DEMONSTRATION OF FUNCTIONALLY DIFFERENT INTERACTIONS BETWEEN PHOSPHOLIPASE C-GAMMA AND THE 2 TYPES OF PLATELET-DERIVED GROWTH-FACTOR RECEPTORS

Phosphorylated tyrosine residues in receptor tyrosine kinases serve as binding sites for signal transduction molecules. We have identified t wo autophosphorylation sites, Tyr-988 and Tyr-1018, in the platelet-de rived growth factor (PDGF) alpha-receptor carboxyl-terminal tail, whic h are involved in binding of phospholipase C-gamma (PLC-gamma). The ca pacities of the Y988F and Y1018F mutant PDGF alpha-receptors, expresse d in porcine aortic endothelial cells, to bind PLC-gamma are 60 and 5% of that of the wild-type receptor, respectively. Phosphorylated but n ot unphosphorylated peptides containing Tyr-1018 are able to compete w ith the intact receptor for binding to immobilized PLC-gamma SH2 domai ns; a phosphorylated Tyr-988 peptide competes 10 times less efficientl y. The complex between PLC-gamma and the PDGF alpha-receptor is more s table than that of PLC-gamma and the PDGF beta-receptor. However, PDGF stimulation results in a smaller fraction of tyrosine-phosphorylated PLC-gamma and a smaller accumulation of inositol trisphosphate in cell s expressing the alpha-receptor as compared with cells expressing the beta-receptor. We conclude that phosphorylated Tyr-988 and Tyr-1018 in the PDGF alpha-receptor carboxyl-terminal tail bind PLC-gamma, but th is association leads to only a relatively low level of tyrosine phosph orylation and activation of PLC-gamma.