RhoA inactivation by p190RhoGAP regulates cell spreading and migration by promoting membrane protrusion and polarity

The binding of extracellular matrix proteins to integrins triggers rearrang ements in the actin cytoskeleton by regulating the Rho family of small GTPa ses. The signaling events that mediate changes in the activity of Rho prote ins in response to the extracellular matrix remain largely unknown. We have demonstrated in previous studies that integrin signaling transiently suppr esses RhoA activity through stimulation of p190RhoGAP. Here, we investigate d the biological significance of adhesion-dependent RhoA inactivation by ma nipulating p190RhoGAP signaling in Rat1 fibroblasts. The inhibition of RhoA activity that is induced transiently by adhesion was antagonized by expres sion of dominant negative p190RhoGAP. This resulted in impaired cell spread ing on a fibronectin substrate, reduced cell protrusion, and premature asse mbly of stress fibers. Conversely, overexpression of p190RhoGAP augmented c ell spreading. Dominant negative p190RhoGAP elevated RhoA activity in cells on fibronectin and inhibited migration, whereas overexpression of the wild -type GA-P decreased RhoA activity, promoted the formation of membrane prot rusions, and enhanced motility. Cells expressing dominant negative p190RhoG AP, but not control cells or cells overexpressing the wild-type GAP, were u nable to establish polarity in the direction of migration. Taken together, these data demonstrate that integrin-triggered RhoA inhibition by p190RhoGA P enhances spreading and migration by regulating cell protrusion and polari ty.