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Nuclear trafficking of retroviral RNAs and Gag proteins during late steps of replication. Viruses 2013; 5:2767-95. [PMID: 24253283 PMCID: PMC3856414 DOI: 10.3390/v5112767] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2013] [Revised: 10/31/2013] [Accepted: 11/12/2013] [Indexed: 11/16/2022] Open
Abstract
Retroviruses exploit nuclear trafficking machinery at several distinct stages in their replication cycles. In this review, we will focus primarily on nucleocytoplasmic trafficking events that occur after the completion of reverse transcription and proviral integration. First, we will discuss nuclear export of unspliced viral RNA transcripts, which serves two essential roles: as the mRNA template for the translation of viral structural proteins and as the genome for encapsidation into virions. These full-length viral RNAs must overcome the cell's quality control measures to leave the nucleus by co-opting host factors or encoding viral proteins to mediate nuclear export of unspliced viral RNAs. Next, we will summarize the most recent findings on the mechanisms of Gag nuclear trafficking and discuss potential roles for nuclear localization of Gag proteins in retrovirus replication.
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Kula A, Marcello A. Dynamic Post-Transcriptional Regulation of HIV-1 Gene Expression. BIOLOGY 2012; 1:116-33. [PMID: 24832221 PMCID: PMC4009772 DOI: 10.3390/biology1020116] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/11/2012] [Revised: 06/15/2012] [Accepted: 06/18/2012] [Indexed: 01/08/2023]
Abstract
Gene expression of the human immunodeficiency virus type 1 (HIV-1) is a highly regulated process. Basal transcription of the integrated provirus generates early transcripts that encode for the viral products Tat and Rev. Tat promotes the elongation of RNA polymerase while Rev mediates the nuclear export of viral RNAs that contain the Rev-responsive RNA element (RRE). These RNAs are exported from the nucleus to allow expression of Gag-Pol and Env proteins and for the production of full-length genomic RNAs. A balance exists between completely processed mRNAs and RRE-containing RNAs. Rev functions as an adaptor that recruits cellular factors to re-direct singly spliced and unspliced viral RNAs to nuclear export. The aim of this review is to address the dynamic regulation of this post-transcriptional pathway in light of recent findings that implicate several novel cellular cofactors of Rev function.
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Affiliation(s)
- Anna Kula
- Laboratory of Molecular Virology, International Centre for Genetic Engineering and Biotechnology (ICGEB), Padriciano, Trieste 99 34012, Italy.
| | - Alessandro Marcello
- Laboratory of Molecular Virology, International Centre for Genetic Engineering and Biotechnology (ICGEB), Padriciano, Trieste 99 34012, Italy.
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Stably integrated and expressed retroviral sequences can influence nuclear location and chromatin condensation of the integration locus. Chromosoma 2012; 121:353-67. [PMID: 22415776 PMCID: PMC3401306 DOI: 10.1007/s00412-012-0366-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2011] [Revised: 02/27/2012] [Accepted: 02/27/2012] [Indexed: 12/24/2022]
Abstract
The large-scale chromatin organization of retrovirus and retroviral gene vector integration loci has attracted little attention so far. We compared the nuclear organization of transcribed integration loci with the corresponding loci on the homologous chromosomes. Loci containing gamma-retroviral gene transfer vectors in mouse hematopoietic precursor cells showed small but significant repositioning of the integration loci towards the nuclear interior. HIV integration loci in human cells showed a significant repositioning towards the nuclear interior in two out of five cases. Notably, repositioned HIV integration loci also showed chromatin decondensation. Transcriptional activation of HIV by sodium butyrate treatment did not lead to a further enhancement of the differences between integration and homologous loci. The positioning relative to splicing speckles was indistinguishable for integration and homologous control loci. Our data show that stable retroviral integration can lead to alterations of the nuclear chromatin organization, and has the potential to modulate chromatin structure of the host cell. We thus present an example where a few kb of exogenous DNA are sufficient to significantly alter the large-scale chromatin organization of an endogenous locus.
