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

Abstract

SummaryInteractions 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-jB (NF-jB) 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-jB 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 IjBa degradation and hence NF-jB 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-jB 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-jB activation albeit weaker cytokine secretion than LPS, suggesting that S100A9 and LPS activated NF-jB in a qualitatively distinct manner.

Transcriptome Assessment Reveals a Dominant Role for TLR4 in the Activation of Human Monocytes by the Alarmin MRP8

“…For isolated MRP14, similar findings were found. Although it could be shown that MRP14 binds to both receptors TLR4 as well as RAGE (19), cytokine induction could only be observed for MRP14-TLR4-dependent activation in a cell line culturing model (39). Studies on phagocytes from TLR4 mutant mice clearly indicate that TLR4 is mainly responsible for MRP8-dependent activation in these cells (9).…”

Human S100A9 potentiates IL‐8 production in response to GM‐CSF or fMLP via activation of a different set of transcription factors in neutrophils

“…Binding of S100A8 and S100A9 to TLR-4 leads to the activation of NF-jB and secretion of inflammatory cytokines in murine BMC and THP-1 cells [6,19]. In addition, studies have reported important roles for S100A8, S100A8/A9 and S100A9 in the regulation of cytokine secretion by monocytes [15,19,20]. However, only one study reported an effect of S100A8 on the secretion of IL-8 and IL-16 by human neutrophils [21].…”

Calgranulins May Contribute Vascular Protection In Atherogenesis

“…68 In contrast, TLR4 is implicated in monocyte and DC activation by S100A9. 81 Another study showed a requirement for Ca 2+ and Zn 2+ to achieve high-affinity S100A9 binding to TLR4/MD2, whereas S100A8/A9 binding was less. 80 S100A12 is also recently reported to activate human monocytes via TLR4 69 rather than RAGE.…”