Non-Transcriptional and Translational Function of Canonical NF- κ B Signaling in Activating ERK1/2 in IL-1 β -Induced COX-2 Expression in Synovial Fibroblasts

The pro-inflammatory cytokine interleukin 1 (IL-1 ) induces the synthesis of prostaglandin E by upregulating cyclooxygenase-2 (COX-2) in the synovial tissue of individuals with autoimmune diseases, such as rheumatoid arthritis (RA). IL-1 -mediated stimulation of NF- B and MAPK signaling is important for the pathogenesis of RA; however, crosstalk(s) between NF- B and MAPK signaling remains to be understood. In this study, we established a model for IL-1 -induced synovitis and investigated the role of NF- B and MAPK signaling in synovitis. We observed an increase in the mRNA and protein levels of COX-2 and prostaglandin E release in cells treated with IL-1 . NF- B and ERK1/2 inhibitors significantly reduced IL-1 -induced COX-2 expression. IL-1 induced the phosphorylation of canonical NF- B complex (p65 and p105) and degradation of I B . IL-1 also induced ERK1/2 phosphorylation but did not affect the phosphorylation levels of p38 MAPK and JNK. IL-1 failed to induce COX-2 expression in cells transfected with siRNA for p65, p105, ERK1, or ERK2. Notably, NF- B inhibitors reduced IL-1 -induced ERK1/2 phosphorylation; however, the ERK1/2 inhibitor had no effect on the phosphorylation of the canonical NF- B complex. Although transcription and translation inhibitors had no effect on IL-1 -induced ERK1/2 phosphorylation, the silencing of canonical NF- B complex in siRNA-transfected fibroblasts prevented IL-1 -induced phosphorylation of ERK1/2. Taken together, our data indicate the importance of the non-transcriptional/translational activity of canonical NF- B in the activation of ERK1/2 signaling involved in the IL-1 -induced development of autoimmune diseases affecting the synovial tissue, such as RA.