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

Abstract

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-κB, C/EBPβ, 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 IκBα, or dominant-negative versions of C/EBPβ or c-Jun, to determine the contribution of each transcription factor to IL-6 and IL-8 expression. Inhibition of NF-κB activation significantly reduced the spontaneous and IL-1β-induced secretion of IL-6 and IL-8 by RA FLS and the IL-1β-induced production of IL-6 and IL-8 by human dermal fibroblasts. Inhibition of C/EBPβ modestly reduced constitutive and IL-1β-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-κB, C/EBPβ, and c-Jun were constitutively activated in RA FLS, but only NF-κB and c-Jun activity increased after IL-1β. The reduction of cytokines by IκBα was mediated through inhibition of NF-κB activation, which resulted in decreased IL-6 and IL-8 mRNA. NF-κB was essential for IL-6 expression, because fibroblasts in which both NF-κB p50/p65 genes were deleted failed to express IL-6 in response to IL-1. These findings document the importance of NF-κB for the regulation of the constitutive and IL-1β-stimulated expression of IL-6 and IL-8 by RA FLS and support the role of inhibition of NF-κB as a therapeutic goal in RA.

Preventive Effects of a Kampo Medicine, Shosaikoto, on Inflammatory Responses in LPS-Treated Human Gingival Fibroblasts

“…Baicalein inhibits CCAAT/enhancer binding protein b (C/EBPb) DNAbinding activity in COX-2 promoter region and suppresses COX-2 expression in mouse macrophages, 18) while C/EBPb plays no or little role in IL-6 and IL-8 transcription in LPStreated dermal fibroblasts and LPS-treated rheumatoid arthritis synovial fibroblasts. 22) Taken together, our results suggest that the mechanism of anti-inflammatory effects of TJ-9 is mainly the suppression of PGE 2 production rather than those of inflammatory cytokines. Moreover, this decreased PGE 2 production will cause substantial reduction of PGE 2 in periodontal tissue because periodontal tissue is mainly occupied by HGFs.…”

Inhibition of NF-κB Activity by a Membrane-Transducing Mutant of IκBα

“…I B␣, in its wild-type or mutated forms, represents a specific inhibitor and has been used in experimental systems to inhibit NF-B activity. Such experiments have shown that TNF-␣ production by macrophages and expression of IL6 and IL8 in RA are NF-B dependent (13), that NF-B provides a link between inflammation and hyperplasia in RA joint (14), and that its inhibition results in TNF-␣-induced apoptosis of RA synovial fibroblasts (33). Also, in type I diabetes, NF-B inhibition protected human islet ␤ cells from the adverse effects of IL-1␤ (34).…”

“…The expression of many proinflammatory genes is regulated by NF-B, such as the cytokines TNF-␣, IL-1␤, IL6, and IL8; adhesion molecules; matrix remodelling enzymes; cyclooxygenase-2; and inducible NO synthase. NF-B activity regulates expression of IL6 and IL8 in RA synovial fibroblasts (13) and links inflammation to hyperplasia in the arthritic joint (14). In addition, a peptide that inhibited nuclear localization of NF-B improved inflammatory disease in an animal model (15).…”

Regulation of IL-1 and TNF Receptor Expression and Function by Endogenous Macrophage Migration Inhibitory Factor

“…Both p38 MAPK and NF-B have been reported to be implicated in the regulation of IL-6 expression (10,25). However, NF-B is essential as NF-B p50/p65-deficient fibroblasts do not express IL-6 in response to IL-1 (47). In our study, IL-1-induced IL-6 remained intact despite a profound reduction in IL-1-induced p38 phosphorylation in MIF Ϫ/Ϫ cells, and NF-B antagonism lead to near complete abrogation of IL-1-induced IL-6.…”