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Raguram A, An M, Chen PZ, Liu DR. Directed evolution of engineered virus-like particles with improved production and transduction efficiencies. Nat Biotechnol 2024:10.1038/s41587-024-02467-x. [PMID: 39537813 DOI: 10.1038/s41587-024-02467-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2024] [Accepted: 10/10/2024] [Indexed: 11/16/2024]
Abstract
Engineered virus-like particles (eVLPs) are promising vehicles for transient delivery of proteins and RNAs, including gene editing agents. We report a system for the laboratory evolution of eVLPs that enables the discovery of eVLP variants with improved properties. The system uses barcoded guide RNAs loaded within DNA-free eVLP-packaged cargos to uniquely label each eVLP variant in a library, enabling the identification of desired variants following selections for desired properties. We applied this system to mutate and select eVLP capsids with improved eVLP production properties or transduction efficiencies in human cells. By combining beneficial capsid mutations, we developed fifth-generation (v5) eVLPs, which exhibit a 2-4-fold increase in cultured mammalian cell delivery potency compared to previous-best v4 eVLPs. Analyses of v5 eVLPs suggest that these capsid mutations optimize packaging and delivery of desired ribonucleoprotein cargos rather than native viral genomes and substantially alter eVLP capsid structure. These findings suggest the potential of barcoded eVLP evolution to support the development of improved eVLPs.
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Affiliation(s)
- Aditya Raguram
- Merkin Institute of Transformative Technologies in Healthcare, Broad Institute of MIT and Harvard, Cambridge, MA, USA.
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA.
- Howard Hughes Medical Institute, Harvard University, Cambridge, MA, USA.
- Whitehead Institute for Biomedical Research, Cambridge, MA, USA.
| | - Meirui An
- Merkin Institute of Transformative Technologies in Healthcare, Broad Institute of MIT and Harvard, Cambridge, MA, USA
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
- Howard Hughes Medical Institute, Harvard University, Cambridge, MA, USA
| | - Paul Z Chen
- Merkin Institute of Transformative Technologies in Healthcare, Broad Institute of MIT and Harvard, Cambridge, MA, USA
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
- Howard Hughes Medical Institute, Harvard University, Cambridge, MA, USA
- Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - David R Liu
- Merkin Institute of Transformative Technologies in Healthcare, Broad Institute of MIT and Harvard, Cambridge, MA, USA.
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA.
- Howard Hughes Medical Institute, Harvard University, Cambridge, MA, USA.
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2
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Matsuoka K, Imahashi N, Ohno M, Ode H, Nakata Y, Kubota M, Sugimoto A, Imahashi M, Yokomaku Y, Iwatani Y. SARS-CoV-2 accessory protein ORF8 is secreted extracellularly as a glycoprotein homodimer. J Biol Chem 2022; 298:101724. [PMID: 35157849 PMCID: PMC8832879 DOI: 10.1016/j.jbc.2022.101724] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Revised: 02/03/2022] [Accepted: 02/04/2022] [Indexed: 01/03/2023] Open
Abstract
ORF8 is an accessory protein encoded by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Consensus regarding the biological functions of ORF8 is lacking, largely because the fundamental characteristics of this protein in cells have not been determined. To clarify these features, we herein established an ORF8 expression system in 293T cells. Using this system, approximately 41% of the ORF8 expressed in 293T cells were secreted extracellularly as a glycoprotein homodimer with inter/intramolecular disulfide bonds. Intracellular ORF8 was sensitive to the glycosidase Endo H, whereas the secreted portion was Endo-H-resistant, suggesting that secretion occurs via a conventional pathway. Additionally, immunoblotting analysis showed that the total amounts of the major histocompatibility complex class Ι (MHC-I), angiotensin-converting enzyme 2 (ACE2), and SARS-CoV-2 spike (CoV-2 S) proteins coexpressed in cells were not changed by the increased ORF8 expression, although FACS analysis revealed that the expression of the cell surface MHC-I protein, but not that of ACE2 and CoV-2 S proteins, was reduced by ORF8 expression. Finally, we demonstrate by RNA-seq analysis that ORF8 had no significant stimulatory effects in human primary monocyte-derived macrophages (MDMs). Taken together, our results provide fundamental evidence that the ORF8 glycoprotein acts as a secreted homodimer, and its functions are likely associated with the intracellular transport and/or extracellular signaling in SARS-CoV-2 infection.
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Affiliation(s)
- Kazuhiro Matsuoka
- Department of Infectious Diseases and Immunology, Clinical Research Center, National Hospital Organization Nagoya Medical Center, Nagoya, Aichi, Japan
| | - Nobuhiko Imahashi
- Department of Hematology, National Hospital Organization Nagoya Medical Center, Nagoya, Aichi, Japan
| | - Miki Ohno
- Department of Infectious Diseases and Immunology, Clinical Research Center, National Hospital Organization Nagoya Medical Center, Nagoya, Aichi, Japan
| | - Hirotaka Ode
- Department of Infectious Diseases and Immunology, Clinical Research Center, National Hospital Organization Nagoya Medical Center, Nagoya, Aichi, Japan
| | - Yoshihiro Nakata
- Department of Infectious Diseases and Immunology, Clinical Research Center, National Hospital Organization Nagoya Medical Center, Nagoya, Aichi, Japan; Department of AIDS Research, Nagoya University Graduate School of Medicine, Nagoya, Aichi, Japan
| | - Mai Kubota
- Department of Infectious Diseases and Immunology, Clinical Research Center, National Hospital Organization Nagoya Medical Center, Nagoya, Aichi, Japan
| | - Atsuko Sugimoto
- Department of Infectious Diseases and Immunology, Clinical Research Center, National Hospital Organization Nagoya Medical Center, Nagoya, Aichi, Japan
| | - Mayumi Imahashi
- Department of Infectious Diseases and Immunology, Clinical Research Center, National Hospital Organization Nagoya Medical Center, Nagoya, Aichi, Japan
| | - Yoshiyuki Yokomaku
- Department of Infectious Diseases and Immunology, Clinical Research Center, National Hospital Organization Nagoya Medical Center, Nagoya, Aichi, Japan
| | - Yasumasa Iwatani
- Department of Infectious Diseases and Immunology, Clinical Research Center, National Hospital Organization Nagoya Medical Center, Nagoya, Aichi, Japan; Department of AIDS Research, Nagoya University Graduate School of Medicine, Nagoya, Aichi, Japan.
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Bernacchi S. Visualization of Retroviral Gag-Genomic RNA Cellular Interactions Leading to Genome Encapsidation and Viral Assembly: An Overview. Viruses 2022; 14:324. [PMID: 35215917 PMCID: PMC8876502 DOI: 10.3390/v14020324] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Revised: 01/25/2022] [Accepted: 02/03/2022] [Indexed: 11/16/2022] Open
Abstract
Retroviruses must selectively recognize their unspliced RNA genome (gRNA) among abundant cellular and spliced viral RNAs to assemble into newly formed viral particles. Retroviral gRNA packaging is governed by Gag precursors that also orchestrate all the aspects of viral assembly. Retroviral life cycles, and especially the HIV-1 one, have been previously extensively analyzed by several methods, most of them based on molecular biology and biochemistry approaches. Despite these efforts, the spatio-temporal mechanisms leading to gRNA packaging and viral assembly are only partially understood. Nevertheless, in these last decades, progress in novel bioimaging microscopic approaches (as FFS, FRAP, TIRF, and wide-field microscopy) have allowed for the tracking of retroviral Gag and gRNA in living cells, thus providing important insights at high spatial and temporal resolution of the events regulating the late phases of the retroviral life cycle. Here, the implementation of these recent bioimaging tools based on highly performing strategies to label fluorescent macromolecules is described. This report also summarizes recent gains in the current understanding of the mechanisms employed by retroviral Gag polyproteins to regulate molecular mechanisms enabling gRNA packaging and the formation of retroviral particles, highlighting variations and similarities among the different retroviruses.
