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Role of pore-forming toxins in bacterial infectious diseases.

ABSTRACT: Pore-forming toxins (PFTs) are the most common bacterial cytotoxic proteins and are required for virulence in a large number of important pathogens, including Streptococcus pneumoniae, group A and B streptococci, Staphylococcus aureus, Escherichia coli, and Mycobacterium tuberculosis. PFTs generally disrupt host cell membranes, but they can have additional effects independent of pore formation. Substantial effort has been devoted to understanding the molecular mechanisms underlying the functions of certain model PFTs. Likewise, specific host pathways mediating survival and immune responses in the face of toxin-mediated cellular damage have been delineated. However, less is known about the overall functions of PFTs during infection in vivo. This review focuses on common themes in the area of PFT biology, with an emphasis on studies addressing the roles of PFTs in in vivo and ex vivo models of colonization or infection. Common functions of PFTs include disruption of epithelial barrier function and evasion of host immune responses, which contribute to bacterial growth and spreading. The widespread nature of PFTs make this group of toxins an attractive target for the development of new virulence-targeted therapies that may have broad activity against human pathogens.

SUBMITTER: Los FC

PROVIDER: S-EPMC3668673 | biostudies-literature | 2013 Jun

REPOSITORIES: biostudies-literature

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Role of pore-forming toxins in bacterial infectious diseases.

Los Ferdinand C O FC Randis Tara M TM Aroian Raffi V RV Ratner Adam J AJ

Microbiology and molecular biology reviews : MMBR 20130601 2

Pore-forming toxins (PFTs) are the most common bacterial cytotoxic proteins and are required for virulence in a large number of important pathogens, including Streptococcus pneumoniae, group A and B streptococci, Staphylococcus aureus, Escherichia coli, and Mycobacterium tuberculosis. PFTs generally disrupt host cell membranes, but they can have additional effects independent of pore formation. Substantial effort has been devoted to understanding the molecular mechanisms underlying the functions ...[more]

PMID: 23699254

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Project description:UnlabelledA subgroup of the cholesterol-dependent cytolysin (CDC) family of pore-forming toxins (PFTs) has an unusually narrow host range due to a requirement for binding to human CD59 (hCD59), a glycosylphosphatidylinositol (GPI)-linked complement regulatory molecule. hCD59-specific CDCs are produced by several organisms that inhabit human mucosal surfaces and can act as pathogens, including Gardnerella vaginalis and Streptococcus intermedius. The consequences and potential selective advantages of such PFT host limitation have remained unknown. Here, we demonstrate that, in addition to species restriction, PFT ligation of hCD59 triggers a previously unrecognized pathway for programmed necrosis in primary erythrocytes (red blood cells [RBCs]) from humans and transgenic mice expressing hCD59. Because they lack nuclei and mitochondria, RBCs have typically been thought to possess limited capacity to undergo programmed cell death. RBC programmed necrosis shares key molecular factors with nucleated cell necroptosis, including dependence on Fas/FasL signaling and RIP1 phosphorylation, necrosome assembly, and restriction by caspase-8. Death due to programmed necrosis in RBCs is executed by acid sphingomyelinase-dependent ceramide formation, NADPH oxidase- and iron-dependent reactive oxygen species formation, and glycolytic formation of advanced glycation end products. Bacterial PFTs that are hCD59 independent do not induce RBC programmed necrosis. RBC programmed necrosis is biochemically distinct from eryptosis, the only other known programmed cell death pathway in mature RBCs. Importantly, RBC programmed necrosis enhances the growth of PFT-producing pathogens during exposure to primary RBCs, consistent with a role for such signaling in microbial growth and pathogenesis.ImportanceIn this work, we provide the first description of a new form of programmed cell death in erythrocytes (RBCs) that occurs as a consequence of cellular attack by human-specific bacterial toxins. By defining a new RBC death pathway that shares important components with necroptosis, a programmed necrosis module that occurs in nucleated cells, these findings expand our understanding of RBC biology and RBC-pathogen interactions. In addition, our work provides a link between cholesterol-dependent cytolysin (CDC) host restriction and promotion of bacterial growth in the presence of RBCs, which may provide a selective advantage to human-associated bacterial strains that elaborate such toxins and a potential explanation for the narrowing of host range observed in this toxin family.

