title: Desensitization of the Y1 cell adrenocorticotropin receptor: evidence for a restricted heterologous mechanism implying a role for receptor-effector complexes.
abstract: Receptor desensitization provides a potential mechanism for the regulation of adrenocortical adrenocorticotropin (ACTH) responsiveness. Using the mouse adrenocortical Y1 cell line we demonstrate that ACTH effectively desensitizes the cAMP response of its own receptor, the melanocortin 2 receptor (MC2R), in these cells with a maximal effect between 30 and 60 min. Neither forskolin nor isoproterenol (in Y1 cells stably transfected with the beta(2)-adrenergic receptor) desensitize this ACTH response. ACTH desensitizes its receptor at concentrations at which only a fraction of receptors are occupied, implying that this mechanism acts on agonist-unoccupied receptors. Y1 cells express G protein-coupled receptor kinase (GRK) 2 and 5, but stable expression of a dominant negative GRK2 (K220W) only marginally reduces the desensitization by ACTH. The protein kinase A (PKA) inhibitor, H89, extinguishes almost the entire desensitization response over the initial 30-min period at all concentrations of ACTH. A mutant MC2R in which the single consensus PKA phosphorylation site has been mutated (S208A) when expressed in MC2R-negative Y6 cells is also unable to desensitize. These data imply a heterologous, PKA-dependent, mode of desensitization, which is restricted to agonist-occupied and -unoccupied MC2R, possibly as a consequence of receptor/effector complexes that functionally compartmentalize this receptor.
authors.affiliation: Department of Endocrinology, Barts & the London, Queen Mary, University of London, EC1A 7BE United Kingdom.
authors.forename: A H
authors.initials: AH
authors.lastname: Baig
authors.forename: F M
authors.initials: FM
authors.lastname: Swords
authors.forename: L A
authors.initials: LA
authors.lastname: Noon
authors.forename: P J
authors.initials: PJ
authors.lastname: King
authors.forename: L
authors.initials: L
authors.lastname: Hunyady
authors.forename: A J
authors.initials: AJ
authors.lastname: Clark
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D054774:G-Protein-Coupled Receptor Kinase 5; D005799:Genes, Dominant; D015151:Immunoblotting; D051379:Mice; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D018043:Receptors, Corticotropin / Q000737:chemistry* / Q000378:metabolism*; D044101:Receptors, Melanocortin; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D014162:Transfection; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D051552:beta-Adrenergic Receptor Kinases
chemical_list: D018076:DNA, Complementary; D018043:Receptors, Corticotropin; D044101:Receptors, Melanocortin; D010566:Virulence Factors, Bordetella; D000324:Adrenocorticotropic Hormone; D000242:Cyclic AMP; D017346:Protein Serine-Threonine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D051552:beta-Adrenergic Receptor Kinases; D054774:G-Protein-Coupled Receptor Kinase 5; C517895:Grk5 protein, mouse