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Affiliation(s)
- Serena Bernacchi
- Architecture et Réactivité de l'ARN-UPR 9002, IBMC, CNRS, Université de Strasbourg, F-67000 Strasbourg, France
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4
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Mougel M, Akkawi C, Chamontin C, Feuillard J, Pessel-Vivares L, Socol M, Laine S. NXF1 and CRM1 nuclear export pathways orchestrate nuclear export, translation and packaging of murine leukaemia retrovirus unspliced RNA. RNA Biol 2020; 17:528-538. [PMID: 31918596 PMCID: PMC7237160 DOI: 10.1080/15476286.2020.1713539] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Revised: 12/16/2019] [Accepted: 12/18/2019] [Indexed: 10/25/2022] Open
Abstract
Cellular mRNAs are exported from the nucleus as fully spliced RNAs. Proofreading mechanisms eliminate unprocessed and irregular pre-mRNAs to control the quality of gene expression. Retroviruses need to export partially spliced and unspliced full-length RNAs to the cytoplasm where they serve as templates for protein synthesis and/or as encapsidated RNA in progeny viruses. Genetically complex retroviruses such as HIV-1 use Rev-equivalent proteins to export intron-retaining RNA from the nucleus using the cellular CRM1-driven nuclear export machinery. By contrast, genetically simpler retroviruses such as murine leukaemia virus (MLV) recruit the NXF1 RNA export machinery. In this study, we reveal for the first time that MLV hijacks both NXF1 and CRM1-dependent pathways to achieve optimal replication capacity. The CRM1-pathway marks the MLV full-length RNA (FL RNA) for packaging, while NXF1-driven nuclear export is coupled to translation. Thus, the cytoplasmic function of the viral RNA is determined early in the nucleus. Depending on the nature of ribonucleoprotein complex formed on FL RNA cargo in the nucleus, the FL RNA will be addressed to the translation machinery sites or to the virus-assembly sites at the plasma membrane.
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Affiliation(s)
- M. Mougel
- Team R2D2: Retroviral RNA Dynamics and Delivery, IRIM, UMR9004, CNRS, University of Montpellier, Montpellier, FranceG
| | - C. Akkawi
- Team R2D2: Retroviral RNA Dynamics and Delivery, IRIM, UMR9004, CNRS, University of Montpellier, Montpellier, FranceG
| | - C. Chamontin
- Team R2D2: Retroviral RNA Dynamics and Delivery, IRIM, UMR9004, CNRS, University of Montpellier, Montpellier, FranceG
| | - J. Feuillard
- Team R2D2: Retroviral RNA Dynamics and Delivery, IRIM, UMR9004, CNRS, University of Montpellier, Montpellier, FranceG
| | - L. Pessel-Vivares
- Team R2D2: Retroviral RNA Dynamics and Delivery, IRIM, UMR9004, CNRS, University of Montpellier, Montpellier, FranceG
| | - M. Socol
- Team R2D2: Retroviral RNA Dynamics and Delivery, IRIM, UMR9004, CNRS, University of Montpellier, Montpellier, FranceG
| | - S. Laine
- Team R2D2: Retroviral RNA Dynamics and Delivery, IRIM, UMR9004, CNRS, University of Montpellier, Montpellier, FranceG
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5
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Dubois N, Marquet R, Paillart JC, Bernacchi S. Retroviral RNA Dimerization: From Structure to Functions. Front Microbiol 2018; 9:527. [PMID: 29623074 PMCID: PMC5874298 DOI: 10.3389/fmicb.2018.00527] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2018] [Accepted: 03/08/2018] [Indexed: 01/18/2023] Open
Abstract
The genome of the retroviruses is a dimer composed by two homologous copies of genomic RNA (gRNA) molecules of positive polarity. The dimerization process allows two gRNA molecules to be non-covalently linked together through intermolecular base-pairing. This step is critical for the viral life cycle and is highly conserved among retroviruses with the exception of spumaretroviruses. Furthermore, packaging of two gRNA copies into viral particles presents an important evolutionary advantage for immune system evasion and drug resistance. Recent studies reported RNA switches models regulating not only gRNA dimerization, but also translation and packaging, and a spatio-temporal characterization of viral gRNA dimerization within cells are now at hand. This review summarizes our current understanding on the structural features of the dimerization signals for a variety of retroviruses (HIVs, MLV, RSV, BLV, MMTV, MPMV…), the mechanisms of RNA dimer formation and functional implications in the retroviral cycle.
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Affiliation(s)
- Noé Dubois
- Architecture et Réactivité de l'ARN, UPR 9002, IBMC, CNRS, Université de Strasbourg, Strasbourg, France
| | - Roland Marquet
- Architecture et Réactivité de l'ARN, UPR 9002, IBMC, CNRS, Université de Strasbourg, Strasbourg, France
| | - Jean-Christophe Paillart
- Architecture et Réactivité de l'ARN, UPR 9002, IBMC, CNRS, Université de Strasbourg, Strasbourg, France
| | - Serena Bernacchi
- Architecture et Réactivité de l'ARN, UPR 9002, IBMC, CNRS, Université de Strasbourg, Strasbourg, France
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6
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Pessel-Vivares L, Houzet L, Lainé S, Mougel M. Insights into the nuclear export of murine leukemia virus intron-containing RNA. RNA Biol 2016; 12:942-9. [PMID: 26158194 DOI: 10.1080/15476286.2015.1065375] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
The retroviral genome consists of an intron-containing transcript that has essential cytoplasmic functions in the infected cell. This viral transcript can escape splicing, circumvent the nuclear checkpoint mechanisms and be transported to the cytoplasm by hijacking the host machinery. Once in the cytoplasm, viral unspliced RNA acts as mRNA to be translated and as genomic RNA to be packaged into nascent viruses. The murine leukemia virus (MLV) is among the first retroviruses discovered and is classified as simple Retroviridae due to its minimal encoding capacity. The oncogenic and transduction abilities of MLV are extensively studied, whereas surprisingly the crucial step of its nuclear export has remained unsolved until 2014. Recent work has revealed the recruitment by MLV of the cellular NXF1/Tap-dependent pathway for export. Unconventionally, MLV uses of Tap to export both spliced and unspliced viral RNAs. Unlike other retroviruses, MLV does not harbor a unique RNA signal for export. Indeed, multiple sequences throughout the MLV genome appear to promote export of the unspliced MLV RNA. We review here the current understanding of the export mechanism and highlight the determinants that influence MLV export. As the molecular mechanism of MLV export is elucidated, we will gain insight into the contribution of the export pathway to the cytoplasmic fate of the viral RNA.
