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Functional diversity: update of the posttranslational modification of Epstein-Barr virus coding proteins. Cell Mol Life Sci 2022; 79:590. [PMID: 36376593 DOI: 10.1007/s00018-022-04561-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Revised: 08/26/2022] [Accepted: 09/14/2022] [Indexed: 11/16/2022]
Abstract
Epstein-Barr virus (EBV), a human oncogenic herpesvirus with a typical life cycle consisting of latent phase and lytic phase, is associated with many human diseases. EBV can express a variety of proteins that enable the virus to affect host cell processes and evade host immunity. Additionally, these proteins provide a basis for the maintenance of viral infection, contribute to the formation of tumors, and influence the occurrence and development of related diseases. Posttranslational modifications (PTMs) are chemical modifications of proteins after translation and are very important to guarantee the proper biological functions of these proteins. Studies in the past have intensely investigated PTMs of EBV-encoded proteins. EBV regulates the progression of the latent phase and lytic phase by affecting the PTMs of its encoded proteins, which are critical for the development of EBV-associated human diseases. In this review, we summarize the PTMs of EBV-encoded proteins that have been discovered and studied thus far with focus on their effects on the viral life cycle.
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Nakada R, Hirano H, Matsuura Y. Structural basis for the regulation of nuclear import of Epstein-Barr virus nuclear antigen 1 (EBNA1) by phosphorylation of the nuclear localization signal. Biochem Biophys Res Commun 2017; 484:113-117. [PMID: 28104399 DOI: 10.1016/j.bbrc.2017.01.063] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2016] [Accepted: 01/13/2017] [Indexed: 11/19/2022]
Abstract
Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) is expressed in every EBV-positive tumor and is essential for the maintenance, replication, and transcription of the EBV genome in the nucleus of host cells. EBNA1 is a serine phosphoprotein, and it has been shown that phosphorylation of S385 in the nuclear localization signal (NLS) of EBNA1 increases the binding affinity to the nuclear import adaptor importin-α1 as well as importin-α5, and stimulates nuclear import of EBNA1. To gain insights into how phosphorylation of the EBNA1 NLS regulates nuclear import, we have determined the crystal structures of two peptide complexes of importin-α1: one with S385-phosphorylated EBNA1 NLS peptide, determined at 2.0 Å resolution, and one with non-phosphorylated EBNA1 NLS peptide, determined at 2.2 Å resolution. The structures show that EBNA1 NLS binds to the major and minor NLS-binding sites of importin-α1, and indicate that the binding affinity of the EBNA1 NLS to the minor NLS-binding site could be enhanced by phosphorylation of S385 through electrostatic interaction between the phosphate group of phospho-S385 and K392 of importin-α1 (corresponding to R395 of importin-α5) on armadillo repeat 8.
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Affiliation(s)
- Ryohei Nakada
- Division of Biological Science, Graduate School of Science, Nagoya University, Japan
| | - Hidemi Hirano
- Division of Biological Science, Graduate School of Science, Nagoya University, Japan; Structural Biology Research Center, Graduate School of Science, Nagoya University, Japan
| | - Yoshiyuki Matsuura
- Division of Biological Science, Graduate School of Science, Nagoya University, Japan; Structural Biology Research Center, Graduate School of Science, Nagoya University, Japan.
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Roscovitine inhibits EBNA1 serine 393 phosphorylation, nuclear localization, transcription, and episome maintenance. J Virol 2011; 85:2859-68. [PMID: 21209116 DOI: 10.1128/jvi.01628-10] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Latent Epstein-Barr virus (EBV) infection causes human lymphomas and carcinomas. EBV usually persists as an episome in malignant cells. EBV episome persistence, replication, and gene expression are dependent on EBNA1 binding to multiple cognate sites in oriP. To search for inhibitors of EBNA1- and oriP-dependent episome maintenance or transcription, a library of 40,550 small molecules was screened for compounds that inhibit EBNA1- and oriP-dependent transcription and do not inhibit EBNA1- and oriP-independent transcription. This screening identified roscovitine, a selective inhibitor of cyclin-dependent kinase 1 (CDK1), CDK2, CDK5, and CDK7. Based on motif predictions of EBNA1 serine 393 as a CDK phosphorylation site and (486)RALL(489) and (580)KDLVM(584) as potential cyclin binding domains, we hypothesized that cyclin binding to EBNA1 may enable CDK1, -2, -5, or -7 to phosphorylate serine 393. We found that Escherichia coli-expressed EBNA1 amino acids 387 to 641 were phosphorylated in vitro by CDK1-, -2-, -5-, and -7/cyclin complexes and serine 393 phosphorylation was roscovitine inhibited. Further, S393A mutation abrogated phosphorylation. S393A mutant EBNA1 was deficient in supporting EBNA1- and oriP-dependent transcription and episome persistence, and roscovitine had little further effect on the diminished S393A mutant EBNA1-mediated transcription or episome persistence. Immunoprecipitated FLAG-EBNA1 was phosphorylated in vitro, and roscovitine inhibited this phosphorylation. Moreover, roscovitine decreased nuclear EBNA1 and often increased cytoplasmic EBNA1, whereas S393A mutant EBNA1 was localized equally in the nucleus and cytoplasm and was unaffected by roscovitine treatment. These data indicate that roscovitine effects are serine 393 specific and that serine 393 is important in EBNA1- and oriPCp-dependent transcription and episome persistence.
