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Graham CI, MacMartin TL, de Kievit TR, Brassinga AKC. Molecular regulation of virulence in Legionella pneumophila. Mol Microbiol 2024; 121:167-195. [PMID: 37908155 DOI: 10.1111/mmi.15172] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 09/15/2023] [Accepted: 09/17/2023] [Indexed: 11/02/2023]
Abstract
Legionella pneumophila is a gram-negative bacteria found in natural and anthropogenic aquatic environments such as evaporative cooling towers, where it reproduces as an intracellular parasite of cohabiting protozoa. If L. pneumophila is aerosolized and inhaled by a susceptible person, bacteria may colonize their alveolar macrophages causing the opportunistic pneumonia Legionnaires' disease. L. pneumophila utilizes an elaborate regulatory network to control virulence processes such as the Dot/Icm Type IV secretion system and effector repertoire, responding to changing nutritional cues as their host becomes depleted. The bacteria subsequently differentiate to a transmissive state that can survive in the environment until a replacement host is encountered and colonized. In this review, we discuss the lifecycle of L. pneumophila and the molecular regulatory network that senses nutritional depletion via the stringent response, a link to stationary phase-like metabolic changes via alternative sigma factors, and two-component systems that are homologous to stress sensors in other pathogens, to regulate differentiation between the intracellular replicative phase and more transmissible states. Together, we highlight how this prototypic intracellular pathogen offers enormous potential in understanding how molecular mechanisms enable intracellular parasitism and pathogenicity.
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Affiliation(s)
- Christopher I Graham
- Department of Microbiology, Faculty of Science, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Teassa L MacMartin
- Department of Microbiology, Faculty of Science, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Teresa R de Kievit
- Department of Microbiology, Faculty of Science, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Ann Karen C Brassinga
- Department of Microbiology, Faculty of Science, University of Manitoba, Winnipeg, Manitoba, Canada
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Comparative Genomics of Legionella pneumophila Isolates from the West Bank and Germany Support Molecular Epidemiology of Legionnaires' Disease. Microorganisms 2023; 11:microorganisms11020449. [PMID: 36838414 PMCID: PMC9965269 DOI: 10.3390/microorganisms11020449] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2022] [Revised: 01/27/2023] [Accepted: 02/07/2023] [Indexed: 02/12/2023] Open
Abstract
Legionella pneumophila is an environmental bacterium and clinical pathogen that causes many life-threating outbreaks of an atypical pneumonia called Legionnaires' disease (LD). Studies of this pathogen have focused mainly on Europe and the United States. A shortage in L. pneumophila data is clearly observed for developing countries. To reduce this knowledge gap, L. pneumophila isolates were studied in two widely different geographical areas, i.e., the West Bank and Germany. For this study, we sequenced and compared the whole genome of 38 clinical and environmental isolates of L. pneumophila covering different MLVA-8(12) genotypes in the two areas. Sequencing was conducted using the Illumina HiSeq 2500 platform. In addition, two isolates (A194 and H3) were sequenced using a Pacific Biosciences (PacBio) RSII platform to generate complete reference genomes from each of the geographical areas. Genome sequences from 55 L. pneumophila strains, including 17 reference strains, were aligned with the genome sequence of the closest strain (L. pneumophila strain Alcoy). A whole genome phylogeny based on single nucleotide polymorphisms (SNPs) was created using the ParSNP software v 1.0. The reference genomes obtained for isolates A194 and H3 consisted of circular chromosomes of 3,467,904 bp and 3,691,263 bp, respectively. An average of 36,418 SNPs (min. 8569, max. 70,708 SNPs) against our reference strain L. pneumophila str. Alcoy, and 2367 core-genes were identified among the fifty-five strains. An analysis of the genomic population structure by SNP comparison divided the fifty-five L. pneumophila strains into six branches. Individual isolates in sub-lineages in these branches differed by less than 120 SNPs if they had the same MLVA genotype and were isolated from the same location. A bioinformatics analysis identified the genomic islands (GIs) for horizontal gene transfer and mobile genetic elements, demonstrating that L. pneumophila showed high genome plasticity. Four L. pneumophila isolates (H3, A29, A129 and L10-091) contained well-defined plasmids. On average, only about half of the plasmid genes could be matched to proteins in databases. In silico phage findings suggested that 43 strains contained at least one phage. However, none of them were found to be complete. BLASTp analysis of proteins from the type IV secretion Dot/Icm system showed those proteins highly conserved, with less than 25% structural differences in the new L. pneumophila isolates. Overall, we demonstrated that whole genome sequencing provides a molecular surveillance tool for L. pneumophila at the highest conceivable discriminatory level, i.e., two to eight SNPs were observed for isolates from the same location but several years apart.
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Zayed AR, Bunk B, Jaber L, Abu-Teer H, Ali M, Steinert M, Höfle MG, Brettar I, Bitar DM. Whole-genome sequencing of the clinical isolate of Legionella pneumophila ALAW1 from the West Bank allows high-resolution typing and determination of pathogenicity mechanisms. Eur Clin Respir J 2023; 10:2168346. [PMID: 36698751 PMCID: PMC9869991 DOI: 10.1080/20018525.2023.2168346] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Background Legionella pneumophila is water-based bacterium causing Legionnaires' disease (LD). We describe the first documented case of nosocomial LD caused by L. pneumophila sequence type (ST) 461 and serogroup 6. The etiology of LD was confirmed by culturing the bronchoalveolar lavage sample retrieving L. pneumophila strain ALAW1. A 7-days treatment of the LD patient with Azithromycin and Levofloxacin allowed complete recovery. Methods In details, we sequenced the whole genome of the L. pneumophila ALAW1 using Illumina HiSeq platform. The sequence of ALAW1 was aligned with the genome sequence from the closely related reference strain Alcoy 2300/99 and a whole-genome phylogeny based on single nucleotide polymorphisms (SNPs) was created using Parsnp software. Also, the TYGS web-server was used in order to compare the genome with type strain. Results An analysis of the population structure by SNP and TYGS comparison clustered ALAW1 with the reference genome Alcoy 2300/99. Blastp analysis of the type IV secretion Dot/Icm system genes showed that these genes were highly conserved with (≤25%) structural differences at the protein level. Conclusions Overall, this study provides insights into detailed genome structure and demonstrated the value of whole-genome sequencing as the ultimate typing tool for Legionella.
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Affiliation(s)
- Ashraf R. Zayed
- CONTACT Ashraf R. Zayed Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, An-Najah National University, Nablus, P. O. Box. 7, Palestine;Microbiology Research laboratory Faculty of Medicine Al-Quds University Abu-Dies, East Jerusalem 9993100, Palestine Zayed
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Budowa IV systemu sekrecji Legionella pneumophilai jego znaczenie w patogenezie. POSTEP HIG MED DOSW 2021. [DOI: 10.2478/ahem-2021-0023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Abstrakt
Bakterie Legionella pneumophila w środowisku naturalnym pasożytują wewnątrz komórek wybranych gatunków pierwotniaków, a po przedostaniu się do sztucznych systemów dystrybucji wody stają się ważnym czynnikiem etiologicznym zapalenia płuc u ludzi. Główną cechą determinującą patogenność tych bakterii jest zdolność do życia i replikacji w makrofagach płucnych, czyli w komórkach wyspecjalizowanych do fagocytozy, zabijania i trawienia mikroorganizmów. Warunkiem wstępnym rozwoju infekcji jest przełamanie mechanizmów bójczych makrofagów i utworzenie wakuoli replikacyjnej LCV (Legionella containing vacuole). Biogeneza wakuoli LCV jest możliwa dzięki sprawnemu funkcjonowaniu IV systemu sekrecji Dot/Icm, który jest wielobiałkowym, złożonym kompleksem umiejscowionym w wewnętrznej i zewnętrznej membranie osłony komórkowej bakterii. System Dot/Icm liczy 27 elementów, na które składają się m.in. kompleks rdzeniowo-transmembranowy, tworzący strukturalny szkielet całego systemu oraz kompleks białek sprzęgających. Geny kodujące komponenty systemu Dot/Icm są zorganizowane na dwóch regionach chromosomu bak-teryjnego. System sekrecji Dot/Icm umożliwia L. pneumophila wprowadzenie do cytozolu komórki gospodarza ponad 300 białek efektorowych, których skoordynowane działanie powoduje utrzymanie integralności błony wakuoli replikacyjnej oraz pozwala na manipulowanie różnymi procesami komórki. Ważnym elementem strategii wewnątrzkomórkowego namnażania się L. pneumophila jest modulowanie transportu pęcherzykowego, interakcja z retikulum endoplazmatycznym oraz zakłócenie biosyntezy białek, procesów autofagii i apoptozy komórki gospodarza. Poznanie złożonych mechanizmów regulacji i funkcji białek efektorowych systemu Dot/Icm ma decydujące znaczenie w zapobieganiu i leczeniu choroby legionistów.
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Cytotoxicity, Intracellular Replication, and Contact-Dependent Pore Formation of Genotyped Environmental Legionella pneumophila Isolates from Hospital Water Systems in the West Bank, Palestine. Pathogens 2021; 10:pathogens10040417. [PMID: 33915921 PMCID: PMC8066006 DOI: 10.3390/pathogens10040417] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2021] [Revised: 03/15/2021] [Accepted: 03/28/2021] [Indexed: 12/02/2022] Open
Abstract
Legionella pneumophila is the causative agent of Legionnaires’ disease. Due to the hot climate and intermittent water supply, the West Bank, Palestine, can be considered a high-risk area for this often fatal atypical pneumonia. L. pneumophila occurs in biofilms of natural and man-made freshwater environments, where it infects and replicates intracellularly within protozoa. To correlate the genetic diversity of the bacteria in the environment with their virulence properties for protozoan and mammalian host cells, 60 genotyped isolates from hospital water systems in the West Bank were analyzed. The L. pneumophila isolates were previously genotyped by high resolution Multi Locus Variable Number of Tandem Repeat Analysis (MLVA-8(12)) and sorted according to their relationship in clonal complexes (VACC). Strains of relevant genotypes and VACCs were compared according to their capacity to infect Acanthamoeba castellanii and THP-1 macrophages, and to mediate pore-forming cytotoxicity in sheep red blood cells (sRBCs). Based on a previous detailed analysis of the biogeographic distribution and abundance of the MLVA-8(12)-genotypes, the focus of the study was on the most abundant L. pneumophila- genotypes Gt4(17), Gt6 (18) and Gt10(93) and the four relevant clonal complexes [VACC1, VACC2, VACC5 and VACC11]. The highly abundant genotypes Gt4(17) and Gt6(18) are affiliated with VACC1 and sequence type (ST)1 (comprising L. pneumophila str. Paris), and displayed seroroup (Sg)1. Isolates of these two genotypes exhibited significantly higher virulence potentials compared to other genotypes and clonal complexes in the West Bank. Endemic for the West Bank was the clonal complex VACC11 (affiliated with ST461) represented by three relevant genotypes that all displayed Sg6. These genotypes unique for the West Bank showed a lower infectivity and cytotoxicity compared to all other clonal complexes and their affiliated genotypes. Interestingly, the L. pneumophila serotypes ST1 and ST461 were previously identified by in situ-sequence based typing (SBT) as main causative agents of Legionnaires’ disease (LD) in the West Bank at a comparable level. Overall, this study demonstrates the site-specific regional diversity of L. pneumophila genotypes in the West Bank and suggests that a combination of MLVA, cellular infection assays and hierarchical agglomerative cluster analysis allows an improved genotype-based risk assessment.
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Visser JG, Van Staden ADP, Smith C. Harnessing Macrophages for Controlled-Release Drug Delivery: Lessons From Microbes. Front Pharmacol 2019; 10:22. [PMID: 30740053 PMCID: PMC6355695 DOI: 10.3389/fphar.2019.00022] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2018] [Accepted: 01/09/2019] [Indexed: 01/15/2023] Open
Abstract
With the effectiveness of therapeutic agents ever decreasing and the increased incidence of multi-drug resistant pathogens, there is a clear need for administration of more potent, potentially more toxic, drugs. Alternatively, biopharmaceuticals may hold potential but require specialized protection from premature in vivo degradation. Thus, a paralleled need for specialized drug delivery systems has arisen. Although cell-mediated drug delivery is not a completely novel concept, the few applications described to date are not yet ready for in vivo application, for various reasons such as drug-induced carrier cell death, limited control over the site and timing of drug release and/or drug degradation by the host immune system. Here, we present our hypothesis for a new drug delivery system, which aims to negate these limitations. We propose transport of nanoparticle-encapsulated drugs inside autologous macrophages polarized to M1 phenotype for high mobility and treated to induce transient phagosome maturation arrest. In addition, we propose a significant shift of existing paradigms in the study of host-microbe interactions, in order to study microbial host immune evasion and dissemination patterns for their therapeutic utilization in the context of drug delivery. We describe a system in which microbial strategies may be adopted to facilitate absolute control over drug delivery, and without sacrificing the host carrier cells. We provide a comprehensive summary of the lessons we can learn from microbes in the context of drug delivery and discuss their feasibility for in vivo therapeutic application. We then describe our proposed "synthetic microbe drug delivery system" in detail. In our opinion, this multidisciplinary approach may hold the solution to effective, controlled drug delivery.
