RHO-MEDIATED PROTEIN-TYROSINE PHOSPHORYLATION IN LYSOPHOSPHATIDIC-ACID-INDUCED TUMOR-CELL INVASION

Rat ascites hepatoma cells (MM1) invade a mesothelial cell monolayer i n vitro in assay medium containing serum, but not in serum-free medium . Serum could be completely replaced by 1-oleoyl lysophosphatidic acid (LPA) in inducing invasion. LPA-induced invasion was inhibited by gen istein, a tyrosine-kinase inhibitor. Protein tyrosine phosphorylation in response to LPA was thus analyzed in order to determine the molecul ar mechanism of invasion. LPA of invasion-inducible concentrations evo ked a transient increase in tyrosine phosphorylation, mainly of 110- t o 130-kDa proteins in MM1 cells but not in mesothelial cells. These co ncentrations of LPA were over 10 times higher (10 to 25 mu M) than tho se necessary to produce a variety of biological actions, such as tyros ine phosphorylation in fibroblasts, neurite retraction and platelet ag gregation. Protein tyrosine phosphorylation and invasion by MM1 cells induced by LPA are largely regulated by rho p21, because both were inh ibited by Clostridium botulinum C3 exo-enzyme, which is known to speci fically inactivate rho p21. Invasion of MCL by MM1 cells induced by se rum and that by B16FE7 cells induced by LPA were inhibited by genistei n or C3 as well. By immunoprecipitation, we detected p125 focal adhesi on kinase (FAK) as a major protein of 110- to 130-kDa tyrosine phospho rylated in response to LPA. Tyrosine phosphorylation of paxillin by LP A was also detected. (C) 1996 Wiley-Liss, Inc.