Ultraviolet light in the oncogenic transformation of cultured C3H/10T1/2 mouse embryo cells

Skin tumors are produced in rats, mice, and humans by exposure to UV light. We developed a mouse embryo fibroblast line C3H/10T1/2, which can be transformed by chemical carcinogens, X-irradiation, UV radiation, and oncornavirus. When we irradiated these cells with 10, 25, 50, 100, 150, or 200 ergs/mm2 of UV light, neither transformation nor cytotoxicity was observed at the two lower doses. When the irradiated cells were cultured in medium containing 0.1 micrograms TPA/1 ml (a potent tumor promoter) starting from 0-120 hours after irradiation, a high frequency of transformation was always produced. When the cells were initiated with subeffective concentrations of 0.1 micrograms MCA/ml followed by UV radiation at different intervals, no transformation occurred; however, these initiated cells were transformed after TPA treatment. When we treated the cells with multiple exposures to UV light, no transformation occurred then nor when the cells were treated with TPA followed by UV irradiation at different intervals. Thus UV in our system acts as a pure initiator in the two-stage process of oncogenic transformation.