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Klein JA, Predeus AV, Greissl AR, Clark-Herrera MM, Cruz E, Cundiff JA, Haeberle AL, Howell M, Lele A, Robinson DJ, Westerman TL, Wrande M, Wright SJ, Green NM, Vallance BA, McClelland M, Mejia A, Goodman AG, Elfenbein JR, Knodler LA. Pathogenic diversification of the gut commensal Providencia alcalifaciens via acquisition of a second type III secretion system. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.06.07.595826. [PMID: 38895369 PMCID: PMC11185699 DOI: 10.1101/2024.06.07.595826] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/21/2024]
Abstract
Providencia alcalifaciens is a Gram-negative bacterium found in a wide variety of water and land environments and organisms. It has been isolated as part of the gut microbiome of animals and insects, as well as from stool samples of patients with diarrhea. Specific P. alcalifaciens strains encode gene homologs of virulence factors found in other pathogenic members of the same Enterobacterales order, such as Salmonella enterica serovar Typhimurium and Shigella flexneri. Whether these genes are also pathogenic determinants in P. alcalifaciens is not known. Here we have used P. alcalifaciens 205/92, a clinical isolate, with in vitro and in vivo infection models to investigate P. alcalifaciens -host interactions at the cellular level. Our particular focus was the role of two type III secretion systems (T3SS) belonging to the Inv-Mxi/Spa family. T3SS 1b is widespread in Providencia spp. and encoded on the chromosome. T3SS 1a is encoded on a large plasmid that is present in a subset of P. alcalifaciens strains, which are primarily isolates from diarrheal patients. Using a combination of electron and fluorescence microscopy and gentamicin protection assays we show that P. alcalifaciens 205/92 is internalized into eukaryotic cells, rapidly lyses its internalization vacuole and proliferates in the cytosol. This triggers caspase-4 dependent inflammasome responses in gut epithelial cells. The requirement for the T3SS 1a in entry, vacuole lysis and cytosolic proliferation is host-cell type specific, playing a more prominent role in human intestinal epithelial cells as compared to macrophages. In a bovine ligated intestinal loop model, P. alcalifaciens colonizes the intestinal mucosa, inducing mild epithelial damage with negligible fluid accumulation. No overt role for T3SS 1a or T3SS 1b was seen in the calf infection model. However, T3SS 1b was required for the rapid killing of Drosophila melanogaster . We propose that the acquisition of two T3SS by horizontal gene transfer has allowed P. alcalifaciens to diversify its host range, from a highly virulent pathogen of insects to an opportunistic gastrointestinal pathogen of animals.
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Egan MS, O’Rourke EA, Mageswaran SK, Zuo B, Martynyuk I, Demissie T, Hunter EN, Bass AR, Chang YW, Brodsky IE, Shin S. Inflammasomes primarily restrict cytosolic Salmonella replication within human macrophages. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.17.549348. [PMID: 37503120 PMCID: PMC10370064 DOI: 10.1101/2023.07.17.549348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/29/2023]
Abstract
Salmonella enterica serovar Typhimurium is a facultative intracellular pathogen that utilizes its type III secretion systems (T3SSs) to inject virulence factors into the host cell and colonize the host. In turn, a subset of cytosolic immune receptors respond to T3SS ligands by forming multimeric signaling complexes called inflammasomes, which activate caspases that induce interleukin-1 (IL-1) family cytokine release and an inflammatory form of cell death called pyroptosis. Human macrophages mount a multifaceted inflammasome response to Salmonella infection that ultimately restricts intracellular bacterial replication. However, how inflammasomes restrict Salmonella replication remains unknown. We find that caspase-1 is essential for mediating inflammasome responses to Salmonella and subsequent restriction of bacterial replication within human macrophages, with caspase-4 contributing as well. We also demonstrate that the downstream pore-forming protein gasdermin D (GSDMD) and ninjurin-1 (NINJ1), a mediator of terminal cell lysis, play a role in controlling Salmonella replication in human macrophages. Notably, in the absence of inflammasome responses, we observed hyperreplication of Salmonella within the cytosol of infected cells, and we also observed increased bacterial replication within vacuoles, suggesting that inflammasomes control Salmonella replication primarily within the cytosol and also within vacuoles. These findings reveal that inflammatory caspases and pyroptotic factors mediate inflammasome responses that restrict the subcellular localization of intracellular Salmonella replication within human macrophages.
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Affiliation(s)
- Marisa S. Egan
- Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
| | - Emily A. O’Rourke
- Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
| | - Shrawan Kumar Mageswaran
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
| | - Biao Zuo
- Electron Microscopy Resource Laboratory, Department of Biochemistry & Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
| | - Inna Martynyuk
- Electron Microscopy Resource Laboratory, Department of Biochemistry & Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
| | - Tabitha Demissie
- Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
| | - Emma N. Hunter
- Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
| | - Antonia R. Bass
- Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
| | - Yi-Wei Chang
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
| | - Igor E. Brodsky
- Department of Pathobiology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, PA
| | - Sunny Shin
- Department of Microbiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
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Browning KR, Merrikh H. Pathogenic bacteria experience pervasive RNA polymerase backtracking during infection. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.12.540596. [PMID: 37215019 PMCID: PMC10197661 DOI: 10.1101/2023.05.12.540596] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Pathogenic bacteria and their eukaryotic hosts are in a constant arms race. Hosts have numerous defense mechanisms at their disposal that not only challenge the bacterial invaders, but have the potential to disrupt molecular transactions along the bacterial chromosome. However, it is unclear how the host impacts association of proteins with the bacterial chromosome at the molecular level during infection. This is partially due to the lack of a method that could detect these events in pathogens while they are within host cells. We developed and optimized a system capable of mapping and measuring levels of bacterial proteins associated with the chromosome while they are actively infecting the host (referred to as PIC-seq). Here, we focused on the dynamics of RNA polymerase (RNAP) movement and association with the chromosome in the pathogenic bacterium Salmonella enterica as a model system during infection. Using PIC-seq, we found that RNAP association patterns with the chromosome change during infection genome-wide, including at regions that encode for key virulence genes. Importantly, we found that infection of a host significantly increases RNAP backtracking on the bacterial chromosome. RNAP backtracking is the most common form of disruption to RNAP progress on the chromosome. Interestingly, we found that the resolution of backtracked RNAPs via the anti-backtracking factors GreA and GreB is critical for pathogenesis, revealing a new class of virulence genes. Altogether, our results strongly suggest that infection of a host significantly impacts transcription by disrupting RNAP movement on the chromosome within the bacterial pathogen. The increased backtracking events have important implications not only for efficient transcription, but also for mutation rates as stalled RNAPs increase the levels of mutagenesis.
