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

Hepatocyte growth factor (HGF) induced motility of cultured mouse keratinocytes (308R cells). This HGF-induced cell motility was inhibited by microinjection of either rho GDI, an inhibitory GDP/GTP exchange protein for rho p21 small GTP-binding protein, or a botulinum exoenzyme C3 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 gamma S)-bound active form of rhoA p21, and the C3 action was prevented by comicroinjection with a rhoA p21 mutant (rhoA(Ile41) p21) which is resistant to the C3 action. The HGF-induced cell motility was not inhibited by microinjection of a dominant negative rac1 p21 mutant (rac1(Asn17) 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 dominant active Ki-ras p21 mutant (Ki-ras(Val12) p21) did not induce cell motility. These results indicate that both rho p21 and who GDI, but neither 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 alone did not induce cell motility in the absence of HGF, suggesting that activation of who p21 is necessary but not sufficient for the HGF-induced cell motility. The HGF-induced cell motility was mimicked by 12-O-tetradecanoylphorbol-13-acetate, a protein kinase C-activating phorbol ester, but not by Ca2+ ionophore. The phorbol ester-induced cell motility was also inhibited by microinjection of rho GDI or C3. These results indicate that both rho p21 and rho GDI are also involved in the phorbol ester-induced cell motility.