Induction of Ornithine Decarboxylase in Specific Subpopulations of Murine Epidermal Cells Following Multiple Exposures to 12-O-Tetradecanoylphorbol-13-Acetate, Mezerein, and Ethyl Phenylpropriolate

The study investigated the effects of multiple exposures to 12-O-tetradecanoylphorbol-13-acetate (TPA), mezerein, and ethyl phenylpropriolate (EPP) on murine epidermal cells, focusing on the induction of ornithine decarboxylase (ODC) activity. While single applications of these agents caused similar hyperplasia and ODC induction, multiple treatments revealed significant differences in ODC activity, with TPA and mezerein inducing more than EPP. Immunocytochemical analysis showed distinct patterns of ODC-positive cells, with TPA prominently affecting perifollicular cells, mezerein affecting both interfollicular and perifollicular areas, and EPP affecting only interfollicular cells. Flow cytometry identified three keratinocyte subpopulations, with TPA causing the expansion of an intermediate-sized subpopulation not seen with EPP or mezerein. The findings suggested that TPA, a potent tumor promoter, selectively expanded a keratinocyte subpopulation hyperinducible for ODC, potentially important for neoplastic transformation, while mezerein and EPP were less effective in this regard.