Identification of the receptor-associated signaling enzymes that are required for platelet-derived growth factor-AA-dependent chemotaxis and DNA synthesis

Activation of the platelet-derived growth factor (PDGF) alpha receptor (alpha PDGFR) leads to cell migration and DNA synthesis. These events are preceded by the ligand-induced tyrosine phosphorylation of the receptor and its association with SH2-containing signaling enzymes including Src family members (Src), the phosphotyrosine phosphatase SHP-2, phosphatidylinositol 3-kinase (PI3K), and phospholipase C-gamma 1 (PLC gamma), In this study, we sought to systematically evaluate the relative roles of the signaling enzymes that are recruited to the alpha PDGFR for DNA synthesis and cell migration. Our approach was to generate and characterize tyrosine to phenylalanine alpha PDGFR mutants that failed to associate with one or more of the above listed signaling enzymes. In a 3T3-like cell line (Ph cells), PDGF-dependent DNA synthesis was strictly dependent on only one of the receptor-associated proteins, PI3K, In contrast, multiple signaling enzymes were required for maximal chemotaxis, as receptors unable to associate with either Src, PI3K, or PLC gamma initiated chemotaxis to 4, 47, or 56% of the wild-type level, respectively. Furthermore, coexpression of mutant receptors revealed that these signaling enzymes do not need to be on the same receptor for a cell to respond chemotactically to PDGF, We conclude that for the alpha PDGFR, PI3K plays a major role in initiating DNA synthesis, whereas PI3K, PLC gamma, and especially Src are required for chemotaxis.