INVOLVEMENT OF RHO-P21 SMALL GTP-BINDING PROTEIN AND ITS REGULATOR INTHE HGF-INDUCED CELL MOTILITY

Hepatocyte growth factor (HGF) induced motility of cultured mouse kera tinocytes (308R cells). This HGF-induced cell motility was inhibited b y microinjection of either rho GDI, an inhibitory GDP/GTP exchange pro tein for rho p21 small GTP-binding protein, or a botulinum exoenzyme C 3 which is known to selectively impair the function of who p21 by ADP- ribosylating its effector domain. The rho GDI action was prevented by comicroinjection with the guanosine 5'-(3-O-thio)triphosphate (GTP gam ma S)-bound active form of rhoA p21, and the C3 action was prevented b y comicroinjection with a rhoA p21 mutant (rhoA(Ile41) p21) which is r esistant to the C3 action. The HGF-induced cell motility was not inhib ited by microinjection of a dominant negative rac1 p21 mutant (rac1(As n17) p21) or a dominant negative Ki-ras p21 mutant (Ki-ras(Asn17) p21) . Microinjection of the GTP gamma S-bound form of rac1 p21 or a domina nt active Ki-ras p21 mutant (Ki-ras(Val12) p21) did not induce cell mo tility. These results indicate that both rho p21 and who GDI, but neit her rac p21 nor ras p21, are involved in the HGF-induced cell motility . However, microinjection of the GTP gamma S-bound form of rhoA p21 al one did not induce cell motility in the absence of HGF, suggesting tha t activation of who p21 is necessary but not sufficient for the HGF-in duced cell motility. The HGF-induced cell motility was mimicked by 12- O-tetradecanoylphorbol-13-acetate, a protein kinase C-activating phorb ol ester, but not by Ca2+ ionophore. The phorbol ester-induced cell mo tility was also inhibited by microinjection of rho GDI or C3. These re sults indicate that both rho p21 and rho GDI are also involved in the phorbol ester-induced cell motility.