Motility and invasion are differentially modulated by Rho family GTPases

Cell migration in vivo often requires invasion through tissue matrices. Cur rently little is known regarding the signaling pathways that regulate cell invasion through three-dimensional matrices. The small GTPases Cdc42, Rac a nd Rho are key regulators of actin cytoskeletal and adhesive structures. We now show that expression of dominant negative forms of either Cdc42, Rac o r Rho inhibited PDGF-BB-stimulated Rat1 fibroblast invasion into 3D collage n matrices, indicating that the activity of each of these GTPases is necess ary for cell. invasion, In contrast, only Rac activation was required for P DGF-BB-stimulated locomotion across a planar substrate in the Boyden chambe r. Interestingly, PDGF-induced invasion was also strongly inhibited by expr ession of constitutively active forms of Cdc42 or Rho, and to a lesser exte nt by constitutively active Rac, We also show that constitutively active V1 2-Rac significantly stimulated basal Rat1 fibroblast invasion, independent of PI-3-kinase activity, and that this effect was suppressed by the effecto r mutant V12/N40-Rac. These results suggest that cellular invasion may requ ire an optimal level of activation of Cdc42, Rho and Rac, and that migratio n and invasion are differentially modulated by Rho family GTPases.