title: Differential desensitization and phosphorylation of three cloned and transfected alpha 2-adrenergic receptor subtypes.
abstract: Genes encoding 3 distinct subtypes of human alpha 2-adrenergic receptor are known and are found, respectively, on chromosome 10, 4, and 2 (alpha 2-C10, alpha 2-C4, and alpha 2-C2 adrenergic receptors). All 3 receptors inhibit adenylyl cyclase via Gi proteins. To study and compare their regulatory properties we assessed the ability of each to undergo agonist-promoted desensitization and phosphorylation. When Chinese hamster ovary cells stably expressing each of the three receptor genes were incubated with epinephrine for 20 min, a marked decrease in sensitivity to subsequent agonist-mediated inhibition of adenylyl cyclase was observed for the alpha 2-C10 and alpha 2-C2 receptors but not for the alpha 2-C4 receptors. When similar incubations were performed with 32Pi-labeled cells and the receptors were immunoprecipitated with specific antibodies, alpha 2-C10 and alpha 2-C2 receptors were found to undergo an approximately 3-fold increase in receptor phosphorylation after epinephrine exposure. When transfected into COS cells epinephrine also stimulated phosphorylation of alpha 2-C10 and alpha 2-C2 receptors while having only a slight effect on alpha 2-C4 receptors. Cotransfection of the cells with the cDNA encoding the beta-adrenergic receptor kinase further increased receptor phosphorylation for alpha 2-C10 and alpha 2-C2 receptors while having little or no effect on alpha 2-C4 receptors. Moreover purified and reconstituted recombinant alpha 2-C10 receptors could be phosphorylated in an agonist-dependent fashion whereas alpha 2-C4 receptors could not. These observations suggest receptor subtype-specific differences in susceptibility to regulatory phosphorylation and desensitization.
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710.
authors.forename: H
authors.initials: H
authors.lastname: Kurose
authors.forename: R J
authors.initials: RJ
authors.lastname: Lefkowitz
mesh_terms: D000067956:Adenylyl Cyclase Inhibitors; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D000068438:Brimonidine Tartrate; D016466:CHO Cells; D002460:Cell Line; D003001:Cloning, Molecular; D005576:Colforsin / Q000494:pharmacology; D006224:Cricetinae; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009638:Norepinephrine / Q000494:pharmacology*; D010710:Phosphates / Q000378:metabolism; D010766:Phosphorylation; D011810:Quinoxalines / Q000494:pharmacology; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism; D014162:Transfection
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D000316:Adrenergic alpha-Agonists; D010710:Phosphates; D011810:Quinoxalines; D018341:Receptors, Adrenergic, alpha-2; D011994:Recombinant Proteins; D005576:Colforsin; D000068438:Brimonidine Tartrate; D009638:Norepinephrine