15-Deoxy-δ12,14-prostaglandin J2 inhibits IL-1β-induced cyclooxygenase-2 expression in mesangial cells

Abstract

Background. Cyclooxygenase-2 (COX-2), a key enzyme in the synthesis of prostaglandins, is induced in mesangial cells in response to proinflammatory cytokines. Recently, 15-deoxy-δ12,14-prostaglandin J2 (15d-PGJ2), one of the natural ligands of peroxisome proliferator-activated receptor γ (PPARγ), has been reported to have an anti-inflammatory effect. Therefore, we examined the effect of 15d-PGJ2 on COX-2 expression in cultured rat mesangial cells. Methods. Mesangial cells were incubated with 15d-PGJ2 for 30 minutes and then exposed to interleukin-1β (IL-1β). The expression of COX-2 mRNA and proteins was determined by Northern blot and immunoblot analyses, respectively. Accumulation of prostaglandin E2 (PGE2) was measured by an enzyme-linked immunosorbent assay (ELISA). Activities of mitogen-activated protein kinases (MAPKs) were evaluated by an immunoblot analysis. DNA binding activities of activator protein-1 (AP-1) or nuclear factor-κB (NF-κB) were examined by an electrophoretic mobility shift assay (EMSA). The activities of PPAR responsive elements (PPRE) and COX-2 promoter were measured by a luciferase reporter assay. Results. 15D-PGJ2 significantly suppressed IL-1β-induced COX-2 expression and PGE2 production, but thiazolidinediones, synthetic PPARγ ligands, did not affect COX-2 expression. Moreover, the cells transfected with a PPRE luciferase reporter did not respond to 15d-PGJ2. IL-1β rapidly activated extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK), which were involved in the up-regulation of COX-2 induction, but 15d-PGJ2 inhibited the activation of these kinases. 15d-PGJ2 inhibited the IL-1β-induced increase in binding activities of nuclear proteins to consensus AP-1 site and AP-1-like site of COX-2 promoter but not of NF-κB. IL-1β was unable to activate the COX-2 promoter when the AP-1-like site was mutated. Conclusions. These data suggest that 15d-PGJ2 inhibits IL-1β-induced COX-2 expression, independent of PPARγ activation, by suppression of ERK and JNK pathways and AP-1 activation in mesangial cells. Thus, 15d-PGJ2 may play an important role in the negative feedback mechanism of COX-2 expression in renal inflammation and may be useful as an anti-inflammatory agent.