Expression of A-type PDGF receptor in cytoplasm of tumor cell lines synthesizing PDGF

Two tumor cell lines, WM 266-4 melanoma and SW 707 colorectal carcinoma, both of which synthesize platelet-derived growth factor (PDGF) but do not express cell surface PDGF receptor, were tested for the presence of intracytoplasmic PDGF receptor. Using a novel method of intracytoplasmic (newly synthesized), receptor precipitation by the growth factor, we identified a 125,000 molecular weight protein crosslinked with 125I-labeled PDGF in a 140,000 molecular weight complex. In vitro translation of the corresponding mRNA revealed a 125,000 molecular weight product which presumably represents the A-type PDGF receptor. Exogenous PDGF was found to activate synthesis of RNA and cell proliferation.