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  • 1. Asghar, Naveed
    et al.
    Lee, Yi-Ping
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Nilsson, Emma
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Lindqvist, Richard
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Melik, Wessam
    Kröger, Andrea
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Johansson, Magnus
    The role of the poly(A) tract in the replication and virulence of tick-borne encephalitis virus2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 39265Article in journal (Refereed)
    Abstract [en]

    The tick-borne encephalitis virus (TBEV) is a flavivirus transmitted to humans, usually via tick bites. The virus causes tick-borne encephalitis (TBE) in humans, and symptoms range from mild flu-like symptoms to severe and long-lasting sequelae, including permanent brain damage. It has been suggested that within the population of viruses transmitted to the mammalian host, quasispecies with neurotropic properties might become dominant in the host resulting in neurological symptoms. We previously demonstrated the existence of TBEV variants with variable poly(A) tracts within a single blood-fed tick. To characterize the role of the poly(A) tract in TBEV replication and virulence, we generated infectious clones of Toro-2003 with the wild-type (A)(3)C(A)(6) sequence (Toro-6A) or with a modified (A)(3)C(A)(38) sequence (Toro-38A). Toro-38A replicated poorly compared to Toro-6A in cell culture, but Toro-38A was more virulent than Toro-6A in a mouse model of TBE. Next-generation sequencing of TBEV genomes after passaging in cell culture and/or mouse brain revealed mutations in specific genomic regions and the presence of quasispecies that might contribute to the observed differences in virulence. These data suggest a role for quasispecies development within the poly(A) tract as a virulence determinant for TBEV in mice.

  • 2. Asghar, Naveed
    et al.
    Lindblom, Pontus
    Melik, Wessam
    Lindqvist, Richard
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Haglund, Mats
    Forsberg, Pia
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Andreassen, Åshild
    Lindgren, Per-Eric
    Johansson, Magnus
    Tick-borne encephalitis virus sequenced directly from questing and blood-feeding ticks reveals quasispecies variance2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 7, p. e103264-Article in journal (Refereed)
    Abstract [en]

    The increased distribution of the tick-borne encephalitis virus (TBEV) in Scandinavia highlights the importance of characterizing novel sequences within the natural foci. In this study, two TBEV strains: the Norwegian Mandal 2009 (questing nymphs pool) and the Swedish Saringe 2009 (blood-fed nymph) were sequenced and phylogenetically characterized. Interestingly, the sequence of Mandal 2009 revealed the shorter form of the TBEV genome, similar to the highly virulent Hypr strain, within the 3' non-coding region (3'NCR). A different genomic structure was found in the 3'NCR of Saringe 2009, as in-depth analysis demonstrated TBEV variants with different lengths within the poly(A) tract. This shows that TBEV quasispecies exists in nature and indicates a putative shift in the quasispecies pool when the virus switches between invertebrate and vertebrate environments. This prompted us to further sequence and analyze the 3'NCRs of additional Scandinavian TBEV strains and control strains, Hypr and Neudoerfl. Toro 2003 and Habo 2011 contained mainly a short (A) 3C(A)6 poly(A) tract. A similar pattern was observed for the human TBEV isolates 1993/783 and 1991/4944; however, one clone of 1991/4944 contained an (A) 3C(A)11 poly(A) sequence, demonstrating that quasispecies with longer poly(A) could be present in human isolates. Neudoerfl has previously been reported to contain a poly(A) region, but to our surprise the resequenced genome contained two major quasispecies variants, both lacking the poly(A) tract. We speculate that the observed differences are important factors for the understanding of virulence, spread, and control of the TBEV.

  • 3. Dobler, G.
    et al.
    Bestehorn, M.
    Antwerpen, M.
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology.
    Complete Genome Sequence of a Low-Virulence Tick-Borne Encephalitis Virus Strain2016In: Microbiology Resource Announcements, ISSN 2576-098X, Vol. 4, no 5, article id e01145-16Article in journal (Refereed)
    Abstract [en]

    We report here the complete genome sequence (GenBank accession no. KX268728) of tick-borne encephalitis strain HB171/11, isolated from an Ixodes ricinus tick from a natural focus where human neurological disease is rare. The strain shows unique characteristics in neuroinvasiveness and neurovirulence.

  • 4. Flick, Kirsten
    et al.
    Katz, Anna
    Överby, Anna
    Ludwig Institute for Cancer Research, Stockholm Branch, Karolinska Institute, Stockholm, Sweden.
    Feldmann, Heinz
    Pettersson, Ralf F
    Flick, Ramon
    Functional analysis of the noncoding regions of the Uukuniemi virus (Bunyaviridae) RNA segments2004In: Journal of Virology, ISSN 0022-538X, E-ISSN 1098-5514, Vol. 78, no 21, p. 11726-11738Article in journal (Refereed)
    Abstract [en]

    The role of the variable portion of the noncoding regions (NCRs) of the three Bunyaviridae RNA segments (L, M, S) in transcription, replication, and packaging was studied using the recently developed plasmid-driven RNA polymerase I minigenome system for Uukuniemi (UUK) virus, genus Phlebovirus (11), as a model. Comparison of the different segments showed that all NCRs were sufficient to mediate transcription/replication of a minigenome but demonstrated decreased promoter strength in the order M > L > S. Chimeric minigenomes with flanking NCRs from different genome segments revealed that the number of total base pairs within the inverted, partially complementary ends was important for transcription and replication. Point mutations increasing the base-pairing potential produced increased reporter expression, indicating that complementarity between the 5' and 3' ends is crucial for promoter activity. The role of the intergenic region (IGR) located between the two open reading frames of the ambisense UUK virus S segment was analyzed by inserting this sequence element downstream of the reporter genes. The presence of the IGR was found to enhance reporter expression, demonstrating that efficient transcription termination, regulated by the IGR, is important for optimal minigenome mRNA translation. Finally, genome packaging efficacy varied for different NCRs and was strongest for L followed by M and S. Strong reporter gene activity was still observed after seven consecutive cell culture passages, indicating a selective rather than random genome-packaging mechanism. In summary, our results demonstrate that the NCRs from all three segments contain the necessary signals to initiate transcription and replication as well as packaging. Based on promoter strength, M-segment NCRs may be the preferred choice for the development of reverse genetics and minigenome rescue systems for bunyaviruses.

  • 5. Habjan, Matthias
    et al.
    Penski, Nicola
    Wagner, Valentina
    Spiegel, Martin
    Överby, Anna K
    Department of Virology, University of Freiburg, D-79008 Freiburg, Germany.
    Kochs, Georg
    Huiskonen, Juha T
    Weber, Friedemann
    Efficient production of Rift Valley fever virus-like particles: the antiviral protein MxA can inhibit primary transcription of bunyaviruses2009In: Virology, ISSN 0042-6822, E-ISSN 1096-0341, Vol. 385, no 2, p. 400-408Article in journal (Refereed)
    Abstract [en]

    Rift Valley fever virus (RVFV) is a highly pathogenic member of the family Bunyaviridae that needs to be handled under biosafety level (BSL) 3 conditions. Here, we describe reverse genetics systems to measure RVFV polymerase activity in mammalian cells and to generate virus-like particles (VLPs). Recombinant polymerase (L) and nucleocapsid protein (N), expressed together with a minireplicon RNA, formed transcriptionally active nucleocapsids. These could be packaged into VLPs by additional expression of viral glycoproteins. The VLPs resembled authentic virus particles and were able to infect new cells. After infection, VLP-associated nucleocapsids autonomously performed primary transcription, and co-expression of L and N in VLP-infected cells allowed subsequent replication and secondary transcription. Bunyaviruses are potently inhibited by a human interferon-induced protein, MxA. However, the affected step in the infection cycle is not entirely characterized. Using the VLP system, we demonstrate that MxA inhibits both primary and secondary transcriptions of RVFV. A set of infection assays distinguishing between virus attachment, entry, and subsequent RNA synthesis confirmed that MxA is able to target immediate early RNA synthesis of incoming RVFV particles. Thus, our reverse genetics systems are useful for dissecting individual steps of RVFV infection under non-BSL3 conditions.