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Affiliation(s)
- Johan Georg Visser
- Department of Physiological Sciences, Stellenbosch University, Matieland, South Africa
| | | | - Carine Smith
- Department of Physiological Sciences, Stellenbosch University, Matieland, South Africa
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Flieger A, Frischknecht F, Häcker G, Hornef MW, Pradel G. Pathways of host cell exit by intracellular pathogens. MICROBIAL CELL 2018; 5:525-544. [PMID: 30533418 PMCID: PMC6282021 DOI: 10.15698/mic2018.12.659] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Host cell exit is a critical step in the life-cycle of intracellular pathogens, intimately linked to barrier penetration, tissue dissemination, inflammation, and pathogen transmission. Like cell invasion and intracellular survival, host cell exit represents a well-regulated program that has evolved during host-pathogen co-evolution and that relies on the dynamic and intricate interplay between multiple host and microbial factors. Three distinct pathways of host cell exit have been identified that are employed by three different taxa of intracellular pathogens, bacteria, fungi and protozoa, namely (i) the initiation of programmed cell death, (ii) the active breaching of host cellderived membranes, and (iii) the induced membrane-dependent exit without host cell lysis. Strikingly, an increasing number of studies show that the majority of intracellular pathogens utilize more than one of these strategies, dependent on life-cycle stage, environmental factors and/or host cell type. This review summarizes the diverse exit strategies of intracellular-living bacterial, fungal and protozoan pathogens and discusses the convergently evolved commonalities as well as system-specific variations thereof. Key microbial molecules involved in host cell exit are highlighted and discussed as potential targets for future interventional approaches.
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Affiliation(s)
- Antje Flieger
- Division of Enteropathogenic Bacteria and Legionella, Robert Koch Institute, Wernigerode, Germany
| | | | - Georg Häcker
- Institute of Medical Microbiology and Hygiene, Medical Center - University of Freiburg, Germany
| | - Mathias W Hornef
- Institute of Medical Microbiology, RWTH Aachen University Hospital, Germany
| | - Gabriele Pradel
- Division of Cellular and Applied Infection Biology, Institute of Biology II, RWTH Aachen University, Germany
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Virulence Traits of Environmental and Clinical Legionella pneumophila Multilocus Variable-Number Tandem-Repeat Analysis (MLVA) Genotypes. Appl Environ Microbiol 2018. [PMID: 29523542 DOI: 10.1128/aem.00429-18] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Legionella pneumophila causes water-based infections resulting in severe pneumonia. Recently, we showed that different MLVA-8 (multilocus variable-number tandem-repeat analysis using 8 loci) genotypes dominated different sites of a drinking-water distribution system. Each genotype displayed a unique temperature-dependent growth behavior. Here we compared the pathogenicity potentials of different MLVA-8 genotypes of environmental and clinical strains. The virulence traits studied were hemolytic activity and cytotoxicity toward amoebae and macrophages. Clinical strains were significantly more hemolytic than environmental strains, while their cytotoxicity toward amoebae was significantly lower at 30°C. No significant differences were detected between clinical and environmental strains in cytotoxicity toward macrophages. Significant differences in virulence were observed between the environmental genotypes (Gt). Gt15 strains showed a significantly higher hemolytic activity. In contrast, Gt4 and Gt6 strains were more infective toward Acanthamoeba castellanii Moreover, Gt4 strains exhibited increased cytotoxicity toward macrophages and demonstrated a broader temperature range of amoebal lysis than Gt6 and Gt15 strains. Understanding the virulence traits of Legionella genotypes may improve the assessment of public health risks of Legionella in drinking water.IMPORTANCELegionella pneumophila is the causative agent of a severe form of pneumonia. Here we demonstrated that clinical strains were significantly more cytotoxic toward red blood cells than environmental strains, while their cytotoxicity toward macrophages was similar. Genotype 4 (Gt4) strains were highly cytotoxic toward amoebae and macrophages and lysed amoebae in a broader temperature range than to the other studied genotypes. The results can explain the relatively high success of Gt4 in the environment and in clinical samples; thus, Gt4 strains should be considered a main factor for the assessment of public health risks of Legionella in drinking water. Our findings shed light on the ecology, virulence, and pathogenicity potential of different L. pneumophila genotypes, which can be a valuable parameter for future modeling and quantitative microbial risk assessment of Legionella in drinking-water systems.
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Feichtmayer J, Deng L, Griebler C. Antagonistic Microbial Interactions: Contributions and Potential Applications for Controlling Pathogens in the Aquatic Systems. Front Microbiol 2017; 8:2192. [PMID: 29184541 PMCID: PMC5694486 DOI: 10.3389/fmicb.2017.02192] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Accepted: 10/25/2017] [Indexed: 12/21/2022] Open
Abstract
Despite the active and intense treatment of wastewater, pathogenic microorganisms and viruses are frequently introduced into the aquatic environment. For most human pathogens, however, this is a rather hostile place, where starvation, continuous inactivation, and decay generally occur, rather than successful reproduction. Nevertheless, a great diversity of the pathogenic microorganisms can be detected, in particular, in the surface waters receiving wastewater. Pathogen survival depends majorly on abiotic factors such as irradiation, changes in water ionic strength, temperature, and redox state. In addition, inactivation is enhanced by the biotic interactions in the environment. Although knowledge of the antagonistic biotic interactions has been available since a long time, certain underlying processes and mechanisms still remain unclear. Others are well-appreciated and increasingly are applied to the present research. Our review compiles and discusses the presently known biotic interactions between autochthonous microbes and pathogens introduced into the aquatic environment, including protozoan grazing, virus-induced bacterial cell lysis, antimicrobial substances, and predatory bacteria. An overview is provided on the present knowledge, as well as on the obvious research gaps. Individual processes that appear promising for future applications in the aquatic environment are presented and discussed.
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Affiliation(s)
- Judith Feichtmayer
- Institute of Groundwater Ecology, Helmholtz Zentrum München GmbH, Neuherberg, Germany
| | - Li Deng
- Institute of Groundwater Ecology, Helmholtz Zentrum München GmbH, Neuherberg, Germany
- Institute of Virology, Helmholtz Zentrum München GmbH, Neuherberg, Germany
| | - Christian Griebler
- Institute of Groundwater Ecology, Helmholtz Zentrum München GmbH, Neuherberg, Germany
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Ye Z, Li Q, Guo Q, Xiong Y, Guo D, Yang H, Shu Y. Ketamine induces hippocampal apoptosis through a mechanism associated with the caspase-1 dependent pyroptosis. Neuropharmacology 2017; 128:63-75. [PMID: 28963039 DOI: 10.1016/j.neuropharm.2017.09.035] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2017] [Revised: 08/24/2017] [Accepted: 09/25/2017] [Indexed: 12/11/2022]
Abstract
Ketamine, a pediatric anesthetic, is widely used in clinical practice. There was growing evidence showing that ketamine can promote neuronal death in developing brains of both humans and animals. In this study, we used in vivo neonatal and juvenile mouse models to induce ketamine-related neurotoxicity in the hippocampus. Active caspase-3 and -9 proteins, which are responsible for the release of cytochrome C, and the mitochondrial translocation of p53, which is associated with mitochondrial apoptosis, were found to be significantly up-regulated in the ketamine-induced hippocampal neurotoxicity. Furthermore, we demonstrated that the levels of pyroptosis-related proteins, including caspase-1 and -11, NOD-like receptor family, pyrin domain containing 3 (NLRP3), and IL-1β and IL-18, significantly increased after multiple doses of ketamine administration. We speculated that ketamine triggered the formation of NLRP3 and caspase-1 complex and its translocation to the mitochondria. In consistent with this, ketamine treatment was found to induce pyroptosis in mouse primary hippocampal neurons, which was characterized by increased pore formation and elevated lactate dehydrogenase release in mitochondria. Silencing caspase-1 with lentivirus-mediated short hairpin RNA (shRNA) significantly decreased the levels of not only pyroptosis-related proteins but also mitochondrial apoptosis-associated proteins in mouse primary hippocampal neurons. We conclude that caspase-1-dependent pyroptosis is an important event which may be an essential pathway involved in the mitochondria-associated apoptosis in ketamine-induced hippocampal neurotoxicity.
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Affiliation(s)
- Zhi Ye
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland at Baltimore, MD, USA; Department of Anesthesiology, Xiangya Hospital, Central South University, Changsha, 410078, China
| | - Qing Li
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland at Baltimore, MD, USA; Institute of Clinical Pharmacology, Central South University, Hunan 410078, China
| | - Qulian Guo
- Department of Anesthesiology, Xiangya Hospital, Central South University, Changsha, 410078, China
| | - Yunchuan Xiong
- Department of Anesthesiology, Xiangya Hospital, Central South University, Changsha, 410078, China
| | - Dong Guo
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland at Baltimore, MD, USA
| | - Hong Yang
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland at Baltimore, MD, USA
| | - Yan Shu
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland at Baltimore, MD, USA.
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Abstract
In this article, we have described several cellular pathological effects caused by the Mycobacterium tuberculosis ESX-1. The effects include induction of necrosis, NOD2 signaling, type I interferon production, and autophagy. We then attempted to suggest that these pathological effects are mediated by the cytosolic access of M. tuberculosis-derived materials as a result of the phagosome-disrupting activity of the major ESX-1 substrate ESAT-6. Such activity of ESAT-6 is most likely due to its pore-forming activity at the membrane. The amyloidogenic characteristic of ESAT-6 is reviewed here as a potential mechanism of membrane pore formation. In addition to ESAT-6, the ESX-1 substrate EspB interferes with membrane-mediated innate immune mechanisms such as efferocytosis and autophagy, most likely through its ability to bind phospholipids. Overall, the M. tuberculosis ESX-1 secretion system appears to be a specialized system for the deployment of host membrane-targeting proteins, whose primary function is to interrupt key steps in innate immune mechanisms against pathogens. Inhibitors that block the ESX-1 system or block host factors critical for ESX-1 toxicity have been identified and should represent attractive potential new antituberculosis drugs.
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Chiaraviglio L, Kang YS, Kirby JE. High Throughput, Real-time, Dual-readout Testing of Intracellular Antimicrobial Activity and Eukaryotic Cell Cytotoxicity. J Vis Exp 2016:54841. [PMID: 27911388 PMCID: PMC5226247 DOI: 10.3791/54841] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Traditional measures of intracellular antimicrobial activity and eukaryotic cell cytotoxicity rely on endpoint assays. Such endpoint assays require several additional experimental steps prior to readout, such as cell lysis, colony forming unit determination, or reagent addition. When performing thousands of assays, for example, during high-throughput screening, the downstream effort required for these types of assays is considerable. Therefore, to facilitate high-throughput antimicrobial discovery, we developed a real-time assay to simultaneously identify inhibitors of intracellular bacterial growth and assess eukaryotic cell cytotoxicity. Specifically, real-time intracellular bacterial growth detection was enabled by marking bacterial screening strains with either a bacterial lux operon (1st generation assay) or fluorescent protein reporters (2nd generation, orthogonal assay). A non-toxic, cell membrane-impermeant, nucleic acid-binding dye was also added during initial infection of macrophages. These dyes are excluded from viable cells. However, non-viable host cells lose membrane integrity permitting entry and fluorescent labeling of nuclear DNA (deoxyribonucleic acid). Notably, DNA binding is associated with a large increase in fluorescent quantum yield that provides a solution-based readout of host cell death. We have used this combined assay to perform a high-throughput screen in microplate format, and to assess intracellular growth and cytotoxicity by microscopy. Notably, antimicrobials may demonstrate synergy in which the combined effect of two or more antimicrobials when applied together is greater than when applied separately. Testing for in vitro synergy against intracellular pathogens is normally a prodigious task as combinatorial permutations of antibiotics at different concentrations must be assessed. However, we found that our real-time assay combined with automated, digital dispensing technology permitted facile synergy testing. Using these approaches, we were able to systematically survey action of a large number of antimicrobials alone and in combination against the intracellular pathogen, Legionella pneumophila.
