Endogenous and heterologous expression of Transforming growth factora in mammalian cells

Two distinct polypeptides have been termed trans-forming growth factors (TGFs): TGF-a is related to ep-idermal growth factor (EGF) and binds to the EGF re-ceptor, and TGF-/3 is a structurally unrelated protein that recognizes a different receptor. TGF-c ~ was origi-nally isolated from murine-sarcoma-virus-transformed fibroblast cultures and was therefore initially called sarcoma growth factor (De Larco and Todaro 1978). Subsequent examination of a variety of cell sources showed that this factor was made by many more trans-formed cell lines but not by adult normal cells in cul-ture (Ozanne et al. 1980; Roberts et al. 1980; Todaro et al. 1980, 1985). The fact that this factor was able to convert normal rat kidney (NRK) cells into phenotypi-cally transformed cells, and its synthesis by variou