Involvement of IL-6 in the pathogenesis of rheumatoid arthritis has recently been demonstrated, but the mechanism of its production by rheumatoid synoviocytes is still poorly defined.
The purpose of this study was to clarify the cellular and molecular mechanisms involved in the spontaneous production of IL-6 by fibroblast-like synoviocytes obtained from patients with rheumatoid arthritis.
Cloned synoviocytes were established by the limiting dilution method. IL-6 synthesis was evaluated by ELISA and Northern blot analysis. IL-6 gene transcription and transcription factors were analyzed by the transient transfection of luciferase reporter plasmids and the electrophoretic mobility shift assay, respectively.
IL-6 synthesis by cloned rheumatoid synoviocytes was spontaneously upregulated at the transcriptional level. Enhanced IL-6 production by high-producing clones was independent of cytokines from other cell populations or autocrine production of tumor necrosis factor-alpha and IL-1. Deletion analysis showed that the IL-6 promoter was regulated by 2 positive elements (-159 to -142 base pair and -77 to -59 base pair). The transcriptional activity of the latter element was upregulated in clones showing high IL-6 production. The binding activity of NF-kappaB p50/p65 heterodimer and RBP-Jkappa was enhanced in these clones.
IL-6 production by rheumatoid synoviocytes is autonomously upregulated at the transcriptional level and spontaneous activation of NF-kappaB and RBP-Jkappa seems to be involved.