1) receptors, and have been proposed to be their endogenous ligands. These receptors are located in the plasma membrane and in subcellular membranes, particularly in the endoplasmic reticulum, where they play a modulatory role in intracellular Ca(2+) signaling. Sigma(1) receptors also play a modulatory role in the activity of some ion channels and in several neurotransmitter systems, mainly in glutamatergic neurotransmission. In accordance with their widespread modulatory role, sigma(1) receptor ligands have been proposed to be useful in several therapeutic fields such as amnesic and cognitive deficits, depression and anxiety, schizophrenia, analgesia, and against some effects of drugs of abuse (such as cocaine and methamphetamine). In this review we provide an overview of the present knowledge of sigma(1) receptors, focussing on sigma(1) ligand neuropharmacology and the role of sigma(1) receptors in behavioral animal studies, which have contributed greatly to the potential therapeutic applications of sigma(1) ligands.

  4. The aryl hydrocarbon receptor (AhR) inhibits vanadate-induced vascular endothelial growth factor (VEGF) production in TRAMP prostates

    PubMed Central

    Fritz, Wayne A.; Lin, Tien-Min; Peterson, Richard E.

    2008-01-01

    Hypoxia-inducible factor-1 alpha (HIF-1α) and aryl hydrocarbon receptor nuclear translocator (ARNT) are basic helix-loop-helix/per-arnt-sim (PAS) family transcription factors. During angiogenesis and tumor growth, HIF-1α dimerizes with ARNT, inducing expression of many genes, including vascular endothelial growth factor (VEGF). ARNT also dimerizes with the aryl hydrocarbon receptor (AhR). AhR-null (Ahr−/−) transgenic adenocarcinoma of the mouse prostate (TRAMP) mice develop prostate tumors with greater frequency than AhR wild-type (Ahr+/+) TRAMP mice, even though prevalence of prostate epithelial hyperplasia is not inhibited. This suggests that Ahr inhibits prostate carcinogenesis. In TRAMP mice, prostatic epithelial hyperplasia results in stabilized HIF-1α, inducing expression of VEGF, a prerequisite for tumor growth and angiogenesis. Since ARNT is a common dimerization partner of AhR and HIF-1α, we hypothesized that the AhR inhibits prostate tumor formation by competing with HIF-1α for ARNT, thereby limiting VEGF production. Prostates from Ahr+/+, Ahr+/− and Ahr−/− C57BL/6J TRAMP mice were cultured in the presence of graded concentrations of vanadate, an inducer of VEGF through the HIF-1α–ARNT pathway. Vanadate induced VEGF protein in a dose-dependent fashion in Ahr+/− and Ahr−/− TRAMP cultures, but not in Ahr+/+ cultures. However, vanadate induced upstream proteins in the phosphatidylinositol 3-kinase-signaling cascade to a similar extent in TRAMPs of each Ahr genotype, evidenced by v-akt murine thymoma viral oncogene homolog (Akt) phosphorylation. These findings suggest that AhR sequesters ARNT, decreasing interaction with HIF-1α reducing VEGF production. Since VEGF is required for tumor vascularization and growth, these studies further suggest that reduction in VEGF correlates with inhibited prostate carcinogenesis in Ahr+/+ TRAMP mice. PMID:18359762

  5. A Natural Mutation in Helix 5 of the Ligand Binding Domain of Glucocorticoid Receptor Enhances Receptor-Ligand Interaction

    PubMed Central

    Reyer, Henry; Ponsuksili, Siriluck; Kanitz, Ellen; Pöhland, Ralf; Wimmers, Klaus; Murani, Eduard

    2016-01-01

    The glucocorticoid receptor (GR) is a central player in the neuroendocrine stress response; it mediates feedback regulation of the hypothalamus-pituitary-adrenal (HPA) axis and physiological actions of glucocorticoids in the periphery. Despite intensive investigations of GR in the context of receptor-ligand interaction, only recently the first naturally occurring gain-of-function substitution, Ala610Val, of the ligand binding domain was identified in mammals. We showed that this mutation underlies a major quantitative trait locus for HPA axis activity in pigs, reducing cortisol production by about 40–50 percent. To unravel the molecular mechanisms behind this gain of function, receptor-ligand interactions were evaluated in silico, in vitro and in vivo. In accordance with previously observed phenotypic effects, the mutant Val610 GR showed significantly increased activation in response to glucocorticoid and non-glucocorticoid steroids, and, as revealed by GR-binding studies in vitro and in pituitary glands, enhanced ligand binding. Concordantly, the protein structure prediction depicted reduced binding distances between the receptor and ligand, and altered interactions in the ligand binding pocket. Consequently, the Ala610Val substitution opens up new structural information for the design of potent GR ligands and to examine effects of the enhanced GR responsiveness to glucocorticoids on the entire organism. PMID:27736993

  6. Optimizing electrostatic affinity in ligand-receptor binding: Theory, computation, and ligand properties

    NASA Astrophysics Data System (ADS)

    Kangas, Erik; Tidor, Bruce

    1998-11-01

    The design of a tight-binding molecular ligand involves a tradeoff between an unfavorable electrostatic desolvation penalty incurred when the ligand binds a receptor in aqueous solution and the generally favorable intermolecular interactions made in the bound state. Using continuum electrostatic models we have developed a theoretical framework for analyzing this problem and have shown that the ligand-charge distribution can be optimized to produce the most favorable balance of these opposing free energy contributions [L.-P. Lee and B. Tidor, J. Chem. Phys. 106, 8681 (1997)]. Herein the theoretical framework is extended and calculations are performed for a wide range of model receptors. We examine methods for computing optimal ligands (including cases where there is conformational change) and the resulting properties of optimized ligands. In particular, indicators are developed to aid in the determination of the deficiencies in a specific ligand or basis. A connection is established between the optimization problem here and a generalized image problem, from which an inverse-image basis set can be defined; this basis is shown to perform very well in optimization calculations. Furthermore, the optimized ligands are shown to have favorable electrostatic binding free energies (in contrast to many natural ligands), there is a strong correlation between the receptor desolvation penalty and the optimized binding free energy for fixed geometry, and the ligand and receptor cannot generally be mutually optimal. Additionally, we introduce the display of complementary desolvation and interaction potentials and the deviation of their relationship from ideal as a useful tool for judging effective complementarity. Scripts for computing and displaying these potentials with GRASP are available at http://mit.edu/tidor.

  7. Development of Benzophenone-Alkyne Bifunctional Sigma Receptor Ligands

    PubMed Central

    Guo, Lian-Wang; Hajipour, Abdol R.; Karaoglu, Kerim; Mavlyutov, Timur A.; Ruoho, Arnold E.

    2012-01-01

    Sigma (σ) receptors represent unique non-opioid binding sites that are associated with a broad range of disease states. Sigma-2 receptors provide a promising target for diagnostic imaging and pharmacological interventions to curb tumor progression. Most recently, the progesterone receptor (PGRMC1, 25 kDa) has been identified to contain σ2 receptor-like binding properties, highlighting the need to understand the biological function of an 18-kDa protein that exhibits σ2-like photoaffinity labeling (herein denoted as σ2-18k) but the amino acid sequence of which is not known. In order to provide novel tools for the study of the σ2-18k protein, we have developed bifunctional sigma receptor ligands that bear a benzophenone photo-crosslinking moiety and an alkyne group, to which an azide-containing biotin affinity tag can be covalently attached via click chemistry following photo-crosslink. While several compounds showed favorable σ2 binding properties, compound 22 exhibited the highest affinity (2 nM) and the greatest potency in blocking photolabeling of the σ2-18k by a radioactive photoaffinity ligand. Thus, these benzophenone-alkyne sigma receptor ligands may be amenable for studying the σ2-18k protein via chemical biology approaches. To our knowledge, these compounds represent the first reported benzophenone-containing clickable sigma receptor ligands, which may potentially serve broad applications by “plugging” in various tags. PMID:23001760

  8. Regulation of ligands for the activating receptor NKG2D

    PubMed Central

    Mistry, Anita R; O'Callaghan, Chris A

    2007-01-01

    The outcome of an encounter between a cytotoxic cell and a potential target cell depends on the balance of signals from inhibitory and activating receptors. Natural Killer group 2D (NKG2D) has recently emerged as a major activating receptor on T lymphocytes and natural killer cells. In both humans and mice, multiple different genes encode ligands for NKG2D, and these ligands are non-classical major histocompatibility complex class I molecules. The NKG2D–ligand interaction triggers an activating signal in the cell expressing NKG2D and this promotes cytotoxic lysis of the cell expressing the ligand. Most normal tissues do not express ligands for NKG2D, but ligand expression has been documented in tumour and virus-infected cells, leading to lysis of these cells. Tight regulation of ligand expression is important. If there is inappropriate expression in normal tissues, this will favour autoimmune processes, whilst failure to up-regulate the ligands in pathological conditions would favour cancer development or dissemination of intracellular infection. PMID:17614877

  9. A Spectroscopic Study of the effect of Ligand Complexation on the Reduction of Uranium(VI) by Anthraquinone-2,6-disulfonate (AH2DS)

    SciTech Connect

    Wang, Zheming; Wagnon, Ken B.; Ainsworth, Calvin C.; Liu, Chongxuan; Rosso, Kevin M.; Fredrickson, Jim K.

    2008-11-03

    In this project, the reduction rate of uranyl complexes with hydroxide, carbonate, EDTA, and Desferriferrioxamine B (DFB) by anthraquinone-2,6-disulfonate (AH2DS), a potential electron shuttle for microbial reduction of metal ions (Newman and Kolter 2000), is studied by stopped-flow kinetics techniques under anoxic atmosphere. The apparent reaction rates varied with ligand type, solution pH, and U(VI) concentration. For each ligand, a single largest kobs within the studied pH range was observed, suggesting the influence of pH-dependent speciation on the U(VI) reduction rate. The maximum reaction rate found in each case followed the order of OH- > CO32- > EDTA > DFB, consistent with the same trend of the thermodynamic stability of the uranyl complexes and ionic sizes of the ligands. Increasing the stability of uranyl complexes and ligand size decreased the maximum reduction rate. The pH-dependent rates were modeled using a second-order rate expression that was assumed to be dependent on a single U(VI) complex and AH2DS species. By quantitatively comparing the calculated and measured apparent rate constants as a function of pH, species AHDS3- was suggested as the primary reductant in all cases examined. Species UO2CO3(aq) , UO2HEDTA-, and (UO2)2(OH)22+ were suggested as the principal electron acceptors among the U(VI) species mixture in carbonate, EDTA, and hydroxyl systems, respectively.

  10. BRCA-1 promoter hypermethylation and silencing induced by the aromatic hydrocarbon receptor-ligand TCDD are prevented by resveratrol in MCF-7 cells.

    PubMed

    Papoutsis, Andreas J; Borg, Jamie L; Selmin, Ornella I; Romagnolo, Donato F

    2012-10-01

    Epigenetic mechanisms may contribute to reduced expression of the tumor suppressor gene BRCA-1 in sporadic breast cancers. Through environmental exposure and diet, humans are exposed to xenobiotics and food compounds that bind the aromatic hydrocarbon receptor (AhR). AhR-ligands include the dioxin-like and tumor promoter 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD). The activated AhR regulates transcription through binding to xenobiotic response elements (XREs=GCGTG) and interactions with transcription cofactors. Previously, we reported on the presence of several XREs in the proximal BRCA-1 promoter and that the expression of endogenous AhR was required for silencing of BRCA-1 expression by TCDD. Here, we document that in estrogen receptor-α-positive and BRCA-1 wild-type MCF-7 breast cancer cells, the treatment with TCDD attenuated 17β-estradiol-dependent stimulation of BRCA-1 protein and induced hypermethylation of a CpG island spanning the BRCA-1 transcriptional start site of exon-1a. Additionally, we found that TCDD enhanced the association of the AhR; DNA methyl transferase (DNMT)1, DNMT3a and DNMT3b; methyl binding protein (MBD)2; and trimethylated H3K9 (H3K9me3) with the BRCA-1 promoter. Conversely, the phytoalexin resveratrol, selected as a prototype dietary AhR antagonist, antagonized at physiologically relevant doses (1 μmol/L) the TCDD-induced repression of BRCA-1 protein, BRCA-1 promoter methylation and the recruitment of the AhR, MBD2, H3K9me3 and DNMTs (1, 3a and 3b). Taken together, these observations provide mechanistic evidence for AhR agonists in the establishment of BRCA-1 promoter hypermethylation and the basis for the development of prevention strategies based on AhR antagonists.

  11. The Principles of Ligand Specificity on beta-2-adrenergic receptor

    PubMed Central

    Chan, H. C. Stephen; Filipek, Slawomir; Yuan, Shuguang

    2016-01-01

    G protein-coupled receptors are recognized as one of the largest families of membrane proteins. Despite sharing a characteristic seven-transmembrane topology, G protein-coupled receptors regulate a wide range of cellular signaling pathways in response to various physical and chemical stimuli, and prevail as an important target for drug discovery. Notably, the recent progress in crystallographic methods led to a breakthrough in elucidating the structures of membrane proteins. The structures of β2-adrenergic receptor bound with a variety of ligands provide atomic details of the binding modes of agonists, antagonists and inverse agonists. In this study, we selected four representative molecules from each functional class of ligands and investigated their impacts on β2-adrenergic receptor through a total of 12 × 100 ns molecular dynamics simulations. From the obtained trajectories, we generated molecular fingerprints exemplifying propensities of protein-ligand interactions. For each functional class of compounds, we characterized and compared the fluctuation of the protein backbone, the volumes in the intracellular pockets, the water densities in the receptors, the domain interaction networks as well as the movements of transmembrane helices. We discovered that each class of ligands exhibits a distinct mode of interactions with mainly TM5 and TM6, altering the shape and eventually the state of the receptor. Our findings provide insightful prospective into GPCR targeted structure-based drug discoveries. PMID:27703221

  12. GPCR drug discovery: novel ligands for CNS receptors.

    PubMed

    Lim, William K

    2007-06-01

    G protein-coupled receptors (GPCRs) are the largest class of cell surface receptors in humans. They convey extracellular signals into the cell interior by activating intracellular processes such as heterotrimeric G protein-dependent signaling pathways. They are widely distributed in the nervous system, and mediate key physiological processes including cognition, mood, appetite, pain and synaptic transmission. With at least 30% of marketed drugs being GPCR modulators, they are a major therapeutic target in the pharmaceutical industry's drug discovery programs. This review will survey recently patented ligands for GPCRs implicated in CNS disorders, in particular the metabotropic glutamate, adenosine and cannabinoid receptors. Metabotropic glutamate receptors regulate signaling by glutamate, the major excitatory brain neurotransmitter, while adenosine is a ubiquitous neuromodulater mediating diverse physiological effects. Recent patents for ligands of these receptors include mGluR5 antagonists and adenosine A(1) receptor agonists. Cannabinoid receptors remain one of the most important GPCR drug discovery target due to the intense interest in CB(1) receptor antagonists for treating obesity and metabolic syndrome. Such small molecule ligands are the outcome of the continuing focus of many pharmaceutical companies to identify novel GPCR agonist, antagonist or allosteric modulators useful for CNS disorders, for which more effective drugs are eagerly awaited.

  13. Fibroblast growth factor (Fgf) 21 is a novel target gene of the aryl hydrocarbon receptor (AhR)

    SciTech Connect

    Cheng, Xingguo; Vispute, Saurabh G.; Liu, Jie; Cheng, Christine; Kharitonenkov, Alexei; Klaassen, Curtis D.

    2014-07-01

    The toxic effects of dioxins, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), mainly through activation of the aryl hydrocarbon receptor (AhR) are well documented. Fibroblast growth factor (Fgf) 21 plays critical roles in metabolic adaptation to fasting by increasing lipid oxidation and ketogenesis in the liver. The present study was performed to determine whether activation of the AhR induces Fgf21 expression. In mouse liver, TCDD increased Fgf21 mRNA in both dose- and time-dependent manners. In addition, TCDD markedly increased Fgf21 mRNA expression in cultured mouse and human hepatocytes. Moreover, TCDD increased mRNA (in liver) and protein levels (in both liver and serum) of Fgf21 in wild-type mice, but not in AhR-null mice. Chromatin immunoprecipitation assays showed that TCDD increased AhR protein binding to the Fgf21 promoter (− 105/+ 1 base pair). Fgf21-null mice administered 200 μg/kg of TCDD died within 20 days, whereas wild-type mice receiving the same treatment were still alive at one month after administration. This indicates that TCDD-induced Fgf21 expression protects against TCDD toxicity. Diethylhexylphthalate (DEHP) pretreatment attenuated TCDD-induced Fgf21 expression in mouse liver and white adipose tissue, which may explain a previous report that DEHP pretreatment decreases TCDD-induced wasting. In conclusion, Fgf21 appears to be a target gene of AhR-signaling pathway in mouse and human liver. - Highlights: • TCDD induced Fgf21 expression at both mRNA and protein levels. • Fgf21 induction by TCDD is AhR-dependent. • DEHP attenuated TCDD-induced Fgf21 expression.

  14. Identification of Ligand-Receptor Interactions: Ligand Molecular Arrays, SPR and NMR Methodologies.

    PubMed

    Day, Christopher J; Hartley-Tassell, Lauren E; Korolik, Victoria

    2017-01-01

    Despite many years of research into bacterial chemotaxis, the only well characterized system to date is that of E. coli. Even for E. coli, the direct ligand binding had been fully characterized only for aspartate and serene receptors Tar and Tsr. In 30 years since, no other direct receptor-ligand interaction had been described for bacteria, until the characterization of the C. jejuni aspartate and multiligand receptors (Hartley-Tassell et al. Mol Microbiol 75:710-730, 2010). While signal transduction components of many sensory pathways have now been characterized, ligand-receptor interactions remain elusive due to paucity of high-throughput screening methods. Here, we describe the use of microarray screening we developed to identify ligands, surface plasmon resonance, and saturation transfer difference nuclear magnetic resonance (STD-NMR) we used to verify the hits and to determine the affinity constants of the interactions, allowing for more targeted verification of ligands with traditional chemotaxis and in vivo assays described in Chapter 13 .

  15. Brain endogenous liver X receptor ligands selectively promote midbrain neurogenesis.

    PubMed

    Theofilopoulos, Spyridon; Wang, Yuqin; Kitambi, Satish Srinivas; Sacchetti, Paola; Sousa, Kyle M; Bodin, Karl; Kirk, Jayne; Saltó, Carmen; Gustafsson, Magnus; Toledo, Enrique M; Karu, Kersti; Gustafsson, Jan-Åke; Steffensen, Knut R; Ernfors, Patrik; Sjövall, Jan; Griffiths, William J; Arenas, Ernest

    2013-02-01

    Liver X receptors (Lxrα and Lxrβ) are ligand-dependent nuclear receptors critical for ventral midbrain neurogenesis in vivo. However, no endogenous midbrain Lxr ligand has so far been identified. Here we used LC/MS and functional assays to identify cholic acid as a new Lxr ligand. Moreover, 24(S),25-epoxycholesterol (24,25-EC) was found to be the most potent and abundant Lxr ligand in the developing mouse midbrain. Both Lxr ligands promoted neural development in an Lxr-dependent manner in zebrafish in vivo. Notably, each ligand selectively regulated the development of distinct midbrain neuronal populations. Whereas cholic acid increased survival and neurogenesis of Brn3a-positive red nucleus neurons, 24,25-EC promoted dopaminergic neurogenesis. These results identify an entirely new class of highly selective and cell type-specific regulators of neurogenesis and neuronal survival. Moreover, 24,25-EC promoted dopaminergic differentiation of embryonic stem cells, suggesting that Lxr ligands may thus contribute to the development of cell replacement and regenerative therapies for Parkinson's disease.

  16. Estrogen Receptor Ligands: A Review (2013–2015)

    PubMed Central

    Farzaneh, Shabnam; Zarghi, Afshin

    2016-01-01

    Estrogen receptors (ERs) are a group of compounds named for their importance in both menstrual and estrous reproductive cycles. They are involved in the regulation of various processes ranging from tissue growth maintenance to reproduction. Their action is mediated through ER nuclear receptors. Two subtypes of the estrogen receptor, ERα and ERβ, exist and exhibit distinct cellular and tissue distribution patterns. In humans, both receptor subtypes are expressed in many cells and tissues, and they control key physiological functions in various organ systems. Estrogens attract great attention due to their wide applications in female reproductive functions and treatment of some estrogen-dependent cancers and osteoporosis. This paper provides a general review of ER ligands published in international journals patented between 2013 and 2015. The broad physiological profile of estrogens has attracted the attention of many researchers to develop new estrogen ligands as therapeutic molecules for various clinical purposes. After the discovery of the ERβ receptor, subtype-selective ligands could be used to elicit beneficial estrogen-like activities and reduce adverse side effects, based on the different distributions and relative levels of the two ER subtypes in different estrogen target tissues. Therefore, recent literature has focused on selective estrogen ligands as highly promising agents for the treatment of some types of cancer, as well as for cardiovascular, inflammatory, and neurodegenerative diseases. Estrogen receptors are nuclear transcription factors that are involved in the regulation of many complex physiological functions in humans. Selective estrogen ligands are highly promising targets for treatment of some types of cancer, as well as for cardiovascular, inflammatory and neurodegenerative diseases. Extensive structure-activity relationship studies of ER ligands based on small molecules indicate that many different structural scaffolds may provide high

  17. Inside job: ligand-receptor pharmacology beneath the plasma membrane

    PubMed Central

    Babcock, Joseph J; Li, Min

    2013-01-01

    Most drugs acting on the cell surface receptors are membrane permeable and thus able to engage their target proteins in different subcellular compartments. However, these drugs' effects on cell surface receptors have historically been studied on the plasma membrane alone. Increasing evidence suggests that small molecules may also modulate their targeted receptors through membrane trafficking or organelle-localized signaling inside the cell. These additional modes of interaction have been reported for functionally diverse ligands of GPCRs, ion channels, and transporters. Such intracellular drug-target engagements affect cell surface expression. Concurrent intracellular and cell surface signaling may also increase the complexity and therapeutic opportunities of small molecule modulation. Here we discuss examples of ligand-receptor interactions that are present in both intra- and extracellular sites, and the potential therapeutic opportunities presented by this phenomenon. PMID:23685953

  18. Tools and techniques to study ligand-receptor interactions and receptor activation by TNF superfamily members.

    PubMed

    Schneider, Pascal; Willen, Laure; Smulski, Cristian R

    2014-01-01

    Ligands and receptors of the TNF superfamily are therapeutically relevant targets in a wide range of human diseases. This chapter describes assays based on ELISA, immunoprecipitation, FACS, and reporter cell lines to monitor interactions of tagged receptors and ligands in both soluble and membrane-bound forms using unified detection techniques. A reporter cell assay that is sensitive to ligand oligomerization can identify ligands with high probability of being active on endogenous receptors. Several assays are also suitable to measure the activity of agonist or antagonist antibodies, or to detect interactions with proteoglycans. Finally, self-interaction of membrane-bound receptors can be evidenced using a FRET-based assay. This panel of methods provides a large degree of flexibility to address questions related to the specificity, activation, or inhibition of TNF-TNF receptor interactions in independent assay systems, but does not substitute for further tests in physiologically relevant conditions.

  19. Ligand-induced ErbB receptor dimerization

    PubMed Central

    Lemmon, Mark A.

    2009-01-01

    Structural studies have provided important new insights into how ligand binding promotes homodimerization and activation of the EGF receptor and the other members of the ErbB family or receptor tyrosine kinases. These structures have also suggested possible explanations for the unique properties of ErbB2, which has no known ligand and can cause cell transformation (and tumorigenesis) by simple overexpression. In parallel with these advances, studies of the EGF receptor at the cell surface increasingly argue that the structural studies are missing key mechanistic components. This is particularly evident in the structural prediction that EGF binding linked to receptor dimerization should be positively cooperative, whereas cell-surface EGF-binding studies suggest negative cooperativity. In this review, I summarize studies of ErbB receptor extracellular regions in solution and of intact receptors at the cell surface, and attempt to reconcile the differences suggested by the two approaches. By combining results obtained with receptor ‘parts’, it is qualitatively possible to explain some models for the properties of the whole receptor. These considerations underline the need to consider the intact ErbB receptors as intact allosterically regulated enzymes, and to combine cellular and structural studies into a complete picture. PMID:19038249

  20. [Endorphines--the endogenous ligands of opiate receptors (author's transl)].

    PubMed

    Teschemacher, H

    1978-01-01

    The demonstration of opiate receptors in the nervous tissue of vertebrates in 1973 was the starting point of an intensive search for the endogenous ligands of these receptors. During the following years, several of such "edogenous opiates", called "endorphines", were isolated from various tissues of the mammalian organism. These are peptides which are able to elicit the same effects as do opiates. Possibly, they play a role in the reaction of the organism to stress.

  1. [Effect of ligand concentration on the precision of determining the parameters of ligand-receptor interaction by serial dilution methods].

    PubMed

    Bobrovnik, S A

    2004-01-01

    Earlier we suggested the method of serial dilution, which allows one to determine the parameters of ligand-receptor interaction even if the reactants are in a mixture and their concentrations are unknown. The method is especially useful if the liability of studied receptor does not allow its separation from corresponding ligand. The important prerequisite of the method's precision is that the concentration of the ligand should be sufficiently high comparing to the concentration of the receptor. In the present paper it was demonstrated that the method allows one to obtain sufficiently good precision even in the case when the concentration of the ligand is only one tenth of the receptor concentration.

  2. [Determining the parameters for receptor-ligand interaction by serial dilution method for the case when the ligand and receptor are in a pre-existing mixture].

    PubMed

    Bobrovnik, S A

    2005-01-01

    New methods of determining the binding parameters for ligand-receptor interaction are considered. The considered approaches are based on the earlier suggested method of serial dilution and application of so-called coordinates of dilution. It was shown that the suggested methods allow to evaluate affinity constant and ligand concentration even for the case, when the receptor and corresponding ligand of unknown concentration are in a mixture and their separation from each other is impossible. In this connection the suggested methods are especially useful for studying the ligand-receptor interaction if the receptor is very liable and its purification from the ligand would cause drastic changes of its binding properties.

  3. Pharmacokinetics and pharmacodynamics of nonsteroidal androgen receptor ligands.

    PubMed

    Gao, Wenqing; Kim, Juhyun; Dalton, James T

    2006-08-01

    Testosterone and structurally related anabolic steroids have been used to treat hypogonadism, muscle wasting, osteoporosis, male contraception, cancer cachexia, anemia, and hormone replacement therapy in aging men or age-related frailty; while antiandrogens may be useful for treatment of conditions like acne, alopecia (male-pattern baldness), hirsutism, benign prostatic hyperplasia (BPH) and prostate cancer. However, the undesirable physicochemical and pharmacokinetic properties of steroidal androgen receptor (AR) ligands limited their clinical use. Nonsteroidal AR ligands with improved pharmacological and pharmacokinetic properties have been developed to overcome these problems. This review focuses on the pharmacokinetics, metabolism, and pharmacology of clinically used and emerging nonsteroidal AR ligands, including antagonists, agonists, and selective androgen receptor modulators.

  4. REACTIVITY PROFILE OF CONFORMATIONALLY-FLEXIBLE RETINOID RECEPTOR LIGANDS

    EPA Science Inventory

    Retinoids and associated derivatives represent a class of endogenousr hormones that bind to and activate different families of retinoic acid receptors (RARs, RXRs), and control many aspects of normal vertebrate development. Identification of potential RAR and RXRs ligands is of i...

  5. Nonsteroidal Androgen Receptor Ligands: Versatile Syntheses and Biological Data

    PubMed Central

    2012-01-01

    We report herein a stereoselective and straightforward methodology for the synthesis of new androgen receptor ligands with (anti)-agonistic activities. Oxygen–nitrogen replacement in bicalutamide-like structures paves the way to the disclosure of a new class of analogues, including cyclized/nitrogen-substituted derivatives, with promising antiandrogen (or anabolic) activity. PMID:24900495

  6. Central nicotinic receptors: structure, function, ligands, and therapeutic potential.

    PubMed

    Romanelli, M Novella; Gratteri, Paola; Guandalini, Luca; Martini, Elisabetta; Bonaccini, Claudia; Gualtieri, Fulvio

    2007-06-01

    The growing interest in nicotinic receptors, because of their wide expression in neuronal and non-neuronal tissues and their involvement in several important CNS pathologies, has stimulated the synthesis of a high number of ligands able to modulate their function. These membrane proteins appear to be highly heterogeneous, and still only incomplete information is available on their structure, subunit composition, and stoichiometry. This is due to the lack of selective ligands to study the role of nAChR under physiological or pathological conditions; so far, only compounds showing selectivity between alpha4beta2 and alpha7 receptors have been obtained. The nicotinic receptor ligands have been designed starting from lead compounds from natural sources such as nicotine, cytisine, or epibatidine, and, more recently, through the high-throughput screening of chemical libraries. This review focuses on the structure of the new agonists, antagonists, and allosteric ligands of nicotinic receptors, it highlights the current knowledge on the binding site models as a molecular modeling approach to design new compounds, and it discusses the nAChR modulators which have entered clinical trials.

  7. Oxytocin receptors: ligand binding, signalling and cholesterol dependence.

    PubMed

    Gimpl, Gerald; Reitz, Julian; Brauer, Sabine; Trossen, Conny

    2008-01-01

    The G protein coupled oxytocin receptor (OTR) reveals some specific molecular and physiological characteristics. Ligand-receptor interaction has been analysed by photoaffinity labelling, site-directed mutagenesis, the construction of receptor chimeras and molecular modelling. Major results of these studies will be summarized. The N-terminus of the OTR is mainly involved in agonist binding. Notably, antagonists that are derived from the ground structure of oxytocin, bind the receptor at distinct sites partly non-overlapping with the agonist binding site. OTRs are able to couple to different G proteins, with a subsequent stimulation of phospholipase C-beta isoforms. In dependence on G protein coupling, OTRs can transduce growth-inhibitory or proliferatory signals. Some evidence is provided that OTRs are also present in form of dimeric or oligomeric complexes at the cell surface. The affinity of the receptor for ligands is strongly dependent on the presence of divalent cations (Mg(2+)) and cholesterol that both act like positive allosteric modulators. While the high-affinity state of the receptor for agonists requires divalent cations and cholesterol, the high-affinity state for antagonists is only dependent on a sufficient amount of cholesterol. Cholesterol affects ligand-binding affinity, receptor signalling and stability. Since the purification of the OTR has never been achieved, alternative methods to study the receptor in its native environment are necessary. Promising strategies for the site-specific labelling of the OTR will be presented. The employment of diverse reporter molecules introduced at different positions within the OTR might allow us in the near future to measure conformational changes of the receptor in its native lipid environment.

  8. Why do cannabinoid receptors have more than one endogenous ligand?

    PubMed Central

    Di Marzo, Vincenzo; De Petrocellis, Luciano

    2012-01-01

    The endocannabinoid system was revealed following the understanding of the mechanism of action of marijuana's major psychotropic principle, Δ9-tetrahydrocannabinol, and includes two G-protein-coupled receptors (GPCRs; the cannabinoid CB1 and CB2 receptors), their endogenous ligands (the endocannabinoids, the best studied of which are anandamide and 2-arachidonoylglycerol (2-AG)), and the proteins that regulate the levels and activity of these receptors and ligands. However, other minor lipid metabolites different from, but chemically similar to, anandamide and 2-AG have also been suggested to act as endocannabinoids. Thus, unlike most other GPCRs, cannabinoid receptors appear to have more than one endogenous agonist, and it has been often wondered what could be the physiological meaning of this peculiarity. In 1999, it was proposed that anandamide might also activate other targets, and in particular the transient receptor potential of vanilloid type-1 (TRPV1) channels. Over the last decade, this interaction has been shown to occur both in peripheral tissues and brain, during both physiological and pathological conditions. TRPV1 channels can be activated also by another less abundant endocannabinoid, N-arachidonoyldopamine, but not by 2-AG, and have been proposed by some authors to act as ionotropic endocannabinoid receptors. This article will discuss the latest discoveries on this subject, and discuss, among others, how anandamide and 2-AG differential actions at TRPV1 and cannabinoid receptors contribute to making this signalling system a versatile tool available to organisms to fine-tune homeostasis. PMID:23108541

  9. Thiophene-Core Estrogen Receptor Ligands Having Superagonist Activity

    PubMed Central

    Min, Jian; Wang, Pengcheng; Srinivasan, Sathish; Nwachukwu, Jerome C.; Guo, Pu; Huang, Minjian; Carlson, Kathryn E.; Katzenellenbogen, John A.; Nettles, Kendall W.; Zhou, Hai-Bing

    2013-01-01

    To probe the importance of the heterocyclic core of estrogen receptor (ER) ligands, we prepared a series of thiophene-core ligands by Suzuki cross-coupling of aryl boronic acids with bromo-thiophenes, and we assessed their receptor binding and cell biological activities. The disposition of the phenol substituents on the thiophene core, at alternate or adjacent sites, and the nature of substituents on these phenols all contribute to binding affinity and subtype selectivity. Most of the bis(hydroxyphenyl)-thiophenes were ERβ selective, whereas the tris(hydroxyphenyl)-thiophenes were ERα selective; analogous furan-core compounds generally have lower affinity and less selectivity. Some diarylthiophenes show distinct superagonist activity in reporter gene assays, giving maximal activities 2–3 times that of estradiol, and modeling suggests that these ligands have a different interaction with a hydrogen-bonding residue in helix-11. Ligand-core modification may be a new strategy for developing ER ligands whose selectivity is based on having transcriptional activity greater than that of estradiol. PMID:23586645

  10. Ligand specificity and evolution of liver X receptors§

    PubMed Central

    Reschly, Erica J.; Ai, Ni; Welsh, William J.; Ekins, Sean; Hagey, Lee R.; Krasowski, Matthew D.

    2008-01-01

    Liver X receptors (LXRs) are key regulators of lipid and cholesterol metabolism in mammals. Little is known, however, about the function and evolution of LXRs in non-mammalian species. The present study reports the cloning of LXRs from African clawed frog (Xenopus laevis), Western clawed frog (Xenopus tropicalis), and zebrafish (Danio rerio), and their functional characterization and comparison with human and mouse LXRs. Additionally, an ortholog of LXR in the chordate invertebrate Ciona intestinalis was cloned and functionally characterized. Ligand specificities of the frog and zebrafish LXRs were very similar to LXRα and LXRβ from human and mouse. All vertebrate LXRs studied were activated robustly by the synthetic ligands T-0901317 and GW3965 and by a variety of oxysterols. In contrast, Ciona LXR was not activated by T-0901317 or GW3965 but was activated by a limited number of oxysterols, as well as some androstane and pregnane steroids. Pharmacophore analysis, homology modeling, and docking studies of Ciona LXR predict a receptor with a more restricted ligand-binding pocket and less intrinsic disorder in the ligand-binding domain compared to vertebrate LXRs. The results suggest that LXRs have a long evolutionary history, with vertebrate LXRs diverging from invertebrate LXRs in ligand specificity. PMID:18395439

  11. Receptor Specific Ligands for Spect Imaging

    SciTech Connect

    Kung, H. F.

    2003-02-25

    In the past funding period we have concentrated in developing new 99mTc labeled MIBG analogs. Basic chemistry of ligand synthesis, radiochemistry of Re and 99mTc complex formation, separation of stereoisomers and in vitro stability were investigated. We have prepared a number of new MIBG derivatives containing chelating moiety N2S2 and additional groups to increase lipophilicity. Unfortunately none of the new 99mTc labeled MIBG analogs showed promise as an imaging agent for myocardial neuronal function. Radioactive-iodine-labeled meta-iodobenzylguanidine (MIBG) is currently being used as an in vivo imaging agent to evaluate neuroendocrine tumors as well as the myocardial sympathetic nervous system in patients with myocardial infarct and cardiomyopathy. It is generally accepted that MIBG is an analog of norepinephrine and its uptake in the heart corresponds to the distribution of norepinephrine and the density of sympathetic neurons. A series of MIBG derivatives containing suitable chelating functional groups N2S2 for the formation of [Tcv0]+3N2S2 complex was successfully synthesized and the 99mTc-labeled complexes were prepared and tested in rats. One of the compounds, [99mTc]M2, tested showed significant, albeit lower, heart uptakes post iv injection in rats (0.18% dose/organ at 4 hours) as compared to [l25l]MIBG (1.4% dose/organ at 4 hours). The heart uptake of the 99mTc-labeled complex, [99mTc]M2, appears to be specific and can be reduced by coinjection with nonradioactive MIBG or by pretreatment with desipramine. a selective norepinephrine transporter inhibitor. Further evaluation of the in vitro uptake of [99mTc]M2 in cultured neuroblastoma cells displayed consistently lower, but measurable uptake (app. 10% of that for [125l]MlBG). These preliminary results suggested that the mechanisms of heart uptake of [99mTc]M2 may be related to those for [125l]MIBG uptake. To improve the heart uptake of the MIBG derivatives we have developed chemistry related to the

  12. Ligands for cannabinoid receptors, promising anticancer agents.

    PubMed

    Nikan, Marjan; Nabavi, Seyed Mohammad; Manayi, Azadeh

    2016-02-01

    Cannabinoid compounds are unique to cannabis and provide some interesting biological properties. These compounds along with endocannabinoids, a group of neuromodulator compounds in the body especially in brain, express their effects by activation of G-protein-coupled cannabinoid receptors, CB1 and CB2. There are several physiological properties attributed to the endocannabinoids including pain relief, enhancement of appetite, blood pressure lowering during shock, embryonic development, and blocking of working memory. On the other hand, activation of endocannabinoid system may be suppresses evolution and progression of several types of cancer. According to the results of recent studies, CB receptors are over-expressed in cancer cell lines and application of multiple cannabinoid or cannabis-derived compounds reduce tumor size through decrease of cell proliferation or induction of cell cycle arrest and apoptosis along with desirable effect on decrease of tumor-evoked pain. Therefore, modulation of endocannabinoid system by inhibition of fatty acid amide hydrolase (FAAH), the enzyme, which metabolized endocannabinoids, or application of multiple cannabinoid or cannabis-derived compounds, may be appropriate for the treatment of several cancer subtypes. This review focuses on how cannabinoid affect different types of cancers.

  13. Aryl Hydrocarbon Receptor Ligand 5F 203 Induces Oxidative Stress That Triggers DNA Damage in Human Breast Cancer Cells

    PubMed Central

    McLean, Lancelot S.; Watkins, Cheri N.; Campbell, Petreena; Zylstra, Dain; Rowland, Leah; Amis, Louisa H.; Scott, Lia; Babb, Crystal E.; Livingston, W. Joel; Darwanto, Agus; Davis, Willie L.; Senthil, Maheswari; Sowers, Lawrence C.; Brantley, Eileen

    2015-01-01

    Breast tumors often show profound sensitivity to exogenous oxidative stress. Investigational agent 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (5F 203) induces aryl hydrocarbon receptor (AhR)-mediated DNA damage in certain breast cancer cells. Since AhR agonists often elevate intracellular oxidative stress, we hypothesize that 5F 203 increases reactive oxygen species (ROS) to induce DNA damage, which thwarts breast cancer cell growth. We found that 5F 203 induced single-strand break formation. 5F 203 enhanced oxidative DNA damage that was specific to breast cancer cells sensitive to its cytotoxic actions, as it did not increase oxidative DNA damage or ROS formation in nontumorigenic MCF-10A breast epithelial cells. In contrast, AhR agonist and procarcinogen benzo[a]pyrene and its metabolite, 1,6-benzo[a]pyrene quinone, induced oxidative DNA damage and ROS formation, respectively, in MCF-10A cells. In sensitive breast cancer cells, 5F 203 activated ROS-responsive kinases: c-Jun-N-terminal kinase (JNK) and p38 mitogen activated protein kinase (p38). AhR antagonists (alpha-naphthoflavone, CH223191) or antioxidants (N-acetyl-l-cysteine, EUK-134) attenuated 5F 203-mediated JNK and p38 activation, depending on the cell type. Pharmacological inhibition of AhR, JNK, or p38 attenuated 5F 203-mediated increases in intracellular ROS, apoptosis, and single-strand break formation. 5F 203 induced the expression of cytoglobin, an oxidative stress-responsive gene and a putative tumor suppressor, which was diminished with AhR, JNK, or p38 inhibition. Additionally, 5F 203-mediated increases in ROS production and cytoglobin were suppressed in AHR100 cells (AhR ligand-unresponsive MCF-7 breast cancer cells). Our data demonstrate 5F 203 induces ROS-mediated DNA damage at least in part via AhR, JNK, or p38 activation and modulates the expression of oxidative stress-responsive genes such as cytoglobin to confer its anticancer action. PMID:25781201

  14. The AXL Receptor is a Sensor of Ligand Spatial Heterogeneity

    PubMed Central

    Meyer, Aaron S.; Zweemer, Annelien J.M.; Lauffenburger, Douglas A.

    2015-01-01

    The AXL receptor is a TAM (Tyro3, AXL, MerTK) receptor tyrosine kinase (RTK) important in physiological inflammatory processes such as blood clotting, viral infection, and innate immune-mediated cell clearance. Overexpression of the receptor in a number of solid tumors is increasingly appreciated as a key drug resistance and tumor dissemination mechanism. Although the ligand-receptor (Gas6-AXL) complex structure is known, literature reports on ligand-mediated signaling have provided conflicting conclusions regarding the influence of other factors such as phosphatidylserine binding, and a detailed, mechanistic picture of AXL activation has not emerged. Integrating quantitative experiments with mathematical modeling, we show here that AXL operates to sense local spatial heterogeneity in ligand concentration, a feature consistent with its physiological role in inflammatory cell responses. This effect arises as a result of an intricate reaction-diffusion interaction. Our results demonstrate that AXL functions distinctly from other RTK families, a vital insight for envisioned design of AXL-targeted therapeutic intervention. PMID:26236777

  15. Metabotropic glutamate receptor ligands as potential therapeutics for addiction

    PubMed Central

    Olive, M. F.

    2009-01-01

    There is now compelling evidence that the excitatory amino acid neurotransmitter glutamate plays a pivotal role in drug addiction and alcoholism. As a result, there has been increasing interest in developing glutamate-based therapies for the treatment of addictive disorders. Receptors for glutamate are primarily divided into two classes: ionotropic glutamate receptors (iGluRs) that mediate fast excitatory glutamate transmission, and metabotropic glutamate receptors (mGluRs), which are G-protein coupled receptors that mediate slower, modulatory glutamate transmission. Most iGluR antagonists, while showing some efficacy in animal models of addiction, exhibit serious side effects when tested in humans. mGluR ligands, on the other hand, which have been advanced to testing in clinical trials for various medical conditions, have demonstrated the ability to reduce drug reward, reinforcement, and relapse-like behaviors in animal studies. mGluR ligands that have been shown to be primarily effective are Group I (mGluR1 and mGluR5) negative allosteric modulators and Group II (mGluR2 and mGluR3) orthosteric presynaptic autoreceptor agonists. In this review, we will summarize findings from animal studies suggesting that these mGluR ligands may be of potential benefit in reducing on-going drug self-administration and may aid in the prevention of relapse. The neuroanatomical distribution of mGluR1, mGluR2/3, and mGluR5 receptors and the pharmacological properties of Group I negative allosteric modulators and Group II agonists will also be overviewed. Finally, we will discuss the current status of mGluR ligands in human clinical trials. PMID:19630739

  16. Probability description of ligand-receptor interactions. Evaluation of reliability of events with small and supersmall doses. I. Kinetics of ligand-receptor interactions.

    PubMed

    Gurevich, K G; Varfolomeev, S D

    1999-09-01

    We have developed mathematical methods for describing ligand-receptor interactions (LRI) using Markov chains. Under some conditions, the mean value of ligand-receptor complexes obtained using Markov chains coincides with that obtained from the law of mass action. Using the calculated ratio of standard deviation to mean number of ligand-receptor complexes, we show that with small concentrations of ligand-receptor complexes LRI must be described using probability methods. Using data from the literature, we show that LRI description using the mass-action law under these conditions can cause significant errors in interpretation of experimental data.

  17. Constitutive and ligand-induced nuclear localization of oxytocin receptor.

    PubMed

    Kinsey, Conan G; Bussolati, Gianni; Bosco, Martino; Kimura, Tadashi; Pizzorno, Marie C; Chernin, Mitchell I; Cassoni, Paola; Novak, Josef F

    2007-01-01

    Oxytocin receptor (OTR) is a membrane protein known to mediate oxytocin (OT) effects, in both normal and neoplastic cells. We report here that human osteosarcoma (U2OS, MG63, OS15 and SaOS2), breast cancer (MCF7), and primary human fibroblastic cells (HFF) all exhibit OTR not only on the cell membrane, but also in the various nuclear compartments including the nucleolus. Both an OTR-GFP fusion protein and the native OTR appear to be localized to the nucleus as detected by transfection and/or confocal immunofluorescence, respectively. Treatment with oxytocin causes internalization of OTR and the resulting vesicles accumulate in the vicinity of the nucleus and some of the perinuclear OTR enters the nucleus. Western blots indicate that OTR in the nucleus and on the plasma membrane are likely to be the same biochemical and immunological entities. It appears that OTR is first visible in the nucleoli and subsequently disperses within the nucleus into 4-20 spots while some of the OTR diffuses throughout the nucleoplasm. The behaviour and kinetics of OTR-GFP and OTR are different, indicating interference by GFP in both OTR entrance into the nucleus and subsequent relocalization of OTR within the nucleus. There are important differences among the tested cells, such as the requirement of a ligand for transfer of OTR in nuclei. A constitutive internalization of OTR was found only in osteosarcoma cells, while the nuclear localization in all other tested cells was dependent on ligand binding. The amount of OTR-positive material within and in the vicinity of the nucleus increased following a treatment with oxytocin in both constitutive and ligand-dependent type of cells. The evidence of OTR compartmentalization at the cell nucleus (either ligand-dependent or constitutive) in different cell types suggests still unknown biological functions of this protein or its ligand and adds this G-protein-coupled receptor to other heptahelical receptors displaying this atypical and unexpected

  18. The inhibition of lung cancer cell migration by AhR-regulated autophagy

    PubMed Central

    Tsai, Chi-Hao; Li, Ching-Hao; Cheng, Yu-Wen; Lee, Chen-Chen; Liao, Po-Lin; Lin, Cheng-Hui; Huang, Shih-Hsuan; Kang, Jaw-Jou

    2017-01-01

    The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that is highly expressed in multiple organs and tissues. Whereas AhR mediates the metabolism of xenobiotic and endogenous compounds, its novel function in cancer epithelial-mesenchymal transition (EMT) remains controversial. Autophagy also participates in tumour progression through its functions in cell homeostasis and facilitates adaptation to EMT progression. In the present study, we found that AhR-regulated autophagy positively modulates EMT in non-small cell lung cancer cells. The motility of A549, H1299, and CL1-5 cells were correlated with different AhR expression levels. Invasive potential and cell morphology also changed when AhR protein expression was altered. Moreover, AhR levels exerted a contrasting effect on autophagy potential. Autophagy was higher in CL1-5 and H1299 cells with lower AhR levels than in A549 cells. Both AhR overexpression and autophagy inhibition decreased CL1-5 metastasis in vivo. Furthermore, AhR promoted BNIP3 ubiquitination for proteasomal degradation. AhR silencing in A549 cells also reduced BNIP3 ubiquitination. Taken together, these results provide a novel insight into the cross-linking between AhR and autophagy, we addressed the mechanistic BNIP3 modulation by endogenous AhR, which affect cancer cell EMT progression. PMID:28195146

  19. Cancer therapy using natural ligands that target estrogen receptor beta

    PubMed Central

    Sareddy, Gangadhara R; Vadlamudi, Ratna K.

    2016-01-01

    Estrogen receptor beta (ERβ) is one of the two key receptors (ERα, ERβ) that facilitate biological actions of 17β-estradiol (E2). ERβ is widely expressed in many tissues, and its expression is reduced or lost during progression of many tumors. ERβ facilitates estrogen signaling by both genomic (classical and non-classical) and extra-nuclear signaling. Emerging evidence suggests that ERβ functions as a tissue-specific tumor suppressor with anti-proliferative actions. Recent studies have identified a number of naturally available selective ERβ agonists. Targeting ERβ using its naturally available ligands is an attractive approach for treating and preventing cancers. This review presents the beneficial actions of ERβ signaling and clinical utility of several natural ERβ ligands as potential cancer therapy. PMID:26614454

  20. High-affinity benzodiazepine receptor ligands among benzodiazepines and betacarbolines with different intrinsic activity

    SciTech Connect

    Yliniemelae, A.; Gynther, J. ); Konschin, H.; Tylli, H. ); Rouvinen, J. )

    1989-01-01

    Structural and electrostatic features of diazepam, flumazenil, and methyl betacarboline-3-carboxylate (BCCM) have been investigated using the molecular superimposition method. These high-affinity benzodiazepine (BZ) receptor ligands are structurally unrelated and they have different intrinsic activity. These ligands are superimposed in such a way that common structural and electrostatic features essential for the high receptor binding affinity overlap. In addition to this binding pharmacophore, there are roughly three separate binding zones in the BZ receptor, one for each class of ligands. The intrinsic activity of BZ receptor ligands depends on the molecular structures and the way the ligand approaches the receptor.

  1. Functionality of aryl hydrocarbon receptors (AhR1 and AhR2) of white sturgeon (Acipenser transmontanus) and implications for the risk assessment of dioxin-like compounds.

    PubMed

    Doering, Jon A; Farmahin, Reza; Wiseman, Steve; Kennedy, Sean W; Giesy, John P; Hecker, Markus

    2014-07-15

    Worldwide, populations of sturgeons are endangered, and it is hypothesized that anthropogenic chemicals, including dioxin-like compounds (DLCs), might be contributing to the observed declines in populations. DLCs elicit their toxic action through activation of the aryl hydrocarbon receptor (AhR), which is believed to regulate most, if not all, adverse effects associated with exposure to these chemicals. Currently, risk assessment of DLCs in fishes uses toxic equivalency factors (TEFs) developed for the World Health Organization (WHO) that are based on studies of embryo-lethality with salmonids. However, there is a lack of knowledge of the sensitivity of sturgeons to DLCs, and it is uncertain whether TEFs developed by the WHO are protective of these fishes. Sturgeons are evolutionarily distinct from salmonids, and the AhRs of sturgeons differ from those of salmonids. Therefore, this study investigated the sensitivity of white sturgeon (Acipenser transmontanus) to DLCs in vitro via the use of luciferase reporter gene assays using COS-7 cells transfected with AhR1 or AhR2 of white sturgeon. Specifically, activation and relative potencies (RePs) of 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachloro-dibenzofuran, 2,3,7,8-tetrachloro-dibenzofuran, 3,3',4,4',5-pentachlorobiphenyl, 3,3',4,4'-tetrachlorobiphenyl, and 2,3,3',4,4'-pentachlorobiphenyl were determined for each AhR. It was demonstrated that white sturgeon expresses AhR1s and AhR2s that are both activated by DLCs with EC50 values for 2,3,7,8-TCDD that are lower than those of any other AhR of vertebrates tested to date. Both AhRs of white sturgeon had RePs for polychlorinated dibenzofurans more similar to TEFs for birds, while RePs for polychlorinated biphenyls were most similar to TEFs for fishes. Measured concentrations of select DLCs in tissues of white sturgeon from British Columbia, Canada, were used to calculate toxic equivalents (TEQs) by use of TEFs for fishes used by the WHO and TCDD

  2. Optimizing Ligand Efficiency of Selective Androgen Receptor Modulators (SARMs).

    PubMed

    Handlon, Anthony L; Schaller, Lee T; Leesnitzer, Lisa M; Merrihew, Raymond V; Poole, Chuck; Ulrich, John C; Wilson, Joseph W; Cadilla, Rodolfo; Turnbull, Philip

    2016-01-14

    A series of selective androgen receptor modulators (SARMs) containing the 1-(trifluoromethyl)benzyl alcohol core have been optimized for androgen receptor (AR) potency and drug-like properties. We have taken advantage of the lipophilic ligand efficiency (LLE) parameter as a guide to interpret the effect of structural changes on AR activity. Over the course of optimization efforts the LLE increased over 3 log units leading to a SARM 43 with nanomolar potency, good aqueous kinetic solubility (>700 μM), and high oral bioavailability in rats (83%).

  3. Optimizing Ligand Efficiency of Selective Androgen Receptor Modulators (SARMs)

    PubMed Central

    2015-01-01

    A series of selective androgen receptor modulators (SARMs) containing the 1-(trifluoromethyl)benzyl alcohol core have been optimized for androgen receptor (AR) potency and drug-like properties. We have taken advantage of the lipophilic ligand efficiency (LLE) parameter as a guide to interpret the effect of structural changes on AR activity. Over the course of optimization efforts the LLE increased over 3 log units leading to a SARM 43 with nanomolar potency, good aqueous kinetic solubility (>700 μM), and high oral bioavailability in rats (83%). PMID:26819671

  4. Peptide ligand recognition by G protein-coupled receptors

    PubMed Central

    Krumm, Brian E.

    2015-01-01

    The past few years have seen spectacular progress in the structure determination of G protein-coupled receptors (GPCRs). We now have structural representatives from classes A, B, C, and F. Within the rhodopsin-like class A, most structures belong to the α group, whereas fewer GPCR structures are available from the β, γ, and δ groups, which include peptide GPCRs such as the receptors for neurotensin (β group), opioids, chemokines (γ group), and protease-activated receptors (δ group). Structural information on peptide GPCRs is restricted to complexes with non-peptidic drug-like antagonists with the exception of the chemokine receptor CXCR4 that has been crystallized in the presence of a cyclic peptide antagonist. Notably, the neurotensin receptor 1 is to date the only peptide GPCR whose structure has been solved in the presence of a peptide agonist. Although limited in number, the current peptide GPCR structures reveal great diversity in shape and electrostatic properties of the ligand binding pockets, features that play key roles in the discrimination of ligands. Here, we review these aspects of peptide GPCRs in view of possible models for peptide agonist binding. PMID:25852552

  5. 5D-QSAR for spirocyclic sigma1 receptor ligands by Quasar receptor surface modeling.

    PubMed

    Oberdorf, Christoph; Schmidt, Thomas J; Wünsch, Bernhard

    2010-07-01

    Based on a contiguous and structurally as well as biologically diverse set of 87 sigma(1) ligands, a 5D-QSAR study was conducted in which a quasi-atomistic receptor surface modeling approach (program package Quasar) was applied. The superposition of the ligands was performed with the tool Pharmacophore Elucidation (MOE-package), which takes all conformations of the ligands into account. This procedure led to four pharmacophoric structural elements with aromatic, hydrophobic, cationic and H-bond acceptor properties. Using the aligned structures a 3D-model of the ligand binding site of the sigma(1) receptor was obtained, whose general features are in good agreement with previous assumptions on the receptor structure, but revealed some novel insights since it represents the receptor surface in more detail. Thus, e.g., our model indicates the presence of an H-bond acceptor moiety in the binding site as counterpart to the ligands' cationic ammonium center, rather than a negatively charged carboxylate group. The presented QSAR model is statistically valid and represents the biological data of all tested compounds, including a test set of 21 ligands not used in the modeling process, with very good to excellent accuracy [q(2) (training set, n=66; leave 1/3 out) = 0.84, p(2) (test set, n=21)=0.64]. Moreover, the binding affinities of 13 further spirocyclic sigma(1) ligands were predicted with reasonable accuracy (mean deviation in pK(i) approximately 0.8). Thus, in addition to novel insights into the requirements for binding of spirocyclic piperidines to the sigma(1) receptor, the presented model can be used successfully in the rational design of new sigma(1) ligands.

  6. Steroid receptors and their ligands: Effects on male gamete functions

    SciTech Connect

    Aquila, Saveria; De Amicis, Francesca

    2014-11-01

    In recent years a new picture of human sperm biology is emerging. It is now widely recognized that sperm contain nuclear encoded mRNA, mitochondrial encoded RNA and different transcription factors including steroid receptors, while in the past sperm were considered incapable of transcription and translation. One of the main targets of steroid hormones and their receptors is reproductive function. Expression studies on Progesterone Receptor, estrogen receptor, androgen receptor and their specific ligands, demonstrate the presence of these systems in mature spermatozoa as surface but also as nuclear conventional receptors, suggesting that both systemic and local steroid hormones, through sperm receptors, may influence male reproduction. However, the relationship between the signaling events modulated by steroid hormones and sperm fertilization potential as well as the possible involvement of the specific receptors are still controversial issues. The main line of this review highlights the current research in human sperm biology examining new molecular systems of response to the hormones as well as specific regulatory pathways controlling sperm cell fate and biological functions. Most significant studies regarding the identification of steroid receptors are reported and the mechanistic insights relative to signaling pathways, together with the change in sperm metabolism energy influenced by steroid hormones are discussed.The reviewed evidences suggest important effects of Progesterone, Estrogen and Testosterone and their receptors on spermatozoa and implicate the involvement of both systemic and local steroid action in the regulation of male fertility potential. - Highlights: • One of the main targets of steroid hormones and their receptors is reproductive function. • Pg/PR co-work to stimulate enzymatic activities to sustain a capacitation process. • E2/ERs regulate sperm motility, capacitation and acrosome reaction and act as survival factors. • Androgens

  7. Structural basis of ligand interaction with atypical chemokine receptor 3

    NASA Astrophysics Data System (ADS)

    Gustavsson, Martin; Wang, Liwen; van Gils, Noortje; Stephens, Bryan S.; Zhang, Penglie; Schall, Thomas J.; Yang, Sichun; Abagyan, Ruben; Chance, Mark R.; Kufareva, Irina; Handel, Tracy M.

    2017-01-01

    Chemokines drive cell migration through their interactions with seven-transmembrane (7TM) chemokine receptors on cell surfaces. The atypical chemokine receptor 3 (ACKR3) binds chemokines CXCL11 and CXCL12 and signals exclusively through β-arrestin-mediated pathways, without activating canonical G-protein signalling. This receptor is upregulated in numerous cancers making it a potential drug target. Here we collected over 100 distinct structural probes from radiolytic footprinting, disulfide trapping, and mutagenesis to map the structures of ACKR3:CXCL12 and ACKR3:small-molecule complexes, including dynamic regions that proved unresolvable by X-ray crystallography in homologous receptors. The data are integrated with molecular modelling to produce complete and cohesive experimentally driven models that confirm and expand on the existing knowledge of the architecture of receptor:chemokine and receptor:small-molecule complexes. Additionally, we detected and characterized ligand-induced conformational changes in the transmembrane and intracellular regions of ACKR3 that elucidate fundamental structural elements of agonism in this atypical receptor.

  8. Structural basis of ligand interaction with atypical chemokine receptor 3

    PubMed Central

    Gustavsson, Martin; Wang, Liwen; van Gils, Noortje; Stephens, Bryan S.; Zhang, Penglie; Schall, Thomas J.; Yang, Sichun; Abagyan, Ruben; Chance, Mark R.; Kufareva, Irina; Handel, Tracy M.

    2017-01-01

    Chemokines drive cell migration through their interactions with seven-transmembrane (7TM) chemokine receptors on cell surfaces. The atypical chemokine receptor 3 (ACKR3) binds chemokines CXCL11 and CXCL12 and signals exclusively through β-arrestin-mediated pathways, without activating canonical G-protein signalling. This receptor is upregulated in numerous cancers making it a potential drug target. Here we collected over 100 distinct structural probes from radiolytic footprinting, disulfide trapping, and mutagenesis to map the structures of ACKR3:CXCL12 and ACKR3:small-molecule complexes, including dynamic regions that proved unresolvable by X-ray crystallography in homologous receptors. The data are integrated with molecular modelling to produce complete and cohesive experimentally driven models that confirm and expand on the existing knowledge of the architecture of receptor:chemokine and receptor:small-molecule complexes. Additionally, we detected and characterized ligand-induced conformational changes in the transmembrane and intracellular regions of ACKR3 that elucidate fundamental structural elements of agonism in this atypical receptor. PMID:28098154

  9. Receptor-based 3D QSAR analysis of estrogen receptor ligands - merging the accuracy of receptor-based alignments with the computational efficiency of ligand-based methods

    NASA Astrophysics Data System (ADS)

    Sippl, Wolfgang

    2000-08-01

    One of the major challenges in computational approaches to drug design is the accurate prediction of binding affinity of biomolecules. In the present study several prediction methods for a published set of estrogen receptor ligands are investigated and compared. The binding modes of 30 ligands were determined using the docking program AutoDock and were compared with available X-ray structures of estrogen receptor-ligand complexes. On the basis of the docking results an interaction energy-based model, which uses the information of the whole ligand-receptor complex, was generated. Several parameters were modified in order to analyze their influence onto the correlation between binding affinities and calculated ligand-receptor interaction energies. The highest correlation coefficient ( r 2 = 0.617, q 2 LOO = 0.570) was obtained considering protein flexibility during the interaction energy evaluation. The second prediction method uses a combination of receptor-based and 3D quantitative structure-activity relationships (3D QSAR) methods. The ligand alignment obtained from the docking simulations was taken as basis for a comparative field analysis applying the GRID/GOLPE program. Using the interaction field derived with a water probe and applying the smart region definition (SRD) variable selection, a significant and robust model was obtained ( r 2 = 0.991, q 2 LOO = 0.921). The predictive ability of the established model was further evaluated by using a test set of six additional compounds. The comparison with the generated interaction energy-based model and with a traditional CoMFA model obtained using a ligand-based alignment ( r 2 = 0.951, q 2 LOO = 0.796) indicates that the combination of receptor-based and 3D QSAR methods is able to improve the quality of the underlying model.

  10. Lighting up G protein-coupled purinergic receptors with engineered fluorescent ligands

    PubMed Central

    Ciruela, Francisco; Fernández-Dueñas, Víctor; Jacobson, Kenneth A.

    2015-01-01

    The use of G protein-coupled receptors fluorescent ligands is undergoing continuous expansion. In line with this, fluorescent agonists and antagonists of high affinity for G protein-coupled adenosine and P2Y receptors have been shown to be useful pharmacological probe compounds. Fluorescent ligands for A1R, A2AR, and A3R (adenosine receptors) and P2Y2R, P2Y4R, P2Y6R, and P2Y14R (nucleotide receptors) have been reported. Such ligands have been successfully applied to drug discovery and to GPCR characterization by flow cytometry, fluorescence correlation spectroscopy, fluorescence microscopy, fluorescence polarization, fluorescence resonance energy transfer and scanning confocal microscopy. Here we summarize recently reported and readily available representative fluorescent ligands of purinergic receptors. In addition, we pay special attention on the use of this family of fluorescent ligands revealing two main aspects of purinergic receptor biology, namely ligand binding and receptor oligomerization. PMID:25890205

  11. Amino Acid Substitutions That Affect Receptor Binding and Stability of the Hemagglutinin of Influenza A/H7N9 Virus

    PubMed Central

    Schrauwen, Eefje J. A.; Burke, David F.; Rimmelzwaan, Guus F.; Herfst, Sander; Fouchier, Ron A. M.

    2016-01-01

    Receptor-binding preference and stability of hemagglutinin have been implicated as crucial determinants of airborne transmission of influenza viruses. Here, amino acid substitutions previously identified to affect these traits were tested in the context of an A/H7N9 virus. Some combinations of substitutions, most notably G219S and K58I, resulted in relatively high affinity for α2,6-linked sialic acid receptor and acid and temperature stability. Thus, the hemagglutinin of the A/H7N9 virus may adopt traits associated with airborne transmission. PMID:26792744

  12. Multiresolution imaging of in-vivo ligand-receptor interactions

    NASA Astrophysics Data System (ADS)

    Thevenaz, Philippe; Millet, Philippe

    2001-05-01

    The aim of this study is to obtain voxel-by-voxel images of binding parameters between [11C]-flumazenil and benzodiazepine receptors using positron emission tomography (PET). We estimate five local parameters (k1, k2, B'max, kon/VR, koff) by fitting a three- compartment ligand-receptor model for each voxel of a PET time series. It proves difficult to fit the ligand-receptor model to the data. We trade noise and spatial resolution to get better results. Our strategy is based on the use of a multiresolution pyramid. It is much easier to solve the problem at coarse resolution because there are fewer data to process. To increase resolution, we expand the parameter maps to the next finer level and use them as initial solution to further optimization, which then proceeds at a fast pace and is more likely to escape false local minima. For this approach to work optimally, the residue between data at a given pyramid level and data at the next level must be as small as possible. We satisfy this constraint by working with spline-based least- squares pyramids. To achieve speed, the optimizer must be efficient, particularly when it is nearing the solution. To that effect, we have developed a Marquardt-Levenberg algorithm that exhibits superlinear convergence properties.

