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Marques M, Ramos B, Albuquerque H, Pereira M, Ribeiro DR, Nunes A, Sarabando J, Brás D, Ferreira AR, Vitorino R, Amorim MJ, Silva AM, Soares AR, Ribeiro D. Influenza A virus propagation requires the activation of the unfolded protein response and the accumulation of insoluble protein aggregates. iScience 2024; 27:109100. [PMID: 38405606 PMCID: PMC10884513 DOI: 10.1016/j.isci.2024.109100] [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] [Received: 07/31/2023] [Revised: 12/11/2023] [Accepted: 01/30/2024] [Indexed: 02/27/2024] Open
Abstract
Influenza A virus (IAV) employs multiple strategies to manipulate cellular mechanisms and support proper virion formation and propagation. In this study, we performed a detailed analysis of the interplay between IAV and the host cells' proteostasis throughout the entire infectious cycle. We reveal that IAV infection activates the inositol requiring enzyme 1 (IRE1) branch of the unfolded protein response, and that this activation is important for an efficient infection. We further observed the accumulation of virus-induced insoluble protein aggregates, containing both viral and host proteins, associated with a dysregulation of the host cell RNA metabolism. Our data indicate that this accumulation is important for IAV propagation and favors the final steps of the infection cycle, more specifically the virion assembly. These findings reveal additional mechanisms by which IAV disrupts host proteostasis and uncovers new cellular targets that can be explored for the development of host-directed antiviral strategies.
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Affiliation(s)
- Mariana Marques
- Institute of Biomedicine – iBiMED, Department of Medical Sciences University of Aveiro, Aveiro, Portugal
| | - Bruno Ramos
- Institute of Biomedicine – iBiMED, Department of Medical Sciences University of Aveiro, Aveiro, Portugal
| | - Hélio Albuquerque
- LAQV-REQUIMTE, Department of Chemistry, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal
| | - Marisa Pereira
- Institute of Biomedicine – iBiMED, Department of Medical Sciences University of Aveiro, Aveiro, Portugal
| | - Diana Roberta Ribeiro
- Institute of Biomedicine – iBiMED, Department of Medical Sciences University of Aveiro, Aveiro, Portugal
| | - Alexandre Nunes
- Institute of Biomedicine – iBiMED, Department of Medical Sciences University of Aveiro, Aveiro, Portugal
| | - Jéssica Sarabando
- Institute of Biomedicine – iBiMED, Department of Medical Sciences University of Aveiro, Aveiro, Portugal
| | - Daniela Brás
- Instituto Gulbenkian de Ciência, 2780-156 Oeiras, Portugal
| | - Ana Rita Ferreira
- Institute of Biomedicine – iBiMED, Department of Medical Sciences University of Aveiro, Aveiro, Portugal
| | - Rui Vitorino
- Institute of Biomedicine – iBiMED, Department of Medical Sciences University of Aveiro, Aveiro, Portugal
| | - Maria João Amorim
- Instituto Gulbenkian de Ciência, 2780-156 Oeiras, Portugal
- Católica Biomedical Research Centre, Católica Medical School, Universidade Católica Portuguesa, 1649-023 Lisboa, Portugal
| | - Artur M.S. Silva
- LAQV-REQUIMTE, Department of Chemistry, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal
| | - Ana Raquel Soares
- Institute of Biomedicine – iBiMED, Department of Medical Sciences University of Aveiro, Aveiro, Portugal
| | - Daniela Ribeiro
- Institute of Biomedicine – iBiMED, Department of Medical Sciences University of Aveiro, Aveiro, Portugal
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2
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Kryvenko V, Vadász I. Alveolar-capillary endocytosis and trafficking in acute lung injury and acute respiratory distress syndrome. Front Immunol 2024; 15:1360370. [PMID: 38533500 PMCID: PMC10963603 DOI: 10.3389/fimmu.2024.1360370] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2023] [Accepted: 02/29/2024] [Indexed: 03/28/2024] Open
Abstract
Acute respiratory distress syndrome (ARDS) is associated with high morbidity and mortality but lacks specific therapeutic options. Diverse endocytic processes play a key role in all phases of acute lung injury (ALI), including the initial insult, development of respiratory failure due to alveolar flooding, as a consequence of altered alveolar-capillary barrier function, as well as in the resolution or deleterious remodeling after injury. In particular, clathrin-, caveolae-, endophilin- and glycosylphosphatidyl inositol-anchored protein-mediated endocytosis, as well as, macropinocytosis and phagocytosis have been implicated in the setting of acute lung damage. This manuscript reviews our current understanding of these endocytic pathways and subsequent intracellular trafficking in various phases of ALI, and also aims to identify potential therapeutic targets for patients with ARDS.
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Affiliation(s)
- Vitalii Kryvenko
- Department of Internal Medicine, Justus Liebig University, Universities of Giessen and Marburg Lung Center (UGMLC), Member of the German Center for Lung Research (DZL), Giessen, Germany
- The Cardio-Pulmonary Institute (CPI), Giessen, Germany
- Institute for Lung Health (ILH), Giessen, Germany
| | - István Vadász
- Department of Internal Medicine, Justus Liebig University, Universities of Giessen and Marburg Lung Center (UGMLC), Member of the German Center for Lung Research (DZL), Giessen, Germany
- The Cardio-Pulmonary Institute (CPI), Giessen, Germany
- Institute for Lung Health (ILH), Giessen, Germany
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3
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Xia M, Wang Y, Xia Y, Zeng J. Forskolin Enhances Antitumor Effect of Oncolytic Measles Virus by Promoting Rab27a Dependent Vesicular Transport System. Curr Microbiol 2024; 81:93. [PMID: 38334775 DOI: 10.1007/s00284-024-03613-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Accepted: 01/06/2024] [Indexed: 02/10/2024]
Abstract
The measles vaccine virus strain (MV-Edm) serves as a potential platform for the development of effective oncolytic vectors. Nevertheless, despite promising pre-clinical data, our comprehension of the factors influencing the efficacy of MV-Edm infection and intratumoral spread, as well as the interactions between oncolytic viruses and specific chemotherapeutics associated with viral infection, remains limited. Therefore, we investigated the potency of Forskolin in enhancing the antitumor effect of oncolytic MV-Edm by promoting the Rab27a-dependent vesicular transport system. After infecting cells with MV-Edm, we observed an increased accumulation of cytoplasmic vesicles. Our study demonstrated that MV-Edm infection and spread in tumors, which are indispensable processes for viral oncolysis, depend on the vesicular transport system of tumor cells. Although tumor cells displayed a responsive mechanism to restrain the MV-Edm spread by down-regulating the expression of Rab27a, a key member of the vesicle transport system, over-expression of Rab27a promoted the oncolytic efficacy of MV-Edm towards A549 tumor cells. Additionally, we found that Forskolin, a Rab27a agonist, was capable of promoting the oncolytic effect of MV-Edm in vitro. Our study revealed that the vesicle transporter Rab27a could facilitate the secretion of MV-Edm and the generation of syncytial bodies in MV-Edm infected cells during the MV-Edm-mediated oncolysis pathway. The results of the study demonstrate that a combination of Forskolin and MV-Edm exerts a synergistic anti-tumor effect in vitro, leading to elevated oncolysis. This finding holds promise for the clinical treatment of patients with tumors.
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Affiliation(s)
- Mao Xia
- Department of Laboratory Medicine, The Affiliated Drum Tower Hospital, Medical School of Nanjing University, Nanjing, 210008, China
| | - Yangbin Wang
- Department of Laboratory Medicine, The Affiliated Drum Tower Hospital, Medical School of Nanjing University, Nanjing, 210008, China
| | - Yongquan Xia
- Department of Laboratory Medicine, The Affiliated Drum Tower Hospital, Medical School of Nanjing University, Nanjing, 210008, China
| | - Jiawei Zeng
- Medical Laboratory of Taizhou Fourth People's Hospital, Taizhou, 225300, China.
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4
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Diot C, Cosentino G, Rameix-Welti MA. Ribonucleoprotein transport in Negative Strand RNA viruses. Biol Cell 2023; 115:e2200059. [PMID: 36192136 DOI: 10.1111/boc.202200059] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Revised: 08/01/2022] [Accepted: 09/09/2022] [Indexed: 01/07/2023]
Abstract
Negative-sense, single-stranded RNA (-ssRNA) viruses comprise some of the deadliest human pathogens (Ebola, rabies, influenza A viruses etc.). Developing therapeutic tools relies on a better understanding of their multiplication cycle. For these viruses, the genome replication and transcription activities most-often segregate in membrane-less environments called inclusion bodies (IBs) or viral factories. These "organelles" usually locate far from the cell surface from where new virions are released, and -ssRNA viruses do not encode for transport factors. The efficient trafficking of the genome progeny toward the cell surface is most often ensured by mechanisms co-opting the cellular machineries. In this review, for each -ssRNA viral family, we cover the methods employed to characterize these host-virus interactions, the strategies used by the viruses to promote the virus genome transport, and the current gaps in the literature. Finally, we highlight how Rab11 has emerged as a target of choice for the intracellular transport of -ssRNA virus genomes.
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Affiliation(s)
- Cédric Diot
- Université Paris-Saclay - Université de Versailles St. Quentin, UMR 1173 (2I), INSERM, Montigny-le-Bretonneux, France
| | - Gina Cosentino
- Université Paris-Saclay - Université de Versailles St. Quentin, UMR 1173 (2I), INSERM, Montigny-le-Bretonneux, France
| | - Marie-Anne Rameix-Welti
- Université Paris-Saclay - Université de Versailles St. Quentin, UMR 1173 (2I), INSERM, Montigny-le-Bretonneux, France.,Assistance Publique des Hôpitaux de Paris, Hôpital Ambroise Paré, Laboratoire de Microbiologie, DMU15, Versailles, France
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5
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Jani RA, Di Cicco A, Keren-Kaplan T, Vale-Costa S, Hamaoui D, Hurbain I, Tsai FC, Di Marco M, Macé AS, Zhu Y, Amorim MJ, Bassereau P, Bonifacino JS, Subtil A, Marks MS, Lévy D, Raposo G, Delevoye C. PI4P and BLOC-1 remodel endosomal membranes into tubules. J Biophys Biochem Cytol 2022; 221:213508. [PMID: 36169638 PMCID: PMC9524204 DOI: 10.1083/jcb.202110132] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Revised: 07/25/2022] [Accepted: 08/31/2022] [Indexed: 12/11/2022] Open
Abstract
Intracellular trafficking is mediated by transport carriers that originate by membrane remodeling from donor organelles. Tubular carriers contribute to the flux of membrane lipids and proteins to acceptor organelles, but how lipids and proteins impose a tubular geometry on the carriers is incompletely understood. Using imaging approaches on cells and in vitro membrane systems, we show that phosphatidylinositol-4-phosphate (PI4P) and biogenesis of lysosome-related organelles complex 1 (BLOC-1) govern the formation, stability, and functions of recycling endosomal tubules. In vitro, BLOC-1 binds and tubulates negatively charged membranes, including those containing PI4P. In cells, endosomal PI4P production by type II PI4-kinases is needed to form and stabilize BLOC-1-dependent recycling endosomal tubules. Decreased PI4KIIs expression impairs the recycling of endosomal cargoes and the life cycles of intracellular pathogens such as Chlamydia bacteria and influenza virus that exploit the membrane dynamics of recycling endosomes. This study demonstrates how a phospholipid and a protein complex coordinate the remodeling of cellular membranes into functional tubules.
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Affiliation(s)
- Riddhi Atul Jani
- Institut Curie, Université PSL, CNRS, UMR144, Structure and Membrane Compartments, Paris, France
| | - Aurélie Di Cicco
- Institut Curie, Université PSL, Sorbonne Université, CNRS UMR168, Laboratoire Physico-Chimie Curie, Paris, France.,Institut Curie, Université PSL, CNRS, UMR144, Cell and Tissue Imaging Facility (PICT-IBiSA), Paris, France
| | - Tal Keren-Kaplan
- Neurosciences and Cellular and Structural Biology Division, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD
| | - Silvia Vale-Costa
- Cell Biology of Viral Infection Lab, Instituto Gulbenkian de Ciência, Oeiras, Portugal
| | - Daniel Hamaoui
- Institut Pasteur, Université de Paris Cité, CNRS UMR3691, Cellular biology of microbial infection, Paris, France
| | - Ilse Hurbain
- Institut Curie, Université PSL, CNRS, UMR144, Structure and Membrane Compartments, Paris, France.,Institut Curie, Université PSL, CNRS, UMR144, Cell and Tissue Imaging Facility (PICT-IBiSA), Paris, France
| | - Feng-Ching Tsai
- Institut Curie, Université PSL, Sorbonne Université, CNRS UMR168, Laboratoire Physico-Chimie Curie, Paris, France
| | - Mathilde Di Marco
- Institut Curie, Université PSL, CNRS, UMR144, Structure and Membrane Compartments, Paris, France
| | - Anne-Sophie Macé
- Institut Curie, Université PSL, CNRS, UMR144, Cell and Tissue Imaging Facility (PICT-IBiSA), Paris, France
| | - Yueyao Zhu
- Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia, Philadelphia, PA.,Department of Biology, University of Pennsylvania, Philadelphia, PA
| | - Maria João Amorim
- Cell Biology of Viral Infection Lab, Instituto Gulbenkian de Ciência, Oeiras, Portugal.,Universidade Católica Portuguesa, Católica Medical School, Católica Biomedical Research Centre, Palma de Cima, Lisboa, Portugal
| | - Patricia Bassereau
- Institut Curie, Université PSL, Sorbonne Université, CNRS UMR168, Laboratoire Physico-Chimie Curie, Paris, France
| | - Juan S Bonifacino
- Neurosciences and Cellular and Structural Biology Division, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD
| | - Agathe Subtil
- Institut Pasteur, Université de Paris Cité, CNRS UMR3691, Cellular biology of microbial infection, Paris, France
| | - Michael S Marks
- Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia, Philadelphia, PA.,Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA.,Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
| | - Daniel Lévy
- Institut Curie, Université PSL, Sorbonne Université, CNRS UMR168, Laboratoire Physico-Chimie Curie, Paris, France.,Institut Curie, Université PSL, CNRS, UMR144, Cell and Tissue Imaging Facility (PICT-IBiSA), Paris, France
| | - Graça Raposo
- Institut Curie, Université PSL, CNRS, UMR144, Structure and Membrane Compartments, Paris, France.,Institut Curie, Université PSL, CNRS, UMR144, Cell and Tissue Imaging Facility (PICT-IBiSA), Paris, France
| | - Cédric Delevoye
- Institut Curie, Université PSL, CNRS, UMR144, Structure and Membrane Compartments, Paris, France.,Institut Curie, Université PSL, CNRS, UMR144, Cell and Tissue Imaging Facility (PICT-IBiSA), Paris, France
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6
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ARHGAP1 Transported with Influenza Viral Genome Ensures Integrity of Viral Particle Surface through Efficient Budozone Formation. mBio 2022; 13:e0072122. [PMID: 35475647 PMCID: PMC9239208 DOI: 10.1128/mbio.00721-22] [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: 11/24/2022] Open
Abstract
Influenza viral particles are assembled at the plasma membrane concomitantly with Rab11a-mediated endocytic transport of viral ribonucleoprotein complexes (vRNPs). The mechanism of spatiotemporal regulation of viral budozone formation and its regulatory molecules on the endocytic vesicles remain unclear. Here, we performed a proximity-based proteomics approach for Rab11a and found that ARHGAP1, a Rho GTPase-activating protein, is transported through the Rab11a-mediated apical transport of vRNP. ARHGAP1 stabilized actin filaments in infected cells for the lateral clustering of hemagglutinin (HA) molecules, a viral surface membrane protein, to the budozone. Disruption of the HA clustering results in the production of virions with low HA content, and such virions were less resistant to protease and had enhanced antigenicity, presumably because reduced clustering of viral membrane proteins exposes hidden surfaces. Collectively, these results demonstrate that Rab11a-mediated endocytic transport of ARHGAP1 with vRNPs stimulates budozone formation to ensure the integrity of virion surface required for viral survival.
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7
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Inferring protein function in an emerging virus: detection of the nucleoprotein in Tilapia Lake Virus. J Virol 2022; 96:e0175721. [PMID: 35107373 DOI: 10.1128/jvi.01757-21] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Emerging viruses impose global threats to animal and human populations and may bear novel genes with limited homology to known sequences, necessitating the development of novel approaches to infer and test protein functions. This challenge is dramatically evident in tilapia lake virus (TiLV), an emerging orthomyxo-like virus that threatens the global tilapia aquaculture and food security of millions of people. The majority of TiLV proteins have no homology to known sequences, impeding functionality assessments. Using a novel bioinformatics approach, we predicted that TiLV's Protein 4 encodes the nucleoprotein - a factor essential for viral RNA replication. Multiple methodologies revealed the expected properties of orthomyxoviral nucleoproteins. A modified yeast three-hybrid assay detected Protein 4-RNA interactions, which were independent of the RNA sequence, and identified specific positively charged residues involved. Protein 4-RNA interactions were uncovered by R-DeeP and XRNAX methodologies. Immunoelectron microscopy found that multiple Protein 4 copies localized along enriched ribonucleoproteins. TiLV RNA from cells and virions co-immunoprecipitated with Protein 4. Immunofluorescence microscopy detected Protein 4 in the cytoplasm and nuclei, and nuclear Protein 4 increased upon CRM1 inhibition, suggesting CRM1-dependent nuclear export of TiLV RNA. Together, these data reveal TiLV's nucleoprotein and highlight the ability to infer protein functionality, including novel RNA-binding proteins, in emerging pathogens. These are important in light of the expected discovery of many unknown viruses and the zoonotic potential of such pathogens. Importance Tilapia is an important source of dietary protein, especially in developing countries. Massive losses of tilapia were identified worldwide, risking the food security of millions of people. Tilapia lake virus (TiLV) is an emerging pathogen responsible for these disease outbreaks. TiLV's genome encodes ten major proteins, nine of which show no homology to other known viral or cellular proteins, hindering functionality assessment of these proteins. Here we describe a novel bioinformatics approach to infer the functionality of TiLV proteins, which predicted Protein 4 as the nucleoprotein - a factor essential for viral RNA replication. We provided experimental support for this prediction by applying multiple molecular, biochemical, and imaging approaches. Overall, we illustrate a strategy for functional analyses in viral discovery. The strategy is important in light of the expected discovery of many unknown viruses and the zoonotic potential of such pathogens.
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8
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The C-terminal domains of the PB2 subunit of the influenza A virus RNA polymerase directly interact with cellular GTPase Rab11a. J Virol 2022; 96:e0197921. [PMID: 35019720 PMCID: PMC8906434 DOI: 10.1128/jvi.01979-21] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Influenza A virus (IAV) contains a segmented RNA genome that is transcribed and replicated by the viral RNA polymerase in the cell nucleus. Replicated RNA segments are assembled with viral polymerase and oligomeric nucleoprotein into viral ribonucleoprotein (vRNP) complexes which are exported from the nucleus and transported across the cytoplasm to be packaged into progeny virions. Host GTPase Rab11a associated with recycling endosomes is believed to contribute to this process by mediating the cytoplasmic transport of vRNPs. However, how vRNPs interact with Rab11a remains poorly understood. In this study, we utilised a combination of biochemical, proteomic, and biophysical approaches to characterise the interaction between the viral polymerase and Rab11a. Using pull-down assays we show that vRNPs but not cRNPs from infected cell lysates bind to Rab11a. We also show that the viral polymerase directly interacts with Rab11a and that the C-terminal two thirds of the PB2 polymerase subunit (PB2-C) comprising the cap-binding, mid-link, 627 and nuclear localization signal (NLS) domains mediate this interaction. Small-angle X-ray scattering (SAXS) experiments confirmed that PB2-C associates with Rab11a in solution forming a compact folded complex with a 1:1 stoichiometry. Furthermore, we demonstrate that the switch I region of Rab11a, that has been shown to be important for binding Rab11 family interacting proteins (Rab11-FIPs), is also important for PB2-C binding suggesting that IAV polymerase and Rab11-FIPs compete for the same binding site. Our findings expand our understanding of the interaction between the IAV polymerase and Rab11a in the cytoplasmic transport of vRNPs. Importance The influenza virus RNA genome segments are replicated in the cell nucleus and are assembled into viral ribonucleoprotein (vRNP) complexes with viral RNA polymerase and nucleoprotein (NP). Replicated vRNPs need to be exported from the nucleus and trafficked across the cytoplasm to the cell membrane where virion assembly takes place. The host GTPase Rab11a plays a role in vRNP trafficking. In this study we show that the viral polymerase directly interacts with Rab11a mediating the interaction between vRNPs and Rab11a. We map this interaction to the C-terminal domains of the PB2 polymerase subunit and the switch I region of Rab11a. Identifying the exact site of Rab11a binding on the viral polymerase could uncover a novel target site for the development of an influenza antiviral drug.
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9
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Staller E, Barclay WS. Host Cell Factors That Interact with Influenza Virus Ribonucleoproteins. Cold Spring Harb Perspect Med 2021; 11:a038307. [PMID: 32988980 PMCID: PMC8559542 DOI: 10.1101/cshperspect.a038307] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Influenza viruses hijack host cell factors at each stage of the viral life cycle. After host cell entry and endosomal escape, the influenza viral ribonucleoproteins (vRNPs) are released into the cytoplasm where the classical cellular nuclear import pathway is usurped for nuclear translocation of the vRNPs. Transcription takes place inside the nucleus at active host transcription sites, and cellular mRNA export pathways are subverted for export of viral mRNAs. Newly synthesized RNP components cycle back into the nucleus using various cellular nuclear import pathways and host-encoded chaperones. Replication of the negative-sense viral RNA (vRNA) into complementary RNA (cRNA) and back into vRNA requires complex interplay between viral and host factors. Progeny vRNPs assemble at the host chromatin and subsequently exit from the nucleus-processes orchestrated by sets of host and viral proteins. Finally, several host pathways appear to play a role in vRNP trafficking from the nuclear envelope to the plasma membrane for egress.
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Affiliation(s)
- Ecco Staller
- Department of Infectious Disease, Faculty of Medicine, Imperial College London, St. Mary's Campus, London W2 1NY, United Kingdom
| | - Wendy S Barclay
- Department of Infectious Disease, Faculty of Medicine, Imperial College London, St. Mary's Campus, London W2 1NY, United Kingdom
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10
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Host factor Rab11a is critical for efficient assembly of influenza A virus genomic segments. PLoS Pathog 2021; 17:e1009517. [PMID: 33970958 PMCID: PMC8136845 DOI: 10.1371/journal.ppat.1009517] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2021] [Revised: 05/20/2021] [Accepted: 04/19/2021] [Indexed: 11/30/2022] Open
Abstract
It is well documented that influenza A viruses selectively package 8 distinct viral ribonucleoprotein complexes (vRNPs) into each virion; however, the role of host factors in genome assembly is not completely understood. To evaluate the significance of cellular factors in genome assembly, we generated a reporter virus carrying a tetracysteine tag in the NP gene (NP-Tc virus) and assessed the dynamics of vRNP localization with cellular components by fluorescence microscopy. At early time points, vRNP complexes were preferentially exported to the MTOC; subsequently, vRNPs associated on vesicles positive for cellular factor Rab11a and formed distinct vRNP bundles that trafficked to the plasma membrane on microtubule networks. In Rab11a deficient cells, however, vRNP bundles were smaller in the cytoplasm with less co-localization between different vRNP segments. Furthermore, Rab11a deficiency increased the production of non-infectious particles with higher RNA copy number to PFU ratios, indicative of defects in specific genome assembly. These results indicate that Rab11a+ vesicles serve as hubs for the congregation of vRNP complexes and enable specific genome assembly through vRNP:vRNP interactions, revealing the importance of Rab11a as a critical host factor for influenza A virus genome assembly. The influenza A virus (IAV) genome is composed of 8 distinct RNA segments. It has remained unclear how these 8 individual RNA segments are assembled together to form infectious virus particles. Our study shows that Rab11a+ vesicles serve as platforms for the congregation and assembly of 8 individual viral RNA segments needed to form infectious virus particles. However, in cells lacking Rab11a, viral RNA segments fail to congregate together, resulting in increased production of defective virus particles, likely due to misassembling of viral RNA segments. Thus, our study reveals the important role for Rab11a in influenza virus genome assembly and production of infectious virus particles.
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11
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Wu J, Gu J, Shen L, Jia X, Yin Y, Chen Y, Wang S, Mao L. The role of host cell Rab GTPases in influenza A virus infections. Future Microbiol 2021; 16:445-452. [PMID: 33847136 DOI: 10.2217/fmb-2020-0092] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Influenza A virus (IAV) is a crucial cause of respiratory infections in humans worldwide. Therefore, studies should clarify adaptation mechanisms of IAV and critical factors of the viral pathogenesis in human hosts. GTPases of the Rab family are the largest branch of the Ras-like small GTPase superfamily, and they regulate almost every step during vesicle-mediated trafficking. Evidence has shown that Rab proteins participate in the lifecycle of IAV. In this mini-review, we outline the regulatory mechanisms of different Rab proteins in the lifecycle of IAV. Understanding the role of Rab proteins in IAV infections is important to develop broad-spectrum host-targeted antiviral strategies.
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Affiliation(s)
- Jing Wu
- Department of Laboratory Medicine, The Affiliated People's Hospital, Jiangsu University, Zhenjiang, China.,Department of Immunology, Jiangsu Key Laboratory of Laboratory Medicine, School of Medicine, Jiangsu University, Zhenjiang, China
| | - Jiaqi Gu
- Department of Laboratory Medicine, The Affiliated People's Hospital, Jiangsu University, Zhenjiang, China.,Department of Immunology, Jiangsu Key Laboratory of Laboratory Medicine, School of Medicine, Jiangsu University, Zhenjiang, China
| | - Li Shen
- Clinical Laboratory, Zhenjiang Center for Disease Control & Prevention, Jiangsu, China
| | - Xiaonan Jia
- Department of Laboratory Medicine, The Affiliated People's Hospital, Jiangsu University, Zhenjiang, China.,Department of Immunology, Jiangsu Key Laboratory of Laboratory Medicine, School of Medicine, Jiangsu University, Zhenjiang, China
| | - Yiqian Yin
- Department of Laboratory Medicine, The Affiliated People's Hospital, Jiangsu University, Zhenjiang, China.,Department of Immunology, Jiangsu Key Laboratory of Laboratory Medicine, School of Medicine, Jiangsu University, Zhenjiang, China
| | - Yiwen Chen
- Department of Laboratory Medicine, The Affiliated People's Hospital, Jiangsu University, Zhenjiang, China.,Department of Immunology, Jiangsu Key Laboratory of Laboratory Medicine, School of Medicine, Jiangsu University, Zhenjiang, China
| | - Shengjun Wang
- Department of Laboratory Medicine, The Affiliated People's Hospital, Jiangsu University, Zhenjiang, China.,Department of Immunology, Jiangsu Key Laboratory of Laboratory Medicine, School of Medicine, Jiangsu University, Zhenjiang, China
| | - Lingxiang Mao
- Department of Laboratory Medicine, The Affiliated People's Hospital, Jiangsu University, Zhenjiang, China
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12
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Etibor TA, Yamauchi Y, Amorim MJ. Liquid Biomolecular Condensates and Viral Lifecycles: Review and Perspectives. Viruses 2021; 13:366. [PMID: 33669141 PMCID: PMC7996568 DOI: 10.3390/v13030366] [Citation(s) in RCA: 53] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2021] [Revised: 02/16/2021] [Accepted: 02/20/2021] [Indexed: 02/06/2023] Open
Abstract
Viruses are highly dependent on the host they infect. Their dependence triggers processes of virus-host co-adaptation, enabling viruses to explore host resources whilst escaping immunity. Scientists have tackled viral-host interplay at differing levels of complexity-in individual hosts, organs, tissues and cells-and seminal studies advanced our understanding about viral lifecycles, intra- or inter-species transmission, and means to control infections. Recently, it emerged as important to address the physical properties of the materials in biological systems; membrane-bound organelles are only one of many ways to separate molecules from the cellular milieu. By achieving a type of compartmentalization lacking membranes known as biomolecular condensates, biological systems developed alternative mechanisms of controlling reactions. The identification that many biological condensates display liquid properties led to the proposal that liquid-liquid phase separation (LLPS) drives their formation. The concept of LLPS is a paradigm shift in cellular structure and organization. There is an unprecedented momentum to revisit long-standing questions in virology and to explore novel antiviral strategies. In the first part of this review, we focus on the state-of-the-art about biomolecular condensates. In the second part, we capture what is known about RNA virus-phase biology and discuss future perspectives of this emerging field in virology.
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Affiliation(s)
- Temitope Akhigbe Etibor
- Cell Biology of Viral Infection Lab, Instituto Gulbenkian de Ciência, 2780-156 Oeiras, Portugal;
| | - Yohei Yamauchi
- School of Cellular and Molecular Medicine, University of Bristol, Bristol BS8 1TL, UK;
| | - Maria João Amorim
- Cell Biology of Viral Infection Lab, Instituto Gulbenkian de Ciência, 2780-156 Oeiras, Portugal;
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13
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Touizer E, Sieben C, Henriques R, Marsh M, Laine RF. Application of Super-Resolution and Advanced Quantitative Microscopy to the Spatio-Temporal Analysis of Influenza Virus Replication. Viruses 2021; 13:233. [PMID: 33540739 PMCID: PMC7912985 DOI: 10.3390/v13020233] [Citation(s) in RCA: 7] [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: 01/04/2021] [Revised: 01/28/2021] [Accepted: 01/28/2021] [Indexed: 02/07/2023] Open
Abstract
With an estimated three to five million human cases annually and the potential to infect domestic and wild animal populations, influenza viruses are one of the greatest health and economic burdens to our society, and pose an ongoing threat of large-scale pandemics. Despite our knowledge of many important aspects of influenza virus biology, there is still much to learn about how influenza viruses replicate in infected cells, for instance, how they use entry receptors or exploit host cell trafficking pathways. These gaps in our knowledge are due, in part, to the difficulty of directly observing viruses in living cells. In recent years, advances in light microscopy, including super-resolution microscopy and single-molecule imaging, have enabled many viral replication steps to be visualised dynamically in living cells. In particular, the ability to track single virions and their components, in real time, now allows specific pathways to be interrogated, providing new insights to various aspects of the virus-host cell interaction. In this review, we discuss how state-of-the-art imaging technologies, notably quantitative live-cell and super-resolution microscopy, are providing new nanoscale and molecular insights into influenza virus replication and revealing new opportunities for developing antiviral strategies.
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Affiliation(s)
- Emma Touizer
- Division of Infection and Immunity, University College London, London WC1E 6AE, UK;
- MRC Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK; (R.H.); (M.M.)
| | - Christian Sieben
- Department of Cell Biology, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany;
| | - Ricardo Henriques
- MRC Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK; (R.H.); (M.M.)
- The Francis Crick Institute, London NW1 1AT, UK
- Instituto Gulbenkian de Ciência, 2780-156 Oeiras, Portugal
| | - Mark Marsh
- MRC Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK; (R.H.); (M.M.)
| | - Romain F. Laine
- MRC Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK; (R.H.); (M.M.)
- The Francis Crick Institute, London NW1 1AT, UK
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14
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Thompson MG, Dittmar M, Mallory MJ, Bhat P, Ferretti MB, Fontoura BM, Cherry S, Lynch KW. Viral-induced alternative splicing of host genes promotes influenza replication. eLife 2020; 9:55500. [PMID: 33269701 PMCID: PMC7735754 DOI: 10.7554/elife.55500] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Accepted: 12/02/2020] [Indexed: 12/17/2022] Open
Abstract
Viral infection induces the expression of numerous host genes that impact the outcome of infection. Here, we show that infection of human lung epithelial cells with influenza A virus (IAV) also induces a broad program of alternative splicing of host genes. Although these splicing-regulated genes are not enriched for canonical regulators of viral infection, we find that many of these genes do impact replication of IAV. Moreover, in several cases, specific inhibition of the IAV-induced splicing pattern also attenuates viral infection. We further show that approximately a quarter of the IAV-induced splicing events are regulated by hnRNP K, a host protein required for efficient splicing of the IAV M transcript in nuclear speckles. Finally, we find an increase in hnRNP K in nuclear speckles upon IAV infection, which may alter accessibility of hnRNP K for host transcripts thereby leading to a program of host splicing changes that promote IAV replication.
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Affiliation(s)
- Matthew G Thompson
- Biochemistry and Molecular Biophysics Graduate Group, University of Pennsylvania, Philadelphia, United States.,Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, United States
| | - Mark Dittmar
- Department of Pathology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, United States
| | - Michael J Mallory
- Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, United States
| | - Prasanna Bhat
- Department of Cell Biology, UT Southwestern Medical Center, Dallas, United States
| | - Max B Ferretti
- Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, United States.,Department of Pathology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, United States
| | - Beatriz Ma Fontoura
- Department of Cell Biology, UT Southwestern Medical Center, Dallas, United States
| | - Sara Cherry
- Biochemistry and Molecular Biophysics Graduate Group, University of Pennsylvania, Philadelphia, United States.,Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, United States.,Department of Pathology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, United States
| | - Kristen W Lynch
- Biochemistry and Molecular Biophysics Graduate Group, University of Pennsylvania, Philadelphia, United States.,Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, United States
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15
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Microtubules in Influenza Virus Entry and Egress. Viruses 2020; 12:v12010117. [PMID: 31963544 PMCID: PMC7020094 DOI: 10.3390/v12010117] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Revised: 01/10/2020] [Accepted: 01/14/2020] [Indexed: 12/14/2022] Open
Abstract
Influenza viruses are respiratory pathogens that represent a significant threat to public health, despite the large-scale implementation of vaccination programs. It is necessary to understand the detailed and complex interactions between influenza virus and its host cells in order to identify successful strategies for therapeutic intervention. During viral entry, the cellular microenvironment presents invading pathogens with a series of obstacles that must be overcome to infect permissive cells. Influenza hijacks numerous host cell proteins and associated biological pathways during its journey into the cell, responding to environmental cues in order to successfully replicate. The cellular cytoskeleton and its constituent microtubules represent a heavily exploited network during viral infection. Cytoskeletal filaments provide a dynamic scaffold for subcellular viral trafficking, as well as virus-host interactions with cellular machineries that are essential for efficient uncoating, replication, and egress. In addition, influenza virus infection results in structural changes in the microtubule network, which itself has consequences for viral replication. Microtubules, their functional roles in normal cell biology, and their exploitation by influenza viruses will be the focus of this review.
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16
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Bhagwat AR, Le Sage V, Nturibi E, Kulej K, Jones J, Guo M, Tae Kim E, Garcia BA, Weitzman MD, Shroff H, Lakdawala SS. Quantitative live cell imaging reveals influenza virus manipulation of Rab11A transport through reduced dynein association. Nat Commun 2020; 11:23. [PMID: 31911620 PMCID: PMC6946661 DOI: 10.1038/s41467-019-13838-3] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2018] [Accepted: 11/20/2019] [Indexed: 11/10/2022] Open
Abstract
Assembly of infectious influenza A viruses (IAV) is a complex process involving transport from the nucleus to the plasma membrane. Rab11A-containing recycling endosomes have been identified as a platform for intracellular transport of viral RNA (vRNA). Here, using high spatiotemporal resolution light-sheet microscopy (~1.4 volumes/second, 330 nm isotropic resolution), we quantify Rab11A and vRNA movement in live cells during IAV infection and report that IAV infection decreases speed and increases arrest of Rab11A. Unexpectedly, infection with respiratory syncytial virus alters Rab11A motion in a manner opposite to IAV, suggesting that Rab11A is a common host component that is differentially manipulated by respiratory RNA viruses. Using two-color imaging we demonstrate co-transport of Rab11A and IAV vRNA in infected cells and provide direct evidence that vRNA-associated Rab11A have altered transport. The mechanism of altered Rab11A movement is likely related to a decrease in dynein motors bound to Rab11A vesicles during IAV infection.
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Affiliation(s)
- Amar R Bhagwat
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, 450 Technology Drive, Pittsburgh, PA, 15219, USA
| | - Valerie Le Sage
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, 450 Technology Drive, Pittsburgh, PA, 15219, USA
| | - Eric Nturibi
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, 450 Technology Drive, Pittsburgh, PA, 15219, USA
| | - Katarzyna Kulej
- The Children's Hospital of Philadelphia Research Institute, 3501 Civic Center Dr., Philadelphia, PA, 19104, USA
| | - Jennifer Jones
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, 450 Technology Drive, Pittsburgh, PA, 15219, USA
| | - Min Guo
- Section on High Resolution Optical Imaging, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, 13 South Drive, Building 13, Bethesda, MD, 20892, USA
| | - Eui Tae Kim
- The Children's Hospital of Philadelphia Research Institute, 3501 Civic Center Dr., Philadelphia, PA, 19104, USA
| | - Benjamin A Garcia
- Department of Biochemistry and Biophysics, University of Pennsylvania Perelman School of Medicine, 3400 Civic Center Blvd, Building 421, Philadelphia, PA, 19104, USA
- Epigenetics Institute, University of Pennsylvania Perelman School of Medicine, 3400, Civic Center Blvd, Philadelphia, PA, 19104, USA
| | - Matthew D Weitzman
- The Children's Hospital of Philadelphia Research Institute, 3501 Civic Center Dr., Philadelphia, PA, 19104, USA
- Epigenetics Institute, University of Pennsylvania Perelman School of Medicine, 3400, Civic Center Blvd, Philadelphia, PA, 19104, USA
- Department of Pathology and Laboratory Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, 19104, USA
| | - Hari Shroff
- Section on High Resolution Optical Imaging, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, 13 South Drive, Building 13, Bethesda, MD, 20892, USA
| | - Seema S Lakdawala
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, 450 Technology Drive, Pittsburgh, PA, 15219, USA.
- Center for Vaccine Research, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15219, USA.
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17
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Alenquer M, Vale-Costa S, Etibor TA, Ferreira F, Sousa AL, Amorim MJ. Influenza A virus ribonucleoproteins form liquid organelles at endoplasmic reticulum exit sites. Nat Commun 2019; 10:1629. [PMID: 30967547 PMCID: PMC6456594 DOI: 10.1038/s41467-019-09549-4] [Citation(s) in RCA: 110] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2018] [Accepted: 03/19/2019] [Indexed: 12/12/2022] Open
Abstract
Influenza A virus has an eight-partite RNA genome that during viral assembly forms a complex containing one copy of each RNA. Genome assembly is a selective process driven by RNA-RNA interactions and is hypothesized to lead to discrete punctate structures scattered through the cytosol. Here, we show that contrary to the accepted view, formation of these structures precedes RNA-RNA interactions among distinct viral ribonucleoproteins (vRNPs), as they assemble in cells expressing only one vRNP type. We demonstrate that these viral inclusions display characteristics of liquid organelles, segregating from the cytosol without a delimitating membrane, dynamically exchanging material and adapting fast to environmental changes. We provide evidence that viral inclusions develop close to endoplasmic reticulum (ER) exit sites, depend on continuous ER-Golgi vesicular cycling and do not promote escape to interferon response. We propose that viral inclusions segregate vRNPs from the cytosol and facilitate selected RNA-RNA interactions in a liquid environment. Influenza A virus forms cytosolic inclusions containing viral ribonucleoproteins. Here, the authors show that viral inclusions form juxtaposed the endoplasmic reticulum and have liquid properties, likely constituting sites of assembly of epidemic and pandemic influenza genomes.
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Affiliation(s)
- Marta Alenquer
- Cell Biology of Viral Infection Lab, Instituto Gulbenkian de Ciência, 2780-156, Oeiras, Portugal
| | - Sílvia Vale-Costa
- Cell Biology of Viral Infection Lab, Instituto Gulbenkian de Ciência, 2780-156, Oeiras, Portugal
| | - Temitope Akhigbe Etibor
- Cell Biology of Viral Infection Lab, Instituto Gulbenkian de Ciência, 2780-156, Oeiras, Portugal
| | - Filipe Ferreira
- Cell Biology of Viral Infection Lab, Instituto Gulbenkian de Ciência, 2780-156, Oeiras, Portugal
| | - Ana Laura Sousa
- Cell Biology of Viral Infection Lab, Instituto Gulbenkian de Ciência, 2780-156, Oeiras, Portugal.,Electron Microscopy Facility, Instituto Gulbenkian de Ciência, 2780-156, Oeiras, Portugal
| | - Maria João Amorim
- Cell Biology of Viral Infection Lab, Instituto Gulbenkian de Ciência, 2780-156, Oeiras, Portugal.
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18
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Bedi S, Ono A. Friend or Foe: The Role of the Cytoskeleton in Influenza A Virus Assembly. Viruses 2019; 11:v11010046. [PMID: 30634554 PMCID: PMC6356976 DOI: 10.3390/v11010046] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2018] [Revised: 01/02/2019] [Accepted: 01/08/2019] [Indexed: 12/12/2022] Open
Abstract
Influenza A Virus (IAV) is a respiratory virus that causes seasonal outbreaks annually and pandemics occasionally. The main targets of the virus are epithelial cells in the respiratory tract. Like many other viruses, IAV employs the host cell’s machinery to enter cells, synthesize new genomes and viral proteins, and assemble new virus particles. The cytoskeletal system is a major cellular machinery, which IAV exploits for its entry to and exit from the cell. However, in some cases, the cytoskeleton has a negative impact on efficient IAV growth. In this review, we highlight the role of cytoskeletal elements in cellular processes that are utilized by IAV in the host cell. We further provide an in-depth summary of the current literature on the roles the cytoskeleton plays in regulating specific steps during the assembly of progeny IAV particles.
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Affiliation(s)
- Sukhmani Bedi
- Department of Microbiology and Immunology, University of Michigan, Ann Arbor, MI 48109, USA.
| | - Akira Ono
- Department of Microbiology and Immunology, University of Michigan, Ann Arbor, MI 48109, USA.
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19
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Amorim MJ. A Comprehensive Review on the Interaction Between the Host GTPase Rab11 and Influenza A Virus. Front Cell Dev Biol 2019; 6:176. [PMID: 30687703 PMCID: PMC6333742 DOI: 10.3389/fcell.2018.00176] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Accepted: 12/17/2018] [Indexed: 12/20/2022] Open
Abstract
This year marks the 100th anniversary of one of the deadliest pandemic outbreaks, commonly referred as the Spanish Flu, that was caused by influenza A virus (IAV). Since then, IAV has been in governmental agendas worldwide, and a lot of effort has been put into understanding the pathogen's lifecycle, predict and mitigate the emergence of the strains that provoke yearly epidemics and pandemic events. Despite decades of research and seminal contributions there is still a lot to be investigated. In particular for this review, IAV lifecycle that takes place inside the host cell is not fully understood. Two steps that need clarification include genome transport to budding sites and genome assembly, the latter a complex process challenged by the nature of IAV genome that is divided into eight distinct parts. Assembly of such segmented genome is crucial to form fully infectious viral particles but is also critical for the emergence of viruses with pandemic potential that arise when avian and human IAV strains co-infect a host. The host GTPase Rab11 was separately implicated in both steps, and, interestingly these processes are beginning to emerge as being intimately related. Rab11 was initially proposed to be involved in the budding/release of IAV virions. It was subsequently shown to transport progeny genome, and later proposed to promote assembly of viral genome, but the underlying bridging mechanism the two is far from clear. For simplicity, this Rab11-centric review provides an initial separate account of Rab11 involvement in genome transport and in assembly. IAV genome assembly is a complicated molecular biology process, and therefore earned a dedicated section on how/if the viral genome forms a genomic supramolecular complex. Both topics present intricate challenges, outstanding questions, and unique controversies. At the end of the review, I will explore possible mechanisms intertwining IAV vRNP transport and genome assembly. Importantly, Rab11 has recently emerged as a key factor subverted by evolutionary unrelated viral families (Paramyxo, Bunya, and Orthomyxoviruses, among many others) and bacteria (Salmonella and Shigella) relevant to human health. This review provides a framework to identify common biological principles among the lifecycles of these pathogens.
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Affiliation(s)
- Maria João Amorim
- Cell Biology of Viral Infection Lab, Instituto Gulbenkian de Ciência, Oeiras, Portugal
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20
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Thompson MG, Lynch KW. Functional and Mechanistic Interplay of Host and Viral Alternative Splicing Regulation during Influenza Infection. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2019; 84:123-131. [PMID: 32703803 DOI: 10.1101/sqb.2019.84.039040] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Alternative splicing is a pervasive gene regulatory mechanism utilized by both mammalian cells and viruses to expand their genomic coding capacity. The process of splicing and the RNA sequences that guide this process are the same in mammalian and viral transcripts; however, viruses lack the splicing machinery and therefore must usurp both the host spliceosome and many of the associated regulatory proteins in order to correctly process their genes. Here, we use the example of the influenza A virus to both describe how viruses utilize host splicing factors to regulate their own splicing and provide examples of how viral infection can, in turn, alter host splicing. Importantly, we show that at least some of the viral-induced changes in host splicing occur in genes that alter the efficiency of influenza replication. We emphasize the importance of increased understanding of the mechanistic interplay between host and viral splicing, and its functional consequences, in uncovering potential antiviral vulnerabilities.
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Affiliation(s)
- Matthew G Thompson
- Department of Biochemistry and Biophysics Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Kristen W Lynch
- Department of Biochemistry and Biophysics Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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21
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Calado J, Santos AR, Aires I, Lebre F, Nolasco F, Rueff J, Ramalho J. The Na + -coupled glucose transporter SGLT2 interacts with its accessory unit MAP17 in vitro and their expressions overlap in the renal proximal tubule. FEBS Lett 2018; 592:3317-3326. [PMID: 30156268 DOI: 10.1002/1873-3468.13233] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2018] [Revised: 08/14/2018] [Accepted: 08/23/2018] [Indexed: 01/10/2023]
Abstract
Na+ -glucose cotransporter 2 is the renal Na+ -coupled glucose transporter responsible for the tubular glucose reabsorption, while MAP17 was recently identified as its accessory unit. Mutations in either of the proteins' coding genes, SLC5A2 and PDZK1IP1, lead to urinary glucose excretion. To investigate whether MAP17 interacts with SGLT2 in vitro, we engineered a V5-tagged SGLT2 construct and evaluated HEK293T cells coexpressing it together with a HA tagged MAP17 construct. MAP17 is shown to colocalize and coimmunoprecipitate with SGLT2. Also, in human kidney sections, the expression of both proteins overlaps at the apical surface of tubular epithelia. This interaction provides the rationale behind SGLT2 activation by MAP17 as well the similarity of the SLC5A2 and PDZK1IP1 glucosuric phenotypes.
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Affiliation(s)
- Joaquim Calado
- Centre for Toxicogenomics and Human Health (ToxOmics), Genetics, Oncology and Human Toxicology, Nova Medical School/Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Lisbon, Portugal
- Nephrology Department, Centro Hospitalar Lisboa Central, Lisbon, Portugal
| | - Ana Rita Santos
- Pathology Department, Nefro Lab, Clara Saúde, Pinhal Novo, Portugal
| | - Inês Aires
- Nephrology Department, Centro Hospitalar Lisboa Central, Lisbon, Portugal
| | - Firmina Lebre
- CEDOC, Chronic Diseases Research Centre, Nova Medical School/Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Lisbon, Portugal
| | - Fernando Nolasco
- Nephrology Department, Centro Hospitalar Lisboa Central, Lisbon, Portugal
| | - José Rueff
- Centre for Toxicogenomics and Human Health (ToxOmics), Genetics, Oncology and Human Toxicology, Nova Medical School/Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Lisbon, Portugal
| | - José Ramalho
- CEDOC, Chronic Diseases Research Centre, Nova Medical School/Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Lisbon, Portugal
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22
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Santarella-Mellwig R, Haselmann U, Schieber NL, Walther P, Schwab Y, Antony C, Bartenschlager R, Romero-Brey I. Correlative Light Electron Microscopy (CLEM) for Tracking and Imaging Viral Protein Associated Structures in Cryo-immobilized Cells. J Vis Exp 2018. [PMID: 30247481 PMCID: PMC6235138 DOI: 10.3791/58154] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Due to its high resolution, electron microscopy (EM) is an indispensable tool for virologists. However, one of the main difficulties when analyzing virus-infected or transfected cells via EM are the low efficiencies of infection or transfection, hindering the examination of these cells. In order to overcome this difficulty, light microscopy (LM) can be performed first to allocate the subpopulation of infected or transfected cells. Thus, taking advantage of the use of fluorescent proteins (FPs) fused to viral proteins, LM is used here to record the positions of the "positive-transfected" cells, expressing a FP and growing on a support with an alphanumeric pattern. Subsequently, cells are further processed for EM via high pressure freezing (HPF), freeze substitution (FS) and resin embedding. The ultra-rapid freezing step ensures excellent membrane preservation of the selected cells that can then be analyzed at the ultrastructural level by transmission electron microscopy (TEM). Here, a step-by-step correlative light electron microscopy (CLEM) workflow is provided, describing sample preparation, imaging and correlation in detail. The experimental design can be also applied to address many cell biology questions.