  • 6. Habjan, Matthias
    et al.
    Pichlmair, Andreas
    Elliott, Richard M
    Överby, Anna K
    Department of Virology, University of Freiburg, Freiburg, Germany.
    Glatter, Timo
    Gstaiger, Matthias
    Superti-Furga, Giulio
    Unger, Hermann
    Weber, Friedemann
    NSs protein of rift valley fever virus induces the specific degradation of the double-stranded RNA-dependent protein kinase2009In: Journal of Virology, ISSN 0022-538X, E-ISSN 1098-5514, Vol. 83, no 9, p. 4365-4375Article in journal (Refereed)
    Abstract [en]

    Rift Valley fever virus (RVFV) continues to cause large outbreaks of acute febrile and often fatal illness among humans and domesticated animals in Africa, Saudi Arabia, and Yemen. The high pathogenicity of this bunyavirus is mainly due to the viral protein NSs, which was shown to prevent transcriptional induction of the antivirally active type I interferons (alpha/beta interferon [IFN-alpha/beta]). Viruses lacking the NSs gene induce synthesis of IFNs and are therefore attenuated, whereas the noninducing wild-type RVFV strains can only be inhibited by pretreatment with IFN. We demonstrate here in vitro and in vivo that a substantial part of the antiviral activity of IFN against RVFV is due to a double-stranded RNA-dependent protein kinase (PKR). PKR-mediated virus inhibition, however, was much more pronounced for the strain Clone 13 with NSs deleted than for the NSs-expressing strain ZH548. In vivo, Clone 13 was nonpathogenic for wild-type (wt) mice but could regain pathogenicity if mice lacked the PKR gene. ZH548, in contrast, killed both wt and PKR knockout mice indiscriminately. ZH548 was largely resistant to the antiviral properties of PKR because RVFV NSs triggered the specific degradation of PKR via the proteasome. The NSs proteins of the related but less virulent sandfly fever Sicilian virus and La Crosse virus, in contrast, had no such anti-PKR activity despite being efficient suppressors of IFN induction. Our data suggest that RVFV NSs has gained an additional anti-IFN function that may explain the extraordinary pathogenicity of this virus.

  • 7. Henningsson, Anna J.
    et al.
    Lindqvist, Richard
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Norberg, Peter
    Lindblom, Pontus
    Roth, Anette
    Forsberg, Pia
    Bergström, Tomas
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology.
    Lindgren, Per-Eric
    Human Tick-Borne Encephalitis and Characterization of Virus from Biting Tick2016In: Emerging Infectious Diseases, ISSN 1080-6040, E-ISSN 1080-6059, Vol. 22, no 8, p. 1485-1487Article in journal (Refereed)
    Abstract [en]

    We report a case of human tick-borne encephalitis (TBE) in which the TBE virus was isolated from the biting tick. Viral growth and sequence were characterized and compared with those of a reference strain. Virus isolation from ticks from patients with TBE may offer a new approach for studies of epidemiology and pathogenicity.

  • 8. Huiskonen, Juha T
    et al.
    Överby, Anna K
    Department of Virology, University of Freiburg, Hermann-Herder-Strasse 11, D-79008 Freiburg, Germany.
    Weber, Friedemann
    Grünewald, Kay
    Electron cryo-microscopy and single-particle averaging of Rift Valley fever virus: evidence for GN-GC glycoprotein heterodimers2009In: Journal of Virology, ISSN 0022-538X, E-ISSN 1098-5514, Vol. 83, no 8, p. 3762-3769Article in journal (Refereed)
    Abstract [en]

    Rift Valley fever virus (RVFV) is a member of the genus Phlebovirus within the family Bunyaviridae. It is a mosquito-borne zoonotic agent that can cause hemorrhagic fever in humans. The enveloped RVFV virions are known to be covered by capsomers of the glycoproteins G(N) and G(C), organized on a T=12 icosahedral lattice. However, the structural units forming the RVFV capsomers have not been determined. Conflicting biochemical results for another phlebovirus (Uukuniemi virus) have indicated the existence of either G(N) and G(C) homodimers or G(N)-G(C) heterodimers in virions. Here, we have studied the structure of RVFV using electron cryo-microscopy combined with three-dimensional reconstruction and single-particle averaging. The reconstruction at 2.2-nm resolution revealed the organization of the glycoprotein shell, the lipid bilayer, and a layer of ribonucleoprotein (RNP). Five- and six-coordinated capsomers are formed by the same basic structural unit. Molecular-mass measurements suggest a G(N)-G(C) heterodimer as the most likely candidate for this structural unit. Both leaflets of the lipid bilayer were discernible, and the glycoprotein transmembrane densities were seen to modulate the curvature of the lipid bilayer. RNP densities were situated directly underneath the transmembrane densities, suggesting an interaction between the glycoprotein cytoplasmic tails and the RNPs. The success of the single-particle averaging approach taken in this study suggests that it is applicable in the study of other phleboviruses, as well, enabling higher-resolution description of these medically important pathogens.

  • 9.
    Islam, Md. Koushikul
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Infectious Diseases.
    Baudin, Maria
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Eriksson, Jonas
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Öberg, Christopher
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Habjan, Matthias
    Weber, Friedemann
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Ahlm, Clas
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Infectious Diseases.
    Evander, Magnus
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    High-Throughput Screening Using a Whole-Cell Virus Replication Reporter Gene Assay to Identify Inhibitory Compounds against Rift Valley Fever Virus Infection2016In: Journal of Biomolecular Screening, ISSN 1087-0571, E-ISSN 1552-454X, Vol. 21, no 4, p. 354-362Article in journal (Refereed)
    Abstract [en]

    Rift Valley fever virus (RVFV) is an emerging virus that causes serious illness in humans and livestock. There are no approved vaccines or treatments for humans. The purpose of the study was to identify inhibitory compounds of RVFV infection without any preconceived idea of the mechanism of action. A whole-cell-based high-throughput drug screening assay was developed to screen 28,437 small chemical compounds targeting RVFV infection. To accomplish both speed and robustness, a replication-competent NSs-deleted RVFV expressing a fluorescent reporter gene was developed. Inhibition of fluorescence intensity was quantified by spectrophotometry and related to virus infection in human lung epithelial cells (A549). Cell toxicity was assessed by the Resazurin cell viability assay. After primary screening, 641 compounds were identified that inhibited RVFV infection by 80%, with 50% cell viability at 50 mu M concentration. These compounds were subjected to a second screening regarding dose-response profiles, and 63 compounds with 60% inhibition of RVFV infection at 3.12 mu M compound concentration and 50% cell viability at 25 mu M were considered hits. Of these, six compounds with high inhibitory activity were identified. In conclusion, the high-throughput assay could efficiently and safely identify several promising compounds that inhibited RVFV infection.

  • 10.
    Kurhade, Chaitanya
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology.
    Lee, Yi-Ping
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology.
    Schreier, Sarah
    Zegenhagen, Loreen
    Kröger, Andrea
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology.
    Correlation of disease severity in human tick-borne encephalitis and pathogenicity in miceManuscript (preprint) (Other academic)
  • 11.
    Kurhade, Chaitanya
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Schreier, Sarah
    Lee, Yi-Ping
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology. National Cheng Kung University, Tainan, Taiwan..
    Zegenhagen, Loreen
    Hjertqvist, Marika
    Dobler, Gerhard
    Kroeger, Andrea
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Correlation of Severity of Human Tick-Borne Encephalitis Virus Disease and Pathogenicity in Mice2018In: Emerging Infectious Diseases, ISSN 1080-6040, E-ISSN 1080-6059, Vol. 24, no 9, p. 1709-1712Article in journal (Refereed)
    Abstract [en]

    We compared 2 tick-borne encephalitis virus strains isolated from 2 different foci that cause different symptoms in tick-borne encephalitis patients, from neurologic to mild gastrointestinal symptoms. We compared neuroinvasiveness, neurovirulence, and proinflammatory cytokine response in mice and found unique differences that contribute to our understanding of pathogenesis.

  • 12.
    Kurhade, Chaitanya
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Zegenhagen, Loreen
    Weber, Elvira
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Nair, Sharmila
    Michaelsen-Preusse, Kristin
    Spanier, Julia
    Gekara, Nelson O.
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Kroeger, Andrea
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Type I Interferon response in olfactory bulb, the site of tick-borne flavivirus accumulation, is primarily regulated by IPS-12016In: Journal of Neuroinflammation, ISSN 1742-2094, E-ISSN 1742-2094, Vol. 13, article id 22Article in journal (Refereed)
    Abstract [en]

    Background: Although type I interferons (IFNs)—key effectors of antiviral innate immunity are known to be induced via different pattern recognition receptors (PRRs), the cellular source and the relative contribution of different PRRs in host protection against viral infection is often unclear. IPS-1 is a downstream adaptor for retinoid-inducible gene I (RIG-I)-like receptor signaling. In this study, we investigate the relative contribution of IPS-1 in the innate immune response in the different brain regions during infection with tick-borne encephalitis virus (TBEV), a flavivirus that causes a variety of severe symptoms like hemorrhagic fevers, encephalitis, and meningitis in the human host.

