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 motility of epithelial cells, initially inducing centrifugal spreading of colonies followed by disruption of cell-cell junctions and subsequent cell scattering. In Madin-Darby canine kidney cells, HGF/SF-induced motility involves actin reorganization mediated by Pas, but whether Pas and 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 intercellular junctions during cell spreading, and the HGF/SF response was blocked by dominant-negative N17Ras. Desmosomes and tight junctions were regulated separately from adherens junctions, because they were not disrupted by V12Ras. MAP kinase, phosphatidylinositide 3-kinase (PI3-kinase), and Pac were required downstream of Pas, because loss of adherens junctions was blocked by the inhibitors PD098059 and LY294002 or by dominant-inhibitory mutants of MAP kinase kinase 1 or Rad. All of these inhibitors also prevented HGF/SF-induced cell scattering. Interestingly, activated Raf or the activated p110 alpha subunit of PI 3-kinase 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.