Protein kinase C-α coordinately regulates cytosolic phospholipase A2 activity and the expression of cyclooxygenase-2 through different mechanisms in mouse keratinocytes

Transgenic mice (K5-PKC alpha) in which the keratin 5 promoter directs the expression of protein kinase C-alpha (PKC alpha) to epidermal keratinocytes display a 10-fold increase in PKC alpha protein in their epidermis and alterations in phorbol ester-induced cutaneous inflammation [J Cell Science 1999;112:3497-3506]. In the current study, we have used these K5-PKC alpha mice to examine the role of PKC alpha in keratinocyte phospholipid metabolism/eicosanoid production and cutaneous inflammation. Primary keratinocytes from wild-type and transgenic mice were prelabeled in culture with [H-3]arachidonic acid (AA) and subsequently treated with TPA. Compared with wild-type keratinocytes, K5-PKC alpha keratinocytes displayed a 2-fold increase in AA release. TPA treatment resulted in the phosphorylation of cPLA(2). PKC inhibitors GF-109203X or H7, but not mitogen-activated protein/extracellular signal-regulated protein kinase (MEK) inhibitor PD 98059, could inhibit phosphorylation and AA release. Topical 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment of K5-PKC alpha mice resulted in a 5-fold increase in epidermal COX-2 induction and a 2- to 3-fold increase in prostaglandin (PG) E-2 levels above that observed in TPA-treated wild-type mice. PD 98059, GF-109203X, or H7 could block cyclooxygenase-2 (COX-2) induction by TPA. Because C/EBP beta, a basic leucine zipper transcription factor, can be activated via a PKC alpha /mitogen-activated protein kinase pathway and can influence COX-2 expression, we examined whether C/EBP beta is involved in TPA-induced epidermal COX-2 expression. TPA-induced COX-2 expression was similar in C/EBP beta nullizygous and wild-type mice. In summary, our results indicate that epidermal PKC alpha coordinately regulates cPLA(2) activity and COX-2 expression resulting in increased levels of AA and PGE(2). Furthermore, PKC alpha -induced AA release and cPLA(2) phosphorylation are independent of MEK, whereas PKC alpha -induced COX-2 expression and PGE(2) production are MEK-dependent and C/EBP beta -independent events.