cdc42 regulates the exit of apical and basolateral proteins from the trans-Golgi network

It is well established that Rho-GTPases regulate vesicle fusion and fission events at the plasma membrane through their modulatory role on the cortica l actin cytoskeleton. In contrast, their effects on intracellular transport processes and actin pools are less clear. It was recently shown that cdc42 associates with the Golgi apparatus in an ARF-dependent manner, similarly to coat proteins involved in vesicle formation and to several actin-binding proteins. We report here that mutants of cdc42 inhibited the exit of basol ateral proteins from the trans-Golgi network (TGN), while stimulating the e xit of an apical marker, in two different transport assays. This regulation may result from modulation of the actin cytoskeleton, as GTPase-deficient cdc42 depleted a perinuclear actin pool that rapidly exchanges with exogeno us fluorescent actin.