Phosphorylation of RGS5 protein by protein kinase C

• Published in: Japanese Journal of Pharmacology 2001, Vol.85 (suppl.1), p.178-178
• Main Authors: Kayoko Moroi, Mariko Nishiyama, Motoko Satoh, Hirokazu Usui, Sadao Kimura
• Format: Article
• Language: Japanese
• ISSN: 0021-5198

RGS (regulator of G-protein signaling) proteins bind to G α subunits, serve as GTPase-activating proteins (GAPs) for them, and negatively regulate G protein-coupled receptor signaling. In this study, we examined phosphorylation of RGS5 as a possible mechanism of regulation of RGS5 activity. RGS5 protein was phosphorylated by HEK 293 (HEK) cell membrane and cytosolic fractions time- and concentration-dependently. The phosphorylation was potentiated by PMA and phosphatidylserine, and inhibited by protein kinase C (PKC) inhibitors, indicating that RGS5 was phosphorylated by PKC. RGS5 protein was phosphorylated by purified PKC and only serine residues were identified as the phosphorylated amino acid. After phosphorylation by PKC, the binding of RGS5 protein to G-protein α subunits (Gi3 α and Gq α) in HEK cell membranes was lowered considerably. Phosphorylation of RGS5 by PKC was markedly reduced when serine 84 and 166, putative phosphorylation sites by PKC, were substituted by alanine. In addition, when serine 166 was substituted by aspartic acid, to mimic the phospho-serine, the mutant RGS5 abolished the ability to bind to G α subunits and GAP activity toward Gi3 α subunit. These results suggest that phosphorylation of RGS5 by PKC may reduce the function of RGS5 as a negative regulator of G-protein-coupled receptor signaling.