In vitro induction of human skin ornithine decarboxylase by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate

A method was developed for the in vitro induction by 12-O-tetradecanoylphorbol-13-acetate (TPA) or ornithine decarboxylase (ODC) activity in human skin punch biopsy samples. Addition of TPA to 1 ml serum-free minimum essential medium containing a single 3-mm human skin punch biopsy sample obtained from a surgical specimen resulted in an induction of ODC activity with a peak activity at 5 hours after TPA addition. In vitro induction of human epidermal ODC activity was dependent on the TPA concentration in the medium; about a twofold increase in ODC activity was observed 6 hours after the addition of 0.1 μM TPA, and about a fivefold increase in ODC activity was observed with 1 μM TPA. TPA also caused about a fivefold to sixfold increase in ODC activity in 3-mm skin punch biopsy samples from healthy volunteers. Human skin punch biopsy samples remained responsive to TPA induction of ODC activity even when stored in serum-free medium at 4°C for 24 hours. A similar degree of induction of ODC activity by TPA was observed whether whole unfractionated human epidermis or a soluble epidermal extract was used for ODC assays. Increased ODC activity was the result of the increase in enzymatically active ODC protein, quantitated by a [³H]difluoromethylornithine-binding assay. Thus human skin, like mouse skin, is responsive to TPA for ODC induction.