REGULATION OF MYOSIN PHOSPHATASE BY RHO AND RHO-ASSOCIATED KINASE (RHO-KINASE)

The small guanosine triphosphatase Rho is implicated in myosin light c hain (MLC) phosphorylation, which results in contraction of smooth mus cle and interaction of actin and myosin in nonmuscle cells. The guanos ine triphosphate (GTP)-bound, active form of RhoA (GTP . RhoA) specifi cally interacted with the myosin-binding subunit (MBS) of myosin phosp hatase, which regulates the extent of phosphorylation of MLC. Rho-asso ciated kinase (Rho-kinase), which is activated by GTP . RhoA, phosphor ylated MBS and consequently inactivated myosin phosphatase. Overexpres sion of RhoA or activated RhoA in NIH 3T3 cells increased phosphorylat ion of MBS and MLC. Thus, Rho appears to inhibit myosin phosphatase th rough the action of Rho-kinase.