Constitutive phosphorylation by protein kinase C regulates D1 dopamine receptor signaling.
The D(1) dopamine receptor (D(1) DAR) is robustly phosphorylated by multiple protein kinases, yet the phosphorylation sites and functional consequences of these modifications are not fully understood. Here, we report that the D(1) DAR is phosphorylated by protein kinase C (PKC) in the absence of agonist stimulation. Phosphorylation of the D(1) DAR by PKC is constitutive in nature, can be induced by phorbol ester treatment or through activation of Gq-mediated signal transduction pathways, and is abolished by PKC inhibitors. We demonstrate that most, but not all, isoforms of PKC are capable of phosphorylating the receptor. To directly assess the functional role of PKC phosphorylation of the D(1) DAR, a site-directed mutagenesis approach was used to identify the PKC sites within the receptor. Five serine residues were found to mediate the PKC phosphorylation. Replacement of these residues had no effect on D(1) DAR expression or agonist-induced desensitization; however, G protein coupling and cAMP accumulation were significantly enhanced in PKC-null D(1) DAR. Thus, constitutive or heterologous PKC phosphorylation of the D(1) DAR dampens dopamine activation of the receptor, most likely occurring in a context-specific manner, mediated by the repertoire of PKC isozymes within the cell.
Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-9405, USA.
Michele L
ML
Rankin
David R
DR
Sibley
D000595:Amino Acid Sequence; D000818:Animals; D004298:Dopamine / Q000378:metabolism / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D011493:Protein Kinase C / Q000502:physiology*; D051381:Rats; D017447:Receptors, Dopamine D1 / Q000819:agonists / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*
D017447:Receptors, Dopamine D1; D011493:Protein Kinase C; D004298:Dopamine