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Affiliation(s)
- Lucie Pessel-Vivares
- a CNRS, UM; CPBS ; Montpellier , France.,b Department of Infectious Diseases ; King's College London ; London , UK
| | - Laurent Houzet
- c Inserm U1085-IRSET; Université de Rennes 1; Structure Fédérative Recherche Biosit ; Rennes , France
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7
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Choi J, Kim HM, Yoon JK, Cho Y, Lee HJ, Kim KC, Kim CK, Kim GW, Kim YB. Identification of Porcine Endogenous Retrovirus (PERV) packaging sequence and development of PERV packaging viral vector system. J Microbiol 2015; 53:348-53. [PMID: 25935307 DOI: 10.1007/s12275-015-5134-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2015] [Revised: 04/09/2015] [Accepted: 04/13/2015] [Indexed: 12/11/2022]
Abstract
Studies of the retroviruses have focused on the specific interaction of the nucleocapsid protein with a packaging signal in the viral RNA as important for this selectivity, but the packaging signal in porcine endogenous retrovirus (PERV) has not been defined. Herein, we identified and analyzed this packaging signal in PERV and found hairpin structures with conserved tetranucleotides in their loops and nucleocapsid recognition sequences; both of which are key elements in the viral packaging signal of MLV. We evaluated packaging efficiency of sequence variants isolated from viral and proviral integrated genomes. All viral packaging sequences (Ψ) were identical, while five distinct packaging sequences were identified from proviral sources. One proviral sequence (Ψ1) was identical to that of the viral Ψ and had the highest packaging efficiency. Three variants (Ψ2, Ψ3, Ψ4) maintained key elements of the viral packaging signal, but had nucleotide replacements and consequently demonstrated reduced packaging efficiency. Despite of the same overall hairpin structure, the proviral variant (Ψ5) had only one GACG sequence in the hairpin loop and showed the lowest packaging efficiency other than ∆Ψ, in which the essential packaging sequence was removed. This result, thus, defined the packaging sequences in PERV and emphasized the importance of nucleotide sequence and RNA structure in the determination of packaging efficiency. In addition, we demonstrate efficient infection and gene expression from the PERV based viral vector, which may serve as a novel alternative to current retroviral expression systems.
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Affiliation(s)
- Jiwon Choi
- Department of Bioindustrial Technologies, Konkuk University, Seoul, 143-701, Korea
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8
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Volkova NA, Fomina EG, Smolnikova VV, Zinovieva NA, Fomin IK. The U3 region of Moloney murine leukemia virus contains position-independent cis-acting sequences involved in the nuclear export of full-length viral transcripts. J Biol Chem 2014; 289:20158-69. [PMID: 24878957 DOI: 10.1074/jbc.m113.545855] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
The distinguishing feature of self-inactivating (SIN) retroviral vectors is the deletion of the enhancer/promoter sequences in the U3 region of the 3' long terminal repeat. This design is used to overcome transcriptional interference and prevent downstream transcription from the 3' long terminal repeat. SIN vectors were derived from a number of different retroviruses. Studies of SIN vectors show that extensive U3 deletions in HIV-based vectors do not alter viral titers or the in vitro and in vivo properties of the vectors. However, deletion of the U3 sequences in γ- and α-retroviruses correlates with defects in 3' RNA processing and reduces viral titers by >10-fold. Here, we studied the steps in the retroviral life cycle that are affected by the deletion of sequences in the 3' U3 region of Moloney murine leukemia virus-derived retroviral vectors. The results show that the amounts of both full-length and internal RNA transcripts of U3-minus vectors are reduced in the nuclei of transfected cells, an effect that is probably due to a general defect in 3' RNA processing. Furthermore, full-length RNA transcripts were also defective in terms of nuclear export. This defect was complemented by transferring the U3 region to another position within the retroviral vector, indicating that the U3 region contains position-independent cis-acting sequences that are required for the transport of full-length viral transcripts. The results also suggest that the leader region of Moloney murine leukemia virus contains inhibitory/regulatory sequences, which prevent export and mediate nuclear retention of full-length viral RNA.
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Affiliation(s)
- Natalia A Volkova
- From the The Laboratory of Cellular Engineering, All-Russian State Research Institute of Animal Breeding, 142132 Moscow region, Russia
| | - Elena G Fomina
- The Laboratory for Biotechnology and Immunodiagnosis, The Republic Research and Practical Center for Epidemiology and Microbiology, 220114 Minsk, Belarus, and
| | - Viktoryia V Smolnikova
- The Republic Center of Hematology and Bone Marrow Transplantation, 220116 Minsk, Belarus
| | - Natalia A Zinovieva
- From the The Laboratory of Cellular Engineering, All-Russian State Research Institute of Animal Breeding, 142132 Moscow region, Russia,
| | - Igor K Fomin
- From the The Laboratory of Cellular Engineering, All-Russian State Research Institute of Animal Breeding, 142132 Moscow region, Russia,
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Pessel-Vivares L, Ferrer M, Lainé S, Mougel M. MLV requires Tap/NXF1-dependent pathway to export its unspliced RNA to the cytoplasm and to express both spliced and unspliced RNAs. Retrovirology 2014; 11:21. [PMID: 24597485 PMCID: PMC4015919 DOI: 10.1186/1742-4690-11-21] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2013] [Accepted: 02/04/2014] [Indexed: 01/12/2023] Open
Abstract
BACKGROUND Eukaryotic cells have evolved stringent proofreading mechanisms to ensure that intron-containing mRNAs do not leave the nucleus. However, all retroviruses must bypass this checkpoint for replication. Indeed, their primary polycistronic transcript (Full-Length) must reach the cytoplasm to be either translated or packaged as genomic RNA in progeny viruses.Murine leukemia virus (MLV) is a prototype of simple retroviruses with only two well-regulated splicing events that directly influence viral leukemogenic properties in mice. Several cis-elements have been identified in the FL RNA that regulate its cytoplasmic accumulation. However, their connection with an export mechanism is yet unknown. Our goal was to identify the cellular pathway used by MLV to export its RNAs into the cytoplasm of the host cells. RESULTS Since other retroviruses use the CRM1 and/or the Tap/NXF1 pathways to export their unspliced RNA from the nucleus, we investigated the role of these two pathways in MLV replication by using specific inhibitors. The effects of export inhibition on MLV protein synthesis, RNA levels and RNA localization were studied by Western blotting, RT-qPCR, fluorescence microscopy and ribonucleoprotein immunoprecipitation assays. Taken together, our results show for the first time that MLV requires the Tap/NXF1-mediated export pathway, and not the CRM1 pathway, for the expression of its spliced and unspliced RNAs and for FL RNA nuclear export. CONCLUSIONS By contrast to HIV-1, MLV recruits the same pathway for the cytoplasmic expression of its spliced and unspliced RNAs. Thus, MLV RNA expression depends upon coordinated splicing/export processes. In addition, FL RNA translation relies on Tap/NXF1-dependent export, raising the critical question of whether the pool of FL RNA to be packaged is also exported by Tap/NXF1.
