title: Phosphorylation and functional desensitization of the alpha2A-adrenergic receptor by protein kinase C.
abstract: We have investigated the potential for protein kinase C (PKC) to phosphorylate and desensitize the alpha2A-adrenergic receptor (alpha2AAR). In whole-cell phosphorylation studies, recombinantly expressed human alpha2AAR displayed an increase in phosphorylation after short-term exposure to 100 nM phorbol 12-myristate-13-acetate (PMA) that was blocked by preincubation with a PKC inhibitor. This increase in receptor phosphorylation over basal amounted to 172 +/- 40% in COS-7 cells and 201 +/- 40% in Chinese hamster ovary cells. In permanently transfected Chinese hamster fibroblast cells, PKC activation by brief exposure of the cells to PMA resulted in a marked desensitization of alpha2AAR function, amounting to a 68 +/- 4% decrease in the maximal agonist (UK14304)-stimulated intracellular calcium release. Such desensitization was blocked by the PKC inhibitor bisindolylmaleimide I and was not evoked by an inactive phorbol ester. The desensitization of this agonist response was not caused by PKC-mediated augmentation of G protein-coupled receptor kinase activity, because PMA-promoted desensitization of a mutated alpha2AAR that lacked G protein-coupled receptor kinase phosphorylation sites was identical to that of wild-type alpha2AAR. To test whether PKC phosphorylation is a mechanism by which alpha2AAR can be regulated by other receptors, the alpha1bAR was co-expressed with the alpha2AAR in Chinese hamster ovary cells. Upon selective activation of alpha1bAR, the function of alpha2AAR underwent a 53 +/- 5% desensitization. Thus, cellular events that result in PKC activation promote phosphorylation of the alpha2AAR and lead to substantial desensitization of receptor function. This heterologous regulation also represents a mechanism by which rapid crosstalk between the alpha2AAR and other receptors can occur.
authors.affiliation: Department of Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0564, USA.
authors.forename: M
authors.initials: M
authors.lastname: Liang
authors.forename: M G
authors.initials: MG
authors.lastname: Eason
authors.forename: E A
authors.initials: EA
authors.lastname: Jewell-Motz
authors.forename: M A
authors.initials: MA
authors.lastname: Williams
authors.forename: C T
authors.initials: CT
authors.lastname: Theiss
authors.forename: G W
authors.initials: GW
authors.lastname: Dorn
authors.forename: S B
authors.initials: SB
authors.lastname: Liggett
mesh_terms: D000818:Animals; D016466:CHO Cells / Q000378:metabolism; D019556:COS Cells / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D006224:Cricetinae; D006801:Humans; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D018341:Receptors, Adrenergic, alpha-2 / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection
chemical_list: D018341:Receptors, Adrenergic, alpha-2; D011493:Protein Kinase C; D002118:Calcium