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Abstract
Viruses employ a variety of strategies to usurp and control cellular activities through the orchestrated recruitment of macromolecules to specific cytoplasmic or nuclear compartments. Formation of such specialized virus-induced cellular microenvironments, which have been termed viroplasms, virus factories, or virus replication centers, complexes, or compartments, depends on molecular interactions between viral and cellular factors that participate in viral genome expression and replication and are in some cases associated with sites of virion assembly. These virus-induced compartments function not only to recruit and concentrate factors required for essential steps of the viral replication cycle but also to control the cellular mechanisms of antiviral defense. In this review, we summarize characteristic features of viral replication compartments from different virus families and discuss similarities in the viral and cellular activities that are associated with their assembly and the functions they facilitate for viral replication.
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52
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Rivera-Molina YA, Martínez FP, Tang Q. Nuclear domain 10 of the viral aspect. World J Virol 2013; 2:110-122. [PMID: 24255882 PMCID: PMC3832855 DOI: 10.5501/wjv.v2.i3.110] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/27/2013] [Revised: 05/31/2013] [Accepted: 07/11/2013] [Indexed: 02/05/2023] Open
Abstract
Nuclear domain 10 (ND10) are spherical bodies distributed throughout the nucleoplasm and measuring around 0.2-1.0 μm. First observed under an electron microscope, they were originally described as dense bodies found in the nucleus. They are known by a number of other names, including Promyelocytic Leukemia bodies (PML bodies), Kremer bodies, and PML oncogenic domains. ND10 are frequently associated with Cajal bodies and cleavage bodies. It has been suggested that they play a role in regulating gene transcription. ND10 were originally characterized using human autoantisera, which recognizes Speckled Protein of 100 kDa, from patients with primary biliary cirrhosis. At the immunohistochemical level, ND10 appear as nuclear punctate structures, with 10 indicating the approximate number of dots per nucleus observed. ND10 do not colocalize with kinetochores, centromeres, sites of mRNA processing, or chromosomes. Resistance of ND10 antigens to nuclease digestion and salt extraction suggest that ND10 are associated with the nuclear matrix. They are often identified by immunofluorescent assay using specific antibodies against PML, Death domain-associated protein, nuclear dot protein (NDP55), and so on. The role of ND10 has long been the subject of investigation, with the specific connection of ND10 and viral infection having been a particular focus for almost 20 years. This review summarizes the relationship of ND10 and viral infection. Some future study directions are also discussed.
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53
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Matlaf LA, Harkins LE, Bezrookove V, Cobbs CS, Soroceanu L. Cytomegalovirus pp71 protein is expressed in human glioblastoma and promotes pro-angiogenic signaling by activation of stem cell factor. PLoS One 2013; 8:e68176. [PMID: 23861869 PMCID: PMC3702580 DOI: 10.1371/journal.pone.0068176] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2013] [Accepted: 05/24/2013] [Indexed: 12/28/2022] Open
Abstract
Glioblastoma multiforme (GBM) is a highly malignant primary central nervous system neoplasm characterized by tumor cell invasion, robust angiogenesis, and a mean survival of 15 months. Human cytomegalovirus (HCMV) infection is present in >90% of GBMs, although the role the virus plays in GBM pathogenesis is unclear. We report here that HCMV pp71, a viral protein previously shown to promote cell cycle progression, is present in a majority of human GBMs and is preferentially expressed in the CD133+, cancer stem-like cell population. Overexpression of pp71 in adult neural precursor cells resulted in potent induction of stem cell factor (SCF), an important pro-angiogenic factor in GBM. Using double immunofluorescence, we demonstrate in situ co-localization of pp71 and SCF in clinical GBM specimens. pp71 overexpression in both normal and transformed glial cells increased SCF secretion and this effect was specific, since siRNA mediated knockdown of pp71 or treatment with the antiviral drug cidofovir resulted in decreased expression and secretion of SCF by HCMV-infected cells. pp71- induced upregulation of SCF resulted in downstream activation of its putative endothelial cell receptor, c-kit, and angiogenesis as measured by increased capillary tube formation in vitro. We demonstrate that pp71 induces a pro-inflammatory response via activation of NFΚB signaling which drives SCF expression. Furthermore, we show that pp71 levels and NFKB activation are selectively augmented in the mesenchymal subtype of human GBMs, characterized by worst patient outcome, suggesting that HCMV pp71-induced paracrine signaling may contribute to the aggressive phenotype of this human malignancy.
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Affiliation(s)
- Lisa A. Matlaf
- California Pacific Medical Center Research Institute, San Francisco, California, United States of America
| | - Lualhati E. Harkins
- Birmingham Veterans Administration Hospital, Birmingham, Alabama, United States of America
| | - Vladimir Bezrookove
- California Pacific Medical Center Research Institute, San Francisco, California, United States of America
| | - Charles S. Cobbs
- California Pacific Medical Center Research Institute, San Francisco, California, United States of America
- University of California San Francisco, Department of Neurological Surgery, San Francisco, California, United States of America
| | - Liliana Soroceanu
- California Pacific Medical Center Research Institute, San Francisco, California, United States of America
- * E-mail:
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54
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Korb E, Wilkinson CL, Delgado RN, Lovero KL, Finkbeiner S. Arc in the nucleus regulates PML-dependent GluA1 transcription and homeostatic plasticity. Nat Neurosci 2013; 16:874-83. [PMID: 23749147 PMCID: PMC3703835 DOI: 10.1038/nn.3429] [Citation(s) in RCA: 107] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Accepted: 05/12/2013] [Indexed: 02/06/2023]
Abstract
The activity-regulated cytoskeletal protein Arc (also known as Arg3.1) is required for long-term memory formation and synaptic plasticity. Arc expression is robustly induced by activity, and Arc protein localizes to both active synapses and the nucleus. Whereas its synaptic function has been examined, it is not clear why or how Arc is localized to the nucleus. We found that murine Arc nuclear expression is regulated by synaptic activity in vivo and in vitro. We identified distinct regions of Arc that control its localization, including a nuclear localization signal, a nuclear retention domain and a nuclear export signal. Arc localization to the nucleus promotes an activity-induced increase in the expression of promyelocytic leukemia nuclear bodies, which decreases GluA1 (also called Gria1) transcription and synaptic strength. We further show that Arc nuclear localization regulates homeostatic plasticity. Thus, Arc mediates the homeostatic response to increased activity by translocating to the nucleus, increasing promyelocytic leukemia protein expression and decreasing GluA1 transcription, ultimately downscaling synaptic strength.
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Affiliation(s)
- Erica Korb
- Gladstone Institutes of Neurological Disease, San Francisco, California, USA
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55
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Mattoscio D, Segré CV, Chiocca S. Viral manipulation of cellular protein conjugation pathways: The SUMO lesson. World J Virol 2013; 2:79-90. [PMID: 24175232 PMCID: PMC3785051 DOI: 10.5501/wjv.v2.i2.79] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Revised: 01/23/2013] [Accepted: 02/06/2013] [Indexed: 02/05/2023] Open
Abstract
Small ubiquitin-like modifier (SUMO)ylation is a key post-translational modification mechanism that controls the function of a plethora of proteins and biological processes. Given its central regulatory role, it is not surprising that it is widely exploited by viruses. A number of viral proteins are known to modify and/or be modified by the SUMOylation system to exert their function, to create a cellular environment more favorable for virus survival and propagation, and to prevent host antiviral responses. Since the SUMO pathway is a multi-step cascade, viral proteins engage with it at many levels, to advance and favor each stage of a typical infection cycle: replication, viral assembly and immune evasion. Here we review the current knowledge on the interplay between the host SUMO system and viral lifecycle.
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56
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Wang K, Li Y, Zhao G, Wu Y, Zhang X, Li H, Zhou T. Inhibition of human cytomegalovirus DNA replication by small interfering RNAs targeted to UL49. Acta Biochim Biophys Sin (Shanghai) 2013; 45:401-7. [PMID: 23507399 DOI: 10.1093/abbs/gmt025] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Human cytomegalovirus (HCMV) is a ubiquitous virus. Although the infection in healthy children and adults is usually asymptomatic, in immunocompromised individuals and newborns it is a significant cause of morbidity and mortality. UL49, an essential gene of HCMV, is highly conserved among various HCMV strains. The expression of UL49 is correlated with the production of virions. When UL49 is inhibited in the HCMV, the production of virions is reduced severely. In this study, RNA interference was applied to further investigate the roles of UL49 in viral replication. Two effective small interfering RNAs against UL49 were selected. Silencing of UL49 in HCMV-infected human foreskin fibroblast cells reduced the transcription levels of early and late genes, but not immediate-early ones. In addition, the viral DNA content was significantly reduced. This is the first time to uncover the role of UL49 in viral DNA synthesis, which indicates that UL49 might play an important role in this period. So the down-regulation of UL49 mRNA using RNAi might be a potential clinical therapy against the virus.
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Affiliation(s)
- Kezhen Wang
- Department of Biotechnology, College of Life Science and Technology, Jinan University, Guangzhou 510632, China
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57
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Everett RD, Boutell C, Hale BG. Interplay between viruses and host sumoylation pathways. Nat Rev Microbiol 2013; 11:400-11. [PMID: 23624814 DOI: 10.1038/nrmicro3015] [Citation(s) in RCA: 136] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Post-translational modification by members of the small ubiquitin-like modifier (SUMO) family of proteins is important for the regulation of many cellular proteins and pathways. As obligate parasites, viruses must engage with the host cell throughout their replication cycles, and it is therefore unsurprising that there are many examples of interplay between viral proteins and the host sumoylation system. This article reviews recent advances in this field, summarizing information on sumoylated viral proteins, the varied ways in which viruses engage with SUMO-related pathways, and the consequences of these interactions for viral replication and engagement with innate and intrinsic immunity.
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Affiliation(s)
- Roger D Everett
- MRC-University of Glasgow Centre for Virus Research, 8 Church Street, Glasgow G11 5JR, UK.
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58
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Pham TH, Kwon KM, Kim YE, Kim KK, Ahn JH. DNA sensing-independent inhibition of herpes simplex virus 1 replication by DAI/ZBP1. J Virol 2013; 87:3076-86. [PMID: 23283962 PMCID: PMC3592125 DOI: 10.1128/jvi.02860-12] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2012] [Accepted: 12/21/2012] [Indexed: 01/01/2023] Open
Abstract
DNA-dependent activator of interferon regulatory factor (DAI) acts as a cytosolic B-form DNA sensor that induces type I interferons. However, DAI is not required for DNA sensing in certain cell types due to redundancy of the DNA sensing system. Here, we investigated the effect of DAI on herpes simplex virus 1 (HSV-1) infection in HepG2 hepatocellular carcinoma cells. DAI transcription was induced after gamma interferon (IFN-γ) treatment or HSV-1 infection. HSV-1 replication was enhanced by DAI knockdown, and ectopic DAI expression repressed viral replication in a manner requiring the Zβ and D3 domains, but not the Zα domain. This activity of DAI was more prominent at low multiplicity of infection (MOI) and correlated with the reduced expression of viral immediate-early genes. Consistently, DAI repressed the activation of ICP0 promoter in reporter gene assays. DAI knockdown did not affect the B-DNA-mediated IFN-β transcription and IRF3 activation, and overexpression of DAI and RIP1 did not enhance NF-κB activation by B-DNA treatment, demonstrating that DAI is not essential for the B-DNA-mediated IFN production in HepG2 cells. DAI colocalized with ICP0 in a subset of nuclear and cytoplasmic foci in infected cells and interacted with ICP0 in coimmunoprecipitation assays. The anti-HSV-1 effect of DAI was not observed in ICP0-deleted mutant virus infection at a high MOI in HepG2 cells and mouse embryonic fibroblasts. Degradation of IFI16 and PML by ICP0 was enhanced in infection of DAI-knockdown cells. Collectively, these results demonstrate that DAI can suppress HSV-1 growth independent of DNA sensing through mechanisms involving suppression of viral genomes and regulation of ICP0.