  13. NKG2D receptor and its ligands in host defense

    PubMed Central

    Lanier, Lewis L.

    2015-01-01

    NKG2D is an activating receptor expressed on the surface of natural killer (NK) cells, CD8+ T cells, and subsets of CD4+ T cells, iNKT cells, and γδ T cells. In humans NKG2D transmits signals by its association with the DAP10 adapter subunit and in mice alternatively spliced isoforms transmit signals either using DAP10 or DAP12 adapter subunits. Although NKG2D is encoded by a highly conserved gene (KLRK1) with limited polymorphism, the receptor recognizes an extensive repertoire of ligands, encoded by at least 8 genes in humans (MICA, MICB, RAET1E, RAET1G, RAET1H, RAET1I, RAET1L, and RAET1N), some with extensive allelic polymorphism. Expression of the NKG2D ligands is tightly regulated at the level of transcription, translation, and post-translation. In general healthy adult tissues do not express NKG2D glycoproteins on the cell surface, but these ligands can be induced by hyper-proliferation and transformation, as well as when cells are infected by pathogens. Thus, the NKG2D pathway serves a mechanism for the immune system to detect and eliminate cells that have undergone “stress”. Viruses and tumor cells have devised numerous strategies to evade detection by the NKG2D surveillance system and diversification of the NKG2D ligand genes likely has been driven by selective pressures imposed by pathogens. NKG2D provides an attractive target for therapeutics in the treatment of infectious diseases, cancer, and autoimmune diseases. PMID:26041808

  14. NKG2D Receptor and Its Ligands in Host Defense.

    PubMed

    Lanier, Lewis L

    2015-06-01

    NKG2D is an activating receptor expressed on the surface of natural killer (NK) cells, CD8(+) T cells, and subsets of CD4(+) T cells, invariant NKT cells (iNKT), and γδ T cells. In humans, NKG2D transmits signals by its association with the DAP10 adapter subunit, and in mice alternatively spliced isoforms transmit signals either using DAP10 or DAP12 adapter subunits. Although NKG2D is encoded by a highly conserved gene (KLRK1) with limited polymorphism, the receptor recognizes an extensive repertoire of ligands, encoded by at least eight genes in humans (MICA, MICB, RAET1E, RAET1G, RAET1H, RAET1I, RAET1L, and RAET1N), some with extensive allelic polymorphism. Expression of the NKG2D ligands is tightly regulated at the level of transcription, translation, and posttranslation. In general, healthy adult tissues do not express NKG2D glycoproteins on the cell surface, but these ligands can be induced by hyperproliferation and transformation, as well as when cells are infected by pathogens. Thus, the NKG2D pathway serves as a mechanism for the immune system to detect and eliminate cells that have undergone "stress." Viruses and tumor cells have devised numerous strategies to evade detection by the NKG2D surveillance system, and diversification of the NKG2D ligand genes likely has been driven by selective pressures imposed by pathogens. NKG2D provides an attractive target for therapeutics in the treatment of infectious diseases, cancer, and autoimmune diseases.

  15. Highly selective CB(1) cannabinoid receptor ligands and novel CB(1)/VR(1) vanilloid receptor "hybrid" ligands.

    PubMed

    Di Marzo, V; Bisogno, T; De Petrocellis, L; Brandi, I; Jefferson, R G; Winckler, R L; Davis, J B; Dasse, O; Mahadevan, A; Razdan, R K; Martin, B R

    2001-02-23

    Anandamide and the metabolically stabler analogs, (R)-1'-methyl-2'-hydroxy-ethyl-arachidonamide (Met-AEA) and N-(3-methoxy-4-hydroxy-benzyl)-arachidonamide (arvanil), are CB(1) cannabinoid and VR(1) vanilloid receptors agonists. We synthesized 1',1'-dimethylheptyl-arvanil (O-1839) and six other AEA analogs obtained by addition of either a hydroxy, cyano, or bromo group on the C-20 atom of 1,1'-dimethylpentyl-Met-AEA (O-1811, O-1812 and O-1860, respectively) or 1,1'-dimethylpentyl-arvanil (O-1856, O-1895 and O-1861, respectively). The compounds were tested for their (i) affinity for CB(1) and CB(2) receptors, (ii) capability to activate VR1 receptors, (iii) inhibitory effect on the anandamide hydrolysis and on the anandamide membrane transporter, and (iv) cannabimimetic activity in the mouse 'tetrad' of in vivo assays. O-1812 is the first ligand ever proven to be highly (500- to 1000-fold) selective for CB(1) vs both VR(1) and CB(2) receptors, while O-1861 is the first true "hybrid" agonist of CB(1)/VR(1) receptors and a compound with potential therapeutic importance. The activities of the seven compounds in vivo did not correlate with their activities at either CB(1) or VR(1) receptors, thus suggesting the existence of other brain sites of action mediating some of their neurobehavioral actions in mice.

  16. Transgenic mouse lines expressing rat AH receptor variants - A new animal model for research on AH receptor function and dioxin toxicity mechanisms

    SciTech Connect

    Pohjanvirta, Raimo

    2009-04-15

    Han/Wistar (Kuopio; H/W) rats are exceptionally resistant to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity mainly because of their mutated aryl hydrocarbon receptor (AHR) gene. In H/W rats, altered splicing of the AHR mRNA generates two AHR proteins: deletion (DEL) and insertion (INS) variants, with the INS isoform being predominantly expressed. To gain further insight into their functional properties, cDNAs of these and rat wild-type (rWT) isoform were transferred into C57BL/6J-derived mice by microinjection. The endogenous mouse AHR was eliminated by selective crossing with Ahr-null mice. A single mouse line was obtained for each of the three constructs. The AHR mRNA levels in tissues were generally close to those of C57BL/6 mice in INS and DEL mice and somewhat higher in rWT mice; in testis, however, all 3 constructs exhibited marked overexpression. The transgenic mouse lines were phenotypically normal except for increased testis weight. Induction of drug-metabolizing enzymes by TCDD occurred similarly to that in C57BL/6 mice, but there tended to be a correlation with AHR concentrations, especially in testis. In contrast to C57BL/6 mice, the transgenics did not display any major gender difference in susceptibility to the acute lethality and hepatotoxicity of TCDD; rWT mice were highly sensitive, DEL mice moderately resistant and INS mice highly resistant. Co-expression of mouse AHR and rWT resulted in augmented sensitivity to TCDD and abolished the natural resistance of female C57BL/6 mice, whereas mice co-expressing mouse AHR and INS were resistant. Thus, these transgenic mouse lines provide a novel promising tool for molecular studies on dioxin toxicity and AHR function.

  17. Tumor necrosis factor-α inhibits effects of aryl hydrocarbon receptor ligands on cell death in human lymphocytes

    PubMed Central

    Ghatrehsamani, Mahdi; Soleimani, Masoud; Esfahani, Behjat A Moayedi; Shirzad, Hedayatollah; Hakemi, Mazdak G; Mossahebimohammadi, Majid; Eskandari, Nahid; Adib, Minoo

    2015-01-01

    Background: Activation of aryl hydrocarbon receptor (AhR) leads to diverse outcome in various kinds of cells. AhR activation may induce apoptosis or prevent of apoptosis and cell death. Recent studies suggest that apoptosis effects of AhR can be modulated by inflammatory cytokine like tumor necrosis factor alpha (TNF-α). In this study, we try to investigate the possible interaction of TNF-α with the 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD), a ligand of AhR, on peripheral lymphocytes. Materials and Methods: Human peripheral blood mononuclear cells (PBMCs) were isolated from peripheral blood by discontinuous density gradient centrifugation on ficoll. Isolated PBMCs were divided into four groups: Control group, TNF-α administered group, TCDD administered group, co-administered group with TCDD and TNF-α. Cells were maintained for a week in lymphocyte culture condition. Then, TNF-α was added to group 2 and 4. Finally, apoptosis and necrosis were analyzed in all samples using flowcytometry. Result: In group 4, the mean percent of necrosis and apoptosis in TCDD treatment groups was significantly larger than other groups; (P < 0.05). Furthermore, there was no significant difference between the mean percent of cell death in TNF-α administered group and TCDD administered group (P > 0.05). However, the mean percent of cell death in co-administered group with TCDD and TNF-α was significantly lower than other groups; (P < 0.05). Conclusion: TNF-α could significantly inhibit effects of TCDD on lymphocytes apoptosis. Combination effects of TNF-α and TCDD on lymphocyte increase cell survival. PMID:26605245

  18. Probing an artificial polypeptide receptor library using a series of novel histamine H3 receptor ligands.

    PubMed

    Bak, Andrzej; Daszykowski, Michal; Kaminski, Zbigniew; Kiec-Kononowicz, Katarzyna; Kuder, Kamil; Fraczyk, Justyna; Kolesinska, Beata; Ciosek, Patrycja; Polanski, Jaroslaw

    2014-02-01

    An artificial polypeptide receptor (APR) library was created by using the self-organization of N-lipidated peptides attached to cellulose via m-aminophenylamino-1,3,5-triazine. The response of the library was probed using a series of novel H3 receptor ligands. Since no guidelines on how to design an APRs selective vs certain receptor types exist, a diverse set of amino acids (Ala, Trp, Pro, Glu, His, Lys and Ser) were used and coupled with one of three gating fatty acids (palmitic, ricinoleic or capric). A competitive adsorption-desorption of an appropriate reporter dye was used for the indirect visualization of the interactions of guests with particular receptors. The resulted library response to individual inhibitors was then arranged in a matrix, preprocessed and analyzed using the principal component analysis (PCA) and partial least squares (PLS) method. The most important conclusion obtained from the PCA analysis is that the library differentiates the probed compounds according to the lipophilicity of the gating unit. The PC3 with a dominant absolute contribution of the receptors containing Glu allowed for the best separation of the ligands with respect to their activity. This conclusion is in agreement with the fact that Glu 206 is a genuine ligand counterpart in the natural histamine receptor.

  19. Modulation of Opioid Receptor Ligand Affinity and Efficacy Using Active and Inactive State Receptor Models

    PubMed Central

    Anand, Jessica P.; Purington, Lauren C.; Pogozheva, Irina D.; Traynor, John R.; Mosberg, Henry I.

    2012-01-01

    Mu opioid receptor (MOR) agonists are widely used for the treatment of pain; however chronic use results in the development of tolerance and dependence. It has been demonstrated that co-administration of a MOR agonist with a delta opioid receptor (DOR) antagonist maintains the analgesia associated with MOR agonists, but with reduced negative side effects. Using our newly refined opioid receptor models for structure-based ligand design, we have synthesized several pentapeptides with tailored affinity and efficacy profiles. In particular, we have obtained pentapeptides 8, Tyr-c(S-S)[DCys-1Nal-Nle-Cys]NH2, and 12, Tyr-c(S-S)[DCys-1Nal-Nle-Cys]OH, which demonstrates high affinity and full agonist behavior at MOR, high affinity but very low efficacy for DOR, and minimal affinity for the kappa opioid receptor (KOR). Functional properties of these peptides as MOR agonists/DOR antagonists lacking undesired KOR activity make them promising candidates for future in vivo studies of MOR/DOR interactions. Subtle structural variation of 12, by substituting D-Cys5 for L-Cys5, generated analog 13 which maintains low nanomolar MOR and DOR affinity, but which displays no efficacy at either receptor. These results demonstrate the power and utility of accurate receptor models for structure-based ligand design, as well as the profound sensitivity of ligand function on its structure. PMID:22882801

  20. [Endomorphins--endogenous ligands of the mu-opioid receptor].

    PubMed

    Perlikowska, Renata; Fichna, Jakub; Janecka, Anna

    2009-01-01

    Two endogenous opioid peptides with extremely high mu-opioid receptor affinity and selectivity, endomorphin-1 and endomorphin-2, were: discovered and isolated from the mammalian brain in 1997. Endomorphins are amidated tetrapeptides, structurally different from so called typical opioids: enkephalins, dynorphins and endorphins. A protein precursor of endomorphins and a gene encoding their sequence remain unknown. Endomorphins are unable to cross the blood-brain barrier because of their low hydrophobicity. In animal models, these peptides turned out to be very potent in relieving neuropathic and inflammatory pain. In comparison with morphine, a prototype opioid receptor ligand, endomorphins produces less undesired side effects. In this article we describe the discovery of endomorphins, their cellular localization and functions in the organism, as well as their structure-activity relationships and biodegradation pathways.

  1. Beta-arrestin-biased ligands at seven-transmembrane receptors.

    PubMed

    Violin, Jonathan D; Lefkowitz, Robert J

    2007-08-01

    Seven-transmembrane receptors (7TMRs), the most common molecular targets of modern drug therapy, are critically regulated by beta-arrestins, which both inhibit classic G-protein signaling and initiate distinct beta-arrestin signaling. The interplay of G-protein and beta-arrestin signals largely determines the cellular consequences of 7TMR-targeted drugs. Until recently, a drug's efficacy for beta-arrestin recruitment was believed to be proportional to its efficacy for G-protein activities. This paradigm restricts 7TMR drug effects to a linear spectrum of responses, ranging from inhibition of all responses to stimulation of all responses. However, it is now clear that 'biased ligands' can selectively activate G-protein or beta-arrestin functions and thus elicit novel biological effects from even well-studied 7TMRs. Here, we discuss the current state of beta-arrestin-biased ligand research and the prospects for beta-arrestin bias as a therapeutic target. Consideration of ligand bias might have profound influences on the way scientists approach 7TMR-targeted drug discovery.

  2. MIPs are ancestral ligands for the sex peptide receptor.

    PubMed

    Kim, Young-Joon; Bartalska, Katarina; Audsley, Neil; Yamanaka, Naoki; Yapici, Nilay; Lee, Ju-Youn; Kim, Yong-Chul; Markovic, Milica; Isaac, Elwyn; Tanaka, Yoshiaki; Dickson, Barry J

    2010-04-06

    Upon mating, females of many animal species undergo dramatic changes in their behavior. In Drosophila melanogaster, postmating behaviors are triggered by sex peptide (SP), which is produced in the male seminal fluid and transferred to female during copulation. SP modulates female behaviors via sex peptide receptor (SPR) located in a small subset of internal sensory neurons that innervate the female uterus and project to the CNS. Although required for postmating responses only in these female sensory neurons, SPR is expressed broadly in the CNS of both sexes. Moreover, SPR is also encoded in the genomes of insects that lack obvious SP orthologs. These observations suggest that SPR may have additional ligands and functions. Here, we identify myoinhibitory peptides (MIPs) as a second family of SPR ligands that is conserved across a wide range of invertebrate species. MIPs are potent agonists for Drosophila, Aedes, and Aplysia SPRs in vitro, yet are unable to trigger postmating responses in vivo. In contrast to SP, MIPs are not produced in male reproductive organs, and are not required for postmating behaviors in Drosophila females. We conclude that MIPs are evolutionarily conserved ligands for SPR, which are likely to mediate functions other than the regulation of female reproductive behaviors.

  3. Identification of Putative Receptors for the Novel Adipokine CTRP3 Using Ligand-Receptor Capture Technology

    PubMed Central

    Li, Ying; Ozment, Tammy; Wright, Gary L.

    2016-01-01

    C1q TNF Related Protein 3 (CTRP3) is a member of a family of secreted proteins that exert a multitude of biological effects. Our initial work identified CTRP3’s promise as an effective treatment for Nonalcoholic fatty liver disease (NAFLD). Specifically, we demonstrated that mice fed a high fat diet failed to develop NAFLD when treated with CTRP3. The purpose of this current project is to identify putative receptors which mediate the hepatic actions of CTRP3. Methods We used Ligand-receptor glycocapture technology with TriCEPS™-based ligand-receptor capture (LRC-TriCEPS; Dualsystems Biotech AG). The LRC-TriCEPS experiment with CTRP3-FLAG protein as ligand and insulin as a control ligand was performed on the H4IIE rat hepatoma cell line. Results Initial analysis demonstrated efficient coupling of TriCEPS to CTRP3. Further, flow cytometry analysis (FACS) demonstrated successful oxidation and crosslinking of CTRP3-TriCEPS and Insulin-TriCEPS complexes to cell surface glycans. Demonstrating the utility of TriCEPS under these conditions, the insulin receptor was identified in the control dataset. In the CTRP3 treated cells a total enrichment of 261 peptides was observed. From these experiments 5 putative receptors for CTRP3 were identified with two reaching statistically significance: Lysosomal-associated membrane protein 1 (LAMP-1) and Lysosome membrane protein 2 (LIMP II). Follow-up Co-immunoprecipitation analysis confirmed the association between LAMP1 and CTRP3 and further testing using a polyclonal antibody to block potential binding sites of LAMP1 prevented CTRP3 binding to the cells. Conclusion The LRC-TriCEPS methodology was successful in identifying potential novel receptors for CTRP3. Relevance The identification of the receptors for CTRP3 are important prerequisites for the development of small molecule drug candidates, of which none currently exist, for the treatment NAFLD. PMID:27727322

  4. Molecular Basis of Ligand Dissociation in β-Adrenergic Receptors

    PubMed Central

    González, Angel; Perez-Acle, Tomas; Pardo, Leonardo; Deupi, Xavier

    2011-01-01

    The important and diverse biological functions of β-adrenergic receptors (βARs) have promoted the search for compounds to stimulate or inhibit their activity. In this regard, unraveling the molecular basis of ligand binding/unbinding events is essential to understand the pharmacological properties of these G protein-coupled receptors. In this study, we use the steered molecular dynamics simulation method to describe, in atomic detail, the unbinding process of two inverse agonists, which have been recently co-crystallized with β1 and β2ARs subtypes, along four different channels. Our results indicate that this type of compounds likely accesses the orthosteric binding site of βARs from the extracellular water environment. Importantly, reconstruction of forces and energies from the simulations of the dissociation process suggests, for the first time, the presence of secondary binding sites located in the extracellular loops 2 and 3 and transmembrane helix 7, where ligands are transiently retained by electrostatic and Van der Waals interactions. Comparison of the residues that form these new transient allosteric binding sites in both βARs subtypes reveals the importance of non-conserved electrostatic interactions as well as conserved aromatic contacts in the early steps of the binding process. PMID:21915263

  5. Molecular modeling studies demonstrate key mutations that could affect the ligand recognition by influenza AH1N1 neuraminidase.

    PubMed

    Ramírez-Salinas, Gema L; García-Machorro, J; Quiliano, Miguel; Zimic, Mirko; Briz, Verónica; Rojas-Hernández, Saul; Correa-Basurto, J

    2015-11-01

    The goal of this study was to identify neuraminidase (NA) residue mutants from human influenza AH1N1 using sequences from 1918 to 2012. Multiple alignment studies of complete NA sequences (5732) were performed. Subsequently, the crystallographic structure of the 1918 influenza (PDB ID: 3BEQ-A) was used as a wild-type structure and three-dimensional (3-D) template for homology modeling of the mutated selected NA sequences. The 3-D mutated NAs were refined using molecular dynamics (MD) simulations (50 ns). The refined 3-D models were used to perform docking studies using oseltamivir. Multiple sequence alignment studies showed seven representative mutations (A232V, K262R, V263I, T264V, S367L, S369N, and S369K). MD simulations applied to 3-D NAs showed that each NA had different active-site shapes according to structural surface visualization and docking results. Moreover, Cartesian principal component analyses (cPCA) show structural differences among these NA structures caused by mutations. These theoretical results suggest that the selected mutations that are located outside of the active site of NA could affect oseltamivir recognition and could be associated with resistance to oseltamivir.

  6. Ligands and receptors: common theme in insect storage protein transport.

    PubMed

    Burmester, T; Scheller, K

    1999-10-01

    The passage of macromolecules through biological membranes is an essential process for all multicellular organisms. Insects have developed a mechanism different from that known for all other eukaryotes investigated so far. This review discusses the function and evolution of this mechanism. Insect pupae do not feed during metamorphosis. Therefore they depend on material that has been accumulated during the larval life. At the end of this period, shortly before pupariation, a rise in titer of ecdysteroid hormones induces the incorporation of a large fraction of storage proteins (hexamerins) from the body fluid into the fat body cells. The transport of hexamerins across the cell-membrane is mediated by a specific ecdysteroid-controlled receptor. It is synthesized as a precursor protein that is subsequently processed into the active receptor. This receptor protein is very unusual because it is closely related to its own hexamerin ligand. Sequence comparison shows that the hexamerins and hexamerin receptors diverged early in insect evolution and derive from a common hemocyanin ancestor.

  7. Ligand and Structure-based Methodologies for the Prediction of the Activity of G Protein-Coupled Receptor Ligands

    PubMed Central

    Costanzi, Stefano; Tikhonova, Irina G.; Harden, T. Kendall; Jacobson, Kenneth A.

    2008-01-01

    Summary Accurate in silico models for the quantitative prediction of the activity of G protein-coupled receptor (GPCR) ligands would greatly facilitate the process of drug discovery and development. Several methodologies have been developed based on the properties of the ligands, the direct study of the receptor-ligand interactions, or a combination of both approaches. Ligand-based three-dimensional quantitative structure-activity relationships (3D-QSAR) techniques, not requiring knowledge of the receptor structure, have been historically the first to be applied to the prediction of the activity of GPCR ligands. They are generally endowed with robustness and good ranking ability; however they are highly dependent on training sets. Structure-based techniques generally do not provide the level of accuracy necessary to yield meaningful rankings when applied to GPCR homology models. However, they are essentially independent from training sets and have a sufficient level of accuracy to allow an effective discrimination between binders and nonbinders, thus qualifying as viable lead discovery tools. The combination of ligand and structure-based methodologies in the form of receptor-based 3D-QSAR and ligand and structure-based consensus models results in robust and accurate quantitative predictions. The contribution of the structure-based component to these combined approaches is expected to become more substantial and effective in the future, as more sophisticated scoring functions are developed and more detailed structural information on GPCRs is gathered. PMID:18483766

  8. Ligand and structure-based methodologies for the prediction of the activity of G protein-coupled receptor ligands

    NASA Astrophysics Data System (ADS)

    Costanzi, Stefano; Tikhonova, Irina G.; Harden, T. Kendall; Jacobson, Kenneth A.

    2009-11-01

    Accurate in silico models for the quantitative prediction of the activity of G protein-coupled receptor (GPCR) ligands would greatly facilitate the process of drug discovery and development. Several methodologies have been developed based on the properties of the ligands, the direct study of the receptor-ligand interactions, or a combination of both approaches. Ligand-based three-dimensional quantitative structure-activity relationships (3D-QSAR) techniques, not requiring knowledge of the receptor structure, have been historically the first to be applied to the prediction of the activity of GPCR ligands. They are generally endowed with robustness and good ranking ability; however they are highly dependent on training sets. Structure-based techniques generally do not provide the level of accuracy necessary to yield meaningful rankings when applied to GPCR homology models. However, they are essentially independent from training sets and have a sufficient level of accuracy to allow an effective discrimination between binders and nonbinders, thus qualifying as viable lead discovery tools. The combination of ligand and structure-based methodologies in the form of receptor-based 3D-QSAR and ligand and structure-based consensus models results in robust and accurate quantitative predictions. The contribution of the structure-based component to these combined approaches is expected to become more substantial and effective in the future, as more sophisticated scoring functions are developed and more detailed structural information on GPCRs is gathered.

  9. Fcγ receptors and ligands and cardiovascular disease.

    PubMed

    Tanigaki, Keiji; Sundgren, Nathan; Khera, Amit; Vongpatanasin, Wanpen; Mineo, Chieko; Shaul, Philip W

    2015-01-16

    Fcγ receptors (FcγRs) classically modulate intracellular signaling on binding of the Fc region of IgG in immune response cells. How FcγR and their ligands affect cardiovascular health and disease has been interrogated recently in both preclinical and clinical studies. The stimulation of activating FcγR in endothelial cells, vascular smooth muscle cells, and monocytes/macrophages causes a variety of cellular responses that may contribute to vascular disease pathogenesis. Stimulation of the lone inhibitory FγcR, FcγRIIB, also has adverse consequences in endothelial cells, antagonizing NO production and reparative mechanisms. In preclinical disease models, activating FcγRs promote atherosclerosis, whereas FcγRIIB is protective, and activating FcγRs also enhance thrombotic and nonthrombotic vascular occlusion. The FcγR ligand C-reactive protein (CRP) has undergone intense study. Although in rodents CRP does not affect atherosclerosis, it causes hypertension and insulin resistance and worsens myocardial infarction. Massive data have accumulated indicating an association between increases in circulating CRP and coronary heart disease in humans. However, Mendelian randomization studies reveal that CRP is not likely a disease mediator. CRP genetics and hypertension warrant further investigation. To date, studies of genetic variants of activating FcγRs are insufficient to implicate the receptors in coronary heart disease pathogenesis in humans. However, a link between FcγRIIB and human hypertension may be emerging. Further knowledge of the vascular biology of FcγR and their ligands will potentially enhance our understanding of cardiovascular disorders, particularly in patients whose greater predisposition for disease is not explained by traditional risk factors, such as individuals with autoimmune disorders.

  10. Highly Pathogenic Influenza A(H5Nx) Viruses with Altered H5 Receptor-Binding Specificity

    PubMed Central

    Guo, Hongbo; de Vries, Erik; McBride, Ryan; Dekkers, Jojanneke; Peng, Wenjie; Bouwman, Kim M.; Nycholat, Corwin; Verheije, M. Helene; Paulson, James C.; van Kuppeveld, Frank J.M.

    2017-01-01

    Emergence and intercontinental spread of highly pathogenic avian influenza A(H5Nx) virus clade 2.3.4.4 is unprecedented. H5N8 and H5N2 viruses have caused major economic losses in the poultry industry in Europe and North America, and lethal human infections with H5N6 virus have occurred in Asia. Knowledge of the evolution of receptor-binding specificity of these viruses, which might affect host range, is urgently needed. We report that emergence of these viruses is accompanied by a change in receptor-binding specificity. In contrast to ancestral clade 2.3.4 H5 proteins, novel clade 2.3.4.4 H5 proteins bind to fucosylated sialosides because of substitutions K222Q and S227R, which are unique for highly pathogenic influenza virus H5 proteins. North American clade 2.3.4.4 virus isolates have retained only the K222Q substitution but still bind fucosylated sialosides. Altered receptor-binding specificity of virus clade 2.3.4.4 H5 proteins might have contributed to emergence and spread of H5Nx viruses. PMID:27869615

  11. Ligand Binding Mechanism in Steroid Receptors: From Conserved Plasticity to Differential Evolutionary Constraints.

    PubMed

    Edman, Karl; Hosseini, Ali; Bjursell, Magnus K; Aagaard, Anna; Wissler, Lisa; Gunnarsson, Anders; Kaminski, Tim; Köhler, Christian; Bäckström, Stefan; Jensen, Tina J; Cavallin, Anders; Karlsson, Ulla; Nilsson, Ewa; Lecina, Daniel; Takahashi, Ryoji; Grebner, Christoph; Geschwindner, Stefan; Lepistö, Matti; Hogner, Anders C; Guallar, Victor

    2015-12-01

    Steroid receptor drugs have been available for more than half a century, but details of the ligand binding mechanism have remained elusive. We solved X-ray structures of the glucocorticoid and mineralocorticoid receptors to identify a conserved plasticity at the helix 6-7 region that extends the ligand binding pocket toward the receptor surface. Since none of the endogenous ligands exploit this region, we hypothesized that it constitutes an integral part of the binding event. Extensive all-atom unbiased ligand exit and entrance simulations corroborate a ligand binding pathway that gives the observed structural plasticity a key functional role. Kinetic measurements reveal that the receptor residence time correlates with structural rearrangements observed in both structures and simulations. Ultimately, our findings reveal why nature has conserved the capacity to open up this region, and highlight how differences in the details of the ligand entry process result in differential evolutionary constraints across the steroid receptors.

  12. Biased ligands at G-protein-coupled receptors: promise and progress.

    PubMed

    Violin, Jonathan D; Crombie, Aimee L; Soergel, David G; Lark, Michael W

    2014-07-01

    Drug discovery targeting G protein-coupled receptors (GPCRs) is no longer limited to seeking agonists or antagonists to stimulate or block cellular responses associated with a particular receptor. GPCRs are now known to support a diversity of pharmacological profiles, a concept broadly referred to as functional selectivity. In particular, the concept of ligand bias, whereby a ligand stabilizes subsets of receptor conformations to engender novel pharmacological profiles, has recently gained increasing prominence. This review discusses how biased ligands may deliver safer, better tolerated, and more efficacious drugs, and highlights several biased ligands that are in clinical development. Biased ligands targeting the angiotensin II type 1 receptor and the μ opioid receptor illustrate the translation of the biased ligand concept from basic biology to clinical drug development.

  13. Binding of aromatic amines to the rat hepatic Ah receptor in vitro and in vivo and the 8S and 4S estrogen receptor of rat uterus and rat liver

    SciTech Connect

    Cikryt, P.; Kaiser, T.; Gottlicher, M. )

    1990-08-01

    Studies on structurally related aromatic amines with different carcinogenic properties have shown that 2-acetylaminofluorene (2-AAF) and 2-acetylaminophenanthrene (AAP) inhibit the binding of 2,3,7,8-tetrachlorodibenzo-p-dioxin to the Ah receptor in vitro. The apparent inhibitor constants (K{sub i}) are 2.3 {mu}M for 2-AAF and 2.7 {mu}M for AAP. In contrast, 4-acetylaminofluorene, an isomer of 2-AAF, and trans-4-acetylaminostilbene do not bind to the rat hepatic cytosolic Ah receptor. Pretreating female Wistar rats with 2-AAF or AAP leads to the induction of the P-450 isoenzymes that are under the control of the Ah receptor. Ornithine decarboxylase activity is induced by all aromatic amines tested irrespective of their Ah receptor affinity. The aromatic amines used as model compounds do not inhibit the binding of 17-{beta}-estradiol to the 8S and 4S estrogen receptor of rat uterus or rat liver in a competition assay analyzed using sucrose density gradient centrifugation. On the other hand, the aromatic amines bind to varying extents to another estrogen-binding protein of rat liver whose function and identity is still unknown. The study demonstrates that structurally related aromatic amines in their unmetabolized form interact differentially with a cellular target protein, the Ah receptor, in vitro as well as in vivo. However, a relationship between these effects and the postulated promoting properties of 2-AAF remains to be established.

  14. Exploration of Bivalent Ligands Targeting Putative Mu Opioid Receptor and Chemokine Receptor CCR5 Dimerization

    PubMed Central

    Arnatt, Christopher K.; Falls, Bethany A.; Yuan, Yunyun; Raborg, Thomas J.; Masvekar, Ruturaj R.; El-Hage, Nazira; Selley, Dana E.; Nicola, Anthony V.; Knapp, Pamela E.; Hauser, Kurt F.; Zhang, Yan

    2016-01-01

    Modern antiretroviral therapies have provided HIV-1 infected patients longer lifespans and better quality of life. However, several neurological complications are now being seen in these patients due to HIV-1 associated injury of neurons by infected microglia and astrocytes. In addition, these effects can be further exacerbated with opiate use and abuse. One possible mechanism for such potentiation effects of opiates is the interaction of the mu opioid receptor (MOR) with the chemokine receptor CCR5 (CCR5), a known HIV-1 co-receptor, to form MOR-CCR5 heterodimer. In an attempt to understand this putative interaction and its relevance to neuroAIDS, we designed and synthesized a series of bivalent ligands targeting the putative CCR5-MOR heterodimer. To understand how these bivalent ligands may interact with the heterodimer, biological studies including calcium mobilization inhibition, binding affinity, HIV-1 invasion, and cell fusion assays were applied. In particular, HIV-1 infection assays using human peripheral blood mononuclear cells, macrophages, and astrocytes revealed a notable synergy in activity for one particular bivalent ligand. Further, a molecular model of the putative CCR5-MOR heterodimer was constructed, docked with the bivalent ligand, and molecular dynamics simulations of the complex was performed in a membrane-water system to help understand the biological observation. PMID:27720326

  15. The emerging roles of AhR in physiology and immunity.

    PubMed

    Hao, Nan; Whitelaw, Murray L

    2013-09-01

    The aryl hydrocarbon receptor (AhR) is traditionally defined as a transcriptional regulator involved in adaptive xenobiotic response, however, emerging evidence supports physiological functions of AhR in normal cell development and immune response. The role of AhR in immunomodulation is multi-dimensional. On the one hand, activation of AhR by TCDD and other ligands leads to profound immunosuppression, potentially via skewed Th1/Th2 cell balance toward Th1 dominance, and boosted Treg cell differentiation. On the other hand, activation of AhR can also induce Th17 cell polarization and increase the severity of autoimmune disease. In addition to T lymphocytes, the AhR also appears to play a vital role in B cell maturation, and regulates the activity of macrophages, dendritic cells and neutrophils following lipopolysaccharide challenge or influenza virus infection. In these scenarios, activation of AhR is associated with decreased host response and reduced survival. Furthermore, gene knock out studies suggest that AhR is indispensable for the postnatal maintenance of intestinal intraepithelial lymphocytes and skin-resident dendritic epidermal gamma delta T cells, providing a potential link between AhR and gut immunity and wound healing. It is well accepted that the magnitude and the type of immune response is dependent on the local cytokine milieu and the AhR appears to be one of the key factors involved in the fine turning of this cytokine balance.

  16. Ah receptor, CYP1A1, CYP1A2 and CYP1B1 gene polymorphisms are not involved in the risk of recurrent pregnancy loss.

    PubMed

    Saijo, Y; Sata, F; Yamada, H; Suzuki, K; Sasaki, S; Kondo, T; Gong, Y Y; Kato, E H; Shimada, S; Morikawa, M; Minakami, H; Kishi, R

    2004-10-01

    The etiology of recurrent pregnancy loss (RPL) remains unclear, but it may be related to a possible genetic predisposition together with involvement of environmental factors. We examined the relation between RPL and polymorphisms in four genes, human aryl hydrocarbon (Ah) receptor, cytochrome P450 (CYP) 1A1, CYP1A2 and CYP1B1, which are involved in the metabolism of a wide range of environmental toxins and carcinogens. All cases and controls were women resident in Sapporo, Japan and the surrounding area. The Ah receptor, CYP1A1, CYP1A2 and CYP1B1 genotypes were assessed in 113 Japanese women with recurrent pregnancy loss (RPL) and 203 ethnically matched women experiencing at least one live birth and no spontaneous abortion (control). No significant differences in Ah receptor, CYP1A1, CYP1A2 and CYP1B1 genotype frequencies were found between the women with RPL and the controls [Ah receptor: Arg/Arg (reference); Arg/Lys and Lys/Lys, odds ratio (OR)=0.67; 95% confidence interval (CI)=0.40-1.11, CYP1A1: m1m1 (reference); m1m2 and m2m2, OR = 0.86; 95% CI = 0.53-1.40, CYP1A2: C/C and C/A (reference); A/A, OR = 1.16; 95% CI = 0.71-1.88, CYP1B1: Leu/Leu (reference); Leu/Val and Val/Val, OR = 1.18; 95% CI = 0.68-2.02]. The present study suggests that the Ah receptor, CYP1A1, CYP1A2 and CYP1B1 gene polymorphisms are not major genetic regulators in RPL.

  17. Structure of the homodimeric androgen receptor ligand-binding domain

    PubMed Central

    Nadal, Marta; Prekovic, Stefan; Gallastegui, Nerea; Helsen, Christine; Abella, Montserrat; Zielinska, Karolina; Gay, Marina; Vilaseca, Marta; Taulès, Marta; Houtsmuller, Adriaan B.; van Royen, Martin E.; Claessens, Frank; Fuentes-Prior, Pablo; Estébanez-Perpiñá, Eva

    2017-01-01

    The androgen receptor (AR) plays a crucial role in normal physiology, development and metabolism as well as in the aetiology and treatment of diverse pathologies such as androgen insensitivity syndromes (AIS), male infertility and prostate cancer (PCa). Here we show that dimerization of AR ligand-binding domain (LBD) is induced by receptor agonists but not by antagonists. The 2.15-Å crystal structure of homodimeric, agonist- and coactivator peptide-bound AR-LBD unveils a 1,000-Å2 large dimerization surface, which harbours over 40 previously unexplained AIS- and PCa-associated point mutations. An AIS mutation in the self-association interface (P767A) disrupts dimer formation in vivo, and has a detrimental effect on the transactivating properties of full-length AR, despite retained hormone-binding capacity. The conservation of essential residues suggests that the unveiled dimerization mechanism might be shared by other nuclear receptors. Our work defines AR-LBD homodimerization as an essential step in the proper functioning of this important transcription factor. PMID:28165461

  18. IDENTIFICATION OF VDR ANTAGONISTS AMONG NUCLEAR RECEPTOR LIGANDS USING VIRTUAL SCREENING

    PubMed Central

    Teske, Kelly; Nandhikonda, Premchendar; Bogart, Jonathan W.; Feleke, Belaynesh; Sidhu, Preetpal; Yuan, Nina; Preston, Joshua; Goy, Robin; Han, Lanlan; Silvaggi, Nicholas R; Singh, Rakesh K.; Bikle, Daniel D.; Cook, James M.; Arnold, Leggy A.

    2014-01-01

    Herein, we described the development of two virtual screens to identify new vitamin D receptor (VDR) antagonists among nuclear receptor (NR) ligands. Therefore, a database of 14330 nuclear receptor ligands and their NR affinities was assembled using the online available “Binding Database”. Two different virtual screens were carried out in conjunction with a reported VDR crystal structure applying a stringent and less stringent pharmacophore model to filter docked NR ligand conformations. The pharmacophore models were based on the spatial orientation of the hydroxyl functionalities of VDR’s natural ligands 1,25(OH2)D3 and 25(OH2)D3. The first virtual screen identified 32 NR ligands with a calculate free energy of VDR binding of more than −6.0 kJ/mol. All but nordihydroguaiaretic acid (NDGA) are VDR ligands, which inhibited the interaction between VDR and coactivator peptide SRC2-3 with an IC50 value of 15.8 µM. The second screen identified 162 NR ligands with a calculate free energy of VDR binding of more than −6.0 kJ/mol. More than half of these ligands were developed to bind VDR followed by ERα/β ligands (26%), TRα/β ligands (7%) and LxRα/β ligands (7%). The binding between VDR and ERα ligand H6036 as well as TRα/β ligand triiodothyronine and a homoserine analog thereof was confirmed by fluorescence polarization. PMID:25419525

  19. Ligand binding by recombinant domains from insect ecdysone receptors.

    PubMed

    Graham, L D; Johnson, W M; Pawlak-Skrzecz, A; Eaton, R E; Bliese, M; Howell, L; Hannan, G N; Hill, R J

    2007-06-01

    The ligand binding domains (LBDs) from the EcR and USP proteins of four insect pests (Lucilia cuprina, Myzus persicae, Bemisia tabaci, Helicoverpa armigera) were purified as recombinant heterodimers. The K(d) values for [(3)H]-ponasterone A binding by LBD heterodimers that included the hinge regions (i.e., DE/F heterodimers) ranged 0.7-2.5 nM, with K(i) values for ecdysteroid and dibenzoylhydrazine ligands ranging from 0.1 nM to >448 microM. The K(d) and K(i) values for a recombinant H. armigera LBD heterodimer that lacked D-regions (i.e., an E/F heterodimer) were approximately 4 times higher than those for its DE/F counterpart. Rate constants were estimated for the L. cuprina LBD heterodimer. A fluorescein-inokosterone conjugate (K(i)~40 nM) was used to develop a novel binding assay based on fluorescence polarization. This assay, which ranked the affinity of competitor ecdysteroids in the same order as the [(3)H]-ponasterone A binding assay, is well suited to high-throughput screening. Ponasterone A had a higher affinity than muristerone A for the recombinant hemipteran LBD heterodimers, whereas the reverse was true for the recombinant dipteran one. The same preference was observed when these ligands were tested as inducers of ecdysone receptor-controlled gene expression in transfected mammalian cells. The binding data obtained in vitro using recombinant LBD heterodimers reflects the ability of agonists to induce transgene expression in recombinant mammalian cells, and can also reflect their efficacy as larvicides.

  20. Novel photoaffinity ligands for the GA-receptor

    SciTech Connect

    Suttle, J.C.; Hultstrand, J.F.; Tanaka, F.S. )

    1990-05-01

    Previous studies from this laboratory have shown that certain N-substituted phthalimides (NSPs) exhibit GA-like activity in a range of specific bioassays and that bioactive NSPs compete with ({sup 3}H)-GA{sub 4} for soluble binding sites in cucumber homogenates. As such, these compounds may prove useful in the purification and characterization of GA receptor proteins. To this end, five azido-NSPs have been synthesized and are currently being screened for biological activity and photochemical stability. Three azido-NSPs elicit {alpha}-amylase production in barley half-seeds and stimulate tissue elongation in d{sub 5} maize, lettuce, sunflower, and soybean. Further evaluations are in progress and these data as well as the utility of these compounds as photo-affinity ligands will be discussed.

  1. Functional phylogenetics reveals contributions of pleiotropic peptide action to ligand-receptor coevolution

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The evolution of peptidergic signaling has been accompanied by a significant degree of ligand-receptor coevolution. Closely related clusters of peptide signaling molecules are observed to activate related groups of receptors, implying that genes encoding these ligands may orchestrate an array of fu...

  2. Autocrine ligand binding to cell receptors. Mathematical analysis of competition by solution "decoys".

    PubMed Central

    Forsten, K E; Lauffenburger, D A

    1992-01-01

    Autocrine ligands have been demonstrated to regulate cell proliferation, cell adhesion, and cell migration in a number of different systems and are believed to be one of the underlying causes of malignant cell transformation. Binding of these ligands to their cellular receptors can be compromised by diffusive transport of ligand away from the secreting cell. Exogenous addition of antibodies or solution receptors capable of competing with cellular receptors for these autocrine ligands has been proposed as a means of inhibiting autocrine-stimulated cell behavioral responses. Such "decoys" complicate cellular binding by offering alternative binding targets, which may also be capable of aiding or abating transport of the ligand away from the cell surface. We present a mathematical model incorporating autocrine ligand production and the presence of competing cellular and solution receptors. We elucidate effects of key system parameters including ligand diffusion rate, binding rate constants, cell density, and secretion rate on the ability of solution receptors to inhibit cellular receptor binding. Both plated and suspension cell systems are considered. An approximate analytical expression relating the key parameters to the critical concentration of solution "decoys" required for inhibition is derived and compared to the numerical calculations. We find that in order to achieve essentially complete inhibition of surface receptor binding, the concentration of decoys may need to be as much as four to eight orders of magnitude greater than the equilibrium disociation constant for ligand binding to surface receptors. PMID:1312367

  3. Imaging of a glioma using peripheral benzodiazepine receptor ligands

    SciTech Connect

    Starosta-Rubinstein, S.; Ciliax, B.J.; Penney, J.B.; McKeever, P.; Young, A.B.

    1987-02-01

    Two types of benzodiazepine receptors have been demonstrated in mammalian tissues, one which is localized on neuronal elements in brain and the other, on glial cells and in peripheral tissues such as kidney. In vivo administration of /sup 3/H-labeled PK 11195 (1-(2-chlorophenyl-N-methyl-N-(1-methylpropyl)-3-isoquinoline carboxamide) or (/sup 3/H)flunitrazepam with 5 mg of clonazepam per kg to rats with intracranial C6 gliomas resulted in high levels of tritiated-drug binding to the tumor as shown by quantitative autoradiography. Pharmacological studies indicated that the bound drugs labeled the peripheral benzodiazepine binding site. Binding to the peripheral benzodiazepine site was confirmed primarily to malignant cells with little binding to adjacent normal brain tissue or to necrotic tissue. Tumor cell binding was completely inhibited by preadministration of the peripheral benzodiazepine blocking agent PK 11195 at 5 mg/kg. The centrally selective benzodiazepine ligand clonazepam had no effect on PK 11195 binding to the tumor cells. When binding to other tumor cell lines grown in nude mice and nude athymic rats was evaluated, little or no peripheral benzodiazepine binding was detected on human pheochromocytoma (RN1) and neuroblastoma (SK-N-MC, SK-N-SH) tumor cells, respectively. However, high densities of peripheral benzodiazepine binding sites were observed on tumors derived from a human glioma cell line (ATCC HTB 14, U-87 MG). The presence of high concentrations of specific peripheral benzodiazepine receptors on glial tumors suggests that human primary central nervous system tumors could be imaged and diagnosed using peripheral benzodiazepine ligands labeled with positron- or gamma-emitting isotopes.

  4. The tryptophan-derived endogenous arylhydrocarbon receptor ligand 6-formylindolo[3,2-b]carbazole (FICZ) is a nanomolar UVA-photosensitizer in epidermal keratinocytes

    PubMed Central

    Williams, Joshua D.; Cabello, Christopher M.; Qiao, Shuxi; Wondrak, Georg T.

    2014-01-01

    Endogenous UVA-chromophores may act as sensitizers of oxidative stress underlying cutaneous photoaging and photocarcinogenesis, but the molecular identity of non-DNA key chromophores displaying UVA-driven photodyamic activity in human skin remains largely undefined. Here we report that 6-formylindolo[3,2-b]carbazole (FICZ), a tryptophan photoproduct and endogenous high affinity aryl hydrocarbon receptor (AhR) agonist, acts as a nanomolar photosensitizer potentiating UVA-induced oxidative stress irrespective of AhR ligand activity. In human HaCaT and primary epidermal keratinocytes, photodynamic induction of apoptosis was elicited by the combined action of solar simulated UVA and FICZ, whereas exposure to the isolated action of UVA or FICZ did not impair viability. In a human epidermal tissue reconstruct, FICZ/UVA-cotreatment caused pronounced phototoxicity inducing keratinocyte cell death, and FICZ photodynamic activity was also substantiated in a murine skin exposure model. Array analysis revealed pronounced potentiation of cellular heat shock, ER stress, and oxidative stress response gene expression observed only upon FICZ/UVA-cotreatment. FICZ photosensitization caused intracellular oxidative stress, and comet analysis revealed introduction of formamidopyrimidine-DNA glycosylase (FPG)-sensitive oxidative DNA lesions suppressible by antioxidant cotreatment. Taken together, our data demonstrate that the endogenous AhR ligand FICZ displays nanomolar photodynamic activity representing a molecular mechanism of UVA-induced photooxidative stress potentially operative in human skin. PMID:25431849

  5. Development of radioiodinated receptor ligands for cerebral single photon emission tomography

    SciTech Connect

    Knapp, F.F. Jr.; McPherson, D.W.

    1992-01-01

    In the last decade the use of radiolabeled ligands for the imaging of cerebral receptors by emission computed tomography (ECT) has seen rapid growth. The opportunity to routinely perform cerebral single photon emission tomography (SPET) with iodine-123-labeled ligands depends on the availability of receptor ligands into which iodine can be introduced without decreasing the required high target receptor specificity. The use of iodine-123-labeled receptor-specific ligands also depends on the availability of high purity iodine-123 at reasonable costs and the necessary imaging instrumentation. In this paper, the development and current stage of evaluation of various iodine-123-labeled ligands for SPET imaging of dopaminergic, serotonergic and muscarinic acetylcholinergic receptor classes are discussed.

  6. Development of radioiodinated receptor ligands for cerebral single photon emission tomography

    SciTech Connect

    Knapp, F.F. Jr.; McPherson, D.W.

    1992-03-01

    In the last decade the use of radiolabeled ligands for the imaging of cerebral receptors by emission computed tomography (ECT) has seen rapid growth. The opportunity to routinely perform cerebral single photon emission tomography (SPET) with iodine-123-labeled ligands depends on the availability of receptor ligands into which iodine can be introduced without decreasing the required high target receptor specificity. The use of iodine-123-labeled receptor-specific ligands also depends on the availability of high purity iodine-123 at reasonable costs and the necessary imaging instrumentation. In this paper, the development and current stage of evaluation of various iodine-123-labeled ligands for SPET imaging of dopaminergic, serotonergic and muscarinic acetylcholinergic receptor classes are discussed.

  7. Ligand Receptor-Mediated Regulation of Growth in Plants.

    PubMed

    Haruta, Miyoshi; Sussman, Michael R

    2017-01-01

    Growth and development of multicellular organisms are coordinately regulated by various signaling pathways involving the communication of inter- and intracellular components. To form the appropriate body patterns, cellular growth and development are modulated by either stimulating or inhibiting these pathways. Hormones and second messengers help to mediate the initiation and/or interaction of the various signaling pathways in all complex multicellular eukaryotes. In plants, hormones include small organic molecules, as well as larger peptides and small proteins, which, as in animals, act as ligands and interact with receptor proteins to trigger rapid biochemical changes and induce the intracellular transcriptional and long-term physiological responses. During the past two decades, the availability of genetic and genomic resources in the model plant species, Arabidopsis thaliana, has greatly helped in the discovery of plant hormone receptors and the components of signal transduction pathways and mechanisms used by these immobile but highly complex organisms. Recently, it has been shown that two of the most important plant hormones, auxin and abscisic acid (ABA), act through signaling pathways that have not yet been recognized in animals. For example, auxins stimulate cell elongation by bringing negatively acting transcriptional repressor proteins to the proteasome to be degraded, thus unleashing the gene expression program required for increasing cell size. The "dormancy" inducing hormone, ABA, binds to soluble receptor proteins and inhibits a specific class of protein phosphatases (PP2C), which activates phosphorylation signaling leading to transcriptional changes needed for the desiccation of the seeds prior to entering dormancy. While these two hormone receptors have no known animal counterparts, there are also many similarities between animal and plant signaling pathways. For example, in plants, the largest single gene family in the genome is the protein kinase

  8. From α4β2 Nicotinic Ligands to the Discovery of σ1 Receptor Ligands: Pharmacophore Analysis and Rational Design.

    PubMed

    Yu, Li-Fang; Zhang, Han-Kun; Gunosewoyo, Hendra; Kozikowski, Alan P

    2012-12-13

    Comparative analyses of the pharmacophoric elements required for σ1 and nicotinic ligands led to the identification of a potent and selective σ1 ligand (15). Compound 15 displayed high selectivity for the σ1 receptor (Ki, σ1 = 4.1 nM, Ki, σ2 = 1312 nM) with moderate binding affinity for the DAT (Ki = 373 nM) and NET (Ki = 203 nM) in the PDSP broad screening panel of common CNS neurotransmitter transporters and receptors. The key finding in this present work is that a subtle structural modifica tion could be used as a tool to switch a ligand's selectivity between nAChRs and sigma receptors.

  9. Muscarinic acetylcholine receptors: location of the ligand binding site

    SciTech Connect

    Hulme, E.; Wheatley, M.; Curtis, C.; Birdsall, N.

    1987-05-01

    The key to understanding the pharmacological specificity of muscarinic acetylcholine receptors (mAChR's) is the location within the receptor sequence of the amino acid residues responsible for ligand binding. To approach this problem, they have purified mAChR's from rat brain to homogeneity by sequential ion-exchange chromatography, affinity chromatography and molecular weight fractionation. Following labelling of the binding site with an alkylating affinity label, /sup 3/H-propylbenzilycholine mustard aziridinium ion (/sup 3/H-PrBCM), the mAChR was digested with a lysine-specific endoproteinase, and a ladder of peptides of increasing molecular weight, each containing the glycosylated N-terminus, isolated by chromatography on wheat-germ agglutinin sepharose. The pattern of labelling showed that a residue in the peptides containing transmembrane helices 2 and/or 3 of the mAChR was alkylated. The linkage was cleaved by 1 M hydroxylamine, showing that /sup 3/H-PrBCM was attached to an acidic residue, whose properties strongly suggested it to be embedded in a hydrophobic intramembrane region of the mAChR. Examination of the cloned sequence of the mAChR reveals several candidate residues, the most likely of which is homologous to an aspartic acid residue thought to protonate the retinal Schiff's base in the congeneric protein rhodopsin.

  10. Labeling of receptor ligands and other compounds with halogen radionuclides

    SciTech Connect

    Welch, M.J. . Edward Mallinckrodt Inst. of Radiology)

    1989-08-01

    Major advances have been made in all the areas. Specifically, patient studies have been carried out. This work has shown that the uptake of fluorine-18 labeled 16{alpha}-fluoroestradiol-17{beta} correlates well with receptor levels measured in vivo and also that the uptake of the tracer is blocked in humans by the administration of the antiestrogen tamoxifen. An image from this work was designated Image of the Year by Dr. Wagner, Jr., following his summary of the 1987 Society of Nuclear Medicine Meeting. We have also evaluated the brain uptake of both estrogen and progesterone, and this work was awarded the Berson-Yalow Award from the Society of Nuclear Medicine in 1988. This publication represents a new application of radiolabeled sex hormones. Hines and coworkers have suggested that hormone levels in the brain are important for sexual differentiation of human behavior. We have shown that both 16{alpha}-(F-18)-fluoroestradiol-17{beta} and 21-(F-18)-fluoro-16{alpha}-ethyl-19-norprogesterone (FENP) accumulate in the hypothalamus and pituitary tissues of primates and humans; and in primates this uptake can be blocked by administration of nonradioactive competing ligands. This presents an opportunity for studying sex hormone receptors in mammalian brain.

  11. Argos inhibits epidermal growth factor receptor signalling by ligand sequestration.

    PubMed

    Klein, Daryl E; Nappi, Valerie M; Reeves, Gregory T; Shvartsman, Stanislav Y; Lemmon, Mark A

    2004-08-26

    The epidermal growth factor receptor (EGFR) has critical functions in development and in many human cancers. During development, the spatial extent of EGFR signalling is regulated by feedback loops comprising both well-understood activators and less well-characterized inhibitors. In Drosophila melanogaster the secreted protein Argos functions as the only known extracellular inhibitor of EGFR, with clearly identified roles in multiple stages of development. Argos is only expressed when the Drosophila EGFR (DER) is activated at high levels, and downregulates further DER signalling. Although there is ample genetic evidence that Argos inhibits DER activation, the biochemical mechanism has not been established. Here we show that Argos inhibits DER signalling without interacting directly with the receptor, but instead by sequestering the DER-activating ligand Spitz. Argos binds tightly to the EGF motif of Spitz and forms a 1:1 (Spitz:Argos) complex that does not bind DER in vitro or at the cell surface. Our results provide an insight into the mechanism of Argos function, and suggest new strategies for EGFR inhibitor design.

  12. Cell-based assays for screening androgen receptor ligands

    PubMed Central

    Campana, Carmela; Pezzi, Vincenzo; Rainey, William E

    2015-01-01

    The androgen receptor (AR, NR3C4), mediates the majority of androgen effects on target cells. The AR is activated following ligand binding that result in activation of target gene transcription. Several cell based model systems have been developed that allow sensitive detection and monitoring of steroids or other compounds with AR bioactivity. Most cell based AR reporter models use transgenic gene constructs that include an androgen response element (ARE) that controls reporter gene expression. The DNA cis-regulatory elements that respond to AR share sequence similarity with cis-regulatory elements for glucocorticoid (GR, NR3C1), mineralocorticoid (MR, NR3C2) and progesterone (PGR, NR3C3) receptors, which has compromised AR selectivity for some models. In recent years, the sensitivity and selectivity of AR bioassays have been significantly improved through careful selection of cell models, utilization of improved reporter genes and the use of yeast two hybrid AR systems. This review summarizes and compares the currently available androgen-responsive cell model systems. PMID:26036905

  13. Development of a photoactivatable allosteric ligand for the m1 muscarinic acetylcholine receptor.

    PubMed

    Davie, Briana J; Sexton, Patrick M; Capuano, Ben; Christopoulos, Arthur; Scammells, Peter J

    2014-10-15

    The field of G protein-coupled receptor drug discovery has benefited greatly from the structural and functional insights afforded by photoactivatable ligands. One G protein-coupled receptor subfamily for which photoactivatable ligands have been developed is the muscarinic acetylcholine receptor family, though, to date, all such ligands have been designed to target the orthosteric (endogenous ligand) binding site of these receptors. Herein we report the synthesis and pharmacological investigation of a novel photoaffinity label, MIPS1455 (4), designed to bind irreversibly to an allosteric site of the M1 muscarinic acetylcholine receptor; a target of therapeutic interest for the treatment of cognitive deficits. MIPS1455 may be a valuable molecular tool for further investigating allosteric interactions at this receptor.

  14. Acetylcholine receptors and cholinergic ligands: biochemical and genetic aspects in Torpedo californica and Drosophila melanogaster

    SciTech Connect

    Rosenthal, L.S.

    1987-01-01

    This study evaluates the biochemical and genetic aspects of the acetylcholine receptor proteins and cholinergic ligands in Drosophila melanogaster and Torpedo californica. Included are (1) a comparative study of nicotinic ligand-induced cation release from acetylcholine receptors isolated from Torpedo californica and from Drosophila melanogaster, (2) solution studies of the cholinergic ligands, nikethamide and ethamivan, aimed at measuring internal molecular rotational barriers in solvents of different polarity; and (3) the isolation and characterization of the gene(s) for the acetylcholine receptor in Drosophila melasogaster. Acetylcholine receptor proteins isolated from Drosphila melanogaster heads were found to behave kinetically similar (with regards to cholinergic ligand-induced /sup 155/Eu:/sup 3 +/ displacement from prelabeled proteins) to receptor proteins isolated from Torpedo californica electric tissue, providing additional biochemical evidence for the existence of a Drosophila acetylcholine receptor.

  15. Design and synthesis of dual 5-HT1A and 5-HT7 receptor ligands.

    PubMed

    Ofori, Edward; Zhu, Xue Y; Etukala, Jagan R; Peprah, Kwakye; Jordan, Kamanski R; Adkins, Adia A; Bricker, Barbara A; Kang, Hye J; Huang, Xi-Ping; Roth, Bryan L; Ablordeppey, Seth Y

    2016-08-15

    5-HT1A and 5-HT7 receptors have been at the center of discussions recently due in part to their major role in the etiology of major central nervous system diseases such as depression, sleep disorders, and schizophrenia. As part of our search to identify dual targeting ligands for these receptors, we have carried out a systematic modification of a selective 5HT7 receptor ligand culminating in the identification of several dual 5-HT1A and 5-HT7 receptor ligands. Compound 16, a butyrophenone derivative of tetrahydroisoquinoline (THIQ), was identified as the most potent agent with low nanomolar binding affinities to both receptors. Interestingly, compound 16 also displayed moderate affinity to other clinically relevant dopamine receptors. Thus, it is anticipated that compound 16 may serve as a lead for further exploitation in our quest to identify new ligands with the potential to treat diseases of CNS origin.

  16. Fluorescent Approaches for Understanding Interactions of Ligands with G Protein Coupled Receptors

    PubMed Central

    Sridharan, Rajashri; Zuber, Jeffrey; Connelly, Sara M.; Mathew, Elizabeth; Dumont, Mark E.

    2014-01-01

    G Protein Coupled Receptors (GPCRs) are responsible for a wide variety of signaling responses in diverse cell types. Despite major advances in the determination of structures of this class of receptors, the underlying mechanisms by which binding of different types of ligands specifically elicits particular signaling responses remains unclear. The use of fluorescence spectroscopy can provide important information about the process of ligand binding and ligand dependent conformational changes in receptors, especially kinetic aspects of these processes, that can be difficult to extract from x-ray structures. We present an overview of the extensive array of fluorescent ligands that have been used in studies of GPCRs and describe spectroscopic approaches for assaying binding and probing the environment of receptor-bound ligands with particular attention to examples involving yeast pheromone receptors. In addition, we discuss the use of fluorescence spectroscopy for detecting and characterizing conformational changes in receptors induced by the binding of ligands. Such studies have provided strong evidence for diversity of receptor conformations elicited by different ligands, consistent with the idea that GPCRs are not simple on and off switches. This diversity of states constitutes an underlying mechanistic basis for biased agonism, the observation that different stimuli can produce different responses from a single receptor. It is likely that continued technical advances will allow fluorescence spectroscopy to play an important role in continued probing of structural transitions in GPCRs. PMID:24055822

  17. Effects of scorched food leachates with or without activated charcoal pretreatment on AhR activation in cultured cells.

    PubMed

    Takahashi, Satoshi; Morita, Koji; Kinoshita, Makoto; Fujimori, Shin; Ishikawa, Toshio

    2015-12-01

    Aryl hydrocarbon receptor (AhR) is a transcription factor activated by xenobiotics, including dioxins and polycyclic aromatic hydrocarbons (PAHs). Although AhR is also activated by some dietary constituents, it has not been completely clarified in what circumstances AhR ligands are ingested in our daily life. Because PAHs are formed by the incomplete combustion of organic materials, we hypothesized that scorched foods might contain and leach out AhR ligands sufficient to stimulate AhR in vitro. To test this hypothesis, scorched foods (bread, cheese, etc.) were mixed vigorously with water, and the supernatants were retrieved as samples. The samples were added to HepG2 cells stably expressing an AhR-responsive reporter gene. Also, expression of CYP1A1, an endogenous AhR-responsive gene, was analyzed by RT-PCR in different cell lines treated with the samples. We further tested whether pretreatment of the samples with activated charcoal would alter their AhR-stimulating activity. All the supernatant samples tested induced AhR-dependent reporter gene activity and CYP1A1 mRNA expression. In some samples, these inductions were inhibited by pretreatment with activated charcoal. Our findings indicate that scorched food leachates stimulate AhR in cultured cells and that activated charcoal adsorbs the AhR-stimulating substances in some leachates. Thus, people who habitually eat scorched foods are exposed to AhR ligands on a regular basis. Further studies are needed to elucidate whether burnt foods actually exert biological effects on our health.

  18. Cellular approaches to the interaction between cannabinoid receptor ligands and nicotinic acetylcholine receptors.

    PubMed

    Oz, Murat; Al Kury, Lina; Keun-Hang, Susan Yang; Mahgoub, Mohamed; Galadari, Sehamuddin

    2014-05-15

    Cannabinoids are among the earliest known drugs to humanity. Cannabis plant contains various phytochemicals that bind to cannabinoid receptors. In addition, synthetic and endogenously produced cannabinoids (endocannabinoids) constitute other classes of cannabinoid receptor ligands. Although many pharmacological effects of these cannabinoids are mediated by the activation of cannabinoid receptors, recent studies indicate that cannabinoids also modulate the functions of various integral membrane proteins including ion channels, receptors, neurotransmitter transporters, and enzymes by mechanism(s) not involving the activation of known cannabinoid receptors. Currently, the mechanisms of these effects were not fully understood. However, it is likely that direct actions of cannabinoids are closely linked to their lipophilic structures. This report will focus on the actions of cannabinoids on nicotinic acetylcholine receptors and will examine the results of recent studies in this field. In addition some mechanistic approaches will be provided. The results discussed in this review indicate that, besides cannabinoid receptors, further molecular targets for cannabinoids exist and that these targets may represent important novel sites to alter neuronal excitability.

  19. Glucagon-Like Peptide-1 Receptor Ligand Interactions: Structural Cross Talk between Ligands and the Extracellular Domain

    PubMed Central

    West, Graham M.; Willard, Francis S.; Sloop, Kyle W.; Showalter, Aaron D.; Pascal, Bruce D.; Griffin, Patrick R.

