Members of the Rho family of Ras-related GTPases, such as ARHE, regulate the organization of the actin cytoskeleton in response to extracellular growth factors. Like Ras, Rho family members appear to cycle between an inactive GDP-bound form and an active GTP-bound form. Three major regulators of Rho activity have been identified: RhoGDIs, which interact with the GDP-bound Rho proteins to keep them in a resting complex; GEFs, which promote GDP/GTP exchange leading to activation of Rho proteins; and GAPs, which stimulate GTP hydrolysis and return the activated Rho protein to its inactive form |