Search of factors that intermediate cytokine-induced group IIA phospholipase A2 expression through the cytosolic phospholipase A2- and 12/15-lipoxygenase-dependent pathway

Abstract

Inducible expression of group IIA secretory phospholipase A2 (SPLA2-IIA) by interleukin-1β (IL-1β) and tumor necrosis factor-α (TNFα) is under the control of group IVA cytosolic PLA 2α and 12/15-lipoxygenase (12/15-LOX) in rat fibroblastic 3Y1 cells. We show here that this cytokine induction of SPLA2-HA mRNA requires de novo protein synthesis. By means of cDNA array analysis, we found that the level of the CXC chemokine MIP-2 (macrophage inflammatory protein-2) was significantly elevated in 12/15-LOX-transfected cells compared with control cells. IL-1β/TNFα-stimulated induction of endogenous MIP-2 preceded that of SPLA2-IIA, and exogenous MIP-2 induced SPLA2-IIA dose-dependently. Moreover, a MIP-2-specific antisense oligonucleotide and small interfering RNA attenuated the IL-1β/TNFα-induced expression of SPLA2-IIA, suggesting that MIP-2 is an absolute intermediate requirement for optimal induction of SPLA2-IIA. In addition, the expression of c-jun and fra-1, which are components of the transcription factor AP-1, was elevated in 12/15-LOX-transfected cells, in which cytokine-dependent binding of AP-1 to the SPLA2-IIA promoter was increased significantly. Conversely, the receptors for transforming growth factor-β and platelet-derived growth factor, which contributed to down-regulation of SPLA2-IIA expression, were decreased following 12/15-LOX overexpression. Taken together, 12/15-LOX-dependent up-regulation of SPLA 2-IIA expression may result from the interplay between accelerated MIP-2 signaling, AP-1 activation, and attenuated transforming growth factor-β and platelet-derived growth factor signaling. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc.