Mode of action of retinol. Involvement in glycosylation reactions of cultured mouse epidermal cells.

Cells from mouse epidermis, a keratinizing tissue, when cultured in the presence of retinyl acetate display the phenotype of a secreting epithelium. Retinyl acetate- treated cultures incorporated labeled galactose, mannose, and glucosamine into glycopeptides to a higher extent than their solvent-treated controls; the stimulation of mannose and galactose incorporation was apparent within 2 to 3 h from the addition of retinyl acetate to the culture medium. Retinyl acetate treatment did not significantly alter the level of [Wlglucose in the culture medium, over a 24-h period, nor did it affect the incorporation of labeled uridine into RNA. Epidermal cells in culture synthesized retinyl phosphate and doubly labeled mannosylretinyl phosphate in the presence of [15-3H]retinol and [Wlmannose. Both products yielded [3H]anhydroretinol by mild alkaline hydrolysis in the lipid phase. [W]Mannosyl phosphate was released in the water phase and yielded [‘TImannose after strong acid hydrolysis. Microsomes from mouse epidermal cells synthesized rC]mannosylretinyl phosphate from GDP-[“Clmannose. The synthesis of this compound in vitro was stimulated by exogenous retinyl phosphate. Epidermal cells actively incorporated radioactively labeled galactose into galactolipids. A minor compound with chromatographic characteristics of a galactosyl derivative of retinyl phosphate was isolated. However, this product was stable to hydrolysis with mild alkali, thus excluding the possibility that it is a derivative of retinyl phosphate. These results demonstrate that retinyl acetate markedly alters glycoprotein synthesis in epidermal cells. It is further suggested that this alteration is mediated via the synthesis of retinyl phosphate and mannosylretinyl phosphate. These biochemical changes are likely to be involved in the altered phenotype induced by retinyl acetate in these cultures.