EFFECT OF 12-O-TETRADECANOYLPHORBOL-13-ACETATE ON INHIBITION OF EXPRESSION OF KERATIN-1 MESSENGER-RNA IN MOUSE KERATINOCYTES MIMICKED BY 12(S)-HYDROXYEICOSATETRAENOIC ACID

Differentiation of cultured keratinocytes is controlled by the calcium concentration of the medium and is marked by the expression of differ entiation-specific keratins. Treatment with 12-O-tetradecanoylphorbol- 13-acetate (TPA) alters the normal differentiation program and suppres ses keratin (K) 1 expression. Based on reported similarities in the ef fects of TPA and the arachidonic acid metabolite 12(S)-hydroxyeicosate traenoic acid (12(S)-HETE), we hypothesized that 12(S)-HETE might supp ress K1 expression in mouse keratinocytes. We also investigated the ef fect of pretreatment with 13(S)-hydroxyoctadecadienoic acid (13(S)-HOD E) because others have reported that 13(S)-HODE prevents 12(S)-HETE-in duced events. In our study, 100 nM 12(S)-HETE mimicked the effect of 5 00 nM TPA in suppressing KI mRNA expression within 24 h of calcium-ind uced 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 r esponse with the PKC inhibitors bryostatin-l or RO-31-8220. Both TPA a nd 12(S)-HETE stimulated keratinocyte PKC activity. Pretreatment With 13(S)-HODE blocked the 12(S)-HETE-induced increase in PKC activity. Im munoblotting showed that whereas TPA caused a rapid, partial transloca tion of the PKC alpha isozyme, it had no effect on the distribution of PKC delta. Conversely, 12(S)-HETE had no effect on the distribution o f PKC alpha but caused a complete translocation of PKC delta. Pretreat ment with 13(S)-HODE prevented 12(S)-HETE-elicited translocation of PK C delta. We conclude that 12(S)-HETE mimics the effect of TPA on K1 mR NA and that the effect is mediated through different isoforms of PKC. (C) 1997 Wiley-Liss, Inc.