    2014-01-01

    Activation of the glucagon-like peptide-1 receptor (GLP-1R) in pancreatic β-cells potentiates insulin production and is a current therapeutic target for the treatment of type 2 diabetes mellitus (T2DM). Like other class B G protein-coupled receptors (GPCRs), the GLP-1R contains an N-terminal extracellular ligand binding domain. N-terminal truncations on the peptide agonist generate antagonists capable of binding to the extracellular domain, but not capable of activating full length receptor. The main objective of this study was to use Hydrogen/deuterium exchange (HDX) to identify how the amide hydrogen bonding network of peptide ligands and the extracellular domain of GLP-1R (nGLP-1R) were altered by binding interactions and to then use this platform to validate direct binding events for putative GLP-1R small molecule ligands. The HDX studies presented here for two glucagon-like peptide-1 receptor (GLP-1R) peptide ligands indicates that the antagonist exendin-4[9-39] is significantly destabilized in the presence of nonionic detergents as compared to the agonist exendin-4. Furthermore, HDX can detect stabilization of exendin-4 and exendin-4[9-39] hydrogen bonding networks at the N-terminal helix [Val19 to Lys27] upon binding to the N-terminal extracellular domain of GLP-1R (nGLP-1R). In addition we show hydrogen bonding network stabilization on nGLP-1R in response to ligand binding, and validate direct binding events with the extracellular domain of the receptor for putative GLP-1R small molecule ligands. PMID:25180755

  20. Potential ligand-binding residues in rat olfactory receptors identified by correlated mutation analysis

    NASA Technical Reports Server (NTRS)

    Singer, M. S.; Oliveira, L.; Vriend, G.; Shepherd, G. M.

    1995-01-01

    A family of G-protein-coupled receptors is believed to mediate the recognition of odor molecules. In order to identify potential ligand-binding residues, we have applied correlated mutation analysis to receptor sequences from the rat. This method identifies pairs of sequence positions where residues remain conserved or mutate in tandem, thereby suggesting structural or functional importance. The analysis supported molecular modeling studies in suggesting several residues in positions that were consistent with ligand-binding function. Two of these positions, dominated by histidine residues, may play important roles in ligand binding and could confer broad specificity to mammalian odor receptors. The presence of positive (overdominant) selection at some of the identified positions provides additional evidence for roles in ligand binding. Higher-order groups of correlated residues were also observed. Each group may interact with an individual ligand determinant, and combinations of these groups may provide a multi-dimensional mechanism for receptor diversity.

  1. Biased ligands for better cardiovascular drugs: dissecting G-protein-coupled receptor pharmacology.

    PubMed

    DeWire, Scott M; Violin, Jonathan D

    2011-07-08

    Drug discovery efforts targeting G-protein-coupled receptors (GPCR) have been immensely successful in creating new cardiovascular medicines. Currently marketed GPCR drugs are broadly classified as either agonists that activate receptors or antagonists that prevent receptor activation by endogenous stimuli. However, GPCR couple to a multitude of intracellular signaling pathways beyond classical G-protein signals, and these signals can be independently activated by biased ligands to vastly expand the potential for new drugs at these classic targets. By selectively engaging only a subset of a receptor's potential intracellular partners, biased ligands may deliver more precise therapeutic benefit with fewer side effects than current GPCR-targeted drugs. In this review, we discuss the history of biased ligand research, the current understanding of how biased ligands exert their unique pharmacology, and how research into GPCR signaling has uncovered previously unappreciated capabilities of receptor pharmacology. We focus on several receptors to illustrate the approaches taken and discoveries made, and how these are steadily illuminating the intricacies of GPCR pharmacology. Discoveries of biased ligands targeting the angiotensin II type 1 receptor and of separable pharmacology suggesting the potential value of biased ligands targeting the β-adrenergic receptors and nicotinic acid receptor GPR109a highlight the powerful clinical promise of this new category of potential therapeutics.

  2. Dose- and time-dependent expression of aryl hydrocarbon receptor (AhR) and aryl hydrocarbon receptor nuclear translocator (ARNT) in PCB-, B[a]P-, and TBT-exposed intertidal copepod Tigriopus japonicus.

    PubMed

    Kim, Bo-Mi; Rhee, Jae-Sung; Hwang, Un-Ki; Seo, Jung Soo; Shin, Kyung-Hoon; Lee, Jae-Seong

    2015-02-01

    The aryl hydrocarbon receptor (AhR) and aryl hydrocarbon nuclear translocator (ARNT) genes from the copepod Tigriopus japonicus (Tj) were cloned to examine their potential functions in the invertebrate putative AhR-CYP signaling pathway. The amino acid sequences encoded by the Tj-AhR and Tj-ARNT genes showed high similarity to homologs of Daphnia and Drosophila, ranging from 68% and 70% similarity for the AhR genes to 56% for the ARNT genes. To determine whether Tj-AhR and Tj-ARNT are modulated by environmental pollutants, transcriptional expression of Tj-AhR and Tj-ARNT was analyzed in response to exposure to five concentrations of polychlorinated biphenyl (PCB 126) (control, 10, 50, 100, 500 μg L(-1)), benzo[a]pyrene (B[a]P) (control, 5, 10, 50, 100 μg L(-1)), and tributyltin (TBT) (control, 1, 5, 10, 20 μg L(-1)) 24h after exposure. A time-course experiment (0, 3, 6, 12, 24h) was performed to analyze mRNA expression patterns after exposure to PCB, B[a]P, and TBT. T. japonicus exhibited dose-dependent and time-dependent upregulation of Tj-AhR and Tj-ARNT in response to pollutant exposure, and the degree of expression was dependent on the pollutant, suggesting that pollutants such as PCB, B[a]P, and TBT modulate expression of Tj-AhR and Tj-ARNT genes in the putative AhR-CYP signaling pathway.

  3. Targeting Ligand-Dependent and Ligand-Independent Androgen Receptor Signaling in Prostate Cancer

    DTIC Science & Technology

    2013-10-01

    sub 10nM range efficacy. Our primary objective was to establish a series of compounds blocking the AR ligand-dependent and ligand-independent gene ...of AR driven genes to be more comprehensive and more in line with what is currently known about AR-driven signaling in prostate cancer. We have...developed a robust panel of genes for AR signaling that is reflective of the clinical findings in both ligand dependent and ligand-independent androgen

  4. Ah Receptor-mediated impairment of interrenal steroidogenesis involves StAR protein and P450scc gene attenuation in rainbow trout.

    PubMed

    Aluru, Neelakanteswar; Renaud, Rick; Leatherland, John F; Vijayan, Mathilakath M

    2005-04-01

    The objective of the study was to investigate the impact of aryl hydrocarbon receptor (AhR) activation on interrenal steroidogenesis in rainbow trout. To this end, fish were fed AhR agonist (beta-naphthoflavone (BNF): 10 mg/kg body mass/day) and antagonist (alpha-naphthoflavone (ANF): 10 mg/kg body mass/day) either singly or in combination (ABNF) for 5 days to elucidate the mechanisms involved in AhR-mediated depression of cortisol production. Liver AhR protein expression was significantly elevated only with ABNF, but not with BNF and ANF compared to the control group. However, all three treatments (BNF, ANF, and ABNF) significantly elevated cytochrome P450 1A1 (CYP1A1) gene and protein expression in the kidney and liver, respectively. Also, these three treatment groups had significantly depressed ACTH-stimulated cortisol production in vitro compared to the control group. This attenuation of interrenal steroidogenesis corresponded with a lower mRNA abundance of steroidogenic acute regulatory (StAR) protein and cytochrome P450 cholesterol side chain cleavage enzyme (P450scc), but not 11beta-hydroxylase. Furthermore, in vitro incubation of head kidney pieces with 7-3H-pregnenolone failed to show any treatment effects on pathways downstream of P450scc, except for a significantly higher conversion to progesterone in the BNF and ANF groups. Plasma cortisol and glucose levels showed no significant change between the treated groups and control, but liver and brain glucocorticoid receptor (GR) protein expression was higher in the BNF group, and ANF abolished this response. Taken together, both BNF and ANF impaired cortisol production, and the mechanism may involve attenuation of StAR and P450scc, the rate limiting steps in steroidogenesis. Overall, endocrine disruption by xenobiotics acting via AhR includes impaired cortisol biosynthesis and abnormal cortisol target tissue GR responses in rainbow trout.

  5. Computational studies of ligand-receptor interactions in bitter taste receptors.

    PubMed

    Miguet, Laurence; Zhang, Ziding; Grigorov, Martin G

    2006-01-01

    Phenylthiocarbamide tastes intensely bitter to some individuals, but others find it completely tasteless. Recently, it was suggested that phenylthiocarbamide elicits bitter taste by interacting with a human G protein-coupled receptor (hTAS2R38) encoded by the PTC gene. The phenylthiocarbamide nontaster trait was linked to three single nucleotide polymorphisms occurring in the PTC gene. Using the crystal structure of bovine rhodopsin as template, we generated the 3D structure of hTAS2R38 bitter taste receptor. We were able to map on the receptor structure the amino acids affected by the genetic polymorphisms and to propose molecular functions for two of them that explained the emergence of the nontaster trait. We used molecular docking simulations to find that phenylthiocarbamide exhibited a higher affinity for the target receptor than the structurally similar molecule 6-n-propylthiouracil, in line with recent experimental studies. A 3D model was constructed for the hTAS2R16 bitter taste receptor as well, by applying the same protocol. We found that the recently published experimental ligand binding affinity data for this receptor correlated well with the binding scores obtained from our molecular docking calculations.

  6. Extracellular loop 2 in the FSH receptor is crucial for ligand mediated receptor activation.

    PubMed

    Dupakuntla, Madhavi; Pathak, Bhakti; Roy, Binita Sur; Mahale, Smita D

    2012-10-15

    The present study aims to determine the role of the specific residues of the extracellular loops (ELs) of the FSH receptor (FSHR) in hormone binding and receptor activation. By substituting the sequences of each of the ELs of human FSHR with those of the luteinizing hormone/choriogonadotropin receptor (LH/CGR), we generated three mutant constructs where the three ELs were individually replaced. A fourth construct had all the three substituted ELs. The receptor expression and hormone binding ability of the mutants were comparable to that of the wild type. Hormone-induced signaling and internalization were lower in the EL2 substitution mutant (EL2M). In this mutant, the EL2 of FSHR was substituted with the corresponding loop of LH/CGR. Interestingly, homology modeling revealed a change in the orientation of EL2 in the mutant receptor. Thus, disruption of EL2 affected overall receptor function, suggesting the role of FSHR specific residues of the loop in ligand mediated signaling.

  7. Ligand binding to nicotinic acetylcholine receptor investigated by surface plasmon resonance.

    PubMed

    Kröger, D; Hucho, F; Vogel, H

    1999-08-01

    Ligand binding to the nicotinic acetylcholine receptor is studied by surface plasmon resonance. Biotinylated bungarotoxin, immobilized on a streptavidin-coated gold film, binds nicotinic acetylcholine receptor both in detergent-solubilized and in lipid vesicle-reconstituted form with high specificity. In the latter case, nonspecific binding to the sensor surface is significantly reduced by reconstituting the receptor into poly(ethylene glycol)-lipid-containing sterically stabilized vesicles. By preincubation of a bulk nicotinic acetylcholine receptor sample with the competing ligands carbamoylcholine and decamethonium bromide, the subsequent specific binding of the receptor to the surface-immobilized bungarotoxin is reduced, depending on the concentration of competing ligand. This competition assay allows the determination of the dissociation constants of the acetylcholine receptor-carbamoylcholine complex. A K(D) = 3.5 × 10(-)(6) M for the detergent-solubilized receptor and a K(D) = 1.4 × 10(-)(5) M for the lipid vesicle-reconstituted receptor are obtained. For decamethonium bromide, a K(D) = 4.5 × 10(-)(5) M is determined for the detergent-solubilized receptor. This approach is of general importance for investigating ligand-receptor interactions in case of small ligand molecules by mass-sensitive techniques.

  8. Trace amine-associated receptors and their ligands

    PubMed Central

    Zucchi, R; Chiellini, G; Scanlan, T S; Grandy, D K

    2006-01-01

    Classical biogenic amines (adrenaline, noradrenaline, dopamine, serotonin and histamine) interact with specific families of G protein-coupled receptors (GPCRs). The term ‘trace amines' is used when referring to p-tyramine, β-phenylethylamine, tryptamine and octopamine, compounds that are present in mammalian tissues at very low (nanomolar) concentrations. The pharmacological effects of trace amines are usually attributed to their interference with the aminergic pathways, but in 2001 a new gene was identified, that codes for a GPCR responding to p-tyramine and β-phenylethylamine but not to classical biogenic amines. Several closely related genes were subsequently identified and designated as the trace amine-associated receptors (TAARs). Pharmacological investigations in vitro show that many TAAR subtypes may not respond to p-tyramine, β-phenylethylamine, tryptamine or octopamine, suggesting the existence of additional endogenous ligands. A novel endogenous thyroid hormone derivative, 3-iodothyronamine, has been found to interact with TAAR1 and possibly other TAAR subtypes. In vivo, micromolar concentrations of 3-iodothyronamine determine functional effects which are opposite to those produced on a longer time scale by thyroid hormones, including reduction in body temperature and decrease in cardiac contractility. Expression of all TAAR subtypes except TAAR1 has been reported in mouse olfactory epithelium, and several volatile amines were shown to interact with specific TAAR subtypes. In addition, there is evidence that TAAR1 is targeted by amphetamines and other psychotropic agents, while genetic linkage studies show a significant association between the TAAR gene family locus and susceptibility to schizophrenia or bipolar affective disorder. PMID:17088868

  9. The Ah regulatory gene product. Survey of nineteen polycyclic aromatic compounds' and fifteen benzo[a]pyrene metabolites' capacity to bind to the cytosolic receptor.

    PubMed

    Bigelow, S W; Nebert, D W

    1982-01-01

    The capacity of 19 polycyclic aromatic compounds and 15 benzo[a]pyrene metabolites to displace [1,6-3H]2,3,7,8-tetrachlorodibenzo-p-dioxine ([3H]TCDD) from the mouse liver cytosolic Ah receptor was examined. We compared our data with various parameters taken from previously published results: the capacity of seven polycyclic hydrocarbons to induce aryl hydrocarbon hydroxylase (AHH) activity in human cell cultures, the capacity of 10 polycyclic hydrocarbons to induce azo dye N-demethylase activity in rat liver, the capacity of 6 polycyclic hydrocarbons to shorten zoxazolamine paralysis times in the intact rat, and the capacity of 15 benzo[a]pyrene metabolites to induce AHH activity in rat hepatoma H-4-II-E cultures. An excellent correlation is seen between the capacity to displace the radioligand from the Ah receptor and the capacity to induce these monooxygenase activities. differences in the rate of cellular uptake and formation of alkali-extractable metabolites of dibenzo[a,h]anthracene, 3-methylcholanthrene, and benzo[a]anthracene in Hepa-1 mouse hepatoma cell cultures do not account for differences in the capacity of these three polycyclic hydrocarbons to displace [3H]TCDD from the Ah receptor.

  10. Triclosan activates aryl hydrocarbon receptor (AhR)-dependent apoptosis and affects Cyp1a1 and Cyp1b1 expression in mouse neocortical neurons.

    PubMed

    Szychowski, Konrad A; Wnuk, Agnieszka; Kajta, Małgorzata; Wójtowicz, Anna K

    2016-11-01

    Triclosan (TCS) is an antimicrobial agent that is used extensively in personal care and in sanitizing products, such as soaps, toothpastes, and hair products. A number of studies have revealed the presence of TCS in human tissues, such as fat, liver and brain, in addition to blood and breast milk. The aim of the present study was to investigate the impact of TCS on AhR and Cyp1a1/Cyp1b1 signaling in mouse neocortical neurons in primary cultures. In addition to the use of selective ligands and siRNAs, expression levels of mRNA and proteins as well as caspase-3 activity, reactive oxygen species (ROS) formation, and lactate dehydrogenase (LDH) release have been measured. We also studied the involvement of the AhR in TCS-induced LDH release and caspase-3 activation as well as the effect of TCS on ROS generation. Cultures of neocortical neurons were prepared from Swiss mouse embryos on day 15/16 of gestation. The cells were cultured in phenol red-free Neurobasal medium with B27 and glutamine, and the neurons were exposed to 1 and 10µM TCS. Our experiments showed that the expression of AhR and Cyp1a1 mRNA decreased in cells exposed to 10µM TCS for 3 or 6h. In the case of Cyp1b1, mRNA expression remained unchanged compared with the control group following 3h of exposure to TCS, but after 6h, the mRNA expression of Cyp1b1 was decreased. Our results confirmed that the AhR is involved in the TCS mechanism of action, and our data demonstrated that after the cells were transfected with AhR siRNA, the cytotoxic and pro-apoptotic properties of TCS were decreased. The decrease in Cyp1a1 mRNA and protein expression levels accompanied by a decrease in its activity. The stimulation of Cyp1a1 activity produced by the application of an AhR agonist (βNF) was attenuated by TCS, whereas the addition of AhR antagonist (αNF) reversed the inhibitory effects of TCS. In our experiments, TCS diminished Cyp1b1 mRNA and enhanced its protein expression. In case of Cyp1a1 we observed

  11. Cell surface receptors for signal transduction and ligand transport - a design principles study

    SciTech Connect

    Shankaran, Harish; Resat, Haluk; Wiley, H. S.

    2007-06-01

    Although many different receptors undergo endocytosis, the system-level design principles that govern the evolution of receptor dynamics are far from fully understood. We have constructed a generalized mathematical model to understand how receptor internalization dynamics encodes receptor function and regulation. Parametric analysis of the response of receptor systems to ligand inputs reveals that receptors can be categorized a being: i) avidity-controlled where the response control depends primarily on the extracelluar ligand capture efficiency, ii) consumption-controlled where the ability to internalize surface-bound ligand is the primary control parameter, and iii) dual-sensitivity where both the avidity and consumption parameters are important. We show that the transferrin and low-density lipoprotein receptors are avidity-controlled, the vitellogenin receptor is consumption-controlled and epidermal growth factor receptor is a dual-sensitivity receptor. Significantly, we show that ligand-induced endocytosis is a mechanism to anhance the accuracy of signaling receptors rather than serving to attenuate signaling. Our analysis reveals that the location of a receptor system in the avidity-consumption parameter space can be used to understand both its function and its regulations.

  12. Ah Receptor Signaling Controls the Expression of Cardiac Development and Homeostasis Genes

    PubMed Central

    Carreira, Vinicius S.; Fan, Yunxia; Wang, Qing; Zhang, Xiang; Kurita, Hisaka; Ko, Chia-I.; Naticchioni, Mindi; Jiang, Min; Koch, Sheryl; Medvedovic, Mario; Xia, Ying; Rubinstein, Jack; Puga, Alvaro

    2015-01-01

    Congenital heart disease (CHD) is the most common congenital abnormality and one of the leading causes of newborn death throughout the world. Despite much emerging scientific information, the precise etiology of this disease remains elusive. Here, we show that the aryl hydrocarbon receptor (AHR) regulates the expression of crucial cardiogenesis genes and that interference with endogenous AHR functions, either by gene ablation or by agonist exposure during early development, causes overlapping structural and functional cardiac abnormalities that lead to altered fetal heart physiology, including higher heart rates, right and left ventricle dilation, higher stroke volume, and reduced ejection fraction. With striking similarity between AHR knockout (Ahr−/−) and agonist-exposed wild type (Ahr+/+) embryos, in utero disruption of endogenous AHR functions converge into dysregulation of molecular mechanisms needed for attainment and maintenance of cardiac differentiation, including the pivotal signals regulated by the cardiogenic transcription factor NKH2.5, energy balance via oxidative phosphorylation and TCA cycle and global mitochondrial function and homeostasis. Our findings suggest that AHR signaling in the developing mammalian heart is central to the regulation of pathways crucial for cellular metabolism, cardiogenesis, and cardiac function, which are potential targets of environmental factors associated with CHD. PMID:26139165

  13. Computational approaches for ligand discovery and design in class-A G protein- coupled receptors.

    PubMed

    Rodríguez, David; Gutiérrez-de-Terán, Hugo

    2013-01-01

    Our structural understanding of the superfamily of G-protein coupled receptors, a group of targets of utmost pharmacological importance, has improved dramatically in the last few years. This was directly translated in an increase of both the number and the relevance of computer-assisted drug design efforts devoted to these receptors. The field, which had been greatly influenced by ligand-based methods, has experienced a radical transformation with a number of successful structure-based ligand design and ligand discovery studies. This revolution has been accompanied by the exponential increase of computational resources, and as a result the scenario in GPCR structural and chemical studies is now more complex and richer than ever. Virtual screens, both structure- and ligand-based, co-exist with accurate computational characterizations of the receptor conformational dynamics and of the energy landscapes of receptor-ligand interactions. We here provide an integrated and updated view of the different computational techniques applied to the ligand design of GPCRs. Particular emphasis is put on the studies that take into account the novel structural information of GPCRs, together with those that consider the enormous amount of chemical information accumulated on these receptors in the last decades. Indeed, we propose that proper combinations of the different computational techniques: ligand-based, structure-based and molecular dynamics studies, should be performed to better integrate all available information whenever possible. With this in mind, a major impact of computational technologies in the ligand design on GPCRs is expected in the forthcoming years.

  14. PPAR-γ receptor ligands: novel therapy for pituitary adenomas

    PubMed Central

    Heaney, Anthony P.; Fernando, Manory; Melmed, Shlomo

    2003-01-01

    Pituitary tumors cause considerable morbidity due to local invasion, hypopituitarism, or hormone hypersecretion. In many cases, no suitable drug therapies are available, and surgical excision is currently the only effective treatment. We show here abundant expression of nuclear hormone receptor PPAR-γ in all of 39 human pituitary tumors. PPAR-γ activating thiazolidinediones (TZDs) rosiglitazone and troglitazone induced G0-G1 cell-cycle arrest and apoptosis in human, rat somatolactotroph, and murine gonadotroph pituitary tumor cells, and suppressed in vitro hormone secretion. In vivo development and growth of murine somatolactotroph and gonadotroph tumors, generated by subcutaneous injection of prolactin-secreting (PRL-secreting) and growth hormone–secreting (GH-secreting) GH3 cells, luteinizing hormone–secreting (LH-secreting) LβT2 cells, and α-T3 cells, was markedly suppressed in rosiglitazone-treated mice, and serum GH, PRL, and LH levels were attenuated in all treated animals (P < 0.009). These results demonstrate that PPAR-γ is an important molecular target in pituitary adenoma cells and PPAR-γ ligands inhibit tumor cell growth and GH, PRL, and LH secretion in vitro and in vivo. TZDs are proposed as novel oral medications for managing pituitary tumors. PMID:12727930

  15. Reliability theory for receptor-ligand bond dissociation

    NASA Astrophysics Data System (ADS)

    Tees, David F. J.; Woodward, John T.; Hammer, David A.

    2001-05-01

    Cell adhesion in the presence of hydrodynamic forces is a critical factor in inflammation, cancer metastasis, and blood clotting. A number of assays have recently been developed to apply forces to small numbers of the receptor-ligand bonds responsible for adhesion. Examples include assays using hydrodynamic shear in flow chambers or elastic probe deflection assays such as the atomic force microscope or the biomembrane force probe. One wishes to use the data on the time distribution of dissociation from these assays to derive information on the force dependence of reaction rates, an important determinant of cell adhesive behavior. The dissociation process can be described using the theory developed for reliability engineering of electronic components and networks. We use this framework along with the Bell model for the reverse reaction rate (kr=kr0exp[r0 f/kT], where f is the applied force and kr0 and r0 are Bell model parameters) to write closed form expressions for the probability distribution of break-up with multiple independent or interacting bonds. These expressions show that the average lifetime of n bonds scales with the nth harmonic number multiplied by the lifetime of a single bond. Results from calculation and simulations are used to describe the effect of experimental procedures in forced unbinding assays on the estimation of parameters for the force dependence of reverse reaction rates.

  16. DDE and PCB 153 independently induce aryl hydrocarbon receptor (AhR) expression in peripheral blood mononuclear cells.

    PubMed

    Gaspar-Ramírez, Octavio; Pérez-Vázquez, Francisco J; Salgado-Bustamante, Mariana; González-Amaro, Roberto; Hernandez-Castro, Berenice; Pérez-Maldonado, Ivan N

    2015-01-01

    Recent studies have demonstrated that compounds inducing pro-inflammatory cytokines enhance AhR expression. The aim of this study was 2-fold: (1) to determine if two pro-inflammatory compounds, dichlorodiphenyldichloroethylene (DDE) and 2,2',4,4',5,5'-hexa-chlorobiphenyl (PCB 153), independently affect AhR gene expression in peripheral blood mononuclear cells (PBMC); and (2) if affected, to determine whether the mechanism involved was due to AhR activation or to a pro-inflammatory effect of the chemicals. PBMC isolated from healthy individuals were incubated in the presence of DDE (10 µg/ml) and PCB 153 (20 ng/ml) over time and AhR and CYP1A1 expression was assessed with a real-time PCR technique. The results indicated there was over-expression of the AhR mRNA in PBMC when the cells were treated with DDE and PCB 153. No changes in expression levels of CYP1A1 mRNA were found. Importantly, when the cells were exposed to DDE and PCB 153 in the presence of an antagonist of tumor necrosis factor (TNF)-α, the over-expression of AhR was abolished; as expected, the expression of CYP1A1 was unaffected. In conclusion, these studies demonstrated for the first time an increment of AhR expression "in vitro" in PBMC treated with two pro-inflammatory environmental pollutants, DDE and PCB153. Moreover, the over-expression of AhR was dependent of TNFα induced by DDE and PCB 153 and was independent of AhR activation.

  17. Transcriptional activation by the thyroid hormone receptor through ligand-dependent receptor recruitment and chromatin remodelling.

    PubMed

    Grøntved, Lars; Waterfall, Joshua J; Kim, Dong Wook; Baek, Songjoon; Sung, Myong-Hee; Zhao, Li; Park, Jeong Won; Nielsen, Ronni; Walker, Robert L; Zhu, Yuelin J; Meltzer, Paul S; Hager, Gordon L; Cheng, Sheue-yann

    2015-04-28

    A bimodal switch model is widely used to describe transcriptional regulation by the thyroid hormone receptor (TR). In this model, the unliganded TR forms stable, chromatin-bound complexes with transcriptional co-repressors to repress transcription. Binding of hormone dissociates co-repressors and facilitates recruitment of co-activators to activate transcription. Here we show that in addition to hormone-independent TR occupancy, ChIP-seq against endogenous TR in mouse liver tissue demonstrates considerable hormone-induced TR recruitment to chromatin associated with chromatin remodelling and activated gene transcription. Genome-wide footprinting analysis using DNase-seq provides little evidence for TR footprints both in the absence and presence of hormone, suggesting that unliganded TR engagement with repressive complexes on chromatin is, similar to activating receptor complexes, a highly dynamic process. This dynamic and ligand-dependent interaction with chromatin is likely shared by all steroid hormone receptors regardless of their capacity to repress transcription in the absence of ligand.

  18. Helix 8 of the ligand binding domain of the glucocorticoid receptor (GR) is essential for ligand binding.

    PubMed

    Deng, Qiong; Waxse, Bennett; Riquelme, Denise; Zhang, Jiabao; Aguilera, Greti

    2015-06-15

    Membrane association of estrogen receptors (ER) depends on cysteine palmitoylation and two leucines in the ligand binding domain (LBD), conserved in most steroid receptors. The role of this region, corresponding to helix 8 of the glucocorticoid receptor (GR) LBD, on membrane association of GR was studied in 4B cells, expressing endogenous GR, and Cos-7 cells transfected EGFP-GR constructs. 4B cells preloaded with radiolabeled palmitic acid showed no radioactivity incorporation into immunoprecipitated GR. Moreover, mutation C683A (corresponding to ER palmitoylation site) did not affect corticosterone-induced membrane association of GR. Mutations L687-690A, L682A, E680G and K685G prevented membrane and also nuclear localization through reduced ligand binding. L687-690A mutation decreased association of GR with heat shock protein 90 and transcriptional activity, without overt effects on receptor protein stability. The data demonstrate that palmitoylation does not mediate membrane association of GR, but that the region 680-690 (helix 8) is critical for ligand binding and receptor function.

  19. Challenges Predicting Ligand-Receptor Interactions of Promiscuous Proteins: The Nuclear Receptor PXR

    PubMed Central

    Ekins, Sean; Kortagere, Sandhya; Iyer, Manisha; Reschly, Erica J.; Lill, Markus A.; Redinbo, Matthew R.; Krasowski, Matthew D.

    2009-01-01

    Transcriptional regulation of some genes involved in xenobiotic detoxification and apoptosis is performed via the human pregnane X receptor (PXR) which in turn is activated by structurally diverse agonists including steroid hormones. Activation of PXR has the potential to initiate adverse effects, altering drug pharmacokinetics or perturbing physiological processes. Reliable computational prediction of PXR agonists would be valuable for pharmaceutical and toxicological research. There has been limited success with structure-based modeling approaches to predict human PXR activators. Slightly better success has been achieved with ligand-based modeling methods including quantitative structure-activity relationship (QSAR) analysis, pharmacophore modeling and machine learning. In this study, we present a comprehensive analysis focused on prediction of 115 steroids for ligand binding activity towards human PXR. Six crystal structures were used as templates for docking and ligand-based modeling approaches (two-, three-, four- and five-dimensional analyses). The best success at external prediction was achieved with 5D-QSAR. Bayesian models with FCFP_6 descriptors were validated after leaving a large percentage of the dataset out and using an external test set. Docking of ligands to the PXR structure co-crystallized with hyperforin had the best statistics for this method. Sulfated steroids (which are activators) were consistently predicted as non-activators while, poorly predicted steroids were docked in a reverse mode compared to 5α-androstan-3β-ol. Modeling of human PXR represents a complex challenge by virtue of the large, flexible ligand-binding cavity. This study emphasizes this aspect, illustrating modest success using the largest quantitative data set to date and multiple modeling approaches. PMID:20011107

  20. From α4β2 Nicotinic Ligands to the Discovery of σ1 Receptor Ligands: Pharmacophore Analysis and Rational Design

    PubMed Central

    2012-01-01

    Comparative analyses of the pharmacophoric elements required for σ1 and nicotinic ligands led to the identification of a potent and selective σ1 ligand (15). Compound 15 displayed high selectivity for the σ1 receptor (Ki, σ1 = 4.1 nM; Ki, σ2 = 1312 nM) with moderate binding affinity for the DAT (Ki = 373 nM) and NET (Ki = 203 nM) in the PDSP broad screening panel of common CNS neurotransmitter transporters and receptors. The key finding in this present work is that a subtle structural modification could be used as a tool to switch a ligand’s selectivity between nAChRs and sigma receptors. PMID:23641311

  1. Sigma-1 receptor ligands: potential in the treatment of neuropsychiatric disorders.

    PubMed

    Hayashi, Teruo; Su, Tsung-Ping

    2004-01-01

    The sigma receptor was originally proposed to be a subtype of the opioid receptor. However, it is now clear that sigma receptors are unique non-opioid, non-phencyclidine brain proteins. Two types of sigma receptor exist, the sigma-1 receptor and the sigma-2 receptor. sigma-1 receptors have been cloned and their distribution, physiological functions and roles in signal transduction were recently characterised. Certain sex hormones in the brain (neurosteroids) are known to interact with sigma-1 receptors. sigma-1 receptors regulate glutamate NMDA receptor function and the release of neurotransmitters such as dopamine. They are thus proposed to be involved in learning and memory as well as in certain neuropsychiatric disorders. Selective sigma-1 receptor ligands have been suggested to represent a new class of therapeutic agents for neuropsychiatric disorders, although none have yet been introduced into therapeutic use. Early studies showed that psychotomimetic benzomorphans, as well as several antipsychotics, can bind to sigma-1 receptors. As a result of these findings, sigma-1 receptor ligands have been proposed as being of potential use in the treatment of schizophrenia. Nevertheless, the relationship of sigma-1 receptors to the underlying pathogenesis of schizophrenia is still unclear. sigma-1 receptor ligands have failed to improve acute psychotic symptoms of schizophrenia in clinical trials, but, interestingly, a few studies have shown an improvement in negative symptoms in schizophrenic patients. A number of preclinical studies have shown that selective agonists of sigma-1 receptors affect higher-ordered brain functions such as learning and memory, cognition and mood. These studies indicate that sigma-1 receptor agonists may exert therapeutic effects in depression and senile dementia. Indeed, the sigma-1 receptor agonist igmesine, has been shown to improve depression in a clinical trial. The most distinctive feature of the action of sigma-1 receptor ligands is

  2. Inhibition of osteoclast formation by 3-methylcholanthrene, a ligand for arylhydrocarbon receptor: suppression of osteoclast differentiation factor in osteogenic cells.

    PubMed

    Naruse, M; Otsuka, E; Naruse, M; Ishihara, Y; Miyagawa-Tomita, S; Hagiwara, H

    2004-01-01

    We investigated the effects of 3-methylcholanthrene (3MC), a ligand for arylhydrocarbon receptor (AhR), on osteoclastogenesis. Osteoclast-like cells, in cocultures with mouse spleen cells and clonal osteogenic stromal ST2 cells, are formed from spleen cells by a combination of the receptor activator of nuclear factor-kappaB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF) produced by ST2 cells in response to 1alpha,25(OH)(2) Vitamin D(3). 3MC dose-dependently inhibited the formation of mono- and multinuclear osteoclast-like cells. However, 3MC did not inhibit the formation of osteoclast-like cells from mouse spleen cells which was supported by the exogenous soluble RANKL and M-CSF. 3MC did not affect the formation of an actin ring and pits on slices of dentine by osteoclast-like cells, both of which are typical indices of osteoclast activity. These results suggest that 3MC affects osteoclast-supporting cells such as ST2 cells but not osteoclast precursor cells and mature osteoclastic cells. When we measured the expression levels of RANKL mRNA in ST2 cells, 3MC dose-dependently decreased the level of this mRNA. However, 3MC did not affect levels of mRNAs for osteoprotegerin (OPG), M-CSF, and the receptor of 1alpha,25(OH)(2) Vitamin D(3) in ST2 cells. Furthermore, soluble RANKL was able to counteract the inhibitory effect of 3MC on the formation of osteoclast-like cells. Our findings indicate that 3MC inhibits osteoclastogenesis via the inhibition of RANKL expression in osteoblastic cells.

  3. Molecular Mechanism of Dioxin Action: Molecular Cloning of the Ah Receptor Using a DNA Recognition Site Probe

    DTIC Science & Technology

    1992-01-13

    analysis of AhR binding to the DRE (see attached manuscript an the following brief description of these results) and have bequn the library screening . Although...relatively rapidly as to whether they represent AhR clones or not. As mentioned above, we have only recently begun the library screening . We have obtained a...DNA oligonucleotides, identify the DRE oligonucleotide with the highest binding affinity, optimize the screening protocol and begin the actual library

  4. Molecular modeling study of the differential ligand-receptor interaction at the μ, δ and κ opioid receptors

    NASA Astrophysics Data System (ADS)

    Filizola, Marta; Carteni-Farina, Maria; Perez, Juan J.

    1999-07-01

    3D models of the opioid receptors μ, δ and κ were constructed using BUNDLE, an in-house program to build de novo models of G-protein coupled receptors at the atomic level. Once the three opioid receptors were constructed and before any energy refinement, models were assessed for their compatibility with the results available from point-site mutations carried out on these receptors. In a subsequent step, three selective antagonists to each of three receptors (naltrindole, naltrexone and nor-binaltorphamine) were docked onto each of the three receptors and subsequently energy minimized. The nine resulting complexes were checked for their ability to explain known results of structure-activity studies. Once the models were validated, analysis of the distances between different residues of the receptors and the ligands were computed. This analysis permitted us to identify key residues tentatively involved in direct interaction with the ligand.

  5. Potential applications for sigma receptor ligands in cancer diagnosis and therapy.

    PubMed

    van Waarde, Aren; Rybczynska, Anna A; Ramakrishnan, Nisha K; Ishiwata, Kiichi; Elsinga, Philip H; Dierckx, Rudi A J O

    2015-10-01

    Sigma receptors (sigma-1 and sigma-2) represent two independent classes of proteins. Their endogenous ligands may include the hallucinogen N,N-dimethyltryptamine (DMT) and sphingolipid-derived amines which interact with sigma-1 receptors, besides steroid hormones (e.g., progesterone) which bind to both sigma receptor subpopulations. The sigma-1 receptor is a ligand-regulated molecular chaperone with various ion channels and G-protein-coupled membrane receptors as clients. The sigma-2 receptor was identified as the progesterone receptor membrane component 1 (PGRMC1). Although sigma receptors are over-expressed in tumors and up-regulated in rapidly dividing normal tissue, their ligands induce significant cell death only in tumor tissue. Sigma ligands may therefore be used to selectively eradicate tumors. Multiple mechanisms appear to underlie cell killing after administration of sigma ligands, and the signaling pathways are dependent both on the type of ligand and the type of tumor cell. Recent evidence suggests that the sigma-2 receptor is a potential tumor and serum biomarker for human lung cancer and an important target for inhibiting tumor invasion and cancer progression. Current radiochemical efforts are focused on the development of subtype-selective radioligands for positron emission tomography (PET) imaging. Right now, the mostpromising tracers are [18F]fluspidine and [18F]FTC-146 for sigma-1 receptors and [11C]RHM-1 and [18F]ISO-1 for the sigma-2 subtype. Nanoparticles coupled to sigma ligands have shown considerable potential for targeted delivery of antitumor drugs in animal models of cancer, but clinical studies exploring this strategy in cancer patients have not yet been reported. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

  6. Computer-aided design of a novel ligand for retinoic acid receptor in cancer chemotherapy

    NASA Astrophysics Data System (ADS)

    Silva, Carlos H. T. P.; Leopoldino, Andreia M.; Silva, Eloiza H. T.; Espinoza, V. A. A.; Taft, C. A.

    The isotypes of RAR and RXR are retinoic acid and retinoid X acid receptors, respectively, whose ligand-binding domain contains the ligand-dependent activation function, with distinct pharmacological targets for retinoids, involved in the treatment of various cancers and skin diseases. Due to the major challenge which cancer treatment and cure still imposes after many decades to the international scientific community, there is actually considerable interest in new ligands with increased bioactivity. We have focused on the retinoid acid receptor, which is considered an interesting target for drug design. In this work, we carried out density functional geometry optimizations and different docking procedures. We performed screening in a large database (hundreds of thousands of molecules which we optimized at the AM1 level) yielding a set of potential bioactive ligands. A new ligand was selected and optimized at the B3LYP/6-31G* level. A flexible docking program was used to investigate the interactions between the receptor and the new ligand. The result of this work is compared with several crystallographic ligands of RAR. Our theoretically more bioactive new ligand indicates stronger and more hydrogen bonds as well as hydrophobic interactions with the receptor.

  7. Computational Exploration of a Protein Receptor Binding Space with Student Proposed Peptide Ligands

    ERIC Educational Resources Information Center

    King, Matthew D.; Phillips, Paul; Turner, Matthew W.; Katz, Michael; Lew, Sarah; Bradburn, Sarah; Andersen, Tim; McDougal, Owen M.

    2016-01-01

    Computational molecular docking is a fast and effective "in silico" method for the analysis of binding between a protein receptor model and a ligand. The visualization and manipulation of protein to ligand binding in three-dimensional space represents a powerful tool in the biochemistry curriculum to enhance student learning. The…

  8. Expression and Purification of Functional Ligand-binding Domains of T1R3 Taste Receptors

    SciTech Connect

    Nie,Y.; Hobbs, J.; Vigues, S.; Olson, W.; Conn, G.; Munger, S.

    2006-01-01

    Chemosensory receptors, including odor, taste, and vomeronasal receptors, comprise the largest group of G protein-coupled receptors (GPCRs) in the mammalian genome. However, little is known about the molecular determinants that are critical for the detection and discrimination of ligands by most of these receptors. This dearth of understanding is due in part to difficulties in preparing functional receptors suitable for biochemical and biophysical analyses. Here we describe in detail two strategies for the expression and purification of the ligand-binding domain of T1R taste receptors, which are constituents of the sweet and umami taste receptors. These class C GPCRs contain a large extracellular N-terminal domain (NTD) that is the site of interaction with most ligands and that is amenable to expression as a separate polypeptide in heterologous cells. The NTD of mouse T1R3 was expressed as two distinct fusion proteins in Escherichia coli and purified by column chromatography. Spectroscopic analysis of the purified NTD proteins shows them to be properly folded and capable of binding ligands. This methodology should not only facilitate the characterization of T1R ligand interactions but may also be useful for dissecting the function of other class C GPCRs such as the large family of orphan V2R vomeronasal receptors.

  9. Ligands Raise the Constraint That Limits Constitutive Activation in G Protein-coupled Opioid Receptors*

    PubMed Central

    Vezzi, Vanessa; Onaran, H. Ongun; Molinari, Paola; Guerrini, Remo; Balboni, Gianfranco; Calò, Girolamo; Costa, Tommaso

    2013-01-01

    Using a cell-free bioluminescence resonance energy transfer strategy we compared the levels of spontaneous and ligand-induced receptor-G protein coupling in δ (DOP) and μ (MOP) opioid receptors. In this assay GDP can suppress spontaneous coupling, thus allowing its quantification. The level of constitutive activity was 4–5 times greater at the DOP than at the MOP receptor. A series of opioid analogues with a common peptidomimetic scaffold displayed remarkable inversions of efficacy in the two receptors. Agonists that enhanced coupling above the low intrinsic level of the MOP receptor were inverse agonists in reducing the greater level of constitutive coupling of the DOP receptor. Yet the intrinsic activities of such ligands are identical when scaled over the GDP base line of both receptors. This pattern is in conflict with the predictions of the ternary complex model and the “two state” extensions. According to this theory, the order of spontaneous and ligand-induced coupling cannot be reversed if a shift of the equilibrium between active and inactive forms raises constitutive activation in one receptor type. We propose that constitutive activation results from a lessened intrinsic barrier that restrains spontaneous coupling. Any ligand, regardless of its efficacy, must enhance this constraint to stabilize the ligand-bound complexed form. PMID:23836900

  10. Ligands raise the constraint that limits constitutive activation in G protein-coupled opioid receptors.

    PubMed

    Vezzi, Vanessa; Onaran, H Ongun; Molinari, Paola; Guerrini, Remo; Balboni, Gianfranco; Calò, Girolamo; Costa, Tommaso

    2013-08-16

    Using a cell-free bioluminescence resonance energy transfer strategy we compared the levels of spontaneous and ligand-induced receptor-G protein coupling in δ (DOP) and μ (MOP) opioid receptors. In this assay GDP can suppress spontaneous coupling, thus allowing its quantification. The level of constitutive activity was 4-5 times greater at the DOP than at the MOP receptor. A series of opioid analogues with a common peptidomimetic scaffold displayed remarkable inversions of efficacy in the two receptors. Agonists that enhanced coupling above the low intrinsic level of the MOP receptor were inverse agonists in reducing the greater level of constitutive coupling of the DOP receptor. Yet the intrinsic activities of such ligands are identical when scaled over the GDP base line of both receptors. This pattern is in conflict with the predictions of the ternary complex model and the "two state" extensions. According to this theory, the order of spontaneous and ligand-induced coupling cannot be reversed if a shift of the equilibrium between active and inactive forms raises constitutive activation in one receptor type. We propose that constitutive activation results from a lessened intrinsic barrier that restrains spontaneous coupling. Any ligand, regardless of its efficacy, must enhance this constraint to stabilize the ligand-bound complexed form.

  11. Insights into Bombesin receptors and ligands: highlighting recent advances

    PubMed Central

    Ramos-Álvarez, Irene; Moreno, Paola; Mantey, Samuel A.; Nakamura, Taichi; Nuche-Berenguer, Bernardo; Moody, Terry W.; Coy, David H.; Jensen, Robert T.

    2015-01-01

    This following article is written for Prof. Abba Kastin’s Festschrift, to add to the tribute to his important role in the advancement of the role of peptides in physiological, as well as pathophysiological processes. There have been many advances during the 35 years of his prominent role in the Peptide field, not only as editor of the journal Peptides, but also as a scientific investigator and editor of two volumes of the Handbook of Biological Active Peptides [146,147]. Similar to the advances with many different peptides, during this 35 year period, there have been much progress made in the understanding of the pharmacology, cell biology and the role of (Bombesin) Bn receptors and their ligands in various disease states, since the original isolation of bombesin from skin of the European frog Bombina bombina in 1970 [76]. This paper will briefly review some of these advances over the time period of Prof Kastin 35 years in the peptide field concentrating on the advances since 2007 when many of the results from earlier studies were summarized [128,129]. It is appropriate to do this because there have been 280 articles published in Peptides during this time on Bombesin-related peptides and it accounts for almost 5% of all publications. Furthermore, 22 Bn publications we have been involved in have been published in either Peptides [14,39,55,58,81,92,93,119,152,216,225,226,231,280,302,309,355,361,362] or in the Prof Kastin’s Handbook of Biological Active Peptides [137,138,331]. PMID:25976083

  12. Oestrogen receptor beta ligand: a novel treatment to enhance endogenous functional remyelination.

    PubMed

    Crawford, Daniel K; Mangiardi, Mario; Song, Bingbing; Patel, Rhusheet; Du, Sienmi; Sofroniew, Michael V; Voskuhl, Rhonda R; Tiwari-Woodruff, Seema K

    2010-10-01

    Demyelinating diseases, such as multiple sclerosis, are characterized by inflammatory demyelination and neurodegeneration of the central nervous system. Therapeutic strategies that induce effective neuroprotection and enhance intrinsic repair mechanisms are central goals for future therapy of multiple sclerosis. Oestrogens and oestrogen receptor ligands are promising treatments to prevent multiple sclerosis-induced neurodegeneration. In the present study we investigated the capacity of oestrogen receptor β ligand treatment to affect callosal axon demyelination and stimulate endogenous myelination in chronic experimental autoimmune encephalomyelitis using electrophysiology, electron microscopy, immunohistochemistry and tract-tracing methods. Oestrogen receptor β ligand treatment of experimental autoimmune encephalomyelitis mice prevented both histopathological and functional abnormalities of callosal axons despite the presence of inflammation. Specifically, there were fewer demyelinated, damaged axons and more myelinated axons with intact nodes of Ranvier in oestrogen receptor β ligand-treated mice. In addition, oestrogen receptor β ligand treatment caused an increase in mature oligodendrocyte numbers, a significant increase in myelin sheath thickness and axon transport. Functional analysis of callosal axon conduction showed a significant improvement in compound action potential amplitudes, latency and in axon refractoriness. These findings show a direct neuroprotective effect of oestrogen receptor β ligand treatment on oligodendrocyte differentiation, myelination and axon conduction during experimental autoimmune encephalomyelitis.

  13. Pharmacophore modeling improves virtual screening for novel peroxisome proliferator-activated receptor-gamma ligands

    PubMed Central

    Lewis, Stephanie N.; Garcia, Zulma; Hontecillas, Raquel; Bassaganya-Riera, Josep; Bevan, David R.

    2015-01-01

    Peroxisome proliferator-activated receptor-gamma (PPARγ) is a nuclear hormone receptor involved in regulating various metabolic and immune processes. The PPAR family of receptors possesses a large binding cavity that imparts promiscuity of ligand binding not common to other nuclear receptors. This feature increases the challenge of using computational methods to identify PPAR ligands that will dock favorably into a structural model. Utilizing both ligand- and structure-based pharmacophore methods, we sought to improve agonist prediction by grouping ligands according to pharmacophore features, and pairing models derived from these features with receptor structures for docking. For 22 of the 33 receptor structures evaluated we observed an increase in true positive rate (TPR) when screening was restricted to compounds sharing molecular features found in rosiglitazone. A combination of structure models used for docking resulted in a higher TPR (40%) when compared to docking with a single structure model (less than 20%). Prediction was also improved when specific protein-ligand interactions between the docked ligands and structure models were given greater weight than the calculated free energy of binding. A large-scale screen of compounds using a marketed drug database verified the predictive ability of the selected structure models. This study highlights the steps necessary to improve screening for PPARγ ligands using multiple structure models, ligand-based pharmacophore data, evaluation of protein-ligand interactions, and comparison of docking datasets. The unique combination of methods presented here holds potential for more efficient screening of compounds with unknown affinity for PPARγ that could serve as candidates for therapeutic development. PMID:25616366

  14. Pharmacophore modeling improves virtual screening for novel peroxisome proliferator-activated receptor-gamma ligands

    NASA Astrophysics Data System (ADS)

    Lewis, Stephanie N.; Garcia, Zulma; Hontecillas, Raquel; Bassaganya-Riera, Josep; Bevan, David R.

    2015-05-01

    Peroxisome proliferator-activated receptor-gamma (PPARγ) is a nuclear hormone receptor involved in regulating various metabolic and immune processes. The PPAR family of receptors possesses a large binding cavity that imparts promiscuity of ligand binding not common to other nuclear receptors. This feature increases the challenge of using computational methods to identify PPAR ligands that will dock favorably into a structural model. Utilizing both ligand- and structure-based pharmacophore methods, we sought to improve agonist prediction by grouping ligands according to pharmacophore features, and pairing models derived from these features with receptor structures for docking. For 22 of the 33 receptor structures evaluated we observed an increase in true positive rate (TPR) when screening was restricted to compounds sharing molecular features found in rosiglitazone. A combination of structure models used for docking resulted in a higher TPR (40 %) when compared to docking with a single structure model (<20 %). Prediction was also improved when specific protein-ligand interactions between the docked ligands and structure models were given greater weight than the calculated free energy of binding. A large-scale screen of compounds using a marketed drug database verified the predictive ability of the selected structure models. This study highlights the steps necessary to improve screening for PPARγ ligands using multiple structure models, ligand-based pharmacophore data, evaluation of protein-ligand interactions, and comparison of docking datasets. The unique combination of methods presented here holds potential for more efficient screening of compounds with unknown affinity for PPARγ that could serve as candidates for therapeutic development.

  15. Histamine H4 receptor ligands: future applications and state of art.

    PubMed

    Corrêa, Michelle Fidelis; dos Santos Fernandes, João Paulo

    2015-04-01

    Histamine is a chemical transmitter found practically in whole organism and exerts its effects through the interaction with H1 to H4 histaminergic receptors. Specifically, H4 receptors are found mainly in immune cells and blood-forming tissues, thus are involved in inflammatory and immune processes, as well as some actions in central nervous system. Therefore, H4 receptor ligands can have applications in the treatment of chronic inflammatory and immune diseases and may be novel therapeutic option in these conditions. Several H4 receptor ligands have been described from early 2000's until nowadays, being imidazole, indolecarboxamide, 2-aminopyrimidine, quinazoline, and quinoxaline scaffolds the most explored and discussed in this review. Moreover, several studies of molecular modeling using homology models of H4 receptor and QSAR data of the ligands are summarized. The increasing and promising therapeutic applications are leading these compounds to clinical trials, which probably will be part of the next generation of blockbuster drugs.

  16. Ligand Activation of TAM Family Receptors-Implications for Tumor Biology and Therapeutic Response

    PubMed Central

    Davra, Viralkumar; Kimani, Stanley G.; Calianese, David; Birge, Raymond B.

    2016-01-01

    The TAM family of receptors (i.e., Tyro3, Axl, and Mertk), and their ligands Growth arrest specific factor 6 (Gas6) and Protein S (Pros1) contribute to several oncogenic processes, such as cell survival, invasion, migration, chemo-resistance, and metastasis, whereby expression often correlates with poor clinical outcomes. In recent years, there has been great interest in the study of TAM receptors in cancer, stemming both from their roles as oncogenic signaling receptors, as well as their roles in tumor immunology. As a result, several classes of TAM inhibitors that include small molecule tyrosine kinase inhibitors, monoclonal antibodies, decoy receptors, as well as novel strategies to target TAM ligands are being developed. This paper will review the biology of TAM receptors and their ligands with a focus on cancer, as well as evidence-based data for the continued pursuit of TAM/Gas6 inhibitors in clinical practice. PMID:27916840

  17. Distinct second extracellular loop structures of the brain cannabinoid CB(1) receptor: implication in ligand binding and receptor function.

    PubMed

    Shim, Joong-Youn; Rudd, James; Ding, Tomas T

    2011-02-01

    The G-protein-coupled receptor (GPCR) second extracellular loop (E2) is known to play an important role in receptor structure and function. The brain cannabinoid (CB(1)) receptor is unique in that it lacks the interloop E2 disulfide linkage to the transmembrane (TM) helical bundle, a characteristic of many GPCRs. Recent mutation studies of the CB(1) receptor, however, suggest the presence of an alternative intraloop disulfide bond between two E2 Cys residues. Considering the oxidation state of these Cys residues, we determine the molecular structures of the 17-residue E2 in the dithiol form (E2(dithiol)) and in the disulfide form (E2(disulfide)) of the CB(1) receptor in a fully hydrated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayer, using a combination of simulated annealing and molecular dynamics simulation approaches. We characterize the CB(1) receptor models with these two E2 forms, CB(1)(E2(dithiol)) and CB(1)(E2(disulfide)), by analyzing interaction energy, contact number, core crevice, and cross correlation. The results show that the distinct E2 structures interact differently with the TM helical bundle and uniquely modify the TM helical topology, suggesting that E2 of the CB(1) receptor plays a critical role in stabilizing receptor structure, regulating ligand binding, and ultimately modulating receptor activation. Further studies on the role of E2 of the CB(1) receptor are warranted, particularly comparisons of the ligand-bound form with the present ligand-free form.

  18. Polycyclic aromatic hydrocarbons (PAHs) mediate transcriptional activation of the ATP binding cassette transporter ABCB6 gene via the aryl hydrocarbon receptor (AhR).

    PubMed

    Chavan, Hemantkumar; Krishnamurthy, Partha

    2012-09-14

    Liver is endowed with a mechanism to induce hepatic cytochromes P450 (CYP450s) in response to therapeutic drugs and environmental contaminants, leading to increased detoxification and elimination of the xenobiotics. Each CYP450 is composed of an apoprotein moiety and a heme prosthetic group, which is required for CYP450 activity. Thus, under conditions of CYP450 induction, there is a coordinate increase in heme biosynthesis to compensate for the increased expression of CYP450s. ABCB6, a mitochondrial ATP binding cassette transporter, which regulates coproporphyrinogen transport from the cytoplasm into the mitochondria to complete heme biosynthesis, represents a previously unrecognized rate-limiting step in heme biosynthesis. However, it is not known if exposure to drugs and environmental contaminants induces ABCB6 expression, to assure an adequate and apparently coordinated supply of heme for the generation of functional cytochrome holoprotein. In the present study, we demonstrate that polycyclic aromatic hydrocarbons (PAHs), the widely distributed environmental toxicants shown to induce porphyrin accumulation causing hepatic porphyria, up-regulate ABCB6 expression in both mice and humans. Using siRNA technology and Abcb6 knock-out mice, we demonstrate that PAH-mediated increase in hepatic porphyrins is compromised in the absence of ABCB6. Moreover, in vivo studies in aryl hydrocarbon receptor (AhR) knock-out mice demonstrate that PAH induction of ABCB6 is mediated by AhR. Promoter activation studies combined with electrophoretic mobility shift assay and chromatin immunoprecipitation assay demonstrate direct interactions between the AhR binding sites in the ABCB6 promoter and the AhR receptor, implicating drug activation mechanisms for ABCB6 similar to those found in inducible cytochrome P450s. These studies are the first to describe direct transcriptional activation of both mouse and human ABCB6 by xenobiotics.

  19. Sigma receptor ligands: possible application as therapeutic drugs and as radiopharmaceuticals.

    PubMed

    Hashimoto, Kenji; Ishiwata, Kiichi

    2006-01-01

    Sigma receptors are classified into sigma(1) and sigma(2) subtypes. These subtypes display a different tissue distribution and a distinct physiological and pharmacological profile in the central and peripheral nervous system. The characterization of these subtypes and the discovery of new specific sigma receptor ligands demonstrated that sigma receptors are novel targets for the therapeutic treatment of neuropsychiatric diseases (schizophrenia, depression, and cognition), brain ischemia, and cocaine addiction. Furthermore, imaging of sigma(1) receptors in the human brain using specific PET radioligands has started. In addition, the two sigma receptor subtypes are also expressed on tumor cells, where they could be of prognostic relevance. The ability of sigma(2) receptor agonists to inhibit tumor cell proliferation through mechanisms that might involve apoptosis, intracellular Ca(2+), and sphingolipids has promoted the development of sigma(2) receptor agonists as novel therapeutic drugs for treating cancer. Consequently, sigma(2) receptor ligands have been demonstrated to be potentially useful tumor imaging ligands. In this article, we focus on the sigma receptor ligands as therapeutic agents and as radiopharmaceuticals.

  20. Direct identification of ligand-receptor interactions on living cells and tissues.

    PubMed

    Frei, Andreas P; Jeon, Ock-Youm; Kilcher, Samuel; Moest, Hansjoerg; Henning, Lisa M; Jost, Christian; Plückthun, Andreas; Mercer, Jason; Aebersold, Ruedi; Carreira, Erick M; Wollscheid, Bernd

    2012-10-01

    Many cellular responses are triggered by proteins, drugs or pathogens binding to cell-surface receptors, but it can be challenging to identify which receptors are bound by a given ligand. Here we describe TRICEPS, a chemoproteomic reagent with three moieties--one that binds ligands containing an amino group, a second that binds glycosylated receptors on living cells and a biotin tag for purifying the receptor peptides for identification by quantitative mass spectrometry. We validated this ligand-based, receptor-capture (LRC) technology using insulin, transferrin, apelin, epidermal growth factor, the therapeutic antibody trastuzumab and two DARPins targeting ErbB2. In some cases, we could also determine the approximate ligand-binding sites on the receptors. Using TRICEPS to label intact mature vaccinia viruses, we identified the cell surface proteins AXL, M6PR, DAG1, CSPG4 and CDH13 as binding factors on human cells. This technology enables the identification of receptors for many types of ligands under near-physiological conditions and without the need for genetic manipulations.

  1. C-type lectin-like receptors of the dectin-1 cluster: ligands and signaling pathways.

    PubMed

    Plato, Anthony; Willment, Janet A; Brown, Gordon D

    2013-04-01

    Innate immunity is constructed around genetically encoded receptors that survey the intracellular and extracellular environments for signs of invading microorganisms. These receptors recognise the invader and through complex intracellular networks of molecular signaling, they destroy the threat whilst instructing effective adaptive immune responses. Many of these receptors, like the Toll-like receptors in particular, are well-known for their ability to mediate downstream responses upon recognition of exogenous or endogenous ligands; however, the emerging family known as the C-type lectin-like receptors contains many members that have a huge impact on immune and homeostatic regulation. Of particular interest here are the C-type lectin-like receptors that make up the Dectin-1 cluster and their intracellular signaling motifs that mediate their functions. In this review, we aim to draw together current knowledge of ligands, motifs and signaling pathways, present downstream of Dectin-1 cluster receptors, and discuss how these dictate their role within biological systems.

  2. Bivalent Ligands Targeting Chemokine Receptor Dimerization: Molecular Design and Functional Studies

    PubMed Central

    Arnatt, Christopher Kent; Zhang, Yan

    2015-01-01

    Increasing evidence has shown that chemokine receptors may form functional dimers with unique pharmacological profiles. A common practice to characterize such G protein-coupled receptor dimerization processes is to apply bivalent ligands as chemical probes which can interact with both receptors simultaneously. Currently, two chemokine receptor dimers have been studied by applying bivalent compounds: the CXCR4-CXCR4 homodimer and the CCR5-MOR heterodimer. These bivalent compounds have revealed how dimerization influences receptor function and may lead to novel therapeutics. Future design of bivalent ligands for chemokine receptor dimers may be aided with the recently available CXCR4 homodimer, and CCR5 monomer crystal structures by more accurately simulating chemokine receptors and their dimers. PMID:25159160

  3. Design, synthesis and X-ray crystallographic study of new nonsecosteroidal vitamin D receptor ligands.

    PubMed

    Demizu, Yosuke; Takahashi, Takeo; Kaneko, Fumiya; Sato, Yukiko; Okuda, Haruhiro; Ochiai, Eiji; Horie, Kyohei; Takagi, Ken-Ichiro; Kakuda, Shinji; Takimoto-Kamimura, Midori; Kurihara, Masaaki

    2011-10-15

    We designed and synthesized nonsecosteroidal vitamin D receptor (VDR) ligands that formed H-bonds with six amino acid residues (Tyr143, Ser233, Arg270, Ser274, His301 and His393) of the VDR ligand-binding domain. The ligand YR335 exhibited potent transcriptional activity, which was comparable to those of 1α,25-dihydroxyvitamin D(3) and YR301. The crystal structure of the complex formed between YR335 and the VDR ligand-binding domain was solved, which revealed that YR335 formed H-bonds with the six amino acid residues mentioned above.

  4. Modulation of Retinoic Acid Receptor-related Orphan Receptor α and γ Activity by 7-Oxygenated Sterol Ligands*

    PubMed Central

    Wang, Yongjun; Kumar, Naresh; Solt, Laura A.; Richardson, Timothy I.; Helvering, Leah M.; Crumbley, Christine; Garcia-Ordonez, Ruben D.; Stayrook, Keith R.; Zhang, Xi; Novick, Scott; Chalmers, Michael J.; Griffin, Patrick R.; Burris, Thomas P.

    2010-01-01

    The retinoic acid receptor-related orphan receptors α and γ (RORα (NR1F1) and RORγ (NR1F3)) are orphan nuclear receptors and perform critical roles in regulation of development, metabolism, and immune function. Cholesterol and cholesterol sulfate have been suggested to be RORα ligands, but the physiological significance is unclear. To date, no endogenous RORγ ligands have been described. Here, we demonstrate that 7-oxygenated sterols function as high affinity ligands for both RORα and RORγ by directly binding to their ligand-binding domains (Ki ∼20 nm), modulating coactivator binding, and suppressing the transcriptional activity of the receptors. One of the 7-oxygenated sterols, 7α-hydroxycholesterol (7α-OHC), serves as a key intermediate in bile acid metabolism, and we show that 7α-OHC modulates the expression of ROR target genes, including Glc-6-Pase and phosphoenolpyruvate carboxykinase, in an ROR-dependent manner. Furthermore, glucose output from hepatocytes is suppressed by 7α-OHC functioning as an RORα/γ ligand. Thus, RORα and RORγ are ligand-regulated members of the NR superfamily and may serve as sensors for 7-oxygenated sterols. PMID:19965867

  5. Revealing a steroid receptor ligand as a unique PPAR[gamma] agonist

    SciTech Connect

    Lin, Shengchen; Han, Ying; Shi, Yuzhe; Rong, Hui; Zheng, Songyang; Jin, Shikan; Lin, Shu-Yong; Lin, Sheng-Cai; Li, Yong

    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 of 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.

  6. Molecular modeling of sigma 1 receptor ligands: a model of binding conformational and electrostatic considerations.

    PubMed

    Gund, Tamara M; Floyd, Jie; Jung, Dawoon

    2004-01-01

    We have performed molecular modeling studies on several sigma 1 specific ligands, including PD144418, spipethiane, haloperidol, pentazocine, and others to develop a pharmacophore for sigma 1 receptor-ligand binding, under the assumption that all the compounds interact at the same receptor binding site. The modeling studies have investigated the conformational and electrostatic properties of the ligands. Superposition of active molecules gave the coordinates of the hypothetical 5-point sigma 1 pharmacophore, as follows: R1 (0.85, 7.26, 0.30); R2 (5.47, 2.40, -1.51); R3 (-2.57, 4.82, -7.10); N (-0.71, 3.29, -6.40); carbon centroid (3.16, 4.83, -0.60), where R1, R2 were constructed onto the aromatic ring of each compound to represent hydrophobic interactions with the receptor; and R3 represents a hydrogen bond between the nitrogen atom and the receptor. Additional analyses were used to describe secondary binding sites to electronegative groups such as oxygen or sulfur atom. Those coordinates are (2.34, 5.08, -4.18). The model was verified by fitting other sigma 1 receptor ligands. This model may be used to search conformational databases for other possibly active ligands. In conjunction with rational drug design techniques the model may be useful in design and synthesis of novel sigma 1 ligands of high selectivity and potency. Calculations were performed using Sybyl 6.5.

  7. Free energy calculations offer insights into the influence of receptor flexibility on ligand-receptor binding affinities.

