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Euller-Nicolas G, Le Mennec C, Schaeffer J, Zeng XL, Ettayebi K, Atmar RL, Le Guyader FS, Estes MK, Desdouits M. Human Sapovirus Replication in Human Intestinal Enteroids. J Virol 2023; 97:e0038323. [PMID: 37039654 PMCID: PMC10134857 DOI: 10.1128/jvi.00383-23] [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: 03/13/2023] [Accepted: 03/15/2023] [Indexed: 04/12/2023] Open
Abstract
Human sapoviruses (HuSaVs), like human noroviruses (HuNoV), belong to the Caliciviridae family and cause acute gastroenteritis in humans. Since their discovery in 1976, numerous attempts to grow HuSaVs in vitro were unsuccessful until 2020, when these viruses were reported to replicate in a duodenal cancer cell-derived line. Physiological cellular models allowing viral replication are essential to investigate HuSaV biology and replication mechanisms such as genetic susceptibility, restriction factors, and immune responses to infection. In this study, we demonstrate replication of two HuSaV strains in human intestinal enteroids (HIEs) known to support the replication of HuNoV and other human enteric viruses. HuSaVs replicated in differentiated HIEs originating from jejunum, duodenum and ileum, but not from the colon, and bile acids were required. Between 2h and 3 to 6 days postinfection, viral RNA levels increased up from 0.5 to 1.8 log10-fold. Importantly, HuSaVs were able to replicate in HIEs independent of their secretor status and histo-blood group antigen expression. The HIE model supports HuSaV replication and allows a better understanding of host-pathogen mechanisms such as cellular tropism and mechanisms of viral replication. IMPORTANCE Human sapoviruses (HuSaVs) are a frequent but overlooked cause of acute gastroenteritis, especially in children. Little is known about this pathogen, whose successful in vitro cultivation was reported only recently, in a cancer cell-derived line. Here, we assessed the replication of HuSaV in human intestinal enteroids (HIEs), which are nontransformed cultures originally derived from human intestinal stem cells that can be grown in vitro and are known to allow the replication of other enteric viruses. Successful infection of HIEs with two strains belonging to different genotypes of the virus allowed discovery that the tropism of these HuSaVs is restricted to the small intestine, does not occur in the colon, and replication requires bile acid but is independent of the expression of histo-blood group antigens. Thus, HIEs represent a physiologically relevant model to further investigate HuSaV biology and a suitable platform for the future development of vaccines and antivirals.
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Affiliation(s)
| | - Cécile Le Mennec
- MASAE Microbiologie Aliment Santé Environnement, Ifremer, Nantes, France
| | - Julien Schaeffer
- MASAE Microbiologie Aliment Santé Environnement, Ifremer, Nantes, France
| | - Xi-Lei Zeng
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, USA
| | - Khalil Ettayebi
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, USA
| | - Robert L. Atmar
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, USA
- Department of Medicine, Baylor College of Medicine, Houston, Texas, USA
| | | | - Mary K. Estes
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, USA
- Department of Medicine, Baylor College of Medicine, Houston, Texas, USA
| | - Marion Desdouits
- MASAE Microbiologie Aliment Santé Environnement, Ifremer, Nantes, France
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Ayyar BV, Ettayebi K, Salmen W, Karandikar UC, Neill FH, Tenge VR, Crawford SE, Bieberich E, Prasad BVV, Atmar RL, Estes MK. CLIC and membrane wound repair pathways enable pandemic norovirus entry and infection. Nat Commun 2023; 14:1148. [PMID: 36854760 PMCID: PMC9974061 DOI: 10.1038/s41467-023-36398-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2022] [Accepted: 01/30/2023] [Indexed: 03/02/2023] Open
Abstract
Globally, most cases of gastroenteritis are caused by pandemic GII.4 human norovirus (HuNoV) strains with no approved therapies or vaccines available. The cellular pathways that these strains exploit for cell entry and internalization are unknown. Here, using nontransformed human jejunal enteroids (HIEs) that recapitulate the physiology of the gastrointestinal tract, we show that infectious GII.4 virions and virus-like particles are endocytosed using a unique combination of endosomal acidification-dependent clathrin-independent carriers (CLIC), acid sphingomyelinase (ASM)-mediated lysosomal exocytosis, and membrane wound repair pathways. We found that besides the known interaction of the viral capsid Protruding (P) domain with host glycans, the Shell (S) domain interacts with both galectin-3 (gal-3) and apoptosis-linked gene 2-interacting protein X (ALIX), to orchestrate GII.4 cell entry. Recognition of the viral and cellular determinants regulating HuNoV entry provides insight into the infection process of a non-enveloped virus highlighting unique pathways and targets for developing effective therapeutics.
