Point mutation in FGF receptor eliminates phosphatidylinositol hydrolysis without affecting mitogenesis

Area of Science:

• Cellular signaling
• Molecular biology
• Receptor tyrosine kinases

Background:

• Growth factor receptors with tyrosine kinase activity initiate signaling cascades upon stimulation.
• Key signaling molecules like phospholipase C gamma (PLC gamma) and ras GTPase-activating protein are phosphorylated.
• Src-homologous SH2 domains mediate the binding of PLC gamma and GTPase-activating protein to phosphorylated growth factor receptors.

Purpose of the Study:

• To investigate the role of tyrosine 766 in the fibroblast growth factor (FGF) receptor.
• To determine the necessity of FGF receptor tyrosine 766 phosphorylation for PLC gamma association and activation.
• To elucidate the contribution of phosphatidylinositol hydrolysis to FGF-induced mitogenesis.

Main Methods:

• Site-directed mutagenesis was used to create an FGF receptor point mutant (Y766F) replacing tyrosine 766 with phenylalanine.
• Assessment of PLC gamma association and tyrosine phosphorylation with the FGF receptor mutant.
• Measurement of phosphatidylinositol hydrolysis and DNA synthesis in cells expressing the FGF receptor mutant.

Main Results:

• The FGF receptor Y766F mutant failed to associate with and tyrosine-phosphorylate PLC gamma.
• Hydrolysis of phosphatidylinositol was not stimulated by the Y766F FGF receptor mutant.
• The Y766F FGF receptor mutant retained autophosphorylation activity and stimulated DNA synthesis, indicating intact mitogenic signaling.

Conclusions:

• Phosphorylation of conserved tyrosine 766 in the FGF receptor is essential for PLC gamma phosphorylation and subsequent phosphatidylinositol hydrolysis.
• FGF-induced mitogenesis can occur independently of phosphatidylinositol hydrolysis mediated by PLC gamma.
• This finding highlights a dissociation between PLC gamma-dependent signaling and FGF-mediated cell proliferation.