ACTIVATION OF BOTH MAP KINASE AND PHOSPHATIDYLINOSITIDE 3-KINASE BY RAS IS REQUIRED FOR HEPATOCYTE GROWTH-FACTOR SCATTER FACTOR-INDUCED ADHERENS JUNCTION DISASSEMBLY

Hepatocyte growth factor/scatter factor (HGF/SF) stimulates the motili ty of epithelial cells, initially inducing centrifugal spreading of co lonies followed by disruption of cell-cell junctions and subsequent ce ll scattering. In Madin-Darby canine kidney cells, HGF/SF-induced moti lity involves actin reorganization mediated by Pas, but whether Pas an d downstream signals regulate the breakdown of intercellular adhesions has not been established. Both HGF/SF and V12Ras induced the loss of the adherens junction proteins E-cadherin and beta-catenin from interc ellular junctions during cell spreading, and the HGF/SF response was b locked by dominant-negative N17Ras. Desmosomes and tight junctions wer e regulated separately from adherens junctions, because they were not disrupted by V12Ras. MAP kinase, phosphatidylinositide 3-kinase (PI3-k inase), and Pac were required downstream of Pas, because loss of adher ens junctions was blocked by the inhibitors PD098059 and LY294002 or b y dominant-inhibitory mutants of MAP kinase kinase 1 or Rad. All of th ese inhibitors also prevented HGF/SF-induced cell scattering. Interest ingly, activated Raf or the activated p110 alpha subunit of PI 3-kinas e alone did not induce disruption of adherens junctions. These results indicate that activation of both MAP kinase and PIS-kinase by Pas is required for adherens junction disassembly and that this is essential for the motile response to HGF/SF.