201
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Coburn GA, Wiegand HL, Kang Y, Ho DN, Georgiadis MM, Cullen BR. Using viral species specificity to define a critical protein/RNA interaction surface. Genes Dev 2001; 15:1194-205. [PMID: 11358864 PMCID: PMC313802 DOI: 10.1101/gad.888201] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The Tap protein mediates the sequence-specific nuclear export of mRNAs bearing the retroviral constitutive transport element (CTE) and also plays a critical role in the sequence nonspecific export of cellular mRNAs. Previously, we have demonstrated that CTE function displays species specificity, that is, the CTE functions in human but not quail cells. Here, we demonstrate that quail Tap fails to support CTE function because it cannot bind the CTE. However, changing a single residue in quail Tap, glutamine 246, to arginine, the residue found in human Tap, rescues both CTE function and CTE binding. This residue, which is located on the exterior of a recently reported molecular structure of Tap, defines a surface on Tap that is critical for CTE binding. These data emphasize the potential importance of cross-species genetic complementation in the identification and characterization of cellular factors that are critical for different aspects of viral replication.
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Affiliation(s)
- G A Coburn
- Howard Hughes Medical Institute, Duke University Medical Center, Durham, North Carolina 27710, USA
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202
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Ruvolo V, Gupta AK, Swaminathan S. Epstein-Barr virus SM protein interacts with mRNA in vivo and mediates a gene-specific increase in cytoplasmic mRNA. J Virol 2001; 75:6033-41. [PMID: 11390605 PMCID: PMC114319 DOI: 10.1128/jvi.75.13.6033-6041.2001] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
SM is an Epstein-Barr virus (EBV) gene expressed during early lytic replication of EBV. SM encodes a nuclear phosphoprotein that functions as a posttranscriptional regulator of gene expression. SM has been implicated in several aspects of gene regulation, including nuclear mRNA stabilization, posttranscriptional processing, and nuclear mRNA export. Activation by SM is promoter independent but gene specific. The mechanism by which SM selectively activates some EBV target genes or heterologous reporter genes remains to be determined. SM binds RNA in vitro, suggesting that sequence- or structure-specific mRNA interactions might mediate SM specificity. We have further analyzed RNA binding by SM and demonstrated that proteolytic cleavage of SM and consequent exposure of an arginine-rich region are necessary to allow RNA binding in vitro. However, SM mutants with deletions of this arginine-rich region localized normally in the nucleus and were fully functional in gene activation. We therefore developed an assay to study in vivo interactions of SM with target mRNAs based on immunoprecipitation of SM from cell lysates followed by RNase protection analysis. Using this assay, we demonstrated that SM forms complexes with specific mRNAs in vivo. SM binds mRNAs from both SM-responsive as well as nonresponsive intronless genes and increases the nuclear accumulation of both types of mRNAs. In addition, SM preferentially associates with newly transcribed mRNAs. These data indicate that SM forms complexes with mRNAs in the nucleus and enhances their nuclear accumulation. However, SM does not enhance cytoplasmic accumulation of all transcripts that it binds to the same degree, suggesting that additional mRNA-specific characteristics, such as nuclear retention motifs or binding sites for cellular proteins, also determine responsiveness to SM.
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Affiliation(s)
- V Ruvolo
- University of Florida Shands Cancer Center, University of Florida, 1600 SW Archer Rd., Gainesville, FL 32610, USA
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203
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Zolotukhin AS, Michalowski D, Smulevitch S, Felber BK. Retroviral constitutive transport element evolved from cellular TAP(NXF1)-binding sequences. J Virol 2001; 75:5567-75. [PMID: 11356964 PMCID: PMC114269 DOI: 10.1128/jvi.75.12.5567-5575.2001] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The constitutive transport element (CTE) of type D retroviruses serves as a signal of nuclear export of unspliced viral RNAs. The human TAP(NXF1) protein, a cellular mRNA export factor, directly binds to CTE and mediates nuclear export of CTE-containing RNAs. Here, we use genomic SELEX (systematic evolution of ligands by exponential enrichment) to show that the human genome encodes a family of high-affinity TAP ligands. These TAP-binding elements (TBE) are 15-bp minisatellite repeats that are homologous to the core TAP-binding sites in CTE. The repeats are positioned similarly in the RNA secondary structures of CTE and TBE. Like CTE, TBE is an active nuclear export signal. CTE elements of different species share sequence similarities to TBE in the regions that are neutral for CTE function. This conservation points to a possible common ancestry of the two elements, and in fact, TBE has properties expected from a primordial CTE. Additionally, a molecular fossil of a TBE-like minisatellite is found in the genome of a modern retroelement. These findings constitute direct evidence of an evolutionary link between TBE-related minisatellites and CTE.
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Affiliation(s)
- A S Zolotukhin
- Human Retrovirus Pathogenesis Section, Basic Research Laboratory, Center for Cancer Research, National Cancer Institute-Frederick, Frederick, Maryland 21702-1201, USA
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204
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Klimatcheva E, Planelles V, Day SL, Fulreader F, Renda MJ, Rosenblatt J. Defective lentiviral vectors are efficiently trafficked by HIV-1 and inhibit its replication. Mol Ther 2001; 3:928-39. [PMID: 11407907 DOI: 10.1006/mthe.2001.0344] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Gene therapy against HIV infection should involve vector-mediated delivery of anti-HIV therapeutic genes into T-lymphocytes and macrophages or, alternatively, hematopoietic progenitors. Transduction of mature cells with defective vectors would have limited success because the vector would disappear with cell turnover. However, if a vector could be trafficked by wild-type HIV, initial transduction of a majority of the population would not be required, as the vector would be able to spread. We describe HIV-1-based lentiviral vectors that are efficiently packaged and trafficked by HIV-1, allowing a small number of cells initially transduced to spread the vector within a nontransduced cell population. We examined whether the presence or absence of the rev gene and the Rev-responsive element (RRE) would have a noticeable effect on the ability of lentiviral vectors to be trafficked and to inhibit HIV-1 replication. We found that replacement of rev/RRE with a constitutive transport element from Mason-Pfizer monkey virus had no apparent effect on trafficking and did not change the intrinsic inhibitory abilities of the vectors. We also constructed a rev/RRE-independent HIV-1-derived vector carrying a trans-dominant negative mutant of HIV-1 Rev, RevM10. This vector was less efficiently trafficked by HIV-1 and, despite the presence of an anti-HIV-1 gene, RevM10, was less efficient at inhibiting HIV-1 replication when introduced into a target T-cell population.
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Affiliation(s)
- E Klimatcheva
- Department of Medicine, University of Rochester Cancer Center, 601 Elmwood Avenue, Rochester, New York 14642, USA
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205
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Browning MT, Schmidt RD, Lew KA, Rizvi TA. Primate and feline lentivirus vector RNA packaging and propagation by heterologous lentivirus virions. J Virol 2001; 75:5129-40. [PMID: 11333894 PMCID: PMC114918 DOI: 10.1128/jvi.75.11.5129-5140.2001] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Development of safe and effective gene transfer systems is critical to the success of gene therapy protocols for human diseases. Currently, several primate lentivirus-based gene transfer systems, such as those based on human and simian immunodeficiency viruses (HIV/SIV), are being tested; however, their use in humans raises safety concerns, such as the generation of replication-competent viruses through recombination with related endogenous retroviruses or retrovirus-like elements. Due to the greater phylogenetic distance from primate lentiviruses, feline immunodeficiency virus (FIV) is becoming the lentivirus of choice for human gene transfer systems. However, the safety of FIV-based vector systems has not been tested experimentally. Since lentiviruses such as HIV-1 and SIV have been shown to cross-package their RNA genomes, we tested the ability of FIV RNA to get cross-packaged into primate lentivirus particles such as HIV-1 and SIV, as well as a nonlentiviral retrovirus such as Mason-Pfizer monkey virus (MPMV), and vice versa. Our results reveal that FIV RNA can be cross-packaged by primate lentivirus particles such as HIV-1 and SIV and vice versa; however, a nonlentivirus particle such as MPMV is unable to package FIV RNA. Interestingly, FIV particles can package MPMV RNA but cannot propagate the vector RNA further for other steps of the retrovirus life cycle. These findings reveal that diverse retroviruses are functionally more similar than originally thought and suggest that upon coinfection of the same host, cross- or copackaging may allow distinct retroviruses to generate chimeric variants with unknown pathogenic potential.
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Affiliation(s)
- M T Browning
- Department of Veterinary Sciences, The University of Texas M.D. Anderson Cancer Center, Bastrop, Texas 78602, USA
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206
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Warashina M, Kuwabara T, Kato Y, Sano M, Taira K. RNA-protein hybrid ribozymes that efficiently cleave any mRNA independently of the structure of the target RNA. Proc Natl Acad Sci U S A 2001; 98:5572-7. [PMID: 11344300 PMCID: PMC33254 DOI: 10.1073/pnas.091411398] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2000] [Indexed: 11/18/2022] Open
Abstract
Ribozyme activity in vivo depends on achieving high-level expression, intracellular stability, target colocalization, and cleavage site access. At present, target site selection is problematic because of unforeseeable secondary and tertiary RNA structures that prevent cleavage. To overcome this design obstacle, we wished to engineer a ribozyme that could access any chosen site. To create this ribozyme, the constitutive transport element (CTE), an RNA motif that has the ability to interact with intracellular RNA helicases, was attached to our ribozymes so that the helicase-bound, hybrid ribozymes would be produced in cells. This modification significantly enhanced ribozyme activity in vivo, permitting cleavage of sites previously found to be inaccessible. To confer cleavage enhancement, the CTE must retain helicase-binding activity. Binding experiments demonstrated the likely involvement of RNA helicase(s). We found that attachment of the RNA motif to our tRNA ribozymes leads to cleavage in vivo at the chosen target site regardless of the local RNA secondary or tertiary structure.
