Motility and invasion are differentially modulated by Rho family GTPases.

Cell migration in vivo often requires invasion through tissue matrices. Currently little is known regarding the signaling pathways that regulate cell invasion through three-dimensional matrices. The small GTPases Cdc42, Rac and Rho are key regulators of actin cytoskeletal and adhesive structures. We now show that expression of dominant negative forms of either Cdc42, Rac or Rho inhibited PDGF-BB-stimulated Rat1 fibroblast invasion into 3D collagen matrices, indicating that the activity of each of these GTPases is necessary for cell invasion. In contrast, only Rac activation was required for PDGF-BB-stimulated locomotion across a planar substrate in the Boyden chamber. Interestingly, PDGF-induced invasion was also strongly inhibited by expression of constitutively active forms of Cdc42 or Rho, and to a lesser extent by constitutively active Rac. We also show that constitutively active V12-Rac significantly stimulated basal Rat1 fibroblast invasion, independent of PI-3-kinase activity, and that this effect was suppressed by the effector mutant V12/H40-Rac. These results suggest that cellular invasion may require an optimal level of activation of Cdc42, Rho and Rac, and that migration and invasion are differentially modulated by Rho family GTPases.