101
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Tasaka M, Sakamoto N, Itakura Y, Nakagawa M, Itsui Y, Sekine-Osajima Y, Nishimura-Sakurai Y, Chen CH, Yoneyama M, Fujita T, Wakita T, Maekawa S, Enomoto N, Watanabe M. Hepatitis C virus non-structural proteins responsible for suppression of the RIG-I/Cardif-induced interferon response. J Gen Virol 2007; 88:3323-3333. [DOI: 10.1099/vir.0.83056-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Viral infections activate cellular expression of type I interferons (IFNs). These responses are partly triggered by RIG-I and mediated by Cardif, TBK1, IKKϵ and IRF-3. This study analysed the mechanisms of dsRNA-induced IFN responses in various cell lines that supported subgenomic hepatitis C virus (HCV) replication. Transfection of dsRNA into Huh7, HeLa and HEK293 cells induced an IFN expression response as shown by IRF-3 dimerization, whilst these responses were abolished in corresponding cell lines that expressed HCV replicons. Similarly, RIG-I-dependent activation of the IFN-stimulated response element (ISRE) was significantly suppressed by cells expressing the HCV replicon and restored in replicon-eliminated cells. Overexpression analyses of individual HCV non-structural proteins revealed that NS4B, as well as NS34A, significantly inhibited RIG-I-triggered ISRE activation. Taken together, HCV replication and protein expression substantially blocked the dsRNA-triggered, RIG-I-mediated IFN expression response and this blockade was partly mediated by HCV NS4B, as well as NS34A. These mechanisms may contribute to the clinical persistence of HCV infection and could constitute a novel antiviral therapeutic target.
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Affiliation(s)
- Megumi Tasaka
- Department of Gastroenterology and Hepatology, Tokyo Medical and Dental University, Tokyo, Japan
| | - Naoya Sakamoto
- Department for Hepatitis Control, Tokyo Medical and Dental University, Tokyo, Japan
- Department of Gastroenterology and Hepatology, Tokyo Medical and Dental University, Tokyo, Japan
| | - Yoshie Itakura
- First Department of Internal Medicine, University of Yamanashi, Yamanashi, Japan
- Department of Gastroenterology and Hepatology, Tokyo Medical and Dental University, Tokyo, Japan
| | - Mina Nakagawa
- Department for Hepatitis Control, Tokyo Medical and Dental University, Tokyo, Japan
- Department of Gastroenterology and Hepatology, Tokyo Medical and Dental University, Tokyo, Japan
| | - Yasuhiro Itsui
- Department of Gastroenterology and Hepatology, Tokyo Medical and Dental University, Tokyo, Japan
| | - Yuko Sekine-Osajima
- Department of Gastroenterology and Hepatology, Tokyo Medical and Dental University, Tokyo, Japan
| | - Yuki Nishimura-Sakurai
- Department of Gastroenterology and Hepatology, Tokyo Medical and Dental University, Tokyo, Japan
| | - Cheng-Hsin Chen
- Department of Gastroenterology and Hepatology, Tokyo Medical and Dental University, Tokyo, Japan
| | - Mitsutoshi Yoneyama
- Laboratory of Molecular Genetics, Department of Genetics and Molecular Biology, Institute for Virus Research, Kyoto University, Kyoto, Japan
| | - Takashi Fujita
- Laboratory of Molecular Genetics, Department of Genetics and Molecular Biology, Institute for Virus Research, Kyoto University, Kyoto, Japan
| | - Takaji Wakita
- Department of Virology II, National Institute of Infectious Diseases, Tokyo, Japan
| | - Shinya Maekawa
- First Department of Internal Medicine, University of Yamanashi, Yamanashi, Japan
| | - Nobuyuki Enomoto
- First Department of Internal Medicine, University of Yamanashi, Yamanashi, Japan
| | - Mamoru Watanabe
- Department of Gastroenterology and Hepatology, Tokyo Medical and Dental University, Tokyo, Japan
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102
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Sutton RE. What does the future hold for viral gene therapy? Future Virol 2007. [DOI: 10.2217/17460794.2.6.543] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
- Richard E Sutton
- Baylor College of Medicine, Department of Molecular Virology & Microbiology, Department of Medicine, Division of Infectious Diseases, Center for Cell & Gene Therapy, 1 Baylor Plaza, Houston, TX 77030, USA
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103
