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Onorini D, Borel N, Schoborg RV, Leonard CA. Neisseria gonorrhoeae Limits Chlamydia trachomatis Inclusion Development and Infectivity in a Novel In Vitro Co-Infection Model. Front Cell Infect Microbiol 2022; 12:911818. [PMID: 35873141 PMCID: PMC9300984 DOI: 10.3389/fcimb.2022.911818] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2022] [Accepted: 06/14/2022] [Indexed: 11/13/2022] Open
Abstract
Chlamydia trachomatis (Ct) and Neisseria gonorrhoeae (Ng) are the most common bacterial sexually transmitted infections (STIs) worldwide. The primary site of infection for both bacteria is the epithelium of the endocervix in women and the urethra in men; both can also infect the rectum, pharynx and conjunctiva. Ct/Ng co-infections are more common than expected by chance, suggesting Ct/Ng interactions increase susceptibility and/or transmissibility. To date, studies have largely focused on each pathogen individually and models exploring co-infection are limited. We aimed to determine if Ng co-infection influences chlamydial infection and development and we hypothesized that Ng-infected cells are more susceptible to chlamydial infection than uninfected cells. To address this hypothesis, we established an in vitro model of Ct/Ng co-infection in cultured human cervical epithelial cells. Our data show that Ng co-infection elicits an anti-chlamydial effect by reducing chlamydial infection, inclusion size, and subsequent infectivity. Notably, the anti-chlamydial effect is dependent on Ng viability but not extracellular nutrient depletion or pH modulation. Though this finding is not consistent with our hypothesis, it provides evidence that interaction of these bacteria in vitro influences chlamydial infection and development. This Ct/Ng co-infection model, established in an epithelial cell line, will facilitate further exploration into the pathogenic interplay between Ct and Ng.
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Affiliation(s)
- Delia Onorini
- Institute of Veterinary Pathology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
| | - Nicole Borel
- Institute of Veterinary Pathology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
| | - Robert V. Schoborg
- Department of Medical Education, Center for Infectious Disease, Inflammation and Immunity, Quillen College of Medicine, East Tennessee State University, Johnson City, TN, United States
| | - Cory Ann Leonard
- Institute of Veterinary Pathology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
- *Correspondence: Cory Ann Leonard,
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Pegg CE, Zaichick SV, Bomba-Warczak E, Jovasevic V, Kim D, Kharkwal H, Wilson DW, Walsh D, Sollars PJ, Pickard GE, Savas JN, Smith GA. Herpesviruses assimilate kinesin to produce motorized viral particles. Nature 2021; 599:662-666. [PMID: 34789877 DOI: 10.1038/s41586-021-04106-w] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2020] [Accepted: 10/07/2021] [Indexed: 01/05/2023]
Abstract
Neurotropic alphaherpesviruses initiate infection in exposed mucosal tissues and, unlike most viruses, spread rapidly to sensory and autonomic nerves where life-long latency is established1. Recurrent infections arise sporadically from the peripheral nervous system throughout the life of the host, and invasion of the central nervous system may occur, with severe outcomes2. These viruses directly recruit cellular motors for transport along microtubules in nerve axons, but how the motors are manipulated to deliver the virus to neuronal nuclei is not understood. Here, using herpes simplex virus type I and pseudorabies virus as model alphaherpesviruses, we show that a cellular kinesin motor is captured by virions in epithelial cells, carried between cells, and subsequently used in neurons to traffic to nuclei. Viruses assembled in the absence of kinesin are not neuroinvasive. The findings explain a critical component of the alphaherpesvirus neuroinvasive mechanism and demonstrate that these viruses assimilate a cellular protein as an essential proviral structural component. This principle of viral assimilation may prove relevant to other virus families and offers new strategies to combat infection.
