THE RAS-RELATED PROTEIN CDC42HS AND BRADYKININ PROMOTE FORMATION OF PERIPHERAL ACTIN MICROSPIKES AND FILOPODIA IN SWISS 3T3 FIBROBLASTS

The Ras-related protein Cdc42 plays a role in yeast cell budding and p olarity. Two related proteins, Rad and RhoA, promote formation in mamm alian cells of membrane ruffles and stress fibers, respectively, which contain actin microfilaments. We now show that microinjection of the related human Cdc42Hs into Swiss 3T3 fibroblasts induced the formation of peripheral actin microspikes, determined by staining,vith phalloid in. A proportion of these microspikes was found to be components of fi lopodia, as analyzed by time-lapse phase-contrast microscopy. The form ation of filopodia was also found to be promoted by Cdc42Hs microinjec tion. This was followed by activation of Rad-mediated membrane rufflin g. Treatment with bradykinin also promoted formation of microspikes an d filopodia as well as subsequent effects similar to that seen upon Cd c42Hs microinjection. These effects of bradykinin were specifically in hibited by prior microinjection of dominant negative Cdc42Hs(T17N), su ggesting that bradykinin acts by activating cellular Cdc42Hs. Since fi lopodia have been ascribed an important sensory function in fibroblast s and are required for guidance of neuronal grow-th cones, these resul ts indicate that Cdc42Hs plays an important role in determining mammal ian cell morphology.