Point mutation in FGF receptor eliminates phosphatidylinositol hydrolysis without affecting mitogenesis

Abstract

STIMULATION of growth factor receptors with tyrosine kinase activity is followed by rapid receptor dimerization, tyrosine autophosphorylation and phosphorylation of signalling molecules such as phospholipase C_γ(PLC_γ) and the ros GTPase-activating protein^1,2. PLC_γ and GTPase-activating protein bind to specific tyrosine-phosphorylated regions in growth factor receptors^3–9through their sir-homologous SH2 domains^7,8,10,11. Growth factor-induced tyrosine phosphorylation of PLC_γ is essential for stimulation of phosphatidylinositol hydrolysis in vitro¹² and in vivo¹³. We have shown that a short phosphorylated peptide containing tyrosine at position 766 from a conserved region^14–18 of the fibre-blast growth factor (FGF) receptor is a binding site for the SH2 domain of PLC_γ (ref. 8). Here we show that an FGF receptor point mutant in which Tyr766 is replaced by a phenylalanine residue (Y766F) is unable to associate with and tyrosine-phosphorylate PLC_γ or to stimulate hydrolysis of phosphatidylinositol. Nevertheless, the Y766F FGF receptor mutant can be autophos-phorylated, and can phosphorylate several cellular proteins and stimulate DNA synthesis. Our data show that phosphorylation of the conserved Tyr 766 of the FGF receptor is essential for phosphorylation of PLC_γ and for hydrolysis of phosphatidylinositol, but that elimination of this hydrolysis does not affect FGF-induced mitogenesis.