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Intracellular HMGB1 transactivates the human IL1B gene promoter through association with an Ets transcription factor PU.1

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Abstract

High mobility group box 1 protein (HMGB1), originally described as a non-histone, DNA binding protein, was recently identified as a late mediator of inflammation via its extracellular release from activated macrophages/monocytes. In the present study, we report that intracellular HMGB1 synergizes with a macrophage/monocyte-specific E26 transformation-specific sequence (Ets) transcription factor PU.1 to transactivate the promoter of the IL1B gene coding a 31-kDa proIL-1β protein. The −131 to +12 IL1B promoter, which possesses a PU.1 binding motif essential for its transactivation, was induced when HMGB1 expression vector was transfected into murine RAW264.7 macrophage cells. Our glutathione S-transferase-pulldown and coimmunoprecipitation assays demonstrated direct physical interaction of HMGB1 with PU.1. Deletion of the PU.1 winged helix-turn-helix DNA-binding domain inhibited the association of the two proteins. In electrophoretic mobility shift assay using recombinant PU.1 protein, a ternary complex of PU.1, HMGB1 and PU.1-binding element within the IL1B promoter was generated. The importance of PU.1 was further supported by our observation that induction of the IL1B promoter was obtained only after PU.1 expression in PU.1-deficient murine EL4 thymoma cells. Thus, our data raise the possibility of a novel mechanism which sustains and amplifies inflammatory reactions through physical interaction of PU.1 with intracellular HMGB1 in macrophages/monocytes.
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Keywords: PU.1; high mobility group box 1; interleukin-1; macrophage

Document Type: Research Article

Affiliations: 1: The first Department of Internal Medicine, School of Medicine, University of Occupational and Environmental Health, Kitakyushu 2: Department of Immunology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu 3: Department of Genome Sciences, Faculty of Medical Sciences, Graduate School of Medicine, Kobe University, Kobe 4: Department of Molecular Biology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu 5: Department of Legal Medicine and Molecular Genetics, Graduate School of Medicine, Gunma University, Maebashi, Japan

Publication date: January 1, 2008

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