Rho family small GTPases, including Rho, Rac and cdc42, act as molecular switches, regulating processes such as cell migration, adhesion, proliferation and differentiation. They are activated by guanine nucleotide exchange factors, which catalyze the exchange of bound GDP for GTP, and inhibited by GTPase activating proteins, which catalyze the hydrolysis of GTP to GDP. A third level of regulation is provided by the stoichiometric binding of Rho GDP dissociation inhibitor. RhoA, RhoB and RhoC are highly homologous, but appear to have divergent biological functions. Carboxy-terminal modifications and differences in subcellular localization allow these three proteins to respond to and act on distinct signaling molecules.RhoB functions in the regulation of cell shape, migration and adhesion. RhoB activity has also been shown to play a role in protein trafficking and in CXCR2-mediated chemotaxis. Inhibition of RhoB activity downstream of PKCι influences the degree of invasion and migration by glioblastoma cells, and RhoB expression has a negative affect on tumor growth in ovarian cancer.
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