Characterization of platelet-derived growth factor-stimulated phosphorylation in cell membranes.

Platelet-derived growth factor (PDGF) stimulated the phosphorylation of a 170,000-Mr protein in membranes prepared from parental and several variant lines of Swiss 3T3 cells as well as from diploid human fibroblasts. The intensity of the phosphorylation of the 170,000-Mr protein paralleled the number of PDGF receptors present on the various cells. The enhanced phosphorylation was the result of an increase in the amount of phosphoserine and phosphotyrosine present in the 170,000-Mr protein. PDGF-stimulated phosphorylation of the 170,000-Mr protein was rapid and showed a dose response to PDGF. Down regulation of the PDGF receptor led to a rapid loss in the PDGF-stimulated phosphorylation of the 170,000-Mr protein. In Swiss 3T3 cell membranes, PDGF as well as epidermal growth factor stimulated the phosphorylation of a synthetic, tyrosine-containing peptide. The effects of the two growth factors were additive, indicating that PDGF and epidermal growth factor stimulate peptide phosphorylation through distinct receptors.