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Affiliation(s)
| | - Yoon-Suk Kang
- Department of Pathology, Beth Israel Deaconess Medical Center
| | - James E Kirby
- Department of Pathology, Beth Israel Deaconess Medical Center;
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Vakulskas CA, Potts AH, Babitzke P, Ahmer BMM, Romeo T. Regulation of bacterial virulence by Csr (Rsm) systems. Microbiol Mol Biol Rev 2015; 79:193-224. [PMID: 25833324 PMCID: PMC4394879 DOI: 10.1128/mmbr.00052-14] [Citation(s) in RCA: 243] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Most bacterial pathogens have the remarkable ability to flourish in the external environment and in specialized host niches. This ability requires their metabolism, physiology, and virulence factors to be responsive to changes in their surroundings. It is no surprise that the underlying genetic circuitry that supports this adaptability is multilayered and exceedingly complex. Studies over the past 2 decades have established that the CsrA/RsmA proteins, global regulators of posttranscriptional gene expression, play important roles in the expression of virulence factors of numerous proteobacterial pathogens. To accomplish these tasks, CsrA binds to the 5' untranslated and/or early coding regions of mRNAs and alters translation, mRNA turnover, and/or transcript elongation. CsrA activity is regulated by noncoding small RNAs (sRNAs) that contain multiple CsrA binding sites, which permit them to sequester multiple CsrA homodimers away from mRNA targets. Environmental cues sensed by two-component signal transduction systems and other regulatory factors govern the expression of the CsrA-binding sRNAs and, ultimately, the effects of CsrA on secretion systems, surface molecules and biofilm formation, quorum sensing, motility, pigmentation, siderophore production, and phagocytic avoidance. This review presents the workings of the Csr system, the paradigm shift that it generated for understanding posttranscriptional regulation, and its roles in virulence networks of animal and plant pathogens.
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Affiliation(s)
- Christopher A Vakulskas
- Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida, USA
| | - Anastasia H Potts
- Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida, USA
| | - Paul Babitzke
- Department of Biochemistry and Molecular Biology, Center for RNA Molecular Biology, Pennsylvania State University, University Park, Pennsylvania, USA
| | - Brian M M Ahmer
- Department of Microbial Infection and Immunity, The Ohio State University, Columbus, Ohio, USA Department of Microbiology, The Ohio State University, Columbus, Ohio, USA
| | - Tony Romeo
- Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida, USA
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Kpadeh ZZ, Day SR, Mills BW, Hoffman PS. Legionella pneumophila utilizes a single-player disulfide-bond oxidoreductase system to manage disulfide bond formation and isomerization. Mol Microbiol 2015; 95:1054-69. [PMID: 25534767 DOI: 10.1111/mmi.12914] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/16/2014] [Indexed: 11/26/2022]
Abstract
Legionella pneumophila uses a single homodimeric disulfide bond (DSB) oxidoreductase DsbA2 to catalyze extracytoplasmic protein folding and to correct DSB errors through protein-disulfide isomerase (PDI) activity. In Escherichia coli, these functions are separated to avoid futile cycling. In L. pneumophila, DsbA2 is maintained as a mixture of disulfides (S-S) and free thiols (SH), but when expressed in E. coli, only the SH form is observed. We provide evidence to suggest that structural differences in DsbB oxidases (LpDsbB1 and LpDsbB2) and DsbD reductases (LpDsbD1 and LpDsbD2) (compared with E. coli) permit bifunctional activities without creating a futile cycle. LpdsbB1 and LpdsbB2 partially complemented an EcdsbB mutant while neither LpdsbD1 nor LpdsbD2 complemented an EcdsbD mutant unless DsbA2 was also expressed. When the dsb genes of E. coli were replaced with those of L. pneumophila, motility was restored and DsbA2 was present as a mixture of redox forms. A dominant-negative approach to interfere with DsbA2 function in L. pneumophila determined that DSB oxidase activity was necessary for intracellular multiplication and assembly/function of the Dot/Icm Type IVb secretion system. Our studies show that a single-player system may escape the futile cycle trap by limiting transfer of reducing equivalents from LpDsbDs to DsbA2.
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Affiliation(s)
- Zegbeh Z Kpadeh
- Department of Medicine, Division of Infectious Diseases & International Health, University of Virginia Health System, Charlottesville, VA, 22901, USA; Department of Microbiology, Immunology and Cancer Biology, University of Virginia School of Medicine, Charlottesville, VA, 22908, USA
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15
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Functional type 1 secretion system involved in Legionella pneumophila virulence. J Bacteriol 2014; 197:563-71. [PMID: 25422301 DOI: 10.1128/jb.02164-14] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Legionella pneumophila is a Gram-negative pathogen found mainly in water, either in a free-living form or within infected protozoans, where it replicates. This bacterium can also infect humans by inhalation of contaminated aerosols, causing a severe form of pneumonia called legionellosis or Legionnaires' disease. The involvement of type II and IV secretion systems in the virulence of L. pneumophila is now well documented. Despite bioinformatic studies showing that a type I secretion system (T1SS) could be present in this pathogen, the functionality of this system based on the LssB, LssD, and TolC proteins has never been established. Here, we report the demonstration of the functionality of the T1SS, as well as its role in the infectious cycle of L. pneumophila. Using deletion mutants and fusion proteins, we demonstrated that the repeats-in-toxin protein RtxA is secreted through an LssB-LssD-TolC-dependent mechanism. Moreover, fluorescence monitoring and confocal microscopy showed that this T1SS is required for entry into the host cell, although it seems dispensable to the intracellular cycle. Together, these results underline the active participation of L. pneumophila, via its T1SS, in its internalization into host cells.
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16
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Shen XF, Ren LB, Teng Y, Zheng S, Yang XL, Guo XJ, Wang XY, Sha KH, Li N, Xu GY, Tian HW, Wang XY, Liu XK, Li J, Huang N. Luteolin decreases the attachment, invasion and cytotoxicity of UPEC in bladder epithelial cells and inhibits UPEC biofilm formation. Food Chem Toxicol 2014; 72:204-11. [PMID: 25051393 DOI: 10.1016/j.fct.2014.07.019] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2014] [Revised: 07/03/2014] [Accepted: 07/09/2014] [Indexed: 01/24/2023]
Abstract
Urinary tract infection (UTI), primarily caused by uropathogenic Escherichia coli (UPEC), is one of the most common infectious diseases worldwide. Emerging antibiotic resistance requires novel treatment strategies. Luteolin, a dietary polyphenolic flavonoid, has been confirmed as a potential antimicrobial agent. Here, we evaluated the sub-MICs of luteolin for potential properties to modulate the UPEC infection. We found that luteolin significantly decreased the attachment and invasion of UPEC J96 or CFT073 in human bladder epithelial cell lines T24. Meanwhile, obvious decreased expression of type 1 fimbriae adhesin fimH gene, lower bacterial surface hydrophobicity and swimming motility, were observed in luteolin-pretreated UPEC. Furthermore, luteolin could attenuate UPEC-induced cytotoxicity in T24 cells, which manifested as decreased activity of lactate dehydrogenase (LDH). Simultaneously, the inhibition of luteolin on UPEC-induced cytotoxicity was confirmed by ethidium bromide/acridine orange staining. Finally, the luteolin-pretreated UPEC showed a lower ability of biofilm formation. Collectively, these results indicated that luteolin decreased the attachment and invasion of UPEC in bladder epithelial cells, attenuated UPEC-induced cytotoxicity and biofilm formation via down-regulating the expression of adhesin fimH gene, reducing the bacterial surface hydrophobicity and motility.
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Affiliation(s)
- Xiao-fei Shen
- Research Unit of Infection and Immunity, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China; Department of Pathophysiology, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China
| | - Lai-bin Ren
- Research Unit of Infection and Immunity, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China; Department of Pathophysiology, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China
| | - Yan Teng
- Research Unit of Infection and Immunity, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China; Department of Pathophysiology, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China
| | - Shuang Zheng
- Research Unit of Infection and Immunity, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China; Department of Pathophysiology, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China
| | - Xiao-long Yang
- Research Unit of Infection and Immunity, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China; Department of Pathophysiology, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China
| | - Xiao-juan Guo
- Research Unit of Infection and Immunity, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China; Department of Pathophysiology, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China
| | - Xin-yuan Wang
- Research Unit of Infection and Immunity, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China; Department of Pathophysiology, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China
| | - Kai-hui Sha
- Research Unit of Infection and Immunity, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China; Department of Pathophysiology, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China
| | - Na Li
- Research Unit of Infection and Immunity, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China; Department of Pathophysiology, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China
| | - Guang-ya Xu
- Department of Pathophysiology, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China
| | - Han-wen Tian
- Department of Pathophysiology, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China; Department of Pharmacology, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China
| | - Xiao-ying Wang
- Department of Pathophysiology, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China
| | - Xiao-kang Liu
- Department of Pharmacology, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China
| | - Jingyu Li
- Department of Pathophysiology, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China.
| | - Ning Huang
- Research Unit of Infection and Immunity, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China; Department of Pathophysiology, West China College of Basic and Forensic Medicine, Sichuan University, Chengdu 610041, China.
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Miller HK, Kwuan L, Schwiesow L, Bernick DL, Mettert E, Ramirez HA, Ragle JM, Chan PP, Kiley PJ, Lowe TM, Auerbuch V. IscR is essential for yersinia pseudotuberculosis type III secretion and virulence. PLoS Pathog 2014; 10:e1004194. [PMID: 24945271 PMCID: PMC4055776 DOI: 10.1371/journal.ppat.1004194] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2013] [Accepted: 05/06/2014] [Indexed: 11/19/2022] Open
Abstract
Type III secretion systems (T3SS) are essential for virulence in dozens of pathogens, but are not required for growth outside the host. Therefore, the T3SS of many bacterial species are under tight regulatory control. To increase our understanding of the molecular mechanisms behind T3SS regulation, we performed a transposon screen to identify genes important for T3SS function in the food-borne pathogen Yersinia pseudotuberculosis. We identified two unique transposon insertions in YPTB2860, a gene that displays 79% identity with the E. coliiron-sulfur cluster regulator, IscR. A Y. pseudotuberculosis iscR in-frame deletion mutant (ΔiscR) was deficient in secretion of Ysc T3SS effector proteins and in targeting macrophages through the T3SS. To determine the mechanism behind IscR control of the Ysc T3SS, we carried out transcriptome and bioinformatic analysis to identify Y. pseudotuberculosis genes regulated by IscR. We discovered a putative IscR binding motif upstream of the Y. pseudotuberculosis yscW-lcrF operon. As LcrF controls transcription of a number of critical T3SS genes in Yersinia, we hypothesized that Yersinia IscR may control the Ysc T3SS through LcrF. Indeed, purified IscR bound to the identified yscW-lcrF promoter motif and mRNA levels of lcrF and 24 other T3SS genes were reduced in Y. pseudotuberculosis in the absence of IscR. Importantly, mice orally infected with the Y. pseudotuberculosis ΔiscR mutant displayed decreased bacterial burden in Peyer's patches, mesenteric lymph nodes, spleens, and livers, indicating an essential role for IscR in Y. pseudotuberculosis virulence. This study presents the first characterization of Yersinia IscR and provides evidence that IscR is critical for virulence and type III secretion through direct regulation of the T3SS master regulator, LcrF. Bacterial pathogens use regulators that sense environmental cues to enhance their fitness. Here, we identify a transcriptional regulator in the human gut pathogen, Yersinia pseudotuberculosis, which controls a specialized secretion system essential for bacterial growth in mammalian tissues. This regulator was shown in other bacterial species to alter its activity in response to changes in iron concentration and oxidative stress, but has never been studied in Yersinia. Importantly, Y. pseudotuberculosis experiences large changes in iron bioavailability upon transit from the gut to deeper tissues and iron is a critical component in Yersinia virulence, as individuals with iron overload disorders have enhanced susceptibility to systemic Yersinia infections. Our work places this iron-modulated transcriptional regulator within the regulatory network that controls virulence gene expression in Y. pseudotuberculosis, identifying it as a potential new target for antimicrobial agents.
