ABSTRACT
Platelet-derived growth factor (PDGF) is the major mitogen in serum for connective tissue-derived cells. The various forms of PDGF-like growth factors exert mitogenic activity via interaction with a specific high-affinity receptor that has been identified on the cell surface of responsive cells. PDGF receptors have been found on cultured fibroblasts, smooth muscle cells, glial cells, and placental cytotrophoblasts, but not on hematopoietic cells and epithelial cells. The identification of such substrates has been difficult due to the profuse background phosphorylation in a metabolically active cell. Immunoprecipitation of metabolically labeled, PDGF-stimulated fibroblasts revealed that the PDGF receptor proper is the major tyrosine-phosphorylated component; the autophosphorylation of the receptor reaches a maximum 5 to 10 min after PDGF stimulation and then declines. Considering the functional homology between many growth factor receptors and oncogene products, it is likely that tyrosine phosphorylation is involved in the transduction of the mitogenic signal from the activated PDGF receptor and further into the cell.