    PubMed

    Dolenc, Jožica; Riniker, Sereina; Gaspari, Roberto; Daura, Xavier; van Gunsteren, Wilfred F

    2011-08-01

    Docking algorithms for computer-aided drug discovery and design often ignore or restrain the flexibility of the receptor, which may lead to a loss of accuracy of the relative free enthalpies of binding. In order to evaluate the contribution of receptor flexibility to relative binding free enthalpies, two host-guest systems have been examined: inclusion complexes of α-cyclodextrin (αCD) with 1-chlorobenzene (ClBn), 1-bromobenzene (BrBn) and toluene (MeBn), and complexes of DNA with the minor-groove binding ligands netropsin (Net) and distamycin (Dist). Molecular dynamics simulations and free energy calculations reveal that restraining of the flexibility of the receptor can have a significant influence on the estimated relative ligand-receptor binding affinities as well as on the predicted structures of the biomolecular complexes. The influence is particularly pronounced in the case of flexible receptors such as DNA, where a 50% contribution of DNA flexibility towards the relative ligand-DNA binding affinities is observed. The differences in the free enthalpy of binding do not arise only from the changes in ligand-DNA interactions but also from changes in ligand-solvent interactions as well as from the loss of DNA configurational entropy upon restraining.

  8. The gamma-chain cytokine/receptor system in fish: more ligands and receptors.

    PubMed

    Wang, Tiehui; Huang, Wenshu; Costa, Maria M; Secombes, Christopher J

    2011-11-01

    The mammalian gamma-chain (γC) cytokine family consists of interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15 and IL-21. They signal through a receptor complex containing the common γC and a private alpha chain, and in the case of IL-2 and IL-15 an additional common IL-2/15Rβ chain. Deficiency of γC signalling in mammals prevents CD4+ T cells from developing effector functions and CD8+ T cells from developing immunological memory. Thus γC cytokines are critical for the generation and peripheral homeostasis of naïve and memory T cells. This review will give an update on the γC ligands and receptor subunits in fish, and also present some new data on the cloning and expression of a second γC and two IL-2Rβ chains in rainbow trout Oncorhynchus mykiss. In recent years, aided by the availability of sequenced fish genomes and expressed sequence tag databases, five of the six mammalian γC cytokines and their cognate receptors have been discovered in fish, with only the IL-9/IL-9R homologues apparently absent. Paralogues have been discovered in diploid fish and all the receptors described in the tetraploid rainbow trout, including γC itself, IL-2Rβ, IL-4Rα, IL-13Rα1, IL-13Rα2 and IL-2/15Rα, have duplicates. As a consequence of the teleost and salmonid whole genome duplications, even more paralogues may yet be discovered. Some of the paralogues have changes in domain structures and show differential expression and modulation, suggesting the potential for a change in function. Functional characterisation of fish γC cytokines is beginning but made more difficult by the co-existence of so many paralogues of the ligands and their receptors. Initial functional studies have shown that fish γC cytokines can modulate the expression of key cytokines (e.g. interferon-γ, IL-10 and IL-22) of the adaptive immune response, and may thus have promise as adjuvants to improve vaccination efficiency in fish.

  9. Visualization and ligand-induced modulation of dopamine receptor dimerization at the single molecule level

    PubMed Central

    Tabor, Alina; Weisenburger, Siegfried; Banerjee, Ashutosh; Purkayastha, Nirupam; Kaindl, Jonas M.; Hübner, Harald; Wei, Luxi; Grömer, Teja W.; Kornhuber, Johannes; Tschammer, Nuska; Birdsall, Nigel J. M.; Mashanov, Gregory I.; Sandoghdar, Vahid; Gmeiner, Peter

    2016-01-01

    G protein–coupled receptors (GPCRs), including dopamine receptors, represent a group of important pharmacological targets. An increased formation of dopamine receptor D2 homodimers has been suggested to be associated with the pathophysiology of schizophrenia. Selective labeling and ligand-induced modulation of dimerization may therefore allow the investigation of the pathophysiological role of these dimers. Using TIRF microscopy at the single molecule level, transient formation of homodimers of dopamine receptors in the membrane of stably transfected CHO cells has been observed. The equilibrium between dimers and monomers was modulated by the binding of ligands; whereas antagonists showed a ratio that was identical to that of unliganded receptors, agonist-bound D2 receptor-ligand complexes resulted in an increase in dimerization. Addition of bivalent D2 receptor ligands also resulted in a large increase in D2 receptor dimers. A physical interaction between the protomers was confirmed using high resolution cryogenic localization microscopy, with ca. 9 nm between the centers of mass. PMID:27615810

  10. Modeling multivalent ligand-receptor interactions with steric constraints on configurations of cell surface receptor aggregates

    SciTech Connect

    Monine, Michael; Posner, Richard; Savage, Paul; Faeder, James; Hlavacek, William S

    2008-01-01

    Signal transduction generally involves multivalent protein-protein interactions, which can produce various protein complexes and post-translational modifications. The reaction networks that characterize these interactions tend to be so large as to challenge conventional simulation procedures. To address this challenge, a kinetic Monte Carlo (KMC) method has been developed that can take advantage of a model specification in terms of reaction rules for molecular interactions. A set of rules implicitly defines the reactions that can occur as a result of the interactions represented by the rules. With the rule-based KMC method, explicit generation of the underlying chemical reaction network implied by rules is avoided. Here, we apply and extend this method to characterize the interactions of a trivalent ligand with a bivalent cell-surface receptor. This system is also studied experimentally. We consider the following kinetic models: an equivalent-site model, an extension of this model, which takes into account steric constraints on the configurations of receptor aggregates, and finally, a model that accounts for cyclic receptor aggregates. Simulation results for the equivalent-site model are consistent with an equilibrium continuum model. Using these models, we investigate the effects of steric constraints and the formation of cyclic aggregates on the kinetics and equilibria of small and large aggregate formation and the percolation phase transition that occurs in this system.

  11. New Insights in Glucocorticoid Receptor Signaling—More Than Just a Ligand-Binding Receptor

    PubMed Central

    Scheschowitsch, Karin; Leite, Jacqueline Alves; Assreuy, Jamil

    2017-01-01

    The clinical use of classical glucocorticoids (GC) is narrowed by the many side effects it causes and the resistance to GC observed in some diseases. Since the great majority of GC effects depend on the activation of a glucocorticoid receptor (GR), many research groups had focused to better understand the signaling pathways involving those receptors. Transgenic animal models and genetic modifications of the receptor brought a huge insight into GR mechanisms of action. This in turn opened a new window for the search of selective GR modulators that ideally may have agonistic and antagonistic combined effects and activate one specific signaling pathway, inducing mostly transrepression or transactivation mechanisms. Another important research field concerns to posttranslational modifications that affect the GR and consequently also affect its signaling and function. In this mini review, we discuss many of those aspects of GR signaling, as well as findings like the ligand-independent activation of GR, which add another layer of complexity in GR signaling pathways. Although several recent data have been added to the GR field, much work has yet to be done, especially to find out the biological relevance of those alternative GR signaling pathways. Improving the knowledge about alternative GR signaling pathways and understanding how these pathways intercommunicate and in which situations they are relevant might help to develop new strategies to take benefit of it and to improve GC or other compounds efficacy causing minimal side effects. PMID:28220107

  12. Heterologous production of death ligands' and death receptors' extracellular domains: structural features and efficient systems.

    PubMed

    Muraki, Michiro

    2012-08-01

    The extracellular domains of death ligands and those of death receptors are closely related to many serious human diseases through the initiation of apoptosis. Recombinant production of the extracellular domains has been investigated due to demand for a large amount of purified samples, which are a prerequisite for their biochemical characterization and constitute the fundamentals of medical applications. This review focuses on the recombinant production of extracellular domains of the major members of death ligand and death receptor families using non-mammalian expression systems with an emphasis on Fas ligand and Fas receptor. In contrast to the efficient production of the functional extracellular domains of TRAIL, TNFα and LTα by intracellular expression systems using Escherichia coli or Pichia pastoris, that of Fas ligand requires the secretory expression systems using P. pastoris or Dictyostelium discoideum, and the productivity in P. pastoris was largely dependent on tag sequence, potential N-glycosylation site and expressed protein region. On the other hand, the exploitation of insect cell systems is generally useful for the preparation of functional extracellular domains of death receptors containing many disulfide bridges in the absence of extended secondary structure, and a Bombyx mori larvae secretion system presented a superior productivity for human Fas receptor extracellular domain. Based on the results obtained so far, further efforts should be devoted to the artificial control of death ligand - death receptor interactions in order to make a contribution to medicine, represented by the development of novel biopharmaceuticals.

  13. Folding and stability of the ligand-binding domain of the glucocorticoid receptor

    PubMed Central

    McLaughlin, Stephen H.; Jackson, Sophie E.

    2002-01-01

    A complex pathway involving many molecular chaperones has been proposed for the folding, assembly, and maintenance of a high-affinity ligand-binding form of steroid receptors in vivo, including the glucocorticoid receptor. To better understand this intricate folding and assembly process, we studied the folding of the ligand-binding domain of the glucocorticoid receptor in vitro. We found that this domain can be refolded into a compact, highly structured state in vitro in the absence of chaperones. However, the presence of zwitterionic detergent is required to maintain the domain in a soluble form. In this state, the protein is dimeric and has considerable helical structure as shown by far-UV circular dichroism. Further investigation of the properties of this in vitro refolded state show that it is stable and resistant to denaturation by heat or low concentrations of chemical denaturants. A detailed analysis of the unfolding equilibria using three different structural probes demonstrated that this state unfolds via a highly populated dimeric intermediate state. Together, these data clearly show that the ligand-binding domain of the glucocorticoid receptor does not require chaperones for folding per se. However, this in vitro refolded state binds the ligand dexamethasone only weakly (Kd = 45 μM) compared to the in vivo assembled receptor (Kd = 3.4 nM). We suggest that the role of Hsp90 and associated chaperones is to bind to, and stabilize, a specific conformational state of the receptor which binds ligand with high affinity. PMID:12142447

  14. Structural and functional characterization of the human formyl peptide receptor ligand-binding region.

    PubMed Central

    Radel, S J; Genco, R J; De Nardin, E

    1994-01-01

    The formyl peptide (N-formyl-1-methionyl-1-leucyl-1-phenylalanine [FMLP]) receptor is involved in the activation of neutrophils and their subsequent response to chemotactic N-formylated peptides. Recently, we found that the first extracellular loop closest to the N-terminal end of the FMLP receptor exhibited the strongest ligand binding compared with that shown by other extracellular regions. By constructing amino acid substitutional variants of this domain, we have determined that residues Arg-84 and Lys-85 on this loop play major roles in ligand-binding activity. Furthermore, random rearrangement of the residues of this receptor region demonstrated that the position of these charged amino acids did not affect their involvement in ligand binding, although their presence was essential for this binding to occur. We propose that the portion of the first N-terminal extracellular loop of the FMLP receptor containing residues Arg-84 and Lys-85 contributes significantly to the active site in ligand-receptor binding. We further propose that this binding is not dependent on defined structure but rather that these charged moieties may function as important "contacts" in receptor-ligand interactions. Images PMID:8168934

  15. Characterization of receptor proteins using affinity cross-linking with biotinylated ligands.

    PubMed

    Shinya, Tomonori; Osada, Tomohiko; Desaki, Yoshitake; Hatamoto, Masahiro; Yamanaka, Yuko; Hirano, Hisashi; Takai, Ryota; Che, Fang-Sik; Kaku, Hanae; Shibuya, Naoto

    2010-02-01

    The plant genome encodes a wide range of receptor-like proteins but the function of most of these proteins is unknown. We propose the use of affinity cross-linking of biotinylated ligands for a ligand-based survey of the corresponding receptor molecules. Biotinylated ligands not only enable the analysis of receptor-ligand interactions without the use of radioactive compounds but also the isolation and identification of receptor molecules by a simple affinity trapping method. We successfully applied this method for the characterization, isolation and identification of the chitin elicitor binding protein (CEBiP). A biocytin hydrazide conjugate of N-acetylchitooctaose (GN8-Bio) was synthesized and used for the detection of CEBiP in the plasma or microsomal membrane preparations from rice and carrot cells. Binding characteristics of CEBiP analyzed by inhibition studies were in good agreement with the previous results obtained with the use of a radiolabeled ligand. The biotin-tagged CEBiP could be purified by avidin affinity chromatography and identified by LC-MALDI-MS/MS after tryptic digestion. We also used this method to detect OsFLS2, a rice receptor-like kinase for the perception of the peptide elicitor flg22, in membrane preparations from rice cells overexpressing OsFLS2. This work demonstrates the applicability of this method to the purification and identification of plant receptor proteins.

  16. Purinergic P2X receptors: structural models and analysis of ligand-target interaction.

    PubMed

    Dal Ben, Diego; Buccioni, Michela; Lambertucci, Catia; Marucci, Gabriella; Thomas, Ajiroghene; Volpini, Rosaria

    2015-01-07

    The purinergic P2X receptors are ligand-gated cation channels activated by the endogenous ligand ATP. They assemble as homo- or heterotrimers from seven cloned subtypes (P2X1-7) and all trimer subunits present a common topology consisting in intracellular N- and C- termini, two transmembrane domains and a large extracellular domain. These membrane proteins are present in virtually all mammalian tissues and regulate a large variety of responses in physio- and pathological conditions. The development of ligands that selectively activate or block specific P2X receptor subtypes hence represents a promising strategy to obtain novel pharmacological tools for the treatment of pain, cancer, inflammation, and neurological, cardiovascular, and endocrine diseases. The publication of the crystal structures of zebrafish P2X4 receptor in inactive and ATP-bound active forms provided structural data for the analysis of the receptor structure, the interpretation of mutagenesis data, and the depiction of ligand binding and receptor activation mechanism. In addition, the availability of ATP-competitive ligands presenting selectivity for P2X receptor subtypes supports the design of new potent and selective ligands with possibly improved pharmacokinetic profiles, with the final aim to obtain new drugs. This study describes molecular modelling studies performed to develop structural models of the human and rat P2X receptors in inactive and active states. These models allowed to analyse the role of some non-conserved residues at ATP binding site and to study the receptor interaction with some non-specific or subtype selective agonists and antagonists.

  17. Regulatory crosstalk and interference between the xenobiotic and hypoxia sensing pathways at the AhR-ARNT-HIF1α signaling node

    PubMed Central

    Vorrink, Sabine U.; Domann, Frederick E.

    2014-01-01

    The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates many of the responses to toxic environmental chemicals such as TCDD or dioxin-like PCBs. To regulate gene expression, the AhR requires its binding partner, the aryl hydrocarbon receptor nuclear translocator (ARNT). ARNT is also required by the hypoxia-inducible factor-1α (HIF-1α), a crucial regulator of responses to conditions of reduced oxygen. The important role of ARNT in both the AhR and HIF-1α signaling pathways establishes a meaningful foundation for a possible crosstalk between these two vitally important signaling pathways. This crosstalk might lead to interference between the two signaling pathways and thus might play a role in the variety of cellular responses after exposure to AhR ligands and reduced oxygen availability. This review focuses on studies that have analyzed the effect of low oxygen environments and hypoxiamimetic agents on AhR signaling and conversely, the effect of AhR ligands, with a special emphasis on PCBs, on HIF-1α signaling. We highlight studies that assess the role of ARNT, elucidate the mechanism of the crosstalk, and discuss the physiological implications for exposure to AhR-inducing compounds in the context of hypoxia. PMID:24824450

  18. Thiophene bioisosteres of spirocyclic σ receptor ligands: relationships between substitution pattern and σ receptor affinity.

    PubMed

    Oberdorf, Christoph; Schepmann, Dirk; Vela, Jose Miguel; Buschmann, Helmut; Holenz, Jörg; Wünsch, Bernhard

    2012-06-14

    On the basis of the 6',7'-dihydrospiro[piperidine-4,4'-thieno[3,2-c]pyran] framework, a series of more than 30 σ ligands with versatile substituents in 1-, 2'-, and 6'-position has been synthesized and pharmacologically evaluated in order to find novel structure-affinity relationships. It was found that a cyclohexylmethyl residue at the piperidine N-atom instead of a benzyl moiety led to increased σ(2) affinity and therefore to decreased σ(1)/σ(2) selectivity. Small substituents (e.g., OH, OCH(3), CN, CH(2)OH) in 6'-position adjacent to the O-atom were well tolerated by the σ(1) receptor. Removal of the substituent in 6'-position resulted in very potent but unselective σ ligands (13). A broad range of substituents with various lipophilic and H-bond forming properties was introduced in 2'-position adjacent to the S-atom without loss of σ(1) affinity. However, very polar and basic substituents in both 2'- and 6'-position decreased the σ(1) affinity considerably. It is postulated that the electron density of the thiophene moiety has a big impact on the σ(1) affinity.

  19. Structure-based discovery of selective serotonin 5-HT(1B) receptor ligands.

    PubMed

    Rodríguez, David; Brea, José; Loza, María Isabel; Carlsson, Jens

    2014-08-05

    The development of safe and effective drugs relies on the discovery of selective ligands. Serotonin (5-hydroxytryptamine [5-HT]) G protein-coupled receptors are therapeutic targets for CNS disorders but are also associated with adverse drug effects. The determination of crystal structures for the 5-HT1B and 5-HT2B receptors provided an opportunity to identify subtype selective ligands using structure-based methods. From docking screens of 1.3 million compounds, 22 molecules were predicted to be selective for the 5-HT1B receptor over the 5-HT2B subtype, a requirement for safe serotonergic drugs. Nine compounds were experimentally verified as 5-HT1B-selective ligands, with up to 300-fold higher affinities for this subtype. Three of the ligands were agonists of the G protein pathway. Analysis of state-of-the-art homology models of the two 5-HT receptors revealed that the crystal structures were critical for predicting selective ligands. Our results demonstrate that structure-based screening can guide the discovery of ligands with specific selectivity profiles.

  20. Theoretical investigation of interaction between the set of ligands and α7 nicotinic acetylcholine receptor

    NASA Astrophysics Data System (ADS)

    Glukhova, O. E.; Prytkova, T. R.; Shmygin, D. S.

    2016-03-01

    Nicotinic acetylcholine receptors (nAChRs) are neuron receptor proteins that provide a transmission of nerve impulse through the synapses. They are composed of a pentametric assembly of five homologous subunits (5 α7 subunits for α7nAChR, for example), oriented around the central pore. These receptors might be found in the chemical synapses of central and peripheral nervous system, and also in the neuromuscular synapses. Transmembrane domain of the one of such receptors constitutes ion channel. The conductive properties of ion channel strongly depend on the receptor conformation changes in the response of binding with some molecule, f.e. acetylcholine. Investigation of interaction between ligands and acetylcholine receptor is important for drug design. In this work we investigate theoretically the interaction between the set of different ligands (such as vanillin, thymoquinone, etc.) and the nicotinic acetylcholine receptor (primarily with subunit of the α7nAChR) by different methods and packages (AutodockVina, GROMACS, KVAZAR, HARLEM, VMD). We calculate interaction energy between different ligands in the subunit using molecular dynamics. On the base of obtained calculation results and using molecular docking we found an optimal location of different ligands in the subunit.

  1. Synthesis and Biological Evaluation of Bivalent Ligands for the CB1 Receptor

    PubMed Central

    Zhang, Yanan; Gilliam, Anne; Maitra, Rangan; Damaj, M. Imad; Tajuba, Julianne M.; Seltzman, Herbert H.; Thomas, Brian F.

    2011-01-01

    Dimerization or oligomerization of many G protein-coupled receptors, including the CB1 receptor, is now widely accepted and may have significant implications towards medications development targeting these receptor complexes. A library of bivalent ligands composed of two identical CB1 antagonist pharmacophores derived from SR141716 linked by spacers of various lengths were developed. The affinities of these bivalent ligands at CB1 and CB2 receptors were determined using radiolabeled binding assays. Their functional activities were measured using GTP-γ-S accumulation and intracellular calcium mobilization assays. The results suggest that the nature of the linker and its length are crucial factors for optimum interactions of these ligands at CB1 receptor binding sites. Finally, selected bivalent ligands (5d and 7b) were able to attenuate the antinociceptive effects of the cannabinoid agonist CP55,940 in a rodent tail-flick assay. These novel compounds as probes will enable further evaluation of CB1 receptor dimerization and oligomerization, its functional significance, and may prove useful in the development of new therapeutic approaches to G protein-coupled receptor mediated disorders. PMID:20845959

  2. Versatility or promiscuity: the estrogen receptors, control of ligand selectivity and an update on subtype selective ligands.

    PubMed

    Ng, Hui Wen; Perkins, Roger; Tong, Weida; Hong, Huixiao

    2014-08-26

    The estrogen receptors (ERs) are a group of versatile receptors. They regulate an enormity of processes starting in early life and continuing through sexual reproduction, development, and end of life. This review provides a background and structural perspective for the ERs as part of the nuclear receptor superfamily and discusses the ER versatility and promiscuity. The wide repertoire of ER actions is mediated mostly through ligand-activated transcription factors and many DNA response elements in most tissues and organs. Their versatility, however, comes with the drawback of promiscuous interactions with structurally diverse exogenous chemicals with potential for a wide range of adverse health outcomes. Even when interacting with endogenous hormones, ER actions can have adverse effects in disease progression. Finally, how nature controls ER specificity and how the subtle differences in receptor subtypes are exploited in pharmaceutical design to achieve binding specificity and subtype selectivity for desired biological response are discussed. The intent of this review is to complement the large body of literature with emphasis on most recent developments in selective ER ligands.

  3. Kappa-opioid receptor-selective dicarboxylic ester-derived salvinorin A ligands.

    PubMed

    Polepally, Prabhakar R; White, Kate; Vardy, Eyal; Roth, Bryan L; Ferreira, Daneel; Zjawiony, Jordan K

    2013-05-15

    Salvinorin A, the active ingredient of the hallucinogenic plant Salvia divinorum is the most potent known naturally occurring hallucinogen and is a selective κ-opioid receptor agonist. To better understand the ligand-receptor interactions, a series of dicarboxylic ester-type of salvinorin A derivatives were synthesized and evaluated for their binding affinity at κ-, δ- and μ-opioid receptors. Most of the analogues show high affinity to the κ-opioid receptor. Methyl malonyl derivative 4 shows the highest binding affinity (Ki=2nM), analogues 5, 7, and 14 exhibit significant affinity for the κ-receptor (Ki=21, 36 and 39nM).

  4. Kappa-Opioid Receptor-Selective Dicarboxylic Ester-Derived Salvinorin A Ligands

    PubMed Central

    Polepally, Prabhakar R.; White, Kate; Vardy, Eyal; Roth, Bryan L.; Ferreira, Daneel; Zjawiony, Jordan K.

    2013-01-01

    Salvinorin A, the active ingredient of the hallucinogenic plant Salvia divinorum is the most potent known naturally occurring hallucinogen and is a selective κ-opioid receptor agonist. To better understand the ligand-receptor interactions, a series of dicarboxylic ester-type of salvinorin A derivatives were synthesized and evaluated for their binding affinity at κ, δ, and μ-opioid receptors. Most of the analogues show high affinity to the κ-opioid receptor. Methyl malonyl derivative 4 shows the highest binding affinity (Ki = 2 nM), analogues 5, 7, and 14 exhibit significant affinity for the κ-receptor (Ki = 21, 36 and 39 nM). PMID:23587424

  5. Development of a unique 3D interaction model of endogenous and synthetic peripheral benzodiazepine receptor ligands

    NASA Astrophysics Data System (ADS)

    Cinone, Nunzia; Höltje, Hans-Dieter; Carotti, Angelo

    2000-11-01

    Different classes of Peripheral-type Benzodiazepine Receptor (PBR) ligands were examined and common structural elements were detected and used to develop a rational binding model based on energetically allowed ligand conformations. Two lipophilic regions and one electrostatic interaction site are essential features for high affinity ligand binding, while a further lipophilic region plays an important modulator role. A comparative molecular field analysis, performed over 130 PBR ligands by means of the GRID/GOLPE methodology, led to a PLS model with both high fitting and predictive values (r2 = 0.898, Q2 = 0.761). The outcome from the 3D QSAR model and the GRID interaction fields computed on the putative endogenous PBR ligands DBI (Diazepam Binding Inhibitor) and TTN (Tetracontatetraneuropeptide) was used to identify the amino acids most probably involved in PBR binding. Three amino acids, bearing lipophilic side chains, were detected in DBI (Phe49, Leu47 and Met46) and in TTN (Phe33, Leu31 and Met30) as likely residues underlying receptor binding. Moreover, a qualitative comparison of the molecular electrostatic potentials of DBI, TTN and selected synthetic ligands indicated also similar electronic properties. Convergent results from the modeling studies of synthetic and endogenous ligands suggest a common binding mode to PBRs. This may help the rational design of new high affinity PBR ligands.

  6. Cell receptor and surface ligand density effects on dynamic states of adhering circulating tumor cells.

    PubMed

    Zheng, Xiangjun; Cheung, Luthur Siu-Lun; Schroeder, Joyce A; Jiang, Linan; Zohar, Yitshak

    2011-10-21

    Dynamic states of cancer cells moving under shear flow in an antibody-functionalized microchannel are investigated experimentally and theoretically. The cell motion is analyzed with the aid of a simplified physical model featuring a receptor-coated rigid sphere moving above a solid surface with immobilized ligands. The motion of the sphere is described by the Langevin equation accounting for the hydrodynamic loadings, gravitational force, receptor-ligand bindings, and thermal fluctuations; the receptor-ligand bonds are modeled as linear springs. Depending on the applied shear flow rate, three dynamic states of cell motion have been identified: (i) free motion, (ii) rolling adhesion, and (iii) firm adhesion. Of particular interest is the fraction of captured circulating tumor cells, defined as the capture ratio, via specific receptor-ligand bonds. The cell capture ratio decreases with increasing shear flow rate with a characteristic rate. Based on both experimental and theoretical results, the characteristic flow rate increases monotonically with increasing either cell-receptor or surface-ligand density within certain ranges. Utilizing it as a scaling parameter, flow-rate dependent capture ratios for various cell-surface combinations collapse onto a single curve described by an exponential formula.

  7. Acetylated deoxycholic (DCA) and cholic (CA) acids are potent ligands of pregnane X (PXR) receptor.

    PubMed

    Carazo, Alejandro; Hyrsova, Lucie; Dusek, Jan; Chodounska, Hana; Horvatova, Alzbeta; Berka, Karel; Bazgier, Vaclav; Gan-Schreier, Hongying; Chamulitrat, Waleé; Kudova, Eva; Pavek, Petr

    2017-01-04

    The Pregnane X (PXR), Vitamin D (VDR) and Farnesoid X (FXR) nuclear receptors have been shown to be receptors of bile acids controlling their detoxification or synthesis. Chenodeoxycholic (CDCA) and lithocholic (LCA) acids are ligands of FXR and VDR, respectively, whereas 3-keto and acetylated derivates of LCA have been described as ligands for all three receptors. In this study, we hypothesized that oxidation or acetylation at position 3, 7 and 12 of bile acids DCA (deoxycholic acid), LCA, CA (cholic acid), and CDCA by detoxification enzymes or microbiome may have an effect on the interactions with bile acid nuclear receptors. We employed reporter gene assays in HepG2 cells, the TR-FRET assay with recombinant PXR and RT-PCR to study the effects of acetylated and keto bile acids on the nuclear receptors activation and their target gene expression in differentiated hepatic HepaRG cells. We demonstrate that the DCA 3,12-diacetate and CA 3,7,12-triacetate derivatives are ligands of PXR and DCA 3,12-diacetate induces PXR target genes such as CYP3A4, CYP2B6 and ABCB1/MDR1. In conclusion, we found that acetylated DCA and CA are potent ligands of PXR. Whether the acetylated bile acid derivatives are novel endogenous ligands of PXR with detoxification or physiological functions should be further studied in ongoing experiments.

  8. Design and synthesis of novel dimeric morphinan ligands for kappa and micro opioid receptors.

    PubMed

    Neumeyer, John L; Zhang, Ao; Xiong, Wennan; Gu, Xiao-Hui; Hilbert, James E; Knapp, Brian I; Negus, S Stevens; Mello, Nancy K; Bidlack, Jean M

    2003-11-20

    A novel series of morphinans were synthesized, and their binding affinity at and functional selectivity for micro, delta, and kappa opioid receptors were evaluated. These dimeric ligands can be viewed as dimeric morphinans, which were formed by coupling two identical morphinan pharmacophores (cyclorphan (1) or MCL 101 (2)) with varying connecting spacers. Ligands 6 and 7 with alkyl spacers on the nitrogen position and ligands 8 and 9 in which the two morphinan pharmacophores were coupled by ether moieties at the 3-hydroxyl positions showed significant decrease in affinity at all three opioid receptors. An improvement in the affinity was achieved by introducing an ester moiety as the spacer in the dimeric morphinans. It was observed that the affinity of these ligands was sensitive to the character and length of the spacer. Compound 13 (MCL-139) with a 4-carbon ester spacer, compound 17 (MCL-144) containing a 10-carbon spacer, and compound 19 (MCL-145) with the conformationally constrained fumaryl spacer were the most potent ligands in this series, displaying excellent affinities at micro and kappa receptors (K(i) = 0.09-0.2 nM at micro and K(i) = 0.078-0.049 nM at kappa), which were comparable to the parent compound 2. Ligand 12, a compound containing only one morphinan pharmacophore and a long-chain ester group, had affinity at both micro and kappa receptors almost identical to that of the parent ligand 2. In the [(35)S]GTPgammaS binding assay, ligands 13, 17, and 19 and their parent morphinans 1 and 2 stimulated [(35)S]GTPgammaS binding mediated by the micro and kappa receptors. Compounds 13 and 17 were full kappa agonists and partial micro agonists, while compound 19 was a partial agonist at both micro and kappa receptors. These novel ligands, as well as their interesting pharmacological properties, will serve as the basis for our continuing investigation of the dimeric ligands as potential probes for the pharmacotherapy of cocaine abuse and may also open new

  9. Antihyperalgesic effects of imidazoline I2 receptor ligands in rat models of inflammatory and neuropathic pain

    PubMed Central

    Li, Jun-Xu; Thorn, David A; Qiu, Yanyan; Peng, Bi-Wen; Zhang, Yanan

    2014-01-01

    Background and Purpose A new imidazoline I2 receptor ligand, CR4056, is effective for chronic inflammatory pain and diabetic neuropathy. However, it is unclear whether other I2 receptor ligands have similar effects and whether antinociceptive tolerance develops with repeated treatment. Experimental Approach The Von Frey filament test was used to measure mechanical hyperalgesia and the plantar test to measure thermal hyperalgesia in rats injected with complete Freund's adjuvant (CFA) treatment or had undergone surgery to induce chronic constriction injury (CCI), models of inflammatory pain and peripheral neuropathic pain respectively. The effects of morphine and I2 receptor ligands, 2-BFI, BU224, tracizoline and CR4056, 3.2–32 mg·kg−1, i.p., on hyperalgesia or affective pain (as measured by a place escape/avoidance paradigm) were studied in separate experiments. Key Results Morphine and the I2 receptor ligands (2-BFI, BU224 and tracizoline) all dose-dependently attenuated mechanical and thermal hyperalgesia in CFA-treated rats. The anti-hyperalgesic effects of 2-BFI in CFA-treated and CCI rats were attenuated by the I2 receptor antagonist idazoxan. The combination of 2-BFI and morphine produced additive effects against mechanical hyperalgesia in CFA-treated rats. Repeated treatment (daily for 7–9 days) with 2-BFI or CR4056 did not produce antinociceptive tolerance in CFA-treated or CCI rats. Morphine and the I2 receptor ligands (2-BFI, BU224 and CR4056) were all effective at attenuating place escape/avoidance behaviour in CFA-treated rats. Conclusions and Implications Imidazoline I2 receptor ligands have antihyperalgesic effects in rat models of inflammatory and neuropathic pain and may represent a new class of pharmacotherapeutics for the management of chronic pain. PMID:24329196

  10. Ligands of the Neuropeptide Y Y2 receptor

    PubMed Central

    Mittapalli, Gopi Kumar; Roberts, Edward

    2015-01-01

    Neuropeptide Y (NPY) is one of the most abundant neuropeptides in the mammalian brain and exerts a variety of physiological processes in humans via four different receptor subtypes Y1, Y2, Y4 and Y5. Y2 receptor is the most abundant Y subtype receptor in the central nervous system and implicated with food intake, bone formation, affective disorders, alcohol and drugs of abuse, epilepsy, pain, and cancer. The lack of small molecule non-peptidic Y2 receptor modulators suitable as in vivo pharmacological tools hampered the progress to uncover the precise pharmacological role of Y2. Only in recent years, several potent, selective and non-peptidic Y2 antagonists have been discovered providing the tools to validate Y2 receptor as a therapeutic target. This article reviews Y2 receptor modulators mainly non-peptidic antagonists and their structure-activity relationships. PMID:24365162

  11. Identification of Receptor Ligands and Receptor Subtypes Using Antagonists in a Capillary Electrophoresis Single-Cell Biosensor Separation System

    NASA Astrophysics Data System (ADS)

    Fishman, Harvey A.; Orwar, Owe; Scheller, Richard H.; Zare, Richard N.

    1995-08-01

    A capillary electrophoresis system with single-cell biosensors as a detector has been used to separate and identify ligands in complex biological samples. The power of this procedure was significantly increased by introducing antagonists that inhibited the cellular response from selected ligand-receptor interactions. The single-cell biosensor was based on the ligand-receptor binding and G-protein-mediated signal transduction pathways in PC12 and NG108-15 cell lines. Receptor activation was measured as increases in cytosolic free calcium ion concentration by using fluorescence microscopy with the intracellular calcium ion indicator fluo-3 acetoxymethyl ester. Specifically, a mixture of bradykinin (BK) and acetylcholine (ACh) was fractionated and the components were identified by inhibiting the cellular response with icatibant (HOE 140), a selective antagonist to the BK B_2 receptor subtype (B_2BK), and atropine, an antagonist to muscarinic ACh receptor subtypes. Structurally related forms of BK were also identified based on inhibiting B_2BK receptors. Applications of this technique include identification of endogenous BK in a lysate of human hepatocellular carcinoma cells (Hep G2) and screening for bioactivity of BK degradation products in human blood plasma. The data demonstrate that the use of antagonists with a single-cell biosensor separation system aids identification of separated components and receptor subtypes.

  12. Programmable Multivalent Display of Receptor Ligands using Peptide Nucleic Acid Nanoscaffolds

    PubMed Central

    Englund, Ethan A.; Wang, Deyun; Fujigaki, Hidetsugu; Sakai, Hiroyasu; Micklitsch, Christopher M.; Ghirlando, Rodolfo; Martin-Manso, Gema; Pendrak, Michael L.; Roberts, David D.; Durell, Stewart R.; Appella, Daniel H.

    2012-01-01

    Multivalent effects dictate the binding affinity of multiple ligands on one molecular entity to receptors. Integrins are receptors that mediate cell attachment through multivalent binding to peptide sequences within the extracellular matrix, and overexpression promotes the metastasis of some cancers. Multivalent display of integrin antagonists enhances their efficacy, but current scaffolds have limited ranges and precision for the display of ligands. Here we present an approach to study multivalent effects across wide ranges of ligand number, density, and three-dimensional arrangement. Using L-lysine γ-substituted peptide nucleic acids, the multivalent effects of an integrin antagonist were examined over a range of 1 to 45 ligands. The optimal construct improves the inhibitory activity of the antagonist by two orders of magnitude against the binding of melanoma cells to the extracellular matrix in both in vitro and in vivo models. PMID:22233624

  13. A new Lamarckian genetic algorithm for flexible ligand-receptor docking.

    PubMed

    Fuhrmann, Jan; Rurainski, Alexander; Lenhof, Hans-Peter; Neumann, Dirk

    2010-07-15

    We present a Lamarckian genetic algorithm (LGA) variant for flexible ligand-receptor docking which allows to handle a large number of degrees of freedom. Our hybrid method combines a multi-deme LGA with a recently published gradient-based method for local optimization of molecular complexes. We compared the performance of our new hybrid method to two non gradient-based search heuristics on the Astex diverse set for flexible ligand-receptor docking. Our results show that the novel approach is clearly superior to other LGAs employing a stochastic optimization method. The new algorithm features a shorter run time and gives substantially better results, especially with increasing complexity of the ligands. Thus, it may be used to dock ligands with many rotatable bonds with high efficiency.

  14. Photomodulation of G Protein-Coupled Adenosine Receptors by a Novel Light-Switchable Ligand

    PubMed Central

    2015-01-01

    The adenosinergic system operates through G protein-coupled adenosine receptors, which have become promising therapeutic targets for a wide range of pathological conditions. However, the ubiquity of adenosine receptors and the eventual lack of selectivity of adenosine-based drugs have frequently diminished their therapeutic potential. Accordingly, here we aimed to develop a new generation of light-switchable adenosine receptor ligands that change their intrinsic activity upon irradiation, thus allowing the spatiotemporal control of receptor functioning (i.e., receptor activation/inactivation dependent on location and timing). Therefore, we synthesized an orthosteric, photoisomerizable, and nonselective adenosine receptor agonist, nucleoside derivative MRS5543 containing an aryl diazo linkage on the N6 substituent, which in the dark (relaxed isomer) behaved as a full adenosine A3 receptor (A3R) and partial adenosine A2A receptor (A2AR) agonist. Conversely, upon photoisomerization with blue light (460 nm), it remained a full A3R agonist but became an A2AR antagonist. Interestingly, molecular modeling suggested that structural differences encountered within the third extracellular loop of each receptor could modulate the intrinsic, receptor subtype-dependent, activity. Overall, the development of adenosine receptor ligands with photoswitchable activity expands the pharmacological toolbox in support of research and possibly opens new pharmacotherapeutic opportunities. PMID:25248077

  15. Ligand-binding dynamics rewire cellular signaling via Estrogen Receptor

    PubMed Central

    Srinivasan, Sathish; Nwachukwu, Jerome C.; Parent, Alex A.; Cavett, Valerie; Nowak, Jason; Hughes, Travis S.; Kojetin, Douglas J.; Katzenellenbogen, John A.; Nettles, Kendall W.

    2013-01-01

    Ligand-binding dynamics control allosteric signaling through the estrogen receptor-α (ERα), but the biological consequences of such dynamic binding orientations are unknown. Here, we compare a set of ER ligands having dynamic binding orientation (dynamic ligands) with a control set of isomers that are constrained to bind in a single orientation (constrained ligands). Proliferation of breast cancer cells directed by constrained ligands is associated with DNA binding, coactivator recruitment and activation of the estrogen-induced gene GREB1, reflecting a highly interconnected signaling network. In contrast, proliferation driven by dynamic ligands is associated with induction of ERα-mediated transcription in a DNA-binding domain (DBD)-dependent manner. Further, dynamic ligands displayed enhanced anti-inflammatory activity. The DBD-dependent profile was predictive of these signaling patterns in a larger diverse set of natural and synthetic ligands. Thus, ligand dynamics directs unique signaling pathways, and reveals a novel role of the DBD in allosteric control of ERα-mediated signaling. PMID:23524984

  16. The unique extracellular disulfide loop of the glycine receptor is a principal ligand binding element.

    PubMed Central

    Rajendra, S; Vandenberg, R J; Pierce, K D; Cunningham, A M; French, P W; Barry, P H; Schofield, P R

    1995-01-01

    A loop structure, formed by the putative disulfide bridging of Cys198 and Cys209, is a principal element of the ligand binding site in the glycine receptor (GlyR). Disruption of the loop's tertiary structure by Ser mutations of these Cys residues either prevented receptor assembly on the cell surface, or created receptors unable to be activated by agonists or to bind the competitive antagonist, strychnine. Mutation of residues Lys200, Tyr202 and Thr204 within this loop reduced agonist binding and channel activation sensitivities by up to 55-, 520- and 190-fold, respectively, without altering maximal current sizes, and mutations of Lys200 and Tyr202 abolished strychnine binding to the receptor. Removal of the hydroxyl moiety from Tyr202 by mutation to Phe profoundly reduced agonist sensitivity, whilst removal of the benzene ring abolished strychnine binding, thus demonstrating that Tyr202 is crucial for both agonist and antagonist binding to the GlyR. Tyr202 also influences receptor assembly on the cell surface, with only large chain substitutions (Phe, Leu and Arg, but not Thr, Ser and Ala) forming functional receptors. Our data demonstrate the presence of a second ligand binding site in the GlyR, consistent with the three-loop model of ligand binding to the ligand-gated ion channel superfamily. Images PMID:7621814

  17. A comprehensive ligand based mapping of the σ₂ receptor binding pocket.

    PubMed

    Rhoades, Derek J; Kinder, David H; Mahfouz, Tarek M

    2014-01-01

    The sigma (σ) receptor system consists of at least two major receptor subtypes: σ₁ and σ₂. Several potential therapeutic applications would benefit from structural knowledge of the σ₂ receptor but gaining this knowledge has been hampered by the difficulties associated with its isolation and, thus, characterization. Here, a ligand based approach has been adopted using the program PHASE® and a group of 41 potent and structurally diverse σ₂ ligands to develop several pharmacophore models for different families of σ₂ ligands. These pharmacophores were analyzed to identify the different binding modes to the receptor and were combined together to construct a comprehensive pharmacophore that was used to develop a structural model for the σ₂ binding pocket. A total of six binding modes were identified and could be classified as neutral or charged modes. The results presented here also indicate the significance of hydrophobic interactions to σ₂ binding and the requirement of hydrogen bonding interactions to increase the affinity for this receptor subtype. This work adds breadth to our knowledge of this receptor's binding site, and should contribute significantly to the development of novel selective σ₂ ligands.

  18. Ligand specificities of recombinant retinoic acid receptors RAR alpha and RAR beta.

    PubMed Central

    Crettaz, M; Baron, A; Siegenthaler, G; Hunziker, W

    1990-01-01

    Binding of retinoic acid (RA) to specific RA receptors alpha and beta (RAR alpha and RAR beta) was studied. Receptors were obtained in two ways: (1) full-length receptors were produced by transient expression of the respective human cDNAs in COS 1 cells; and (2) the ligand-binding domains of RAR alpha and RAR beta were produced in Escherichia coli. RA binding to the wild-type and truncated forms of the receptor was identical for both RAR alpha and RAR beta, indicating that the ligand-binding domains have retained the binding characteristics of the intact receptors. Furthermore, RA bound with the same affinity to both RAR alpha and RAR beta. Only retinoid analogues with an acidic end-group were able to actively bind to both receptors. On measuring the binding of various retinoids, we have found that the properties of the ligand-binding sites of RAR alpha and RAR beta were rather similar. Two retinoid analogues were capable of binding preferentially to either RAR alpha or RAR beta, suggesting that it may be possible to synthesize specific ligands for RAR alpha and RAR beta. PMID:2176462

  19. Identification of a ligand-dependent switch within a muscarinic receptor.

    PubMed

    Spalding, T A; Burstein, E S; Henderson, S C; Ducote, K R; Brann, M R

    1998-08-21

    G-protein-coupled receptors spontaneously switch between active and inactive conformations. Agonists stabilize the active conformation, whereas antagonists stabilize the inactive conformation. In a systematic search for residues that participate in receptor function, several regions of the m5 muscarinic receptor were randomly mutated and tested for their functional properties. Mutations spanning one face of transmembrane 6 (TM6) were found to induce high levels of receptor activity in the absence of agonists (constitutive activity). The same face of TM6 contained several residues crucial for receptor activation by agonists and one residue identified as a contact site for both agonists and antagonists. In addition, one mutation induced agonist-like responses from the receptor when exposed to classical antagonists. These results suggest that TM6 is a switch that defines the activation state of the receptor, and that ligand interactions with TM6 stabilize the receptor in either an active or an inactive conformation.

  20. Targeting Ligand-Dependent and Ligand-Independent Androgen Receptor Signaling in Prostate Cancer

    DTIC Science & Technology

    2015-10-01

    Pugh M, Raj GV, Brown GD, D’Santos C, Robinson JL, Silva G, Launchbury R, Perou CM, Stingl J, Caldas C, Tilley WD, Carroll JS. Progesterone receptor... Peng Y, Raj GV, Yee D, Lange CA. Progesterone receptor-B enhances estrogen responsiveness of breast cancer cells via scaffolding PELP1- and estrogen

  1. Disruption of Ah Receptor Signaling during Mouse Development Leads to Abnormal Cardiac Structure and Function in the Adult

    PubMed Central

    Carreira, Vinicius S.; Fan, Yunxia; Kurita, Hisaka; Wang, Qin; Ko, Chia-I; Naticchioni, Mindi; Jiang, Min; Koch, Sheryl; Zhang, Xiang; Biesiada, Jacek; Medvedovic, Mario; Xia, Ying; Rubinstein, Jack; Puga, Alvaro

    2015-01-01

    The Developmental Origins of Health and Disease (DOHaD) Theory proposes that the environment encountered during fetal life and infancy permanently shapes tissue physiology and homeostasis such that damage resulting from maternal stress, poor nutrition or exposure to environmental agents may be at the heart of adult onset disease. Interference with endogenous developmental functions of the aryl hydrocarbon receptor (AHR), either by gene ablation or by exposure in utero to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a potent AHR ligand, causes structural, molecular and functional cardiac abnormalities and altered heart physiology in mouse embryos. To test if embryonic effects progress into an adult phenotype, we investigated whether Ahr ablation or TCDD exposure in utero resulted in cardiac abnormalities in adult mice long after removal of the agent. Ten-months old adult Ahr-/- and in utero TCDD-exposed Ahr+/+ mice showed sexually dimorphic abnormal cardiovascular phenotypes characterized by echocardiographic findings of hypertrophy, ventricular dilation and increased heart weight, resting heart rate and systolic and mean blood pressure, and decreased exercise tolerance. Underlying these effects, genes in signaling networks related to cardiac hypertrophy and mitochondrial function were differentially expressed. Cardiac dysfunction in mouse embryos resulting from AHR signaling disruption seems to progress into abnormal cardiac structure and function that predispose adults to cardiac disease, but while embryonic dysfunction is equally robust in males and females, the adult abnormalities are more prevalent in females, with the highest severity in Ahr-/- females. The findings reported here underscore the conclusion that AHR signaling in the developing heart is one potential target of environmental factors associated with cardiovascular disease. PMID:26555816

  2. Generating "fragment-based virtual library" using pocket similarity search of ligand-receptor complexes.

    PubMed

    Khashan, Raed S

    2015-01-01

    As the number of available ligand-receptor complexes is increasing, researchers are becoming more dedicated to mine these complexes to aid in the drug design and development process. We present free software which is developed as a tool for performing similarity search across ligand-receptor complexes for identifying binding pockets which are similar to that of a target receptor. The search is based on 3D-geometric and chemical similarity of the atoms forming the binding pocket. For each match identified, the ligand's fragment(s) corresponding to that binding pocket are extracted, thus forming a virtual library of fragments (FragVLib) that is useful for structure-based drug design. The program provides a very useful tool to explore available databases.

  3. Sliding tethered ligands add topological interactions to the toolbox of ligand–receptor design

    PubMed Central

    Bauer, Martin; Kékicheff, Patrick; Iss, Jean; Fajolles, Christophe; Charitat, Thierry; Daillant, Jean; Marques, Carlos M.

    2015-01-01

    Adhesion in the biological realm is mediated by specific lock-and-key interactions between ligand–receptor pairs. These complementary moieties are ubiquitously anchored to substrates by tethers that control the interaction range and the mobility of the ligands and receptors, thus tuning the kinetics and strength of the binding events. Here we add sliding anchoring to the toolbox of ligand–receptor design by developing a family of tethered ligands for which the spacer can slide at the anchoring point. Our results show that this additional sliding degree of freedom changes the nature of the adhesive contact by extending the spatial range over which binding may sustain a significant force. By introducing sliding tethered ligands with self-regulating length, this work paves the way for the development of versatile and reusable bio-adhesive substrates with potential applications for drug delivery and tissue engineering. PMID:26350224

  4. NMR and computational methods in the structural and dynamic characterization of ligand-receptor interactions.

    PubMed

    Ghitti, Michela; Musco, Giovanna; Spitaleri, Andrea

    2014-01-01

    The recurrent failures in drug discovery campaigns, the asymmetry between the enormous financial investments and the relatively scarce results have fostered the development of strategies based on complementary methods. In this context in recent years the rigid lock-and-key binding concept had to be revisited in favour of a dynamic model of molecular recognition accounting for conformational changes of both the ligand and the receptor. The high level of complexity required by a dynamic description of the processes underlying molecular recognition requires a multidisciplinary investigation approach. In this perspective, the combination of nuclear magnetic resonance spectroscopy with molecular docking, conformational searches along with molecular dynamics simulations has given new insights into the dynamic mechanisms governing ligand receptor interactions, thus giving an enormous contribution to the identification and design of new and effective drugs. Herein a succinct overview on the applications of both NMR and computational methods to the structural and dynamic characterization of ligand-receptor interactions will be presented.

  5. Tuned-Affinity Bivalent Ligands for the Characterization of Opioid Receptor Heteromers

    PubMed Central

    2012-01-01

    Opioid receptors, including the μ- and δ-opioid receptors (MOR and DOR), are important targets for the treatment of pain. Although there is mounting evidence that these receptors form heteromers, the functional role of the MOR/DOR heteromer remains unresolved. We have designed and synthesized bivalent ligands as tools to elucidate the functional role of the MOR/DOR heteromer. Our ligands (L2 and L4) are comprised of a compound with low affinity at the DOR tethered to a compound with high affinity at the MOR, with the goal of producing ligands with “tuned affinity” at MOR/DOR heteromers as compared to DOR homomers. Here, we show that both L2 and L4 demonstrate enhanced affinity at MOR/DOR heteromers as compared to DOR homomers, thereby providing unique pharmacological tools to dissect the role of the MOR/DOR heteromer in pain. PMID:23585918

  6. Muscarinic receptors as model targets and antitargets for structure-based ligand discovery.

    PubMed

    Kruse, Andrew C; Weiss, Dahlia R; Rossi, Mario; Hu, Jianxin; Hu, Kelly; Eitel, Katrin; Gmeiner, Peter; Wess, Jürgen; Kobilka, Brian K; Shoichet, Brian K

    2013-10-01

    G protein-coupled receptors (GPCRs) regulate virtually all aspects of human physiology and represent an important class of therapeutic drug targets. Many GPCR-targeted drugs resemble endogenous agonists, often resulting in poor selectivity among receptor subtypes and restricted pharmacologic profiles. The muscarinic acetylcholine receptor family exemplifies these problems; thousands of ligands are known, but few are receptor subtype-selective and nearly all are cationic in nature. Using structure-based docking against the M2 and M3 muscarinic receptors, we screened 3.1 million molecules for ligands with new physical properties, chemotypes, and receptor subtype selectivities. Of 19 docking-prioritized molecules tested against the M2 subtype, 11 had substantial activity and 8 represented new chemotypes. Intriguingly, two were uncharged ligands with low micromolar to high nanomolar Ki values, an observation with few precedents among aminergic GPCRs. To exploit a single amino-acid substitution among the binding pockets between the M2 and M3 receptors, we selected molecules predicted by docking to bind to the M3 and but not the M2 receptor. Of 16 molecules tested, 8 bound to the M3 receptor. Whereas selectivity remained modest for most of these, one was a partial agonist at the M3 receptor without measurable M2 agonism. Consistent with this activity, this compound stimulated insulin release from a mouse β-cell line. These results support the ability of structure-based discovery to identify new ligands with unexplored chemotypes and physical properties, leading to new biologic functions, even in an area as heavily explored as muscarinic pharmacology.

  7. Unnatural agrochemical ligands for engineered abscisic acid receptors.

    PubMed

    Rodriguez, Pedro L; Lozano-Juste, Jorge

    2015-06-01

    Existing agrochemicals can be endowed with new applications through protein engineering of plant receptors. A recent study shows an engineered PYR1 ABA receptor can be activated by mandipropamid. Plants engineered with such PYR1 variant are responsive to this agrochemical, which confers protection against drought through activation of ABA signaling.

  8. Photoaffinity ligand for dopamine D2 receptors: azidoclebopride

    SciTech Connect

    Niznik, H.B.; Guan, J.H.; Neumeyer, J.L.; Seeman, P.

    1985-02-01

    In order to label D2 dopamine receptors selectively and covalently by means of a photosensitive compound, azidoclebopride was synthesized directly from clebopride. The dissociation constant (KD) of clebopride for the D2 dopamine receptor (canine brain striatum) was 1.5 nM, while that for azidoclebopride was 21 nM. The affinities of both clebopride and azidoclebopride were markedly reduced in the absence of sodium chloride. In the presence of ultraviolet light, azidoclebopride inactivated D2 dopamine receptors irreversibly, as indicated by the inability of the receptors to bind (/sup 3/H)spiperone. Maximal photoinactivation of about 60% of the D2 dopamine receptors occurred at 1 microM azidoclebopride; 30% of the receptors were inactivated at 80 nM azidoclebopride (pseudo-IC50). Dopamine agonists selectively protected the D2 receptors from being inactivated by azidoclebopride, the order of potency being (-)-N-n-propylnorapomorphine greater than apomorphine greater than (+/-)-6,7-dihydroxy-2-aminotetralin greater than (+)-N-n-propylnorapomorphine greater than dopamine greater than noradrenaline greater than serotonin. Similarly, dopaminergic antagonists prevented the photoinactivation of D2 receptors by azidoclebopride with the following order of potency: spiperone greater than (+)-butaclamol greater than haloperidol greater than clebopride greater than (-)-sulpiride greater than (-)-butaclamol.

  9. Could sigma receptor ligands be a treatment for methamphetamine addiction?

    PubMed

    Rodvelt, Kelli R; Miller, Dennis K

    2010-09-01

    Methamphetamine's effects are generally considered to be mediated via monoamine transporters; however, it has comparable affinity for sigma receptors. Sigma receptors influence the downstream dopamine systems that are targeted by methamphetamine treatment. Research investigating the effect of sigma receptor agonists on methamphetamine-associated neurochemical and behavioral properties remains controversial; however, the general trend indicates an enhancement of stimulant effects. In contrast, sigma receptor antagonists attenuate methamphetamine-induced neurotoxic and behavioral properties. Together, these studies highlight an important role for sigma receptors in methamphetamine's addictive properties and the consequences of methamphetamine intoxication. Additional research is necessary to elucidate the precise mechanisms underlying their involvement and their role as a potential target for anti-methamphetamine pharmacotherapies.

  10. A Simple Method for Improving Torsion Optimization of Ligand Molecules in Receptor Binding Sites.

    PubMed

    Che, Jianwei

    2005-07-01

    A simple but effective method is introduced for optimizing ligand molecules in torsion space within receptor binding sites. The algorithm makes use of geometric constraints of ligand molecules to search for energetically favorable conformations. It is applied to a conjugate gradient (CG) method as an example. During conformational energy optimization, new line search directions are modified according to the spatial span of rotational groups in ligand molecules. Significant improvements were observed in terms of the abilities both to recover global optimal structures and to obtain lower energy ensembles. This simple algorithm allows rapid implementation and can be incorporated into other conformational energy optimization techniques.

  11. Structure-based design of estrogen receptor-beta selective ligands.

    PubMed

    Manas, Eric S; Unwalla, Rayomand J; Xu, Zhang B; Malamas, Michael S; Miller, Chris P; Harris, Heather A; Hsiao, Chulai; Akopian, Tatos; Hum, Wah-Tung; Malakian, Karl; Wolfrom, Scott; Bapat, Ashok; Bhat, Ramesh A; Stahl, Mark L; Somers, William S; Alvarez, Juan C

    2004-11-24

    We present the structure-based optimization of a series of estrogen receptor-beta (ERbeta) selective ligands. X-ray cocrystal structures of these ligands complexed to both ERalpha and ERbeta are described. We also discuss how molecular modeling was used to take advantage of subtle differences between the two binding cavities in order to optimize selectivity for ERbeta over ERalpha. Quantum chemical calculations are utilized to gain insight into the mechanism of selectivity enhancement. Despite only two relatively conservative residue substitutions in the ligand binding pocket, the most selective compounds have greater than 100-fold selectivity for ERbeta relative to ERalpha when measured using a competitive radioligand binding assay.

  12. Conserved residues in RF-NH₂ receptor models identify predicted contact sites in ligand-receptor binding.

    PubMed

    Bass, C; Katanski, C; Maynard, B; Zurro, I; Mariane, E; Matta, M; Loi, M; Melis, V; Capponi, V; Muroni, P; Setzu, M; Nichols, R

    2014-03-01

    Peptides in the RF-NH2 family are grouped together based on an amidated dipeptide C terminus and signal through G-protein coupled receptors (GPCRs) to influence diverse physiological functions. By determining the mechanisms underlying RF-NH2 signaling targets can be identified to modulate physiological activity; yet, how RF-NH2 peptides interact with GPCRs is relatively unexplored. We predicted conserved residues played a role in Drosophila melanogaster RF-NH2 ligand-receptor interactions. In this study D. melanogaster rhodopsin-like family A peptide GPCRs alignments identified eight conserved residues unique to RF-NH2 receptors. Three of these residues were in extra-cellular loops of modeled RF-NH2 receptors and four in transmembrane helices oriented into a ligand binding pocket to allow contact with a peptide. The eighth residue was unavailable for interaction; yet its conservation suggested it played another role. A novel hydrophobic region representative of RF-NH2 receptors was also discovered. The presence of rhodopsin-like family A GPCR structural motifs including a toggle switch indicated RF-NH2s signal classically; however, some features of the DMS receptors were distinct from other RF-NH2 GPCRs. Additionally, differences in RF-NH2 receptor structures which bind the same peptide explained ligand specificity. Our novel results predicted conserved residues as RF-NH2 ligand-receptor contact sites and identified unique and classic structural features. These discoveries will aid antagonist design to modulate RF-NH2 signaling.

  13. Importance of the pharmacological profile of the bound ligand in enrichment on nuclear receptors: toward the use of experimentally validated decoy ligands.

    PubMed

    Lagarde, Nathalie; Zagury, Jean-François; Montes, Matthieu

    2014-10-27

    The evaluation of virtual ligand screening methods is of major importance to ensure their reliability. Taking into account the agonist/antagonist pharmacological profile should improve the quality of the benchmarking data sets since ligand binding can induce conformational changes in the nuclear receptor structure and such changes may vary according to the agonist/antagonist ligand profile. We indeed found that splitting the agonist and antagonist ligands into two separate data sets for a given nuclear receptor target significantly enhances the quality of the evaluation. The pharmacological profile of the ligand bound in the binding site of the target structure was also found to be an additional critical parameter. We also illustrate that active compound data sets for a given pharmacological activity can be used as a set of experimentally validated decoy ligands for another pharmacological activity to ensure a reliable and challenging evaluation of virtual screening methods.

  14. Functional interaction of nuclear receptor coactivator 4 with aryl hydrocarbon receptor

    SciTech Connect

    Kollara, Alexandra; Brown, Theodore J. . E-mail: brown@mshri.on.ca

    2006-07-28

    Aryl hydrocarbon receptor (AhR) transcriptional activity is enhanced by interaction with p160 coactivators. We demonstrate here that NcoA4, a nuclear receptor coactivator, interacts with and amplifies AhR action. NcoA4-AhR and NcoA4-ARNT interactions were demonstrated by immunoprecipitation in T47D breast cancer and COS cells and was independent of ligand. Overexpression of NcoA4 enhanced AhR transcriptional activity 3.2-fold in the presence of dioxin, whereas overexpression of a splice variant, NcoA4{beta}, as well as a variant lacking the C-terminal region enhanced AhR transcriptional activity by only 1.6-fold. Enhanced AhR signaling by NcoA4 was independent of the LXXLL and FXXLF motifs or of the activation domain. NcoA4 protein localized to cytoplasm in the absence of dioxin and in both the cytoplasm and nucleus following dioxin treatment. NcoA4-facilitation of AhR activity was abolished by overexpression of androgen receptor, suggesting a potential competition of AhR and androgen receptor for NcoA4. These findings thus demonstrate a functional interaction between NcoA4 and AhR that may alter AhR activity to affect disease development and progression.

  15. The Aryl Hydrocarbon Receptor: A Key Bridging Molecule of External and Internal Chemical Signals

    PubMed Central

    Tian, Jijing; Feng, Yu; Fu, Hualing; Xie, Heidi Qunhui; Jiang, Joy Xiaosong; Zhao, Bin

    2015-01-01

    The aryl hydrocarbon receptor (AhR) is a highly evolutionary conserved, ligand-activated transcription factor that is best known to mediate the toxicities of dioxins and dioxin-like compounds. Phenotype of AhR-null mice, together with the recent discovery of a variety of endogenous and plant-derived ligands, point to the integral roles of AhR in normal cell physiology, in addition to its roles in sensing the environmental chemicals. Here, we summarize the current knowledge about AhR signaling pathways, its ligands and AhR-mediated effects on cell specialization, host defense and detoxification. AhR-mediated health effects particularly in liver, immune, and nervous systems, as well as in tumorgenesis are discussed. Dioxin-initiated embryotoxicity and immunosuppressive effects in fish and birds are reviewed. Recent data demonstrate that AhR is a convergence point of multiple signaling pathways that inform the cell of its external and internal environments. As such, AhR pathway is a promising potential target for therapeutics targeting nervous, liver, and autoimmune diseases through AhR ligand-mediated interventions and other perturbations of AhR signaling. Additionally, using available laboratory data obtained on animal models, AhR-centered adverse outcome pathway analysis is useful in reexamining known and potential adverse outcomes of specific or mixed compounds on wildlife. PMID:26079192

  16. Human NK cells in acute myeloid leukaemia patients: analysis of NK cell-activating receptors and their ligands.

    PubMed

    Sanchez-Correa, Beatriz; Morgado, Sara; Gayoso, Inmaculada; Bergua, Juan M; Casado, Javier G; Arcos, Maria Jose; Bengochea, Maria Luisa; Duran, Esther; Solana, Rafael; Tarazona, Raquel

    2011-08-01

    Natural killer (NK) cell activation is strictly regulated to ensure that healthy cells are preserved, but tumour-transformed or virus-infected cells are recognized and eliminated. To carry out this selective killing, NK cells have an ample repertoire of receptors on their surface. Signalling by inhibitory and activating receptors by interaction with their ligands will determine whether the NK cell becomes activated and kills the target cell. Here, we show reduced expression of NKp46, NKp30, DNAM-1, CD244 and CD94/NKG2C activating receptors on NK cells from acute myeloid leukaemia patients. This reduction may be induced by chronic exposure to their ligands on leukaemic blasts. The analysis of ligands for NK cell-activating receptors showed that leukaemic blasts from the majority of patients express ligands for NK cell-activating receptors. DNAM-1 ligands are frequently expressed on blasts, whereas the expression of the NKG2D ligand MICA/B is found in half of the patients and CD48, a ligand for CD244, in only one-fourth of the patients. The decreased expression of NK cell-activating receptors and/or the heterogeneous expression of ligands for major receptors on leukaemic blasts can lead to an inadequate tumour immunosurveillance by NK cells. A better knowledge of the activating receptor repertoire on NK cells and their putative ligands on blasts together with the possibility to modulate their expression will open new possibilities for the use of NK cells in immunotherapy against leukaemia.

  17. Segregation of receptor-ligand complexes in cell adhesion zones: phase diagrams and the role of thermal membrane roughness

    NASA Astrophysics Data System (ADS)

    Różycki, B.; Lipowsky, R.; Weikl, T. R.

    2010-09-01

    The adhesion zone of immune cells, the 'immunological synapse', exhibits characteristic domains of receptor-ligand complexes. The domain formation is probably caused by a length difference of the receptor-ligand complexes, and has been investigated in experiments in which T cells adhere to supported membranes with anchored ligands. For supported membranes with two types of anchored ligands, MHCp and ICAM1, which bind to the T-cell receptor (TCR) and the receptor LFA1 in the cell membrane, the coexistence of domains of the TCR-MHCp and LFA1-ICAM1 complexes in the cell adhesion zone has been observed for a wide range of ligand concentrations and affinities. For supported membranes with long and short ligands that bind to the same cell receptor CD2, in contrast, domain coexistence has been observed for a quite narrow ratio of ligand concentrations. In this paper, we determine detailed phase diagrams for cells adhering to supported membranes with a statistical-physical model of cell adhesion. We find a characteristic difference between the adhesion scenarios in which two types of ligands in a supported membrane bind (i) to the same cell receptor or (ii) to two different cell receptors, which helps us to explain the experimental observations. Our phase diagrams fully include thermal shape fluctuations of the cell membranes on nanometer scales, which lead to a critical point for the domain formation and to a cooperative binding of the receptors and ligands.