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Affiliation(s)
- M Warashina
- Gene Discovery Research Center, National Institute of Advanced Industrial Science and Technology, 1-1-4 Higashi, Tsukuba Science City 305-8562, Japan
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207
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Pandya S, Boris-Lawrie K, Leung NJ, Akkina R, Planelles V. Development of an Rev-independent, minimal simian immunodeficiency virus-derived vector system. Hum Gene Ther 2001; 12:847-57. [PMID: 11339901 DOI: 10.1089/104303401750148847] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Lentiviral vectors are attractive candidates for gene therapy because of their ability to integrate into nondividing cells. To date, conventional HIV-1-based vectors can be produced at higher titers, but concerns regarding their safety for human use exist because of the possibility of recombination leading to production of infectious virions with pathogenic potential. Development of lentivirus vectors based on nonhuman lentiviruses constitutes an active area of research. We described a novel HIV-SIV hybrid vector system in which an HIV-1-derived transfer vector is encapsidated by SIVmac1A11 core particles and pseudotyped with VSV glycoprotein G. In an effort to further develop this vector system, we modified the packaging plasmid by deletion of the SIV accessory genes. Specifically, versions of the packaging plasmid (SIVpack) lacking vif, vpr, vpx, and/or nef were constructed. Our results indicate that, as with HIV-1-based packaging plasmids, deletion of accessory genes has no significant effect on transduction in either dividing or nondividing cells. The SIV packaging plasmid was also modified with regard to the requirement for RRE and rev. Deletion of the RRE and rev from SIVpack led to dramatic loss of transduction ability. Introduction of the 5' LTR from the spleen necrosis virus to packaging plasmids lacking RRE/Rev was then sufficient to fully restore vector titer. A minimal SIV transfer vector was also developed, which does not require RRE/Rev and exhibits no reduction in transduction efficiency in two packaging systems. The SIV-based vector system described here recapitulates the biological properties of minimal HIV-1-derived systems and is expected to provide an added level of safety for human gene transfer. We suggest that the SIV-derived vector system will also be useful to deliver anti-HIV-1 gene therapy reagents that would inhibit an HIV-1-derived vector.
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Affiliation(s)
- S Pandya
- Department of Medicine, University of Rochester Cancer Center, Rochester, NY 14642, USA
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208
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Nappi F, Schneider R, Zolotukhin A, Smulevitch S, Michalowski D, Bear J, Felber BK, Pavlakis GN. Identification of a novel posttranscriptional regulatory element by using a rev- and RRE-mutated human immunodeficiency virus type 1 DNA proviral clone as a molecular trap. J Virol 2001; 75:4558-69. [PMID: 11312326 PMCID: PMC114209 DOI: 10.1128/jvi.75.10.4558-4569.2001] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2000] [Accepted: 02/20/2001] [Indexed: 01/28/2023] Open
Abstract
Human immunodeficiency virus (HIV) and all other lentiviruses utilize the essential viral protein Rev, which binds to RRE RNA, to export their unspliced and partially spliced mRNAs from the nucleus. We used a rev- and RRE-defective HIV type 1 (HIV-1) molecular clone in complementation experiments to establish a method for the rapid isolation of posttranscriptional regulatory elements from the mammalian genome by selecting for rescue of virus replication. Viruses rescued by this method contained a novel element with homology to rodent intracisternal A-particle (IAP) retroelements. A functional element was contained within a 247-nucleotide fragment named RNA transport element (RTE), which was able to promote replication of the Rev- and RRE-defective HIV-1 in both human lymphoid cell lines and primary lymphocytes, demonstrating its potent posttranscriptional function. RTE was functional in many cell types, indicating that the cellular factors that recognize RTE are widely expressed and evolutionarily conserved. RTE also promoted RNA export from Xenopus oocyte nuclei. RTE-mediated RNA transport was CRM1 independent, and RTE did not show high affinity for binding to mRNA export factor TAP/NXF1. Since CRM1 and TAP/NXF1 are critical export receptors associated with the two recognized mRNA export pathways, these results suggest that RTE functions via a distinct export mechanism. Taken together, our results identify a novel posttranscriptional control element that uses a conserved cellular export mechanism.
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MESH Headings
- Active Transport, Cell Nucleus
- Animals
- Base Sequence
- Carrier Proteins/metabolism
- Cloning, Molecular
- DNA, Viral
- Gene Products, rev/genetics
- Genes, Intracisternal A-Particle
- Genes, Regulator
- Genes, env/genetics
- HIV-1/genetics
- Humans
- Jurkat Cells
- Karyopherins
- Mice
- Molecular Sequence Data
- Mutagenesis
- Nuclear Proteins/metabolism
- Nucleocytoplasmic Transport Proteins
- Proviruses/genetics
- RNA/metabolism
- RNA Processing, Post-Transcriptional
- RNA, Messenger/metabolism
- RNA-Binding Proteins/metabolism
- Receptors, Cytoplasmic and Nuclear
- Regulatory Sequences, Nucleic Acid
- Xenopus laevis
- rev Gene Products, Human Immunodeficiency Virus
- Exportin 1 Protein
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Affiliation(s)
- F Nappi
- Human Retrovirus Section, Basic Research Laboratory, National Cancer Institute-Frederick, Frederick, Maryland 21702-1201, USA
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209
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Yoshizawa I, Soda Y, Mizuochi T, Yasuda S, Rizvi TA, Mizuochi T, Takemori T, Tsunetsugu-Yokota Y. Enhancement of mucosal immune response against HIV-1 Gag by DNA immunization. Vaccine 2001; 19:2995-3003. [PMID: 11282211 DOI: 10.1016/s0264-410x(00)00539-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In order to examine the feasibility of Gag-expression DNA as a potential candidate for HIV vaccine using a mouse model, we injected DNA into mice either intramuscularly or by using a gene gun. Both methods induced a low level of antibody production. However, after booster immunization with p24 protein emulsified with complete Freund's adjuvant via a footpad, we found that only the preceding intramuscular DNA immunization induced an anti-Gag Th1-type (IgG(2a)) antibody response, in addition to the enhancement of a Th2-type (IgG(1)) antibody response. Importantly, when mice were boosted intranasally with p24 and cholera toxin, intramuscular DNA injection was found to enhance both systemic and mucosal Gag-specific immune responses. These results indicate that intramuscular DNA immunization confers the inducibility of memory cells, which circulate around various mucosal tissues. Therefore, intramuscular DNA priming, followed by a mucosal booster immunization, could be considered as a regimen applicable to HIV vaccine.
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Affiliation(s)
- I Yoshizawa
- Department of Immunology, National Institute of Infectious Diseases, 1-23-1 Toyama-cho, Shinjuku-ku, Tokyo 162-8640, Japan
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210
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Guzik BW, Levesque L, Prasad S, Bor YC, Black BE, Paschal BM, Rekosh D, Hammarskjöld ML. NXT1 (p15) is a crucial cellular cofactor in TAP-dependent export of intron-containing RNA in mammalian cells. Mol Cell Biol 2001; 21:2545-54. [PMID: 11259602 PMCID: PMC86886 DOI: 10.1128/mcb.21.7.2545-2554.2001] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
TAP, the human homologue of the yeast protein Mex67p, has been proposed to serve a role in mRNA export in mammalian cells. We have examined the ability of TAP to mediate export of Rev response element (RRE)-containing human immunodeficiency virus (HIV) RNA, a well-characterized export substrate in mammalian cells. To do this, the TAP gene was fused in frame to either RevM10 or RevDelta78-79. These proteins are nonfunctional Rev mutant proteins that can bind to HIV RNA containing the RRE in vivo but are unable to mediate the export of this RNA to the cytoplasm. However, the fusion of TAP to either of these mutant proteins gave rise to chimeric proteins that were able to complement Rev function. Significantly, cotransfection with a vector expressing NXT1 (p15), an NTF2-related cellular factor that binds to TAP, led to dramatic enhancement of the ability of the chimeric proteins to mediate RNA export. Mutant-protein analysis demonstrated that the domain necessary for nuclear export mapped to the C-terminal region of TAP and required the domain that interacts with NXT1, as well as the region that has been shown to interact with nucleoporins. RevM10-TAP function was leptomycin B insensitive. In contrast, the function of this protein was inhibited by DeltaCAN, a protein consisting of part of the FG repeat domain of CAN/Nup214. These results show that TAP can complement Rev nuclear export signal function and redirect the export of intron-containing RNA to a CRM1-independent pathway. These experiments support the role of TAP as an RNA export factor in mammalian cells. In addition, they indicate that NXT1 serves as a crucial cellular cofactor in this process.
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Affiliation(s)
- B W Guzik
- Myles H. Thaler Center for AIDS and Human Retrovirus Research and Department of Microbiology, University of Virginia, Charlottesville, Virginia 22908, USA
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211
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Abstract
We have uncovered a novel function for two members of the SR protein family in mRNA export. Using UV cross-linking, transient transfection, and Xenopus oocyte microinjection, we find that the nucleocytoplasmic shuttling proteins SRp20 and 9G8 interact specifically with a 22-nt RNA element from the histone H2a gene to promote the export of intronless RNAs in both mammalian cells and Xenopus oocytes. Antibodies to SRp20 or 9G8 eliminate RNA binding and significantly inhibit the export of RNAs carrying the element from oocyte nuclei. Our observation that SRp20 and 9G8 can be UV cross-linked to polyadenylated RNA in both the nucleus and cytoplasm of HeLa cells suggests a more general role for these SR proteins in mRNA export.
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Affiliation(s)
- Y Huang
- Department of Molecular Biophysics and Biochemistry, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06536, USA
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212
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Pacchia AL, Adelson ME, Kaul M, Ron Y, Dougherty JP. An inducible packaging cell system for safe, efficient lentiviral vector production in the absence of HIV-1 accessory proteins. Virology 2001; 282:77-86. [PMID: 11259192 DOI: 10.1006/viro.2000.0787] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Lentiviral vectors based on human immunodeficiency virus type 1 (HIV-1) possess the ability to deliver exogenous genes to both dividing and nondividing cells and to subsequently establish a stable provirus in these target cells, which can allow long-term expression of the transferred gene. Herein we describe a stable packaging cell line that is devoid of HIV-1 tat, vif, vpr, vpu, and nef. In order to avoid any risk of cytotoxicity associated with constitutive expression of HIV-1 protease or the VSV-G envelope protein, transcription of the packaging and envelope constructs was tightly controlled by employing the ecdysone-inducible system. Using this cell line, we have been able to consistently generate concentrated pseudotyped vector virus stocks with titers in the range of 10(8) IU/ml, which can efficiently transduce actively dividing and growth-arrested cells in vitro. This novel packaging cell line for lentiviral vectors facilitates the production of high-titer virus stocks in the absence of replication-competent virus and provides us with an important tool for use in future gene transfer studies.