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Affiliation(s)
- Thanh H Pham
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
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59
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Scherer M, Reuter N, Wagenknecht N, Otto V, Sticht H, Stamminger T. Small ubiquitin-related modifier (SUMO) pathway-mediated enhancement of human cytomegalovirus replication correlates with a recruitment of SUMO-1/3 proteins to viral replication compartments. J Gen Virol 2013; 94:1373-1384. [PMID: 23407422 DOI: 10.1099/vir.0.051078-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Recent studies have suggested that the small ubiquitin-related modifier (SUMO) conjugation pathway may play an important role in intrinsic antiviral resistance and thus for repression of herpesviral infections. In particular, it was shown that the herpes simplex virus type-1 regulatory protein ICP0 acts as a SUMO-targeted ubiquitin ligase (STUbL), inducing the widespread degradation of SUMO-conjugated proteins during infection. As the IE1 protein of human cytomegalovirus (HCMV) is known to mediate a de-SUMOylation of PML, we investigated whether HCMV uses a similar mechanism to counteract intrinsic antiviral resistance. We generated primary human fibroblasts stably expressing FLAG-SUMO-1 or FLAG-SUMO-3 and analysed the SUMOylation pattern after HCMV infection or isolated IE1 expression. However, Western blot experiments did not reveal a global loss of SUMO conjugates, either in HCMV-infected or in IE1-expressing cells, arguing against a function of IE1 as an STUbL. Interestingly, we observed that FLAG-SUMO-1 and FLAG-SUMO-3, subsequent to IE1-mediated promyelocytic leukemia protein (PML) de-SUMOylation and the consequent disruption of PML nuclear bodies, were recruited into viral replication compartments. This raised the question of whether FLAG-SUMO-1/3 might promote HCMV replication. Intriguingly, overexpression of FLAG-SUMO-1/3 enhanced accumulation of viral DNA, which correlated with an increase in viral replication and in virus particle release. Together, these data indicate that HCMV, in contrast to other herpesviruses, has evolved subtle mechanisms enabling it to utilize the SUMO conjugation pathway for its own benefit, resulting in an overall positive effect of SUMO conjugation for HCMV replication.
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Affiliation(s)
- Myriam Scherer
- Institute for Clinical and Molecular Virology, University of Erlangen-Nuremberg, Schlossgarten 4, 91054 Erlangen, Germany
| | - Nina Reuter
- Institute for Clinical and Molecular Virology, University of Erlangen-Nuremberg, Schlossgarten 4, 91054 Erlangen, Germany
| | - Nadine Wagenknecht
- Institute for Clinical and Molecular Virology, University of Erlangen-Nuremberg, Schlossgarten 4, 91054 Erlangen, Germany
| | - Victoria Otto
- Institute for Clinical and Molecular Virology, University of Erlangen-Nuremberg, Schlossgarten 4, 91054 Erlangen, Germany
| | - Heinrich Sticht
- Institute of Biochemistry, University of Erlangen-Nuremberg, Fahrstr. 17, 91054 Erlangen, Germany
| | - Thomas Stamminger
- Institute for Clinical and Molecular Virology, University of Erlangen-Nuremberg, Schlossgarten 4, 91054 Erlangen, Germany
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60
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Glass M, Everett RD. Components of promyelocytic leukemia nuclear bodies (ND10) act cooperatively to repress herpesvirus infection. J Virol 2013; 87:2174-85. [PMID: 23221561 PMCID: PMC3571464 DOI: 10.1128/jvi.02950-12] [Citation(s) in RCA: 90] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Accepted: 11/28/2012] [Indexed: 01/12/2023] Open
Abstract
Upon the entry of the viral genome into the nucleus, herpes simplex virus type 1 (HSV-1) gene expression is rapidly repressed by constitutively expressed cellular proteins. This intrinsic antiviral defense is normally counteracted by ICP0, which allows virus infection to proceed efficiently. Replication of ICP0-null mutant HSV-1, however, is severely repressed by mechanisms that are conferred, at least in part, by nuclear domain 10 (ND10) components, including hDaxx, the promyelocytic leukemia (PML) protein, and Sp100. To investigate if these ND10 components repress viral gene expression in a cooperative manner, we simultaneously depleted host cells for hDaxx, PML, and Sp100 by multiple short hairpin RNA (shRNA) knockdown from a single lentivirus vector. We found that replication and gene expression of ICP0-null mutant HSV-1 were cooperatively repressed by hDaxx, PML, and Sp100 immediately upon infection, and all stages of virus replication were inhibited. Plaque-forming efficiency was enhanced at least 50-fold in the triple-depleted cells, a much larger increase than achieved by depletion of any single ND10 protein. Similar effects were also observed during infection of triple-depleted cells with human cytomegalovirus (HCMV). Moreover, using a cell culture model of quiescent infection, we found that triple depletion resulted in a much larger number of viral genomes escaping repression. However, triple depletion was unable to fully overcome the ICP0-null phenotype, implying the presence of additional repressive host factors, possibly components of the SUMO modification or DNA repair pathways. We conclude that several ND10 components cooperate in an additive manner to regulate HSV-1 and HCMV infection.
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Affiliation(s)
- Mandy Glass
- MRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland, United Kingdom
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61
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Everett RD, Bell AJ, Lu Y, Orr A. The replication defect of ICP0-null mutant herpes simplex virus 1 can be largely complemented by the combined activities of human cytomegalovirus proteins IE1 and pp71. J Virol 2013; 87:978-90. [PMID: 23135716 PMCID: PMC3554063 DOI: 10.1128/jvi.01103-12] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2012] [Accepted: 10/29/2012] [Indexed: 12/26/2022] Open
Abstract
Herpes simplex virus 1 (HSV-1) immediate-early protein ICP0 is required for efficient lytic infection and productive reactivation from latency and induces derepression of quiescent viral genomes. Despite being unrelated at the sequence level, ICP0 and human cytomegalovirus proteins IE1 and pp71 share some functional similarities in their abilities to counteract antiviral restriction mediated by components of cellular nuclear structures known as ND10. To investigate the extent to which IE1 and pp71 might substitute for ICP0, cell lines were developed that express either IE1 or pp71, or both together, in an inducible manner. We found that pp71 dissociated the hDaxx-ATRX complex and inhibited accumulation of these proteins at sites juxtaposed to HSV-1 genomes but had no effect on the promyelocytic leukemia protein (PML) or Sp100. IE1 caused loss of the small ubiquitin-like modifier (SUMO)-conjugated forms of PML and Sp100 and inhibited the recruitment of these proteins to HSV-1 genome foci but had little effect on hDaxx or ATRX in these assays. Both IE1 and pp71 stimulated ICP0-null mutant plaque formation, but neither to the extent achieved by ICP0. The combination of IE1 and pp71, however, inhibited recruitment of all ND10 proteins to viral genome foci, stimulated ICP0-null mutant HSV-1 plaque formation to near wild-type levels, and efficiently induced derepression of quiescent HSV-1 genomes. These results suggest that ND10-related intrinsic resistance results from the additive effects of several ND10 components and that the effects of IE1 and pp71 on subsets of these components combine to mirror the overall activities of ICP0.
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Affiliation(s)
- Roger D Everett
- MRC-University of Glasgow Centre for Virus Research 8, Glasgow, Scotland.
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62
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Nordén R, Nyström K, Aurelius J, Brisslert M, Olofsson S. Virus-induced appearance of the selectin ligand sLeX in herpes simplex virus type 1-infected T-cells: Involvement of host and viral factors. Glycobiology 2012; 23:310-21. [DOI: 10.1093/glycob/cws160] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
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63
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Geng Y, Monajembashi S, Shao A, Cui D, He W, Chen Z, Hemmerich P, Tang J. Contribution of the C-terminal regions of promyelocytic leukemia protein (PML) isoforms II and V to PML nuclear body formation. J Biol Chem 2012; 287:30729-42. [PMID: 22773875 PMCID: PMC3436317 DOI: 10.1074/jbc.m112.374769] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2012] [Revised: 06/25/2012] [Indexed: 12/12/2022] Open
Abstract
Promyelocytic leukemia protein (PML) nuclear bodies are dynamic and heterogeneous nuclear protein complexes implicated in various important functions, most notably tumor suppression. PML is the structural component of PML nuclear bodies and has several nuclear splice isoforms that share a common N-terminal region but differ in their C termini. Previous studies have suggested that the coiled-coil motif within the N-terminal region is sufficient for PML nuclear body formation by mediating homo/multi-dimerization of PML molecules. However, it has not been investigated whether any of the C-terminal variants of PML may contribute to PML body assembly. Here we report that the unique C-terminal domains of PML-II and PML-V can target to PML-NBs independent of their N-terminal region. Strikingly, both domains can form nuclear bodies in the absence of endogenous PML. The C-terminal domain of PML-II interacts transiently with unknown binding sites at PML nuclear bodies, whereas the C-terminal domain of PML-V exhibits hyperstable binding to PML bodies via homo-dimerization. This strong interaction is mediated by a putative α-helix in the C terminus of PML-V. Moreover, nuclear bodies assembled from the C-terminal domain of PML-V also recruit additional PML body components, including Daxx and Sp100. These observations establish the C-terminal domain of PML-V as an additional important contributor to the assembly mechanism(s) of PML bodies.