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Poole E, Strappe P, Mok HP, Hicks R, Lever AML. HIV-1 Gag-RNA interaction occurs at a perinuclear/centrosomal site; analysis by confocal microscopy and FRET. Traffic 2005; 6:741-55. [PMID: 16101678 DOI: 10.1111/j.1600-0854.2005.00312.x] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The Gag polyprotein is the major structural protein of human immunodeficiency virus-1 (HIV-1) constituting the viral core. Between translation on cytoplasmic polysomes and assembly into viral particles at the plasma membrane, it specifically captures the RNA genome of the virus through binding RNA structural motifs (packaging signals -Psi) in the RNA. RNA is believed to be a structural facilitator of Gag assembly. Using a combined approach of immunofluorescence detection of Gag protein and in situ hybridisation detection of viral genomic RNA, we demonstrate that Gag protein colocalises early after expression with Psi+ RNA in the perinuclear region and also colocalises with centrioles. Colocalised RNA and protein subsequently traffic through the cytoplasm to the plasma membrane of the cell. Gag expressed from Psi- RNA diffuses throughout the cell. It is not found at centrioles and shows delayed cytoplasmic colocalisation with the RNA genome. RNA capture through Psi does not influence binding of Gag to microfilaments. Gag does not bind to tubulin during export. The presence of the packaging signal may coordinate capture of Psi+ RNA by Gag protein at the centrosome followed by their combined transport to the site of budding. HIV-1 Psi thus acts as a subcellular localisation signal as well as a high-affinity-binding site for Gag.
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Affiliation(s)
- Emma Poole
- Department of Medicine, University of Cambridge, Addenbrooke's Hospital, Cambridge, CB2 2QQ, UK
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Marcello A, Lusic M, Pegoraro G, Pellegrini V, Beltram F, Giacca M. Nuclear organization and the control of HIV-1 transcription. Gene 2004; 326:1-11. [PMID: 14729258 DOI: 10.1016/j.gene.2003.10.018] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The regulation of transcription of the human immunodeficiency virus (HIV) is a complex event of significant pathological relevance, which recapitulates general concepts of cellular transcription with some peculiarities. The viral promoter is embedded in a chromatin structure that exerts powerful repression on transcription; activation of gene expression relies on the combined activity of a series of cellular factors that respond to different external stimuli, and on the function of a single viral regulatory protein, the Tat transactivator. Transcriptional activation is consequent to both chromatin remodeling and to the recruitment of elongation-competent RNA polymerase II complexes onto the integrated promoter, two events that require the coordinate, but transient, assembly of different protein complexes. Application of optical imaging techniques now allows us to appreciate the spatial and temporal evolvement of these reactions in vivo. The picture that is emerging is not only descriptive, but also relevant to the understanding of the regulation of the process. In particular, it appears that the confinement of biomolecules within specific subcellular compartments represents a way to control and coordinate the assembly of functional complexes that regulate viral gene expression.
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Affiliation(s)
- Alessandro Marcello
- Molecular Medicine Laboratory, International Centre for Genetic Engineering and Biotechnology, Area Science Park, Padriciano 99, 34012 Trieste, Italy
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Cmarko D, Bøe SO, Scassellati C, Szilvay AM, Davanger S, Fu XD, Haukenes G, Kalland KH, Fakan S. Rev inhibition strongly affects intracellular distribution of human immunodeficiency virus type 1 RNAs. J Virol 2002; 76:10473-84. [PMID: 12239324 PMCID: PMC136536 DOI: 10.1128/jvi.76.20.10473-10484.2002] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2002] [Accepted: 06/27/2002] [Indexed: 11/20/2022] Open
Abstract
To define the human immunodeficiency virus type 1 (HIV-1) RNA maturation pathways, we analyzed the intracellular distribution of HIV-1 RNA and the viral regulatory proteins Rev and Tat in transfected COS cells and HIV-1-infected lymphoid C8166 cells by means of ultrastructural in situ hybridization using antisense RNA probes and immunoelectron microscopy. The intranuclear viral RNA occurs in ribonucleoprotein fibrils in the perichromatin and interchromatin regions. The simultaneous demonstration of Rev, Tat, Br-labeled RNA, and cellular proteins SC35 and CRM1 in such fibrils reveals the potential of Rev to associate with nascent HIV pre-mRNA and its splicing complex and transport machinery. In a rev-minus system, the env intron-containing, incompletely spliced viral RNAs are revealed only in the nucleus, indicating that Rev is required to initiate the transport to the cytoplasm. Moreover, env intron sequences frequently occur in the periphery of interchromatin granule clusters, while the probe containing the rev exon sequence does not associate with this nucleoplasmic domain. When cells were treated with the CRM1 inhibitor leptomycin B in the presence of Rev protein, the env intron containing HIV RNAs formed clusters throughout the nucleoplasm and accumulated at the nuclear pores. This suggests that Rev is necessary and probably also sufficient for the accumulation of incompletely spliced HIV RNAs at the nuclear pores while CRM1 is needed for translocation across the nuclear pore complex.
