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Isomura H, Stinski MF. Coordination of late gene transcription of human cytomegalovirus with viral DNA synthesis: recombinant viruses as potential therapeutic vaccine candidates. Expert Opin Ther Targets 2012; 17:157-66. [PMID: 23231449 DOI: 10.1517/14728222.2013.740460] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
INTRODUCTION During productive infection, human cytomegalovirus (HCMV) genes are expressed in a temporal cascade, with temporal phases designated as immediate-early (IE), early, and late. The major IE (MIE) genes, UL123 and UL122 (IE1/IE2), play a critical role in subsequent viral gene expression and the efficiency of viral replication. The early viral genes encode proteins necessary for viral DNA replication. Following viral DNA replication, delayed-early and late viral genes are expressed which encode structural proteins for the virion. The late genes can be divided into two broad classes. At early times the gamma-1 or leaky-late class are expressed at low levels after infection and are dramatically upregulated at late times. In contrast, the gamma-2 or 'true' late genes are expressed exclusively after viral DNA replication. Expression of true late (gamma-2 class) viral genes is completely prevented by inhibition of viral DNA synthesis. AREAS COVERED This review addresses the viral genes required for HCMV late gene transcription. Recombinant viruses that are defective for late gene transcription allow for early viral gene expression and viral DNA synthesis, but not infectious virus production. Since current HCMV prophylaxis is limited by several shortcomings, the use of defective recombinant viruses to induce HCMV cell-mediated and humoral immunity is discussed. EXPERT OPINION HCMV DNA replication and late gene transcription are not completely linked. Viral-encoded trans-acting factors are required. Recombinant viruses proficient in MIE and early viral gene expression and defective in late gene expression may be an alternative therapeutic vaccine candidates for the induction of cell-mediated and humoral immunity.
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Affiliation(s)
- Hiroki Isomura
- Gunma University Graduate School of Medicine, Department of Virology and Preventive Medicine, 3-39-22 Showa-machi, Maebashi, Gunma, 371-8511, Japan.
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Strang BL, Bender BJ, Sharma M, Pesola JM, Sanders RL, Spector DH, Coen DM. A mutation deleting sequences encoding the amino terminus of human cytomegalovirus UL84 impairs interaction with UL44 and capsid localization. J Virol 2012; 86:11066-77. [PMID: 22855486 PMCID: PMC3457161 DOI: 10.1128/jvi.01379-12] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2012] [Accepted: 07/23/2012] [Indexed: 01/10/2023] Open
Abstract
Protein-protein interactions are required for many biological functions. Previous work has demonstrated an interaction between the human cytomegalovirus DNA polymerase subunit UL44 and the viral replication factor UL84. In this study, glutathione S-transferase pulldown assays indicated that residues 1 to 68 of UL84 are both necessary and sufficient for efficient interaction of UL84 with UL44 in vitro. We created a mutant virus in which sequences encoding these residues were deleted. This mutant displayed decreased virus replication compared to wild-type virus. Immunoprecipitation assays showed that the mutation decreased but did not abrogate association of UL84 with UL44 in infected cell lysate, suggesting that the association in the infected cell can involve other protein-protein interactions. Further immunoprecipitation assays indicated that IRS1, TRS1, and nucleolin are candidates for such interactions in infected cells. Quantitative real-time PCR analysis of viral DNA indicated that the absence of the UL84 amino terminus does not notably affect viral DNA synthesis. Western blotting experiments and pulse labeling of infected cells with [(35)S]methionine demonstrated a rather modest downregulation of levels of multiple proteins and particularly decreased levels of the minor capsid protein UL85. Electron microscopy demonstrated that viral capsids assemble but are mislocalized in nuclei of cells infected with the mutant virus, with fewer cytoplasmic capsids detected. In sum, deletion of the sequences encoding the amino terminus of UL84 affects interaction with UL44 and virus replication unexpectedly, not viral DNA synthesis. Mislocalization of viral capsids in infected cell nuclei likely contributes to the observed decrease in virus replication.
