101
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El-Guindy AS, Paek SY, Countryman J, Miller G. Identification of constitutive phosphorylation sites on the Epstein-Barr virus ZEBRA protein. J Biol Chem 2005; 281:3085-95. [PMID: 16321978 DOI: 10.1074/jbc.m506076200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ZEBRA, the product of the Epstein-Barr virus gene bzlf1, and a member of the AP-1 subfamily of basic zipper (bZIP) transcription factors, is necessary and sufficient to disrupt viral latency and to initiate the viral lytic cycle. Two serine residues of ZEBRA, Ser167 and Ser173, are substrates for casein kinase 2 (CK2) and are constitutively phosphorylated in vivo. Phosphorylation of ZEBRA at its CK2 sites is required for proper temporal regulation of viral gene expression. Phosphopeptide analysis indicated that ZEBRA contains additional constitutive phosphorylation sites. Here we employed a co-migration strategy to map these sites in vivo. The cornerstone of this strategy was to correlate the migration of 32P- and 35S-labeled tryptic peptides of ZEBRA. The identity of the peptides was revealed by mutagenesis of methionine and cysteine residues present in each peptide. Phosphorylation sites within the peptide were identified by mutagenesis of serines and threonines. ZEBRA was shown to be phosphorylated at serine and threonine residues, but not tyrosine. Two previously unrecognized phosphorylation sites of ZEBRA were identified in the NH2-terminal region of the transactivation domain: a cluster of weak phosphorylation sites at Ser6, Thr7, and Ser8 and a strong phosphorylation site at Thr14. Thr14 was embedded in a MAP kinase consensus sequence and could be phosphorylated in vitro by JNK, despite the absence of a canonical JNK docking site. Thus ZEBRA is now known to be constitutively phosphorylated at three distinct sites.
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Affiliation(s)
- Ayman S El-Guindy
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, Connecticut 06520, USA
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102
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Adamson AL. Effects of SUMO-1 upon Epstein-Barr virus BZLF1 function and BMRF1 expression. Biochem Biophys Res Commun 2005; 336:22-8. [PMID: 16112644 DOI: 10.1016/j.bbrc.2005.08.036] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2005] [Accepted: 08/04/2005] [Indexed: 11/28/2022]
Abstract
Epstein-Barr virus (EBV) is a human herpesvirus that has infected at least 90% of the world population. This very successful virus causes infectious mononucleosis and is associated with many different types of cancer. The EBV BZLF1 protein is a transcription factor that has also been shown to interact with many host cell proteins and pathways. BZLF1 (Z) is tagged by the small ubiquitin-related modifier-1 (SUMO-1) protein. Here, we present studies of the functional consequences of SUMO-1 modification of Z. We found that SUMO-1 modification of Z has no apparent effect upon the stability and localization of the Z protein. We did find, however, that SUMO-1 modification decreases the transactivation activity of Z on specific promoters. In addition, when SUMO-1 is supplied to cells when lytic replication is induced, EBV BMRF1 levels greatly increase, suggesting that SUMO-1 enhances EBV lytic replication. Therefore, SUMO-1 modification of proteins appears to have an important role in EBV lytic replication.
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Affiliation(s)
- Amy L Adamson
- Department of Biology, University of North Carolina at Greensboro, Greensboro, NC 27402, USA.
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103
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Izumiya Y, Ellison TJ, Yeh ETH, Jung JU, Luciw PA, Kung HJ. Kaposi's sarcoma-associated herpesvirus K-bZIP represses gene transcription via SUMO modification. J Virol 2005; 79:9912-25. [PMID: 16014952 PMCID: PMC1181544 DOI: 10.1128/jvi.79.15.9912-9925.2005] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Kaposi's sarcoma-associated herpesvirus (KSHV) is a human gammaherpesvirus implicated in AIDS-related neoplasms. Previously, we demonstrated that the early lytic gene product K-bZIP is a transcriptional repressor that affects a subset of viral gene transcriptions mediated by the viral transactivator K-Rta (Y. Izumiya et al. J. Virol. 77:1441-1451, 2003). Sumoylation has emerged as an important posttranslational modification that affects the location and function of cellular and viral proteins and also plays a significant role in transcriptional repression along with Ubc9, the E2 SUMO conjugation enzyme. Here, we provide evidence that K-bZIP is sumoylated at the lysine 158 residue and associates with Ubc9 both in a cell-free system and in virus-infected BCBL-1 cells. Reporter assays showed that the expression of SUMO-specific protease 1 attenuated the transcriptional repression activity of K-bZIP. The expression of a K-bZIPK158R mutant, which was no longer sumoylated, exhibited the reduced transcriptional repression activity. This indicates that sumoylation plays an important part in the transcriptional repression activity of K-bZIP. Finally, chromatin immunoprecipitation experiments demonstrated that K-bZIP interacts with and recruits Ubc9 to specific KSHV promoters. Thus, our data indicate that K-bZIP is a SUMO adaptor, which recruits Ubc9 to specific viral target promoters, thereby exerting its transcriptional repression activity.
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Affiliation(s)
- Yoshihiro Izumiya
- Department of Biological Chemistry, University of California--Davis (UC Davis), School of Medicine, Sacramento, 95817, USA
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104
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Prichard MN, Lawlor H, Duke GM, Mo C, Wang Z, Dixon M, Kemble G, Kern ER. Human cytomegalovirus uracil DNA glycosylase associates with ppUL44 and accelerates the accumulation of viral DNA. Virol J 2005; 2:55. [PMID: 16022730 PMCID: PMC1185570 DOI: 10.1186/1743-422x-2-55] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2005] [Accepted: 07/15/2005] [Indexed: 11/10/2022] Open
Abstract
Background Human cytomegalovirus UL114 encodes a uracil-DNA glycosylase homolog that is highly conserved in all characterized herpesviruses that infect mammals. Previous studies demonstrated that the deletion of this nonessential gene delays significantly the onset of viral DNA synthesis and results in a prolonged replication cycle. The gene product, pUL114, also appears to be important in late phase DNA synthesis presumably by introducing single stranded breaks. Results A series of experiments was performed to formally assign the observed phenotype to pUL114 and to characterize the function of the protein in viral replication. A cell line expressing pUL114 complemented the observed phenotype of a UL114 deletion virus in trans, confirming that the observed defects were the result of a deficiency in this gene product. Stocks of recombinant viruses without elevated levels of uracil were produced in the complementing cells; however they retained the phenotype of poor growth in normal fibroblasts suggesting that poor replication was unrelated to uracil content of input genomes. Recombinant viruses expressing epitope tagged versions of this gene demonstrated that pUL114 was expressed at early times and that it localized to viral replication compartments. This protein also coprecipitated with the DNA polymerase processivity factor, ppUL44 suggesting that these proteins associate in infected cells. This apparent interaction did not appear to require other viral proteins since ppUL44 could recruit pUL114 to the nucleus in uninfected cells. An analysis of DNA replication kinetics revealed that the initial rate of DNA synthesis and the accumulation of progeny viral genomes were significantly reduced compared to the parent virus. Conclusion These data suggest that pUL114 associates with ppUL44 and that it functions as part of the viral DNA replication complex to increase the efficiency of both early and late phase viral DNA synthesis.
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Affiliation(s)
- Mark N Prichard
- Department of Pediatrics, University of Alabama at Birmingham, Birmingham AL, USA
| | - Heather Lawlor
- Department of Research, MedImmune Vaccines Inc., Mountain View, CA, USA
| | - Gregory M Duke
- Department of Research, MedImmune Vaccines Inc., Mountain View, CA, USA
| | - Chengjun Mo
- Department of Research, MedImmune Vaccines Inc., Mountain View, CA, USA
| | - Zhaoti Wang
- Department of Research, MedImmune Vaccines Inc., Mountain View, CA, USA
| | - Melissa Dixon
- Department of Research, MedImmune Vaccines Inc., Mountain View, CA, USA
| | - George Kemble
- Department of Research, MedImmune Vaccines Inc., Mountain View, CA, USA
| | - Earl R Kern
- Department of Pediatrics, University of Alabama at Birmingham, Birmingham AL, USA
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105
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Chiou SH, Chow KC, Yang CH, Chiang SF, Lin CH. Discovery of Epstein–Barr virus (EBV)-encoded RNA signal and EBV nuclear antigen leader protein DNA sequence in pet dogs. J Gen Virol 2005; 86:899-905. [PMID: 15784884 DOI: 10.1099/vir.0.80792-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The aim of this study was to investigate Epstein–Barr virus (EBV)-related virus infection in pet dogs. The presence of antibodies to EBV antigens and EBV-related DNA was determined by Western blot analysis and PCR, respectively. Among 36 pet dogs examined for serum antibodies, 32 (88·9 %) were positive for EBV-specific thymidine kinase, 15 (41·7 %) for EBV-encoded DNA-binding protein and 10 (27·8 %) for EBV-specific DNA polymerase. A BamHI W fragment sequence encoding part of the EBV nuclear antigen leader protein was detected by PCR in corresponding leukocyte DNA samples. Among 21 dogs tested, 15 (71·4 %) were positive for the BamHI W fragment sequence. The specificity of the amplified DNA fragments was confirmed by DNA sequencing. Within the amplified region of the BamHI W fragment (241 bp), DNA sequences detected in 10 dogs had 99·2 % (two nucleotide variations), 99·6 % (one nucleotide variation) or 100 % identity to that of EBV. Furthermore, an EBV-encoded RNA signal was detected by in situ hybridization in dog lymphocytes, as well as in bone-marrow sections, indicating a latent infection with EBV or an EBV-like virus. In conclusion, although the sample size was small, these results showed that a widespread EBV-related gammaherpesvirus could be detected in the peripheral blood and bone marrow of pet dogs. Although no evident zoonotic transmission was detected, further studies are imperative for disclosing the biological significance of this canine EBV-like virus, which may correlate with human disorders.
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Affiliation(s)
- Shiow-Her Chiou
- Graduate Institute of Veterinary Microbiology, National Chung Hsing University, Taichung 40227, Taiwan, Republic of China
| | - Kuan-Chih Chow
- Institute of Biomedical Sciences, National Chung Hsing University, Taichung 40227, Taiwan, Republic of China
| | - Chih-Huan Yang
- Department of Veterinary Medicine, National Chung Hsing University, Taichung 40227, Taiwan, Republic of China
| | - Shu-Fen Chiang
- Graduate Institute of Veterinary Microbiology, National Chung Hsing University, Taichung 40227, Taiwan, Republic of China
| | - Chun-Hao Lin
- Graduate Institute of Veterinary Microbiology, National Chung Hsing University, Taichung 40227, Taiwan, Republic of China
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106
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Holley-Guthrie EA, Seaman WT, Bhende P, Merchant JL, Kenney SC. The Epstein-Barr virus protein BMRF1 activates gastrin transcription. J Virol 2005; 79:745-55. [PMID: 15613302 PMCID: PMC538557 DOI: 10.1128/jvi.79.2.745-755.2005] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The Epstein-Barr virus (EBV) BMRF1 gene encodes an early lytic protein that functions not only as the viral DNA polymerase processivity factor but also as a transcriptional activator. BMRF1 has been previously shown to activate transcription of an EBV early promoter, BHLF1, though a GC-rich motif which binds to SP1 and ZBP-89, although the exact mechanism for this effect is not known (D. J. Law, S. A. Tarle, and J. L. Merchant, Mamm. Genome 9:165-167, 1998). Here we demonstrate that BMRF1 activates transcription of the cellular gastrin gene in telomerase-immortalized keratinocytes. Furthermore, BMRF1 activated a reporter gene construct driven by the gastrin promoter in a variety of cell types, and this effect was mediated by two SP1/ZBP-89 binding sites in the gastrin promoter. ZBP-89 has been previously shown to negatively regulate the gastrin promoter. However, ZBP-89 can function as either a negative or positive regulator of transcription, depending upon the promoter and perhaps other, as-yet-unidentified factors. BMRF1 increased the binding of ZBP-89 to the gastrin promoter, and a ZBP-89-GAL4 fusion protein was converted into a positive transcriptional regulator by cotransfection with BMRF1. BMRF1 also enhanced the transcriptional activity of an SP1-GAL4 fusion protein. These results suggest that BMRF1 activates target promoters through its effect on both the SP1 and ZBP-89 transcription factors. Furthermore, as the EBV genome is present in up to 10% of gastric cancers, and the different forms of gastrin are growth factors for gastrointestinal epithelium, our results suggest a mechanism by which lytic EBV infection could promote the growth of gastric cells.