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Duellman SJ, Thompson KL, Coon JJ, Burgess RR. Phosphorylation sites of Epstein-Barr virus EBNA1 regulate its function. J Gen Virol 2009; 90:2251-9. [PMID: 19439552 DOI: 10.1099/vir.0.012260-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Epstein-Barr virus (EBV) is the causative agent of infectious mononucleosis and a risk factor for developing a variety of lymphomas and carcinomas. EBV nuclear antigen 1 (EBNA1) is the only viral protein found in all EBV-related malignancies. It plays a key role in establishing and maintaining the altered state of cells transformed with EBV. EBNA1 is required for a variety of functions, including gene regulation, replication and maintenance of the viral genome, but the regulation of EBNA1's functions is poorly understood. We demonstrate that phosphorylation affects the functions of EBNA1. By using electron-transfer dissociation tandem mass spectrometry, ten specific phosphorylated EBNA1 residues were identified. A mutant derivative preventing the phosphorylation of all ten phosphosites retained the unusually long half-life and the ability to translocate into the nucleus of wild-type EBNA1. This phosphorylation-deficient mutant, however, had a significantly reduced ability to activate transcription and to maintain EBV's plasmids in cells.
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Affiliation(s)
- Sarah J Duellman
- McArdle Laboratory for Cancer Research, 1400 University Ave., University of Wisconsin-Madison, Madison, WI 53706, USA
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Shire K, Kapoor P, Jiang K, Hing MNT, Sivachandran N, Nguyen T, Frappier L. Regulation of the EBNA1 Epstein-Barr virus protein by serine phosphorylation and arginine methylation. J Virol 2006; 80:5261-72. [PMID: 16699006 PMCID: PMC1472174 DOI: 10.1128/jvi.02682-05] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2005] [Accepted: 03/13/2006] [Indexed: 11/20/2022] Open
Abstract
The Epstein-Barr virus (EBV) EBNA1 protein is important for the replication and mitotic segregation of EBV genomes in latently infected cells and also activates the transcription of some of the viral latency genes. A Gly-Arg-rich region between amino acids 325 and 376 is required for both the segregation and transcriptional activation functions of EBNA1. Here we show that this region is modified by both arginine methylation and serine phosphorylation. Mutagenesis of the four potentially phosphorylated serines in this region indicated that phosphorylation of multiple serines contributes to the efficient segregation of EBV-based plasmids by EBNA1, at least in part by increasing EBNA1 binding to hEBP2. EBNA1 was also found to bind the arginine methyltransferases PRMT1 and PRMT5. Multiple arginines in the 325-376 region were methylated in vitro by PRMT1 and PRMT5, as was an N-terminal Gly-Arg-rich region between amino acids 41 and 50. EBNA1 was also shown to be methylated in vivo, predominantly in the 325-376 region. Treatment of cells with a methylation inhibitor or down-regulation of PRMT1 altered EBNA1 localization, resulting in the formation of EBNA1 rings around the nucleoli. The results indicate that EBNA1 function is influenced by both serine phosphorylation and arginine methylation.
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Affiliation(s)
- Kathy Shire
- Department of Medical Genetics and Microbiology, University of Toronto, 1 Kings College Circle, Toronto, Ontario, Canada M5S 1A8
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Kitamura R, Sekimoto T, Ito S, Harada S, Yamagata H, Masai H, Yoneda Y, Yanagi K. Nuclear import of Epstein-Barr virus nuclear antigen 1 mediated by NPI-1 (Importin alpha5) is up- and down-regulated by phosphorylation of the nuclear localization signal for which Lys379 and Arg380 are essential. J Virol 2006; 80:1979-91. [PMID: 16439554 PMCID: PMC1367128 DOI: 10.1128/jvi.80.4.1979-1991.2006] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA-1) is essential for replication of episomal EBV DNAs and maintenance of latency. Multifunctional EBNA-1 is phosphorylated, but the significance of EBNA-1 phosphorylation is not known. Here, we examined the effects on nuclear translocation of Ser phosphorylation of the EBNA-1 nuclear localization signal (NLS) sequence, 379Lys-Arg-Pro-Arg-Ser-Pro-Ser-Ser386. We found that Lys379Ala and Arg380Ala substitutions greatly reduced nuclear transport and steady-state levels of green fluorescent protein (GFP)-EBNA1, whereas Pro381Ala, Arg382Ala, Pro384Ala, and Glu378Ala substitutions did not. Microinjection of modified EBNA-1 NLS peptide-inserted proteins and NLS peptides cross-linked to bovine serum albumin (BSA) showed that Ala substitution for three NLS Ser residues reduced the efficiency of nuclear import. Similar microinjection analyses demonstrated that phosphorylation of Ser385 accelerated the rate of nuclear import, but phosphorylation of Ser383 and Ser386 reduced it. However, transfection analyses of GFP-EBNA1 mutants with the Ser-to-Ala substitution causing reduced nuclear import efficiency did not result in a decrease in the nuclear accumulation level of EBNA-1. The results suggest dynamic nuclear transport control of phosphorylated EBNA-1 proteins, although the nuclear localization level of EBNA-1 that binds to cellular chromosomes and chromatin seems unchanged. The karyopherin alpha NPI-1 (importin alpha5), a nuclear import adaptor, bound more strongly to Ser385-phosphorylated NLS than to any other phosphorylated or nonphosphorylated forms. Rch1 (importin alpha1) bound only weakly and Qip1 (importin alpha3) did not bind to the Ser385-phosphorylated NLS. These findings suggest that the amino-terminal 379Lys-Arg380 is essential for the EBNA-1 NLS and that Ser385 phosphorylation up-regulates nuclear transport efficiency of EBNA-1 by increasing its binding affinity to NPI-1, while phosphorylation of Ser386 and Ser383 down-regulates it.
