GERMICIDAL ULTRAVIOLET LIGHT INDUCES ORNITHINE DECARBOXYLASE IN MOUSE EPIDERMAL CELLS AND MODIFIES THE INDUCTION CAUSED BY PHORBOL ESTER TUMOR PROMOTERS

Germicidal ultraviolet light (UVC. 8–10 J/m²) induces ornithine decarboxylase (ODC) in mouse epidermal cells in vitro in a biphasic manner with maxima of 2–3 fold induction at 4–6 h and of 10–20 fold induction at 15–18 h after irradiation. At this dose of UVC overall protein synthesis is inhibited by 10–30% and RNA synthesis by 40–50%. Induction of both ODC peaks is prevented by actinomycin D or cycloheximide. Similar culture factors appear to influence the extent of ODC induction by UVC and by the tumor promoter, 12-O-tetradecanoyl phorbol-13-acetate (TPA), since the ratio of peak activities is approximately constant at 2, whereas absolute values vary considerably between experiments. If cells are irradiated with UVC and then exposed to TPA, the effects are additive at 10 J/m², less than additive at higher and enhanced at lower doses of UVC.