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Affiliation(s)
- Halie K. Miller
- Department of Microbiology and Environmental Toxicology, University of California Santa Cruz, Santa Cruz, California, United States of America
| | - Laura Kwuan
- Department of Microbiology and Environmental Toxicology, University of California Santa Cruz, Santa Cruz, California, United States of America
| | - Leah Schwiesow
- Department of Microbiology and Environmental Toxicology, University of California Santa Cruz, Santa Cruz, California, United States of America
| | - David L. Bernick
- Biomolecular Engineering, University of California Santa Cruz, Santa Cruz, California, United States of America
| | - Erin Mettert
- Department of Biomolecular Chemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States of America
| | - Hector A. Ramirez
- Department of Microbiology and Environmental Toxicology, University of California Santa Cruz, Santa Cruz, California, United States of America
| | - James M. Ragle
- Department of Molecular, Cell, and Developmental Biology, University of California Santa Cruz, Santa Cruz, California, United States of America
| | - Patricia P. Chan
- Biomolecular Engineering, University of California Santa Cruz, Santa Cruz, California, United States of America
| | - Patricia J. Kiley
- Department of Biomolecular Chemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States of America
| | - Todd M. Lowe
- Biomolecular Engineering, University of California Santa Cruz, Santa Cruz, California, United States of America
| | - Victoria Auerbuch
- Department of Microbiology and Environmental Toxicology, University of California Santa Cruz, Santa Cruz, California, United States of America
- * E-mail:
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18
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Nasrallah GK, Abdelhady H, Tompkins NP, Carson KR, Garduño RA. Deletion of potD, encoding a putative spermidine-binding protein, results in a complex phenotype in Legionella pneumophila. Int J Med Microbiol 2014; 304:703-16. [PMID: 24928741 DOI: 10.1016/j.ijmm.2014.05.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2014] [Revised: 03/16/2014] [Accepted: 05/11/2014] [Indexed: 11/28/2022] Open
Abstract
L. pneumophila is an intracellular pathogen that replicates in a membrane-bound compartment known as the Legionella-containing vacuole (LCV). We previously observed that the polyamine spermidine, produced by host cells or added exogenously, enhances the intracellular growth of L. pneumophila. To study this enhancing effect and determine whether polyamines are used as nutrients, we deleted potD from L. pneumophila strain JR32. The gene potD encodes a spermidine-binding protein that in other bacteria is essential for the function of the PotABCD polyamine transporter. Deletion of potD did not affect L. pneumophila growth in vitro in the presence or absence of spermidine and putrescine, suggesting that PotD plays a redundant or no role in polyamine uptake. However, deletion of potD resulted in a puzzlingly complex phenotype that included defects in L. pneumophila's ability to form filaments, tolerate Na(+), associate with macrophages and amoeba, recruit host vesicles to the LCV, and initiate intracellular growth. Moreover, the ΔpotD mutant was completely unable to grow in L929 cells treated with a pharmacological inhibitor of spermidine synthesis. These complex and disparate effects suggest that the L. pneumophila potD encodes either: (i) a multifunctional protein, (ii) a protein that interacts with, or regulates a, multifunctional protein, or (iii) a protein that contributes (directly or indirectly) to a regulatory network. Protein function studies with the L. pneumophila PotD protein are thus warranted.
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Affiliation(s)
- Gheyath K Nasrallah
- Department of Health Sciences, Biomedical Sciences Program, College of Arts and Sciences, Qatar University, Doha, Qatar.
| | - Hany Abdelhady
- Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Nicholas P Tompkins
- Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Kaitlyn R Carson
- Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Rafael A Garduño
- Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada; Department of Medicine - Division of Infectious Diseases, Dalhousie University, Halifax, Nova Scotia, Canada
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19
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Pei J, Kahl-McDonagh M, Ficht TA. Brucella dissociation is essential for macrophage egress and bacterial dissemination. Front Cell Infect Microbiol 2014; 4:23. [PMID: 24634889 PMCID: PMC3942807 DOI: 10.3389/fcimb.2014.00023] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2013] [Accepted: 02/10/2014] [Indexed: 12/24/2022] Open
Abstract
It has long been observed that smooth Brucella can dissociate into rough mutants that are cytotoxic to macrophages. However, the in vivo biological significance and/or mechanistic details of Brucella dissociation and cytotoxicity remain incomplete. In the current report, a plaque assay was developed using Brucella strains exhibiting varying degrees of cytotoxicity. Infected monolayers were observed daily using phase contrast microscopy for plaque formation while Brucella uptake and replication were monitored using an immunofluorescence assay (IFA). Visible plaques were detected at 4-5 days post infection (p.i.) with cytotoxic Brucella 16MΔmanBA at an MOI of 0.1. IFA staining demonstrated that the plaques consisted of macrophages with replicating Brucella. Visible plaques were not detected in monolayers infected with non-cytotoxic 16MΔmanBAΔvirB2 at an MOI of 0.1. However, IFA staining did reveal small groups of macrophages (foci) with replicating Brucella in the monolayers infected with 16MΔmanBAΔvirB2. The size of the foci observed in macrophage monolayers infected with rough Brucella correlated directly with cytotoxicity measured in liquid culture, suggesting that cytotoxicity was essential for Brucella egress and dissemination. In monolayers infected with 16M, small and large foci were observed. Double antibody staining revealed spontaneous rough mutants within the large, but not the small foci in 16M infected monolayers. Furthermore, plaque formation was observed in the large foci derived from 16M infections. Finally, the addition of gentamicin to the culture medium inhibited plaque formation, suggesting that cell-to-cell spread occurred only following release of the organisms from the cells. Taken together, these results demonstrate that Brucella-induced cytotoxicity is critical for Brucella egress and dissemination.
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Affiliation(s)
| | | | - Thomas A. Ficht
- Department of Veterinary Pathobiology, Texas A&M University and Texas Agricultural Experiment StationCollege Station, TX, USA
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20
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Fredlund J, Enninga J. Cytoplasmic access by intracellular bacterial pathogens. Trends Microbiol 2014; 22:128-37. [PMID: 24530174 DOI: 10.1016/j.tim.2014.01.003] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Revised: 01/08/2014] [Accepted: 01/10/2014] [Indexed: 02/08/2023]
Abstract
Entry into host cells is a strategy widely used by bacterial pathogens, after which they either remain within membrane-bound compartments or rupture the endocytic vacuole to reach the cytoplasm. During recent years, cytoplasmic access has been documented for an increasing number of pathogens. Here we review how classical cytoplasmic bacterial pathogens rupture their endocytic vacuoles as well as the mechanisms used to accomplish this task by bacterial species for which host cytoplasmic localization has only recently been identified. We also discuss the consequences for pathogenesis resulting from this change in intracellular localization, with a particular focus on the role of the host. What emerges is that cytoplasmic access plays an important role in the pathophysiology of an increasing number of intracellular bacterial pathogens.
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Affiliation(s)
- Jennifer Fredlund
- Unité 'Dynamique des interactions hôte-pathogène', Institut Pasteur, 25 rue du Dr. Roux, 75724 Paris, France
| | - Jost Enninga
- Unité 'Dynamique des interactions hôte-pathogène', Institut Pasteur, 25 rue du Dr. Roux, 75724 Paris, France.
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21
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Yang JR, Yao FH, Zhang JG, Ji ZY, Li KL, Zhan J, Tong YN, Lin LR, He YN. Ischemia-reperfusion induces renal tubule pyroptosis via the CHOP-caspase-11 pathway. Am J Physiol Renal Physiol 2013; 306:F75-84. [PMID: 24133119 DOI: 10.1152/ajprenal.00117.2013] [Citation(s) in RCA: 160] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The apoptotic or necrotic death of renal tubule epithelial cells is the main pathogenesis of renal ischemia-reperfusion-induced acute kidney injury (AKI). Pyroptosis is a programmed cell death pathway that depends on the activation of the caspase cascade and IL-1 cytokine family members. However, the role of pyroptosis in AKI induced by ischemia-reperfusion remains unclear. In this study, we found that the levels of the pyroptosis-related proteins, including caspase-1, caspase-11, and IL-1β, were significantly increased after 6 h of renal ischemia-reperfusion injury (IRI) and peaked at 12 h after IRI. Enhanced pyroptosis was accompanied by elevated renal structural and functional injury. Similarly, hypoxia-reoxygenation injury (HRI) also induced pyroptosis in renal tubule epithelial NRK-52E cells, which was characterized by increased pore formation and elevated lactate dehydrogenase release. In addition, obvious upregulation of the endoplasmic reticulum (ER) stress biomarkers glucose-regulated protein 78 and C/EBP homologous protein (CHOP) preceded the incidence of pyroptosis in cells treated with IRI or HRI. Pretreatment with a low dose of tunicamycin, an inducer of ER stress, relieved IRI-induced pyroptosis and renal tissue injury. Silencing of CHOP by small interfering RNA significantly decreased HRI-induced pyroptosis of NRK-52E cells, as evidenced by reduced caspase-11 activity and IL-1β generation. Therefore, we conclude that pyroptosis of renal tubule epithelial cells is a key event during IRI and that CHOP-caspase-11 triggered by overactivated ER stress may be an essential pathway involved in pyroptosis.
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Affiliation(s)
- Ju-Rong Yang
- Dept. of Nephrology, Daping Hospital, Research Institute of Surgery, the Third Military Medical Univ., Chongqing 400042, China.
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22
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Abstract
The transcriptional regulator RovA positively regulates transcription of the Yersinia enterocolitica virulence gene inv. Invasin, encoded by inv, is important for establishment of Y. enterocolitica infection. However, a rovA mutant is more attenuated for virulence than an inv mutant, implying that RovA regulates additional virulence genes. When the Y. enterocolitica RovA regulon was defined by microarray analysis, YE1984 and YE1985 were among the genes identified as being upregulated by RovA. Since these genes are homologous to Xenorhabdus nematophila cytotoxin genes xaxA and xaxB, we named them yaxA and yaxB, respectively. In this work, we demonstrate the effects of YaxAB on the course of infection in the murine model. While a yaxAB mutant (ΔyaxAB) is capable of colonizing mice at the same level as the wild type, it slightly delays the course of infection and results in differing pathology in the spleen. Further, we found that yaxAB encode a probable cytotoxin capable of lysing mammalian cells, that both YaxA and YaxB are required for cytotoxic activity, and that the two proteins associate. YaxAB-mediated cell death occurs via osmotic lysis through the formation of distinct membrane pores. In silico tertiary structural analysis identified predicted structural homology between YaxA and proteins in pore-forming toxin complexes from Bacillus cereus (HBL-B) and Escherichia coli (HlyE). Thus, it appears that YaxAB function as virulence factors by inducing cell lysis through the formation of pores in the host cell membrane. This characterization of YaxAB supports the hypothesis that RovA regulates expression of multiple virulence factors in Y. enterocolitica.
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23
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Induction of rapid cell death by an environmental isolate of Legionella pneumophila in mouse macrophages. Infect Immun 2013; 81:3077-88. [PMID: 23753633 DOI: 10.1128/iai.00252-13] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Legionella pneumophila, the etiological agent for Legionnaires' disease, is ubiquitous in the aqueous environment, where it replicates as an intracellular parasite of free-living protozoa. Our understanding of L. pneumophila pathogenicity is obtained mostly from study of derivatives of several clinical isolates, which employ almost identical virulent determinants to exploit host functions. To determine whether environmental L. pneumophila isolates interact similarly with the model host systems, we analyzed intracellular replication of several recently isolated such strains and found that these strains cannot productively grow in bone marrow-derived macrophages of A/J mice, which are permissive for all examined laboratory strains. By focusing on one strain called LPE509, we found that its deficiency in intracellular replication in primary A/J macrophages is not caused by the lack of important pathogenic determinants because this strain replicates proficiently in two protozoan hosts and the human macrophage U937 cell. We also found that in the early phase of infection, the trafficking of this strain in A/J macrophages is similar to that of JR32, a derivative of strain Philadelphia 1. Furthermore, infection of these cells by LPE509 caused extensive cell death in a process that requires the Dot/Icm type IV secretion system. Finally, we showed that the cell death is caused neither by the activation of the NAIP5/NLRC4 inflammasome nor by the recently described caspase 11-dependent pathway. Our results revealed that some environmental L. pneumophila strains are unable to overcome the defense conferred by primary macrophages from mice known to be permissive for laboratory L. pneumophila strains. These results also suggest the existence of a host immune surveillance mechanism differing from those currently known in responding to L. pneumophila infection.