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Affiliation(s)
- B Vijayalakshmi Ayyar
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA
| | - Khalil Ettayebi
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA
| | - Wilhelm Salmen
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX, USA
| | - Umesh C Karandikar
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA
| | - Frederick H Neill
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA
| | - Victoria R Tenge
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA
| | - Sue E Crawford
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA
| | - Erhard Bieberich
- Department of Physiology, University of Kentucky, Lexington, KY 40506 and VAMC, Lexington, KY, 40502, USA
| | - B V Venkataram Prasad
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX, USA
| | - Robert L Atmar
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA
- Department of Medicine, Baylor College of Medicine, Houston, TX, USA
| | - Mary K Estes
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA.
- Department of Medicine, Baylor College of Medicine, Houston, TX, USA.
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Mostafa-Hedeab G, Allayeh AK, Elhady HA, Eledrdery AY, Mraheil MA, Mostafa A. Viral Eco-Genomic Tools: Development and Implementation for Aquatic Biomonitoring. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2022; 19:ijerph19137707. [PMID: 35805367 PMCID: PMC9265447 DOI: 10.3390/ijerph19137707] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/21/2022] [Revised: 06/21/2022] [Accepted: 06/21/2022] [Indexed: 12/17/2022]
Abstract
Enteric viruses (EVs) occurrence within aquatic environments varies and leads to significant risk on public health of humans, animals, and diversity of aquatic taxa. Early and efficacious recognition of cultivable and fastidious EVs in aquatic systems are important to ensure the sanitary level of aquatic water and implement required treatment strategies. Herein, we provided a comprehensive overview of the conventional and up-to-date eco-genomic tools for aquatic biomonitoring of EVs, aiming to develop better water pollution monitoring tools. In combination with bioinformatics techniques, genetic tools including cloning sequencing analysis, DNA microarray, next-generation sequencing (NGS), and metagenomic sequencing technologies are implemented to make informed decisions about the global burden of waterborne EVs-associated diseases. The data presented in this review are helpful to recommend that: (1) Each viral pollution detection method has its own merits and demerits; therefore, it would be advantageous for viral pollution evaluation to be integrated as a complementary platform. (2) The total viral genome pool extracted from aquatic environmental samples is a real reflection of pollution status of the aquatic eco-systems; therefore, it is recommended to conduct regular sampling through the year to establish an updated monitoring system for EVs, and quantify viral peak concentrations, viral typing, and genotyping. (3) Despite that conventional detection methods are cheaper, it is highly recommended to implement molecular-based technologies to complement aquatic ecosystems biomonitoring due to numerous advantages including high-throughput capability. (4) Continuous implementation of the eco-genetic detection tools for monitoring the EVs in aquatic ecosystems is recommended.
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Affiliation(s)
- Gomaa Mostafa-Hedeab
- Pharmacology Department and Health Research Unit, Medical College, Jouf University, Skaka 11564, Saudi Arabia
- Correspondence: (G.M.-H.); (M.A.M.); (A.M.)
| | - Abdou Kamal Allayeh
- Water Pollution Department, Virology Laboratory, National Research Centre, Dokki, Giza 12622, Egypt;
| | | | - Abozer Y. Eledrdery
- Department of Clinical Laboratory Sciences, College of Applied Medical Sciences, Jouf University, Sakaka 11564, Saudi Arabia;
| | - Mobarak Abu Mraheil
- German Center for Infection Research (DZIF), Institute of Medical Microbiology, Justus-Liebig University, 35392 Giessen, Germany
- Correspondence: (G.M.-H.); (M.A.M.); (A.M.)
| | - Ahmed Mostafa
- Center of Scientific Excellence for Influenza Viruses, National Research Centre, Giza 12622, Egypt
- Correspondence: (G.M.-H.); (M.A.M.); (A.M.)