  18. A semisynthetic Eph receptor tyrosine kinase provides insight into ligand-induced kinase activation

    PubMed Central

    Singla, Nikhil; Erdjument-Bromage, Hediye; Himanen, Juha P.; Muir, Tom W.; Nikolov, Dimitar B.

    2011-01-01

    SUMMARY We have developed a methodology for generating milligram amounts of functional Eph tyrosine kinase receptor using the protein engineering approach of expressed protein ligation. Stimulation with ligand induces efficient autophosphorylation of the semisynthetic Eph construct. The in vitro phosphorylation of key Eph tyrosine residues upon ligand-induced activation was monitored via time-resolved, quantitative phosphoproteomics, suggesting a precise and unique order of phosphorylation of the Eph tyrosines in the kinase activation process. To our knowledge, this work represents the first reported semisynthesis of a receptor tyrosine kinase and provides a potentially general method for producing single-pass membrane proteins for structural and biochemical characterization. PMID:21439481

  19. Budded baculoviruses as a tool for a homogeneous fluorescence anisotropy-based assay of ligand binding to G protein-coupled receptors: the case of melanocortin 4 receptors.

    PubMed

    Veiksina, Santa; Kopanchuk, Sergei; Rinken, Ago

    2014-01-01

    We present here the implementation of budded baculoviruses that display G protein-coupled receptors on their surfaces for the investigation of ligand-receptor interactions using fluorescence anisotropy (FA). Melanocortin 4 (MC4) receptors and the fluorescent ligand Cy3B-NDP-α-MSH were used as the model system. The real-time monitoring of reactions and the high assay quality allow the application of global data analysis with kinetic mechanistic models that take into account the effect of nonspecific interactions and the depletion of the fluorescent ligand during the reaction. The receptor concentration, affinity and kinetic parameters of fluorescent ligand binding as well as state anisotropies for different fluorescent ligand populations were determined. At low Cy3B-NDP-α-MSH concentrations, a one-site receptor-ligand binding model described the processes, whereas divergence from this model was observed at higher ligand concentrations, which indicated a more complex mechanism of interactions similar to those mechanisms that have been found in experiments with radioactive ligands. The information obtained from our kinetic experiments and the inherent flexibility of FA assays also allowed the estimation of binding parameters for several MC4 receptor-specific unlabelled compounds. In summary, the FA assay that was developed with budded baculoviruses led the experimental data to a level that would solve complex models of receptor-ligand interactions also for other receptor systems and would become as a valuable tool for the screening of pharmacologically active compounds.

  20. Dual Role of the Second Extracellular Loop of the Cannabinoid Receptor 1: Ligand Binding and Receptor Localization

    PubMed Central

    Ahn, Kwang H.; Bertalovitz, Alexander C.; Mierke, Dale F.

    2009-01-01

    The seven transmembrane α-helices of G protein-coupled receptors (GPCRs) are the hallmark of this superfamily. Intrahelical interactions are critical to receptor assembly and, for the GPCR subclass that binds small molecules, ligand binding. Most research has focused on identifying the ligand binding pocket within the helical bundle, whereas the role of the extracellular loops remains undefined. Molecular modeling of the cannabinoid receptor 1 (CB1) extracellular loop 2 (EC2), however, suggests that EC2 is poised for key interactions. To test this possibility, we employed alanine scanning mutagenesis of CB1 EC2 and identified two distinct regions critical for ligand binding, G protein coupling activity, and receptor trafficking. Receptors with mutations in the N terminus of EC2 (W255A, N256A) were retained in the endoplasmic reticulum and did not bind the agonist (1R,3R,4R)-3-[2-hydroxy-4-(1,1-dimethylheptyl)-phenyl]-4-(3-hydroxypropyl)cyclohexan-1-ol (CP55940) or the inverse agonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide(SR141716A). In contrast, the C terminus of EC2 differentiates agonist and inverse agonist; the P269A, H270A, and I271A receptors exhibited diminished binding for several agonists but bound inverse agonists SR141716A, N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251), and 4-[6-methoxy-2-(4-methoxyphenyl)benzofuran-3-carbonyl]benzonitrile (LY320135) with wild-type receptor affinity. The F268A receptor involving substitution in the Cys-X-X-X-Ar motif, displayed both impaired localization and ligand binding. Other amino acid substitutions at position 268 revealed that highly hydrophobic residues are required to accomplish both functions. It is noteworthy that a F268W receptor was trafficked to the cell surface yet displayed differential binding preference for inverse agonists comparable with the P269A, H270A, and I271A receptors. The findings

  1. DEPENDENCE OF PPAR LIGAND-INDUCED MAPK SIGNALING ON EPIDERMAL GROWTH FACTOR RECEPTOR TRANSACTIVATION HEPARIN-BINDING EGF CLEAVAGE MEDIATES ZINC-INDUCED EGF RECEPTOR PHOSPHORYLATION

    EPA Science Inventory

    Peroxisome proliferator-activated receptors (PPARs) are nuclear hormone receptors that function as ligand-activated transcription factors regulating lipid metabolism and homeostasis. In addition to their ability to regulate PPAR-mediated gene transcription, PPARalpha and gamma li...

  2. A nonplanar porphyrin-based receptor molecule for chiral amine ligands

    SciTech Connect

    MUZZI,CINZIA M.; MEDFORTH,CRAIG J.; SMITH,KEVIN M.; JIA,SONG-LING; SHELNUTT,JOHN A.

    2000-03-06

    A novel porphyrin-based receptor molecule for chiral amine ligands is described in which nonplanarity of the porphyrin macrocycle is used to orient the ligand and to enhance porphyrin-ligand interactions. The porphyrin macrocycle provides a versatile platform upon which to build elaborate superstructures, and this feature coupled with a rich and well-developed synthetic chemistry has led to the synthesis of many elegant models of heme protein active sites and numerous porphyrin-based receptor molecules. One design feature which is not usually considered in the design of porphyrin-based receptor molecules is nonplanarity of the porphyrin ring, although there are a few systems such as the pyridine sensitive Venus Flytrap and the chirality-memory molecule which illustrate that nonplanar porphyrin-based receptors can display unique and interesting behavior. Given the novel properties of these receptors and the continuing interest in the effects of nonplanarity on the properties of porphyrins the authors decided to investigate in more detail the potential applications of nonplanarity in the design of porphyrin-based receptors. Herein, they describe the design, synthesis, and characterization of a new kind of nonplanar porphyrin-based receptor molecule for chiral amines.

  3. Expression of a glycosylphosphatidylinositol-anchored ligand, growth hormone, blocks receptor signalling

    PubMed Central

    Guesdon, François; Kaabi, Yahia; Riley, Aiden H.; Wilkinson, Ian R.; Gray, Colin; James, David C.; Artymiuk, Peter J.; Sayers, Jon R.; Ross, Richard J.

    2012-01-01

    We have investigated the interaction between GH (growth hormone) and GHR (GH receptor). We previously demonstrated that a truncated GHR that possesses a transmembrane domain but no cytoplasmic domain blocks receptor signalling. Based on this observation we investigated the impact of tethering the receptor's extracellular domain to the cell surface using a native lipid GPI (glycosylphosphatidylinositol) anchor. We also investigated the effect of tethering GH, the ligand itself, to the cell surface and demonstrated that tethering either the ecGHR (extracellular domain of GHR) or the ligand itself to the cell membrane via a GPI anchor greatly attenuates signalling. To elucidate the mechanism for this antagonist activity, we used confocal microscopy to examine the fluorescently modified ligand and receptor. GH–GPI was expressed on the cell surface and formed inactive receptor complexes that failed to internalize and blocked receptor activation. In conclusion, contrary to expectation, tethering an agonist to the cell surface can generate an inactive hormone receptor complex that fails to internalize. PMID:23013472

  4. Expression of a glycosylphosphatidylinositol-anchored ligand, growth hormone, blocks receptor signalling.

    PubMed

    Guesdon, François; Kaabi, Yahia; Riley, Aiden H; Wilkinson, Ian R; Gray, Colin; James, David C; Artymiuk, Peter J; Sayers, Jon R; Ross, Richard J

    2012-12-01

    We have investigated the interaction between GH (growth hormone) and GHR (GH receptor). We previously demonstrated that a truncated GHR that possesses a transmembrane domain but no cytoplasmic domain blocks receptor signalling. Based on this observation we investigated the impact of tethering the receptor's extracellular domain to the cell surface using a native lipid GPI (glycosylphosphatidylinositol) anchor. We also investigated the effect of tethering GH, the ligand itself, to the cell surface and demonstrated that tethering either the ecGHR (extracellular domain of GHR) or the ligand itself to the cell membrane via a GPI anchor greatly attenuates signalling. To elucidate the mechanism for this antagonist activity, we used confocal microscopy to examine the fluorescently modified ligand and receptor. GH-GPI was expressed on the cell surface and formed inactive receptor complexes that failed to internalize and blocked receptor activation. In conclusion, contrary to expectation, tethering an agonist to the cell surface can generate an inactive hormone receptor complex that fails to internalize.

  5. The Role of AhR in Breast Cancer Development

    DTIC Science & Technology

    2006-07-01

    other cell types, galangin is a potent inhibitor of the aryl hydrocarbon receptor (AhR), an environmental carcinogen-responsive transcription factor...constitutively active AhR. Constitutive and environmental chemical-inducible AhR activity was profoundly suppressed by galangin as was cell growth...However, the failure of a-naphthoflavone or FhAhRR transfection to block growth indicated that galangin -mediated AhR inhibition was either insufficient

  6. Divergent Label-free Cell Phenotypic Pharmacology of Ligands at the Overexpressed β2-Adrenergic Receptors

    NASA Astrophysics Data System (ADS)

    Ferrie, Ann M.; Sun, Haiyan; Zaytseva, Natalya; Fang, Ye

    2014-01-01

    We present subclone sensitive cell phenotypic pharmacology of ligands at the β2-adrenergic receptor (β2-AR) stably expressed in HEK-293 cells. The parental cell line was transfected with green fluorescent protein (GFP)-tagged β2-AR. Four stable subclones were established and used to profile a library of sixty-nine AR ligands. Dynamic mass redistribution (DMR) profiling resulted in a pharmacological activity map suggesting that HEK293 endogenously expresses functional Gi-coupled α2-AR and Gs-coupled β2-AR, and the label-free cell phenotypic activity of AR ligands are subclone dependent. Pathway deconvolution revealed that the DMR of epinephrine is originated mostly from the remodeling of actin microfilaments and adhesion complexes, to less extent from the microtubule networks and receptor trafficking, and certain agonists displayed different efficacy towards the cAMP-Epac pathway. We demonstrate that receptor signaling and ligand pharmacology is sensitive to the receptor expression level, and the organization of the receptor and its signaling circuitry.

  7. Identifying and quantifying two ligand-binding sites while imaging native human membrane receptors by AFM

    NASA Astrophysics Data System (ADS)

    Pfreundschuh, Moritz; Alsteens, David; Wieneke, Ralph; Zhang, Cheng; Coughlin, Shaun R.; Tampé, Robert; Kobilka, Brian K.; Müller, Daniel J.

    2015-11-01

    A current challenge in life sciences is to image cell membrane receptors while characterizing their specific interactions with various ligands. Addressing this issue has been hampered by the lack of suitable nanoscopic methods. Here we address this challenge and introduce multifunctional high-resolution atomic force microscopy (AFM) to image human protease-activated receptors (PAR1) in the functionally important lipid membrane and to simultaneously localize and quantify their binding to two different ligands. Therefore, we introduce the surface chemistry to bifunctionalize AFM tips with the native receptor-activating peptide and a tris-N-nitrilotriacetic acid (tris-NTA) group binding to a His10-tag engineered to PAR1. We further introduce ways to discern between the binding of both ligands to different receptor sites while imaging native PAR1s. Surface chemistry and nanoscopic method are applicable to a range of biological systems in vitro and in vivo and to concurrently detect and localize multiple ligand-binding sites at single receptor resolution.

  8. AIP mutations impair AhR signaling in pituitary adenoma patients fibroblasts and in GH3 cells.

    PubMed

    Lecoq, Anne-Lise; Viengchareun, Say; Hage, Mirella; Bouligand, Jérôme; Young, Jacques; Boutron, Audrey; Zizzari, Philippe; Lombès, Marc; Chanson, Philippe; Kamenický, Peter

    2016-05-01

    Germline mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene predispose humans to pituitary adenomas through unknown molecular mechanisms. The best-known interacting partner of AIP is the aryl hydrocarbon receptor (AhR), a transcription factor that mediates the effects of xenobiotics implicated in carcinogenesis. As 75% of AIP mutations disrupt the physical and/or functional interaction with AhR, we postulated that the tumorigenic potential of AIP mutations might result from altered AhR signaling. We evaluated the impact of AIP mutations on the AhR signaling pathway, first in fibroblasts from AIP-mutated patients with pituitary adenomas, by comparison with fibroblasts from healthy subjects, then in transfected pituitary GH3 cells. The AIP protein level in mutated fibroblasts was about half of that in cells from healthy subjects, but AhR expression was unaffected. Gene expression analyses showed significant modifications in the expression of the AhR target genes CYP1B1 and AHRR in AIP-mutated fibroblasts, both before and after stimulation with the endogenous AhR ligand kynurenine. Kynurenine increased Cyp1b1 expression to a greater extent in GH3 cells overexpressing wild type compared with cells expressing mutant AIP Knockdown of endogenous Aip in these cells attenuated Cyp1b1 induction by the AhR ligand. Both mutant AIP expression and knockdown of endogenous Aip affected the kynurenine-dependent GH secretion of GH3 cells. This study of human fibroblasts bearing endogenous heterozygous AIP mutations and transfected pituitary GH3 cells shows that AIP mutations affect the AIP protein level and alter AhR transcriptional activity in a gene- and tissue-dependent manner.

  9. A constitutively active dioxin/aryl hydrocarbon receptor induces stomach tumors

    NASA Astrophysics Data System (ADS)

    Andersson, Patrik; McGuire, Jacqueline; Rubio, Carlos; Gradin, Katarina; Whitelaw, Murray L.; Pettersson, Sven; Hanberg, Annika; Poellinger, Lorenz

    2002-07-01

    The dioxin/aryl hydrocarbon receptor (AhR) functions as a ligand-activated transcription factor regulating transcription of a battery of genes encoding xenobiotic metabolizing enzymes. Known receptor ligands are environmental pollutants including polycyclic aromatic hydrocarbons and polychlorinated dioxins. Loss-of-function (gene-disruption) studies in mice have demonstrated that the AhR is involved in toxic effects of dioxins but have not yielded unequivocal results concerning the physiological function of the receptor. Gain-of-function studies therefore were performed to unravel the biological functions of the AhR. A constitutively active AhR expressed in transgenic mice reduced the life span of the mice and induced tumors in the glandular part of the stomach, demonstrating the oncogenic potential of the AhR and implicating the receptor in regulation of cell proliferation.

  10. A constitutively active dioxin/aryl hydrocarbon receptor induces stomach tumors

    PubMed Central

    Andersson, Patrik; McGuire, Jacqueline; Rubio, Carlos; Gradin, Katarina; Whitelaw, Murray L.; Pettersson, Sven; Hanberg, Annika; Poellinger, Lorenz

    2002-01-01

    The dioxin/aryl hydrocarbon receptor (AhR) functions as a ligand-activated transcription factor regulating transcription of a battery of genes encoding xenobiotic metabolizing enzymes. Known receptor ligands are environmental pollutants including polycyclic aromatic hydrocarbons and polychlorinated dioxins. Loss-of-function (gene-disruption) studies in mice have demonstrated that the AhR is involved in toxic effects of dioxins but have not yielded unequivocal results concerning the physiological function of the receptor. Gain-of-function studies therefore were performed to unravel the biological functions of the AhR. A constitutively active AhR expressed in transgenic mice reduced the life span of the mice and induced tumors in the glandular part of the stomach, demonstrating the oncogenic potential of the AhR and implicating the receptor in regulation of cell proliferation. PMID:12107286

  11. The CXC Chemokine Receptor 4 Ligands Ubiquitin and Stromal Cell-derived Factor-1α Function through Distinct Receptor Interactions*

    PubMed Central

    Saini, Vikas; Staren, Daniel M.; Ziarek, Joshua J.; Nashaat, Zayd N.; Campbell, Edward M.; Volkman, Brian F.; Marchese, Adriano; Majetschak, Matthias

    2011-01-01

    Recently, we identified extracellular ubiquitin as an endogenous CXC chemokine receptor (CXCR) 4 agonist. However, the receptor selectivity and molecular basis of the CXCR4 agonist activity of ubiquitin are unknown, and functional consequences of CXCR4 activation with ubiquitin are poorly defined. Here, we provide evidence that ubiquitin and the cognate CXCR4 ligand stromal cell-derived factor (SDF)-1α do not share CXCR7 as a receptor. We further demonstrate that ubiquitin does not utilize the typical two-site binding mechanism of chemokine-receptor interactions, in which the receptor N terminus is important for ligand binding. CXCR4 activation with ubiquitin and SDF-1α lead to similar Gαi-responses and to a comparable magnitude of phosphorylation of ERK-1/2, p90 ribosomal S6 kinase-l and Akt, although phosphorylations occur more transiently after activation with ubiquitin. Despite the similarity of signal transduction events after activation of CXCR4 with both ligands, ubiquitin possesses weaker chemotactic activity than SDF-lα in cell migration assays and does not interfere with productive entry of HIV-1 into P4.R5 multinuclear activation of galactosidase indicator cells. Unlike SDF-1α, ubiquitin lacks interactions with an N-terminal CXCR4 peptide in NMR spectroscopy experiments. Binding and signaling studies in the presence of antibodies against the N terminus and extracellular loops 2/3 of CXCR4 confirm that the ubiquitin CXCR4 interaction is independent of the N-terminal receptor domain, whereas blockade of extracellular loops 2/3 prevents receptor binding and activation. Our findings define ubiquitin as a CXCR4 agonist, which does not interfere with productive cellular entry of HIV-1, and provide new mechanistic insights into interactions between CXCR4 and its natural ligands. PMID:21757744

  12. Molecular dynamics simulations and molecular flooding studies of the retinoid X-receptor ligand binding domain.

    PubMed

    Gray, Geoffrey M; Ma, Ning; Wagner, Carl E; van der Vaart, Arjan

    2017-03-01

    Bexarotene is an FDA approved retinoid X-receptor (RXR) agonist for the treatment of cutaneous T-cell lymphoma, and its use in other cancers and Alzheimer's disease is being investigated. The drug causes serious side effects, which might be reduced by chemical modifications of the molecule. To rationalize known agonists and to help identify sites for potential substitutions we present molecular simulations in which the RXR ligand-binding domain was flooded with a large number of drug-like molecules, and molecular dynamics simulations of a series of bexarotene-like ligands bound to the RXR ligand-binding domain. Based on the flooding simulations, two regions of interest for ligand modifications were identified: a hydrophobic area near the bridgehead and another near the fused ring. In addition, positional fluctuations of the phenyl ring were generally smaller than fluctuations of the fused ring of the ligands. Together, these observations suggest that the fused ring might be a good target for the design of higher affinity bexarotene-like ligands, while the phenyl ring is already optimized. In addition, notable differences in ligand position and interactions between the RXRα and RXRβ were observed, as well as differences in hydrogen bonding and solvation, which might be exploited in the development of subspecies-specific ligands.

  13. A selective sigma-2 receptor ligand antagonizes cocaine-induced hyperlocomotion in mice.

    PubMed

    Lever, John R; Miller, Dennis K; Green, Caroline L; Fergason-Cantrell, Emily A; Watkinson, Lisa D; Carmack, Terry L; Fan, Kuo-Hsien; Lever, Susan Z

    2014-02-01

    Cocaine functions, in part, through agonist actions at sigma-1 (σ1 ) receptors, while roles played by sigma-2 (σ2 ) receptors are less established. Attempts to discriminate σ2 receptor-mediated effects of cocaine in locomotor hyperactivity assays have been hampered by the lack of potent and selective antagonists. Certain tetrahydroisoquinolinyl benzamides display high σ2 receptor affinity, and excellent selectivity for binding to σ2 over σ1 receptors. The behavioral properties of this structural class of σ ligands have not yet been investigated. The present study evaluated 5-bromo-N-[4-(6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)-butyl)]-2,3-dimethoxy-benzamide, 1, a ligand shown by others to bind preferentially to σ2 over σ1 receptors, as well as dopamine D2 and D3 sites. First, we determined binding to monoamine transporters and opioid receptors, and noted 57-fold selectivity for σ2 receptors over the serotonin transporter, and >800-fold selectivity for σ2 receptors over the other sites tested. We then examined 1 in locomotor activity studies using male CD-1® mice, and saw no alteration of basal activity at doses up to 31.6 µmol/kg. Cocaine produced a fivefold increase in locomotor activity, which was attenuated by 66% upon pretreatment of mice with 1 at 31.6 µmol/kg. In vivo radioligand binding studies also were performed, and showed no occupancy of σ1 receptors or the dopamine transporter by 1, or its possible metabolites, at the 31.6 µmol/kg dose. Thus, ligand 1 profiles behaviorally as a σ2 receptor-selective antagonist that is able to counteract cocaine's motor stimulatory effects.

  14. Distinct Second Extracellular Loop Structures of the Brain Cannabinoid CB1 Receptor: Implication in Ligand Binding and Receptor Function

    PubMed Central

    Shim, Joong-Youn; Rudd, James; Ding, Tomas T.

    2010-01-01

    The G-protein coupled receptor (GPCR) second extracellular loop (E2) is known to play an important role in receptor structure and function. The brain cannabinoid (CB1) receptor is unique in that it lacks the inter-loop E2 disulfide linkage to the transmembrane (TM) helical bundle, a characteristic of many GPCRs. Recent mutation studies of the CB1 receptor, however, suggest the presence of an alternative intra-loop disulfide bond between two E2 Cys residues. Considering the oxidation state of these Cys residues, we determine the molecular structures of the 17-residue E2 in the dithiol form (E2dithiol) and in the disulfide form (E2disulfide) of the CB1 receptor in a fully hydrated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer, employing a combination of simulated annealing (SA) and molecular dynamics (MD) simulation approaches. We characterize the CB1 receptor models with these two E2 forms, CB1(E2dithiol) and CB1(E2disulfide), by analyzing interaction energy, contact number, core crevice and cross-correlation. The results show that the distinct E2 structures interact differently with the TM helical bundle and uniquely modify the TM helical topology, suggesting that E2 plays a critical role in stabilizing receptor structure, regulating ligand binding, and ultimately modulating receptor activation. Further studies on the role of E2 of the CB1 receptor are warranted; particularly comparisons of the ligand-bound form with the present ligand-free form. PMID:21120862

  15. Localization of ligand-binding domains of human corticotropin-releasing factor receptor: a chimeric receptor approach.

    PubMed

    Liaw, C W; Grigoriadis, D E; Lovenberg, T W; De Souza, E B; Maki, R A

    1997-06-01

    Two CRF receptors, CRFR1 and CRFR2, have recently been cloned and characterized. CRFR1 shares 70% sequence identity with CRFR2, yet has much higher affinity for rat/human CRF (r/hCRF) than CRFR2. As a first step toward understanding the interactions between rat/human CRF and its receptor, the regions that are involved in receptor-ligand binding and/or receptor activation were determined by using chimeric receptor constructs of the two human CRFR subtypes, CRFR1 and CRFR2, followed by generating point mutations of the receptor. The EC50 values in stimulation of intracellular cAMP of the chimeric and mutant receptors for the peptide ligand were determined using a cAMP-dependent reporter system. Three regions of the receptor were found to be important for optimal binding of r/hCRF and/or receptor activation. The first region was mapped to the junction of the third extracellular domain and the fifth transmembrane domain; substitution of three amino acids of CRFR1 in this region (Val266, Tyr267, and Thr268) by the corresponding CRFR2 amino acids (Asp266, Leu267, and Val268) increased the EC50 value by approximately 10-fold. The other two regions were localized to the second extracellular domain of the CRFR1 involving amino acids 175-178 and His189 residue. Substitutions in these two regions each increased the EC50 value for r/hCRF by approximately 7- to 8-fold only in the presence of the amino acid 266-268 mutation involving the first region, suggesting that their roles in peptide ligand binding might be secondary.

  16. Allergic responses and aryl hydrocarbon receptor novel pathway of mast cell activation.

    PubMed

    Sibilano, Riccardo; Pucillo, Carlo E; Gri, Giorgia

    2015-01-01

    The activation of the transcription factor aryl hydrocarbon receptor (AhR) is modulated by a wide variety of xenobiotics and ligands deriving from products of metabolism. The study of the contribution of AhR to allergic diseases has gained much interest in recent years. Here we discuss the role that environmental factors and metabolic products, particularly acting on AhR-expressing mast cells (MCs), could have in the development of local allergic/atopic response. Thus, this review will cover: a brief overview of the AhR mechanism of action in the immune system; a description of different AhR ligands and their effects to IgE-mediated MC activation in the allergic response, with particular attention to the role of IL-17; a discussion about the potential involvement of AhR in immune tolerance; and a conclusion on human diseases in which direct AhR activation of MC might have a major impact.

  17. Modulation of the ligand-independent activation of the human estrogen receptor by hormone and antihormone.

    PubMed Central

    Smith, C L; Conneely, O M; O'Malley, B W

    1993-01-01

    It has been previously demonstrated that several members of the steroid receptor superfamily may be activated by the neurotransmitter dopamine in the apparent absence of cognate ligand. We have examined wild-type and mutant human estrogen receptors (ERs, [Gly400]ER and [Val400]ER, respectively) for their abilities to activate ER-dependent transcription of a transgene in a ligand-independent manner. In cells expressing the wild-type ER, dopamine was nearly as effective as 17 beta-estradiol at inducing the chloramphenicol acetyltransferase activity of the reporter gene in a dose-dependent manner; simultaneous addition of suboptimal concentrations of 17 beta-estradiol and dopamine stimulated transcription more than either compound alone. Dopamine alone was unable to induce gene expression in cells expressing [Val400]ER mutant receptors, but concomitant treatment with 17 beta-estradiol produced a synergistic increase in transcription, suggesting that the ligand may alter the mutant receptor's conformation such that it can be activated subsequently by a dopaminergic signaling mechanism. In the presence of the antiestrogen ICI 164,384, dopamine-stimulated gene expression was undetectable in cells expressing either form of ER. However, simultaneous treatment of cells expressing wild-type ER with trans-4-hydroxytamoxifen and dopamine resulted in transgene expression that was additive in nature compared to either compound alone; similar treatment of cells expressing [Val400]ER produced a synergistic increase. Our results suggest that ligand and ligand-independent activation of the ER initiate from distinct pathways and that the latter may occur in a variety of target tissues subject to modulation by receptor ligands. Images Fig. 5 PMID:8327492

  18. Doubling the Size of the Glucocorticoid Receptor Ligand Binding Pocket by Deacylcortivazol

    SciTech Connect

    Suino-Powell, Kelly; Xu, Yong; Zhang, Chenghai; Tao, Yong-guang; Tolbert, W. David; Simons, Jr., S. Stoney; Xu, H. Eric

    2010-03-08

    A common feature of nuclear receptor ligand binding domains (LBD) is a helical sandwich fold that nests a ligand binding pocket within the bottom half of the domain. Here we report that the ligand pocket of glucocorticoid receptor (GR) can be continuously extended into the top half of the LBD by binding to deacylcortivazol (DAC), an extremely potent glucocorticoid. It has been puzzling for decades why DAC, which contains a phenylpyrazole replacement at the conserved 3-ketone of steroid hormones that are normally required for activation of their cognate receptors, is a potent GR activator. The crystal structure of the GR LBD bound to DAC and the fourth LXXLL motif of steroid receptor coactivator 1 reveals that the GR ligand binding pocket is expanded to a size of 1,070 {angstrom}{sup 3}, effectively doubling the size of the GR dexamethasone-binding pocket of 540 {angstrom}{sup 3} and yet leaving the structure of the coactivator binding site intact. DAC occupies only {approx}50% of the space of the pocket but makes intricate interactions with the receptor around the phenylpyrazole group that accounts for the high-affinity binding of DAC. The dramatic expansion of the DAC-binding pocket thus highlights the conformational adaptability of GR to ligand binding. The new structure also allows docking of various nonsteroidal ligands that cannot be fitted into the previous structures, thus providing a new rational template for drug discovery of steroidal and nonsteroidal glucocorticoids that can be specifically designed to reach the unoccupied space of the expanded pocket.

  19. Ligand-Based Peptide Design and Combinatorial Peptide Libraries to Target G Protein-Coupled Receptors

    PubMed Central

    Gruber, Christian W.; Muttenthaler, Markus; Freissmuth, Michael

    2016-01-01

    G protein-coupled receptors (GPCRs) are considered to represent the most promising drug targets; it has been repeatedly said that a large fraction of the currently marketed drugs elicit their actions by binding to GPCRs (with cited numbers varying from 30–50%). Closer scrutiny, however, shows that only a modest fraction of (~60) GPCRs are, in fact, exploited as drug targets, only ~20 of which are peptide-binding receptors. The vast majority of receptors in the humane genome have not yet been explored as sites of action for drugs. Given the drugability of this receptor class, it appears that opportunities for drug discovery abound. In addition, GPCRs provide for binding sites other than the ligand binding sites (referred to as the “orthosteric site”). These additional sites include (i) binding sites for ligands (referred to as “allosteric ligands”) that modulate the affinity and efficacy of orthosteric ligands, (ii) the interaction surface that recruits G proteins and arrestins, (iii) the interaction sites of additional proteins (GIPs, GPCR interacting proteins that regulate G protein signaling or give rise to G protein-independent signals). These sites can also be targeted by peptides. Combinatorial and natural peptide libraries are therefore likely to play a major role in identifying new GPCR ligands at each of these sites. In particular the diverse natural peptide libraries such as the venom peptides from marine cone-snails and plant cyclotides have been established as a rich source of drug leads. High-throughput screening and combinatorial chemistry approaches allow for progressing from these starting points to potential drug candidates. This will be illustrated by focusing on the ligand-based drug design of oxytocin (OT) and vasopressin (AVP) receptor ligands using natural peptide leads as starting points. PMID:20687879

  20. Antibodies and carbohydrate ligands binding to DC-SIGN differentially modulate receptor trafficking.

    PubMed

    Tacken, Paul J; Ter Huurne, Menno; Torensma, Ruurd; Figdor, Carl G

    2012-08-01

    DCs are regarded as key APCs that initiate humoral and cellular immune responses. Consequently, targeted delivery of Ag toward DC-specific receptors enhances vaccine efficacy. DC-SIGN is a C-type lectin receptor that facilitates DC-specific delivery of Ag. This is accomplished by conjugating Ag to receptor-specific Ab or carbohydrate ligands that bind to its carbohydrate recognition domain. Here, we investigated the fate of DC-SIGN following receptor triggering with Ab. Both whole and single-chain Ab induced rapid internalization of about half of the surface receptor molecules. Biochemical studies showed that about half of the receptor molecules were still intracellular after 3 h, while minimal or no resurfacing of internalized or newly synthesized unbound DC-SIGN molecules was observed. Prolonged exposure of DCs to DC-SIGN Ab, but not carbohydrate ligands, resulted in reduced receptor expression levels, which lasted up to 2 days following removal of the Ab. In addition, exposure to DC-SIGN Ab reduced the ability of the receptor to internalize. Consequently, DC-SIGN showed a poor ability to accumulate targeting Abs within DCs. Vaccine efficacy may therefore be enhanced by strategies increasing the amount of Ag entering via a single receptor molecule, such as the use of targeting moieties allowing DC-SIGN recycling or Ab-coated vaccine carriers.

  1. Controlling the Dissociation of Ligands from the Adenosine A2A Receptor through Modulation of Salt Bridge Strength.

    PubMed

    Segala, Elena; Guo, Dong; Cheng, Robert K Y; Bortolato, Andrea; Deflorian, Francesca; Doré, Andrew S; Errey, James C; Heitman, Laura H; IJzerman, Adriaan P; Marshall, Fiona H; Cooke, Robert M

    2016-07-14

    The association and dissociation kinetics of ligands binding to proteins vary considerably, but the mechanisms behind this variability are poorly understood, limiting their utilization for drug discovery. This is particularly so for G protein-coupled receptors (GPCRs) where high resolution structural information is only beginning to emerge. Engineering the human A2A adenosine receptor has allowed structures to be solved in complex with the reference compound ZM241385 and four related ligands at high resolution. Differences between the structures are limited, with the most pronounced being the interaction of each ligand with a salt bridge on the extracellular side of the receptor. Mutagenesis experiments confirm the role of this salt bridge in controlling the dissociation kinetics of the ligands from the receptor, while molecular dynamics simulations demonstrate the ability of ligands to modulate salt bridge stability. These results shed light on a structural determinant of ligand dissociation kinetics and identify a means by which this property may be optimized.

  2. Human formyl peptide receptor ligand binding domain(s). Studies using an improved mutagenesis/expression vector reveal a novel mechanism for the regulation of receptor occupancy.

    PubMed

    Perez, H D; Vilander, L; Andrews, W H; Holmes, R

    1994-09-09

    Recently, we reported the domain requirements for the binding of formyl peptide to its specific receptor. Based on experiments using receptor chimeras, we also postulated an importance for the amino-terminal domain of the receptor in ligand binding (Perez, H. D., Holmes, R., Vilander, L., Adams, R., Manzana, W., Jolley, D., and Andrews, W. H. (1993) J. Biol. Chem. 268, 2292-2295). We have begun to perform a detailed analysis of the regions within the formyl peptide receptor involved in ligand binding. To address the importance of the receptor amino-terminal domain, we substituted (or inserted) hydrophilic sequences within the amino-terminal domain, expressed the receptors, and determined their ability to bind ligand. A stretch of nine amino acids next to the initial methionine was identified as crucial for receptor occupancy. A peptide containing such a sequence specifically completed binding of the ligand to the receptor. Alanine screen mutagenesis of the second extracellular domain also identified amino acids involved in ligand binding as well as a disulfide bond (Cys98 to Cys176) crucial for maintaining the binding pocket. These studies provide evidence for a novel mechanism involved in regulation of receptor occupancy. Binding of the ligand induces conformational changes in the receptor that result in the apposition of the amino-terminal domain over the ligand, providing a lid to the binding pocket.

  3. The Nuclear Receptor HIZR-1 Uses Zinc as a Ligand to Mediate Homeostasis in Response to High Zinc

    PubMed Central

    Warnhoff, Kurt; Roh, Hyun C.; Kocsisova, Zuzana; Tan, Chieh-Hsiang; Morrison, Andrew; Croswell, Damari; Schneider, Daniel L.; Kornfeld, Kerry

    2017-01-01

    Nuclear receptors were originally defined as endocrine sensors in humans, leading to the identification of the nuclear receptor superfamily. Despite intensive efforts, most nuclear receptors have no known ligand, suggesting new ligand classes remain to be discovered. Furthermore, nuclear receptors are encoded in the genomes of primitive organisms that lack endocrine signaling, suggesting the primordial function may have been environmental sensing. Here we describe a novel Caenorhabditis elegans nuclear receptor, HIZR-1, that is a high zinc sensor in an animal and the master regulator of high zinc homeostasis. The essential micronutrient zinc acts as a HIZR-1 ligand, and activated HIZR-1 increases transcription of genes that promote zinc efflux and storage. The results identify zinc as the first inorganic molecule to function as a physiological ligand for a nuclear receptor and direct environmental sensing as a novel function of nuclear receptors. PMID:28095401

  4. Nuclear receptor ligand-binding domains: reduction of helix H12 dynamics to favour crystallization

    SciTech Connect

    Nahoum, Virginie; Lipski, Alexandra; Quillard, Fabien; Guichou, Jean-François; Boublik, Yvan; Pérez, Efrèn; Germain, Pierre; Lera, Angel R. de; Bourguet, William

    2008-07-01

    Attempts have been made to crystallize the ligand-binding domain of the human retinoid X receptor in complex with a variety of newly synthesized ligands. An inverse correlation was observed between the ‘crystallizability’ and the structural dynamics of the various receptor–ligand complexes. Crystallization trials of the human retinoid X receptor α ligand-binding domain (RXRα LBD) in complex with various ligands have been carried out. Using fluorescence anisotropy, it has been found that when compared with agonists these small-molecule effectors enhance the dynamics of the RXRα LBD C-terminal helix H12. In some cases, the mobility of this helix could be dramatically reduced by the addition of a 13-residue co-activator fragment (CoA). In keeping with these observations, crystals have been obtained of the corresponding ternary RXRα LBD–ligand–CoA complexes. In contrast, attempts to crystallize complexes with a highly mobile H12 remained unsuccessful. These experimental observations substantiate the previously recognized role of co-regulator fragments in facilitating the crystallization of nuclear receptor LBDs.

  5. Novel selective allosteric and bitopic ligands for the S1P(3) receptor.

    PubMed

    Jo, Euijung; Bhhatarai, Barun; Repetto, Emanuela; Guerrero, Miguel; Riley, Sean; Brown, Steven J; Kohno, Yasushi; Roberts, Edward; Schürer, Stephan C; Rosen, Hugh

    2012-12-21

    Sphingosine 1-phosphate (S1P) is a lysophospholipid signaling molecule that regulates important biological functions, including lymphocyte trafficking and vascular development, by activating G protein-coupled receptors for S1P, namely, S1P(1) through S1P(5). Here, we map the S1P(3) binding pocket with a novel allosteric agonist (CYM-5541), an orthosteric agonist (S1P), and a novel bitopic antagonist (SPM-242). With a combination of site-directed mutagenesis, ligand competition assay, and molecular modeling, we concluded that S1P and CYM-5541 occupy different chemical spaces in the ligand binding pocket of S1P(3). CYM-5541 allowed us to identify an allosteric site where Phe263 is a key gate-keeper residue for its affinity and efficacy. This ligand lacks a polar moiety, and the novel allosteric hydrophobic pocket permits S1P(3) selectivity of CYM-5541 within the highly similar S1P receptor family. However, a novel S1P(3)-selective antagonist, SPM-242, in the S1P(3) pocket occupies the ligand binding spaces of both S1P and CYM-5541, showing its bitopic mode of binding. Therefore, our coordinated approach with biochemical data and molecular modeling, based on our recently published S1P(1) crystal structure data in a highly conserved set of related receptors with a shared ligand, provides a strong basis for the successful optimization of orthosteric, allosteric, and bitopic modulators of S1P(3).

  6. Nociceptin/Orphanin FQ Receptor Structure, Signaling, Ligands, Functions, and Interactions with Opioid Systems

    PubMed Central

    Bruchas, Michael R.; Calo', Girolamo; Cox, Brian M.; Zaveri, Nurulain T.

    2016-01-01

    The NOP receptor (nociceptin/orphanin FQ opioid peptide receptor) is the most recently discovered member of the opioid receptor family and, together with its endogenous ligand, N/OFQ, make up the fourth members of the opioid receptor and opioid peptide family. Because of its more recent discovery, an understanding of the cellular and behavioral actions induced by NOP receptor activation are less well developed than for the other members of the opioid receptor family. All of these factors are important because NOP receptor activation has a clear modulatory role on mu opioid receptor-mediated actions and thereby affects opioid analgesia, tolerance development, and reward. In addition to opioid modulatory actions, NOP receptor activation has important effects on motor function and other physiologic processes. This review discusses how NOP pharmacology intersects, contrasts, and interacts with the mu opioid receptor in terms of tertiary structure and mechanism of receptor activation; location of receptors in the central nervous system; mechanisms of desensitization and downregulation; cellular actions; intracellular signal transduction pathways; and behavioral actions with respect to analgesia, tolerance, dependence, and reward. This is followed by a discussion of the agonists and antagonists that have most contributed to our current knowledge. Because NOP receptors are highly expressed in brain and spinal cord and NOP receptor activation sometimes synergizes with mu receptor-mediated actions and sometimes opposes them, an understanding of NOP receptor pharmacology in the context of these interactions with the opioid receptors will be crucial to the development of novel therapeutics that engage the NOP receptor. PMID:26956246

  7. Retinoid X receptor-selective ligands produce malformations in Xenopus embryos.

    PubMed Central

    Minucci, S; Saint-Jeannet, J P; Toyama, R; Scita, G; DeLuca, L M; Tiara, M; Levin, A A; Ozato, K; Dawid, I B

    1996-01-01

    Retinoids exert pleiotropic effects on the development of vertebrates through the action of retinoic acid receptors (RAR) and retinoid X receptors (RXR). We have investigated the effect of synthetic retinoids selective for RXR and RAR on the development of Xenopus and zebrafish embryos. In Xenopus, both ligands selective for RAR and RXR caused striking malformations along the anterior-posterior axis, whereas in zebrafish only ligands specific for RAR caused embryonic malformations. In Xenopus, RAR- and RXR-selective ligands regulated the expression of the Xlim-1, gsc, and HoxA1 genes similarly as all-trans-retinoic acid. Nevertheless, RXR-selective ligands activated only an RXR responsive reporter but not an RAR responsive reporter introduced by microinjection into the Xenopus embryo, consistent with our failure to detect conversion of an RXR-selective ligand to different derivatives in the embryo. These results suggest that Xenopus embryos possess a unique response pathway in which liganded RXR can control gene expression. Our observations further illustrate the divergence in retinoid responsiveness between different vertebrate species. Images Fig. 1 Fig. 2 Fig. 3 Fig. 5 PMID:8700839

  8. Synthetic Multivalent Ligands as Probes of Inter-Receptor Communication in Bacterial Chemotaxis

    NASA Astrophysics Data System (ADS)

    Gestwicki, Jason

    2004-03-01

    Bacteria can sense chemotactic signals, such as nutrients and toxins, with remarkable sensitivity. Escherichia coli, respond to changes in stimulant concentration of less than 10to maintain sensitivity, the relationship between ligand concentration and output response must be non-linear. For example, at low ligand levels, substantial amplification of the chemotactic signal is required to trigger locomotion. Signal amplification must be quickly suppressed, however, to restore proper sensitivity to small changes in ligand at higher concentrations. Because of the rapid flexibility of this system, it has been hypothesized that alterations in the organization of the chemotactic signaling proteins, rather than changes in their expression, provide this exquisite sensitivity. The interaction between chemoreceptors within lattices has been proposed to play a role in this process. Using a series of synthetic multivalent ligands directed at the chemoreceptors, we have demonstrated a requirement for dynamic changes in inter-receptor interactions for amplification and integration of sensory information. Multivalent ligands that interact through the galactose-sensing receptor Trg, enforce proximal interactions between chemoreceptors and enhance signal output. Further, upon treatment with multivalent ligands, the response to the attractant serine is amplified by at least 100-fold. These results, and those from genetic and structural studies by other laboratories, suggest that the entire array is involved in sensing. These results support general strategy by which biological responses may be regulated.

  9. Kinetics of membrane adhesion mediated by ligand-receptor interaction studied with a biomimetic system.

    PubMed Central

    Boulbitch, A; Guttenberg, Z; Sackmann, E

    2001-01-01

    We report the first measurement of the kinetics of adhesion of a single giant vesicle controlled by the competition between membrane-substrate interaction mediated by ligand-receptor interaction, gravitation, and Helfrich repulsion. To model the cell-tissue interaction, we doped the vesicles with lipid-coupled polymers (mimicking the glycocalix) and the reconstituted ligands selectively recognized by alpha(IIb)beta(3) integrin-mediating specific attraction forces. The integrin was grafted on glass substrates to act as a target cell. The adhesion of the vesicle membrane to the integrin-covered surface starts with the spontaneous formation of a small (approximately 200 nm) domain of tight adhesion, which then gradually grows until the whole adhesion area is in the state of tight adhesion. The time of adhesion varies from few tens of seconds to about one hour depending on the ligand and lipopolymer concentration. At small ligand concentrations, we observed the displacement xi of the front of tight adhesion following the square root law xi approximately t(1/2), whereas, at high concentrations, we found a linear law xi approximately t. We show both experimentally and theoretically that the t(1/2)-regime is dominated by diffusion of ligands, and the xi approximately t-regime by the kinetics of ligands-receptors association. PMID:11606287

  10. A Nuclear Receptor Ligand-based Probe Enables Temporal Control of C. elegans Development

    PubMed Central

    Judkins, Joshua C.; Mahanti, Parag; Hoffman, Jacob; Yim, Isaiah; Antebi, Adam; Schroeder, Frank C.

    2014-01-01

    C. elegans development and lifespan are controlled by the nuclear hormone receptor DAF-12, an important model for vertebrate vitamin D and liver-X receptors. Similar to its mammalian homologs, DAF-12 function is regulated by bile acid-like steroidal ligands, the dafachronic acids; however, tools for investigating their biosynthesis and function in vivo are lacking. We report a flexible synthesis for DAF-12 ligands and masked ligand derivatives that enable precise temporal control of DAF-12 function. For ligand masking, we introduce photocleavable amides of 5-methoxy-N-methyl-2-nitroaniline (MMNA). MMNA-masked ligands are bioavailable and after incorporation into the worm can be used to trigger expression of DAF-12 target genes and initiate development from dauer larvae to adults by brief, innocuous UV-irradiation. In-vivo release of DAF-12 ligands and other small-molecule signals using MMNA-based probes will enable functional studies with precise spatial and temporal resolution. PMID:24453122

  11. Functional studies of host-specific ephrin-B ligands as Henipavirus receptors.

    PubMed

    Bossart, Katharine N; Tachedjian, Mary; McEachern, Jennifer A; Crameri, Gary; Zhu, Zhongyu; Dimitrov, Dimiter S; Broder, Christopher C; Wang, Lin-Fa

    2008-03-15

    Hendra virus (HeV) and Nipah virus (NiV) are closely related paramyxoviruses that infect and cause disease in a wide range of mammalian hosts. To determine whether host receptor molecules play a role in species-specific and/or virus-specific infection we have cloned and characterized ephrin-B2 and ephrin-B3 ligands from a range of species, including human, horse, pig, cat, dog, bats (Pteropus alecto and Pteropus vampyrus) and mouse. HeV and NiV were both able to infect cells expressing any of the ephrin-B2 and ephrin-B3 molecules. There did not appear to be significant differences in receptor function from different species or receptor usage by HeV and NiV. Soluble ephrin ligands, their receptors and G-specific human monoclonal antibodies differentially blocked henipavirus infections suggesting different receptor affinities, overlapping receptor binding domains of the henipavirus attachment glycoprotein (G) and that the functional domains of the ephrin ligands may be important for henipavirus binding.

  12. Ligand-induced IFN gamma receptor tyrosine phosphorylation couples the receptor to its signal transduction system (p91).

    PubMed Central

    Greenlund, A C; Farrar, M A; Viviano, B L; Schreiber, R D

    1994-01-01

    Herein we report that interferon-gamma (IFN gamma) induces the rapid and reversible tyrosine phosphorylation of the IFN gamma receptor. Using a panel of receptor intracellular domain mutants, we show that a membrane-proximal LPKS sequence (residues 266-269) is required for ligand-induced tyrosine kinase activation and/or kinase-receptor association and biological responsiveness, and a functionally critical membrane-distal tyrosine residue (Y440) is a target of the activated enzyme. The biological significance of Y440 phosphorylation was demonstrated by showing that a receptor-derived nonapeptide corresponding to receptor residues 436-444 and containing phosphorylated Y440 bound specifically to p91, blocked p91 phosphorylation and inhibited the generation of an active p91-containing transcription factor complex. In contrast, nonphosphorylated wild-type, phosphorylated mutant, or phosphorylated irrelevant peptides did not. Moreover, the phosphorylated Y440-containing peptide did not interact with a related but distinct latent transcription factor (p113) which is activatible by IFN alpha but not IFN gamma. These results thus document the specific and inducible association of p91 with the phosphorylated IFN gamma receptor and thereby elucidate the mechanism by which ligand couples the IFN gamma receptor to its signal transduction system. Images PMID:8156998

  13. Selective nonpeptidic fluorescent ligands for oxytocin receptor: design, synthesis, and application to time-resolved FRET binding assay.

    PubMed

    Karpenko, Iuliia A; Margathe, Jean-François; Rodriguez, Thiéric; Pflimlin, Elsa; Dupuis, Elodie; Hibert, Marcel; Durroux, Thierry; Bonnet, Dominique

    2015-03-12

    The design and the synthesis of the first high-affinity fluorescent ligands for oxytocin receptor (OTR) are described. These compounds enabled the development of a TR-FRET based assay for OTR, readily amenable to high throughput screening. The validation of the assay was achieved by competition experiments with both peptide and nonpeptide OTR ligands as competitors. These probes represent the first selective fluorescent ligands for the oxytocin G protein-coupled receptor.

  14. The Aryl Hydrocarbon Receptor Complex and the Control of Gene Expression

    PubMed Central

    Beischlag, Timothy V.; Morales, J. Luis; Hollingshead, Brett D.; Perdew, Gary H.

    2008-01-01

    The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that controls the expression of a diverse set of genes. The toxicity of the potent AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin is almost exclusively mediated through this receptor. However, the key alterations in gene expression that mediate toxicity are poorly understood. It has been established through characterization of AhR-null mice that the AhR has a required physiological function, yet how endogenous mediators regulate this orphan receptor remains to be established. A picture as to how the AhR/ARNT heterodimer actually mediates gene transcription is starting to emerge. The AhR/ARNT complex can alter transcription both by binding to its cognate response element and through tethering to other transcription factors. In addition, many of the coregulatory proteins necessary for AhR-mediated transcription have been identified. Cross talk between the estrogen receptor and the AhR at the promoter of target genes appears to be an important mode of regulation. Inflammatory signaling pathways and the AhR also appear to be another important site of cross talk at the level of transcription. A major focus of this review is to highlight experimental efforts to characterize nonclassical mechanisms of AhR-mediated modulation of gene transcription. PMID:18540824

  15. Structure- and conformation-activity studies of nociceptin/orphanin FQ receptor dimeric ligands

    PubMed Central

    Pacifico, Salvatore; Carotenuto, Alfonso; Brancaccio, Diego; Novellino, Ettore; Marzola, Erika; Ferrari, Federica; Cerlesi, Maria Camilla; Trapella, Claudio; Preti, Delia; Salvadori, Severo; Calò, Girolamo; Guerrini, Remo

    2017-01-01

    The peptide nociceptin/orphanin FQ (N/OFQ) and the N/OFQ receptor (NOP) constitute a neuropeptidergic system that modulates various biological functions and is currently targeted for the generation of innovative drugs. In the present study dimeric NOP receptor ligands with spacers of different lengths were generated using both peptide and non-peptide pharmacophores. The novel compounds (12 peptide and 7 nonpeptide ligands) were pharmacologically investigated in a calcium mobilization assay and in the mouse vas deferens bioassay. Both structure- and conformation-activity studies were performed. Results demonstrated that dimerization did not modify the pharmacological activity of both peptide and non-peptide pharmacophores. Moreover, when dimeric compounds were obtained with low potency peptide pharmacophores, dimerization recovered ligand potency. This effect depends on the doubling of the C-terminal address sequence rather than the presence of an additional N-terminal message sequence or modifications of peptide conformation. PMID:28383520

  16. Using GFP--ligand fusions to measure receptor-mediated endocytosis in living cells.

    PubMed

    Medina-Kauwe, Lali K; Chen, Xinhua

    2002-01-01

    Recombinant DNA technology has enabled the production of many types of chimeric proteins containing heterologous functional domains that have served a variety of useful capacities for cell biology research. Among proteins gaining wide use as a fusion partner is Aequorea victoria green fluorescent protein (GFP). GFP has been employed by numerous groups as a reporter gene for cell transfection and as an autofluorescent tag by recombinant fusion to foreign sequences. Here we describe the use of GFP as a tag for ligands, and provide examples of how purified recombinant GFP-ligand fusion proteins may be used to detect ligand-receptor interactions, including receptor-mediated endocytosis. Both its utility and limitations are discussed.

  17. Calculations of distance distributions and probabilities of binding by ligands between parallel plane membranes comprising receptors

    NASA Astrophysics Data System (ADS)

    Plante, Ianik; Devroye, Luc; Cucinotta, Francis A.

    2014-03-01

    Cell communication through biochemical signaling pathways is a key determinant of tissue responses to radiation. Several molecules, such as the transforming growth factor β (TGFβ), are implicated in radiation-induced signaling between cells. Brownian Dynamics (BD) algorithms have recently been used to simulate the interaction of ligands with receptors and to elucidate signal transduction and autocrine loops in ligand-receptors systems. In this paper, we discuss the simulation of particle diffusion and binding kinetics in a space bounded by two parallel plane membranes, using an exact algorithm to sample the propagator (Green’s function) of a particle located between 2 membranes. We also show that the simulation results are independent of the number of time steps used, in accordance with time discretization equations. These simulations could be used to simulate the motion and binding of ligand molecules in a cell culture, and possibly in neuronal synapses.

  18. Structural basis for ligand and innate immunity factor uptake by the trypanosome haptoglobin-haemoglobin receptor

    PubMed Central

    Lane-Serff, Harriet; MacGregor, Paula; Lowe, Edward D; Carrington, Mark; Higgins, Matthew K

    2014-01-01

    The haptoglobin-haemoglobin receptor (HpHbR) of African trypanosomes allows acquisition of haem and provides an uptake route for trypanolytic factor-1, a mediator of innate immunity against trypanosome infection. In this study, we report the structure of Trypanosoma brucei HpHbR in complex with human haptoglobin-haemoglobin (HpHb), revealing an elongated ligand-binding site that extends along its membrane distal half. This contacts haptoglobin and the β-subunit of haemoglobin, showing how the receptor selectively binds HpHb over individual components. Lateral mobility of the glycosylphosphatidylinositol-anchored HpHbR, and a ∼50o kink in the receptor, allows two receptors to simultaneously bind one HpHb dimer. Indeed, trypanosomes take up dimeric HpHb at significantly lower concentrations than monomeric HpHb, due to increased ligand avidity that comes from bivalent binding. The structure therefore reveals the molecular basis for ligand and innate immunity factor uptake by trypanosomes and identifies adaptations that allow efficient ligand uptake in the context of the complex trypanosome cell surface. DOI: http://dx.doi.org/10.7554/eLife.05553.001 PMID:25497229

  19. Binding kinetics of membrane-anchored receptors and ligands: Molecular dynamics simulations and theory.

    PubMed

    Hu, Jinglei; Xu, Guang-Kui; Lipowsky, Reinhard; Weikl, Thomas R

    2015-12-28

    The adhesion of biological membranes is mediated by the binding of membrane-anchored receptor and ligand proteins. Central questions are how the binding kinetics of these proteins is affected by the membranes and by the membrane anchoring of the proteins. In this article, we (i) present detailed data for the binding of membrane-anchored proteins from coarse-grained molecular dynamics simulations and (ii) provide a theory that describes how the binding kinetics depends on the average separation and thermal roughness of the adhering membranes and on the anchoring, lengths, and length variations of the proteins. An important element of our theory is the tilt of bound receptor-ligand complexes and transition-state complexes relative to the membrane normals. This tilt results from an interplay of the anchoring energy and rotational entropy of the complexes and facilitates the formation of receptor-ligand bonds at membrane separations smaller than the preferred separation for binding. In our simulations, we have considered both lipid-anchored and transmembrane receptor and ligand proteins. We find that the binding equilibrium constant and binding on-rate constant of lipid-anchored proteins are considerably smaller than the binding constant and on-rate constant of rigid transmembrane proteins with identical binding domains.

  20. Structural basis for ligand and innate immunity factor uptake by the trypanosome haptoglobin-haemoglobin receptor.

    PubMed

    Lane-Serff, Harriet; MacGregor, Paula; Lowe, Edward D; Carrington, Mark; Higgins, Matthew K

    2014-12-12

    The haptoglobin-haemoglobin receptor (HpHbR) of African trypanosomes allows acquisition of haem and provides an uptake route for trypanolytic factor-1, a mediator of innate immunity against trypanosome infection. In this study, we report the structure of Trypanosoma brucei HpHbR in complex with human haptoglobin-haemoglobin (HpHb), revealing an elongated ligand-binding site that extends along its membrane distal half. This contacts haptoglobin and the β-subunit of haemoglobin, showing how the receptor selectively binds HpHb over individual components. Lateral mobility of the glycosylphosphatidylinositol-anchored HpHbR, and a ∼50° kink in the receptor, allows two receptors to simultaneously bind one HpHb dimer. Indeed, trypanosomes take up dimeric HpHb at significantly lower concentrations than monomeric HpHb, due to increased ligand avidity that comes from bivalent binding. The structure therefore reveals the molecular basis for ligand and innate immunity factor uptake by trypanosomes and identifies adaptations that allow efficient ligand uptake in the context of the complex trypanosome cell surface.

  1. REACTIVITY PROFILE OF LIGANDS OF MAMMALIAN RETINOIC ACID RECEPTORS: A PRELIMINARY COREPA ANALYSIS

    EPA Science Inventory

    Retinoic acid and associated derivatives comprise a class of endogenous hormones that bind to and activate different families of retinoic acid receptors (RARs, RXRs), and control many aspects of vertebrate development. Identification of potential RAR and RXR ligands is of interes...

  2. Tension-compression asymmetry in the binding affinity of membrane-anchored receptors and ligands.

    PubMed

    Xu, Guang-Kui; Liu, Zishun; Feng, Xi-Qiao; Gao, Huajian

    2016-03-01

    Cell adhesion plays a crucial role in many biological processes of cells, e.g., immune responses, tissue morphogenesis, and stem cell differentiation. An essential problem in the molecular mechanism of cell adhesion is to characterize the binding affinity of membrane-anchored receptors and ligands under different physiological conditions. In this paper, a theoretical model is presented to study the binding affinity between a large number of anchored receptors and ligands under both tensile and compressive stresses, and corroborated by demonstrating excellent agreement with Monte Carlo simulations. It is shown that the binding affinity becomes lower as the magnitude of the applied stress increases, and drops to zero at a critical tensile or compressive stress. Interestingly, the critical compressive stress is found to be substantially smaller than the critical tensile stress for relatively long and flexible receptor-ligand complexes. This counterintuitive finding is explained by using the Euler instability theory of slender columns under compression. The tension-compression asymmetry in the binding affinity of anchored receptors and ligands depends subtly on the competition between the breaking and instability of their complexes. This study helps in understanding the role of mechanical forces in cell adhesion mediated by specific binding molecules.

  3. NEW DEVELOPMENTS IN A HAZARD IDENTIFICATION ALGORITHM FOR HORMONE RECEPTOR LIGANDS

    EPA Science Inventory

    Recently we described the COmmon REactivity PAttern (COREPA) techniques to screen data sets of diverse structures for their ability to serve as ligands for steroid hormone receptors (Environ. Sci. Technol. 31:3702-3711). The approach identifies and quantifies similar global and l...

  4. Chemical Genetics: receptor-ligand pairs for rapid manipulation of neuronal activity

    PubMed Central

    Wulff, Peer; Arenkiel, Benjamin R.

    2012-01-01

    Towards the functional dissection of neuronal circuits, a number of new genetic tools have been developed that enable rapid and reversible manipulation of genetically defined neuronal subtypes in intact mammalian brain circuits. Alongside the breakthrough technology of optogenetics, receptor-ligand pairs provide complementary approaches to modulate neuronal activity using chemical-genetics. PMID:22119143

  5. CADASIL-associated Notch3 mutations have differential effects both on ligand binding and ligand-induced Notch3 receptor signaling through RBP-Jk.

    PubMed

    Peters, Nils; Opherk, Christian; Zacherle, Simone; Capell, Anja; Gempel, Petra; Dichgans, Martin

    2004-10-01

    Mutations in the NOTCH3 gene are the cause of cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), a hereditary angiopathy leading to strokes and dementia. Pathogenic mutations remove or insert cysteine residues within epidermal growth factor (EGF) repeats in the extracellular domain of the Notch3 receptor (N3ECD). Vascular smooth muscle cells (VSMC) are the predominant site of Notch3 expression in adults. In CADASIL patients, VSMC degenerate and N3ECD is deposited within the vasculature. However, the mechanisms underlying VSMC degeneration and N3ECD accumulation are still unknown. In this study, we investigated the consequences of three pathogenic Notch3 mutations on the biological activity of the receptor by analyzing ligand (Delta-/Jagged-)-induced signaling via RBP-Jk. Two mutations (R133C and C183R) that are located outside the putative ligand binding domain (LBD) of the receptor were found to result in normal Jagged1-induced signaling in A7r5 VSMC, whereas the third mutation (C455R located within the putative LBD) showed strongly reduced signaling activity. Ligand binding assays with soluble Delta1 and Jagged1 revealed that C455R interferes with ligand binding through disruption of the LBD which, as we show here, is located in EGF repeats 10/11 of Notch3. All mutant receptors including Notch3C455R were targeted to the cell surface but showed an elevated ratio between the unprocessed full-length 280-kDa receptor and S1-cleaved receptor fragments. Taken together, these data indicate that CADASIL-associated Notch3 mutations differ with respect to their consequences both on ligand binding and ligand-induced signaling through RBP-Jk, whereas they have similar effects on receptor maturation. Moreover, the data suggest that ligand-induced receptor shedding may not be required for N3ECD deposition in CADASIL.

  6. Ligand-Driven T Cell Receptor Selection in Celiac Disease.

    PubMed

    Singh, Nishant K; Baker, Brian M

    2016-10-04

    Recognition of antigens by T cell receptors (TCRs) underlies cellular immunity. By comparing how different TCRs recognize the key antigens associated with celiac disease, Petersen et al. (2016), in this issue of Structure, show how celiac antigen properties select immunologically distinct yet structurally and physically compatible TCRs, ultimately driving autoimmunity.

  7. Genetic variability of aryl hydrocarbon receptor (AhR)-mediated regulation of the human UDP glucuronosyltransferase (UGT) 1A4 gene

    SciTech Connect

    Erichsen, Thomas J.; Ehmer, Ursula; Kalthoff, Sandra; Lankisch, Tim O.; Mueller, Tordis M.; Munzel, Peter A.; Manns, Michael P.; Strassburg, Christian P.

    2008-07-15

    UDP glucuronosyltransferases (UGTs) play an important role for drug detoxification and toxicity. UGT function is genetically modulated by single nucleotide polymorphisms (SNPs) which lead to the expression of functionally altered protein, or altered expression levels. UGT1A4 activity includes anticonvulsants, antidepressants and environmental mutagens. In this study the induction of the human UGT1A4 gene and a potential influence of genetic variation in its promoter region were analyzed. SNPs at bp - 219 and - 163 occurred in 9% among 109 blood donors reducing UGT1A4 transcription by 40%. UGT1A4 transcription was dioxin inducible. Reporter gene experiments identified 2 xenobiotic response elements (XRE), which were functionally confirmed by mutagenesis analyses, and binding was demonstrated by electromobility shift assays. Constitutive human UGT1A4 gene expression and induction was aryl hydrocarbon receptor (AhR)-dependent, and reduced in the presence of SNPs at bp - 219 and - 163. AhR-mediated regulation of the human UGT1A4 gene by two XRE and a modulation by naturally occurring genetic variability by SNPs is demonstrated, which indicates gene-environment interaction with potential relevance for drug metabolism.

  8. Evaluation of the ecotoxicity of sediments from Yangtze river estuary and contribution of priority PAHs to ah receptor--mediated activities.