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Salgado-Pabón W, Jain S, Turner N, van der Does C, Dillard JP. A novel relaxase homologue is involved in chromosomal DNA processing for type IV secretion in Neisseria gonorrhoeae. Mol Microbiol 2007; 66:930-47. [PMID: 17927698 PMCID: PMC2586181 DOI: 10.1111/j.1365-2958.2007.05966.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The Neisseria gonorrhoeae type IV secretion system secretes chromosomal DNA that acts in natural transformation. To examine the mechanism of DNA processing for secretion, we made mutations in the putative relaxase gene traI and used nucleases to characterize the secreted DNA. The nuclease experiments demonstrated that the secreted DNA is single-stranded and blocked at the 5' end. Mutation of traI identified Tyr93 as required for DNA secretion, while substitution of Tyr201 resulted in intermediate levels of DNA secretion. TraI exhibits features of relaxases, but also has features that are absent in previously characterized relaxases, including an HD phosphohydrolase domain and an N-terminal hydrophobic region. The HD domain residue Asp120 was required for wild-type levels of DNA secretion. Subcellular localization studies demonstrated that the TraI N-terminal region promotes membrane interaction. We propose that Tyr93 initiates DNA processing and Tyr201 is required for termination or acts in DNA binding. Disruption of an inverted-repeat sequence eliminated DNA secretion, suggesting that this sequence may serve as the origin of transfer for chromosomal DNA secretion. The TraI domain architecture, although not previously described, is present in 53 uncharacterized proteins, suggesting that the mechanism of TraI function is a widespread process for DNA donation.
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Affiliation(s)
- Wilmara Salgado-Pabón
- Department of Medical Microbiology and Immunology, University of Wisconsin-Madison, Madison, WI 53706, USA
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104
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Abstract
Hepatitis C virus (HCV) encodes a single polyprotein, which is processed by cellular and viral proteases to generate 10 polypeptides. The HCV genome also contains an overlapping +1 reading frame that may lead to the synthesis of an additional protein. Until recently, studies of HCV have been hampered by the lack of a productive cell culture system. Since the identification of HCV genome approximately 17 years ago, structural, biochemical and biological information on HCV proteins has mainly been obtained with proteins produced by heterologous expression systems. In addition, some functional studies have also been confirmed with replicon systems or with retroviral particles pseudotyped with HCV envelope glycoproteins. The data that have accumulated on HCV proteins begin to provide a framework for understanding the molecular mechanisms involved in the major steps of HCV life cycle. Moreover, the knowledge accumulated on HCV proteins is also leading to the development of antiviral drugs among which some are showing promising results in early-phase clinical trials. This review summarizes the current knowledge on the functions and biochemical features of HCV proteins.
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Affiliation(s)
- Jean Dubuisson
- Hepatitis C Laboratory, CNRS-UMR8161, Institut de Biologie de Lille I & II, Université de Lille, 1 rue Calmette, BP447, 59021 Lille Cedex, France.
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105
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Pawlotsky JM, Chevaliez S, McHutchison JG. The hepatitis C virus life cycle as a target for new antiviral therapies. Gastroenterology 2007; 132:1979-98. [PMID: 17484890 DOI: 10.1053/j.gastro.2007.03.116] [Citation(s) in RCA: 247] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/22/2007] [Accepted: 03/23/2007] [Indexed: 12/11/2022]
Abstract
The burden of disease consequent to hepatitis C virus (HCV) infection has been well described and is expected to increase dramatically over the next decade. Current approved antiviral therapies are effective in eradicating the virus in approximately 50% of infected patients. However, pegylated interferon and ribavirin-based therapy is costly, prolonged, associated with significant adverse effects, and not deemed suitable for many HCV-infected patients. As such, there is a clear and pressing need for the development of additional agents that act through alternate or different mechanisms, in the hope that such regimens could lead to enhanced response rates more broadly applicable to patients with hepatitis C infection. Recent basic science enhancements in HCV cell culture systems and replication assays have led to a broadening of our understanding of many of the mechanisms of HCV replication and, therefore, potential novel antiviral targets. In this article, we have attempted to highlight important new information as it relates to our understanding of the HCV life cycle. These steps broadly encompass viral attachment, entry, and fusion; viral RNA translation; posttranslational processing; HCV replication; and viral assembly and release. In each of these areas, we present up-to-date knowledge of the relevant aspects of that component of the viral life cycle and then describe the preclinical and clinical development targets and pathways being explored in the translational and clinical settings.