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Affiliation(s)
- Elizabeth A Holley-Guthrie
- Lineberger Comprehensive Cancer Center, CB # 7295, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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107
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Xu Y, Cei SA, Rodriguez Huete A, Colletti KS, Pari GS. Human cytomegalovirus DNA replication requires transcriptional activation via an IE2- and UL84-responsive bidirectional promoter element within oriLyt. J Virol 2004; 78:11664-77. [PMID: 15479808 PMCID: PMC523242 DOI: 10.1128/jvi.78.21.11664-11677.2004] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Amplification of the human cytomegalovirus (HCMV) lytic origin (oriLyt) in human fibroblasts is dependent upon six core replication proteins and UL84, IE2, and UL36-38. Using a telomerase-immortalized human fibroblast cell line (T-HFs), oriLyt-dependent DNA replication no longer required the gene products of UL36-38. To determine the role of IE2 in DNA replication in human fibroblasts, we examined potential IE2-binding sites within HCMV oriLyt. We now show that a strong bidirectional promoter (oriLyt(PM)) (nucleotides 91754 to 92030) is located in the previously identified core region of the origin and is required for efficient amplification of oriLyt. It was determined that a 14-bp novel DNA motif (oriLyt promoter activation element), which was initially identified as a binding element for the immediate-early protein IE2, was essential for oriLyt(PM) activity. In Vero cells the oriLyt(PM) was constitutively active and strongly repressed by IE2, but it was reactivated by UL84. In contrast, transfection of the oriLyt(PM) into human fibroblasts resulted in a very low basal level of promoter activity that was dramatically up-regulated upon infection with HCMV. Cotransfection assays demonstrated that the transfection of UL84 along with IE2 transactivated the oriLyt(PM) in human fibroblasts. Further activation was observed upon cotransfection of the set of plasmids expressing the entire replication complex. Efficient oriLyt amplification in the absence of IE2 in human fibroblasts was observed by replacing the oriLyt(PM) with the simian virus 40 early promoter. Under these conditions, however, UL84 was still required for amplification of oriLyt. These results suggest that the mechanism of initiation of HCMV lytic replication in part involves transcriptional activation.
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Affiliation(s)
- Yiyang Xu
- Department of Microbiology and Cell and Molecular Biology Program, University of Nevada-Reno, Howard Bldg., Reno, NV 89557, USA
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108
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Deng H, Chu JT, Park NH, Sun R. Identification of cis sequences required for lytic DNA replication and packaging of murine gammaherpesvirus 68. J Virol 2004; 78:9123-31. [PMID: 15308708 PMCID: PMC506910 DOI: 10.1128/jvi.78.17.9123-9131.2004] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Human gammaherpesviruses are associated with lymphomas and other malignancies. Murine gammaherpesvirus 68 (MHV-68) infection of mice has emerged as a model for understanding gammaherpesvirus pathogenesis in vivo. In contrast to human gammaherpesviruses, MHV-68 replicates in permissive cell lines in a robust manner, presenting an efficient model to study the basic mechanisms for DNA replication and recombination processes. In addition, MHV-68 also infects a broad range of cells of different tissue types and from different host species, and the viral genome persists as an episome in infected cells. These features make MHV-68 an attractive system on which to build gene delivery vectors. We have therefore undertaken a study to identify the cis elements required for MHV-68 genome replication and packaging. Here we report that an 8.4-kb MHV-68 genomic fragment between ORF66 and ORF73 conferred on the plasmid the ability to replicate; replication required the presence of either de novo viral infection or viral reactivation from latency. We further mapped the origin of lytic replication (oriLyt) to a 1.25-kb region. Moreover, we demonstrated that the terminal repeat of the viral genome is sufficient for packaging of the replicated oriLyt plasmid into mature viral particles. Functional identification of the MHV-68 oriLyt and packaging signal has laid a foundation for investigating the mechanisms controlling gammaherpesvirus DNA replication during the viral lytic phase and will also serve as a base on which to design gene delivery vectors.
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Affiliation(s)
- Hongyu Deng
- Department of Molecular & Medical Pharmacology, Dental Research Intsitute, UCLA AIDS Institute, Jonsson Comprehensive Cancer Center, University of California at Los Angeles, Los Angeles 90095-1735, USA.
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109
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Colletti KS, Xu Y, Cei SA, Tarrant M, Pari GS. Human cytomegalovirus UL84 oligomerization and heterodimerization domains act as transdominant inhibitors of oriLyt-dependent DNA replication: evidence that IE2-UL84 and UL84-UL84 interactions are required for lytic DNA replication. J Virol 2004; 78:9203-14. [PMID: 15308715 PMCID: PMC506931 DOI: 10.1128/jvi.78.17.9203-9214.2004] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Human cytomegalovirus (HCMV) UL84 encodes a 75-kDa protein required for oriLyt-dependent DNA replication and interacts with IE2 in infected and transfected cells. UL84 localizes to the nucleus of transfected and infected cells and is found in viral replication compartments. In transient assays it was shown that UL84 can interfere with the IE2-mediated transactivation of the UL112/113 promoter of HCMV. To determine whether UL84 protein-protein interactions are necessary for lytic DNA synthesis, we purified UL84 and used this protein to generate a monoclonal antibody. Using this antibody, we now show that UL84 forms a stable interaction with itself in vivo. The point of self-interaction maps to a region of the protein between amino acids 151 and 200, a domain that contains a series of highly charged amino acid residues. Coimmunoprecipitation assays determined that UL84 interacts with a protein domain present within the first 215 amino acids of IE2. We also show that an intact leucine zipper domain of UL84 is required for a stable interaction with IE2 and UL84 leucine zipper mutants fail to complement oriLyt-dependent DNA replication. UL84 leucine zipper mutants no longer interfere with IE2-mediated transactivation of the UL112/113 promoter, confirming that the leucine zipper is essential for a functional interaction with IE2. In addition, we demonstrate that both the leucine zipper and oligomerization domains of UL84 can act as transdominant-negative inhibitors of lytic replication in the transient assay, strongly suggesting that both an IE2-UL84 and a UL84-UL84 interaction are required for DNA synthesis.
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Affiliation(s)
- Kelly S Colletti
- Department of Microbiology and Immunology, University of Nevada-Reno, Reno, Nevada, USA
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110
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Makhov AM, Subramanian D, Holley-Guthrie E, Kenney SC, Griffith JD. The Epstein-Barr Virus Polymerase Accessory Factor BMRF1 Adopts a Ring-shaped Structure as Visualized by Electron Microscopy. J Biol Chem 2004; 279:40358-61. [PMID: 15286084 DOI: 10.1074/jbc.m408733200] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Epstein-Barr virus (EBV) encodes a set of core replication factors used during lytic infection in human cells that parallels the factors used in many other systems. These include a DNA polymerase and its accessory factor, a helicase/primase, and a single strand binding protein. The EBV polymerase accessory factor has been identified as the product of the BMRF1 gene and has been shown by functional assays to increase the activity and processivity of the polymerase. Unlike other members of this class of factors, BMRF1 is also a transcription factor regulating certain EBV genes. Although several polymerase accessory factors, including eukaryotic proliferating cell nuclear antigen, Escherichia coli beta protein, and T4 gene 45 protein have been shown to form oligomeric rings termed sliding clamps, nothing is known about the oligomeric state of BMRF1 or whether it forms a ring. In this work, BMRF1 was purified directly from human cells infected with an adenovirus vector expressing the BMRF1 gene product. The protein was purified to near homogeneity, and examination by negative staining electron microscopy revealed large, flat, ring-shaped molecules with a diameter of 15.5 +/- 0.8 nm and a distinct 5.3-nm diameter hole in the center. The size of these rings is consistent with an oligomer of 6 monomers, nearly twice as large as the trimeric proliferating cell nuclear antigen ring. Unlike the herpes simplex virus UL42 homologue, BMRF1 was found to self-associate in solution. These findings extend the theme of polymerase accessory factors adopting ring-shaped structures and provide an example in which the ring is significantly larger than any previously described sliding clamp.
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Affiliation(s)
- Alexander M Makhov
- Department of Microbiology and Immunology, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599-7295, USA
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111
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Zhang J, Das SC, Kotalik C, Pattnaik AK, Zhang L. The latent membrane protein 1 of Epstein-Barr virus establishes an antiviral state via induction of interferon-stimulated genes. J Biol Chem 2004; 279:46335-42. [PMID: 15322136 DOI: 10.1074/jbc.m403966200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Epstein-Barr virus (EBV) infection is associated with several human cancers. Latent membrane protein 1 (LMP-1) is one of the key viral proteins required for transformation of primary B cells in vitro and establishment of EBV latency. In this report, we show that LMP-1 is able to induce the expression of several interferon (IFN)-stimulated genes (ISGs) with antiviral properties such as 2'-5' oligoadenylate synthetase (OAS), stimulated trans-acting factor of 50 kDa (STAF-50), and ISG-15. LMP-1 inhibits vesicular stomatitis virus (VSV) replication at low multiplicity of infection (0.1 pfu/cell). The antiviral effect of LMP-1 is associated with the ability of LMP-1 to induce ISGs; an LMP-1 mutant that cannot induce ISGs fails to induce an antiviral state. High levels of ISGs are expressed in EBV latency cells in which LMP-1 is expressed. EBV latency cells have antiviral activity that inhibits replication of superinfecting VSV. The antiviral activity of LMP-1 is apparently not related to IFN production in our experimental systems. In addition, EBV latency is responsive to viral superinfection: LMP-1 is induced and EBV latency is disrupted by EBV lytic replication during VSV superinfection of EBV latency cells. These data suggest that LMP-1 has antiviral effect, which may be an intrinsic part of EBV latency program to assist the establishment and/or maintenance of EBV latency.
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Affiliation(s)
- Jun Zhang
- Nebraska Center for Virology, University of Nebraska, Lincoln, NE 68588, USA
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112
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El-Guindy AS, Miller G. Phosphorylation of Epstein-Barr virus ZEBRA protein at its casein kinase 2 sites mediates its ability to repress activation of a viral lytic cycle late gene by Rta. J Virol 2004; 78:7634-44. [PMID: 15220438 PMCID: PMC434091 DOI: 10.1128/jvi.78.14.7634-7644.2004] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
ZEBRA, a member of the bZIP family, serves as a master switch between latent and lytic cycle Epstein-Barr virus (EBV) gene expression. ZEBRA influences the activity of another viral transactivator, Rta, in a gene-specific manner. Some early lytic cycle genes, such as BMRF1, are activated in synergy by ZEBRA and Rta. However, ZEBRA suppresses Rta's ability to activate a late gene, BLRF2. Here we show that this repressive activity is dependent on the phosphorylation state of ZEBRA. We find that two residues of ZEBRA, S167 and S173, that are phosphorylated by casein kinase 2 (CK2) in vitro are also phosphorylated in vivo. Inhibition of ZEBRA phosphorylation at the CK2 substrate motif, either by serine-to-alanine substitutions or by use of a specific inhibitor of CK2, abolished ZEBRA's capacity to repress Rta activation of the BLRF2 gene, but did not alter its ability to initiate the lytic cycle or to synergize with Rta in activation of the BMRF1 early-lytic-cycle gene. These studies illustrate how the phosphorylation state of a transcriptional activator can modulate its behavior as an activator or repressor of gene expression. Phosphorylation of ZEBRA at its CK2 sites is likely to play an essential role in proper temporal control of the EBV lytic life cycle.
