Pore-Forming Bacterial Protein Toxins: An Overview

Alouf, Joseph E.

doi:10.1007/978-3-642-56508-3_1

Cited by 50 publications

(53 citation statements)

References 106 publications

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“…S. pneumoniae and S. aureus can secrete pore-forming toxins during infection that aid in bacterial invasion. PFTs are the largest single class of proteinaceous bacterial toxins (19,20), and many PFTs gain access to the host cell through binding to cholesterol or lipid derivatives in lipid rafts on the cell surface, resulting in subsequent oligomerization and pore formation (21,22). Pneumolysin (PLY), a member of the cholesteroldependent cytolysin family, is a major virulence factor that is expressed by virtually all clinical isolates of S. pneumoniae.…”

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confidence: 99%

Statin-Conferred Enhanced Cellular Resistance against Bacterial Pore-Forming Toxins in Airway Epithelial Cells

Statt

Ruan

Hung

et al. 2015

Am J Respir Cell Mol Biol

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Statins are widely used to prevent cardiovascular disease. In addition to their inhibitory effects on cholesterol synthesis, statins have beneficial effects in patients with sepsis and pneumonia, although molecular mechanisms have mostly remained unclear. Using human airway epithelial cells as a proper in vitro model, we show that prior exposure to physiological nanomolar serum concentrations of simvastatin (ranging from 10-1,000 nM) confers significant cellular resistance to the cytotoxicity of pneumolysin, a pore-forming toxin and the main virulence factor of Streptococcus pneumoniae. This protection could be demonstrated with a different statin, pravastatin, or on a different toxin, a-hemolysin. Furthermore, through the use of gene silencing, pharmacological inhibitors, immunofluorescence microscopy, and biochemical and metabolic rescue approaches, we demonstrate that the mechanism of protection conferred by simvastatin at physiological nanomolar concentrations could be different from the canonical mevalonate pathways seen in most other mechanistic studies conducted with statins at micromolar levels. All of these data are integrated into a protein synthesis-dependent, calcium-dependent model showing the interconnected pathways used by statins in airway epithelial cells to elicit an increased resistance to pore-forming toxins. This research fills large gaps in our understanding of how statins may confer host cellular protection against bacterial infections in the context of airway epithelial cells without the confounding effect from the presence of immune cells. In addition, our discovery could be potentially developed into a host-centric strategy for the adjuvant treatment of pore-forming toxin associated bacterial infections.Keywords: airway epithelium; pneumolysin; simvastatin; cholesterol; pneumonia Clinical RelevanceOur study dissects the cellular and molecular protection mechanisms of statins in an isolated airway epithelial cell-bacterial pore-forming toxin context. This research can fill large gaps in our understanding of how statins contribute to the reduced pathology observed during pneumonia and other bacterial infections. The better understanding of the molecular mechanisms in the statin-mediated protection will further affect the therapeutic development of host-centric approach therapies in combating microbial infections.

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confidence: 99%

Statin-Conferred Enhanced Cellular Resistance against Bacterial Pore-Forming Toxins in Airway Epithelial Cells

Statt

Ruan

Hung

et al. 2015

Am J Respir Cell Mol Biol

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“…Members of a large family of pore-forming toxins called the cholesterol-dependent cytolysins, LLO monomers bind cholesterol-containing host membranes. Upon binding, the monomers oligomerize and the resultant complex inserts into the membrane, producing pores up to 30 nm in diameter (1,68). Bacteria deficient for LLO production or activity remain trapped within a phagosome (17,68) and are unable to replicate in cells, resulting in a 5-log decrease in virulence in mice compared to the virulence of wild-type (WT) bacteria (12,36,57).…”

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Development of amariner-Based Transposon and Identification ofListeria monocytogenesDeterminants, Including the Peptidyl-Prolyl Isomerase PrsA2, That Contribute to Its Hemolytic Phenotype