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Affiliation(s)
- Blair L. Strang
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA
| | - Brian J. Bender
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA
| | - Mayuri Sharma
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA
| | - Jean M. Pesola
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA
| | - Rebecca L. Sanders
- Department of Cellular and Molecular Medicine and Skaggs School of Pharmacy and Pharmaceutical Sciences
- Division of Biological Sciences, University of California, San Diego, La Jolla, California, USA
| | - Deborah H. Spector
- Department of Cellular and Molecular Medicine and Skaggs School of Pharmacy and Pharmaceutical Sciences
| | - Donald M. Coen
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA
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Internal deletions of IE2 86 and loss of the late IE2 60 and IE2 40 proteins encoded by human cytomegalovirus affect the levels of UL84 protein but not the amount of UL84 mRNA or the loading and distribution of the mRNA on polysomes. J Virol 2008; 82:11383-97. [PMID: 18787008 DOI: 10.1128/jvi.01293-08] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The major immediate-early (IE) region of human cytomegalovirus encodes two IE proteins, IE1 72 and IE2 86, that are translated from alternatively spliced transcripts that differ in their 3' ends. Two other proteins that correspond to the C-terminal region of IE2 86, IE2 60 and IE2 40, are expressed at late times. In this study, we used IE2 mutant viruses to examine the mechanism by which IE2 86, IE2 60, and IE2 40 affect the expression of a viral DNA replication factor, UL84. Deletion of amino acids (aa) 136 to 290 of IE2 86 results in a significant decrease in UL84 protein during the infection. This loss of UL84 is both proteasome and calpain independent, and the stability of the protein in the context of infection with the mutant remains unaffected. The RNA for UL84 is expressed to normal levels in the mutant virus-infected cells, as are the RNAs for two other proteins encoded by this region, UL85 and UL86. Moreover, nuclear-to-cytoplasmic transport and the distribution of the UL84 mRNA on polysomes are unaffected. A region between aa 290 and 369 of IE2 86 contributes to the UL84-IE2 86 interaction in vivo and in vitro. IE2 86, IE2 60, and IE2 40 are each able to interact with UL84 in the mutant-infected cells, suggesting that these interactions may be important for the roles of UL84 and the IE2 proteins. Thus, these data have defined the contribution of IE2 86, IE2 60, and IE2 40 to the efficient expression of UL84 throughout the infection.
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Kronschnabl M, Marschall M, Stamminger T. Efficient and tightly regulated expression systems for the human cytomegalovirus major transactivator protein IE2p86 in permissive cells. Virus Res 2002; 83:89-102. [PMID: 11864743 DOI: 10.1016/s0168-1702(01)00422-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
The 86-kDa IE2 protein (IE2p86) of human cytomegalovirus is a pleiotropic regulatory polypeptide that is essential for activation of viral early promoters and thus, for the entire viral replication cycle. Moreover, this protein modulates cellular gene expression and contributes to the pathogenic features of HCMV. The full spectrum of IE2p86 mediated effects on cellular gene expression has not been defined yet, since efficient expression systems for this protein in HCMV permissive cells are, so far, limited. Here, we report the establishment of two efficient model systems that allow a tightly regulated expression of IE2p86 in various permissive cell types including primary human fibroblasts, primary endothelial cells and U373MG cells. Firstly, we generated a tetracycline-regulated U373MG cell line, which expresses high levels of IE2p86 upon tetracycline removal from the culture medium. Secondly, a recombinant baculovirus was constructed, which expresses IE2p86 under the control of the HCMV major immediate early enhancer/promoter upon transduction of various cell types. Importantly, IE2p86 was functional in both systems, since strong transactivation of luciferase promoter constructs could be measured. Furthermore, a cell cycle arrest was detectable after infection of primary human fibroblasts with IE2p86-expressing baculoviruses. Both expression systems represent useful tools to fully define the effects of this pleiotropic transactivator on cellular gene expression and to establish screening systems for novel antiviral drugs targeting this critical immediate early protein of HCMV.