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MESH Headings
- Cell Line
- Ecdysone/pharmacology
- Gene Products, tat/deficiency
- Gene Products, tat/genetics
- Gene Products, vif/deficiency
- Gene Products, vif/genetics
- Gene Products, vpr/deficiency
- Gene Products, vpr/genetics
- Genetic Vectors
- Green Fluorescent Proteins
- HIV-1/genetics
- Human Immunodeficiency Virus Proteins
- Humans
- Lentivirus/genetics
- Luminescent Proteins/genetics
- Membrane Glycoproteins
- Transduction, Genetic
- Transfection
- Viral Envelope Proteins/genetics
- Viral Proteins/genetics
- Viral Regulatory and Accessory Proteins/deficiency
- Viral Regulatory and Accessory Proteins/genetics
- Virus Replication
- tat Gene Products, Human Immunodeficiency Virus
- vif Gene Products, Human Immunodeficiency Virus
- vpr Gene Products, Human Immunodeficiency Virus
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Affiliation(s)
- A L Pacchia
- Department of Molecular Genetics and Microbiology, Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, New Jersey 08854, USA
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213
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Hofmann W, Reichart B, Ewald A, Müller E, Schmitt I, Stauber RH, Lottspeich F, Jockusch BM, Scheer U, Hauber J, Dabauvalle MC. Cofactor requirements for nuclear export of Rev response element (RRE)- and constitutive transport element (CTE)-containing retroviral RNAs. An unexpected role for actin. J Cell Biol 2001; 152:895-910. [PMID: 11238447 PMCID: PMC2198816 DOI: 10.1083/jcb.152.5.895] [Citation(s) in RCA: 177] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2000] [Accepted: 01/16/2001] [Indexed: 11/22/2022] Open
Abstract
Nuclear export of proteins containing leucine-rich nuclear export signals (NESs) is mediated by the export receptor CRM1/exportin1. However, additional protein factors interacting with leucine-rich NESs have been described. Here, we investigate human immunodeficiency virus type 1 (HIV-1) Rev-mediated nuclear export and Mason-Pfizer monkey virus (MPMV) constitutive transport element (CTE)-mediated nuclear export in microinjected Xenopus laevis oocytes. We show that eukaryotic initiation factor 5A (eIF-5A) is essential for Rev and Rev-mediated viral RNA export, but not for nuclear export of CTE RNA. In vitro binding studies demonstrate that eIF-5A is required for efficient interaction of Rev-NES with CRM1/exportin1 and that eIF-5A interacts with the nucleoporins CAN/nup214, nup153, nup98, and nup62. Quite unexpectedly, nuclear actin was also identified as an eIF-5A binding protein. We show that actin is associated with the nucleoplasmic filaments of nuclear pore complexes and is critically involved in export processes. Finally, actin- and energy-dependent nuclear export of HIV-1 Rev is reconstituted by using a novel in vitro egg extract system. In summary, our data provide evidence that actin plays an important functional role in nuclear export not only of retroviral RNAs but also of host proteins such as protein kinase inhibitor (PKI).
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Affiliation(s)
- Wilma Hofmann
- Department of Cell and Developmental Biology, Biocenter of the University of Würzburg, D-97074 Würzburg, Germany
| | - Beate Reichart
- Department of Cell and Developmental Biology, Biocenter of the University of Würzburg, D-97074 Würzburg, Germany
| | - Andrea Ewald
- Department of Cell and Developmental Biology, Biocenter of the University of Würzburg, D-97074 Würzburg, Germany
| | - Eleonora Müller
- Department of Cell and Developmental Biology, Biocenter of the University of Würzburg, D-97074 Würzburg, Germany
| | - Iris Schmitt
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037
| | - Roland H. Stauber
- Institute for Clinical and Molecular Virology, University Erlangen-Nürnberg, D-91054 Erlangen, Germany
| | | | - Brigitte M. Jockusch
- Cell Biology, Zoological Institute, Technical University of Braunschweig, D-38092 Braunschweig, Germany
| | - Ulrich Scheer
- Department of Cell and Developmental Biology, Biocenter of the University of Würzburg, D-97074 Würzburg, Germany
| | - Joachim Hauber
- Institute for Clinical and Molecular Virology, University Erlangen-Nürnberg, D-91054 Erlangen, Germany
| | - Marie-Christine Dabauvalle
- Department of Cell and Developmental Biology, Biocenter of the University of Würzburg, D-97074 Würzburg, Germany
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214
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Mouland AJ, Xu H, Cui H, Krueger W, Munro TP, Prasol M, Mercier J, Rekosh D, Smith R, Barbarese E, Cohen EA, Carson JH. RNA trafficking signals in human immunodeficiency virus type 1. Mol Cell Biol 2001; 21:2133-43. [PMID: 11238947 PMCID: PMC86835 DOI: 10.1128/mcb.21.6.2133-2143.2001] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Intracellular trafficking of retroviral RNAs is a potential mechanism to target viral gene expression to specific regions of infected cells. Here we show that the human immunodeficiency virus type 1 (HIV-1) genome contains two sequences similar to the hnRNP A2 response element (A2RE), a cis-acting RNA trafficking sequence that binds to the trans-acting trafficking factor, hnRNP A2, and mediates a specific RNA trafficking pathway characterized extensively in oligodendrocytes. The two HIV-1 sequences, designated A2RE-1, within the major homology region of the gag gene, and A2RE-2, in a region of overlap between the vpr and tat genes, both bind to hnRNP A2 in vitro and are necessary and sufficient for RNA transport in oligodendrocytes in vivo. A single base change (A8G) in either sequence reduces hnRNP A2 binding and, in the case of A2RE-2, inhibits RNA transport. A2RE-mediated RNA transport is microtubule and hnRNP A2 dependent. Differentially labelled gag and vpr RNAs, containing A2RE-1 and A2RE-2, respectively, coassemble into the same RNA trafficking granules and are cotransported to the periphery of the cell. tat RNA, although it contains A2RE-2, is not transported as efficiently as vpr RNA. An A2RE/hnRNP A2-mediated trafficking pathway for HIV RNA is proposed, and the role of RNA trafficking in targeting HIV gene expression is discussed.
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Affiliation(s)
- A J Mouland
- Laboratory of Human Retrovirology, Department of Microbiology and Immunology, University of Montreal, Montreal, Quebec, Canada
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215
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Flick R, Pettersson RF. Reverse genetics system for Uukuniemi virus (Bunyaviridae): RNA polymerase I-catalyzed expression of chimeric viral RNAs. J Virol 2001; 75:1643-55. [PMID: 11160662 PMCID: PMC114073 DOI: 10.1128/jvi.75.4.1643-1655.2001] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2000] [Accepted: 11/07/2000] [Indexed: 12/28/2022] Open
Abstract
We describe here the development of a reverse genetics system for the phlebovirus Uukuniemi virus, a member of the Bunyaviridae family, by using RNA polymerase I (pol I)-mediated transcription. Complementary DNAs containing the coding sequence for either chloramphenicol acetyltransferase (CAT) or green fluorescent protein (GFP) (both in antisense orientation) were flanked by the 5'- and 3'-terminal untranslated regions of the Uukuniemi virus sense or complementary RNA derived from the medium-sized (M) RNA segment. This chimeric cDNA (pol I expression cassette) was cloned between the murine pol I promoter and terminator and the plasmid transfected into BHK-21 cells. When such cells were either superinfected with Uukuniemi virus or cotransfected with expression plasmids encoding the L (RNA polymerase), N (nucleoprotein), and NSs (nonstructural protein) viral proteins, strong CAT activity or GFP expression was observed. CAT activity was consistently stronger in cells expressing L plus N than following superinfection. No activity was seen without superinfection, nor was activity detected when either the L or N expression plasmid was omitted. Omitting NSs expression had no effect on CAT activity or GFP expression, indicating that this protein is not needed for viral RNA replication or transcription. CAT activity could be serially passaged to fresh cultures by transferring medium from CAT-expressing cells, indicating that recombinant virus containing the reporter construct had been produced. In summary, we demonstrate that the RNA pol I system, originally developed for influenza virus, which replicates in the nucleus, has strong potential for the development of an efficient reverse genetics system also for Bunyaviridae members, which replicate in the cytoplasm.
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Affiliation(s)
- R Flick
- Ludwig Institute for Cancer Research, Stockholm Branch, Karolinska Institute, S-17177 Stockholm, Sweden
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216
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Tan W, Zolotukhin AS, Bear J, Patenaude DJ, Felber BK. The mRNA export in Caenorhabditis elegans is mediated by Ce-NXF-1, an ortholog of human TAP/NXF and Saccharomyces cerevisiae Mex67p. RNA (NEW YORK, N.Y.) 2000; 6:1762-72. [PMID: 11142376 PMCID: PMC1370046 DOI: 10.1017/s1355838200000832] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Human TAP and Saccharomyces cerevisiae Mex67p belong to a family of proteins that mediate mRNA export. Computer searches identified previously two Caenorhabditis elegans genes, C15H11.3 and C115H11.6, that encode putative homologs of hTAP and Mex67p (Segref et al., EMBO J, 1997, 16:3256-3271). Using RNA interference experiments in C. elegans, we found that functional knockout of C15H11.3 resulted in nuclear accumulation of poly(A)-containing RNAs and was lethal for both embryos and adult nematodes. No embryonic or progeny abnormality was observed in functional knockout of C15H11.6. Taken together, these data established that the C15H11.3 gene product is an ortholog of hTAP and Mex67p; thus, it was named Ce-NXF-1. Ce-NXF-1 binds RNA directly and is a nucleocytoplasmic shuttle protein accumulating in the nucleoplasm and at the nuclear rim. The rim association is mediated via unique signals present in the C-terminal portion of all TAP/NXF and Mex67p proteins. This region was shown to interact with the FG-repeat domains of nucleoporins Nup98, Nup153, and Nup214, indicating that the rim association occurs through components of the nuclear pore complex. In summary, Ce-NXF-1 belongs together with hTAP and Mex67p to a family of proteins that participate in mRNA export and can provide a direct molecular link between mRNAs and components of the nuclear pore complex. Therefore, despite differences in mRNA metabolism between these species, they utilize a conserved mRNA transport mechanism.
