Cold-inducible RNA-binding protein induces inflammatory responses via NF-κB signaling pathway in normal human bronchial epithelial cells infected with streptococcus pneumoniae

Abstract

Abstract Background Community-acquired pneumonia is a significant cause of morbidity and mortality worldwide, with substantial clinical implications that warrant further investigation and intervention. The invasion of Streptococcus pneumoniae (S. pneumoniae, S.p) can result in serious conditions such as meningitis, sepsis or pneumonia. Extracellular Cold-inducible RNA-binding protein (eCIRP) acts as a damage-associated molecular pattern that triggers inflammatory responses and plays an important role in both acute and chronic inflammatory diseases. It remains unclear whether CIRP is involved in the process of S. pneumoniae infection in normal human bronchial epithelial cells (BEAS-2B). Methods Cell counting kit (CCK)-8 assay was used to detect the activity of BEAS-2B cells after Streptococcus pneumoniae infection. The distribution of CIRP in BEAS-2B cells was detected by immunofluorescence. Quantitative real-time PCR (PCR) and Western Blot (WB) were used to detect the expression of CIRP, nuclear factor kappa-B (NF-κB) p65, toll like receptor-4 (TLR4), interleukin-6 (IL-6), etc. The expressions of CIRP, IL-1β, IL-6, tumor necrosis factor-α (TNF-α) and monocyte chemoattractant protein-1 (MCP-1) were assessed by enzyme linked immunosorbent assay (ELISA). Results We discovered that CIRP affected the activity of BEAS-2B cells that were induced by S. pneumoniae infection. After S. pneumoniae infection, CIRP transferred from the nucleus to the cytoplasm, and pro-inflammatory cytokines (IL-1, IL-6, TNF-α and MCP-1) were then produced. We further found that a significant increase in the expression of NF-κB p65 protein following S. pneumoniae infection of BEAS-2B cells, which was significantly reduced upon si-CIRP interference. Treatment with TLR4 neutralizing antibodies and an NF-κB inhibitor resulted in a significant decrease in the expressions of IL-1β, IL-6, TNF-α and MCP-1 in BEAS-2B cells. Conclusions Infection with S. pneumoniae induces an upregulation of CIRP expression and translocation from the nucleus to the cytoplasm in BEAS-2B cells, which subsequently leads to the release of proinflammatory factors via activation of NF-κB signaling pathway. The identification of CIRP as a key mediator in S. pneumoniae-induced inflammation provides potential targets for therapeutic intervention against community-acquired pneumonia.