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Affiliation(s)
- Martina Kronschnabl
- Institut für Klinische und Molekulare Virologie, Schlossgarten 4, 91054 Erlangen, Germany
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Tenney DJ, Yamanaka G, Voss SM, Cianci CW, Tuomari AV, Sheaffer AK, Alam M, Colonno RJ. Lobucavir is phosphorylated in human cytomegalovirus-infected and -uninfected cells and inhibits the viral DNA polymerase. Antimicrob Agents Chemother 1997; 41:2680-5. [PMID: 9420038 PMCID: PMC164188 DOI: 10.1128/aac.41.12.2680] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Lobucavir (LBV) is a deoxyguanine nucleoside analog with broad-spectrum antiviral activity. LBV was previously shown to inhibit herpes simplex virus (HSV) DNA polymerase after phosphorylation by the HSV thymidine kinase. Here we determined the mechanism of action of LBV against human cytomegalovirus (HCMV). LBV inhibited HCMV DNA synthesis to a degree comparable to that of ganciclovir (GCV), a drug known to target the viral DNA polymerase. The expression of late proteins and RNA, dependent on viral DNA synthesis, was also inhibited by LBV. Immediate-early and early HCMV gene expression was unaffected, suggesting that LBV acts temporally coincident with HCMV DNA synthesis and not through cytotoxicity. In vitro, the triphosphate of LBV was a potent inhibitor of HCMV DNA polymerase with a Ki of 5 nM. LBV was phosphorylated to its triphosphate form intracellularly in both infected and uninfected cells, with phosphorylated metabolite levels two- to threefold higher in infected cells. GCV-resistant HCMV isolates, with deficient GCV phosphorylation due to mutations in the UL97 protein kinase, remained sensitive to LBV. Overall, these results suggest that LBV-triphosphate halts HCMV DNA replication by inhibiting the viral DNA polymerase and that LBV phosphorylation can occur in the absence of viral factors including the UL97 protein kinase. Furthermore, LBV may be effective in the treatment of GCV-resistant HCMV.
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Affiliation(s)
- D J Tenney
- Department of Virology, Bristol-Myers Squibb Pharmaceutical Research Institute, Wallingford, Connecticut 06492, USA.
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Winkler M, Rice SA, Stamminger T. UL69 of human cytomegalovirus, an open reading frame with homology to ICP27 of herpes simplex virus, encodes a transactivator of gene expression. J Virol 1994; 68:3943-54. [PMID: 8189530 PMCID: PMC236900 DOI: 10.1128/jvi.68.6.3943-3954.1994] [Citation(s) in RCA: 148] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The UL69 open reading frame of human cytomegalovirus (HCMV) is homologous to the immediate-early protein ICP27 of herpes simplex virus, an essential viral regulatory protein involved in the transition from early to late gene expression. Genes with homology to ICP27 have been detected in all subclasses of herpesviruses so far. While the respective proteins in alpha- and gammaherpesviruses have been defined as trans-regulatory molecules, nothing is known about these genes in betaherpesviruses. This study was therefore undertaken in order to investigate expression from the UL69 gene locus of HCMV. Northern (RNA) blot experiments revealed a complex pattern of transcripts that changed during the time course of the HCMV replicative cycle: two transcripts of 2.7 and 3.5 kb that were regulated differentially could be detected as early as 7 h after infection. However, these transcripts could not be detected in the presence of cycloheximide. Additional, larger transcripts were present exclusively at late times after infection. To analyze protein expression from the UL69 gene region, the UL69 open reading frame was expressed as a histidine-tagged protein in Escherichia coli. A specific antiserum was generated and used to detect the UL69 protein in HCMV-infected cells which revealed its localization within the intranuclear inclusions that are characteristic for HCMV infection. In cotransfection experiments, an HCMV true late promoter could not be activated by UL69, whereas an early promoter and several heterologous promoters were stimulated about 10-fold. Complementation studies showed that the UL69 protein cannot substitute for ICP27 in the context of the HSV infection, suggesting functional differences between these two proteins. In summary, these experiments define a novel regulatory protein encoded by HCMV that is expressed as an early-late gene and appears to exert a broad stimulatory effect on gene expression.
