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 (MIM 190020), 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 (see MIM 601925); GEFs, which promote GDP/GTP exchange leading to activation of Rho proteins (see MIM 601855); and GAPs, which stimulate GTP hydrolysis and return the activated Rho protein to its inactive form (see MIM 602680) (Nobes et al., 1998 [PubMed 9531558]).