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Affiliation(s)
- Ryo Kitamura
- AIDS Research Center, National Institute of Infectious Diseases, Toyama 1-23-1, Shinjuku, Tokyo 162-8640, Japan
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Duellman SJ, Burgess RR. Overproduction in Escherichia coli and purification of Epstein-Barr virus EBNA-1. Protein Expr Purif 2005; 47:434-40. [PMID: 16403648 DOI: 10.1016/j.pep.2005.11.023] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2005] [Revised: 11/22/2005] [Accepted: 11/23/2005] [Indexed: 11/17/2022]
Abstract
Epstein-Barr virus nuclear antigen 1 (EBNA-1) is a multi-functional protein of the Epstein-Barr virus (EBV). Due to its low abundance in EBV-transformed cells, overproduction in a foreign host is preferred to obtain purified EBNA-1 protein. The EBNA-1 gene possesses a large number of Escherichia coli rare codons (23%). By using E. coli BL21(DE3)Rosetta2 cells that augment the low-abundance tRNA genes, the expression level of EBNA-1 in E. coli was greatly enhanced. EBNA-1 was then purified by applying the whole cell extract soluble fraction to a Ni-NTA Superflow column and eluting with an imidazole gradient. The improved overexpression in E. coli followed by a one-step Ni-NTA purification resulted in a sufficient amount of pure EBNA-1 protein to test DNA binding activity, and prepare and test EBNA-1-specific monoclonal antibodies (mAbs).
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Affiliation(s)
- Sarah J Duellman
- McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, USA.
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Lu CC, Wu CW, Chang SC, Chen TY, Hu CR, Yeh MY, Chen JY, Chen MR. Epstein-Barr virus nuclear antigen 1 is a DNA-binding protein with strong RNA-binding activity. J Gen Virol 2004; 85:2755-2765. [PMID: 15448336 DOI: 10.1099/vir.0.80239-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA-1) plays key roles in both the regulation of gene expression and the replication of the EBV genome in latently infected cells. To characterize the RNA-binding activity of EBNA-1, it was demonstrated that EBNA-1 binds efficiently to RNA homopolymers that are composed of poly(G) and weakly to those composed of poly(U). All three RGG boxes of EBNA-1 contributed additively to poly(G)-binding activity and could mediate RNA binding when attached to a heterologous protein in an RNA gel mobility-shift assay. In vitro-transcribed EBV and non-EBV RNA probes revealed that EBNA-1 bound to most RNAs examined and the affinity increased as the content of G and U increased, as demonstrated in competition assays. Among these probes, the 5' non-coding region (NCR) (nt 131-278) of hepatitis C virus RNA appeared to be the strongest competitor for EBNA-1 binding to the EBV-encoded small nuclear RNA 1 (EBER1) probe, whereas a mutant 5' NCR RNA with partially disrupted secondary structure was a weak competitor. Furthermore, the interaction of endogenous EBNA-1 and EBER1 in EBV-infected cells was demonstrated by a ribonucleoprotein immunoprecipitation assay. These results revealed that EBNA-1 is a DNA-binding protein with strong binding activity to a relatively broad spectrum of RNA and suggested an additional biological impact of EBNA-1 through its ability to bind to RNA.
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Affiliation(s)
- Chih-Chung Lu
- Graduate Institute of Microbiology, College of Medicine, No. 1, Jen-Ai Road, 1st Section, National Taiwan University, Taipei, Taiwan
| | - Chia-Wei Wu
- Graduate Institute of Microbiology, College of Medicine, No. 1, Jen-Ai Road, 1st Section, National Taiwan University, Taipei, Taiwan
| | - Shin C Chang
- Graduate Institute of Microbiology, College of Medicine, No. 1, Jen-Ai Road, 1st Section, National Taiwan University, Taipei, Taiwan
| | - Tzu-Yi Chen
- Graduate Institute of Microbiology, College of Medicine, No. 1, Jen-Ai Road, 1st Section, National Taiwan University, Taipei, Taiwan
| | - Chwan-Ren Hu
- Graduate Institute of Microbiology, College of Medicine, No. 1, Jen-Ai Road, 1st Section, National Taiwan University, Taipei, Taiwan
| | - Ming-Yi Yeh
- Graduate Institute of Microbiology, College of Medicine, No. 1, Jen-Ai Road, 1st Section, National Taiwan University, Taipei, Taiwan
| | - Jen-Yang Chen
- National Health Research Institutes, Taipei, Taiwan
- Graduate Institute of Microbiology, College of Medicine, No. 1, Jen-Ai Road, 1st Section, National Taiwan University, Taipei, Taiwan
| | - Mei-Ru Chen
- Graduate Institute of Microbiology, College of Medicine, No. 1, Jen-Ai Road, 1st Section, National Taiwan University, Taipei, Taiwan
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9
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Chuang TC, Way TD, Lin YS, Lee YC, Law SL, Kao MC. The Epstein-Barr virus nuclear antigen-1 may act as a transforming suppressor of the HER2/neu oncogene. FEBS Lett 2002; 532:135-42. [PMID: 12459478 DOI: 10.1016/s0014-5793(02)03658-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It is known that the HER2/neu proto-oncogene is associated with a wide variety of human cancers and considered to be an attractive target for developing anti-cancer agents. We report here for the first time that the Epstein-Barr virus nuclear antigen-1 (EBNA1) suppresses the HER2/neu oncogene expression at the transcriptional level. Recombinant clones of EBNA1 were subcloned and stably transfected into HER2/neu-overexpressing human ovarian cancer SKOV3.ip1 cells. These EBNA1-containing clones down-regulated the endogenous production of p185(HER2/neu). In addition, the EBNA1-expressing stable transfectants showed reduced growth rate, low soft agarose colony-forming ability and tumorigenic potential as compared with the parental line. These data suggest that EBNA1 may act as a transforming suppressor of the HER2/neu oncogene.
