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Special Issue "Bacterial Protein Toxins: Enemies within or Unexpected Friends"

A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Molecular Toxicology".

Deadline for manuscript submissions: closed (31 January 2019).

Special Issue Editors

Prof. Dr. Carla Fiorentini
E-Mail Website
Guest Editor
National Center for Global Health, Istituto Superiore di Sanità, Rome, Italy
Interests: bacterial protein toxins; Rho GTPases; cytoskeleton; mitochondria; cancer; toxins as therapeutics
Special Issues and Collections in MDPI journals
Dr. Alessia Fabbri
E-Mail
Co-Guest Editor
Italian Center for Global Health, Istituto Superiore di Sanità, Rome, Italy
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

Bacterial protein toxins are the principal virulence factors of pathogenic bacteria and their production represents one of the main bacterial strategies to interact with mammalian cells. Using diverse and sophisticated mechanisms, bacterial toxins manipulate the host cell functions to suit their own needs, favoring the spreading, colonization, and survival of the microbes. However, toxins play a negative role in human health, not only because implicated in infectious diseases but also because potentially involved in harmful situations, such as cancer development. Under all these aspects, bacterial toxins can certainly be considered as “enemies”.

On the other hand, knowledge of their modes of action has permitted their beneficial use, not only as high selective tools in cell biology, but also as potential new drugs for medical applications. For example, some toxins can be “engineered” as the cell-killing component of immuno-toxins, while others toxins or their derivatives have been incorporated into human vaccines because of their adjuvant properties. Paradigmatic is the use of botulinum toxin, the most powerful candidate as a biological weapon, which is used for human disorders characterized by hyperactivity of nerve terminals of whatever origin and is today very popular for its ability to reduce wrinkles. Thus, the scientific research has permitted to convert these harmful bacterial molecules into “friends”.

In this Special Issue of IJMS, the focus will be on bacterial protein toxins pointing to both their pathogenetic strategies and their therapeutic potentials, thus highlighting the Janus aspect of such virulence factors.

Dr. Carla Fiorentini
Dr. Alessia Fabbri
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. International Journal of Molecular Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. There is an Article Processing Charge (APC) for publication in this open access journal. For details about the APC please see here. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • bacterial protein toxins
  • pathogenesis
  • molecular target
  • drug discovery
  • therapy

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Published Papers (8 papers)

