SHP-2 is involved in heterodimer specific loss of phosphorylation of Tyr771 in the PDGF β-receptor

We have previously shown that the binding site for GTPase activating protein of Ras (RasGAP) in the PDGF beta-receptor, Tyr771, is phosphorylated to a much lower extent in the heterodimeric configuration of PDGF alpha- and beta-receptors, compared to the PDGF beta-receptor homodimer. The decreased recruitment of the RasGAP to the receptor leads to prolonged activation of the Ras/MAP kinase pathway, which could explain the increase in mitogenicity seen upon induction of heterodimers. The molecular mechanism underlying these differences was investigated. We could show that the loss of phosphorylation of Tyr771 was dependent on presence of intact binding sites for the protein tyrosine phosphatase SHP-2 on the PDGF beta-receptor. Thus, in PDGF receptor mutants in which binding of SHP-2 was lost, a higher degree of phosphorylation of Tyr771 was seen, while other phosphorylation sites in the receptor remained virtually unaffected. Thus, SHP-2 appears to play an important role in modulating phosphorylation of Y771, thereby controlling RasGAP recruitment and Ras/MAP kinase signaling in the heterodimeric configuration of the PDGF receptors.