Role of Protein Kinase C Isoforms in the Regulation of Interleukin-13-induced 15-Lipoxygenase Gene Expression in Human Monocytes

Abstract We reported previously that interleukin-13 (IL-13) induces tyrosine phosphorylation/activation of Jak2 and Tyk2 kinases and Stats 1, 3, 5, and 6 in primary human monocytes. We recently revealed that p38 MAPK-mediated serine phosphorylation of both Stat1 and Stat3 is required for the induction of 15-lipoxygenase (15-LO) expression by IL-13. In this study, we present data indicating that another serine/threonine kinase, PKCδ, is also required for IL-13-induced 15-LO expression. PKCδ, a member of the novel protein kinase C (PKC) subclass, was rapidly phosphorylated and activated upon exposure to IL-13. Treatment of cells with rottlerin, a PKCδ inhibitor, blocked IL-13-induced 15-LO mRNA and protein expression, whereas Go6976, an inhibitor of the conventional PKC subclass, had no inhibitory effects. Down-regulation of cellular PKCδ protein levels by PKCδ-specific antisense oligodeoxyribonucleotides also inhibited 15-LO expression markedly. IL-13-induced 15-LO expression resulted in significant inhibition of synthesis of the potent chemotactic factor leukotriene B4, and that process was reversed by rottlerin, presumably through the blockage of PKCδ-dependent 15-LO expression. Furthermore, our data demonstrate that IL-13-mediated activation of PKCδ and p38 MAPK are independent pathways, because inhibition of one kinase activity had no effect on the other, suggesting that the two pathways act in parallel to regulate the downstream targets necessary for 15-LO expression. Inhibition of PKCδ activation by rottlerin also markedly attenuated IL-13-induced Stat3 DNA binding activity. Our findings indicate that PKCδ plays an important role in regulating IL-13-induced 15-LO expression in human monocytes and subsequently modulates the inflammatory responses mediated by 15-LO products.