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Affiliation(s)
- W Tan
- Basic Research Laboratory, Human Retrovirus Pathogenesis Section, National Cancer Institute-Frederick Cancer Research and Development Center, Maryland 21702-1201, USA
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217
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Schambach A, Wodrich H, Hildinger M, Bohne J, Kräusslich HG, Baum C. Context dependence of different modules for posttranscriptional enhancement of gene expression from retroviral vectors. Mol Ther 2000; 2:435-45. [PMID: 11082317 DOI: 10.1006/mthe.2000.0191] [Citation(s) in RCA: 163] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We present a systematic comparison of three modules that enhance expression from retroviral gene transfer vectors at a posttranscriptional level: (i) splice signals (SS) that create an intron in the 5' untranslated region; (ii) constitutive RNA transport elements (CTE), originally discovered in D-type retroviruses; and (iii) the posttranscriptional regulatory element of woodchuck hepatitis virus (WPRE). Here we show that enhancement of expression depends not only on the specific element, but also on the gene of interest, implying context-dependent activity of the RNA elements. Interestingly, different results were obtained for genes that normally require or do not require such control elements. Expression of the HIV-1 gag-protease gene, which normally depends on the viral export factor Rev, was strongly enhanced by an oligomeric CTE, while WPRE had only a marginal effect. On the other hand, both CTE and WPRE compensated for the lack of an intron in the expression of human beta-globin. In this case, the strongest stimulation of RNA production was observed when functional SS were combined with the WPRE. Both CTE and, in particular, WPRE also enhanced expression of cDNAs that do not normally require any such element (green fluorescent protein, human multidrug resistance-1). In this study, functional SS and WPRE acted in an additive manner, resulting in a 10-fold higher level of expression. Our results indicate that the described modules act on different levels of RNA processing, transport, and translation and that the correct choice of a posttranscriptional enhancer configuration depends on the type of cDNA to be expressed.
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Affiliation(s)
- A Schambach
- Abteilung Virologie, Heinrich-Pette-Institut für Experimentelle Virologie und Immunologie, Martinistrasse 52, Hamburg, D-20251, Germany
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218
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Yang J, Bogerd H, Le SY, Cullen BR. The human endogenous retrovirus K Rev response element coincides with a predicted RNA folding region. RNA (NEW YORK, N.Y.) 2000; 6:1551-1564. [PMID: 11105755 PMCID: PMC1370025 DOI: 10.1017/s135583820000100x] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Human endogenous retrovirus K (HERV-K) is the name given to an approximately 30-million-year-old family of endogenous retroviruses present at >50 copies per haploid human genome. Previously, the HERV-K were shown to encode a nuclear RNA export factor, termed K-Rev, that is the functional equivalent of the H-Rev protein encoded by human immunodeficiency virus type 1. HERV-K was also shown to contain a cis-acting target element, the HERV-K Rev response element (K-RRE), that allowed the nuclear export of linked RNA transcripts in the presence of either K-Rev or H-Rev. Here, we demonstrate that the functionally defined K-RRE coincides with a statistically highly significant unusual RNA folding region and present a potential RNA secondary structure for the approximately 416-nt K-RRE. Both in vitro and in vivo assays of sequence specific RNA binding were used to map two primary binding sites for K-Rev, and one primary binding site for H-Rev, within the K-RRE. Of note, all three binding sites map to discrete predicted RNA stem-loop subdomains within the larger K-RRE structure. Although almost the entire 416-nt K-RRE was required for the activation of nuclear RNA export in cells expressing K-Rev, mutational inactivation of the binding sites for K-Rev resulted in the selective loss of the K-RRE response to K-Rev but not to H-Rev. Together, these data strongly suggest that the K-RRE, like the H-RRE, coincides with an extensive RNA secondary structure and identify specific sites within the K-RRE that can recruit either K-Rev or H-Rev to HERV-K RNA transcripts.
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Affiliation(s)
- J Yang
- Department of Genetics and Howard Hughes Medical Institute, Duke University Medical Center, Durham, North Carolina 27710, USA
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219
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Tang H, Wong-Staal F. Specific interaction between RNA helicase A and Tap, two cellular proteins that bind to the constitutive transport element of type D retrovirus. J Biol Chem 2000; 275:32694-700. [PMID: 10924507 DOI: 10.1074/jbc.m003933200] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Constitutive transport element (CTE) facilitates retroviral RNA export by interacting with the cellular RNA export machinery. Two cellular proteins, RNA helicase A (RHA) and Tip-associated protein (Tap) were identified as binding to CTE and were proposed to function as CTE co-factors (1,2). Here, we report that these two CTE-binding proteins interact with each other in vitro and in vivo. The in vitro binding of RHA to Tap is direct and independent of either CTE or the nuclear transport domain of RHA. The removal of the first 60 amino acids of Tap significantly diminishes the binding to RHA. The activity of this Tap mutant to enhance CTE-mediated gene expression is also markedly reduced. A transdominant mutant of Tap inhibited RHA-mediated up-regulation of CTE function in mammalian cells. The nuclear transport domain of RHA also interfered with Tap-mediated transactivation of the CTE function in quail cells, in which the function of CTE is dependent on the expression of a functional human Tap cDNA.
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Affiliation(s)
- H Tang
- Departments of Biology and Medicine, University of California, San Diego, La Jolla, California 92093-0665, USA
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220
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Paca RE, Ogert RA, Hibbert CS, Izaurralde E, Beemon KL. Rous sarcoma virus DR posttranscriptional elements use a novel RNA export pathway. J Virol 2000; 74:9507-14. [PMID: 11000220 PMCID: PMC112380 DOI: 10.1128/jvi.74.20.9507-9514.2000] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Rous sarcoma virus (RSV), a simple retrovirus, needs to export unspliced viral RNA from the nucleus to the cytoplasm, circumventing the host cell restriction on cytoplasmic expression of intron-containing RNA. The cytoplasmic accumulation of full-length viral RNA is promoted by two cis-acting direct repeat (DR) elements that flank the src gene; at least one copy of the DR sequence is necessary for viral replication. We show here that the DR mediates export of a reporter construct from the nucleus, suggesting it is a constitutive transport element (CTE). In contrast, human immunodeficiency virus type 1 (HIV-1) and other complex retroviruses encode accessory proteins, Rev or Rex, which promote export of incompletely spliced viral transcripts. This RNA export pathway is CRM1 dependent and can be blocked by the cytotoxic agent leptomycin B. We show here that DR-mediated export is CRM1 independent, suggesting that RSV uses a different export pathway from that of HIV-1 and other complex retroviruses. The simian retroviruses have a CTE which interacts with the cellular Tap export protein. However, we were unable to detect binding of the RSV DR RNA to Tap, suggesting it may use a different export pathway from that of the simian retroviruses. These data suggest that the RSV DR element uses a novel nucleocytoplasmic export pathway.
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Affiliation(s)
- R E Paca
- Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA
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221
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Abstract
Human immunodeficiency virus type-1 (HIV-1) integrase catalyzes the irreversible insertion of the viral genome into host chromosomal DNA. We have developed a mammalian expression system for the synthesis of authentic HIV-1 integrase in the absence of other viral proteins. Integrase, which bears a N-terminal phenylalanine, was found to be a short-lived protein in human embryo kidney 293T cells. The degradation of integrase could be suppressed by proteasome inhibitors. N-terminal phenylalanine is recognized as a degradation signal by a ubiquitin-proteasome proteolytic system known as the N-end rule pathway. The replacement of N-terminal phenylalanine with methionine, valine, or glycine, which are stabilizing residues in the N-end rule, resulted in metabolically stabilized integrase proteins (half-life of N-terminal Met-integrase was at least 3 h). Conversely, the substitution of N-terminal phenylalanine with other destabilizing residues retained the metabolic instability of integrase. These findings indicate that the HIV-1 integrase is a physiological substrate of the N-end rule. We discuss a possible functional similarity to the better understood turnover of the bacteriophage Mu transposase and functions of integrase instability to the maintenance and integrity of the host cell genome.
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Affiliation(s)
- L C Mulder
- Aaron Diamond AIDS Research Center, The Rockefeller University, New York, New York 10016, USA
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222
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Roberts TM, Boris-Lawrie K. The 5' RNA terminus of spleen necrosis virus stimulates translation of nonviral mRNA. J Virol 2000; 74:8111-8. [PMID: 10933721 PMCID: PMC112344 DOI: 10.1128/jvi.74.17.8111-8118.2000] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The RU5 region at the 5' RNA terminus of spleen necrosis virus (SNV) has been shown to facilitate expression of human immunodeficiency virus type 1 (HIV) unspliced RNA independently of the Rev-responsive element (RRE) and Rev. The SNV sequences act as a distinct posttranscriptional control element to stimulate gag RNA nuclear export and association with polyribosomes. Here we sought to determine whether RU5 functions to neutralize the cis-acting inhibitory sequences (INSs) in HIV RNA that confer RRE/Rev dependence or functions as an independent stimulatory sequence. Experiments with HIV gag reporter plasmids that contain inactivated INS-1 indicated that neutralization of INSs does not account for RU5 function. Results with luciferase reporter gene (luc) plasmids further indicated that RU5 stimulates expression of a nonretroviral RNA that lacks INSs. Northern blot and RT-PCR analyses indicated that RU5 does not increase the steady-state levels or nuclear export of the luc transcript but rather that the U5 region facilitates efficient polyribosomal association of the mRNA. RU5 does not function as an internal ribosome entry site in bicistronic reporter plasmids, and it requires the 5'-proximal position for efficient function. Our results indicate that RU5 contains stimulatory sequences that function in a 5'-proximal position to enhance initiation of translation of a nonretroviral reporter gene RNA. We speculate that RU5 evolved to overcome the translation-inhibitory effect of the highly structured encapsidation signal and other replication motifs in the 5' untranslated region of the retroviral RNA.