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Affiliation(s)
- Yunyun Geng
- From the State Key Laboratory of Agrobiotechnology and
- College of Veterinary Medicine, China Agricultural University, Beijing 100193, China
| | | | - Anwen Shao
- College of Veterinary Medicine, China Agricultural University, Beijing 100193, China
| | - Di Cui
- From the State Key Laboratory of Agrobiotechnology and
- College of Veterinary Medicine, China Agricultural University, Beijing 100193, China
| | - Weiyong He
- College of Veterinary Medicine, China Agricultural University, Beijing 100193, China
| | - Zhongzhou Chen
- From the State Key Laboratory of Agrobiotechnology and
- the College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - Peter Hemmerich
- the Leibniz Institute for Age Research, 07743 Jena, Germany, and
| | - Jun Tang
- From the State Key Laboratory of Agrobiotechnology and
- College of Veterinary Medicine, China Agricultural University, Beijing 100193, China
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64
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Herpes simplex virus is equipped with RNA- and protein-based mechanisms to repress expression of ATRX, an effector of intrinsic immunity. J Virol 2012; 86:10093-102. [PMID: 22787211 DOI: 10.1128/jvi.00930-12] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Intrinsic immunity is a first-line intracellular defense against virus infection, and viruses have evolved mechanisms to counteract it. During herpes simplex virus (HSV) infection, nuclear domain 10 (ND10) components localize adjacent to incoming viral genomes and generate a repressive environment for viral gene expression. Here, we found that the ND10 component, alpha-thalassemia/mental retardation syndrome X-linked (ATRX) protein, is predicted to be a target of HSV-1 miR-H1 and HSV-2 miR-H6. These microRNAs (miRNAs) share a seed sequence and are abundant during lytic infection. Mimics of both miRNAs could deplete endogenous ATRX, and an miR-H1 mimic could repress the expression of a reporter linked to the 3' untranslated region of ATRX mRNA, identifying a cellular mRNA targeted by an HSV miRNA. Interestingly, ATRX protein and its mRNA were depleted in cells lytically infected with HSV, and ATRX protein was also depleted in cells infected with human cytomegalovirus. However, infection with an HSV-1 mutant lacking miR-H1 still resulted in ATRX depletion. This depletion was sensitive to a proteasome inhibitor and was largely ablated by a deletion of the gene encoding the immediate-early ICP0 protein. Additionally, a deletion of the gene encoding the tegument protein Vhs ablated most of the depletion of ATRX mRNA. Thus, HSV is equipped with multiple mechanisms to limit the expression of ATRX. As ATRX is implicated in repression of lytic viral gene expression, our results suggest roles for these different mechanisms during various phases of HSV infection.
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65
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Wilson VG. Sumoylation at the host-pathogen interface. Biomolecules 2012; 2:203-27. [PMID: 23795346 PMCID: PMC3685863 DOI: 10.3390/biom2020203] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Revised: 03/21/2012] [Accepted: 03/27/2012] [Indexed: 12/11/2022] Open
Abstract
Many viral proteins have been shown to be sumoylated with corresponding regulatory effects on their protein function, indicating that this host cell modification process is widely exploited by viral pathogens to control viral activity. In addition to using sumoylation to regulate their own proteins, several viral pathogens have been shown to modulate overall host sumoylation levels. Given the large number of cellular targets for SUMO addition and the breadth of critical cellular processes that are regulated via sumoylation, viral modulation of overall sumoylation presumably alters the cellular environment to ensure that it is favorable for viral reproduction and/or persistence. Like some viruses, certain bacterial plant pathogens also target the sumoylation system, usually decreasing sumoylation to disrupt host anti-pathogen responses. The recent demonstration that Listeria monocytogenes also disrupts host sumoylation, and that this is required for efficient infection, extends the plant pathogen observations to a human pathogen and suggests that pathogen modulation of host sumoylation may be more widespread than previously appreciated. This review will focus on recent aspects of how pathogens modulate the host sumoylation system and how this benefits the pathogen.
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Affiliation(s)
- Van G Wilson
- Department of Microbial & Molecular Pathogenesis, College of Medicine, Texas A&M Health Science Center, 8447 HWY 47, Bryan, TX 77807-1359
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66
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Full F, Reuter N, Zielke K, Stamminger T, Ensser A. Herpesvirus saimiri antagonizes nuclear domain 10-instituted intrinsic immunity via an ORF3-mediated selective degradation of cellular protein Sp100. J Virol 2012; 86:3541-53. [PMID: 22278248 PMCID: PMC3302493 DOI: 10.1128/jvi.06992-11] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Accepted: 01/09/2012] [Indexed: 01/28/2023] Open
Abstract
In recent studies, the nuclear domain 10 (ND10) components PML, Sp100, human Daxx (hDaxx), and ATRX were identified to be cellular restriction factors that are able to inhibit the replication of several herpesviruses. The antiviral function of ND10, however, is antagonized by viral effector proteins by a variety of strategies, including degradation of PML or relocalization of ND10 proteins. In this study, we analyzed the interplay between infection with herpesvirus saimiri (HVS), the prototypic rhadinovirus, and cellular defense by ND10. In contrast to other herpesviruses, we found that HVS specifically degraded the cellular ND10 component Sp100, whereas other factors like PML or hDaxx remained intact. We could further identify the ORF3 tegument protein of HVS, which shares homology with the cellular formylglycinamide ribotide amidotransferase (FGARAT) enzyme, to be the viral factor that induces the proteasomal degradation of Sp100. Interestingly, recent studies showed that the ORF3-homologous proteins ORF75c of murine gammaherpesvirus 68 and BNRF-1 of Epstein-Barr virus modulate the ND10 proteins PML and ATRX, respectively, suggesting that the ND10 targets of viral FGARAT-homologous proteins diversified during evolution. Furthermore, a virus with the ORF3 deletion was efficiently complemented in Sp100-depleted cells, indicating that Sp100 is able to inhibit HVS in the absence of antagonistic mechanisms. In contrast, we observed that PML, which was neither degraded nor redistributed after HVS infection, strongly restricted both wild-type HVS and virus with the ORF3 deletion. Thus, HVS may lack a factor that efficiently counteracts the repressive function of PML, which may foster latency as the outcome of infection.
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Affiliation(s)
- Florian Full
- Institut für Klinische und Molekulare Virologie, Universitätsklinikum, Friedrich Alexander Universität, Erlangen, Germany
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Shin HJ, Kim YE, Kim ET, Ahn JH. The chromatin-tethering domain of human cytomegalovirus immediate-early (IE) 1 mediates associations of IE1, PML and STAT2 with mitotic chromosomes, but is not essential for viral replication. J Gen Virol 2011; 93:716-721. [PMID: 22158879 DOI: 10.1099/vir.0.037986-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Human cytomegalovirus (HCMV) immediate-early (IE) 1 protein associates with chromosomes in mitotic cells using its carboxyl-terminal 16 aa region. However, the role of this IE1 activity in viral growth has not been evaluated in the context of mutant virus infection. We produced a recombinant HCMV encoding mutant IE1 with the carboxyl-terminal chromosome-tethering domain (CTD) deleted. This IE1(ΔCTD) virus grew like the wild-type virus in fibroblasts, indicating that the CTD is not essential for viral replication in permissive cells. Unlike wild-type virus infections, PML and STAT2, which interact with IE1, did not accumulate at mitotic chromosomes in IE1(ΔCTD) virus-infected fibroblasts, demonstrating that their associations with chromosomes are IE1 CTD-dependent. IE1 SUMOylation did not affect IE1 association with chromosomes. Our results provide genetic evidence that the CTD is required for the associations of IE1, PML and STAT2 with mitotic chromosomes, but that these IE1-related activities are not essential for viral replication in fibroblasts.
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Affiliation(s)
- Hye Jin Shin
- Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea
| | - Young-Eui Kim
- Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea
| | - Eui Tae Kim
- Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea
| | - Jin-Hyun Ahn
- Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea
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Abstract
Since posttranslational modification (PTM) by the small ubiquitin-related modifiers (SUMOs) was discovered over a decade ago, a huge number of cellular proteins have been found to be reversibly modified, resulting in alteration of differential cellular pathways. Although the molecular consequences of SUMO attachment are difficult to predict, the underlying principle of SUMOylation is altering inter- and/or intramolecular interactions of the modified substrate, changing localization, stability, and/or activity. Unsurprisingly, many different pathogens have evolved to exploit the cellular SUMO modification system due to its functional flexibility and far-reaching functional downstream consequences. Although the extensive knowledge gained so far is impressive, a definitive conclusion about the role of SUMO modification during virus infection in general remains elusive and is still restricted to a few, yet promising concepts. Based on the available data, this review aims, first, to provide a detailed overview of the current state of knowledge and, second, to evaluate the currently known common principles/molecular mechanisms of how human pathogenic microbes, especially viruses and their regulatory proteins, exploit the host cell SUMO modification system.
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Kim YE, Lee JH, Kim ET, Shin HJ, Gu SY, Seol HS, Ling PD, Lee CH, Ahn JH. Human cytomegalovirus infection causes degradation of Sp100 proteins that suppress viral gene expression. J Virol 2011; 85:11928-37. [PMID: 21880768 PMCID: PMC3209270 DOI: 10.1128/jvi.00758-11] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2011] [Accepted: 08/18/2011] [Indexed: 01/02/2023] Open
Abstract
The interferon-inducible Sp100 proteins are thought to play roles in the chromatin pathway and in transcriptional regulation. Sp100A, the smallest isoform, is one of the major components of PML nuclear bodies (NBs) that exhibit intrinsic antiviral activity against several viruses. Since PML NBs are disrupted by the immediate-early 1 (IE1) protein during human cytomegalovirus (HCMV) infection, the modulation of Sp100 protein expression or activity during infection has been suggested. Here, we show that Sp100 proteins are lost largely in the late stages of HCMV infection. This event required viral gene expression and involved posttranscriptional control. The mutant virus with deletion of the sequence for IE1 (CR208) did not have Sp100 loss. In CR208 infection, PML depletion by RNA interference abrogated the accumulation of SUMO-modified Sp100A and of certain high-molecular-weight Sp100 isoforms but did not significantly affect unmodified Sp100A, suggesting that the IE1-induced disruption of PML NBs is not sufficient for the complete loss of Sp100 proteins. Sp100A loss was found to require proteasome activity. Depletion of all Sp100 proteins by RNA silencing enhanced HCMV replication and major IE (MIE) gene expression. Sp100 knockdown enhanced the acetylation level of histones associated with the MIE promoter, demonstrating that the repressive effect of Sp100 proteins may involve, at least in part, the epigenetic control of the MIE promoter. Sp100A was found to interact directly with IE1 through the N-terminal dimerization domain. These findings indicate that the IE1-dependent loss of Sp100 proteins during HCMV infection may represent an important requirement for efficient viral growth.
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Affiliation(s)
- Young-Eui Kim
- Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon
| | - Jin-Hyoung Lee
- Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon
| | - Eui Tae Kim
- Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon
| | - Hye Jin Shin
- Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon
| | - Su Yeon Gu
- Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon
| | - Hyang Sook Seol
- Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon
| | - Paul D. Ling
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas
| | - Chan Hee Lee
- Division of Life Sciences, Chungbuk National University, Cheongju, Republic of Korea
| | - Jin-Hyun Ahn
- Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon
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Sánchez-Durán MA, Dallas MB, Ascencio-Ibañez JT, Reyes MI, Arroyo-Mateos M, Ruiz-Albert J, Hanley-Bowdoin L, Bejarano ER. Interaction between geminivirus replication protein and the SUMO-conjugating enzyme is required for viral infection. J Virol 2011; 85:9789-800. [PMID: 21775461 PMCID: PMC3196459 DOI: 10.1128/jvi.02566-10] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2010] [Accepted: 07/08/2011] [Indexed: 12/11/2022] Open
Abstract
Geminiviruses are small DNA viruses that replicate in nuclei of infected plant cells by using plant DNA polymerases. These viruses encode a protein designated AL1, Rep, or AC1 that is essential for viral replication. AL1 is an oligomeric protein that binds to double-stranded DNA, catalyzes the cleavage and ligation of single-stranded DNA, and induces the accumulation of host replication machinery. It also interacts with several host proteins, including the cell cycle regulator retinoblastoma-related protein (RBR), the DNA replication protein PCNA (proliferating cellular nuclear antigen), and the sumoylation enzyme that conjugates SUMO to target proteins (SUMO-conjugating enzyme [SCE1]). The SCE1-binding motif was mapped by deletion to a region encompassing AL1 amino acids 85 to 114. Alanine mutagenesis of lysine residues in the binding region either reduced or eliminated the interaction with SCE1, but no defects were observed for other AL1 functions, such as oligomerization, DNA binding, DNA cleavage, and interaction with AL3 or RBR. The lysine mutations reduced or abolished virus infectivity in plants and viral DNA accumulation in transient-replication assays, suggesting that the AL1-SCE1 interaction is required for viral DNA replication. Ectopic AL1 expression did not result in broad changes in the sumoylation pattern of plant cells, but specific changes were detected, indicating that AL1 modifies the sumoylation state of selected host proteins. These results established the importance of AL1-SCE1 interactions during geminivirus infection of plants and suggested that AL1 alters the sumoylation of selected host factors to create an environment suitable for viral infection.
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Affiliation(s)
- Miguel A. Sánchez-Durán
- Instituto de Hortofruticultura Subtropical y Mediterránea La Mayora, Universidad de Málaga-Consejo Superior de Investigaciones Científicas (IHSM-UMA-CSIC), Departmento de Biología Celular, Genética y Fisiología, Universidad de Málaga, Campus Teatinos, 29071 Málaga, Spain
| | - Mary B. Dallas
- Department of Molecular and Structural Biochemistry, North Carolina State University, Raleigh, North Carolina 27695-7622
| | - José T. Ascencio-Ibañez
- Department of Molecular and Structural Biochemistry, North Carolina State University, Raleigh, North Carolina 27695-7622
| | - Maria Ines Reyes
- Department of Molecular and Structural Biochemistry, North Carolina State University, Raleigh, North Carolina 27695-7622
| | - Manuel Arroyo-Mateos
- Instituto de Hortofruticultura Subtropical y Mediterránea La Mayora, Universidad de Málaga-Consejo Superior de Investigaciones Científicas (IHSM-UMA-CSIC), Departmento de Biología Celular, Genética y Fisiología, Universidad de Málaga, Campus Teatinos, 29071 Málaga, Spain
| | - Javier Ruiz-Albert
- Instituto de Hortofruticultura Subtropical y Mediterránea La Mayora, Universidad de Málaga-Consejo Superior de Investigaciones Científicas (IHSM-UMA-CSIC), Departmento de Biología Celular, Genética y Fisiología, Universidad de Málaga, Campus Teatinos, 29071 Málaga, Spain
| | - Linda Hanley-Bowdoin
- Department of Molecular and Structural Biochemistry, North Carolina State University, Raleigh, North Carolina 27695-7622
| | - Eduardo R. Bejarano
- Instituto de Hortofruticultura Subtropical y Mediterránea La Mayora, Universidad de Málaga-Consejo Superior de Investigaciones Científicas (IHSM-UMA-CSIC), Departmento de Biología Celular, Genética y Fisiología, Universidad de Málaga, Campus Teatinos, 29071 Málaga, Spain
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Tavalai N, Adler M, Scherer M, Riedl Y, Stamminger T. Evidence for a dual antiviral role of the major nuclear domain 10 component Sp100 during the immediate-early and late phases of the human cytomegalovirus replication cycle. J Virol 2011; 85:9447-58. [PMID: 21734036 PMCID: PMC3165758 DOI: 10.1128/jvi.00870-11] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2011] [Accepted: 06/27/2011] [Indexed: 12/20/2022] Open
Abstract
In recent studies, the nuclear domain 10 (ND10) components PML and hDaxx were identified as cellular restriction factors that inhibit the initiation of human cytomegalovirus (HCMV) replication. The antiviral function of ND10, however, is antagonized by the IE1 protein, which induces ND10 disruption. Here we show that IE1 not only de-SUMOylates PML immediately upon infection but also directly targets Sp100. IE1 expression alone was sufficient to downregulate endogenous Sp100 independently of the presence of PML. Moreover, cotransfection experiments revealed that IE1 negatively interferes with the SUMOylation of all Sp100 isoforms. The modulation of Sp100 at immediate-early (IE) times of infection, indeed, seemed to have an in vivo relevance for HCMV replication, since knockdown of Sp100 resulted in more cells initiating the viral gene expression program. In addition, we observed that Sp100 was degraded in a proteasome-dependent manner at late times postinfection, suggesting that Sp100 may play an additional antiviral role during the late phase. Infection experiments conducted with Sp100 knockdown human foreskin fibroblasts (HFFs) confirmed this hypothesis: depletion of Sp100 resulted in augmented release of progeny virus particles compared to that from control cells. Consistent with this observation, we noted increased amounts of viral late gene products in the absence of Sp100. Importantly, this elevated late gene expression was not dependent on enhanced viral IE gene expression. Taken together, our data provide evidence that Sp100 is the first ND10-related factor identified that not only possesses the potential to restrict the initial stage of infection but also inhibits HCMV replication during the late phase.
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Affiliation(s)
- Nina Tavalai
- Institute for Clinical and Molecular Virology, University Erlangen-Nuremberg, Schlossgarten 4, 91054 Erlangen, Germany
| | - Martina Adler
- Institute for Clinical and Molecular Virology, University Erlangen-Nuremberg, Schlossgarten 4, 91054 Erlangen, Germany
| | - Myriam Scherer
- Institute for Clinical and Molecular Virology, University Erlangen-Nuremberg, Schlossgarten 4, 91054 Erlangen, Germany
| | - Yvonne Riedl
- Institute for Clinical and Molecular Virology, University Erlangen-Nuremberg, Schlossgarten 4, 91054 Erlangen, Germany
| | - Thomas Stamminger
- Institute for Clinical and Molecular Virology, University Erlangen-Nuremberg, Schlossgarten 4, 91054 Erlangen, Germany
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Arcangeletti MC, Rodighiero I, Mirandola P, De Conto F, Covan S, Germini D, Razin S, Dettori G, Chezzi C. Cell-cycle-dependent localization of human cytomegalovirus UL83 phosphoprotein in the nucleolus and modulation of viral gene expression in human embryo fibroblasts in vitro. J Cell Biochem 2011; 112:307-17. [PMID: 21053310 DOI: 10.1002/jcb.22928] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The nucleolus is a multifunctional nuclear compartment widely known to be involved in several cellular processes, including mRNA maturation and shuttling to cytoplasmic sites, control of the cell cycle, cell proliferation, and apoptosis; thus, it is logical that many viruses, including herpesvirus, target the nucleolus in order to exploit at least one of the above-mentioned functions. Recent studies from our group demonstrated the early accumulation of the incoming ppUL83 (pp65), the major tegument protein of human cytomegalovirus (HCMV), in the nucleolus. The obtained results also suggested that a functional relationship might exist between the nucleolar localization of pp65, rRNA synthesis, and the development of the lytic program of viral gene expression. Here we present new data which support the hypothesis of a potentially relevant role of HCMV pp65 and its nucleolar localization for the control of the cell cycle by HCMV (arrest of cell proliferation in G1-G1/S), and for the promotion of viral infection. We demonstrated that, although the incoming pp65 amount in the infected cells appears to be constant irrespective of the cell-cycle phase, its nucleolar accumulation is prominent in G1 and G1/S, but very poor in S or G2/M. This correlates with the observation that only cells in G1 and G1/S support an efficient development of the HCMV lytic cycle. We propose that HCMV pp65 might be involved in regulatory/signaling pathways related to nucleolar functions, such as the cell-cycle control. Co-immunoprecipitation experiments have permitted to identify nucleolin as one of the nucleolar partners of pp65.
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73
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Cosme-Cruz R, Martínez FP, Perez KJ, Tang Q. H2B homology region of major immediate-early protein 1 is essential for murine cytomegalovirus to disrupt nuclear domain 10, but is not important for viral replication in cell culture. J Gen Virol 2011; 92:2006-2019. [PMID: 21632568 DOI: 10.1099/vir.0.033225-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Cytomegalovirus (CMV) major immediate-early protein 1 (IE1) has multiple functions and is important for efficient viral infection. As does its counterpart in human CMV, murine CMV (MCMV) IE1 also functions as a disruptor of mouse-cell nuclear domain 10 (ND10), where many different gene-regulation proteins congregate. It still remains unclear how MCMV IE1 disperses ND10 and whether this dispersion could have any effect on viral replication. MCMV IE1 is 595 aa long and has multiple functional domains that have not yet been fully analysed. In this study, we dissected the IE1 molecule by truncation and/or deletion and found that the H2B homology domain (amino acid sequence NDIFERI) is required for the dispersion of ND10 by IE1. Furthermore, we made additional deletions and point mutations and found that the minimal truncation in the H2B homology domain required for IE1 to lose the ability to disperse ND10 is just 3 aa (IFE). Surprisingly, the mutated IE1 still interacted with PML and co-localized with ND10 but failed to disperse ND10. This suggests that binding to ND10 key protein is essential to, but not sufficient for, the dispersal of ND10, and that some other unknown mechanism must be involved in this biological procedure. Finally, we generated MCMV with IFE-deleted IE1 (MCMVdlIFE) and its revertant (MCMVIFERQ). Although MCMVdlIFE lost the ability to disperse ND10, plaque assays and viral gene production assays showed that the deletion of IFE did not increase viral replication in cell culture. We conclude that the dispersion of ND10 appears not to be important for MCMV replication in a mouse-cell culture.