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Abu Khweek A, Fernández Dávila NS, Caution K, Akhter A, Abdulrahman BA, Tazi M, Hassan H, Novotny LA, Bakaletz LO, Amer AO. Biofilm-derived Legionella pneumophila evades the innate immune response in macrophages. Front Cell Infect Microbiol 2013; 3:18. [PMID: 23750338 PMCID: PMC3664316 DOI: 10.3389/fcimb.2013.00018] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2013] [Accepted: 04/27/2013] [Indexed: 01/11/2023] Open
Abstract
Legionella pneumophila, the causative agent of Legionnaire's disease, replicates in human alveolar macrophages to establish infection. There is no human-to-human transmission and the main source of infection is L. pneumophila biofilms established in air conditioners, water fountains, and hospital equipments. The biofilm structure provides protection to the organism from disinfectants and antibacterial agents. L. pneumophila infection in humans is characterized by a subtle initial immune response, giving time for the organism to establish infection before the patient succumbs to pneumonia. Planktonic L. pneumophila elicits a strong immune response in murine, but not in human macrophages enabling control of the infection. Interactions between planktonic L. pneumophila and murine or human macrophages have been studied for years, yet the interface between biofilm-derived L. pneumophila and macrophages has not been explored. Here, we demonstrate that biofilm-derived L. pneumophila replicates significantly more in murine macrophages than planktonic bacteria. In contrast to planktonic L. pneumophila, biofilm-derived L. pneumophila lacks flagellin expression, do not activate caspase-1 or -7 and trigger less cell death. In addition, while planktonic L. pneumophila is promptly delivered to lysosomes for degradation, most biofilm-derived bacteria were enclosed in a vacuole that did not fuse with lysosomes in murine macrophages. This study advances our understanding of the innate immune response to biofilm-derived L. pneumophila and closely reproduces the natural mode of infection in human.
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Affiliation(s)
- Arwa Abu Khweek
- Department of Microbial Infection and Immunity, Center for Microbial Interface Biology, College of Medicine, The Ohio State University Columbus, OH, USA
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25
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Rao C, Benhabib H, Ensminger AW. Phylogenetic reconstruction of the Legionella pneumophila Philadelphia-1 laboratory strains through comparative genomics. PLoS One 2013; 8:e64129. [PMID: 23717549 PMCID: PMC3661481 DOI: 10.1371/journal.pone.0064129] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2013] [Accepted: 04/10/2013] [Indexed: 01/03/2023] Open
Abstract
Over 20 years ago, two groups independently domesticated Legionella pneumophila from a clinical isolate of bacteria collected during the first recognized outbreak of Legionnaires' disease (at the 1976 American Legion's convention in Philadelphia). These two laboratory strains, JR32 and Lp01, along with their derivatives, have been disseminated to a number of laboratories around the world and form the cornerstone of much of the research conducted on this important pathogen to date. Nevertheless, no exhaustive examination of the genetic distance between these strains and their clinical progenitor has been performed thus far. Such information is of paramount importance for making sense of several phenotypic differences observed between these strains. As environmental replication of L. pneumophila is thought to exclusively occur within natural protozoan hosts, retrospective analysis of the domestication and axenic culture of the Philadelphia-1 progenitor strain by two independent groups also provides an excellent opportunity to uncover evidence of adaptation to the laboratory environment. To reconstruct the phylogenetic relationships between the common laboratory strains of L. pneumophila Philadelphia-1 and their clinical ancestor, we performed whole-genome Illumina resequencing of the two founders of each laboratory lineage: JR32 and Lp01. As expected from earlier, targeted studies, Lp01 and JR32 contain large deletions in the lvh and tra regions, respectively. By sequencing additional strains derived from Lp01 (Lp02 and Lp03), we retraced the phylogeny of these strains relative to their reported ancestor, thereby reconstructing the evolutionary dynamics of each laboratory lineage from genomic data.
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Affiliation(s)
- Chitong Rao
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
| | - Hadas Benhabib
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
| | - Alexander W. Ensminger
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
- Public Health Ontario, Toronto, Ontario, Canada
- * E-mail:
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Erken M, Lutz C, McDougald D. The rise of pathogens: predation as a factor driving the evolution of human pathogens in the environment. MICROBIAL ECOLOGY 2013; 65:860-8. [PMID: 23354181 PMCID: PMC3637895 DOI: 10.1007/s00248-013-0189-0] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2012] [Accepted: 01/14/2013] [Indexed: 05/08/2023]
Abstract
Bacteria in the environment must survive predation from bacteriophage, heterotrophic protists, and predatory bacteria. This selective pressure has resulted in the evolution of a variety of defense mechanisms, which can also function as virulence factors. Here we discuss the potential dual function of some of the mechanisms, which protect against heterotrophic protists, and how predation pressure leads to the evolution of pathogenicity. This is in accordance with the coincidental evolution hypothesis, which suggests that virulence factors arose as a response to other selective pressures, for example, predation rather than for virulence per se. In this review we discuss some of those environmental factors that may be associated with the rise of pathogens in the marine environment. In particular, we will discuss the role of heterotrophic protists in the evolution of virulence factors in marine bacteria. Finally, we will discuss the implications for expansion of current pathogens and emergence of new pathogens.
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Affiliation(s)
- Martina Erken
- Centre for Marine Bio-Innovation, School of Biotechnology and Biomolecular Science, University of New South Wales, Sydney, New South Wales 2052 Australia
| | - Carla Lutz
- Centre for Marine Bio-Innovation, School of Biotechnology and Biomolecular Science, University of New South Wales, Sydney, New South Wales 2052 Australia
| | - Diane McDougald
- Centre for Marine Bio-Innovation, School of Biotechnology and Biomolecular Science, University of New South Wales, Sydney, New South Wales 2052 Australia
- Advanced Environmental Biotechnology Centre, Nanyang Environment and Water Research Institute, School of Biological Sciences, Nanyang Technological University, Nanyang Avenue, Singapore, 637551 Singapore
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Aurass P, Schlegel M, Metwally O, Harding CR, Schroeder GN, Frankel G, Flieger A. The Legionella pneumophila Dot/Icm-secreted effector PlcC/CegC1 together with PlcA and PlcB promotes virulence and belongs to a novel zinc metallophospholipase C family present in bacteria and fungi. J Biol Chem 2013; 288:11080-92. [PMID: 23457299 PMCID: PMC3630882 DOI: 10.1074/jbc.m112.426049] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2012] [Revised: 02/19/2013] [Indexed: 11/06/2022] Open
Abstract
Legionella pneumophila is a water-borne bacterium that causes pneumonia in humans. PlcA and PlcB are two previously defined L. pneumophila proteins with homology to the phosphatidylcholine-specific phospholipase C (PC-PLC) of Pseudomonas fluorescens. Additionally, we found that Lpg0012 shows similarity to PLCs and has been shown to be a Dot/Icm-injected effector, CegC1, which is designated here as PlcC. It remained unclear, however, whether these L. pneumophila proteins exhibit PLC activity. PlcC expressed in Escherichia coli hydrolyzed a broad phospholipid spectrum, including PC, phosphatidylglycerol (PG), and phosphatidylinositol. The addition of Zn(2+) ions activated, whereas EDTA inhibited, PlcC-derived PLC activity. Protein homology search revealed that the three Legionella enzymes and P. fluorescens PC-PLC share conserved domains also present in uncharacterized fungal proteins. Fifteen conserved amino acids were essential for enzyme activity as identified via PlcC mutagenesis. Analysis of defined L. pneumophila knock-out mutants indicated Lsp-dependent export of PG-hydrolyzing PLC activity. PlcA and PlcB exhibited PG-specific activity and contain a predicted Sec signal sequence. In line with the reported requirement of host cell contact for Dot/Icm-dependent effector translocation, PlcC showed cell-associated PC-specific PLC activity after bacterial growth in broth. A PLC triple mutant, but not single or double mutants, exhibited reduced host killing in a Galleria mellonella infection model, highlighting the importance of the three PLCs in pathogenesis. In summary, we describe here a novel Zn(2+)-dependent PLC family present in Legionella, Pseudomonas, and fungi with broad substrate preference and function in virulence.
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Affiliation(s)
- Philipp Aurass
- From the Division of Bacterial Infections, Robert Koch-Institut, Burgstrasse 37, 38855 Wernigerode, Germany and
| | - Maren Schlegel
- From the Division of Bacterial Infections, Robert Koch-Institut, Burgstrasse 37, 38855 Wernigerode, Germany and
| | - Omar Metwally
- From the Division of Bacterial Infections, Robert Koch-Institut, Burgstrasse 37, 38855 Wernigerode, Germany and
| | - Clare R. Harding
- the MRC Centre for Molecular Bacteriology and Infection, Division of Cell and Molecular Biology, Imperial College London, London SW7 2AZ, United Kingdom
| | - Gunnar N. Schroeder
- the MRC Centre for Molecular Bacteriology and Infection, Division of Cell and Molecular Biology, Imperial College London, London SW7 2AZ, United Kingdom
| | - Gad Frankel
- the MRC Centre for Molecular Bacteriology and Infection, Division of Cell and Molecular Biology, Imperial College London, London SW7 2AZ, United Kingdom
| | - Antje Flieger
- From the Division of Bacterial Infections, Robert Koch-Institut, Burgstrasse 37, 38855 Wernigerode, Germany and
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Khweek AA, Caution K, Akhter A, Abdulrahman BA, Tazi M, Hassan H, Majumdar N, Doran A, Guirado E, Schlesinger LS, Shuman H, Amer AO. A bacterial protein promotes the recognition of the Legionella pneumophila vacuole by autophagy. Eur J Immunol 2013; 43:1333-44. [PMID: 23420491 DOI: 10.1002/eji.201242835] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2012] [Revised: 01/09/2013] [Accepted: 02/13/2013] [Indexed: 11/07/2022]
Abstract
Legionella pneumophila (L. pneumophila) is an intracellular bacterium of human alveolar macrophages that causes Legionnaires' disease. In contrast to humans, most inbred mouse strains are restrictive to L. pneumophila replication. We demonstrate that autophagy targets L. pneumophila vacuoles to lysosomes and that this process requires ubiquitination of L. pneumophila vacuoles and the subsequent binding of the autophagic adaptor p62/SQSTM1 to ubiquitinated vacuoles. The L. pneumophila legA9 encodes for an ankyrin-containing protein with unknown role. We show that the legA9 mutant replicate in WT mice and their bone marrow-derived macrophages. This is the first L. pneumophila mutant to be found to replicate in WT bone marrow-derived macrophages other than the Fla mutant. Less legA9 mutant-containing vacuoles acquired ubiquitin labeling and p62/SQSTM1 staining, evading autophagy uptake and avoiding lysosomal fusion. Thus, we describe a bacterial protein that targets the L. pneumophila-containing vacuole for autophagy uptake.
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Affiliation(s)
- Arwa A Khweek
- Department of Microbial Infection and Immunity, Center for Microbial Interface Biology, Columbus, OH 43210, USA
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Impact of host membrane pore formation by the Yersinia pseudotuberculosis type III secretion system on the macrophage innate immune response. Infect Immun 2013; 81:905-14. [PMID: 23297383 DOI: 10.1128/iai.01014-12] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Type III secretion systems (T3SSs) are used by Gram-negative pathogens to form pores in host membranes and deliver virulence-associated effector proteins inside host cells. In pathogenic Yersinia, the T3SS pore-forming proteins are YopB and YopD. Mammalian cells recognize the Yersinia T3SS, leading to a host response that includes secretion of the inflammatory cytokine interleukin-1β (IL-1β), Toll-like receptor (TLR)-independent expression of the stress-associated transcription factor Egr1 and the inflammatory cytokine tumor necrosis factor alpha (TNF-α), and host cell death. The known Yersinia T3SS effector proteins are dispensable for eliciting these responses, but YopB is essential. Three models describe how the Yersinia T3SS might trigger inflammation: (i) mammalian cells sense YopBD-mediated pore formation, (ii) innate immune stimuli gain access to the host cytoplasm through the YopBD pore, and/or (iii) the YopB-YopD translocon itself or its membrane insertion is proinflammatory. To test these models, we constructed a Yersinia pseudotuberculosis mutant expressing YopD devoid of its predicted transmembrane domain (YopD(ΔTM)) and lacking the T3SS cargo proteins YopHEMOJTN. This mutant formed pores in macrophages, but it could not mediate translocation of effector proteins inside host cells. Importantly, this mutant did not elicit rapid host cell death, IL-1β secretion, or TLR-independent Egr1 and TNF-α expression. These data suggest that YopBD-mediated translocation of unknown T3SS cargo leads to activation of host pathways influencing inflammation, cell death, and response to stress. As the YopD(ΔTM) Y. pseudotuberculosis mutant formed somewhat smaller pores with delayed kinetics, an alternative model is that the wild-type YopB-YopD translocon is specifically sensed by host cells.
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Sutherland MC, Nguyen TL, Tseng V, Vogel JP. The Legionella IcmSW complex directly interacts with DotL to mediate translocation of adaptor-dependent substrates. PLoS Pathog 2012; 8:e1002910. [PMID: 23028312 PMCID: PMC3441705 DOI: 10.1371/journal.ppat.1002910] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2012] [Accepted: 08/01/2012] [Indexed: 01/30/2023] Open
Abstract
Legionella pneumophila is a Gram-negative bacterium that replicates within human alveolar macrophages by evasion of the host endocytic pathway through the formation of a replicative vacuole. Generation of this vacuole is dependent upon the secretion of over 275 effector proteins into the host cell via the Dot/Icm type IVB secretion system (T4SS). The type IV coupling protein (T4CP) subcomplex, consisting of DotL, DotM, DotN, IcmS and IcmW, was recently defined. DotL is proposed to be the T4CP of the L. pneumophila T4SS based on its homology to known T4CPs, which function as inner-membrane receptors for substrates. As a result, DotL is hypothesized to play an integral role(s) in the L. pneumophila T4SS for the engagement and translocation of substrates. To elucidate this role, a genetic approach was taken to screen for dotL mutants that were unable to survive inside host cells. One mutant, dotLY725Stop, did not interact with the type IV adaptor proteins IcmS/IcmW (IcmSW) leading to the identification of an IcmSW-binding domain on DotL. Interestingly, the dotLY725Stop mutant was competent for export of one class of secreted effectors, the IcmSW-independent substrates, but exhibited a specific defect in secretion of IcmSW-dependent substrates. This differential secretion illustrates that DotL requires a direct interaction with the type IV adaptor proteins for the secretion of a major class of substrates. Thus, by identifying a new target for IcmSW, we have discovered that the type IV adaptors perform an additional role in the export of substrates by the L. pneumophila Dot/Icm T4SS.
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Affiliation(s)
- Molly C. Sutherland
- Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Thuy Linh Nguyen
- Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Victor Tseng
- New York Medical College, Valhalla, New York, United States of America
| | - Joseph P. Vogel
- Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, United States of America
- * E-mail:
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Abstract
Two-signal models have a rich history in immunology. In the classic two-signal model of T-cell activation, signal one consists of engagement of the T-cell receptor by antigen/major histocompatibility complex, whereas signal two arises from costimulatory ligands on antigen-presenting cells. A requirement for two independent signals helps to ensure that T-cell responses are initiated only in response to bona fide infectious threats. Our studies have led us to conclude that initiation of innate immune responses to pathogens also often requires two signals: signal one is initiated by a microbe-derived ligand, such as lipopolysaccharide (LPS) or flagellin, whereas signal two conveys additional contextual information that often accompanies infectious microbes. Although signal one alone is sufficient to initiate many innate responses, certain responses-particularly ones with the potential for self-damage-require two signals for activation. Many of our studies have employed the intracellular bacterial pathogen Legionella pneumophila, which has been established as a valuable model for understanding innate immune responses. In this review, we discuss how the innate immune system integrates multiple signals to generate an effective response to L. pneumophila and other bacterial pathogens.
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Affiliation(s)
- Mary F Fontana
- Division of Immunology & Pathogenesis, Department of Molecular & Cell Biology, University of California, Berkeley, CA 94720, USA
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RpkA, a highly conserved GPCR with a lipid kinase domain, has a role in phagocytosis and anti-bacterial defense. PLoS One 2011; 6:e27311. [PMID: 22073313 PMCID: PMC3206951 DOI: 10.1371/journal.pone.0027311] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2011] [Accepted: 10/13/2011] [Indexed: 12/03/2022] Open
Abstract
RpkA (Receptor phosphatidylinositol kinase A) is an unusual seven-helix transmembrane protein of Dictyostelium discoideum with a G protein coupled receptor (GPCR) signature and a C-terminal lipid kinase domain (GPCR-PIPK) predicted as a phosphatidylinositol-4-phosphate 5-kinase. RpkA-homologs are present in all so far sequenced Dictyostelidae as well as in several other lower eukaryotes like the oomycete Phytophthora, and in the Legionella host Acanthamoeba castellani. Here we show by immunofluorescence that RpkA localizes to endosomal membranes and is specifically recruited to phagosomes. RpkA interacts with the phagosomal protein complex V-ATPase as proteins of this complex co-precipitate with RpkA-GFP as well as with the GST-tagged PIPK domain of RpkA. Loss of RpkA leads to a defect in phagocytosis as measured by yeast particle uptake. The uptake of the pathogenic bacterium Legionella pneumophila was however unaltered whereas its intra-cellular replication was significantly enhanced in rpkA-. The difference between wild type and rpkA- was even more prominent when L. hackeliae was used. When we investigated the reason for the enhanced susceptibility for L. pneumophila of rpkA- we could not detect a difference in endosomal pH but rpkA- showed depletion of phosphoinositides (PIP and PIP2) when we compared metabolically labeled phosphoinositides from wild type and rpkA-. Furthermore rpkA- exhibited reduced nitrogen starvation tolerance, an indicator for a reduced autophagy rate. Our results indicate that RpkA is a component of the defense system of D. discoideum as well as other lower eukaryotes.
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de Pace F, Boldrin de Paiva J, Nakazato G, Lancellotti M, Sircili MP, Guedes Stehling E, Dias da Silveira W, Sperandio V. Characterization of IcmF of the type VI secretion system in an avian pathogenic Escherichia coli (APEC) strain. MICROBIOLOGY (READING, ENGLAND) 2011. [PMID: 21778203 DOI: 10.1099/mic.0.050005–0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The intracellular multiplication factor (IcmF) protein is a component of the recently described type VI secretion system (T6SS). IcmF has been shown to be required for intra-macrophage replication and inhibition of phagosome-lysosome fusion in Legionella pneumophila. In Vibrio cholerae it is involved in motility, adherence and conjugation. Given that we previously reported that two T6SS genes (hcp and clpV) contribute to the pathogenesis of a septicaemic strain (SEPT362) of avian pathogenic Escherichia coli (APEC), we investigated the function of IcmF in this strain. Further elucidation of the virulence mechanisms of APEC is important because this pathogen is responsible for financial losses in the poultry industry, and is closely related to human extraintestinal pathogenic E. coli (ExPEC) strains, representing a potential zoonotic risk, as well as serving as a reservoir of virulence genes. Here we show that an APEC icmF mutant has decreased adherence to and invasion of epithelial cells, as well as decreased intra-macrophage survival. The icmF mutant is also defective for biofilm formation on abiotic surfaces. Additionally, expression of the flagella operon is decreased in the icmF mutant, leading to decreased motility. The combination of these phenotypes culminates in this mutant being altered for infection in chicks. These results suggest that IcmF in APEC may play a role in disease, and potentially also in the epidemiological spread of this pathogen through enhancement of biofilm formation.
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Affiliation(s)
- Fernanda de Pace
- Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | - Jacqueline Boldrin de Paiva
- Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | | | - Marcelo Lancellotti
- Department of Biochemistry, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | | | - Eliana Guedes Stehling
- Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | - Wanderley Dias da Silveira
- Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | - Vanessa Sperandio
- University of Texas Southwestern Medical Center, Dallas, TX 75390-9048, USA
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de Pace F, Boldrin de Paiva J, Nakazato G, Lancellotti M, Sircili MP, Guedes Stehling E, Dias da Silveira W, Sperandio V. Characterization of IcmF of the type VI secretion system in an avian pathogenic Escherichia coli (APEC) strain. MICROBIOLOGY-SGM 2011; 157:2954-2962. [PMID: 21778203 DOI: 10.1099/mic.0.050005-0] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The intracellular multiplication factor (IcmF) protein is a component of the recently described type VI secretion system (T6SS). IcmF has been shown to be required for intra-macrophage replication and inhibition of phagosome-lysosome fusion in Legionella pneumophila. In Vibrio cholerae it is involved in motility, adherence and conjugation. Given that we previously reported that two T6SS genes (hcp and clpV) contribute to the pathogenesis of a septicaemic strain (SEPT362) of avian pathogenic Escherichia coli (APEC), we investigated the function of IcmF in this strain. Further elucidation of the virulence mechanisms of APEC is important because this pathogen is responsible for financial losses in the poultry industry, and is closely related to human extraintestinal pathogenic E. coli (ExPEC) strains, representing a potential zoonotic risk, as well as serving as a reservoir of virulence genes. Here we show that an APEC icmF mutant has decreased adherence to and invasion of epithelial cells, as well as decreased intra-macrophage survival. The icmF mutant is also defective for biofilm formation on abiotic surfaces. Additionally, expression of the flagella operon is decreased in the icmF mutant, leading to decreased motility. The combination of these phenotypes culminates in this mutant being altered for infection in chicks. These results suggest that IcmF in APEC may play a role in disease, and potentially also in the epidemiological spread of this pathogen through enhancement of biofilm formation.
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Affiliation(s)
- Fernanda de Pace
- Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | - Jacqueline Boldrin de Paiva
- Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | | | - Marcelo Lancellotti
- Department of Biochemistry, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | | | - Eliana Guedes Stehling
- Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | - Wanderley Dias da Silveira
- Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas - Unicamp, Campinas, SP CP6109, Brazil
| | - Vanessa Sperandio
- University of Texas Southwestern Medical Center, Dallas, TX 75390-9048, USA
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Hilbi H, Hoffmann C, Harrison CF. Legionella spp. outdoors: colonization, communication and persistence. ENVIRONMENTAL MICROBIOLOGY REPORTS 2011; 3:286-296. [PMID: 23761274 DOI: 10.1111/j.1758-2229.2011.00247.x] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Bacteria of the genus Legionella persist in a wide range of environmental habitats, including biofilms, protozoa and nematodes. Legionellaceae are 'accidental' human pathogens that upon inhalation cause a severe pneumonia termed 'Legionnaires' disease'. The interactions of L. pneumophila with eukaryotic hosts are governed by the Icm/Dot type IV secretion system (T4SS) and more than 150 'effector proteins', which subvert signal transduction pathways and promote the formation of the replication-permissive 'Legionella-containing vacuole'. The Icm/Dot T4SS is essential to infect free-living protozoa, such as the amoeba Dictyostelium discoideum, as well as the nematode Caenorhabditis elegans, or mammalian macrophages. To adapt to different niches, L. pneumophila not only responds to exogenous cues, but also to endogenous signals, such as the α-hydroxyketone compound LAI-1 (Legionella autoinducer-1). The long-term adaptation of Legionella spp. is based on extensive horizontal DNA transfer. In fact, Legionella spp. have acquired canonical 'genomic islands' of prokaryotic origin, but also a number of eukaryotic genes. Since many aspects of Legionella virulence against environmental predators and immune phagocytes are similar, an understanding of Legionella ecology provides valuable insights into the pathogenesis of legionellaceae for humans.
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Affiliation(s)
- Hubert Hilbi
- Max von Pettenkofer Institute, Ludwig-Maximilian University Munich, Pettenkoferstrasse 9a, 80336 Munich, Germany
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Jameson-Lee M, Garduño RA, Hoffman PS. DsbA2 (27 kDa Com1-like protein) of Legionella pneumophila catalyses extracytoplasmic disulphide-bond formation in proteins including the Dot/Icm type IV secretion system. Mol Microbiol 2011; 80:835-52. [PMID: 21375592 DOI: 10.1111/j.1365-2958.2011.07615.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In Gram-negative bacteria, thiol oxidoreductases catalyse the formation of disulphide bonds (DSB) in extracytoplasmic proteins. In this study, we sought to identify DSB-forming proteins required for assembly of macromolecular structures in Legionella pneumophila. Here we describe two DSB-forming proteins, one annotated as dsbA1 and the other annotated as a 27 kDa outer membrane protein similar to Com1 of Coxiella burnetii, which we designate as dsbA2. Both proteins are predicted to be periplasmic, and while dsbA1 mutants were readily isolated and without phenotype, dsbA2 mutants were not obtained. To advance studies of DsbA2, a cis-proline residue at position 198 was replaced with threonine that enables formation of stable disulphide-bond complexes with substrate proteins. Expression of DsbA2 P198T mutant protein from an inducible promoter produced dominant-negative effects on DsbA2 function that resulted in loss of infectivity for amoeba and HeLa cells and loss of Dot/Icm T4SS-mediated contact haemolysis of erythrocytes. Analysis of captured DsbA2 P198T-substrate complexes from L. pneumophila by mass spectrometry identified periplasmic and outer membrane proteins that included components of the Dot/Icm T4SS. More broadly, our studies establish a DSB oxidoreductase function for the Com1 lineage of DsbA2-like proteins which appear to be conserved among those bacteria also expressing T4SS.
