Intracellular type III secretion by cytoplasmic Shigella flexneri promotes caspase-1-dependent macrophage cell death

Schroeder, Gunnar N.; Jann, Naja J.; Hilbi, Hubert

doi:10.1099/mic.0.2007/007427-0

Cited by 35 publications

(31 citation statements)

References 64 publications

(100 reference statements)

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“…This hypothesis was supported by a previous study demonstrating that NMI and NMII differentially activated primary human alveolar macrophages, which produced different levels of pro-IL-1␤ and mature IL-1␤ (46). It has been reported that Shigella flexneri induced caspase-1-dependent host cell death, leading to the release of IL-1␤, which causes acute inflammation and ultimately helps clear the infection (47). However, Salmonella-induced apoptosis was correlated to the severity of disease in vivo (48).…”

Section: Discussionsupporting

confidence: 73%

Coxiella burnetii Avirulent Nine Mile Phase II Induces Caspase-1-Dependent Pyroptosis in Murine Peritoneal B1a B Cells

et al. 2016

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Our recent study demonstrated that virulentCoxiella burnetiiNine Mile phase I (NMI) is capable of infecting and replicating within peritoneal B1a cells and that B1a cells play an important role in host defense againstC. burnetiiinfection in mice. However, it remains unknown if avirulent Nine Mile phase II (NMII) can infect and replicate in B1a cells and whether NMI and NMII can differentially interact with B1a cells. In this study, we examined if NMI and NMII can differentially modulate host cell apoptotic signaling in B1a cells. The results showed that NMII induced dose-dependent cell death in murine peritoneal B1a cells but NMI did not, suggesting that NMI and NMII may differentially activate host cell apoptotic signaling in B1a cells. Western blotting indicated that NMII-induced B1a cell death was not dependent on either caspase-3 or PARP-1 cleavage, but cleavage of caspase-1 was detected in NMII-infected B1a cells. In addition, inhibition or deficiency of caspase-1 activity blocked NMII-induced B1a cell death. These results suggest that NMII induces a caspase-1-dependent pyroptosis in murine peritoneal B1a cells. We also found that heat-killed NMII and type 4 secretion system (T4SS) mutant NMII were unable to induce B1a cell death and that NMII infection did not induce cell death in peritoneal B1a cells from Toll-like receptor 2 (TLR-2)- or NLRP3 inflammasome-deficient mice. These data suggest that NMII-induced caspase-1-dependent pyroptosis may require its T4SS and activation of the TLR-2 and NLRP3 signaling pathways.

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Section: Discussionsupporting

confidence: 73%

Coxiella burnetii Avirulent Nine Mile Phase II Induces Caspase-1-Dependent Pyroptosis in Murine Peritoneal B1a B Cells

et al. 2016

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“…S4 in the supplemental material). Moreover, WR30 efficiently kills macrophages, a process that requires a TTSS that can secrete functional translocators (IpaB and -C) (37,38). The phenotype for WR30 in epithelial cells may be a pleiotropic effect resulting from its filamentous morphology, even though log-phase cultures contain similar numbers of viable bacteria.…”

Section: Vol 78 2010 Characterization Of S Flexneri Msbb Mutants 409mentioning

confidence: 99%

Virulence, Inflammatory Potential, and Adaptive Immunity Induced by Shigella flexneri msbB Mutants