    PubMed

    Liu, Li; Chen, Ling; Shao, Ying; Zhang, Lili; Floehr, Tilman; Xiao, Hongxia; Yan, Yan; Eichbaum, Kathrin; Hollert, Henner; Wu, Lingling

    2014-01-01

    In this study, in vitro bioassays were performed to assess the ecotoxicological potential of sediments from Yangtze River estuary. The cytotoxicity and aryl hydrocarbon receptor (AhR)-mediated toxicity of sediment extracts with rainbow trout (Oncorhynchus mykiss) liver cells were determined by neutral red retention and 7-ethoxyresorufin-O-deethylase assays. The cytotoxicity and AhR-mediated activity of sediments from the Yangtze River estuary ranged from low level to moderate level compared with the ecotoxicity of sediments from other river systems. However, Yangtze River releases approximately 14 times greater water discharge compared with Rhine, a major river in Europe. Thus, the absolute pollution mass transfer of Yangtze River may be detrimental to the environmental quality of estuary and East China Sea. Effect-directed analysis was applied to identify substances causing high dioxin-like activities. To identify unknown substances contributing to dioxin-like potencies of whole extracts, we fractionated crude extracts by open column chromatography. Non-polar paraffinic components (F1), weakly and moderately polar components (F2), and highly polar substances (F3) were separated from each crude extract of sediments. F2 showed the highest dioxin-like activities. Based on the results of mass balance calculation of chemical toxic equivalent concentrations (TEQs), our conclusion is that priority polycyclic aromatic hydrocarbons indicated a low portion of bio-TEQs ranging from 1% to 10% of crude extracts. Further studies should be conducted to identify unknown pollutants.

  9. Polychlorinated biphenyls (PCBs) contamination and aryl hydrocarbon receptor (AhR) agonist activity of Omega-3 polyunsaturated fatty acid supplements: implications for daily intake of dioxins and PCBs.

    PubMed

    Bourdon, J A; Bazinet, T M; Arnason, T T; Kimpe, L E; Blais, J M; White, P A

    2010-11-01

    Omega-3 polyunsaturated fatty acid (n-3 PUFA) rich oils derived primarily from fish are frequently consumed as supplements. Due to the tendency of persistent organic pollutants (POPs) to accumulate in exposed organisms, n-3 PUFA supplements can contain sufficient POPs to present a risk to consumers. Here we investigated PCB concentrations and aryl hydrocarbon receptor (AhR) agonist activity in 17 n-3 PUFA supplements available in Canada. PCBs ranged from <0.8 to 793 ng g(-1) oil, with salmon- and seal-derived products yielding the highest values. AhR agonist activity from a reporter gene assay ranged from 1.3 to 72.2 pg TEQ g(-1) oil, with salmon and tuna yielding the highest values. When consumed at the recommended doses and as a supplement to the average Canadian diet, seal-derived oil can contribute to exceedance of the tolerable daily intake of 20 ng PCBs kg-BW(-1)day(-1), and salmon-, tuna-, and sea herring-derived oils can contribute to exceedance of the tolerable daily intake limit of 2.3 pg TEQ kg-BW(-1)day(-1). The beneficial properties of fish and n-3 PUFA supplements, and the results of this study suggest that it is prudent to consume supplements derived from small, cold-water fatty fish. Further research will be necessary to draw firm conclusions.

  10. The glucocorticoid receptor hormone binding domain mediates transcriptional activation in vitro in the absence of ligand.

    PubMed Central

    Schmitt, J; Stunnenberg, H G

    1993-01-01

    We show that recombinant rat glucocorticoid receptor (vvGR) expressed using vaccinia virus is indistinguishable from authentic GR with respect to DNA and hormone binding. In the absence of hormone, vvGR is mainly found in the cytoplasm in a complex with heat shock protein 90. Upon incubation with ligand, vvGR is released from this complex and translocated to the nucleus. Thus, the ligand binding domain displays the known biochemical properties. However, in vitro, transcription from a synthetic promoter and from the mouse mammary tumor virus (MMTV) promoter is enhanced by recombinant GR in a ligand independent manner. Both transactivation domains contribute to the transcriptional activity, additively on a synthetic promoter and cooperatively on the MMTV promoter. We thus provide the first evidence that in vitro the hormone binding domain has a transcriptional activity even in the absence of ligand. Images PMID:8392705

  11. Functional Selectivity and Antidepressant Activity of Serotonin 1A Receptor Ligands.

    PubMed

    Chilmonczyk, Zdzisław; Bojarski, Andrzej Jacek; Pilc, Andrzej; Sylte, Ingebrigt

    2015-08-07

    Serotonin (5-HT) is a monoamine neurotransmitter that plays an important role in physiological functions. 5-HT has been implicated in sleep, feeding, sexual behavior, temperature regulation, pain, and cognition as well as in pathological states including disorders connected to mood, anxiety, psychosis and pain. 5-HT1A receptors have for a long time been considered as an interesting target for the action of antidepressant drugs. It was postulated that postsynaptic 5-HT1A agonists could form a new class of antidepressant drugs, and mixed 5-HT1A receptor ligands/serotonin transporter (SERT) inhibitors seem to possess an interesting pharmacological profile. It should, however, be noted that 5-HT1A receptors can activate several different biochemical pathways and signal through both G protein-dependent and G protein-independent pathways. The variables that affect the multiplicity of 5-HT1A receptor signaling pathways would thus result from the summation of effects specific to the host cell milieu. Moreover, receptor trafficking appears different at pre- and postsynaptic sites. It should also be noted that the 5-HT1A receptor cooperates with other signal transduction systems (like the 5-HT1B or 5-HT2A/2B/2C receptors, the GABAergic and the glutaminergic systems), which also contribute to its antidepressant and/or anxiolytic activity. Thus identifying brain specific molecular targets for 5-HT1A receptor ligands may result in a better targeting, raising a hope for more effective medicines for various pathologies.

  12. Functional Selectivity and Antidepressant Activity of Serotonin 1A Receptor Ligands

    PubMed Central

    Chilmonczyk, Zdzisław; Bojarski, Andrzej Jacek; Pilc, Andrzej; Sylte, Ingebrigt

    2015-01-01

    Serotonin (5-HT) is a monoamine neurotransmitter that plays an important role in physiological functions. 5-HT has been implicated in sleep, feeding, sexual behavior, temperature regulation, pain, and cognition as well as in pathological states including disorders connected to mood, anxiety, psychosis and pain. 5-HT1A receptors have for a long time been considered as an interesting target for the action of antidepressant drugs. It was postulated that postsynaptic 5-HT1A agonists could form a new class of antidepressant drugs, and mixed 5-HT1A receptor ligands/serotonin transporter (SERT) inhibitors seem to possess an interesting pharmacological profile. It should, however, be noted that 5-HT1A receptors can activate several different biochemical pathways and signal through both G protein-dependent and G protein-independent pathways. The variables that affect the multiplicity of 5-HT1A receptor signaling pathways would thus result from the summation of effects specific to the host cell milieu. Moreover, receptor trafficking appears different at pre- and postsynaptic sites. It should also be noted that the 5-HT1A receptor cooperates with other signal transduction systems (like the 5-HT1B or 5-HT2A/2B/2C receptors, the GABAergic and the glutaminergic systems), which also contribute to its antidepressant and/or anxiolytic activity. Thus identifying brain specific molecular targets for 5-HT1A receptor ligands may result in a better targeting, raising a hope for more effective medicines for various pathologies. PMID:26262615

  13. Synthesis and evaluation of bivalent ligands for binding to the human melanocortin-4 receptor

    PubMed Central

    Fernandes, Steve M.; Lee, Yeon Sun; Gillies, Robert J.; Hruby, Victor J.

    2014-01-01

    Membrane proteins, especially G-protein coupled receptors (GPCRs), are interesting and important theragnostic targets since many of them serve in intracellular signaling critical for all aspects of health and disease. The potential utility of designed bivalent ligands as targeting agents for cancer diagnosis and/or therapy can be evaluated by determining their binding to the corresponding receptors. As proof of concept, GPCR cell surface proteins are shown to be targeted specifically using multivalent ligands. We designed, synthesized, and tested a series of bivalent ligands targeting the over-expressed human melanocortin 4 receptor (hMC4R) in human embryonic kidney (HEK) 293 cells. Based on our data suggesting an optimal linker length of 25±10 Å inferred from the bivalent melanocyte stimulating hormone (MSH) agonist, the truncated heptapeptide, referred to as MSH(7): Ac-Ser-Nle-Glu-His-D-Phe-Arg-Trp-NH2 was used to construct a set of bivalent ligands incorporating a hMC4R antagonist, SHU9119: Ac-Nle-c[Asp-His-2′-D-Nal-Arg-Trp-Lys]-NH2 and another set of bivalent ligands containing the SHU9119 antagonist pharmacophore on both side of the optimized linkers. These two binding motifs within the bivalent constructs were conjoined by semi-rigid (Pro-Gly)3 units with or without the flexible poly(ethylene glycol) (PEGO) moieties. Lanthanide-based competitive binding assays showed bivalent ligands binds to the hMC4R with up to 240-fold higher affinity than the corresponding linked monovalent ligands. PMID:25438759

  14. Synthesis and evaluation of bivalent ligands for binding to the human melanocortin-4 receptor.

    PubMed

    Fernandes, Steve M; Lee, Yeon Sun; Gillies, Robert J; Hruby, Victor J

    2014-11-15

    Membrane proteins, especially G-protein coupled receptors (GPCRs), are interesting and important theragnostic targets since many of them serve in intracellular signaling critical for all aspects of health and disease. The potential utility of designed bivalent ligands as targeting agents for cancer diagnosis and/or therapy can be evaluated by determining their binding to the corresponding receptors. As proof of concept, GPCR cell surface proteins are shown to be targeted specifically using multivalent ligands. We designed, synthesized, and tested a series of bivalent ligands targeting the over-expressed human melanocortin 4 receptor (hMC4R) in human embryonic kidney (HEK) 293 cells. Based on our data suggesting an optimal linker length of 25±10Å inferred from the bivalent melanocyte stimulating hormone (MSH) agonist, the truncated heptapeptide, referred to as MSH(7): Ac-Ser-Nle-Glu-His-D-Phe-Arg-Trp-NH2 was used to construct a set of bivalent ligands incorporating a hMC4R antagonist, SHU9119: Ac-Nle-c[Asp-His-2'-D-Nal-Arg-Trp-Lys]-NH2 and another set of bivalent ligands containing the SHU9119 antagonist pharmacophore on both side of the optimized linkers. These two binding motifs within the bivalent constructs were conjoined by semi-rigid (Pro-Gly)3 units with or without the flexible poly(ethylene glycol) (PEGO) moieties. Lanthanide-based competitive binding assays showed bivalent ligands binds to the hMC4R with up to 240-fold higher affinity than the corresponding linked monovalent ligands.

  15. CoMFA and docking study of novel estrogen receptor subtype selective ligands

    NASA Astrophysics Data System (ADS)

    Wolohan, Peter; Reichert, David E.

    2003-05-01

    We present the results from a Comparative Molecular Field Analysis (CoMFA) and docking study of a diverse set of 36 estrogen receptor ligands whose relative binding affinities (RBA) with respect to 17β-Estradiol were available in both isoforms of the nuclear estrogen receptors (ERα, ERβ). Initial CoMFA models exhibited a correlation between the experimental relative binding affinities and the molecular steric and electrostatic fields; ERα: r2=0.79, q2=0.44 ERβ: r2=0.93, q2=0.63. Addition of the solvation energy of the isolated ligand improved the predictive nature of the ERβ model initially; r2=0.96, q2=0.70 but upon rescrambling of the data-set and reselecting the training set at random, inclusion of the ligand solvation energy was found to have little effect on the predictive nature of the CoMFA models. The ligands were then docked inside the ligand binding domain (LBD) of both ERα and ERβ utilizing the docking program Gold, after-which the program CScore was used to rank the resulting poses. Inclusion of both the Gold and CScore scoring parameters failed to improve the predictive ability of the original CoMFA models. The subtype selectivity expressed as RBA(ERα/ERβ) of the test sets was predicted using the most predictive CoMFA models, as illustrated by the cross-validated r2. In each case the most selective ligands were ranked correctly illustrating the utility of this method as a prescreening tool in the development of novel estrogen receptor subtype selective ligands.

  16. A structural feature of the non-peptide ligand interactions with mice mu-opioid receptors.

    PubMed

    Noori, Hamid R; Mucksch, Christian; Urbassek, Herbert M

    2014-01-01

    By binding to and activating the G-protein coupled μ-, κ- and δ-opioid receptors in the central nervous system, opiates are known to induce analgesic and sedative effects. In particular, non-peptide opioid ligands are often used in clinical applications to induce these therapeutically beneficial effects, due to their superior pharmacokinetics and bioavailability in comparison to endogenous neuropeptides. However, since opioid alkaloids are highly addictive substances, it is necessary to understand the exact mechanisms of their actions, specifically the ligand-binding properties of the target receptors, in order to safely apply opiates for therapeutic purposes. Using an in silico molecular docking approach (AutoDock Vina) combined with two-step cluster analysis, we have computationally obtained the docking scores and the ligand-binding pockets of twelve representative non-peptide nonendogenous agonists and antagonists at the crystallographically identified μ-opioid receptor. Our study predicts the existence of two main binding sites that are congruently present in all opioid receptor types. Interestingly, in terms of the agonist or antagonist properties of the substances on the receptors, the clustering analysis suggests a relationship with the position of the ligand-binding pockets, particularly its depth within the receptor structure. Furthermore, the binding affinity of the substances is directly correlated to the proximity of the binding pockets to the extracellular space. In conclusion, the results provide further insights into the structural features of the functional pharmacology of opioid receptors, suggesting the importance of the binding position of non-peptide agonists and antagonists- specifically the distance and the level of exposure to the extracellular space- to their dissociation kinetics and subsequent potency.

  17. Ligand-induced interaction between. alpha. - and. beta. -type platelet-derived growth factor (PDGF) receptors: Role of receptor heterodimers in kinase activation

    SciTech Connect

    Kanakaraj, P.; Raj, S.; Bishayee, S. ); Khan, S.A. )

    1991-02-19

    Two types of PDGF receptors have been cloned and sequenced. Both receptors are transmembrane glycoproteins with a ligand-stimulatable tyrosine kinase site. The authors have shown earlier that ligand-induced activation of the {beta}-type PDGF receptor is due to the conversion of the monomeric form of the receptor to the dimeric form. In the present studies, they have established the ligand-binding specificity of two receptor types and extended it further to investigate the ligand-induced association state of the {alpha}-receptor and the role of {alpha}-receptor in the activation of {beta}-receptor. These studies were conducted with cells that express one or the other type of PDGF receptor as well as with cells that express both types of receptors. Moreover, ligand-binding characteristics of the receptor were confirmed by immunoprecipitation of the receptor-{sup 125}I-PDGF covalent complex with type-specific anti-PDGF receptor antibodies. These studies revealed that all three isoforms of PDGF bind to {alpha}-receptor, and such binding leads to dimerization as well as activation of the receptor. In contrast, {beta}-receptor can be activated only by PDGF BB and not by PDGF AB or PDGF AA. However, by using antipeptide antibodies that are specific for {alpha}- or {beta}-type PDGF receptor, they demonstrated that in the presence of {alpha}-receptor, {beta}-receptor kinase can be activated by PDGF AB. They present here direct evidence that strongly suggests that such PDGF AB induced activation of {beta}-receptor is due to the formation of a noncovalently linked {alpha}-{beta} receptor heterodimer.

  18. A python-based docking program utilizing a receptor bound ligand shape: PythDock.

    PubMed

    Chung, Jae Yoon; Cho, Seung Joo; Hah, Jung-Mi

    2011-09-01

    PythDock is a heuristic docking program that uses Python programming language with a simple scoring function and a population based search engine. The scoring function considers electrostatic and dispersion/repulsion terms. The search engine utilizes a particle swarm optimization algorithm. A grid potential map is generated using the shape information of a bound ligand within the active site. Therefore, the searching area is more relevant to the ligand binding. To evaluate the docking performance of PythDock, two well-known docking programs (AutoDock and DOCK) were also used with the same data. The accuracy of docked results were measured by the difference of the ligand structure between x-ray structure, and docked pose, i.e., average root mean squared deviation values of the bound ligand were compared for fourteen protein-ligand complexes. Since the number of ligands' rotational flexibility is an important factor affecting the accuracy of a docking, the data set was chosen to have various degrees of flexibility. Although PythDock has a scoring function simpler than those of other programs (AutoDock and DOCK), our results showed that PythDock predicted more accurate poses than both AutoDock4.2 and DOCK6.2. This indicates that PythDock could be a useful tool to study ligand-receptor interactions and could also be beneficial in structure based drug design.

  19. Noncontiguous domains of the alpha-factor receptor of yeasts confer ligand specificity.

    PubMed

    Sen, M; Marsh, L

    1994-01-14

    The Saccharomyces cerevisiae alpha-factor receptor has a 3400-fold higher affinity for the S. cerevisiae alpha-factor peptide (c-alpha-f) than for the Saccharomyces kluyveri alpha-factor peptide (k-alpha-f) as determined by competition for [3H] c-alpha-f binding. The S. kluyveri alpha-factor receptor has an approximately 2-fold higher affinity for k-alpha-f than for c-alpha-f. The S. kluyveri receptor gene (k-STE2) is incompletely regulated by S. cerevisiae mating type and poorly expressed on the surface of an S. cerevisiae mating type a strain. A chimeric receptor (c/k1) with amino acid residues 1-45 derived from S. cerevisiae and amino acid residues 46-427 from S. kluyveri exhibits the binding specificity of the S. kluyveri receptor. However, chimeric receptors containing residues 1-168 (c/k2) or 1-250 (c/k3) from S. cerevisiae and the remainder from the S. kluyveri receptor exhibit specificities similar to one another, but intermediate between the parent S. cerevisiae and S. kluyveri receptors. The relative ability of c-alpha-f and k-alpha-f to induce growth arrest in strains expressing chimeric receptors parallels relative affinity. Thus, two noncontiguous domains that include putative extracellular loops 1 and 3 and associated transmembrane segments, but exclude the extracellular NH2 terminus and loop 2, appear to contribute to alpha-factor receptor ligand specificity. COOH-terminal regions of the S. kluyveri receptor appear to confer a desensitization defect when expressed in S. cerevisiae. The S. cerevisiae receptor truncated at residue 296 retains ligand specificity for growth arrest.

  20. Ligand binding and signalling pathways of PTH receptors in sea bream (Sparus auratus) enterocytes.

    PubMed

    Rotllant, J; Guerreiro, P M; Redruello, B; Fernandes, H; Apolónia, L; Anjos, L; Canario, A V M; Power, D M

    2006-02-01

    Whole animal studies have indicated that Ca(2+) uptake by the gastrointestinal tract is regulated by the action of parathyroid hormone-related peptide (PTHrP) in teleost fish. We have characterised PTH receptors (PTHR) in piscine enterocytes and established, by using amino-terminal PTHrP peptides, the amino acid residues important for receptor activation and for stabilising the ligand/receptor complex. Ligand binding of (125)I-(1-35(tyr)) PTHrP to the membrane fraction of isolated sea bream enterocytes revealed the existence of a single saturable high-affinity receptor (K (D)=2.59 nM; B (max)=71 fmol/mg protein). Reverse transcription/polymerase chain reaction with specific primers for sea bream PTH1R and PTH3R confirmed the mRNA expression of only the later receptor. Fugu (1-34)PTHrP increased cAMP levels in enterocytes but had no effect on total inositol phosphate accumulation. The amino-terminal peptides (2-34)PTHrP, (3-34)PTHrP and (7-34)PTHrP bound efficiently to the receptor but were severely defective in stimulating cAMP in enterocyte cells indicating that the first six residues of piscine (1-34)PTHrP, although not important for receptor binding, are essential for activation of the adenylate cyclase/phosphokinase A (AC-PKA)-receptor-coupled intracellular signalling pathway. Therefore, PTHrP in teleosts acts on the gastrointestinal tract through PTH3R and the AC-PKA intracellular signalling pathway and might regulate Ca(2+) uptake at this site. Ligand-receptor binding and activity throughout the vertebrates appears to be allocated to the same amino acid residues of the amino-terminal domain of the PTHrP molecule.

  1. The aryl hydrocarbon receptor promotes aging phenotypes across species

    PubMed Central

    Eckers, Anna; Jakob, Sascha; Heiss, Christian; Haarmann-Stemmann, Thomas; Goy, Christine; Brinkmann, Vanessa; Cortese-Krott, Miriam M.; Sansone, Roberto; Esser, Charlotte; Ale-Agha, Niloofar; Altschmied, Joachim; Ventura, Natascia; Haendeler, Judith

    2016-01-01

    The ubiquitously expressed aryl hydrocarbon receptor (AhR) induces drug metabolizing enzymes as well as regulators of cell growth, differentiation and apoptosis. Certain AhR ligands promote atherosclerosis, an age-associated vascular disease. Therefore, we investigated the role of AhR in vascular functionality and aging. We report a lower pulse wave velocity in young and old AhR-deficient mice, indicative of enhanced vessel elasticity. Moreover, endothelial nitric oxide synthase (eNOS) showed increased activity in the aortas of these animals, which was reflected in increased NO production. Ex vivo, AhR activation reduced the migratory capacity of primary human endothelial cells. AhR overexpression as well as treatment with a receptor ligand, impaired eNOS activation and reduced S-NO content. All three are signs of endothelial dysfunction. Furthermore, AhR expression in blood cells of healthy human volunteers positively correlated with vessel stiffness. In the aging model Caenorhabditis elegans, AhR-deficiency resulted in increased mean life span, motility, pharynx pumping and heat shock resistance, suggesting healthier aging. Thus, AhR seems to have a negative impact on vascular and organismal aging. Finally, our data from human subjects suggest that AhR expression levels could serve as an additional, new predictor of vessel aging. PMID:26790370

  2. 3-Methylcholanthrene and other aryl hydrocarbon receptor agonists directly activate estrogen receptor alpha.

    PubMed

    Abdelrahim, Maen; Ariazi, Eric; Kim, Kyounghyun; Khan, Shaheen; Barhoumi, Rola; Burghardt, Robert; Liu, Shengxi; Hill, Denise; Finnell, Richard; Wlodarczyk, Bogdan; Jordan, V Craig; Safe, Stephen

    2006-02-15

    3-Methylcholanthrene (3MC) is an aryl hydrocarbon receptor (AhR) agonist, and it has been reported that 3MC induces estrogenic activity through AhR-estrogen receptor alpha (ER alpha) interactions. In this study, we used 3MC and 3,3',4,4',5-pentachlorobiphenyl (PCB) as prototypical AhR ligands, and both compounds activated estrogen-responsive reporter genes/gene products (cathepsin D) in MCF-7 breast cancer cells. The estrogenic responses induced by these AhR ligands were inhibited by the antiestrogen ICI 182780 and by the transfection of a small inhibitory RNA for ER alpha but were not affected by the small inhibitory RNA for AhR. These results suggest that 3MC and PCB directly activate ER alpha, and this was confirmed in a competitive ER alpha binding assay and in a fluorescence resonance energy transfer experiment in which PCB and 3MC induced CFP-ER alpha/YFP-ER alpha interactions. In a chromatin immunoprecipitation assay, PCB and 3MC enhanced ER alpha (but not AhR) association with the estrogen-responsive region of the pS2 gene promoter. Moreover, in AhR knockout mice, 3MC increased uterine weights and induced expression of cyclin D1 mRNA levels. These results show that PCB and 3MC directly activate ER alpha-dependent transactivation and extend the number of ligands that activate both AhR and ER alpha.

  3. Proliferating cell nuclear antigen is a novel inhibitory ligand for the natural cytotoxicity receptor NKp44.

    PubMed

    Rosental, Benyamin; Brusilovsky, Michael; Hadad, Uzi; Oz, Dafna; Appel, Michael Y; Afergan, Fabian; Yossef, Rami; Rosenberg, Lior Ann; Aharoni, Amir; Cerwenka, Adelheid; Campbell, Kerry S; Braiman, Alex; Porgador, Angel

    2011-12-01

    NK cells play an important role in the early immune response to cancer. The NKp44 activating receptor is the only natural cytotoxicity receptor that is expressed exclusively by primate NK cells, yet its cellular ligands remain largely unknown. Proliferating cell nuclear Ag (PCNA) is overexpressed in cancer cells. In this study, we show that the NKp44 receptor recognizes PCNA. Their interaction inhibits NK cell function through NKp44/ITIM. The physical interaction of NKp44 and PCNA is enabled by recruitment of target cell PCNA to the NK immunological synapse. We demonstrate that PCNA promotes cancer survival by immune evasion through inhibition of NKp44-mediated NK cell attack.

  4. 3-Chlorotyramine Acting as Ligand of the D2 Dopamine Receptor. Molecular Modeling, Synthesis and D2 Receptor Affinity.

    PubMed

    Angelina, Emilio; Andujar, Sebastian; Moreno, Laura; Garibotto, Francisco; Párraga, Javier; Peruchena, Nelida; Cabedo, Nuria; Villecco, Margarita; Cortes, Diego; Enriz, Ricardo D

    2015-01-01

    We synthesized and tested 3-chlorotyramine as a ligand of the D2 dopamine receptor. This compound displayed a similar affinity by this receptor to that previously reported for dopamine. In order to understand further the experimental results we performed a molecular modeling study of 3-chlorotyramine and structurally related compounds. By combining molecular dynamics simulations with semiempirical (PM6), ab initio and density functional theory calculations, a simple and generally applicable procedure to evaluate the binding energies of these ligands interacting with the D2 dopamine receptors is reported here. These results provided a clear picture of the binding interactions of these compounds from both structural and energetic view points. A reduced model for the binding pocket was used. This approach allowed us to perform more accurate quantum mechanical calculations as well as to obtain a detailed electronic analysis using the Quantum Theory of Atoms in Molecules (QTAIM) technique. Molecular aspects of the binding interactions between ligands and the D2 dopamine receptor are discussed in detail. A good correlation between the relative binding energies obtained from theoretical calculations and experimental IC50 values was obtained. These results allowed us to predict that 3-chlorotyramine possesses a significant affinity by the D2 -DR. Our theoretical predictions were experimentally corroborated when we synthesized and tested 3-chlorotyramine which displayed a similar affinity by the D2 -DR to that reported for DA.

  5. A photoregulated ligand for the nuclear import receptor karyopherin alpha.

    PubMed

    Park, S B; Standaert, R F

    2001-12-01

    The ability to orchestrate the transport of proteins between nucleus and cytoplasm provides cells with a powerful regulatory mechanism. Selective translocation between these compartments is often used to propagate cellular signals, and it is an intimate part of the processes that control cell division, viral replication, and other cellular events. Therefore, precise experimental control over protein localization, through the agency of light, would provide a powerful tool for the study and manipulation of these events. To this end, a prototype photoregulated nuclear localization signal (NLS) was derived from a native NLS. A library of 30 mutants of the bipartite NLS from Xenopus laevis nucleoplasmin containing a novel, photoisomerizable amino acid was prepared by parallel, solid-phase synthesis and screened in vitro for binding to the nuclear import receptor karyopherin alpha, which mediates the nuclear import of cellular proteins. A single peptide was identified in which the cis and trans photoisomers bind the receptor differentially. The strategy used to obtain this peptide is systematic and empirical; therefore, it is potentially applicable to any peptide-receptor system.

  6. Molecular Modelling Approaches for the Analysis of Histamine Receptors and Their Interaction with Ligands.

    PubMed

    Strasser, Andrea; Wittmann, Hans-Joachim

    2017-01-22

    Several experimental techniques to analyse histamine receptors are available, e.g. pharmacological characterisation of known or new compounds by different types of assays or mutagenesis studies. To obtain insights into the histamine receptors on a molecular and structural level, crystal structures have to be determined and molecular modelling studies have to be performed. It is widely accepted to generate homology models of the receptor of interest based on an appropriate crystal structure as a template and to refine the resulting models by molecular dynamic simulations. A lot of modelling techniques, e.g. docking, QSAR or interaction fingerprint methods, are used to predict binding modes of ligands and pharmacological data, e.g. affinity or even efficacy. However, within the last years, molecular dynamic simulations got more and more important: First of all, molecular dynamic simulations are very helpful to refine the binding mode of a ligand to a histamine receptor, obtained by docking studies. Furthermore, with increasing computational performance it got possible to simulate complete binding pathways of ions or ligands from the aqueous extracellular phase into the allosteric or orthosteric binding pocket of histamine receptors.

  7. Ligand-induced EGF Receptor Oligomerization Is Kinase-dependent and Enhances Internalization*

    PubMed Central

    Hofman, Erik G.; Bader, Arjen N.; Voortman, Jarno; van den Heuvel, Dave J.; Sigismund, Sara; Verkleij, Arie J.; Gerritsen, Hans C.; van Bergen en Henegouwen, Paul M. P.

    2010-01-01

    The current activation model of the EGF receptor (EGFR) predicts that binding of EGF results in dimerization and oligomerization of the EGFR, leading to the allosteric activation of the intracellular tyrosine kinase. Little is known about the regulatory mechanism of receptor oligomerization. In this study, we have employed FRET between identical fluorophores (homo-FRET) to monitor the dimerization and oligomerization state of the EGFR before and after receptor activation. Our data show that, in the absence of ligand, ∼40% of the EGFR molecules were present as inactive dimers or predimers. The monomer/predimer ratio was not affected by deletion of the intracellular domain. Ligand binding induced the formation of receptor oligomers, which were found in both the plasma membrane and intracellular structures. Ligand-induced oligomerization required tyrosine kinase activity and nine different tyrosine kinase substrate residues. This indicates that the binding of signaling molecules to activated EGFRs results in EGFR oligomerization. Induction of EGFR predimers or pre-oligomers using the EGFR fused to the FK506-binding protein did not affect signaling but was found to enhance EGF-induced receptor internalization. Our data show that EGFR oligomerization is the result of EGFR signaling and enhances EGFR internalization. PMID:20940297

  8. Expression of ARNT, ARNT2, HIF1 alpha, HIF2 alpha and Ah receptor mRNAs in the developing mouse.

    PubMed

    Jain, S; Maltepe, E; Lu, M M; Simon, C; Bradfield, C A

    1998-04-01

    The basic helix-loop-helix-PAS (bHLH-PAS) protein ARNT is a dimeric partner of the Ah receptor (AHR) and hypoxia inducible factor 1 alpha(HIF1 alpha). These dimers mediate biological responses to xenobiotic exposure and low oxygen tension. The recent cloning of ARNT and HIF1(homologues (ARNT2 and HIF2 alpha) indicates that at least six distinct bHLH-PAS heterodimeric combinations can occur in response to a number of environmental stimuli. In an effort to understand the biological relevance of this combinatorial complexity, we characterized their relative expression at a number of developmental time points by parallel in situ hybridization of adjacent tissue sections. Our results reveal that in general there is limited redundancy in the expression of these six transcription factors and that each of these bHLH-PAS members displays a unique pattern of developmental expression emerging as early as embryonic day 9.5.

  9. Cholinesterase inhibitory activity of chlorophenoxy derivatives-Histamine H3 receptor ligands.

    PubMed

    Łażewska, Dorota; Jończyk, Jakub; Bajda, Marek; Szałaj, Natalia; Więckowska, Anna; Panek, Dawid; Moore, Caitlin; Kuder, Kamil; Malawska, Barbara; Kieć-Kononowicz, Katarzyna

    2016-08-15

    In recent years, multitarget-directed ligands have become an interesting strategy in a search for a new treatment of Alzheimer's disease. Combination of both: a histamine H3 receptor antagonist/inverse agonist and a cholinesterases inhibitor in one molecule could provide a new therapeutic opportunity. Here, we present biological evaluation of histamine H3 receptor ligands-chlorophenoxyalkylamine derivatives against cholinesterases: acetyl- and butyrylcholinesterase. The target compounds showed cholinesterase inhibitory activity in a low micromolar range. The most potent in this group was 1-(7-(4-chlorophenoxy)heptyl)homopiperidine (18) inhibiting the both enzymes (EeAChE IC50=1.93μM and EqBuChE IC50=1.64μM). Molecular modeling studies were performed to explain the binding mode of 18 with histamine H3 receptor as well as with cholinesterases.

  10. The active analog approach applied to the pharmacophore identification of benzodiazepine receptor ligands

    NASA Astrophysics Data System (ADS)

    Tebib, Souhail; Bourguignon, Jean-Jacques; Wermuth, Camille-Georges

    1987-07-01

    Applied to seven potent benzodiazepine-receptor ligands belonging to chemically different classes, the active analog approach allowed the stepwise identification of the pharmacophoric pattern associated with the recognition by the benzodiazepine receptor. A unique pharmacophore model was derived which involves six critical zones: (a) a π-electron rich aromatic (PAR) zone; (b) two electron-rich zones δ1 and δ2 placed at 5.0 and 4.5 Å respectively from the reference centroid in the PAR zone; (c) a freely rotating aromatic ring (FRA) region; (d) an out-of-plane region (OPR), strongly associated with agonist properties; and (e) an additional hydrophobic region (AHR). The model accommodates all presently known ligands of the benzodiazepine receptor, identifies sensitivity to steric hindrance close to the δ1 zone, accounts for R and S differential affinities and distinguishes requirements for agonist versus non-agonist activity profiles.

  11. The thrombin receptor extracellular domain contains sites crucial for peptide ligand-induced activation.

    PubMed Central

    Bahou, W F; Coller, B S; Potter, C L; Norton, K J; Kutok, J L; Goligorsky, M S

    1993-01-01

    A thrombin receptor (TR) demonstrating a unique activation mechanism has recently been isolated from a megakaryocytic (Dami) cell line. To further study determinants of peptide ligand-mediated activation phenomenon, we have isolated, cloned, and stably expressed the identical receptor from a human umbilical vein endothelial cell (HUVEC) library. Chinese hamster ovary (CHO) cells expressing a functional TR (CHO-TR), platelets, and HUVECs were then used to specifically characterize alpha-thrombin- and peptide ligand-induced activation responses using two different antibodies: anti-TR34-52 directed against a 20-amino acid peptide spanning the thrombin cleavage site, and anti-TR1-160 generated against the NH2-terminal 160 amino acids of the TR expressed as a chimeric protein in Escherichia coli. Activation-dependent responses to both alpha-thrombin (10 nM) and peptide ligand (20 microM) were studied using fura 2-loaded cells and microspectrofluorimetry. Whereas preincubation of CHO-TR with anti-TR34-52 abolished only alpha-thrombin-induced [Ca2+]i transients, preincubation with anti-TR1-160 abrogated both alpha-thrombin- and peptide ligand-induced responses. This latter inhibitory effect was dose dependent and similar for both agonists, with an EC50 of approximately 90 micrograms/ml. Anti-TR1-160 similarly abolished peptide ligand-induced [Ca2+]i transients in platelets and HUVECs, whereas qualitatively different responses characterized by delayed but sustained elevations in [Ca2+]i transients were evident using alpha-thrombin. Platelet aggregation to low concentrations of both ligands was nearly abolished by anti-TR1-160, although some shape change remained; anti-TR34-52 only inhibited alpha-thrombin-induced aggregation. These data establish that a critical recognition sequence for peptide ligand-mediated receptor activation is contained on the NH2-terminal portion of the receptor, upstream from the first transmembrane domain. Furthermore, alpha

  12. Only high-affinity receptors for interleukin 2 mediate internalization of ligand

    SciTech Connect

    Weissman, A.M.; Harford, J.B.; Svetlik, P.B.; Leonard, W.L.; Depper, J.M.; Waldmann, T.A.; Greene, W.C.; Klausner, R.D.

    1986-03-01

    Interleukin 2 (IL-2) receptors are expressed on activated T cells and in select T-cell leukemias. Recently, it has been demonstrated that at least two classes of receptor for IL-2 exist with markedly different affinities for ligand. All known biological actions of IL-2 have been correlated with occupancy of high-affinity sites; the function of the low-affinity sites remains unknown. Receptor-mediated endocytosis is the primary means of internalization of cell-surface receptors and their ligands. The internalization of IL-2 bound to high- and low-affinity receptor sites was studied in a human T-cell lymphotrophic virus type 1 (HTLV-1)-infected human T-cell leukemia cell line and in a cloned murine cytotoxic T-cell line (CTLL). Internalization of IL-2 occurred only when bound to high-affinity sites. In addition, an anti-receptor antibody (anti-Tac), which binds equally well to high- and low-affinity sites, demonstrated no detectable internalization. The implications of these findings as they relate to IL-2 receptor structure and function are discussed.

  13. Aryl Hydrocarbon Receptor Ligand Effects in RBL2H3 Cells

    PubMed Central

    Maaetoft-Udsen, Kristina; Shimoda, Lori M.N.; Frøkiær, Hanne; Turner, Helen

    2012-01-01

    The aryl hydrocarbon receptor (AHR) mediates toxic effects of dioxin and xenobiotic metabolism. AHR has an emerging role in the immune system but its physiological ligands and functional role in immunocytes remain poorly understood. Mast cells are immunocytes that are central to inflammatory responses and release a spectrum of pro-inflammatory mediators including histamine, mast cell proteases, and pro-inflammatory cytokines such as IL-6 upon stimulation. Our aim was to investigate the AHR in model mast cells and examine how both putative and known AHR ligands, e.g., kynurenine, kynurenic acid (KA), Resveratrol, indolmycin, and violacein, affect mast cell activation and signaling. We tested these ligands on calcium signaling, degranulation, and gene expression. Our data show that AHR is present in three model mast cell lines, and that various known and putative AHR ligands regulate gene expression of Cyp1a1, a gene down-stream of AHR. Furthermore, we found that calcium influxes and mast cell secretory responses were enhanced or suppressed after chronic treatment with AHR agonists or antagonists, and that AHR ligands modified RBL2H3 cell degranulation. AHR ligands can chronically change cytokine gene expression in activated mast cells, as exemplified by IL-6. The antagonist Resveratrol repressed expression of induced IL-6 gene expression. Though KA and kynurenine are both AHR agonists, these ligands behaved differently in regards to degranulation and IL-6 expression, indicating that they may function outside of AHR pathways. These data suggest considerable complexity in RBL2H3 responses to AHR ligands, with implications for our understanding of both dioxin pathology and the immunological effects of endogenous AHR ligands. PMID:22471748

  14. Chemical modification of Class II G-protein coupled receptor ligands

    PubMed Central

    Chapter, Megan C.; White, Caitlin M.; De Ridder, Angela; Chadwick, Wayne; Martin, Bronwen; Maudsley, Stuart

    2009-01-01

    Recent research and clinical data have begun to demonstrate the huge potential therapeutic importance of ligands that modulate the activity of the secretin-like, Class II, G-protein coupled receptors (GPCRs). Ligands that can modulate the activity of these Class II GPCRs may have important clinical roles in the treatment of a wide variety of conditions such as osteoporosis, diabetes, amyotrophic lateral sclerosis and autism spectrum disorders. While these receptors present important new therapeutic targets, the large glycoprotein nature of their cognate ligands poses many problems with respect to therapeutic peptidergic drug design. These native peptides often exhibit poor bioavailability, metabolic instability, poor receptor selectivity and resultant low potencies in vivo. Recently, increased attention has been paid to the structural modification of these peptides to enhance their therapeutic efficacy. Successful modification strategies have included D-amino acid substitutions, selective truncation, and fatty acid acylation of the peptide. Through these and other processes, these novel peptide ligand analogs can demonstrate enhanced receptor subtype selectivity, directed signal transduction pathway activation, resistance to proteolytic degradation, and improved systemic bioavailability. In the future, it is likely, through additional modification strategies such as addition of circulation-stabilizing transferrin moieties, that the therapeutic pharmacopeia of drugs targeted towards Class II secretin-like receptors may rival that of the Class I rhodopsin-like receptors that currently provide the majority of clinically used GPCR-based therapeutics. Currently, Class II-based drugs include synthesized analogues of vasoactive intestinal peptide for type 2 diabetes or parathyroid hormone for osteoporosis. PMID:19686775

  15. The pyrokinin/ pheromone biosynthesis-activating neuropeptide (PBAN) family of peptides and their receptors in Insecta: evolutionary trace indicates potential receptor ligand-binding domains.

    PubMed

    Jurenka, R; Nusawardani, T

    2011-06-01

    The pyrokinin/pheromone biosynthesis-activating neuropeptide (PBAN) family of G-protein-coupled receptors and their ligands have been identified in various insects. Physiological functions of pyrokinin peptides include muscle contraction, whereas PBAN regulates, among other functions, pheromone production in moths which indicates the pleiotropic nature of these peptides. Based on the alignment of annotated genomic sequences, the pyrokinin/PBAN family of receptors have similarity with the corresponding structures of the capa or periviscerokinin receptors of insects and the neuromedin U receptors of vertebrates. In our study, evolutionary trace (ET) analysis on the insect receptor sequences was conducted to predict the putative ligand recognition and binding sites. The ET analysis of four class-specific receptors indicated several amino acid residues that are conserved in the transmembrane domains. The receptor extracellular domains exhibit several class-specific amino acid residues, which could indicate putative domains for activation of these receptors by ligand recognition and binding.

  16. The aryl hydrocarbon receptor: Regulation of hematopoiesis and involvement in the progression of blood diseases

    PubMed Central

    Casado, Fanny L.; Singh, Kameshwar P.; Gasiewicz, Thomas A.

    2010-01-01

    The aryl hydrocarbon receptor (AhR) is a basic helix-loop-helix protein that belongs to the superfamily of environment-sensing PAS (Per-ARNT-Sim) proteins. A large number of ligands have been described to bind AhR and promote its nuclear translocation. In the nucleus, the AhR and its dimerization partner the AhR nuclear translocase (ARNT), also known as HIF1β, form a DNA-binding complex that acts as a transcriptional regulator. Animal and human data suggest that, beyond its mediating responses to xenobiotic and/or unknown endogenous ligands, the AhR has a role, although as yet undefined, in the regulation of cell cycle and inflammation. The AhR also appears to regulate the hematopoietic and immune systems during development and adult life in a cell-specific manner. While accidental exposure to xenobiotic AhR ligands has been associated with leukemia in humans, the specific mechanisms of AhR involvement are still not completely understood. However, recent data are consistent with a functional role of the AhR in the maintenance of hematopoietic stem and/or progenitor cells (HSCs/HPCs). Studies highlighting AhR-regulation of HSCs/HPCs provide a rational framework to understand their biology, a role of the AhR in hematopoietic diseases, and a means to develop interventions for these diseases. PMID:20171126

  17. The aryl hydrocarbon receptor: regulation of hematopoiesis and involvement in the progression of blood diseases.

    PubMed

    Casado, Fanny L; Singh, Kameshwar P; Gasiewicz, Thomas A

    2010-04-15

    The aryl hydrocarbon receptor (AhR) is a basic helix-loop-helix protein that belongs to the superfamily of environment-sensing PAS (Per-ARNT-Sim) proteins. A large number of ligands have been described to bind AhR and promote its nuclear translocation. In the nucleus, the AhR and its dimerization partner the AhR nuclear translocator (ARNT) form a DNA-binding complex that acts as a transcriptional regulator. Animal and human data suggest that, beyond its mediating responses to xenobiotic and/or unknown endogenous ligands, the AhR has a role, although as yet undefined, in the regulation of cell cycle and inflammation. The AhR also appears to regulate the hematopoietic and immune systems during development and adult life in a cell-specific manner. While accidental exposure to xenobiotic AhR ligands has been associated with leukemia in humans, the specific mechanisms of AhR involvement are still not completely understood. However, recent data are consistent with a functional role of the AhR in the maintenance of hematopoietic stem and/or progenitor cells (HSCs/HPCs). Studies highlighting AhR regulation of HSCs/HPCs provide a rational framework to understand their biology, a role of the AhR in hematopoietic diseases, and a means to develop interventions for these diseases.

  18. Hypersensitivity of Aryl Hydrocarbon Receptor-Deficient Mice to Lipopolysaccharide-Induced Septic Shock▿ †

    PubMed Central

    Sekine, Hiroki; Mimura, Junsei; Oshima, Motohiko; Okawa, Hiromi; Kanno, Jun; Igarashi, Katsuhide; Gonzalez, Frank J.; Ikuta, Togo; Kawajiri, Kaname; Fujii-Kuriyama, Yoshiaki

    2009-01-01

    Aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, is known to mediate a wide variety of pharmacological and toxicological effects caused by polycyclic aromatic hydrocarbons. Recent studies have revealed that AhR is involved in the normal development and homeostasis of many organs. Here, we demonstrate that AhR knockout (AhR KO) mice are hypersensitive to lipopolysaccharide (LPS)-induced septic shock, mainly due to the dysfunction of their macrophages. In response to LPS, bone marrow-derived macrophages (BMDM) of AhR KO mice secreted an enhanced amount of interleukin-1β (IL-1β). Since the enhanced IL-1β secretion was suppressed by supplementing Plasminogen activator inhibitor-2 (Pai-2) expression through transduction with Pai-2-expressing adenoviruses, reduced Pai-2 expression could be a cause of the increased IL-1β secretion by AhR KO mouse BMDM. Analysis of gene expression revealed that AhR directly regulates the expression of Pai-2 through a mechanism involving NF-κB but not AhR nuclear translocator (Arnt), in an LPS-dependent manner. Together with the result that administration of the AhR ligand 3-methylcholanthrene partially protected mice with wild-type AhR from endotoxin-induced death, these results raise the possibility that an appropriate AhR ligand may be useful for treating patients with inflammatory disorders. PMID:19822660

  19. Deciphering Dimerization Modes of PAS Domains: Computational and Experimental Analyses of the AhR:ARNT Complex Reveal New Insights Into the Mechanisms of AhR Transformation

    PubMed Central

    Corrada, Dario; Soshilov, Anatoly A.; Denison, Michael S.

    2016-01-01

    The Aryl hydrocarbon Receptor (AhR) is a transcription factor that mediates the biochemical response to xenobiotics and the toxic effects of a number of environmental contaminants, including dioxins. Recently, endogenous regulatory roles for the AhR in normal physiology and development have also been reported, thus extending the interest in understanding its molecular mechanisms of activation. Since dimerization with the AhR Nuclear Translocator (ARNT) protein, occurring through the Helix-Loop-Helix (HLH) and PER-ARNT-SIM (PAS) domains, is needed to convert the AhR into its transcriptionally active form, deciphering the AhR:ARNT dimerization mode would provide insights into the mechanisms of AhR transformation. Here we present homology models of the murine AhR:ARNT PAS domain dimer developed using recently available X-ray structures of other bHLH-PAS protein dimers. Due to the different reciprocal orientation and interaction surfaces in the different template dimers, two alternative models were developed for both the PAS-A and PAS-B dimers and they were characterized by combining a number of computational evaluations. Both well-established hot spot prediction methods and new approaches to analyze individual residue and residue-pairwise contributions to the MM-GBSA binding free energies were adopted to predict residues critical for dimer stabilization. On this basis, a mutagenesis strategy for both the murine AhR and ARNT proteins was designed and ligand-dependent DNA binding ability of the AhR:ARNT heterodimer mutants was evaluated. While functional analysis disfavored the HIF2α:ARNT heterodimer-based PAS-B model, most mutants derived from the CLOCK:BMAL1-based AhR:ARNT dimer models of both the PAS-A and the PAS-B dramatically decreased the levels of DNA binding, suggesting this latter model as the most suitable for describing AhR:ARNT dimerization. These novel results open new research directions focused at elucidating basic molecular mechanisms underlying the

  20. [Drug discrimination properties and cytotoxicity of the cannabinoid receptor ligands].

    PubMed

    Tomiyama, Ken-ichi; Funada, Masahiko

    2012-06-01

    The worldwide distribution of smokable herbal mixtures called "Spice" that contain synthetic cannabinoids with a pharmacological activity similar to delta 9-tetrahydrocannabinol (delta 9-THC) has been reported. The synthetic cannabinoids induce behavior and have biochemical properties similar to naturally occurring cannabinoids such as delta 9-THC. In drug discrimination procedures, animal behavior is differentially reinforced depending on the presence or absence of specific drug stimuli. This review seeks to establish an animal model to serve as a discriminative stimulus of the synthetic cannabinoids, to determine whether this discriminative stimulus is identical to that of delta 9-THC. Much data have been obtained in drug discrimination experiments with various synthetic cannabinoids. In the discriminative study, synthetic cannabinoids such as CP-55,940 and WIN-55,212-2 were substituted for delta 9-THC in rats trained to discriminate delta 9-THC from the vehicle. These discriminative effects of synthetic cannabinoids were antagonized by CB1 antagonist SR-141,716A. The discriminative effects of synthetic cannabinoids may overlap with the delta 9-THC cue mediated by CB1 receptors. In in vitro study using NG 108-15 cell lines, synthetic cannabinoids have produced strong cytotoxicities that were suppressed by pretreatment with the CB1 receptor antagonist. Furthermore, pretreatment with caspase inhibitors suppressed these synthetic-cannabinoid-induced cytotoxicities in NG 108-15 cells. These findings indicate that the cytotoxicity of synthetic cannabinoids towards NG 108-15 cells is mediated by the CB1 receptors and further suggest that caspase cascades may play an important role in the cytotoxicities induced by these synthetic cannabinoids. In conclusion, synthetic cannabinoid abuse could be a health hazard for humans.

  1. A multi-protein receptor-ligand complex underlies combinatorial dendrite guidance choices in C. elegans

    PubMed Central

    Zou, Wei; Shen, Ao; Dong, Xintong; Tugizova, Madina; Xiang, Yang K; Shen, Kang

    2016-01-01

    Ligand receptor interactions instruct axon guidance during development. How dendrites are guided to specific targets is less understood. The C. elegans PVD sensory neuron innervates muscle-skin interface with its elaborate dendritic branches. Here, we found that LECT-2, the ortholog of leukocyte cell-derived chemotaxin-2 (LECT2), is secreted from the muscles and required for muscle innervation by PVD. Mosaic analyses showed that LECT-2 acted locally to guide the growth of terminal branches. Ectopic expression of LECT-2 from seam cells is sufficient to redirect the PVD dendrites onto seam cells. LECT-2 functions in a multi-protein receptor-ligand complex that also contains two transmembrane ligands on the skin, SAX-7/L1CAM and MNR-1, and the neuronal transmembrane receptor DMA-1. LECT-2 greatly enhances the binding between SAX-7, MNR-1 and DMA-1. The activation of DMA-1 strictly requires all three ligands, which establishes a combinatorial code to precisely target and pattern dendritic arbors. DOI: http://dx.doi.org/10.7554/eLife.18345.001 PMID:27705746

  2. The Molecular Basis of Ligand Interaction at Free Fatty Acid Receptor 4 (FFA4/GPR120)*

    PubMed Central

    Hudson, Brian D.; Shimpukade, Bharat; Milligan, Graeme; Ulven, Trond

    2014-01-01

    The long-chain fatty acid receptor FFA4 (previously GPR120) is receiving substantial interest as a novel target for the treatment of metabolic and inflammatory disease. This study examines for the first time the detailed mode of binding of both long-chain fatty acid and synthetic agonist ligands at FFA4 by integrating molecular modeling, receptor mutagenesis, and ligand structure-activity relationship approaches in an iterative format. In doing so, residues required for binding of fatty acid and synthetic agonists to FFA4 have been identified. This has allowed for the refinement of a well validated model of the mode of ligand-FFA4 interaction that will be invaluable in the identification of novel ligands and the future development of this receptor as a therapeutic target. The model reliably predicted the effects of substituent variations on agonist potency, and it was also able to predict the qualitative effect of binding site mutations in the majority of cases. PMID:24860101

  3. Acetylation of pregnane X receptor protein determines selective function independent of ligand activation

    SciTech Connect

    Biswas, Arunima; Pasquel, Danielle; Tyagi, Rakesh Kumar; Mani, Sridhar

    2011-03-18

    Research highlights: {yields} Pregnane X receptor (PXR), a major regulatory protein, is modified by acetylation. {yields} PXR undergoes dynamic deacetylation upon ligand-mediated activation. {yields} SIRT1 partially mediates PXR deacetylation. {yields} PXR deacetylation per se induces lipogenesis mimicking ligand-mediated activation. -- Abstract: Pregnane X receptor (PXR), like other members of its class of nuclear receptors, undergoes post-translational modification [PTM] (e.g., phosphorylation). However, it is unknown if acetylation (a major and common form of protein PTM) is observed on PXR and, if it is, whether it is of functional consequence. PXR has recently emerged as an important regulatory protein with multiple ligand-dependent functions. In the present work we show that PXR is indeed acetylated in vivo. SIRT1 (Sirtuin 1), a NAD-dependent class III histone deacetylase and a member of the sirtuin family of proteins, partially mediates deacetylation of PXR. Most importantly, the acetylation status of PXR regulates its selective function independent of ligand activation.

  4. G protein-coupled receptor 56 and collagen III, a receptor-ligand pair, regulates cortical development and lamination.

    PubMed

    Luo, Rong; Jeong, Sung-Jin; Jin, Zhaohui; Strokes, Natalie; Li, Shihong; Piao, Xianhua

    2011-08-02

    GPR56, an orphan G protein-coupled receptor (GPCR) from the family of adhesion GPCRs, plays an indispensable role in cortical development and lamination. Mutations in the GPR56 gene cause a malformed cerebral cortex in both humans and mice that resembles cobblestone lissencephaly, which is characterized by overmigration of neurons beyond the pial basement membrane. However, the molecular mechanisms through which GPR56 regulates cortical development remain elusive due to the unknown status of its ligand. Here we identify collagen, type III, alpha-1 (gene symbol Col3a1) as the ligand of GPR56 through an in vitro biotinylation/proteomics approach. Further studies demonstrated that Col3a1 null mutant mice exhibit overmigration of neurons beyond the pial basement membrane and a cobblestone-like cortical malformation similar to the phenotype seen in Gpr56 null mutant mice. Functional studies suggest that the interaction of collagen III with its receptor GPR56 inhibits neural migration in vitro. As for intracellular signaling, GPR56 couples to the Gα(12/13) family of G proteins and activates RhoA pathway upon ligand binding. Thus, collagen III regulates the proper lamination of the cerebral cortex by acting as the major ligand of GPR56 in the developing brain.

  5. Ligand-induced internalization of the type 1 cholecystokinin receptor independent of recognized signaling activity.

    PubMed

    Cawston, Erin E; Harikumar, Kaleeckal G; Miller, Laurence J

    2012-02-01

    Receptor ligands, identified as antagonists, based on the absence of stimulation of signaling, can rarely stimulate receptor internalization. d-Tyr-Gly-[(Nle(28,31),d-Trp(30))CCK-26-32]-2-phenylethyl ester (d-Trp-OPE) is such a ligand that binds to the cholecystokinin (CCK) receptor and stimulates internalization. Here, the molecular basis of this trafficking event is explored, with the assumption that ligand binding initiates conformational change, exposing an epitope to direct endocytosis. Ligand-stimulated internalization was studied morphologically using fluorescent CCK and d-Trp-OPE. d-Trp-OPE occupation of Chinese hamster ovary cell receptors stimulated internalization into the same region as CCK. Arrestin-biased action was ruled out using morphological translocation of fluorescent arrestin 2 and arrestin 3, moving to the membrane in response to CCK, but not d-Trp-OPE. Possible roles of the carboxyl terminus were studied using truncated receptor constructs, eliminating the proline-rich distal tail, the serine/threonine-rich midregion, and the remainder to the vicinal cysteines. None of these constructs disrupted d-Trp-OPE-stimulated internalization. Possible contributions of transmembrane segments were studied using competitive inhibition with peptides that also had no effect. Intracellular regions were studied with a similar strategy using coexpressing cell lines. Peptides corresponding to ends of each loop region were studied, with only the peptide at the carboxyl end of the third loop inhibiting d-Trp-OPE-stimulated internalization but having no effect on CCK-stimulated internalization. The region contributing to this effect was refined to peptide 309-323, located below the recognized G protein-association motif. While a receptor in which this segment was deleted did internalize in response to d-Trp-OPE, it exhibited abnormal ligand binding and did not signal in response to CCK, suggesting an abnormal conformation and possible mechanism of internalization

  6. High resolution structures of the bone morphogenetic protein type II receptor in two crystal forms: Implications for ligand binding

    SciTech Connect

    Mace, Peter D.; Cutfield, John F.; Cutfield, Sue M. . E-mail: sue.cutfield@otago.ac.nz

    2006-12-29

    BMPRII is a type II TGF-{beta} serine threonine kinase receptor which is integral to the bone morphogenetic protein (BMP) signalling pathway. It is known to bind BMP and growth differentiation factor (GDF) ligands, and has overlapping ligand specificity with the activin type II receptor, ActRII. In contrast to activin and TGF-{beta} type ligands, BMPs bind to type II receptors with lower affinity than type I receptors. Crystals of the BMPRII ectodomain were grown in two different forms, both of which diffracted to high resolution. The tetragonal form exhibited some disorder, whereas the entire polypeptide was seen in the orthorhombic form. The two structures retain the basic three-finger toxin fold of other TGF-{beta} receptor ectodomains, and share the main hydrophobic patch used by ActRII to bind various ligands. However, they present different conformations of the A-loop at the periphery of the proposed ligand-binding interface, in conjunction with rearrangement of a disulfide bridge within the loop. This particular disulfide (Cys94-Cys117) is only present in BMPRII and activin receptors, suggesting that it is important for their likely shared mode of binding. Evidence is presented that the two crystal forms represent ligand-bound and free conformations of BMPRII. Comparison with the solved structure of ActRII bound to BMP2 suggests that His87, unique amongst TGF-{beta} receptors, may play a key role in ligand recognition.

  7. Receptor Crosslinking: A General Method to Trigger Internalization and Lysosomal Targeting of Therapeutic Receptor:Ligand Complexes.

    PubMed

    Moody, Paul R; Sayers, Edward J; Magnusson, Johannes P; Alexander, Cameron; Borri, Paola; Watson, Peter; Jones, Arwyn T

    2015-12-01

    A major unmet clinical need is a universal method for subcellular targeting of bioactive molecules to lysosomes. Delivery to this organelle enables either degradation of oncogenic receptors that are overexpressed in cancers, or release of prodrugs from antibody-drug conjugates. Here, we describe a general method that uses receptor crosslinking to trigger endocytosis and subsequently redirect trafficking of receptor:cargo complexes from their expected route, to lysosomes. By incubation of plasma membrane receptors with biotinylated cargo and subsequent addition of streptavidin to crosslink receptor:cargo-biotin complexes, we achieved rapid and selective lysosomal targeting of transferrin, an anti-MHC class I antibody, and the clinically approved anti-Her2 antibody trastuzumab. These three protein ligands each target a receptor with a distinct cellular function and intracellular trafficking profile. Importantly, we confirmed that crosslinking of trastuzumab increased lysosomal degradation of its cognate oncogenic receptor Her2 in breast cancer cell lines SKBR3 and BT474. These data suggest that crosslinking could be exploited for a wide range of target receptors, for navigating therapeutics through the endolysosomal pathway, for significant therapeutic benefit.

  8. Receptor Crosslinking: A General Method to Trigger Internalization and Lysosomal Targeting of Therapeutic Receptor:Ligand Complexes

    PubMed Central

    Moody, Paul R; Sayers, Edward J; Magnusson, Johannes P; Alexander, Cameron; Borri, Paola; Watson, Peter; Jones, Arwyn T

    2015-01-01

    A major unmet clinical need is a universal method for subcellular targeting of bioactive molecules to lysosomes. Delivery to this organelle enables either degradation of oncogenic receptors that are overexpressed in cancers, or release of prodrugs from antibody–drug conjugates. Here, we describe a general method that uses receptor crosslinking to trigger endocytosis and subsequently redirect trafficking of receptor:cargo complexes from their expected route, to lysosomes. By incubation of plasma membrane receptors with biotinylated cargo and subsequent addition of streptavidin to crosslink receptor:cargo–biotin complexes, we achieved rapid and selective lysosomal targeting of transferrin, an anti-MHC class I antibody, and the clinically approved anti-Her2 antibody trastuzumab. These three protein ligands each target a receptor with a distinct cellular function and intracellular trafficking profile. Importantly, we confirmed that crosslinking of trastuzumab increased lysosomal degradation of its cognate oncogenic receptor Her2 in breast cancer cell lines SKBR3 and BT474. These data suggest that crosslinking could be exploited for a wide range of target receptors, for navigating therapeutics through the endolysosomal pathway, for significant therapeutic benefit. PMID:26412588

  9. Metabotropic glutamatergic receptors and their ligands in drug addiction.

    PubMed

    Pomierny-Chamioło, Lucyna; Rup, Kinga; Pomierny, Bartosz; Niedzielska, Ewa; Kalivas, Peter W; Filip, Małgorzata

    2014-06-01

    Glutamatergic excitatory transmission is implicated in physiological and pathological conditions like learning, memory, neuronal plasticity and emotions, while glutamatergic abnormalities are reported in numerous neurological and psychiatric disorders, including neurodegenerative diseases, epilepsy, stroke, traumatic brain injury, depression, anxiety, schizophrenia and pain. Also, several lines of evidence have accumulated indicating a pivotal role for glutamatergic neurotransmission in mediating addictive behaviors. Among the proteins regulating glutamatergic transmission, the metabotropic glutamate receptors (mGluR) are being developed as pharmacological targets for treating many neuropsychiatric disorders, including drug addiction. In this review we describe the molecular structure of mGluRs and their distribution, physiology and pharmacology in the central nervous system, as well as their use as targets in preclinical studies of drug addiction.

  10. Ligands for SPECT and PET imaging of muscarinic-cholinergic receptors of the heart and brain

    SciTech Connect

    Knapp, F.F. Jr.; McPherson, D.W.; Luo, H.

    1995-06-01

    Interest in the potential use of cerebral SPECT and PET imaging for determination of the density and activity of muscarinic-cholinergic receptors (mAChR) has been stimulated by the changes in these receptors which occur in many neurological diseases. In addition, the important involvement of mAChR in modulating negative inotropic cardiac activity suggests that such receptor ligands may have important applications in evaluation of changes which may occur in cardiac disease. In this paper, the properties of several key muscarinic receptor ligands being developed or which have been used for clinical SPECT and PET are discussed. In addition, the ORNL development of the new iodinated IQNP ligand based on QNB and the results of in vivo biodistribution studies in rats, in vitro competitive binding studies and ex vivo autoradiographic experiments are described. The use of radioiodinated IQNP may offer several advantages in comparison to IQNB because of its easy and high yield preparation and high brain uptake and the potential usefulness of the {open_quotes}partial{close_quotes} subtype selective IONP isomers. We also describe the development of new IQNP-type analogues which offer the opportunity for radiolabeling with positron-emitting radioisotopes (carbon-11, fluorine-18 and bromine-76) for potential use with PET.

  11. Measuring two-dimensional receptor-ligand binding kinetics by micropipette.

    PubMed Central

    Chesla, S E; Selvaraj, P; Zhu, C

    1998-01-01

    We report a novel method for measuring forward and reverse kinetic rate constants, kf0 and kr0, for the binding of individual receptors and ligands anchored to apposing surfaces in cell adhesion. Not only does the method examine adhesion between a single pair of cells; it also probes predominantly a single receptor-ligand bond. The idea is to quantify the dependence of adhesion probability on contact duration and densities of the receptors and ligands. The experiment was an extension of existing micropipette protocols. The analysis was based on analytical solutions to the probabilistic formulation of kinetics for small systems. This method was applied to examine the interaction between Fc gamma receptor IIIA (CD16A) expressed on Chinese hamster ovary cell transfectants and immunoglobulin G (IgG) of either human or rabbit origin coated on human erythrocytes, which were found to follow a monovalent biomolecular binding mechanism. The measured rate constants are Ackf0 = (2.6 +/- 0.32) x 10(-7) micron 4 s-1 and kr0 = (0.37 +/- 0.055) s-1 for the CD16A-hIgG interaction and Ackf0 = (5.7 +/- 0.31) X 10(-7) micron 4 s-1 and kr0 = (0.20 +/- 0.042) s-1 for the CD16A-rIgG interaction, respectively, where Ac is the contact area, estimated to be a few percent of 3 micron 2. PMID:9726957

  12. Phytosphingosine 1-phosphate: a high affinity ligand for the S1P(4)/Edg-6 receptor.

    PubMed

    Candelore, Mari Rios; Wright, Michael J; Tota, Laurie M; Milligan, James; Shei, Gan-ju; Bergstrom, James D; Mandala, Suzanne M

    2002-09-27

    It has been reported recently that the phosphorylated form of the immunomodulator FTY720 activates sphingosine 1-phosphate G protein-coupled receptors. Therefore, understanding the biology of this new class of receptors will be important in clarifying the immunological function of bioactive lysosphingolipid ligands. The S1P(4) receptor has generated interest due to its lymphoid tissue distribution. While the S1P(4) receptor binds the prototypical ligand, S1P, a survey of other lysosphingolipids demonstrated that 4D-hydroxysphinganine 1-phosphate, more commonly known as phytosphingosine 1-phosphate (PhS1P), binds to S1P(4) with higher affinity. Using radiolabeled S1P (S133P), the affinity of PhS1P for the S1P(4) receptor is 1.6nM, while that of S1P is nearly 50-fold lower (119+/-20nM). Radiolabeled PhS1P proved to be superior to S133P in routine binding assays due to improved signal-to-noise ratio. The present study demonstrates the utility of a novel radiolabeled probe, PhS133P, for in vitro studies of the S1P(4) receptor pharmacology.

