title: Agonist-dependent phosphorylation of the mouse delta-opioid receptor: involvement of G protein-coupled receptor kinases but not protein kinase C.
abstract: With chronic opiate use, opioid receptor desensitization may be one of the important mechanisms underlying the development of opiate tolerance and addiction. Opioid receptors belong to the G protein-coupled receptor superfamily. In this study, the mouse delta-opioid receptor (delta OR) was used in a model system to investigate the role of opioid receptor phosphorylation in receptor desensitization. When expressed in 293 cells and exposed to agonist, the delta OR underwent receptor-specific desensitization within 10 min. This agonist-induced desensitization corresponded temporally to a 3-fold increase in receptor phosphorylation. Phorbol ester, but not forskolin, also stimulated phosphorylation of the delta OR in 293 cells. Although down-regulation of protein kinase C failed to affect agonist-induced receptor phosphorylation, it abolished phorbol ester-induced receptor phosphorylation. Agonist-induced delta OR phosphorylation must therefore involve kinases other than protein kinase C. Whereas overexpression of a dominant negative mutant (K220R) of beta-adrenergic receptor kinase-1 (beta ARK1) in 293 cells significantly reduced agonist-dependent phosphorylation of the delta OR, overexpression of beta ARK1 or G protein-coupled receptor kinase-5 significantly enhanced this phosphorylation. Concordantly, beta ARK1-K220R overexpression reduced agonist-dependent delta OR desensitization, whereas beta ARK1 overexpression enhanced this densensitization. We conclude that short term desensitization of the delta OR involves phosphorylation of the receptor by one or more G protein-coupled receptor kinases.
authors.affiliation: Howard Hughes Medical Institute, Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: G
authors.initials: G
authors.lastname: Pei
authors.forename: B L
authors.initials: BL
authors.lastname: Kieffer
authors.forename: R J
authors.initials: RJ
authors.lastname: Lefkowitz
authors.forename: N J
authors.initials: NJ
authors.lastname: Freedman
mesh_terms: D000700:Analgesics / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins / Q000494:pharmacology; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D051379:Mice; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D017465:Receptors, Opioid, delta / Q000819:agonists* / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D051552:beta-Adrenergic Receptor Kinases
chemical_list: D000700:Analgesics; D004745:Enkephalins; D017465:Receptors, Opioid, delta; D020881:Enkephalin, D-Penicillamine (2,5)-; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D051552:beta-Adrenergic Receptor Kinases; D019204:GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate