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Jiao M, Danthi P, Yu Y. Cholesterol-Dependent Membrane Deformation by Metastable Viral Capsids Facilitates Entry. ACS Infect Dis 2024; 10:2728-2740. [PMID: 38873897 DOI: 10.1021/acsinfecdis.4c00085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2024]
Abstract
Nonenveloped viruses employ unique entry mechanisms to breach and infect host cells. Understanding these mechanisms is crucial for developing antiviral strategies. Prevailing perspective suggests that nonenveloped viruses release membrane pore-forming peptides to breach host membranes. However, the precise involvement of the viral capsid in this entry remains elusive. Our study presents direct observations elucidating the dynamically distinctive steps through which metastable reovirus capsids disrupt host lipid membranes as they uncoat into partially hydrophobic intermediate particles. Using both live cells and model membrane systems, our key finding is that reovirus capsids actively deform and permeabilize lipid membranes in a cholesterol-dependent process. Unlike membrane pore-forming peptides, these metastable viral capsids induce more extensive membrane perturbations, including budding, bridging between adjacent membranes, and complete rupture. Notably, cholesterol enhances subviral particle adsorption, resulting in the formation of pores equivalent to the capsid size. This cholesterol dependence is attributed to the lipid condensing effect, particularly prominent at an intermediate cholesterol level. Furthermore, our results reveal a positive correlation between membrane disruption extent and efficiency of viral variants in establishing infection. This study unveils the crucial role of capsid-lipid interaction in nonenveloped virus entry, providing new insights into how cholesterol homeostasis influences virus infection dynamics.
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Affiliation(s)
- Mengchi Jiao
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405-7102, United States
| | - Pranav Danthi
- Department of Biology, Indiana University, Bloomington, Indiana 47405-7102, United States
| | - Yan Yu
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405-7102, United States
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Jiao M, Danthi P, Yu Y. Cholesterol-Dependent Membrane Deformation by Metastable Viral Capsids Facilitates Entry. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.10.575085. [PMID: 38260524 PMCID: PMC10802578 DOI: 10.1101/2024.01.10.575085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
Non-enveloped viruses employ unique entry mechanisms to breach and infect host cells. Understanding these mechanisms is crucial for developing antiviral strategies. Prevailing perspective suggests that non-enveloped viruses release membrane lytic peptides to breach host membranes. However, the precise involvement of the viral capsid in this entry remains elusive. Our study presents direct observations elucidating the dynamically distinctive steps through which metastable reovirus capsids disrupt host lipid membranes as they uncoat into partially hydrophobic intermediate particles. Using both live cells and model membrane systems, our key finding is that reovirus capsids actively deform and permeabilize lipid membranes in a cholesterol-dependent process. Unlike membrane lytic peptides, these metastable viral capsids induce more extensive membrane perturbations, including budding, bridging between adjacent membranes, and complete rupture. Notably, cholesterol enhances subviral particle adsorption, resulting in the formation of pores equivalent to the capsid size. This cholesterol dependence is attributed to the lipid condensing effect, particularly prominent at intermediate cholesterol level. Furthermore, our results reveal a positive correlation between membrane disruption extent and efficiency of viral variants in establishing infection. This study unveils the crucial role of capsid-lipid interaction in non-enveloped virus entry, providing new insights into how cholesterol homeostasis influences virus infection dynamics.
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Affiliation(s)
- Mengchi Jiao
- Department of Chemistry, Indiana University, Bloomington, IN 47405-7102
| | - Pranav Danthi
- Department of Biology, Indiana University, Bloomington, IN 47405-7102
| | - Yan Yu
- Department of Chemistry, Indiana University, Bloomington, IN 47405-7102
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Abad AT, McNamara AJ, Danthi P. Proteasome activity is required for reovirus entry into cells. J Virol 2023; 97:e0134823. [PMID: 37830819 PMCID: PMC10617490 DOI: 10.1128/jvi.01348-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2023] [Accepted: 09/04/2023] [Indexed: 10/14/2023] Open
Abstract
IMPORTANCE Due to their limited genetic capacity, viruses are reliant on multiple host systems to replicate successfully. Mammalian orthoreovirus (reovirus) is commonly used as a model system for understanding host-virus interactions. In this study, we identify that the proteasome system, which is critical for cellular protein turnover, affects reovirus entry. Inhibition of the proteasome using a chemical inhibitor blocks reovirus uncoating. Blocking these events reduces subsequent replication of the virus. This work identifies that additional host factors control reovirus entry.
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Affiliation(s)
- Andrew T. Abad
- Department of Biology, Indiana University, Bloomington, Indiana, USA
| | | | - Pranav Danthi
- Department of Biology, Indiana University, Bloomington, Indiana, USA
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Garcia ML, Danthi P. The Reovirus σ1 Attachment Protein Influences the Stability of Its Entry Intermediate. J Virol 2023; 97:e0058523. [PMID: 37167564 PMCID: PMC10231251 DOI: 10.1128/jvi.00585-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Accepted: 04/19/2023] [Indexed: 05/13/2023] Open
Abstract
Structural metastability of viral capsids is pivotal for viruses to survive in harsh environments and to undergo timely conformational changes required for cell entry. Mammalian orthoreovirus (reovirus) is a model to study capsid metastability. Following initial disassembly of the reovirus particle mediated by proteases, a metastable intermediate called the infectious subvirion particle (ISVP) is generated. Using a σ1 monoreassortant virus, we recently showed that σ1 properties affect its encapsidation on particles and the metastability of ISVPs. How metastability is impacted by σ1 and whether the lower encapsidation level of σ1 is connected to this property is unknown. To define a correlation between encapsidation of σ1 and ISVP stability, we generated mutant viruses with single amino acid polymorphisms in σ1 or those that contain chimeric σ1 molecules composed of σ1 portions from type 1 and type 3 reovirus strains. We found that under most conditions where σ1 encapsidation on the particle was lower, ISVPs displayed lower stability. Characterization of mutant viruses selected for enhanced stability via a forward genetic approach also revealed that in some cases, σ1 properties influence stability without influencing σ1 encapsidation. These data indicate that σ1 can also influence ISVP stability independent of its level of incorporation. Together, our work reveals an underappreciated effect of the σ1 attachment protein on the properties of the reovirus capsid. IMPORTANCE Reovirus particles are comprised of eight proteins. Among them, the reovirus σ1 protein functions engages cellular receptors. σ1 also influences the stability of an entry intermediate called ISVP. Here, we sought to define the basis of the link between σ1 properties and stability of ISVPs. Using variety of mutant strains, we determined that when virus preparations contain particles with a high amount of encapsidated σ1, ISVP stability is higher. Additionally, we identified portions of σ1 that impact its encapsidation and consequently the stability of ISVPs. We also determined that in some cases, σ1 properties alter stability of ISVPs without affecting encapsidation. This work highlights that proteins of these complex particles are arranged in an intricate, interconnected manner such that changing the properties of these proteins has a profound impact on the remainder of the particle.
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Affiliation(s)
| | - Pranav Danthi
- Department of Biology, Indiana University, Bloomington, Indiana, USA
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5
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McNamara A, Roebke K, Danthi P. Cell Killing by Reovirus: Mechanisms and Consequences. Curr Top Microbiol Immunol 2023; 442:133-153. [PMID: 32986138 DOI: 10.1007/82_2020_225] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Infection of host cells by mammalian reovirus in culture or in tissues of infected animals results in cell death. Cell death of infected neurons and myocytes contributes to the pathogenesis of reovirus-induced encephalitis and myocarditis in a newborn mouse model. Thus, reovirus-induced cell death has been used to investigate the basis of viral disease. Depending on the cell type, infection of host cells by reovirus results in one of two forms of cell death-apoptosis and necroptosis. In addition to the obvious differences in how these two forms of cell death are executed, the mechanisms by which reovirus infection initiates and transduces signals that lead to each of these types of cell death are distinct. In this review, we discuss how apoptosis and necroptosis are triggered by events at different stages of infection. We also describe how innate immune recognition of reovirus genomic material and type I interferon signaling pathways connect with the core components of the apoptosis and necroptosis machinery. The impact of different cell death mediators on viral pathogenesis and the potential of reovirus as an oncolytic vector are also outlined.
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Affiliation(s)
- Andrew McNamara
- Department of Biology, Indiana University, Bloomington, IN, 47405, USA
| | - Katherine Roebke
- Department of Biology, Indiana University, Bloomington, IN, 47405, USA
| | - Pranav Danthi
- Department of Biology, Indiana University, Bloomington, IN, 47405, USA.
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Identification of putative binding interface of PI(3,5)P2 lipid on rice black-streaked dwarf virus (RBSDV) P10 protein. Virology 2022; 570:81-95. [DOI: 10.1016/j.virol.2022.03.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Revised: 03/15/2022] [Accepted: 03/27/2022] [Indexed: 11/18/2022]
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A CRISPR-Cas9 screen reveals a role for WD repeat-containing protein 81 (WDR81) in the entry of late penetrating viruses. PLoS Pathog 2022; 18:e1010398. [PMID: 35320319 PMCID: PMC8942271 DOI: 10.1371/journal.ppat.1010398] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Accepted: 02/25/2022] [Indexed: 12/02/2022] Open
Abstract
Successful initiation of infection by many different viruses requires their uptake into the endosomal compartment. While some viruses exit this compartment early, others must reach the degradative, acidic environment of the late endosome. Mammalian orthoreovirus (reovirus) is one such late penetrating virus. To identify host factors that are important for reovirus infection, we performed a CRISPR-Cas9 knockout (KO) screen that targets over 20,000 genes in fibroblasts derived from the embryos of C57/BL6 mice. We identified seven genes (WDR81, WDR91, RAB7, CCZ1, CTSL, GNPTAB, and SLC35A1) that were required for the induction of cell death by reovirus. Notably, CRISPR-mediated KO of WD repeat-containing protein 81 (WDR81) rendered cells resistant to reovirus infection. Susceptibility to reovirus infection was restored by complementing KO cells with human WDR81. Although the absence of WDR81 did not affect viral attachment efficiency or uptake into the endosomal compartments for initial disassembly, it reduced viral gene expression and diminished infectious virus production. Consistent with the role of WDR81 in impacting the maturation of endosomes, WDR81-deficiency led to the accumulation of reovirus particles in dead-end compartments. Though WDR81 was dispensable for infection by VSV (vesicular stomatitis virus), which exits the endosomal system at an early stage, it was required for VSV-EBO GP (VSV that expresses the Ebolavirus glycoprotein), which must reach the late endosome to initiate infection. These results reveal a previously unappreciated role for WDR81 in promoting the replication of viruses that transit through late endosomes. Viruses are obligate intracellular parasites that require the contributions of numerous host factors to complete the viral life cycle. Thus, the host-pathogen interaction can regulate cell death signaling and virus entry, replication, assembly, and egress. Functional genetic screens are useful tools to identify host factors that are important for establishing infection. Such information can also be used to understand cell biology. Notably, genome-scale CRISPR-Cas9 knockout screens are robust due to their specificity and the loss of host gene expression. Mammalian orthoreovirus (reovirus) is a tractable model system to investigate the pathogenesis of neurotropic and cardiotropic viruses. Using a CRISPR-Cas9 screen, we identified WD repeat-containing protein 81 (WDR81) as a host factor required for efficient reovirus infection of murine cells. Ablation of WDR81 blocked a late step in the viral entry pathway. Further, our work indicates that WDR81 is required for the entry of vesicular stomatitis virus that expresses the Ebolavirus glycoprotein.
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Ortega-Gonzalez P, Taylor G, Jangra RK, Tenorio R, Fernandez de Castro I, Mainou BA, Orchard RC, Wilen CB, Brigleb PH, Sojati J, Chandran K, Sachse M, Risco C, Dermody TS. Reovirus infection is regulated by NPC1 and endosomal cholesterol homeostasis. PLoS Pathog 2022; 18:e1010322. [PMID: 35263388 PMCID: PMC8906592 DOI: 10.1371/journal.ppat.1010322] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Accepted: 01/28/2022] [Indexed: 11/19/2022] Open
Abstract
Cholesterol homeostasis is required for the replication of many viruses, including Ebola virus, hepatitis C virus, and human immunodeficiency virus-1. Niemann-Pick C1 (NPC1) is an endosomal-lysosomal membrane protein involved in cholesterol trafficking from late endosomes and lysosomes to the endoplasmic reticulum. We identified NPC1 in CRISPR and RNA interference screens as a putative host factor for infection by mammalian orthoreovirus (reovirus). Following internalization via clathrin-mediated endocytosis, the reovirus outer capsid is proteolytically removed, the endosomal membrane is disrupted, and the viral core is released into the cytoplasm where viral transcription, genome replication, and assembly take place. We found that reovirus infection is significantly impaired in cells lacking NPC1, but infection is restored by treatment of cells with hydroxypropyl-β-cyclodextrin, which binds and solubilizes cholesterol. Absence of NPC1 did not dampen infection by infectious subvirion particles, which are reovirus disassembly intermediates that bypass the endocytic pathway for infection of target cells. NPC1 is not required for reovirus attachment to the plasma membrane, internalization into cells, or uncoating within endosomes. Instead, NPC1 is required for delivery of transcriptionally active reovirus core particles from endosomes into the cytoplasm. These findings suggest that cholesterol homeostasis, ensured by NPC1 transport activity, is required for reovirus penetration into the cytoplasm, pointing to a new function for NPC1 and cholesterol homeostasis in viral infection.
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Affiliation(s)
- Paula Ortega-Gonzalez
- Cell Structure Laboratory, National Center for Biotechnology, CNB-CSIC, campus UAM, Cantoblanco, Madrid, Spain
- PhD Program in Molecular Biosciences, Autonoma de Madrid University, Madrid, Spain
- Department of Pediatrics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States of America
- Institute of Infection, Inflammation, and Immunity, UPMC Children’s Hospital of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Gwen Taylor
- Department of Pediatrics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States of America
- Institute of Infection, Inflammation, and Immunity, UPMC Children’s Hospital of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Rohit K. Jangra
- Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - Raquel Tenorio
- Cell Structure Laboratory, National Center for Biotechnology, CNB-CSIC, campus UAM, Cantoblanco, Madrid, Spain
| | - Isabel Fernandez de Castro
- Cell Structure Laboratory, National Center for Biotechnology, CNB-CSIC, campus UAM, Cantoblanco, Madrid, Spain
| | - Bernardo A. Mainou
- Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, Tennessee, United States of America
| | - Robert C. Orchard
- Department of Immunology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Craig B. Wilen
- Departments of Laboratory Medicine and Immunobiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Pamela H. Brigleb
- Institute of Infection, Inflammation, and Immunity, UPMC Children’s Hospital of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States of America
| | - Jorna Sojati
- Institute of Infection, Inflammation, and Immunity, UPMC Children’s Hospital of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States of America
| | - Kartik Chandran
- Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - Martin Sachse
- Cell Structure Laboratory, National Center for Biotechnology, CNB-CSIC, campus UAM, Cantoblanco, Madrid, Spain
| | - Cristina Risco
- Cell Structure Laboratory, National Center for Biotechnology, CNB-CSIC, campus UAM, Cantoblanco, Madrid, Spain
| | - Terence S. Dermody
- Department of Pediatrics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States of America
- Institute of Infection, Inflammation, and Immunity, UPMC Children’s Hospital of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States of America
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Gummersheimer SL, Snyder AJ, Danthi P. Control of Capsid Transformations during Reovirus Entry. Viruses 2021; 13:v13020153. [PMID: 33494426 PMCID: PMC7911961 DOI: 10.3390/v13020153] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2020] [Revised: 01/15/2021] [Accepted: 01/19/2021] [Indexed: 02/04/2023] Open
Abstract
Mammalian orthoreovirus (reovirus), a dsRNA virus with a multilayered capsid, serves as a model system for studying the entry of similar viruses. The outermost layer of this capsid undergoes processing to generate a metastable intermediate. The metastable particle undergoes further remodeling to generate an entry-capable form that delivers the genome-containing inner capsid, or core, into the cytoplasm. In this review, we highlight capsid proteins and the intricacies of their interactions that control the stability of the capsid and consequently impact capsid structural changes that are prerequisites for entry. We also discuss a novel proviral role of host membranes in promoting capsid conformational transitions. Current knowledge gaps in the field that are ripe for future investigation are also outlined.
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Reovirus Core Proteins λ1 and σ2 Promote Stability of Disassembly Intermediates and Influence Early Replication Events. J Virol 2020; 94:JVI.00491-20. [PMID: 32581098 DOI: 10.1128/jvi.00491-20] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2020] [Accepted: 06/15/2020] [Indexed: 12/11/2022] Open
Abstract
The capsids of mammalian reovirus contain two concentric protein shells, the core and the outer capsid. The outer capsid is composed of μ1-σ3 heterohexamers which surround the core. The core is composed of λ1 decamers held in place by σ2. After entry into the endosome, σ3 is proteolytically degraded and μ1 is cleaved and exposed to form infectious subvirion particles (ISVPs). ISVPs undergo further conformational changes to form ISVP*s, resulting in the release of μ1 peptides, which facilitate the penetration of the endosomal membrane to release transcriptionally active core particles into the cytoplasm. Previous work identified regions or specific residues within reovirus outer capsid proteins that impact the efficiency of cell entry. We examined the functions of the core proteins λ1 and σ2. We generated a reovirus T3D reassortant that carries strain T1L-derived σ2 and λ1 proteins (T3D/T1L L3S2). This virus displays lower ISVP stability and therefore converts to ISVP*s more readily. To identify the molecular basis for lability of T3D/T1L L3S2, we screened for hyperstable mutants of T3D/T1L L3S2 and identified three point mutations in μ1 that stabilize ISVPs. Two of these mutations are located in the C-terminal ϕ region of μ1, which has not previously been implicated in controlling ISVP stability. Independent of compromised ISVP stability, we also found that T3D/T1L L3S2 launches replication more efficiently and produces higher yields in infected cells than T3D. In addition to identifying a new role for the core proteins in disassembly events, these data highlight the possibility that core proteins may influence multiple stages of infection.IMPORTANCE Protein shells of viruses (capsids) have evolved to undergo specific changes to ensure the timely delivery of genetic material to host cells. The 2-layer capsid of reovirus provides a model system to study the interactions between capsid proteins and the changes they undergo during entry. We tested a virus in which the core proteins were derived from a different strain than the outer capsid. In comparison to the parental T3D strain, we found that this mismatched virus was less stable and completed conformational changes required for entry prematurely. Capsid stability was restored by introduction of specific changes to the outer capsid, indicating that an optimal fit between inner and outer shells maintains capsid function. Separate from this property, mismatch between these protein layers also impacted the capacity of the virus to initiate infection and produce progeny. This study reveals new insights into the roles of capsid proteins and their multiple functions during viral replication.
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Components of the Reovirus Capsid Differentially Contribute to Stability. J Virol 2019; 93:JVI.01894-18. [PMID: 30381491 DOI: 10.1128/jvi.01894-18] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2018] [Accepted: 10/24/2018] [Indexed: 12/13/2022] Open
Abstract
The mammalian orthoreovirus (reovirus) outer capsid is composed of 200 μ1-σ3 heterohexamers and a maximum of 12 σ1 trimers. During cell entry, σ3 is degraded by luminal or intracellular proteases to generate the infectious subviral particle (ISVP). When ISVP formation is prevented, reovirus fails to establish a productive infection, suggesting proteolytic priming is required for entry. ISVPs are then converted to ISVP*s, which is accompanied by μ1 rearrangements. The μ1 and σ3 proteins confer resistance to inactivating agents; however, neither the impact on capsid properties nor the mechanism (or basis) of inactivation is fully understood. Here, we utilized T1L/T3D M2 and T3D/T1L S4 to investigate the determinants of reovirus stability. Both reassortants encode mismatched subunits. When μ1-σ3 were derived from different strains, virions resembled wild-type particles in structure and protease sensitivity. T1L/T3D M2 and T3D/T1L S4 ISVPs were less thermostable than wild-type ISVPs. In contrast, virions were equally susceptible to heating. Virion associated μ1 adopted an ISVP*-like conformation concurrent with inactivation; σ3 preserves infectivity by preventing μ1 rearrangements. Moreover, thermostability was enhanced by a hyperstable variant of μ1. Unlike the outer capsid, the inner capsid (core) was highly resistant to elevated temperatures. The dual layered architecture allowed for differential sensitivity to inactivating agents.IMPORTANCE Nonenveloped and enveloped viruses are exposed to the environment during transmission to a new host. Protein-protein and/or protein-lipid interactions stabilize the particle and protect the viral genome. Mammalian orthoreovirus (reovirus) is composed of two concentric, protein shells. The μ1 and σ3 proteins form the outer capsid; contacts between neighboring subunits are thought to confer resistance to inactivating agents. We further investigated the determinants of reovirus stability. The outer capsid was disrupted concurrent with the loss of infectivity; virion associated μ1 rearranged into an altered conformation. Heat sensitivity was controlled by σ3; however, particle integrity was enhanced by a single μ1 mutation. In contrast, the inner capsid (core) displayed superior resistance to heating. These findings reveal structural components that differentially contribute to reovirus stability.
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Protein Mismatches Caused by Reassortment Influence Functions of the Reovirus Capsid. J Virol 2018; 92:JVI.00858-18. [PMID: 30068646 DOI: 10.1128/jvi.00858-18] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2018] [Accepted: 07/26/2018] [Indexed: 12/22/2022] Open
Abstract
Following attachment to host receptors via σ1, reovirus particles are endocytosed and disassembled to generate infectious subvirion particles (ISVPs). ISVPs undergo conformational changes to form ISVP*, releasing σ1 and membrane-targeting peptides from the viral μ1 protein. ISVP* formation is required for delivery of the viral core into the cytoplasm for replication. We characterized the properties of T3DF/T3DCS1, an S1 gene monoreassortant between two laboratory isolates of prototype reovirus strain T3D: T3DF and T3DC T3DF/T3DCS1 is poorly infectious. This deficiency is a consequence of inefficient encapsidation of S1-encoded σ1 on T3DF/T3DCS1 virions. Additionally, compared to T3DF, T3DF/T3DCS1 undergoes ISVP-to-ISVP* conversion more readily, revealing an unexpected role for σ1 in regulating ISVP* formation. The σ1 protein is held within turrets formed by the λ2 protein. To test if the altered properties of T3DF/T3DCS1 are due to a mismatch between σ1 and λ2 proteins from T3DF and T3DC, properties of T3DF/T3DCL2 and T3DF/T3DCS1L2, which express a T3DC-derived λ2, were compared. The presence of T3DC λ2 allowed more efficient σ1 incorporation, producing particles that exhibit T3DF-like infectivity. Compared to T3DF, T3DF/T3DCL2 prematurely converts to ISVP*, uncovering a role for λ2 in regulating ISVP* formation. Importantly, a virus with matching σ1 and λ2 displayed a more regulated conversion to ISVP* than either T3DF/T3DCS1 or T3DF/T3DCL2. In addition to identifying new regulators of ISVP* formation, our results highlight that protein mismatches produced by reassortment can alter virus assembly and thereby influence subsequent functions of the virus capsid.IMPORTANCE Cells coinfected with viruses that possess a multipartite or segmented genome reassort to produce progeny viruses that contain a combination of gene segments from each parent. Reassortment places new pairs of genes together, generating viruses in which mismatched proteins must function together. To test if such forced pairing of proteins that form the virus shell or capsid alters the function of the particle, we investigated properties of reovirus variants in which the σ1 attachment protein and the λ2 protein that anchors σ1 on the particle are mismatched. Our studies demonstrate that a σ1-λ2 mismatch produces particles with lower levels of encapsidated σ1, consequently decreasing virus attachment and infectivity. The mismatch between σ1 and λ2 also altered the capacity of the viral capsid to undergo conformational changes required for cell entry. These studies reveal new functions of reovirus capsid proteins and illuminate both predictable and novel implications of reassortment.
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Staring J, Raaben M, Brummelkamp TR. Viral escape from endosomes and host detection at a glance. J Cell Sci 2018; 131:131/15/jcs216259. [PMID: 30076240 DOI: 10.1242/jcs.216259] [Citation(s) in RCA: 105] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
In order to replicate, most pathogens need to enter their target cells. Many viruses enter the host cell through an endocytic pathway and hijack endosomes for their journey towards sites of replication. For delivery of their genome to the host cell cytoplasm and to avoid degradation, viruses have to escape this endosomal compartment without host detection. Viruses have developed complex mechanisms to penetrate the endosomal membrane and have evolved to co-opt several host factors to facilitate endosomal escape. Conversely, there is an extensive variety of cellular mechanisms to counteract or impede viral replication. At the level of cell entry, there are cellular defense mechanisms that recognize endosomal membrane damage caused by virus-induced membrane fusion and pore formation, as well as restriction factors that block these processes. In this Cell Science at a Glance article and accompanying poster, we describe the different mechanisms that viruses have evolved to escape the endosomal compartment, as well as the counteracting cellular protection mechanisms. We provide examples for enveloped and non-enveloped viruses, for which we discuss some unique and unexpected cellular responses to virus-entry-induced membrane damage.
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Affiliation(s)
- Jacqueline Staring
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.,Department of Biochemistry, Oncode Institute, Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
| | - Matthijs Raaben
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
| | - Thijn R Brummelkamp
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands .,Department of Biochemistry, Oncode Institute, Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.,CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, 1090 Vienna, Austria.,CGC.nl, Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
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Differential Delivery of Genomic Double-Stranded RNA Causes Reovirus Strain-Specific Differences in Interferon Regulatory Factor 3 Activation. J Virol 2018; 92:JVI.01947-17. [PMID: 29437975 DOI: 10.1128/jvi.01947-17] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Accepted: 02/02/2018] [Indexed: 12/17/2022] Open
Abstract
Serotype 3 (T3) reoviruses induce substantially more type 1 interferon (IFN-I) secretion than serotype 1 (T1) strains. However, the mechanisms underlying differences in IFN-I production between T1 and T3 reoviruses remain undefined. Here, we found that differences in IFN-I production between T1 and T3 reoviruses correlate with activation of interferon regulatory factor 3 (IRF3), a key transcription factor for the production of IFN-I. T3 strain rsT3D activated IRF3 more rapidly and to a greater extent than the T1 strain rsT1L, in simian virus 40 (SV40) immortalized endothelial cells (SVECs). Differences in IRF3 activation between rsT1L and rsT3D were observed in the first hours of infection and were independent of de novo viral RNA and protein synthesis. NF-κB activation mirrored IRF3 activation, with rsT3D inducing more NF-κB activity than rsT1L. We also found that IRF3 and NF-κB are activated in a mitochondrial antiviral-signaling protein (MAVS)-dependent manner. rsT1L does not suppress IRF3 activation, as IRF3 phosphorylation could be induced in rsT1L-infected cells. Transfected rsT1L and rsT3D RNA induced IRF3 phosphorylation, indicating that genomic RNA from both strains has the capacity to activate IRF3. Finally, bypassing the normal route of reovirus entry by transfecting in vitro-generated viral cores revealed that rsT1L and rsT3D core particles induced equivalent IRF3 activation. Taken together, our findings indicate that entry-related events that occur after outer capsid disassembly, but prior to deposition of viral cores into the cytoplasm, influence the efficiency of IFN-I responses to reovirus. This work provides further insight into mechanisms by which nonenveloped viruses activate innate immune responses.IMPORTANCE Detection of viral nucleic acids by the host cell triggers type 1 interferon (IFN-I) responses, which are critical for containing and clearing viral infections. Viral RNA is sensed in the cytoplasm by cellular receptors that initiate signaling pathways, leading to the activation of interferon regulatory factor 3 (IRF3) and NF-κB, key transcription factors required for IFN-I induction. Serotype 3 (T3) reoviruses induce significantly more IFN-I than serotype 1 (T1) strains. In this work, we found that differences in IFN-I production by T1 and T3 reoviruses correlate with differential IRF3 activation. Differences in IRF3 activation are not caused by a blockade of the IRF3 activation by a T1 strain. Rather, differences in events during the late stages of viral entry determine the capacity of reovirus to activate host IFN-I responses. Together, our work provides insight into mechanisms of IFN-I induction by nonenveloped viruses.
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Cleavage of the C-Terminal Fragment of Reovirus μ1 Is Required for Optimal Infectivity. J Virol 2018; 92:JVI.01848-17. [PMID: 29298891 DOI: 10.1128/jvi.01848-17] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2017] [Accepted: 12/20/2017] [Indexed: 12/12/2022] Open
Abstract
The mammalian orthoreovirus (reovirus) outer capsid, which is composed of 200 μ1/σ3 heterohexamers and a maximum of 12 σ1 trimers, contains all of the proteins that are necessary for attaching to and entering host cells. Following attachment, reovirus is internalized by receptor-mediated endocytosis and acid-dependent cathepsin proteases degrade the σ3 protein. This process generates a metastable intermediate, called infectious subviral particle (ISVP), in which the μ1 membrane penetration protein is exposed. ISVPs undergo a second structural rearrangement to deposit the genome-containing core into the host cytoplasm. The conformationally altered particle is called ISVP*. ISVP-to-ISVP* conversion culminates in the release of μ1 N- and C-terminal fragments, μ1N and Φ, respectively. Released μ1N is thought to facilitate core delivery by generating size-selective pores within the endosomal membrane, whereas the precise role of Φ, particularly in the context of viral entry, is undefined. In this report, we characterize a recombinant reovirus that fails to cleave Φ from μ1 in vitro Φ cleavage, which is not required for ISVP-to-ISVP* conversion, enhances the disruption of liposomal membranes and facilitates the recruitment of ISVP*s to the site of pore formation. Moreover, the Φ cleavage-deficient strain initiates infection of host cells less efficiently than the parental strain. These results indicate that μ1N and Φ contribute to reovirus pore forming activity.IMPORTANCE Host membranes represent a physical barrier that prevents infection. To overcome this barrier, viruses utilize diverse strategies, such as membrane fusion or membrane disruption, to access internal components of the cell. These strategies are characterized by discrete protein-protein and protein-lipid interactions. The mammalian orthoreovirus (reovirus) outer capsid undergoes a series of well-defined conformational changes, which conclude with pore formation and delivery of the viral genetic material. In this report, we characterize the role of the small, reovirus-derived Φ peptide in pore formation. Φ cleavage from the outer capsid enhances membrane disruption and facilitates the recruitment of virions to membrane-associated pores. Moreover, Φ cleavage promotes the initiation of infection. Together, these results reveal an additional component of the reovirus pore forming apparatus and highlight a strategy for penetrating host membranes.
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Snyder AJ, Danthi P. Infectious Subviral Particle to Membrane Penetration Active Particle (ISVP-to-ISVP*) Conversion Assay for Mammalian Orthoreovirus. Bio Protoc 2018; 8:e2700. [PMID: 29399600 DOI: 10.21769/bioprotoc.2700] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The mammalian orthoreovirus (reovirus) outer capsid undergoes a series of conformational changes prior to or during viral entry. These transitions are necessary for delivering the genome-containing core across host cell membranes. This protocol describes an in vitro assay for monitoring the transition into a membrane penetration-active form (i.e., ISVP*).
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Affiliation(s)
- Anthony J Snyder
- Department of Biology, Indiana University, Bloomington, Indiana, USA
| | - Pranav Danthi
- Department of Biology, Indiana University, Bloomington, Indiana, USA
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Snyder AJ, Danthi P. Infectious Subviral Particle-induced Hemolysis Assay for Mammalian Orthoreovirus. Bio Protoc 2018; 8:e2701. [PMID: 29552594 DOI: 10.21769/bioprotoc.2701] [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: 11/02/2022] Open
Abstract
Mammalian orthoreovirus (reovirus) utilizes pore forming peptides to penetrate host cell membranes. This step is essential for delivering its genome containing core particle during viral entry. This protocol describes an in vitro assay for measuring reovirus-induced pore formation.