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Affiliation(s)
- Tzu-Chao Chuang
- Graduate Institute of Life Sciences, National Defense Medical Center, National Defense University, Taipei, Taiwan
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10
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Van Craenenbroeck K, Vanhoenacker P, Haegeman G. Episomal vectors for gene expression in mammalian cells. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:5665-78. [PMID: 10971576 DOI: 10.1046/j.1432-1327.2000.01645.x] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
An important reason for preferring mammalian cells for heterologous gene expression is their ability to make authentic proteins containing post-translational modifications similar to those of the native protein. The development of expression systems for mammalian cells has been ongoing for several years, resulting in a wide variety of effective expression vectors. The aim of this review is to highlight episomal expression vectors. Such episomal plasmids are usually based on sequences from DNA viruses, such as BK virus, bovine papilloma virus 1 and Epstein-Barr virus. In this review we will mainly focus on the improvements made towards the usefulness of these systems for gene expression studies and gene therapy.
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Ito S, Ikeda M, Kato N, Matsumoto A, Ishikawa Y, Kumakubo S, Yanagi K. Epstein-barr virus nuclear antigen-1 binds to nuclear transporter karyopherin alpha1/NPI-1 in addition to karyopherin alpha2/Rch1. Virology 2000; 266:110-9. [PMID: 10612665 DOI: 10.1006/viro.1999.0054] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
We searched for cellular proteins that interact with Epstein-Barr (EBV) virus nuclear antigen-1, which is a latent EBV origin-binding protein detected in all EBV latently infected cells and essential for maintenance of the latent EBV genome, by a yeast two-hybrid screening of a B lymphocyte cDNA library in this study. Interaction of polypeptides synthesized from three selected cDNA clones with EBNA-1 proteins was confirmed in vitro using their glutathione-S-transferase-fusion polypeptides and by coimmunoprecipitation analyses of B cell extracts with anti-EBNA-1 monoclonal antibodies and monospecific antibodies against cellular proteins of interest. We report the following: (i) Karyopherin alpha (karyopherin alpha1, hSRP1, and NPI-1), an adaptor subunit of nuclear localization signal receptors, which direct proteins to the nuclear pore, interacted with EBNA-1. (ii) EBNA-1 proteins endogenous in the B cell line Raji of Burkitt lymphoma origin bound to another adaptor protein, karyopherin alpha2 (hSRP1alpha, hRch1), interactions of which to recombinant EBNA-1 polypeptides were previously reported. (iii) Nearly 90% of all the cDNA clones examined was p32 (SF2-associated P32, p32/TAP, and gC1q-R), and endogenous EBNA-1 proteins in the Raji cells bound to p32, a potential of which to affect localization of EBNA-1 in transfected Vero cells has been recently suggested. These results suggest that EBNA-1, which has the unique NLS containing Lys-Arg and overlapping with one of the phosphorylation domains, is recognized and transported to the nuclei by these two distinct karyopherin alpha proteins, which are differentially expressed in different cell types, implying a regulatory localization system for EBNA-1.
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Affiliation(s)
- S Ito
- Department of Virology I, National Institute of Infectious Diseases, Tokyo, 162-8640, Japan
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12
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Fischer N, Voss MD, Mueller-Lantzsch N, Grässer FA. A potential NES of the Epstein-Barr virus nuclear antigen 1 (EBNA1) does not confer shuttling. FEBS Lett 1999; 447:311-4. [PMID: 10214968 DOI: 10.1016/s0014-5793(99)00313-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Epstein-Barr virus nuclear antigen 1 (EBNA1) is a multifunctional protein involved in the replication and maintenance of the viral episome. We identified a potential Rev-like nuclear export signal (NES) which, however, does not confer the export of EBNA1. In the yeast two-hybrid system EBNA1 does not bind to the nuclear exporter Crm1p. In spite of the RNA-binding ability of EBNA1 and its structural homologies to RNA binding proteins like hnRNP U and/or A1, EBNA1 does not shuttle to the cytoplasm in heterokaryon analysis. We propose the function of the RNA binding of EBNA1 in retaining RNAs to the nucleus.
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Affiliation(s)
- N Fischer
- Institut für Mikrobiologie und Hygiene, Abteilung Virologie, Universitätskliniken, Homburg/Saar, Germany
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13
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Lehman CW, Botchan MR. Segregation of viral plasmids depends on tethering to chromosomes and is regulated by phosphorylation. Proc Natl Acad Sci U S A 1998; 95:4338-43. [PMID: 9539738 PMCID: PMC22490 DOI: 10.1073/pnas.95.8.4338] [Citation(s) in RCA: 137] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Eukaryotic viruses can maintain latency in dividing cells as extrachromosomal nuclear plasmids. Segregation and nuclear retention of DNA is, therefore, a key issue in retaining copy number. The E2 enhancer protein of the papillomaviruses is required for viral DNA replication and transcription. Viral mutants that prevent phosphorylation of the bovine papillomavirus type 1 (BPV) E2 protein are transformation-defective, despite normal viral gene expression and replication function. Cell colonies harboring such mutants show sectoring of viral DNA and are unable to maintain the episome. We find that transforming viral DNA attaches to mitotic chromosomes, in contrast to the mutant genome encoding the E2 phosphorylation mutant. Second-site suppressor mutations were uncovered in both E1 and E2 genes that allow for transformation, maintenance, and chromosomal attachment. E2 protein was also found to colocalize to mitotic chromosomes, whereas the mutant did not, suggesting a direct role for E2 in viral attachment to chromosomes. Such viral hitch-hiking onto cellular chromosomes is likely to provide a general mechanism for maintaining nuclear plasmids.