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Affiliation(s)
- Ruth Cosme-Cruz
- Department of Microbiology/RCMI Program, Ponce School of Medicine and Health Sciences, Ponce 00716, Puerto Rico
| | - Francisco Puerta Martínez
- Department of Microbiology/RCMI Program, Ponce School of Medicine and Health Sciences, Ponce 00716, Puerto Rico
| | - Kareni J Perez
- Department of Microbiology/RCMI Program, Ponce School of Medicine and Health Sciences, Ponce 00716, Puerto Rico
| | - Qiyi Tang
- Department of Microbiology/RCMI Program, Ponce School of Medicine and Health Sciences, Ponce 00716, Puerto Rico
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74
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Intrinsic cellular defense mechanisms targeting human cytomegalovirus. Virus Res 2011; 157:128-33. [DOI: 10.1016/j.virusres.2010.10.002] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2010] [Revised: 09/30/2010] [Accepted: 10/04/2010] [Indexed: 11/20/2022]
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75
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Shi-Chen Ou D, Lee SB, Chu CS, Chang LH, Chung BC, Juan LJ. Transcriptional activation of endoplasmic reticulum chaperone GRP78 by HCMV IE1-72 protein. Cell Res 2011; 21:642-53. [PMID: 21221131 PMCID: PMC3203653 DOI: 10.1038/cr.2011.10] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Glucose-regulated protein 78 (GRP78), a key regulator of endoplasmic reticulum (ER) stress, facilitates cancer cell growth and viral replication. The mechanism leading to grp78 gene activation during viral infection is largely unknown. In this study, we show that the immediate-early 1 (IE1-72) protein of the human cytomegalovirus (HCMV) is essential for HCMV-mediated GRP78 activation. IE1-72 upregulated grp78 gene expression depending on the ATP-binding site, the zinc-finger domain and the putative leucine-zipper motif of IE1-72, as well as the ER stress response elements (ERSEs) on the grp78 promoter. The purified IE1-72 protein bound to the CCAAT box within ERSE in vitro, whereas deletion mutants of IE1-72 deficient in grp78 promoter stimulation failed to do so. Moreover, IE1-72 binding to the grp78 promoter in infected cells accompanied the recruitment of TATA box-binding protein-associated factor 1 (TAF1), a histone acetyltransferase, and the increased level of acetylated histone H4, an indicator of active-state chromatin. These results provide evidence that HCMV IE1-72 activates grp78 gene expression through direct promoter binding and modulation of the local chromatin structure, indicating an active viral mechanism of cellular chaperone induction for viral growth.
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Affiliation(s)
- Derick Shi-Chen Ou
- Institute of Molecular and Cellular Biology, National Tsing Hua University, 101, Section 2, Kuang-Fu Road, Hsinchu 300
- Genomics Research Center, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 115
| | - Sung-Bau Lee
- Genomics Research Center, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 115
| | - Chi-Shuen Chu
- Genomics Research Center, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 115
| | - Liang-Hao Chang
- Genomics Research Center, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 115
| | - Bon-chu Chung
- Institute of Molecular and Cellular Biology, National Tsing Hua University, 101, Section 2, Kuang-Fu Road, Hsinchu 300
- Institute of Molecular Biology, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 115
- Tel: +886-2-2789-9215; Fax: +886-2-27826085
E-mail:
| | - Li-Jung Juan
- Genomics Research Center, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 115
- Institute of Molecular Medicine, National Taiwan University, No.7, Chung San South Road, Taipei 100
- Tel: +886-2-27871234; Fax: +886-2-27898811
E-mail:
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76
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Abstract
BK virus (BKV) is the causative agent for polyomavirus-associated nephropathy, a severe disease found in renal transplant patients due to reactivation of a persistent BKV infection. BKV replication relies on the interactions of BKV with many nuclear components, and subnuclear structures such as promyelocytic leukemia nuclear bodies (PML-NBs) are known to play regulatory roles during a number of DNA virus infections. In this study, we investigated the relationship between PML-NBs and BKV during infection of primary human renal proximal tubule epithelial (RPTE) cells. While the levels of the major PML-NB protein components remained unchanged, BKV infection of RPTE cells resulted in dramatic alterations in both the number and the size of PML-NBs. Furthermore, two normally constitutive components of PML-NBs, Sp100 and hDaxx, became dispersed from PML-NBs. To define the viral factors responsible for this reorganization, we examined the cellular localization of the BKV large tumor antigen (TAg) and viral DNA. TAg colocalized with PML-NBs during early infection, while a number of BKV chromosomes were adjacent to PML-NBs during late infection. We demonstrated that TAg alone was not sufficient to reorganize PML-NBs and that active viral DNA replication is required. Knockdown of PML protein did not dramatically affect BKV growth in culture. BKV infection, however, was able to rescue the growth of an ICP0-null herpes simplex virus 1 mutant whose growth defect was partially due to its inability to disrupt PML-NBs. We hypothesize that the antiviral functions of PML-NBs are inactivated through reorganization during normal BKV infection. BK virus (BKV) is a human pathogen that causes severe diseases, including polyomavirus-associated nephropathy in kidney transplant patients and hemorrhagic cystitis in bone marrow transplant recipients. How BKV replication is regulated and the effects of a lytic BKV infection on host cells at the molecular level are not well understood. Currently, there is no specific antiviral treatment for BKV-associated disease, and a better understanding of the complete life cycle of the virus is necessary. Here, we report the interplay between BKV and one of the regulatory structures in the host cell nucleus, promyelocytic leukemia nuclear bodies (PML-NBs). Our results show that BKV infection reorganizes PML-NBs as a strategy to inactivate the negative functions of PML-NBs.
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77
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Geoffroy MC, Chelbi-Alix MK. Role of promyelocytic leukemia protein in host antiviral defense. J Interferon Cytokine Res 2011; 31:145-58. [PMID: 21198351 DOI: 10.1089/jir.2010.0111] [Citation(s) in RCA: 150] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Several pathways have been implicated in the establishment of antiviral state in response to interferon (IFN), one of which implicates the promyelocytic leukemia (PML) protein. The PML gene has been discovered 20 years ago and has led to new insights into oncogenesis, apoptosis, cell senescence, and antiviral defense. PML is induced by IFN, leading to a marked increase of expression of PML isoforms and the number of PML nuclear bodies (NBs). PML is the organizer of the NBs that contains at least 2 permanent NB-associated proteins, the IFN-stimulated gene product Speckled protein of 100 kDa (Sp100) and death-associated dead protein (Daxx), as well as numerous other transient proteins recruited in these structures in response to different stimuli. Accumulating reports have implicated PML in host antiviral defense and revealed various strategies developed by viruses to disrupt PML NBs. This review will focus on the regulation of PML and the implication of PML NBs in conferring resistance to DNA and RNA viruses. The role of PML in mediating an IFN-induced antiviral state will also be discussed.
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78
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Cuchet D, Sykes A, Nicolas A, Orr A, Murray J, Sirma H, Heeren J, Bartelt A, Everett RD. PML isoforms I and II participate in PML-dependent restriction of HSV-1 replication. J Cell Sci 2010; 124:280-91. [PMID: 21172801 DOI: 10.1242/jcs.075390] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Intrinsic antiviral resistance mediated by constitutively expressed cellular proteins is one arm of defence against virus infection. Promyelocytic leukaemia nuclear bodies (PML-NBs, also known as ND10) contribute to host restriction of herpes simplex virus type 1 (HSV-1) replication via mechanisms that are counteracted by viral regulatory protein ICP0. ND10 assembly is dependent on PML, which comprises several different isoforms, and depletion of all PML isoforms decreases cellular resistance to ICP0-null mutant HSV-1. We report that individual expression of PML isoforms I and II partially reverses the increase in ICP0-null mutant HSV-1 plaque formation that occurs in PML-depleted cells. This activity of PML isoform I is dependent on SUMO modification, its SUMO interaction motif (SIM), and each element of its TRIM domain. Detailed analysis revealed that the punctate foci formed by individual PML isoforms differ subtly from normal ND10 in terms of composition and/or Sp100 modification. Surprisingly, deletion of the SIM motif from PML isoform I resulted in increased colocalisation with other major ND10 components in cells lacking endogenous PML. Our observations suggest that complete functionality of PML is dependent on isoform-specific C-terminal sequences acting in concert.
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Affiliation(s)
- Delphine Cuchet
- MRC-University of Glasgow Centre for Virus Research, Church Street, Glasgow G11 5JR, Scotland, UK
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79
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Abstract
Nonstructural protein 1 (NS1) is one of the major factors resulting in the efficient infection rate and high level of virulence of influenza A virus. Although consisting of only approximately 230 amino acids, NS1 has the ability to interfere with several systems of the host viral defense. In the present study, we demonstrate that NS1 of the highly pathogenic avian influenza A/Duck/Hubei/L-1/2004 (H5N1) virus interacts with human Ubc9, which is the E2 conjugating enzyme for sumoylation, and we show that SUMO1 is conjugated to H5N1 NS1 in both transfected and infected cells. Furthermore, two lysine residues in the C terminus of NS1 were identified as SUMO1 acceptor sites. When the SUMO1 acceptor sites were removed by mutation, NS1 underwent rapid degradation. Studies of different influenza A virus strains of human and avian origin showed that the majority of viruses possess an NS1 protein that is modified by SUMO1, except for the recently emerged swine-origin influenza A virus (S-OIV) (H1N1). Interestingly, growth of a sumoylation-deficient WSN virus mutant was retarded compared to that of wild-type virus. Together, these results indicate that sumoylation enhances NS1 stability and thus promotes rapid growth of influenza A virus.
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80
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Dimitropoulou P, Caswell R, McSharry BP, Greaves RF, Spandidos DA, Wilkinson GWG, Sourvinos G. Differential relocation and stability of PML-body components during productive human cytomegalovirus infection: detailed characterization by live-cell imaging. Eur J Cell Biol 2010; 89:757-68. [PMID: 20599291 DOI: 10.1016/j.ejcb.2010.05.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2010] [Revised: 05/14/2010] [Accepted: 05/26/2010] [Indexed: 01/30/2023] Open
Abstract
In controlling the switch from latency to lytic infection, the immediate early (IE) genes lie at the core of herpesvirus pathogenesis. To image the 72kDa human cytomegalovirus (HCMV) major IE protein (IE1-72K), a recombinant virus encoding IE1 fused with EGFP was constructed. Using this construct, the IE1-EGFP fusion was detected at ND10 (PML-bodies) within 2h post infection (p.i.) and the complete disruption of ND10 imaged through to 6h p.i. HCMV genomes and IE2-86K protein could be detected adjacent to the slowly degrading IE1-72K/ND10 foci. IE1-72K associates with metaphase chromatin, recruiting both PML and STAT2. hDaxx, STAT1 and IE2-86K did not re-locate to metaphase chromatin; the fate of hDaxx is particularly important as this protein contributes to an intrinsic barrier to HCMV infection. While IE1-72K participates in a complex with chromatin, PML, STAT2 and Sp100, IE1-72K releases hDaxx from ND10 yet does not appear to remain associated with it.