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Affiliation(s)
- Max Jameson-Lee
- Department of Medicine, Division of Infectious Diseases and International Health, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
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Cyclic diguanylate signaling proteins control intracellular growth of Legionella pneumophila. mBio 2011; 2:e00316-10. [PMID: 21249170 PMCID: PMC3023162 DOI: 10.1128/mbio.00316-10] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2010] [Accepted: 12/07/2010] [Indexed: 11/20/2022] Open
Abstract
Proteins that metabolize or bind the nucleotide second messenger cyclic diguanylate regulate a wide variety of important processes in bacteria. These processes include motility, biofilm formation, cell division, differentiation, and virulence. The role of cyclic diguanylate signaling in the lifestyle of Legionella pneumophila, the causative agent of Legionnaires' disease, has not previously been examined. The L. pneumophila genome encodes 22 predicted proteins containing domains related to cyclic diguanylate synthesis, hydrolysis, and recognition. We refer to these genes as cdgS (cyclic diguanylate signaling) genes. Strains of L. pneumophila containing deletions of all individual cdgS genes were created and did not exhibit any observable growth defect in growth medium or inside host cells. However, when overexpressed, several cdgS genes strongly decreased the ability of L. pneumophila to grow inside host cells. Expression of these cdgS genes did not affect the Dot/Icm type IVB secretion system, the major determinant of intracellular growth in L. pneumophila. L. pneumophila strains overexpressing these cdgS genes were less cytotoxic to THP-1 macrophages than wild-type L. pneumophila but retained the ability to resist grazing by amoebae. In many cases, the intracellular-growth inhibition caused by cdgS gene overexpression was independent of diguanylate cyclase or phosphodiesterase activities. Expression of the cdgS genes in a Salmonella enterica serovar Enteritidis strain that lacks all diguanylate cyclase activity indicated that several cdgS genes encode potential cyclases. These results indicate that components of the cyclic diguanylate signaling pathway play an important role in regulating the ability of L. pneumophila to grow in host cells.
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Morinaga Y, Yanagihara K, Nakamura S, Hasegawa H, Seki M, Izumikawa K, Kakeya H, Yamamoto Y, Yamada Y, Kohno S, Kamihira S. Legionella pneumophila induces cathepsin B-dependent necrotic cell death with releasing high mobility group box1 in macrophages. Respir Res 2010; 11:158. [PMID: 21092200 PMCID: PMC3003236 DOI: 10.1186/1465-9921-11-158] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2010] [Accepted: 11/22/2010] [Indexed: 11/16/2022] Open
Abstract
BACKGROUND Legionella pneumophila (LPN) can cause a lethal infectious disease with a marked inflammatory response in humans. However, the mechanism of this severe inflammation remains poorly understood. Since necrosis is known to induce inflammation, we investigated whether LPN induces necrosis in macrophages. We also analyzed the involvement of lysosomal cathepsin B in LPN-induced cell death. METHODS The human monocytic cell line THP-1 was infected with LPN, NUL1 strain. MG132-treated cells were used as apoptotic control cells. After infection, the type of cell death was analyzed by using microscopy, LDH release and flow cytometry. As a proinflammatory mediator, high-mobility group box 1 (HMGB-1), was measured. Cathepsin B activity was also measured and the inhibitory effects of cathepsin B on LPN-induced cell death were analyzed. RESULTS THP-1 cells after treatment with high dose of LPN showed necrotic features with releasing HMGB-1. This necrosis and the HMGB-1 release were inhibited by a specific lysosomal cathepsin B inhibitor and were characterized by a rapid and high activation of cathepsin B that was not observed in apoptotic control cells. The necrosis was also accompanied by cathepsin B-dependent poly(ADP-ribose) polymerase (PARP) cleavage. CONCLUSIONS We demonstrate here that L. pneumophila rapidly induces cathepsin B-dependent necrosis in a dose-dependent manner and releases a proinflammatory mediator, HMGB-1, from macrophages. This report describes a novel aspect of the pathogenesis of Legionnaires' disease and provides a possible therapeutic target for the regulation of inflammation.
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Affiliation(s)
- Yoshitomo Morinaga
- Department of Laboratory Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki, 851-2128, Japan
- Second Department of Internal Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki, 851-2128, Japan
| | - Katsunori Yanagihara
- Department of Laboratory Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki, 851-2128, Japan
- Second Department of Internal Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki, 851-2128, Japan
| | - Shigeki Nakamura
- Second Department of Internal Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki, 851-2128, Japan
| | - Hiroo Hasegawa
- Department of Laboratory Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki, 851-2128, Japan
| | - Masafumi Seki
- Second Department of Internal Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki, 851-2128, Japan
| | - Koichi Izumikawa
- Second Department of Internal Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki, 851-2128, Japan
| | - Hiroshi Kakeya
- Second Department of Internal Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki, 851-2128, Japan
| | - Yoshihiro Yamamoto
- Second Department of Internal Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki, 851-2128, Japan
| | - Yasuaki Yamada
- Department of Laboratory Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki, 851-2128, Japan
| | - Shigeru Kohno
- Second Department of Internal Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki, 851-2128, Japan
- Global COE Program, Nagasaki University, 1-7-1 Sakamoto, Nagasaki, 851-2128, Japan
| | - Shimeru Kamihira
- Department of Laboratory Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki, 851-2128, Japan
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Didodecyldimethylammonium bromide (DDAB) induces caspase-mediated apoptosis in human leukemia HL-60 cells. J Control Release 2010; 147:246-52. [DOI: 10.1016/j.jconrel.2010.07.114] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2010] [Revised: 07/19/2010] [Accepted: 07/21/2010] [Indexed: 11/21/2022]
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Vats V, Agrawal T, Salhan S, Mittal A. Characterization of Apoptotic Activities DuringChlamydia trachomatisInfection in Primary Cervical Epithelial Cells. Immunol Invest 2010; 39:674-87. [DOI: 10.3109/08820139.2010.485626] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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41
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Abstract
The genus Legionella contains more than 50 species, of which at least 24 have been associated with human infection. The best-characterized member of the genus, Legionella pneumophila, is the major causative agent of Legionnaires' disease, a severe form of acute pneumonia. L. pneumophila is an intracellular pathogen, and as part of its pathogenesis, the bacteria avoid phagolysosome fusion and replicate within alveolar macrophages and epithelial cells in a vacuole that exhibits many characteristics of the endoplasmic reticulum (ER). The formation of the unusual L. pneumophila vacuole is a feature of its interaction with the host, yet the mechanisms by which the bacteria avoid classical endosome fusion and recruit markers of the ER are incompletely understood. Here we review the factors that contribute to the ability of L. pneumophila to infect and replicate in human cells and amoebae with an emphasis on proteins that are secreted by the bacteria into the Legionella vacuole and/or the host cell. Many of these factors undermine eukaryotic trafficking and signaling pathways by acting as functional and, in some cases, structural mimics of eukaryotic proteins. We discuss the consequences of this mimicry for the biology of the infected cell and also for immune responses to L. pneumophila infection.
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Vp1659 is a Vibrio parahaemolyticus type III secretion system 1 protein that contributes to translocation of effector proteins needed to induce cytolysis, autophagy, and disruption of actin structure in HeLa cells. J Bacteriol 2010; 192:3491-502. [PMID: 20418402 DOI: 10.1128/jb.01493-09] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Vibrio parahaemolyticus harbors two type III secretion systems (T3SSs; T3SS1 and T3SS2), of which T3SS1 is involved in host cell cytotoxicity. T3SS1 expression is positively regulated by ExsA, and it is negatively regulated by ExsD. We compared the secretion profiles of a wild-type strain (NY-4) of V. parahaemolyticus with those of an ExsD deletion mutant (DeltaexsD) and with a strain of NY-4 that overexpresses T3SS1 (NY-4:pexsA). From this comparison, we detected a previously uncharacterized protein, Vp1659, which shares some sequence homology with LcrV from Yersinia. We show that vp1659 expression is positively regulated by ExsA and is negatively regulated by ExsD. Vp1659 is specifically secreted by T3SS1 of V. parahaemolyticus, and Vp1659 is not required for the successful extracellular secretion of another T3SS1 protein, Vp1656. Mechanical fractionation showed that Vp1659 is translocated into HeLa cells in a T3SS1-dependent manner and that deletion of Vp1659 does not prevent VopS from being translocated into HeLa cells during infection. Deletion of vp1659 significantly reduces cytotoxicity when HeLa cells are infected by V. parahaemolyticus, while complementation of the Deltavp1659 strain restores cytotoxicity. Differential staining showed that Vp1659 is required to induce membrane permeability in HeLa cells. We also show evidence that Vp1659 is required for actin rearrangement and the induction of autophagy. On the basis of these data, we conclude that Vp1659 is a T3SS1-associated protein that is a component of the secretion apparatus and that it is necessary for the efficient translocation of effector proteins into epithelial cells.
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Hilbi H, Jarraud S, Hartland E, Buchrieser C. Update on Legionnaires' disease: pathogenesis, epidemiology, detection and control. Mol Microbiol 2010; 76:1-11. [PMID: 20149105 PMCID: PMC2914503 DOI: 10.1111/j.1365-2958.2010.07086.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Legionellosis or Legionnaires' disease is an emerging and often-fatal form of pneumonia that is most severe in elderly and immunocompromised people, an ever-increasing risk group for infection. In recent years, the genomics of Legionella spp. has significantly increased our knowledge of the pathogenesis of this disease by providing new insights into the evolution and genetic and physiological basis of Legionella-host interactions. The seventh international conference on Legionella, Legionella 2009, illustrated many recent conceptual advances in epidemiology, pathogenesis and ecology. Experts in different fields presented new findings on basic mechanisms of pathogen-host interactions and bacterial evolution, as well as the clinical management and environmental prevalence and persistence of Legionella. The presentations revealed remarkable facts about the genetic and metabolic basis of the intracellular lifestyle of Legionella and reported on its striking ability to manipulate host cell processes by molecular mimicry. Together, these investigations will lead to new approaches for the treatment and prevention of Legionnaires' disease.
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Affiliation(s)
- Hubert Hilbi
- Institute of Molecular Life Sciences, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
| | - Sophie Jarraud
- Centre National de Référence des Legionella, Université de Lyon, INSERM U851, Faculté de Médecine, IFR 128, Lyon, France
| | - Elizabeth Hartland
- Department of Microbiology and Immunology, University of Melbourne, Victoria 3010, Australia
| | - Carmen Buchrieser
- Institut Pasteur, Biologie des Bactéries Intracellulaires, Paris, France
- CNRS URA 2171, Paris, France
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Sawada K, Ariki S, Kojima T, Saito A, Yamazoe M, Nishitani C, Shimizu T, Takahashi M, Mitsuzawa H, Yokota SI, Sawada N, Fujii N, Takahashi H, Kuroki Y. Pulmonary collectins protect macrophages against pore-forming activity of Legionella pneumophila and suppress its intracellular growth. J Biol Chem 2010; 285:8434-43. [PMID: 20056602 DOI: 10.1074/jbc.m109.074765] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Pulmonary collectins, surfactant proteins A (SP-A) and D (SP-D), play important roles in innate immunity of the lung. Legionella pneumophila is a bacterial respiratory pathogen that can replicate within macrophages and causes opportunistic infections. L. pneumophila possesses cytolytic activity, resulting from insertion of pores in the macrophage membrane upon contact. We examined whether pulmonary collectins play protective roles against L. pneumophila infection. SP-A and SP-D bound to L. pneumophila and its lipopolysaccharide (LPS) and inhibited the bacterial growth in a Ca(2+)-dependent manner. The addition of LPS in the culture blocked the inhibitory effects on L. pneumophila growth by the collectins, indicating the importance of LPS-collectin interaction. When differentiated THP-1 cells were infected with L. pneumophila in the presence of SP-A and SP-D, the number of permeable cells was significantly decreased, indicating that pulmonary collectins inhibit pore-forming activity of L. pneumophila. The number of live bacteria within the macrophages on days 1-4 after infection was significantly decreased when infection was performed in the presence of pulmonary collectins. The phagocytosis experiments with the pH-sensitive dye-labeled bacteria revealed that pulmonary collectins promoted bacterial localization to an acidic compartment. In addition, SP-A and SP-D significantly increased the number of L. pneumophila co-localized with LAMP-1. These results indicate that pulmonary collectins protect macrophages against contact-dependent cytolytic activity of L. pneumophila and suppress intracellular growth of the phagocytosed bacteria. The promotion of lysosomal fusion with Legionella-containing phagosomes constitutes a likely mechanism of L. pneumophila growth suppression by the collectins.
