Sarcoma growth factor from conditioned medium of virally transformed cells is composed of both type alpha and type beta transforming growth factors.

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Abstract
Sarcoma growth factor (SGF) derived from conditioned medium of Moloney sarcoma virus-transformed cells and partially purified by gel filtration (crude SGF) was characterized by its ability both to compete with epidermal growth factor (EGF) for binding to membrane receptors and to induce anchorage-independent growth of untransformed cells. Further purification of crude SGF by reverse-phase high-pressure liquid chromatography on .mu.Bondapak C18 and CN columns at pH 2 resolves it into 2 distinctly different polypeptides, types .alpha. and .beta. transforming growth factors (TGF). Type .alpha. TGF (TGF-.alpha.), but not type .beta. TGF (TGF-.beta.), competes for binding to the EGF receptor and induces the formation of small colonies (1000-2000 .mu.m2) of normal rat kidney cells in soft agar. Both TGF-.beta. and EGF or TGF-.alpha. must be present in order to induce the formation of large colonies (7000-15,000 .mu.m2). Based on EGF competing equivalents as determined from a radioreceptor assay with 125I-labeled EGF in normal rat kidney cells, the relative ability of EGF and TGF-.alpha. to potentiate TGF-.beta.-dependent colony formation is in the order conditioned-medium TGF-.alpha. > EGF > intracellular TGF-.alpha.. Suboptimal concentrations of the same polypeptides give additive potentiation of the TGF-.beta.-dependent colony-forming response; saturating levels potentiate a similar maximum response whether used alone or in various combinations. The data indicate that the EGF-competing activity of crude SGF is due to its TGF-.alpha. component alone; the soft-agar colony-forming activity is due to the combined action of 2 distinct polypeptides, TGF-.alpha. and TGF-.beta.

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