Regulation of IL-6 and IL-8 expression in rheumatoid arthritis synovial fibroblasts:: the dominant role for NF-κB but not C/EBPβ or c-jun

Rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS) produce IL-6 and IL-8, which contribute to inflammation and joint damage, The promoters of both cytokines possess binding sites for NF-kappaB, C/EBP beta, and c-Jun, but the contribution of each to the regulation of IL-6 and IL-8 in RA FLS is unknown, We employed adenoviral-mediated gene delivery of a nondegradable I kappaB alpha, or dominant-negative versions of C/EBP beta or c-Jun, to determine the contribution of each transcription factor to IL-6 and IL-8 expression. Inhibition of NF-kappaB activation significantly reduced the spontaneous and IL-1 beta -induced secretion of IL-6 and n-8 by RA FLS and the IL-1 beta -induced production of IL-6 and IL-8 by human dermal fibroblasts. Inhibition of C/EBP beta modestly reduced constitutive and IL-1 beta -induced IL-6 by RA FLS, but not by human dermal fibroblasts, and had no effect on IL-8, Inhibition of c-Jun/AP-1 had no effect on the production of either IL-6 or IL-8, Employing gel shift assays, NF-kappaB, C/EBP beta, and c-Jun were constitutively activated in RA FLS, but only NF-kappaB and c-Jun activity increased after IL-1 beta, The reduction of cytokines by I kappaB alpha was mediated through inhibition of NF-kappaB activation, which resulted in decreased IL-6 and IL-8 mRNA, NF-kappaB was essential for IL-6 expression, because fibroblasts in which both NF-kappaB p50/p65 genes were deleted failed to express IL-6 in response to IL-1, These findings document the importance of NF-kappaB for the regulation of the constitutive and IL-1 beta -stimulated expression of IL-6 and IL-8 by RA FLS and support the role of inhibition of NF-kappaB as a therapeutic goal in RA.