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Research

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Open AccessArticle
Bacillus anthracis Edema Toxin Inhibits Efferocytosis in Human Macrophages and Alters Efferocytic Receptor Signaling
Int. J. Mol. Sci. 2019, 20(5), 1167; https://doi.org/10.3390/ijms20051167 - 07 Mar 2019
Cited by 3 | Viewed by 2028
Abstract
The Bacillus anthracis Edema Toxin (ET), composed of a Protective Antigen (PA) and the Edema Factor (EF), is a cellular adenylate cyclase that alters host responses by elevating cyclic adenosine monophosphate (cAMP) to supraphysiologic levels. However, the role of ET in systemic anthrax [...] Read more.
The Bacillus anthracis Edema Toxin (ET), composed of a Protective Antigen (PA) and the Edema Factor (EF), is a cellular adenylate cyclase that alters host responses by elevating cyclic adenosine monophosphate (cAMP) to supraphysiologic levels. However, the role of ET in systemic anthrax is unclear. Efferocytosis is a cAMP-sensitive, anti-inflammatory process of apoptotic cell engulfment, the inhibition of which may promote sepsis in systemic anthrax. Here, we tested the hypothesis that ET inhibits efferocytosis by primary human macrophages and evaluated the mechanisms of altered efferocytic signaling. ET, but not PA or EF alone, inhibited the efferocytosis of early apoptotic neutrophils (PMN) by primary human M2 macrophages (polarized with IL-4, IL-10, and/or dexamethasone) at concentrations relevant to those encountered in systemic infection. ET inhibited Protein S- and MFGE8-dependent efferocytosis initiated by signaling through MerTK and αVβ5 receptors, respectively. ET inhibited Rac1 activation as well as the phosphorylation of Rac1 and key activating sites of calcium calmodulin-dependent kinases CamK1α, CamK4, and vasodilator-stimulated phosphoprotein, that were induced by the exposure of M2(Dex) macrophages to Protein S-opsonized apoptotic PMN. These results show that ET impairs macrophage efferocytosis and alters efferocytic receptor signaling. Full article
(This article belongs to the Special Issue Bacterial Protein Toxins: Enemies within or Unexpected Friends)
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Open AccessCommunication
The Bacterial Protein CNF1 as a Potential Therapeutic Strategy against Mitochondrial Diseases: A Pilot Study
Int. J. Mol. Sci. 2018, 19(7), 1825; https://doi.org/10.3390/ijms19071825 - 21 Jun 2018
Cited by 7 | Viewed by 1415
Abstract
The Escherichia coli protein toxin cytotoxic necrotizing factor 1 (CNF1), which acts on the Rho GTPases that are key regulators of the actin cytoskeleton, is emerging as a potential therapeutic tool against certain neurological diseases characterized by cellular energy homeostasis impairment. In this [...] Read more.
The Escherichia coli protein toxin cytotoxic necrotizing factor 1 (CNF1), which acts on the Rho GTPases that are key regulators of the actin cytoskeleton, is emerging as a potential therapeutic tool against certain neurological diseases characterized by cellular energy homeostasis impairment. In this brief communication, we show explorative results on the toxin’s effect on fibroblasts derived from a patient affected by myoclonic epilepsy with ragged-red fibers (MERRF) that carries a mutation in the m.8344A>G gene of mitochondrial DNA. We found that, in the patient’s cells, besides rescuing the wild-type-like mitochondrial morphology, CNF1 administration is able to trigger a significant increase in cellular content of ATP and of the mitochondrial outer membrane marker Tom20. These results were accompanied by a profound F-actin reorganization in MERRF fibroblasts, which is a typical CNF1-induced effect on cell cytoskeleton. These results point at a possible role of the actin organization in preventing or limiting the cell damage due to mitochondrial impairment and at CNF1 treatment as a possible novel strategy against mitochondrial diseases still without cure. Full article
(This article belongs to the Special Issue Bacterial Protein Toxins: Enemies within or Unexpected Friends)
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Open AccessArticle
Cell Propagation of Cholera Toxin CTA ADP-Ribosylating Factor by Exosome Mediated Transfer
Int. J. Mol. Sci. 2018, 19(5), 1521; https://doi.org/10.3390/ijms19051521 - 19 May 2018
Cited by 2 | Viewed by 2022
Abstract
In this study, we report how the cholera toxin (CT) A subunit (CTA), the enzyme moiety responsible for signaling alteration in host cells, enters the exosomal pathway, secretes extracellularly, transmits itself to a cell population. The first evidence for long-term transmission of CT’s [...] Read more.