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Affiliation(s)
- Caitlin E Pegg
- Department of Microbiology-Immunology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
| | - Sofia V Zaichick
- Department of Microbiology-Immunology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA.,Gene Therapy Program, Department of Pathology and Laboratory Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, USA
| | - Ewa Bomba-Warczak
- Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
| | - Vladimir Jovasevic
- Department of Microbiology-Immunology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA.,Department of Pharmacology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
| | - DongHo Kim
- Department of Microbiology-Immunology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
| | - Himanshu Kharkwal
- Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, NY, USA.,Agenus, Lexington, MA, USA
| | - Duncan W Wilson
- Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, NY, USA.,Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY, USA
| | - Derek Walsh
- Department of Microbiology-Immunology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
| | - Patricia J Sollars
- School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln, Lincoln, NE, USA
| | - Gary E Pickard
- School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln, Lincoln, NE, USA.,Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, NE, USA
| | - Jeffrey N Savas
- Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
| | - Gregory A Smith
- Department of Microbiology-Immunology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA.
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Pharmacokinetic/pharmacodynamic considerations for new and current therapeutic drugs for uncomplicated gonorrhoea-challenges and opportunities. Clin Microbiol Infect 2020; 26:1630-1635. [PMID: 32798687 DOI: 10.1016/j.cmi.2020.08.006] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Revised: 07/10/2020] [Accepted: 08/06/2020] [Indexed: 11/20/2022]
Abstract
BACKGROUND Increasing multidrug resistance rates in Neisseria gonorrhoeae have raised concerns and an urgent call for new antibiotics for treatment of gonorrhoea. Several decades of subdued drug development in this field and the recent failures of two new antibiotics to show non-inferiority compared with the current first-line antibiotics ceftriaxone plus azithromycin highlight the need for improved preclinical tools to predict clinical outcome of new drugs in the development process. OBJECTIVES To summarize current pharmacokinetic/pharmacodynamic (PK/PD) knowledge and dose-finding strategies for antibiotics against gonorrhoea. SOURCES Literature review of published papers and discussions by global experts at a special workshop on this topic. CONTENT We review current knowledge of gonococcal specific PK/PD principles and provide an update on new in vitro and in vivo models to correlate drug exposure with clinical outcome, and identify challenges and gaps in gonococcal therapeutic research. IMPLICATIONS Identifying the ideal antimicrobial agent and dose for treating uncomplicated urogenital and pharyngeal gonococcal disease requires appropriate validated non-clinical PK/PD models. Recent advances in adapting in vitro and in vivo models for use in gonorrhoea are an important step for enabling the development of new drugs with reduced risk of failure in Phase 3 clinical development and diminish the risk of emergence of resistance.
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Rodriguez DC, Ocampo M, Salazar LM, Patarroyo MA. Quantifying intracellular Mycobacterium tuberculosis: An essential issue for in vitro assays. Microbiologyopen 2018; 7:e00588. [PMID: 29484835 PMCID: PMC5911991 DOI: 10.1002/mbo3.588] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2017] [Revised: 12/21/2017] [Accepted: 12/28/2017] [Indexed: 12/12/2022] Open
Abstract
Many studies about intracellular microorganisms which are important regarding diseases affecting public health have been focused on the recognition of host–pathogen interactions, thereby ascertaining the mechanisms by which the pathogen invades a cell and makes it become its host. Such knowledge enables understanding the immunological response triggered by these interactions for obtaining useful information for developing vaccines and drugs. Quantitative cell infection assay protocols are indispensable regarding studies involving Mycobacterium tuberculosis, which takes the lives of more than 2 million people worldwide every year; however, sometimes these are limited by the pathogen's slow growth. Concerning such limitation, a detailed review is presented here regarding the different methods for quantifying and differentiating an intracellular pathogen, the importance of mycobacteria aggregate dissociation and multiplicity of infection (MOI) in infection assays. The methods’ differences, advantages, and disadvantages are discussed regarding intra and extracellular bacteria (on cell surface) differentiation, current problems are outlined, as are the solutions provided using fluorophores and projections made concerning quantitative infection assays.
