Rho is a member of the Ras-related family of small molecular weight GTP-binding 
proteins, and Rho works as a molecular switch by shuttling between the GDP-bound 
inactive form and the GTP-bound active form. Rho is involved in cell motility, 
cell adhesion, and cytokinesis through the reorganization of the actin 
cytoskeleton. In addition to this, Rho also regulates Ras-induced 
transformation, transcriptional activation and cell cycle progression. These 
actions through the Rho signaling are mediated by downstream Rho effectors. 
Several putative Rho effectors including ROCK and mDia have been isolated on the 
basis of their selective binding to the GTP-bound form of Rho. Among them, the 
ROCK family of Rho-associated serine/threonine protein kinases inactivates 
myosin phosphatase and actin depolymerizing factor (cofilin/Destrin) to induce 
stabilization of filamentous actin and increase in the actomyosin-based 
contractility. mDia binds profilin likely to promote actin polymerization. Thus, 
these effectors are supposed to work in organization of the actin cytoskeleton. 
Furthermore, analyses using a ROCK specific inhibitor Y-27632 have suggested 
that the Rho-ROCK pathway works in contractions of vascular smooth muscles and 
is involved in malignant cell transformation and tumor invasion and metastasis.