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Affiliation(s)
- Kaku Sawada
- Departments of Biochemistry, Sapporo Medical University School of Medicine, Sapporo 060-8556, Japan
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Pore formation triggered by Legionella spp. is an Nlrc4 inflammasome-dependent host cell response that precedes pyroptosis. Infect Immun 2010; 78:1403-13. [PMID: 20048047 DOI: 10.1128/iai.00905-09] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Legionella pneumophila, the etiological agent of Legionnaires disease, is known to trigger pore formation in bone marrow-derived macrophages (BMMs) by mechanisms dependent on the type IVB secretion system known as Dot/Icm. Here, we used several mutants of L. pneumophila in combination with knockout mice to assess the host and bacterial factors involved in pore formation in BMMs. We found that regardless of Dot/Icm activity, pore formation does not occur in BMMs deficient in caspase-1 and Nlrc4/Ipaf. Pore formation was temporally associated with interleukin-1beta secretion and preceded host cell lysis and pyroptosis. Pore-forming ability was dependent on bacterial Dot/Icm but independent of several effector proteins, multiplication, and de novo protein synthesis. Flagellin, which is known to trigger the Nlrc4 inflammasome, was required for pore formation as flaA mutant bacteria failed to induce cell permeabilization. Accordingly, transfection of purified flagellin was sufficient to trigger pore formation independent of infection. By using 11 different Legionella species, we found robust pore formation in response to L. micdadei, L. bozemanii, L. gratiana, L. jordanis, and L. rubrilucens, and this trait correlated with flagellin expression by these species. Together, the results suggest that pore formation is neither L. pneumophila specific nor the result of membrane damage induced by Dot/Icm activity; instead, it is a highly coordinated host cell response dependent on host Nlrc4 and caspase-1 and on bacterial flagellin and type IV secretion system.
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46
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Mouse macrophages are permissive to motile Legionella species that fail to trigger pyroptosis. Infect Immun 2009; 78:423-32. [PMID: 19841075 DOI: 10.1128/iai.00070-09] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Legionella pneumophila, a motile opportunistic pathogen of humans, is restricted from replicating in the lungs of C57BL/6 mice. Resistance of mouse macrophages to L. pneumophila depends on recognition of cytosolic flagellin. Once detected by the NOD-like receptors Naip5 and Ipaf (Nlrc4), flagellin triggers pyroptosis, a proinflammatory cell death. In contrast, motile strains of L. parisiensis and L. tucsonensis replicate profusely within C57BL/6 macrophages, similar to flagellin-deficient L. pneumophila. To gain insight into how motile species escape innate defense mechanisms of mice, we compared their impacts on macrophages. L. parisiensis and L. tucsonensis do not induce proinflammatory cell death, as measured by lactate dehydrogenase (LDH) release and interleukin-1beta (IL-1beta) secretion. However, flagellin isolated from L. parisiensis and L. tucsonensis triggers cell death and IL-1beta secretion when transfected into the cytosol of macrophages. Neither strain displays three characteristics of the canonical L. pneumophila Dot/Icm type IV secretion system: sodium sensitivity, LAMP-1 evasion, and pore formation. Therefore, we postulate that when L. parisiensis and L. tucsonensis invade a mouse macrophage, flagellin is confined to the phagosome, protecting the bacteria from recognition by the cytosolic surveillance system and allowing Legionella to replicate. Despite their superior capacity to multiply in mouse macrophages, L. parisiensis and L. tucsonensis have been associated with only two cases of disease, both in renal transplant patients. These results point to the complexity of disease, a product of the pathogenic potential of the microbe, as defined in the laboratory, and the capacity of the host to mount a measured defense.
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A Legionella type IV effector activates the NF-kappaB pathway by phosphorylating the IkappaB family of inhibitors. Proc Natl Acad Sci U S A 2009; 106:13725-30. [PMID: 19666608 DOI: 10.1073/pnas.0907200106] [Citation(s) in RCA: 123] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
NF-kappaB is critical in innate immune defense responses against invading microbial pathogens. Legionella pneumophila infection of lung macrophages causes Legionnaire's disease with pneumonia symptoms. A set of NF-kappaB-controlled genes involved in inflammation and anti-apoptosis are up-regulated in macrophages upon L. pneumophila infection in a Legionella Dot/Icm type IV secretion system-dependent manner. Among approximately 100 Dot/Icm substrates screened, we identified LegK1 as the sole Legionella protein that harbors a highly potent NF-kappaB-stimulating activity. LegK1 does not affect MAPK and IFN pathways. Activation of the NF-kappaB pathway by LegK1 requires its eukaryotic-like Ser/Thr kinase activity and is independent of upstream components in the NF-kappaB pathway, including TRAFs, NIK, MEKK3, and TAK1. Cell-free reconstitution revealed that LegK1 stimulated NF-kappaB activation in the absence of IKKalpha and IKKbeta, and LegK1 efficiently phosphorylated IkappaBalpha on Ser-32 and Ser-36 both in vitro and in cells. LegK1 seems to mimic the host IKK as LegK1 also directly phosphorylated other IkappaB family of inhibitors including p100 in the noncanonical NF-kappaB pathway. Phosphorylation of p100 by LegK1 led to its maturation into p52. Thus, LegK1 is a bacterial effector that directly activates the host NF-kappaB signaling and likely plays important roles in modulating macrophage defense or inflammatory responses during L. pneumophila infection.
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Bender J, Rydzewski K, Broich M, Schunder E, Heuner K, Flieger A. Phospholipase PlaB of Legionella pneumophila represents a novel lipase family: protein residues essential for lipolytic activity, substrate specificity, and hemolysis. J Biol Chem 2009; 284:27185-94. [PMID: 19640837 DOI: 10.1074/jbc.m109.026021] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Legionella pneumophila possesses several phospholipases capable of host cell manipulation and lung damage. Recently, we discovered that the major cell-associated hemolytic phospholipase A (PlaB) shares no homology to described phospholipases and is dispensable for intracellular replication in vitro. Nevertheless, here we show that PlaB is the major lipolytic activity in L. pneumophila cell infections and that PlaB utilizes a typical catalytic triad of Ser-Asp-His for effective hydrolysis of phospholipid substrates. Crucial residues were found to be located within the N-terminal half of the protein, and amino acids embedding these active sites were unique for PlaB and homologs. We further showed that catalytic activity toward phosphatidylcholine but not phosphatidylglycerol is directly linked to hemolytic potential of PlaB. Although the function of the prolonged PlaB C terminus remains to be elucidated, it is essential for lipolysis, since the removal of 15 amino acids already abolishes enzyme activity. Additionally, we determined that PlaB preferentially hydrolyzes long-chain fatty acid substrates containing 12 or more carbon atoms. Since phospholipases play an important role as bacterial virulence factors, we examined cell-associated enzymatic activities among L. pneumophila clinical isolates and non-pneumophila species. All tested clinical isolates showed comparable activities, whereas of the non-pneumophila species, only Legionella gormanii and Legionella spiritensis possessed lipolytic activities similar to those of L. pneumophila and comprised plaB-like genes. Interestingly, phosphatidylcholine-specific phospholipase A activity and hemolytic potential were more pronounced in L. pneumophila. Therefore, hydrolysis of the eukaryotic membrane constituent phosphatidylcholine triggered by PlaB could be an important virulence tool for Legionella pathogenicity.
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Affiliation(s)
- Jennifer Bender
- Division of Bacterial Infections, FG11, Robert Koch-Institut, Burgstrasse 37, Wernigerode 38855, Germany
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Charpentier X, Gabay JE, Reyes M, Zhu JW, Weiss A, Shuman HA. Chemical genetics reveals bacterial and host cell functions critical for type IV effector translocation by Legionella pneumophila. PLoS Pathog 2009; 5:e1000501. [PMID: 19578436 PMCID: PMC2698123 DOI: 10.1371/journal.ppat.1000501] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2008] [Accepted: 06/05/2009] [Indexed: 11/18/2022] Open
Abstract
Delivery of effector proteins is a process widely used by bacterial pathogens to subvert host cell functions and cause disease. Effector delivery is achieved by elaborate injection devices and can often be triggered by environmental stimuli. However, effector export by the L. pneumophila Icm/Dot Type IVB secretion system cannot be detected until the bacterium encounters a target host cell. We used chemical genetics, a perturbation strategy that utilizes small molecule inhibitors, to determine the mechanisms critical for L. pneumophila Icm/Dot activity. From a collection of more than 2,500 annotated molecules we identified specific inhibitors of effector translocation. We found that L. pneumophila effector translocation in macrophages requires host cell factors known to be involved in phagocytosis such as phosphoinositide 3-kinases, actin and tubulin. Moreover, we found that L. pneumophila phagocytosis and effector translocation also specifically require the receptor protein tyrosine phosphate phosphatases CD45 and CD148. We further show that phagocytosis is required to trigger effector delivery unless intimate contact between the bacteria and the host is artificially generated. In addition, real-time analysis of effector translocation suggests that effector export is rate-limited by phagocytosis. We propose a model in which L. pneumophila utilizes phagocytosis to initiate an intimate contact event required for the translocation of pre-synthesized effector molecules. We discuss the need for host cell participation in the initial step of the infection and its implications in the L. pneumophila lifestyle. Chemical genetic screening provides a novel approach to probe the host cell functions and factors involved in host-pathogen interactions.
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Affiliation(s)
- Xavier Charpentier
- Department of Microbiology, Columbia University Medical Center, New York, New York, United States of America
| | - Joëlle E. Gabay
- Department of Microbiology, Columbia University Medical Center, New York, New York, United States of America
| | - Moraima Reyes
- Department of Microbiology, Columbia University Medical Center, New York, New York, United States of America
| | - Jing W. Zhu
- Departments of Medicine and of Microbiology and Immunology, Howard Hughes Medical Institute, Rosalind Russell Medical Research Center for Arthritis, University of California, San Francisco, California, United States of America
| | - Arthur Weiss
- Departments of Medicine and of Microbiology and Immunology, Howard Hughes Medical Institute, Rosalind Russell Medical Research Center for Arthritis, University of California, San Francisco, California, United States of America
| | - Howard A. Shuman
- Department of Microbiology, Columbia University Medical Center, New York, New York, United States of America
- * E-mail:
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50
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Zhou X, Konkel ME, Call DR. Type III secretion system 1 of Vibrio parahaemolyticus induces oncosis in both epithelial and monocytic cell lines. MICROBIOLOGY-SGM 2009; 155:837-851. [PMID: 19246755 DOI: 10.1099/mic.0.024919-0] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The Vibrio parahaemolyticus type III secretion system 1 (T3SS1) induces cytotoxicity in mammalian epithelial cells. We characterized the cell death phenotype in both epithelial (HeLa) and monocytic (U937) cell lines following infection with V. parahaemolyticus. Using a combination of the wild-type strain and gene knockouts, we confirmed that V. parahaemolyticus strain NY-4 was able to induce cell death in both cell lines via a T3SS1-dependent mechanism. Bacterial contact, but not internalization, was required for T3SS1-induced cytotoxicity. The mechanism of cell death involves formation of a pore structure on the surface of infected HeLa and U937 cells, as demonstrated by cellular swelling, uptake of cell membrane-impermeable dye and protection of cytotoxicity by osmoprotectant (PEG3350). Western blot analysis showed that poly ADP ribose polymerase (PARP) was not cleaved and remained in its full-length active form. This result was evident for seven different V. parahaemolyticus strains. V. parahaemolyticus-induced cytotoxicity was not inhibited by addition of the pan-caspase inhibitor carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone (Z-VAD-FMK) or the caspase-1 inhibitor N-acetyl-tyrosyl-valyl-alanyl-aspartyl-aldehyde (Ac-YVAD-CHO); thus, caspases were not involved in T3SS1-induced cytotoxicity. DNA fragmentation was not evident following infection and autophagic vacuoles were not observed after monodansylcadaverine staining. We conclude that T3SS1 of V. parahaemolyticus strain NY-4 induces a host cell death primarily via oncosis rather than apoptosis, pyroptosis or autophagy.
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Affiliation(s)
- Xiaohui Zhou
- Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA, USA
| | - Michael E Konkel
- School of Molecular Biosciences, Washington State University, Pullman, WA, USA
| | - Douglas R Call
- Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA, USA
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