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Affiliation(s)
| | - Mireia Ferrer
- UMR5236 CNRS, UM1, UM2, CPBS, 1919 Route de Mende, Montpellier, France
| | - Sébastien Lainé
- UMR5236 CNRS, UM1, UM2, CPBS, 1919 Route de Mende, Montpellier, France
| | - Marylène Mougel
- UMR5236 CNRS, UM1, UM2, CPBS, 1919 Route de Mende, Montpellier, France
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Choo YC, Seki Y, Machinaga A, Ogita N, Takase-Yoden S. The 0.3-kb fragment containing the R-U5-5'leader sequence of Friend murine leukemia virus influences the level of protein expression from spliced mRNA. Virol J 2013; 10:124. [PMID: 23602143 PMCID: PMC3651342 DOI: 10.1186/1743-422x-10-124] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2013] [Accepted: 04/12/2013] [Indexed: 12/04/2022] Open
Abstract
Background A neuropathogenic variant of Friend murine leukemia virus (Fr-MLV) clone A8 induces spongiform neurodegeneration when infected into neonatal rats. Studies with chimeras constructed from the A8 virus and the non-neuropathogenic Fr-MLV clone 57 identified a 0.3-kb KpnI-AatII fragment containing a R-U5-5’leader sequence as an important determinant for inducing spongiosis, in addition to the env gene of A8 as the primary determinant. This 0.3-kb fragment contains a 17-nucleotide difference between the A8 and 57 sequences. We previously showed that the 0.3-kb fragment influences expression levels of Env protein in both cultured cells and rat brain, but the corresponding molecular mechanisms are not well understood. Results Studies with expression vectors constructed from the full-length proviral genome of Fr-MLV that incorporated the luciferase (luc) gene instead of the env gene found that the vector containing the A8-0.3-kb fragment yielded a larger amount of spliced luc-mRNA and showed higher expression of luciferase when compared to the vector containing the 57-0.3-kb fragment. The amount of total transcripts from the vectors, the poly (A) tail length of their mRNAs, and the nuclear-cytoplasm distribution of luc-mRNA in transfected cells were also evaluated. The 0.3-kb fragment did not influence transcription efficiency, mRNA polyadenylation or nuclear export of luc-mRNA. Mutational analyses were carried out to determine the importance of nucleotides that differ between the A8 and 57 sequences within the 0.3-kb fragment. In particular, seven nucleotides upstream of the 5’splice site (5’ss) were found to be important in regulating the level of protein expression from spliced messages. Interestingly, these nucleotides reside within the stem-loop structure that has been speculated to limit the recognition of 5’ss. Conclusions The 0.3-kb fragment containing the R-U5-5’leader sequence of Fr-MLV influences the level of protein expression from the spliced-mRNA by regulating the splicing efficiency rather than transcription, nuclear export of spliced-mRNA, or poly (A) addition to mRNA. Seven nucleotides in the 0.3-kb fragment, which reside within the stem-loop structure that has been speculated to limit recognition of the 5’ss, could pinpoint the function of this region.
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Affiliation(s)
- Yeng Cheng Choo
- Department of Bioinformatics, Faculty of Engineering, Soka University, Hachioji, Tokyo 192-8577, Japan
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11
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Sequences within both the 5' UTR and Gag are required for optimal in vivo packaging and propagation of mouse mammary tumor virus (MMTV) genomic RNA. PLoS One 2012; 7:e47088. [PMID: 23077548 PMCID: PMC3473059 DOI: 10.1371/journal.pone.0047088] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2012] [Accepted: 09/07/2012] [Indexed: 01/31/2023] Open
Abstract
Background This study mapped regions of genomic RNA (gRNA) important for packaging and propagation of mouse mammary tumor virus (MMTV). MMTV is a type B betaretrovirus which preassembles intracellularly, a phenomenon distinct from retroviruses that assemble the progeny virion at cell surface just before budding such as the type C human and feline immunodeficiency viruses (HIV and FIV). Studies of FIV and Mason-Pfizer monkey virus (MPMV), a type D betaretrovirus with similar intracellular virion assembly processes as MMTV, have shown that the 5′ untranslated region (5′ UTR) and 5′ end of gag constitute important packaging determinants for gRNA. Methodology Three series of MMTV transfer vectors containing incremental amounts of gag or 5′ UTR sequences, or incremental amounts of 5′ UTR in the presence of 400 nucleotides (nt) of gag were constructed to delineate the extent of 5′ sequences that may be involved in MMTV gRNA packaging. Real time PCR measured the packaging efficiency of these vector RNAs into MMTV particles generated by co-transfection of MMTV Gag/Pol, vesicular stomatitis virus envelope glycoprotein (VSV-G Env), and individual transfer vectors into human 293T cells. Transfer vector RNA propagation was monitored by measuring transduction of target HeLaT4 cells following infection with viral particles containing a hygromycin resistance gene expression cassette on the packaged RNA. Principal Findings MMTV requires the entire 5′ UTR and a minimum of ∼120 nucleotide (nt) at the 5′ end of gag for not only efficient gRNA packaging but also propagation of MMTV-based transfer vector RNAs. Vector RNAs without the entire 5′ UTR were defective for both efficient packaging and propagation into target cells. Conclusions/Significance These results reveal that the 5′ end of MMTV genome is critical for both gRNA packaging and propagation, unlike the recently delineated FIV and MPMV packaging determinants that have been shown to be of bipartite nature.
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12
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Clemens K, Bilanchone V, Beliakova-Bethell N, Larsen LSZ, Nguyen K, Sandmeyer S. Sequence requirements for localization and packaging of Ty3 retroelement RNA. Virus Res 2012; 171:319-31. [PMID: 23073180 DOI: 10.1016/j.virusres.2012.10.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2012] [Revised: 10/06/2012] [Accepted: 10/08/2012] [Indexed: 12/22/2022]
Abstract
Retroviruses and retrotransposons package genomic RNA into virus-like particles (VLPs) in a poorly understood process. Expression of the budding yeast retrotransposon Ty3 results in the formation of cytoplasmic Ty3 VLP assembly foci comprised of Ty3 RNA and proteins, and cellular factors associated with RNA processing body (PB) components, which modulate translation and effect nonsense-mediated decay (NMD). A series of Ty3 RNA variants were tested to understand the effects of read-through translation via programmed frameshifting on RNA localization and packaging into VLPs, and to identify the roles of coding and non-coding sequences in those processes. These experiments showed that a low level of read-through translation of the downstream open reading frame (as opposed to no translation or translation without frameshifting) is important for localization of full-length Ty3 RNA to foci. Ty3 RNA variants associated with PB components via independent determinants in the native Ty3 untranslated regions (UTRs) and in GAG3-POL3 sequences flanked by UTRs adapted from non-Ty3 transcripts. However, despite localization, RNAs containing GAG3-POL3 but lacking Ty3 UTRs were not packaged efficiently. Surprisingly, sequences within Ty3 UTRs, which bind the initiator tRNA(Met) proposed to provide the dimerization interface, were not required for packaging of full-length Ty3 RNA into VLPs. In summary, our results demonstrate that Gag3 is sufficient and required for localization and packaging of RNAs containing Ty3 UTRs and support a role for POL3 sequences, translation of which is attenuated by programmed frameshifting, in both localization and packaging of the Ty3 full-length gRNA.