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Affiliation(s)
- Jean-Michel Pawlotsky
- French National Reference Center for Viral Hepatitis B, C, and delta, Department of Virology, Hôpital Henri Mondor, Université Paris 12, Créteil, France.
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106
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Welker MW, Hofmann WP, Welsch C, von Wagner M, Herrmann E, Lengauer T, Zeuzem S, Sarrazin C. Correlation of amino acid variations within nonstructural 4B protein with initial viral kinetics during interferon-alpha-based therapy in HCV-1b-infected patients. J Viral Hepat 2007; 14:338-49. [PMID: 17439523 DOI: 10.1111/j.1365-2893.2006.00798.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Chronic hepatitis C is a major cause of liver cirrhosis leading to chronic liver failure and hepatocellular carcinoma. Different hepatitis C virus (HCV) proteins have been associated with resistance to interferon-alpha-based therapy. However, the exact mechanisms of virus-mediated interferon resistance are not completely understood. The importance of amino acid (aa) variations within the HCV nonstructural (NS)4B protein for replication efficiency and viral decline during the therapy is unknown. We investigated pretreatment sera from 42 patients with known outcome to interferon-based therapy. The complete NS4B gene was amplified and sequenced. Mutational analyses of predicted conformational, functional, structural and phylogenetic properties of the deduced aa sequences were performed. The complete NS4B protein was highly conserved with a median frequency of 0.015 +/- 0.009 aa exchanges (median +/- SD, 4.00 +/- 2.31). Especially within the predicted transmembranous domains of the NS4B protein, the mean number of aa variations was low (median frequency, 0.013 +/- 0.013). Neither the number of aa variations nor specific aa exchanges were correlated with HCV RNA serum concentration at baseline. A rapid initial HCV RNA decline of >/=1.5 log(10) IU/mL at week 2 of interferon-based therapy was associated with a higher frequency of nonconservative aa exchanges within the complete NS4B protein in comparison with patients with a nonrapid HCV RNA decline (median frequency, 0.011 +/- 0.005 vs 0.004 +/- 0.003, P = 0.006). Overall, the aa sequence of the NS4B protein was highly conserved, indicating an important role for replication in vivo. Amino acid variations with relevant changes of physicochemical properties may influence replication efficiency, associated with a rapid early virological response.
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Affiliation(s)
- M-W Welker
- Klinik für Innere Medizin II, Universitätsklinikum des Saarlandes, Homburg/Saar, Germany
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107
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Welsch C, Albrecht M, Maydt J, Herrmann E, Welker MW, Sarrazin C, Scheidig A, Lengauer T, Zeuzem S. Structural and functional comparison of the non-structural protein 4B in flaviviridae. J Mol Graph Model 2007; 26:546-57. [PMID: 17507273 DOI: 10.1016/j.jmgm.2007.03.012] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2006] [Revised: 03/23/2007] [Accepted: 03/28/2007] [Indexed: 12/27/2022]
Abstract
Flaviviridae are evolutionarily related viruses, comprising the hepatitis C virus (HCV), with the non-structural protein 4B (NS4B) as one of the least characterized proteins. NS4B is located in the endoplasmic reticulum membrane and is assumed to be a multifunctional protein. However, detailed structure information is missing. The hydrophobic nature of NS4B is a major difficulty for many experimental techniques. We applied bioinformatics methods to analyse structural and functional properties of NS4B in different viruses. We distinguish a central non-globular membrane portion with four to five transmembrane regions from an N- and C-terminal part with non-transmembrane helical elements. We demonstrate high similarity in sequence and structure for the C-terminal part within the flaviviridae family. A palmitoylation site contained in the C-terminal part of HCV is equally conserved in GB virus B. Furthermore, we identify and characterize an N-terminal basic leucine zipper (bZIP) motif in HCV, which is suggestive of a functionally important interaction site. In addition, we model the interaction of the bZIP region with the recently identified interaction partner CREB-RP/ATF6beta, a human activating transcription factor involved in ER-stress. In conclusion, the versatile structure, together with functional sites and motifs, possibly enables NS4B to adopt a role as protein hub in the membranous web interaction network of virus and host proteins. Important structural and functional properties of NS4B are predicted with implications for ER-stress response, altered gene expression and replication efficacy.
