Cdc42 controls secretory and endocytic transport to the basolateral plasmamembrane of MDCK cells

Cdc42 is a Rho-family GTPase that in yeast is important in establishing pol arized bud growth. Here we show that Cdc42 is also essential in establishin g and maintaining polarity in epithelial cells. Functional deletion of Cdc4 2 in Madin-Darby canine kidney (MDCK) cells results in the selective depola rization of basolateral membrane proteins; the polarity of apical proteins remains unaffected. This phenotype does not reflect major alterations in th e actin cytoskeleton, but rather results from the selective inhibition of m embrane traffic to the basolateral plasma membrane in both the endocytic an d the secretory pathways. Thus, Cdc42 plays a critical part in epithelial-c ell polarity, by, unexpectedly, regulating the fidelity of membrane transpo rt.