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Affiliation(s)
- Deisy Carolina Rodriguez
- Universidad Nacional de Colombia, Bogotá, Colombia.,Fundación Instituto de Inmunología de Colombia (FIDIC), Bogotá, Colombia
| | - Marisol Ocampo
- Fundación Instituto de Inmunología de Colombia (FIDIC), Bogotá, Colombia.,Universidad del Rosario, Bogotá, Colombia
| | | | - Manuel Alfonso Patarroyo
- Fundación Instituto de Inmunología de Colombia (FIDIC), Bogotá, Colombia.,Universidad del Rosario, Bogotá, Colombia
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Abstract
Bacterial-bacterial interactions play a critical role in promoting biofilm formation. Here we show that NagZ, a protein associated with peptidoglycan recycling, has moonlighting activity that allows it to modulate biofilm accumulation by Neisseria gonorrhoeae. We characterize the biochemical properties of NagZ and demonstrate its ability to function as a dispersing agent for biofilms formed on abiotic surfaces. We extend these observations to cell culture and tissue explant models and show that in nagZ mutants, the biofilms formed in cell culture and on human tissues contain significantly more biomass than those formed by a wild-type strain. Our results demonstrate that an enzyme thought to be restricted to peptidoglycan recycling is able to disperse preformed biofilms.
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Determination of In Vitro Activities of Solithromycin at Different pHs and Its Intracellular Activity against Clinical Isolates of Neisseria gonorrhoeae from a Laboratory Collection. Antimicrob Agents Chemother 2013; 57:4322-4328. [PMID: 23796936 DOI: 10.1128/aac.00564-13] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Accepted: 06/20/2013] [Indexed: 11/20/2022] Open
Abstract
We evaluated the activity of solithromycin against 196 clinical gonococcal isolates collected at the Public Health Ontario Laboratories, Toronto, Canada, including isolates with different levels of azithromycin resistance, as well as the role of pH in MIC determinations using pH-adjusted agar plates (pH range, 5.6 to 7.6). In vitro invasion assays were performed using monolayers of HeLa epithelial cells and clinical gonococci displaying different azithromycin MICs; infected cultures were treated with solithromycin, and its intracellular activity was determined by CFU assays after 3 and 20 h of exposure. Solithromycin displayed a MIC50 and MIC90 of 0.0625 and 0.125 μg/ml, respectively, making its activity at least 4-fold higher than that of azithromycin. Clinical isolates with elevated MICs for azithromycin (MICs of ≥2,048 μg/ml and 4 to 8 μg/ml) showed solithromycin MIC values of 8 and 0.5 μg/ml, respectively. In contrast to azithromycin, solithromycin MICs were not significantly affected by acidic pHs, suggesting more stability at lower pH. Moreover, when intracellular Neisseria gonorrhoeae isolates were incubated with solithromycin at 4 times, 1 times, and one-fourth of the MIC, the exposure to solithromycin resulted in the progressive loss of viability of most isolates over time. The intracellular activity of solithromycin, combined with the low MICs to this agent, indicates that it may be an attractive option for gonorrhea treatment if clinical trials in development reveal that this drug can be used safely in adult indications, especially when multidrug-resistant clinical isolates are now emerging.