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Affiliation(s)
- Christoph Welsch
- Internal Medicine II, Saarland University Hospital, Kirrberger Strasse, 66421 Homburg/Saar, Germany.
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108
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Blight KJ. Allelic variation in the hepatitis C virus NS4B protein dramatically influences RNA replication. J Virol 2007; 81:5724-36. [PMID: 17360748 PMCID: PMC1900245 DOI: 10.1128/jvi.02481-06] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
In the Huh-7.5 hepatoma cell line, replication of the genotype 1a H77 strain of hepatitis C virus (HCV) is attenuated compared to that of the genotype 1b Con1 strain. This study identifies the poorly characterized integral membrane protein, NS4B, as a major determinant for this replication difference. Chimeric H77 subgenomic replicons containing the entire NS4B gene from Con1 in place of the H77 NS4B sequence replicated approximately 10-fold better than the H77 parent and to levels similar to that of the adapted Con1 replicon. An intermediate level of replication enhancement was conferred by H77 chimeras containing the poorly conserved N-terminal 47 residues or the remaining less-divergent C terminus of Con1 NS4B. The replication-enhancing activity within the N terminus of NS4B was further mapped to two Con1-specific amino acids. Experiments to elucidate the mechanism of enhanced H77 replication revealed that Con1 NS4B primarily increased H77 RNA synthesis on a per cell basis, as indicated by the similar capacities of chimeric and parental replicons to establish replication in Huh-7.5 cells and the higher levels of both positive- and negative-strand RNAs for the chimeras than for the H77 parent. Additionally, enhanced H77 replication was not the result of Con1 NS4B-mediated effects on HCV translation efficiency or alterations in polyprotein processing. Expression of Con1 NS4B in trans did not improve the replication of the H77 parental replicon, suggesting a cis-dominant role for NS4B in HCV replication. These results provide the first evidence that allelic variation in the NS4B sequence between closely related isolates significantly impacts HCV replication in cell culture.
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Affiliation(s)
- Keril J Blight
- Department of Molecular Microbiology, Center for Infectious Disease Research, Washington University School of Medicine, 660 South Euclid Ave., Campus Box 8230, St. Louis, MO 63110, USA.
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109
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Van Wynsberghe PM, Chen HR, Ahlquist P. Nodavirus RNA replication protein a induces membrane association of genomic RNA. J Virol 2007; 81:4633-44. [PMID: 17301137 PMCID: PMC1900146 DOI: 10.1128/jvi.02267-06] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Positive-strand RNA virus genome replication occurs in membrane-associated RNA replication complexes, whose assembly remains poorly understood. Here we show that prior to RNA replication, the multifunctional, transmembrane RNA replication protein A of the nodavirus flock house virus (FHV) recruits FHV genomic RNA1 to a membrane-associated state in both Drosophila melanogaster and Saccharomyces cerevisiae cells. Protein A has mitochondrial membrane-targeting, self-interaction, RNA-dependent RNA polymerase (RdRp), and RNA capping domains. In the absence of RdRp activity due to an active site mutation (A(D692E)), protein A stimulated RNA1 accumulation by increasing RNA1 stability. Protein A(D692E) stimulated RNA1 accumulation in wild-type cells and in xrn1(-) yeast defective in decapped RNA decay, showing that increased RNA1 stability was not due to protein A-mediated RNA1 recapping. Increased RNA1 stability was closely linked with protein A-induced membrane association of the stabilized RNA and was highly selective for RNA1. Substantial N- and C-proximal regions of protein A were dispensable for these activities. However, increased RNA1 accumulation was eliminated by deleting protein A amino acids (aa) 1 to 370 but was restored completely by adding back the transmembrane domain (aa 1 to 35) and partially by adding back peripheral membrane association sequences in aa 36 to 370. Moreover, although RNA polymerase activity was not required, even small deletions in or around the RdRp domain abolished increased RNA1 accumulation. These and other results show that prior to negative-strand RNA synthesis, multiple domains of mitochondrially targeted protein A cooperate to selectively recruit FHV genomic RNA to membranes where RNA replication complexes form.
