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Abstract
Human cytomegalovirus (HCMV) persists as a subclinical, lifelong infection in the normal human host, maintained at least in part by its carriage in the absence of detectable infectious virus – the hallmark of latent infection. Reactivation from latency in immunocompromised individuals, in contrast, often results in serious disease. Latency and reactivation are defining characteristics of the herpesviruses and key to understanding their biology. However, the precise cellular sites in which HCMV is carried and the mechanisms regulating its latency and reactivation during natural infection remain poorly understood. This review will detail our current knowledge of where HCMV is carried in healthy individuals, which viral genes are expressed upon carriage of the virus and what effect this has on cellular gene expression. It will also address the accumulating evidence suggesting that reactivation of HCMV from latency appears to be linked intrinsically to the differentiation status of the myeloid cell, and how the cellular mechanisms that normally control host gene expression play a critical role in the differential regulation of viral gene expression during latency and reactivation.
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Affiliation(s)
- John Sinclair
- Department of Medicine, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK
| | - Patrick Sissons
- Department of Medicine, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK
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52
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Petrik DT, Schmitt KP, Stinski MF. Inhibition of cellular DNA synthesis by the human cytomegalovirus IE86 protein is necessary for efficient virus replication. J Virol 2006; 80:3872-83. [PMID: 16571804 PMCID: PMC1440472 DOI: 10.1128/jvi.80.8.3872-3883.2006] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Human cytomegalovirus (HCMV) expresses several proteins that manipulate normal cellular functions, including cellular transcription, apoptosis, immune response, and cell cycle control. The IE2 gene, which is expressed from the HCMV major immediate-early (MIE) promoter, encodes the IE86 protein. IE86 is a multifunctional protein that is essential for viral replication. The functions of IE86 include transactivation of cellular and viral early genes, negative autoregulation of the MIE promoter, induction of cell cycle progression from G0/G1 to G1/S, and arresting cell cycle progression at the G1/S transition in p53-positive human foreskin fibroblast (HFF) cells. Mutations were introduced into the IE2 gene in the context of the viral genome using bacterial artificial chromosomes (BACs). From these HCMV BACs, a recombinant virus (RV) with a single amino acid substitution in the IE86 protein was isolated that replicates slower and to lower titers than wild-type HCMV. HFF cells infected with the Q548R RV undergo cellular DNA synthesis and do not arrest at any point in the cell cycle. The Q548R RV is able to negatively autoregulate the MIE promoter, transactivate viral early genes, activate cellular E2F-responsive genes, and produce infectious virus. This is the first report of a viable recombinant HCMV that is unable to inhibit cellular DNA synthesis in infected HFF cells.
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Affiliation(s)
- Dustin T Petrik
- Interdisciplinary Graduate Program in Molecular Biology, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA
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53
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Boomker JM, The TH, de Leij LFMH, Harmsen MC. The human cytomegalovirus-encoded receptor US28 increases the activity of the major immediate-early promoter/enhancer. Virus Res 2006; 118:196-200. [PMID: 16448715 DOI: 10.1016/j.virusres.2005.12.011] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2005] [Revised: 12/23/2005] [Accepted: 12/23/2005] [Indexed: 11/18/2022]
Abstract
The activation of the major immediate-early promoter (MIEP) is a key event in the cytomegalovirus replication cycle and is dependent on cellular transcription factors which are partially activated by viral proteins. Expression of the viral chemokine receptor homolog US28 results in constitutive activation of pro-inflammatory transcription factors that may be involved in the activation of the major immediate-early promoter/enhancer. Using reporter gene assays in human embryonic kidney cells, we found that US28 signaling was responsible for increased major immediate-early promoter/enhancer activity which was independent of beta-chemokine binding. Inhibition of nuclear factor-kappaB (NF-kappaB) only partially blocked the effect of US28, whereas treatment with a specific p38 mitogen activated kinase (MAPK) inhibitor fully abrogated the US28-induced enhancement of promoter activity. Our results suggest that during human cytomegalovirus (HCMV) infection, US28 in epithelial cells transactivates the major immediate-early promoter/enhancer via the activation of p38 MAPK and downstream signaling that partially involves NF-kappaB.
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Affiliation(s)
- Jasper M Boomker
- Department of Pathology and Laboratory Medicine, Medical Biology Section, University Medical Center Groningen, Hanzeplein 1, 9713 GZ Groningen, The Netherlands.
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54
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Isomura H, Stinski MF, Kudoh A, Daikoku T, Shirata N, Tsurumi T. Two Sp1/Sp3 binding sites in the major immediate-early proximal enhancer of human cytomegalovirus have a significant role in viral replication. J Virol 2005; 79:9597-607. [PMID: 16014922 PMCID: PMC1181558 DOI: 10.1128/jvi.79.15.9597-9607.2005] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2005] [Accepted: 04/06/2005] [Indexed: 01/29/2023] Open
Abstract
We previously demonstrated that the major immediate early (MIE) proximal enhancer containing one GC box and the TATA box containing promoter are minimal elements required for transcription and viral replication in human fibroblast cells (H. Isomura, T. Tsurumi, M. F. Stinski, J. Virol. 78:12788-12799, 2004). After infection, the level of Sp1 increased while Sp3 remained constant. Here we report that either Sp1 or Sp3 transcription factors bind to the GC boxes located at approximately positions -55 and -75 relative to the transcription start site (+1). Both the Sp1 and Sp3 binding sites have a positive and synergistic effect on the human cytomegalovirus (HCMV) major immediate-early (MIE) promoter. There was little to no change in MIE transcription or viral replication for recombinant viruses with one or the other Sp1 or Sp3 binding site mutated. In contrast, mutation of both the Sp1 and Sp3 binding sites caused inefficient MIE transcription and viral replication. These data indicate that the Sp1 and Sp3 binding sites have a significant role in HCMV replication in human fibroblast cells.
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Affiliation(s)
- Hiroki Isomura
- Division of Virology, Aichi Cancer Center Research Institute, Chikusa-ku, Nagoya, Japan
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55
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Wright E, Bain M, Teague L, Murphy J, Sinclair J. Ets-2 repressor factor recruits histone deacetylase to silence human cytomegalovirus immediate-early gene expression in non-permissive cells. J Gen Virol 2005; 86:535-544. [PMID: 15722512 DOI: 10.1099/vir.0.80352-0] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Previous work from this laboratory has shown that expression of human cytomegalovirus (HCMV) immediate-early (IE) genes from the major immediate-early promoter (MIEP) is likely to be regulated by chromatin remodelling around the promoter affecting the acetylation state of core histone tails. The HCMV MIEP contains sequences that bind cellular transcription factors responsible for its negative regulation in undifferentiated, non-permissive cells. Ets-2 repressor factor (ERF) is one such factor that binds to such sequences and represses IE gene expression. Although it is not known how cellular transcription factors such as ERF mediate transcriptional repression of the MIEP, it is likely to involve differentiation-specific co-factors. In this study, the mechanism by which ERF represses HCMV IE gene expression was analysed. ERF physically interacts with the histone deacetylase, HDAC1, both in vitro and in vivo and this physical interaction between ERF and HDAC1 mediates repression of the MIEP. This suggests that silencing of viral IE gene expression, associated with histone deacetylation events around the MIEP, is mediated by differentiation-dependent cellular factors such as ERF, which specifically recruit chromatin remodellers to the MIEP in non-permissive cells.