In this study, we report how the cholera toxin (CT) A subunit (CTA), the enzyme moiety responsible for signaling alteration in host cells, enters the exosomal pathway, secretes extracellularly, transmits itself to a cell population. The first evidence for long-term transmission of CT’s toxic effect via extracellular vesicles was obtained in Chinese hamster ovary (CHO) cells. To follow the CT intracellular route towards exosome secretion, we used a novel strategy for generating metabolically-labeled fluorescent exosomes that can be counted by flow cytometry assay (FACS) and characterized. Our results clearly show the association of CT with exosomes, together with the heat shock protein 90 (HSP90) and Protein Disulfide Isomerase (PDI) molecules, proteins required for translocation of CTA across the ER membrane into the cytoplasm. Confocal microscopy showed direct internalization of CT containing fluorescent exo into CHO cells coupled with morphological changes in the recipient cells that are characteristic of CT action. Moreover, Me665 cells treated with CT-containing exosomes showed an increase in Adenosine 3’,5’-Cyclic Monophosphate (cAMP) level, reaching levels comparable to those seen in cells exposed directly to CT. Our results prompt the idea that CT can exploit an exosome-mediated cell communication pathway to extend its pathophysiological action beyond an initial host cell, into a multitude of cells. This finding could have implications for cholera disease pathogenesis and epidemiology. Full article
(This article belongs to the Special Issue Bacterial Protein Toxins: Enemies within or Unexpected Friends)
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Open AccessArticle
The Bacterial Toxin CNF1 Induces Activation and Maturation of Human Monocyte-Derived Dendritic Cells
Int. J. Mol. Sci. 2018, 19(5), 1408; https://doi.org/10.3390/ijms19051408 - 08 May 2018
Cited by 1 | Viewed by 2577
Abstract
Cytotoxic necrotizing factor 1 (CNF1) is a bacterial protein toxin primarily expressed by pathogenic Escherichia coli strains, causing extraintestinal infections. The toxin is believed to enhance the invasiveness of E. coli by modulating the activity of Rho GTPases in host cells, but it [...] Read more.
Cytotoxic necrotizing factor 1 (CNF1) is a bacterial protein toxin primarily expressed by pathogenic Escherichia coli strains, causing extraintestinal infections. The toxin is believed to enhance the invasiveness of E. coli by modulating the activity of Rho GTPases in host cells, but it has interestingly also been shown to promote inflammation, stimulate host immunity and function as a potent immunoadjuvant. The mechanisms underlying the immunostimulatory properties of CNF1 are, however, poorly characterized, and little is known about the direct effects of the toxin on immune cells. Here, we show that CNF1 induces expression of maturation markers on human immature monocyte-derived dendritic cells (moDCs) without compromising cell viability. Consistent with the phenotypic maturation, CNF1 further triggered secretion of proinflammatory cytokines and increased the capacity of moDCs to stimulate proliferation of allogenic naïve CD4+ T cells. A catalytically inactive form of the toxin did not induce moDC maturation, indicating that the enzymatic activity of CNF1 triggers immature moDCs to undergo phenotypic and functional maturation. As the maturation of dendritic cells plays a central role in initiating inflammation and activating the adaptive immune response, the present findings shed new light on the immunostimulatory properties of CNF1 and may explain why the toxin functions as an immunoadjuvant. Full article
(This article belongs to the Special Issue Bacterial Protein Toxins: Enemies within or Unexpected Friends)
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Open AccessArticle
Commensal Staphylococcus aureus Provokes Immunity to Protect against Skin Infection of Methicillin-Resistant Staphylococcus aureus
Int. J. Mol. Sci. 2018, 19(5), 1290; https://doi.org/10.3390/ijms19051290 - 25 Apr 2018
Cited by 11 | Viewed by 2787
Abstract
Unlike USA300, a strain of community-acquired methicillin-resistant Staphylococcus aureus (MRSA), commensal Staphylococcus aureus (S. aureus) bacteria isolated from human skin demonstrated the ability to mediate the glycerol fermentation to produce short-chain fatty acids (SCFAs). Quantitative proteomic analysis of enzymes involved in [...] Read more.
Unlike USA300, a strain of community-acquired methicillin-resistant Staphylococcus aureus (MRSA), commensal Staphylococcus aureus (S. aureus) bacteria isolated from human skin demonstrated the ability to mediate the glycerol fermentation to produce short-chain fatty acids (SCFAs). Quantitative proteomic analysis of enzymes involved in glycerol fermentation demonstrated that the expression levels of six enzymes, including glycerol-3-phosphate dehydrogenase (GPDH) and phosphoglycerate mutase (PGM), in commensal S. aureus are more than three-fold higher than those in USA300. Western blotting validated the low expression levels of GPDH in USA300, MRSA252 (a strain of hospital-acquired MRSA), and invasive methicillin-susceptible S. aureus (MSSA). In the presence of glycerol, commensal S. aureus effectively suppressed the growth of USA300 in vitro and in vivo. Active immunization of mice with lysates or recombinant α-hemolysin of commensal S. aureus or passive immunization with neutralizing sera provided immune protection against the skin infection of USA300. Our data illustrate for the first time that commensal S. aureus elicits both innate and adaptive immunity via glycerol fermentation and systemic antibody production, respectively, to fight off the skin infection of pathogenic MRSA. Full article
(This article belongs to the Special Issue Bacterial Protein Toxins: Enemies within or Unexpected Friends)
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Review

