| Abstract: | Differentiation of cultured keratinocytes is controlled by the calcium concentration of the medium and is marked by the expression of differentiation-specific keratins. Treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) alters the normal differentiation program and suppresses keratin (K) 1 expression. Based on reported similarities in the effects of TPA and the arachidonic acid metabolite 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE), we hypothesized that 12(S)-HETE might suppress K1 expression in mouse keratinocytes. We also investigated the effect of pretreatment with 13(S)-hydroxyoctadecadienoic acid (13(S)-HODE) because others have reported that 13(S)-HODE prevents 12(S)-HETE–induced events. In our study, 100 nM 12(S)-HETE mimicked the effect of 500 nM TPA in suppressing K1 mRNA expression within 24 h of calcium-induced differentiation. Pretreatment with 100 nM 13(S)-HODE blocked the 12(S)-HETE effect but not the TPA effect. A role for protein kinase C (PKC) was suggested for both TPA and 12(S)-HETE based on the loss of response with the PKC inhibitors bryostatin-1 or RO-31-8220. Both TPA and 12(S)-HETE stimulated keratinocyte PKC activity. Pretreatment with 13(S)-HODE blocked the 12(S)-HETE–induced increase in PKC activity. Immunoblotting showed that whereas TPA caused a rapid, partial translocation of the PKCα isozyme, it had no effect on the distribution of PKCδ. Conversely, 12(S)-HETE had no effect on the distribution of PKCα but caused a complete translocation of PKCδ. Pretreatment with 13(S)-HODE prevented 12(S)-HETE–elicited translocation of PKCδ. We conclude that 12(S)-HETE mimics the effect of TPA on K1 mRNA and that the effect is mediated through different isoforms of PKC. Mol. Carcinog. 19:157–164, 1997. © 1997 Wiley-Liss, Inc. |