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Affiliation(s)
- Edward Wright
- Department of Medicine, University of Cambridge, PO Box 157, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK
| | - Mark Bain
- Department of Medicine, University of Cambridge, PO Box 157, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK
| | - Linda Teague
- Department of Medicine, University of Cambridge, PO Box 157, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK
| | - Jane Murphy
- Department of Medicine, University of Cambridge, PO Box 157, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK
| | - John Sinclair
- Department of Medicine, University of Cambridge, PO Box 157, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK
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56
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Britt WJ, Boppana S. Human cytomegalovirus virion proteins. Hum Immunol 2005; 65:395-402. [PMID: 15172437 DOI: 10.1016/j.humimm.2004.02.008] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2003] [Revised: 01/15/2004] [Accepted: 02/03/2004] [Indexed: 12/16/2022]
Abstract
Human cytomegalovirus (HCMV) is the largest member of the family of human herpesviruses. The number of virus encoded proteins and the complexity of their functions in the life cycle of this virus are reflected in the size of its genome. There continues to be some controversy surrounding the exact protein coding capacity of the virus with estimates ranging from 160 open reading frames to more than 200 open reading frames. Very recent studies using mass spectrometry to determine the viral proteome suggests that the number of viral proteins may be even greater than previous estimates. The proteins of the virion capsid have readily identifiable homologous proteins in the capsid of the more extensively studied herpes simplex virus, likely because of similar capsid structure and assembly pathways. In contrast, the tegument and the envelope of HCMV contain a significant number of proteins that lack structural homology to proteins found in either alpha or gamma-herpesviruses. This brief overview discusses some of the general features and possible functions of the HCMV virion structural proteins in the replicative cycle of this virus.
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Affiliation(s)
- William J Britt
- Department of Pediatrics, University of Alabama at Birmingham, AL, USA.
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57
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Reeves MB, MacAry PA, Lehner PJ, Sissons JGP, Sinclair JH. Latency, chromatin remodeling, and reactivation of human cytomegalovirus in the dendritic cells of healthy carriers. Proc Natl Acad Sci U S A 2005; 102:4140-5. [PMID: 15738399 PMCID: PMC554799 DOI: 10.1073/pnas.0408994102] [Citation(s) in RCA: 286] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Human cytomegalovirus (HCMV) persists as a subclinical, lifelong infection in the normal human host, but reactivation from latency in immunocompromised subjects results in serious disease. Latency and reactivation are defining characteristics of the herpesviruses and are key to understanding their biology; however, the precise cellular sites in which HCMV is carried and the mechanisms regulating its latency and reactivation during natural infection remain poorly understood. Here we present evidence, based entirely on direct analysis of material isolated from healthy virus carriers, to show that myeloid dendritic cell (DC) progenitors are sites of HCMV latency and that their ex vivo differentiation to a mature DC phenotype is linked with reactivation of infectious virus resulting from differentiation-dependent chromatin remodeling of the viral major immediate-early promoter. Thus, myeloid DC progenitors are a site of HCMV latency during natural persistence, and there is a critical linkage between their differentiation to DC and transcriptional reactivation of latent virus, which is likely to play an important role in the pathogenesis of HCMV infection.
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Affiliation(s)
- M B Reeves
- Department of Medicine, School of Clinical Medicine, University of Cambridge, Hills Road, Cambridge CB2 2QQ, United Kingdom
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58
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Tang Q, Li L, Maul GG. Mouse cytomegalovirus early M112/113 proteins control the repressive effect of IE3 on the major immediate-early promoter. J Virol 2005; 79:257-63. [PMID: 15596821 PMCID: PMC538721 DOI: 10.1128/jvi.79.1.257-263.2005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The mouse cytomegalovirus major immediate-early (IE) transcript is differentially spliced to produce two IE proteins: IE1, which functions partly to maintain its own promoter, the major IE promoter (MIEP), free from repression, and IE3, which functions partly as a repressor of MIEP. Paradoxically, the site where transcription of the viral genome occurs is also the site where the greatest amounts of IE3 accumulate. This raises the question of how the repression capabilities of IE3 are controlled so soon after infection. We detected IE3, an activator of early proteins, contemporaneously with gene products of the early M112/113 locus. Both IE3 and the early M112/113 gene products colocalize and coimmunoprecipitate. Protein interaction most likely occurs between IE3 and the 87-kDa splice form of M112/113, because only the 87-kDa component coimmunoprecipitated with IE3. The complex also includes PML. Transiently expressed M112/113 can form large domains alone, even in the absence of full viral genomes or PML. Coexpression of M112/113 products and IE3 results in segregation of IE3 into newly formed M112/113-based domains. Importantly, coexpression eliminates the IE3-based repressive effect on MIEP, as determined by MIEP-driven reporter assays. The consequence of segregating IE3 into the M112/113-containing prereplication domains appears to make IE3 unavailable for binding and repressing MIEP during the earliest stages of infection. These findings establish a new feedback mechanism between IE and early proteins, a new mechanism of promoter control via segregation of the repressor, and a new function for proteins from the M112/113 locus.
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Affiliation(s)
- Qiyi Tang
- The Wistar Institute, Philadelphia, Pennsylvania 19104, USA
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59
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Isomura H, Tsurumi T, Stinski MF. Role of the proximal enhancer of the major immediate-early promoter in human cytomegalovirus replication. J Virol 2004; 78:12788-99. [PMID: 15542631 PMCID: PMC525030 DOI: 10.1128/jvi.78.23.12788-12799.2004] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2004] [Accepted: 07/19/2004] [Indexed: 11/20/2022] Open
Abstract
The human cytomegalovirus (CMV) enhancer has a distal component (positions -550 to -300) and a proximal component (-300 to -39) relative to the transcription start site (+1) of the major immediate-early (MIE) promoter. Without the distal enhancer, human CMV replicates slower and has a small-plaque phenotype. We determined the sequence requirements of the proximal enhancer by making 5'-end deletions to positions -223, -173, -116, -67, and -39. Even though recombinant virus with the proximal enhancer deleted to -39 has the minimal TATA box-containing MIE promoter element, it cannot replicate independently in human fibroblast cells. Recombinant virus with a deletion to -67 has an Sp-1 transcription factor binding site which may represent a minimal enhancer element for recombinant virus replication in human fibroblast cells. Although recombinant virus with a deletion to -223 replicates to titers at least 100-fold less than that of the wild-type virus, it replicates to titers 8-fold higher than that of recombinant virus with a deletion to -173 and 20-fold higher than that of virus with a deletion to -67. Recombinant virus with a deletion to -173 replicates more efficiently than that with a deletion to -116. There was a direct correlation between the level of infectious virus replication and time after infection, amount of MIE gene transcription, MIE and early viral protein synthesis, and viral DNA synthesis. The extent of the proximal enhancer determines the efficiency of viral replication.
