FOS and arthritic joint disease: Another major transcription factor that contributes to the pathogenesis of arthritis is c-fos/AP-1, since c-fos/AP-1 not only directly controls the expression of inflammatory cytokines and MMPs by binding to AP-1 motifs in the promoters of these genes [31], but participates in a cross-talk with IL-1β to influence each other's gene expression and activity [32], [33].