title: Ligand binding to somatostatin receptors induces receptor-specific oligomer formation in live cells.
abstract: Heptahelical receptors (HHRs) are generally thought to function as monomeric entities. Several HHRs such as somatostatin receptors (SSTRs), however, form homo- and heterooligomers when activated by ligand binding. By using dual fluorescent ligands simultaneously applied to live cells monotransfected with SSTR5 (R5) or SSTR1 (R1), or cotransfected with R5 and R1, we have analyzed the ligand receptor stoichiometry and aggregation states for the three receptor systems by fluorescence resonance energy transfer and fluorescence correlation spectroscopy. Both homo- and heterooligomeric receptors are occupied by two ligand molecules. We find that monomeric, homooligomeric, and heterooligomeric receptor species occur in the same cell cotransfected with two SSTRs, and that oligomerization of SSTRs is regulated by ligand binding by a selective process that is restricted to some (R5) but not other (R1) SSTR subtypes. We propose that induction by ligand of different oligomeric states of SSTRs represents a unique mechanism for generating signaling specificity not only within the SSTR family but more generally in the HHR family.
authors.affiliation: Fraser Laboratories, Department of Medicine, McGill University, and Royal Victoria Hospital, Montreal, QC, Canada H3A 1A1.
authors.forename: Ramesh C
authors.initials: RC
authors.lastname: Patel
authors.forename: Ujendra
authors.initials: U
authors.lastname: Kumar
authors.forename: Don C
authors.initials: DC
authors.lastname: Lamb
authors.forename: John S
authors.initials: JS
authors.lastname: Eid
authors.forename: Magalie
authors.initials: M
authors.lastname: Rocheville
authors.forename: Michael
authors.initials: M
authors.lastname: Grant
authors.forename: Aruna
authors.initials: A
authors.lastname: Rani
authors.forename: Theodore
authors.initials: T
authors.lastname: Hazlett
authors.forename: Shutish C
authors.initials: SC
authors.lastname: Patel
authors.forename: Enrico
authors.initials: E
authors.lastname: Gratton
authors.forename: Yogesh C
authors.initials: YC
authors.lastname: Patel
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D005456:Fluorescent Dyes; D008024:Ligands; D009842:Oligopeptides; D011485:Protein Binding; D017481:Receptors, Somatostatin / Q000235:genetics / Q000378:metabolism*; D013050:Spectrometry, Fluorescence / Q000379:methods
chemical_list: D005456:Fluorescent Dyes; D008024:Ligands; D009842:Oligopeptides; D017481:Receptors, Somatostatin; C101130:somatostatin receptor type 1; C094573:somatostatin receptor 5