Evidence for Functional Platelet-derived Growth Factor Receptors on MG-63 Human Osteosarcoma Cells1

The specific interaction of platelet-derived growth factor (PDGF) with the human osteosarcoma cell line MG-63 was studied. Scatchard analysis of 125I-PDGFbinding to MG-63 cells indicated there were 32,000 specific PDGF-binding sites per cell with a K<jof 2.4 x 10~11M. Unlabeled PDGF blocked the specific binding of labeled PDGF to MG-63 cells at concentrations greater than 1 ng/ml. When assayed for phosphorylation of MG-63 membrane vesicles, PDGF was shown to stimulate a dosedependent phosphorylation of a protein (phosphoprotein with a molecular weight of 185,000) which was stable in 1 M NaOH. In the absence of PDGF, a prominent alkali-stable phosphoprotein with a molecular weight of 116,000 was noted. PDGF also stimulated a dose-dependent increase in [3H]aminoisobutyric acid uptake, [3H]thymidine incorporation, and cell proliferation. When tested for secretion of PDGF-like factors, the mitogenic activity of MG-63-conditioned serum-free medium was not blocked by anti-PDGF antiserum. Concentrated MG-63-conditioned medium did not compete with 125I-PDGF for specific receptor sites on diploid fibroblasts. Therefore, MG-63 osteosar coma cells have functional PDGF receptors and do not secrete PDGF-like mitogens.