An 11-Amino Acid Sequence from c-met Initiates Epithelial Chemotaxis via Phosphatidylinositol 3-Kinase and Phospholipase C (*)

Abstract

Interaction of hepatocyte growth factor with its high affinity receptor c-met initiates a cascade of intracellular events leading to epithelial motility. An 11-amino acid sequence from the c-met receptor has been found to cause cell transformation in transfected fibroblasts (Ponzetto, C., Bardelli, A., Zhen, Z., Maina, F., Dalla, Z. P., Giordano, S., Graziani, A., Panayotou, G., and Comoglio, P. M.(1994) Cell 77, 261-271). We inserted this sequence into a mutant platelet-derived growth factor receptor (F5) to determine if this region of c-met can initiate cell motility and which signaling pathways it activates. The platelet-derived growth factor (PDGF) receptor/c-met hybrid (F5 met) initiated PDGF-dependent chemotaxis in renal epithelial cells (8.0 ± 2.3 versus 70.5 ± 4.8 cells/mm²), while the parental construct, F5, did not. Addition of PDGF to cells expressing F5 met caused activation of the phosphatidylinositol (PI) 3-kinase (control 2.0 ± 0.8, +PDGF 17.1 ± 5.1, n = 3, p < 0.05) and phospholipase C (control 478.5 ± 67 dpm/well, +PDGF 1049.3 ± 93, n = 4, p = 0.003), while neither pathway was activated in cells expressing F5. The chemotactic response of F5 met was inhibited by both the PI 3-kinase inhibitor wortmannin and the phospholipase C inhibitor U-71322. Selective activation of the PI 3-kinase utilizing a PDGF receptor mutant (F3) containing the native high affinity PI 3-kinase binding site also resulted in PDGF stimulated chemotaxis, although less than that generated by the c-met sequence.

These findings demonstrate that the 11-amino acid sequence from c-met initiates epithelial motility via coincident activation of the PI 3-kinase and phospholipase C and that selective activation of the PI 3-kinase can initiate a partial chemotactic response.