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Affiliation(s)
- Kaitlyn R. Browning
- Vanderbilt University School of Medicine, Department of Biochemistry, Nashville, TN 37232, USA
| | - Houra Merrikh
- Vanderbilt University School of Medicine, Department of Biochemistry, Nashville, TN 37232, USA
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Roy Chowdhury A, Sah S, Varshney U, Chakravortty D. Salmonella Typhimurium outer membrane protein A (OmpA) renders protection from nitrosative stress of macrophages by maintaining the stability of bacterial outer membrane. PLoS Pathog 2022; 18:e1010708. [PMID: 35969640 PMCID: PMC9410544 DOI: 10.1371/journal.ppat.1010708] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2021] [Revised: 08/25/2022] [Accepted: 06/27/2022] [Indexed: 11/18/2022] Open
Abstract
Bacterial porins are highly conserved outer membrane proteins used in the selective transport of charged molecules across the membrane. In addition to their significant contributions to the pathogenesis of Gram-negative bacteria, their role(s) in salmonellosis remains elusive. In this study, we investigated the role of outer membrane protein A (OmpA), one of the major outer membrane porins of Salmonella, in the pathogenesis of Salmonella Typhimurium (STM). Our study revealed that OmpA plays an important role in the intracellular virulence of Salmonella. An ompA deficient strain of Salmonella (STM ΔompA) showed compromised proliferation in macrophages. We found that the SPI-2 encoded virulence factors such as sifA and ssaV are downregulated in STM ΔompA. The poor colocalization of STM ΔompA with LAMP-1 showed that disruption of SCV facilitated its release into the cytosol of macrophages, where it was assaulted by reactive nitrogen intermediates (RNI). The enhanced recruitment of nitrotyrosine on the cytosolic population of STM ΔompAΔsifA and ΔompAΔssaV compared to STM ΔsifA and ΔssaV showed an additional role of OmpA in protecting the bacteria from host nitrosative stress. Further, we showed that the generation of greater redox burst could be responsible for enhanced sensitivity of STM ΔompA to the nitrosative stress. The expression of several other outer membrane porins such as ompC, ompD, and ompF was upregulated in STM ΔompA. We found that in the absence of ompA, the enhanced expression of ompF increased the outer membrane porosity of Salmonella and made it susceptible to in vitro and in vivo nitrosative stress. Our study illustrates a novel mechanism for the strategic utilization of OmpA by Salmonella to protect itself from the nitrosative stress of macrophages. Salmonella Typhimurium majorly uses SPI-1 and SPI-2 encoded T3SS and virulence factors for thriving in the host macrophages. But the role of non-SPI genes in Salmonella pathogenesis remains unknown. This article illustrates a novel mechanism of how a non-SPI virulent protein, OmpA, helps Salmonella Typhimurium to survive in murine macrophages. Our data revealed that Salmonella lacking OmpA (STM ΔompA) is deficient in producing SPI-2 effector proteins and has a severe defect in maintaining the stability of its outer membrane. It is released into the cytosol of macrophages during infection after disrupting the SCV membrane. STM ΔompA was severely challenged with reactive nitrogen intermediates in the cytosol, which reduced their proliferation in macrophages. We further showed that the deletion of OmpA increased the expression of other larger porins (ompC, ompD, and ompF) on the surface of Salmonella. It was observed that the enhanced expression of OmpF in STM ΔompA increased the outer membrane permeability and made the bacteria more susceptible to in vitro and in vivo nitrosative stress. Altogether our study proposes new insights into the role of Salmonella OmpA as an essential virulence factor.
