PU.1 and ICSBP control constitutive and IFN-gamma-regulated Tlr9 gene expression in mouse macrophages

Kate Schroder, Monika Lichtinger, Katharine M Irvine, Kristian Brion, Angela Trieu, Ian L Ross, Timothy Ravasi, Katryn J Stacey, Michael Rehli, David A Hume, Matthew J Sweet

Research output: Contribution to journalArticlepeer-review

Abstract

Macrophages are activated by unmethylated CpG-containing DNA (CpG DNA) via TLR9. IFN-gamma and LPS can synergize with CpG DNA to enhance proinflammatory responses in murine macrophages. Here, we show that LPS and IFN-gamma up-regulated Tlr9 mRNA in murine bone marrow-derived macrophages (BMM). The ability of LPS and IFN-gamma 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-gamma activated the Tlr9 promoter directly and only marginally affected cell surface CSF-1R expression. An approximately 100-bp proximal promoter of the murine Tlr9 gene was sufficient to confer basal and IFN-gamma-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-gamma 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-gamma-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-gamma amplifies mouse macrophage responses to CpG DNA.
Original languageEnglish
Pages (from-to)1577-90
Number of pages14
JournalJournal of Leukocyte Biology
Volume81
Issue number6
DOIs
Publication statusPublished - Jun 2007

Keywords

  • Animals
  • Base Sequence
  • Cells, Cultured
  • CpG Islands
  • Gene Expression Regulation
  • Interferon Regulatory Factors
  • Interferon-gamma
  • Lipopolysaccharides
  • Macrophage Colony-Stimulating Factor
  • Macrophages
  • Mice
  • Molecular Sequence Data
  • Promoter Regions, Genetic
  • Proto-Oncogene Proteins
  • Receptor, Macrophage Colony-Stimulating Factor
  • Recombinant Proteins
  • Response Elements
  • Toll-Like Receptor 9
  • Trans-Activators

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