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MESH Headings
- Active Transport, Cell Nucleus
- Animals
- COS Cells
- Cell Nucleus/metabolism
- Chlorocebus aethiops
- Exons
- Gene Products, rev/genetics
- Gene Products, rev/metabolism
- Gene Products, tat/genetics
- Genes, env
- HIV-1/genetics
- Humans
- Intracellular Fluid/metabolism
- Introns
- Karyopherins/metabolism
- Nuclear Proteins/metabolism
- Plasmids
- RNA Splicing
- RNA, Messenger
- RNA, Viral/metabolism
- Receptors, Cytoplasmic and Nuclear
- Ribonucleoproteins
- Serine-Arginine Splicing Factors
- Transfection
- Virion
- rev Gene Products, Human Immunodeficiency Virus
- tat Gene Products, Human Immunodeficiency Virus
- Exportin 1 Protein
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Affiliation(s)
- Dusan Cmarko
- Centre of Electron Microscopy, University of Lausanne, 27 Bugnon, CH-1005 Lausanne, Switzerland
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Affiliation(s)
- A Michienzi
- Molecular Biology Department, Beckman Research Institute of the City of Hope, Duarte, California 91010, USA
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Bell P, Montaner LJ, Maul GG. Accumulation and intranuclear distribution of unintegrated human immunodeficiency virus type 1 DNA. J Virol 2001; 75:7683-91. [PMID: 11462040 PMCID: PMC115003 DOI: 10.1128/jvi.75.16.7683-7691.2001] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2001] [Accepted: 05/09/2001] [Indexed: 12/12/2022] Open
Abstract
The RNA genome of human immunodeficiency virus type 1 (HIV-1) is converted into DNA after infection in order to integrate into the host cell DNA. However, a large number of these reverse-transcribed genomes remain unintegrated in the nucleus of infected cells. Currently, there are no data available about the intranuclear distribution pattern of unintegrated HIV-1 DNA in relation to nuclear structures as observed on the single-cell level. In the present study, we investigated the intranuclear fate of unintegrated viral DNA in cell lines expressing CD4 and coreceptors (HOS-CD4.CCR5 and U373-MAGI-CXCR4(CEM)) infected with HIV-1 (strain 89.6). We used a novel approach to distinguish in situ unintegrated from integrated viral DNA by performing fluorescent in situ hybridization on cells in which stress-induced chromosome condensation had been induced, a procedure that contracts chromosomes independent of the cell cycle. Cells infected for 15 h accumulated large amounts of HIV-1 DNA which was located between the condensed chromosome strands, allowing the identification of this viral DNA as unintegrated. In contrast, in HeLa/LAV, a cell line carrying integrated HIV-1 genomes, the great majority of viral DNA colocalized with the cellular DNA. We show that unintegrated HIV-1 DNA does not evenly distribute within the host cell nucleus but tends to aggregate into clusters containing many copies of the viral genomes. The formation of these DNA clusters was independent of viral DNA replication and thus appeared to result solely from multiple infections. The DNA aggregates remained in the nuclei of infected cells for at least 25 h after the infection was stopped. The emergence of transcription sites, which most likely denote sites of the integrated provirus, lagged clearly behind the accumulation of viral DNA. These transcription foci could not be linked to unintegrated DNA molecules, suggesting that this DNA type is unable to transcribe, at least at levels comparable to those of integrated DNA. Neither unintegrated HIV-1 DNA nor transcription foci nor integrated DNA was observed to associate with nuclear domain 10 (ND10), a nuclear structure known to represent the site where several DNA viruses replicate and transcribe. Also, HIV-1 does not modify ND10 at early or late times of infection. There was no specific association of HIV-1 transcripts with splicing factor SC35 domains, in contrast to what has been reported for a number of both cellular and viral genes. Surprisingly, unintegrated HIV-1 DNA was found to accumulate within or in close association with SC35 domains, demonstrating a specific distribution of the viral DNA within the host cell nucleus. Taken together, our results demonstrate that unintegrated proviral HIV-1 DNA does not randomly localize within infected cells but preferentially aggregates in the nucleus within SC35 domains.