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Affiliation(s)
| | - Uta Haselmann
- Department of Infectious Diseases, Molecular Virology, Heidelberg University
| | | | - Paul Walther
- Central Facility for Electron Microscopy, Ulm University
| | | | | | - Ralf Bartenschlager
- Department of Infectious Diseases, Molecular Virology, Heidelberg University; Heidelberg Partner Site, German Center for Infection Research;
| | - Inés Romero-Brey
- Department of Infectious Diseases, Molecular Virology, Heidelberg University;
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23
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Zheng J, Perlman S. Immune responses in influenza A virus and human coronavirus infections: an ongoing battle between the virus and host. Curr Opin Virol 2018; 28:43-52. [PMID: 29172107 PMCID: PMC5835172 DOI: 10.1016/j.coviro.2017.11.002] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2017] [Accepted: 11/02/2017] [Indexed: 12/25/2022]
Abstract
Respiratory viruses, especially influenza A viruses and coronaviruses such as MERS-CoV, represent continuing global threats to human health. Despite significant advances, much needs to be learned. Recent studies in virology and immunology have improved our understanding of the role of the immune system in protection and in the pathogenesis of these infections and of co-evolution of viruses and their hosts. These findings, together with sophisticated molecular structure analyses, omics tools and computer-based models, have helped delineate the interaction between respiratory viruses and the host immune system, which will facilitate the development of novel treatment strategies and vaccines with enhanced efficacy.
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Affiliation(s)
- Jian Zheng
- Department of Microbiology and Immunology, The University of Iowa, Iowa City, IA 52242, United States
| | - Stanley Perlman
- Department of Microbiology and Immunology, The University of Iowa, Iowa City, IA 52242, United States.
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24
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Abstract
Influenza, a serious illness of humans and domesticated animals, has been studied intensively for many years. It therefore provides an example of how much we can learn from detailed studies of an infectious disease and of how even the most intensive scientific research leaves further questions to answer. This introduction is written for researchers who have become interested in one of these unanswered questions, but who may not have previously worked on influenza. To investigate these questions, researchers must not only have a firm grasp of relevant methods and protocols; they must also be familiar with the basic details of our current understanding of influenza. This article therefore briefly covers the burden of disease that has driven influenza research, summarizes how our thinking about influenza has evolved over time, and sets out key features of influenza viruses by discussing how we classify them and what we understand of their replication. It does not aim to be comprehensive, as any researcher will read deeply into the specific areas that have grasped their interest. Instead, it aims to provide a general summary of how we came to think about influenza in the way we do now, in the hope that the reader's own research will help us to understand it better.
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Affiliation(s)
| | - Yohei Yamauchi
- School of Cellular and Molecular Medicine, University of Bristol, Bristol, UK.
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25
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Romero-Brey I. 3D Electron Microscopy (EM) and Correlative Light Electron Microscopy (CLEM) Methods to Study Virus-Host Interactions. Methods Mol Biol 2018; 1836:213-236. [PMID: 30151576 DOI: 10.1007/978-1-4939-8678-1_11] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Viruses use different strategies to interact with their host and perform a successful viral infection that results in the formation of new infectious viral particles and their propagation to new hosts. Understanding how viruses interact with their hosts requires the use of high-resolution techniques for the direct visualization of these interactions. Here electron microscopy (EM) methods are described that allow the 3D ultrastructural analysis of virus-infected cells. These methods can be implemented with light microscopy (LM) to certainly allocate virus-infected cells or cells displaying a specific/interesting phenotype caused by the interaction of viral proteins with the cellular machinery. Some sample preparation procedures where LM is integrated, known as correlative light electron microscopy (CLEM), are also explained in this chapter. All of these methods are applicable to any kind of cultured cells, including influenza virus-infected cells.
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Affiliation(s)
- Inés Romero-Brey
- Department of Infectious Diseases, Molecular Virology, University of Heidelberg, Heidelberg, Germany.
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26
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Influenza virus genome reaches the plasma membrane via a modified endoplasmic reticulum and Rab11-dependent vesicles. Nat Commun 2017; 8:1396. [PMID: 29123131 PMCID: PMC5680169 DOI: 10.1038/s41467-017-01557-6] [Citation(s) in RCA: 59] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2017] [Accepted: 09/27/2017] [Indexed: 12/05/2022] Open
Abstract
Transport of neo-synthesized influenza A virus (IAV) viral ribonucleoproteins (vRNPs) from the nucleus to the plasma membrane involves Rab 11 but the precise mechanism remains poorly understood. We used metal-tagging and immunolabeling to visualize viral proteins and cellular endomembrane markers by electron microscopy of IAV-infected cells. Unexpectedly, we provide evidence that the vRNP components and the Rab11 protein are present at the membrane of a modified, tubulated endoplasmic reticulum (ER) that extends all throughout the cell, and on irregularly coated vesicles (ICVs). Some ICVs are found very close to the ER and to the plasma membrane. ICV formation is observed only in infected cells and requires an active Rab11 GTPase. Against the currently accepted model in which vRNPs are carried onto Rab11-positive recycling endosomes across the cytoplasm, our findings reveal that the endomembrane organelle that is primarily involved in the transport of vRNPs is the ER. Transport of neo-synthesized influenza A virus viral ribonucleoproteins (vRNPs) from the nucleus to the plasma membrane involves Rab 11 but the mechanism is unclear. Here the authors show that vRNPs are transported through a modified Rab11-positive endoplasmic reticulum and Rab11-dependent vesicles.
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Yeganeh B, Ghavami S, Rahim MN, Klonisch T, Halayko AJ, Coombs KM. Autophagy activation is required for influenza A virus-induced apoptosis and replication. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2017; 1865:364-378. [PMID: 29108912 DOI: 10.1016/j.bbamcr.2017.10.014] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 10/23/2017] [Accepted: 10/30/2017] [Indexed: 01/07/2023]
Abstract
Autophagy and apoptosis are two major interconnected host cell responses to viral infection, including influenza A virus (IAV). Thus, delineating these events could facilitate the development of better treatment options and provide an effective anti-viral strategy for controlling IAV infection. We used A549 cells and mouse embryonic fibroblasts (MEF) to study the role of virus-induced autophagy and apoptosis, the cross-talk between both pathways, and their relation to IAV infection [ATCC strain A/Puerto Rico/8/34(H1N1) (hereafter; PR8)]. PR8-infected and mock-infected cells were analyzed by immunoblotting, immunofluorescence confocal microscopy, electron microscopy and flow cytometry (FACS). We found that PR8 infection simultaneously induced autophagy and apoptosis in A549 cells. Autophagy was associated with Bax and Bak activation, intrinsic caspase cleavage and subsequent PARP-1 and BID cleavage. Both Bax knockout (KO) and Bax/Bak double knockout MEFs displayed inhibition of virus-induced cytopathology and cell death and diminished virus-mediated caspase activation, suggesting that virus-induced apoptosis is Bax/Bak-dependent. Biochemical inhibition of autophagy induction with 3-methyladenine blocked both virus replication and apoptosis pathways. These effects were replicated using autophagy-refractory Atg3 KO and Atg5 KO cells. Taken together, our data indicate that PR8 infection simultaneously induces autophagy and Bax/caspase-dependent apoptosis, with autophagy playing a role to support PR8 replication, in part, by modulating virus-induced apoptosis.
