Chemical and biological properties of a growth factor from human‐cultured osteosarcoma cells: Resemblance with platelet‐derived growth factor

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Abstract
A human osteosarcoma cell line, U‐2 OS, cultured under serumfree conditions, was shown to produce a growth factor (osteosarcoma‐derived growth factor, ODGF) for human‐cultured glial cells, fibroblasts, and other cells. ODGF, collected from the spent medium of 2 OS cultures, was purified by a sequence involving heparin‐Sepharose chromatography, hydrophobic chromatography, gel chromatography, and preparative gel electrophoresis in SDS. Purified ODGF, at a concentration of 3 ng/ml, elicited a mitogenic response in human glial cells equivalent to 50% of that afforded by human serum at a final concentration of 1%. The preparation was estimated to be > 50% pure. The biological activity of ODGF resided in a cationic, relatively heat‐resistant, reduction‐susceptible protein with a molecular weight of 30,000 (by gel chromatography and SDS‐gel electrophoresis). The electrophoretic behaviour of radioiodinated ODGF suggested that the protein was composed of two different polypeptide chains (about 13,000‐14,000 and 16,000‐17,000 daltons, respectively) linked via disulphide bonds. The molecular makeup of ODGF was thus similar to that of platelet‐derived growth factor. 125I‐ODGF could be precipitated by an antibody to platelet‐derived growth factor, indicating that the two factors were immunologically related. Resemblance with platelet‐derived growth factor was also indicated by the finding that the latter (but not, e.g., fibroblast growth factor or epidermal growth factor) competed with 125I‐ODGF for binding to human‐cultured glial cells.