JUN and rheumatoid arthritis: The synthesis is regulated mainly by the transcription factors NF-IL-6, CAAT-enhancer-binding protein (C/EBP)-β, AP-1, and nuclear factor-kappa-B (NF-κB) [8,10,11], which are constitutively activated in RA synovial tissue (for a review, see [12]) and have binding sites in the promoter region of the IL-6 gene.