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Differential growth response to exogenous calcium in normal and carcinogen-exposed primary human keratinocyte cell cultures.

The purpose of these studies was to examine an early carcinogen-induced change in primary human epithelial cell cultures and to attempt to reverse this change with retinoic acid. Primary cultures of human foreskin keratinocytes were prepared and exposed to the carcinogen, propane sultone. After each passage, a portion of cells were plated into medium containing increasing amounts of calcium. In a series of experiments it became evident that carcinogen exposed cells continued to grow in the presence of added calcium. Solvent control cell growth was decreased under such conditions. This new phenotype became apparent after the third subculture, but was pronounced after the fourth subculture. The addition of retinoic acid to the culture medium at each medium change reduced this effect and the keratinocytes grew more slowly, similar to control cells, in the presence of added calcium. The results suggest that carcinogen-exposed human keratinocytes acquire a resistance to calcium-induced differentiation or growth cessation and that retinoic acid can ameliorate this process. Although the mechanism of retinoic acid's inhibition remains unclear, these studies do provide a human cell model system which can be used to screen potential chemopreventive agents and for further mechanistic research.