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Keller C, Mellouk N, Danckaert A, Simeone R, Brosch R, Enninga J, Bobard A. Single cell measurements of vacuolar rupture caused by intracellular pathogens. J Vis Exp 2013:e50116. [PMID: 23792688 PMCID: PMC3727297 DOI: 10.3791/50116] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Shigella flexneri are pathogenic bacteria that invade host cells entering into an endocytic vacuole. Subsequently, the rupture of this membrane-enclosed compartment allows bacteria to move within the cytosol, proliferate and further invade neighboring cells. Mycobacterium tuberculosis is phagocytosed by immune cells, and has recently been shown to rupture phagosomal membrane in macrophages. We developed a robust assay for tracking phagosomal membrane disruption after host cell entry of Shigella flexneri or Mycobacterium tuberculosis. The approach makes use of CCF4, a FRET reporter sensitive to β-lactamase that equilibrates in the cytosol of host cells. Upon invasion of host cells by bacterial pathogens, the probe remains intact as long as the bacteria reside in membrane-enclosed compartments. After disruption of the vacuole, β-lactamase activity on the surface of the intracellular pathogen cleaves CCF4 instantly leading to a loss of FRET signal and switching its emission spectrum. This robust ratiometric assay yields accurate information about the timing of vacuolar rupture induced by the invading bacteria, and it can be coupled to automated microscopy and image processing by specialized algorithms for the detection of the emission signals of the FRET donor and acceptor. Further, it allows investigating the dynamics of vacuolar disruption elicited by intracellular bacteria in real time in single cells. Finally, it is perfectly suited for high-throughput analysis with a spatio-temporal resolution exceeding previous methods. Here, we provide the experimental details of exemplary protocols for the CCF4 vacuolar rupture assay on HeLa cells and THP-1 macrophages for time-lapse experiments or end points experiments using Shigella flexneri as well as multiple mycobacterial strains such as Mycobacterium marinum, Mycobacterium bovis, and Mycobacterium tuberculosis.
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Affiliation(s)
- Charlotte Keller
- Dynamique des Interactions Hôte Pathogène, Institut Pasteur, Paris, France
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Edwards VL, Wang LC, Dawson V, Stein DC, Song W. Neisseria gonorrhoeae breaches the apical junction of polarized epithelial cells for transmigration by activating EGFR. Cell Microbiol 2013; 15:1042-57. [PMID: 23279089 PMCID: PMC5584544 DOI: 10.1111/cmi.12099] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2012] [Revised: 12/13/2012] [Accepted: 12/17/2012] [Indexed: 12/24/2022]
Abstract
Neisseria gonorrhoeae initiates infection at the apical surface of columnar endocervical epithelial cells in the female reproductive tract. These cells provide a physical barrier against pathogens by forming continuous apical junctional complexes between neighbouring cells. This study examines the interaction of gonococci (GC) with polarized epithelial cells. We show that viable GC preferentially localize at the apical side of the cell-cell junction in polarized endometrial and colonic epithelial cells, HEC-1-B and T84. In GC-infected cells, continuous apical junctional complexes are disrupted, and the junction-associated protein β-catenin is redistributed from the apical junction to the cytoplasm and to GC adherent sites; however, overall cellular levels remain unchanged. This redistribution of junctional proteins is associated with a decrease in the 'fence' function of the apical junction but not its 'gate' function. Disruption of the apical junction by removing calcium increases GC transmigration across the epithelial monolayer. GC inoculation induces the phosphorylation of both epidermal growth factor receptor (EGFR) and β-catenin, while inhibition of EGFR kinase activity significantly reduces both GC-induced β-catenin redistribution and GC transmigration. Therefore, the gonococcus is capable of weakening the apical junction and polarity of epithelial cells by activating EGFR, which facilitates GC transmigration across the epithelium.
