Differentiation of cultured epidermal keratinocytes related to sterol metabolism and its retardation by chemical carcinogens.

The amount of 5 beta-cholest-7-en-3 beta-ol of mouse dorsal skin was increased after parturition until 10 days of age, reaching a maximum 5 beta-cholest-7-en-3 beta-ol/5-cholesten-3 beta-ol ratio of 0.43. [2-14C]Acetate was incorporated almost exclusively into 5-cholesten-3 beta-ol in the basal cell culture of epidermal keratinocytes. However, when the concentration of calcium was changed from 0.07 to 1.9 mM to induce terminal differentiation of keratinocytes, a definite amount of radioactive acetate was incorporated into 5 beta-cholest-7-en-3 beta-ol. The extent of the incorporation was increased at least until 72 h after changing medium, and the ratio of radioactive 5 beta-cholest-7-en-3 beta-ol/radioactive 5-cholesten-3 beta-ol was constantly increased in this period, indicating that the accumulation of 5 beta-cholest-7-en-3 beta-ol in the cell is concomitant with the differentiation of the cell. Pretreatment with chemical carcinogens such as 7,12-dimethylbenz[a]anthracene and 20-methylcholanthrene inhibited the incorporation of radioactive acetate into 5 beta-cholest-7-en-3 beta-ol in the high calcium medium at least for the initial 24 h. After that, the incorporation was gradually restored to the normal level. Pretreatment with a tumor promoter, such as 12-O-tetradecanoyl-phorbol 13-acetate, however, did not inhibit the incorporation. Thus, sterol metabolism is suggested to be a useful indicator for differentiation of epidermal keratinocytes.