Synthesis of biologically active transforming growth factor alpha

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Abstract
A 50-amino acid residue transforming growth factor, type alpha (TGFα), secreted in culture by feline-sarcoma-virus-transformed rat embryo fibroblasts, was synthesized by an improved stepwise solid-phase method with an overall yield of 31%. A deprotection strategy based on the SN2 mechanism using either a low concentration of HF or CF3SO3H-CF3CO2H in dimethylsulfide was employed to remove most of the benzyl-derived protecting groups. The more acid resistant protecting groups of Cys and Arg were removed by the SN2 condition using a high concentration of HF. Synthetic TGFα was purified to homogeneity in three steps. Synthetic and natural TGFα were indistinguishable from each other in HPLC and in different assays, including the assay for anchorage-independent growth of normal rat kidney fibroblasts in soft agar, binding, and stimulating to epidermal growth factor (EGF)-receptor protein kinase. Furthermore, synthetic TGFα showed similar biological activities when compared with EGF in these assays. Thus, the chemical synthesis of TGFα provided convincing evidence that TGFα is functionally related to EGF and is one of the active principles required for cellular transformation.