Cell cycle implications in the pathogenesis of rheumatoid arthritis.

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by hyperplasia of the synovial lining cells, angiogenesis, and infiltration of mononuclear cells resulting in pannus formation, cartilage erosion and ultimately joint destruction. Synovial tissue (ST) fibroblast hyperplasia is reminiscent of tumor-like proliferation and is a major cause of cartilage destruction in the RA joint. The RA joint is replete with cytokines and growth factors which exert a synergistic mitogenic effect on ST fibroblasts. As a result, RA ST fibroblasts exhibit elevated gene expression of proto- oncogenes, such as c-Myc, c-Ras, and c-Jun and apoptosis inhibitors such as Bcl-2. At the same time, RA ST fibroblasts contain mutations in tumor suppressor genes such as p53. The altered rates of proliferation and apoptosis of RA synovial cells result in the hyperplasia of synovial tissue and in concert with the chronic inflammatory environment ultimately lead to the destruction of the RA joint.