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Affiliation(s)
- Priscilla M Van Wynsberghe
- Institute for Molecular Virology, University of Wisconsin-Madison, 1525 Linden Drive, Madison, WI 53706-1596, USA
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110
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Lundin M, Lindström H, Grönwall C, Persson MAA. Dual topology of the processed hepatitis C virus protein NS4B is influenced by the NS5A protein. J Gen Virol 2006; 87:3263-3272. [PMID: 17030859 DOI: 10.1099/vir.0.82211-0] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Among the least-known hepatitis C virus proteins is the non-structural protein 4B (NS4B). It localizes to the endoplasmic reticulum (ER) membrane and induces membrane changes, resulting in a membranous web that is reported to be the locale for virus replication. A model was presented previously for the topology of recombinant HCV NS4B of the 1a genotype based on in vitro data. In this model, the N-terminal tail of a considerable fraction of the NS4B molecules was translocated into the ER lumen via a post-translational process, giving the protein a dual transmembrane topology. It is now reported that translocation of the N terminus also occurs for processed NS4B expressed in cells in the context of the polyprotein. In the presence of NS5A, however, a lower degree of translocation was observed, which may indicate that NS5A influences the topology of NS4B. In vitro expression studies of NS4B from all major genotypes demonstrated that translocation of the N terminus to the ER lumen is conserved across genotypes. This clearly suggests an important function for this feature. Furthermore, when disrupting a previously reported amphipathic helix (AH) in the N terminus of NS4B, translocation was inhibited. As a disrupted AH also abolished the ability of NS4B to rearrange membranes, these data indicate for the first time an association between translocation of the N terminus and membrane rearrangement. Finally, the present experiments also confirm the predicted location of the first luminal loop to be around aa 112.
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Affiliation(s)
- Marika Lundin
- Karolinska Institutet, Department of Medicine at Center for Molecular Medicine (L8 : 01), Karolinska University Hospital Solna, S-171 76 Stockholm, Sweden
| | - Hannah Lindström
- Karolinska Institutet, Department of Medicine at Center for Molecular Medicine (L8 : 01), Karolinska University Hospital Solna, S-171 76 Stockholm, Sweden
| | - Caroline Grönwall
- The Royal Institute of Technology, Department of Biotechnology, Alba Nova University Centre, Stockholm, Sweden
| | - Mats A A Persson
- Karolinska Institutet, Department of Medicine at Center for Molecular Medicine (L8 : 01), Karolinska University Hospital Solna, S-171 76 Stockholm, Sweden
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111
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Qureshi SA. Hepatitis C virus-biology, host evasion strategies, and promising new therapies on the horizon. Med Res Rev 2006; 27:353-73. [PMID: 16958135 DOI: 10.1002/med.20063] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Hepatitis C reduces the quality of life for some 170 million people around the globe and is one of the most prevalent diseases on the planet. It is caused by the hepatitis C virus (HCV) that is replicated by an error-prone polymerase and therefore undergoes rapid evolution. To date, although much has been learned about the biology of HCV, only a partially effective combination therapy comprised of ribavirin and pegylated-interferon-alpha is available to hepatitis C sufferers. Given the prevalence of hepatitis C, together with the fact that almost half the chronically infected HCV patients are refractory to current therapy, there is an urgent need for an efficacious immunoprophylactic that protects individuals from HCV infection, as well as drugs that impede the viral life cycle effectively and eradicate infection. Herein, I provide an overview of the molecular biology of HCV, highlighting the functions of different virally encoded proteins in terms of how they alter signaling pathways of host cell to establish an infection and discuss whether a more promising therapy for treating hepatitis C is anywhere in sight.
