DNA synthesis in U‐2 OS human osteosarcoma cells is independent of PDGF binding to functional cell surface receptors

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Abstract
Previous studies have shown that suramin reveals specific PDGF binding sites on U‐2 OS human osteosarcoma cells. Stud es presented here indicate that U‐2 OS cells pretreated with suramin internalize and degrade 125l‐PDGF and respond to PDGF by increased tyrosine kinase activity and amino acid transport. However, DNA synthesis in these cells is not reduced by incubation with the PDGF blocking agent suramin and is not stimulated by exogenous PDGF. These data indicate that U‐2 OS cells possess functional PDGF receptors but that high levels of DNA synthesis in these cells is unrelated to the binding of secreted PDGF to these cell surface receptors. Thus, it is unlikely that the PDGF mitogen produced by U‐2 OS cells stimulates proliferation through an autocrine mechanism involving secretion and subsequent binding to PDGF receptors.