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Affiliation(s)
- Ayman S El-Guindy
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, CT 06520-8064, USA
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113
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Lan K, Kuppers DA, Verma SC, Robertson ES. Kaposi's sarcoma-associated herpesvirus-encoded latency-associated nuclear antigen inhibits lytic replication by targeting Rta: a potential mechanism for virus-mediated control of latency. J Virol 2004; 78:6585-94. [PMID: 15163750 PMCID: PMC416549 DOI: 10.1128/jvi.78.12.6585-6594.2004] [Citation(s) in RCA: 162] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Like other herpesviruses, Kaposi's sarcoma-associated herpesvirus (KSHV, also designated human herpesvirus 8) can establish a latent infection in the infected host. During latency a small number of genes are expressed. One of those genes encodes latency-associated nuclear antigen (LANA), which is constitutively expressed in cells during latent as well as lytic infection. LANA has previously been shown to be important for the establishment of latent episome maintenance through tethering of the viral genome to the host chromosomes. Under specific conditions, KSHV can undergo lytic replication, with the production of viral progeny. The immediate-early Rta, encoded by open reading frame 50 of KSHV, has been shown to play a critical role in switching from viral latent replication to lytic replication. Overexpression of Rta from a heterologous promoter is sufficient for driving KSHV lytic replication and the production of viral progeny. In the present study, we show that LANA down-modulates Rta's promoter activity in transient reporter assays, thus repressing Rta-mediated transactivation. This results in a decrease in the production of KSHV progeny virions. We also found that LANA interacts physically with Rta both in vivo and in vitro. Taken together, our results demonstrate that LANA can inhibit viral lytic replication by inhibiting expression as well as antagonizing the function of Rta. This suggests that LANA may play a critical role in maintaining latency by controlling the switch between viral latency and lytic replication.
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Affiliation(s)
- Ke Lan
- Department of Microbiology and the Abramson Comprehensive Cancer Center, University of Pennsylvania Medical School, 201E Johnson Pavilion, 3610 Hamilton Walk, Philadelphia, PA 19104, USA
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114
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Wu FY, Wang SE, Chen H, Wang L, Hayward SD, Hayward GS. CCAAT/enhancer binding protein alpha binds to the Epstein-Barr virus (EBV) ZTA protein through oligomeric interactions and contributes to cooperative transcriptional activation of the ZTA promoter through direct binding to the ZII and ZIIIB motifs during induction of the EBV lytic cycle. J Virol 2004; 78:4847-65. [PMID: 15078966 PMCID: PMC387681 DOI: 10.1128/jvi.78.9.4847-4865.2004] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
The Epstein-Barr virus (EBV)-encoded ZTA protein interacts strongly with and stabilizes the cellular CCAAT/enhancer binding protein alpha (C/EBPalpha), leading to the induction of p21-mediated G(1) cell cycle arrest. Despite the strong interaction between these two basic leucine zipper (bZIP) family proteins, the ZTA and C/EBPalpha subunits do not heterodimerize, as indicated by an in vitro cross-linking assay with in vitro-cotranslated (35)S-labeled C/EBPalpha and (35)S-labeled ZTA protein. Instead, they evidently form a higher-order oligomeric complex that competes with C/EBPalpha binding but not with ZTA binding in electrophoretic mobility shift assays (EMSAs). Glutathione S-transferase affinity assays with mutant ZTA proteins revealed that the basic DNA binding domain and the key leucine zipper residues required for homodimerization are all required for the interaction with C/EBPalpha. ZTA is known to bind to two ZRE sites within the ZTA promoter and to positively autoregulate its own expression in transient cotransfection assays, but there is conflicting evidence about whether it does so in vivo. Examination of the proximal ZTA upstream promoter region by in vitro EMSA analysis revealed two high-affinity C/EBP binding sites (C-2 and C-3), which overlap the ZII and ZIIIB motifs, implicated as playing a key role in lytic cycle induction. A chromatin immunoprecipitation assay confirmed the in vivo binding of both endogenous C/EBPalpha and ZTA protein to the ZTA promoter after lytic cycle induction but not during the latent state in EBV-infected Akata cells. Reporter assays revealed that cotransfected C/EBPalpha activated the ZTA promoter even more effectively than cotransfected ZTA. However, synergistic activation of the ZTA promoter was not observed when ZTA and C/EBPalpha were cotransfected together in either HeLa or DG75 cells. Mutagenesis of either the ZII or the ZIIIB sites in the ZTA promoter strongly reduced C/EBPalpha transactivation, suggesting that these sites act cooperatively. Furthermore, the introduction of exogenous C/EBPalpha into EBV-infected HeLa-BX1 cells induced endogenous ZTA mRNA and protein expression, as demonstrated by both reverse transcription-PCR and immunoblotting assays. Finally, double-label immunofluorescence assays suggested that EAD protein expression was activated even better than ZTA expression in latently infected C/EBPalpha-transfected Akata cells, perhaps because of the presence of a strong B-cell-specific repressed chromatin conformation on the ZTA promoter itself during EBV latency.
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Affiliation(s)
- Frederick Y Wu
- Molecular Virology Laboratories, Department of Pharmacology and Molecular Sciences, School of dicine, The Johns Hopkins University, Baltimore, Maryland 21231-1000, USA
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115
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AuCoin DP, Colletti KS, Cei SA, Papousková I, Tarrant M, Pari GS. Amplification of the Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8 lytic origin of DNA replication is dependent upon a cis-acting AT-rich region and an ORF50 response element and the trans-acting factors ORF50 (K-Rta) and K8 (K-bZIP). Virology 2004; 318:542-55. [PMID: 14972523 DOI: 10.1016/j.virol.2003.10.016] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2003] [Revised: 10/14/2003] [Accepted: 10/15/2003] [Indexed: 11/22/2022]
Abstract
Kaposi's sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus 8 (HHV8), has significant sequence homology to Epstein-Barr virus (EBV). In cell culture, HHV8 is primarily latent, and viral genes associated with lytic replication are not expressed. Two lytic origins of DNA replication (oriLyt) are present within the HHV8 genome and are composed of an AT-rich region adjacent to GC-rich DNA sequences. We have now identified essential cis- and trans-acting elements required for oriLyt-dependent DNA replication. The transient replication assay was used to show that two AT-rich elements, three consensus AP1 transcription factor-binding sites, an ORF50 response element (RE), and a consensus TATA box motif are essential for efficient origin-dependent DNA replication. Transient transfection of luciferase reporter constructs indicated that the downstream region of the HHV8 oriLyt responds to ORF50 and suggests that part of the oriLyt may be an enhancer/promoter. In addition, a transient cotransfection-replication assay elucidated the set of trans-acting factors required for lytic DNA replication. These factors consist of homologues to the core replication proteins: ORF6 (ssDNA binding protein), ORF9 (DNA polymerase), ORF40-41 (primase-associated factor), ORF44 (helicase), ORF56 (primase), and ORF59 (polymerase processivity factor) common to all herpesviruses along with ORF50 (K-Rta) and K8 (K-bZIP).
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Affiliation(s)
- David P AuCoin
- Department of Microbiology and the Cell and Molecular Biology Program, University of Nevada School of Medicine, Reno, NV 89557, USA
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116
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Izumiya Y, Lin SF, Ellison TJ, Levy AM, Mayeur GL, Izumiya C, Kung HJ. Cell cycle regulation by Kaposi's sarcoma-associated herpesvirus K-bZIP: direct interaction with cyclin-CDK2 and induction of G1 growth arrest. J Virol 2003; 77:9652-61. [PMID: 12915577 PMCID: PMC187423 DOI: 10.1128/jvi.77.17.9652-9661.2003] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In order to cope with hostile host environments, many viruses have developed strategies to perturb the cellular machinery to suit their replication needs. Some herpesvirus genes protect cells from undergoing apoptosis to prolong the lives of infected cells, while others, such as Epstein-Barr virus Zta, slow down the G(1)/S transition phase to allow ample opportunity for transcription and translation of viral genes before the onset of cellular genomic replication. In this study, we investigated whether Kaposi's sarcoma-associated herpesvirus (KSHV) K-bZIP, a homologue of the Epstein-Barr virus transcription factor BZLF1 (Zta), plays a role in cell cycle regulation. Here we show that K-bZIP physically associates with cyclin-CDK2 and downmodulates its kinase activity. The association can be detected in the natural environment of KSHV-infected cells without artificial overexpression of either component. With purified protein, it can be shown that the interaction between K-bZIP and cyclin-CDK2 is direct and that K-bZIP alone is sufficient to inhibit CDK2 activity. The interacting domain of K-bZIP has been mapped to the basic region. The result of these associations is a prolonged G(1) phase, accompanied by the induction of p21 and p27 in a naturally infected B-cell line. Thus, in addition to the previously described transcription and genome replication functions, a new role of K-bZIP in KSHV replication is identified in this report.
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Affiliation(s)
- Yoshihiro Izumiya
- Department of Biological Chemistry, School of Medicine, University of California, Davis, UC Davis Cancer Center, Sacramento, California 95817, USA
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117
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Schäfer A, Lengenfelder D, Grillhösl C, Wieser C, Fleckenstein B, Ensser A. The latency-associated nuclear antigen homolog of herpesvirus saimiri inhibits lytic virus replication. J Virol 2003; 77:5911-25. [PMID: 12719584 PMCID: PMC154051 DOI: 10.1128/jvi.77.10.5911-5925.2003] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Herpesvirus saimiri (HVS), a T-lymphotropic tumor virus of neotropical primates, and the Kaposi's sarcoma-associated human herpesvirus 8 (KSHV) belong to the gamma-(2)-herpesvirus (Rhadinovirus) subfamily and share numerous features of genome structure and organization. The KSHV latency-associated nuclear antigen (LANA) protein appears to be relevant for viral persistence, latency, and transformation. It binds to DNA, colocalizes with viral episomal DNA, and presumably mediates efficient persistence of viral genomes. LANA further represses the transcriptional and proapoptotic activities of the p53 tumor suppressor protein. Here we report on the ORF73 gene of HVS strain C488, which is the positional and structural homolog of KSHV LANA. The ORF73 gene in OMK cells can encode a 62-kDa protein that localizes to the nucleus in a pattern similar to that of LANA. We show that the ORF73 gene product can regulate viral gene expression by acting as a transcriptional modulator of latent and lytic viral promoters. To define the HVS ORF73 function in the background of a replication-competent virus, we constructed a viral mutant that expresses ORF73 under the transcriptional control of a mifepristone (RU-486)-inducible promoter. The HVS ORF73 gene product efficiently suppresses lytic viral replication in permissive cells, indicating that it defines a critical control point between viral persistence and lytic replication.
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Affiliation(s)
- Alexandra Schäfer
- Institut für Klinische und Molekulare Virologie, Universität Erlangen-Nürnberg, 91054 Erlangen, Germany
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118
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Lin CL, Li H, Wang Y, Zhu FX, Kudchodkar S, Yuan Y. Kaposi's sarcoma-associated herpesvirus lytic origin (ori-Lyt)-dependent DNA replication: identification of the ori-Lyt and association of K8 bZip protein with the origin. J Virol 2003; 77:5578-88. [PMID: 12719550 PMCID: PMC154033 DOI: 10.1128/jvi.77.10.5578-5588.2003] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Herpesviruses utilize different origins of replication during lytic versus latent infection. Latent DNA replication depends on host cellular DNA replication machinery, whereas lytic cycle DNA replication requires virally encoded replication proteins. In lytic DNA replication, the lytic origin (ori-Lyt) is bound by a virus-specified origin binding protein (OBP) that recruits the core replication machinery. In this report, we demonstrated that DNA sequences in two noncoding regions of the Kaposi's sarcoma-associated herpesvirus (KSHV) genome, between open reading frames (ORFs) K4.2 and K5 and between K12 and ORF71, are able to serve as origins for lytic cycle-specific DNA replication. The two ori-Lyt domains share an almost identical 1,153-bp sequence and a 600-bp downstream GC-rich repeat sequence, and the 1.7-kb DNA sequences are sufficient to act as a cis signal for replication. We also showed that an AT-palindromic sequence in the ori-Lyt domain is essential for the DNA replication. In addition, a virally encoded bZip protein, namely K8, was found to bind to a DNA sequence within the ori-Lyt by using a DNA binding site selection assay. The binding of K8 to this region was confirmed in cells by using a chromatin immunoprecipitation method. Further analysis revealed that K8 binds to an extended region, and the entire region is 100% conserved between two KSHV ori-Lyt's. K8 protein displays significant similarity to the Zta protein of Epstein-Barr virus (EBV), which is a known OBP of EBV. This notion, together with the ability of K8 to bind to the KSHV ori-Lyt, suggests that K8 may function as an OBP in KSHV.
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Affiliation(s)
- Cui Li Lin
- Department of Microbiology, University of Pennsylvania School of Dental Medicine, Philadelphia, Pennsylvania 19104, USA
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119
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Reid GG, Ellsmore V, Stow ND. An analysis of the requirements for human cytomegalovirus oriLyt-dependent DNA synthesis in the presence of the herpes simplex virus type 1 replication fork proteins. Virology 2003; 308:303-16. [PMID: 12706080 DOI: 10.1016/s0042-6822(03)00005-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Activation of the human cytomegalovirus (HCMV) origin of replication (oriLyt) was previously demonstrated in transient transfection assays in permissive human fetal fibroblasts and nonpermissive Vero cells, and shown to require six viral proteins that function at the replication fork plus a number of HCMV products that perform auxiliary roles. The six replication fork proteins could be substituted by their Epstein-Barr virus homologues. In this paper we demonstrate that the corresponding herpes simplex virus type 1 replication fork proteins can similarly replace those of HCMV in Vero cells. Under these conditions the essential auxiliary functions were mapped to two plasmids: pSVH (containing the major immediate-early locus) and pZP8 (spanning genes UL32-UL38). Mutants of pSVH and pZP8 and cloned cDNAs encoding the IE1-p72 and IE2-p86 proteins were tested for their ability to support DNA synthesis. The results showed that IE2-p86 was necessary for activation of the origin, and that the UL37x1 and IE1-p72 products exerted strong stimulatory effects. In contrast to the previous work, omission of the UL84 protein had no effect upon oriLyt-dependent DNA synthesis.
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Affiliation(s)
- G Gordon Reid
- MRC Virology Unit, Institute of Virology, Church Street, Glasgow G11 5JR, UK
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120
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Prince S, Keating S, Fielding C, Brennan P, Floettmann E, Rowe M. Latent membrane protein 1 inhibits Epstein-Barr virus lytic cycle induction and progress via different mechanisms. J Virol 2003; 77:5000-7. [PMID: 12663807 PMCID: PMC152124 DOI: 10.1128/jvi.77.8.5000-5007.2003] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Epstein-Barr virus (EBV) is a potent growth-transforming agent of human B cells. It has previously been shown that viral latent membrane protein 1 (LMP1) is essential for EBV-induced transformation of normal B cells and contributes to maintenance of latency in vitro. Using the EBV-positive Burkitt's lymphoma line P3HR1-c16, which lacks LMP1 during latency and which can readily be activated into virus-productive lytic cycle, we found that LMP1 inhibits lytic cycle induction via the transcription factor NF-kappa B. In addition, LMP1 inhibits lytic cycle progress via two distinct NF-kappa B-independent mechanisms: one involving the cytosolic C-terminal activating regions and the other involving the transmembrane region of LMP1. These findings indicate that in B cells EBV self-limits its lytic cycle via three distinct LMP1-mediated mechanisms.
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Affiliation(s)
- Stuart Prince
- Section of Infection and Immunity, University of Wales College of Medicine, Cardiff CF14 4XX, United Kingdom
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121
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Hiriart E, Farjot G, Gruffat H, Nguyen MVC, Sergeant A, Manet E. A novel nuclear export signal and a REF interaction domain both promote mRNA export by the Epstein-Barr virus EB2 protein. J Biol Chem 2003; 278:335-42. [PMID: 12403791 DOI: 10.1074/jbc.m208656200] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A striking characteristic of mRNA export factors is that they shuttle continuously between the cytoplasm and the nucleus. This shuttling is mediated by specific factors interacting with peptide motifs called nuclear export signals (NES) and nuclear localization signals. We have identified a novel CRM-1-independent transferable NES and two nuclear localization signals in the Epstein-Barr virus mRNA export factor EB2 (also called BMLF1, Mta, or SM) localized at the N terminus of the protein between amino acids 61 and 146. We have also found that a previously described double NES (amino acids 213-236) does not mediate the nuclear shuttling of EB2, but is an interaction domain with the cellular export factor REF in vitro. This newly characterized REF interaction domain is essential for EB2-mediated mRNA export. Accordingly, in vivo, EB2 is found in complexes containing REF as well as the cellular factor TAP. However, these interactions are RNase-sensitive, suggesting that the RNA is an essential component of these complexes.
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Affiliation(s)
- Edwige Hiriart
- Unité de Virologie Humaine, U412 INSERM, Ecole Normale Supérieure de Lyon, 46 allée d'Italie, 69364 Lyon Cedex 07, France
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122
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Wu FY, Chen H, Wang SE, ApRhys CMJ, Liao G, Fujimuro M, Farrell CJ, Huang J, Hayward SD, Hayward GS. CCAAT/enhancer binding protein alpha interacts with ZTA and mediates ZTA-induced p21(CIP-1) accumulation and G(1) cell cycle arrest during the Epstein-Barr virus lytic cycle. J Virol 2003; 77:1481-500. [PMID: 12502863 PMCID: PMC140856 DOI: 10.1128/jvi.77.2.1481-1500.2003] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Cellular CCAAT/enhancer binding protein alpha (C/EBPalpha) promotes cellular differentiation and has antimitotic activities involving cell cycle arrest at G(1)/S through stabilization of p21(CIP-1)/WAF1 and through transcriptional activation of the p21 promoter. The Epstein-Barr virus lytic-cycle transactivator protein ZTA is known to arrest the host cell cycle at G(1)/S via a p53-independent p21 pathway, but the detailed molecular mechanisms involved have not been defined. To further evaluate the role of ZTA in cell cycle arrest, we constructed a recombinant adenovirus vector expressing ZTA (Ad-ZTA), whose level of expression at a low multiplicity of infection in normal human diploid fibroblast (HF) cells was lower than or equal to the physiological level seen in Akata cells lytically induced by EBV (EBV-Akata cells). Fluorescence-activated cell sorting analysis of HF cells infected with Ad-ZTA confirmed that G(1)/S cell cycle arrest occurred in the majority of ZTA-positive cells, but not with an adenovirus vector expressing green fluorescent protein. Double-label immunofluorescence assays (IFA) performed with Ad-ZTA-infected HF cells revealed that only ZTA-positive cells induced the expression of both endogenous C/EBPalpha and p21 and blocked the progression into S phase, as detected by a lack of incorporation of bromodeoxyuridine. The stimulation of endogenous ZTA protein expression either through treatment with tetradecanoyl phorbol acetate in D98/HR1 cells or through B-cell receptor cross-linking with anti-immunoglobulin G antibody in EBV-Akata cells also coincided with the induction of both C/EBPalpha and p21 and their mRNAs, as assayed by Northern blot, Western blot, and IFA experiments. Mechanistically, the ZTA protein proved to directly interact with C/EBPalpha by coimmunoprecipitation in EBV-Akata cells and with DNA-bound C/EBPalpha in electrophoretic mobility shift assay experiments, and the in vitro interaction domain encompassed the basic leucine zipper domain of ZTA. ZTA also specifically protected C/EBPalpha from degradation in a protein stability assay with a non-EBV-induced Akata cell proteasome extract. Furthermore, both C/EBPalpha and ZTA were found to specifically associate with the C/EBPalpha promoter in chromatin immunoprecipitation assays, but the interaction with ZTA appeared to be mediated by C/EBPalpha because it was abolished by clearing with anti-C/EBPalpha antibody. ZTA did not bind to or activate the C/EBPalpha promoter directly but cooperatively enhanced the positive autoregulation of the C/EBPalpha promoter by cotransfected C/EBPalpha in transient luciferase reporter gene assays with Vero and HeLa cells as well as with DG75 B lymphocytes. Similarly, ZTA alone had little effect on the p21 promoter in transient reporter gene assays, but in the presence of cotransfected C/EBPalpha, ZTA enhanced the level of C/EBPalpha activation. This effect proved to require a previously unrecognized region in the proximal p21 promoter that contains three high-affinity C/EBPalpha binding sites. Finally, in C/EBPalpha-deficient mouse embryonic fibroblasts (MEF), Ad-ZTA was unable to induce either p21 or G(1) arrest, whereas it was able to induce both in wild-type MEF. Overall, we conclude that C/EBPalpha is essential for at least one pathway of ZTA-induced G(1) arrest during EBV lytic-cycle DNA replication and that this process involves a physical piggyback interaction between ZTA and C/EBPalpha leading to greatly enhanced C/EBPalpha and p21 levels through both transcriptional and posttranslational mechanisms.
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Affiliation(s)
- Frederick Y Wu
- Molecular Virology Laboratories, Department of Pharmacology and Molecular Sciences, School of Medicine, The Johns Hopkins University, Baltimore, Maryland 21231-1000, USA
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123
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Feng WH, Westphal E, Mauser A, Raab-Traub N, Gulley ML, Busson P, Kenney SC. Use of adenovirus vectors expressing Epstein-Barr virus (EBV) immediate-early protein BZLF1 or BRLF1 to treat EBV-positive tumors. J Virol 2002; 76:10951-9. [PMID: 12368338 PMCID: PMC136642 DOI: 10.1128/jvi.76.21.10951-10959.2002] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Epstein-Barr virus (EBV) genome is present in a variety of tumor types, including virtually all undifferentiated nasopharyngeal carcinomas (NPC) and a portion of gastric carcinomas. The uniform presence of the EBV genome in certain tumors (versus only a very small number of normal B cells) suggests that novel therapies which specifically target EBV-positive cells for destruction might be effective for treating such tumors. Although the great majority of EBV-positive tumor cells are infected with one of the latent forms of EBV infection, expression of either viral immediate-early protein (BZLF1 or BRLF1) is sufficient to convert the virus to the lytic form of infection. Induction of the lytic form of EBV infection could potentially result in death of the tumor cell. Here we have examined the efficacy of adenovirus vectors expressing the BZLF1 or BRLF1 proteins for treatment of EBV-positive epithelial tumors. The BZLF1 and BRLF1 vectors induced preferential killing of EBV-positive, versus EBV-negative, gastric carcinoma cells in vitro. Infection of C18 NPC tumors (grown in nude mice) with either the BZLF1 or BRLF1 vector, but not a control adenovirus vector, induced expression of early lytic EBV genes in tumor cells. Injection of C18 tumors with the BZLF1 or BRLF1 adenovirus vector, but not the control vector, also significantly inhibited growth of the tumors in nude mice. The addition of ganciclovir did not significantly affect the antitumor effect of the BZLF1 and BRLF1 adenovirus vectors. These results suggest a potential cancer therapy against EBV-related tumors.
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Affiliation(s)
- Wen-hai Feng
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, North Carolina 27599-7295, USA
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124
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Gruffat H, Batisse J, Pich D, Neuhierl B, Manet E, Hammerschmidt W, Sergeant A. Epstein-Barr virus mRNA export factor EB2 is essential for production of infectious virus. J Virol 2002; 76:9635-44. [PMID: 12208942 PMCID: PMC136519 DOI: 10.1128/jvi.76.19.9635-9644.2002] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The splicing machinery which positions a protein export complex near the exon-exon junction mediates nuclear export of mRNAs generated from intron-containing genes. Many Epstein-Barr virus (EBV) early and late genes are intronless, and an alternative pathway, independent of splicing, must export the corresponding mRNAs. Since the EBV EB2 protein induces the cytoplasmic accumulation of intronless mRNA, it is tempting to speculate that EB2 is a viral adapter involved in the export of intronless viral mRNA. If this is true, then the EB2 protein is essential for the production of EBV infectious virions. To test this hypothesis, we generated an EBV mutant in which the BMLF1 gene, encoding the EB2 protein, has been deleted (EBV(BMLF1-KO)). Our studies show that EB2 is necessary for the production of infectious EBV and that its function cannot be transcomplemented by a cellular factor. In the EBV(BMLF1-KO) 293 cells, oriLyt-dependent DNA replication was greatly enhanced by EB2. Accordingly, EB2 induced the cytoplasmic accumulation of a subset of EBV early mRNAs coding for essential proteins implicated in EBV DNA replication during the productive cycle. Two herpesvirus homologs of the EB2 protein, the herpes simplex virus type 1 protein ICP27 and, the human cytomegalovirus protein UL69, only partly rescued the phenotype of the EBV(BMLF1-KO) mutant, indicating that some EB2 functions in virus production cannot be transcomplemented by ICP27 and UL69.