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Affiliation(s)
- Atish Roy Chowdhury
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, Karnataka, India
| | - Shivjee Sah
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, Karnataka, India
| | - Umesh Varshney
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, Karnataka, India
| | - Dipshikha Chakravortty
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, Karnataka, India
- * E-mail:
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Chandra K, Roy Chowdhury A, Chatterjee R, Chakravortty D. GH18 family glycoside hydrolase Chitinase A of Salmonella enhances virulence by facilitating invasion and modulating host immune responses. PLoS Pathog 2022; 18:e1010407. [PMID: 35482710 PMCID: PMC9049553 DOI: 10.1371/journal.ppat.1010407] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Accepted: 02/28/2022] [Indexed: 11/22/2022] Open
Abstract
Salmonella is a facultative intracellular pathogen that has co-evolved with its host and has also developed various strategies to evade the host immune responses. Salmonella recruits an array of virulence factors to escape from host defense mechanisms. Previously chitinase A (chiA) was found to be upregulated in intracellular Salmonella. Although studies show that several structurally similar chitinases and chitin-binding proteins (CBP) of many human pathogens have a profound role in various aspects of pathogenesis, like adhesion, virulence, and immune evasion, the role of chitinase in the intravacuolar pathogen Salmonella has not yet been elucidated. Therefore, we made chromosomal deletions of the chitinase encoding gene (chiA) to study the role of chitinase of Salmonella enterica in the pathogenesis of the serovars, Typhimurium, and Typhi using in vitro cell culture model and two different in vivo hosts. Our data indicate that ChiA removes the terminal sialic acid moiety from the host cell surface, and facilitates the invasion of the pathogen into the epithelial cells. Interestingly we found that the mutant bacteria also quit the Salmonella-containing vacuole and hyper-proliferate in the cytoplasm of the epithelial cells. Further, we found that ChiA aids in reactive nitrogen species (RNS) and reactive oxygen species (ROS) production in the phagocytes, leading to MHCII downregulation followed by suppression of antigen presentation and antibacterial responses. Notably, in the murine host, the mutant shows compromised virulence, leading to immune activation and pathogen clearance. In continuation of the study in C. elegans, Salmonella Typhi ChiA was found to facilitate bacterial attachment to the intestinal epithelium, intestinal colonization, and persistence by downregulating antimicrobial peptides. This study provides new insights on chitinase as an important and novel virulence determinant that helps in immune evasion and increased pathogenesis of Salmonella. Chitinases and chitin-binding proteins have been implicated in the pathogenesis of several human pathogens associated with the mucosal barrier. Interestingly, chitinases from the major enteric pathogen, Salmonella enterica, were reported to be upregulated during macrophage and epithelial cell infection. Although Salmonella Chitinase ChiA (encoded by STM14_0022) shares sequence similarity with the pathogenic chitinases, its role as a virulence determinant remained obscured. Here we aim to investigate the role of chitinase in the context of Salmonella pathogenesis using cell culture, mouse, and nematode models. We found that Salmonella requires ChiA to remodel the intestinal epithelium and access the host system. In the phagocytes, chitinase-mediated upregulation of nitric oxide (NO) leads to inhibition of MHC-I bound antigen presentation and CD8+ T cell proliferation. Furthermore, the absence of ChiA impairs bacterial adhesion and colonization in vivo. During the systemic phase in the murine host, Salmonella Typhimurium chitinase prevents immune activation and antimicrobial responses. Additionally, in the Caenorhabditis elegans, Salmonella Typhi chitinase promotes bacterial attachment to the intestinal epithelium and enhances pathogen colonization and persistence in the intestine by downregulating the antimicrobial peptides SPP1 and ABF2. In conclusion, our study provides novel insights into the role of Salmonella chitinase as a novel virulence factor.
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Affiliation(s)
- Kasturi Chandra
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
| | - Atish Roy Chowdhury
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
| | - Ritika Chatterjee
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
| | - Dipshikha Chakravortty
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
- Centre for BioSystems Science and Engineering, Indian Institute of Science, Bangalore, India
- * E-mail:
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6
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Lau N, Thomas DR, Lee YW, Knodler LA, Newton HJ. Perturbation of ATG16L1 function impairs the biogenesis of Salmonella and Coxiella replication vacuoles. Mol Microbiol 2022; 117:235-251. [PMID: 34874584 PMCID: PMC8844213 DOI: 10.1111/mmi.14858] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2021] [Accepted: 12/03/2021] [Indexed: 02/03/2023]
Abstract
Anti-bacterial autophagy, known as xenophagy, is a host innate immune response that targets invading pathogens for degradation. Some intracellular bacteria, such as the enteric pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium), utilize effector proteins to interfere with autophagy. One such S. Typhimurium effector, SopF, inhibits recruitment of ATG16L1 to damaged Salmonella-containing vacuoles (SCVs), thereby inhibiting the host xenophagic response. SopF is also required to maintain the integrity of the SCV during the early stages of infection. Here we show disruption of the SopF-ATG16L1 interaction leads to an increased proportion of cytosolic S. Typhimurium. Furthermore, SopF was utilized as a molecular tool to examine the requirement for ATG16L1 in the intracellular lifestyle of Coxiella burnetii, a bacterium that requires a functional autophagy pathway to replicate efficiently and form a single, spacious vacuole called the Coxiella-containing vacuole (CCV). ATG16L1 is required for CCV expansion and fusion but does not influence C. burnetii replication. In contrast, SopF did not affect CCV formation or replication, demonstrating that the contribution of ATG16L1 to CCV biogenesis is via its role in autophagy, not xenophagy. This study highlights the diverse capabilities of bacterial effector proteins to dissect the molecular details of host-pathogen interactions.