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Affiliation(s)
- M Winkler
- Institut für Klinische und Molekulare Virologie, Universität Erlangen-Nürnberg, Germany
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Gozlan J, Caburet F, Tancrede C, Petit JC. A reverse polymerase chain reaction method for detection of human cytomegalovirus late transcripts in cells infected in vitro. J Virol Methods 1992; 40:1-10. [PMID: 1331156 DOI: 10.1016/0166-0934(92)90002-u] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
A rapid and simple application of the polymerase chain reaction is described for the detection of human cytomegalovirus (HCMV) mRNAs in cells infected in-vitro. The method was first used to study the transcription of two HCMV genes, and confirm the link between the transcription of one, encoding for the major capsid protein, and viral replication. The oligonucleotides chosen in this region were specific for HCMV genome and sensitivity experiments showed that a single infected cell in 5 x 10(5) can be detected. Detection of this transcript should be suitable for diagnostic purposes, permitting the distinction between latency and active infection.
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Affiliation(s)
- J Gozlan
- Hôpital Saint-Antoine, Laboratoire de Bactériologie-Virologie, Paris, France
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Tenney DJ, Colberg-Poley AM. Human cytomegalovirus UL36-38 and US3 immediate-early genes: temporally regulated expression of nuclear, cytoplasmic, and polysome-associated transcripts during infection. J Virol 1991; 65:6724-34. [PMID: 1658371 PMCID: PMC250752 DOI: 10.1128/jvi.65.12.6724-6734.1991] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
During permissive in vitro infection, the human cytomegalovirus (HCMV) UL36-38 and US3 immediate-early (IE) regions give rise to multiple distinct species of RNA in a temporally regulated manner. We have compared the temporally regulated expression of the UL36-38 and US3 regions with that of the well-characterized major IE (MIE) region. Northern (RNA) blot hybridizations with antisense RNA probes were used to examine RNA isolated from infected cells at IE, early, and late times after infection and from cells infected in the presence of anisomycin (used to block de novo viral protein synthesis) or in the presence of phosphonoformate (used to block HCMV DNA synthesis). Different US3 region transcripts were expressed in the cytoplasm during the IE and late phases of infection, with kinetics similar to those of the MIE region. In contrast, various cytoplasmic transcripts from the UL36-38 region were expressed during each of the IE, early, and late phases of infection, including some expressed from IE through late times. The levels of steady-state RNA from the US3 and MIE regions were increased dramatically by infection in the presence of anisomycin, predominantly because of an increase in multiply spliced transcripts. Two of the three UL36-38 IE transcripts were largely unaffected by anisomycin and were expressed abundantly throughout infection, but a third, multiply spliced UL36-38 IE transcript was abundant only during infection in the presence of anisomycin. Nuclear, cytoplasmic, and polysome-associated transcripts from the three IE regions were not significantly different qualitatively or quantitatively. These results suggest that posttranscriptional controls at the levels of nuclear retention or polysome exclusion of transcripts are not operative for the IE region genes. Overall, these results indicate common features of expression of US3, MIE, and UL36-38, in addition to distinctive expression of the UL36-38 region during all temporal phases of expression.