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Furlong K, Biering SB, Choi J, Wilen CB, Orchard RC, Wobus CE, Nelson CA, Fremont DH, Baldridge MT, Randall G, Hwang S. CD300LF Polymorphisms of Inbred Mouse Strains Confer Resistance to Murine Norovirus Infection in a Cell Type-Dependent Manner. J Virol 2020; 94:e00837-20. [PMID: 32581099 PMCID: PMC7431780 DOI: 10.1128/jvi.00837-20] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Accepted: 06/16/2020] [Indexed: 02/07/2023] Open
Abstract
Human norovirus is the leading cause of gastroenteritis worldwide, yet basic questions about its life cycle remain unanswered due to an historical lack of robust experimental systems. Recent studies on the closely related murine norovirus (MNV) have identified CD300LF as an indispensable entry factor for MNV. We compared the MNV susceptibilities of cells from different mouse strains and identified polymorphisms in murine CD300LF which are critical for its function as an MNV receptor. Bone marrow-derived macrophages (BMDMs) from I/LnJ mice were resistant to infection from multiple MNV strains which readily infect BMDMs from C57BL/6J mice. The resistance of I/LnJ BMDMs was specific to MNV, since the cells supported infection of other viruses comparably to C57BL/6J BMDMs. Transduction of I/LnJ BMDMs with C57BL/6J CD300LF made the cells permissible to MNV infection, suggesting that the cause of resistance lies in the entry step of MNV infection. In fact, we mapped this phenotype to a 4-amino-acid difference at the CC' loop of CD300LF; swapping of these amino acids between C57BL/6J and I/LnJ CD300LF proteins made the mutant C57BL/6J CD300LF functionally impaired and the corresponding mutant of I/LnJ CD300LF functional as an MNV entry factor. Surprisingly, expression of the I/LnJ CD300LF in other cell types made the cells infectible by MNV, even though the I/LnJ allele did not function as an MNV receptor in macrophage-like cells. Correspondingly, I/LnJ CD300LF bound MNV virions in permissive cells but not in nonpermissive cells. Collectively, our data suggest the existence of a cell type-specific modifier of MNV entry.IMPORTANCE MNV is a prevalent model system for studying human norovirus, which is the leading cause of gastroenteritis worldwide and thus a sizeable public health burden. Elucidating mechanisms underlying susceptibility of host cells to MNV infection can lead to insights on the roles that specific cell types play during norovirus pathogenesis. Here, we show that different alleles of the proteinaceous receptor for MNV, CD300LF, function in a cell type-dependent manner. In contrast to the C57BL/6J allele, which functions as an MNV entry factor in all tested cell types, including human cells, I/LnJ CD300LF does not function as an MNV entry factor in macrophage-like cells but does allow MNV entry in other cell types. Together, these observations indicate the existence of cell type-specific modifiers of CD300LF-dependent MNV entry.
