Objective: To determine the effect of the human T cell leukemia virus type I (HTLV-I) tax gene on interleukin-6 (IL-6) production and gene transcription in synovial cells, we established the synovial cell line, E-11, from a patient with rheumatoid arthritis.
Methods: E-11 cells were transfected with tax expression vector using the calcium phosphate coprecipitation method. IL-6 production and gene expression were investigated by ELISA and Northern blot analysis, respectively. To clarify how tax induces IL-6 gene expression, we used deletion analysis and chloramphenicol acetyltransferase (CAT) assay, and electrophoretic mobility shift assay (EMSA).
Results: Transfection of the tax gene induced markedly high levels of IL-6 mRNA. Furthermore, the tax gene strongly transactivated IL-6 gene promoter activity assayed by CAT assay. By using deletion and site specific mutations, we have identified a nuclear factor (NF)-kappa B sequence (positions -73 to -63) which is essential for tax transaction. EMSA demonstrated the induction of specific binding of nuclear extracts to the NF-kappa B sequence by HTLV-I tax.
Conclusion: The HTLV-1 tax gene may transactivate IL-6 gene in the synovial cells through NF-kappa B and may contribute in the pathophysiology of HTLV-I associated arthritis.