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Affiliation(s)
- Kristina Clemens
- Department of Biological Chemistry, University of California, Irvine, CA 92697, USA
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13
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Abstract
Foamy viruses (FVs) are distinct members of the retrovirus (RV) family. In this chapter, the molecular regulation of foamy viral transcription, splicing, polyadenylation, and RNA export will be compared in detail to the orthoretroviruses. Foamy viral transcription is regulated in early and late phases, which are separated by the usage of two promoters. The viral transactivator protein Tas activates both promoters. The nature of this early-late switch and the molecular mechanism used by Tas are unique among RVs. RVs duplicate the long terminal repeats (LTRs) during reverse transcription. These LTRs carry both a promoter region and functional poly(A) sites. In order to express full-length transcripts, RVs have to silence the poly(A) signal in the 5' LTR and to activate it in the 3' LTR. FVs have a unique R-region within these LTRs with a major splice donor (MSD) at +51 followed by a poly(A) signal. FVs use a MSD-dependent mechanism to inactivate the polyadenylation. Most RVs express all their genes from a single primary transcript. In order to allow expression of more than one gene from this RNA, differential splicing is extensively used in complex RVs. The splicing pattern of FV is highly complex. In contrast to orthoretroviruses, FVs synthesize the Pol precursor protein from a specific and spliced transcript. The LTR and IP-derived primary transcripts are spliced into more than 15 different mRNA species. Since the RNA ratios have to be balanced, a tight regulation of splicing is required. Cellular quality control mechanisms retain and degrade unspliced or partially spliced RNAs in the nucleus. In this review, I compare the RNA export pathways used by orthoretroviruses with the distinct RNA export pathway used by FV. All these steps are highly regulated by host and viral factors and set FVs apart from all other RVs.
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Affiliation(s)
- Jochen Bodem
- Institute of Virology and Immunobiology, University of Würzburg, Würzburg, Germany
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14
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Karimian Pour N, Adeli K. Insulin silences apolipoprotein B mRNA translation by inducing intracellular traffic into cytoplasmic RNA granules. Biochemistry 2011; 50:6942-50. [PMID: 21721546 DOI: 10.1021/bi200711v] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Insulin is a potent inducer of global mRNA translation and protein synthesis, yet it negatively regulates apolipoprotein B (apoB) mRNA translation, via an unknown mechanism. ApoB mRNA has a long half-life of 16 h, suggesting intracellular storage as mRNPs likely in the form of RNA granules. The availability of apoB mRNA for translation may be regulated by the rate of release from translationally silenced mRNPs within cytoplasmic foci called processing bodies (P bodies). In this report, we directly imaged intracellular apoB mRNA traffic and determined whether insulin silences apoB mRNA translation by entering cytoplasmic P bodies. We assessed the colocalization of apoB mRNA and β-globin mRNA (as a control) with P body (PB) markers using a strong interaction between the bacteriophage capsid protein MS2 and a sequence specific RNA stem-loop structure. We observed statistically significant increases in the localization of apoB mRNA into P bodies 4-16 h after insulin treatment (by 72-89%). The movement of apoB mRNA into cytoplasmic P bodies correlated with reduced translational efficiency as assessed by polysomal profiling and measurement of apoB mRNA abundance. PB localization of β-globin mRNA was insensitive to insulin treatment, suggesting selective regulation of apoB mRNA by insulin. Overall, our data suggest that insulin may specifically silence apoB mRNA translation by reprogramming its mRNA into P bodies and reducing the size of translationally competent mRNA pools. Translational control via traffic into cytoplasmic RNA granules may be an important mechanism for controlling the rate of apoB synthesis and hepatic lipoprotein production.
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Affiliation(s)
- Navaz Karimian Pour
- Molecular Structure and Function, Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada
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15
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Rein A, Datta SAK, Jones CP, Musier-Forsyth K. Diverse interactions of retroviral Gag proteins with RNAs. Trends Biochem Sci 2011; 36:373-80. [PMID: 21550256 PMCID: PMC3130074 DOI: 10.1016/j.tibs.2011.04.001] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2011] [Revised: 03/31/2011] [Accepted: 04/04/2011] [Indexed: 10/18/2022]
Abstract
Retrovirus particles are constructed from a single virus-encoded protein, termed Gag. Given that assembly is an essential step in the viral replication cycle, it is a potential target for antiviral therapy. However, such an approach has not yet been exploited because of the lack of fundamental knowledge concerning the structures and interactions responsible for assembly. Assembling an infectious particle entails a remarkably diverse array of interactions, both specific and nonspecific, between Gag proteins and RNAs. These interactions are essential for the construction of the particle, for packaging of the viral RNA into the particle, and for placement of the primer for viral DNA synthesis. Recent results have provided some new insights into each of these interactions. In the case of HIV-1 Gag, it is clear that more than one domain of the protein contributes to Gag-RNA interaction.
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Affiliation(s)
- Alan Rein
- HIV Drug Resistance Program, National Cancer Institute-Frederick, Frederick, MD 21702, USA.
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16
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Bodem J, Schied T, Gabriel R, Rammling M, Rethwilm A. Foamy virus nuclear RNA export is distinct from that of other retroviruses. J Virol 2011; 85:2333-41. [PMID: 21159877 PMCID: PMC3067772 DOI: 10.1128/jvi.01518-10] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2010] [Accepted: 12/07/2010] [Indexed: 01/09/2023] Open
Abstract
Most retroviruses express all of their genes from a single primary transcript. In order to allow expression of more than one gene from this RNA, differential splicing is extensively used. Cellular quality control mechanisms retain and degrade unspliced or partially spliced RNAs in the nucleus. Two pathways have been described that explain how retroviruses circumvent this nuclear export inhibition. One involves a constitutive transport element in the viral RNA that interacts with the cellular mRNA transporter proteins NXF1 and NXT1 to facilitate nuclear export. The other pathway relies on the recognition of a viral RNA element by a virus-encoded protein that interacts with the karyopherin CRM1. In this report, we analyze the protein factors required for the nuclear export of unspliced foamy virus (FV) mRNA. We show that this export is CRM1 dependent. In contrast to other complex retroviruses, FVs do not encode an export-mediating protein. Cross-linking experiments indicated that the cellular protein HuR binds to the FV RNA. Inhibition studies showed that both ANP32A and ANP32B, which are known to bridge HuR and CRM1, are essential for FV RNA export. By using this export pathway, FVs solve a central problem of viral replication.
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Affiliation(s)
- Jochen Bodem
- Universität Würzburg, Institut für Virologie und Immunbiologie, Versbacher Str. 7, 97078 Würzburg, Germany
| | - Tanja Schied
- Universität Würzburg, Institut für Virologie und Immunbiologie, Versbacher Str. 7, 97078 Würzburg, Germany
| | - Richard Gabriel
- Universität Würzburg, Institut für Virologie und Immunbiologie, Versbacher Str. 7, 97078 Würzburg, Germany
| | - Matthias Rammling
- Universität Würzburg, Institut für Virologie und Immunbiologie, Versbacher Str. 7, 97078 Würzburg, Germany
| | - Axel Rethwilm
- Universität Würzburg, Institut für Virologie und Immunbiologie, Versbacher Str. 7, 97078 Würzburg, Germany
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17
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Abstract
Long terminal repeat (LTR) retrotransposons are not only the ancient predecessors of retroviruses, but they constitute significant fractions of the genomes of many eukaryotic species. Studies of their structure and function are motivated by opportunities to gain insight into common functions of retroviruses and retrotransposons, diverse mechanisms of intracellular genomic mobility, and host factors that diminish or enhance retrotransposition. This review focuses on the nucleocapsid (NC) protein of a Saccharomyces cerevisiae LTR retrotransposon, the metavirus, Ty3. Retrovirus NC promotes genomic (g)RNA dimerization and packaging, tRNA primer annealing, reverse transcription strand transfers, and host protein interactions with gRNA. Studies of Ty3 NC have revealed key roles for Ty3 NC in formation of retroelement assembly sites (retrosomes), and in chaperoning primer tRNA to both dimerize and circularize Ty3 gRNA. We speculate that Ty3 NC, together with P-body and stress-granule proteins, plays a role in transitioning Ty3 RNA from translation template to gRNA, and that interactions between the acidic spacer domain of Ty3 Gag3 and the adjacent basic NC domain control condensation of the virus-like particle.
