RESUMO
The p38 MAPK mediates transcriptional and post-transcriptional control of cyclooxygenase-2 (COX-2) mRNA following interleukin-1(IL-1)/lipopolysaccharide cellular activation. We explored a positive feedback, prostaglandin E(2) (PGE(2))-dependent stabilization of COX-2 mRNA mediated by the p38 MAPK cascade in IL-1 beta-stimulated human synovial fibroblasts. We observed a rapid (5 min), massive (>30-fold), and sustained (>48 h) increase in COX-2 mRNA, protein, and PGE(2) release following a recombinant human (rh) IL-1 beta signal that was inhibited by NS-398, a COX-2 inhibitor, and SB202190, a selective, cell-permeable p38 MAPK inhibitor. PGE(2) completely reversed NS-398-mediated inhibition but not SB202190-dependent inhibition. The eicosanoid didn't potentiate IL-1 beta-induced COX-2 expression nor did it activate COX-2 gene expression in quiescent cells. Transfection experiments with a human COX-2 promoter construct revealed a minor element of p38 MAPK-dependent transcriptional control after IL-1 beta stimulation. p38 MAPK synergized with the cAMP/cAMP-dependent protein kinase cascade to transactivate the COX-2 promoter. When human synovial fibroblasts were activated with rhIL-1 beta for 3-4 h (steady state) followed by washout, the elevated levels of COX-2 mRNA declined rapidly (<2 h) to control levels. If PGE(2), unlike EP2/3 agonists butaprost and sulprostone, was added to fresh medium, COX-2 mRNA levels remained elevated for up to 16 h. SB202190 or anti-PGE(2) monoclonal antibody compromised the stabilization of COX-2 mRNA by PGE(2). Deletion analysis using transfected chimeric luciferase-COX-2 mRNA 3'-untranslated region reporter constructs revealed that IL-1 beta increased reporter gene mRNA stability and translation via AU-containing distal regions of the untranslated region. This response was mediated entirely by a PGE(2)/p38 MAPK-dependent process. We conclude that the magnitude and duration of the induction of COX-2 mRNA, protein, and PGE(2) release by rhIL-1 beta is primarily the result of PGE(2)-dependent stabilization of COX-2 mRNA and stimulation of translation, a process involving a positive feedback loop mediated by the EP4 receptor and the downstream kinases p38 MAPK and, perhaps, cAMP-dependent protein kinase.
