JUN and rheumatoid arthritis: The mechanisms involved in RA FLS phenotype are still unclear, with some contributions from c-Jun, a member of the activator protein 1 (AP-1) (19), nuclear factor κB (NF-κB) pathway (20), p53 or B-cell lymphoma 2 (Bcl-2) family members involved in apoptosis regulation (20, 21), and/or epigenetic alterations (22).