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Affiliation(s)
- Suzanne B Sandmeyer
- Department of Biological Chemistry, School of Medicine, University of California, Irvine, CA USA.
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18
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Rizvi TA, Kenyon JC, Ali J, Aktar SJ, Phillip PS, Ghazawi A, Mustafa F, Lever AML. Optimal packaging of FIV genomic RNA depends upon a conserved long-range interaction and a palindromic sequence within gag. J Mol Biol 2010; 403:103-119. [PMID: 20732330 PMCID: PMC2987497 DOI: 10.1016/j.jmb.2010.08.019] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2010] [Revised: 08/09/2010] [Accepted: 08/10/2010] [Indexed: 02/06/2023]
Abstract
The feline immunodeficiency virus (FIV) is a lentivirus that is related to human immunodeficiency virus (HIV), causing a similar pathology in cats. It is a potential small animal model for AIDS and the FIV-based vectors are also being pursued for human gene therapy. Previous studies have mapped the FIV packaging signal (ψ) to two or more discontinuous regions within the 5' 511 nt of the genomic RNA and structural analyses have determined its secondary structure. The 5' and 3' sequences within ψ region interact through extensive long-range interactions (LRIs), including a conserved heptanucleotide interaction between R/U5 and gag. Other secondary structural elements identified include a conserved 150 nt stem-loop (SL2) and a small palindromic stem-loop within gag open reading frame that might act as a viral dimerization initiation site. We have performed extensive mutational analysis of these sequences and structures and ascertained their importance in FIV packaging using a trans-complementation assay. Disrupting the conserved heptanucleotide LRI to prevent base pairing between R/U5 and gag reduced packaging by 2.8-5.5 fold. Restoration of pairing using an alternative, non-wild type (wt) LRI sequence restored RNA packaging and propagation to wt levels, suggesting that it is the structure of the LRI, rather than its sequence, that is important for FIV packaging. Disrupting the palindrome within gag reduced packaging by 1.5-3-fold, but substitution with a different palindromic sequence did not restore packaging completely, suggesting that the sequence of this region as well as its palindromic nature is important. Mutation of individual regions of SL2 did not have a pronounced effect on FIV packaging, suggesting that either it is the structure of SL2 as a whole that is necessary for optimal packaging, or that there is redundancy within this structure. The mutational analysis presented here has further validated the previously predicted RNA secondary structure of FIV ψ.
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Affiliation(s)
- Tahir A Rizvi
- Departments of Microbiology & Immunology, Faculty of Medicine and Health Sciences (FMHS), United Arab Emirates University (UAEU), Al Ain, UAE.
| | - Julia C Kenyon
- Department of Medicine, Addenbrooke's Hospital, University of Cambridge, Cambridge CB2 2QQ, UK
| | - Jahabar Ali
- Departments of Microbiology & Immunology, Faculty of Medicine and Health Sciences (FMHS), United Arab Emirates University (UAEU), Al Ain, UAE
| | - Suriya J Aktar
- Departments of Microbiology & Immunology, Faculty of Medicine and Health Sciences (FMHS), United Arab Emirates University (UAEU), Al Ain, UAE
| | - Pretty S Phillip
- Departments of Microbiology & Immunology, Faculty of Medicine and Health Sciences (FMHS), United Arab Emirates University (UAEU), Al Ain, UAE
| | - Akela Ghazawi
- Departments of Microbiology & Immunology, Faculty of Medicine and Health Sciences (FMHS), United Arab Emirates University (UAEU), Al Ain, UAE
| | - Farah Mustafa
- Department of Biochemistry, Faculty of Medicine and Health Sciences (FMHS), United Arab Emirates University (UAEU), Al Ain, UAE
| | - Andrew M L Lever
- Department of Medicine, Addenbrooke's Hospital, University of Cambridge, Cambridge CB2 2QQ, UK
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19
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Maurel S, Mougel M. Murine leukemia virus RNA dimerization is coupled to transcription and splicing processes. Retrovirology 2010; 7:64. [PMID: 20687923 PMCID: PMC2925334 DOI: 10.1186/1742-4690-7-64] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2010] [Accepted: 08/05/2010] [Indexed: 11/16/2022] Open
Abstract
Most of the cell biological aspects of retroviral genome dimerization remain unknown. Murine leukemia virus (MLV) constitutes a useful model to study when and where dimerization occurs within the cell. For instance, MLV produces a subgenomic RNA (called SD') that is co-packaged with the genomic RNA predominantly as FLSD' heterodimers. This SD' RNA is generated by splicing of the genomic RNA and also by direct transcription of a splice-associated retroelement of MLV (SDARE). We took advantage of these two SD' origins to study the effects of transcription and splicing events on RNA dimerization. Using genetic approaches coupled to capture of RNA heterodimer in virions, we determined heterodimerization frequencies in different cellular contexts. Several cell lines were stably established in which SD' RNA was produced by either splicing or transcription from SDARE. Moreover, SDARE was integrated into the host chromosome either concomitantly or sequentially with the genomic provirus. Our results showed that transcribed genomic and SD' RNAs preferentially formed heterodimers when their respective proviruses were integrated together. In contrast, heterodimerization was strongly affected when the two proviruses were integrated independently. Finally, dimerization was enhanced when the transcription sites were expected to be physically close. For the first time, we report that splicing and RNA dimerization appear to be coupled. Indeed, when the RNAs underwent splicing, the FLSD' dimerization reached a frequency similar to co-transcriptional heterodimerization. Altogether, our results indicate that randomness of heterodimerization increases when RNAs are co-expressed during either transcription or splicing. Our results strongly support the notion that dimerization occurs in the nucleus, at or near the transcription and splicing sites, at areas of high viral RNA concentration.