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Affiliation(s)
- T M Roberts
- Center for Retrovirus Research, Comprehensive Cancer Center, The Ohio State University, Columbus, Ohio 43210-1093, USA
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223
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Guo W, Winistorfer SC, Stoltzfus CM. Selective inhibition of splicing at the avian sarcoma virus src 3' splice site by direct-repeat posttranscriptional cis elements. J Virol 2000; 74:8513-23. [PMID: 10954552 PMCID: PMC116363 DOI: 10.1128/jvi.74.18.8513-8523.2000] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The direct-repeat elements (dr1) of avian sarcoma virus (ASV) and leukosis virus have the properties of constitutive transport elements (CTEs), which facilitate cytoplasmic accumulation of unspliced RNA. It is thought that these elements represent binding sites for cellular factors. Previous studies have indicated that in the context of the avian sarcoma virus genome, precise deletion of both ASV dr1 elements results in a very low level of virus replication. This is characterized by a decreased cytoplasmic accumulation of unspliced RNA and a selective increase in spliced src mRNA. Deletion of either the upstream or downstream dr1 results in a delayed-replication phenotype. To determine if the same regions of the dr1 mediate inhibition of src splicing and unspliced RNA transport, point mutations in the upstream and downstream elements were studied. In the context of viral genomes with single dr1 elements, the effects of the mutations on virus replication and increases in src splicing closely paralleled the effects of the mutations on CTE activity. For mutants strongly affecting CTE activity and splicing, unspliced RNA but not spliced RNA turned over in the nucleus more rapidly than wild-type RNA. In the context of wild-type virus containing two dr1 elements, mutations of either element that strongly affect CTE activity caused a marked delay of virus replication and a selective increase in src splicing. However, the turnover of the mutant unspliced RNA as well as the spliced mRNA species did not differ significantly from that of the wild type. These results suggest the dr1 elements in ASV act to selectively inhibit src splicing and that both elements contribute to the fitness of the wild-type virus. However, a single dr1 element is sufficient to stabilize unspliced RNA.
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Affiliation(s)
- W Guo
- Department of Microbiology, University of Iowa, Iowa City, Iowa 52242, USA
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224
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Kataoka N, Yong J, Kim VN, Velazquez F, Perkinson RA, Wang F, Dreyfuss G. Pre-mRNA splicing imprints mRNA in the nucleus with a novel RNA-binding protein that persists in the cytoplasm. Mol Cell 2000; 6:673-82. [PMID: 11030346 DOI: 10.1016/s1097-2765(00)00065-4] [Citation(s) in RCA: 283] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
We describe a novel RNA binding protein, Y14, a predominantly nuclear nucleocytoplasmic shuttling protein. Interestingly, Y14 associates preferentially with mRNAs produced by splicing but not with pre-mRNAs, introns, or mRNAs produced from intronless cDNAs. Y14 associates with both nuclear mRNAs and newly exported cytoplasmic mRNAs. Splicing of a single intron is sufficient for Y14 association. Y14-containing nuclear complexes are different from general hnRNP complexes. They contain hnRNP proteins and several unique proteins including the mRNA export factor TAP. Thus, Y14 defines novel intermediates in the pathway of gene expression, postsplicing nuclear preexport mRNPs, and newly exported cytoplasmic mRNPs, whose composition is established by splicing. These findings suggest that pre-mRNA splicing imprints mRNA with a unique set of proteins that persists in the cytoplasm and thereby communicates the history of the transcript.
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Affiliation(s)
- N Kataoka
- Howard Hughes Medical Institute and Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia 19104, USA
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225
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Abstract
In eukaryotic cells, the nuclear membrane creates a barrier between the nucleus and the cytoplasm. Whereas RNA synthesis occurs in the nucleus, they mostly function in the cytoplasm; thus export of RNA molecules from the nucleus to the cytoplasm is indispensable for normal function of the cells. The molecular mechanisms involved in each kind of cellular RNA export is gradually understood. The focus of this review will be mRNA export. mRNAs are multiformed. In order to ensure that this variety of mRNA molecules are all exported, cells are probably equipped with multiple export pathways. A number of proteins is predicted to be involved in mRNA export. Ascertaining which proteins play crucial roles in the pathways is the key point in the study of mRNA export.
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Affiliation(s)
- M C Siomi
- Institute for Genome Research, University of Tokushima, Japan.
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226
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Jehle C, Lipkin WI, Staeheli P, Marion RM, Schwemmle M. Authentic Borna disease virus transcripts are spliced less efficiently than cDNA-derived viral RNAs. J Gen Virol 2000; 81:1947-1954. [PMID: 10900032 DOI: 10.1099/0022-1317-81-8-1947] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Borna disease virus (BDV) is a non-segmented, negative-strand RNA virus that replicates and transcribes its genome in the nucleus of infected cells. It uses the cellular splicing machinery to generate a set of alternatively spliced mRNAs from the 2.8 and 7.1 kb primary transcripts, each harbouring two introns. To determine whether splicing of these transcripts is regulated by viral factors, the extent of splicing was studied in infected cells and COS-7 cells transiently transfected with plasmids encoding the 2.8 kb RNA of BDV. Unspliced RNA was found to be the most abundant RNA species in infected cells, whereas viral transcripts lacking both introns were only found in minute amounts. In sharp contrast, plasmid-derived 2.8 kb RNA was predominantly intron 1-spliced and double-spliced. Co-expression of the BDV proteins P, N and X did not influence splicing of plasmid-expressed 2.8 kb RNA. Furthermore, the splicing pattern did not change when the 2.8 kb RNA was expressed in BDV-infected cells. Based on these results we speculate that splicing of authentic BDV transcripts is tightly linked to transcription by the viral polymerase.
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Affiliation(s)
- Christian Jehle
- Department of Virologie, Institute for Medical Microbiology & Hygiene, University of Freiburg, Hermann-Herder Str. 11, D-79104 Freiburg, Germany1
| | - W Ian Lipkin
- Emerging Diseases Laboratory, Departments of Neurology, Anatomy and Neurobiology, and Microbiology and Molecular Genetics, University of California-Irvine, Irvine, CA 92697-4292, USA2
| | - Peter Staeheli
- Department of Virologie, Institute for Medical Microbiology & Hygiene, University of Freiburg, Hermann-Herder Str. 11, D-79104 Freiburg, Germany1
| | - Rosa M Marion
- Centro Nacional de Biotecnologia (CSIC), Cantoblanco, 28049 Madrid, Spain3
| | - Martin Schwemmle
- Department of Virologie, Institute for Medical Microbiology & Hygiene, University of Freiburg, Hermann-Herder Str. 11, D-79104 Freiburg, Germany1
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227
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Reddy TR, Tang H, Xu W, Wong-Staal F. Sam68, RNA helicase A and Tap cooperate in the post-transcriptional regulation of human immunodeficiency virus and type D retroviral mRNA. Oncogene 2000; 19:3570-5. [PMID: 10951562 DOI: 10.1038/sj.onc.1203676] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Unlike cellular mRNA, retroviral mRNA bypasses the tight coupling of the splicing and nuclear export steps to allow the export of intron-containing viral RNA transcripts to the cytoplasm. Two distinct nuclear export pathways for retroviral mRNA have been described: a CRM-1 dependent pathway mediated by the HIV-1 Rev protein and the Rev Response Element (RRE), and a CRM-1 independent pathway mediated by the Constitutive Transport Element (CTE) of type D retroviruses. Two CTE-binding proteins, RNA helicase A (RHA) and Tap, have been implicated in the nuclear export of CTE-containing RNA. Recently, we reported that expression of RRE-containing RNA could also be mediated by a cellular protein, Sam68, independently of Rev. Here we report evidence that Sam68, RHA and Tap cooperate in the nuclear export of both CTE- and RRE-containing RNA. RHA binds to Sam68 and to Tap both in vivo and in vitro. Over-expression of Sam68 activates both RRE- and CTE-regulated reporter gene expression in human cells and in quail cells in the presence of human Tap. This activation was competitively inhibited by the nuclear transport domain (NTD) of RHA and a transdominant negative mutant of Tap. Conversely, the activation of CTE by Tap in quail cells was inhibited by a transdominant mutant of Sam68 and NTD. We propose that both HIV and type D retroviruses may access the same constitutive RNA nuclear export pathway involving RHA, Tap and Sam68, even though HIV also utilizes the Rev protein for more efficient nuclear export. it is likely that this constitutive export pathway is also used by cellular mRNA, but at a different interface with the splicing process.
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Affiliation(s)
- T R Reddy
- Department of Medicine, University of California, San Diego, La Jolla 92093-0665, USA
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228
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Westberg C, Yang JP, Tang H, Reddy TR, Wong-Staal F. A novel shuttle protein binds to RNA helicase A and activates the retroviral constitutive transport element. J Biol Chem 2000; 275:21396-401. [PMID: 10748171 DOI: 10.1074/jbc.m909887199] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The constitutive transport element (CTE) of type D retroviruses mediates the nuclear export of unspliced viral transcripts. We previously showed that RNA helicase A functionally interacts with CTE and contains a bidirectional nuclear transport domain at the carboxyl terminus. Here we report the identification of a novel human protein, helicase A-binding protein 95 (HAP95), which specifically binds to the carboxyl terminus of RNA helicase A. HAP95 is partially homologous to AKAP95, a member of the A kinase-anchoring protein family, but lacks the protein kinase A binding domain characteristic of this family. HAP95 is a nuclear protein at steady state but shuttles between the nucleus and cytoplasm. Overexpression of HAP95 significantly increases CTE-dependent gene expression but has no effect on general gene expression or that mediated by the Rev/Rev response element of human immunodeficiency virus type 1.
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Affiliation(s)
- C Westberg
- Departments of Biology and Medicine, University of California, San Diego, La Jolla, California 92093-0665, USA
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229
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Srinivasakumar N, Schuening F. Novel Tat-encoding bicistronic human immunodeficiency virus type 1-based gene transfer vectors for high-level transgene expression. J Virol 2000; 74:6659-68. [PMID: 10864682 PMCID: PMC112178 DOI: 10.1128/jvi.74.14.6659-6668.2000] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We describe bicistronic single-exon Tat (72-amino-acid Tat [Tat72])- and full-length Tat (Tat86)-encoding gene transfer vectors based on human immunodeficiency virus type 1 (HIV-1). We created versions of these vectors that were rendered Rev independent by using the constitutive transport element (CTE) from Mason-Pfizer monkey virus (MPMV). Tat72-encoding vectors performed better than Tat86-expressing vectors in gene transfer experiments. CTE-containing vectors, produced in a Rev-independent packaging system, had gene transfer efficiencies nearly equivalent to those produced using a combination RNA transport (CTE and Rev-Rev response element)-based packaging system. The Tat72-encoding vectors could be efficiently transduced into a variety of cell types, showed higher levels of transgene expression than vectors with the simian cytomegalovirus immediate-early or the simian virus 40 early promoter, and provide an alternative to HIV-1 vectors with internal promoters.