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Affiliation(s)
- Henri Gruffat
- Laboratoire de Virologie Humaine, INSERM U412, ENS-Lyon, F-69364 Lyon Cedex 07, France.
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125
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Keating S, Prince S, Jones M, Rowe M. The lytic cycle of Epstein-Barr virus is associated with decreased expression of cell surface major histocompatibility complex class I and class II molecules. J Virol 2002; 76:8179-88. [PMID: 12134023 PMCID: PMC155144 DOI: 10.1128/jvi.76.16.8179-8188.2002] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Human herpesviruses utilize an impressive range of strategies to evade the immune system during their lytic replicative cycle, including reducing the expression of cell surface major histocompatibility complex (MHC) and immunostimulatory molecules required for recognition and lysis by virus-specific cytotoxic T cells. Study of possible immune evasion strategies by Epstein-Barr virus (EBV) in lytically infected cells has been hampered by the lack of an appropriate permissive culture model. Using two-color immunofluorescence staining of cell surface antigens and EBV-encoded lytic cycle antigens, we examined EBV-transformed B-cell lines in which a small subpopulation of cells had spontaneously entered the lytic cycle. Cells in the lytic cycle showed a four- to fivefold decrease in cell surface expression of MHC class I molecules relative to that in latently infected cells. Expression of MHC class II molecules, CD40, and CD54 was reduced by 40 to 50% on cells in the lytic cycle, while no decrease was observed in cell surface expression of CD19, CD80, and CD86. Downregulation of MHC class I expression was found to be an early-lytic-cycle event, since it was observed when progress through late lytic cycle was blocked by treatment with acyclovir. The immediate-early transactivator of the EBV lytic cycle, BZLF1, did not directly affect expression of MHC class I molecules. However, BZLF1 completely inhibited the upregulation of MHC class I expression mediated by the EBV cell-transforming protein, LMP1. This novel function of BZLF1 elucidates the paradox of how MHC class I expression can be downregulated when LMP1, which upregulates MHC class I expression in latent infection, remains expressed in the lytic cycle.
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Affiliation(s)
- Sinéad Keating
- Section of Infection and Immunity, University of Wales College of Medicine, Cardiff CF14 4XX, United Kingdom
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126
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Abstract
The human cytomegalovirus (HCMV) UL70, UL102, and UL105 genes are predicted to encode essential proteins that assemble the replicative helicase-primase complex based on sequence and genome position similarities to putative herpes simplex virus type 1 (HSV-1) counterparts. Consistent with this prediction, they are required for transient complementation of DNA synthesis. However, little is known about their physical interactions and biochemical activities, primarily because of their restricted expression in HCMV-infected cells. To look for assembly of the predicted complexes, we prepared rabbit polyclonal antisera and used Semliki Forest Virus (SFV) vectors to express untagged and glutathione-S-transferase (GST)-tagged UL70, UL102 and UL105 proteins. The UL70 and UL105 proteins co-purified with the GST-tagged UL102 protein from triply-infected baby hamster kidney cells (BHK-21), and pUL70, but not pUL105, co-purified with pGST-UL102 from dually infected BHK-21 cells. In immunoprecipitation experiments with untagged SFV-expressed proteins, pUL70 or pUL105 coprecipitated with pUL102, pUL102 or pUL70 co-precipitated with pUL105; and pUL102 or pUL105 coprecipitated with pUL70. Comparison of the GST-pull down and immunoprecipitation experiments suggested that the amino-terminal GST-tag interfered with certain pairwise interactions. These results support the prediction that the HCMV helicase-primase proteins assemble a three-protein heteromeric complex, and show that each protein contacts both partners.
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Affiliation(s)
- Timothy P McMahon
- Department of Biomedical Sciences, University at Albany School of Public Health, Albany, NY 12201-2002, USA
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127
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Affiliation(s)
- T Tsurumi
- Division of Virology, Aichi Cancer Center Research Institute, 1-1, Kanokoden, Chikusa-ku, Nagoya 464-8681, Japan
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128
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Coulter LJ, Reid HW. Isolation and expression of three open reading frames from ovine herpesvirus-2. J Gen Virol 2002; 83:533-543. [PMID: 11842248 DOI: 10.1099/0022-1317-83-3-533] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Ovine herpesvirus-2 (OvHV-2), a member of the gammaherpesviruses (genus Rhadinovirus), asymptomatically infects its natural host, the sheep, but causes malignant catarrhal fever (MCF) in susceptible hosts, such as cattle, deer and pigs. A permissive cell culture system for virus replication has not been identified but viral DNA is present within lymphoblastoid cell lines (LCLs) established from cases of MCF. During this study, a cDNA expression library generated from LCLs was screened with sheep sera and two cDNAs were isolated. One cDNA contained two open reading frames (ORFs) that show similarity to ORFs 58 and 59 of alcelaphine herpesvirus-1 (AlHV-1), a closely related gammaherpesvirus that also causes MCF. Both ORFs 58 and 59 are conserved throughout the gammaherpesviruses. ORF 58 is predicted to be a membrane protein, while ORF 59 has been shown to be an early lytic gene that functions as a DNA polymerase processivity factor. The second cDNA clone contained a partial ORF showing limited similarity to AlHV-1 ORF 73, a homologue of the latency-associated nuclear antigen of human herpesvirus-8, which is associated with latent infections. The full-length OvHV-2 ORF 73 was cloned subsequently by PCR. The ORFs isolated from the library were cloned into a bacterial expression vector and the recombinant proteins tested for their reactivity to sera from OvHV-2-infected animals. An ORF 59 fusion protein was recognized specifically by sera from OvHV-2-infected cattle and will be used to develop a sero-diagnostic test.
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Affiliation(s)
- Lesley J Coulter
- Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik, Midlothian EH26 0PZ, UK1
| | - Hugh W Reid
- Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik, Midlothian EH26 0PZ, UK1
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129
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Gershburg E, Pagano JS. Phosphorylation of the Epstein-Barr virus (EBV) DNA polymerase processivity factor EA-D by the EBV-encoded protein kinase and effects of the L-riboside benzimidazole 1263W94. J Virol 2002; 76:998-1003. [PMID: 11773375 PMCID: PMC135851 DOI: 10.1128/jvi.76.3.998-1003.2002] [Citation(s) in RCA: 65] [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
A member of the family of L-riboside benzimidazole compounds, 1263W94, was shown recently to inhibit replication of Epstein-Barr virus (EBV) (V. L. Zacny, E. Gershburg, M. G. Davis, K. K. Biron, and J. S. Pagano, J. Virol. 73:7271-7277, 1999). In the present report the effect of 1263W94 on the phosphorylation pattern of the EBV DNA polymerase processivity factor, EA-D, during viral reactivation in latently EBV-infected Akata cells is analyzed. This pattern specifically changes with progression of cytolytic infection. In the presence of 1263W94 the appearance of the hyperphosphorylated form of EA-D is mainly affected. Next, coexpression of the cloned EBV-encoded protein kinase (EBV PK), BGLF4, with EA-D demonstrated the ability of EBV PK to phosphorylate EA-D to its hyperphosphorylated form in transient assays. However, the phosphorylation of EA-D was not directly inhibited by 1263W94 in these coexpression assays. The results indicate that the EBV PK appears to be responsible for the hyperphosphorylation of EA-D, imply that the phosphorylation status of EA-D is important for viral replication, and suggest that 1263W94 acts at a level other than direct inhibition of EA-D phosphorylation by EBV PK.
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Affiliation(s)
- Edward Gershburg
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA
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130
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AuCoin DP, Pari GS. The human herpesvirus-8 (Kaposi's sarcoma-associated herpesvirus) ORF 40/41 region encodes two distinct transcripts. J Gen Virol 2002; 83:189-193. [PMID: 11752716 DOI: 10.1099/0022-1317-83-1-189] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The human herpesvirus-8 (HHV-8) locus encoding ORFs 40/41 is a candidate homologue for the Epstein-Barr virus BBLF 2/3 gene, which encodes the putative primase-associated factor. Northern blot data revealed that two transcripts originated from the HHV-8 ORF 40/41 region. The sizes of these transcripts (2.2 and 0.7 kb) suggested that one transcript was the result of a spliced form of ORFs 40 and 41 and the second transcript originated from a region within ORF 41. cDNA sequence and 5' RACE analysis revealed the removal of an intron between ORFs 40 and 41 and a transcriptional start site 82 nt upstream of ORF 40. The start of transcription for the smaller transcript was mapped to within ORF 41. Regions upstream of the transcriptional start sites were subcloned into a luciferase reporter vector, and transient luciferase assays indicated that distinct promoters drive the expression of each transcript.
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Affiliation(s)
- David P AuCoin
- Department of Microbiology and the Cell and Molecular Biology Program, School of Medicine, University of Nevada-Reno, Howard Building, Reno, NV 89557, USA1
| | - Gregory S Pari
- Department of Microbiology and the Cell and Molecular Biology Program, School of Medicine, University of Nevada-Reno, Howard Building, Reno, NV 89557, USA1
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131
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Morrison TE, Mauser A, Wong A, Ting JP, Kenney SC. Inhibition of IFN-gamma signaling by an Epstein-Barr virus immediate-early protein. Immunity 2001; 15:787-99. [PMID: 11728340 DOI: 10.1016/s1074-7613(01)00226-6] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Viruses have evolved elaborate mechanisms to target many aspects of the host's immune response. The cytokine IFN-gamma plays a central role in resistance of the host to infection via direct antiviral effects as well as modulation of the immune response. In this study, we demonstrate that the Epstein-Barr virus (EBV) immediate-early protein, BZLF1, inhibits the IFN-gamma signaling pathway. BZLF1 decreases the ability of IFN-gamma to activate a variety of important downstream target genes, such as IRF-1, p48, and CIITA, and prevents IFN-gamma-induced class II MHC surface expression. Additionally, BZLF1 inhibits IFN-gamma-induced STAT1 tyrosine phosphorylation and nuclear translocation. Finally, we demonstrate that BZLF1 decreases expression of the IFN-gamma receptor, suggesting a mechanism by which EBV may escape antiviral immune responses during primary infection.
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Affiliation(s)
- T E Morrison
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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132
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Delecluse HJ, Kost M, Feederle R, Wilson L, Hammerschmidt W. Spontaneous activation of the lytic cycle in cells infected with a recombinant Kaposi's sarcoma-associated virus. J Virol 2001; 75:2921-8. [PMID: 11222717 PMCID: PMC115918 DOI: 10.1128/jvi.75.6.2921-2928.2001] [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
The genetic analysis of human herpesvirus 8 (HHV8), also termed Kaposi's sarcoma-associated virus, has been hampered by severe difficulties in producing infectious viral particles and modifying the viral genome. In this article, we report the successful cloning of the HHV8 complete genome onto a prokaryotic F-plasmid replicon which allows the propagation of the recombinant viral DNA in Escherichia coli. The insertion of the F-plasmid into the HHV8 genome interrupts the ORF56 gene, whose expression product-by homology with the Epstein-Barr virus BSLF1 gene--is supposed to be necessary for lytic DNA replication. After introduction of the recombinant HHV8 DNA into 293 cells, early viral antigens are expressed, suggesting that spontaneous lytic replication is initiated. However, completion of the lytic program is prevented by the absence of the ORF56 protein, and a quasi-latent state is established. Upon reintroduction of the ORF56 viral gene, the block is overcome and infectious HHV8 virions are produced. As the recombinant HHV8 genome can be easily modified in E. coli, this experimental system opens the way to an extensive genetic analysis of other HHV8 functions.