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Affiliation(s)
- B Yeganeh
- Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, MB, Canada; Biology of Breathing Group, Children's Hospital Research Institute of Manitoba, Winnipeg, MB, Canada
| | - S Ghavami
- Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, MB, Canada; Biology of Breathing Group, Children's Hospital Research Institute of Manitoba, Winnipeg, MB, Canada; Department of Human Anatomy and Cell Science, University of Manitoba, Winnipeg, MB, Canada
| | - Md N Rahim
- Department of Medical Microbiology and Infectious Diseases, University of Manitoba, Winnipeg, MB, Canada
| | - T Klonisch
- Department of Human Anatomy and Cell Science, University of Manitoba, Winnipeg, MB, Canada; Department of Medical Microbiology and Infectious Diseases, University of Manitoba, Winnipeg, MB, Canada
| | - A J Halayko
- Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, MB, Canada; Biology of Breathing Group, Children's Hospital Research Institute of Manitoba, Winnipeg, MB, Canada; Department of Internal Medicine, University of Manitoba, Winnipeg, MB, Canada
| | - K M Coombs
- Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, MB, Canada; Biology of Breathing Group, Children's Hospital Research Institute of Manitoba, Winnipeg, MB, Canada; Department of Medical Microbiology and Infectious Diseases, University of Manitoba, Winnipeg, MB, Canada; Manitoba Centre for Proteomics and Systems Biology, University of Manitoba, Winnipeg, MB, Canada.
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Ramos-Nascimento A, Kellen B, Ferreira F, Alenquer M, Vale-Costa S, Raposo G, Delevoye C, Amorim MJ. KIF13A mediates trafficking of influenza A virus ribonucleoproteins. J Cell Sci 2017; 130:4038-4050. [PMID: 29061883 DOI: 10.1242/jcs.210807] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2017] [Accepted: 10/18/2017] [Indexed: 01/18/2023] Open
Abstract
Influenza A is a rapidly evolving virus that is successful in provoking periodic epidemics and occasional pandemics in humans. Viral assembly is complex as the virus incorporates an eight-partite genome of RNA (in the form of viral ribonucleoproteins, vRNPs), and viral genome assembly - with its implications to public health - is not completely understood. It has previously been reported that vRNPs are transported to the cell surface on Rab11-containing vesicles by using microtubules but, so far, no molecular motor has been assigned to the process. Here, we have identified KIF13A, a member of the kinesin-3 family, as the first molecular motor to efficiently transport vRNP-Rab11 vesicles during infection with influenza A. Depletion of KIF13A resulted in reduced viral titers and less accumulation of vRNPs at the cell surface, without interfering with the levels of other viral proteins at sites of viral assembly. In addition, when overexpressed and following two separate approaches to displace vRNP-Rab11 vesicles, KIF13A increased levels of vRNP at the plasma membrane. Together, our results show that KIF13A plays an important role in the transport of influenza A vRNPs, a crucial step for viral assembly.This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Ana Ramos-Nascimento
- Cell Biology of Viral Infection Lab, Instituto Gulbenkian de Ciência (IGC), 2780-156 Oeiras, Portugal.,Institute of Virology, Hannover Medical School, 30625 Hannover, Germany
| | - Bárbara Kellen
- Science4U, MARL Espaços CC02 e CC03, São Julião do Tojal, 2660-421, Loures, Portugal
| | - Filipe Ferreira
- Cell Biology of Viral Infection Lab, Instituto Gulbenkian de Ciência (IGC), 2780-156 Oeiras, Portugal
| | - Marta Alenquer
- Cell Biology of Viral Infection Lab, Instituto Gulbenkian de Ciência (IGC), 2780-156 Oeiras, Portugal
| | - Sílvia Vale-Costa
- Cell Biology of Viral Infection Lab, Instituto Gulbenkian de Ciência (IGC), 2780-156 Oeiras, Portugal
| | - Graça Raposo
- Institut Curie, PSL Research University, CNRS, UMR144, Structure and Membrane Compartments, 75005 Paris, France
| | - Cédric Delevoye
- Institut Curie, PSL Research University, CNRS, UMR144, Structure and Membrane Compartments, 75005 Paris, France
| | - Maria João Amorim
- Cell Biology of Viral Infection Lab, Instituto Gulbenkian de Ciência (IGC), 2780-156 Oeiras, Portugal
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Neefjes J, Jongsma MML, Berlin I. Stop or Go? Endosome Positioning in the Establishment of Compartment Architecture, Dynamics, and Function. Trends Cell Biol 2017; 27:580-594. [PMID: 28363667 DOI: 10.1016/j.tcb.2017.03.002] [Citation(s) in RCA: 61] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2016] [Revised: 03/03/2017] [Accepted: 03/06/2017] [Indexed: 02/03/2023]
Abstract
The endosomal system constitutes a key negotiator between the environment of a cell and its internal affairs. Comprised of a complex membranous network, wherein each vesicle can in principle move autonomously throughout the cell, the endosomal system operates as a coherent unit to optimally face external challenges and maintain homeostasis. Our appreciation of how individual endosomes are controlled in time and space to best serve their collective purpose has evolved dramatically in recent years. In light of these efforts, the endoplasmic reticulum (ER) - with its expanse of membranes permeating the cytoplasmic space - has emerged as a potent spatiotemporal organizer of endosome biology. We review the latest advances in our understanding of the mechanisms underpinning endosomal transport and positioning, with emphasis on the contributions from the ER, and offer a perspective on how the interplay between these aspects shapes the architecture and dynamics of the endosomal system and drives its myriad cellular functions.
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Affiliation(s)
- Jacques Neefjes
- Department of Chemical Immunology, Leiden University Medical Center (LUMC), Einthovenweg 20, 2333 ZC Leiden, The Netherlands
| | - Marlieke M L Jongsma
- Department of Immunopathology, Sanquin Research and Landsteiner Laboratory, Academic Medical Center (AMC)/Universiteit van Amsterdam (UvA), Plesmanlaan 125, 1066 CX Amsterdam, The Netherlands
| | - Ilana Berlin
- Department of Chemical Immunology, Leiden University Medical Center (LUMC), Einthovenweg 20, 2333 ZC Leiden, The Netherlands.
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Vale-Costa S, Amorim MJ. Clustering of Rab11 vesicles in influenza A virus infected cells creates hotspots containing the 8 viral ribonucleoproteins. Small GTPases 2016; 8:71-77. [PMID: 27337591 PMCID: PMC5464114 DOI: 10.1080/21541248.2016.1199190] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Abstract
Influenza A virus is an important human pathogen causative of yearly epidemics and occasional pandemics. The ability to replicate within the host cell is a determinant of virulence, amplifying viral numbers for host-to-host transmission. This process requires multiple rounds of entering permissive cells, replication, and virion assembly at the plasma membrane, the site of viral budding and release. The assembly of influenza A virus involves packaging of several viral (and host) proteins and of a segmented genome, composed of 8 distinct RNAs in the form of viral ribonucleoproteins (vRNPs). The selective assembly of the 8-segment core remains one of the most interesting unresolved problems in virology. The recycling endosome regulatory GTPase Rab11 was shown to contribute to the process, by transporting vRNPs to the periphery, giving rise to enlarged cytosolic puncta rich in Rab11 and the 8 vRNPs. We recently reported that vRNP hotspots were formed of clustered vesicles harbouring protruding electron-dense structures that resembled vRNPs. Mechanistically, vRNP hotspots were formed as vRNPs outcompeted the cognate effectors of Rab11, the Rab11-Family-Interacting-Proteins (FIPs) for binding, and as a consequence impair recycling sorting at an unknown step. Here, we speculate on the impact that such impairment might have in host immunity, membrane architecture and viral assembly.
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Affiliation(s)
- Sílvia Vale-Costa
- a Cell Biology of Viral Infection Lab , Instituto Gulbenkian de Ciência , Oeiras , Portugal
| | - Maria João Amorim
- a Cell Biology of Viral Infection Lab , Instituto Gulbenkian de Ciência , Oeiras , Portugal
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Abstract
Influenza A viruses (IAVs) harbor a segmented RNA genome that is organized into eight distinct viral ribonucleoprotein (vRNP) complexes. Although a segmented genome may be a major advantage to adapt to new host environments, it comes at the cost of a highly sophisticated genome packaging mechanism. Newly synthesized vRNPs conquer the cellular endosomal recycling machinery to access the viral budding site at the plasma membrane. Genome packaging sequences unique to each RNA genome segment are thought to be key determinants ensuring the assembly and incorporation of eight distinct vRNPs into progeny viral particles. Recent studies using advanced fluorescence microscopy techniques suggest the formation of vRNP sub-bundles (comprising less than eight vRNPs) during their transport on recycling endosomes. The formation of such sub-bundles might be required for efficient packaging of a bundle of eight different genomes segments at the budding site, further highlighting the complexity of IAV genome packaging.
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