PHOSPHOINOSITIDE 3-KINASE INDUCES SCATTERING AND TUBULOGENESIS IN EPITHELIAL-CELLS THROUGH A NOVEL PATHWAY

Hepatocyte growth factor/scatter factor (HGF/SF) treatment of the Madi n-Darby canine kidney epithelial cell line causes scattering of cells grown in monolayer culture and the formation of branching tubules by c ells grown in collagen gels. HGF/SF causes prolonged activation of bot h the mitogen-activated protein (MAP) kinase extracellular signal-regu lated kinase 2 (ERK2) and the phosphoinositide 3-OH kinase (PI 3-kinas e) target protein kinase B (PKB)/ Akt; inhibition of either the MAP ki nase pathway by the MAP kinase/ERK kinase inhibitor PD98059 or the PI 3-kinase pathway by LY294002 blocks HGF/SF induction of scattering, al though in morphologically distinct ways. Expression of constitutively activated PI 3-kinase, Pas, or R-Ras will cause scattering, but activa ted Raf will not, indicating that activation of the MAP kinase pathway is not sufficient for this response. Downstream of PI 3-kinase, activ ated PKB/Akt and Pac are both unable to induce scattering, implicating a novel pathway. Scattering induced by Pas or PI 3-kinase is sensitiv e to PD98059, as well as to LY294002, suggesting that basal MAP kinase activity is required, but not sufficient, for the scattering response . Induction of MDCk cell tubulogenesis in collagen gels by HGF/SF is i nhibited by PD98059; expression of activated Pas and Raf causes disorg anized growth in this system, but activated PI 3-kinase or R-Ras cause s branching tubule formation similar to that seen with HGF/SF treatmen t. These data indicate that multiple signaling pathways acting downstr eam of Met and Pas are needed for these morphological effects; scatter ing is induced primarily by the PI 3-kinase pathway, which acts throug h effecters, other than PKB/Akt or Pac and requires at least basal MAP kinase function. Elevated PI 3-kinase activity induces tubulogenesis, but total inhibition and excess activation of the MAP kinase pathway both oppose this effect.