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TLR9 ligands induce S100A8 in macrophages via a STAT3-dependent pathway which requires IL-10 and PGE2
Kenneth Hsu1, Yuen Ming Chung1, Yasumi Endoh1
1Inflammation and Infection Research Centre, School of Medical Sciences, University of New South Wales, Sydney, New South Wales, Australia.
Abstract:
S100A8 and S100A9 are highly-expressed calcium-binding proteins in neutrophils and monocytes, and in subsets of macrophages in inflammatory lesions. Unmethylated CpG motifs found in bacterial and viral DNA are potent activators of innate immunity via Toll-like receptor 9 (TLR9). S100A8, but not S100A9, mRNA and protein was directly induced by CpG-DNA in murine and human macrophages. Induction in murine macrophages peaked at 16 h. CpG-DNA-induced S100A8 required de novo protein synthesis; IL-10 and Prostaglandin E2 (PGE2) synergistically enhanced expression and promoted earlier gene induction. Inhibitors of endogenous IL-10, PGE2, and the E prostanoid (EP) 4 receptor strongly suppressed S100A8 expression, particularly when combined. Thus, S100A8 induction by E. coli DNA required both IL-10 and PGE2/EP4 signaling. The MAPKs, PI3K and JAK pathways were essential, whereas ERK1/2 appeared to play a direct role. S100A8 induction by CpG-DNA was controlled at the transcriptional level. The promoter region responsible for activation, either directly, or indirectly via IL-10 and PGE2, was located within a -178 to -34-bp region and required STAT3 binding. Because of the robust links connecting IL-10 and PGE2 with an anti-inflammatory macrophage phenotype, the induction profile of S100A8 strongly indicates a role for this protein in resolution of inflammation.
Insights
CpG-DNA directly induces S100A8 protein in macrophages, requiring IL-10 and PGE2 signaling for optimal expression. This suggests S100A8 plays a role in resolving inflammation.
Area of Science:
- Immunology
- Molecular Biology
Background:
- S100A8 and S100A9 are calcium-binding proteins crucial in innate immunity.
- Bacterial DNA's unmethylated CpG motifs activate Toll-like receptor 9 (TLR9), a key immune sensor.
Purpose of the Study:
- To investigate the direct induction of S100A8 by CpG-DNA in macrophages.
- To elucidate the signaling pathways and regulatory mechanisms involved in S100A8 expression.
Main Methods:
- Treatment of murine and human macrophages with CpG-DNA.
- Analysis of S100A8 mRNA and protein induction.
- Investigation of synergistic effects of IL-10 and Prostaglandin E2 (PGE2).
- Assessment of signaling pathway involvement (MAPKs, PI3K, JAK, ERK1/2).
- Identification of the transcriptional regulatory region and STAT3 binding site.
Main Results:
- CpG-DNA directly induced S100A8 mRNA and protein in macrophages, peaking at 16 hours.
- IL-10 and PGE2 synergistically enhanced S100A8 expression and promoted earlier induction.
- Inhibition of IL-10, PGE2, and EP4 receptor signaling suppressed S100A8 expression.
- MAPK, PI3K, and JAK pathways were essential, with ERK1/2 playing a direct role.
- Transcriptional analysis identified a -178 to -34-bp promoter region requiring STAT3 binding for activation.
Conclusions:
- CpG-DNA induction of S100A8 in macrophages is dependent on IL-10 and PGE2/EP4 signaling.
- S100A8 expression is transcriptionally regulated via a STAT3-binding promoter region.
- The induction profile of S100A8 suggests a role in the resolution of inflammation.
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