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Affiliation(s)
- Sohail A Qureshi
- Department of Biological & Biomedical Sciences, The Aga Khan University Hospital, Karachi 74800, Pakistan.
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112
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Yu GY, Lee KJ, Gao L, Lai MMC. Palmitoylation and polymerization of hepatitis C virus NS4B protein. J Virol 2006; 80:6013-23. [PMID: 16731940 PMCID: PMC1472571 DOI: 10.1128/jvi.00053-06] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Hepatitis C Virus (HCV) NS4B protein induces a specialized membrane structure which may serve as the replication platform for HCV RNA replication. In the present study, we demonstrated that NS4B has lipid modifications (palmitoylation) on two cysteine residues (cysteines 257 and 261) at the C-terminal end. Site-specific mutagenesis of these cysteine residues on individual NS4B proteins and on an HCV subgenomic replicon showed that the lipid modifications, particularly of Cys261, are important for protein-protein interaction in the formation of the HCV RNA replication complex. We further demonstrated that NS4B can undergo polymerization. The main polymerization determinants were mapped in the N-terminal cytosolic domain of NS4B protein; however, the lipid modifications on the C terminus also facilitate the polymerization process. The lipid modification and the polymerization activity could be two properties of NS4B important for its induction of the specialized membrane structure involved in viral RNA replication.
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Affiliation(s)
- Guann-Yi Yu
- Department of Molecular Microbiology and Immunology, University of Southern California Keck School of Medicine, Los Angeles, CA 90033-1054, USA
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113
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Lindström H, Lundin M, Häggström S, Persson MAA. Mutations of the Hepatitis C virus protein NS4B on either side of the ER membrane affect the efficiency of subgenomic replicons. Virus Res 2006; 121:169-78. [PMID: 16806556 DOI: 10.1016/j.virusres.2006.05.008] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2006] [Revised: 05/12/2006] [Accepted: 05/24/2006] [Indexed: 11/19/2022]
Abstract
The non-structural protein NS4B of the Hepatitis C virus (HCV) is an integral membrane protein located in the endoplasmic reticulum (ER). Although the function of the NS4B in the viral life cycle is unknown a critical role in replication has been indicated. In order to investigate which components are involved we initially introduced restriction sites near the extremities of the NS4B in a subgenomic replicon that resulted in the alterations of six amino acid residues. This totally abolished replication. We subsequently introduced 14 single point mutations into different regions of NS4B based on the current topology model. One mutation abolished replication, while most conferred reduced replicon establishment and one mutation resulted in improved efficiency. Neither the protein processing nor the membrane altering capacity of NS4B was affected. Surprisingly, mutations situated in the ER lumen also conferred strong effects, despite the fact that replication occurs on the cytosolic side of the ER membrane. We conclude that the molecular integrity of NS4B is vital for HCV replication. Our results suggest that NS4B interacts with itself and with other viral and cellular factors, and may carry intrinsic capacities in order to allow replication.
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Affiliation(s)
- Hannah Lindström
- Karolinska Institutet, Department of Medicine at Center for Molecular Medicine (L8:01), Karolinska Hospital, Stockholm, Sweden
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114
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von Lindern JJ, Aroner S, Barrett ND, Wicker JA, Davis CT, Barrett ADT. Genome analysis and phylogenetic relationships between east, central and west African isolates of Yellow fever virus. J Gen Virol 2006; 87:895-907. [PMID: 16528039 DOI: 10.1099/vir.0.81236-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Yellow fever virus (YFV), a reemerging disease agent in Africa and South America, is the prototype member of the genus Flavivirus. Based on examination of the prM/M, E and 3′ non-coding regions of the YFV genome, previous studies have identified seven genotypes of YFV, including the Angolan, east/central African and east African genotypes, which are highly divergent from the prototype strain Asibi. In this study, full genome analysis was used to expand upon these genetic relationships as well as on the very limited full genome database for YFV. This study was the first to investigate genomic sequences of YFV strains from east and central Africa (Angola71, Uganda48a and Ethiopia61b). All three viruses had genomes of 10 823 nt in length. Compared with the prototype strain Asibi (from west Africa) they were approximately 25 % divergent in nucleotide sequence and 7 % divergent in amino acid sequence. Comparison of multiple flaviviruses in the N-terminal region of NS4B showed that amino acid sequences were variable and that west African strains of YFV had an amino acid deletion at residue 21. Additionally, N-linked glycosylation sites were conserved between viral genotypes, while codon usage varied between strains.