Zemansky¹,

Kline²,

Woodward³

et al. 2009

J Bacteriol

146

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Listeriolysin O (LLO) is a pore-forming toxin that mediates phagosomal escape and cell-to-cell spread of the intracellular pathogen Listeria monocytogenes. In order to identify factors that control the production, activity, or secretion of this essential virulence factor, we constructed a Himar1 mariner transposon delivery system and screened 50,000 mutants for a hypohemolytic phenotype on blood agar plates. Approximately 200 hypohemolytic mutants were identified, and the 51 most prominent mutants were screened ex vivo for intracellular growth defects. Eight mutants with a phenotype were identified, and they contained insertions in the following genes: lmo0964 (similar to yjbH), lmo1268 (clpX), lmo1401 (similar to ymdB), lmo1575 (similar to ytqI), lmo1695 (mprF), lmo1821 (similar to prpC), lmo2219 (prsA2), and lmo2460 (similar to cggR). Some of these genes are involved in previously unexplored areas of research with L. monocytogenes: the genes yjbH and clpX regulate the disulfide stress response in Bacillus subtilis, and the prpC phosphatase has been implicated in virulence in other gram-positive pathogens. Here we demonstrate that prsA2, an extracytoplasmic peptidylprolyl cis/trans isomerase, is critical for virulence and contributes to the folding of LLO and to the activity of another virulence factor, the broad-range phospholipase C (PC-PLC). Furthermore, although it has been shown that prsA2 expression is linked to PrfA, the master virulence transcription factor in L. monocytogenes pathogenesis, we demonstrate that prsA2 is not directly controlled by PrfA. Finally, we show that PrsA2 is involved in flagellum-based motility, indicating that this factor likely serves a broad physiological role.Listeria monocytogenes is a gram-positive, facultative intracellular pathogen capable of infecting a broad range of animal hosts, including humans (84). The cell biology of infection has been well characterized and is a model for pathogenesis. Upon internalization into host cells, including macrophages and nonprofessional phagocytes, L. monocytogenes organisms are initially enclosed in a single-membrane vacuole. Bacteria rapidly lyse this primary vacuole and replicate in the cytosol, exploiting actin-based motility as a means to move within the cytoplasm and to spread from cell to cell. Actin-based propulsion of bacteria from the cytoplasm of one cell into the cytoplasm of a neighboring cell results in the formation of a double-membrane vacuole or secondary vacuole. Bacteria lyse the secondary vacuole, and intracellular growth continues (81, 84).Central to the virulence of L. monocytogenes is the ability to lyse the primary and secondary vacuoles in order to gain entry into the host cytosol. Escape from both types of vacuoles is primarily mediated by the secretion of the cytolysin listeriolysin O (LLO) (68). Members of a large family of pore-forming toxins called the cholesterol-dependent cytolysins, LLO monomers bind cholesterol-containing host membranes. Upon binding, the monomers oligomerize and the resultant complex ...

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“…LLO is a member of a large family of toxins, called cholesterol-dependent cytolysins, that are secreted by gram-positive bacterial pathogens (1,62). Secreted toxin monomers bind cholesterol-containing membranes, oligomerize, and thereafter insert themselves into the membranes, forming pores of up to 30 nm in diameter (62).…”

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confidence: 99%

Listeriolysin O Secreted byListeria monocytogenesinto the Host Cell Cytosol Is Degraded by the N-End Rule Pathway

et al. 2007

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The intracellular pathogen Listeria monocytogenes escapes from a phagosomal compartment into the cytosol by secreting the pore-forming cytolysin listeriolysin O (LLO). During the proliferation of L. monocytogenes bacteria in the mammalian cell cytosol, the secreted LLO is targeted for degradation by the ubiquitin system. We report here that LLO is a substrate of the ubiquitin-dependent N-end rule pathway, which recognizes LLO through its N-terminal Lys residue. Specifically, we demonstrated by reverse-genetic and pharmacological methods that LLO was targeted for degradation by the N-end rule pathway in reticulocyte extracts and mouse NIH 3T3 cells and after its secretion by intracellular bacteria into the mouse cell cytosol. Replacing the N-terminal Lys of LLO with a stabilizing residue such as Val increased the in vivo half-life of LLO but did not strongly affect the intracellular growth or virulence of L. monocytogenes. Nevertheless, this replacement decreased the virulence of L. monocytogenes by nearly twofold, suggesting that a destabilizing N-terminal residue of LLO may stem from positive selection during the evolution of this and related bacteria. A double mutant strain of L. monocytogenes in which upregulated secretion of LLO was combined with a stabilizing N-terminal residue was severely toxic to infected mammalian cells, resulting in reduced intracellular growth of bacteria and an ϳ100-fold-lower level of virulence. In summary, we showed that LLO is degraded by the N-end rule pathway and that the degradation of LLO can reduce the toxicity of L. monocytogenes during infection, a property of LLO that may have been selected for its positive effects on fitness during the evolution of L. monocytogenes.Listeria monocytogenes is a gram-positive, facultative, intracytosolic bacterial pathogen of humans and animals. In humans, L. monocytogenes infections are typically food borne and cause an invasive, sometimes fatal, disease in pregnant women, the elderly, newborns, and immunocompromised individuals (51, 66). Following internalization into mammalian cells, bacteria are initially contained within host vacuoles but rapidly escape into the cytosol, largely through the perforation of the phagosomal membrane by the pore-forming toxin called listeriolysin O (LLO) (46,66). LLO is an essential virulence factor, as hly⌬ bacteria, which lack LLO, fail to escape from the phagosomal compartment and are attenuated 10,000-fold in comparison to their wild-type counterparts in the murine model of listeriosis (20,33,45,46). Once in the host cytosol, L. monocytogenes cells grow and divide, exploiting a host mechanism of actin-based motility to move within the cytosol and to spread from cell to cell through the formation of long plasma membrane extensions that are taken up by neighboring cells (18,34,61). LLO is also required for productive cell-to-cell spread because it facilitates the disruption of bacterium-containing double-membrane vesicles within the secondarily infected cells (23).LLO is a member of a large family of toxin...

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Pore-Forming Bacterial Protein Toxins: An Overview

Cited by 50 publications

References 106 publications

Statin-Conferred Enhanced Cellular Resistance against Bacterial Pore-Forming Toxins in Airway Epithelial Cells

Statin-Conferred Enhanced Cellular Resistance against Bacterial Pore-Forming Toxins in Airway Epithelial Cells

Development of amariner-Based Transposon and Identification ofListeria monocytogenesDeterminants, Including the Peptidyl-Prolyl Isomerase PrsA2, That Contribute to Its Hemolytic Phenotype

Listeriolysin O Secreted byListeria monocytogenesinto the Host Cell Cytosol Is Degraded by the N-End Rule Pathway

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