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Kruppel-like factor 4 is a mediator of proinflammatory signaling in macrophages

Mark W Feinberg1, Zhuoxiao Cao, Akm Khyrul Wara

  • 1Program in Cardiovascular Transcriptional Biology, Cardiovascular Division, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA. mfeinberg@rics.bwh.harvard.edu

The Journal of Biological Chemistry
|September 20, 2005
PubMed

Insights

Kruppel-like factor 4 (KLF4) regulates macrophage activation by balancing pro-inflammatory and anti-inflammatory signals. This study identifies KLF4 as a key mediator in chronic inflammatory diseases like atherosclerosis.

Area of Science:

  • Immunology
  • Molecular Biology
  • Cell Biology

Background:

  • Macrophage activation is crucial in chronic inflammatory diseases, including atherosclerosis.
  • Pro-inflammatory cytokines (interferon-gamma, lipopolysaccharide, tumor necrosis factor-alpha) promote activation, while anti-inflammatory factors (transforming growth factor-beta1) suppress it.
  • The molecular regulators balancing these opposing pathways are not fully understood.

Purpose of the Study:

  • To identify novel molecular mediators that regulate the balance between pro-inflammatory and anti-inflammatory signaling in macrophages.
  • To elucidate the role of Kruppel-like factor 4 (KLF4) in controlling macrophage activation pathways.

Main Methods:

  • Investigated KLF4 expression in response to various cytokines in macrophages.
  • Utilized gene overexpression and knockdown techniques to assess KLF4's functional impact on macrophage activation markers (inducible nitric-oxide synthase - iNOS) and cytokine signaling pathways (TGF-beta1/Smad3).
  • Analyzed KLF4's interaction with signaling proteins (p65/RelA, Smad3) and its effect on gene promoter activity (iNOS, plasminogen activator inhibitor-1 - PAI-1).

Main Results:

  • KLF4 expression is induced by pro-inflammatory stimuli (IFN-gamma, LPS, TNF-alpha) and suppressed by TGF-beta1.
  • KLF4 overexpression activates the iNOS promoter and inhibits the TGF-beta1/Smad3-mediated PAI-1 promoter.
  • KLF4 knockdown attenuates pro-inflammatory induction of iNOS and enhances TGF-beta1/Smad3 signaling.
  • KLF4 interacts with p65/RelA to induce the iNOS promoter and antagonizes Smad3 for p300/CBP to inhibit PAI-1 induction.

Conclusions:

  • KLF4 is a critical regulator of macrophage activation, integrating pro-inflammatory and anti-inflammatory signals.
  • KLF4 plays a significant role in pathways relevant to chronic inflammatory conditions like atherosclerosis.
  • KLF4's distinct mechanisms of action on iNOS and PAI-1 promoters highlight its complex regulatory function.

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