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Affiliation(s)
- Panagiota Dimitropoulou
- Department of Virology, Faculty of Medicine, University of Crete, Heraklion 71003, Crete, Greece
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81
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Reeves M, Woodhall D, Compton T, Sinclair J. Human cytomegalovirus IE72 protein interacts with the transcriptional repressor hDaxx to regulate LUNA gene expression during lytic infection. J Virol 2010; 84:7185-94. [PMID: 20444888 PMCID: PMC2898242 DOI: 10.1128/jvi.02231-09] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
A putative latency-associated transcript (LUNA) complementary to the human cytomegalovirus (HCMV) UL81-82 region previously identified in seropositive donors' monocytes is also expressed during lytic infection. Thus, the LUNA promoter is active during both lytic and latent infection. Consequently, the mechanisms regulating this promoter may provide further insight into factors that determine whether the outcome of HCMV infection is latent or lytic. By transfection, the LUNA promoter exhibited low but reproducible activity. Substantial activation by virus infection suggested that a viral factor was important for LUNA expression during lytic infection. IE72, a known transactivator of viral promoters, activated the LUNA promoter in cotransfection assays. Furthermore, coinfection with wild-type HCMV but not an IE72 deletion virus (CR208) also activated the LUNA promoter. Finally, diminished LUNA gene expression in CR208 virus-infected cells supported a role for IE72 in LUNA gene expression. The initial regulation of herpesvirus immediate-early gene expression is associated with proteins found at cellular nuclear domain 10 (ND10) bodies, such as PML, hDaxx, and ATRX. hDaxx transfection repressed LUNA promoter activity. Furthermore, we observed binding of hDaxx to the LUNA promoter, which was abrogated by IE72 gene expression via direct interaction. Finally, we show that small interfering RNA (siRNA) knockdown of the hDaxx interaction partner ATRX rescued LUNA gene expression in CR208-infected cells. Overall, these data show that hDaxx/ATRX-mediated repression of LUNA during lytic infection absolutely requires IE72 gene expression. It also suggests that the targeting of cellular factors by IE72 is important throughout the different phases of HCMV gene expression during productive infection.
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Affiliation(s)
- Matthew Reeves
- Novartis Institutes for Biomedical Research, 500 Technology Square, Cambridge, Massachusetts, Department of Medicine, Addenbrooke's Hospital, Cambridge CB2 2QQ, United Kingdom
| | - David Woodhall
- Novartis Institutes for Biomedical Research, 500 Technology Square, Cambridge, Massachusetts, Department of Medicine, Addenbrooke's Hospital, Cambridge CB2 2QQ, United Kingdom
| | - Teresa Compton
- Novartis Institutes for Biomedical Research, 500 Technology Square, Cambridge, Massachusetts, Department of Medicine, Addenbrooke's Hospital, Cambridge CB2 2QQ, United Kingdom
| | - John Sinclair
- Novartis Institutes for Biomedical Research, 500 Technology Square, Cambridge, Massachusetts, Department of Medicine, Addenbrooke's Hospital, Cambridge CB2 2QQ, United Kingdom
- Corresponding author. Mailing address: Department of Medicine, Level 5, Box 157, Addenbrooke's Hospital, Cambridge CB2 2QQ, United Kingdom. Phone: 44 1223 336850. Fax: 44 1223 336846. E-mail:
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82
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Role of the specific interaction of UL112-113 p84 with UL44 DNA polymerase processivity factor in promoting DNA replication of human cytomegalovirus. J Virol 2010; 84:8409-21. [PMID: 20538862 DOI: 10.1128/jvi.00189-10] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human cytomegalovirus (HCMV) UL112-113 region encodes four phosphoproteins with common amino termini (p34, p43, p50, and p84) via alternative splicing and is thought to be required for efficient viral DNA replication. We have previously shown that interactions among the four UL112-113 proteins regulate their intranuclear targeting and enable the recruitment of the UL44 DNA polymerase processivity factor to viral prereplication foci. Here, we show that in virus-infected cells, the UL112-113 proteins form a complex with UL44 and other replication proteins, such as UL84 and IE2. In vitro assays showed that all four phosphoproteins interacted with UL44. Interestingly, p84 required both the shared amino-terminal region and the specific near-carboxy-terminal region for UL44 binding. UL44 required both the carboxy-terminal region and the central region, including the dimerization domain for p84 binding. The production of recombinant virus from mutant Towne bacterial artificial chromosome (BAC) DNA, which encodes intact p34, p43, and p50 and a carboxy-terminally truncated p84 defective in UL44 binding, was severely impaired compared to wild-type BAC DNA. A similar defect was observed when mutant BAC DNA encoded a carboxy-terminally truncated UL44 defective in p84 binding. In cotransfection replication assays using six replication core proteins, UL84, IE2, and UL112-113, the efficient replication of an HCMV oriLyt-containing plasmid required the regions of p84 and UL44 necessary for their interaction. Our data suggest that the UL112-113 proteins form a complex with other replication proteins such as UL44, UL84, and IE2 and that the specific interaction of UL112-113 p84 with UL44 is necessary for efficient viral DNA replication.
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83
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Role of noncovalent SUMO binding by the human cytomegalovirus IE2 transactivator in lytic growth. J Virol 2010; 84:8111-23. [PMID: 20519406 DOI: 10.1128/jvi.00459-10] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The 86-kDa immediate-early 2 (IE2) protein of human cytomegalovirus (HCMV) is a promiscuous transactivator essential for viral gene expression. IE2 is covalently modified by SUMO at two lysine residues (K175 and K180) and also interacts noncovalently with SUMO. Although SUMOylation of IE2 has been shown to enhance its transactivation activity, the role of SUMO binding is not clear. Here we showed that SUMO binding by IE2 is necessary for its efficient transactivation function and for viral growth. IE2 bound physically to SUMO-1 through a SUMO-interacting motif (SIM). Mutations in SIM (mSIM) or in both SUMOylation sites and SIM (KR/mSIM), significantly reduced IE2 transactivation effects on viral early promoters. The replication of IE2 SIM mutant viruses (mSIM or KR/mSIM) was severely depressed in normal human fibroblasts. Analysis of viral growth curves revealed that the replication defect of the mSIM virus correlated with low-level accumulation of SUMO-modified IE2 and of viral early and late proteins. Importantly, both the formation of viral transcription domains and the association of IE2 with viral promoters in infected cells were significantly reduced in IE2 SIM mutant virus infection. Furthermore, IE2 was found to interact with the SUMO-modified form of TATA-binding protein (TBP)-associated factor 12 (TAF12), a component of the TFIID complex, in a SIM-dependent manner, and this interaction enhanced the transactivation activity of IE2. Our data demonstrate that the interaction of IE2 with SUMO-modified proteins plays an important role for the progression of the HCMV lytic cycle, and they suggest a novel viral mechanism utilizing the cellular SUMO system.
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84
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Sumoylation of the Epstein-Barr virus BZLF1 protein inhibits its transcriptional activity and is regulated by the virus-encoded protein kinase. J Virol 2010; 84:4383-94. [PMID: 20181712 DOI: 10.1128/jvi.02369-09] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The Epstein-Barr virus (EBV) immediate-early protein BZLF1 (Z) mediates the switch between latent and lytic EBV infection. Z not only activates early lytic viral gene transcription but also plays a direct role in lytic viral genome replication. Although a small fraction of Z is known to be sumoylated, the effects of this posttranslational modification on various different Z functions have not been well defined. In this report, we show that only the lysine at amino acid residue 12 is required for the sumoylation of Z, and that Z can be sumoylated by SUMO isoforms 1, 2, and 3. We also demonstrate that the sumo-defective Z mutants ZK12A and ZK12R have enhanced transcriptional activity. The sumoylated and nonsumoylated forms of Z were found to have a similar cellular location, both being localized primarily within the nuclear matrix. The Z sumo-defective mutants were, however, partially defective for disrupting promyelocytic leukemia (PML) bodies compared to the ability of wild-type Z. In addition, we show that lytic viral genome replication does not require the sumoylation of Z, although a Z mutant altered at both amino acids 12 and 13 is replication defective. Furthermore, we show that the sumoylation of Z is greatly increased (from less than 1 to about 11%) in lytically induced 293 cells infected with an EBV mutant virus deleted for the EBV-encoded protein kinase (EBV-PK) compared to that of 293 cells infected with wild-type EBV, and that the overexpression of EBV-PK leads to the reduced sumoylation of Z in EBV-negative cells. Our results suggest that the sumoylation of Z helps to promote viral latency, and that EBV-PK inhibits Z sumoylation during viral reactivation.
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85
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Biphasic recruitment of transcriptional repressors to the murine cytomegalovirus major immediate-early promoter during the course of infection in vivo. J Virol 2010; 84:3631-43. [PMID: 20106920 DOI: 10.1128/jvi.02380-09] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Our previous studies showed that establishment of murine cytomegalovirus (MCMV) latency in vivo is associated with repression of immediate-early gene expression, deacetylation of histones bound to the major immediate-early promoter (MIEP), changes in patterns of methylation of histones, and recruitment of cellular repressors of transcription to the MIEP. Here, we have quantitatively analyzed the kinetics of changes in viral RNA expression, DNA copy number, and recruitment of repressors and activators of transcription to viral promoters during the course of infection. Our results show that changes in viral gene expression correlate with changes in recruitment of RNA polymerase and acetylated histones to viral promoters. Binding of the transcriptional repressors histone deacetylase type 2 (HDAC2), HDAC3, YY1, CBF-1/RBP-Jk, Daxx, and CIR to the MIEP and HDACs to other promoters showed a biphasic pattern: some binding was detectable prior to activation of viral gene expression, then decreased with the onset of transcription and increased again as repression of viral gene expression occurred. Potential binding sites for CBF-1/RBP-Jk and YY1 in the MIEP and for YY1 in the M100 promoter (M100P) were identified by in silico analysis. While recruitment of HDACs was not promoter specific, binding of CBF-1/RBP-Jk and YY1 was restricted to promoters with their cognate sites. Our results suggest that sequences within viral promoters may contribute to establishment of latency through recruitment of transcriptional repressors to these genes. The observation that repressors are bound to the MIEP and other promoters immediately upon infection suggests that latency may be established in some cells very early in infection.
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86
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Tavalai N, Stamminger T. Interplay between Herpesvirus Infection and Host Defense by PML Nuclear Bodies. Viruses 2009; 1:1240-64. [PMID: 21994592 PMCID: PMC3185544 DOI: 10.3390/v1031240] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2009] [Revised: 12/10/2009] [Accepted: 12/14/2009] [Indexed: 12/17/2022] Open
Abstract
In recent studies we and others have identified the cellular proteins PML, hDaxx, and Sp100, which form a subnuclear structure known as nuclear domain 10 (ND10) or PML nuclear bodies (PML-NBs), as host restriction factors that counteract herpesviral infections by inhibiting viral replication at different stages. The antiviral function of ND10, however, is antagonized by viral regulatory proteins (e.g., ICP0 of herpes simplex virus; IE1 of human cytomegalovirus) which induce either a modification or disruption of ND10. This review will summarize the current knowledge on how viral replication is inhibited by ND10 proteins. Furthermore, herpesviral strategies to defeat this host defense mechanism are discussed.