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Affiliation(s)
- H J Delecluse
- Department of Gene Vectors, GSF-National Research Center for Environment and Health, D-81377 Munich, Germany.
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133
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Wu FY, Ahn JH, Alcendor DJ, Jang WJ, Xiao J, Hayward SD, Hayward GS. Origin-independent assembly of Kaposi's sarcoma-associated herpesvirus DNA replication compartments in transient cotransfection assays and association with the ORF-K8 protein and cellular PML. J Virol 2001; 75:1487-506. [PMID: 11152521 PMCID: PMC114054 DOI: 10.1128/jvi.75.3.1487-1506.2001] [Citation(s) in RCA: 132] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Six predicted Kaposi's sarcoma virus herpesvirus (KSHV) proteins have homology with other well-characterized herpesvirus core DNA replication proteins and are expected to be essential for viral DNA synthesis. Intact Flag-tagged protein products from all six were produced from genomic expression vectors, although the ORF40/41 transcript encoding a primase-helicase component proved to be spliced with a 127-bp intron. The intracellular localization of these six KSHV replication proteins and the mechanism of their nuclear translocation were investigated. SSB (single-stranded DNA binding protein, ORF6) and PPF (polymerase processivity factor, ORF59) were found to be intrinsic nuclear proteins, whereas POL (polymerase, ORF9), which localized in the cytoplasm on its own, was translocated to the nucleus when cotransfected with PPF. PAF (primase-associated factor, ORF40/41), a component of the primase-helicase tripartite subcomplex together with PRI (primase, ORF56) and HEL (helicase, ORF44), required the presence of all five other replication proteins for efficient nuclear translocation. Surprisingly, even in the absence of a lytic cycle replication origin (ori-Lyt) and any known initiator or origin binding protein, the protein products of all six KSHV core replication genes cooperated in a transient cotransfection assay to form large globular shaped pseudo-replication compartments (pseudo-RC), which excluded cellular DNA. These pseudo-RC structures were confirmed to include POL, SSB, PRI, and PAF but did not contain any newly synthesized DNA. Similar to the human cytomegalovirus system, the peripheries of these KSHV pre-RC were also found to be surrounded by punctate PML oncogenic domains (PODs). Furthermore, by transient cotransfection, the six KSHV core replication machinery proteins successfully replicated a plasmid containing EBV ori-Lyt in the presence of the Epstein-Barr virus-encoded DNA binding initiator protein, ZTA. The KSHV-encoded K8 (ORF-K8) protein, which is a distant evolutionary homologue to ZTA, was incorporated into pseudo-RC structures formed by transient cotransfection with the six core KSHV replication genes. However, unlike ZTA, K8 displayed a punctate nuclear pattern both in transfected cells and at early stages of lytic infection and colocalized with the cellular PML proteins in PODs. Finally, K8 was also found to accumulate in functional viral RC, detected by incorporation of pulse-labeled bromodeoxyuridine into newly synthesized DNA in both tetradecanoyl phorbol acetate-induced JSC-1 primary effusion lymphoblasts and in KSHV lytically infected endothelial cells.
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Affiliation(s)
- F Y Wu
- Molecular Virology Laboratories, Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21231-1000, USA
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134
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Coulter LJ, Wright H, Reid HW. Molecular genomic characterization of the viruses of malignant catarrhal fever. J Comp Pathol 2001; 124:2-19. [PMID: 11428184 DOI: 10.1053/jcpa.2000.0524] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- L J Coulter
- Moredun Research Institute, International Research Centre, Pentlands Science Park, Bush Loan, Penicuik, Midlothian EH26 0PZ, UK
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135
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Abstract
Several of the gamma-herpesviruses are known to have cellular transforming and oncogenic properties. The genomes of eight distinct gamma-herpesviruses have been sequenced, and the resulting database of information has enabled the identification of genetic similarities and differences between evolutionarily closely related and distant viruses of the subfamily and between the gamma-herpesviruses and other members of the herpesvirus family. The recognition of coincident loci of genetic divergence between individual gamma-herpesviruses and the identification of novel genes and cellular gene homologues in these genomic regions has delineated a subset of genes that are likely to contribute to the unique biological properties of these viruses. These genes, together with gamma-herpesvirus conserved genes not found in viruses outside the family, might be responsible for virus specific pathogenicity and pathogenic effects, such as viral associated neoplasia, characteristic of the subfamily. The presence of the gamma-herpesvirus major divergent genomic loci and the apparent increased mutational frequencies of homologous genes (where they occur) within these regions, indicates that these loci possess particular features that drive genetic divergence. Whatever the mechanisms underlying this phenomenon, it potentially provides the basis for the relatively rapid adaptation and evolution of gamma-herpesviruses and the diversity of biological and pathogenic properties.
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Affiliation(s)
- J Nicholas
- Department of Oncology, John Hopkins University School of Medicine, Baltimore, Maryland 21231, USA.
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136
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Yokoyama N, Hirata M, Ohtsuka K, Nishiyama Y, Fujii K, Fujita M, Kuzushima K, Kiyono T, Tsurumi T. Co-expression of human chaperone Hsp70 and Hsdj or Hsp40 co-factor increases solubility of overexpressed target proteins in insect cells. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1493:119-24. [PMID: 10978513 DOI: 10.1016/s0167-4781(00)00170-6] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The insect-baculovirus expression system has proved particularly useful for producing recombinant proteins that are biologically active. Overexpression of foreign proteins using the recombinant baculovirus system is often accompanied by aggregation of the overexpressed protein, which is thought to be due to a limitation of the translated protein folding in the infected cells. Co-infection of a recombinant baculovirus capable of expressing the human chaperone Hsp70 slightly increased the solubility of the overexpressed Epstein-Barr virus replication protein, BZLF1. Co-expression of Hsp70 and its co-factor, Hsdj or Hsp40, was here found to improve the solubility of the target protein several fold. Thus, a baculovirus expression system producing these molecular chaperones may find application for improved production of target foreign gene products in insect cells.
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Affiliation(s)
- N Yokoyama
- Division of Virology, Aichi Cancer Center Research Institute, 1-1 Kanokoden, Chikusa-ku, Nagoya 464-8681, Japan
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137
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Feederle R, Kost M, Baumann M, Janz A, Drouet E, Hammerschmidt W, Delecluse HJ. The Epstein-Barr virus lytic program is controlled by the co-operative functions of two transactivators. EMBO J 2000; 19:3080-9. [PMID: 10856251 PMCID: PMC203345 DOI: 10.1093/emboj/19.12.3080] [Citation(s) in RCA: 322] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
The propagation of herpesviruses has long been viewed as a temporally regulated sequential process that results from the consecutive expression of specific viral transactivators. As a key step in this process, lytic viral DNA replication is considered as a checkpoint that controls the expression of the late structural viral genes. In a novel genetic approach, we show that both hypotheses do not hold true for the Epstein-Barr virus (EBV). The study of viral mutants of EBV in which the early genes BZLF1 and BRLF1 are deleted allowed a precise assignment of the function of these proteins. Both transactivators were absolutely essential for viral DNA replication. Both BZLF1 and BRLF1 were required for full expression of the EBV proteins expressed during the lytic program, although the respective influence of these molecules on the expression of various viral target genes varied greatly. In replication-defective viral mutants, neither early gene expression nor DNA replication was a prerequisite for late gene expression. This work shows that BRLF1 and BZLF1 harbor distinct but complementary functions that influence all stages of viral production.
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Affiliation(s)
- R Feederle
- GSF-National Research Center for Environment and Health, Institute of Clinical Molecular Biology and Tumor Genetics, D-81377 Munich, Germany
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138
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Ellwood KB, Yen YM, Johnson RC, Carey M. Mechanism for specificity by HMG-1 in enhanceosome assembly. Mol Cell Biol 2000; 20:4359-70. [PMID: 10825199 PMCID: PMC85803 DOI: 10.1128/mcb.20.12.4359-4370.2000] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Assembly of enhanceosomes requires architectural proteins to facilitate the DNA conformational changes accompanying cooperative binding of activators to a regulatory sequence. The architectural protein HMG-1 has been proposed to bind DNA in a sequence-independent manner, yet, paradoxically, it facilitates specific DNA binding reactions in vitro. To investigate the mechanism of specificity we explored the effect of HMG-1 on binding of the Epstein-Barr virus activator ZEBRA to a natural responsive promoter in vitro. DNase I footprinting, mutagenesis, and electrophoretic mobility shift assay reveal that HMG-1 binds cooperatively with ZEBRA to a specific DNA sequence between two adjacent ZEBRA recognition sites. This binding requires a strict alignment between two adjacent ZEBRA sites and both HMG boxes of HMG-1. Our study provides the first demonstration of sequence-dependent binding by a nonspecific HMG-box protein. We hypothesize how a ubiquitous, nonspecific architectural protein can function in a specific context through the use of rudimentary sequence recognition coupled with cooperativity. The observation that an abundant architectural protein can bind DNA cooperatively and specifically has implications towards understanding HMG-1's role in mediating DNA transactions in a variety of enzymological systems.
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Affiliation(s)
- K B Ellwood
- Department of Biological Chemistry, University of California at Los Angeles School of Medicine, Los Angeles, California 90095-1737, USA
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139
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Fujii K, Yokoyama N, Kiyono T, Kuzushima K, Homma M, Nishiyama Y, Fujita M, Tsurumi T. The Epstein-Barr virus pol catalytic subunit physically interacts with the BBLF4-BSLF1-BBLF2/3 complex. J Virol 2000; 74:2550-7. [PMID: 10684269 PMCID: PMC111743 DOI: 10.1128/jvi.74.6.2550-2557.2000] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The Epstein-Barr virus (EBV)-encoded replication proteins that account for the basic reactions at the replication fork are thought to be the EBV Pol holoenzyme, consisting of the BALF5 Pol catalytic and the BMRF1 Pol accessory subunits, the putative helicase-primase complex, comprising the BBLF4, BSLF1, and BBLF2/3 proteins, and the BALF2 single-stranded DNA-binding protein. Immunoprecipitation analyses using anti-BSLF1 or anti-BBLF2/3 protein-specific antibody with clarified lysates of B95-8 cells in a viral productive cycle suggested that the EBV Pol holoenzyme physically interacts with the BBLF4-BSLF1-BBLF2/3 complex to form a large complex. Although the complex was stable in 500 mM NaCl and 1% NP-40, the BALF5 protein became dissociated in the presence of 0.1% sodium dodecyl sulfate. Experiments using lysates from insect cells superinfected with combinations of recombinant baculoviruses capable of expressing each of viral replication proteins showed that not the BMRF1 Pol accessory subunit but rather the BALF5 Pol catalytic subunit directly interacts with the BBLF4-BSLF1-BBLF2/3 complex. Furthermore, double infection with pairs of recombinant viruses revealed that each component of the BBLF4-BSLF1-BBLF2/3 complex makes contact with the BALF5 Pol catalytic subunit. The interactions of the EBV DNA polymerase with the EBV putative helicase-primase complex warrant particular attention because they are thought to coordinate leading- and lagging-strand DNA synthesis at the replication fork.