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Affiliation(s)
- Anthony J Snyder
- Department of Biology, Indiana University, Bloomington, Indiana, USA
| | - Pranav Danthi
- Department of Biology, Indiana University, Bloomington, Indiana, USA
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The Loop Formed by Residues 340 to 343 of Reovirus μ1 Controls Entry-Related Conformational Changes. J Virol 2017; 91:JVI.00898-17. [PMID: 28794028 DOI: 10.1128/jvi.00898-17] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2017] [Accepted: 08/02/2017] [Indexed: 12/13/2022] Open
Abstract
Reovirus particles are covered with 200 μ1/σ3 heterohexamers. Following attachment to cell surface receptors, reovirus is internalized by receptor-mediated endocytosis. Within the endosome, particles undergo a series of stepwise disassembly events. First, the σ3 protector protein is degraded by cellular proteases to generate infectious subviral particles (ISVPs). Second, the μ1 protein rearranges into a protease-sensitive conformation to generate ISVP*s and releases two virus-encoded peptides, μ1N and Φ. The released peptides promote delivery of the genome-containing core by perforating the endosomal membrane. Thus, to establish a productive infection, virions must be stable in the environment but flexible to disassemble in response to the appropriate cellular cue. The reovirus outer capsid is stabilized by μ1 intratrimer, intertrimer, and trimer-core interactions. As a consequence of ISVP-to-ISVP* conversion, neighboring μ1 trimers unwind and separate. Located within the μ1 jelly roll β barrel domain, which is a known regulator of ISVP* formation, residues 340 to 343 form a loop and have been proposed to facilitate viral entry. To test this idea, we generated recombinant reoviruses that encoded deletions within this loop (Δ341 and Δ342). Both deletions destabilized the outer capsid. Notably, Δ342 impaired the viral life cycle; however, replicative fitness was restored by an additional change (V403A) within the μ1 jelly roll β barrel domain. In the Δ341 and Δ342 backgrounds, V403A also rescued defects in ISVP-to-ISVP* conversion. Together, these findings reveal a new region that regulates reovirus disassembly and how perturbing a metastable capsid can compromise replicative fitness.IMPORTANCE Capsids of nonenveloped viruses are composed of protein complexes that encapsulate, or form a shell around, nucleic acid. The protein-protein interactions that form this shell must be stable to protect the viral genome but also sufficiently flexible to disassemble during cell entry. Thus, capsids adopt conformations that undergo rapid disassembly in response to a specific cellular cue. In this work, we identify a new region within the mammalian orthoreovirus outer capsid that regulates particle stability. Amino acid deletions that destabilize this region impair the viral replication cycle. Nonetheless, replicative fitness is restored by a compensatory mutation that restores particle stability. Together, this work demonstrates the critical balance between assembling virions that are stable and maintaining conformational flexibility. Any factor that perturbs this balance has the potential to block a productive infection.
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Abstract
Purpose of Review The ability of viruses to infect host cells is dependent on several factors including the availability of cell-surface receptors, antiviral state of cells, and presence of host factors needed for viral replication. Here, we review findings from in vitro and in vivo studies using mammalian orthoreovirus (reovirus) that have identified an intricate group of molecules and mechanisms used by the virus to attach and enter cells. Recent Findings Recent findings provide an improved mechanistic understanding of reovirus cell entry. Of special note is the identification of a cellular mediator of cell entry in neuronal and non-neuronal cells, the effect of cell entry on the outcome of infection and cytopathic effects on the host cell, and an improved understanding of the components that promote viral penetration of cellular membranes. Summary A mechanistic understanding of the interplay between host and viral factors has enhanced our view of how viruses usurp cellular processes during infection.
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Affiliation(s)
- Bernardo A Mainou
- Department of Pediatrics, Emory University School of Medicine, Atlanta, GA 30322.,Children's Healthcare of Atlanta, Atlanta, GA, 30322
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Snyder AJ, Danthi P. Lipids Cooperate with the Reovirus Membrane Penetration Peptide to Facilitate Particle Uncoating. J Biol Chem 2016; 291:26773-26785. [PMID: 27875299 DOI: 10.1074/jbc.m116.747477] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Revised: 11/14/2016] [Indexed: 12/24/2022] Open
Abstract
Virus-host interactions play a role in many stages of the viral lifecycle, including entry. Reovirus, a model system for studying the entry mechanisms of nonenveloped viruses, undergoes a series of regulated structural transitions that culminate in delivery of the viral genetic material. Lipids can trigger one of these conformational changes, infectious subviral particle (ISVP)-to-ISVP* conversion. ISVP* formation releases two virally encoded peptides, myristoylated μ1N (myr-μ1N) and Φ. Among these, myr-μ1N is sufficient to form pores within membranes. Released myr-μ1N can also promote ISVP* formation in trans Using thermal inactivation as a readout for ISVP-to-ISVP* conversion, we demonstrate that lipids render ISVPs less thermostable in a virus concentration-dependent manner. Under conditions in which neither lipids alone nor myr-μ1N alone promotes ISVP-to-ISVP* conversion, myr-μ1N induces particle uncoating when lipids are present. These data suggest that the pore-forming activity and the ISVP*-promoting activity of myr-μ1N are linked. Lipid-associated myr-μ1N interacts with ISVPs and triggers efficient ISVP* formation. The cooperativity between a reovirus component and lipids reveals a distinct virus-host interaction in which membranes can facilitate nonenveloped virus entry.
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Affiliation(s)
- Anthony J Snyder
- From the Department of Biology, Indiana University, Bloomington, Indiana 47405
| | - Pranav Danthi
- From the Department of Biology, Indiana University, Bloomington, Indiana 47405
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