Tumor Necrosis Factor-α Promotes Sustained Cyclooxygenase-2 Expression: Attenuation by Dexamethasone and NSAIDs

Prostaglandin (PG) release is characteristic of most inflammatory diseases. The committed step in the formation of free arachidonic acid into PG products is catalyzed by cyclooxygenase (COX, prostaglandin H₂ synthase, PGHS), which exists as two genetically distinct isoforms. COX-1 is constitutively expressed and produces PGs and thromboxane A₂ during normal physiologic activities, while COX-2 is an inducible enzyme stimulated by growth factors, lipopolysaccharide, and cytokines during inflammation or cell injury. Proinflammatory cytokines such as tumor necrosis factor-α (TNF-α) released into the amniotic fluid in the setting of infection have been proposed to signal amnion and decidual cells to produce PGs that may culminate in preterm labor. However, since the molecular control of this phenomenon has not been established, this study used amnion-derived WISH cells to determine if TNF-α promoted the formation of PGs through COX-2 activity. Treatment of WISH cells with TNF-α (0.1 ng/mL–100 ng/mL) caused a dose-dependent increase in COX-2 expression and the subsequent biosynthesis of PGE₂ that persisted for at least 48 hrs. In contrast, COX-1 mRNA and protein levels were unaltered by TNF-α treatment as determined by RT-PCR and immunoblot analysis, respectively. TNF-α-stimulated COX-2 expression and the subsequent formation of PGE₂ were inhibited by dexamethasone (0.1 μM). In addition, indomethacin (1 μM) and the novel COX-2-selective inhibitor, NS-398 (IC₅₀ ∼ 1.1 × 10⁻⁹ M), attenuated TNF-α-elicited PGE₂ production. Results presented here demonstrate that TNF-α elicits prolonged and regulatable induction of COX-2 in WISH cells, while COX-1 is constitutively expressed and unchanged in response to TNF-α stimulation.