Human transforming growth factor type alpha (TGF-alpha) was synthesized by a stepwise solid-phase method with an overall yield of 26%. Synthetic TGF-alpha, consisting of 50 amino acid residues deduced from a cDNA precursor sequence, was purified in a single HPLC step. The homogeneity and primary structure were confirmed by several criteria including Edman degradation and mass spectrometry. Synthetic TGF-alpha was as active as murine epidermal growth factor in binding to the epidermal growth factor receptor and in stimulation of anchorage-dependent and of anchorage-independent growth of normal indicator cells in culture. Synthetic TGF-alpha stimulated plasminogen activator production in A 431 and HeLa cells; the stimulation was similar to that induced by epidermal growth factor. Furthermore, synthetic human TGF-alpha showed similar immunoreactivity when compared with rat TGF-alpha. Thus, the 50-amino acid TGF-alpha is likely to be the bioactive principle produced and secreted by tumor cell lines.
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Tam et al. (1986) studied this question.