    Methods: IPS-1 knockout mice were infected with TBEV/Langat virus (LGTV), and viral burden in the peripheral and the central nervous systems, type I IFN induction, brain infiltrating cells, and inflammatory response was analyzed.

    Results: We show that IPS-1 is indispensable for controlling TBEV and LGTV infections in the peripheral and central nervous system. Our data indicate that IPS-1 regulates neuropathogenicity in mice. IFN response is differentially regulated in distinct regions of the central nervous system (CNS) influencing viral tropism, as LGTV replication was mainly restricted to olfactory bulb in wild-type (WT) mice. In contrast to the other brain regions, IFN upregulation in the olfactory bulb was dependent on IPS-1 signaling. IPS-1 regulates basal levels of antiviral interferon-stimulated genes (ISGs) like viperin and IRF-1 which contributes to the establishment of early viral replication which inhibits STAT1 activation. This diminishes the antiviral response even in the presence of high IFN-β levels. Consequently, the absence of IPS-1 causes uncontrolled virus replication, in turn resulting in apoptosis, activation of microglia and astrocytes, elevated proinflammatory response, and recruitment of inflammatory cells into the CNS.

    Conclusions: We show that LGTV replication is restricted to the olfactory bulb and that IPS-1 is a very important player in the olfactory bulb in shaping the innate immune response by inhibiting early viral replication and viral spread throughout the central nervous system. In the absence of IPS-1, higher viral replication leads to the evasion of antiviral response by inhibiting interferon signaling. Our data suggest that the local microenvironment of distinct brain regions is critical to determine virus permissiveness.

  • 13. Lindgren, Lena
    et al.
    Lindkvist, Marie
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Infectious Diseases.
    Överby, Anna
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Ahlm, Clas
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Infectious Diseases.
    Bucht, Göran
    Holmström, Anna
    Swedish Defence Research Agency, Division of CBRN Defence and Security, SE-901 82 Umeå, Sweden.
    Regions of importance for interaction of puumala virus nucleocapsid subunits2006In: Virus genes, ISSN 0920-8569, E-ISSN 1572-994X, Vol. 33, no 2, p. 169-174Article in journal (Refereed)
    Abstract [en]

    Puumala virus (PUUV) is a hantavirus that causes a mild form of hemorrhagic fever with renal syndrome in northern and central Europe, and in large parts of Russia. The nucleocapsid (N) protein encoded by hantaviruses plays an important role in the life-cycle of these viruses, and one important function for the N-protein is to oligomerize, surround and protect the viral RNAs. We have identified amino- and carboxy-terminal regions involved in PUUV N-N interactions, which comprise amino acids 100-120 and 330-405. Our findings strengthen the hypothesis that the amino-terminus of the N-protein of hantaviruses holds a more regulatory function regarding N-N interactions, while conserved residues in the carboxy-terminal region, F335 together with F336 and W392, in concert with Y388 and/or F400 seems to play a more critical role in the PUUV N-N formation. This study provides evidence that the amino-terminal regions involved in the N-N interaction of Puumala virus are similar to those reported for Seoul virus (SEOV) and to some extent Hantaan virus (HTNV), even though the identity between PUUV N and SEOV/HTNV N is markedly lower than between PUUV N and Tula virus (TULV) N or Sin Nombre virus (SNV) N.

  • 14.
    Lindquist, Richard
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    The Role of Viperin in Antiflavivirus Responses2018In: DNA and Cell Biology, ISSN 1044-5498, E-ISSN 1557-7430, Vol. 37, no 9, p. 725-730Article in journal (Refereed)
    Abstract [en]

    Viperin is an interferon (IFN)-stimulated gene product, which is part of the first line of the intracellular response against viral infection. It is a potent antiviral protein, strongly upregulated after IFN-stimulation and virus infection. Viperin is antivirally active against many different viruses from different families and has been shown to inhibit several flaviviruses. Flaviviruses are an important group of arthropod-borne viruses that cause millions of infections annually. In this review, we focus on the recent advances of the antiviral mechanisms of viperin against these flaviviruses, both pointing to similarities and differences between viruses within the same genera.

  • 15.
    Lindqvist, Richard
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Department of Pharmacology and Clinical Neuroscience, Clinical Neuroscience.
    Kurhade, Chaitanya
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Gilthorpe, Jonathan D.
    Umeå University, Faculty of Medicine, Department of Pharmacology and Clinical Neuroscience.
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Cell-type- and region-specific restriction of neurotropic flavivirus infection by viperin2018In: Journal of Neuroinflammation, ISSN 1742-2094, E-ISSN 1742-2094, Vol. 15, article id 80Article in journal (Refereed)
    Abstract [en]

    Background: Flaviviruses are a group of diverse and emerging arboviruses and an immense global health problem. A number of flaviviruses are neurotropic, causing severe encephalitis and even death. Type I interferons (IFNs) are the first line of defense of the innate immune system against flavivirus infection. IFNs elicit the concerted action of numerous interferon-stimulated genes (ISGs) to restrict both virus infection and replication. Viperin (virus-inhibitory protein, endoplasmic reticulum-associated, IFN-inducible) is an ISG with broad-spectrum antiviral activity against multiple flaviviruses in vitro. Its activity in vivo restricts neurotropic infections to specific regions of the central nervous system (CNS). However, the cell types in which viperin activity is required are unknown. Here we have examined both the regional and cell-type specificity of viperin in the defense against infection by several model neurotropic flaviviruses.

    Methods: Viral burden and IFN induction were analyzed in vivo in wild-type and viperin(-/-) mice infected with Langat virus (LGTV). The effects of IFN pretreatment were tested in vitro in primary neural cultures from different brain regions in response to infection with tick-borne encephalitis virus (TBEV), West Nile virus (WNV), and Zika virus (ZIKV).

    Results: Viperin activity restricted nonlethal LGTV infection in the spleen and the olfactory bulb following infection via a peripheral route. Viperin activity was also necessary to restrict LGTV replication in the olfactory bulb and the cerebrum following CNS infection, but not in the cerebellum. In vitro, viperin could restrict TBEV replication in primary cortical neurons, but not in the cerebellar granule cell neurons. Interferon-induced viperin was also very important in primary cortical neurons to control TBEV, WNV, and ZIKV.

    Conclusions: Our findings show that viperin restricts replication of neurotropic flaviviruses in the CNS in a region- and cell-type-specific manner. The most important sites of activity are the olfactory bulb and cerebrum. Activity within the cerebrum is required in the cortical neurons in order to restrict spread. This study exemplifies cell type and regional diversity of the IFN response within the CNS and shows the importance of a potent broad-spectrum antiviral ISG.

  • 16.
    Lindqvist, Richard
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology.
    Kurhade, Chaitanya
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology.
    Gilthorpe, Jonathan
    Umeå University, Faculty of Medicine, Department of Pharmacology and Clinical Neuroscience.
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology.
    Viperin restrict neurotropic flavivirus infection in cell type and region-specific mannerManuscript (preprint) (Other academic)
  • 17.
    Lindqvist, Richard
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Mundt, Filip
    Gilthorpe, Jonathan D.
    Umeå University, Faculty of Medicine, Department of Pharmacology and Clinical Neuroscience, Clinical Neuroscience.
    Woelfel, Silke
    Gekara, Nelson O.
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Kroeger, Andrea
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Fast type I interferon response protects astrocytes from flavivirus infection and virus-induced cytopathic effects2016In: Journal of Neuroinflammation, ISSN 1742-2094, E-ISSN 1742-2094, Vol. 13, article id 277Article in journal (Refereed)
    Abstract [en]

    Background: Neurotropic flaviviruses such as tick-borne encephalitis virus (TBEV), Japanese encephalitis virus (JEV), West Nile virus (WNV), and Zika virus (ZIKV) are causative agents of severe brain-related diseases including meningitis, encephalitis, and microcephaly. We have previously shown that local type I interferon response within the central nervous system (CNS) is involved in the protection of mice against tick-borne flavivirus infection. However, the cells responsible for mounting this protective response are not defined. Methods: Primary astrocytes were isolated from wild-type (WT) and interferon alpha receptor knock out (IFNAR(-/-)) mice and infected with neurotropic flaviviruses. Viral replication and spread, IFN induction and response, and cellular viability were analyzed. Transcriptional levels in primary astrocytes treated with interferon or supernatant from virus-infected cells were analyzed by RNA sequencing and evaluated by different bioinformatics tools. Results: Here, we show that astrocytes control viral replication of different TBEV strains, JEV, WNV, and ZIKV. In contrast to fibroblast, astrocytes mount a rapid interferon response and restrict viral spread. Furthermore, basal expression levels of key interferon-stimulated genes are high in astrocytes compared to mouse embryonic fibroblasts. Bioinformatic analysis of RNA-sequencing data reveals that astrocytes have established a basal antiviral state which contributes to the rapid viral recognition and upregulation of interferons. The most highly upregulated pathways in neighboring cells were linked to type I interferon response and innate immunity. The restriction in viral growth was dependent on interferon signaling, since loss of the interferon receptor, or its blockade in wild-type cells, resulted in high viral replication and virus-induced cytopathic effects. Astrocyte supernatant from TBEV-infected cells can restrict TBEV growth in astrocytes already 6 h post infection, the effect on neurons is highly reinforced, and astrocyte supernatant from 3 h post infection is already protective. Conclusions: These findings suggest that the combination of an intrinsic constitutive antiviral response and the fast induction of type I IFN production by astrocytes play an important role in self-protection of astrocytes and suppression of flavivirus replication in the CNS.

  • 18.
    Lindqvist, Richard
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Upadhyay, Arunkumar S.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Tick-Borne Flaviviruses and the Type I Interferon Response2018In: Viruses, ISSN 1999-4915, E-ISSN 1999-4915, Vol. 10, no 7, article id 340Article, review/survey (Refereed)
    Abstract [en]

    Flaviviruses are globally distributed pathogens causing millions of human infections every year. Flaviviruses are arthropod-borne viruses and are mainly transmitted by either ticks or mosquitoes. Mosquito-borne flaviviruses and their interactions with the innate immune response have been well-studied and reviewed extensively, thus this review will discuss tick-borne flaviviruses and their interactions with the host innate immune response.

  • 19. Lozach, Pierre-Yves
    et al.
    Mancini, Roberta
    Bitto, David
    Meier, Roger
    Oestereich, Lisa
    Överby, Anna K
    Ludwig Institute for Cancer Research, Stockholm Branch, Karolinska Institute, Box 10 240, SE-17177 Stockholm, Sweden.
    Pettersson, Ralf F
    Helenius, Ari
    Entry of bunyaviruses into mammalian cells2010In: Cell host & microbe, ISSN 1934-6069, Vol. 7, no 6, p. 488-499Article in journal (Refereed)
    Abstract [en]

    The Bunyaviridae constitute a large family of enveloped animal viruses, many members of which cause serious diseases. However, early bunyavirus-host cell interactions and entry mechanisms remain largely uncharacterized. Investigating Uukuniemi virus, a bunyavirus of the genus Phlebovirus, we found that virus attachment to the cell surface was specific but inefficient, with 25% of bound viruses being endocytosed within 10 min, mainly via noncoated vesicles. The viruses entered Rab5a+ early endosomes and, subsequently, Rab7a+ and LAMP-1+ late endosomes. Acid-activated penetration, occurring 20-40 min after internalization, required maturation of early to late endosomes. The pH threshold for viral membrane fusion was 5.4, and entry was sensitive to temperatures below 25 degrees C. Together, our results indicate that Uukuniemi virus penetrates host cells by acid-activated membrane fusion from late endosomal compartments. This study also highlights the importance of the degradative branch of the endocytic pathway in facilitating entry of late-penetrating viruses.

  • 20. Lund, Harald
    et al.
    Pieber, Melanie
    Parsa, Roham
    Han, Jinming
    Grommisch, David
    Ewing, Ewoud
    Kular, Lara
    Needhamsen, Maria
    Espinosa, Alexander
    Nilsson, Emma
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Butovsky, Oleg
    Jagodic, Maja
    Zhang, Xing-Mei
    Harris, Robert A.
    Competitive repopulation of an empty microglial niche yields functionally distinct subsets of microglia-like cells2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 4845Article in journal (Refereed)
    Abstract [en]

    Circulating monocytes can compete for virtually any tissue macrophage niche and become long-lived replacements that are phenotypically indistinguishable from their embryonic counterparts. As the factors regulating this process are incompletely understood, we studied niche competition in the brain by depleting microglia with >95% efficiency using Cx3cr1CreER/+R26DTA/+ mice and monitored long-term repopulation. Here we show that the microglial niche is repopulated within weeks by a combination of local proliferation of CX3CR1+F4/80lowClec12a microglia and infiltration of CX3CR1+F4/80hiClec12a+ macrophages that arise directly from Ly6Chi monocytes. This colonization is independent of blood brain barrier breakdown, paralleled by vascular activation, and regulated by type I interferon. Ly6Chi monocytes upregulate microglia gene expression and adopt microglia DNA methylation signatures, but retain a distinct gene signature from proliferating microglia, displaying altered surface marker expression, phagocytic capacity and cytokine production. Our results demonstrate that monocytes are imprinted by the CNS microenvironment but remain transcriptionally, epigenetically and functionally distinct.

  • 21.
    Panayiotou, Christakis
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Lindqvist, Richard
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Kurhade, Chaitanya
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Vonderstein, Kirstin
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Pasto, Jenny
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Edlund, Karin
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Upadhyay, Arunkumar S.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Viperin restricts Zika virus and tick-borne encephalitis virus replication by targeting NS3 for proteasomal degradation2018In: Journal of Virology, ISSN 0022-538X, E-ISSN 1098-5514, Vol. 92, no 7, article id e02054-17Article in journal (Refereed)
    Abstract [en]

    Flaviviruses are arthropod-borne viruses that constitute a major global health problem, with millions of human infections annually. Their pathogenesis ranges from mild illness to severe manifestations such as hemorrhagic fever and fatal encephalitis. Type I interferons (IFNs) are induced in response to viral infection and stimulate the expression of interferon-stimulated genes (ISGs), including that encoding viperin (virus-inhibitory protein, endoplasmic reticulum associated, IFN inducible), which shows antiviral activity against a broad spectrum of viruses, including several flaviviruses. Here we describe a novel antiviral mechanism employed by viperin against two prominent flaviviruses, tick-borne encephalitis virus (TBEV) and Zika virus (ZIKV). Viperin was found to interact and colocalize with the structural proteins premembrane (prM) and envelope (E) of TBEV, as well as with nonstructural (NS) proteins NS2A, NS2B, and NS3. Interestingly, viperin expression reduced the NS3 protein level, and the stability of the other interacting viral proteins, but only in the presence of NS3. We also found that although viperin interacted with NS3 of mosquito-borne flaviviruses (ZIKV, Japanese encephalitis virus, and yellow fever virus), only ZIKV was sensitive to the antiviral effect of viperin. This sensitivity correlated with viperin's ability to induce proteasome-dependent degradation of NS3. ZIKV and TBEV replication was rescued completely when NS3 was overexpressed, suggesting that the viral NS3 is the specific target of viperin. In summary, we present here a novel antiviral mechanism of viperin that is selective for specific viruses in the genus Flavivirus, affording the possible availability of new drug targets that can be used for therapeutic intervention.

    IMPORTANCE Flaviviruses are a group of enveloped RNA viruses that cause severe diseases in humans and animals worldwide, but no antiviral treatment is yet available. Viperin, a host protein produced in response to infection, effectively restricts the replication of several flaviviruses, but the exact molecular mechanisms have not been elucidated. Here we have identified a novel mechanism employed by viperin to inhibit the replication of two flaviviruses: tick-borne encephalitis virus (TBEV) and Zika virus (ZIKV). Viperin induced selective degradation via the proteasome of TBEV and ZIKV non-structural 3 (NS3) protein, which is involved in several steps of the viral life cycle. Furthermore, viperin also reduced the stability of several other viral proteins in a NS3-dependent manner, suggesting a central role of NS3 in viperin's antiflavivirus activity. Taking the results together, our work shows important similarities and differences among the members of the genus Flavivirus and could lead to the possibility of therapeutic intervention.

