Cholesterol sulfate activates multiple protein kinase C isoenzymes and induces granular cell differentiation in cultured murine keratinocytes.

The accumulation of cholesterol sulfate (CS) in differentiating keratinocytes coincides with the expression of protein kinase C (PKC)-regulated granular layer differentiation markers both in vitro and in vivo. In this study, we examined the ability of Cs to induce differentiation marker expression in primary mouse keratinocytes and to modulate keratinocyte PKC isozymes (alpha, delta, epsilon, eta, and sigma). Treatment of basal keratinocytes with CS induced the expression of the granular layer proteins filaggrin and loricrin and decreased the level of the spinous keratin K1. CS stimulated cornification and blocked the induction of K10 in keratinocytes induced to differentiate by calcium. The induction of filaggrin and loricrin by CS corresponds to a granular layer differentiation program, where PKC activation occurs and was blocked by the PKC inhibitor GF 109203X. Treatment of keratinocytes with CS caused PKC epsilon, eta, and sigma to be selectively lost from the cytosol fraction and increased in the cytoskeletal fraction. The loss of soluble PKC epsilon, eta, and sigma was rapid (1 h) and sustained (44 h). PKC alpha and delta were not redistributed. In vitro, CS induced kinase activity of PKC epsilon, eta, and sigma to a greater extent than did the phorbol ester 12-O-tetradecanoylphorbol-13-acetate for these isoforms. PKC alpha and delta were activated to a lesser extent by CS than by 12-O-tetradecanoylphorbol-13-acetate. The translocation of PKC epsilon, eta, and sigma in intact cells treated with CS, together with the in vitro activation of recombinant PKC epsilon, eta, and sigma preferentially by CS, suggests a role for these isoforms in the induction of keratinocyte differentiation by CS.