Rho proteins: Linking signaling with membrane trafficking

Rho proteins are well known for their effects on the actin cytoskeleton, an d are activated in response to a variety of extracellular stimuli. Several Rho family members are localized to vesicular compartments, and increasing evidence suggests that they play important roles in the trafficking of vesi cles on both endocytic and exocytic pathways. In particular, RhoA, RhoB, Rh oD, Rac and Cdc42 have been shown to affect various steps of membrane traff icking. The underlying molecular basis for these effects of Rho proteins ar e incompletely understood, but in the case of Cdc42 it appears that it can drive vesicle movement through Arp2/3 complex-mediated actin polymerization at the surface of the vesicle. This is similar to what is believed to happ en when Rac and Cdc42 stimulate actin polymerization at the plasma membrane . Rho proteins may also affect membrane trafficking by altering phosphatidy linositide composition of membrane compartments, or through interactions wi th microtubules.