  • 22. Peña Cárcamo, José R.
    et al.
    Morell, María L.
    Vázquez, Cecilia A.
    Vatansever, Sezen
    Upadhyay, Arunkumar S.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Cordo, Sandra M.
    García, Cybele C.
    The interplay between viperin antiviral activity, lipid droplets and Junín mammarenavirus multiplication2018In: Virology, ISSN 0042-6822, E-ISSN 1096-0341, Vol. 514, p. 216-229Article in journal (Refereed)
    Abstract [en]

    Junín arenavirus infections are associated with high levels of interferons in both severe and fatal cases. Upon Junín virus (JUNV) infection a cell signaling cascade initiates, that ultimately attempts to limit viral replication and prevent infection progression through the expression of host antiviral proteins. The interferon stimulated gene (ISG) viperin has drawn our attention as it has been highlighted as an important antiviral protein against several viral infections. The studies of the mechanistic actions of viperin have described important functional domains relating its antiviral and immune-modulating actions through cellular lipid structures. In line with this, through silencing and overexpression approaches, we have identified viperin as an antiviral ISG against JUNV. In addition, we found that lipid droplet structures are modulated during JUNV infection, suggesting its relevance for proper virus multiplication. Furthermore, our confocal microscopy images, bioinformatics and functional results also revealed viperin-JUNV protein interactions that might be participating in this antiviral pathway at lipid droplet level. Altogether, these results will help to better understand the factors mediating innate immunity in arenavirus infection and may lead to the development of pharmacological agents that can boost their effectiveness thereby leading to new treatments for this viral disease.

  • 23. Rezelj, Veronica V
    et al.
    Överby, Anna K
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Elliott, Richard M
    Generation of mutant Uukuniemi viruses lacking the nonstructural protein NSs by reverse genetics indicates that NSs is a weak interferon antagonist.2015In: Journal of Virology, ISSN 0022-538X, E-ISSN 1098-5514, Vol. 89, no 9, p. 4849-4856Article in journal (Refereed)
    Abstract [en]

    Uukuniemi virus (UUKV) is a tick-borne member of the Phlebovirus genus (family Bunyaviridae) and has been widely used as a safe laboratory model to study aspects of bunyavirus replication. Recently, a number of new tick-borne phleboviruses have been discovered, some of which, like severe fever with thrombocytopenia syndrome virus and Heartland virus, are highly pathogenic in man. UUKV could now serve as a useful comparator to understand the molecular basis for the different pathogenicities of these related viruses. We established a reverse genetics system to recover UUKV entirely from cDNA clones. We generated two recombinant viruses, one in which the nonstructural protein NSs open reading frame was deleted from the S segment and one in which the NSs gene was replaced with GFP, allowing convenient visualization of viral infection. We show that the UUKV NSs protein acts as a weak interferon antagonist in human cells, but it is unable to completely counteract the interferon response, which could serve as an explanation for its inability to cause disease in man.

    IMPORTANCE: Uukuniemi virus (UUKV) is a tick-borne phlebovirus that is apathogenic for man and has been used as a convenient model to investigate aspects of phlebovirus replication. Recently new tick-borne phleboviruses have emerged, such as severe fever with thrombocytopenia syndrome virus in China and Heartland virus in the US, that are highly pathogenic, and UUKV will now serve as a comparison to aid understanding of the molecular basis for the virulence of these new viruses. To help such investigations, we have developed a reverse genetics system for UUKV that permits manipulation of the viral genome. We generated viruses lacking the nonstructural protein NSs and show that UUKV NSs is a weak interferon antagonist. In addition, we created a virus that expresses GFP and thus allows convenient monitoring of virus replication. These new tools represent a significant advance in the study of tick-borne phleboviruses.

  • 24.
    Rodrigues, Raquel
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Section of Virology.
    Danskog, Katarina
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Section of Virology.
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Section of Virology.
    Arnberg, Niklas
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Section of Virology.
    Characterizing the cellular attachment receptor for Langat virus2019In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 14, no 6, article id e0217359Article in journal (Refereed)
    Abstract [en]

    Tick-borne encephalitis infections have increased the last 30 years. The mortality associated to this viral infection is 0.5 to 30% with a risk of permanent neurological sequelae, however, no therapeutic is currently available. The first steps of virus-cell interaction, such as attachment and entry, are of importance to understand pathogenesis and tropism. Several molecules have been shown to interact with tick-borne encephalitis virus (TBEV) at the plasma membrane surface, yet, no studies have proven that these are specific entry receptors. In this study, we set out to characterize the cellular attachment receptor(s) for TBEV using the naturally attenuated member of the TBEV complex, Langat virus (LGTV), as a model. Inhibiting or cleaving different molecules from the surface of A549 cells, combined with inhibition assays using peptide extracts from high LGTV binding cells, revealed that LGTV attachment to host cells is dependent on plasma membrane proteins, but not on glycans or glycolipids, and suggested that LGTV might use different cellular attachment factors on different cell types. Based on this, we developed a transcriptomic approach to generate a list of candidate attachment and entry receptors. Our findings shed light on the first step of the flavivirus life-cycle and provide candidate receptors that might serve as a starting point for future functional studies to identify the specific attachment and/or entry receptor for LGTV and TBEV.

  • 25. Ruzek, Daniel
    et al.
    Zupanc, Tatjana Avsic
    Borde, Johannes
    Chrdle, Ales
    Eyer, Ludek
    Karganova, Galina
    Kholodilov, Ivan
    Knap, Natasa
    Kozlovskaya, Liubov
    Matveev, Andrey
    Miller, Andrew D.
    Osolodkin, Dmitry I.
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Section of Virology.
    Tikunova, Nina
    Tkachev, Sergey
    Zajkowska, Joanna
    Tick-borne encephalitis in Europe and Russia: review of pathogenesis, clinical features, therapy, and vaccines2019In: Antiviral Research, ISSN 0166-3542, E-ISSN 1872-9096, Vol. 164, p. 23-51Article, review/survey (Refereed)
    Abstract [en]

    Tick-borne encephalitis (TBE) is an illness caused by tick-borne encephalitis virus (TBEV) infection which is often limited to a febrile illness, but may lead to very aggressive downstream neurological manifestations. The disease is prevalent in forested areas of Europe and northeastern Asia, and is typically caused by infection involving one of three TBEV subtypes, namely the European (TBEV-Eu), the Siberian (TBEV-Sib), or the Far Eastern (TBEV-FE) subtypes. In addition to the three main TBEV subtypes, two other subtypes; i.e., the Baikalian (TBEV-Bkl) and the Himalayan subtype (TBEV-Him), have been described recently. In Europe, TBEV-Eu infection usually results in only mild TBE associated with a mortality rate of < 2%. TBEV-Sib infection also results in a generally mild TBE associated with a non-paralytic febrile form of encephalitis, although there is a tendency towards persistent TBE caused by chronic viral infection. TBE-FE infection is considered to induce the most severe forms of TBE. Importantly though, viral subtype is not the sole determinant of TBE severity; both mild and severe cases of TBE are in fact associated with infection by any of the subtypes. In keeping with this observation, the overall TBE mortality rate in Russia is similar to 2%, in spite of the fact that TBEV-Sib and TBEV-FE subtypes appear to be inducers of more severe TBE than TBEV-Eu. On the other hand, TBEV-Sib and TBEV-FE subtype infections in Russia are associated with essentially unique forms of TBE rarely seen elsewhere if at all, such as the hemorrhagic and chronic (progressive) forms of the disease. For post-exposure prophylaxis and TBE treatment in Russia and Kazakhstan, a specific anti-TBEV immunoglobulin is currently used with well-documented efficacy, but the use of specific TBEV immunoglobulins has been discontinued in Europe due to concerns regarding antibody-enhanced disease in naive individuals. Therefore, new treatments are essential. This review summarizes available data on the pathogenesis and clinical features of TBE, plus different vaccine preparations available in Europe and Russia. In addition, new treatment possibilities, including small molecule drugs and experimental immunotherapies are reviewed. The authors caution that their descriptions of approved or experimental therapies should not be considered to be recommendations for patient care.