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Affiliation(s)
- Nina Tavalai
- Institute for Clinical and Molecular Virology, University of Erlangen-Nuremberg, Schlossgarten 4, 91054 Erlangen, Germany; E-Mail:
| | - Thomas Stamminger
- Institute for Clinical and Molecular Virology, University of Erlangen-Nuremberg, Schlossgarten 4, 91054 Erlangen, Germany; E-Mail:
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87
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Sandford GR, Schumacher U, Ettinger J, Brune W, Hayward GS, Burns WH, Voigt S. Deletion of the rat cytomegalovirus immediate-early 1 gene results in a virus capable of establishing latency, but with lower levels of acute virus replication and latency that compromise reactivation efficiency. J Gen Virol 2009; 91:616-21. [PMID: 19923265 DOI: 10.1099/vir.0.016022-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The immediate-early 1 (IE1) and IE2 proteins encoded by the major immediate-early (MIE) transcription unit of cytomegaloviruses are thought to play key roles in the switch between latent- and lytic-cycle infection. Whilst IE2 is essential for triggering the lytic cycle, the exact roles of IE1 have not been resolved. An MIE-exon 4-deleted rat cytomegalovirus (DeltaIE1) failed to synthesize the IE1 protein and did not disperse promyelocytic leukaemia bodies early post-infection, but was still capable of normal replication in fibroblast cell culture. However, DeltaIE1 had a diminished ability to infect salivary glands persistently in vivo and to reactivate from spleen explant cultures ex vivo. Quantification of viral genomes in spleens of infected animals revealed a reduced amount of DeltaIE1 virus produced during acute infection, suggesting a role for IE1 as a regulator in establishing a chronic or persistent infection, rather than in influencing the latency or reactivation processes more directly.
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Affiliation(s)
- Gordon R Sandford
- The Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University School of Medicine, Baltimore, MD, USA
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88
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Paulus C, Nevels M. The human cytomegalovirus major immediate-early proteins as antagonists of intrinsic and innate antiviral host responses. Viruses 2009; 1:760-79. [PMID: 21994568 PMCID: PMC3185523 DOI: 10.3390/v1030760] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2009] [Revised: 11/04/2009] [Accepted: 11/05/2009] [Indexed: 12/21/2022] Open
Abstract
The major immediate-early (IE) gene of human cytomegalovirus (CMV) is believed to have a decisive role in acute infection and its activity is an important indicator of viral reactivation from latency. Although a variety of gene products are expressed from this region, the 72-kDa IE1 and the 86-kDa IE2 nuclear phosphoproteins are the most abundant and important. Both proteins have long been recognized as promiscuous transcriptional regulators. More recently, a critical role of the IE1 and IE2 proteins in counteracting non-adaptive host cell defense mechanisms has been revealed. In this review we will briefly summarize the available literature on IE1- and IE2-dependent mechanisms contributing to CMV evasion from intrinsic and innate immune responses.
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Affiliation(s)
- Christina Paulus
- Institute for Medical Microbiology and Hygiene, University of Regensburg, Franz-Josef-Strauss-Allee 11, D-93053 Regensburg, Germany; E-Mail:
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89
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Kim ET, Kim KK, Matunis MJ, Ahn JH. Enhanced SUMOylation of proteins containing a SUMO-interacting motif by SUMO-Ubc9 fusion. Biochem Biophys Res Commun 2009; 388:41-5. [PMID: 19635459 DOI: 10.1016/j.bbrc.2009.07.103] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2009] [Accepted: 07/22/2009] [Indexed: 11/27/2022]
Abstract
Identifying new targets for SUMO and understanding the function of protein SUMOylation are largely limited by low level of SUMOylation. It was found recently that Ubc9, the SUMO E2 conjugating enzyme, is covalently modified by SUMO at a lysine 14 in the N-terminal alpha helix, and that SUMO-modified Ubc9 has enhanced conjugation activity for certain target proteins containing a SUMO-interacting motif (SIM). Here, we show that, compared to intact Ubc9, the SUMO-Ubc9 fusion protein has higher conjugating activity for SIM-containing targets such as Sp100 and human cytomegalovirus IE2. Assays using an IE2 SIM mutant revealed the requirement of SIM for the enhanced IE2 SUMOylation by SUMO-Ubc9. In pull-down assays with cell extracts, the SUMO-Ubc9 fusion protein bound to more diverse cellular proteins and interacted with some SIM-containing proteins with higher affinities than Ubc9. Therefore, the devised SUMO-Ubc9 fusion will be useful for identifying SIM-containing SUMO targets and producing SUMO-modified proteins.
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Affiliation(s)
- Eui Tae Kim
- Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Cheoncheondong Jangangu, Suwon, Gyeonggido, Republic of Korea
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90
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Physical requirements and functional consequences of complex formation between the cytomegalovirus IE1 protein and human STAT2. J Virol 2009; 83:12854-70. [PMID: 19812155 DOI: 10.1128/jvi.01164-09] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Our previous work has shown that efficient evasion from type I interferon responses by human cytomegalovirus (hCMV) requires expression of the 72-kDa immediate-early 1 (IE1) protein. It has been suggested that IE1 inhibits interferon signaling through intranuclear sequestration of the signal transducer and activator of transcription 2 (STAT2) protein. Here we show that physical association and subnuclear colocalization of IE1 and STAT2 depend on short acidic and serine/proline-rich low-complexity motifs in the carboxy-terminal region of the 491-amino-acid viral polypeptide. These motifs compose an essential core (amino acids 373 to 420) and an adjacent ancillary site (amino acids 421 to 445) for STAT2 interaction that are predicted to form part of a natively unstructured domain. The presence of presumably "disordered" carboxy-terminal domains enriched in low-complexity motifs is evolutionarily highly conserved across all examined mammalian IE1 orthologs, and the murine cytomegalovirus IE1 protein appears to interact with STAT2 just like the human counterpart. A recombinant hCMV specifically mutated in the IE1 core STAT2 binding site displays hypersensitivity to alpha interferon, delayed early viral protein accumulation, and attenuated growth in fibroblasts. However, replication of this mutant virus is specifically restored by knockdown of STAT2 expression. Interestingly, complex formation with STAT2 proved to be entirely separable from disruption of nuclear domain 10 (ND10), another key activity of IE1. Finally, our results demonstrate that IE1 counteracts the antiviral interferon response and promotes viral replication by at least two distinct mechanisms, one depending on sequestration of STAT2 and the other one likely involving ND10 interaction.
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91
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Isaacson MK, Ploegh HL. Ubiquitination, ubiquitin-like modifiers, and deubiquitination in viral infection. Cell Host Microbe 2009; 5:559-70. [PMID: 19527883 PMCID: PMC7103382 DOI: 10.1016/j.chom.2009.05.012] [Citation(s) in RCA: 224] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2009] [Accepted: 05/27/2009] [Indexed: 11/26/2022]
Abstract
Ubiquitin is important for nearly every aspect of cellular physiology. All viruses rely extensively on host machinery for replication; therefore, it is not surprising that viruses connect to the ubiquitin pathway at many levels. Viral involvement with ubiquitin occurs either adventitiously because of the unavoidable usurpation of cellular processes, or for some specific purpose selected for by the virus to enhance viral replication. Here, we review current knowledge of how the ubiquitin pathway alters viral replication and how viruses influence the ubiquitin pathway to enhance their own replication.
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Affiliation(s)
- Marisa K Isaacson
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
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92
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Reineke EL, Kao HY. Targeting promyelocytic leukemia protein: a means to regulating PML nuclear bodies. Int J Biol Sci 2009; 5:366-76. [PMID: 19471587 PMCID: PMC2686094 DOI: 10.7150/ijbs.5.366] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2009] [Accepted: 05/06/2009] [Indexed: 01/17/2023] Open
Abstract
The promyelocytic leukemia protein (PML) is involved in many cellular processes including cell cycle progression, DNA damage response, transcriptional regulation, viral infection, and apoptosis. These cellular activities often rely on the localization of PML to unique subnuclear structures known as PML nuclear bodies (NBs). More than 50 cellular proteins are known to traffic in and out of PML NBs, either transiently or constitutively. In order to understand the dynamics of these NBs, it is important to delineate the regulation of PML itself. PML is subject to extensive regulation at transcriptional, post-transcriptional, and post-translational levels. Many of these modes of regulation depend on the cellular context and the presence of extracellular signals. This review focuses on the current knowledge of regulation of PML under normal cellular conditions as well as the role for regulation of PML in viral infection and cancer.
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Affiliation(s)
- Erin L Reineke
- Department of Biochemistry, School of Medicine, Case Western Reserve University and the Comprehensive Cancer Center of CWRU, Cleveland, Ohio 44106, USA
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93
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Busche A, Marquardt A, Bleich A, Ghazal P, Angulo A, Messerle M. The mouse cytomegalovirus immediate-early 1 gene is not required for establishment of latency or for reactivation in the lungs. J Virol 2009; 83:4030-8. [PMID: 19211741 PMCID: PMC2668463 DOI: 10.1128/jvi.02520-08] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2008] [Accepted: 02/03/2009] [Indexed: 01/01/2023] Open
Abstract
The immediate-early protein IE1 of human and mouse cytomegalovirus (MCMV) is one of the first proteins expressed during the productive infection cycle and upon reactivation from latency. The CMV IE1 proteins have been found to inhibit histone deacetylases, suggesting a role in the epigenetic regulation of viral gene expression. Consequently, the IE1 protein is considered to have a profound effect on reactivation, because small amounts of IE1 may be decisive for the switch to lytic replication. Here we asked if an MCMV Deltaie1 mutant is able both to establish latency and to reactivate from the lungs of latently infected mice. Since the Deltaie1 mutant was known to be attenuated during acute infection, we first defined conditions that led to comparable levels of viral genomes during latent infection with mutant and wild-type (wt) MCMV. Viral genome copy numbers dropped considerably at the onset of the latent infection but then remained steady for both viruses even after several months. Reactivation of the Deltaie1 mutant and of wt MCMV from latency occurred with similar incidences in lung explant cultures at 4, 7, and 12 months postinfection. The increase in the frequency of a subset of MCMV-specific memory T cells, a possible indicator of frequent transcriptional reactivation events during latency, was in a comparable range for both viruses. Recurrence of the Deltaie1 virus infection in vivo could also be induced by hematoablative treatment of latently infected mice. We conclude that the ie1 gene is not essential for the establishment of latency or for the reactivation of MCMV.
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Affiliation(s)
- Andreas Busche
- Department of Virology, Hannover Medical School, Hannover, Germany
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94
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Koh K, Lee K, Ahn JH, Kim S. Human cytomegalovirus infection downregulates the expression of glial fibrillary acidic protein in human glioblastoma U373MG cells: identification of viral genes and protein domains involved. J Gen Virol 2009; 90:954-962. [PMID: 19264642 DOI: 10.1099/vir.0.006486-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Human cytomegalovirus (HCMV) has tropism for glial cells, among many other cell types. It was reported previously that the stable expression of HCMV immediate-early protein 1 (IE1) could dramatically reduce the RNA level of glial fibrillary acidic protein (GFAP), an astroglial cell-specific intermediate filament protein, which is progressively lost with an increase in glioma malignancy. To understand this phenomenon in the context of virus infection, a human glioblastoma cell line, U373MG, was infected with HCMV (strain AD169 or Towne). The RNA level of GFAP was reduced by more than 10-fold at an m.o.i. of 3 at 48 h post-infection, whilst virus treated with neutralizing antibody C23 or with UV light had a much-reduced effect. Treatment of infected cells with ganciclovir did not prevent HCMV-mediated downregulation of GFAP. Although the expression of GFAP RNA is downregulated in IE1-expressing cells, a mutant HCMV strain lacking IE1 still suppressed GFAP, indicating that other IE proteins may be involved. IE2 is also proposed to be involved in GFAP downregulation, as an adenoviral vector expressing IE2 could also reduce the RNA level of GFAP. Data from the mutational analysis indicated that HCMV infection might affect the expression of this structural protein significantly, primarily through the C-terminal acidic region of the IE1 protein.
