The purification of an acid- and heat-labile transforming growth factor from an avian sarcoma virus- transformed rat cell line

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Abstract
A new class of transforming growth factor (TGF), with chemical characteristics differing from previously reported TGFs, was isolated and purified from an avian sarcoma virus-transformed rat cell line, 77N1. Purification steps were simple and consisted of ion-exchange chromatography on diethylaminoethyl (DEAE)-Sephacel, ammonium sulfate precipitation, Chromatofocusing, and DEAE-Sephadex A-25 chromatography. The purified TGF is a heat- and acidlabile protein with a molecular mass of 12,000 daltons and isoelectric point of 5.2–5.4. Because of the acid lability of this TGF, purification was carried out at neutral pH. The TGF induced DNA synthesis in growth-arrested BALB 3T3 cells and promoted anchorage-independent growth of nontransformed BALB 3T3 cells in soft agar; the latter activity is specific for the peptide growth factors, called TGFs, but it did not compete with epidermal growth factor (EGF) for binding to the EGF membrane receptors. The TGF activity was not potentiated by EGF. The purified preparation of the TGF stimulated BALB 3T3 cells to grow progressively in soft agar at a dose of 20 ng/ml.