PIP3 inhibition of RGS protein and its reversal by Ca2+/calmodulin mediate voltage-dependent control of the G protein cycle in a cardiac K+ channel.
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.
Ishii
Masaru
M
Department of Pharmacology II, Graduate School of Medicine, Osaka University, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan.
Inanobe
Atsushi
A
Kurachi
Yoshihisa
Y
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002147:Calmodulin / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000502:physiology*; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*; D020710:RGS Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D051381:Rats; D011921:Rats, Inbred WKY
D002147:Calmodulin; D010716:Phosphatidylinositols; D015221:Potassium Channels; D020710:RGS Proteins; C118303:phosphoinositide-3,4,5-triphosphate; C098799:RGS4 protein; D019204:GTP-Binding Proteins; D002118:Calcium