title: The Norovirus NS3 Protein Is a Dynamic Lipid- and Microtubule-Associated Protein Involved in Viral RNA Replication.
abstract: Norovirus (NoV) infections are a significant health burden to society, yet the lack of reliable tissue culture systems has hampered the development of appropriate antiviral therapies. Here we show that the NoV NS3 protein, derived from murine NoV (MNV), is intimately associated with the MNV replication complex and the viral replication intermediate double-stranded RNA (dsRNA). We observed that when expressed individually, MNV NS3 and NS3 encoded by human Norwalk virus (NV) induced the formation of distinct vesicle-like structures that did not colocalize with any particular protein markers to cellular organelles but localized to cellular membranes, in particular those with a high cholesterol content. Both proteins also showed some degree of colocalization with the cytoskeleton marker β-tubulin. Although the distribution of MNV and NV NS3s were similar, NV NS3 displayed a higher level of colocalization with the Golgi apparatus and the endoplasmic reticulum (ER). However, we observed that although both proteins colocalized in membranes counterstained with filipin, an indicator of cholesterol content, MNV NS3 displayed a greater association with flotillin and stomatin, proteins known to associate with sphingolipid- and cholesterol-rich microdomains. Utilizing time-lapse epifluorescence microscopy, we observed that the membrane-derived vesicular structures induced by MNV NS3 were highly motile and dynamic in nature, and their movement was dependent on intact microtubules. These results begin to interrogate the functions of NoV proteins during virus replication and highlight the conserved properties of the NoV NS3 proteins among the seven Norovirus genogroups.
  
  
  OBJECTIVE
  Many mechanisms involved in the replication of norovirus still remain unclear, including the role for the NS3 protein, one of seven nonstructural viral proteins, which remains to be elucidated. This study reveals that murine norovirus (MNV) NS3 is intimately associated with the viral replication complex and dsRNA. We observed that the NS3 proteins of both MNV and Norwalk virus (NV) induce prominent vesicular structures and that this formation is dependent on microtubules and cellular cholesterol. Thus, this study contributes to our understanding of protein function within different Norovirus genogroups and expands a growing knowledge base on the interaction between positive-strand RNA [(+)RNA] viruses and cellular membranes that contribute to the biogenesis of virus-induced membrane organelles. This study contributes to our understanding of viral protein function and the ability of a viral protein to recruit specific cellular organelles and lipids that enable replication.
authors.affiliation: Department of Physiology, Anatomy and Microbiology, La Trobe University, Melbourne, Victoria, Australia.|Department of Microbiology and Immunology, University of Melbourne, Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia.
authors.forename: Ben T
authors.initials: BT
authors.lastname: Cotton
authors.affiliation: Department of Physiology, Anatomy and Microbiology, La Trobe University, Melbourne, Victoria, Australia.|School of Chemical and Biological Sciences, University of Queensland, Brisbane, Queensland, Australia.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Hyde
authors.affiliation: Department of Microbiology and Immunology, University of Melbourne, Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia.
authors.forename: Soroush T
authors.initials: ST
authors.lastname: Sarvestani
authors.affiliation: Norovirus Gastroenteritis Unit, Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Stanislav V
authors.initials: SV
authors.lastname: Sosnovtsev
authors.affiliation: Norovirus Gastroenteritis Unit, Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Kim Y
authors.initials: KY
authors.lastname: Green
authors.affiliation: School of Biotechnology and Biomolecular Sciences, Faculty of Science, University of New South Wales, Sydney, New South Wales, Australia.
authors.forename: Peter A
authors.initials: PA
authors.lastname: White
authors.affiliation: Department of Microbiology and Immunology, University of Melbourne, Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia jason.mackenzie@unimelb.edu.au.
authors.forename: Jason M
authors.initials: JM
authors.lastname: Mackenzie
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017250:Caliciviridae Infections / Q000378:metabolism* / Q000821:virology*; D002460:Cell Line; D002522:Chlorocebus aethiops; D002784:Cholesterol / Q000378:metabolism; D054884:Host-Pathogen Interactions; D042541:Intracellular Space; D050356:Lipid Metabolism; D021962:Membrane Microdomains / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008870:Microtubules / Q000378:metabolism*; D029322:Norovirus / Q000502:physiology*; D011485:Protein Binding; D021381:Protein Transport; D012330:RNA, Double-Stranded / Q000378:metabolism; D012367:RNA, Viral / Q000378:metabolism; D014709:Vero Cells; D017361:Viral Nonstructural Proteins / Q000737:chemistry / Q000378:metabolism*; D014779:Virus Replication
chemical_list: D008565:Membrane Proteins; D012330:RNA, Double-Stranded; D012367:RNA, Viral; D017361:Viral Nonstructural Proteins; D002784:Cholesterol
keywords: cellular lipids; cytoskeleton; norovirus; virus replication