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Affiliation(s)
- Stéphan Maurel
- Université Montpellier 1, Centre d'études d'agents Pathogènes et Biotechnologies pour la Santé (CPBS), CNRS, UMR 5236, 4 Bd Henri IV, 34965 Montpellier, France
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20
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Abstract
Human immunodeficiency virus type 1 (HIV-1) Gag and genomic RNA determinants required for encapsidation are well established, but where and when encapsidation occurs in the cell is unknown. We constructed MS2 phage coat protein labeling systems to track spatial dynamics of primate and nonprimate lentiviral genomic RNAs (HIV-1 and feline immunodeficiency virus [FIV]) vis-à-vis their Gag proteins in live cells. Genomic RNAs of both lentiviral genera were observed to traffic into the cytoplasm, and this was Rev dependent. In transit, FIV Gag and genomic RNA accumulated independently of each other at the nuclear envelope, and focal colocalizations of genomic RNA with an intact packaging signal (psi) and Gag were observed to extend outward from the cytoplasmic face. In contrast, although HIV-1 genomic RNA was detected at the nuclear envelope, HIV-1 Gag was not. For both lentiviruses, genomic RNAs were seen at the plasma membrane if and only if Gag was present and psi was intact. In addition, HIV-1 and FIV genomes accumulated with Gag in late endosomal foci, again, only psi dependently. Thus, lentiviral genomic RNAs require specific Gag binding to accumulate at the plasma membrane, packaged genomes cointernalize with Gag into the endosomal pathway, and plasma membrane RNA incorporation by Gag does not trigger committed lentiviral particle egress from the cell. Based on the FIV results, we hypothesize that the Gag-genome association may initiate at the nuclear envelope.
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21
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Kharytonchyk S, Pedersen FS. A unique, thermostable dimer linkage structure of RD114 retroviral RNA. RNA (NEW YORK, N.Y.) 2010; 16:572-584. [PMID: 20075164 PMCID: PMC2822922 DOI: 10.1261/rna.1495110] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2008] [Accepted: 11/13/2009] [Indexed: 05/28/2023]
Abstract
Retroviruses package their genome as RNA dimers linked together primarily by base-pairing between palindromic stem-loop (psl) sequences at the 5' end of genomic RNA. Retroviral RNA dimers usually melt in the range of 55 degrees C-70 degrees C. However, RNA dimers from virions of the feline endogenous gammaretrovirus RD114 were reported to melt only at 87 degrees C. We here report that the high thermal stability of RD114 RNA dimers generated from in vitro synthesized RNA is an effect of multiple dimerization sites located in the 5' region from the R region to sequences downstream from the splice donor (SD) site. By antisense oligonucleotide probing we were able to map at least five dimerization sites. Computational prediction revealed a possibility to form stems with autocomplementary loops for all of the mapped dimerization sites. Three of them were located upstream of the SD site. Mutant analysis supported a role of all five loop sequences in the formation and thermal stability of RNA dimers. Four of the five psls were also predicted in the RNA of two baboon endogenous retroviruses proposed to be ancestors of RD114. RNA fragments of the 5' R region or prolonged further downstream could be efficiently dimerized in vitro. However, this was not the case for the 3' R region linked to upstream U3 sequences, suggesting a specific mechanism of negative regulation of dimerization at the 3' end of the genome, possibly explained by a long double-stranded RNA region at the U3-R border. Altogether, these data point to determinants of the high thermostability of the dimer linkage structure of the RD114 genome and reveal differences from other retroviruses.
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22
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Lehmann M, Milev MP, Abrahamyan L, Yao XJ, Pante N, Mouland AJ. Intracellular transport of human immunodeficiency virus type 1 genomic RNA and viral production are dependent on dynein motor function and late endosome positioning. J Biol Chem 2009; 284:14572-85. [PMID: 19286658 PMCID: PMC2682905 DOI: 10.1074/jbc.m808531200] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2008] [Revised: 03/03/2009] [Indexed: 11/06/2022] Open
Abstract
Our earlier work indicated that the human immunodeficiency virus type 1 (HIV-1) genomic RNA (vRNA) is trafficked to the microtubule-organizing center (MTOC) when heterogeneous nuclear ribonucleoprotein A2/B1 is depleted from cells. Also, Rab7-interacting lysosomal protein promoted dynein motor complex, late endosome and vRNA clustering at the MTOC suggesting that the dynein motor and late endosomes were involved in vRNA trafficking. To investigate the role of the dynein motor in vRNA trafficking, dynein motor function was disrupted by small interference RNA-mediated depletion of the dynein heavy chain or by p50/dynamitin overexpression. These treatments led to a marked relocalization of vRNA and viral structural protein Gag to the cell periphery with late endosomes and a severalfold increase in HIV-1 production. In contrast, rerouting vRNA to the MTOC reduced virus production. vRNA localization depended on Gag membrane association as shown using both myristoylation and Gag nucleocapsid domain proviral mutants. Furthermore, the cytoplasmic localization of vRNA and Gag was not attributable to intracellular or internalized endocytosed virus particles. Our results demonstrate that dynein motor function is important for regulating Gag and vRNA egress on endosomal membranes in the cytoplasm to directly impact on viral production.
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Affiliation(s)
- Martin Lehmann
- HIV-1 RNA Trafficking Laboratory, Lady Davis Institute for Medical Research, Quebec
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23
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Yamamoto N, Takase-Yoden S. Analysis of cis-regulatory elements in the 5' untranslated region of murine leukemia virus controlling protein expression. Microbiol Immunol 2009; 53:140-8. [PMID: 19302524 DOI: 10.1111/j.1348-0421.2008.00103.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
It has previously been reported by us that high-level expression of the Env protein of Fr-MLV clone A8 in brains is crucial for induction of spongiform neurodegeneration, and that the 0.3-kb fragment containing the R, U5, and the 5' leader sequence of A8 is responsible for neuropathogenicity. In the present study, the role of the 5' untranslated region in protein expression was investigated. Luciferase expression vectors containing the LTR (R-U3-U5) and 5' leader sequence of A8 and non-neuropathogenic 57 Fr-MLV, designated gl-A8 and gl-57, and their chimeric vectors, were constructed, and transfected into rat glial cells F10. Replacement of the region containing the 3' half of R, U5, and 5' leader sequence of gl-A8 with that of 57 showed a reduction in luciferase activities, and replacement of this region of gl-57 with that of A8 showed increased luciferase activity. These results show that the region containing the 3' half of R, U5, and 5' leader sequence of A8 more efficiently up-regulates protein expression than 57. In particular, the 3' half of 5' leader of A8 was most responsible for the up-regulation of protein expression. Of interest, after replacement of the fragments between A8 and 57, changes in the activities of vectors containing A8-U3 paralleled the amount of mRNA, but the activities of vectors containing 57-U3 did not. Furthermore, it is suggested that the region containing R, U5, and the 5' leader sequence influences transcriptional or post-transcriptional steps, depending on the upstream sequence containing enhancer elements and promoter.
