Active Rho kinase (ROK-α) associates with insulin receptor substrate-1 and inhibits insulin signaling in vascular smooth muscle cells

Recent studies from our laboratory have shown that insulin stimulates myosin-bound phosphatase (MBP) in vascular smooth muscle cells (VSMCs) by decreasing site-specific phosphorylation of the myosin-bound subunit (MBS) of MBP via nitric oxide/cGMP-mediated Rho/Rho kinase inactivation. Here we tested potential interactions between Rho kinase and insulin signaling pathways. In control VSMCs, insulin inactivates ROK-alpha, the major Rho kinase isoform in VSMCs, and inhibits thrombin-induced increase in ROK-alpha association with the insulin receptor substrate-1 (IRS-1). Hypertension (in spontaneous hypertensive rats) or expression of an active RhoA(V14) up-regulates Rho kinase activity and increases ROK-alpha/IRS-1 association resulting in ERS-1 serine phosphorylation that leads to inhibition of both insulin-induced IRS-1 tyrosine phosphorylation and phosphatidylinositol 3-kinase (P13-kinase) activation. In contrast, expression of dominant negative RhoA or cGMP-dependent protein kinase type Ialpha inactivates Rho kinase, abolishes ROK-alpha/IRS-1 association, and potentiates insulin-induced tyrosine phosphorylation and P13-kinase activation leading to decreased MBST695. phosphorylation and decreased MBP inhibition. Collectively, these results suggest a novel function for ROK-alpha in insulin signal transduction at the level of IRS-1 and potential cross-talk between cGMP-dependent protein kinase type Ialpha, Rho/Rho kinase signaling, and insulin signaling at the level of ERS-I/P13-kinase.