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Affiliation(s)
- Hiroki Isomura
- Department of Microbiology, Carver College of Medicine, 3-772 BSB, University of Iowa, Iowa City, IA 52242, USA
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60
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Lashmit PE, Lundquist CA, Meier JL, Stinski MF. Cellular repressor inhibits human cytomegalovirus transcription from the UL127 promoter. J Virol 2004; 78:5113-23. [PMID: 15113893 PMCID: PMC400324 DOI: 10.1128/jvi.78.10.5113-5123.2004] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2004] [Accepted: 01/28/2004] [Indexed: 02/07/2023] Open
Abstract
The region of the human cytomegalovirus (HCMV) genome between the UL127 promoter and the major immediate-early (MIE) enhancer is referred to as the unique region. The role of this region during a viral infection is not known. In wild-type HCMV-infected permissive fibroblasts, there is no transcription from the UL127 promoter at any time during productive infection. Our investigators previously reported that the region upstream of the UL127 TATA box repressed expression from the UL127 promoter (C. A. Lundquist et al., J. Virol. 73:9039-9052, 1999). The region was reported to contain functional NF1 DNA binding sites (L. Hennighausen and B. Fleckenstein, EMBO J. 5:1367-1371, 1986). Sequence analysis of this region detected additional consensus binding sites for three transcriptional regulatory proteins, FoxA (HNF-3), suppressor of Hairy wing, and CAAT displacement protein. The cis-acting elements in the unique region prevented activation of the early UL127 promoter by the HCMV MIE proteins. In contrast, deletion of the region permitted very high activation of the UL127 promoter by the viral MIE proteins. Mutation of the NF1 sites had no effect on the basal activity of the promoter. To determine the role of the other sites in the context of the viral genome, recombinant viruses were generated in which each putative repressor site was mutated and the effect on the UL127 promoter was analyzed. Mutation of the putative Fox-like site resulted in a significant increase in expression from the viral early UL127 promoter. Insertion of wild-type Fox-like sites between the HCMV immediate-early (IE) US3 TATA box and the upstream NF-kappaB-responsive enhancer (R2) also significantly decreased gene expression, but mutated Fox-like sites did not. The wild-type Fox-like site inhibits activation of a viral IE enhancer-containing promoter. Cellular protein, which is present in uninfected or infected permissive cell nuclear extracts, binds to the wild-type Fox-like site but not to mutated sites. Reasons for repression of UL127 gene transcription during productive infection are discussed.
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Affiliation(s)
- Philip E Lashmit
- Department of Microbiology, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
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61
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Nerheim PL, Meier JL, Vasef MA, Li WG, Hu L, Rice JB, Gavrila D, Richenbacher WE, Weintraub NL. Enhanced cytomegalovirus infection in atherosclerotic human blood vessels. THE AMERICAN JOURNAL OF PATHOLOGY 2004; 164:589-600. [PMID: 14742264 PMCID: PMC1602282 DOI: 10.1016/s0002-9440(10)63148-3] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 10/22/2003] [Indexed: 12/17/2022]
Abstract
Human cytomegalovirus (CMV) is a possible co-factor in atherogenesis and vascular occlusion, but its ability to actively infect medium and large blood vessels is unclear. A vascular explant model was adapted to investigate CMV infection in human coronary artery, internal mammary artery (IMA), and saphenous vein (SV). Vascular explants were inoculated with CMV Towne or low-passage clinical isolate and examined in situ for CMV cytopathic effect and immediate-early and early antigens, as indicators of active infection. At 5 to 7 days after inoculation, we found that CMV Towne actively infected eight of eight different atherosclerotic blood vessel explants (coronary artery, n = 4; SV and IMA grafts, n = 4), whereas it only infected 2 of 14 nonatherosclerotic blood vessel explants (SV, n = 10; IMA, n = 4) (P = 0.001). The CMV clinical isolate actively infected none of six sets of nonatherosclerotic SV explants at 5 to 7 days after inoculation. The active CMV infections involved adventitial and, less frequently, intimal cells. A small subset of infected cells in atherosclerotic tissue expresses the endothelial cell marker CD31. Smooth muscle cells residing in both atherosclerotic and nonatherosclerotic blood vessels were free of active CMV infections even after all vascular tissue layers were exposed to the virus. In contrast, active CMV Towne infection was evident at 2 days after inoculation in smooth muscle cells and endothelial cells previously isolated from the SV tissues. We conclude that active CMV infection is enhanced in atherosclerotic blood vessels compared to atherosclerosis-free vascular equivalents, and this viral activity is restricted to subpopulations of intimal and adventitial cells.
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Affiliation(s)
- Pamela L Nerheim
- Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52242, USA
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62
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Liang Y, Ganem D. Lytic but not latent infection by Kaposi's sarcoma-associated herpesvirus requires host CSL protein, the mediator of Notch signaling. Proc Natl Acad Sci U S A 2003; 100:8490-5. [PMID: 12832621 PMCID: PMC166256 DOI: 10.1073/pnas.1432843100] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Infection by Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) is a key factor in the development of KS. Both latent and lytic KSHV infection is observed in KS tumor cells, and both genetic programs contribute importantly to KS pathogenesis. The viral replication and transcription activator (RTA) protein is a transcription factor that controls the switch from latency to lytic replication. We have previously shown that RTA can activate the expression of several lytic viral genes in transfected cells by interaction with recombination signal sequence-binding protein-J kappa (RBP-J kappa, also called CSL), which in uninfected cells is a transcriptional repressor that is the target of the Notch-signaling pathway. The recognition that many KSHV lytic genes, including RTA itself, contain RBP-J kappa-binding sites raised the possibility that RBP-J kappa-mediated repression may be central to the establishment of latency. Here, we have tested this hypothesis by examining KSHV infection of RBP-J kappa-null murine fibroblasts. Our results show that KSHV latency is efficiently induced in such cells; however, the reactivation of lytic gene expression, viral DNA replication, and the release of progeny viruses are dramatically inhibited in the absence of RBP-J kappa. RBP-J kappa-mediated repression is therefore not essential for establishment of latent infection, but the RTA-mediated redirection of RBP-J kappa activity from repression to activation is critical for lytic viral replication.