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Affiliation(s)
- Naoki Yamamoto
- Department of Bioinformatics, Faculty of Engineering, Soka University, Hachioji, Tokyo 192-8577, Japan
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24
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Sinck L, Richer D, Howard J, Alexander M, Purcell DFJ, Marquet R, Paillart JC. In vitro dimerization of human immunodeficiency virus type 1 (HIV-1) spliced RNAs. RNA (NEW YORK, N.Y.) 2007; 13:2141-2150. [PMID: 17925344 PMCID: PMC2080610 DOI: 10.1261/rna.678307] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2007] [Accepted: 08/28/2007] [Indexed: 05/25/2023]
Abstract
The human immunodeficiency virus type 1 (HIV-1) packages its genomic RNA as a dimer of homologous RNA molecules that has to be selected among a multitude of cellular and viral RNAs. Interestingly, spliced viral mRNAs are packaged into viral particles with a relatively low efficiency despite the fact that they contain most of the extended packaging signal found in the 5' untranslated region of the genomic RNA, including the dimerization initiation site (DIS). As a consequence, HIV-1 spliced viral RNAs can theoretically homodimerize and heterodimerize with the genomic RNA, and thus they should directly compete with genomic RNA for packaging. To shed light on this issue, we investigated for the first time the in vitro dimerization properties of spliced HIV-1 RNAs. We found that singly spliced (env, vpr) and multispliced (tat, rev, and nef) RNA fragments are able to dimerize in vitro, and to efficiently form heterodimers with genomic RNA. Chemical probing experiments and inhibition of RNA dimerization by an antisense oligonucleotide directed against the DIS indicated that the DIS is structurally functional in spliced HIV-1 RNA, and that RNA dimerization occurs through a loop-loop interaction. In addition, by combining in vitro transcription and dimerization assays, we show that heterodimers can be efficiently formed only when the two RNA fragments are synthesized simultaneously, in the same environment. Together, our results support a model in which RNA dimerization would occur during transcription in the nucleus and could thus play a major role in splicing, transport, and localization of HIV-1 RNA.
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Affiliation(s)
- Lucile Sinck
- Architecture et Réactivité de l'ARN, Université Louis Pasteur, CNRS, IBMC, 67084, Strasbourg cedex, France
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25
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Freed EO, Mouland AJ. The cell biology of HIV-1 and other retroviruses. Retrovirology 2006; 3:77. [PMID: 17083721 PMCID: PMC1635732 DOI: 10.1186/1742-4690-3-77] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2006] [Accepted: 11/03/2006] [Indexed: 12/23/2022] Open
Abstract
In recognition of the growing influence of cell biology in retrovirus research, we recently organized a Summer conference sponsored by the American Society for Cell Biology (ASCB) on the Cell Biology of HIV-1 and other Retroviruses (July 20–23, 2006, Emory University, Atlanta, Georgia). The meeting brought together a number of leading investigators interested in the interplay between cell biology and retrovirology with an emphasis on presentation of new and unpublished data. The conference was arranged from early to late events in the virus replication cycle, with sessions on viral fusion, entry, and transmission; post-entry restrictions to retroviral infection; nuclear import and integration; gene expression/regulation of retroviral Gag and genomic RNA; and assembly/release. In this review, we will attempt to touch briefly on some of the highlights of the conference, and will emphasize themes and trends that emerged at the meeting.
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Affiliation(s)
- Eric O Freed
- Virus-Cell Interaction Section, HIV Drug Resistance Program, National Cancer Institute, Frederick, MD. 21702-1201, USA
| | - Andrew J Mouland
- HIV-1 RNA Trafficking Laboratory, Lady Davis Institute for Medical Research-Sir Mortimer B. Davis Jewish General Hospital, Departments of Medicine, Microbiology and Immunology, McGill University, Montréal, Québec, H3T 1E2, Canada
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26
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Abstract
Full-length retroviral RNA has three well-established functions: it constitutes the genomic RNA that is packaged into virions and is transmitted to target cells by infection, it is the messenger RNA (mRNA) template for viral Gag and Pol protein synthesis and it serves as the pre-mRNA for the production of subgenomic spliced mRNAs that encode additional viral proteins such as Env. More recent work indicates that these full-length RNAs also play important roles in the assembly of virus particles, not only as a structural scaffold that facilitates viral core formation but also as a potential regulator of the assembly process itself. Here, we discuss how these assorted activities may be coupled with each other, paying particular attention to the importance of RNA trafficking and subcellular localization in the cytoplasm, possible points of regulation, and the role(s) played by cellular RNA-binding proteins.
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Affiliation(s)
- Chad M Swanson
- Department of Infectious Diseases, King's College London School of Medicine, 2nd Floor New Guy's House, Guy's Hospital, London Bridge, London, SE1 9RT, UK
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27
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Rasmussen SV, Pedersen FS. Co-localization of gammaretroviral RNAs at their transcription site favours co-packaging. J Gen Virol 2006; 87:2279-2289. [PMID: 16847124 DOI: 10.1099/vir.0.81759-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A retroviral vector-rescue system in which co-packaging of the two co-expressed vectors is required for transduction of one of the vectors has been established previously. By using this rescue system, two distinct packaging-cell populations have been generated. One cell population expressed retroviral RNA from co-localized transcription sites, resulting in local and overlapping accumulation of both RNA transcripts. In the other cell population, the two transcription cassettes were introduced separately, leading to distinct transcription sites of the two RNAs and no significant co-localization of the RNAs. Titre measurements from the two distinct cell populations showed large differences in rescue titre, which is an indirect measure of co-packaging efficiency. Thus, the cell populations with overlapping RNA accumulation gave rise to 15-80-fold-higher rescue titres than cell populations with non-overlapping RNA accumulation. These data show that the spatial position of proviral transcription sites affects the level of retroviral RNA co-packaging and suggest that there is already a linkage of RNAs for co-packaging at the transcription site. It is hypothesized that this linkage is due to RNA dimerization taking place at the transcription site.
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Affiliation(s)
- Søren Vestergaard Rasmussen
- Department of Molecular Biology, University of Aarhus, C. F. Møllers Allé, Building 130, DK-8000 Aarhus C, Denmark
| | - Finn Skou Pedersen
- Department of Medical Microbiology and Immunology, University of Aarhus, C. F. Møllers Allé, Building 130, DK-8000 Aarhus C, Denmark
- Department of Molecular Biology, University of Aarhus, C. F. Møllers Allé, Building 130, DK-8000 Aarhus C, Denmark
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Cochrane AW, McNally MT, Mouland AJ. The retrovirus RNA trafficking granule: from birth to maturity. Retrovirology 2006; 3:18. [PMID: 16545126 PMCID: PMC1475878 DOI: 10.1186/1742-4690-3-18] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2005] [Accepted: 03/17/2006] [Indexed: 11/10/2022] Open
Abstract
Post-transcriptional events in the life of an RNA including RNA processing, transport, translation and metabolism are characterized by the regulated assembly of multiple ribonucleoprotein (RNP) complexes. At each of these steps, there is the engagement and disengagement of RNA-binding proteins until the RNA reaches its final destination. For retroviral genomic RNA, the final destination is the capsid. Numerous studies have provided crucial information about these processes and serve as the basis for studies on the intracellular fate of retroviral RNA. Retroviral RNAs are like cellular mRNAs but their processing is more tightly regulated by multiple cis-acting sequences and the activities of many trans-acting proteins. This review describes the viral and cellular partners that retroviral RNA encounters during its maturation that begins in the nucleus, focusing on important events including splicing, 3' end-processing, RNA trafficking from the nucleus to the cytoplasm and finally, mechanisms that lead to its compartmentalization into progeny virions.
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Affiliation(s)
- Alan W Cochrane
- Department of Medical Genetics and Microbiology, University of Toronto, 1 King's College Circle, Toronto, Ontario, M5S 1A8, Canada
| | - Mark T McNally
- Department of Microbiology and Molecular Genetics, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - Andrew J Mouland
- HIV-1 RNA Trafficking Laboratory, Lady Davis Institute for Medical Research-Sir Mortimer B. Davis Jewish General Hospital and McGill University, 3755 Côte-Ste-Catherine Road, H3T 1E2, Canada
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