Project description:Bacterial pathogens use various strategies to interfere with host cell functions. Among these strategies, bacteria induce transcriptional changes, in order to modify the set of proteins synthetized by the host cell, or target pre-existing proteins by modulating their post-translational modifications or by triggering their degradation. Protein levels variations in host cells during infection integrates both transcriptional and post-transcriptional regulations induced by pathogens. Here, we focused on host proteome alterations induced by the bacterial pathogen Listeria monocytogenes, and more specifically the Listeria toxin Listeriolysin O (LLO). In order to characterize host proteome alterations induced by LLO, we performed a shotgun proteomics analysis on HeLa cells treated or not with the LLO toxin. To this end, we used SILAC labelling (stable isotope labelling by amino acids in cell culture) to compared in a quantitative manner the protein content from two differentially treated cell populations: one control population and one population incubated with a sublytic dose of LLO (3 nM). We decided to expose cells to LLO during only 20 min to limit protein level changes resulting from transcriptional changes. We performed two independent experiments (experiment #1 and experiment #2) with swapped SILAC labelling to rule out putative labelling-dependent effects. A total of 2009 and 1684 proteins was quantified in each independent experiment, respectively, and 1360 proteins were quantified in both experiments. Among these 1360 proteins, we identified a total of 91 proteins for which protein levels were consistently decreased in cells treated with LLO (i.e. with a log2 control/LLO ratio >0.5 in both experiments). To assess whether the host proteasome was involved in the decrease of these 91 proteins, we repeated our proteomics analysis on SILAC-labelled HeLa cells pre-treated with proteasome inhibitors before exposure to LLO. Two independent experiments were similarly performed with swapped SILAC labelling (experiment #3 and experiment #4). Interestingly, we observed that the vast majority of host proteins identified as strongly downregulated in response to LLO also displayed significant decreased levels in the presence of proteasome inhibitors, indicating that the majority of observed decreases in host protein levels induced by LLO are not due to proteasome-mediated degradation. In follow-up experiments, we identified that LLO decreases in particular the protein level of two E2 ubiquitin enzymes, UBE2K and UBE2N, leading to major changes in the host ubiquitylome. This toxin-induced proteome remodeling involves post-transcriptional regulations, as no modification in the transcription levels of the corresponding genes was observed. These decreases in host protein levels were observed in different epithelial cell lines but not in macrophages. In addition, we could show that Perfringolysin O, another bacterial pore-forming toxin similar to LLO, also induces host proteome changes. Taken together, our data show that different bacterial pore-forming toxins induce deep proteome remodeling, that may impair host epithelial cell functions.

Project description:Bacterial pathogens use various strategies to interfere with host cell functions. Among these strategies, bacteria induce transcriptional changes, in order to modify the set of proteins synthetized by the host cell, or target pre-existing proteins by modulating their post-translational modifications or by triggering their degradation. Protein levels variations in host cells during infection integrates both transcriptional and post-transcriptional regulations induced by pathogens. Here, we focused on host proteome alterations induced by the bacterial pathogen Listeria monocytogenes, and more specifically the Listeria toxin Listeriolysin O (LLO). In order to characterize host proteome alterations induced by LLO, we performed a shotgun proteomics analysis on HeLa cells treated or not with the LLO toxin. To this end, we used SILAC labelling (stable isotope labelling by amino acids in cell culture) to compared in a quantitative manner the protein content from two differentially treated cell populations: one control population and one population incubated with a sublytic dose of LLO (3 nM). We decided to expose cells to LLO during only 20 min to limit protein level changes resulting from transcriptional changes. We performed two independent experiments (experiment #1 and experiment #2) with swapped SILAC labelling to rule out putative labelling-dependent effects. A total of 2009 and 2577 proteins was quantified in each independent experiment, respectively, and 1834 proteins were quantified in both experiments. Among these 1834 proteins, we identified a total of 151 proteins for which protein levels were consistently decreased in cells treated with LLO (i.e. with a log2 control/LLO ratio >0.5 in both experiments). To assess whether the host proteasome was involved in the decrease of these 151 proteins, we repeated our proteomics analysis on SILAC-labelled HeLa cells pre-treated with proteasome inhibitors before exposure to LLO. Two independent experiments were similarly performed with swapped SILAC labelling (experiment #3 and experiment #4). Interestingly, we observed that the vast majority of host proteins identified as strongly downregulated in response to LLO also displayed significant decreased levels in the presence of proteasome inhibitors, indicating that the majority of observed decreases in host protein levels induced by LLO are not due to proteasome-mediated degradation. In follow-up experiments, we validated that LLO decreases in particular the protein level of two E2 ubiquitin enzymes, UBE2K and UBE2N, leading to major changes in the host ubiquitylome. This toxin-induced proteome remodeling involves post-transcriptional regulations, as no modification in the transcription levels of the corresponding genes was observed. These decreases in host protein levels were observed in different epithelial cell lines but not in macrophages. In addition, we could show that Perfringolysin O, another bacterial pore-forming toxin similar to LLO, also induces host proteome changes. Taken together, our data show that different bacterial pore-forming toxins induce deep proteome remodeling, that may impair host epithelial cell functions.

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Role of pore-forming toxins in bacterial infectious diseases.

Publications

Role of pore-forming toxins in bacterial infectious diseases.

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