title: The role of subtype-specific ligand binding and the C-tail domain in dimer formation of human somatostatin receptors.
abstract: G-protein-coupled receptors (GPCRs) represent the largest and most diverse family of cell surface receptors. Several GPCRs have been documented to dimerize with resulting changes in pharmacology. We have previously reported by means of photobleaching fluorescence resonance energy transfer (pbFRET) microscopy and fluorescence correlation spectroscopic (FCS) analysis in live cells, that human somatostatin receptor (hSSTR) 5 could both homodimerize and heterodimerize with hSSTR1 in the presence of the agonist SST-14. In contrast, hSSTR1 remained monomeric when expressed alone regardless of agonist exposure in live cells. In an effort to elucidate the role of ligand and receptor subtypes in heterodimerization, we have employed both pb-FRET microscopy and Western blot on cells stably co-expressing hSSTR1 and hSSTR5 treated with subtype-specific agonists. Here we provide evidence that activation of hSSTR5 but not hSSTR1 is necessary for heterodimeric assembly. This property was also reflected in signaling as shown by increases in adenylyl cyclase coupling efficiencies. Furthermore, receptor C-tail chimeras allowed for the identification of the C-tail as a determinant for dimerization. Finally, we demonstrate that heterodimerization is subtype-selective involving ligand-induced conformational changes in hSSTR5 but not hSSTR1 and could be attributed to molecular events occurring at the C-tail. Understanding the mechanisms by which GPCRs dimerize holds promise for improvements in drug design and efficacy.
authors.affiliation: Fraser Laboratories For Diabetes Research, Royal Victoria Hospital, Department of Medicine, McGill University, Montreal, Quebec H3A 1A1, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Grant
authors.forename: Ramesh C
authors.initials: RC
authors.lastname: Patel
authors.forename: Ujendra
authors.initials: U
authors.lastname: Kumar
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D007150:Immunohistochemistry; D007700:Kinetics; D008024:Ligands; D018613:Microscopy, Confocal; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017481:Receptors, Somatostatin / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013997:Time Factors; D014162:Transfection
chemical_list: D008024:Ligands; D017481:Receptors, Somatostatin; D000242:Cyclic AMP; D000262:Adenylyl Cyclases