  13. International Union of Basic and Clinical Pharmacology. LXXIX. Cannabinoid Receptors and Their Ligands: Beyond CB1 and CB2

    PubMed Central

    Howlett, A. C.; Abood, M. E.; Alexander, S. P. H.; Di Marzo, V.; Elphick, M. R.; Greasley, P. J.; Hansen, H. S.; Kunos, G.; Mackie, K.; Mechoulam, R.; Ross, R. A.

    2010-01-01

    There are at least two types of cannabinoid receptors (CB1 and CB2). Ligands activating these G protein-coupled receptors (GPCRs) include the phytocannabinoid Δ9-tetrahydrocannabinol, numerous synthetic compounds, and endogenous compounds known as endocannabinoids. Cannabinoid receptor antagonists have also been developed. Some of these ligands activate or block one type of cannabinoid receptor more potently than the other type. This review summarizes current data indicating the extent to which cannabinoid receptor ligands undergo orthosteric or allosteric interactions with non-CB1, non-CB2 established GPCRs, deorphanized receptors such as GPR55, ligand-gated ion channels, transient receptor potential (TRP) channels, and other ion channels or peroxisome proliferator-activated nuclear receptors. From these data, it is clear that some ligands that interact similarly with CB1 and/or CB2 receptors are likely to display significantly different pharmacological profiles. The review also lists some criteria that any novel “CB3” cannabinoid receptor or channel should fulfil and concludes that these criteria are not currently met by any non-CB1, non-CB2 pharmacological receptor or channel. However, it does identify certain pharmacological targets that should be investigated further as potential CB3 receptors or channels. These include TRP vanilloid 1, which possibly functions as an ionotropic cannabinoid receptor under physiological and/or pathological conditions, and some deorphanized GPCRs. Also discussed are 1) the ability of CB1 receptors to form heteromeric complexes with certain other GPCRs, 2) phylogenetic relationships that exist between CB1/CB2 receptors and other GPCRs, 3) evidence for the existence of several as-yet-uncharacterized non-CB1, non-CB2 cannabinoid receptors; and 4) current cannabinoid receptor nomenclature. PMID:21079038

  14. International Union of Basic and Clinical Pharmacology. LXXIX. Cannabinoid receptors and their ligands: beyond CB₁ and CB₂.

    PubMed

    Pertwee, R G; Howlett, A C; Abood, M E; Alexander, S P H; Di Marzo, V; Elphick, M R; Greasley, P J; Hansen, H S; Kunos, G; Mackie, K; Mechoulam, R; Ross, R A

    2010-12-01

    There are at least two types of cannabinoid receptors (CB(1) and CB(2)). Ligands activating these G protein-coupled receptors (GPCRs) include the phytocannabinoid Δ(9)-tetrahydrocannabinol, numerous synthetic compounds, and endogenous compounds known as endocannabinoids. Cannabinoid receptor antagonists have also been developed. Some of these ligands activate or block one type of cannabinoid receptor more potently than the other type. This review summarizes current data indicating the extent to which cannabinoid receptor ligands undergo orthosteric or allosteric interactions with non-CB(1), non-CB(2) established GPCRs, deorphanized receptors such as GPR55, ligand-gated ion channels, transient receptor potential (TRP) channels, and other ion channels or peroxisome proliferator-activated nuclear receptors. From these data, it is clear that some ligands that interact similarly with CB(1) and/or CB(2) receptors are likely to display significantly different pharmacological profiles. The review also lists some criteria that any novel "CB(3)" cannabinoid receptor or channel should fulfil and concludes that these criteria are not currently met by any non-CB(1), non-CB(2) pharmacological receptor or channel. However, it does identify certain pharmacological targets that should be investigated further as potential CB(3) receptors or channels. These include TRP vanilloid 1, which possibly functions as an ionotropic cannabinoid receptor under physiological and/or pathological conditions, and some deorphanized GPCRs. Also discussed are 1) the ability of CB(1) receptors to form heteromeric complexes with certain other GPCRs, 2) phylogenetic relationships that exist between CB(1)/CB(2) receptors and other GPCRs, 3) evidence for the existence of several as-yet-uncharacterized non-CB(1), non-CB(2) cannabinoid receptors; and 4) current cannabinoid receptor nomenclature.

  15. Conformational Rearrangement Within the Soluble Domains of the CD4 Receptor is Ligand-Specific

    SciTech Connect

    Ashish,F.; Juncadella, I.; Garg, R.; Boone, C.; Anguita, J.; Krueger, J.

    2008-01-01

    Ligand binding induces shape changes within the four modular ectodomains (D1-D4) of the CD4 receptor, an important receptor in immune signaling. Small angle x-ray scattering (SAXS) on both a two-domain and a four-domain construct of the soluble CD4 (sCD4) is consistent with known crystal structures demonstrating a bilobal and a semi-extended tetralobal Z conformation in solution, respectively. Detection of conformational changes within sCD4 as a result of ligand binding was followed by SAXS on sCD4 bound to two different glycoprotein ligands: the tick saliva immunosuppressor Salp15 and the HIV-1 envelope protein gp120. Ab initio modeling of these data showed that both Salp15 and gp120 bind to the D1 domain of sCD4 and yet induce drastically different structural rearrangements. Upon binding, Salp15 primarily distorts the characteristic lobal architecture of the sCD4 without significantly altering the semi-extended shape of the sCD4 receptor. In sharp contrast, the interaction of gp120 with sCD4 induces a shape change within sCD4 that can be described as a Z-to-U bi-fold closure of the four domains across its flexible D2-D3 linker. Placement of known crystal structures within the boundaries of the SAXS-derived models suggests that the ligand-induced shape changes could be a result of conformational changes within this D2-D3 linker. Functionally, the observed shape changes in CD4 receptor causes dissociation of lymphocyte kinase from the cytoplasmic domain of Salp15-bound CD4 and facilitates an interaction between the exposed V3 loops of CD4-bound gp120 molecule to the extracellular loops of its co-receptor, a step essential for HIV-1 viral entry.

  16. Two-photon excitation fluorescence cross-correlation assay for ligand-receptor binding: cell membrane nanopatches containing the human micro-opioid receptor.

    PubMed

    Swift, Jody L; Burger, Melanie C; Massotte, Dominique; Dahms, Tanya E S; Cramb, David T

    2007-09-01

    Current ligand-receptor binding assays for G-protein coupled receptors cannot directly measure the system's dissociation constant, Kd, without purification of the receptor protein. Accurately measured Kd's are essential in the development of a molecular level understanding of ligand-receptor interactions critical in rational drug design. Here we report the introduction of two-photon excitation fluorescence cross-correlation spectroscopy (TPE-FCCS) to the direct analysis of ligand-receptor interactions of the human micro opioid receptor (hMOR) for both agonists and antagonists. We have developed the use of fluorescently distinct, dye-labeled hMOR-containing cell membrane nanopatches ( approximately 100-nm radius) and ligands, respectively, for this assay. We show that the output from TPE-FCCS data sets can be converted to the conventional Hill format, which provides Kd and the number of active receptors per nanopatch. When ligands are labeled with quantum dots, this assay can detect binding with ligand concentrations in the subnanomolar regime. Interestingly, conjugation to a bulky quantum dot did not adversely affect the binding propensity of the hMOR pentapeptide ligand, Leu-enkephalin.

  17. Aryl hydrocarbon receptor activation inhibits in vitro differentiation of human monocytes and Langerhans dendritic cells.

    PubMed

    Platzer, Barbara; Richter, Susanne; Kneidinger, Doris; Waltenberger, Darina; Woisetschläger, Maximilian; Strobl, Herbert

    2009-07-01

    The transcription factor aryl hydrocarbon receptor (AhR) represents a promising therapeutic target in allergy and autoimmunity. AhR signaling induced by the newly described ligand VAF347 inhibits allergic lung inflammation as well as suppresses pancreatic islet allograft rejection. These effects are likely mediated via alterations in dendritic cell (DC) function. Moreover, VAF347 induces tolerogenic DCs. Langerhans cells (LCs) are immediate targets of exogenous AhR ligands at epithelial surfaces; how they respond to AhR ligands remained undefined. We studied AhR expression and function in human LCs and myelopoietic cell subsets using a lineage differentiation and gene transduction model of human CD34(+) hematopoietic progenitors. We found that AhR is highly regulated during myeloid subset differentiation. LCs expressed highest AhR levels followed by monocytes. Conversely, neutrophil granulocytes lacked AhR expression. AhR ligands including VAF347 arrested the differentiation of monocytes and LCs at an early precursor cell stage, whereas progenitor cell expansion or granulopoiesis remained unimpaired. AhR expression was coregulated with the transcription factor PU.1 during myeloid subset differentiation. VAF347 inhibited PU.1 induction during initial monocytic differentiation, and ectopic PU.1 restored monocyte and LC generation in the presence of this compound. AhR ligands failed to interfere with cytokine receptor signaling during LC differentiation and failed to impair LC activation/maturation. VAF347-mediated antiproliferative effect on precursors undergoing LC lineage differentiation occurred in a clinically applicable serum-free culture model and was not accompanied by apoptosis induction. In conclusion, AhR agonist signaling interferes with transcriptional processes leading to monocyte/DC lineage commitment of human myeloid progenitor cells.

  18. Quantitative Analysis of STD-NMR Spectra of Reversibly Forming Ligand-Receptor Complexes

    NASA Astrophysics Data System (ADS)

    Krishna, N. Rama; Jayalakshmi, V.

    We describe our work on the quantitative analysis of STD-NMR spectra of reversibly forming ligand-receptor complexes. This analysis is based on the theory of complete relaxation and conformational exchange matrix analysis of saturation transfer (CORCEMA-ST) effects. As part of this work, we have developed two separate versions of the CORCEMA-ST program. The first version predicts the expected STD intensities for a given model of a ligand-protein complex, and compares them quantitatively with the experimental data. This version is very useful for rapidly determining if a model for a given ligand-protein complex is compatible with the STD-NMR data obtained in solution. It is also useful in determining the optimal experimental conditions for undertaking the STD-NMR measurements on a given complex by computer simulations. In the second version of the CORCEMA-ST program, we have implemented a torsion angle refinement feature for the bound ligand within the protein binding pocket. In this approach, the global minimum for the bound ligand conformation is obtained by a hybrid structure refinement protocol involving CORCEMA-ST calculation of intensities and simulated annealing refinement of torsion angles of the bound ligand using STD-NMR intensities as experimental constraints to minimize a pseudo-energy function. This procedure is useful in refining and improving the initial models based on crystallography, computer docking, or other procedures to generate models for the bound ligand within the protein binding pocket compatible with solution STD-NMR data. In this chapter we describe the properties of the STD-NMR spectra, including the dependence of the intensities on various parameters. We also describe the results of the CORCEMA-ST analyses of experimental STD-NMR data on some ligand-protein complexes to illustrate the quantitative analysis of the data using this method. This CORCEMA-ST program is likely to be useful in structure-based drug design efforts.

  19. Modeling the epidermal growth factor -- epidermal growth factor receptor l2 domain interaction: implications for the ligand binding process.

    PubMed

    Jorissen, Robert N; Treutlein, Herbert R; Epa, V Chandana; Burgess, Antony W

    2002-06-01

    Signaling from the epidermal growth factor (EGF) receptor is triggered by the binding of ligands such as EGF or transforming growth factor alpha (TGF-alpha) and subsequent receptor dimerization. An understanding of these processes has been hindered by the lack of structural information about the ligand-bound, dimerized EGF receptor. Using an NMR-derived structure of EGF and a homology model of the major ligand binding domain of the EGF receptor and experimental data, we modeled the binding of EGF to this EGF receptor fragment. In this low resolution model of the complex, EGF sits across the second face of the EGF receptor L2 domain and EGF residues 10-16, 36-37, 40-47 bind to this face. The structural model is largely consistent with previously published NMR data describing the residues of TGF-alpha which interact strongly with the EGF receptor. Other EGF residues implicated in receptor binding are accounted by our proposal that the ligand binding is a two-step process with the EGF binding to at least one other site of the receptor. This three-dimensional model is expected to be useful in the design of ligand-based antagonists of the receptor.

  20. Evidence that Argos is an antagonistic ligand of the EGF receptor.

    PubMed

    Vinós, J; Freeman, M

    2000-07-20

    Argos, the inhibitor of the Drosophila epidermal growth factor (EGF) receptor, remains the only known extracellular inhibitor of this family of receptors in any organism. The functional domain of Argos includes an atypical EGF domain and it is not clear whether it binds to the EGF receptor or if it acts via a distinct receptor to reduce Egfr activity indirectly. Here we present two lines of evidence that strongly suggest that Argos directly interacts with the EGF receptor. First, Argos is unable to inhibit a chimeric receptor that contains an extracellular domain from an unrelated RTK, indicating the need for the EGF receptor extracellular domain. Second, Argos can inhibit the Drosophila EGF receptor even when expressed in human cells, implying that no other Drosophila protein is necessary for inhibition. We also report that Argos and the Drosophila activating ligand, Spitz, can influence mammalian RTK activation, albeit in a cell-type specific manner. This includes the first evidence that Argos can inhibit signalling in mammalian cells, raising the possibility of engineering an effective human EGF receptor/ErbB antagonist. Oncogene (2000) 19, 3560 - 3562

  1. Investigation on critical structural motifs of ligands for triggering glucocorticoid receptor nuclear migration through molecular docking simulations.

    PubMed

    Liu, Ya-Lin; Jang, Soonmin; Wang, Shih-Min; Chen, Chiu-Hao; Li, Feng-Yin

    2016-06-01

    The glucocorticoid receptor (GR), a transcription factor regulating gene expression in a ligand-dependent fashion, is known for flexibility in adapting various ligands with their structures ranging from steroid to non-steroid. However, in our previous study, GR shows a stringent discrimination against a set of steroid ligands with highly similar structures for triggering its nuclear migration. In order to resolve this puzzle, we employed molecular docking simulations to investigate the origin of this structural discrimination. By analyzing the docking orientations and the related ligand-GR interaction patterns, we found that the hydrophilicity mismatch between the docking ligand and the GR ligand-binding site is the main cause combined with the steric hindrance and structural rigidness of these steroid ligands. Furthermore, we utilized this knowledge to rationalize how the structure-binding interaction of non-steroid ligands triggers GR nuclear migration with their structures available in Protein Data Bank.

  2. A Structural Switch between Agonist and Antagonist Bound Conformations for a Ligand-Optimized Model of the Human Aryl Hydrocarbon Receptor Ligand Binding Domain

    PubMed Central

    Perkins, Arden; Phillips, Jessica L.; Kerkvliet, Nancy I.; Tanguay, Robert L.; Perdew, Gary H.; Kolluri, Siva K.; Bisson, William H.

    2014-01-01

    The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that regulates the expression of a diverse group of genes. Exogenous AHR ligands include the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which is a potent agonist, and the synthetic AHR antagonist N-2-(1H-indol-3yl)ethyl)-9-isopropyl-2-(5-methylpyridin-3-yl)-9H-purin-6-amine (GNF351). As no experimentally determined structure of the ligand binding domain exists, homology models have been utilized for virtual ligand screening (VLS) to search for novel ligands. Here, we have developed an “agonist-optimized” homology model of the human AHR ligand binding domain, and this model aided in the discovery of two human AHR agonists by VLS. In addition, we performed molecular dynamics simulations of an agonist TCDD-bound and antagonist GNF351-bound version of this model in order to gain insights into the mechanics of the AHR ligand-binding pocket. These simulations identified residues 307–329 as a flexible segment of the AHR ligand pocket that adopts discrete conformations upon agonist or antagonist binding. This flexible segment of the AHR may act as a structural switch that determines the agonist or antagonist activity of a given AHR ligand. PMID:25329374

  3. NMR spectroscopy of the ligand binding core of ionotropic glutamate receptor 2 bound to 5-substituted willardiine partial agonists

    PubMed Central

    Fenwick, Michael K.; Oswald, Robert E.

    2008-01-01

    Glutamate receptors mediate neuronal intercommunication in the central nervous system by coupling extracellular neurotransmitter-receptor interactions to ion channel conductivity. To gain insight into structural and dynamical factors that underlie this coupling, solution NMR experiments were performed on the bi-lobed ligand-binding core of glutamate receptor 2 in complexes with a set of willardiine partial agonists. These agonists are valuable for studying structure-function relationships because their 5-position substituent size is correlated with ligand efficacy and extent of receptor desensitization whereas the substituent electronegativity is correlated with ligand potency. NMR results show that the protein backbone amide chemical shift deviations correlate mainly with efficacy and extent of desensitization. Pronounced deviations occur at specific residues in the ligand-binding site and in the two helical segments that join the lobes by a disulfide bond. Experiments detecting conformational exchange show that micro- to millisecond timescale motions also occur near the disulfide bond and vary largely with efficacy and extent of desensitization. These results thus identify regions displaying structural and dynamical dissimilarity arising from differences in ligand-protein interactions and lobe closure which may play a critical role in receptor response. Furthermore, measures of line broadening and conformational exchange for a portion of the ligand-binding site correlate with ligand EC50 data. These results do not have any correlate in the currently available crystal structures and thus provide a novel view of ligand-binding events that may be associated with agonist potency differences. PMID:18387631

  4. Novel Chalcone-Based Fluorescent Human Histamine H3 Receptor Ligands as Pharmacological Tools

    PubMed Central

    Tomasch, Miriam; Schwed, J. Stephan; Weizel, Lilia; Stark, Holger

    2012-01-01

    Novel fluorescent chalcone-based ligands at human histamine H3 receptors (hH3R) have been designed, synthesized, and characterized. Compounds described are non-imidazole analogs of ciproxifan with a tetralone motif. Tetralones as chemical precursors and related fluorescent chalcones exhibit affinities at hH3R in the same concentration range like the reference antagonist ciproxifan (hH3R pKi value of 7.2). Fluorescence characterization of our novel ligands shows emission maxima about 570 nm for yellow fluorescent chalcones and ≥600 nm for the red fluorescent derivatives. Interferences to cellular autofluorescence could be excluded. All synthesized chalcone compounds could be used to visualize hH3R proteins in stably transfected HEK-293 cells using confocal laser scanning fluorescence microscopy. These novel fluorescent ligands possess high potential to be used as pharmacological tools for hH3R visualization in different tissues. PMID:22470321

  5. Antioxidant Functions of the Aryl Hydrocarbon Receptor

    PubMed Central

    2016-01-01

    The aryl hydrocarbon receptor (AhR) is a transcription factor belonging to the basic helix-loop-helix/PER-ARNT-SIM family. It is activated by a variety of ligands, such as environmental contaminants like polycyclic aromatic hydrocarbons or dioxins, but also by naturally occurring compounds and endogenous ligands. Binding of the ligand leads to dimerization of the AhR with aryl hydrocarbon receptor nuclear translocator (ARNT) and transcriptional activation of several xenobiotic phase I and phase II metabolizing enzymes. It is generally accepted that the toxic responses of polycyclic aromatic hydrocarbons, dioxins, and structurally related compounds are mediated by activation of the AhR. A multitude of studies indicate that the AhR operates beyond xenobiotic metabolism and exerts pleiotropic functions. Increasing evidence points to a protective role of the AhR against carcinogenesis and oxidative stress. Herein, I will highlight data demonstrating a causal role of the AhR in the antioxidant response and present novel findings on potential AhR-mediated antioxidative mechanisms. PMID:27829840

  6. Pharmacological characterization of the cannabinoid CB₁ receptor PET ligand ortholog, [³H]MePPEP.

    PubMed

    Suter, Todd M; Chesterfield, Amy K; Bao, Chun; Schaus, John M; Krushinski, Joseph H; Statnick, Michael A; Felder, Christian C

    2010-12-15

    MePPEP ((3R,5R)-5-(3-methoxy-phenyl)-3-((R)-1-phenyl-ethylamino)-1-(4-trifluoromethyl-phenyl)-pyrrolidin-2-one) is an inverse agonist shown to be an effective PET ligand for labeling cannabinoid CB₁ receptors in vivo. [¹¹C]MePPEP and structurally related analogs have been reported to specifically and reversibly label cannabinoid CB₁ receptors in rat and non-human primate brains, and [¹¹C]MePPEP has been used in human subjects as a PET tracer. We have generated [³H]MePPEP, an ortholog of [¹¹C]MePPEP, to characterize the molecular pharmacology of the cannabinoid CB₁ receptor across preclinical and clinical species. [³H]MePPEP demonstrates saturable, reversible, and single-site high affinity binding to cannabinoid CB₁ receptors. In cerebellar membranes purified from brains of rat, non-human primate and human, and cells ectopically expressing recombinant human cannabinoid CB₁ receptor, [³H]MePPEP binds cannabinoid CB₁ receptors with similar affinity with K(d) values of 0.09 nM, 0.19 nM, 0.14 nM and 0.16 nM, respectively. Both agonist and antagonist cannabinoid ligands compete [³H]MePPEP with predicted rank order potency. No specific binding is present in autoradiographic sections from cannabinoid CB₁ receptor knockout mouse brains, demonstrating that [³H]MePPEP selectively binds cannabinoid CB₁ receptors in native mouse tissue. Furthermore, [³H]MePPEP binding to anatomical sites in mouse and rat brain is comparable to the anatomical profiles of [¹¹C]MePPEP in non-human primate and human brain in vivo, as well as the binding profiles of other previously described cannabinoid CB₁ receptor agonist and antagonist radioligands. Therefore, [³H]MePPEP is a promising tool for translation of preclinical cannabinoid CB₁ receptor pharmacology to clinical PET ligand and cannabinoid CB₁ receptor inverse agonist therapeutic development.

  7. Aryl hydrocarbon receptor mediates both proinflammatory and anti-inflammatory effects in lipopolysaccharide-activated microglia.

    PubMed

    Lee, Yi-Hsuan; Lin, Chun-Hua; Hsu, Pei-Chien; Sun, Yu-Yo; Huang, Yu-Jie; Zhuo, Jiun-Horng; Wang, Chen-Yu; Gan, Yu-Ling; Hung, Chia-Chi; Kuan, Chia-Yi; Shie, Feng-Shiun

    2015-07-01

    The aryl hydrocarbon receptor (AhR) regulates peripheral immunity; but its role in microglia-mediated neuroinflammation in the brain remains unknown. Here, we demonstrate that AhR mediates both anti-inflammatory and proinflammatory effects in lipopolysaccharide (LPS)-activated microglia. Activation of AhR by its ligands, formylindolo[3,2-b]carbazole (FICZ) or 3-methylcholanthrene (3MC), attenuated LPS-induced microglial immune responses. AhR also showed proinflammatory effects, as evidenced by the findings that genetic silence of AhR ameliorated the LPS-induced microglial immune responses and LPS-activated microglia-mediated neurotoxicity. Similarly, LPS-induced expressions of tumor necrosis factor α (TNFα) and inducible nitric oxide synthase (iNOS) were reduced in the cerebral cortex of AhR-deficient mice. Intriguingly, LPS upregulated and activated AhR in the absence of AhR ligands via the MEK1/2 signaling pathway, which effects were associated with a transient inhibition of cytochrome P450 1A1 (CYP1A1). Although AhR ligands synergistically enhance LPS-induced AhR activation, leading to suppression of LPS-induced microglial immune responses, they cannot do so on their own in microglia. Chromatin immunoprecipitation results further revealed that LPS-FICZ co-treatment, but not LPS alone, not only resulted in co-recruitment of both AhR and NFκB onto the κB site of TNFα gene promoter but also reduced LPS-induced AhR binding to the DRE site of iNOS gene promoter. Together, we provide evidence showing that microglial AhR, which can be activated by LPS, exerts bi-directional effects on the regulation of LPS-induced neuroinflammation, depending on the availability of external AhR ligands. These findings confer further insights into the potential link between environmental factors and the inflammatory brain disorders.

  8. Hepatic microsomal cytochrome p450s and chlorinated hydrocarbons in largha and ribbon seals from Hokkaido, Japan: differential response of seal species to Ah receptor agonist exposure.

    PubMed

    Chiba, Issei; Sakakibara, Akihito; Iwata, T Hisato; Ishizuka, Mayumi; Tanabe, Shinsuke; Akahori, Fumiaki; Kazusaka, Akio; Fujita, Shoichi

    2002-04-01

    From 16 largha seals (Phoca largha) and 15 ribbon seals (Phoca fasciata) in the coastal waters of Hokkaido, Japan, blubber chlorinated hydrocarbon (CHC) levels and hepatic cytochrome P450 (CYP) catalytic activities and their immunochemically detected protein content levels were measured. Concentrations of DDTs (2,2-bis(4-chlorophenyl)-1,1-dichloroethylene,p,p'-DDE; 2,2-bis(4-chlorophenyl)-1,1-dichloroethane, p,p'-DDD; dichlorodiphenyltrichloroethane, p,p'-DDT), polychlorinated biphenyl congeners (PCBs), and chlordane compounds (oxychlordane, chlordanes, and nonachlors) in both species were in the range of 290 to 5,300, 420 to 4,000, and 130 to 1,500 ng/g lipid weight, respectively. Aryl hydrocarbon receptor (AhR) agonists, non-ortho (IUPAC 77 and 126) and mono-ortho (IUPAC 105, 118, and 156) coplanar PCB congeners, were also detected, and the 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD) toxic equivalents (TEQs) were 4.9 to 120 pg TEQ/g lipid weight. Cross-reactive proteins with polyclonal antibodies against rat CYP1A1 and CYP3A2 were notably detected in seal liver microsomes. Interestingly, a polyclonal antibody against rat CYP2B1 recognized proteins only at trace levels. In largha seals, both levels of alkoxyresorufin- (methoxy-, ethoxy-, pentoxy-, and benzyloxyresorufin) O-dealkylase (AROD) activities and proteins detected by polyclonal antibodies against rat CYP1A1 were significantly correlated with the concentrations of individual coplanar PCB congeners, total TEQs, and total PCBs. Threshold concentrations for TEQs in blubber of the largha seal to induce hepatic CYP1A protein and EROD activity were estimated to be 8.5 and 19 pg TEQ/g fat weight, respectively. In ribbon seals, similar correlations were not detected, although the TEQ levels were not significantly lower than those in largha seals. These results suggest that AROD activity and CYP1A1 protein in the liver of the largha seal could be a biomarker for the exposure to AhR agonists such as coplanar PCB

  9. In vivo and in vitro Ah-receptor activation by commercial and fractionated pentabromodiphenylether using zebrafish (Danio rerio) and the DR-CALUX assay.

    PubMed

    Kuiper, R V; Murk, A J; Leonards, P E G; Grinwis, G C M; van den Berg, M; Vos, J G

    2006-10-12

    The present study addresses the toxicity of a commercial pentabrominated diphenylether (PeBDE) flame retardant mixture, DE-71, in a model aquatic vertebrate. Four weeks' exposure of juvenile zebrafish (Danio rerio) to water-borne DE-71 resulted in dose-dependent induction of CYP1A immunoreactivity, predominantly in the endocardium and the endothelium of larger blood vessels, such as ventral aorta and branchial arteries, as well as the larger hepatic and pancreatic blood vessels. To investigate the impact of possible contaminating PBDD/Fs in the DE-71 product, the study was repeated after DE-71 had been fractionated into a non-planar (cleaned PBDEs) and a planar fraction (PBDD/Fs). Zebrafish were exposed under similar conditions to the planar and cleaned DE-71 fractions, and to uncleaned DE-71. In addition, the above fractions were chemically analyzed and tested in a reporter gene assay (DR-CALUX) for their aromatic hydrocarbon-receptor (AhR) stimulating potencies. A relatively strong CALUX response was detected from the planar DE-71 fraction (19.7ng TCDD equivalent (TEQ)/g DE-71), coinciding with a strong induction of CYP1A immunoreactivity in zebrafish. CYP1A immunoreactivity in zebrafish exposed to uncleaned DE-71 was intense, although the CALUX response was 10-fold less compared to the planar fraction. Only weak CYP1A immunoreactivity was found in fish exposed to cleaned DE-71, and none in control animals; no CALUX response was detected in cleaned DE-71. The present findings indicate that chemical impurities of the commercial PeBDE product account for AhR-mediated effects. Analytical isolation of a planar fraction from the commercial product increased the in vitro (DR-CALUX) signal 10 times. Immunohistochemistry showed a strong tissue specific reaction to DE-71 in vivo at these relatively low TEQ levels regardless of chemical pretreatment of the mix, reflecting the sensitivity of CYP1A induction in juvenile zebrafish to AhR agonists.

  10. Exploring Flexibility of Progesterone Receptor Ligand Binding Domain Using Molecular Dynamics

    PubMed Central

    Zheng, Liangzhen; Mu, Yuguang

    2016-01-01

    Progesterone receptor (PR), a member of nuclear receptor (NR) superfamily, plays a vital role for female reproductive tissue development, differentiation and maintenance. PR ligand, such as progesterone, induces conformation changes in PR ligand binding domain (LBD), thus mediates subsequent gene regulation cascades. PR LBD may adopt different conformations upon an agonist or an antagonist binding. These different conformations would trigger distinct transcription events. Therefore, the dynamics of PR LBD would be of general interest to biologists for a deep understanding of its structure-function relationship. However, no apo-form (non-ligand bound) of PR LBD model has been proposed either by experiments or computational methods so far. In this study, we explored the structural dynamics of PR LBD using molecular dynamics simulations and advanced sampling tools in both ligand-bound and the apo-forms. Resolved by the simulation study, helix 11, helix 12 and loop 895–908 (the loop between these two helices) are quite flexible in antagonistic conformation. Several residues, such as Arg899 and Glu723, could form salt-bridging interaction between helix 11 and helix 3, and are important for the PR LBD dynamics. And we also propose that helix 12 in apo-form PR LBD, not like other NR LBDs, such as human estrogen receptor α (ERα) LBD, may not adopt a totally extended conformation. With the aid of umbrella sampling and metadynamics simulations, several stable conformations of apo-form PR LBD have been sampled, which may work as critical structural models for further large scale virtual screening study to discover novel PR ligands for therapeutic application. PMID:27824891

  11. PEGylated Dendritic Unimolecular Micelles as Versatile Carriers for Ligands of G Protein-Coupled Receptors

    PubMed Central

    Kim, Yoonkyung; Hechler, Béatrice; Gao, Zhan-Guo; Gachet, Christian; Jacobson, Kenneth A.

    2009-01-01

    Despite its widespread application in nanomedicine, poly(ethylene glycol) (PEG) is seldom used for covalent modification of ligands for G protein-coupled receptors (GPCRs) due to potential steric complications. In order to study the influence of PEG chains on the biological activity of GPCR ligands bound to a common macromolecular carrier, we prepared a series of G3 polyamidoamine (PAMAM) dendrimers derivatized with Alexa Fluor 488, varying numbers of PEG550/PEG750/PEG2000, and nucleoside moieties derived from the A2A adenosine receptor (AR) agonist CGS21680 (2-[4-(2-carboxylethyl)phenylethylamino]-5′-N-ethylcarboxamidoadenosine). These dendrimer conjugates were purified by size exclusion chromatography and characterized by 1H NMR and MALDI MS. In radioligand binding assays, some PAMAM-PEG conjugates showed enhanced subtype-selectivity at the human A2A AR compared to monomeric ligands of comparable affinity. The functional potency was measured in the A2A AR-mediated activation of adenylate cyclase and inhibition of ADP-induced platelet aggregation. Interestingly, the dendrimer conjugate 10c bearing 11 PEG750 chains (out of theo. 32 amino end groups) and 14 nucleoside moieties was 5-fold more potent in A2A AR–mediated stimulation of cyclic AMP formation than 10d with four PEG2000 chains and 21 nucleosides, although the binding affinities of these two compounds were similar. Thus, a relatively small (≤10 nm) multivalent ligand 10c modified for water solubility maintained high potency and displayed increased A2A AR binding selectivity over the monomeric nucleosides. Longer PEG chains reduced affinity at the A2A AR. The current study demonstrates the feasiblity of using short PEG chains in the design of carriers that target ligand-receptor interactions. PMID:19785401

  12. Reconstruction of ligand-dependent transactivation of Choristoneura fumiferana ecdysone receptor in yeast.

    PubMed

    Tran, H T; Askari, H B; Shaaban, S; Price, L; Palli, S R; Dhadialla, T S; Carlson, G R; Butt, T R

    2001-07-01

    Ecdysteroids play an important role in regulating development and reproduction in insects. Interaction of 20-hydroxyecdysone (20E) with ecdysone receptor (EcR) as a heterodimer with ultraspiracle (USP) protein triggers the activation of 20E-responsive genes. In this paper we describe a ligand-mediated transactivation system in yeast using the spruce budworm Choristoneura fumiferana ecdysone receptor (CfEcR). Coexpression of C. fumiferana USP (CfUSP) with CfEcR in yeast led to constitutive transcription of the reporter gene. However, deletion of the A/B domain of CfUSP abolished constitutive activity observed for the CfUSP:CfEcR complex. Replacement of USP with its mammalian homolog retinoid X receptors (RXRs) abolished the constitutive activity of the heterodimer but it did not restore EcR ligand-mediated transactivation. These data suggest that USP and its A/B domain play a role in the constitutive function of CfEcR:USP in yeast. A ligand-mediated transactivation was observed when GRIP1, a mouse coactivator gene, was added to EcR:RXR or EcR:DeltaA/BUSP complexes. Deletion of the A/B domain of EcR in the context of DeltaA/BEcR:RXR:GRIP1 or DeltaA/BEcR:DeltaA/BUSP:GRIP1 dramatically improved the ligand-dependent transactivation. This is the first example of highly efficient ligand-dependent transactivation of insect EcR in yeast. Analysis of transactivation activity of different ecdysteroidal compounds showed that the yeast system remarkably mimics the response observed in insect tissue culture cells and whole insect systems. The results open the way to develop assays that can be used to screen novel species-specific ecdysone agonist/antagonist insecticides.

  13. Evolutionary diversification of retinoic acid receptor ligand-binding pocket structure by molecular tinkering

    PubMed Central

    Gutierrez-Mazariegos, Juliana; Nadendla, Eswar Kumar; Studer, Romain A.; Alvarez, Susana; de Lera, Angel R.; Kuraku, Shigehiro; Bourguet, William; Laudet, Vincent

    2016-01-01

    Whole genome duplications (WGDs) have been classically associated with the origin of evolutionary novelties and the so-called duplication–degeneration–complementation model describes the possible fates of genes after duplication. However, how sequence divergence effectively allows functional changes between gene duplicates is still unclear. In the vertebrate lineage, two rounds of WGDs took place, giving rise to paralogous gene copies observed for many gene families. For the retinoic acid receptors (RARs), for example, which are members of the nuclear hormone receptor (NR) superfamily, a unique ancestral gene has been duplicated resulting in three vertebrate paralogues: RARα, RARβ and RARγ. It has previously been shown that this single ancestral RAR was neofunctionalized to give rise to a larger substrate specificity range in the RARs of extant jawed vertebrates (also called gnathostomes). To understand RAR diversification, the members of the cyclostomes (lamprey and hagfish), jawless vertebrates representing the extant sister group of gnathostomes, provide an intermediate situation and thus allow the characterization of the evolutionary steps that shaped RAR ligand-binding properties following the WGDs. In this study, we assessed the ligand-binding specificity of cyclostome RARs and found that their ligand-binding pockets resemble those of gnathostome RARα and RARβ. In contrast, none of the cyclostome receptors studied showed any RARγ-like specificity. Together, our results suggest that cyclostome RARs cover only a portion of the specificity repertoire of the ancestral gnathostome RARs and indicate that the establishment of ligand-binding specificity was a stepwise event. This iterative process thus provides a rare example for the diversification of receptor–ligand interactions of NRs following WGDs. PMID:27069642

  14. E-selectin ligands as mechanosensitive receptors on neutrophils in health and disease

    PubMed Central

    Chase, S. D.; Magnani, J. L.; Simon, S. I.

    2012-01-01

    Application of mechanical force to bonds between selectins and their ligands is a requirement for these adhesion receptors to optimally perform functions that include leukocyte tethering and activation of stable adhesion. Although all three selectins are reported to signal from the outside-in subsequent to ligand binding, E-selectin is unique in its capacity to bind multiple sialyl Lewisx presenting ligands and mediate slow rolling on the order of a micron per second. A diverse set of ligands are recognized by E-selectin in the mouse, including ESL-1, CD44, and PSGL-1 which are critical in transition from slow rolling to arrest and for efficient transendothelial migration. The molecular recognition process is different in humans as L-selectin is a major ligand, which along with glycolipids constitute more than half of the E-selectin receptors on human polymorphonuclear neutrophils (PMN). In addition, E-selectin is most efficient at raising the affinity and avidity of CD18 integrins that supports PMN deceleration and trafficking to sites of acute inflammation. The mechanism is only partially understood but known to involve a rise in cytosolic calcium and tyrosine phosphorylation that activates p38 MAP kinase and Syk kinase, both of which transduce signals from clustered E-selectin ligands. In this review we highlight the molecular recognition and mechanical requirements of this process to reveal how E-selectin confers selectivity and efficiency of signaling for extravasation at sites of inflammation and the mechanism of action of a new glycomimetic antagonist targeted to the lectin domain that has shown efficacy in blocking neutrophil activation and adhesion on inflamed endothelium. PMID:22271244

  15. Identification and functional analysis of ligands for natural killer cell activating receptors in colon carcinoma.

    PubMed

    Zhang, Zhang; Su, Tao; He, Liang; Wang, Hongtao; Ji, Gang; Liu, Xiaonan; Zhang, Yun; Dong, Guanglong

    2012-01-01

    Natural killer (NK) cells play important roles in the immune defense against tumor cells. The function of NK cells is determined by a balance between activating and inhibitory signals. DNAX accessory molecule-1 (DNAM-1) and NK group 2 member D (NKG2D) are major NK cell activating receptors, which transduce activating signals after binding their ligands CD155, CD112 and major histocompatibility complex class I-related chains A and B (MICA/B). However, the expression and functions of these ligands in colon carcinoma are still elusive. Here, we show the higher expression of CD155, CD112 and MICA/B in colon carcinoma tissues, although no correlations between the ligands expression and patient clinicopathological parameters were found. The subsequent cytotoxicity assay indicated that NK cells effectively kill colon carcinoma cells. Functional blocking of these ligands and/or receptors with antibodies led to significant inhibition of NK cell cytotoxicity. Importantly, expression of DNAM-1 and NKG2D was reduced in NK cells of colon cancer patients, and this reduction could directly suppress the activation of NK cells. Moreover, colon cancer patients have higher serum concentrations of sCD155 and sMICA/B (soluble ligands, secreted or shed from cells) than those in healthy donors (sCD155, 127.82 ± 44.12 vs. 63.67 ± 22.30 ng/ml; sMICA, 331.51 ± 65.23 vs. 246.74 ± 20.76 pg/ml; and sMICB, 349.42 ± 81.69 vs. 52.61 ± 17.56 pg/ml). The up-regulation of these soluble ligands may down-regulate DNAM-1 and NKG2D on NK cells, ultimately leading to the inhibition of NK cytotoxicity. Colon cancer might be a promising target for NK cell-based adoptive immunotherapy.

  16. Protein Kinase Cβ Modulates Ligand-induced Cell Surface Death Receptor Accumulation

    PubMed Central

    Meng, Xue Wei; Heldebrant, Michael P.; Flatten, Karen S.; Loegering, David A.; Dai, Haiming; Schneider, Paula A.; Gomez, Timothy S.; Peterson, Kevin L.; Trushin, Sergey A.; Hess, Allan D.; Smith, B. Douglas; Karp, Judith E.; Billadeau, Daniel D.; Kaufmann, Scott H.

    2010-01-01

    Although treatment with the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) is known to protect a subset of cells from induction of apoptosis by death ligands such as Fas ligand and tumor necrosis factor-α-related apoptosis-inducing ligand, the mechanism of this protection is unknown. This study demonstrated that protection in short term apoptosis assays and long term proliferation assays was maximal when Jurkat or HL-60 human leukemia cells were treated with 2–5 nm PMA. Immunoblotting demonstrated that multiple PKC isoforms, including PKCα, PKCβ, PKCϵ, and PKCθ, translocated from the cytosol to a membrane-bound fraction at these PMA concentrations. When the ability of short hairpin RNA (shRNA) constructs that specifically down-regulated each of these isoforms was examined, PKCβ shRNA uniquely reversed PMA-induced protection against cell death. The PKCβ-selective small molecule inhibitor enzastaurin had a similar effect. Although mass spectrometry suggested that Fas is phosphorylated on a number of serines and threonines, mutation of these sites individually or collectively had no effect on Fas-mediated death signaling or PMA protection. Further experiments demonstrated that PMA diminished ligand-induced cell surface accumulation of Fas and DR5, and PKCβ shRNA or enzastaurin reversed this effect. Moreover, enzastaurin sensitized a variety of human tumor cell lines and clinical acute myelogenous leukemia isolates, which express abundant PKCβ, to tumor necrosis factor-α related apoptosis-inducing ligand-induced death in the absence of PMA. Collectively, these results identify a specific PKC isoform that modulates death receptor-mediated cytotoxicity as well as a small molecule inhibitor that mitigates the inhibitory effects of PKC activation on ligand-induced death receptor trafficking and cell death. PMID:19887445

  17. Evolution of Parathyroid Hormone Receptor Family and Their Ligands in Vertebrate

    PubMed Central

    On, Jason S. W.; Chow, Billy K. C.; Lee, Leo T. O.

    2015-01-01

    The presence of the parathyroid hormones in vertebrates, including PTH, PTH-related peptide (PTHrP), and tuberoinfundibular peptide of 39 residues (TIP39), has been proposed to be the result of two rounds of whole genome duplication in the beginning of vertebrate diversification. Bioinformatics analyses, in particular chromosomal synteny study and the characterization of the PTH ligands and their receptors from various vertebrate species, provide evidence that strongly supports this hypothesis. In this mini-review, we summarize recent advances in studies regarding the molecular evolution and physiology of the PTH ligands and their receptors, with particular focus on non-mammalian vertebrates. In summary, the PTH family of peptides probably predates early vertebrate evolution, indicating a more ancient existence as well as a function of these peptides in invertebrates. PMID:25806022

  18. Biased mu-opioid receptor ligands: a promising new generation of pain therapeutics.

    PubMed

    Siuda, Edward R; Carr, Richard; Rominger, David H; Violin, Jonathan D

    2016-12-06

    Opioid chemistry and biology occupy a pivotal place in the history of pharmacology and medicine. Morphine offers unmatched efficacy in alleviating acute pain, but is also associated with a host of adverse side effects. The advent of biased agonism at G protein-coupled receptors has expanded our understanding of intracellular signaling and highlighted the concept that certain ligands are able to differentially modulate downstream pathways. The ability to target one pathway over another has allowed for the development of biased ligands with robust clinical efficacy and fewer adverse events. In this review we summarize these concepts with an emphasis on biased mu opioid receptor pharmacology and highlight how far opioid pharmacology has evolved.

  19. Pannexin-1 as a potentiator of ligand-gated receptor signaling.

    PubMed

    Isakson, Brant E; Thompson, Roger J

    2014-01-01

    Pannexins are a class of plasma membrane spanning proteins that presumably form a hexameric, non-selective ion channel. Although similar in secondary structure to the connexins, pannexins notably do not form endogenous gap junctions and act as bona fide ion channels. The pannexins have been primarily studied as ATP-release channels, but the overall diversity of their functions is still being elucidated. There is an intriguing theme with pannexins that has begun to develop. In this review we analyze several recent reports that converge on the idea that pannexin channels (namely Panx1) can potentiate ligand-gated receptor signaling. Although the literature remains sparse, this emerging concept appears consistent between both ionotropic and metabotropic receptors of several ligand families.

  20. Communication: Free energy of ligand-receptor systems forming multimeric complexes

    NASA Astrophysics Data System (ADS)

    Di Michele, Lorenzo; Bachmann, Stephan J.; Parolini, Lucia; Mognetti, Bortolo M.

    2016-04-01

    Ligand-receptor interactions are ubiquitous in biology and have become popular in materials in view of their applications to programmable self-assembly. Although complex functionalities often emerge from the simultaneous interaction of more than just two linker molecules, state of the art theoretical frameworks enable the calculation of the free energy only in systems featuring one-to-one ligand/receptor binding. In this Communication, we derive a general formula to calculate the free energy of systems featuring simultaneous direct interaction between an arbitrary number of linkers. To exemplify the potential and generality of our approach, we apply it to the systems recently introduced by Parolini et al. [ACS Nano 10, 2392 (2016)] and Halverson and Tkachenko [J. Chem. Phys. 144, 094903 (2016)], both featuring functionalized Brownian particles interacting via three-linker complexes.

  1. Communication: Free energy of ligand-receptor systems forming multimeric complexes.

    PubMed

    Di Michele, Lorenzo; Bachmann, Stephan J; Parolini, Lucia; Mognetti, Bortolo M

    2016-04-28

    Ligand-receptor interactions are ubiquitous in biology and have become popular in materials in view of their applications to programmable self-assembly. Although complex functionalities often emerge from the simultaneous interaction of more than just two linker molecules, state of the art theoretical frameworks enable the calculation of the free energy only in systems featuring one-to-one ligand/receptor binding. In this Communication, we derive a general formula to calculate the free energy of systems featuring simultaneous direct interaction between an arbitrary number of linkers. To exemplify the potential and generality of our approach, we apply it to the systems recently introduced by Parolini et al. [ACS Nano 10, 2392 (2016)] and Halverson and Tkachenko [J. Chem. Phys. 144, 094903 (2016)], both featuring functionalized Brownian particles interacting via three-linker complexes.

  2. Sigma Receptor Ligand, (+)-Pentazocine, Suppresses Inflammatory Responses of Retinal Microglia

    PubMed Central

    Zhao, Jing; Ha, Yonju; Liou, Gregory I.; Gonsalvez, Graydon B.; Smith, Sylvia B.; Bollinger, Kathryn E.

    2014-01-01

    Purpose. To evaluate the effects of the σ 1 receptor (σR1) agonist, (+)-pentazocine, on lipopolysaccharide (LPS)–induced inflammatory changes in retinal microglia cells. Methods. Retinal microglia cells were isolated from Sprague-Dawley rat pups. Cells were treated with LPS with or without (+)-pentazocine and with or without the σR1 antagonist BD1063. Morphologic changes were assayed. Cell viability was assessed by using MTT assay. Supernatant levels of tumor necrosis factor α (TNF-α), interleukin 10, (IL-10), monocyte chemoattractant protein-1 (MCP-1), and nitric oxide (NO) were determined. Reactive oxygen species (ROS) formation was assayed, and levels of mitogen-activated protein kinases (MAPKs) were analyzed by using Western blot. Results. The σR1 protein was expressed in retinal microglia. Incubation with LPS and/or (+)-pentazocine did not alter cell viability or σR1 protein levels. Incubation with LPS for 24 hours induced a marked change in microglial morphology and a significant increase in secreted levels of TNF-α, IL-10, MCP-1, and NO. Pretreatment with (+)-pentazocine inhibited the LPS-induced morphologic changes. Release of TNF-α, IL-10, MCP-1, and NO was reduced with (+)-pentazocine. Intracellular ROS formation was suppressed with (+)-pentazocine. Phosphorylation of extracellular signal–regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) was reduced in the presence of (+)-pentazocine. The σR1 antagonist BD1063 blocked the (+)-pentazocine–mediated inhibition of LPS-induced morphologic changes. In addition, BD1063 treatment blocked (+)-pentazocine–mediated suppression of LPS-induced TNF-α, IL-10, MCP-1, NO, and intracellular ROS release. Conclusions. Treatment with (+)-pentazocine suppressed inflammatory responses of retinal microglia and inhibited LPS-induced activation of ERK/JNK MAPK. In neurodegenerative disease, (+)-pentazocine may exert neuroprotective effects through manipulation of microglia. PMID:24812552

  3. Ligand-receptor binding kinetics in surface plasmon resonance cells: a Monte Carlo analysis

    NASA Astrophysics Data System (ADS)

    Carroll, Jacob; Raum, Matthew; Forsten-Williams, Kimberly; Täuber, Uwe C.

    2016-12-01

    Surface plasmon resonance (SPR) chips are widely used to measure association and dissociation rates for the binding kinetics between two species of chemicals, e.g., cell receptors and ligands. It is commonly assumed that ligands are spatially well mixed in the SPR region, and hence a mean-field rate equation description is appropriate. This approximation however ignores the spatial fluctuations as well as temporal correlations induced by multiple local rebinding events, which become prominent for slow diffusion rates and high binding affinities. We report detailed Monte Carlo simulations of ligand binding kinetics in an SPR cell subject to laminar flow. We extract the binding and dissociation rates by means of the techniques frequently employed in experimental analysis that are motivated by the mean-field approximation. We find major discrepancies in a wide parameter regime between the thus extracted rates and the known input simulation values. These results underscore the crucial quantitative importance of spatio-temporal correlations in binary reaction kinetics in SPR cell geometries, and demonstrate the failure of a mean-field analysis of SPR cells in the regime of high Damköhler number {{Da}}\\gt 0.1, where the spatio-temporal correlations due to diffusive transport and ligand-receptor rebinding events dominate the dynamics of SPR systems.

  4. Immunological Visibility: Posttranscriptional Regulation of Human NKG2D Ligands by the EGF Receptor Pathway

    PubMed Central

    Vantourout, Pierre; Willcox, Carrie; Turner, Andrea; Swanson, Chad; Haque, Yasmin; Sobolev, Olga; Grigoriadis, Anita; Tutt, Andrew; Hayday, Adrian

    2014-01-01

    Human cytolytic T lymphocytes and NK cells can limit tumor growth and are being increasingly harnessed for tumor immunotherapy. One way cytolytic lymphocytes recognize tumor cells is by engagement of their activating receptor, NKG2D, by stress-antigens of the MICA/B and ULBP families. This study shows that surface upregulation of NKG2D ligands by human epithelial cells in response to ultraviolet irradiation, osmotic shock, oxidative stress, and growth factor provision, is attributable to activation of the EGF-receptor (EGFR). EGFR activation causes intracellular re-localisation of AUF1 proteins that ordinarily destabilise NKG2D ligand mRNAs by targeting an AU-rich element conserved within the 3′ ends of most human but not murine NKG2D ligand genes. Consistent with these findings, NKG2D ligand expression by primary human carcinomas positively correlated with EGFR expression that is commonly hyper-activated in such tumours, and was reduced by clinical EGFR inhibitors. Thus, stress-induced activation of EGFR not only regulates cell growth but concomitantly regulates the cells’ immunological visibility. Thus, therapeutics designed to limit cancer cell growth should also be considered in terms of their impact on immunosurveillance. PMID:24718859

  5. Endosulfine, an endogenous peptidic ligand for the sulfonylurea receptor: purification and partial characterization from ovine brain.

    PubMed Central

    Virsolvy-Vergine, A; Leray, H; Kuroki, S; Lupo, B; Dufour, M; Bataille, D

    1992-01-01

    Antidiabetic sulfonylureas act through receptors coupled to ATP-dependent potassium channels. Using the binding of [3H]glibenclamide, a highly potent sulfonylurea, to rat brain membranes to follow the purification procedure, we extracted from ovine brain, purified, and partially characterized two peptides that are endogenous ligands for the central nervous system sulfonylurea receptors. These peptides, referred to as alpha and beta endosulfine, differ by their isoelectric points, the beta form being more basic. Each form of endosulfine is recognized equally by the sulfonylurea receptors from the central nervous system and from insulin-secreting beta cells. In the same concentration range that is active on the receptors, beta endosulfine releases insulin from a beta-cell line. Endosulfine is a good candidate for being implicated in the physiology of beta cells and their disorders (e.g., type II diabetes) and in certain pathologies related to modifications of ion fluxes. Images PMID:1631165

  6. Cbln1 and the δ2 glutamate receptor--an orphan ligand and an orphan receptor find their partners.

    PubMed

    Matsuda, Keiko; Yuzaki, Michisuke

    2012-03-01

    Cerebellin was originally discovered as a Purkinje cell-specific peptide more than two decades ago. Later, its precursor protein precerebellin (Cbln1) was found to be produced in cerebellar granule cells. It has become increasingly clear that although the cerebellin peptide may have certain functions, Cbln1 is an actual signaling molecule that belongs to the C1q family. However, the precise function of Cbln1 has been unresolved. Cbln1 is released from granule cells, and disruption of the cbln1 gene in mice causes a severe reduction in the number of synapses between Purkinje cells and parallel fibers (PFs; axons of granule cells) and results in cerebellar ataxia. The glutamate receptor δ2 (GluD2) is highly expressed on Purkinje cells' dendritic spines which make synapses with PFs. Although GluD2 was identified as a member of the ionotropic glutamate receptors more than 15 years ago, it has been referred to as an orphan receptor because its endogenous ligands are unclear. Interestingly, GluD2-null mice phenocopy cbln1-null mice precisely. Cbln1 and GluD2 have therefore been thought to participate in a common signaling pathway that is required for the formation of PF synapses. We recently established a direct ligand-receptor relationship between Cbln1 and GluD2. The Cbln1-GluD2 complex is located at the cleft of PF-Purkinje cell synapses and bidirectionally regulates both presynaptic and postsynaptic differentiation.

  7. Structure of the Ligand-Binding Domain of the EphB2 Receptor of 2 Angstrom Resolution

    SciTech Connect

    Goldgur, Y.; Paavilainen, S; Nikolov, D; Himanen, J

    2009-01-01

    Eph tyrosine kinase receptors, the largest group of receptor tyrosine kinases, and their ephrin ligands are important mediators of cell-cell communication regulating cell attachment, shape and mobility. Recently, several Eph receptors and ephrins have also been found to play important roles in the progression of cancer. Structural and biophysical studies have established detailed information on the binding and recognition of Eph receptors and ephrins. The initial high-affinity binding of Eph receptors to ephrin occurs through the penetration of an extended G-H loop of the ligand into a hydrophobic channel on the surface of the receptor. Consequently, the G-H loop-binding channel of Eph receptors is the main target in the search for Eph antagonists that could be used in the development of anticancer drugs and several peptides have been shown to specifically bind Eph receptors and compete with the cognate ephrin ligands. However, the molecular details of the conformational changes upon Eph/ephrin binding have remained speculative, since two of the loops were unstructured in the original model of the free EphB2 structure and their conformational changes upon ligand binding could consequently not be analyzed in detail. In this study, the X-ray structure of unbound EphB2 is reported at a considerably higher 2 A resolution, the conformational changes that the important receptor loops undergo upon ligand binding are described and the consequences that these findings have for the development of Eph antagonists are discussed.

  8. Effects of coumestrol on lipid and glucose metabolism as a farnesoid X receptor ligand

    SciTech Connect

    Takahashi, Miki; Kanayama, Tomohiko; Yashiro, Takuya; Kondo, Hidehiko; Murase, Takatoshi; Hase, Tadashi; Tokimitsu, Ichiro; Nishikawa, Jun-ichi; Sato, Ryuichiro

    2008-08-01

    In the course of an effort to identify novel agonists of the farnesoid X receptor (FXR), coumestrol was determined to be one such ligand. Reporter and in vitro coactivator interaction assays revealed that coumestrol bound and activated FXR. Treatment of Hep G2 cells with coumestrol stimulated the expression of FXR target genes, thereby regulating the expression of target genes of the liver X receptor and hepatocyte nuclear factor-4{alpha}. Through these actions, coumestrol is expected to exert beneficial effects on lipid and glucose metabolism.

  9. Arylpiperazines with N-acylated amino acids as 5-HT1A receptor ligands.

    PubMed

    Zajdel, Paweł; Subra, Gilles; Bojarski, Andrzej J; Duszyńska, Beata; Pawłowski, Maciej; Martinez, Jean

    2006-07-01

    A library consisting of 60 arylpiperazines modified with N-acylated amino acids was prepared on BAL linker SynPhasetrade mark Lanterns and evaluated in vitro for 5-HT(1A) receptor affinity. Biological screening, followed by a simple Fujita-Ban analysis, enabled the description of structure-activity relationships and allowed the selection of some potent, high-affinity ligands for in vivo pharmacological investigations.

  10. Dopamine D3 receptor ligands for drug addiction treatment: update on recent findings.

    PubMed

    Le Foll, Bernard; Collo, Ginetta; Rabiner, Eugenii A; Boileau, Isabelle; Merlo Pich, Emilio; Sokoloff, Pierre

    2014-01-01

    The dopamine D3 receptor is located in the limbic area and apparently mediates selective effects on motivation to take drugs and drug-seeking behaviors, so that there has been considerable interest on the possible use of D3 receptor ligands to treat drug addiction. However, only recently selective tools allowing studying this receptor have been developed. This chapter presents an overview of findings that were presented at a symposium on the conference Dopamine 2013 in Sardinia in May 2013. Novel neurobiological findings indicate that drugs of abuse can lead to significant structural plasticity in rodent brain and that this is dependent on the availability of functional dopamine D3 autoreceptor, whose activation increased phosphorylation in the ERK pathway and in the Akt/mTORC1 pathway indicating the parallel engagement of a series of intracellular signaling pathways all involved in cell growth and survival. Preclinical findings using animal models of drug-seeking behaviors confirm that D3 antagonists have a promising profile to treat drug addiction across drugs of abuse type. Imaging the D3 is now feasible in human subjects. Notably, the development of (+)-4-propyl-9-hydroxynaphthoxazine ligand used in positron emission tomography (PET) studies in humans allows to measure D3 and D2 receptors based on the area of the brain under study. This PET ligand has been used to confirm up-regulation of D3 sites in psychostimulant users and to reveal that tobacco smoking produces elevation of dopamine at the level of D3 sites. There are now novel antagonists being developed, but also old drugs such as buspirone, that are available to test the D3 hypothesis in humans. The first results of clinical investigations are now being provided. Overall, those recent findings support further exploration of D3 ligands to treat drug addiction.

  11. The prelude on novel receptor and ligand targets involved in the treatment of diabetes mellitus.

    PubMed

    Jonnalagadda, Venu Gopal; Ram Raju, Allam Venkata Sita; Pittala, Srinivas; Shaik, Afsar; Selkar, Nilakash Annaji

    2014-01-01

    Metabolic disorders are a group of disorders, due to the disruption of the normal metabolic process at a cellular level. Diabetes Mellitus and Tyrosinaemia are the majorly reported metabolic disorders. Among them, Diabetes Mellitus is a one of the leading metabolic syndrome, affecting 5 to 7 % of the population worldwide and mainly characterised by elevated levels of glucose and is associated with two types of physiological event disturbances such as impaired insulin secretion and insulin resistance. Up to now, various treatment strategies are like insulin, alphaglucosidase inhibitors, biguanides, incretins were being followed. Concurrently, various novel therapeutic strategies are required to advance the therapy of Diabetes mellitus. For the last few decades, there has been an extensive research in understanding the metabolic pathways involved in Diabetes Mellitus at the cellular level and having the profound knowledge on cell-growth, cell-cycle, and apoptosis at a molecular level provides new targets for the treatment of Diabetes Mellitus. Receptor signalling has been involved in these mechanisms, to translate the information coming from outside. To understand the various receptors involved in these pathways, we must have a sound knowledge on receptors and ligands involved in it. This review mainly summarises the receptors and ligands which are involved the Diabetes Mellitus. Finally, researchers have to develop the alternative chemical moieties that retain their affinity to receptors and efficacy. Diabetes Mellitus being a metabolic disorder due to the glucose surfeit, demands the need for regular exercise along with dietary changes.

  12. High-affinity interactions of ligands at recombinant Guinea pig 5HT7 receptors

    NASA Astrophysics Data System (ADS)

    Wilcox, R. E.; Ragan, J. E.; Pearlman, R. S.; Brusniak, M. Y.-. K.; Eglen, R. M.; Bonhaus, D. W.; Tenner, T. E., Jr.; Miller, J. D.

    2001-10-01

    The serotonin 5HT7 receptor has been implicated in numerous physiological and pathological processes from circadian rhythms [1] to depression and schizophrenia. Clonal cell lines heterologously expressing recombinant receptors offer good models for understanding drug-receptor interactions and development of quantitative structure-activity relationships (QSAR). Comparative Molecular Field Analysis (CoMFA) is an important modern QSAR procedure that relates the steric and electrostatic fields of a set of aligned compounds to affinity. Here, we utilized CoMFA to predict affinity for a number of high-affinity ligands at the recombinant guinea pig 5HT7 receptor. Using R-lisuride as the template, a final CoMFA model was derived using procedures similar to those of our recent papers [2, 3, 4] The final cross-validated model accounted for >85% of the variance in the compound affinity data, while the final non-cross validated model accounted for >99% of the variance. Model evaluation was done using cross-validation methods with groups of 5 ligands. Twenty cross-validation runs yielded an average predictive r2(q2) of 0.779 ± 0.015 (range: 0.669-0.867). Furthermore, 3D-chemical database search queries derived from the model yielded hit lists of promising agents with high structural similarity to the template. Together, these results suggest a possible basis for high-affinity drug action at 5HT7 receptors.

  13. Dimeric Arrangement of the Parathyroid Hormone Receptor and a Structural Mechanism for Ligand-induced Dissociation

    SciTech Connect

    Pioszak, Augen A.; Harikumar, Kaleeckal G.; Parker, Naomi R.; Miller, Laurence J.; Xu, H. Eric

    2010-06-25

    The parathyroid hormone receptor (PTH1R) is a class B G protein-coupled receptor that is activated by parathyroid hormone (PTH) and PTH-related protein (PTHrP). Little is known about the oligomeric state of the receptor and its regulation by hormone. The crystal structure of the ligand-free PTH1R extracellular domain (ECD) reveals an unexpected dimer in which the C-terminal segment of both ECD protomers forms an {alpha}-helix that mimics PTH/PTHrP by occupying the peptide binding groove of the opposing protomer. ECD-mediated oligomerization of intact PTH1R was confirmed in living cells by bioluminescence and fluorescence resonance energy transfer experiments. As predicted by the structure, PTH binding disrupted receptor oligomerization. A receptor rendered monomeric by mutations in the ECD retained wild-type PTH binding and cAMP signaling ability. Our results are consistent with the hypothesis that PTH1R forms constitutive dimers that are dissociated by ligand binding and that monomeric PTH1R is capable of activating G protein.

