Epidermal growth factor, like tumor promoters, enhances viral and radiation-induced cell transformation

The polypeptide hormone epidermal growth factor (EGF) has been shown to enhance adenovirus type 5 transformation of a cloned culture of rat embryo cells (CREF) and X-ray or u.v.-light induced transformation of 10T1/2 mouse embryo cells. In both systems, the degree of enhancement was quantitatively similar to that observed in treated rats grown in the presence of the potent tumor promoting agent 12-O-tetradecanoyl-phorbol-13-acetate (TPA). An increase in viral transformation was also observed in cells continuously exposed to phorbol esters with known promoting activity on mouse skin, but not structurally related analogs, inactive or weakly active in the two-stage mouse skin carcinogenesis assay. In addition, the appearance of transformed foci was accelerated and colonies tended to be larger in cultures grown in the presence of EGF or TPA. The present studies suggest the possibility that EGF may function as an endogenous promoter of carcinogenesis and further indicates that in vitro cell transformation systems may prove useful in identifying such agents.