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Affiliation(s)
- Nicole Lau
- The Department of Microbiology and Immunology at the Peter Doherty Institute for Infection and Immunity, University of Melbourne, Melbourne, Victoria, Australia
| | - David R Thomas
- The Department of Microbiology and Immunology at the Peter Doherty Institute for Infection and Immunity, University of Melbourne, Melbourne, Victoria, Australia
| | - Yi Wei Lee
- The Department of Microbiology and Immunology at the Peter Doherty Institute for Infection and Immunity, University of Melbourne, Melbourne, Victoria, Australia
| | - Leigh A Knodler
- The Department of Microbiology and Immunology at the Peter Doherty Institute for Infection and Immunity, University of Melbourne, Melbourne, Victoria, Australia.,Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, USA
| | - Hayley J Newton
- The Department of Microbiology and Immunology at the Peter Doherty Institute for Infection and Immunity, University of Melbourne, Melbourne, Victoria, Australia
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Walch P, Selkrig J, Knodler LA, Rettel M, Stein F, Fernandez K, Viéitez C, Potel CM, Scholzen K, Geyer M, Rottner K, Steele-Mortimer O, Savitski MM, Holden DW, Typas A. Global mapping of Salmonella enterica-host protein-protein interactions during infection. Cell Host Microbe 2021; 29:1316-1332.e12. [PMID: 34237247 PMCID: PMC8561747 DOI: 10.1016/j.chom.2021.06.004] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Revised: 02/24/2021] [Accepted: 05/21/2021] [Indexed: 11/16/2022]
Abstract
Intracellular bacterial pathogens inject effector proteins to hijack host cellular processes and promote their survival and proliferation. To systematically map effector-host protein-protein interactions (PPIs) during infection, we generated a library of 32 Salmonella enterica serovar Typhimurium (STm) strains expressing chromosomally encoded affinity-tagged effectors and quantified PPIs in macrophages and epithelial cells. We identified 446 effector-host PPIs, 25 of which were previously described, and validated 13 by reciprocal co-immunoprecipitation. While effectors converged on the same host cellular processes, most had multiple targets, which often differed between cell types. We demonstrate that SseJ, SseL, and SifA modulate cholesterol accumulation at the Salmonella-containing vacuole (SCV) partially via the cholesterol transporter Niemann-Pick C1 protein. PipB recruits the organelle contact site protein PDZD8 to the SCV, and SteC promotes actin bundling by phosphorylating formin-like proteins. This study provides a method for probing host-pathogen PPIs during infection and a resource for interrogating STm effector mechanisms.
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Affiliation(s)
- Philipp Walch
- European Molecular Biology Laboratory (EMBL), Genome Biology Unit, Heidelberg, Germany; Heidelberg University, Faculty of Biosciences, Heidelberg, Germany
| | - Joel Selkrig
- European Molecular Biology Laboratory (EMBL), Genome Biology Unit, Heidelberg, Germany
| | - Leigh A Knodler
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, USA; Laboratory of Intracellular Parasites, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, USA
| | - Mandy Rettel
- EMBL, Proteomics Core Facility, Heidelberg, Germany
| | - Frank Stein
- EMBL, Proteomics Core Facility, Heidelberg, Germany
| | - Keith Fernandez
- European Molecular Biology Laboratory (EMBL), Genome Biology Unit, Heidelberg, Germany
| | - Cristina Viéitez
- European Molecular Biology Laboratory (EMBL), Genome Biology Unit, Heidelberg, Germany; EMBL European Bioinformatics Institute, (EMBL-EBI), Hinxton, UK
| | - Clément M Potel
- European Molecular Biology Laboratory (EMBL), Genome Biology Unit, Heidelberg, Germany
| | - Karoline Scholzen
- European Molecular Biology Laboratory (EMBL), Genome Biology Unit, Heidelberg, Germany
| | - Matthias Geyer
- Institute of Structural Biology, University of Bonn, Bonn, Germany
| | - Klemens Rottner
- Division of Molecular Cell Biology, Zoological Institute, TU Braunschweig, Braunschweig, Germany; Molecular Cell Biology Group, Helmholtz Centre for Infection Research, Braunschweig, Germany
| | - Olivia Steele-Mortimer
- Laboratory of Intracellular Parasites, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, USA
| | - Mikhail M Savitski
- European Molecular Biology Laboratory (EMBL), Genome Biology Unit, Heidelberg, Germany; EMBL, Proteomics Core Facility, Heidelberg, Germany
| | - David W Holden
- MRC Centre for Molecular Bacteriology and Infection, Imperial College, London, UK
| | - Athanasios Typas
- European Molecular Biology Laboratory (EMBL), Genome Biology Unit, Heidelberg, Germany.
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8
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Powers TR, Haeberle AL, Predeus AV, Hammarlöf DL, Cundiff JA, Saldaña-Ahuactzi Z, Hokamp K, Hinton JCD, Knodler LA. Intracellular niche-specific profiling reveals transcriptional adaptations required for the cytosolic lifestyle of Salmonella enterica. PLoS Pathog 2021; 17:e1009280. [PMID: 34460873 PMCID: PMC8432900 DOI: 10.1371/journal.ppat.1009280] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Revised: 09/10/2021] [Accepted: 08/06/2021] [Indexed: 11/18/2022] Open
Abstract
Salmonella enterica serovar Typhimurium (S. Typhimurium) is a zoonotic pathogen that causes diarrheal disease in humans and animals. During salmonellosis, S. Typhimurium colonizes epithelial cells lining the gastrointestinal tract. S. Typhimurium has an unusual lifestyle in epithelial cells that begins within an endocytic-derived Salmonella-containing vacuole (SCV), followed by escape into the cytosol, epithelial cell lysis and bacterial release. The cytosol is a more permissive environment than the SCV and supports rapid bacterial growth. The physicochemical conditions encountered by S. Typhimurium within the epithelial cytosol, and the bacterial genes required for cytosolic colonization, remain largely unknown. Here we have exploited the parallel colonization strategies of S. Typhimurium in epithelial cells to decipher the two niche-specific bacterial virulence programs. By combining a population-based RNA-seq approach with single-cell microscopic analysis, we identified bacterial genes with cytosol-induced or vacuole-induced expression signatures. Using these genes as environmental biosensors, we defined that Salmonella is exposed to oxidative stress and iron and manganese deprivation in the cytosol and zinc and magnesium deprivation in the SCV. Furthermore, iron availability was critical for optimal S. Typhimurium replication in the cytosol, as well as entC, fepB, soxS, mntH and sitA. Virulence genes that are typically associated with extracellular bacteria, namely Salmonella pathogenicity island 1 (SPI1) and SPI4, showed increased expression in the cytosol compared to vacuole. Our study reveals that the cytosolic and vacuolar S. Typhimurium virulence gene programs are unique to, and tailored for, residence within distinct intracellular compartments. This archetypical vacuole-adapted pathogen therefore requires extensive transcriptional reprogramming to successfully colonize the mammalian cytosol.
