Glucocorticoid-mediated repression of inflammatory cytokine production in fibroblast-like rheumatoid synoviocytes is independent of nuclear factor-κB activation induced by tumour necrosis factor α

Abstract

Objective. To determine whether steroids inhibit the production of inflammatory cytokines by the inhibition of nuclear factor κB (NF-κB) activation in fibroblast-like rheumatoid synoviocytes (FLSs) under inflammatory conditions, and to determine whether steroids stimulate the induction of synthesis of the inhibitory protein IκB-α in the anti-inflammatory immune response of these cells. Methods. Expression of the interleukin-6 (IL-6) and interleukin-1 β (IL-1β) genes was measured by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR), and the secreted IL-6 was measured with the enzyme-linked immunosorbent assay. Inhibition of the NF-κB activation was examined with the electrophoretic mobility shift assay (EMSA). In order to study dexamethasone (DEX)-dependent regulation of IκB-α expression, we performed Western blotting before and after stimulation with tumour necrosis factor α (TNF-α). Results. The inflammatory cytokine study showed that DEX suppressed gene expression and the production of protein in FLSs. EMSA demonstrated that identical amounts of NF-κB were present in the nucleus of the FLSs stimulated by TNF-α, with or without pretreatment with DEX. Treatment of FLSs with DEX did not induce an increase in IκB-α sufficient to prevent nuclear translocation of NF-κB on stimulation with TNF-α. Conclusion. DEX may suppress the production of inflammatory cytokines, such as IL-6 and IL-1β, but it neither prevents the translocation of NF-κB to the nucleus nor induces the synthesis of IκB-α protein in FLSs stimulated by TNF-α.