To investigate the expression of the transcription factor Ets-1 in synovial tissue and cultured synovial fibroblasts from patients with rheumatoid arthritis (RA) and osteoarthritis (OA) and to study the regulation of Ets-1 expression and activation in synovial fibroblasts by proinflammatory cytokines.
In situ expression of Ets-1 in synovial tissue from RA and OA patients was examined by double immunohistochemistry. The effects of interleukin-1 (IL-1) or tumor necrosis factor alpha (TNFalpha) on Ets-1 expression and 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.
Pronounced expression of Ets-1 was detected in synovial tissues from all RA patients evaluated, particularly in the synovial lining layer and the sublining areas. Ets-1 was expressed by both fibroblasts and macrophages as well as by endothelial cells, while only a few T cells stained positive 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 from RA and OA patients, as demonstrated by reverse transcriptase-polymerase chain reaction and Western blotting. Both IL-1 and TNFalpha induced pronounced up-regulation of Ets-1 in synovial fibroblasts. Moreover, binding of Ets-1 to its specific DNA binding site was induced by both cytokines, although with different time courses. Immunofluorescence staining revealed a dominant nuclear localization of Ets-1 in IL-1- or TNFalpha-stimulated synovial fibroblasts.
The overexpression of Ets-1 observed in RA synovial tissue appears to be caused by TNFalpha and IL-1, suggesting that Ets-1 may be an important factor in the cytokine-mediated inflammatory and destructive cascade characteristic of RA.