Inhibition of DNA synthesis and sugar uptake and lack of induction of ornithine decarboxylase in human epidermal cells treated with mouse skin tumor promoters.

The present study was undertaken to investigate the possibility that 12-O-tetradecanoylphorbol-13-acetate (TPA) is active as a tumor promoter in human skin. Human epidermal and dermal cells were isolated from the skin of normal subjects by trypsinization and separation of the epidermis from the dermis. Cells in primary culture were exposed to a wide range of TPA concentrations (0.001 to 1000 ng/ml) for various time intervals, and its effect on DNA synthesis, sugar uptake, and polyamine synthesis was measured. Results obtained using human cells were compared with those for the corresponding cells isolated from Sencar mice. In human epidermal cells, TPA did not stimulate but instead inhibited DNA synthesis and uptake of 2-deoxy-D-glucose (DG), a glucose analogue. Inhibition of DNA synthesis could be detected at a dose of TPA as low as 0.1 ng/ml, while at 10 ng/ml DNA synthesis was 50 to 70% of the control. Inhibition of DG uptake depended on concentration of and length of exposure to TPA. Exposure to TPA (10 ng/ml) for 3 hr resulted in a 35% inhibition of DG uptake. Furthermore, exposure of human epidermal cells to TPA under various conditions, including the use of uncultured, freshly isolated cells and of a low-calcium medium, did not result in induction of ornithine decarboxylase, a key enzyme in the synthesis of polyamine. Teleocidin B, a tumor promoter, structurally unrelated to TPA but with an ornithine decarboxylase inducibility in mouse skin similar to that of TPA, also failed to induce ornithine decarboxylase activity in human epidermal cells. Mouse epidermal cells reacted differently from human epidermal cells on addition of TPA. DNA synthesis, sugar uptake, and polyamine synthesis were all stimulated. DG uptake alone was stimulated in human and mouse dermal cells treated with TPA.