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Affiliation(s)
- TuShun R. Powers
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, United States of America
| | - Amanda L. Haeberle
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, United States of America
| | - Alexander V. Predeus
- Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, United Kingdom
| | - Disa L. Hammarlöf
- Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, United Kingdom
| | - Jennifer A. Cundiff
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, United States of America
| | - Zeus Saldaña-Ahuactzi
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, United States of America
| | - Karsten Hokamp
- Smurfit Institute of Genetics, School of Genetics and Microbiology, Trinity College Dublin, Dublin, Ireland
| | - Jay C. D. Hinton
- Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, United Kingdom
| | - Leigh A. Knodler
- Paul G. Allen School for Global Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, United States of America
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9
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Type I interferon remodels lysosome function and modifies intestinal epithelial defense. Proc Natl Acad Sci U S A 2020; 117:29862-29871. [PMID: 33172989 DOI: 10.1073/pnas.2010723117] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Organelle remodeling is critical for cellular homeostasis, but host factors that control organelle function during microbial infection remain largely uncharacterized. Here, a genome-scale CRISPR/Cas9 screen in intestinal epithelial cells with the prototypical intracellular bacterial pathogen Salmonella led us to discover that type I IFN (IFN-I) remodels lysosomes. Even in the absence of infection, IFN-I signaling modified the localization, acidification, protease activity, and proteomic profile of lysosomes. Proteomic and genetic analyses revealed that multiple IFN-I-stimulated genes including IFITM3, SLC15A3, and CNP contribute to lysosome acidification. IFN-I-dependent lysosome acidification was associated with elevated intracellular Salmonella virulence gene expression, rupture of the Salmonella-containing vacuole, and host cell death. Moreover, IFN-I signaling promoted in vivo Salmonella pathogenesis in the intestinal epithelium where Salmonella initiates infection, indicating that IFN-I signaling can modify innate defense in the epithelial compartment. We propose that IFN-I control of lysosome function broadly impacts host defense against diverse viral and microbial pathogens.
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Goddard PJ, Sanchez-Garrido J, Slater SL, Kalyan M, Ruano-Gallego D, Marchès O, Fernández LÁ, Frankel G, Shenoy AR. Enteropathogenic Escherichia coli Stimulates Effector-Driven Rapid Caspase-4 Activation in Human Macrophages. Cell Rep 2020; 27:1008-1017.e6. [PMID: 31018119 PMCID: PMC6486487 DOI: 10.1016/j.celrep.2019.03.100] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2018] [Revised: 02/20/2019] [Accepted: 03/27/2019] [Indexed: 12/20/2022] Open
Abstract
Microbial infections can stimulate the assembly of inflammasomes, which activate caspase-1. The gastrointestinal pathogen enteropathogenic Escherichia coli (EPEC) causes localized actin polymerization in host cells. Actin polymerization requires the binding of the bacterial adhesin intimin to Tir, which is delivered to host cells via a type 3 secretion system (T3SS). We show that EPEC induces T3SS-dependent rapid non-canonical NLRP3 inflammasome activation in human macrophages. Notably, caspase-4 activation by EPEC triggers pyroptosis and cytokine processing through the NLRP3-caspase-1 inflammasome. Mechanistically, caspase-4 activation requires the detection of LPS and EPEC-induced actin polymerization, either via Tir tyrosine phosphorylation and the phosphotyrosine-binding adaptor NCK or Tir and the NCK-mimicking effector TccP. An engineered E. coli K12 could reconstitute Tir-intimin signaling, which is necessary and sufficient for inflammasome activation, ruling out the involvement of other virulence factors. Our studies reveal a crosstalk between caspase-4 and caspase-1 that is cooperatively stimulated by LPS and effector-driven actin polymerization. EPEC bacteria expressing virulence genes induce rapid human macrophage pyroptosis Bacterial LPS sensing by caspase-4 activates NLRP3-caspase-1 inflammasomes Actin polymerization driven by Tir-intimin signaling promotes pyroptosis Caspase-1 mediates cytokine processing and gasdermin D cleavage, leading to pyroptosis
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Affiliation(s)
- Philippa J Goddard
- Department of Life Sciences, Medical Research Council Centre for Molecular Bacteriology & Infection, Imperial College London, London, UK; Department of Medicine, Medical Research Council Centre for Molecular Bacteriology & Infection, Imperial College London, London, UK
| | - Julia Sanchez-Garrido
- Department of Medicine, Medical Research Council Centre for Molecular Bacteriology & Infection, Imperial College London, London, UK
| | - Sabrina L Slater
- Department of Life Sciences, Medical Research Council Centre for Molecular Bacteriology & Infection, Imperial College London, London, UK
| | - Mohini Kalyan
- Department of Medicine, Medical Research Council Centre for Molecular Bacteriology & Infection, Imperial College London, London, UK
| | - David Ruano-Gallego
- Department of Microbial Biotechnology, Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
| | - Olivier Marchès
- Department of Life Sciences, Medical Research Council Centre for Molecular Bacteriology & Infection, Imperial College London, London, UK
| | - Luis Ángel Fernández
- Department of Microbial Biotechnology, Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
| | - Gad Frankel
- Department of Life Sciences, Medical Research Council Centre for Molecular Bacteriology & Infection, Imperial College London, London, UK
| | - Avinash R Shenoy
- Department of Medicine, Medical Research Council Centre for Molecular Bacteriology & Infection, Imperial College London, London, UK.
