Overexpression of transcription factor Ets-1 in rheumatoid arthritis synovial membrane - Regulation of expression and activation by interleukin-1 andtumor necrosis factor alpha

Objective. To investigate the expression of the transcription factor Ets-1 in synovial tissue and cultured synovial fibroblasts from patients with rhe umatoid arthritis (RA) and osteoarthritis (OA) and to study the regulation of Ets-1 expression and activation in synovial fibroblasts by proinflammato ry cytokines. Methods. In situ expression of Ets-1 in synovial tissue from RA and OA pati ents was examined by double immunohistochemistry. The effects of interleuki n-1 (IL-1) or tumor necrosis factor alpha (TNF alpha) on Ets-1 expression a nd activation (DNA binding) in cultured synovial fibroblasts were analyzed by Western blotting and DNA gel shift assay, respectively. In addition, the intracellular location of Ets-1 in synovial fibroblasts was determined by immunofluorescence. Results. Pronounced expression of Ets-1 was detected in synovial tissues fr om all RA patients evaluated, particularly in the synovial lining layer and the sublining areas. Ets-1 was expressed by both fibroblasts and macrophag es as well as by endothelial cells, while only a few T cells stained positi ve for Ets-1. In synovial specimens from OA patients, Ets-1 expression was much less frequently observed and was largely restricted to vascular cells. Ets-1 was expressed to a similar degree in cultured synovial fibroblasts f rom RA and OA patients, as demonstrated by reverse transcriptase-polymerase chain reaction and Western blotting. Both IL-I and TNF alpha induced prono unced up-regulation of Ets-1 in synovial fibroblasts. Moreover, binding of Ets-1 to its specific DNA binding site was induced by both cytokines, altho ugh with different time courses. Immunofluorescence staining revealed a dom inant nuclear localization of Ets-1 in IL-1- or TNF alpha -stimulated synov ial fibroblasts. Conclusion. The overexpression of Ets-1 observed in RA synovial tissue appe ars to be caused by TNF alpha and IL-1, suggesting that Ets-1 may be an imp ortant factor in the cytokine-mediated inflammatory and destructive cascade characteristic of RA.