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Affiliation(s)
- Vonetta L. Edwards
- Department of Cell Biology & Molecular Genetics, University of Maryland, College Park, MD 20742, USA
| | - Liang-Chun Wang
- Department of Cell Biology & Molecular Genetics, University of Maryland, College Park, MD 20742, USA
| | - Valerie Dawson
- Department of Cell Biology & Molecular Genetics, University of Maryland, College Park, MD 20742, USA
| | - Daniel C. Stein
- Department of Cell Biology & Molecular Genetics, University of Maryland, College Park, MD 20742, USA
| | - Wenxia Song
- Department of Cell Biology & Molecular Genetics, University of Maryland, College Park, MD 20742, USA
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9
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Swanson KV, Griffiss JM, Edwards VL, Stein DC, Song W. Neisseria gonorrhoeae-induced transactivation of EGFR enhances gonococcal invasion. Cell Microbiol 2011; 13:1078-90. [PMID: 21501367 DOI: 10.1111/j.1462-5822.2011.01603.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Neisseria gonorrhoeae, the causative agent of the sexually transmitted infection gonorrhoea, adheres to and invades into genital epithelial cells. Here, we investigate host components that are used by the bacteria for their entry into epithelial cells. We found that gonococcal microcolony formation on the surface of HEC-1-B cells disrupted the polarized, basolateral distribution of both epidermal growth factor receptor (EGFR) and ErbB2, a related family member, and induced their accumulation under the microcolonies at the apical membrane. Gonococcal infection increased EGFR and ErbB2 phosphorylation. The EGFR kinase inhibitor, AG1478, reduced gonococcal invasion by 80%, but had no effect on adherence or the recruitment of EGFR and ErbB2 to the microcolonies. Gonococcal inoculation upregulated the mRNA levels of several ligands of EGFR. Prevention of EGFR ligand shedding by blocking matrix metalloproteinase activation reduced gonococcal invasion without altering their adherence, while the addition of the EGFR ligand, HB-EGF, was able to restore invasion to 66% of control levels. These data indicate that N. gonorrhoeae modulates the activity and cellular distribution of host EGFR, facilitating their invasion. EGFR activation does not appear to be due to direct gonococcal binding to EGFR, but instead by its transactivation by gonococcal induced increases in EGFR ligands.
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Affiliation(s)
- Karen V Swanson
- Department of Cell Biology & Molecular Genetics, and Maryland Pathogen Research Institute, University of Maryland, College Park, MD, USA
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10
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Razgulin A, Ma N, Rao J. Strategies for in vivo imaging of enzyme activity: an overview and recent advances. Chem Soc Rev 2011; 40:4186-216. [DOI: 10.1039/c1cs15035a] [Citation(s) in RCA: 226] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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Bobard A, Mellouk N, Enninga J. Spotting the right location- imaging approaches to resolve the intracellular localization of invasive pathogens. Biochim Biophys Acta Gen Subj 2010; 1810:297-307. [PMID: 21029766 DOI: 10.1016/j.bbagen.2010.10.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2010] [Revised: 10/16/2010] [Accepted: 10/18/2010] [Indexed: 10/18/2022]
Abstract
BACKGROUND A common strategy of microbial pathogens is to invade host cells during infection. The invading microbes explore different intracellular compartments to find their preferred niche. SCOPE OF REVIEW Imaging has been instrumental to unravel paradigms of pathogen entry, to identify their exact intracellular location, and to understand the underlying mechanisms for the formation of pathogen-containing niches. Here, we provide an overview of imaging techniques that have been applied to monitor the intracellular lifestyle of pathogens, focusing mainly on bacteria that either remain in vacuolar-bound compartments or rupture the endocytic vacuole to escape into the host's cellular cytoplasm. MAJOR CONCLUSIONS We will depict common molecular and cellular paradigms that are preferentially exploited by pathogens. A combination of electron microscopy, fluorescence microscopy, and time-lapse microscopy has been the driving force to reveal underlying cell biological processes. Furthermore, the development of highly sensitive and specific fluorescent sensor molecules has allowed for the identification of functional aspects of niche formation by intracellular pathogens. GENERAL SIGNIFICANCE Currently, we are beginning to understand the sophistication of the invasion strategies used by bacterial pathogens during the infection process- innovative imaging has been a key ingredient for this. This article is part of a Special Issue entitled Nanotechnologies - Emerging Applications in Biomedicine.