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MESH Headings
- Animals
- Binding Sites
- Caliciviridae Infections/virology
- Disease Resistance/genetics
- Gastroenteritis/virology
- Macrophages/virology
- Mice
- Mice, Inbred C57BL
- Mice, Inbred Strains
- Models, Molecular
- Norovirus
- Polymorphism, Genetic
- Protein Conformation
- Receptors, Immunologic/chemistry
- Receptors, Immunologic/genetics
- Receptors, Immunologic/metabolism
- Receptors, Virus/genetics
- Receptors, Virus/metabolism
- Sequence Analysis, Protein
- Virus Internalization
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Affiliation(s)
- Kevin Furlong
- Committee on Microbiology, The University of Chicago, Chicago, Illinois, USA
| | - Scott B Biering
- Committee on Microbiology, The University of Chicago, Chicago, Illinois, USA
| | - Jayoung Choi
- Department of Pathology, The University of Chicago, Chicago, Illinois, USA
| | - Craig B Wilen
- Department of Laboratory Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
- Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Robert C Orchard
- Department of Immunology, The University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Christiane E Wobus
- Department of Microbiology and Immunology, University of Michigan, Ann Arbor, Michigan, USA
| | - Christopher A Nelson
- Department of Pathology & Immunology, Washington University, St. Louis, Missouri, USA
- Department of Biochemistry & Molecular Biophysics, Washington University, St. Louis, Missouri, USA
- Department of Molecular Microbiology, Washington University, St. Louis, Missouri, USA
| | - Daved H Fremont
- Department of Pathology & Immunology, Washington University, St. Louis, Missouri, USA
- Department of Biochemistry & Molecular Biophysics, Washington University, St. Louis, Missouri, USA
- Department of Molecular Microbiology, Washington University, St. Louis, Missouri, USA
| | - Megan T Baldridge
- Department of Molecular Microbiology, Washington University, St. Louis, Missouri, USA
- Division of Infectious Diseases, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Glenn Randall
- Department of Microbiology, The University of Chicago, Chicago, Illinois, USA
| | - Seungmin Hwang
- Committee on Microbiology, The University of Chicago, Chicago, Illinois, USA
- Department of Pathology, The University of Chicago, Chicago, Illinois, USA
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Sriwilaijaroen N, Suzuki Y. Sialoglycovirology of Lectins: Sialyl Glycan Binding of Enveloped and Non-enveloped Viruses. Methods Mol Biol 2020; 2132:483-545. [PMID: 32306355 PMCID: PMC7165297 DOI: 10.1007/978-1-0716-0430-4_47] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/24/2023]
Abstract
On the cell sur "face", sialoglycoconjugates act as receptionists that have an important role in the first step of various cellular processes that bridge communication between the cell and its environment. Loss of Sia production can cause the developmental of defects and lethality in most animals; hence, animal cells are less prone to evolution of resistance to interactions by rapidly evolved Sia-binding viruses. Obligative intracellular viruses mostly have rapid evolution that allows escape from host immunity, leading to an epidemic variant, and that allows emergence of a novel strain, occasionally leading to pandemics that cause health-social-economic problems. Recently, much attention has been given to the mutual recognition systems via sialosugar chains between viruses and their host cells and there has been rapid growth of the research field "sialoglycovirology." In this chapter, the structural diversity of sialoglycoconjugates is overviewed, and enveloped and non-enveloped viruses that bind to Sia are reviewed. Also, interactions of viral lectins-host Sia receptors, which determine viral transmission, host range, and pathogenesis, are presented. The future direction of new therapeutic routes targeting viral lectins, development of easy-to-use detection methods for diagnosis and monitoring changes in virus binding specificity, and challenges in the development of suitable viruses to use in virus-based therapies for genetic disorders and cancer are discussed.
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Affiliation(s)
- Nongluk Sriwilaijaroen
- Department of Preclinical Sciences, Faculty of Medicine, Thammasat University, Pathumthani, Thailand
- College of Life and Health Sciences, Chubu University, Kasugai, Aichi, Japan
| | - Yasuo Suzuki
- College of Life and Health Sciences, Chubu University, Kasugai, Aichi, Japan.
