Ishii Masaru, Inanobe Atsushi, Kurachi Yoshihisa
Department of Pharmacology II, Graduate School of Medicine, Osaka University, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan.
Proc Natl Acad Sci U S A. 2002 Apr 2;99(7):4325-30. doi: 10.1073/pnas.072073399. Epub 2002 Mar 19.
Regulators of G protein signaling (RGS) accelerate intrinsic GTP hydrolysis on alpha subunits of trimeric G proteins and play crucial roles in the physiological regulation of G protein-mediated cell signaling. The control mechanisms of the action of RGS proteins per se are poorly clarified, however. We recently showed a physiological mode of action of a RGS protein in cardiac myocytes. The voltage-dependent formation of Ca2+/calmodulin facilitated the GTPase activity of RGS by an unidentified mechanism, which underlay the "relaxation" behavior of G protein-gated K+ (K(G)) channels. Here we report the mechanism which is the reversal by Ca2+/calmodulin of phosphatidylinositol-3,4,5,-trisphosphate (PIP3)-mediated inhibition of RGS. Purified RGS4 protein alone inhibited GTP-induced K(G) channel activity in inside-out patches from atrial myocytes. The inhibitory effect of RGS4 was reduced by PIP3 and restored by addition of Ca2+/calmodulin. The intracellular application of anti-PIP3 antibody abolished the RGS-dependent relaxation behavior of K(G) current in atrial myocytes. This study, therefore, reveals a general physiological control mechanism of RGS proteins by lipid-protein interaction.
G蛋白信号调节因子（RGS）可加速三聚体G蛋白α亚基上的内源性GTP水解，并在G蛋白介导的细胞信号传导的生理调节中发挥关键作用。然而，RGS蛋白本身作用的控制机制尚不清楚。我们最近展示了一种RGS蛋白在心肌细胞中的生理作用模式。电压依赖性的Ca2+/钙调蛋白形成通过一种未知机制促进了RGS的GTP酶活性，这是G蛋白门控K+（K(G)）通道“舒张”行为的基础。在此，我们报告了Ca2+/钙调蛋白逆转磷脂酰肌醇-3,4,5-三磷酸（PIP3）介导的RGS抑制作用的机制。单独纯化的RGS4蛋白可抑制来自心房肌细胞的内向外膜片中GTP诱导的K(G)通道活性。PIP3可降低RGS4的抑制作用，添加Ca2+/钙调蛋白可恢复该作用。细胞内应用抗PIP3抗体可消除心房肌细胞中K(G)电流的RGS依赖性舒张行为。因此，本研究揭示了通过脂-蛋白相互作用对RGS蛋白进行普遍生理控制的机制。