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Affiliation(s)
| | - Don Ganem
- To whom correspondence should be addressed at: Departments of Microbiology and
Medicine, Howard Hughes Medical Institute, University of California, 513
Parnassus Avenue, Room Hse 401, San Francisco, CA 94143-0414. E-mail:
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63
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Keller MJ, Wheeler DG, Cooper E, Meier JL. Role of the human cytomegalovirus major immediate-early promoter's 19-base-pair-repeat cyclic AMP-response element in acutely infected cells. J Virol 2003; 77:6666-75. [PMID: 12767986 PMCID: PMC156166 DOI: 10.1128/jvi.77.12.6666-6675.2003] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2003] [Accepted: 03/18/2003] [Indexed: 01/08/2023] Open
Abstract
Prior studies have suggested a role of the five copies of the 19-bp-repeat cyclic AMP (cAMP)-response element (CRE) in major immediate-early (MIE) promoter activation, the rate-limiting step in human cytomegalovirus (HCMV) replication. We used two different HCMV genome modification strategies to test this hypothesis in acutely infected cells. We report the following: (i) the CREs do not govern basal levels of MIE promoter activity at a high or low multiplicity of infection (MOI) in human foreskin fibroblast (HFF)- or NTera2-derived neuronal cells; (ii) serum and virion components markedly increase MIE promoter-dependent transcription at a low multiplicity of infection (MOI), but this increase is not mediated by the CREs; (iii) forskolin stimulation of the cAMP signaling pathway induces a two- to threefold increase in MIE RNA levels in a CRE-specific manner at a low MOI in both HFF- and NTera2-derived neuronal cells; and (iv) the CREs do not regulate basal levels of HCMV DNA replication at a high or low MOI in HFF. Their presence does impart a forskolin-induced increase in viral DNA replication at a low MOI but only when basal levels of MIE promoter activity are experimentally diminished. In conclusion, the 19-bp-repeat CREs add to the robust MIE promoter activity that occurs in the acutely infected stimulated cells, although the CREs' greater role may be in other settings.
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Affiliation(s)
- M J Keller
- Department of Internal Medicine and the Helen C. Levitt Center for Viral Pathogenesis and Disease, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, USA
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64
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Abstract
Human cytomegalovirus (HCMV), a betaherpesvirus, represents the major infectious cause of birth defects, as well as an important pathogen for immunocompromised individuals. The viral nucleocapsid containing a linear double-stranded DNA of 230 kb is surrounded by a proteinaceous tegument, which is itself enclosed by a loosely applied lipid bilayer. Expression of the HCMV genome is controlled by a cascade of transcriptional events that leads to the synthesis of three categories of viral proteins designated as immediate-early, early, and late. Clinical manifestations can be seen following primary infection, reinfection, or reactivation. About 10% of infants are infected by the age of 6 months following transmission from their mothers via the placenta, during delivery, or by breastfeeding. HCMV is a significant post-allograft pathogen and contributes to graft loss independently from graft rejection. Histopathologic examination of necropsy tissues demonstrates that the virus enters via the epithelium of the upper alimentary, respiratory, or genitourinary tracts. Hematogenous spreading is typically followed by infection of ductal epithelial cells. Infections are kept under control by the immune system. However, total HCMV clearance is rarely achieved, and the viral genome remains at selected sites in a latent state. Virological and molecular detection of HCMV, as well as serological demonstration of a specific immune response, are used for diagnosis. Treatment of HCMV infections is difficult because there are few options. The presently available drugs produced a significant clinical improvement, but suffer from poor oral bioavailability, low potency, development of resistance in clinical practice, and dose-limiting toxicities.
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Affiliation(s)
- Santo Landolfo
- Department of Public Health and Microbiology, University of Turin, Via Santena 9, 10126 Turin, Italy.
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65
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Isomura H, Stinski MF. The human cytomegalovirus major immediate-early enhancer determines the efficiency of immediate-early gene transcription and viral replication in permissive cells at low multiplicity of infection. J Virol 2003; 77:3602-14. [PMID: 12610136 PMCID: PMC149520 DOI: 10.1128/jvi.77.6.3602-3614.2003] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
To determine the effect of the human cytomegalovirus (CMV) major immediate-early (MIE) enhancer or promoter on the efficiency of viral replication in permissive human cells, we constructed recombinant viruses with their human MIE promoter, enhancer, and promoter plus enhancer replaced with the murine CMV components. After a low multiplicity of infection (MOI) (0.01 PFU/cell), recombinant human CMV with the murine CMV promoter replicated like the wild type but recombinant virus with the murine enhancer replicated less efficiently. Immediate-early (IE) viral protein pIE72 (UL123), early viral protein (UL44), and viral DNA synthesis were significantly decreased. The effect of the human CMV enhancer substitution with the murine CMV enhancer was also demonstrated in different cell types by using recombinant virus with the UL127 promoter, driving the expression of green fluorescent protein (GFP). After an MOI of 1, GFP expression was high with the human CMV enhancer and significantly lower with the murine CMV enhancer. Even though at a high MOI (10 PFU/cell), the murine CMV enhancer was as efficient as the human CMV enhancer for the transcription of IE genes in human foreskin fibroblast cells, at lower MOIs, the murine CMV enhancer was less efficient. Proximal and distal chimeras of the human and murine enhancers also replicated less efficiently at a low MOI and expressed lower levels of GFP from the UL127 promoter. These experiments demonstrate that the entire human CMV enhancer has evolved for the efficient expression of the viral IE and early genes in human cells. Possible functions of the human CMV enhancer and promoter at a low MOI are discussed.
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Affiliation(s)
- Hiroki Isomura
- Department of Microbiology, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA
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66
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Bain M, Mendelson M, Sinclair J. Ets-2 Repressor Factor (ERF) mediates repression of the human cytomegalovirus major immediate-early promoter in undifferentiated non-permissive cells. J Gen Virol 2003; 84:41-49. [PMID: 12533699 DOI: 10.1099/vir.0.18633-0] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The repression of human cytomegalovirus immediate-early (IE) lytic gene expression is crucial for the maintenance of the latent viral state. By using conditionally permissive cell lines, which provide a good model for the differentiation state-dependent repression of IE gene expression, we have identified several cellular factors that bind to the major immediate-early promoter (MIEP) and whose expression is down-regulated after differentiation to a permissive phenotype. Here we show that the cellular protein Ets-2 Repressor Factor (ERF) physically interacts with the MIEP and represses MIEP activity in undifferentiated non-permissive T2 embryonal carcinoma cells. This factor binds to the dyad element and the 21 bp repeats within the MIEP - regions known to be important for the negative regulation of MIEP activity. Finally, we show that following differentiation to a permissive phenotype ERF's repressive effects are severely abrogated.