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Affiliation(s)
- C W Lehman
- Molecular and Cell Biology Department, University of California, Berkeley, CA 94720, USA
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14
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Wang Y, Finan JE, Middeldorp JM, Hayward SD. P32/TAP, a cellular protein that interacts with EBNA-1 of Epstein-Barr virus. Virology 1997; 236:18-29. [PMID: 9299613 DOI: 10.1006/viro.1997.8739] [Citation(s) in RCA: 127] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The Epstein-Barr virus (EBV) EBNA-1 protein has a central role in the maintenance of a latent EBV infection and is the only virus-encoded protein expressed in all EBV-associated tumors. EBNA-1 is required for replication of the episomal form of the latent viral genome and transactivates the latency C and LMP-1 promoters. The mechanisms by which EBNA-1 performs these functions are not known. Here we describe the cloning, expression, and characterization of a cellular protein, P32/TAP, which strongly interacts with EBNA-1. We show that P32/TAP is expressed at high levels in Raji cells and is synthesized as a proprotein of 282 amino acids (aa) that is posttranslationally processed by a two-step cleavage process to yield a mature protein of 209 aa. It has been previously reported that P32/TAP is expressed on the cell surface. Our transient expression assays detected full-length P32/TAP (1-282 aa) in the cytoplasm while mature P32/TAP protein localized to the nucleus. Three lines of evidence support P32/TAP interaction with EBNA-1. First, in the yeast two-hybrid system we mapped two interactive N-terminal regions of EBNA-1, aa 40-60 and aa 325-376, each of which contains arginine-glycine repeats. These regions interact with the C-terminal half of P32/TAP. Second, the full-length cytoplasmic P32/TAP protein can translocate nuclear EBNA-1 into the cytoplasm. Third, P32/TAP co-immunoprecipitated with EBNA-1. We have confirmed that a Gal4 fusion protein containing the C-terminal region of P32/TAP (aa 244-282) transactivates expression from a reporter containing upstream Gal4-binding sites. Deletion of the P32/TAP interactive regions of EBNA-1 severely diminished EBNA-1 transactivation of FRTKCAT in transient expression assays. Our data suggest that interaction with P32/TAP may contribute to EBNA-1-mediated transactivation.
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Affiliation(s)
- Y Wang
- Department of Pharmacology and Molecular Sciences, Johns Hopkins School of Medicine, Baltimore, Maryland 21205-2185, USA
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15
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Fischer N, Kremmer E, Lautscham G, Mueller-Lantzsch N, Grässer FA. Epstein-Barr virus nuclear antigen 1 forms a complex with the nuclear transporter karyopherin alpha2. J Biol Chem 1997; 272:3999-4005. [PMID: 9020106 DOI: 10.1074/jbc.272.7.3999] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The Epstein-Barr virus (EBV) is implicated in the induction of several malignancies. The nuclear antigen 1 (EBNA1) is the only viral protein that is expressed consistently in all EBV-associated tumors. EBNA1 is involved in the replication and maintenance of the viral episome in the infected cell and exhibits oncogenic activity in transgenic mice. Here we report the identification of the nuclear transporter karyopherin alpha2 as a cellular partner of EBNA1 using the yeast "two-hybrid system." Karyopherin alpha2 is also called importin alpha or Rch1. The binding to karyopherin alpha2 was mediated through a C-terminal region of EBNA1 encompassing the nuclear localization signal, whereas clones of EBNA1 devoid of the nuclear localization signal failed to bind to karyopherin alpha2. The interaction was biochemically confirmed by far-Western analysis using bacterially expressed karyopherin alpha2 and karyopherin alpha2-specific monoclonal antibodies. The nuclear transport of EBNA1 was impaired by expression of N-terminally truncated karyopherin alpha2. Zone velocity sedimentation in a sucrose gradient indicated that: (i) EBNA1 and Rch1 colocalize; and (ii) the association of karyopherin alpha2 with high molecular weight protein complexes might be impeded by the presence of EBNA1.
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Affiliation(s)
- N Fischer
- Institut für Mikrobiologie und Hygiene, Abteilung Virologie, Haus 47, Universitätskliniken, D-66421 Homburg/Saar, Germany
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16
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Ermakova OV, Frappier L, Schildkraut CL. Role of the EBNA-1 protein in pausing of replication forks in the Epstein-Barr virus genome. J Biol Chem 1996; 271:33009-17. [PMID: 8955146 DOI: 10.1074/jbc.271.51.33009] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We have previously shown that replication forks stall at a family of repeated sequences (FR) within the Epstein-Barr virus latent origin of replication oriP, both in a small plasmid and in the intact Epstein-Barr virus genome. Each of the 20 repeated sequences within the FR contains a binding site for Epstein-Barr nuclear antigen 1 (EBNA-1), the only viral protein required for latent replication. We showed that the EBNA-1 protein enhances the accumulation of paused replication forks at the FR. In this study, we have investigated a series of truncated EBNA-1 proteins to determine the portion of the EBNA-1 protein that is responsible for pausing of forks at the FR. Two-dimensional agarose gel electrophoresis was performed on the products of in vitro replication reactions in the presence of full-length EBNA-1 or proteins with various deletions to assess the extent of fork pausing at the FR. We conclude that a portion of the DNA binding domain is important for fork pausing. We also present evidence indicating that phosphorylation of the EBNA-1 protein or EBNA-1-truncated derivatives is not essential for pausing. To investigate the mechanism of EBNA-1-mediated pausing of replication forks, we asked whether EBNA-1 could inhibit the DNA unwinding activity of replicative helicases. We found that EBNA-1, when bound to the FR, inhibits DNA unwinding in vitro by SV40 T antigen and Escherichia coli dnaB helicases in an orientation-independent manner.