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11
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Chamoun-Emanuelli AM, Bryan LK, Cohen ND, Tetrault TL, Szule JA, Barhoumi R, Whitfield-Cargile CM. NSAIDs disrupt intestinal homeostasis by suppressing macroautophagy in intestinal epithelial cells. Sci Rep 2019; 9:14534. [PMID: 31601922 PMCID: PMC6787209 DOI: 10.1038/s41598-019-51067-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Accepted: 09/20/2019] [Indexed: 12/24/2022] Open
Abstract
Small intestinal damage induced by nonsteroidal anti-inflammatory drugs (NSAIDs) remains an under-recognized clinical disorder. The incomplete understanding of the pathophysiology has hampered the development of prevention and treatment strategies leading to the high morbidity and mortality rates. NSAIDs are known to modulate macroautophagy, a process indispensable for intestinal homeostasis. Whether NSAIDs stimulate or repress macroautophagy and how this correlates with the clinical manifestations of NSAID enteropathy, however, remains unknown. The objectives of this study were to determine whether NSAIDs impaired macroautophagy and how this affects macroautophagy-regulated intestinal epithelial cell (IEC) processes essential for intestinal homeostasis (i.e., clearance of invading pathogens, secretion and composition of mucus building blocks, and inflammatory response). We show that NSAID treatment of IECs inhibits macroautophagy in vitro and in vivo. This inhibition was likely attributed to a reduction in the area and/or distribution of lysosomes available for degradation of macroautophagy-targeted cargo. Importantly, IEC regulatory processes necessary for intestinal homeostasis and dependent on macroautophagy were dysfunctional in the presence of NSAIDs. Since macroautophagy is essential for gastrointestinal health, NSAID-induced inhibition of macroautophagy might contribute to the severity of intestinal injury by compromising the integrity of the mucosal barrier, preventing the clearance of invading microbes, and exacerbating the inflammatory response.
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Affiliation(s)
- Ana M Chamoun-Emanuelli
- Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America
| | - Laura K Bryan
- Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America
| | - Noah D Cohen
- Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America
| | - Taylor L Tetrault
- Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America
| | - Joseph A Szule
- Department of Veterinary Pathobiology, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America
| | - Rola Barhoumi
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America
| | - Canaan M Whitfield-Cargile
- Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America.
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12
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Lau N, Haeberle AL, O’Keeffe BJ, Latomanski EA, Celli J, Newton HJ, Knodler LA. SopF, a phosphoinositide binding effector, promotes the stability of the nascent Salmonella-containing vacuole. PLoS Pathog 2019; 15:e1007959. [PMID: 31339948 PMCID: PMC6682159 DOI: 10.1371/journal.ppat.1007959] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2019] [Revised: 08/05/2019] [Accepted: 07/02/2019] [Indexed: 12/19/2022] Open
Abstract
The enteric bacterial pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium), utilizes two type III secretion systems (T3SSs) to invade host cells, survive and replicate intracellularly. T3SS1 and its dedicated effector proteins are required for bacterial entry into non-phagocytic cells and establishment and trafficking of the nascent Salmonella-containing vacuole (SCV). Here we identify the first T3SS1 effector required to maintain the integrity of the nascent SCV as SopF. SopF associates with host cell membranes, either when translocated by bacteria or ectopically expressed. Recombinant SopF binds to multiple phosphoinositides in protein-lipid overlays, suggesting that it targets eukaryotic cell membranes via phospholipid interactions. In yeast, the subcellular localization of SopF is dependent on the activity of Mss4, a phosphatidylinositol 4-phosphate 5-kinase that generates PI(4,5)P2 from PI(4)P, indicating that membrane recruitment of SopF requires specific phospholipids. Ectopically expressed SopF partially colocalizes with specific phosphoinositide pools present on the plasma membrane in mammalian cells and with cytoskeletal-associated markers at the leading edge of cells. Translocated SopF concentrates on plasma membrane ruffles and around intracellular bacteria, presumably on the SCV. SopF is not required for bacterial invasion of non-phagocytic cells but is required for maintenance of the internalization vacuole membrane as infection with a S. Typhimurium ΔsopF mutant led to increased lysis of the SCV compared to wild type bacteria. Our structure-function analysis shows that the carboxy-terminal seven amino acids of SopF are essential for its membrane association in host cells and to promote SCV membrane stability. We also describe that SopF and another T3SS1 effector, SopB, act antagonistically to modulate nascent SCV membrane dynamics. In summary, our study highlights that a delicate balance of type III effector activities regulates the stability of the Salmonella internalization vacuole.