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Affiliation(s)
- N Srinivasakumar
- Division of Hematology-Oncology, Department of Medicine, Vanderbilt University, Nashville, Tennessee 37232-6305, USA.
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230
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Kang Y, Bogerd HP, Cullen BR. Analysis of cellular factors that mediate nuclear export of RNAs bearing the Mason-Pfizer monkey virus constitutive transport element. J Virol 2000; 74:5863-71. [PMID: 10846066 PMCID: PMC112081 DOI: 10.1128/jvi.74.13.5863-5871.2000] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2000] [Accepted: 04/05/2000] [Indexed: 11/20/2022] Open
Abstract
There is now convincing evidence that the human Tap protein plays a critical role in mediating the nuclear export of mRNAs that contain the Mason-Pfizer monkey virus constitutive transport element (CTE) and significant evidence that Tap also participates in global poly(A)(+) RNA export. Previously, we had mapped carboxy-terminal sequences in Tap that serve as an essential nucleocytoplasmic shuttling domain, while others had defined an overlapping Tap sequence that can bind to the FG repeat domains of certain nucleoporins. Here, we demonstrate that these two biological activities are functionally correlated. Specifically, mutations in Tap that block nucleoporin binding also block both nucleocytoplasmic shuttling and the Tap-dependent nuclear export of CTE-containing RNAs. In contrast, mutations that do not inhibit nucleoporin binding also fail to affect Tap shuttling. Together, these data indicate that Tap belongs to a novel class of RNA export factors that can target bound RNA molecules directly to the nuclear pore without the assistance of an importin beta-like cofactor. In addition to nucleoporins, Tap has also been proposed to interact with a cellular cofactor termed p15. Although we were able to confirm that Tap can indeed bind p15 specifically both in vivo and in vitro, a mutation in Tap that blocked p15 binding only modestly inhibited CTE-dependent nuclear RNA export. However, p15 did significantly enhance the affinity of Tap for the CTE in vitro and readily formed a ternary complex with Tap on the CTE. This result suggests that p15 may play a significant role in the recruitment of the Tap nuclear export factor to target RNA molecules in vivo.
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Affiliation(s)
- Y Kang
- Department of Genetics, Duke University Medical Center, Durham, North Carolina 27710, USA
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231
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Cherepanov P, Pluymers W, Claeys A, Proost P, Clercq E, Debyser Z. High‐level expression of active HIV‐1 integrase from a synthetic gene in human cells. FASEB J 2000. [DOI: 10.1096/fasebj.14.10.1389] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Peter Cherepanov
- Rega Institute for Medical Research K.U. Leuven B‐3000 Leuven Belgium
| | - Wim Pluymers
- Rega Institute for Medical Research K.U. Leuven B‐3000 Leuven Belgium
| | - Anje Claeys
- Rega Institute for Medical Research K.U. Leuven B‐3000 Leuven Belgium
| | - Paul Proost
- Rega Institute for Medical Research K.U. Leuven B‐3000 Leuven Belgium
| | - Erik Clercq
- Rega Institute for Medical Research K.U. Leuven B‐3000 Leuven Belgium
| | - Zeger Debyser
- Rega Institute for Medical Research K.U. Leuven B‐3000 Leuven Belgium
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232
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Ristea S, Dobbelstein M, Roth J. Rev protein of human immunodeficiency virus type 1 and cellular exportin 1 protein relocalize each other to a subnucleolar structure. AIDS Res Hum Retroviruses 2000; 16:857-65. [PMID: 10875611 DOI: 10.1089/08892220050042792] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The exportin 1/crml protein associates with leucine-rich nuclear export signals (NESs) and mediates nuclear export in various experimental systems. We show here that exportin 1 and the NES-containing human immunodeficiency virus (HIV) type 1 Rev protein relocalize each other to a characteristic dotlike structure within the nucleoli of human cells. On treatment with actinomycin D, Rev remains in these dots longer than in the rest of the nucleoli, arguing that the nucleolar dots do not represent sites of high transport turnover. Transient expression of exportin 1 strongly reduces the expression of a reporter that depends on the export of HIV RNA. When export of hepatitis B virus RNA and simple retrovirus RNA, as well as spliced mRNA, was assayed in this way, exportin 1 inhibited reporter expression to a lesser extent. Thus, an excess of exportin 1 may downregulate Rev-mediated RNA export by sequestering Rev to a subnucleolar structure.
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Affiliation(s)
- S Ristea
- Institut für Virologie, Universität Marburg, Germany
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233
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Affiliation(s)
- B R Cullen
- Howard Hughes Medical Institute and Department of Genetics, Duke University Medical Center, Durham, North Carolina 27710, USA.
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234
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Bacharach E, Gonsky J, Lim D, Goff SP. Deletion of a short, untranslated region adjacent to the polypurine tract in Moloney murine leukemia virus leads to formation of aberrant 5' plus-strand DNA ends in vivo. J Virol 2000; 74:4755-64. [PMID: 10775614 PMCID: PMC111998 DOI: 10.1128/jvi.74.10.4755-4764.2000] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Experiments were performed to determine the function of a 28-nucleotide untranslated sequence lying between the envelope gene and the polypurine tract (PPT) sequence in the Moloney murine leukemia virus (Mo-MuLV) genome. A mutant virus carrying a deletion of this sequence (Mo-MuLVDelta28) replicated more slowly than wild-type (wt) virus and reverted by recombination with endogenous sequences during growth in NIH 3T3 cells. We show that this deletion did not affect the level of viral protein expression or genomic RNA packaging. Mo-MuLVDelta28 served as a helper virus as efficiently as the wt virus; in contrast, a retroviral vector harboring this mutation exhibited reduced transduction efficiency, indicating that the mutation acts not in trans but in cis. Analysis of acutely infected cells revealed that reduced levels of viral DNA were generated by reverse transcription of the Mo-MuLVDelta28 RNA as compared to the wt RNA. Analysis of DNA circle junctions revealed that plus-strand DNA of Mo-MuLVDelta28 but not wt virus often retained the PPT and additional upstream sequences. These structures suggest that aberrant 5' ends of plus-strand DNA were generated by a failure to remove the PPT RNA primer and/or by mispriming at sites upstream of the PPT. These data demonstrate that the major role of the sequences immediately upstream of the PPT is specifying efficient and accurate plus-strand DNA synthesis.
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Affiliation(s)
- E Bacharach
- Department of Biochemistry and Molecular Biophysics, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA
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235
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Abstract
Lentiviruses are associated with chronic diseases of the hematological and neurological systems in animals and man. In particular, human immunodeficiency virus type 1 (HIV-1) is the etiological agent of the global AIDS epidemic. The genomes of lentiviruses are complex, encoding a number of regulatory and accessory proteins not found in other retroviruses. This complexity is reflected in their replication cycle, which reveals intricate regulatory pathways and unique mechanisms for viral persistence. In this review, we highlight some of these unique features for HIV-1, with particular focus on the transcriptional and posttranscriptional control of gene expression. Although our understanding of the biology of HIV-1 is far from complete, the knowledge gained thus far has already led to novel strategies for both virus intervention and exploiting the lentiviruses for therapeutic applications.
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Affiliation(s)
- H Tang
- Department of Medicine and Biology, University of California, San Diego 92093-0665, USA.
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236
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Wodrich H, Schambach A, Kräusslich HG. Multiple copies of the Mason-Pfizer monkey virus constitutive RNA transport element lead to enhanced HIV-1 Gag expression in a context-dependent manner. Nucleic Acids Res 2000; 28:901-10. [PMID: 10648781 PMCID: PMC102582 DOI: 10.1093/nar/28.4.901] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Retroviral gene expression requires nuclear export and translation of incompletely spliced RNA. In the case of human immunodeficiency virus (HIV), this is facilitated by the viral Rev protein binding to its cognate RNA response element (RRE), while other retroviruses contain constitutive transport elements (CTE) binding to cellular factors. These CTE can substitute for the HIV-1 Rev/RRE system, albeit with reduced efficiency. Here, we show that multimeric copies of the CTE restore HIV-1 protein expression to levels comparable to or higher than Rev/RRE in various cell lines from different species. We suggest that multimerization of export factors is important for CTE function, as reported for Rev. CTE function was not affected when the element was displaced from its natural position close to the poly(A) signal, while insertion of an intron into the 3'-untranslated region (3'-UTR) severely reduced CTE activity. In this case, cytoplasmic RNA degradation was observed, which may be mediated by nonsense-mediated RNA decay. In contrast, Rev-dependent gene expression was insensitive to an intron in the 3'-UTR. Finally, we show that the putative CTE-binding protein RNA helicase A is not specifically translocated into the cytoplasm upon overexpression of CTE-containing RNA.
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Affiliation(s)
- H Wodrich
- Heinrich-Pette-Institut für experimentelle Virologie und Immunologie an der Universität Hamburg, Martinstrasse 52, D-20251 Hamburg, Germany
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237
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Zhao Y, Low W, Collins MK. Improved safety and titre of murine leukaemia virus (MLV)-based retroviral vectors. Gene Ther 2000; 7:300-5. [PMID: 10694810 DOI: 10.1038/sj.gt.3301081] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Many retroviral vectors based on murine leukaemia virus (MLV) contain the first 420 nucleotides of the gag gene, as this was reported to increase vector titre by increasing the efficiency of RNA packaging. In this study, deletion of this gag sequence from its original location did not decrease the titre of two retroviral vectors, pBabe puro and MFG-S-. The two vectors could be improved by replacing the gag sequence with a CTE from Mason-Pfizer monkey virus (MPMV). This substitution improved vector titre, while eliminating a region of homology between vector and packaging constructs. Gene Therapy (2000) 7, 300-305.
