Regulation of the expression of epidermal keratinocyte proliferation and differentiation by vitamin A analogs

A number of vitamin A analogs (retinoids) were used to manipulate the growth of epidermal keratinocytes in culture. The retinoids used were the TMMP analog of ethyl retinoate (Ro 10-9359), 13-cis retinoic acid, all trans retinoic acid and retinol (trans). These were added to primarily neonatal mouse epidermal keratinocyte cultures that proliferate, stratify, and differentiate over 2-3 weeks. [3H]Tdr labeling technics were used to quantitate proliferation. A histologic stain, and a four buffer protein extraction protocol, used in conjunction with polyacrylamide gel electrophoresis and fluorographic technics, were used to assess the differentiation of the cultures. Our results showed that all of the vitamin A analogs we tested inhibited keratinocyte proliferation. Quantitation of specific differentiation proteins showed that Ro 10-9359 and 13-cis retinoic acid partially inhibited the differentiation of the cultures. The Ro 10-9359 retinoid was unusual in that it increased the synthesis of keratohyalin granule-related proteins. These studies showed that inhibition of basal cell proliferation did not result in the obligatory expression of cell differentiation and that at least one of the events that is a part of epidermal keratinocyte differentiation can be separately controlled.