Inflammatory cytokines such as tumour necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) synergistically activate expression of the RANTES (regulated upon activation, normal T-cell expressed and secreted) gene, which plays a crucial role in the chemoattraction of leukocytes during the inflammatory response. To understand at the molecular level the mechanism by which the two cytokines activate RANTES gene expression, we determined the requirement of cis-acting elements in the RANTES promoter and trans-acting factors. The murine RANTES promoter contained one putative interferon regulatory factor, IRF, and three putative nuclear factor κB (NF-κB) binding sites. Specific destruction of the IRF binding site and one of the three NF-κB binding sites abolished the inducibility of promoter activity by IFN-γ and TNF-α, respectively. In contrast, mutation of the other two putative NF-κB binding sites did not affect RANTES promoter activity significantly. In addition, the RANTES promoter was stimulated by co-transfection of plasmids that expressed either p65, an NF-κB family protein, or the IRF-1 transcription factor. RANTES promoters with mutations in the NF-κB or IRF binding sites were not stimulated by p65 or IRF-1 expression, respectively. In electrophoretic mobility-shift and immunologic assays, we showed that IRF-1 was induced after cells were treated with IFN-γ and that NF-κB was activated by TNF-α treatment. These results demonstrate that both NF-κB and IRF-1 transcription factors mediate the induction of RANTES expression via their cognate cis-acting elements when cells are stimulated by TNF-α and IFN-γ.

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