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Affiliation(s)
- Mark Bain
- Department of Medicine, University of Cambridge, PO Box 157, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK
| | - Marc Mendelson
- Department of Medicine, University of Cambridge, PO Box 157, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK
| | - John Sinclair
- Department of Medicine, University of Cambridge, PO Box 157, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK
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67
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Chen J, Stinski MF. Role of regulatory elements and the MAPK/ERK or p38 MAPK pathways for activation of human cytomegalovirus gene expression. J Virol 2002; 76:4873-85. [PMID: 11967304 PMCID: PMC136149 DOI: 10.1128/jvi.76.10.4873-4885.2002] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A series of recombinant viruses with either site-specific mutations or various deletions of the early UL4 promoter of human cytomegalovirus were used to determine the roles of regulatory elements and the effects of the mitogen-activated protein kinase (MAPK) pathways. Viral gene expression was regulated by upstream cis-acting sites and by basic promoter elements that respond to the MAPK signal transduction pathways. Inhibitors of either the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway or the p38 MAPK pathway affected expression equally with either wild-type or mutant early UL4 promoters in the viral genome, indicating that the effects of the inhibitors are not exclusive for a single transcription factor. The minimal responsive element is the TATA box-containing early viral promoter.
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Affiliation(s)
- Jiping Chen
- Department of Microbiology, College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA
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68
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Assogba BD, Choi BH, Rho HM. Transcriptional activation of the promoter of human cytomegalovirus immediate early gene (CMV-IE) by the hepatitis B viral X protein (HBx) through the NF-kappaB site. Virus Res 2002; 84:171-9. [PMID: 11900849 DOI: 10.1016/s0168-1702(01)00445-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The reactivation of latent cytomegalovirus (CMV) in a human by another viral infection may induce virus-related symptoms. Based on this presumption, we investigated the effect of HBx on the activation of the CMV-IE, which is also known as a transactivator and potential oncogene. The HBx transactivated the CMV-IE promoter by up to 4- and 18-fold factors in human liver HepG2 and lung fibroblast MRC-5 cells, respectively. Cotransfection of HBx with each transcription factor presented in the CMV-IE promoter showed that only NF-kappaB synergistically activated the promoter by up to a 14-fold factor. Serial deletion assays and point mutation analysis showed that the third NF-kappaB site (nt -267 to -258) and the second one (nt -162 to -153) appeared as the major responsible site and minor one, respectively, for the transactivation. These results suggest the possibility that the HBV infection of a cell previously infected by CMV would exert influence on the reactivation of the latent cytomegalovirus in a human to induce virus-related symptoms.
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Affiliation(s)
- Barnabe Dossou Assogba
- Department of Molecular Biology and Research, School of Biological Sciences, Seoul National University, 151-742 Seoul, South Korea
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69
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Meier JL, Keller MJ, McCoy JJ. Requirement of multiple cis-acting elements in the human cytomegalovirus major immediate-early distal enhancer for viral gene expression and replication. J Virol 2002; 76:313-26. [PMID: 11739696 PMCID: PMC135711 DOI: 10.1128/jvi.76.1.313-326.2002] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
We have shown previously that the human cytomegalovirus (HCMV) major immediate-early (MIE) distal enhancer is needed for MIE promoter-dependent transcription and viral replication at low multiplicities of infection (MOI). To understand how this region works, we constructed and analyzed a series of HCMVs with various distal enhancer mutations. We show that the distal enhancer is composed of at least two parts that function independently to coordinately activate MIE promoter-dependent transcription and viral replication. One such part is contained in a 47-bp segment that has consensus binding sites for CREB/ATF, SP1, and YY1. At low MOI, these working parts likely function in cis to directly activate MIE gene expression, thus allowing viral replication to ensue. Three findings support the view that these working parts are likely cis-acting elements. (i) Deletion of either part of a bisegmented distal enhancer only slightly alters MIE gene transcription and viral replication. (ii) Reversing the distal enhancer's orientation largely preserves MIE gene transcription and viral replication. (iii) Placement of stop codons at -300 or -345 in all reading frames does not impair MIE gene transcription and viral replication. Lastly, we show that these working parts are dispensable at high MOI, partly because of compensatory stimulation of MIE promoter activity and viral replication that is induced by a virion-associated component(s) present at a high viral particle/cell ratio. We conclude that the distal enhancer is a complex multicomponent cis-acting region that is required to augment both MIE promoter-dependent transcription and HCMV replication.
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Affiliation(s)
- Jeffery L Meier
- Department of Internal Medicine and the Helen C. Levitt Center for Viral Pathogenesis and Disease, University of Iowa College of Medicine, Iowa City, Iowa, 52242, USA.
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70
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Bullock GC, Lashmit PE, Stinski MF. Effect of the R1 element on expression of the US3 and US6 immune evasion genes of human cytomegalovirus. Virology 2001; 288:164-74. [PMID: 11543669 DOI: 10.1006/viro.2001.1084] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Human cytomegalovirus (HCMV) has several gene products that are important for escape from immune surveillance. These viral gene products downregulate the expression of HLA molecules on the cell surface. The viral US3 and US6 gene products are expressed at immediate-early and early times after infection, respectively. There are two regulatory regions between the US3 and the US6 transcription units. The first region is an NF-kappaB responsive enhancer that promotes the immediate-early expression of the US3 gene and is designated the R2 enhancer. Upstream of the R2 enhancer is a region designated the R1 element that in transient transfection assays behaves as a silencer by repressing the effect of the enhancer on downstream gene expression (A. R. Thrower et al., J. Virol. 1996, 70, 91; Y.-J. Chan et al., J. Virol. 1996, 70, 5312). We constructed recombinant viruses with wild-type or mutated R1 elements. The expression of the US3 gene at 6 h after infection and the US6 gene at 24 h was higher when the R1 element was present. The R1 element in the context of the viral genome is not a silencer of US3 or US6 gene expression. The R1 element has multiple effects on the US3 and US6 RNAs. It enhances the level of US3 and US6 mRNA; it determines the 3'-end cleavage and polyadenylation of US6 RNA, and it stabilizes read-through viral RNAs. The potential mechanisms of R1 enhancement of US3 and US6 gene expression are discussed.
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Affiliation(s)
- G C Bullock
- Program in Molecular Biology, College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA
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71
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Pizzorno MC. Nuclear cathepsin B-like protease cleaves transcription factor YY1 in differentiated cells. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1536:31-42. [PMID: 11335102 DOI: 10.1016/s0925-4439(01)00032-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Differentiation of pluripotent cells into differentiated cell types involves changes in many aspects of cellular biochemistry. Many of these changes result in alterations of gene expression, which may occur by changing the activity of transcription factors. The cell line NTERA-2 (NT2) can be differentiated into various cell types by incubation with retinoic acid. The differentiated cell type is also permissive for infection with the human herpesvirus cytomegalovirus (CMV). The transcription factor YY1 has been shown to regulate the immediate-early promoter of CMV in a differentiation specific manner by binding to one site at -958 to -950 and to at least two sites in the enhancer. It is demonstrated here that there is a second YY1 site in the modulator between -995 and -987. Levels of YY1 DNA binding activity and protein decrease in NT2 cells as they are differentiated with retinoic acid. This decrease in protein is due to the degradation of YY1 by a cathepsin B-like activity found in nuclear extracts. The cleavage products of YY1 include the intact C-terminal half of the protein, which contains the zinc fingers and the DNA binding activity. This suggests a mechanism that allows expression of the CMV immediate-early promoter in differentiated cells.
