ACTIVATION OF BETA-1 INTEGRIN SIGNALING STIMULATES TYROSINE PHOSPHORYLATION OF P190(RHOGAP) AND MEMBRANE-PROTRUSIVE ACTIVITIES AT INVADOPODIA

The ligation of available alpha 6 beta 1 integrin in adherent LOX mela noma cells by laminin G peptides and integrin stimulatory antibodies i nduced cell invasiveness, independent of adhesion activity of integrin s that were prebound to extracellular matrix (Nakahara, H, Nomizu, M., Akiyama, S. K,, Yamada, Y., Yeh, Y., and Chen, W,-T, (1996) J. Biol. Chem. 271, 27221-27224). Here, we show that this induced invasion invo lves an increase in tyrosine phosphorylation of a 190-kDa GTPase-activ ating protein for Rho family members (p190(RhoGAP); p190) and membrane -protrusive activities at invadopodia, This tyrosine phosphorylation d oes not occur when the adherent cells are treated with non-activating antibody against pi integrin, control laminin peptides, or tyrosine ki nase inhibitors genistein and herbimycin A, Although p190 and F-actin co-distribute in all cell cortex extensions, tyrosine-phosphorylated p roteins including p190 appear to associate with F-actin specifically i n invadopodia. In addition, the localized matrix degradation and membr ane-protrusive activities were blocked by treatment of LOX cells with tyrosine kinase inhibitors as well as microinjection of antibodies dir ected against p190 but not by non-perturbing antibodies or control buf fers, We suggest that activation of the alpha 6 beta 1 integrin signal ing regulates the tyrosine phosphorylation state of p190 which in turn connects downstream signaling pathways through Rho family GTPases to actin cytoskeleton in invadopodia, thus promoting membrane-protrusive and degradative activities necessary for cell invasion.