Sustained recruitment of phospholipase C-gamma to Gab1 is required for HGF-induced branching tubulogenesis

A distinctive property of Hepatocyte Growth Factor (HGF) is its ability to induce differentiation of tubular structures from epithelial and endothelia l cells (branching tubulogenesis), The HGF receptor directly activates PI3 kinase, Ras and STAT signalling pathways and phosphorylates the adaptator G RB2 Associated Binder-1 (Gab1), Gab1 is also phosphorylated in response to Epidermal Growth Factor (EGF) but is unable to induce tubule formation. Com parison of P-32-peptide maps of Gab1 from EGF- versus HGF-treated cells, de monstrates that the same sites are phosphorylated in vivo. However, while b oth EGF and HGF induce rapid tyrosine phosphorylation of Gab1 with a peak a t 15 min, the phosphorylation persists for over 1 h, only in response to HG F. Nine tyrosines are phosphorylated by both receptors, Three of them (Y307 , Y373, Y407) bind phospholipase C-gamma (PLC-gamma), Interestingly, the ov erexpression of a Gab1 mutant unable to bind PLC-gamma (Gab1 Y307/373/407F) did not alter HGF-stimulated cell scattering, only partially reduced the g rowth stimulation but completely abolished HGF-mediated tubulogenesis, It i s concluded that sustained recruitment of PLC gamma to Gab1 plays an import ant role in branching tubulogenesis.