Inhibition of ROCK by RhoE.

RhoE belongs to the Rnd subfamily of small Rho-related GTP-binding proteins. Similar to other Rho proteins, RhoE regulates actin cytoskeleton dynamics. Expression of RhoE induces loss of actin stress fibers, and it also increases cell migration speed. In part, this is due to RhoE interaction with the RhoA effector ROCK I, a serine/threonine kinase that regulates the formation and contractility of stress fibers. Interestingly, RhoE does not interact with the highly homologous kinase ROCK II. RhoE binding inhibits ROCK I from phosphorylating its downstream target myosin light chain phosphatase, thus increasing the activity of the phosphatase to dephosphorylate myosin II, which results in reduced actomyosin contractility. RhoE itself is phosphorylated by ROCK I, and this may enhance RhoE regulation of ROCK I function. This chapter describes the method used for studying ROCK inhibition by RhoE.