Effects of tumor promoters on the rate and commitment to terminal differentiation of subpopulations of murine keratinocytes

The effects of skin-tumor-promoting and -nonpromoting agents on the kinetics of terminal differentiation of subpopulations of keratinocytes differing in buoyant density isolated from mice (SENCAR) that are very sensitive to 12-O-tetradecanoylphorbol-13-acetate (TPA) promotion were investigated. Topical pretreatment of dorsal skin with complete (TPA), first-stage (calcium ionophore A23187) and second-stage (mezerein) tumor promoters, but not the hyperplastic agent ethylphenylpropiolate, accelerated the rate of terminal differentiation of keratinocytes with densities less than 1.074 g/cm³, but had little effect on cells with a greater density. Within 8.5 hr of TPA treatment, a period preceding mitosis, a large percentage of the most dense basal-cell keratinocytes (≥1.074 g/cm³) were converted to cells with a lower density, with a reduced plating efficiency and with an increased rate of differentiation, suggesting that TPA induces a subpopulation of basal cells to commit to terminal differentiation, and accelerates the rate of differentiation of committed cells.