DIFFERENTIAL REQUIREMENT OF GRB2 AND PI3-KINASE IN HCF SF-INDUCED CELL MOTILITY AND TUBULOGENESIS/

Hepatocyte growth factor/scatter factor (HGF/SF) is a multifunctional cytokine that induces mitogenesis, motility, invasion, and morphogenes is of several epithelial and endothelial cell lines in culture. The re ceptor for HGF/SF has been identified as the Met tyrosine kinase. To i nvestigate the signaling pathways that are involved in these events, w e have generated chimeric receptors containing the extracellular domai n of the colony stimulating factor-1 (CSF-1) receptor fused to the tra nsmembrane and intracellular domains of the Met receptor (MET). Madin- Darby canine kidney (MDCK) epithelial cells, expressing the CSF-MET ch imera dissociate, scatter and form branching tubules in response to CS F-1. However, cells expressing a mutant CSF-MET receptor containing a phenylalanine substitution for tyrosine 1356 (Y1356F) are unable to sc atter or form branching tubules following stimulation with CSF-1. Tyro sine 1356 is essential for the recruitment of multiple substrates incl uding Grb2, the p85 subunit of PI3-kinase, and PLC gamma. To investiga te the role of these signaling pathways, Lye have generated a mutant r eceptor that selectively fails to associate with Grb2, and have treate d MDCK cells with potent inhibitors of PLC gamma, PI3-kinase, and p70( S6K), a downstream target of PI3-kinase. Our results implicate pathway s downstream from PI3-kinase in cell dissociation and scatter, whereas pathways downstream from Grb2 are required for branching tubulogenesi s in MDCK cells. (C) 1997 Wiley-Liss, Inc.