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Affiliation(s)
- Y Zhao
- Department of Immunology, Windeyer Building, 46 Cleveland St, London WIP 6DB, UK
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238
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Weigel S, Dobbelstein M. The nuclear export signal within the E4orf6 protein of adenovirus type 5 supports virus replication and cytoplasmic accumulation of viral mRNA. J Virol 2000; 74:764-72. [PMID: 10623738 PMCID: PMC111596 DOI: 10.1128/jvi.74.2.764-772.2000] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
During the late phase of adenovirus infection, viral mRNA is efficiently transported from the nucleus to the cytoplasm while most cellular mRNA species are retained in the nucleus. Two viral proteins, E1B-55 kDa and E4orf6, are both necessary for these effects. The E4orf6 protein of adenovirus type 5 binds and relocalizes E1B-55 kDa, and the complex of the two proteins was previously shown to shuttle continuously between the nucleus and cytoplasm. Nucleocytoplasmic transport of the complex is achieved by a nuclear export signal (NES) within E4orf6. Mutation of this signal sequence severely reduces the ability of the E1B-55 kDa-E4orf6 complex to leave the nucleus. Here, we examined the role of functional domains within E4orf6 during virus infection. E4orf6 or mutants derived from it were transiently expressed, followed by infection with recombinant adenovirus lacking the E4 region and determination of virus yield. An arginine-rich putative alpha helix near the carboxy terminus of E4orf6 contributes to E1B-55 kDa binding and relocalization as well as to the synthesis of viral DNA, mRNA, and proteins. Further mutational analysis revealed that mutation of the NES within E4orf6 considerably reduces its ability to support virus production. The same effect was observed when nuclear export was blocked with a competitor. Further, a functional NES within E4orf6 contributed to the efficiency of late virus protein synthesis and viral DNA replication, as well as total and cytoplasmic accumulation of viral late mRNA. Our data support the view that NES-mediated nucleocytoplasmic shuttling strongly enhances most, if not all, intracellular activities of E4orf6 during the late phase of adenovirus infection.
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Affiliation(s)
- S Weigel
- Institut für Virologie, Zentrum für Mikrobiologie und Hygiene, Philipps-Universität Marburg, 35037 Marburg, Germany
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239
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Curran MA, Kaiser SM, Achacoso PL, Nolan GP. Efficient transduction of nondividing cells by optimized feline immunodeficiency virus vectors. Mol Ther 2000; 1:31-8. [PMID: 10933909 DOI: 10.1006/mthe.1999.0007] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Second- and third-generation three-plasmid vector systems, termed FELIX, were constructed from feline immunodeficiency virus (FIV). To enhance vector production, the weak FIV long terminal repeat promoter was replaced with the human cytomegalovirus enhancer/promoter. To construct a minimal system in which Gag-Pol was the only viral protein present, the cytoplasmic transport element was used in place of the FIV Rev-RRE system to facilitate nuclear export of Gag-Pol and the transfer vector. Unconcentrated vector titers routinely exceeded 1 x 10(6) IU/mL for most constructs tested. Second- and optimized third-generation vectors were capable of efficiently infecting G1/S- and G2/M-arrested cells. FIV-based FELIX vectors transduced human dendritic cells, hepatocytes, and aortic smooth muscle with efficiencies similar to that of a control 3T3 cell line. All three of these primary cell types were transducible by both the second- and third-generation FELIX vectors, demonstrating that FIV Gag-Pol alone contains the determinants necessary for transduction of primary cells. In cross-packaging tests, we observed that HIV Gag-Pol does not substantially package FIV vectors; consequently, use of such vectors in human immunodeficiency virus-infected cells should not lead to efficient mobilization of the inserted gene. Thus, this FIV-based vector system offers high efficiency and stable delivery of genes to numerous nondividing and primary cell types, opening new avenues for biological inquiry into normal human cells.
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Affiliation(s)
- M A Curran
- Program in Immunology, Stanford University Medical Center, California 94305-5332, USA.
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240
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Abstract
The compartmentation of eukaryotic cells requires all nuclear proteins to be imported from the cytoplasm, whereas, for example, transfer RNAs, messenger RNAs, and ribosomes are made in the nucleus and need to be exported to the cytoplasm. Nuclear import and export proceed through nuclear pore complexes and can occur along a great number of distinct pathways, many of which are mediated by importin beta-related nuclear transport receptors. These receptors shuttle between nucleus and cytoplasm, and they bind transport substrates either directly or via adapter molecules. They all cooperate with the RanGTPase system to regulate the interactions with their cargoes. Another focus of our review is nuclear export of messenger RNA, which apparently largely relies on export mediators distinct from importin beta-related factors. We discuss mechanistic aspects and the energetics of transport receptor function and describe a number of pathways in detail.
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Affiliation(s)
- D Görlich
- Zentrum für Molekulare Biologie, Universität Heidelberg, Federal Republic of Germany.
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241
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Affiliation(s)
- S W Peltz
- Department of Molecular Genetics, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway,New Jersey 08854, USA.
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242
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Yang J, Cullen BR. Structural and functional analysis of the avian leukemia virus constitutive transport element. RNA (NEW YORK, N.Y.) 1999; 5:1645-1655. [PMID: 10606274 PMCID: PMC1369885 DOI: 10.1017/s1355838299991616] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The observation that cells restrict the nuclear export of incompletely spliced transcripts via the canonical nuclear mRNA export pathway implies that all retroviruses should have evolved a way to direct the unspliced form of their genomic RNA into an alternate export pathway. While the Crm1-dependent pathway used by complex retroviruses to export incompletely spliced viral transcripts is now fairly well understood, less is known about how simple retroviruses accomplish this task. However, the Mason-Pfizer monkey virus (MPMV) has been shown to encode a structured RNA sequence, termed the constitutive transport element (CTE), that recruits a cellular RNA export factor termed Tap. Here we demonstrate that a CTE previously proposed to be present in the avian sarcoma/leukemia (ASV/ALV) family of retroviruses indeed functions as a potent RNA export signal. We have mapped single- and double-stranded regions present in the ASV/ALV CTE in vitro and report that this CTE is predicted to fold into a structure bearing three distinct RNA stem-loops. However, only the central stem-loop is critical for CTE function and this 69-nt structure is, in fact, sufficient when present as a dimer. While the ASV/ALV CTE is shown to function independently of Crm1, as also previously reported for the MPMV CTE, it lacks any evident sequence homology to the highly conserved MPMV CTE sequence. Together, these data define the secondary structure and biological activity of an avian CTE sequence that may access a novel nuclear RNA export pathway.
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Affiliation(s)
- J Yang
- Howard Hughes Medical Institute and Department of Genetics, Duke University Medical Center, Durham, North Carolina 27710, USA
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243
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Li B, Wyman TE, Moudgil T, Marracci GH, Ju CF, Machida CA. Nucleocytoplasmic export of type D simian retrovirus genomic RNA: identification of important genetic subregions and interacting cellular proteins. Virology 1999; 264:37-54. [PMID: 10544128 DOI: 10.1006/viro.1999.9938] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The simian retrovirus (SRV) genome contains a constitutive transport element (CTE) within its 3' intergenic region (IR) that mediates the nuclear export of unspliced SRV RNA. The serogroup 2 SRV CTE is predicted to form a stable stem-loop structure containing two major internal loops exhibiting 180 degrees inverse symmetry, with loop face sequences A, A', B, and B' and additional minor internal and terminal loops. To begin the identification of potential CTE-interacting proteins and to assess structural requirements for protein interaction, we conducted RNA mobility shift assays using IR fragments that obliterated this region's known stable stem-loop structure. Using immunoblotting assays, we have determined that RNA helicase A, implicated in the nuclear export of unspliced SRV genomic RNA, does not appear to interact directly with either the complete serogroup 2 SRV 3' IR or the subregion RNAs and that formation of RNA-protein complexes is conferred by interaction with other novel proteins. UV crosslinking of RNA-protein complexes, coupled with RNase T1/A digestion, indicates that a novel protein of 120 kDa molecular weight interacts with the complete CTE or with individual subregion RNAs. Transfection analyses indicate that SRV recombinants containing A, A', B, or B' sequences forming the faces for two open loops undergo RNA export; only the complete sense CTE recombinant or a second recombinant containing two subregions in sense orientation that reconstitute the 3' two-thirds of the 3' IR, and contain only A' and B that form the faces for two terminal loops, are capable of SRV RNA export. These experiments indicate that secondary structural determinants of the 3' IR and multiple protein interactions may be important factors in the nuclear export of unspliced SRV RNA.
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Affiliation(s)
- B Li
- Division of Neuroscience, Oregon Regional Primate Research Center, Beaverton, Oregon 97006, USA
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244
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Yang J, Bogerd HP, Peng S, Wiegand H, Truant R, Cullen BR. An ancient family of human endogenous retroviruses encodes a functional homolog of the HIV-1 Rev protein. Proc Natl Acad Sci U S A 1999; 96:13404-8. [PMID: 10557333 PMCID: PMC23960 DOI: 10.1073/pnas.96.23.13404] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/1999] [Indexed: 11/18/2022] Open
Abstract
The human endogenous retrovirus K (HERV-K) family of endogenous retroviruses consists of approximately 50 proviral copies per haploid human genome. Herein, the HERV-Ks are shown to encode a sequence-specific nuclear RNA export factor, termed K-Rev, that is functionally analogous to the HIV-1 Rev protein. Like HIV-1 Rev, K-Rev binds to both the Crm1 nuclear export factor and to a cis-acting viral RNA target to activate nuclear export of unspliced RNAs. Surprisingly, this HERV-K RNA sequence, which is encoded within the HERV-K long terminal repeat, is also recognized by HIV-1 Rev. These data provide surprising evidence for an evolutionary link between HIV-1 and a group of endogenous retroviruses that first entered the human genome approximately 30 million years ago.
