A Cross-Disciplinary Perspective on the Innate Immune Responses to Bacterial Lipopolysaccharide

Ya, Tan; Kagan, Jonathan C.

doi:10.1016/j.molcel.2014.03.012

Cited by 166 publications

(140 citation statements)

References 109 publications

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“…MrpJ regulates expression or modification of cell surface molecules, such as lipoproteins and LPS, which have been associated with virulence by other bacterial pathogens (78)(79)(80)(81), and we hypothesize these changes aid P. mirabilis survival in the urinary tract by bolstering bacterial defenses against the innate immune response.…”

Section: Discussionmentioning

confidence: 95%

Transcriptional Analysis of the MrpJ Network: Modulation of Diverse Virulence-Associated Genes and Direct Regulation of mrp Fimbrial and flhDC Flagellar Operons in Proteus mirabilis

et al. 2015

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The enteric bacterium Proteus mirabilis is associated with a significant number of catheter-associated urinary tract infections (UTIs). Strict regulation of the antagonistic processes of adhesion and motility, mediated by fimbriae and flagella, respectively, is essential for disease progression. Previously, the transcriptional regulator MrpJ, which is encoded by the mrp fimbrial operon, has been shown to repress both swimming and swarming motility. Here we show that MrpJ affects an array of cellular processes beyond adherence and motility. Microarray analysis found that expression of mrpJ mimicking levels observed during UTIs leads to differential expression of 217 genes related to, among other functions, bacterial virulence, type VI secretion, and metabolism. We probed the molecular mechanism of transcriptional regulation by MrpJ using transcriptional reporters and chromatin immunoprecipitation (ChIP). Binding of MrpJ to two virulence-associated target gene promoters, the promoters of the flagellar master regulator flhDC and mrp itself, appears to be affected by the condensation state of the native chromosome, although both targets share a direct MrpJ binding site proximal to the transcriptional start. Furthermore, an mrpJ deletion mutant colonized the bladders of mice at significantly lower levels in a transurethral model of infection. Additionally, we observed that mrpJ is widely conserved in a collection of recent clinical isolates. Altogether, these findings support a role of MrpJ as a global regulator of P. mirabilis virulence. Bacterial pathogens utilize a myriad of complex regulatory networks to adapt gene expression in response to environmental cues encountered in the host. Trying to walk a fine balance of avoiding detection by the host immune system, while ensuring acquisition of all essential nutrients and promoting growth, bacteria employ transcriptional and posttranscriptional strategies to combat the host's defenses. A prominent example is the specific induction of iron and zinc uptake systems during infection, regulated by Fur and Zur, respectively, which allows pathogens to gain access to these essential transition metals in the restricted host environment (1, 2).Urinary tract infections (UTIs) are among the most common bacterial infections (3), presenting a significant public health burden amounting to annual costs of about 3.5 billion dollars in the United States alone (4). Although Proteus mirabilis causes a relatively small proportion of UTIs in healthy individuals, it is a common cause of cystitis and pyelonephritis in individuals with indwelling catheters or anatomical abnormalities of the urinary tract (4, 5).UTIs occur almost exclusively in an ascending route, meaning that bacteria of fecal origin gain entry to the bladder via the urethra and then spread to the kidneys via the ureters (4). Initially, bacteria adhere to host epithelial cells via proteinaceous supramolecular structures referred to as fimbriae (or pili) (6), which allow pathogens to withstand the mechanical flow of urine (5)...

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Section: Discussionmentioning

confidence: 95%

Transcriptional Analysis of the MrpJ Network: Modulation of Diverse Virulence-Associated Genes and Direct Regulation of mrp Fimbrial and flhDC Flagellar Operons in Proteus mirabilis

et al. 2015

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“…An excessive inflammatory response can lead to tissue damage and inflammatory disorders, such as atherosclerosis or arthritis. 1,2 Macrophages sense microbial pathogen infection mainly through the toll-like receptor (TLR) family. TLR4 recognizes lipopolysaccharides (LPS) in the outer membrane of gram-negative bacteria.…”

Section: Introductionmentioning

confidence: 99%

miR-155 targets Caspase-3 mRNA in activated macrophages

et al. 2015

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To secure the functionality of activated macrophages in the innate immune response, efficient life span control is required. Recognition of bacterial lipopolysaccharides (LPS) by toll-like receptor 4 (TLR4) induces downstream signaling pathways, which merge to induce the expression of cytokine genes and anti-apoptotic genes. MicroRNAs (miRNAs) have emerged as important inflammatory response modulators, but information about their functional impact on apoptosis is scarce. To identify miRNAs differentially expressed in response to LPS, cDNA libraries from untreated and LPSactivated murine macrophages were analyzed by deep sequencing and regulated miRNA expression was verified by Northern blotting and qPCR. Employing TargetScan TM we identified CASPASE-3 (CASP-3) mRNA that encodes a key player in apoptosis as potential target of LPSinduced miR-155. LPS-dependent primary macrophage activation revealed TLR4-mediated enhancement of miR-155 expression and CASP-3 mRNA reduction. Endogenous CASP-3 and cleaved CASP-3 protein declined in LPS-activated macrophages. Accumulation of miR-155 and CASP-3 mRNA in miRNA-induced silencing complexes (miRISC) was demonstrated by ARGONAUTE 2 (AGO2) immunoprecipitation. Importantly, specific antagomir transfection effectively reduced mature miR-155 and resulted in significantly elevated CASP-3 mRNA levels in activated macrophages. In vitro translation assays demonstrated that the target site in the CASP-3 mRNA 3'UTR mediates miR-155-dependent Luciferase reporter mRNA destabilization. Strikingly, Annexin V staining of macrophages transfected with antagomir-155 and stimulated with LPS prior to staurosporine (SSP) treatment implied that LPS-induced miR-155 prevents apoptosis through CASP-3 mRNA down-regulation. In conclusion, we report that miR-155-mediated CASP-3 mRNA destabilization in LPS-activated RAW 264.7 macrophages suppresses apoptosis, as a prerequisite to maintain their crucial function in inflammation.

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“…LPS are composed of O-antigen biological repeats, core oligosaccharide, and lipid A (Knirel et al, 2006). LORE binds LPS mainly through lipid A, which is similar to the recognition of LPS lipid A moiety by mammalian immune receptor TLR4 that activates proinflammatory responses (Park et al, 2009;Tan and Kagan, 2014). However, TLR4 carries an LRR ECD instead of a Lectin ECD.…”

Section: Rks and Rps As Prrsmentioning

confidence: 99%

Plant pattern-recognition receptors controlling innate immunity

Zhou

et al. 2016

Sci. China Life Sci.

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A Cross-Disciplinary Perspective on the Innate Immune Responses to Bacterial Lipopolysaccharide

Cited by 166 publications

References 109 publications

Transcriptional Analysis of the MrpJ Network: Modulation of Diverse Virulence-Associated Genes and Direct Regulation of mrp Fimbrial and flhDC Flagellar Operons in Proteus mirabilis

Transcriptional Analysis of the MrpJ Network: Modulation of Diverse Virulence-Associated Genes and Direct Regulation of mrp Fimbrial and flhDC Flagellar Operons in Proteus mirabilis

miR-155 targets Caspase-3 mRNA in activated macrophages

Plant pattern-recognition receptors controlling innate immunity

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