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Open AccessReview
Bacterial Toxins and Targeted Brain Therapy: New Insights from Cytotoxic Necrotizing Factor 1 (CNF1)
Int. J. Mol. Sci. 2018, 19(6), 1632; https://doi.org/10.3390/ijms19061632 - 31 May 2018
Cited by 3 | Viewed by 1616
Abstract
Pathogenic bacteria produce toxins to promote host invasion and, therefore, their survival. The extreme potency and specificity of these toxins confer to this category of proteins an exceptionally strong potential for therapeutic exploitation. In this review, we deal with cytotoxic necrotizing factor (CNF1), [...] Read more.
Pathogenic bacteria produce toxins to promote host invasion and, therefore, their survival. The extreme potency and specificity of these toxins confer to this category of proteins an exceptionally strong potential for therapeutic exploitation. In this review, we deal with cytotoxic necrotizing factor (CNF1), a cytotoxin produced by Escherichia coli affecting fundamental cellular processes, including cytoskeletal dynamics, cell cycle progression, transcriptional regulation, cell survival and migration. First, we provide an overview of the mechanisms of action of CNF1 in target cells. Next, we focus on the potential use of CNF1 as a pharmacological treatment in central nervous system’s diseases. CNF1 appears to impact neuronal morphology, physiology, and plasticity and displays an antineoplastic activity on brain tumors. The ability to preserve neural functionality and, at the same time, to trigger senescence and death of proliferating glioma cells, makes CNF1 an encouraging new strategy for the treatment of brain tumors. Full article
(This article belongs to the Special Issue Bacterial Protein Toxins: Enemies within or Unexpected Friends)
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Open AccessReview
Experimental Intrastriatal Applications of Botulinum Neurotoxin-A: A Review
Int. J. Mol. Sci. 2018, 19(5), 1392; https://doi.org/10.3390/ijms19051392 - 07 May 2018
Cited by 3 | Viewed by 1942
Abstract
Parkinson’s disease (PD) is one of the most frequent neurodegenerative disorders. Its main pathophysiological characteristic is the loss of dopaminergic neurons in the substantia nigra pars compacta followed by a lack of striatal dopaminergic input and a consequent disinhibition of tonically active cholinergic [...] Read more.
Parkinson’s disease (PD) is one of the most frequent neurodegenerative disorders. Its main pathophysiological characteristic is the loss of dopaminergic neurons in the substantia nigra pars compacta followed by a lack of striatal dopaminergic input and a consequent disinhibition of tonically active cholinergic interneurons. The resulting striatal hypercholinism causes major motor symptoms in PD. Anticholinergic pharmacotherapies have antiparkinsonian effects on motor symptoms, but, due to systemic actions, also numerous severe side effects occur on a regular basis. To circumvent these side effects, a local anticholinergic therapy acting exclusively in the striatum would be reasonable. Botulinum neurotoxin-A (BoNT-A) is synthesized by Clostridium botulinum and blocks the release of acetylcholine from the presynaptic bouton. For several decades, BoNT-A has been used successfully for medical and cosmetic purposes to induce controlled paralyses of single muscles. Our group and others investigated the experimental treatment of striatal hypercholinism by the direct injection of BoNT-A into the striatum of rats and mice as well as of hemiparkinsonian animal models. This review gives an overview of the most important results of the experimental intrastriatal BoNT-A application, with a focus on hemiparkinsonian rats. Full article
(This article belongs to the Special Issue Bacterial Protein Toxins: Enemies within or Unexpected Friends)
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Open AccessReview
Multifaceted Role of Pneumolysin in the Pathogenesis of Myocardial Injury in Community-Acquired Pneumonia
Int. J. Mol. Sci. 2018, 19(4), 1147; https://doi.org/10.3390/ijms19041147 - 11 Apr 2018
Cited by 16 | Viewed by 2178
Abstract
Pneumolysin (PLY), a member of the family of Gram-positive bacterial, cholesterol-dependent, β-barrel pore-forming cytolysins, is the major protein virulence factor of the dangerous respiratory pathogen, Streptococcus pneumoniae (pneumococcus). PLY plays a major role in the pathogenesis of community-acquired pneumonia (CAP), promoting colonization and [...] Read more.
Pneumolysin (PLY), a member of the family of Gram-positive bacterial, cholesterol-dependent, β-barrel pore-forming cytolysins, is the major protein virulence factor of the dangerous respiratory pathogen, Streptococcus pneumoniae (pneumococcus). PLY plays a major role in the pathogenesis of community-acquired pneumonia (CAP), promoting colonization and invasion of the upper and lower respiratory tracts respectively, as well as extra-pulmonary dissemination of the pneumococcus. Notwithstanding its role in causing acute lung injury in severe CAP, PLY has also been implicated in the development of potentially fatal acute and delayed-onset cardiovascular events, which are now recognized as being fairly common complications of this condition. This review is focused firstly on updating mechanisms involved in the immunopathogenesis of PLY-mediated myocardial damage, specifically the direct cardiotoxic and immunosuppressive activities, as well as the indirect pro-inflammatory/pro-thrombotic activities of the toxin. Secondly, on PLY-targeted therapeutic strategies including, among others, macrolide antibiotics, natural product antagonists, cholesterol-containing liposomes, and fully humanized monoclonal antibodies, as well as on vaccine-based preventive strategies. These sections are preceded by overviews of CAP in general, the role of the pneumococcus as the causative pathogen, the occurrence and types of CAP-associated cardiac complication, and the structure and biological activities of PLY. Full article
(This article belongs to the Special Issue Bacterial Protein Toxins: Enemies within or Unexpected Friends)
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