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Affiliation(s)
- J Yang
- Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710, USA
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245
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Truant R, Kang Y, Cullen BR. The human tap nuclear RNA export factor contains a novel transportin-dependent nuclear localization signal that lacks nuclear export signal function. J Biol Chem 1999; 274:32167-71. [PMID: 10542253 DOI: 10.1074/jbc.274.45.32167] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human Tap protein mediates the sequence-specific nuclear export of RNAs containing the constitutive transport element and is likely also critical for general mRNA export. Here, we demonstrate that a previously defined arginine-rich nuclear localization signal (NLS) present in Tap acts exclusively via the transportin import factor. Previously, transportin has been shown to mediate the nuclear import of several heterogeneous nuclear ribonucleoproteins, including heterogeneous nuclear ribonucleoprotein (hnRNP) A1, by binding to a sequence element termed M9. Although the Tap NLS and the hnRNP A1 M9 element are shown to compete for transportin binding, they show no sequence homology, and the Tap NLS does not conform to the recently defined M9 consensus. The Tap NLS also differs from M9 in that only the latter is able to act as a nuclear export signal. The Tap NLS is therefore the first member of a novel class of transportin-specific NLSs that lack nuclear export signal function.
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Affiliation(s)
- R Truant
- Howard Hughes Medical Institute, Duke University Medical Center, Durham, North Carolina 27710, USA
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246
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Kordower JH, Bloch J, Ma SY, Chu Y, Palfi S, Roitberg BZ, Emborg M, Hantraye P, Déglon N, Aebischer P. Lentiviral gene transfer to the nonhuman primate brain. Exp Neurol 1999; 160:1-16. [PMID: 10630186 DOI: 10.1006/exnr.1999.7178] [Citation(s) in RCA: 168] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Lentiviral vectors infect quiescent cells and allow for the delivery of genes to discrete brain regions. The present study assessed whether stable lentiviral gene transduction can be achieved in the monkey nigrostriatal system. Three young adult Rhesus monkeys received injections of a lentiviral vector encoding for the marker gene beta galatosidase (beta Gal). On one side of the brain, each monkey received multiple lentivirus injections into the caudate and putamen. On the opposite side, each animal received a single injection aimed at the substantia nigra. The first two monkeys were sacrificed 1 month postinjection, while the third monkey was sacrificed 3 months postinjection. Robust incorporation of the beta Gal gene was seen in the striatum of all three monkeys. Stereological counts revealed that 930,218; 1,192,359; and 1,501,217 cells in the striatum were beta Gal positive in monkeys 1 (n = 2) and 3 (n = 1) months later, respectively. Only the third monkey had an injection placed directly into the substantia nigra and 187,308 beta Gal-positive cells were identified in this animal. The injections induced only minor perivascular cuffing and there was no apparent inflammatory response resulting from the lentivirus injections. Double label experiments revealed that between 80 and 87% of the beta Gal-positive cells were neurons. These data indicate that robust transduction of striatal and nigral cells can occur in the nonhuman primate brain for up to 3 months. Studies are now ongoing testing the ability of lentivirus encoding for dopaminergic trophic factors to augment the nigrostriatal system in nonhuman primate models of Parkinson's disease.
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Affiliation(s)
- J H Kordower
- Department of Neurological Sciences, Rush Presbyterian-St. Luke's Medical Center, Chicago, Illinois 60612, USA
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247
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Qiu JT, Song R, Dettenhofer M, Tian C, August T, Felber BK, Pavlakis GN, Yu XF. Evaluation of novel human immunodeficiency virus type 1 Gag DNA vaccines for protein expression in mammalian cells and induction of immune responses. J Virol 1999; 73:9145-52. [PMID: 10516021 PMCID: PMC112947 DOI: 10.1128/jvi.73.11.9145-9152.1999] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes (CTL) are an important parameter of host defenses that limit viral replication after infection. Induction of effective CTL against conserved viral proteins such as Gag may be essential to the development of a safe and effective HIV type 1 (HIV-1) vaccine. DNA vaccination represents a novel strategy for inducing potent CD8(+) CTL responses in vivo. However, expression of HIV-1 structural proteins by DNA vectors has been hampered by a stringent requirement for coexpression with other viral components, such as Rev and RRE. Furthermore, even with Rev and RRE present, the level of expression of HIV-1 Gag, Pol, or Env is very low in murine cells. These problems have limited our ability to address the key issue of how to generate effective CTL responses to Gag in a mouse model. To overcome this problem, we compared several novel DNA expression vectors for HIV-1 Gag protein expression in primate and mouse cells and for generating immune responses in mice after DNA vaccination. A DNA vector containing wild type HIV-1 gag coding sequences did not induce detectable Gag expression in any of the cells tested. Attempts to increase nuclear export of Gag expression RNA by adding the constitutive transport element yielded only a moderate increase in Gag expression in monkey-derived COS cells and an even lower increase in Gag expression in HeLa cells or several mouse cell lines. In contrast, silent-site mutations in the HIV-1 gag coding sequences significantly increased Gag expression levels in all cells tested. Furthermore, this construct induced both Gag-specific antibody and CTL responses in mice after DNA vaccination. Using this construct, we achieved stable expression of HIV-1 Gag in the mouse cell line p815, which can now be used as a target cell for measuring HIV-1 Gag-specific CTL responses in immunized mice. The DNA vectors described in this study should make it possible to systematically evaluate the approaches for maximizing the induction of CTL responses against HIV-1 Gag in mouse and other animal systems.
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Affiliation(s)
- J T Qiu
- Department of Molecular Microbiology, The Johns Hopkins School of Hygiene and Public Health, Baltimore, Maryland 21205, USA
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248
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Srinivasakumar N, Schuening FG. A lentivirus packaging system based on alternative RNA transport mechanisms to express helper and gene transfer vector RNAs and its use to study the requirement of accessory proteins for particle formation and gene delivery. J Virol 1999; 73:9589-98. [PMID: 10516068 PMCID: PMC112994 DOI: 10.1128/jvi.73.11.9589-9598.1999] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A lentivirus-based packaging system was designed to reduce the chance of recombination between helper and gene transfer vector sequences by using the constitutive transport element (CTE) derived from Mason-Pfizer monkey virus for expression of the viral proteins and the Rev-Rev response element (RRE) combination for expression of the gene transfer vector. Using this approach, we evaluated a series of human immunodeficiency virus type 1 packaging constructs that express one or more accessory proteins (Vif, Vpr, and Vpu), in addition to the Gag and Pol proteins, for particle formation and virus stock production for gene transfer. Constructs that also express Vpr or both Vpr and Vpu produced more particles, as measured by a p24 assay, than did plasmids that did not contain these sequences. Transactivation experiments showed that the packaging plasmids that encode Vpr or both Vpr and Vpu also expressed a functional single-exon Tat protein. For these constructs, high-titer virus stocks could be prepared in the absence of a cotransfected Tat-expressing plasmid. Amphotropic-envelope-pseudotyped virus stocks prepared with all of the packaging constructs, irrespective of whether any of the accessory proteins were coexpressed, were equally efficient in transducing growth-arrested HeLa cells. The combination/mixed packaging system was compared to systems that were based on either the CTE alone or Rev and RRE for expression of both the packaging plasmid as well as the gene transfer vector. The combination/mixed packaging system was comparable to the other systems for production of virus stocks, suggesting that this design may prove to be safer for the eventual deployment of lentivirus vectors for therapeutic purposes.
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Affiliation(s)
- N Srinivasakumar
- Bone Marrow Transplant Program, Department of Medicine, University of Wisconsin, Madison, USA
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249
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Mitrophanous K, Yoon S, Rohll J, Patil D, Wilkes F, Kim V, Kingsman S, Kingsman A, Mazarakis N. Stable gene transfer to the nervous system using a non-primate lentiviral vector. Gene Ther 1999; 6:1808-18. [PMID: 10602376 DOI: 10.1038/sj.gt.3301023] [Citation(s) in RCA: 226] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We have constructed a non-primate lentiviral vector system based on the equine infectious anaemia virus (EIAV). This system is able to transduce both dividing and non-dividing cells, including primary cultured hippocampal neurons and neurons and glia in the adult rat central nervous system (CNS), at efficiencies comparable with HIV-based vectors. We demonstrate that the only EIAV proteins required for this activity are gag/pol and that the only accessory protein required for vector production is rev. In addition, we show that the pol encoded dUTPase activity that is found in all non-primate lentiviruses is not required. The vectors can be pseudotyped with a range of envelopes including rabies G and MLV 4070A and can be concentrated to high titres. The ability of EIAV to infect mitotically inactive cells makes this vector an attractive alternative to the immunodeficiency viruses for gene therapy.
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250
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D'Agostino DM, Ciminale V, Zotti L, Chieco-Bianchi L. Influence of Rex and intronic sequences on expression of spliced mRNAs produced by human T cell leukemia virus type I. AIDS Res Hum Retroviruses 1999; 15:1351-63. [PMID: 10515151 DOI: 10.1089/088922299310061] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Expression of the incompletely spliced HTLV-I mRNAs relies on the viral posttranscriptional activator Rex, whose interaction with the Rex-responsive element (RXRE) overcomes effects of cis-acting repressive sequences (CRSs). Studies based on heterologous reporter plasmids identified an intronic CRS in the 5' LTR and a CRS that overlaps with the RXRE. The present study investigated the effects of these elements in the context of spliced viral mRNAs encoding p21Rex (mRNA 1-3), Tax/Rex (mRNA 1-2-3), and Tof (mRNA 1-2-B). All three mRNAs were inefficiently expressed when transcribed in their mature intronless form, with the p21Rex mRNA showing the weakest expression. In contrast, efficient expression of p21Rex was obtained from a plasmid containing the 5' LTR and 3' portion of the genome that encoded a spliceable RNA. The defective expression of the intronless mRNAs reflected the inhibitory activity of the RXRE and the lack of 5' intronic sequences. Insertion of an intronic 5' LTR segment located upstream of the 5' CRS overcame Rex dependence conferred by the RXRE. The activity of this segment was mapped to the major splice donor and sequences overlapping with, but functionally distinct from, a previously described transcriptional enhancer. The three mRNAs responded differently to Rex and to insertion of the constitutive transport element of simian retrovirus type 1. Taken together, these results suggest that expression of the spliced mRNAs is controlled by the relative influence of positive and negative sequences present on the primary transcript as well as the Rex-RXRE interaction.
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Affiliation(s)
- D M D'Agostino
- Department of Oncology and Surgical Sciences, University of Padova, Italy.
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