title: Involvement of the carboxyl terminus of the third intracellular loop of the cannabinoid CB1 receptor in constitutive activation of Gs.
abstract: The human cannabinoid receptor CB1 functionally couples primarily to Gi-, but also to Gs-mediated pathways to modulate intracellular cyclic AMP (cAMP) levels. To probe the features of the receptor that may be involved in promoting interactions with one G protein type over another, we generated the L341A/A342L mutant CB1 receptor. The double mutation involved the swap in position of two adjacent residues in the carboxyl-terminal segment of the third intracellular loop of CB1. This resulted in partial constitutive activation of the receptor and an agonist-independent enhancement in cAMP levels. Characterization following treatment with either pertussis or cholera toxin indicated that the constitutive activity is selective for a Gs- and not a Gi-mediated pathway. Treatment with the CB1-specific inverse agonist SR141716A inhibited the basal accumulation of cAMP in the presence of pertussis toxin, establishing that the effect is CB1 mediated. The binding of the agonist CP-55,940 to the L341A/A342L receptor was not markedly different from that for the wild-type receptor despite the constitutive Gs activity. This may reflect a preference of this ligand for an activated receptor state associated with the Gi coupling form and underscores the potential for developing therapeutics that selectively activate one pathway over another.
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs 06269, USA.
authors.forename: V
authors.initials: V
authors.lastname: Abadji
authors.forename: J M
authors.initials: JM
authors.lastname: Lucas-Lenard
authors.forename: C
authors.initials: C
authors.lastname: Chin
authors.forename: D A
authors.initials: DA
authors.lastname: Kendall
mesh_terms: D000818:Animals; D016466:CHO Cells; D002772:Cholera Toxin / Q000494:pharmacology; D006224:Cricetinae; D000242:Cyclic AMP / Q000037:antagonists & inhibitors / Q000378:metabolism; D003511:Cyclohexanols / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000502:physiology*; D006801:Humans; D009154:Mutation / Q000502:physiology; D010446:Peptide Fragments / Q000502:physiology*; D037342:Pertussis Toxin; D010880:Piperidines / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000077285:Rimonabant; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D003511:Cyclohexanols; D010446:Peptide Fragments; D010880:Piperidines; D011720:Pyrazoles; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug; D010566:Virulence Factors, Bordetella; C054649:3-(2-hydroxy-4-(1,1-dimethylheptyl)phenyl)-4-(3-hydroxypropyl)cyclohexanol; D002772:Cholera Toxin; D000242:Cyclic AMP; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D000077285:Rimonabant