  • 26.
    Upadhyay, Arunkumar S.
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Stehling, Oliver
    Panayiotou, Christakis
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Roesser, Ralf
    Lill, Roland
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Cellular requirements for iron-sulfur cluster insertion into the antiviral radical SAM protein viperin2017In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 292, no 33, p. 13879-13889Article in journal (Refereed)
    Abstract [en]

    Viperin (RSAD2) is an interferon-stimulated antiviral protein that belongs to the radical S-adenosylmethionine (SAM) enzyme family. Viperin's iron-sulfur (Fe/S) cluster is critical for its antiviral activity against many different viruses. CIA1 (CIAO1), an essential component of the cytosolic iron-sulfur protein assembly (CIA) machinery, is crucial for Fe/S cluster insertion into viperin and hence for viperin's antiviral activity. In the CIA pathway, CIA1 cooperates with CIA2A, CIA2B, and MMS19 targeting factors to form various complexes that mediate the dedicated maturation of specific Fe/S recipient proteins. To date, however, the mechanisms of how viperin acquires its radical SAM Fe/S cluster to gain antiviral activity are poorly understood. Using co-immunoprecipitation and Fe-55-radiolabeling experiments, we therefore studied the roles of CIA2A, CIA2B, and MMS19 for Fe/S cluster insertion. CIA2B and MMS19 physically interacted with the C terminus of viperin and used CIA1 as the primary viperin-interacting protein. In contrast, CIA2A bound to viperin's N terminus in a CIA1-, CIA2B-, and MMS19-independent fashion. Of note, the observed interaction of both CIA2 isoforms with a single Fe/S target protein is unprecedented in the CIA pathway. Fe-55-radiolabeling experiments with human cells depleted of CIA1, CIA2A, CIA2B, or MMS19 revealed that CIA1, but none of the other CIA factors, is predominantly required for (55F)e/S cluster incorporation into viperin. Collectively, viperin maturation represents a novel CIA pathway with a minimal requirement of the CIA-targeting factors and represents a new paradigm for the insertion of the Fe/S cofactor into a radical SAM protein.

  • 27.
    Upadhyay, Arunkumar S.
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Vonderstein, Kirstin
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Pichlmair, Andreas
    Stehling, Oliver
    Bennett, Keiryn L.
    Dobler, Gerhard
    Guo, Ju-Tao
    Superti-Furga, Giulio
    Lill, Roland
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Department of Virology, University Freiburg, D-79008Freiburg, Germany.
    Weber, Friedemann
    Viperin is an iron-sulfur protein that inhibits genome synthesis of tick-borne encephalitis virus via radical SAM domain activity2014In: Cellular Microbiology, ISSN 1462-5814, E-ISSN 1462-5822, Vol. 16, no 6, p. 834-848Article in journal (Refereed)
    Abstract [en]

    Viperin is an interferon-induced protein with a broad antiviral activity. This evolutionary conserved protein contains a radical S-adenosyl-l-methionine (SAM) domain which has been shown in vitro to hold a [4Fe-4S] cluster. We identified tick-borne encephalitis virus (TBEV) as a novel target for which human viperin inhibits productionof the viral genome RNA. Wt viperin was found to require ER localization for full antiviral activity and to interact with the cytosolic Fe/S protein assembly factor CIAO1. Radiolabelling in vivo revealed incorporation of Fe-55, indicative for the presence of an Fe-S cluster. Mutation of the cysteine residues ligating the Fe-S cluster in the central radical SAM domain entirely abolished both antiviral activity and incorporation of Fe-55. Mutants lacking the extreme C-terminal W361 did not interact with CIAO1, were not matured, and were antivirally inactive. Moreover, intracellular removal of SAM by ectopic expression of the bacteriophage T3 SAMase abolished antiviral activity. Collectively, our data suggest that viperin requires CIAO1 for [4Fe-4S] cluster assembly, and acts through an enzymatic, Fe-S cluster- and SAM-dependent mechanism to inhibit viral RNA synthesis.

  • 28.
    Upadhyay, Arunkumar S.
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Vonderstein, Kirstin
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Pichlmair, Andreas
    Stehling, Oliver
    Guo, Ju-Tao
    Lill, Roland
    Weber, Friedemann
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Viperin vs. tick-borne encephalitis virus: Mechanisms of a potent antiviral protein2013In: Cytokine, ISSN 1043-4666, E-ISSN 1096-0023, Vol. 63, no 3, p. 305-305Article in journal (Other academic)
  • 29. Verbruggen, Paul
    et al.
    Ruf, Marius
    Blakqori, Gjon
    Överby, Anna K
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Heidemann, Martin
    Eick, Dirk
    Weber, Friedemann
    Interferon antagonist NSs of La Crosse virus triggers a DNA damage response-like degradation of transcribing RNA polymerase II2011In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 286, no 5, p. 3681-3692Article in journal (Refereed)
    Abstract [en]

    La Crosse encephalitis virus (LACV) is a mosquito-borne member of the negative-strand RNA virus family Bunyaviridae. We have previously shown that the virulence factor NSs of LACV is an efficient inhibitor of the antiviral type I interferon system. A recombinant virus unable to express NSs (rLACVdelNSs) strongly induced interferon transcription, whereas the corresponding wt virus (rLACV) suppressed it. Here, we show that interferon induction by rLACVdelNSs mainly occurs through the signaling pathway leading from the pattern recognition receptor RIG-I to the transcription factor IRF-3. NSs expressed by rLACV, however, acts downstream of IRF-3 by specifically blocking RNA polymerase II-dependent transcription. Further investigations revealed that NSs induces proteasomal degradation of the mammalian RNA polymerase II subunit RPB1. NSs thereby selectively targets RPB1 molecules of elongating RNA polymerase II complexes, the so-called IIo form. This phenotype has similarities to the cellular DNA damage response, and NSs was indeed found to transactivate the DNA damage response gene pak6. Moreover, NSs expressed by rLACV boosted serine 139 phosphorylation of histone H2A.X, one of the earliest cellular reactions to damaged DNA. However, other DNA damage response markers such as up-regulation and serine 15 phosphorylation of p53 or serine 1524 phosphorylation of BRCA1 were not triggered by LACV infection. Collectively, our data indicate that the strong suppression of interferon induction by LACV NSs is based on a shutdown of RNA polymerase II transcription and that NSs achieves this by exploiting parts of the cellular DNA damage response pathway to degrade IIo-borne RPB1 subunits.

  • 30.
    Vonderstein, Kirstin
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Nilsson, Emma
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Hubel, Philipp
    Nygård Skalman, Lars
    Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics. Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Upadhyay, Arunkumar
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Pasto, Jenny
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Pichlmair, Andreas
    Lundmark, Richard
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics. Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Viperin targets flavivirus virulence by inducing assembly of non-infectious capsid particles2018In: Journal of Virology, ISSN 0022-538X, E-ISSN 1098-5514, Vol. 92, no 1, article id e01751-17Article in journal (Refereed)
    Abstract [en]

    Efficient antiviral immunity requires interference with virus replication at multiple layers targeting diverse steps in the viral life cycle. Here we describe a novel flavivirus inhibition mechanism that results in interferon-mediated obstruction of tick-borne encephalitis virus particle assembly, and involves release of malfunctional membrane associated capsid (C) particles. This mechanism is controlled by the activity of the interferon-induced protein viperin, a broad spectrum antiviral interferon stimulated gene. Through analysis of the viperin-interactome, we identified the Golgi Brefeldin A resistant guanine nucleotide exchange factor 1 (GBF1), as the cellular protein targeted by viperin. Viperin-induced antiviral activity as well as C-particle release was stimulated by GBF1 inhibition and knock down, and reduced by elevated levels of GBF1. Our results suggest that viperin targets flavivirus virulence by inducing the secretion of unproductive non-infectious virus particles, by a GBF1-dependent mechanism. This yet undescribed antiviral mechanism allows potential therapeutic intervention.Importance The interferon response can target viral infection on almost every level, however, very little is known about interference of flavivirus assembly. Here we show that interferon, through the action of viperin, can disturb assembly of tick-borne encephalitis virus. The viperin protein is highly induced after viral infection and exhibit broad-spectrum antiviral activity. However, the mechanism of action is still elusive and appear to vary between the different viruses, indicating that cellular targets utilized by several viruses might be involved. In this study we show that viperin induce capsid particle release by interacting and inhibiting the function of the cellular protein Golgi Brefeldin A resistant guanine nucleotide exchange factor 1 (GBF1). GBF1 is a key protein in the cellular secretory pathway and essential in the life cycle of many viruses, also targeted by viperin, implicating GBF1 as a novel putative drug target.

