Cdc42-dependent modulation of tight junctions and membrane protein trafficin polarized Madin-Darby canine kidney cells

Polarized epithelial cells maintain the asymmetric composition of their api cal and basolateral membrane domains by at least two different processes. T hese include the regulated trafficking of macromolecules from the biosynthe tic and endocytic pathway to the appropriate membrane domain and the abilit y of the tight junction to prevent free mixing of membrane domain-specific proteins and lipids. Cdc42, a Rho family GTPase, is known to govern cellula r polarity and membrane traffic in several cell types. We examined whether this protein regulated tight junction function in Madin-Darby canine kidney cells and pathways that direct proteins to the apical and basolateral surf ace of these cells. We used Madin-Darby canine kidney cells that expressed dominant-active or dominant-negative mutants of Cdc42 under the control of a tetracycline-repressible system. Here we report that expression of domina nt-active Cdc42N12 or dominant-negative Cdc42N17 altered tight junction fun ction. Expression of Cdc42N12 slowed endocytic and biosynthetic traffic, an d expression of Cdc42N17 slowed apical endocytosis and basolateral to apica l transcytosis but stimulated biosynthetic traffic. These results indicate that Cdc42 may modulate multiple cellular pathways required for the mainten ance of epithelial cell polarity.