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Affiliation(s)
- Nicole Lau
- The Department of Microbiology and Immunology at the Peter Doherty Institute for Infection and Immunity, University of Melbourne, Melbourne, Victoria, Australia
- Paul G. Allen School for Global Animal Health, College of Veterinary Medicine, Washington State University, Pullman, WA, United States of America
| | - Amanda L. Haeberle
- Paul G. Allen School for Global Animal Health, College of Veterinary Medicine, Washington State University, Pullman, WA, United States of America
| | - Brittany J. O’Keeffe
- Paul G. Allen School for Global Animal Health, College of Veterinary Medicine, Washington State University, Pullman, WA, United States of America
| | - Eleanor A. Latomanski
- The Department of Microbiology and Immunology at the Peter Doherty Institute for Infection and Immunity, University of Melbourne, Melbourne, Victoria, Australia
| | - Jean Celli
- Paul G. Allen School for Global Animal Health, College of Veterinary Medicine, Washington State University, Pullman, WA, United States of America
| | - Hayley J. Newton
- The Department of Microbiology and Immunology at the Peter Doherty Institute for Infection and Immunity, University of Melbourne, Melbourne, Victoria, Australia
- * E-mail: (LAK); (HJN)
| | - Leigh A. Knodler
- The Department of Microbiology and Immunology at the Peter Doherty Institute for Infection and Immunity, University of Melbourne, Melbourne, Victoria, Australia
- Paul G. Allen School for Global Animal Health, College of Veterinary Medicine, Washington State University, Pullman, WA, United States of America
- * E-mail: (LAK); (HJN)
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13
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Khandia R, Dadar M, Munjal A, Dhama K, Karthik K, Tiwari R, Yatoo MI, Iqbal HMN, Singh KP, Joshi SK, Chaicumpa W. A Comprehensive Review of Autophagy and Its Various Roles in Infectious, Non-Infectious, and Lifestyle Diseases: Current Knowledge and Prospects for Disease Prevention, Novel Drug Design, and Therapy. Cells 2019; 8:cells8070674. [PMID: 31277291 PMCID: PMC6678135 DOI: 10.3390/cells8070674] [Citation(s) in RCA: 133] [Impact Index Per Article: 26.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Revised: 06/04/2019] [Accepted: 06/04/2019] [Indexed: 02/05/2023] Open
Abstract
Autophagy (self-eating) is a conserved cellular degradation process that plays important roles in maintaining homeostasis and preventing nutritional, metabolic, and infection-mediated stresses. Autophagy dysfunction can have various pathological consequences, including tumor progression, pathogen hyper-virulence, and neurodegeneration. This review describes the mechanisms of autophagy and its associations with other cell death mechanisms, including apoptosis, necrosis, necroptosis, and autosis. Autophagy has both positive and negative roles in infection, cancer, neural development, metabolism, cardiovascular health, immunity, and iron homeostasis. Genetic defects in autophagy can have pathological consequences, such as static childhood encephalopathy with neurodegeneration in adulthood, Crohn's disease, hereditary spastic paraparesis, Danon disease, X-linked myopathy with excessive autophagy, and sporadic inclusion body myositis. Further studies on the process of autophagy in different microbial infections could help to design and develop novel therapeutic strategies against important pathogenic microbes. This review on the progress and prospects of autophagy research describes various activators and suppressors, which could be used to design novel intervention strategies against numerous diseases and develop therapeutic drugs to protect human and animal health.
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Affiliation(s)
- Rekha Khandia
- Department of Genetics, Barkatullah University, Bhopal 462 026, Madhya Pradesh, India
| | - Maryam Dadar
- Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj 31975/148, Iran
| | - Ashok Munjal
- Department of Genetics, Barkatullah University, Bhopal 462 026, Madhya Pradesh, India.
| | - Kuldeep Dhama
- Division of Pathology, ICAR-Indian Veterinary Research Institute, Izatnagar, Bareilly 243 122, Uttar Pradesh, India.
| | - Kumaragurubaran Karthik
- Central University Laboratory, Tamil Nadu Veterinary and Animal Sciences University, Madhavaram Milk Colony, Chennai, Tamil Nadu 600051, India
| | - Ruchi Tiwari
- Department of Veterinary Microbiology and Immunology, College of Veterinary Sciences, UP Pandit Deen Dayal Upadhayay Pashu Chikitsa Vigyan Vishwavidyalay Evum Go-Anusandhan Sansthan (DUVASU), Mathura, Uttar Pradesh 281 001, India
| | - Mohd Iqbal Yatoo
- Sher-E-Kashmir University of Agricultural Sciences and Technology of Kashmir, Shalimar, Srinagar 190025, Jammu and Kashmir, India
| | - Hafiz M N Iqbal
- Tecnologico de Monterrey, School of Engineering and Sciences, Campus Monterrey, Ave. Eugenio Garza Sada 2501, Monterrey, N. L., CP 64849, Mexico
| | - Karam Pal Singh
- Division of Pathology, ICAR-Indian Veterinary Research Institute, Izatnagar, Bareilly 243 122, Uttar Pradesh, India
| | - Sunil K Joshi
- Department of Pediatrics, Division of Hematology, Oncology and Bone Marrow Transplantation, University of Miami School of Medicine, Miami, FL 33136, USA.
