Elk-3 is a KLF4-regulated gene that modulates the phagocytosis of bacteria by macrophages

J Leukoc Biol. 2015 Jan;97(1):171-80. doi: 10.1189/jlb.4A0214-087R. Epub 2014 Oct 28.

Abstract

ETS family proteins play a role in immune responses. A unique member of this family, Elk-3, is a transcriptional repressor that regulates the expression of HO-1. Elk-3 is very sensitive to the effects of inflammatory mediators and is down-regulated by bacterial endotoxin (LPS). In the present study, exposure of mouse macrophages to Escherichia coli LPS resulted in decreased, full-length, and splice-variant isoforms of Elk-3. We isolated the Elk-3 promoter and demonstrated that LPS also decreased promoter activity. The Elk-3 promoter contains GC-rich regions that are putative binding sites for zinc-finger transcription factors, such as Sp1 and KLFs. Mutation of the GC-rich region from bp -613 to -603 blunted LPS-induced down-regulation of the Elk-3 promoter. Similar to the LPS response, coexpression of KLF4 led to repression of Elk-3 promoter activity, whereas coexpression of Sp1 increased activity. ChIP assays revealed that KLF4 binding to the Elk-3 promoter was increased by LPS exposure, and Sp1 binding was decreased. Thus, down-regulation of Elk-3 by bacterial LPS is regulated, in part, by the transcriptional repressor KLF4. Overexpression of Elk-3, in the presence of E. coli bacteria, resulted in decreased macrophage phagocytosis. To determine whether limited expression of HO-1 may contribute to this response, we exposed HO-1-deficient bone marrow-derived macrophages to E. coli and found a comparable reduction in bacterial phagocytosis. These data suggest that down-regulation of Elk-3 and the subsequent induction of HO-1 are important for macrophage function during the inflammatory response to infection.

Keywords: gene regulation; heme oxygenase-1; infection; inflammation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blotting, Western
  • Cell Line
  • Chromatin Immunoprecipitation
  • Escherichia coli Infections / immunology
  • Gene Expression Regulation / immunology*
  • Heme Oxygenase-1 / immunology
  • Inflammation / immunology
  • Kruppel-Like Transcription Factors / genetics
  • Kruppel-Like Transcription Factors / immunology*
  • Macrophages / immunology*
  • Membrane Proteins / immunology
  • Mice
  • Mice, Knockout
  • Mutagenesis, Site-Directed
  • Phagocytosis / genetics
  • Phagocytosis / immunology*
  • Proto-Oncogene Proteins c-ets / genetics
  • Proto-Oncogene Proteins c-ets / immunology*
  • Real-Time Polymerase Chain Reaction
  • Transfection

Substances

  • Elk3 protein, mouse
  • GKLF protein
  • Kruppel-Like Transcription Factors
  • Membrane Proteins
  • Proto-Oncogene Proteins c-ets
  • Heme Oxygenase-1
  • Hmox1 protein, mouse