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Affiliation(s)
- M C Pizzorno
- Department of Biology, Bucknell University, Lewisburg, PA 17837, USA.
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72
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Meier JL. Reactivation of the human cytomegalovirus major immediate-early regulatory region and viral replication in embryonal NTera2 cells: role of trichostatin A, retinoic acid, and deletion of the 21-base-pair repeats and modulator. J Virol 2001; 75:1581-93. [PMID: 11160656 PMCID: PMC114067 DOI: 10.1128/jvi.75.4.1581-1593.2001] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2000] [Accepted: 11/14/2000] [Indexed: 01/29/2023] Open
Abstract
Inactivity of the human cytomegalovirus (HCMV) major immediate-early regulatory region (MIERR), which is composed of promoter, enhancer, unique region, and modulator, is linked to lack of HCMV replication in latently infected cells and in other nonpermissive cell types, including human embryonal NTera2 carcinoma (NT2) cells. I refined the embryonal NT2 cell model to enable characterization of the unknown mechanistic basis for silencing of HCMV MIERR-dependent transcription and viral replication in nonpermissive cells. These infected NT2 cells contain nonreplicating viral genomes with electrophoretic mobility equivalent to a supercoiled, bacterial artificial chromosome of comparable molecular weight. MIERR-dependent transcription is minimal to negligible. Increasing the availability of positive-acting transcription factors by retinoic acid (RA) treatment after infection is largely insufficient in reactivating the MIERR. In contrast, trichostatin A (TSA), a histone deacetylase inhibitor, reactivates MIERR-dependent transcription. Contrary to prior findings produced from transfected MIERR segments, deletion of the 21-bp repeats and modulator from the MIERR in the viral genome does not relieve MIERR silencing. To demonstrate that MIERR silencing likely results from enhancer inactivity, I examined an HCMV with a heterologous MIERR promoter that is enhancer dependent but exempt from IE2 p86-mediated negative autoregulation. This heterologous promoter, like its neighboring native MIERR promoter, exhibits immediate-early transcriptional kinetics in fibroblasts. In embryonal NT2 cells, the heterologous MIERR promoter is transcriptionally inactive. This silence is relieved by TSA but not by RA. Remarkably, TSA-induced reactivation of MIERR-dependent transcription from quiescent viral genomes is followed by release of infectious virus. I conclude that a mechanism of active repression imposes a block to MIERR-dependent transcription and viral replication in embryonal NT2 cells. Because TSA overcomes the block, viral gene silencing may involve histone deacetylase-based modification of viral chromatin, which might account for the covalently closed circular conformation of quiescent HCMV genomes.
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Affiliation(s)
- J L Meier
- Department of Internal Medicine, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA.
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73
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Chen J, Stinski MF. Activation of transcription of the human cytomegalovirus early UL4 promoter by the Ets transcription factor binding element. J Virol 2000; 74:9845-57. [PMID: 11024111 PMCID: PMC102021 DOI: 10.1128/jvi.74.21.9845-9857.2000] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The human cytomegalovirus (HCMV) early UL4 promoter has served as a useful model for studying the activation of early viral gene expression. Previous transient-transfection experiments detected cis-acting elements (the NF-Y site and site 2) upstream of the transcriptional start site (L. Huang and M. F. Stinski, J. Virol. 69:7612-7621, 1995). The roles of two of these sites, the NF-Y site and site 2, in the context of the viral genome were investigated further by comparing mRNA levels from the early UL4 promoter in human foreskin fibroblasts infected by recombinant viruses with either wild-type or mutant cis-acting elements. Steady-state mRNA levels from the UL4 promoter with a mutation in the NF-Y site were comparable to that of wild type. A mutation in an Elk-1 site plus putative IE86 protein binding sites decreased the steady-state mRNA levels compared to the wild type at early times after infection. Electrophoretic mobility shift assays and antibody supershifts detected the binding of cellular transcription factor Elk-1 to site 2 DNA with infected nuclear extracts but not with mock-infected nuclear extracts. The role of cellular transcription factors activated by the mitogen activated protein kinase/extracellular signal-regulated kinase pathway in activating transcription from early viral promoters is discussed.
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Affiliation(s)
- J Chen
- Department of Microbiology, College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA
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74
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Murphy EA, Streblow DN, Nelson JA, Stinski MF. The human cytomegalovirus IE86 protein can block cell cycle progression after inducing transition into the S phase of permissive cells. J Virol 2000; 74:7108-18. [PMID: 10888651 PMCID: PMC112229 DOI: 10.1128/jvi.74.15.7108-7118.2000] [Citation(s) in RCA: 115] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Human cytomegalovirus (HCMV) infection of permissive cells has been reported to induce a cell cycle halt. One or more viral proteins may be involved in halting progression at different stages of the cell cycle. We investigated how HCMV infection, and specifically IE86 protein expression, affects the cell cycles of permissive and nonpermissive cells. We used a recombinant virus that expresses the green fluorescent protein (GFP) to determine the effects of HCMV on the cell cycle of permissive cells. Fluorescence by GFP allowed us to select for only productively infected cells. Replication-defective adenovirus vectors expressing the IE72 or IE86 protein were also used to efficiently transduce 95% or more of the cells. The adenovirus-expressed IE86 protein was determined to be functional by demonstrating negative autoregulation of the major immediate-early promoter and activation of an early viral promoter in the context of the viral genome. To eliminate adenovirus protein effects, plasmids expressing GFP for fluorescent selection of only transfected cells and wild-type IE86 protein or a mutant IE86 protein were tested in permissive and nonpermissive cells. HCMV infection induced the entry of U373 cells into the S phase. All permissive cells infected with HCMV were blocked in cell cycle progression and could not divide. After either transduction or transfection and IE86 protein expression, the number of all permissive or nonpermissive cell types in the S phase increased significantly, but the cells could no longer divide. The IE72 protein did not have a significant effect on the S phase. Since IE86 protein inhibits cell cycle progression, the IE2 gene in a human fibroblast IE86 protein-expressing cell line was sequenced. The IE86 protein in these retrovirus-transduced cells has mutations in a critical region of the viral protein. The locations of the mutations and the function of the IE86 protein in controlling cell cycle progression are discussed.
