부산대학교 도서관

Excitatory receptor agonists such as noradrenaline stimulate the activity of the small G protein Rho and inhibit myosin phosphatase (MP) through mechanisms involving Rho kinase-dependent phosphorylation of the MP regulatory subunit MYPT1 in VSM. We have recently demonstrated that a novel, Ca2+-dependent mechanism for Rho activation and myosin phosphatase (MP) inhibition is operating in receptor agonist- and membrane depolarization-induced vascular smooth muscle (VSM) contraction. We found that phosphoinositide 3-kinase (PI3K) was required for Ca2+-dependent Rho activation; the PI3K inhibitors wortmannin and LY294002 inhibited all of the Ca2+-dependent Rho activation, MYPT1 phosphorylation, MP inhibition, MLC phosphorylation and contraction. We tried to identify a PI3K isoform by adopting RNA interference and cultured VSM cells. The selective down-regulation of the expression of class II alfa isoform (PI3K-C2&alpha), but not the class I p110&alpha, by a specific siRNA markedly inhibited Rho kinase-dependent MYPT1 phosphorylation, MLC phosphorylation and contraction in differentiated VSM cultures. Noradrenaline as well as membrane depolarization stimulated the activity of PI3K-C2&alpha, but not p110&alpha, in a Ca2+-dependent manner. Thus, these observations unveiled a novel role of the PI3K-C2&alpha as an upstream regulator of Rho and consequently MP and contraction. [J Physiol Sci. 2006;56 Suppl:S41]