Cdc42 regulates microtubule-dependent Golgi positioning.

The molecular mechanisms underlying cytoskeleton-dependent Golgi positioning are poorly understood. In mammalian cells, the Golgi apparatus is localized near the juxtanuclear centrosome via dynein-mediated motility along microtubules. Previous studies implicate Cdc42 in regulating dynein-dependent motility. Here we show that reduced expression of the Cdc42-specific GTPase-activating protein, ARHGAP21, inhibits the ability of dispersed Golgi membranes to reposition at the centrosome following nocodazole treatment and washout. Cdc42 regulation of Golgi positioning appears to involve ARF1 and a binding interaction with the vesicle-coat protein coatomer. We tested whether Cdc42 directly affects motility, as opposed to the formation of a trafficking intermediate, using a Golgi capture and motility assay in permeabilized cells. Disrupting Cdc42 activation or the coatomer/Cdc42 binding interaction stimulated Golgi motility. The coatomer/Cdc42-sensitive motility was blocked by the addition of an inhibitory dynein antibody. Together, our results reveal that dynein and microtubule-dependent Golgi positioning is regulated by ARF1-, coatomer-, and ARHGAP21-dependent Cdc42 signaling.