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Affiliation(s)
- O V Ermakova
- Department of Cell Biology, Albert Einstein College of Medicine, New York, New York 10461, USA
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17
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Abstract
Epstein-Barr virus nuclear antigen 1 (EBNA1) can bind specifically to two clusters of sites within the Epstein-Barr virus plasmid origin of DNA replication (oriP). EBNA1 activates DNA replication mediated by oriP and can also activate transcription and retain DNA in cells when bound site specifically. EBNA1 bound to oriP physically links the two clusters of EBNA1-binding sites, resulting in loop formation by the intervening DNA. To elucidate the contribution of DNA linking by EBNA1 to its biological activities, we identified regions within it that can independently link DNAs to which they are bound. An electrophoretic mobility shift assay was used to detect this activity. Proteins which link DNA aggregate that DNA into large lattices. Proteins which cannot link DNA but still bind to DNA retard the mobility of that DNA but do not cause it to form lattices. Amino-terminal truncations were used to map the amino-terminal limit of a minimal DNA-linking domain approximately to amino acid 372 of EBNA1. To map the carboxy-terminal limit of this minimal domain, fusion proteins containing the DNA-binding domain of GAL4 and fragments of EBNA1 were generated and studied. This approach identified the carboxy-terminal limit of this minimal domain to be approximately amino acid 391 and verified its amino-terminal limit. Internal deletions within a truncated EBNA1 derivative verified the importance of this region. Two additional fragments of EBNA1, each of which independently conferred DNA-linking activity on the domain of GAL4 which binds DNA, were identified within amino acids 54 to 89 and amino acids 331 to 361. Therefore, EBNA1 contains at least three regions that can act independently to link DNAs and that may act in concert within intact EBNA1.
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Affiliation(s)
- D Mackey
- McArdle Laboratory for Cancer Research, Department of Oncology, Medical School, University of Wisconsin-Madison, USA
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18
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[5] Epstein-barr viral plasmid vectors and their amplifiable derivatives. ACTA ACUST UNITED AC 1995. [DOI: 10.1016/s1067-2389(06)80037-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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19
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Harrison S, Fisenne K, Hearing J. Sequence requirements of the Epstein-Barr virus latent origin of DNA replication. J Virol 1994; 68:1913-25. [PMID: 8107251 PMCID: PMC236653 DOI: 10.1128/jvi.68.3.1913-1925.1994] [Citation(s) in RCA: 85] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The Epstein-Barr virus (EBV) latent origin of DNA replication (oriP) is composed of two elements that contain binding sites for the sole viral gene product required for latent cycle replication, EBNA-1. One of these elements, region I, functions as an EBNA-1-dependent enhancer for RNA polymerase II-transcribed genes, may play a role in plasmid segregation, and is required for origin function in B cells latently infected with EBV. The second element, region II, contains or is very near the site of initiation of DNA replication. A genetic approach was taken to determine the contribution of the EBNA-1 binding sites in oriP to origin function. Although region I is required for the transient replication of plasmids bearing region II in EBV-infected B cells, a plasmid lacking region I but containing region II, was observed to replicate transiently in both D98/Raji and HeLa cells expressing EBNA-1. Thus, binding of EBNA-1 to region I is not absolutely required for the molecular events that lead to initiation of DNA replication at region II. Site-directed mutagenesis of the four EBNA-1-binding sites in region II, individually and in various combinations, demonstrated that only two EBNA-1-binding sites are required for region II function. The results obtained with these mutants, together with the analysis of the replicative ability of plasmids containing insertions between EBNA-1-binding sites, suggested that the spatial relationship of the two sites is critical. Mutants that contain only two EBNA-1-binding sites separated by 26 to 31 bp in region II were not maintained as plasmids over many cell generations and were greatly reduced in their ability to replicate transiently in D98/Raji cells. The EBNA-1-induced bending or untwisting of the DNA in EBNA-1-binding sites 1 and 4 in region II did not, however, demonstrate this spatial constraint. It may be concluded from these results that specific protein-protein interactions between EBNA-1 and/or between EBNA-1 and a cellular protein(s) are required for origin function.
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Affiliation(s)
- S Harrison
- Department of Microbiology, State University of New York, Stony Brook 11794-5222
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20
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Sample J, Henson EB, Sample C. The Epstein-Barr virus nuclear protein 1 promoter active in type I latency is autoregulated. J Virol 1992; 66:4654-61. [PMID: 1321268 PMCID: PMC241289 DOI: 10.1128/jvi.66.8.4654-4661.1992] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The only member of the Epstein-Barr virus family of nuclear proteins (EBNAs) expressed during type I and type II latent infections is EBNA-1. This is in contrast to type III latency, during which all six nuclear proteins are expressed from a common transcription unit. The exclusive expression of EBNA-1 during type I and II latency is mediated through a recently identified promoter, Fp. The objective of this study was to characterize Fp in the Burkitt lymphoma cell background, where it is known to be differentially utilized. Using a short-term transfection assay and reporter gene plasmids containing Fp linked to the human growth hormone, we examined Fp activity in type I and type III latently infected and virus-negative Burkitt lymphoma cells. The data suggested that Fp is predominantly regulated through two distinct elements located between +24 and +270 relative to the transcription start site. One element positively mediates Fp activity, probably at the level of transcription, and acts in a virus-independent manner. The second element contains the EBNA-1 DNA binding domain III and negatively regulates Fp-directed gene expression in trans with EBNA-1 in type III as well as type I latency. Thus, we have identified a third function of EBNA-1, i.e., that of a repressor of gene expression, in addition to its known role in viral DNA replication and its ability to trans-activate gene expression. The overall activity of Fp in type I latently infected Burkitt cells was approximately sixfold lower than in virus-negative Burkitt cells, in which there is no autoregulation, suggesting that there is a fine balance between these two opposing regulatory elements during type I latency.
