Induction of nuclear factor-κB responses by the S100A9 protein is Toll-like receptor-4-dependent

Immunology. 2012 Oct;137(2):172-82. doi: 10.1111/j.1365-2567.2012.03619.x.

Abstract

Interactions between danger-associated molecular patterns (DAMP) and pathogen-associated molecular patterns (PAMP) and pattern recognition receptors such as Toll-like receptors (TLRs) are critical for the regulation of the inflammatory process via activation of nuclear factor-κB (NF-κB) and cytokine secretion. In this report, we investigated the capacity of lipopolysaccharide (LPS) -free S100A9 (DAMP) protein to activate human and mouse cells compared with lipoprotein-free LPS (PAMP). First, we showed that LPS and S100A9 were able to increase NF-κB activity followed by increased cytokine and nitric oxide (NO) secretion both in human THP-1 cells and in mouse bone marrow-derived dendritic cells. Surprisingly, although S100A9 triggered a weaker cytokine response than LPS, we found that S100A9 more potently induced IκBα degradation and hence NF-κB activation. Both the S100A9-induced response and the LPS-induced response were completely absent in TLR4 knockout mice, whereas it was only slightly affected in RAGE knockout mice. Also, we showed that LPS and S100A9 NF-κB induction were strongly reduced in the presence of specific inhibitors of TLR-signalling. Chloroquine reduced S100A9 but not LPS signalling, indicating that S100A9 may need to be internalized to be fully active as a TLR4 inducer. This was confirmed using A488-labelled S100A9 that was internalized in THP-1 cells, showing a raise in fluorescence after 30 min at 37°. Chloroquine treatment significantly reduced the fluorescence. In summary, our data indicate that both human and mouse S100A9 are TLR4 agonists. Importantly, S100A9 induced stronger NF-κB activation albeit weaker cytokine secretion than LPS, suggesting that S100A9 and LPS activated NF-κB in a qualitatively distinct manner.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calgranulin B / genetics
  • Calgranulin B / immunology*
  • Calgranulin B / metabolism
  • Cells, Cultured
  • Dendritic Cells / immunology
  • Dendritic Cells / metabolism
  • Humans
  • Lipopolysaccharides / immunology
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • NF-kappa B / immunology*
  • NF-kappa B / metabolism
  • Nitric Oxide / metabolism
  • Signal Transduction
  • Toll-Like Receptor 4 / deficiency
  • Toll-Like Receptor 4 / immunology*

Substances

  • Calgranulin B
  • Lipopolysaccharides
  • NF-kappa B
  • Tlr4 protein, mouse
  • Toll-Like Receptor 4
  • Nitric Oxide