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Affiliation(s)
- Alexandre Bobard
- Institut Pasteur, Groupe "Dynamique des Interactions Hôte-Pathogène, Paris, France
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Ray K, Bobard A, Danckaert A, Paz-Haftel I, Clair C, Ehsani S, Tang C, Sansonetti P, Tran GVN, Enninga J. Tracking the dynamic interplay between bacterial and host factors during pathogen-induced vacuole rupture in real time. Cell Microbiol 2010; 12:545-56. [PMID: 20070313 DOI: 10.1111/j.1462-5822.2010.01428.x] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Escape into the host cell cytosol following invasion of mammalian cells is a common strategy used by invasive pathogens. This requires membrane rupture of the vesicular or vacuolar compartment formed around the bacteria after uptake into the host cell. The mechanism of pathogen-induced disassembly of the vacuolar membrane is poorly understood. We established a novel, robust and sensitive fluorescence microscopy method that tracks the precise time point of vacuole rupture upon uptake of Gram-negative bacteria. This revealed that the enteroinvasive pathogen Shigella flexneri escapes rapidly, in less than 10 min, from the vacuole. Our method demonstrated the recruitment of host factors, such as RhoA, to the bacterial entry site and their continued presence at the point of vacuole rupture. We found a novel host marker for ruptured vacuoles, galectin-3, which appears instantly in the proximity of bacteria after escape into the cytosol. Furthermore, we show that the Salmonella effector proteins, SifA and PipB2, stabilize the vacuole membrane inhibiting bacterial escape from the vacuole. Our novel approach to track vacuole rupture is ideally suited for high-content and high-throughput approaches to identify the molecular and cellular mechanisms of membrane rupture during invasion by pathogens such as viruses, bacteria and parasites.
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Affiliation(s)
- Katrina Ray
- Institut Pasteur, Groupe Dynamique des interactions hôte-pathogène, 75724, Paris, France
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Hu H, Leppla SH. Anthrax toxin uptake by primary immune cells as determined with a lethal factor-beta-lactamase fusion protein. PLoS One 2009; 4:e7946. [PMID: 19956758 PMCID: PMC2775957 DOI: 10.1371/journal.pone.0007946] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2009] [Accepted: 10/27/2009] [Indexed: 12/28/2022] Open
Abstract
Background To initiate infection, Bacillus anthracis needs to overcome the host innate immune system. Anthrax toxin, a major virulence factor of B. anthracis, impairs both the innate and adaptive immune systems and is important in the establishment of anthrax infections. Methodology/Principal Findings To measure the ability of anthrax toxin to target immune cells, studies were performed using a fusion of the anthrax toxin lethal factor (LF) N-terminal domain (LFn, aa 1–254) with β-lactamase (LFnBLA). This protein reports on the ability of the anthrax toxin protective antigen (PA) to mediate LF delivery into cells. Primary immune cells prepared from mouse spleens were used in conjunction with flow cytometry to assess cleavage and resulting FRET disruption of a fluorescent β-lactamase substrate, CCF2/AM. In spleen cell suspensions, the macrophages, dendritic cells, and B cells showed about 75% FRET disruption of CCF2/AM due to cleavage by the PA–delivered LFnBLA. LFnBLA delivery into CD4+ and CD8+ T cells was lower, with 40% FRET disruption. When the analyses were done on purified samples of individual cell types, similar results were obtained, with T cells again having lower LFnBLA delivery than macrophages, dendritic cells, and B cells. Relative expression levels of the toxin receptors CMG2 and TEM8 on these cells were determined by real-time PCR. Expression of CMG2 was about 1.5-fold higher in CD8+ cells than in CD4+ and B cells, and 2.5-fold higher than in macrophages. Conclusions/Significance Anthrax toxin entry and activity differs among immune cells. Macrophages, dendritic cells, and B cells displayed higher LFnBLA activity than CD4+ and CD8+ T cells in both spleen cell suspension and the purified samples of individual cell types. Expression of anthrax toxin receptor CMG2 is higher in CD4+ and CD8+ T cells, which is not correlated to the intracellular LFnBLA activity.
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Affiliation(s)
- Haijing Hu
- Bacterial Toxins and Therapeutics Section, Laboratory of Bacterial Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Stephen H. Leppla
- Bacterial Toxins and Therapeutics Section, Laboratory of Bacterial Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
- * E-mail:
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