PLATELET-DERIVED GROWTH-FACTOR STIMULATES GROWTH-FACTOR RECEPTOR-BINDING PROTEIN-2 ASSOCIATION WITH SHC IN VASCULAR SMOOTH-MUSCLE CELLS

Platelet-derived growth factor (PDGF) stimulates smooth muscle cell pr oliferation and migration in vascular disorders such as atherosclerosi s and restenosis. Growth factor receptor binding protein-2 (GRB2) and Shc have been shown to link growth factor receptor activation with gua nine nucleotide exchange on p21-ras. We have examined this pathway in cultures of rat A10 vascular smooth muscle cells. Our data demonstrate that PDGF stimulates tyrosine phosphorylation on Shc in a concentrati on- and time-dependent manner that parallels PDGF beta-receptor activa tion. Immunoprecipitates of Shc from cells exposed to PDGF revealed Sh c.GRB2 complexes. She immune complexes also contained PDGF beta-recept ors. Complex formation was maximal with 30 ng/ml PDGF and peaked withi n 10 min of exposure. Although PDGF beta-receptors contain a putative GRB2 binding site, activated receptors failed to bind GRB2 directly. E valuation of Shc from membrane and cytosolic fractions of A10 cells sh owed little redistribution of Shc following PDGF exposure. Cytosolic S hc bound only GRB2, whereas, membrane-associated Shc complexed with GR B2, the PDGF beta-receptor, Src, and additional tyrosine phosphorylate d proteins. We conclude that Shc serves as a primary docking protein f or GRB2 in smooth muscle cells and is critical for proliferation in re sponse to PDGF.