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Affiliation(s)
- K Fujii
- Division of Virology, Aichi Cancer Center Research Institute, Chikusa-ku, Nagoya 464-8681, Japan
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140
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Salamon D, Takacs M, Myöhänen S, Marcsek Z, Berencsi G, Minarovits J. De novo DNA methylation at nonrandom founder sites 5' from an unmethylated minimal origin of DNA replication in latent Epstein-Barr virus genomes. Biol Chem 2000; 381:95-105. [PMID: 10746740 DOI: 10.1515/bc.2000.014] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Latent episomal genomes of Epstein-Barr virus, a human gammaherpesvirus, represent a suitable model system for studying replication and methylation of chromosomal DNA in mammals. We analyzed the methylation patterns of CpG dinucleotides in the latent origin of DNA replication of Epstein-Barr virus using automated fluorescent genomic sequencing of bisulfite-modified DNA samples. We observed that the minimal origin of DNA replication was unmethylated in 8 well-characterized human cell lines or clones carrying latent Epstein-Barr virus genomes as well as in a prototype virus producer marmoset cell line. This observation suggests that unmethylated DNA domains can function as initiation sites or zones of DNA replication in human cells. Furthermore, 5' from this unmethylated region we observed focal points of de novo DNA methylation in nonrandom positions in the majority of Burkitt's lymphoma cell lines and clones studied while the corresponding CpG dinucleotides in viral genomes carried by lymphoblastoid cell lines and marmoset cells were completely unmethylated. Clustering of highly methylated CpG dinucleotides suggests that de novo methylation of unmethylated double-stranded episomal viral genomes starts at discrete founder sites in vivo. This is the first comparative high-resolution methylation analysis of a latent viral origin of DNA replication in human cells.
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Affiliation(s)
- D Salamon
- 2nd Department of Pathology, Semmelweis University of Medicine, Budapest, Hungary
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141
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Ahn JH, Jang WJ, Hayward GS. The human cytomegalovirus IE2 and UL112-113 proteins accumulate in viral DNA replication compartments that initiate from the periphery of promyelocytic leukemia protein-associated nuclear bodies (PODs or ND10). J Virol 1999; 73:10458-71. [PMID: 10559364 PMCID: PMC113101 DOI: 10.1128/jvi.73.12.10458-10471.1999] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
During human cytomegalovirus (HCMV) infection, the periphery of promyelocytic leukemia protein (PML)-associated nuclear bodies (also known as PML oncogenic domains [PODs] or ND10) are sites for both input viral genome deposition and immediate-early (IE) gene transcription. At very early times after infection, the IE1 protein localizes to and subsequently disrupts PODs, whereas the IE2 protein localizes within or adjacent to PODs. This process appears to be required for efficient viral gene expression and DNA replication. We have investigated the initiation of viral DNA replication compartment formation by studying the localization of viral IE proteins, DNA replication proteins, and the PML protein during productive infection. Localization of IE2 adjacent to PODs between 2 and 6 h after infection was confirmed by confocal microscopy of human fibroblasts (HF cells) infected with both wild-type HCMV(Towne) and with an IE1-deletion mutant HCMV(CR208) that fails to disrupt PODs. In HCMV(Towne)-infected HF cells at 24 to 48 h, IE2 also accumulated in newly formed viral DNA replication compartments containing the polymerase processivity factor (UL44), the single-stranded DNA binding protein (SSB; UL57), the UL112-113 accessory protein, and newly incorporated bromodeoxyuridine (BrdU). Double labeling of the HCMV(CR208)-infected HF cells demonstrated that formation of viral DNA replication compartments initiates within granular structures that bud from the periphery of some of the PODs and subsequently coalesce into larger structures that are flanked by PODs. In transient DNA transfection assays, both the N terminus (codons 136 to 290) and the C terminus (codons 379 to 579) of IE2 exon 5, but not the central region between them, were found to be necessary for both the punctate distribution of IE2 and its association with PODs. Like IE2, the UL112-113 accessory replication protein was also distributed in a POD-associated pattern in both DNA-transfected and virus-infected cells beginning at 6 h. Furthermore, when all six replication core machinery proteins (polymerase complex, SSB, and helicase-primase complex) were expressed together in the presence of UL112-113, they also accumulated at POD-associated sites, suggesting that the UL112-113 protein (but not IE2) may play a role in recruitment of viral replication fork proteins into the periphery of PODs. These results show that (i) subsequent to accumulating at the periphery of PODs, IE2 is incorporated together with the core proteins into viral DNA replication compartments that initiate from the periphery of PODs and then grow to fill the space between groups of PODs, and (ii) the UL112-113 protein appears to have a key role in assembling and recruiting the core replication machinery proteins in the initial stages of viral replication compartment formation.
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Affiliation(s)
- J H Ahn
- Molecular Virology Laboratories, Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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142
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Yokoyama N, Fujii K, Hirata M, Tamai K, Kiyono T, Kuzushima K, Nishiyama Y, Fujita M, Tsurumi T. Assembly of the epstein-barr virus BBLF4, BSLF1 and BBLF2/3 proteins and their interactive properties. J Gen Virol 1999; 80 ( Pt 11):2879-2887. [PMID: 10580049 DOI: 10.1099/0022-1317-80-11-2879] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Epstein-Barr virus (EBV) encodes putative helicase-primase proteins BBLF4, BSLF1 and BBLF2/3, which are essential for the lytic phase of viral DNA replication. The BSLF1, BBLF4 and BBLF2/3 proteins were expressed in B95-8 cells after induction of a virus productive cycle, possessing apparent molecular masses of 89 kDa, 90 kDa and 80 kDa, respectively. The anti-BSLF1 or anti-BBLF2/3 protein-specific antibody, which recognizes its target protein in both Western blotting and immunoprecipitation analyses, immunoprecipitated all of the BSLF1, BBLF4 and BBLF2/3 proteins from the extract of the cells with a virus productive cycle, indicating that these viral proteins are assembled together in vivo. To characterize their protein-protein interactions in detail, recombinant baculoviruses capable of expressing each of these viral gene products in insect cells were constructed. The assembly of the three virus replication proteins was reproduced in insect cells co- infected with the three recombinant baculoviruses, indicating that complex formation does not require other EBV replication proteins. Furthermore, experiments performed by using the extracts from insect cells co-infected with each pair of the recombinant viruses demonstrated that the BSLF1 protein could interact separately with both the BBLF4 and BBLF2/3 proteins and that the BBLF2/3 protein also interacted with the BBLF4 protein. These observations strongly suggest that within the BBLF4-BSLF1-BBLF2/3 complex each component interacts directly with the other two, resulting in helicase-primase enzyme activity.
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Affiliation(s)
- Naoaki Yokoyama
- Division of Virology, Aichi Cancer Center Research Institute, 1-1 Kanokoden, Chikusa-ku, Nagoya 464-8681, Japan1
| | - Ken Fujii
- Division of Virology, Aichi Cancer Center Research Institute, 1-1 Kanokoden, Chikusa-ku, Nagoya 464-8681, Japan1
| | - Mineo Hirata
- Division of Virology, Aichi Cancer Center Research Institute, 1-1 Kanokoden, Chikusa-ku, Nagoya 464-8681, Japan1
| | - Katsuyuki Tamai
- Research and Development Department, Medical and Biological Laboratories, Ohara, Terasawaoka, Ina 396-0002, Japan2
| | - Tohru Kiyono
- Division of Virology, Aichi Cancer Center Research Institute, 1-1 Kanokoden, Chikusa-ku, Nagoya 464-8681, Japan1
| | - Kiyotaka Kuzushima
- Division of Virology, Aichi Cancer Center Research Institute, 1-1 Kanokoden, Chikusa-ku, Nagoya 464-8681, Japan1
| | - Yukihiro Nishiyama
- Laboratory of Virology, Nagoya University School of Medicine, 65 Tsuruma-cho, Showa-ku, Nagoya 466-8550, Japan3
| | - Masatoshi Fujita
- Division of Virology, Aichi Cancer Center Research Institute, 1-1 Kanokoden, Chikusa-ku, Nagoya 464-8681, Japan1
| | - Tatsuya Tsurumi
- Division of Virology, Aichi Cancer Center Research Institute, 1-1 Kanokoden, Chikusa-ku, Nagoya 464-8681, Japan1
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143
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Abstract
BALF2, which encodes the major DNA-binding protein of Epstein-Barr virus (EBV), is expressed during the early stage of the lytic cycle. The location of the BALF2 promoter was identified by primer extension, which indicated that the transcription start is located at nucleotide 164,782 of the EBV genome. Transfection analyses revealed that, similar to other EBV early promoters, the BALF2 promoter is activated by the EBV-encoded transcription factors Rta and Zta. The promoter is also synergistically activated if both transcription factors are present in B lymphocytes and in epithelial cells. Deletion analysis and electrophoretic mobility-shift assay revealed that the region between nucleotides -134 and -64 contains Zta-response elements and the region between nucleotides -287 and -254 contains Rta-response elements. This study demonstrates the importance of Rta and Zta in regulating the transcription of EBV early genes.
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Affiliation(s)
- Chien-Hui Hung
- Molecular Genetics Laboratory, Department of Microbiology and Immunology, Chang-Gung University, 259 Wen-Hwa 1st Road, Kwei-Shan, Taoyuan 333, Taiwan2
- Graduate Institute of Microbiology and Immunology, National Yang- Ming University, Shih-Pai, Taipei 112, Taiwan1
| | - Shih-Tung Liu
- Molecular Genetics Laboratory, Department of Microbiology and Immunology, Chang-Gung University, 259 Wen-Hwa 1st Road, Kwei-Shan, Taoyuan 333, Taiwan2
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144
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Zacny VL, Gershburg E, Davis MG, Biron KK, Pagano JS. Inhibition of Epstein-Barr virus replication by a benzimidazole L-riboside: novel antiviral mechanism of 5, 6-dichloro-2-(isopropylamino)-1-beta-L-ribofuranosyl-1H-benzimidazole. J Virol 1999; 73:7271-7. [PMID: 10438815 PMCID: PMC104252 DOI: 10.1128/jvi.73.9.7271-7277.1999] [Citation(s) in RCA: 64] [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
Although a number of antiviral drugs inhibit replication of Epstein-Barr virus (EBV) in cell culture, and acyclovir (ACV) suppresses replication in vivo, currently available drugs have not proven effective for treatment of EBV-associated diseases other than oral hairy leukoplakia. Benzimidazole riboside compounds represent a new class of antiviral compounds that are potent inhibitors of human cytomegalovirus (HCMV) replication but not of other herpesviruses. Here we characterize the effects of two compounds in this class against lytic replication of EBV induced in a Burkitt lymphoma cell line latently infected with EBV. We analyzed linear forms of EBV genomes, indicative of lytic replication, and episomal forms present in latently infected cells by terminal probe analysis followed by Southern blot hybridization as well as the high-molecular-weight unprocessed viral DNA by pulsed-field gel electrophoresis. D-Ribofuranosyl benzimidazole compounds that act as inhibitors of HCMV DNA maturation, including BDCRB (5, 6-dichloro-2-bromo-1-beta-D-ribofuranosyl-1H-benzimidazole), did not affect the accumulation of high-molecular-weight or monomeric forms of EBV DNA in the induced cells. In contrast, the generation of linear EBV DNA as well as precursor viral DNA was sensitive to the L-riboside 1263W94 [5, 6-dichloro-2-(isopropylamino)-1-beta-L-ribofuranosyl-1H-benzimidazole]. The 50% inhibitory concentration range for 1263W94 was 0.15 to 1. 1 microM, compared with 10 microM for ACV. Thus, 1263W94 is a potent inhibitor of EBV. In addition, 1263W94 inhibited the phosphorylation and the accumulation of the essential EBV replicative cofactor, early antigen D.
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Affiliation(s)
- V L Zacny
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA
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145
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Menet A, Speth C, Larcher C, Prodinger WM, Schwendinger MG, Chan P, Jäger M, Schwarzmann F, Recheis H, Fontaine M, Dierich MP. Epstein-Barr virus infection of human astrocyte cell lines. J Virol 1999; 73:7722-33. [PMID: 10438862 PMCID: PMC104299 DOI: 10.1128/jvi.73.9.7722-7733.1999] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Epstein-Barr virus (EBV) is implicated in different central nervous system syndromes. The major cellular receptor for EBV, complement receptor type 2 (CR2) (CD21), is expressed by different astrocyte cell lines and human fetal astrocytes, suggesting their susceptibility to EBV infection. We demonstrated the infection of two astrocyte cell lines, T98 and CB193, at low levels. As infection was mediated by CR2, we used two stable CR2 transfectant astrocyte cell lines (T98CR2 and CB193CR2) to achieve a more efficient infection. We have monitored EBV gene expression for 2 months and observed the transient infection of T98 and T98CR2 cells and persistent infection of CB193 and CB193CR2 cells. The detection of BZLF1, BALF2, and BcLF1 mRNA expression suggests that the lytic cycle is initiated at early time points postinfection. At later time points the pattern of mRNA expressed (EBER1, EBNA1, EBNA2, and LMP1) differs from latency type III in the absence of LMP2A transcription and in the expression of BALF2 and BcLF1 but not BZLF1. A reactivation of the lytic cycle was achieved in CB193CR2 cells by the addition of phorbol esters. These studies identify astrocyte cell lines as targets for EBV infection and suggest that this infection might play a role in the pathology of EBV in the brain.
