Differential contributions of protein kinase C isoforms in the regulation of group IIA secreted phospholipase A2 expression in cytokine-stimulated rat fibroblasts.

Protein kinase C (PKC) is a family of serine/threonine kinases involved in various signal transduction pathways. We investigated the roles of PKC in the regulation of group IIA secreted phospholipase A(2) (sPLA(2)-IIA) expression in cytokine-stimulated rat fibroblastic 3Y1 cells. Here we show that the induction of sPLA(2)-IIA by proinflammatory cytokines was under the control of both classical cPKCalpha and atypical aPKClambda/iota pathways by using PKC inhibitors, a PKC activator, and PKC knockdowns. Treatment of 3Y1 cells with PKC selective inhibitors having broad specificity, such as chelerythrine chloride and GF109203X, blocked IL-1beta/TNFalpha-dependent induction of sPLA(2)-IIA protein in a dose-dependent manner. Treatment with the PKC activator phorbol 12-myristate 13-acetate (PMA), which activates cPKC and novel nPKC isoforms, markedly attenuated the cytokine-dependent induction of sPLA(2)-IIA expression. In comparison, 24-h pretreatment with PMA, which down-regulates these PKC isoforms, markedly enhanced sPLA(2)-IIA expression. Results with short hairpin RNA (shRNA)-mediated knockdown of PKC isoforms revealed that the cytokine-induced sPLA(2)-IIA expression was markedly enhanced in cPKCalpha knockdown cells compared to those in replicate control cells. In contrast, knockdown of the aPKClambda/iota isoform reduced the cytokine-induced expression of sPLA(2)-IIA. These results suggest that the aPKClambda/iota pathway is required for the induction of sPLA(2)-IIA expression and that the cPKCalpha pathway acts as a negative regulator of sPLA(2)-IIA expression in cytokine-stimulated rat fibroblasts.