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 kerati nocytes coincides with the expression of protein kinase C (PKC)-regula ted 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 kera tinocyte PKC isozymes (alpha, delta, epsilon, eta, and zeta). Treatmen t of basal keratinocytes with CS induced the expression of the granula r layer proteins filaggrin and loricrin and decreased the level of the spinous keratin K1. CS stimulated cornification and blocked the induc tion of K10 in keratinocytes induced to differentiate by calcium. The induction of filaggrin and loricrin by CS corresponds to a granular la yer differentiation program, where PKC activation occurs and was block ed by the PKC inhibitor GF 109203X. Treatment of keratinocytes with CS caused PKC epsilon, eta, and zeta to be selectively lost from the cyt osol fraction and increased in the cytoskeletal fraction. The loss of soluble PKC epsilon, eta, and zeta was rapid (1 h) and sustained (44 h ). PKC alpha and delta were not redistributed. In vitro, CS induced ki nase activity of PKC epsilon, eta, and zeta to a greater extent than d id the phorbol ester 12-O-tetradecanoylphorbol-13-acetate for these is oforms. PKC ru and delta were activated to a lesser extent by CS than by 12-O-tetradecanoylphorbol-13-acetate. The translocation of PKC epsi lon, eta, and zeta in intact cells treated with CS, together with the in vitro activation of recombinant PKC epsilon, eta, and zeta preferen tially by CS, suggests a role for these isoforms in the induction of k eratinocyte differentiation by CS.