  • 31.
    Weber, Elvira
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Finsterbusch, Katja
    Innate Immunity and Infection, Helmholtz Centre for Infection Research, Braunschweig, Germany.
    Lindquist, Richard
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Nair, Sharmila
    Innate Immunity and Infection, Helmholtz Centre for Infection Research, Braunschweig, Germany.
    Lienenklaus, Stefan
    Department of Molecular Immunology, Helmholtz Centre for Infection Research, Braunschweig, Germany.
    Gekara, Nelson O
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Janik, Dirk
    Institute of Pathology, Helmholtz Center Munich, Neuherberg, Germany.
    Weiss, Siegfried
    Department of Molecular Immunology, Helmholtz Centre for Infection Research, Braunschweig, Germany.
    Kalinke, Ulrich
    Institute for Experimental Infection Research, TWINCORE, Hannover, Germany.
    Överby, Anna K
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Kröger, Andrea
    Innate Immunity and Infection, Helmholtz Centre for Infection Research, Braunschweig, Germany.
    Type I interferon protects mice from fatal neurotropic infection with Langat virus by systemic and local antiviral responses2014In: Journal of Virology, ISSN 0022-538X, E-ISSN 1098-5514, Vol. 89, no 21, p. 12202-12212Article in journal (Refereed)
    Abstract [en]

    Vector-borne flaviviruses, such as tick-borne encephalitis virus (TBEV), West Nile virus, and dengue virus, cause millions of infections in humans. TBEV causes a broad range of pathological symptoms, ranging from meningitis to severe encephalitis or even hemorrhagic fever, with high mortality. Despite the availability of an effective vaccine, the incidence of TBEV infections is increasing. Not much is known about the role of the innate immune system in the control of TBEV infections. Here, we show that the type I interferon (IFN) system is essential for protection against TBEV and Langat virus (LGTV) in mice. In the absence of a functional IFN system, mice rapidly develop neurological symptoms and succumb to LGTV and TBEV infections. Type I IFN system deficiency results in severe neuroinflammation in LGTV-infected mice, characterized by breakdown of the blood-brain barrier and infiltration of macrophages into the central nervous system (CNS). Using mice with tissue-specific IFN receptor deletions, we show that coordinated activation of the type I IFN system in peripheral tissues as well as in the CNS is indispensable for viral control and protection against virus induced inflammation and fatal encephalitis. IMPORTANCE: The type I interferon (IFN) system is important to control viral infections; however, the interactions between tick-borne encephalitis virus (TBEV) and the type I IFN system are poorly characterized. TBEV causes severe infections in humans that are characterized by fever and debilitating encephalitis, which can progress to chronic illness or death. No treatment options are available. An improved understanding of antiviral innate immune responses is pivotal for the development of effective therapeutics. We show that type I IFN, an effector molecule of the innate immune system, is responsible for the extended survival of TBEV and Langat virus (LGTV), an attenuated member of the TBE serogroup. IFN production and signaling appeared to be essential in two different phases during infection. The first phase is in the periphery, by reducing systemic LGTV replication and spreading into the central nervous system (CNS). In the second phase, the local IFN response in the CNS prevents virus-induced inflammation and the development of encephalitis.

  • 32.
    Weber, Elvira
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology.
    Finsterbusch, Katja
    Lindqvist, Richard
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Kroger, Andrea
    Överby, Anna
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Type I interferon protects against lethal Langat virus infection2013In: Cytokine, ISSN 1043-4666, E-ISSN 1096-0023, Vol. 63, no 3, p. 308-308Article in journal (Other academic)
  • 33. Zegenhagen, Loreen
    et al.
    Kurhade, Chaitanya
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Koniszewski, Nikolaus
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Kroeger, Andrea
    Brain heterogeneity leads to differential innate immune responses and modulates pathogenesis of viral infections2016In: Cytokine & growth factor reviews, ISSN 1359-6101, E-ISSN 1879-0305, Vol. 30, p. 95-101Article, review/survey (Refereed)
    Abstract [en]

    The central nervous system (CNS) is a highly complex organ with highly specialized cell subtypes. Viral infections often target specific structures of the brain and replicate in certain regions. Studies in mice deficient in type I Interferon (IFN) receptor or IFN-I3 have highlighted the importance of the type I IFN system against viral infections and non-viral autoimmune disorders in the CNS. Direct antiviral effects of type I IFNs appear to be crucial in limiting early spread of a number of viruses in CNS tissues. Increased efforts have been made to characterize IFN expression and responses in the brain. In this context, it is important to identify cells that produce IFN, decipher pathways leading to type I IFN expression and to characterize responding cells. In this review we give an overview about region specific aspects that influence local innate immune responses. The route of entry is critical, but also the susceptibility of different cell types, heterogeneity in subpopulations and micro-environmental cues play an important role in antiviral responses. Recent work has outlined the tremendous importance of type I IFNs, particularly in the limitation of viral spread within the CNS. This review will address recent advances in understanding the mechanisms of local type I IFN production and response, in the particular context of the CNS. 

  • 34. Zegenhagen, Loreen
    et al.
    Weber, Elvira
    Kurade, Chaitanya
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Nair, Sharmila
    Överby, Anna K.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Kroeger, Andrea
    Differential innate immune responses in various brain regions regulate antiviral response in the CNS during Tick-borne encephalitis virus infection2015In: Cytokine, ISSN 1043-4666, E-ISSN 1096-0023, Vol. 76, no 1, p. 91-91Article in journal (Other academic)
  • 35.
    Överby, Anna K
    et al.
    Ludwig Institute for Cancer Research, Stockholm Branch, Karolinska Institute, P.O. Box 240, S-17177 Stockholm, Sweden.
    Pettersson, R F
    Grünewald, K
    Huiskonen, J T
    Insights into bunyavirus architecture from electron cryotomography of Uukuniemi virus2008In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 105, no 7, p. 2375-2379Article in journal (Refereed)
    Abstract [en]

    Bunyaviridae is a large family of viruses that have gained attention as "emerging viruses" because many members cause serious disease in humans, with an increasing number of outbreaks. These negative-strand RNA viruses possess a membrane envelope covered by glycoproteins. The virions are pleiomorphic and thus have not been amenable to structural characterization using common techniques that involve averaging of electron microscopic images. Here, we determined the three-dimensional structure of a member of the Bunyaviridae family by using electron cryotomography. The genome, incorporated as a complex with the nucleoprotein inside the virions, was seen as a thread-like structure partially interacting with the viral membrane. Although no ordered nucleocapsid was observed, lateral interactions between the two membrane glycoproteins determine the structure of the viral particles. In the most regular particles, the glycoprotein protrusions, or "spikes," were seen to be arranged on an icosahedral lattice, with T = 12 triangulation. This arrangement has not yet been proven for a virus. Two distinctly different spike conformations were observed, which were shown to depend on pH. This finding is reminiscent of the fusion proteins of alpha-, flavi-, and influenza viruses, in which conformational changes occur in the low pH of the endosome to facilitate fusion of the viral and host membrane during viral entry.

  • 36.
    Överby, Anna K
    et al.
    Ludwig Institute for Cancer Research, Stockholm Branch, Karolinska Institute, Box 240, SE-17177 Stockholm, Sweden.
    Pettersson, Ralf F
    Neve, Etienne P A
    The glycoprotein cytoplasmic tail of Uukuniemi virus (Bunyaviridae) interacts with ribonucleoproteins and is critical for genome packaging2007In: Journal of Virology, ISSN 0022-538X, E-ISSN 1098-5514, Vol. 81, no 7, p. 3198-3205Article in journal (Refereed)
    Abstract [en]

    We have analyzed the importance of specific amino acids in the cytoplasmic tail of the glycoprotein G(N) for packaging of ribonucleoproteins (RNPs) into virus-like particles (VLPs) of Uukuniemi virus (UUK virus), a member of the Bunyaviridae family. In order to study packaging, we added the G(N)/G(C) glycoprotein precursor (p110) to a polymerase I-driven minigenome rescue system to generate VLPs that are released into the supernatant. These particles can infect new cells, and reporter gene expression can be detected. To determine the role of UUK virus glycoproteins in RNP packaging, we performed an alanine scan of the glycoprotein G(N) cytoplasmic tail (amino acids 1 to 81). First, we discovered three regions in the tail (amino acids 21 to 25, 46 to 50, and 71 to 81) which are important for minigenome transfer by VLPs. Further mutational analysis identified four amino acids that were important for RNP packaging. These amino acids are essential for the binding of nucleoproteins and RNPs to the glycoprotein without affecting the morphology of the particles. No segment-specific interactions between the RNA and the cytoplasmic tail could be observed. We propose that VLP systems are useful tools for analyzing protein-protein interactions important for packaging of viral genome segments, assembly, and budding of other members of the Bunyaviridae family.

