Pathogenesis of rheumatoid arthritis and c-Fos/AP-1.

c-Fos/AP-1 controls the expression of inflammatory cytokines and matrix-degrading matrix metalloproteinases (MMPs) important in arthritis via promoter AP-1 binding motif. Among inflammatory cytokines, IL-1beta is the most important inducer of a variety of MMPs, and mainly responsible for cartilage breakdown and osteoclastogenesis. IL-1beta and c-Fos/AP-1 influence each other's gene expression and activity, resulting in an orchestrated cross-talk that is crucial to arthritic joint destruction, where TNFalpha can act synergistically with them. While how to stop the degradation of bone and cartilage, i.e., to control MMP, has long been the central issue in the research of rheumatoid arthritis (RA), selective inhibition of c-Fos/AP-1 does resolve arthritic joint destruction. Thus, the blockade of IL-1beta and/or c-Fos/AP-1 can be promising as an effective therapy for rheumatoid joint destruction in addition to the currently available TNFalpha blocking agents that act mainly on arthritis.