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Affiliation(s)
- E A Murphy
- Molecular Biology Program, College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA
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75
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Angulo A, Kerry D, Huang H, Borst EM, Razinsky A, Wu J, Hobom U, Messerle M, Ghazal P. Identification of a boundary domain adjacent to the potent human cytomegalovirus enhancer that represses transcription of the divergent UL127 promoter. J Virol 2000; 74:2826-39. [PMID: 10684299 PMCID: PMC111773 DOI: 10.1128/jvi.74.6.2826-2839.2000] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/1999] [Accepted: 12/13/1999] [Indexed: 11/20/2022] Open
Abstract
Transcriptional repression within a complex modular promoter may play a key role in determining the action of enhancer elements. In human cytomegalovirus, the major immediate-early promoter (MIEP) locus contains a highly potent and complex modular enhancer. Evidence is presented suggesting that sequences of the MIEP between nucleotide positions -556 and -673 function to prevent transcription activation by enhancer elements from the UL127 open reading frame divergent promoter. Transient transfection assays of reporter plasmids revealed repressor sequences located between nucleotides -556 and -638. The ability of these sequences to confer repression in the context of an infection was shown using recombinant viruses generated from a bacterial artificial chromosome containing an infectious human cytomegalovirus genome. In addition to repressor sequences between -556 and -638, infection experiments using recombinant virus mutants indicated that sequences between -638 and -673 also contribute to repression of the UL127 promoter. On the basis of in vitro transcription and transient transfection assays, we further show that interposed viral repressor sequences completely inhibit enhancer-mediated activation of not only the homologous but also heterologous promoters. These and other experiments suggest that repression involves an interaction of host-encoded regulatory factors with defined promoter sequences that have the property of proximally interfering with upstream enhancer elements in a chromatin-independent manner. Altogether, our findings establish the presence of a boundary domain that efficiently blocks enhancer-promoter interactions, thus explaining how the enhancer can work to selectively activate the MIEP.
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Affiliation(s)
- A Angulo
- Department of Immunology and Molecular Biology, Division of Virology, The Scripps Research Institute, La Jolla, California 92037, USA
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76
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Meier JL, Pruessner JA. The human cytomegalovirus major immediate-early distal enhancer region is required for efficient viral replication and immediate-early gene expression. J Virol 2000; 74:1602-13. [PMID: 10644329 PMCID: PMC111634 DOI: 10.1128/jvi.74.4.1602-1613.2000] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human cytomegalovirus (HCMV) major immediate-early (MIE) genes, encoding IE1 p72 and IE2 p86, are activated by a complex enhancer region (base positions -65 to -550) that operates in a cell type- and differentiation-dependent manner. The expression of MIE genes is required for HCMV replication. Previous studies analyzing functions of MIE promoter-enhancer segments suggest that the distal enhancer region variably modifies MIE promoter activity, depending on cell type, stimuli, or state of differentiation. To further understand the mechanism by which the MIE promoter is regulated, we constructed and analyzed several different recombinant HCMVs that lack the distal enhancer region (-300 to -582, -640, or -1108). In human fibroblasts, the HCMVs without the distal enhancer replicate normally at high multiplicity of infection (MOI) but replicate poorly at low MOI in comparison to wild-type virus (WT) or HCMVs that lack the neighboring upstream unique region and modulator (-582 or -640 to -1108). The growth aberrancy was normalized after restoring the distal enhancer in a virus lacking this region. For HCMVs without a distal enhancer, the impairment in replication at low MOI corresponds to a deficiency in production of MIE RNAs compared to WT or virus lacking the unique region and modulator. An underproduction of viral US3 RNA was also evident at low MOI. Whether lower production of IE1 p72 and IE2 p86 causes a reduction in expression of the immediate-early (IE) class US3 gene remains to be determined. We conclude that the MIE distal enhancer region possesses a mechanism for augmenting viral IE gene expression and genome replication at low MOI, but this regulatory function is unnecessary at high MOI.
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Affiliation(s)
- J L Meier
- Department of Internal Medicine and the Helen C. Levitt Center for Viral Pathogenesis and Disease, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA.
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77
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Affiliation(s)
- E A Fortunato
- Department of Biology and Center for Molecular Genetics, University of California, San Diego, La Jolla 92093-0366, USA
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78
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Lundquist CA, Meier JL, Stinski MF. A strong negative transcriptional regulatory region between the human cytomegalovirus UL127 gene and the major immediate-early enhancer. J Virol 1999; 73:9039-52. [PMID: 10516010 PMCID: PMC112936 DOI: 10.1128/jvi.73.11.9039-9052.1999] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The region of the human cytomegalovirus (CMV) genome between the UL127 open reading frame and the major immediate-early (MIE) enhancer is referred to as the unique region. DNase I protection analysis with human cell nuclear extracts demonstrated multiple protein binding sites in this region of the viral genome (P. Ghazal, H. Lubon, C. Reynolds-Kohler, L. Hennighausen, and J. A. Nelson, Virology 174:18-25, 1990). However, the function of this region in the context of the viral genome is not known. In wild-type human CMV-infected human fibroblasts, cells permissive for viral replication, there is little to no transcription from UL127. We determined that the unique region prevented transcription from the UL127 promoter but had no effect on the divergent MIE promoter. In transient-transfection assays, the basal level of expression from the UL127 promoter increased significantly when the wild-type unique sequences were mutated. In recombinant viruses with similar mutations in the unique region, expression from the UL127 promoter occurred only after de novo viral protein synthesis, typical of an early viral promoter. A 111-bp deletion-substitution of the unique sequence caused approximately a 20-fold increase in the steady-state level of RNA from the UL127 promoter and a 245-fold increase in the expression of a downstream indicator gene. This viral negative regulatory region was also mutated at approximately 50-bp regions proximal and distal to the UL127 promoter. Although some repressive effects were detected in the distal region, mutations of the region proximal to the UL127 promoter had the most significant effects on transcription. Within the proximal and distal regions, there are potential cis sites for known eucaryotic transcriptional repressor proteins. This region may also bind unknown viral proteins. We propose that the unique region upstream of the UL127 promoter and the MIE enhancer negatively regulates the expression from the UL127 promoter in permissive human fibroblast cells. This region may be a regulatory boundary preventing the effects of the very strong MIE enhancer on this promoter.