| | - Wanpen Chaicumpa
- Center of Research Excellence on Therapeutic Proteins and Antibody Engineering, Department of Parasitology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand
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14
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Martínez-Cortés I, Acevedo-Domínguez NA, Olguin-Alor R, Cortés-Hernández A, Álvarez-Jiménez V, Campillo-Navarro M, Sumano-López HS, Gutiérrez-Olvera L, Martínez-Gómez D, Maravillas-Montero JL, Loor JJ, García-Zepeda EA, Soldevila G. Tilmicosin modulates the innate immune response and preserves casein production in bovine mammary alveolar cells during Staphylococcus aureus infection. J Anim Sci 2019; 97:644-656. [PMID: 30517644 DOI: 10.1093/jas/sky463] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2018] [Accepted: 12/01/2018] [Indexed: 12/15/2022] Open
Abstract
Tilmicosin is an antimicrobial agent used to treat intramammary infections against Staphylococcus aureus and has clinical anti-inflammatory effects. However, the mechanism by which it modulates the inflammatory process in the mammary gland is unknown. We evaluated the effect of tilmicosin treatment on the modulation of the mammary innate immune response after S. aureus infection and its effect on casein production in mammary epithelial cells. To achieve this goal, we used immortalized mammary epithelial cells (MAC-T), pretreated for 12 h or treated with tilmicosin after infection with S. aureus (ATCC 27543). Our data showed that tilmicosin decreases intracellular infection (P < 0.01) and had a protective effect on MAC-T reducing apoptosis after infection by 80% (P < 0.01). Furthermore, tilmicosin reduced reactive oxygen species (ROS) (P < 0.01), IL-1β (P < 0.01), IL-6 (P < 0.01), and TNF-α (P < 0.05) production. In an attempt to investigate the signaling pathways involved in the immunomodulatory effect of tilmicosin, mitogen-activated protein kinase (MAPK) phosphorylation was measured by fluorescent-activated cell sorting. Pretreatment with tilmicosin increased ERK1/2 (P < 0.05) but decreased P38 phosphorylation (P < 0.01). In addition, the anti-inflammatory effect of tilmicosin helped to preserve casein synthesis in mammary epithelial cells (P < 0.01). This result indicates that tilmicosin could be an effective modulator inflammation in the mammary gland. Through regulation of MAPK phosphorylation, ROS production and pro-inflammatory cytokine secretion tilmicosin can provide protection from cellular damage due to S. aureus infection and help to maintain normal physiological functions of the bovine mammary epithelial cell.
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Affiliation(s)
- Ismael Martínez-Cortés
- Chemokine Biology Research Laboratory, UNAM, Ciudad de México, Mexico.,Departamento de Inmunología, Instituto de Investigaciones Biomédicas, UNAM, Ciudad de México, Mexico
| | - Naray A Acevedo-Domínguez
- Chemokine Biology Research Laboratory, UNAM, Ciudad de México, Mexico.,Departamento de Inmunología, Instituto de Investigaciones Biomédicas, UNAM, Ciudad de México, Mexico
| | - Roxana Olguin-Alor
- Departamento de Inmunología, Instituto de Investigaciones Biomédicas, UNAM, Ciudad de México, Mexico
| | - Arimelek Cortés-Hernández
- Departamento de Inmunología, Instituto de Investigaciones Biomédicas, UNAM, Ciudad de México, Mexico
| | - Violeta Álvarez-Jiménez
- Chemokine Biology Research Laboratory, UNAM, Ciudad de México, Mexico.,Departamento de Inmunología, Instituto de Investigaciones Biomédicas, UNAM, Ciudad de México, Mexico
| | - Marcia Campillo-Navarro
- Laboratorio de Inmunología Integrativa-INER, Ismael Cosio Villegas. Ciudad de México, Mexico
| | | | | | | | | | - Juan J Loor
- Mammalian NutriPhysioGenomics-University of Illinois, Urbana, IL
| | - Eduardo A García-Zepeda
- Chemokine Biology Research Laboratory, UNAM, Ciudad de México, Mexico.,Departamento de Inmunología, Instituto de Investigaciones Biomédicas, UNAM, Ciudad de México, Mexico
| | - Gloria Soldevila
- Departamento de Inmunología, Instituto de Investigaciones Biomédicas, UNAM, Ciudad de México, Mexico
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15
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Castanheira S, García-Del Portillo F. Salmonella Populations inside Host Cells. Front Cell Infect Microbiol 2017; 7:432. [PMID: 29046870 PMCID: PMC5632677 DOI: 10.3389/fcimb.2017.00432] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Accepted: 09/20/2017] [Indexed: 11/13/2022] Open
Abstract
Bacteria of the Salmonella genus cause diseases ranging from gastroenteritis to life-threatening typhoid fever and are among the most successful intracellular pathogens known. After the invasion of the eukaryotic cell, Salmonella exhibits contrasting lifestyles with different replication rates and subcellular locations. Although Salmonella hyper-replicates in the cytosol of certain host cell types, most invading bacteria remain within vacuoles in which the pathogen proliferates at moderate rates or persists in a dormant-like state. Remarkably, these cytosolic and intra-vacuolar intracellular lifestyles are not mutually exclusive and can co-exist in the same infected host cell. The mechanisms that direct the invading bacterium to follow the cytosolic or intra-vacuolar “pathway” remain poorly understood. In vitro studies show predominance of either the cytosolic or the intra-vacuolar population depending on the host cell type invaded by the pathogen. The host and pathogen factors controlling phagosomal membrane integrity and, as consequence, the egress into the cytosol, are intensively investigated. Other aspects of major interest are the host defenses that may affect differentially the cytosolic and intra-vacuolar populations and the strategies used by the pathogen to circumvent these attacks. Here, we summarize current knowledge about these Salmonella intracellular subpopulations and discuss how they emerge during the interaction of this pathogen with the eukaryotic cell.
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Affiliation(s)
- Sónia Castanheira
- Laboratory of Intracellular Bacterial Pathogens, Departamento de Biotecnología Microbiana, Centro Nacional de Biotecnología-Consejo Superior de Investigaciones Científicas (CNB-CSIC), Madrid, Spain
| | - Francisco García-Del Portillo
- Laboratory of Intracellular Bacterial Pathogens, Departamento de Biotecnología Microbiana, Centro Nacional de Biotecnología-Consejo Superior de Investigaciones Científicas (CNB-CSIC), Madrid, Spain
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