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6
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Li M, Yan P, Liu Z, Cai D, Luo Y, Wu X, Wang Q, Huang Y, Wu Y. Muscovy duck reovirus enters susceptible cells via a caveolae-mediated endocytosis-like pathway. Virus Res 2019; 276:197806. [PMID: 31704247 DOI: 10.1016/j.virusres.2019.197806] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2019] [Revised: 10/21/2019] [Accepted: 11/04/2019] [Indexed: 01/27/2023]
Abstract
Muscovy duck reovirus (MDRV) causes immunosuppression and results in high mortality among Muscovy ducklings. Cell entry is the first step of virus infection and represents a potential therapeutic target. However, very little is known about the mechanism by which MDRV penetrates the cells. The aim of this study was to explore the mechanism of MDRV cell entry and subsequent infection. DF-1 and Vero cells were pretreated with the inhibitors chlorpromazine (CPZ), cytochalasin D, methyl-beta-cyclodextrin (M-β-CD), genistein, dynasore, nocodazole, or NH4Cl, and then infected with MDRV. The copy number of the MDRV p10.8 gene and the expression of viral sigma A protein were determined by RT-PCR and western blot, respectively. Both sigma A expression and p10.8 gene copy number were decreased by treatment with M-β-CD, genistein, dynasore, nocodazole, and NH4Cl. In contrast, no effects on virus infection were detected when inhibitors of clathrin-mediated endocytosis or macropinocytosis were used. In addition, the colocalization between MDRV sigma A protein and caveolin-1 was evaluated by double-label immunofluorescence. Collectively, our data revealed that MDRV can enter susceptible cells through caveolin-dependent endocytosis involving dynamin and microtubules. Moreover, the acidic environment of the endosomes was found to be critical for efficient infection. Our findings provide new insights into the infection process of MDRV.
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Affiliation(s)
- Minghui Li
- College of Animal Science, Fujian Agriculture and Forestry University, Fuzhou 350002, People's Republic of China
| | - Ping Yan
- College of Animal Science, Fujian Agriculture and Forestry University, Fuzhou 350002, People's Republic of China
| | - Zhenni Liu
- College of Animal Science, Fujian Agriculture and Forestry University, Fuzhou 350002, People's Republic of China
| | - Dongling Cai
- College of Animal Science, Fujian Agriculture and Forestry University, Fuzhou 350002, People's Republic of China
| | - Yu Luo
- College of Animal Science, Fujian Agriculture and Forestry University, Fuzhou 350002, People's Republic of China
| | - Xiaoping Wu
- College of Animal Science, Fujian Agriculture and Forestry University, Fuzhou 350002, People's Republic of China; Fujian Key Laboratory of Traditional Chinese Veterinary Medicine and Animal Health (Fujian Agricultural and Forestry University), Fuzhou 350002, People's Republic of China
| | - Quanxi Wang
- College of Animal Science, Fujian Agriculture and Forestry University, Fuzhou 350002, People's Republic of China; Fujian Key Laboratory of Traditional Chinese Veterinary Medicine and Animal Health (Fujian Agricultural and Forestry University), Fuzhou 350002, People's Republic of China
| | - Yifan Huang
- College of Animal Science, Fujian Agriculture and Forestry University, Fuzhou 350002, People's Republic of China; Fujian Key Laboratory of Traditional Chinese Veterinary Medicine and Animal Health (Fujian Agricultural and Forestry University), Fuzhou 350002, People's Republic of China
| | - Yijian Wu
- College of Animal Science, Fujian Agriculture and Forestry University, Fuzhou 350002, People's Republic of China; Fujian Key Laboratory of Traditional Chinese Veterinary Medicine and Animal Health (Fujian Agricultural and Forestry University), Fuzhou 350002, People's Republic of China.
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7
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Desselberger U. Caliciviridae Other Than Noroviruses. Viruses 2019; 11:v11030286. [PMID: 30901945 PMCID: PMC6466229 DOI: 10.3390/v11030286] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2019] [Revised: 03/08/2019] [Accepted: 03/11/2019] [Indexed: 12/24/2022] Open
Abstract
Besides noroviruses, the Caliciviridae family comprises four other accepted genera: Sapovirus, Lagovirus, Vesivirus, and Nebovirus. There are six new genera proposed: Recovirus, Valovirus, Bavovirus, Nacovirus, Minovirus, and Salovirus. All Caliciviridae have closely related genome structures, but are genetically and antigenically highly diverse and infect a wide range of mammalian host species including humans. Recombination in nature is not infrequent for most of the Caliciviridae, contributing to their diversity. Sapovirus infections cause diarrhoea in pigs, humans and other mammalian hosts. Lagovirus infections cause systemic haemorrhagic disease in rabbits and hares, and vesivirus infections lead to lung disease in cats, vesicular disease in swine, and exanthema and diseases of the reproductive system in large sea mammals. Neboviruses are an enteric pathogen of cattle, differing from bovine norovirus. At present, only a few selected caliciviruses can be propagated in cell culture (permanent cell lines or enteroids), and for most of the cultivatable caliciviruses helper virus-free, plasmid only-based reverse genetics systems have been established. The replication cycles of the caliciviruses are similar as far as they have been explored: viruses interact with a multitude of cell surface attachment factors (glycans) and co-receptors (proteins) for adsorption and penetration, use cellular membranes for the formation of replication complexes and have developed mechanisms to circumvent innate immune responses. Vaccines have been developed against lagoviruses and vesiviruses, and are under development against human noroviruses.