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MESH Headings
- Astrocytes/metabolism
- Astrocytes/virology
- DNA, Viral
- DNA-Binding Proteins/genetics
- Gene Expression
- Genes, Viral
- Genetic Vectors
- Herpesvirus 4, Human/metabolism
- Herpesvirus 4, Human/pathogenicity
- Humans
- RNA, Messenger
- Receptors, Complement 3d/genetics
- Receptors, Complement 3d/metabolism
- Receptors, Virus/genetics
- Receptors, Virus/metabolism
- Trans-Activators/genetics
- Transcription, Genetic
- Transfection
- Tumor Cells, Cultured
- Viral Proteins
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Affiliation(s)
- A Menet
- INSERM U519, 76000 Rouen, France.
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146
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Adamson AL, Kenney S. The Epstein-Barr virus BZLF1 protein interacts physically and functionally with the histone acetylase CREB-binding protein. J Virol 1999; 73:6551-8. [PMID: 10400751 PMCID: PMC112738 DOI: 10.1128/jvi.73.8.6551-6558.1999] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Epstein-Barr virus (EBV) immediate-early protein BZLF1 (Z) is a key regulator of the EBV latent-to-lytic switch. Z is a transcriptional activator which induces EBV early gene expression. We demonstrate here that Z interacts with CREB-binding protein (CBP), a histone acetylase and transcriptional coactivator. This interaction requires the amino-terminal region of CBP as well as the transactivation and leucine zipper domains of Z. We show that CBP enhances Z-mediated transactivation of EBV early promoters, in reporter gene assays and in the context of the endogenous genome. We also demonstrate that Z decreases CREB transactivation function and that this inhibitory effect is reversed by overexpression of CBP. We show that Z also interacts directly with CREB. However, mutational analysis indicates that Z inhibition of CREB activity requires the direct interaction between Z and CBP but not the direct interaction between Z and CREB. We propose that Z interacts with CBP to enhance viral early gene transcription. In addition, the Z-CBP interaction may control host cellular transcription factor activity through competition for limiting amounts of cellular CBP.
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Affiliation(s)
- A L Adamson
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295, USA
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147
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Ellwood K, Huang W, Johnson R, Carey M. Multiple layers of cooperativity regulate enhanceosome-responsive RNA polymerase II transcription complex assembly. Mol Cell Biol 1999; 19:2613-23. [PMID: 10082527 PMCID: PMC84054 DOI: 10.1128/mcb.19.4.2613] [Citation(s) in RCA: 40] [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
Two coordinate forms of transcriptional synergy mediate eukaryotic gene regulation: the greater-than-additive transcriptional response to multiple promoter-bound activators, and the sigmoidal response to increasing activator concentration. The mechanism underlying the sigmoidal response has not been elucidated but is almost certainly founded on the cooperative binding of activators and the general machinery to DNA. Here we explore that mechanism by using highly purified transcription factor preparations and a strong Epstein-Barr virus promoter, BHLF-1, regulated by the virally encoded activator ZEBRA. We demonstrate that two layers of cooperative binding govern transcription complex assembly. First, the architectural proteins HMG-1 and -2 mediate cooperative formation of an enhanceosome containing ZEBRA and cellular Sp1. This enhanceosome then recruits transcription factor IIA (TFIIA) and TFIID to the promoter to form the DA complex. The DA complex, however, stimulates assembly of the enhanceosome itself such that the entire reaction can occur in a highly concerted manner. The data reveal the importance of reciprocal cooperative interactions among activators and the general machinery in eukaryotic gene regulation.
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Affiliation(s)
- K Ellwood
- Department of Biological Chemistry, UCLA School of Medicine, Los Angeles, California 90095-1737, USA
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148
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Fingeroth JD, Diamond ME, Sage DR, Hayman J, Yates JL. CD21-Dependent infection of an epithelial cell line, 293, by Epstein-Barr virus. J Virol 1999; 73:2115-25. [PMID: 9971794 PMCID: PMC104456 DOI: 10.1128/jvi.73.3.2115-2125.1999] [Citation(s) in RCA: 66] [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
Epstein-Barr virus (EBV) is invariably present in undifferentiated nasopharyngeal carcinomas, is found sporadically in other carcinomas, and replicates in the differentiated layer of the tongue epithelium in lesions of oral hairy leukoplakia. However, it is not clear how frequently or by what mechanism EBV infects epithelial cells normally. Here, we report that a human epithelial cell line, 293, can be stably infected by EBV that has been genetically marked with a selectable gene. We show that 293 cells express a relatively low level of CD21, that binding of fluorescein-labeled EBV to 293 cells can be detected, and that both the binding of virus to cells and infection can be blocked with antibodies specific for CD21. Two proteins known to form complexes with CD21 on the surface of lymphoid cells, CD35 and CD19, could not be detected at the surface of 293 cells. All infected clones of 293 cells exhibited tight latency with a pattern of gene expression similar to that of type II latency, but productive EBV replication and release of infectious virus could be induced inefficiently by forced expression of the lytic transactivators, R and Z. Low levels of mRNA specific for the transforming membrane protein of EBV, LMP-1, as well as for LMP-2, were detected; however, LMP-1 protein was either undetectable or near the limit of detection at less than 5% of the level typical of EBV-transformed B cells. A slight increase in expression of the receptor for epidermal growth factor, which can be induced in epithelial cells by LMP-1, was detected at the cell surface with two EBV-infected 293 cell clones. These results show that low levels of surface CD21 can support infection of an epithelial cell line by EBV. The results also raise the possibility that in a normal infection of epithelial cells by EBV, the LMP-1 protein is not expressed at levels that are high enough to be oncogenic and that there might be differences in the cells of EBV-associated epithelial cancers that have arisen to allow for elevated expression of LMP-1.
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Affiliation(s)
- J D Fingeroth
- Divisions of Infectious Disease and Experimental Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA
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149
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Sono H, Teshigawara K, Sasada T, Takagi Y, Nishiyama A, Ohkubo Y, Maeda Y, Tatsumi E, Kanamaru A, Yodoi J. Redox control of Epstein-Barr virus replication by human thioredoxin/ATL-derived factor: differential regulation of lytic and latent infection. Antioxid Redox Signal 1999; 1:155-65. [PMID: 11228744 DOI: 10.1089/ars.1999.1.2-155] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Human thioredoxin (hTRX)/adult T-cell leukemia (ATL)-derived factor (ADF) was originally reported as an interleukin-2 (IL-2) receptor-alpha-inducing factor produced by human T-cell lymphotropic virus-1-positive (HTLV-1+) cell lines. Growing evidence indicates that hTRX/ADF plays important roles in cellular responses against oxidative stress and is involved in a variety of cellular functions. A high level of hTRX/ADF expression is also observed in other human virus-infected cell lines including those of Epstein-Barr virus (EBV) and human papillomavirus. In this report, we analyzed the effect of hTRX/ADF on lytic amplification and persistent replication of EBV as a model for lytic versus latent phase of viral replication in host cells. Addition of hTRX/ADF clearly suppressed lytic replication of EBV in Raji cells and B95-8 cells induced to the lytic phase of 12-O-tetradecanoylphorbol-13-acetate (TPA), and it prevented the death of these cells evoked by the lytic induction. In contrast, hTRX/ADF did not have any effect on persistent replication in the latent phase. These data indicated that hTRX/ADF prevents EBV-transformed cells from proceeding into the lytic phase and regulates cohabitation of EBV and its host cells.
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MESH Headings
- Carcinogens/pharmacology
- Cell Death/drug effects
- Cell Line, Transformed/virology
- Cell Transformation, Viral/genetics
- Cytokines/genetics
- Cytokines/metabolism
- Cytokines/physiology
- DNA Replication/genetics
- DNA, Viral/antagonists & inhibitors
- DNA, Viral/genetics
- Gene Amplification
- Gene Expression Regulation, Viral
- Herpesvirus 4, Human/genetics
- Herpesvirus 4, Human/metabolism
- Herpesvirus 4, Human/pathogenicity
- Herpesvirus 4, Human/physiology
- Humans
- Infectious Mononucleosis/genetics
- Infectious Mononucleosis/metabolism
- Infectious Mononucleosis/virology
- Leukemia-Lymphoma, Adult T-Cell/virology
- Neoplasm Proteins/genetics
- Neoplasm Proteins/metabolism
- Neoplasm Proteins/physiology
- Oxidation-Reduction
- Suppression, Genetic
- Tetradecanoylphorbol Acetate/pharmacology
- Thioredoxins/pharmacology
- Virus Replication/genetics
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Affiliation(s)
- H Sono
- Department of Biological Responses, Institute for Virus Research, Kyoto University, Kyoto, Japan
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150
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Semmes OJ, Chen L, Sarisky RT, Gao Z, Zhong L, Hayward SD. Mta has properties of an RNA export protein and increases cytoplasmic accumulation of Epstein-Barr virus replication gene mRNA. J Virol 1998; 72:9526-34. [PMID: 9811685 PMCID: PMC110453 DOI: 10.1128/jvi.72.12.9526-9534.1998] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/1998] [Accepted: 09/09/1998] [Indexed: 11/20/2022] Open
Abstract
The Epstein-Barr virus (EBV) Zta and Mta regulatory proteins were previously found to be required for efficient replication of oriLyt in cotransfection-replication assays, but the contribution of Mta to the replication process was unknown. We now demonstrate that Mta regulates replication gene expression. Using the polymerase processivity factor BMRF1 as an example, we found that in transfected cells, total BMRF1 mRNA levels were unaffected by Mta but that the amounts of cytoplasmic BMRF1 RNA and protein were greatly increased in the presence of Mta. Mta also increased cytoplasmic accumulation of the BALF2, BALF5, BSLF1, and BBLF4 replication gene mRNAs but did not affect cytoplasmic levels of BBLF2/3 mRNA. Thus, five of the six core replication genes require Mta for efficient accumulation of cytoplasmic RNA. The contribution of Mta to posttranscriptional RNA processing was examined. Examination of Mta localization in transfected cells by indirect immunofluorescence revealed that Mta colocalized with the splicing factor SC35. We also found that Mta has RNA binding activity. Glutathione S-transferase-Mta bound to BMRF1 and BMLF1 transcripts but not to a control cellular gene RNA. Mta contains a consensus leucine-rich nuclear export signal. Such signal sequences are characteristic of proteins that undergo nuclear export. Examination of Mta localization in a heterokaryon assay provided evidence that Mta shuttles between the nucleus and the cytoplasm. Our experiments indicate that Mta functions in RNA processing and transport and mediates cytoplasmic accumulation of a number of EBV early mRNAs.
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MESH Headings
- Amino Acid Sequence
- Animals
- Base Sequence
- Biological Transport, Active
- Cell Line
- Cell Nucleus/metabolism
- Cell Nucleus/virology
- Chlorocebus aethiops
- Cytoplasm/metabolism
- Cytoplasm/virology
- DNA Primers/genetics
- Genes, Viral
- Herpesvirus 4, Human/genetics
- Herpesvirus 4, Human/metabolism
- Herpesvirus 4, Human/physiology
- Humans
- RNA Processing, Post-Transcriptional
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Viral/genetics
- RNA, Viral/metabolism
- Trans-Activators/genetics
- Trans-Activators/metabolism
- Transfection
- Vero Cells
- Viral Proteins/genetics
- Viral Proteins/metabolism
- Virus Replication/genetics
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Affiliation(s)
- O J Semmes
- Molecular Virology Laboratories, Department of Pharmacology and Molecular Sciences, Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA
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