Increase of Cyclooxygenase-2 Expression by Interleukin 15 in Rheumatoid Synoviocytes

Objective. To determine the effect of interleukin 15 (IL-15) on cyclooxygenase-2 (COX-2) expression in rheumatoid synoviocytes. Methods. Fibroblast-like synoviocytes (FLS) were prepared from the synovial tissues of patients with rheumatoid arthritis (RA) and cultured in the presence of IL-15. Levels of COX-2 mRNA and protein expression were determined by reverse transcription-polymerase chain reaction and Western blot, respectively. ELISA was used to measure concentrations of IL-1β tumor necrosis factor-α (TNF-α), and prostaglandin E₂ (PGE₂) in the culture supernatants. Results. EL-15 dose-dependently increased COX-2 mRNA and protein expression in FLS, but not the COX-1 mRNA level. Both IL-1β and TNF-α upregulated COX-2 mRNA comparably to IL-15, but neither IL-2 nor interferon-γ had any effect on the COX-2 mRNA level. Treatment with anti-IL-1β or anti-TNF-α antibodies partially reduced the IL-15-stimulated COX-2 mRNA expression, suggesting that these cytokines may take part in modulating COX-2 by IL-15. Dexamethasone and pyrolidine dithiocarbamate, but not curcumin, completely blocked the IL-15-induced upregulation of COX-2 mRNA. A gel mobility shift assay revealed that nuclear factor-κB (NF-κB) was one of the major signal molecules to mediate IL-15-induced COX-2 upregulation. The increase of COX-2 by IL-15 is PGE2-dependent because exogenous PGE2 reversed the suppressive effect of NS-398, a selective COX-2 inhibitor, on COX-2 mRNA and protein expression. Conclusion. This study confirms the effect of IL-15 on upregulation of COX-2 in a PGE ₂-dependent manner. The activation of NF-κB bound to the COX-2 promoter appears to be a downstream target of IL-15 stimulation in FLS, exerted either directly or through the increase in IL-1β and TNF-α production.