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PU.1 and ICSBP control constitutive and IFN‐γ‐regulated Tlr9 gene expression in mouse macrophages
Author(s) -
Schroder Kate,
Lichtinger Monika,
Irvine Katharine M.,
Brion Kristian,
Trieu Angela,
Ross Ian L.,
Ravasi Timothy,
Stacey Katryn J.,
Rehli Michael,
Hume David A.,
Sweet Matthew J.
Publication year - 2007
Publication title -
journal of leukocyte biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.819
H-Index - 191
eISSN - 1938-3673
pISSN - 0741-5400
DOI - 10.1189/jlb.0107036
Subject(s) - tlr9 , biology , microbiology and biotechnology , gene expression , promoter , regulation of gene expression , cpg site , irf8 , gene , dna methylation , genetics
Macrophages are activated by unmethylated CpG‐containing DNA (CpG DNA) via TLR9. IFN‐γ and LPS can synergize with CpG DNA to enhance proinflammatory responses in murine macrophages. Here, we show that LPS and IFN‐γ up‐regulated Tlr9 mRNA in murine bone marrow‐derived macrophages (BMM). The ability of LPS and IFN‐γ to induce Tlr9 mRNA expression in BMM was dependent on the presence of the growth factor, CSF‐1, which is constitutively present in vivo. However, there were clear differences in mechanisms of Tlr9 mRNA induction. LPS stimulation rapidly removed the CSF‐1 receptor (CSF‐1R) from the cell surface, thereby blocking CSF‐1‐mediated transcriptional repression and indirectly inducing Tlr9 mRNA expression. By contrast, IFN‐γ activated the Tlr9 promoter directly and only marginally affected cell surface CSF‐1R expression. An ∼100‐bp proximal promoter of the murine Tlr9 gene was sufficient to confer basal and IFN‐γ‐inducible expression in RAW264.7 cells. A composite IFN regulatory factor (IRF)/PU.1 site upon the major transcription start site was identified. Mutation of the binding sites for PU.1 or IRF impaired basal promoter activity, but only the IRF‐binding site was required for IFN‐γ induction. The mRNA expression of the IRF family member IFN consensus‐binding protein [(ICSBP)/IRF8] was coregulated with Tlr9 in macrophages, and constitutive and IFN‐γ‐inducible Tlr9 mRNA expression was reduced in ICSBP‐deficient BMM. This study therefore characterizes the regulation of mouse Tlr9 expression and defines a molecular mechanism by which IFN‐γ amplifies mouse macrophage responses to CpG DNA.