Rheumatoid arthritis synoviocyte survival is dependent on Stat3

Rheumatoid arthritis (RA) synovial fibroblasts (SFs) are relatively resistant to apoptosis and exhibit dysregulated growth secondary to production of autocrine-acting growth factors and the accumulation of cell-autonomous defects. Many of the cytokines and growth factors expressed during RA synovitis, including IL-6, epidermal growth factor (EGF), and platelet-derived growth factor, activate the transcription factor Stat3 that has been implicated in promoting cell growth and survival. We analyzed the role of Stat3 in mediating the abnormal growth and survival properties of RA synoviocytes using retroviral-mediated gene transfer of a dominant negative mutant of Stat3, termed Stat3-YF. Approximately 3- to 5-fold overexpression of Stat3-YF effectively blocked endogenous Stat3 activation and Stat3-dependent gene expression, including expression of the socs3 and myc genes. Stat3-YF-transduced RA synoviocytes failed to grow in culture, exhibited markedly diminished [H-3]thymidine incorporation (>90% decreased), and died spontaneously. Cell death occurred by apoptosis, as confirmed by annexin V staining, propidium iodide exclusion, and identification of cells with subdiploid levels of DNA. In marked contrast to control cells, EGF accelerated death of Stat3-YF-transduced SFs, such that >90% of cells were dead within 24-48 h of transduction. These results indicate that ablation of Stat3 function converts EGF from a growth/survival factor for RA synoviocytes to a death factor. Stat3-YF also induced apoptosis in osteoarthritis synoviocytes, and levels of apoptosis were increased by exogenous EGF. Apoptosis in Stat3-YF-transduced osteoarthritis synoviocytes was suppressed when Stat1 activity was blocked using a dominant negative Stat1 mutant. Our results identify Stat3 as an important molecule for RA SF survival, and suggest that Stat3 may represent a good target for gene therapy.