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MESH Headings
- Antigens, Viral/genetics
- Blotting, Northern
- Cell Nucleus/physiology
- Cells, Cultured
- Cytomegalovirus/genetics
- Cytoplasm/physiology
- DNA, Viral/genetics
- DNA, Viral/isolation & purification
- Gene Expression Regulation, Viral
- Genes, Viral
- Genome, Viral
- Humans
- Immediate-Early Proteins
- Kinetics
- Polyribosomes/metabolism
- RNA Probes
- RNA, Viral/genetics
- RNA, Viral/isolation & purification
- Skin
- Time Factors
- Transcription, Genetic
- Viral Matrix Proteins/genetics
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Affiliation(s)
- D J Tenney
- Du Pont Merck Pharmaceutical Company, Wilmington, Delaware 19880-0328
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Puchtler E, Stamminger T. An inducible promoter mediates abundant expression from the immediate-early 2 gene region of human cytomegalovirus at late times after infection. J Virol 1991; 65:6301-6. [PMID: 1656096 PMCID: PMC250338 DOI: 10.1128/jvi.65.11.6301-6306.1991] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
An abundant late transcript of 1.5 kb originates from the immediate-early 2 (IE-2) gene region of human cytomegalovirus (HCMV) at late times after infection. The transcriptional start of this RNA was precisely mapped, and the putative promoter region was cloned in front of the CAT gene as reporter. This region, which comprises 78 nucleotides of IE-2 sequence upstream of the determined cap site, was strongly activated by viral superinfection at late times in the replicative cycle. As shown by RNase protection analyses, the authentic transcription start is used. No activation of this late promoter was observed after cotransfection with an expression plasmid containing the HCMV IE-1 and -2 gene region. This result suggests that, compared with early and early late promoters of HCMV, different or additional viral functions are required for the activation of true late promoters.
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MESH Headings
- Base Sequence
- Blotting, Northern
- Cell Transformation, Viral
- Cells, Cultured
- Cloning, Molecular
- Cytomegalovirus/genetics
- Enhancer Elements, Genetic
- Exons
- Gene Expression Regulation, Viral
- Genes, Viral
- Genome, Viral
- Humans
- Molecular Sequence Data
- Promoter Regions, Genetic
- RNA Splicing
- RNA, Viral/genetics
- Restriction Mapping
- Skin
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Affiliation(s)
- E Puchtler
- Institut für Klinische und Molekulare Virologie, Universität Erlangen-Nürnberg, Germany
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Leatham MP, Witte PR, Stinski MF. Alternate promoter selection within a human cytomegalovirus immediate-early and early transcription unit (UL119-115) defines true late transcripts containing open reading frames for putative viral glycoproteins. J Virol 1991; 65:6144-53. [PMID: 1717716 PMCID: PMC250299 DOI: 10.1128/jvi.65.11.6144-6153.1991] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The human cytomegalovirus open reading frames (ORFs) UL119 through UL115 (UL119-115) are located downstream of the immediate-early 1 and 2 transcription units. The promoter upstream of UL119 is active at all times after infection and drives the synthesis of a spliced 3.1-kb mRNA. The viral mRNA initiates in UL119, contains UL119-117 and UL116, and terminates just downstream of UL115. True late transcripts that are detected only after viral DNA synthesis originate from this transcription unit. True late mRNAs of 2.1 kb, containing ORFs UL116 and UL115, and 1.2 kb, containing ORF UL115 only, are synthesized. The true late viral mRNAs are 3' coterminal with the 3.1-kb mRNA. This transcription unit is an example of late promoters nested within an immediate-early-early transcription unit. The gene products of UL119-117, UL116, and UL115 are predicted to be glycoproteins. Efficient expression of the downstream ORFs at late times after infection may be related to alternate promoter usage and downstream cap site selection.
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MESH Headings
- Amino Acid Sequence
- Cells, Cultured
- Cloning, Molecular
- Cytomegalovirus/genetics
- DNA Replication
- DNA, Viral/genetics
- DNA, Viral/isolation & purification
- Genes, Viral
- Glycoproteins/genetics
- Humans
- Molecular Sequence Data
- Oligodeoxyribonucleotides
- Open Reading Frames
- Plasmids
- Promoter Regions, Genetic
- RNA/genetics
- RNA/isolation & purification
- RNA, Messenger/genetics
- RNA, Viral/genetics
- RNA, Viral/isolation & purification
- Restriction Mapping
- Skin
- Transcription, Genetic
- Viral Proteins/genetics
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Affiliation(s)
- M P Leatham
- Department of Microbiology, School of Medicine, University of Iowa, Iowa City 52242
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