Differential sensitivities of transplacentally initiated newborn mouse epidermal cells to different tumor promoters.

Epidermal cells isolated from newborn mice and cultured in low Ca2+ (0.02 mM) medium showed typical basal cell morphology and proliferated as monolayer. An increase in the medium Ca2+ concentration to normal level (1.8 mM) induced terminal differentiation of epidermal cells. Epidermal cells obtained from newborn mice transplacentally initiated with 7,12-dimethylbenz[a]anthracene (DMBA) produced a small number of rapidly growing cellular foci with epidermal morphology when the medium Ca2+ concentration was raised to normal level. The number of these Ca(2+)-induced differentiation-resistant colonies increased with increasing doses of DMBA, indicating that the differentiation-resistant colonies are the cells initiated by DMBA. Three differentiation-resistant colonies were cloned and designated as WY-1, WY-18 and WY-20 cells. All of these cell lines grew rapidly in the normal Ca2+ medium but not in the low Ca2+ medium. A potent skin tumor promoter, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), and other TPA-type second-stage tumor promoters such as mezerein and 12-O-retinoylphorbol-13-acetate, stimulated the growth of WY-18 and WY-20 cells in the low Ca2+ medium, but did not stimulate the growth of WY-1 cells. TPA stimulated DNA synthesis and ornithine decarboxylase induction in WY-18 and WY-20 cells but not in WY-1 cells. A non-TPA-type tumor promoter, okadaic acid, failed to stimulate the growth of these three cell lines. Another non-TPA-type tumor-promoting agent, 7-bromo-methylbenz[a]anthracene, also failed to stimulate the growth of WY-1 and WY-20 cells but stimulated the growth of WY-18 cells. WY-18 and WY-20 cells formed colonies in soft agar but WY-1 cells did not form colonies. When these cell lines were injected s.c. into nude mice, WY-1 cells produced fast-growing tumors, whereas WY-18 and WY-20 cells produced relatively slow-growing tumors. Our present results indicate that each initiated cell has different sensitivities for different types of tumor promoters, and each type of promoter acts on corresponding types of initiated cells.