Transforming growth factor and epidermal growth factor stimulate the phosphorylation of a synthetic, tyrosine-containing peptide in a similar manner

A partially purified preparation of a transforming growth factor (TGF) obtained from serum-free growth medium conditioned by a human melanoma tumor line was found to stimulate the phosphorylation of a synthetic tyrosine-containing peptide. The sequence of the peptide is related to that of the known site of tyrosine phosphorylation in the Rous sarcoma virus-encoded transforming protein, pp60(src). In A431 membranes, the characteristics of TGF- and epidermal growth factor (EGF)-stimulated peptide phosphorylation are nearly identical. The effects of the two growth factors are not additive, suggesting that TGF and EGF stimulate peptide phosphorylation through the same EGF receptor system. This conclusion is supported by the finding that both TGF and EGF stimulate peptide phosphorylation in wild type Swiss 3T3 cell membranes, but neither factor is effective in stimulating peptide phosphorylation in membranes prepared from EGF receptor-deficient NR6 3T3 cells.