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Affiliation(s)
- Jana J von Lindern
- Department of Pathology, University of Texas Medical Branch at Galveston, 301 University Blvd, Galveston, TX 77555-0609, USA
| | - Sarah Aroner
- University of California at Berkeley, Berkeley, CA 94720, USA
| | | | - Jason A Wicker
- Department of Microbiology and Immunology, University of Texas Medical Branch at Galveston, 301 University Blvd, Galveston, TX 77555-0609, USA
| | - C Todd Davis
- Department of Pathology, University of Texas Medical Branch at Galveston, 301 University Blvd, Galveston, TX 77555-0609, USA
| | - Alan D T Barrett
- Sealy Center for Vaccine Development and Center for Biodefense and Emerging Infectious Diseases, University of Texas Medical Branch at Galveston, 301 University Blvd, Galveston, TX 77555-0609, USA
- Department of Microbiology and Immunology, University of Texas Medical Branch at Galveston, 301 University Blvd, Galveston, TX 77555-0609, USA
- Department of Pathology, University of Texas Medical Branch at Galveston, 301 University Blvd, Galveston, TX 77555-0609, USA
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115
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Villanueva RA, Rouillé Y, Dubuisson J. Interactions between virus proteins and host cell membranes during the viral life cycle. ACTA ACUST UNITED AC 2006; 245:171-244. [PMID: 16125548 PMCID: PMC7112339 DOI: 10.1016/s0074-7696(05)45006-8] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The structure and function of cells are critically dependent on membranes, which not only separate the interior of the cell from its environment but also define the internal compartments. It is therefore not surprising that the major steps of the life cycle of viruses of animals and plants also depend on cellular membranes. Indeed, interactions of viral proteins with host cell membranes are important for viruses to enter into host cells, replicate their genome, and produce progeny particles. To replicate its genome, a virus first needs to cross the plasma membrane. Some viruses can also modify intracellular membranes of host cells to create a compartment in which genome replication will take place. Finally, some viruses acquire an envelope, which is derived either from the plasma membrane or an internal membrane of the host cell. This paper reviews recent findings on the interactions of viral proteins with host cell membranes during the viral life cycle.
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Affiliation(s)
- Rodrigo A Villanueva
- CNRS-UPR2511, Institut de Biologie de Lille, Institut Pasteur de Lille, 59021 Lille Cedex, France
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116
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Miller S, Sparacio S, Bartenschlager R. Subcellular localization and membrane topology of the Dengue virus type 2 Non-structural protein 4B. J Biol Chem 2006; 281:8854-63. [PMID: 16436383 DOI: 10.1074/jbc.m512697200] [Citation(s) in RCA: 207] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Dengue virus (DV) is a member of the family Flaviviridae. These positive strand RNA viruses encode a polyprotein that is processed in case of DV into 10 proteins. Although for most of these proteins distinct functions have been defined, this is less clear for the highly hydrophobic non-structural protein (NS) 4B. Despite its possible role as an antagonist of the interferon-induced antiviral response, this protein may play an additional more direct role for viral replication. In this study we determined the subcellular localization, membrane association, and membrane topology of DV NS4B. We found that NS4B resides primarily in cytoplasmic foci originating from the endoplasmic reticulum. NS4B colocalizes with NS3 and double-stranded RNA, an intermediate of viral replication, arguing that NS4B is part of the membrane-bound viral replication complex. Biochemical analysis revealed that NS4B is an integral membrane protein, and that its preceding 2K signal sequence is not required for this integration. We identified three membrane-spanning segments in the COOH-terminal part of NS4B that are sufficient to target a cytosolic marker protein to intracellular membranes. Furthermore, we established a membrane topology model of NS4B in which the NH2-terminal part of the protein is localized in the endoplasmic reticulum lumen, whereas the COOH-terminal part is composed of three trans-membrane domains with the COOH-terminal tail localized in the cytoplasm. This topology model provides a good starting point for a detailed investigation of the function of NS4B in the DV life cycle.
