Molecular mechanisms regulating induction of interleukin‐6 gene transcription by interferon‐γ

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Abstract
The multifunctional cytokine interleukin-6 (IL-6) plays a central role in host defence mechanisms and hematopoiesis. Furthermore, dysregulation of IL-6 gene expression is associated with the pathogenesis of various immunologically related diseases such as myeloma, systemic lupus erythematosus, rheumatoid arthritis, psoriasis and Kaposi's sarcoma. The regulation of IL-6 gene expression occurs mainly at transcriptional level, although mechanisms of post-transcriptional regulation have also been described. In the present study we demonstrate that in HeLa cells, induction of IL-6 by interferon-γ (IFN-γ) is transcriptionally controlled, as shown by run on assays and analysis of the IL-6 mRNA stability. Gel-retardation experiments using antibodies specific for factors of the IRF family identified four protein-DNA complexes, which bind to the interferon regulatory factor (IRF) binding site at position −267 to −254, in nuclear extracts from IFN-γ treated cells. Furthermore, transient transfection analyses of the 5′-flanking region of IL-6 gene linked to the chloramphenicol acetyltransferase (CAT) reporter gene demonstrated that the −267 to −254 IRF site is necessary for IL-6 induction by IFN-γ. However, transfection experiments in which IRF-1 and IxBα were overexpressed show that full-scale transcriptional activation of the IL-6 promoter directing CAT expression requires the co-operation between IRF-1 and NF-xB at a low constitutive level.