Faculty Bibliography

Rheumatoid arthritis (RA) is a complex multisystem disease, the hallmark of which is pannus, the abnormal proliferative synovial tissue that serves as both propagator of the immune response and as the engine of tissue damage. Conceptually, pannus may be divided into two compartments (Fig. 1). The first, comprised by T cells, B cells, macrophages, and dendritic cells, is an immune compartment that exists in what was formerly the subintimal layer of normal synovium. These immune cells partake in antigen presentation, immunoglobulin production (including rheumatoid factor and anti-cyclic citrullinated protein [CCP] antibodies) and cytokine generation; the T cell is thought by many investigators to be the driving force coordinating these various activities

NF-kappaB transcription factors regulate inflammatory responses to cytokines such as IL-1beta and TNF-alpha. We tested whether PGE2 regulated nuclear localization of individual NF-kappaB subunits, p65 and p50, in synovial fibroblasts harvested from patients with rheumatoid arthritis (RA). IL-1beta/TNF-alpha stimulated the translocation of p65 and p50 from the cytosol to the nucleus of human RA synovial fibroblasts, as well as NF-kappaB activation measured by luciferase reporter assay. PGE2 (10 nM, 6 h) enhanced p50, but inhibited p65 translocation and NF-kappaB activation. In contrast, depletion of endogenous PGE2 by ibuprofen (100 microM) and celecoxib (5 microM) enhanced p65, but inhibited p50 nuclear translocation as well as binding to NF-kappaB DNA binding sites. PGE2 also blocked IL-1beta/TNF-alpha-stimulated ERK activation, and the ERK inhibitor, PD98059, mimicked PGE2 in blocking p65, but enhancing p50 nuclear translocation, suggesting that the effects of PGE2 on p65 and p50 are mediated via effects on ERK. PGE2 also enhanced the expression of IkappaBalpha in an ERK-independent manner, suggesting that PGE2 inhibits NF-kappaB activation by both ERK-dependent and -independent mechanisms. Our data indicate that PGE2 may act to attenuate cytokine-induced inflammatory responses in RA synovial fibroblasts via regulation of the localization of specific NF-kappaB family dimers