  • 37.
    Överby, Anna K
    et al.
    Department of Virology, Institute for Medical Microbiology and Hygiene, University of Freiburg, D-79008 Freiburg, Germany.
    Popov, Vsevolod L
    Niedrig, Matthias
    Weber, Friedemann
    Tick-borne encephalitis virus delays interferon induction and hides its double-stranded RNA in intracellular membrane vesicles2010In: Journal of Virology, ISSN 0022-538X, E-ISSN 1098-5514, Vol. 84, no 17, p. 8470-8483Article in journal (Refereed)
    Abstract [en]

    Tick-borne encephalitis virus (TBEV) (family Flaviviridae, genus Flavivirus) accounts for approximately 10,000 annual cases of severe encephalitis in Europe and Asia. Here, we investigated the induction of the antiviral type I interferons (IFNs) (alpha/beta IFN [IFN-alpha/beta]) by TBEV. Using strains Neudörfl, Hypr, and Absettarov, we demonstrate that levels of IFN-beta transcripts and viral RNA are strictly correlated. Moreover, IFN induction by TBEV was dependent on the transcription factor IFN regulatory factor 3 (IRF-3). However, even strain Hypr, which displayed the strongest IFN-inducing activity and the highest RNA levels, substantially delayed the activation of IRF-3. As a consequence, TBEV can keep the level of IFN transcripts below the threshold value that would permit the release of IFN by the cell. Only after 24 h of infection have cells accumulated sufficient IFN transcripts to produce detectable amounts of secreted IFNs. The delay in IFN induction appears not to be caused by a specific viral protein, since the individual expressions of TBEV C, E, NS2A, NS2B, NS3, NS4A, NS4B, NS5, and NS2B-NS3, as well as TBEV infection itself, had no apparent influence on specific IFN-beta induction. We noted, however, that viral double-stranded RNA (dsRNA), an important trigger of the IFN response, is immunodetectable only inside intracellular membrane compartments. Nonetheless, the dependency of IFN induction on IFN promoter stimulator 1 (IPS-1) as well as the phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2alpha) suggest the cytoplasmic exposure of some viral dsRNA late in infection. Using ultrathin-section electron microscopy, we demonstrate that, similar to other flaviviruses, TBEV rearranges intracellular membranes. Virus particles and membrane-connected vesicles (which most likely represent sites of virus RNA synthesis) were observed inside the endoplasmic reticulum. Thus, apparently, TBEV rearranges internal cell membranes to provide a compartment for its dsRNA, which is largely inaccessible for detection by cytoplasmic pathogen receptors. This delays the onset of IFN induction sufficiently to give progeny particle production a head start of approximately 24 h.

  • 38.
    Överby, Anna K
    et al.
    Ludwig Institute for Cancer Research, Stockholm Branch, Karolinska Institute, Box 240, SE-17177 Stockholm, Sweden.
    Popov, Vsevolod L
    Pettersson, Ralf F
    Neve, Etienne P A
    The cytoplasmic tails of Uukuniemi Virus (Bunyaviridae) G(N) and G(C) glycoproteins are important for intracellular targeting and the budding of virus-like particles2007In: Journal of Virology, ISSN 0022-538X, E-ISSN 1098-5514, Vol. 81, no 20, p. 11381-11391Article in journal (Refereed)
    Abstract [en]

    Functional motifs within the cytoplasmic tails of the two glycoproteins G(N) and G(C) of Uukuniemi virus (UUK) (Bunyaviridae family) were identified with the help of our recently developed virus-like particle (VLP) system for UUK virus (A. K. Overby, V. Popov, E. P. Neve, and R. F. Pettersson, J. Virol. 80:10428-10435, 2006). We previously reported that information necessary for the packaging of ribonucleoproteins into VLPs is located within the G(N) cytoplasmic tail (A. K. Overby, R. F. Pettersson, and E. P. Neve, J. Virol. 81:3198-3205, 2007). The G(N) glycoprotein cytoplasmic tail specifically interacts with the ribonucleoproteins and is critical for genome packaging. In addition, two other regions in the G(N) cytoplasmic tail, encompassing residues 21 to 25 and 46 to 50, were shown to be important for particle generation and release. By the introduction of point mutations within these two regions, we demonstrate that leucines at positions 23 and 24 are crucial for the initiation of VLP budding, while leucine 46, glutamate 47, and leucine 50 are important for efficient exit from the endoplasmic reticulum and subsequent transport to the Golgi complex. We found that budding and particle generation are highly dependent on the intracellular localization of both glycoproteins. The short cytoplasmic tail of UUK G(C) contains a lysine at position -3 from the C terminus that is highly conserved among members of the Phlebovirus, Hantavirus, and Orthobunyavirus genera. Mutating this single amino acid residue in G(C) resulted in the mislocalization of not only G(C) but also G(N) to the plasma membrane, and VLP generation was compromised in cells expressing this mutant. Together, these results demonstrate that the cytoplasmic tails of both G(N) and G(C) contain specific information necessary for efficient virus particle generation.

  • 39.
    Överby, Anna K
    et al.
    Ludwig Institute for Cancer Research, Stockholm Branch, Karolinska Institute, Stockholm, Sweden.
    Popov, Vsevolod
    Neve, Etienne P A
    Pettersson, Ralf F
    Generation and analysis of infectious virus-like particles of uukuniemi virus (bunyaviridae): a useful system for studying bunyaviral packaging and budding2006In: Journal of Virology, ISSN 0022-538X, E-ISSN 1098-5514, Vol. 80, no 21, p. 10428-10435Article in journal (Refereed)
    Abstract [en]

    In the present report we describe an infectious virus-like particle (VLP) system for the Uukuniemi (UUK) virus, a member of the Bunyaviridae family. It utilizes our recently developed reverse genetic system based on the RNA polymerase I minigenome system for UUK virus used to study replication, encapsidation, and transcription by monitoring reporter gene expression. Here, we have added the glycoprotein precursor expression plasmid together with the minigenome, nucleoprotein, and polymerase to generate VLPs, which incorporate the minigenome and are released into the supernatant. The particles are able to infect new cells, and reporter gene expression can be monitored if the trans-acting viral proteins (RNA polymerase and nucleoprotein) are also expressed in these cells. No minigenome transfer occurred in the absence of glycoproteins, demonstrating that the glycoproteins are absolutely required for the generation of infectious particles. Moreover, expression of glycoproteins alone was sufficient to produce and release VLPs. We show that the ribonucleoproteins (RNPs) are incorporated into VLPs but are not required for the generation of particles. Morphological analysis of the particles by electron microscopy revealed that VLPs, either with or without minigenomes, display a surface morphology indistinguishable from that of the authentic UUK virus and that they bud into Golgi vesicles in the same way as UUK virus does. This infectious VLP system will be very useful for studying the bunyaviral structural components required for budding and packaging of RNPs and receptor binding and may also be useful for the development of new vaccines for the human pathogens from this family.

  • 40.
    Överby, Anna
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Nilsson, Emma
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Virology.
    Det tidiga immunförsvaret nyckel i kampen mot TBE-virus2014In: Neurologi i Sverige, ISSN 2000-8538, Vol. 2, no 14, p. 68-74Article in journal (Other academic)
  • 41.
    Överby Wernstedt, Anna
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology.
    Weber, Friedemann
    Hiding from intracellular pattern recognition receptors, a passive strategy of flavivirus immune evasion2011In: Virulence, ISSN 2150-5594, E-ISSN 2150-5608, Vol. 2, no 3, p. 238-240Article in journal (Refereed)
    Abstract [en]

    Tick-borne encephalitis virus (TBEV) is a medically important flavivirus in Europe and Asia, causing meningitis and encephalitis in thousands of people annually. Despite its relevance for public health, the interaction of TBEV with the type I interferon (IFN) system is poorly characterized. Induction of these antiviral cytokines is normally triggered by cytoplasmic recognition of viral signature molecules such as double-stranded (ds) RNA. In a recent paper, we showed that TBEV infection leads to formation of intracellular membrane vesicles which protect the viral dsRNA from cellular recognition. This delays the onset of antiviral IFN production sufficiently enough for an unhindered release of progeny viruses over 24 h. Thus, TBEV has evolved a stealth strategy to outrun the antiviral IFN response.

  • 42.
    Överby Wernstedt, Anna
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Microbiology.
    Weber, Friedemann
    Hiding from intracellular pattern recognition receptors, a passive strategy of flavivirus immune evasion2011Conference paper (Refereed)
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