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Affiliation(s)
- C A Lundquist
- Department of Microbiology, College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA
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79
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Selective neuronal expression of green fluorescent protein with cytomegalovirus promoter reveals entire neuronal arbor in transgenic mice. J Neurosci 1999. [PMID: 9852599 DOI: 10.1523/jneurosci.18-24-10640.1998] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
In simple nervous systems, identified groups of neurons can be studied in depth. To allow the same advantage in the mammalian brain, we have generated green fluorescent protein (GFP) transgenic mice in which only a few types of neurons are strongly labeled with a fluorescent molecule, which the neurons synthesize internally, allowing the cells, their dendrites, filopodia, and axons to be identified in both living and fixed CNS, in slices and culture. The same neurons, with GFP expression controlled by part of the major immediate early promoter of human cytomegalovirus (CMV), show GFP beginning early in development, from one generation to the next, allowing cellular and physiological studies of axonal and dendritic growth, fate mapping, anatomical connections, and synapse formation in identified neurons. The human CMV promoter sequence we used was different from that used in previous work with other reporter genes and gave a dramatically different pattern of expression. Two transgenic lines with the same CMV promoter show similar anatomical patterns of expression in the present study. Strong GFP labeling was found in a subpopulation of mossy fibers that innervated parasagittal bands in the cerebellar cortex and olfactory axons that projected into the olfactory bulb, subsets of motoneurons and dorsal root ganglion cells, granule but not mitral cells of the olfactory bulb, and a group of neurons in the hypothalamic suprachiasmatic nucleus. A novel type of neuron was strongly labeled in the olfactory bulb external plexiform layer. In normal brains, CMV does not constitute a threat, but in the developing brain, CMV can cause debilitating neurodegeneration and death; studies using the CMV promoter aid in understanding the affinity of CMV that has been suggested for specific brain regions.
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80
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van den Pol AN, Ghosh PK. Selective neuronal expression of green fluorescent protein with cytomegalovirus promoter reveals entire neuronal arbor in transgenic mice. J Neurosci 1998; 18:10640-51. [PMID: 9852599 PMCID: PMC6793373] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023] Open
Abstract
In simple nervous systems, identified groups of neurons can be studied in depth. To allow the same advantage in the mammalian brain, we have generated green fluorescent protein (GFP) transgenic mice in which only a few types of neurons are strongly labeled with a fluorescent molecule, which the neurons synthesize internally, allowing the cells, their dendrites, filopodia, and axons to be identified in both living and fixed CNS, in slices and culture. The same neurons, with GFP expression controlled by part of the major immediate early promoter of human cytomegalovirus (CMV), show GFP beginning early in development, from one generation to the next, allowing cellular and physiological studies of axonal and dendritic growth, fate mapping, anatomical connections, and synapse formation in identified neurons. The human CMV promoter sequence we used was different from that used in previous work with other reporter genes and gave a dramatically different pattern of expression. Two transgenic lines with the same CMV promoter show similar anatomical patterns of expression in the present study. Strong GFP labeling was found in a subpopulation of mossy fibers that innervated parasagittal bands in the cerebellar cortex and olfactory axons that projected into the olfactory bulb, subsets of motoneurons and dorsal root ganglion cells, granule but not mitral cells of the olfactory bulb, and a group of neurons in the hypothalamic suprachiasmatic nucleus. A novel type of neuron was strongly labeled in the olfactory bulb external plexiform layer. In normal brains, CMV does not constitute a threat, but in the developing brain, CMV can cause debilitating neurodegeneration and death; studies using the CMV promoter aid in understanding the affinity of CMV that has been suggested for specific brain regions.
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Affiliation(s)
- A N van den Pol
- Department of Neurosurgery, Yale University School of Medicine, New Haven, Connecticut 06520, USA
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81
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Lashmit PE, Stinski MF, Murphy EA, Bullock GC. A cis repression sequence adjacent to the transcription start site of the human cytomegalovirus US3 gene is required to down regulate gene expression at early and late times after infection. J Virol 1998; 72:9575-84. [PMID: 9811691 PMCID: PMC110467 DOI: 10.1128/jvi.72.12.9575-9584.1998] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/1998] [Accepted: 08/25/1998] [Indexed: 11/20/2022] Open
Abstract
Human cytomegalovirus has two enhancer-containing immediate-early (IE) promoters with a cis repression sequence (CRS) positioned immediately upstream of the transcription start site, designated the major IE (MIE) promoter and the US3 promoter. The role of the CRS upstream of the US3 transcription start site in the context of the viral genome was determined by comparing the levels of transcription from these two enhancer-containing promoters in recombinant viruses with a wild-type or mutant CRS. Upstream of the CRS of the US3 promoter was either the endogenous enhancer (R2) or silencer (R1). The downstream US3 gene was replaced with the indicator gene chloramphenicol acetyltransferase (CAT). Infected permissive human fibroblast cells or nonpermissive, undifferentiated monocytic THP-1 cells were analyzed for expression from the US3 promoter containing either the wild-type or mutant CRS. With the wild-type CRS, the maximum level of transcription in permissive cells was detected within 4 to 6 h after infection and then declined. With the mutant CRS and the R2 enhancer upstream, expression from the US3 promoter continued to increase throughout the viral replication cycle to levels 20- to 40-fold higher than for the wild type. In nonpermissive or permissive monocytic THP-1 cells, expression from the US3 promoter was also significantly higher when the CRS was mutated. Less expression was obtained when only the R1 element was present, but expression was higher when the CRS was mutated. Thus, the CRS in the enhancer-containing US3 promoter appears to allow for a short burst of US3 gene expression followed by repression at early and late times after infection. Overexpression of US3 may be detrimental to viral replication, and its level of expression must be stringently controlled. The role of the CRS and the viral IE86 protein in controlling enhancer-containing promoters is discussed.
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Affiliation(s)
- P E Lashmit
- Department of Microbiology, College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA
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Angulo A, Messerle M, Koszinowski UH, Ghazal P. Enhancer requirement for murine cytomegalovirus growth and genetic complementation by the human cytomegalovirus enhancer. J Virol 1998; 72:8502-9. [PMID: 9765387 PMCID: PMC110259 DOI: 10.1128/jvi.72.11.8502-8509.1998] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The cytomegalovirus (CMV) enhancer is a highly complex regulatory region containing multiple elements that interact with a variety of host-encoded transcription factors. Many of these sequence elements are conserved among the different species strains of CMV, although the arrangement of the various elements and overall sequence composition of the CMV enhancers differ remarkably. To delineate the importance of this region to a productive infection and to explore the possibility of generating a murine CMV (MCMV) under the control of human CMV (HCMV) genetic elements, the MCMV enhancer was resected and replaced either with nonregulatory sequences or with paralogous sequences from HCMV. The effects of these various deletions and substitutions on viral growth in transfected or infected tissue-culture cells were evaluated. We found that mutations in MCMV that eliminate or substitute for the enhancer with nonregulatory sequences showed a severe deficiency in virus synthesis. This growth defect is effectively complemented by the homologous MCMV enhancer as well as the HCMV enhancer. In the latter case, the chimeric viruses (hybrid MCMV strains) containing the molecularly shuffled human enhancer exhibit infectious kinetics similar to that of parental wild-type and wild-type revertant MCMV. These results also show that open reading frames m124, m124.1, and m125 located within the enhancer region are nonessential for growth of MCMV in cells. Most importantly, we conclude that the enhancer of MCMV is required for optimal infection and that its diverged human counterpart can advantageously replace its role in promoting viral infectivity.
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Affiliation(s)
- A Angulo
- Departments of Immunology and Molecular Biology, Division of Virology, The Scripps Research Institute, La Jolla, California 92037, USA
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