Induction of 15-Lipoxygenase Expression by IL-13 Requires Tyrosine Phosphorylation of Jak2 and Tyk2 in Human Monocytes

The enzyme 15-lipoxygenase (15-LO) participates in the dioxygenation of polyenoic fatty acids. This activity leads to the degradation of mitochondrial membranes during reticulocyte differentiation, the production of pro- and anti-inflammatory mediators by a variety of cell types, and the oxidation of lipids in atherosclerotic lesions. The cytokines, IL-4 and IL-13, are reported to induce the expression of 15-LO in human peripheral blood monocytes. In this report we explore the signaling mechanisms involved in the IL-13-mediated induction of 15-LO expression. First we demonstrate that the delayed induction of 15-LO requires continuous stimulation of monocytes for a minimum period of 12 h. We also found that tyrosine kinase inhibitors blocked the induction of 15-LO in a dose-dependent manner. By immunoprecipitation and antiphosphotyrosine blotting experiments, IL-13 was shown to induce tyrosine phosphorylation of Jak2 and Tyk2, but not Jak1 or Jak3, within 5 min of treatment in human monocytes. To investigate whether the early induction of tyrosine phosphorylation of both Jak2 and Tyk2 was ultimately involved in 15-LO expression, we generated antisense oligodeoxyribonucleotides (ODNs) against Tyk2 and Jak2. We employed a cationic lipid-mediated delivery technique to transfect the monocytes and found that both antisense ODNs inhibited expression of their target proteins by 75–85%. The treatments were specific and did not affect the expression of each other. Furthermore, the antisense ODNs to Jak2 and Tyk2 both inhibited the induction of expression of 15-LO in monocytes treated with IL-13. Parallel experiments with sense ODNs to Jak2 and Tyk2 did not affect their protein levels or the induction of 15-LO by IL-13, and down-regulation of Jak1 also did not affect expression of 15-LO. Our results suggest the novel finding that IL-13 can induce tyrosine phosphorylation of both Jak2 and Tyk2 in primary human monocytes. This occurs as an early and essential signal transduction event for the IL-13-mediated induction of 15-LO expression. These data represent the first characterization of upstream kinases involved in the induced expression of 15-LO.