et al. 2010

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The ability of genetically detoxified lipopolysaccharide (LPS) to stimulate adaptive immune responses is an ongoing area of investigation with significant consequences for the development of safe and effective bacterial vaccines and adjuvants. One approach to genetic detoxification is the deletion of genes whose products modify LPS. The msbB1 and msbB2 genes, which encode late acyltransferases, were deleted in the Shigella flexneri 2a human challenge strain 2457T to evaluate the virulence, inflammatory potential, and acquired immunity induced by strains producing underacylated lipid A. Consistent with a reduced endotoxic potential, S. flexneri 2a msbB mutants were attenuated in an acute mouse pulmonary challenge model. Attenuation correlated with decreases in the production of proinflammatory cytokines and in chemokine release without significant changes in lung histopathology. The levels of specific proinflammatory cytokines (interleukin-1␤ [IL-1␤], macrophage inflammatory protein 1␣ [MIP-1␣], and tumor necrosis factor alpha [TNF-␣]) were also significantly reduced after infection of mouse macrophages with either single or double msbB mutants. Surprisingly, the msbB double mutant displayed defects in the ability to invade, replicate, and spread within epithelial cells. Complementation restored these phenotypes, but the exact nature of the defects was not determined. Acquired immunity and protective efficacy were also assayed in the mouse lung model, using a vaccination-challenge study. Both humoral and cellular responses were generally robust in msbB-immunized mice and afforded significant protection from lethal challenge. These data suggest that the loss of either msbB gene reduces the endotoxicity of Shigella LPS but does not coincide with a reduction in protective immune responses.Shigellosis, or bacillary dysentery, is an acute colitis caused by Shigella flexneri, a gram-negative enteroinvasive bacterium that is transmitted to humans via the fecal-oral route. Shigella triggers its uptake into the M cells of the lower intestine, where they are taken up by the underlying antigen-presenting cells (macrophages and dendritic cells) (18). Shigella bacteria are released from macrophages after inducing cell death (12,29) and invade the surrounding enterocytes, where they begin to multiply and spread to adjacent cells. Effector proteins secreted through a molecular-needle-like complex called the type III secretion system (TTSS) mediate the processes of macrophage cytotoxicity, enterocyte invasion, and modulation of the host cell immune response. The TTSS and associated effector proteins are encoded on a large virulence plasmid that is present in all invasive strains of Shigella (46). During replication and dissemination in host cells, components of the bacterial cell wall (lipopolysaccharide [LPS] and peptidoglycan) are released, inducing proinflammatory cytokines and chemokines which activate the innate immune response (reviewed in reference 31). Although the immune mechanisms of protection remain relatively undef...

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“…The "entry region" of the virulence plasmid contains the mxi, spa, and ipa operons that code for the type III secretion apparatus (T3SA) itself (12). The T3SA resembles a nano-needle and syringe, which consists of a basal body that spans the inner and outer Shigella membranes, a ϳ2.5-nm inner diameter needle that extends from the bacterial surface to provide a passageway for protein translocation and a tip complex that regulates secretion and interacts with the host cell membrane (13,14). The mechanisms supporting protein secretion through the Shigella T3SA remain largely unclear; however, we recently characterized Spa47 as an active T3SS ATPase, suggesting that it may provide the energy necessary to power secretion (15).…”

mentioning

confidence: 99%

Structural and Biochemical Characterization of Spa47 Provides Mechanistic Insight into Type III Secretion System ATPase Activation and Shigella Virulence Regulation

Burgess¹,

Burgess²,

Morales

et al. 2016

Journal of Biological Chemistry

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Edited by Patrick SungLike many Gram-negative pathogens, Shigella rely on a complex type III secretion system (T3SS) to inject effector proteins into host cells, take over host functions, and ultimately establish infection. Despite these critical roles, the energetics and regulatory mechanisms controlling the T3SS and pathogen virulence remain largely unclear. In this study, we present a series of high resolution crystal structures of Spa47 and use the structures to model an activated Spa47 oligomer, finding that ATP hydrolysis may be supported by specific side chain contributions from adjacent protomers within the complex. Follow-up mutagenesis experiments targeting the predicted active site residues validate the oligomeric model and determined that each of the tested residues are essential for Spa47 ATPase activity, although they are not directly responsible for stable oligomer formation. Although N-terminal domain truncation was necessary for crystal formation, it resulted in strictly monomeric Spa47 that is unable to hydrolyze ATP, despite maintaining the canonical ATPase core structure and active site residues. Coupled with studies of ATPase inactive full-length Spa47 point mutants, we find that Spa47 oligomerization and ATP hydrolysis are needed for complete T3SS apparatus formation, a proper translocator secretion profile, and Shigella virulence. This work represents the first structure-function characterization of Spa47, uniquely complementing the multitude of included Shigella T3SS phenotype assays and providing a more complete understanding of T3SS ATPase-mediated pathogen virulence. Additionally, these findings provide a strong platform for follow-up studies evaluating regulation of Spa47 oligomerization in vivo as a much needed means of treating and perhaps preventing shigellosis.

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Intracellular type III secretion by cytoplasmic Shigella flexneri promotes caspase-1-dependent macrophage cell death

Cited by 35 publications

References 64 publications

Coxiella burnetii Avirulent Nine Mile Phase II Induces Caspase-1-Dependent Pyroptosis in Murine Peritoneal B1a B Cells

Coxiella burnetii Avirulent Nine Mile Phase II Induces Caspase-1-Dependent Pyroptosis in Murine Peritoneal B1a B Cells

Virulence, Inflammatory Potential, and Adaptive Immunity Induced by Shigella flexneri msbB Mutants

Structural and Biochemical Characterization of Spa47 Provides Mechanistic Insight into Type III Secretion System ATPase Activation and Shigella Virulence Regulation

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