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Affiliation(s)
- Kyungmi Koh
- School of Biological Sciences, Seoul National University, Seoul 151-747, Republic of Korea
| | - Karim Lee
- School of Biological Sciences, Seoul National University, Seoul 151-747, Republic of Korea
| | - Jin-Hyun Ahn
- Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, Kyonggido 440-746, Republic of Korea
| | - Sunyoung Kim
- School of Biological Sciences, Seoul National University, Seoul 151-747, Republic of Korea
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95
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Echendu CW, Ling PD. Regulation of Sp100A subnuclear localization and transcriptional function by EBNA-LP and interferon. J Interferon Cytokine Res 2008; 28:667-78. [PMID: 18844582 PMCID: PMC2988464 DOI: 10.1089/jir.2008.0023] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2008] [Accepted: 04/30/2008] [Indexed: 01/12/2023] Open
Abstract
Epstein-Barr virus (EBV) efficiently immortalizes human B cells and is associated with several human malignancies. The EBV transcriptional activating protein EBNA2 and the EBNA2 coactivator EBNA-leader protein (EBNA-LP) are important for B cell immortalization. Recent observations from our laboratory indicate that EBNA-LP coactivation function is mediated through interactions with the interferon-inducible gene (ISG) Sp100, resulting in displacement from its normal location in promyelocytic leukemia nuclear bodies (PML NBs) into the nucleoplasm. The EBNA-LP- and interferon-mediated mechanisms that regulate Sp100 subnuclear localization and transcriptional function remain undefined. To clarify these issues, we generated a panel of Sp100 mutant proteins to ascertain whether EBNA-LP induces Sp100 displacement from PML NBs by interfering with Sp100 dimerization or through other domains. In addition, we tested EBNA-LP function in interferon-treated cells. Our results indicate that Sp100 dimerization, PML NB localization, and EBNA-LP interaction domains overlap significantly. We also show that IFN-beta does not inhibit EBNA-LP coactivation function. The results suggest that EBNA-LP might play a role in EBV-evasion of IFN-mediated antiviral responses.
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Affiliation(s)
- Chisaroka W Echendu
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030, USA
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96
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Human cytomegalovirus protein pp71 displaces the chromatin-associated factor ATRX from nuclear domain 10 at early stages of infection. J Virol 2008; 82:12543-54. [PMID: 18922870 DOI: 10.1128/jvi.01215-08] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The human cytomegalovirus (HCMV) tegument protein pp71, encoded by gene UL82, stimulates viral immediate-early (IE) transcription. pp71 interacts with the cellular protein hDaxx at nuclear domain 10 (ND10) sites, resulting in the reversal of hDaxx-mediated repression of viral transcription. We demonstrate that pp71 displaces an hDaxx-binding protein, ATRX, from ND10 prior to any detectable effects on hDaxx itself and that this event contributes to the role of pp71 in alleviating repression. Introduction of pp71 into cells by transfection, infection with a pp71-expressing herpes simplex virus type 1 vector, or by generation of transformed cell lines promoted the rapid relocation of ATRX from ND10 to the nucleoplasm without alteration of hDaxx levels or localization. A pp71 mutant protein unable to interact with hDaxx did not affect the intranuclear distribution of ATRX. Infection with HCMV at a high multiplicity of infection resulted in rapid displacement of ATRX from ND10, the effect being observed maximally by 2 h after adsorption, whereas infection with the UL82-null HCMV mutant ADsubUL82 did not affect ATRX localization even at 7 h postinfection. Cell lines depleted of ATRX by transduction with shRNA-expressing lentiviruses supported increased IE gene expression and virus replication after infection with ADsubUL82, demonstrating that ATRX has a role in repressing IE transcription. The results show that ATRX, in addition to hDaxx, is a component of cellular intrinsic defenses that limit HCMV IE transcription and that displacement of ATRX from ND10 by pp71 is important for the efficient initiation of viral gene expression.
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97
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Yu Y, Pilgrim P, Yan J, Zhou W, Jenkins M, Gagliano N, Bumm K, Cannon M, Milzani A, Dalle-Donne I, Kast WM, Cobos E, Chiriva-Internati M. Protective CD8+ T-cell responses to cytomegalovirus driven by rAAV/GFP/IE1 loading of dendritic cells. J Transl Med 2008; 6:56. [PMID: 18834548 PMCID: PMC2570669 DOI: 10.1186/1479-5876-6-56] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2008] [Accepted: 10/05/2008] [Indexed: 12/26/2022] Open
Abstract
Background Recent studies demonstrate that recombinant adeno-associated virus (rAAV)-based antigen loading of dendritic cells (DCs) generates in vitro, significant and rapid cytotoxic T-lymphocyte (CTL) responses against viral antigens. Methods We used the rAAV system to induce specific CTLs against CVM antigens for the development of cytomegalovirus HCMV) gene therapy. As an extension of the versatility of the rAAV system, we incorporated immediate-early 1 (IE1), expressed in HCMV. Our rAAV vector induced a strong stimulation of CTLs directed against the HCMV antigen IE1. We then investigated the efficiency of the CTLs in killing IE1 targeted cells. Results A significant MHC Class I-restricted, anti-IE1-specific CTL killing was demonstrated against IE1 positive peripheral blood mononuclear cells (PBMC) after one, in vitro, stimulation. Conclusion In summary, single PBMC stimulation with rAAV/IE1 pulsed DCs induces strong antigen specific-CTL generation. CTLs were capable to lyse low doses of peptides pulsed into target cells. These data suggest that AAV-based antigen loading of DCs is highly effective for generating human CTL responses against HCMV antigens.
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Affiliation(s)
- Yuefei Yu
- Division of Hematology & Oncology, Texas Tech University Health Sciences Center and Southwest Cancer Treatment and Research Center, Lubbock, TX, USA.
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98
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Moon JS, Lee MY, Park SW, Han WK, Hong SW, Ahn JH, Kim KS. Androgen-dependent activation of human cytomegalovirus major immediate-early promoter in prostate cancer cells. Prostate 2008; 68:1450-60. [PMID: 18615458 DOI: 10.1002/pros.20817] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
BACKGROUND Human cytomegalovirus (HCMV) major immediate early (MIE) promoter, which is involved in viral reactivation, is specifically activated by androgen in LNCaP prostate cancer cells. METHODS Androgen-dependent transcriptional activities of the HCMV MIE promoter were measured by transient transfection assay. Expression levels of genes related to protein kinase A (PKA)-signaling pathway was measured by RT-PCR. RESULTS Activation of the HCMV MIE promoter by androgen results from an increase in PKA activities. The expression level of PKA catalytic (C) subunit beta transcript variant 2 (PKA-C beta 2) was decreased by serum deprivation and was increased by R1881 treatment, in a pattern similar to changes of the HCMV MIE promoter activities. Furthermore the exogenous expression of PKA-C beta 2 strongly activated the HCMV MIE promoter, indicating that regulation of the PKA-C beta 2 expression might be a direct upstream factor in the HCMV MIE promoter regulation by androgen in LNCaP cells. CONCLUSIONS The data elucidated the mechanisms by which androgen activates PKA in androgen-dependent prostate cancer cells, resulting in activation of the HCMV MIE promoter. These results support the possibility that activation of the HCMV MIE promoter by androgen in the prostate could cause the productive infection, which might contribute to oncomodulation in prostate cancers.
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Affiliation(s)
- Jong-Seok Moon
- Department of Biochemistry and Molecular Biology, Institute of Genetic Science, Center for Chronic Metabolic Disease Research, Brain Korea 21 Project for Medical Science, Yonsei University, College of Medicine, Seodaemungu, Seoul, Korea
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99
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Tavalai N, Stamminger T. New insights into the role of the subnuclear structure ND10 for viral infection. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1783:2207-21. [PMID: 18775455 DOI: 10.1016/j.bbamcr.2008.08.004] [Citation(s) in RCA: 144] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2008] [Revised: 08/06/2008] [Accepted: 08/07/2008] [Indexed: 12/12/2022]
Abstract
Nuclear domains 10 (ND10), alternatively termed PML nuclear bodies (PML-NBs) or PML oncogenic domains (PODs), have been discovered approximately 15 years ago as a nuclear substructure that is targeted by a variety of viruses belonging to different viral families. This review will summarize the most important structural and functional characteristics of ND10 and its major protein constituents followed by a discussion of the current view regarding the role of this subnuclear structure for various DNA and RNA viruses with an emphasis on herpesviruses. It is concluded that accumulating evidence argues for an involvement of ND10 in host antiviral defenses either via mediating an intrinsic immune response against specific viruses or via acting as a component of the cellular interferon pathway.
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Affiliation(s)
- Nina Tavalai
- Institute for Clinical and Molecular Virology, University Erlangen-Nuremberg, Schlossgarten 4, 91054 Erlangen, Germany
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Binding STAT2 by the acidic domain of human cytomegalovirus IE1 promotes viral growth and is negatively regulated by SUMO. J Virol 2008; 82:10444-54. [PMID: 18701593 DOI: 10.1128/jvi.00833-08] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The human cytomegalovirus (HCMV) 72-kDa immediate-early 1 (IE1) protein is thought to modulate cellular antiviral functions impacting on promyelocytic leukemia (PML) nuclear bodies and signal transducer and activator of transcription (STAT) signaling. IE1 consists of four distinct regions: an amino-terminal region required for nuclear localization, a large central hydrophobic region responsible for PML targeting and transactivation activity, an acidic domain, and a carboxyl-terminal chromatin tethering domain. We found that the acidic domain of IE1 is required for binding to STAT2. A mutant HCMV encoding IE1(Delta421-475) with the acidic domain deleted was generated. In mutant virus-infected cells, IE1(Delta421-475) failed to bind to STAT2. The growth of mutant virus was only slightly delayed at a high multiplicity of infection (MOI) but was severely impaired at a low MOI with low-level accumulation of viral proteins. When cells were pretreated with beta interferon, the mutant virus showed an additional 1,000-fold reduction in viral growth, even at a high MOI, compared to the wild type. The inhibition of STAT2 loading on the target promoter upon infection was markedly reduced with mutant virus. Furthermore, sumoylation of IE1 at this acidic domain was found to abolish the activity of IE1 to bind to STAT2 and repress the interferon-stimulated genes. Our results provide genetic evidence that IE1 binding to STAT2 requires the 55-amino-acid acidic domain and promotes viral growth by interfering with interferon signaling and demonstrate that this viral activity is negatively regulated by a cellular sumoylation pathway.
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