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Affiliation(s)
- P Bell
- The Wistar Institute, Philadelphia, Pennsylvania 19104, USA
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Hauber J. Nuclear export mediated by the Rev/Rex class of retroviral Trans-activator proteins. Curr Top Microbiol Immunol 2001; 259:55-76. [PMID: 11417127 DOI: 10.1007/978-3-642-56597-7_3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/20/2023]
Affiliation(s)
- J Hauber
- Institute for Clinical and Molecular Virology, University of Erlangen-Nürnberg, Schlossgarten 4, 91054 Erlangen, Germany
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Michienzi A, Cagnon L, Bahner I, Rossi JJ. Ribozyme-mediated inhibition of HIV 1 suggests nucleolar trafficking of HIV-1 RNA. Proc Natl Acad Sci U S A 2000; 97:8955-60. [PMID: 10922055 PMCID: PMC16803 DOI: 10.1073/pnas.97.16.8955] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The HIV regulatory proteins Tat and Rev have a nucleolar localization property in human cells. However, no functional role has been attributed to this localization. Recently it has been demonstrated that expression of Rev induces nucleolar relocalization of some protein factors involved in Rev export. Because the function of Rev is to bind HIV RNA and facilitate transport of singly spliced and unspliced RNA to the cytoplasm, it is likely that the nucleolus plays a critical role in HIV-1 RNA export. As a test for trafficking of HIV-1 RNAs into the nucleolus, a hammerhead ribozyme that specifically cleaves HIV-1 RNA was inserted into the body of the U16 small nucleolar RNA, resulting in accumulation of the ribozyme within the nucleoli of human cells. HeLa CD4(+) and T cells expressing this nucleolar localized ribozyme exhibit dramatically suppressed HIV-1 replication. The results presented here suggest a trafficking of HIV-1 RNA through the nucleoli of human cells, thus posing a different paradigm for lentiviral RNA processing.
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Affiliation(s)
- A Michienzi
- Department of Molecular Biology, Beckman Research Institute of the City of Hope, and Graduate School of Biological Sciences, City of Hope, Duarte, CA 91010-3011, USA
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Kjems J, Askjaer P. Rev protein and its cellular partners. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2000; 48:251-98. [PMID: 10987094 DOI: 10.1016/s1054-3589(00)48009-9] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- J Kjems
- Department of Molecular and Structural Biology, University of Aarhus, Denmark
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Favaro JP, Maldarelli F, Arrigo SJ, Schmidt MG. Effect of rev on the cytoplasmic localization of intron-containing human immunodeficiency virus type 1 RNA. Virology 1999; 255:237-49. [PMID: 10069949 DOI: 10.1006/viro.1998.9584] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Human immunodeficiency virus type 1 (HIV-1) proteins are expressed from both intron-containing and completely spliced RNAs. Rev, an HIV-1 regulatory protein, is necessary for the expression of intron-containing RNAs. The effect of Rev on the subcellular localization of intron-containing HIV-1 RNA was examined by in situ RNA hybridization. In the presence of Rev, intron-containing HIV-1 RNA accumulated at the nuclear membrane and within the cytoplasm of transfected cells. In the absence of Rev, intron-containing HIV-1 RNA accumulated within the nucleus. In approximately 20% of the cells transfected in the absence of Rev, intron-containing HIV-1 RNA was also found in the cytoplasm. Differences in the subcytoplasmic localization of intron-containing HIV-1 RNA in the presence and absence of Rev were not observed using in situ RNA hybridization. To determine the effect of Rev on RNA localization within the cytoplasm, an extensive fractionation protocol involving both hypotonic and detergent lysis was used. In the presence of Rev, 40.9 +/- 4.6% of the cytoplasmic intron-containing HIV-1 RNA was released by hypotonic lysis. A similar fractionation profile was seen for several other translated viral and cellular RNAs. However, in the absence of Rev, only 16.5 +/- 5.1% of the cytoplasmic intron-containing HIV-1 RNA was released on hypotonic lysis (P < 0. 005). Thus the cytoplasmic fractionation pattern of this RNA was altered in the absence of Rev.
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Affiliation(s)
- J P Favaro
- Department of Microbiology and Immunology, Medical University of South Carolina, Charleston, South Carolina, 29425-2230, USA
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