Phosphorylation of CPI-17, an inhibitory phosphoprotein of smooth muscle myosin phosphatase, by Rho-kinase

Phosphorylation of CPI-17 by Rho-associated kinase (Rho-kinase) and its eff ect on myosin phosphatase (MP) activity were investigated. CPI-17 was phosp horylated by Rho-kinase to 0.92 mol of P/mol of CPI-17 in vitro. The inhibi tory phosphorylation site was Thr(38) (as reported previously) and was iden tified using a point mutant of CPI-17 and a phosphorylation state-specific antibody. Phosphorylation by Rho-kinase dramatically increased the inhibito ry effect of CPI-17 on MP activity. Thus, CPI-17 as a substrate of Rho-kina se could be involved in the Ca2+ sensitization of smooth muscle contraction as a downstream effector of Rho-kinase. (C) 2000 Federation of European Bi ochemical Societies. Published by Elsevier Science B.V. All rights reserved .