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Affiliation(s)
- Ulrich Desselberger
- Department of Medicine, University of Cambridge, Addenbrooke's Hospital, Cambridge CB2 0QQ, UK.
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8
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Phosphatidylinositol 3-Kinase/Akt and MEK/ERK Signaling Pathways Facilitate Sapovirus Trafficking and Late Endosomal Acidification for Viral Uncoating in LLC-PK Cells. J Virol 2018; 92:JVI.01674-18. [PMID: 30282712 PMCID: PMC6258943 DOI: 10.1128/jvi.01674-18] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Accepted: 09/22/2018] [Indexed: 12/24/2022] Open
Abstract
Sapovirus, an important cause of acute gastroenteritis in humans and animals, travels from the early to the late endosomes and requires late endosomal acidification for viral uncoating. However, the signaling pathways responsible for these viral entry processes remain unknown. Here we demonstrate the receptor-mediated early activation of phosphatidylinositol 3-kinase (PI3K)/Akt and mitogen-activated protein extracellular signal-regulated kinase/extracellular signal-regulated kinase (MEK/ERK) signaling pathways involved in sapovirus entry processes. Both signaling pathways were activated during the early stage of porcine sapovirus (PSaV) infection. However, depletion of the cell surface carbohydrate receptors by pretreatment with sodium periodate or neuraminidase reduced the PSaV-induced early activation of these signaling pathways, indicating that PSaV binding to the cell surface carbohydrate receptors triggered these cascades. Addition of bile acid, known to be essential for PSaV escape from late endosomes, was also found to exert a stiffening effect to stimulate both pathways. Inhibition of these signaling pathways by use of inhibitors specific for PI3K or MEK or small interfering RNAs (siRNAs) against PI3K or MEK resulted in entrapment of PSaV particles in early endosomes and prevented their trafficking to late endosomes. Moreover, phosphorylated PI3K and ERK coimmunoprecipitated subunit E of the V-ATPase proton pump that is important for endosomal acidification. Based on our data, we conclude that receptor binding of PSaV activates both PI3K/Akt and MEK/ERK signaling pathways, which in turn promote PSaV trafficking from early to late endosomes and acidification of late endosomes for PSaV uncoating. These signaling cascades may provide a target for potent therapeutics against infections by PSaV and other caliciviruses.IMPORTANCE Sapoviruses cause acute gastroenteritis in both humans and animals. However, the host signaling pathway(s) that facilitates host cell entry by sapoviruses remains largely unknown. Here we demonstrate that porcine sapovirus (PSaV) activates both PI3K/Akt and MEK/ERK cascades at an early stage of infection. Removal of cell surface receptors decreased PSaV-induced early activation of both cascades. Moreover, blocking of PI3K/Akt and MEK/ERK cascades entrapped PSaV particles in early endosomes and prevented their trafficking to the late endosomes. PSaV-induced early activation of PI3K and ERK molecules further mediated V-ATPase-dependent late endosomal acidification for PSaV uncoating. This work unravels a new mechanism by which receptor-mediated early activation of both cascades may facilitate PSaV trafficking from early to late endosomes and late endosomal acidification for PSaV uncoating, which in turn can be a new target for treatment of sapovirus infection.
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