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-PKCα) in which the keratin 5 promoter directs the expression of protein kinase C-α (PKCα) to epidermal keratinocytes display a 10-fold increase in PKCα 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-PKCα mice to examine the role of PKCα in keratinocyte phospholipid metabolism/eicosanoid production and cutaneous inflammation. Primary keratinocytes from wild-type and transgenic mice were prelabeled in culture with [ 3 H]arachidonic acid (AA) and subsequently treated with TPA. Compared with wild-type keratinocytes, K5-PKCα 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-PKCα 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/EBPβ, a basic leucine zipper transcription factor, can be activated via a PKCα/mitogen-activated protein kinase pathway and can influence COX-2 expression, we examined whether C/EBPβ is involved in TPA-induced epidermal COX-2 expression. TPA-induced COX-2 expression was similar in C/EBPβ nullizygous and wild-type mice. In summary, our results indicate that epidermal PKCα coordinately regulates cPLA 2 activity and COX-2 expression resulting in increased levels of AA and PGE 2 . Furthermore, PKCα-induced AA release and cPLA 2 phosphorylation are independent of MEK, whereas PKCα-induced COX-2 expression and PGE 2 production are MEK-dependent and C/EBPβ-independent events.