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Affiliation(s)
- J Sample
- Department of Virology and Molecular Biology, St. Jude Children's Research Hospital, Memphis, Tennessee 38101
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21
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Polvino-Bodnar M, Schaffer PA. DNA binding activity is required for EBNA 1-dependent transcriptional activation and DNA replication. Virology 1992; 187:591-603. [PMID: 1312270 DOI: 10.1016/0042-6822(92)90461-w] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Epstein-Barr virus nuclear antigen 1 (EBNA 1) has been shown to be a sequence-specific DNA binding protein that is required for the replication of episomal elements carrying the viral origin of DNA replication, oriP, as well as for the activation of a specific transcriptional enhancer. We have constructed and analyzed a series of deletion and nonsense mutants in a cloned copy of the EBNA 1 gene and have tested mutant peptides for the ability (a) to bind to a synthetic oligonucleotide containing a consensus EBNA 1 binding site, (b) to activate the EBNA 1-specific enhancer, and (c) to drive replication of an oriP-bearing plasmid in a transient replication assay. The presence of a DNA binding domain in the carboxy-terminal third of the protein was confirmed. Interestingly, neither the acidic tail nor the Gly-Ala copolymer of EBNA 1 contributes significantly to binding. In addition to sequences in the carboxy-terminal portion of the protein, our data indicate that sequences in the amino-terminal portion of the polypeptide affect the binding of EBNA 1 to its target sequence. Further, we show that EBNA 1 binds to its recognition sequence as a dimer. Results of transient expression assays indicate that the ability of EBNA 1 species to activate the transcriptional enhancer and to drive the replication of oriP plasmids is directly dependent on the ability of the polypeptides to bind to the EBNA 1 consensus binding sequence.
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Affiliation(s)
- M Polvino-Bodnar
- Department of Biology, Northeastern University, Boston, Massachusetts 02115
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22
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Tommasino M, Contorni M, Cavalieri F. HPV16 E7 phosphorylation in fission yeast: characterization and biological effects. Gene 1992; 111:93-8. [PMID: 1547958 DOI: 10.1016/0378-1119(92)90607-q] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Human papillomavirus type 16 E7 protein (HPV-16 E7), synthesised in Schizosaccharomyces pombe, is both phosphorylated and targeted to the nucleus [Tommasino et al., Gene 93 (1990) 265-270] as is E7 protein synthesized in primate cells. Further analysis of E7 expression in fission yeast indicates that: (i) E7 protein synthesised in S. pombe is phosphorylated only on the Ser residues which are part of a casein kinase II consensus site, as it has been shown to be the cause in human cells, and is tightly associated with the nuclear matrix; (ii) synthesis of wild type, phosphorylated E7 is responsible for a significant increase in S. pombe doubling time; and (iii) E7 phosphorylation is not required for the tight association of the protein with the nuclear matrix, but E7 mutants, in which one (Ser31) or both phosphorylated serines (Ser31 and Ser32) have been substituted, lack any effect on cell-cycle duration.
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Affiliation(s)
- M Tommasino
- Molecular Virology, Sclavo Research Centre, Siena, Italy
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23
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Frappier L, O'Donnell M. Epstein-Barr nuclear antigen 1 mediates a DNA loop within the latent replication origin of Epstein-Barr virus. Proc Natl Acad Sci U S A 1991; 88:10875-9. [PMID: 1660154 PMCID: PMC53034 DOI: 10.1073/pnas.88.23.10875] [Citation(s) in RCA: 93] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Epstein-Barr virus-encoded nuclear antigen 1 (EBNA-1) binds and activates the viral latent origin of DNA replication, oriP. We have used electron microscopy to examine the assembly of EBNA-1 onto oriP. The oriP region consists of two essential elements separated by approximately 1 kilobase pair of DNA. One element contains 20 tandom EBNA-1 binding sites [called the family of repeats (FR)] and serves to activate initiation of replication at the dyad symmetry (DS) element, which contains 4 EBNA-1 binding sites. Titration of homogeneous EBNA-1 produced in baculovirus (bEBNA-1) onto oriP DNA showed an order to the assembly of bEBNA-1 onto oriP. At low concentrations, bEBNA-1 was located exclusively on the FR element. As the level of bEBNA-1 was raised, a loop between the FR and DS elements became the most prevalent DNA-protein complex. These data suggest protein-mediated DNA looping may play a role in activating latent-phase replication of the Epstein-Barr virus.