  14. The Prelude on Novel Receptor and Ligand Targets Involved in the Treatment of Diabetes Mellitus

    PubMed Central

    Jonnalagadda, Venu Gopal; Ram Raju, Allam Venkata Sita; Pittala, Srinivas; Shaik, Afsar; Selkar, Nilakash Annaji

    2014-01-01

    Metabolic disorders are a group of disorders, due to the disruption of the normal metabolic process at a cellular level. Diabetes Mellitus and Tyrosinaemia are the majorly reported metabolic disorders. Among them, Diabetes Mellitus is a one of the leading metabolic syndrome, affecting 5 to 7 % of the population worldwide and mainly characterised by elevated levels of glucose and is associated with two types of physiological event disturbances such as impaired insulin secretion and insulin resistance. Up to now, various treatment strategies are like insulin, alphaglucosidase inhibitors, biguanides, incretins were being followed. Concurrently, various novel therapeutic strategies are required to advance the therapy of Diabetes mellitus. For the last few decades, there has been an extensive research in understanding the metabolic pathways involved in Diabetes Mellitus at the cellular level and having the profound knowledge on cell-growth, cell-cycle, and apoptosis at a molecular level provides new targets for the treatment of Diabetes Mellitus. Receptor signalling has been involved in these mechanisms, to translate the information coming from outside. To understand the various receptors involved in these pathways, we must have a sound knowledge on receptors and ligands involved in it. This review mainly summarises the receptors and ligands which are involved the Diabetes Mellitus. Finally, researchers have to develop the alternative chemical moieties that retain their affinity to receptors and efficacy. Diabetes Mellitus being a metabolic disorder due to the glucose surfeit, demands the need for regular exercise along with dietary changes. PMID:24754003

  15. Molecular mechanisms of the physiological functions of the aryl hydrocarbon (dioxin) receptor, a multifunctional regulator that senses and responds to environmental stimuli

    PubMed Central

    Fujii-Kuriyama, Yoshiaki; Kawajiri, Kaname

    2010-01-01

    The aryl hydrocarbon receptor (AhR) was originally identified as a ligand-activated transcription factor that is involved in the induction of xenobiotic-metabolizing Cytochrome P4501A1 (CYP1A1). For several decades, AhR has been studied in relation to toxicology and pharmacology. With recent discoveries on novel AhR functions, AhR research has expanded into multiple aspects of physiology, such as reproduction, innate immunity and tumor suppression. In this review, we summarize and discuss recent progress in mechanistic and functional studies on AhR with particular emphasis on physiological processes. PMID:20075607

  16. Peripheral-type benzodiazepine receptor: a protein of mitochondrial outer membranes utilizing porphyrins as endogenous ligands

    SciTech Connect

    Snyder, S.H.; Verma, A.; Trifiletti, R.R.

    1987-10-01

    The peripheral-type benzodiazepine receptor is a site identified by its nanomolar affinity for (/sup 3/H)diazepam, similar to the affinity of diazepam for the central-type benzodiazepine receptor in the brain. The peripheral type benzodiazepine receptor occurs in many peripheral tissues but has discrete localizations as indicated by autoradiographic studies showing uniquely high densities of the receptors in the adrenal cortex and in Leydig cells of the testes. Subcellular localization studies reveal a selective association of the receptors with the outer membrane of mitochondria. Photoaffinity labeling of the mitochondrial receptor with (/sup 3/H)flunitrazepam reveals two discrete labeled protein bands of 30 and 35 kDa, respectively. The 35-kDa band appears to be identical with the voltage-dependent anion channel protein porin. Fractionation of numerous peripheral tissues reveals a single principal endogenous ligand for the receptor, consisting of porphyrins, which display nanomolar affinity. Interactions of porphyrins with the mitochondrial receptor may clarify its physiological role and account for many pharmacological actions of benzodiazepines.

  17. Vibrational spectroscopic investigation of the ligand binding domain of kainate receptors.

    PubMed

    Du, Mei; Rambhadran, Anu; Jayaraman, Vasanthi

    2009-08-01

    Fourier transform infrared spectroscopy has been used to probe the agonist-protein interactions in the ligand binding domain of the GluR6 subunit, one subunit of the kainate subtype of glutamate receptors. In order to study the changes in the interactions over a range of activations the investigations were performed using the wild type, N690S, and T661E mutations. These studies show that the strength of the interactions at the alpha-amine group of the agonist, as probed by studying the environment of the nondisulphide bonded Cys 432, acts as a switch with weaker interactions at lower activations and stronger interactions at higher activations. The alpha-carboxylate interactions of the agonist, however, are not significantly different over the wide range of activations, as measured by the maximum currents mediated by the receptors at saturating concentrations of agonists. Previous investigations of AMPA receptors show a similar dependence of the alpha-amine interactions on activation indicating that the roles of the alpha-amine interactions in mediating receptor activation are similar for both subtypes of receptors; however, in the case of the AMPA receptors a tug of war type of change was observed between the alpha-amine and alpha-carboxylate interactions and this is not observed in kainate receptors. This decoupling of the two interactions could arise due to the larger cleft observed in kainate receptors, which allows for a more flexible interaction for the alpha-amine and alpha-carboxylate groups of the agonists.

  18. Endogenous ligands of imidazoline receptors: classic and immunoreactive clonidine-displacing substance and agmatine.

    PubMed

    Reis, D J; Li, G; Regunathan, S

    1995-07-12

    1. There are several endogenous ligands that bind to I-receptors of both the I1 and I2 subclass. These include: (a) classic CDS, a partially purified entity isolated by the criteria that it displaces binding ligands to alpha 2- and I-receptors; (b) immunoreactive (ir)-CDS, a moiety that binds to antibodies raised against clonidine, para-amino-clonidine, or idazoxan; and (c) agmatine. 2. Classic-CDS, not yet defined structurally, binds to I1, I2, and alpha 2-adrenergic receptors, is neither a peptide nor a catecholamine, and has purportedly a molecular weight of 588 Da. By ligand binding assays, it was found in brain, serum, CSF, and placenta and in a neural-glial cell line. Partially purified classic CDS is bioactive. Like clonidine, it contracts aorta and vas deferens and inhibits platelet aggregation, effects largely attributable to agonism at alpha 2-adrenergic receptors. Unlike clonidine, it contracts rat gastric fundus and releases catecholamines from chromaffin cells, effects attributable to actions at I-receptors. Injected into the RVL, classic CDS alters arterial pressure, but the direction of change of pressure has differed between groups of investigators. However, in the absence of structure, it is possible that ligand binding and bioactivity may be attributable to different molecules. 3. Ir-CDS, also of unknown structure, is a material(s) that binds to antibodies raised against clonidine, PAC, or idazoxan. Ir-CDS, measured by radioimmunoassay, is unevenly distributed in brain with highest concentrations in the hypothalamus, midbrain, and dorsal medulla. It is contained in the gastric fundus, adrenal gland, heart, kidney, and serum in amounts substantially higher than found in brain. Ir-CDS may be elevated in the serum of some patients with hypertension and in the CSF of patients with structural brain disease. The concentration of ir-CDS and bioactivity on gastric fundus directly correlates, suggesting that it may share similarities with classic

  19. Identification of N‐arachidonoyl dopamine as a highly biased ligand at cannabinoid CB1 receptors

    PubMed Central

    Redmond, William J.; Cawston, Erin E.; Grimsey, Natasha L.; Stuart, Jordyn; Edington, Amelia R.; Glass, Michelle

    2015-01-01

    Background and Purpose N‐arachidonyl dopamine (NADA) has been identified as a putative endocannabinoid, but there is little information about which signalling pathways it activates. The purpose of this study was to identify the signalling pathways activated by NADA in vitro. Experimental Approach Human or rat cannabinoid CB1 receptors were expressed in AtT20, CHO or HEK 293 cells. NADA displacement of radiolabelled cannabinoids, and CB1 receptor mediated activation of K channels or ERK phosphorylation, release of intracellular calcium ([Ca]i) and modulation of adenylyl cyclase were measured in addition to NADA effects on CB1 receptor trafficking. Key Results At concentrations up to 30 μM, NADA failed to activate any signalling pathways via CB1 receptors, with the exception of mobilization of [Ca]i. The elevations of [Ca]i were insensitive to pertussis toxin, and reduced or abolished by blockers of Gq/11‐dependent processes including U73122, thapsigargin and a peptide antagonist of Gq/11 activation. Prolonged NADA incubation produced modest loss of cell surface CB1 receptors. The prototypical cannabinoid agonist CP55940 signalled as expected in all assays. Conclusions and Implications NADA is an ineffective agonist at most canonical cannabinoid receptor signalling pathways, but did promote mobilization of [Ca]i via Gq‐dependent processes and some CB1 receptor trafficking. This signalling profile is distinct from that of any known cannabinoid, and suggests that NADA may have a unique spectrum of effects in vivo. Our results also indicate that it may be possible to identify highly biased CB1 receptor ligands displaying a subset of the pharmacological or therapeutic effects usually attributed to CB1 ligands. PMID:26398720

  20. Ligand-guided homology modelling of the GABAB2 subunit of the GABAB receptor.

    PubMed

    Freyd, Thibaud; Warszycki, Dawid; Mordalski, Stefan; Bojarski, Andrzej J; Sylte, Ingebrigt; Gabrielsen, Mari

    2017-01-01

    γ-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the central nervous system, and disturbances in the GABAergic system have been implicated in numerous neurological and neuropsychiatric diseases. The GABAB receptor is a heterodimeric class C G protein-coupled receptor (GPCR) consisting of GABAB1a/b and GABAB2 subunits. Two GABAB receptor ligand binding sites have been described, namely the orthosteric GABA binding site located in the extracellular GABAB1 Venus fly trap domain and the allosteric binding site found in the GABAB2 transmembrane domain. To date, the only experimentally solved three-dimensional structures of the GABAB receptor are of the Venus fly trap domain. GABAB receptor allosteric modulators, however, show great therapeutic potential, and elucidating the structure of the GABAB2 transmembrane domain may lead to development of novel drugs and increased understanding of the allosteric mechanism of action. Despite the lack of x-ray crystal structures of the GABAB2 transmembrane domain, multiple crystal structures belonging to other classes of GPCRs than class A have been released within the last years. More closely related template structures are now available for homology modelling of the GABAB receptor. Here, multiple homology models of the GABAB2 subunit of the GABAB receptor have been constructed using templates from class A, B and C GPCRs, and docking of five clusters of positive allosteric modulators and decoys has been undertaken to select models that enrich the active compounds. Using this ligand-guided approach, eight GABAB2 homology models have been chosen as possible structural representatives of the transmembrane domain of the GABAB2 subunit. To the best of our knowledge, the present study is the first to describe homology modelling of the transmembrane domain of the GABAB2 subunit and the docking of positive allosteric modulators in the receptor.

  1. Ligand-guided homology modelling of the GABAB2 subunit of the GABAB receptor

    PubMed Central

    Freyd, Thibaud; Warszycki, Dawid; Mordalski, Stefan; Bojarski, Andrzej J.; Gabrielsen, Mari

    2017-01-01

    γ-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the central nervous system, and disturbances in the GABAergic system have been implicated in numerous neurological and neuropsychiatric diseases. The GABAB receptor is a heterodimeric class C G protein-coupled receptor (GPCR) consisting of GABAB1a/b and GABAB2 subunits. Two GABAB receptor ligand binding sites have been described, namely the orthosteric GABA binding site located in the extracellular GABAB1 Venus fly trap domain and the allosteric binding site found in the GABAB2 transmembrane domain. To date, the only experimentally solved three-dimensional structures of the GABAB receptor are of the Venus fly trap domain. GABAB receptor allosteric modulators, however, show great therapeutic potential, and elucidating the structure of the GABAB2 transmembrane domain may lead to development of novel drugs and increased understanding of the allosteric mechanism of action. Despite the lack of x-ray crystal structures of the GABAB2 transmembrane domain, multiple crystal structures belonging to other classes of GPCRs than class A have been released within the last years. More closely related template structures are now available for homology modelling of the GABAB receptor. Here, multiple homology models of the GABAB2 subunit of the GABAB receptor have been constructed using templates from class A, B and C GPCRs, and docking of five clusters of positive allosteric modulators and decoys has been undertaken to select models that enrich the active compounds. Using this ligand-guided approach, eight GABAB2 homology models have been chosen as possible structural representatives of the transmembrane domain of the GABAB2 subunit. To the best of our knowledge, the present study is the first to describe homology modelling of the transmembrane domain of the GABAB2 subunit and the docking of positive allosteric modulators in the receptor. PMID:28323850

  2. Biophysical investigations of complement receptor 2 (CD21 and CR2)-ligand interactions reveal amino acid contacts unique to each receptor-ligand pair.

    PubMed

    Kovacs, James M; Hannan, Jonathan P; Eisenmesser, Elan Z; Holers, V Michael

    2010-08-27

    Human complement receptor type 2 (CR2 and CD21) is a cell membrane receptor, with 15 or 16 extracellular short consensus repeats (SCRs), that promotes B lymphocyte responses and bridges innate and acquired immunity. The most distally located SCRs, SCR1-2, mediate the interaction of CR2 with its four known ligands (C3d, EBV gp350, IFNalpha, and CD23). To ascertain specific interacting residues on CR2, we utilized NMR studies wherein gp350 and IFNalpha were titrated into (15)N-labeled SCR1-2, and chemical shift changes indicative of specific inter-molecular interactions were identified. With backbone assignments made, the chemical shift changes were mapped onto the crystal structure of SCR1-2. With regard to gp350, the binding region of CR2 is primarily focused on SCR1 and the inter-SCR linker, specifically residues Asn(11), Arg(13), Ala(22), Arg(28), Ser(32), Arg(36), Lys(41), Lys(57), Tyr(64), Lys(67), Tyr(68), Arg(83), Gly(84), and Arg(89). With regard to IFNalpha, the binding is similar to the CR2-C3d interaction with specific residues being Arg(13), Tyr(16), Arg(28), Ser(42), Lys(48), Lys(50), Tyr(68), Arg(83), Gly(84), and Arg(89). We also report thermodynamic properties of each ligand-receptor pair determined using isothermal titration calorimetry. The CR2-C3d interaction was characterized as a two-mode binding interaction with K(d) values of 0.13 and 160 microm, whereas the CR2-gp350 and CR2-IFNalpha interactions were characterized as single site binding events with affinities of 0.014 and 0.035 microm, respectively. The compilation of chemical binding maps suggests specific residues on CR2 that are uniquely important in each of these three binding interactions.

  3. CHARMM Force Field Parameterization of Peroxisome Proliferator-Activated Receptor γ Ligands

    PubMed Central

    Mottin, Melina; Souza, Paulo C. T.; Ricci, Clarisse G.; Skaf, Munir S.

    2016-01-01

    The peroxisome proliferator-activated receptor γ (PPARγ) ligands are important therapeutic drugs for the treatment of type 2 diabetes, obesity and cardiovascular diseases. In particular, partial agonists and non-agonists are interesting targets to reduce glucose levels, presenting few side effects in comparison to full agonists. In this work, we present a set of CHARMM-based parameters of a molecular mechanics force field for two PPARγ ligands, GQ16 and SR1664. GQ16 belongs to the thiazolidinedione class of drugs and it is a PPARγ partial agonist that has been shown to promote the “browning” of white adipose tissue. SR1664 is the precursor of the PPARγ non-agonist class of ligands that activates PPARγ in a non-classical manner. Here, we use quantum chemical calculations consistent with the CHARMM protocol to obtain bonded and non-bonded parameters, including partial atomic charges and effective torsion potentials for both molecules. The newly parameterized models were evaluated by examining the behavior of GQ16 and SR1664 free in water and bound to the ligand binding pocket of PPARγ using molecular dynamics simulations. The potential parameters derived here are readily transferable to a variety of pharmaceutical compounds and similar PPARγ ligands. PMID:28025495

  4. Ligand-specific regulation of the extracellular surface of a G-protein-coupled receptor

    SciTech Connect

    Bokoch, Michael P.; Zou, Yaozhong; Rasmussen, Søren G.F.; Liu, Corey W.; Nygaard, Rie; Rosenbaum, Daniel M.; Fung, Juan José; Choi, Hee-Jung; Thian, Foon Sun; Kobilka, Tong Sun; Puglisi, Joseph D.; Weis, William I.; Pardo, Leonardo; Prosser, R. Scott; Mueller, Luciano; Kobilka, Brian K.

    2010-01-14

    G-protein-coupled receptors (GPCRs) are seven-transmembrane proteins that mediate most cellular responses to hormones and neurotransmitters. They are the largest group of therapeutic targets for a broad spectrum of diseases. Recent crystal structures of GPCRs have revealed structural conservation extending from the orthosteric ligand-binding site in the transmembrane core to the cytoplasmic G-protein-coupling domains. In contrast, the extracellular surface (ECS) of GPCRs is remarkably diverse and is therefore an ideal target for the discovery of subtype-selective drugs. However, little is known about the functional role of the ECS in receptor activation, or about conformational coupling of this surface to the native ligand-binding pocket. Here we use NMR spectroscopy to investigate ligand-specific conformational changes around a central structural feature in the ECS of the {beta}{sub 2} adrenergic receptor: a salt bridge linking extracellular loops 2 and 3. Small-molecule drugs that bind within the transmembrane core and exhibit different efficacies towards G-protein activation (agonist, neutral antagonist and inverse agonist) also stabilize distinct conformations of the ECS. We thereby demonstrate conformational coupling between the ECS and the orthosteric binding site, showing that drugs targeting this diverse surface could function as allosteric modulators with high subtype selectivity. Moreover, these studies provide a new insight into the dynamic behaviour of GPCRs not addressable by static, inactive-state crystal structures.

  5. Ligand-binding properties of a juvenile hormone receptor, Methoprene-tolerant

    PubMed Central

    Charles, Jean-Philippe; Iwema, Thomas; Epa, V. Chandana; Takaki, Keiko; Rynes, Jan; Jindra, Marek

    2011-01-01

    Juvenile hormone (JH) is a sesquiterpenoid of vital importance for insect development, yet the molecular basis of JH signaling remains obscure, mainly because a bona fide JH receptor has not been identified. Mounting evidence points to the basic helix–loop–helix (bHLH)/Per-Arnt-Sim (PAS) domain protein Methoprene-tolerant (Met) as the best JH receptor candidate. However, details of how Met transduces the hormonal signal are missing. Here, we demonstrate that Met specifically binds JH III and its biologically active mimics, methoprene and pyriproxyfen, through its C-terminal PAS domain. Substitution of individual amino acids, predicted to form a ligand-binding pocket, with residues possessing bulkier side chains reduces JH III binding likely because of steric hindrance. Although a mutation that abolishes JH III binding does not affect a Met–Met complex that forms in the absence of methoprene, it prevents both the ligand-dependent dissociation of the Met–Met dimer and the ligand-dependent interaction of Met with its partner bHLH-PAS protein Taiman. These results show that Met can sense the JH signal through direct, specific binding, thus establishing a unique class of intracellular hormone receptors. PMID:22167806

  6. Ligand-binding properties of a juvenile hormone receptor, Methoprene-tolerant.

    PubMed

    Charles, Jean-Philippe; Iwema, Thomas; Epa, V Chandana; Takaki, Keiko; Rynes, Jan; Jindra, Marek

    2011-12-27

    Juvenile hormone (JH) is a sesquiterpenoid of vital importance for insect development, yet the molecular basis of JH signaling remains obscure, mainly because a bona fide JH receptor has not been identified. Mounting evidence points to the basic helix-loop-helix (bHLH)/Per-Arnt-Sim (PAS) domain protein Methoprene-tolerant (Met) as the best JH receptor candidate. However, details of how Met transduces the hormonal signal are missing. Here, we demonstrate that Met specifically binds JH III and its biologically active mimics, methoprene and pyriproxyfen, through its C-terminal PAS domain. Substitution of individual amino acids, predicted to form a ligand-binding pocket, with residues possessing bulkier side chains reduces JH III binding likely because of steric hindrance. Although a mutation that abolishes JH III binding does not affect a Met-Met complex that forms in the absence of methoprene, it prevents both the ligand-dependent dissociation of the Met-Met dimer and the ligand-dependent interaction of Met with its partner bHLH-PAS protein Taiman. These results show that Met can sense the JH signal through direct, specific binding, thus establishing a unique class of intracellular hormone receptors.

  7. Tyrosine Kinase Ligand-Receptor Pair Prediction by Using Support Vector Machine

    PubMed Central

    Yarimizu, Masayuki; Wei, Cao; Komiyama, Yusuke; Ueki, Kokoro; Nakamura, Shugo; Sumikoshi, Kazuya; Terada, Tohru; Shimizu, Kentaro

    2015-01-01

    Receptor tyrosine kinases are essential proteins involved in cellular differentiation and proliferation in vivo and are heavily involved in allergic diseases, diabetes, and onset/proliferation of cancerous cells. Identifying the interacting partner of this protein, a growth factor ligand, will provide a deeper understanding of cellular proliferation/differentiation and other cell processes. In this study, we developed a method for predicting tyrosine kinase ligand-receptor pairs from their amino acid sequences. We collected tyrosine kinase ligand-receptor pairs from the Database of Interacting Proteins (DIP) and UniProtKB, filtered them by removing sequence redundancy, and used them as a dataset for machine learning and assessment of predictive performance. Our prediction method is based on support vector machines (SVMs), and we evaluated several input features suitable for tyrosine kinase for machine learning and compared and analyzed the results. Using sequence pattern information and domain information extracted from sequences as input features, we obtained 0.996 of the area under the receiver operating characteristic curve. This accuracy is higher than that obtained from general protein-protein interaction pair predictions. PMID:26347773

  8. Somatostatin receptor staining in FFPE sections using a ligand derivative dye as an alternative to immunostaining

    PubMed Central

    Kudoh, Shinji; Ito, Takaaki

    2017-01-01

    The confirmation of target expression in tissues is a prerequisite for molecular-targeted therapy. However, difficulties are sometimes associated with the production of appropriate antibodies against receptors. We herein developed a ligand derivative dye for the staining of receptors. The somatostatin receptor (sstr) was selected as the target and FITC-octreotate as the detective agent. We performed a blot analysis to detect sstr in the transfer membrane. The sstr2 recombinant protein or cell lysate from a small cell lung carcinoma cell line (H69) was boiled and loaded onto SDS-PAGE, and the proteins were transferred to a membrane. Even after denaturing processes, FITC-octreotate still bound sstr on the membrane. Furthermore, FITC-octreotate depicted the expression of sstr in formalin-fixed and paraffin-embedded (FFPE) sections, a method that we named ligand derivative staining (LDS). The accuracies of immunostaining and LDS were compared at the points of the detection of sstr using FFPE sections of 30 neuroendocrine tumor specimens. The sensitivity of LDS was 81.8%, while those of immunostaining using anti-sstr2 and sstr5 antibodies were 72.7% and 63.6%, respectively. Thus, LDS appears to be superior to immunostaining. A ligand derivative may be used as a substitute for antibodies, and has the potential to support economical, simple, and accurate detection methods. PMID:28182792

  9. Synthesis and opioid receptor binding affinities of 2-substituted and 3-aminomorphinans: ligands for mu, kappa, and delta opioid receptors.

    PubMed

    Decker, Michael; Si, Yu-Gui; Knapp, Brian I; Bidlack, Jean M; Neumeyer, John L

    2010-01-14

    The phenolic group of the potent mu and kappa opioid morphinan agonist/antagonists cyclorphan and butorphan was replaced by phenylamino and benzylamino groups including compounds with para-substituents in the benzene ring. These compounds are highly potent mu and kappa ligands, e.g., p-methoxyphenylaminocyclorphan showing a K(i) of 0.026 nM at the mu receptor and a K(i) of 0.03 nM at the kappa receptor. Phenyl carbamates and phenylureas were synthesized and investigated. Selective o-formylation of butorphan and levorphanol was achieved. This reaction opened the way to a large set of 2-substituted 3-hydroxymorphinans, including 2-hydroxymethyl-, 2-aminomethyl-, and N-substituted 2-aminomethyl-3-hydroxymorphinans. Bivalent ligands bridged in the 2-position were also synthesized and connected with secondary and tertiary aminomethyl groups, amide bonds, and hydroxymethylene groups, respectively. Although most of the 2-substituted morphinans showed considerably lower affinities compared to their parent compounds, the bivalent ligand approach led to significantly higher affinities compared to the univalent 2-substituted morphinans.

  10. MODELING THE BINDING OF THE METABOLITES OF SOME POLYCYCLIC AROMTIC HYDROCARBONS TO THE LIGAND BINDING DOMAIN OF THE ESTROGEN RECEPTOR

    EPA Science Inventory

    Modeling the binding of the metabolites of some Polycyclic Aromatic Hydrocarbons to the ligand binding domain of the estrogen receptor
    James Rabinowitz, Stephen Little, Katrina Brown, National Health and Environmental Effects Research Laboratory, Research Triangle Park, NC; Un...

  11. AFM imaging of ligand binding to platelet integrin alphaIIbbeta3 receptors reconstituted into planar lipid bilayers.

    PubMed

    Hussain, Mohammad A; Agnihotri, Aashiish; Siedlecki, Christopher A

    2005-07-19

    The platelet integrin alphaIIbbeta3 plays a key role in platelet adhesion, activation, and aggregation at the subendothelium and at protein-coated synthetic biomaterials. In this study, interactions between alphaIIbbeta3 and both protein and peptide ligands for the receptor were imaged under physiological conditions by high-resolution atomic force microscopy (AFM). To directly image the ligand-receptor interactions, alphaIIbbeta3 receptors were reconstituted into a supported lipid bilayer formed on a mica surface in the AFM fluid cell assembly and subsequently activated with Mn2+. Fibrinogen, the natural protein ligand for the integrin, as well as a nanogold-labeled peptide ligand (an RGD-containing heptamer) were infused into the AFM fluid cell, incubated with the reconstituted and activated receptors, and imaged under buffer. Height images illustrating topographical features showed the integrin reconstituted in the bilayer. Fibrinogen molecules binding to the receptors were easily observed in the height images, with fibrinogen showing its characteristic trinodular structure and occasionally bridging integrin receptors. Fibrinogen was observed to bind to integrins at the D-domain consistent with the location of the gamma-chain dodecapeptide, while fibrinogen bridging integrins bound to receptors on opposite sides of the protein consistent with a 2-fold axis of symmetry. Peptide ligands were not visible in height images; however, phase images that map the mechanical properties detected the nanogold labels and demonstrated the presence of peptide ligands bound to the receptors. The results demonstrate the ability of this high-resolution microscopy technique to directly visualize single ligand/receptor interactions in a dynamic and physiologically relevant environment, and establish a framework for future fundamental studies of single protein/receptor interactions during normal pathological processes as well as biomaterial surface-induced thrombosis.

  12. Diversity and Inter-Connections in the CXCR4 Chemokine Receptor/Ligand Family: Molecular Perspectives

    PubMed Central

    Pawig, Lukas; Klasen, Christina; Weber, Christian; Bernhagen, Jürgen; Noels, Heidi

    2015-01-01

    CXCR4 and its ligand CXCL12 mediate the homing of progenitor cells in the bone marrow and their recruitment to sites of injury, as well as affect processes such as cell arrest, survival, and angiogenesis. CXCL12 was long thought to be the sole CXCR4 ligand, but more recently the atypical chemokine macrophage migration inhibitory factor (MIF) was identified as an alternative, non-cognate ligand for CXCR4 and shown to mediate chemotaxis and arrest of CXCR4-expressing T-cells. This has complicated the understanding of CXCR4-mediated signaling and associated biological processes. Compared to CXCL12/CXCR4-induced signaling, only few details are known on MIF/CXCR4-mediated signaling and it remains unclear to which extent MIF and CXCL12 reciprocally influence CXCR4 binding and signaling. Furthermore, the atypical chemokine receptor 3 (ACKR3) (previously CXCR7) has added to the complexity of CXCR4 signaling due to its ability to bind CXCL12 and MIF, and to evoke CXCL12- and MIF-triggered signaling independently of CXCR4. Also, extracellular ubiquitin (eUb) and the viral protein gp120 (HIV) have been reported as CXCR4 ligands, whereas viral chemokine vMIP-II (Herpesvirus) and human β3-defensin (HBD-3) have been identified as CXCR4 antagonists. This review will provide insight into the diversity and inter-connections in the CXCR4 receptor/ligand family. We will discuss signaling pathways initiated by binding of CXCL12 vs. MIF to CXCR4, elaborate on how ACKR3 affects CXCR4 signaling, and summarize biological functions of CXCR4 signaling mediated by CXCL12 or MIF. Also, we will discuss eUb and gp120 as alternative ligands for CXCR4, and describe vMIP-II and HBD-3 as antagonists for CXCR4. Detailed insight into biological effects of CXCR4 signaling und underlying mechanisms, including diversity of CXCR4 ligands and inter-connections with other (chemokine) receptors, is clinically important, as the CXCR4 antagonist AMD3100 has been approved as stem cell mobilizer in specific

  13. Altered expression of the receptor-ligand pair CXCR5/CXCL13 in B cells during chronic HIV-1 infection.

    PubMed

    Cagigi, Alberto; Mowafi, Frida; Phuong Dang, Linh V; Tenner-Racz, Klara; Atlas, Ann; Grutzmeier, Sven; Racz, Paul; Chiodi, Francesca; Nilsson, Anna

    2008-12-01

    HIV-1 infection is associated with B-cell abnormalities, such as hypergammaglobulinemia, poor immunization responses, and loss of serologic memory. To determine whether altered expression of chemokine receptors and their ligands may play a role in B-cell dysfunctions during HIV-1 infection, the expression of CXC chemokine receptor 4 (CXCR4), CXCR5, and CC chemokine receptor 7 (CCR7) and their respective ligands on CD19(+) B cells were examined in HIV-1-infected patients and controls. We report a decreased CXCR5 expression on B cells from patients (P < .05), a phenomenon associated with a low CD4 T-cell count (< 350 cells/microL). Interestingly, an increased expression of CXC chemokine ligand 13 (CXCL13), the ligand for CXCR5, was found in peripheral B cells from HIV-1-infected patients. Moreover, on B-cell activation in vitro, CXCL13 was secreted in culture. CXCL13(+) B cells were also found in the lymph nodes of HIV-1-infected patients, but not in control tissue. B-cell migration toward CXCL13, CXCL12, and CC chemokine ligand 21 (CCL21), ligands for CXCR5, CXCR4, and CCR7 was also evaluated. In patients with a low CD4 T-cell count, migration toward all ligands was increased. Our findings indicate that altered expression of the chemokine receptor-ligand pair, CXCR5/CXCL13, may participate in the establishment of B-cell dysfunctions during HIV-1 infection.

  14. Decavanadate, a P2X receptor antagonist, and its use to study ligand interactions with P2X7 receptors.

    PubMed

    Michel, Anton D; Xing, Mengle; Thompson, Kyla M; Jones, Clare A; Humphrey, Patrick P A

    2006-03-18

    In this study we have studied decavanadate effects at P2X receptors. Decavanadate competitively blocked 2'- and 3'-O-(4benzoylbenzoyl) ATP (BzATP) stimulated ethidium accumulation in HEK293 cells expressing human recombinant P2X7 receptors (pK(B) 7.5). The effects of decavanadate were rapid (minutes) in both onset and offset and contrasted with the much slower kinetics of pyridoxal 5-phosphate (P5P), Coomassie brilliant blue (CBB) and 1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine (KN62). Decavanadate competitively blocked the slowly reversible, or irreversible, blockade of the P2X7 receptor produced by P5P and oxidised ATP suggesting competition for a common binding site. However, the interaction between decavanadate and KN62 was non-competitive. Decavanadate also blocked P2X2 and P2X4 receptors but with slightly lower potency. These data demonstrate that decavanadate is the first reversible and competitive antagonist of the P2X7 receptor and is a useful tool for studying the mechanism of interaction of ligands with the P2X7 receptor.

  15. Chemically engineering ligand selectivity at the free fatty acid receptor 2 based on pharmacological variation between species orthologs

    PubMed Central

    Hudson, Brian D.; Christiansen, Elisabeth; Tikhonova, Irina G.; Grundmann, Manuel; Kostenis, Evi; Adams, David R.; Ulven, Trond; Milligan, Graeme

    2012-01-01

    When it is difficult to develop selective ligands within a family of related G-protein-coupled receptors (GPCRs), chemically engineered receptors activated solely by synthetic ligands (RASSLs) are useful alternatives for probing receptor function. In the present work, we explored whether a RASSL of the free fatty acid receptor 2 (FFA2) could be developed on the basis of pharmacological variation between species orthologs. For this, bovine FFA2 was characterized, revealing distinct ligand selectivity compared with human FFA2. Homology modeling and mutational analysis demonstrated a single mutation in human FFA2 of C4.57G resulted in a human FFA2 receptor with ligand selectivity similar to the bovine receptor. This was exploited to generate human FFA2-RASSL by the addition of a second mutation at a known orthosteric ligand interaction site, H6.55Q. The resulting FFA2-RASSL displayed a >100-fold loss of activity to endogenous ligands, while responding to the distinct ligand sorbic acid with pEC50 values for inhibition of cAMP, 5.83 ± 0.11; Ca2+ mobilization, 4.63 ± 0.05; ERK phosphorylation, 5.61 ± 0.06; and dynamic mass redistribution, 5.35 ± 0.06. This FFA2-RASSL will be useful in future studies on this receptor and demonstrates that exploitation of pharmacological variation between species orthologs is a powerful method to generate novel chemically engineered GPCRs.—Hudson, B. D., Christiansen, E., Tikhonova, I. G., Grundmann, M., Kostenis, E., Adams, D. R., Ulven, T., Milligan, G. Chemically engineering ligand selectivity at the free fatty acid receptor 2 based on pharmacological variation between species orthologs. PMID:22919070

  16. Evaluation of N-Phenyl Homopiperazine Analogs as Potential Dopamine D3 Receptor Selective Ligands

    PubMed Central

    Li, Aixiao; Mishra, Yogesh; Malik, Maninder; Wang, Qi; Li, Shihong; Taylor, Michelle; Reichert, David E.; Luedtke, Robert R.; Mach, Robert H.

    2013-01-01

    A series of N-(2-methoxyphenyl)homopiperazine analogs was prepared and their affinities for dopamine D2, D3, and D4 receptors were measured using competitive radioligand binding assays. Several ligands exhibited high binding affinity and selectivity for the D3 dopamine receptor compared to the D2 receptor subtype. Compounds 11a, 11b, 11c, 11f, 11j and 11k had Ki values ranging from 0.7–3.9 nM for the D3 receptor with 30- to 170-fold selectivity for the D3 vs. D2 receptor. Calculated log P values (log P = 2.6–3.6) are within the desired range for passive transport across the blood brain barrier. When the binding and the intrinsic efficacy of these phenylhomopiperazines was compared to those of previously published phenylpiperazine analogues, it was found that a) affinity at D2 and D3 dopamine receptors generally decreased, b) the D3 receptor binding selectivity (D2:D3 Ki value ratio) decreased and, c) the intrinsic efficacy, measured using a forskolin-dependent adenylyl cyclase inhibition assay, generally increased. PMID:23618707

  17. Peripheral benzodiazepine receptor ligands reverse apoptosis resistance of cancer cells in vitro and in vivo.

    PubMed

    Decaudin, Didier; Castedo, Maria; Nemati, Fariba; Beurdeley-Thomas, Arnaud; De Pinieux, Gonzague; Caron, Antoine; Pouillart, Pierre; Wijdenes, John; Rouillard, Dany; Kroemer, Guido; Poupon, Marie-France

    2002-03-01

    The mitochondrial peripheral benzodiazepine receptor (mPBR) is involved in a functional structure designated as the permeability transition pore, which controls apoptosis. Binding of Fas/APO-1/CD95 triggers a prototypic apoptosis-inducing pathway. Using four different human tumor cell lines (T-cell Jurkat, neuroblastoma SHEP, osteosarcoma 143N2, and glioblastoma SNB79 cell lines), all of which express CD95 and mPBR, we investigated the potential role of mPBR ligands in CD95-induced apoptosis. We show that, in vitro, the three mPBR ligands tested (RO5-4864, PK11195, and diazepam) enhanced apoptosis induced by anti-CD95 antibody in Jurkat cells, as demonstrated by mitochondrial transmembrane potential drop and DNA fragmentation. In contrast, RO5-4864, but not PK11195 or diazepam, enhanced anti-CD95 apoptosis in all other cell lines. These effects were obtained in Bcl-2-overexpressing SHEP cell lines, but not in Bcl-X(L) SHEP cell lines. Enhancement of anti-CD95 antibody-induced apoptosis by RO5-4864 was characterized by an increased mitochondrial release of cytochrome c and Smac/DIABLO proteins and an enhanced activation of caspases 9 and 3, suggesting a mitochondrion-dependent mechanism. Preincubation of cells with the different mPBR ligands or anti-CD95 did not affect the levels of expression of either mPBR or CD95. In vivo, we found that the RO5-4864 mPBR ligand significantly increased the growth inhibition induced by two chemotherapeutic agents, etoposide and ifosfamide, using two human small cell lung cancers xenografted into nude mice. Peripheral benzodiazepine receptor ligands may therefore act as chemosensitizing agents for the treatment of human neoplasms.

  18. Importance of the extracellular loops in G protein-coupled receptors for ligand recognition and receptor activation.

    PubMed

    Peeters, M C; van Westen, G J P; Li, Q; IJzerman, A P

    2011-01-01

    G protein-coupled receptors (GPCRs) are the major drug target of medicines on the market today. Therefore, much research is and has been devoted to the elucidation of the function and three-dimensional structure of this large family of membrane proteins, which includes multiple conserved transmembrane domains connected by intra- and extracellular loops. In the last few years, the less conserved extracellular loops have garnered increasing interest, particularly after the publication of several GPCR crystal structures that clearly show the extracellular loops to be involved in ligand binding. This review will summarize the recent progress made in the clarification of the ligand binding and activation mechanism of class-A GPCRs and the role of extracellular loops in this process.

  19. Exactly the Same but Different: Promiscuity and Diversity in the Molecular Mechanisms of Action of the Aryl Hydrocarbon (Dioxin) Receptor

    PubMed Central

    Denison, Michael S.; Soshilov, Anatoly A.; He, Guochun; DeGroot, Danica E.; Zhao, Bin

    2011-01-01

    The Ah receptor (AhR) is a ligand-dependent transcription factor that mediates a wide range of biological and toxicological effects that result from exposure to a structurally diverse variety of synthetic and naturally occurring chemicals. Although the overall mechanism of action of the AhR has been extensively studied and involves a classical nuclear receptor mechanism of action (i.e., ligand-dependent nuclear localization, protein heterodimerization, binding of liganded receptor as a protein complex to its specific DNA recognition sequence and activation of gene expression), details of the exact molecular events that result in most AhR-dependent biochemical, physiological, and toxicological effects are generally lacking. Ongoing research efforts continue to describe an ever-expanding list of ligand-, species-, and tissue-specific spectrum of AhR-dependent biological and toxicological effects that seemingly add even more complexity to the mechanism. However, at the same time, these studies are also identifying and characterizing new pathways and molecular mechanisms by which the AhR exerts its actions and plays key modulatory roles in both endogenous developmental and physiological pathways and response to exogenous chemicals. Here we provide an overview of the classical and nonclassical mechanisms that can contribute to the differential sensitivity and diversity in responses observed in humans and other species following ligand-dependent activation of the AhR signal transduction pathway. PMID:21908767

  20. Rifampicin-Independent Interactions between the Pregnane X Receptor Ligand Binding Domain and Peptide Fragments of Coactivator and Corepressor Proteins

    PubMed Central

    Navaratnarajah, Punya; Steele, Bridgett L.; Redinbo, Matthew R.; Thompson, Nancy L.

    2015-01-01

    The pregnane X receptor (PXR), a member of the nuclear receptor superfamily, regulates the expression of drug-metabolizing enzymes in a ligand-dependent manner. The conventional view of nuclear receptor action is that ligand binding enhances the receptor’s affinity for coactivator proteins, while decreasing its affinity for corepressors. To date, however, no known rigorous biophysical studies have been conducted to investigate the interaction among PXR, its coregulators, and ligands. In this work, steady-state total internal reflection fluorescence microscopy (TIRFM) and total internal reflection with fluorescence recovery after photobleaching were used to measure the thermodynamics and kinetics of the interaction between the PXR ligand binding domain and a peptide fragment of the steroid receptor coactivator-1 (SRC-1) in the presence and absence of the established PXR agonist, rifampicin. Equilibrium dissociation and dissociation rate constants of ~5 μM and ~2 s−1, respectively, were obtained in the presence and absence of rifampicin, indicating that the ligand does not enhance the affinity of the PXR and SRC-1 fragments. Additionally, TIRFM was used to examine the interaction between PXR and a peptide fragment of the corepressor protein, the silencing mediator for retinoid and thyroid receptors (SMRT). An equilibrium dissociation constant of ~70 μM was obtained for SMRT in the presence and absence of rifampicin. These results strongly suggest that the mechanism of ligand-dependent activation in PXR differs significantly from that seen in many other nuclear receptors. PMID:22185585

  1. The membrane proximal region of the cannabinoid receptor CB1 N-terminus can allosterically modulate ligand affinity.

    PubMed

    Fay, Jonathan F; Farrens, David L

    2013-11-19

    The human cannabinoid receptor, CB1, a G protein-coupled receptor (GPCR), contains a relatively long (∼110 a.a.) amino terminus, whose function is still not defined. Here we explore a potential role for the CB1 N-terminus in modulating ligand binding to the receptor. Although most of the CB1 N-terminus is not necessary for ligand binding, previous studies have found that mutations introduced into its conserved membrane proximal region (MPR) do impair the receptors ability to bind ligand. Moreover, within the highly conserved MPR (∼ residues 90-110) lie two cysteine residues that are invariant in all CB1 receptors. We find these two cysteines (C98 and C107) form a disulfide in heterologously expressed human CB1, and this C98-C107 disulfide is much more accessible to reducing agents than the previously known disulfide in extracellular loop 2 (EL2). Interestingly, the presence of the C98-C107 disulfide modulates ligand binding to the receptor in a way that can be quantitatively analyzed by an allosteric model. The C98-C107 disulfide also alters the effects of allosteric ligands for CB1, Org 27569 and PSNCBAM-1. Together, these results provide new insights into how the N-terminal MPR and EL2 act together to influence the high-affinity orthosteric ligand binding site in CB1 and suggest that the CB1 N-terminal MPR may be an area through which allosteric modulators can act.

  2. Monitoring Solution Structures of Peroxisome Proliferator-Activated Receptor β/δ upon Ligand Binding

    PubMed Central

    Schwarz, Rico; Tänzler, Dirk; Ihling, Christian H.; Sinz, Andrea

    2016-01-01

    Peroxisome proliferator-activated receptors (PPARs) have been intensively studied as drug targets to treat type 2 diabetes, lipid disorders, and metabolic syndrome. This study is part of our ongoing efforts to map conformational changes in PPARs in solution by a combination of chemical cross-linking and mass spectrometry (MS). To our best knowledge, we performed the first studies addressing solution structures of full-length PPAR-β/δ. We monitored the conformations of the ligand-binding domain (LBD) as well as full-length PPAR-β/δ upon binding of two agonists. (Photo-) cross-linking relied on (i) a variety of externally introduced amine- and carboxyl-reactive linkers and (ii) the incorporation of the photo-reactive amino acid p-benzoylphenylalanine (Bpa) into PPAR-β/δ by genetic engineering. The distances derived from cross-linking experiments allowed us to monitor conformational changes in PPAR-β/δ upon ligand binding. The cross-linking/MS approach proved highly advantageous to study nuclear receptors, such as PPARs, and revealed the interplay between DBD (DNA-binding domain) and LDB in PPAR-β/δ. Our results indicate the stabilization of a specific conformation through ligand binding in PPAR-β/δ LBD as well as full-length PPAR-β/δ. Moreover, our results suggest a close distance between the N- and C-terminal regions of full-length PPAR-β/δ in the presence of GW1516. Chemical cross-linking/MS allowed us gaining detailed insights into conformational changes that are induced in PPARs when activating ligands are present. Thus, cross-linking/MS should be added to the arsenal of structural methods available for studying nuclear receptors. PMID:26992147

  3. Identification of a chemoreceptor for tricarboxylic acid cycle intermediates: differential chemotactic response towards receptor ligands.

    PubMed

    Lacal, Jesús; Alfonso, Carlos; Liu, Xianxian; Parales, Rebecca E; Morel, Bertrand; Conejero-Lara, Francisco; Rivas, Germán; Duque, Estrella; Ramos, Juan L; Krell, Tino

    2010-07-23

    We report the identification of McpS as the specific chemoreceptor for 6 tricarboxylic acid (TCA) cycle intermediates and butyrate in Pseudomonas putida. The analysis of the bacterial mutant deficient in mcpS and complementation assays demonstrate that McpS is the only chemoreceptor of TCA cycle intermediates in the strain under study. TCA cycle intermediates are abundantly present in root exudates, and taxis toward these compounds is proposed to facilitate the access to carbon sources. McpS has an unusually large ligand-binding domain (LBD) that is un-annotated in InterPro and is predicted to contain 6 helices. The ligand profile of McpS was determined by isothermal titration calorimetry of purified recombinant LBD (McpS-LBD). McpS recognizes TCA cycle intermediates but does not bind very close structural homologues and derivatives like maleate, aspartate, or tricarballylate. This implies that functional similarity of ligands, such as being part of the same pathway, and not structural similarity is the primary element, which has driven the evolution of receptor specificity. The magnitude of chemotactic responses toward these 7 chemoattractants, as determined by qualitative and quantitative chemotaxis assays, differed largely. Ligands that cause a strong chemotactic response (malate, succinate, and fumarate) were found by differential scanning calorimetry to increase significantly the midpoint of protein unfolding (T(m)) and unfolding enthalpy (DeltaH) of McpS-LBD. Equilibrium sedimentation studies show that malate, the chemoattractant that causes the strongest chemotactic response, stabilizes the dimeric state of McpS-LBD. In this respect clear parallels exist to the Tar receptor and other eukaryotic receptors, which are discussed.

  4. Ligand binding to thromboxane receptors on human platelets: correlation with biological activity.

    PubMed Central

    Armstrong, R. A.; Jones, R. L.; Wilson, N. H.

    1983-01-01

    The preparation of enantiomerically pure [3H]-15 (S) 9, 11-epoxymethano PGH2 (a thromboxane A2-like agonist) has enabled the binding of ligands to the thromboxane receptor of the human platelet to be studied. The binding of the radio-ligand to washed human platelets has 3 components. One component is not displaceable by 'cold' 9, 11-epoxymethano PGH2 and its concentration-binding plot is roughly linear. The other 2 components are displaceable and saturable, and the larger of the two, which is sensitive to the stereochemistry of the C15 secondary alcohol, appears to represent the thromboxane receptor. About 1700 15(S)9, 11-epoxymethano PGH2 molecules are specifically bound to a single platelet and 50% of this binding is achieved with a concentration of 75 nM. Displacement of [3H]-15(S)9, 11-epoxymethano PGH2 is effected by (a) TXA2 and PGH2 and a number of bicyclic stable analogues (e.g. 9,11-azo PGH2), all of which produce irreversible aggregation of human platelets; (b) analogues of PGF2 alpha with potent thromboxane-like activity (e.g. ICI 79939); (c) compounds with partial agonist activity on the platelet thromboxane system (e.g. CTA2); (d) Thromboxane/endoperoxide analogues which specifically antagonize thromboxane-like actions on the human platelet (e.g. PTA2 and EP 045). Displacement is not achieved with the natural prostaglandins PGE2, PGD2 and PGF2 alpha. Neither the thromboxane-synthetase inhibitor dazoxiben nor R(+)-trimethoquinol have high displacing activity. The correlation of radio-ligand displacement with the biological activity of the competing ligands is discussed in relation to the nature of the thromboxane receptor on the human platelet. PMID:6317122

  5. Data for amino acid alignment of Japanese stingray melanocortin receptors with other gnathostome melanocortin receptor sequences, and the ligand selectivity of Japanese stingray melanocortin receptors.

    PubMed

    Takahashi, Akiyoshi; Davis, Perry; Reinick, Christina; Mizusawa, Kanta; Sakamoto, Tatsuya; Dores, Robert M

    2016-06-01

    This article contains structure and pharmacological characteristics of melanocortin receptors (MCRs) related to research published in "Characterization of melanocortin receptors from stingray Dasyatis akajei, a cartilaginous fish" (Takahashi et al., 2016) [1]. The amino acid sequences of the stingray, D. akajei, MC1R, MC2R, MC3R, MC4R, and MC5R were aligned with the corresponding melanocortin receptor sequences from the elephant shark, Callorhinchus milii, the dogfish, Squalus acanthias, the goldfish, Carassius auratus, and the mouse, Mus musculus. These alignments provide the basis for phylogenetic analysis of these gnathostome melanocortin receptor sequences. In addition, the Japanese stingray melanocortin receptors were separately expressed in Chinese Hamster Ovary cells, and stimulated with stingray ACTH, α-MSH, β-MSH, γ-MSH, δ-MSH, and β-endorphin. The dose response curves reveal the order of ligand selectivity for each stingray MCR.

  6. Reversible sequential-binding probe receptor-ligand interactions in single cells.

    PubMed

    Schreiter, Christoph; Gjoni, Marinela; Hovius, Ruud; Martinez, Karen L; Segura, Jean-Manuel; Vogel, Horst

    2005-12-01

    With the reversible sequential (ReSeq) binding assay,we present a novel approach for the ultrasensitive profiling of receptor function in single living cells. This assay is based on the repetitive application of fluorescent ligands that have fast association-dissociation kinetics. We chose the nicotinic-acetylcholine receptor (nAChR) as a prototypical example and performed ReSeq equilibrium, kinetic, and competition-binding assays using fluorescent derivatives of the antagonist alpha-conotoxin GI (alpha-CnTx). Thereby, we determined the binding constants of unlabeled alpha-CnTx and d-tubocurarine. The high selectivity of alpha-CnTx for muscle-type nAChR made it possible to observe specific binding even in the presence of other nAChR subtypes. Imaging of individual nAChRs and ligand-binding cycles to single cells in microfluidic devices demonstrated the ultimate miniaturization and accuracy of ReSeq-binding assays even at low receptor-expression levels. We expect our approach to be of generic importance for functional screening of compounds or membrane receptors, and for the detailed characterization of rare primary cells.

  7. Sub-millisecond ligand probing of cell receptors with multiple solution exchange.

    PubMed

    Sylantyev, Sergiy; Rusakov, Dmitri A

    2013-01-01

    The accurate knowledge of receptor kinetics is crucial to our understanding of cell signal transduction in general and neural function in particular. The classical technique of probing membrane receptors on a millisecond scale involves placing a recording micropipette with a membrane patch in front of a double-barrel (θ-glass) application pipette mounted on a piezo actuator. Driven by electric pulses, the actuator can rapidly shift the θ-glass pipette tip, thus exposing the target receptors to alternating ligand solutions. However, membrane patches survive for only a few minutes, thus normally restricting such experiments to a single-application protocol. In order to overcome this deficiency, we have introduced pressurized supply microcircuits in the θ-glass channels, thus enabling repeated replacement of application solutions within 10-15 s. This protocol, which has been validated in our recent studies and takes 20-60 min to implement, allows the characterization of ligand-receptor interactions with high sensitivity, thereby also enabling a powerful paired-sample statistical design.

  8. Dynamics of the Ligand Binding Domain Layer during AMPA Receptor Activation

    PubMed Central

    Baranovic, Jelena; Chebli, Miriam; Salazar, Hector; Carbone, Anna L.; Faelber, Katja; Lau, Albert Y.; Daumke, Oliver; Plested, Andrew J.R.

    2016-01-01

    Ionotropic glutamate receptors are postsynaptic tetrameric ligand-gated channels whose activity mediates fast excitatory transmission. Glutamate binding to clamshell-shaped ligand binding domains (LBDs) triggers opening of the integral ion channel, but how the four LBDs orchestrate receptor activation is unknown. Here, we present a high-resolution x-ray crystal structure displaying two tetrameric LBD arrangements fully bound to glutamate. Using a series of engineered metal ion trapping mutants, we showed that the more compact of the two assemblies corresponds to an arrangement populated during activation of full-length receptors. State-dependent cross-linking of the mutants identified zinc bridges between the canonical active LBD dimers that formed when the tetramer was either fully or partially bound by glutamate. These bridges also stabilized the resting state, consistent with the recently published full-length apo structure. Our results provide insight into the activation mechanism of glutamate receptors and the complex conformational space that the LBD layer can sample. PMID:26910426

  9. Characterization of opiate receptor heterogeneity using affinity ligands and phospholipase A/sub 2/

    SciTech Connect

    Reichman, M.

    1985-01-01

    The primary aim of the dissertation was to study the heterogeneity of opiate receptors by utilizing affinity ligands, and by modification of the receptor lipid-microenvironment with phospholipase A/sub 2/ (PLA/sub 2/). The affinity ligands, 14-bromacetamidomorphine (BAM) and 14-chloroacetylnaltrexone (CAN), selectively inactivated high affinity dihydromorphine binding sites in an apparently irreversible manner (the inhibition was resistant to extensive washes of treated neural membrane homogenates). The inhibitory effect of PLA/sub 2/ (10 ng/ml) on opiate receptor subtypes was determined using (/sup 3/H)-dihydromorphine (..mu..-type agonist), (/sup 3/H)-enkephalin (delta agonist) and (/sup 3/H)-naloxone (..mu.. antagonist). PLA/sub 2/ abolished the high affinity antagonist binding site, whereas it inhibited high and low affinity agonist binding sites similarly. The results suggest that high affinity antagonist binding sites are different from high affinity agonist binding sites. Indirect binding assays demonstrated that the selectivities of ..mu..- and delta receptors are not affected significantly by PLA/sub 2/ treatment.

  10. Tumor necrosis factor inhibits ligand-stimulated EGF receptor activation through a TNF receptor 1-dependent mechanism

    PubMed Central

    McElroy, Steven J.; Frey, Mark R.; Yan, Fang; Edelblum, Karen L.; Goettel, Jeremy A.; John, Sutha; Polk, D. Brent

    2008-01-01

    Tumor necrosis factor (TNF) and epidermal growth factor (EGF) are key regulators in the intricate balance maintaining intestinal homeostasis. Previous work from our laboratory shows that TNF attenuates ligand-driven EGF receptor (EGFR) phosphorylation in intestinal epithelial cells. To identify the mechanisms underlying this effect, we examined EGFR phosphorylation in cells lacking individual TNF receptors. TNF attenuated EGF-stimulated EGFR phosphorylation in wild-type and TNFR2−/−, but not TNFR1−/−, mouse colon epithelial (MCE) cells. Reexpression of wild-type TNFR1 in TNFR1−/− MCE cells rescued TNF-induced EGFR inhibition, but expression of TNFR1 deletion mutant constructs lacking the death domain (DD) of TNFR1 did not, implicating this domain in EGFR downregulation. Blockade of p38 MAPK, but not MEK, activation of ERK rescued EGF-stimulated phosphorylation in the presence of TNF, consistent with the ability of TNFR1 to stimulate p38 phosphorylation. TNF promoted p38-dependent EGFR internalization in MCE cells, suggesting that desensitization is achieved by reducing receptor accessible to ligand. Taken together, these data indicate that TNF activates TNFR1 by DD- and p38-dependent mechanisms to promote EGFR internalization, with potential impact on EGF-induced proliferation and migration key processes that promote healing in inflammatory intestinal diseases. PMID:18467504

  11. Identification of common ligand binding determinants of the insulin and insulin-like growth factor 1 receptors. Insights into mechanisms of ligand binding.

    PubMed

    Mynarcik, D C; Williams, P F; Schaffer, L; Yu, G Q; Whittaker, J

    1997-07-25

    Insulin and insulin-like growth factor 1 (IGF-1) are peptides that share nearly 50% sequence homology. However, although their cognate receptors also exhibit significant overall sequence homology, the affinity of each peptide for the non-cognate receptor is 2-3 orders of magnitude lower than for the cognate receptor. The molecular basis for this discrimination is unclear, as are the molecular mechanisms underlying ligand binding. We have recently identified a major ligand binding site of the insulin receptor by alanine scannning mutagenesis. These studies revealed that a number of amino acids critical for insulin binding are conserved in the IGF-1 receptor, suggesting that they may play a role in ligand binding. We therefore performed alanine mutagenesis of these amino acids to determine whether this is the case. cDNAs encoding alanine-substituted secreted recombinant IGF-1 receptors were expressed in 293 EBNA cells, and the ligand binding properties of the expressed proteins were evaluated. Mutation of Phe701 resulted in a receptor with undetectable IGF-1 binding; alanine substitution of the corresponding amino acid of the insulin receptor, Phe714, produces a 140-fold reduction in affinity for insulin. Mutation of Asp8, Asn11, Phe58, Phe692, Glu693, His697, and Asn698 produces a 3.5-6-fold reduction in affinity for IGF-1. In contrast, alanine mutation of the corresponding amino acids of the insulin receptor with the exception of Asp12 produces reductions in affinity that are 50-fold or greater. The affinity of insulin for these mutants relative to wild type receptor was similar to that of their relative affinity for IGF-1 with two exceptions; the IC50 values for insulin binding to the mutants of Arg10, which has normal affinity for IGF-1, and His697, which has a 6-fold reduction in affinity for IGF-1, were both at least 2 orders of magnitude greater than for wild type receptor. The Kd values for insulin of the corresponding alanine mutants of the insulin receptor

  12. Endogenous hallucinogens as ligands of the trace amine receptors: a possible role in sensory perception.

    PubMed

    Wallach, J V

    2009-01-01

    While the endogenous hallucinogens, N,N-dimethyltryptamine, 5-hydroxy-N,N-dimethyl-tryptamine and 5-methoxy-N,N-dimethyltryptamine, have been acknowledged as naturally occurring components of the mammalian body for decades, their biological function remains as elusive now as it was at the time of their discovery. The recent discovery of the trace amine associated receptors and the activity of DMT and other hallucinogenic compounds at these receptor sites leads to the hypothesis that the endogenous hallucinogens act as neurotransmitters of a subclass of these trace amine receptors. Additionally, while activity at the serotonin 5-HT2A receptor has been proposed as being responsible for the hallucinogenic affects of administered hallucinogens, in their natural setting the 5-HT2A receptor may not interact with the endogenous hallucinogens at all. Additionally 5-HT2A agonist activity is unable to account for the visual altering effects of many of the administered hallucinogens; these effects may be mediated by one of the endogenous hallucinogen trace amine receptors rather than the serotonin 5-HT2A receptor. Therefore, activity at the trace amine receptors, in addition to serotonin receptors, may play a large role in the sensory altering effects of administered hallucinogens and the trace amine receptors along with their endogenous hallucinogen ligands may serve an endogenous role in mediating sensory perception in the mammalian central nervous system. Thus the theory proposed states that these compounds act as true endogenous hallucinogenic transmitters acting in regions of the central nervous system involved in sensory perception.

  13. [Ligands of glutamate and dopamine receptors evenly labeled with hydrogen isotopes].

    PubMed

    Zolotarev, Iu A; Firstova, Iu Iu; Abaimov, D A; Dadaian, A K; Kosik, V S; Novikov, A V; Krasnov, N V; Vas'kovskiĭ, B V; Nazimov, I V; Kovalev, G I; Miasoedov, N F

    2009-01-01

    A reaction of high-temperature solid-phase catalytic isotope exchange (HSCIE) was studied for the preparation of tritium- and deuterium-labeled ligands of glutamate and dopamine receptors. Tritium-labeled (5S,10R)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclopenten-5,10-imine ([G-(3)H]MK-801) and R(+)-7-hydroxy-N,N-di-n-propyl-2-aminotetraline ([G-(3)H]-7-OH-DPAT) were obtained with a specific activity of 210 and 120 Ci/mol, respectively. The isotopomeric distribution of deuterium-labeled ligands was studied using time-of-flight mass-spectrometer MX 5310 (ESI-o-TOF) with electrospray and orthogonal ion injection. Mean deuterium incorporation per ligand molecule was 11.09 and 3.21 atoms for [G-(2)H]MK-801 and [G-(2)H]-7-OH-DPAT, respectively. The isotope label was shown to be distributed all over the ligand molecule. The radioreceptor binding of tritium-labeled ligands [G-(3)H]MK-801 and [G-(3)H]-7-OH-DPAT was analyzed using the brain structure of Vistar rats. It was demonstrated that [G-(3)H]MK-801 specifically binds to hippocampus membranes with K(d) 8.3 +/- 1.4 nM, B(max) being 3345 +/- 300 fmol/mg protein. The [G-(3)H]-7-OH-DPAT ligand specifically binds to rat striatum membranes with K(d) 10.01 +/- 0.91 nM and B(max) 125 +/- 4.5 fmol/mg protein. It was concluded that the HSCIE reaction can be used for the preparation of highly tritium-labeled (+)-MK-801 and 7-OH-DPAT with retention of their physiological activities.

  14. A new method for ligand docking to flexible receptors by dual alanine scanning and refinement (SCARE)

    NASA Astrophysics Data System (ADS)

    Bottegoni, Giovanni; Kufareva, Irina; Totrov, Maxim; Abagyan, Ruben

    2008-05-01

    Protein binding sites undergo ligand specific conformational changes upon ligand binding. However, most docking protocols rely on a fixed conformation of the receptor, or on the prior knowledge of multiple conformations representing the variation of the pocket, or on a known bounding box for the ligand. Here we described a general induced fit docking protocol that requires only one initial pocket conformation and identifies most of the correct ligand positions as the lowest score. We expanded a previously used diverse "cross-docking" benchmark to thirty ligand-protein pairs extracted from different crystal structures. The algorithm systematically scans pairs of neighbouring side chains, replaces them by alanines, and docks the ligand to each `gapped' version of the pocket. All docked positions are scored, refined with original side chains and flexible backbone and re-scored. In the optimal version of the protocol pairs of residues were replaced by alanines and only one best scoring conformation was selected from each `gapped' pocket for refinement. The optimal SCARE (SCan Alanines and REfine) protocol identifies a near native conformation (under 2 Å RMSD) as the lowest rank for 80% of pairs if the docking bounding box is defined by the predicted pocket envelope, and for as many as 90% of the pairs if the bounding box is derived from the known answer with ˜5 Å margin as used in most previous publications. The presented fully automated algorithm takes about 2 h per pose of a single processor time, requires only one pocket structure and no prior knowledge about the binding site location. Furthermore, the results for conformationally conserved pockets do not deteriorate due to substantial increase of the pocket variability.

  15. Non-peptide oxytocin receptor ligands and hamster circadian wheel running rhythms.

    PubMed

    Gannon, Robert L

    2014-10-17

    The synchronization of circadian rhythms in sleep, endocrine and metabolic functions with the environmental light cycle is essential for health, and dysfunction of this synchrony is thought to play a part in the development of many neurological disorders. There is a demonstrable need to develop new therapeutics for the treatment of neurological disorders such as depression and schizophrenia, and oxytocin is currently being investigated for this purpose. There are no published reports describing activity of oxytocin receptor ligands on mammalian circadian rhythms and that, then, is the purpose of this study. Non-peptide oxytocin receptor ligands that cross the blood brain barrier were systemically injected in hamsters to determine their ability to modulate light-induced phase advances and delays of circadian wheel running rhythms. The oxytocin receptor agonist WAY267464 (10 mg/kg) inhibited light induced phase advances of wheel running rhythms by 55%, but had no effect on light-induced phase delays. In contrast, the oxytocin receptor antagonist WAY162720 (10 mg/kg) inhibited light-induced phase delays by nearly 75%, but had no effect on light-induced phase advances. Additionally, WAY162720 was able to antagonize the inhibitory effects of WAY267464 on light-induced phase advances. These results are consistent for a role of oxytocin in the phase-delaying effects of light on circadian activity rhythms early in the night. Therefore, oxytocin may prove to be useful in developing therapeutics for the treatment of mood disorders with a concomitant dysfunction in circadian rhythms. Investigators should also be cognizant that oxytocin ligands may negatively affect circadian rhythms during clinical trials for other conditions.

  16. Characterization of the Ligand Binding Functionality of the Extracellular Domain of Activin Receptor Type IIB

    PubMed Central

    Sako, Dianne; Grinberg, Asya V.; Liu, June; Davies, Monique V.; Castonguay, Roselyne; Maniatis, Silas; Andreucci, Amy J.; Pobre, Eileen G.; Tomkinson, Kathleen N.; Monnell, Travis E.; Ucran, Jeffrey A.; Martinez-Hackert, Erik; Pearsall, R. Scott; Underwood, Kathryn W.; Seehra, Jasbir; Kumar, Ravindra

    2010-01-01

    The single transmembrane domain serine/threonine kinase activin receptor type IIB (ActRIIB) has been proposed to bind key regulators of skeletal muscle mass development, including the ligands GDF-8 (myostatin) and GDF-11 (BMP-11). Here we provide a