ExoU Activates NF-κB and Increases IL-8/KC Secretion during Pseudomonas aeruginosa Infection

Abstract

ExoU, a Pseudomonas aeruginosa cytotoxin injected into host cytosol by type III secretion system, exhibits a potent proinflammatory activity that leads to a marked recruitment of neutrophils to infected tissues. To evaluate the mechanisms that account for neutrophil infiltration, we investigated the effect of ExoU on IL-8 secretion and NF-κB activation. We demonstrate that ExoU increases IL-8 mRNA and protein levels in P. aeruginosa-infected epithelial and endothelial cell lines. Also, ExoU induces the nuclear translocation of p65/p50 NF-κB transactivator heterodimer as well as NF-κB-dependent transcriptional activity. ChIP assays clearly revealed that ExoU promotes p65 binding to NF-κB site in IL-8 promoter and the treatment of cultures with the NF-κB inhibitor Bay 11-7082 led to a significant reduction in IL-8 mRNA levels and protein secretion induced by ExoU. These results were corroborated in a murine model of pneumonia that revealed a significant reduction in KC secretion and neutrophil infiltration in bronchoalveolar lavage when mice were treated with Bay 11-7082 before infection with an ExoU-producing strain. In conclusion, our data demonstrate that ExoU activates NF-κB, stimulating IL-8 expression and secretion during P. aeruginosa infection, and unveils a new mechanism triggered by this important virulence factor to interfere in host signaling pathways.

Adaptation-Based Resistance to Siderophore-Conjugated Antibacterial Agents by Pseudomonas aeruginosa

“…While its frequency and persistence within the lungs of cystic fibrosis (CF) patients have been the focus of a substantial amount of research effort, its virulence has also been linked to other non-CF disease states or conditions such as burns (15), wound infections (16), and nosocomial pneumonia (17). The pathogenic versatility of P. aeruginosa can be attributed to the myriad of virulence factors that it is capable of producing, including multiple toxins (18,19), degradative enzymes (20), a functional type III secretion system (21), and several different polysaccharides (22)(23)(24), each of which have been demonstrated to protect this pathogen in various stages of its life cycle. Also included in that list of important virulence factors is the extensive iron acquisition system encoded within the genome of P. aeruginosa strains.…”

Bacterial Sphingomyelinases and Phospholipases as Virulence Factors

“…ExoU contributes to promote the host inflammatory response and oxidative stress through different mechanisms (151,(155)(156)(157)(158). ExoU releases arachidonic acid from cell membranes, leading to a subsequent increase in eicosanoid production by endothelial cells and airway epithelial cells (156).…”

“…ExoU inhibits caspase-1 activation and thereby the secretion of interleukin-1␤ and interleukin-18 (151). ExoU induces NF-B activation through the canonical pathway by platelet activating factor (PAF) receptor signaling, leading to IL-8 production and neutrophil recruitment (158). The ExoU-mediated activation of NF-B in turn favors PAF receptor expression, which amplifies its effects (159).…”

Thrombin-Induced CCAAT/Enhancer-Binding Protein β Activation and IL-8/CXCL8 Expression via MEKK1, ERK, and p90 Ribosomal S6 Kinase 1 in Lung Epithelial Cells

“…Many studies revealed that IL-8/CXCL8 expression is regulated by activation of several transcription factors, including NF-kB and C/EBPb (14,29). Our previous studies showed that NF-kB activation plays a role in thrombin-induced IL-8/CXCL8 expression (12,13).…”