Cdc42Hs and Rac1 GTPases induce the collapse of the vimentin intermediate filament network

In this study we show that expression of active Cdc42Hs and Rac1 GTPases, t wo Rho family members, leads to the reorganization of the vimentin intermed iate filament (IF) network, showing a perinuclear collapse. Cdc42Hs display s a stronger effect than Rad as 90% versus 75% of GTPase-expressing cells s how vimentin collapse. Similar vimentin IF modifications were observed when endogenous Cdc42Hs was activated by bradykinin treatment, endogenous Rad b y platelet-derived growth factor/epidermal growth factor, or both endogenou s proteins upon expression of active RhoG. This reorganization of the vimen tin IF network is not associated with any significant increase in soluble v imentin. Using effector loop mutants of Cdc42Hs and Rac1, we show that the vimentin collapse is mostly independent of CRIB (Cdc42Hs or Rac-interacting binding)-mediated pathways such as JNK or PAK activation but is associated with actin reorganization. This does not result from F-actin depolymerizat ion, because cytochalasin D treatment or Scar-WA expression have merely no effect on vimentin organization. Finally, we show that genistein treatment of Cdc42 and Rac1-expressing cells strongly reduces vimentin collapse, wher eas staurosporin, wortmannin, LY-294002, R-p-cAMP, or RII, the regulatory s ubunit of protein kinase A, remain ineffective. Moreover, we detected an in crease in cellular tyrosine phosphorylation content after Cdc42Hs and Rad e xpression without modification of the vimentin phosphorylation status. Thes e data indicate that Cdc42Hs and Rad GTPases control vimentin IF organizati on involving tyrosine phosphorylation events.