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Affiliation(s)
- Sven Miller
- Department of Molecular Virology, The University of Heidelberg, 69120 Heidelberg, Germany
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117
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Abstract
The study of hepatitis C virus (HCV) molecular virology is helping to shape the future of our anti-HCV strategies by identifying new antiviral targets. With the advent of agents that specifically target individual HCV proteins, HCV-specific therapy has arrived. Key to these efforts is the development of high-efficiency HCV replicons. The future effective pharmacologic control of HCV will likely consist of a cocktail of simultaneously administered virus-specific agents with independent targets. This should minimize the emergence of resistance against any single agent. The way we treat HCV should change dramatically over the next few years.
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Affiliation(s)
- Jeffrey S Glenn
- Division of Gastroenterology and Hepatology, Stanford University School of Medicine and Palo Alto Veterans Administration Medical Center, CCSR Building, Room 3115, 269 Campus Drive, Palo Alto, CA 94305-5187, USA.
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118
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Svitkin YV, Pause A, Lopez-Lastra M, Perreault S, Sonenberg N. Complete translation of the hepatitis C virus genome in vitro: membranes play a critical role in the maturation of all virus proteins except for NS3. J Virol 2005; 79:6868-81. [PMID: 15890926 PMCID: PMC1112104 DOI: 10.1128/jvi.79.11.6868-6881.2005] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
We developed an in vitro translation extract from Krebs-2 cells that translates the entire open reading frame of the hepatitis C virus (HCV) strain H77 and properly processes the viral protein precursors when supplemented with canine microsomal membranes (CMMs). Translation of the C-terminal portion of the viral polyprotein in this system is documented by the synthesis of NS5B. Evidence for posttranslational modification of the viral proteins, the N-terminal glycosylation of E1 and the E2 precursor (E2-p7), and phosphorylation of NS5A is presented. With the exception of NS3, efficient generation of all virus-specific proteins is CMM dependent. A time course of the appearance of HCV products indicates that the viral polyprotein is cleaved cotranslationally. A competitive inhibitor of the NS3 protease inhibited accumulation of NS3, NS4B, NS5A, and NS5B, but not that of NS2 or structural proteins. CMMs also stabilized HCV mRNA during translation. Finally, the formyl-[35S]methionyl moiety of the initiator tRNA(Met) was incorporated exclusively into the core protein portion of the polyprotein, demonstrating that translation initiation in this system occurs with high fidelity.
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Affiliation(s)
- Yuri V Svitkin
- Department of Biochemistry, McGill University, 3655 Promenade Sir William Osler, Montreal, Quebec, Canada H3G 1Y6.
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119
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Einav S, Elazar M, Danieli T, Glenn JS. A nucleotide binding motif in hepatitis C virus (HCV) NS4B mediates HCV RNA replication. J Virol 2004; 78:11288-95. [PMID: 15452248 PMCID: PMC521822 DOI: 10.1128/jvi.78.20.11288-11295.2004] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Hepatitis C virus (HCV) is a major cause of viral hepatitis. There is no effective therapy for most patients. We have identified a nucleotide binding motif (NBM) in one of the virus's nonstructural proteins, NS4B. This structural motif binds and hydrolyzes GTP and is conserved across HCV isolates. Genetically disrupting the NBM impairs GTP binding and hydrolysis and dramatically inhibits HCV RNA replication. These results have exciting implications for the HCV life cycle and novel antiviral strategies.
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Affiliation(s)
- Shirit Einav
- Division of Gastroenterology and Hepatology, Stanford University School of Medicine, CCSR Building, Room 3115, 269 Campus Drive, Palo Alto, CA 94305-5187, USA
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