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Affiliation(s)
- L Frappier
- Howard Hughes Medical Institute, Microbiology Department, Cornell University Medical College, New York, NY 10021
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24
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Cheng HM, Foong YT, Sam CK, Prasad U, Dillner J. Epstein-Barr virus nuclear antigen 1 linear epitopes that are reactive with immunoglobulin A (IgA) or IgG in sera from nasopharyngeal carcinoma patients or from healthy donors. J Clin Microbiol 1991; 29:2180-6. [PMID: 1719023 PMCID: PMC270294 DOI: 10.1128/jcm.29.10.2180-2186.1991] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The entire amino acid sequence of the unique region of the EBNA 1 protein was synthesized as a set of 41 20-residue peptides with an overlap of 10 amino acids. The peptides were tested in the enzyme-linked immunosorbent assay for reactivity with immunoglobulin A (IgA) and IgG in sera from 50 patients with nasopharyngeal carcinoma (NPC) as compared with 36 serum samples from healthy Epstein-Barr virus (EBV)-seropositive donors and 5 serum samples from EBV-negative donors. The most immunoreactive peptide for both IgA and IgG binding was localized to the glycine-alanine repeat domain of the antigen. In the unique regions, 16 immunoreactive peptides were found. Of these, four were reactive with IgG but not IgA and three peptides were reactive with IgA but not IgG in NPC sera. In addition, several IgA and IgG epitopes on the carboxy-terminal region were specifically reactive with NPC sera, but unreactive with sera from healthy EBV-positive donors. The results suggest that EBV serology specific for individual epitopes may provide additional useful information not available by conventional serology with whole antigens or the EBNA complex.
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Affiliation(s)
- H M Cheng
- Department of Virology, Karolinska Institute, Stockholm, Sweden
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25
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Horvath J, Faxing C, Weber JM. Complementation of adenovirus early region 1a and 2a mutants by Epstein-Barr virus immortalized lymphoblastoid cell lines. Virology 1991; 184:141-8. [PMID: 1651589 DOI: 10.1016/0042-6822(91)90830-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Human B-lymphocytes may be infected by both adenoviruses and the Epstein-Barr virus (EBV). Some of the immediate early and early proteins in the two viruses are similar in function even though their primary structures are different. As these viruses might infect the same B-cells in man, we asked if complementation could take place. The adenovirus mutant H5ts125 has a thermolabile DNA-binding protein and is defective in DNA replication at 39 degrees. Several EBV-transformed human lymphoblastoid cell lines and a tamarin cell line B95-8 were infected with H5ts125 and incubated at either the nonpermissive or the permissive temperatures. Adenoviral DNA replication and assembly of new virions were observed at both temperatures, suggesting complementation by the resident EBV gene products. The adenovirus E1a region is deleted in the mutant d1312. Complementation of this mutant was only obtained in the EBV producer B95-8 cells. Immortalization by EBV was apparently not sufficient for effective complementation. This supports an earlier observation that one of the EBV early proteins (MS-EA) behaves like adenovirus E1a and can transactivate the E4 promoter in a CAT assay. The complementation of mutant adenoviruses in EBV-transformed lymphocytes may help the rescue of new adenovirus serotypes in immunosuppressed patients.
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Affiliation(s)
- J Horvath
- Departement de Microbiologie, Faculte de Medecine, Universite de Sherbrooke, Quebec, Canada
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26
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Inoue N, Harada S, Honma T, Kitamura T, Yanagi K. The domain of Epstein-Barr virus nuclear antigen 1 essential for binding to oriP region has a sequence fitted for the hypothetical basic-helix-loop-helix structure. Virology 1991; 182:84-93. [PMID: 1850915 DOI: 10.1016/0042-6822(91)90651-q] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The domain of Epstein-Barr virus nuclear antigen 1 (EBNA-1) which is essential for binding to a region containing oriP, an episomal replication origin of EBV DNA, was analyzed by DNA binding assay with beta-galactosidase-EBNA-1 fusion proteins. It was revealed that a 159-amino acid (aa) domain, 460-618 aa, of EBNA-1 retained the oriP-binding activity and the domain's activity was abolished by a deletion of 29 aa from its amino-terminal end and by a 38 aa deletion from its carboxyl-end as well. One of five monoclonal antibodies against EBNA-1 specifically inhibited the binding of the beta-galactosidase-EBNA-1 fusion protein to the oriP region. The epitope recognized by the monoclonal antibody was mapped in the crucial 29 aa region. An analysis of the domain's putative secondary structure and a computer search of amino acid sequence homology indicated that the 159-aa domain contains the hypothetical basic-helix-loop-helix structure which is considered to be a common characteristic structure of a family of DNA binding proteins. Examinations of DNA binding activity of the other EBNA polypeptides with a series of fusion proteins and similar structural analyses of their amino acid sequences were also performed. This study suggests that EBNA-1 is a constituent of the family of DNA binding proteins which are involved in transcriptional regulation critical for cell differentiation or cell-type determination.
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Affiliation(s)
- N Inoue
- Department of Virology and Rickettsiology, National Institute of Health, Tokyo, Japan
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27
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Frappier L, O'Donnell M. Overproduction, purification, and characterization of EBNA1, the origin binding protein of Epstein-Barr virus. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(20)89523-4] [Citation(s) in RCA: 113] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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28
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Orlowski R, Miller G. Single-stranded structures are present within plasmids containing the Epstein-Barr virus latent origin of replication. J Virol 1991; 65:677-86. [PMID: 1846191 PMCID: PMC239807 DOI: 10.1128/jvi.65.2.677-686.1991] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The Epstein-Barr virus (EBV) latent origin of plasmid replication (oriP) contains two essential regions, a family of repeats with 20 imperfect copies of a 30-bp sequence and a dyad symmetry element with four similar 30-bp repeats. Each of the repeats has an internal palindromic sequence and can bind EBNA 1, a protein that together with oriP constitutes the only viral element necessary for EBV maintenance and replication. Using single-strand-specific nucleases, we have probed plasmids containing oriP-derived sequences for the presence of secondary structural elements. Multiple single-stranded structures were detected within the oriP region. Of the two essential elements of oriP, the family of repeats seemed to extrude these structures at a much higher frequency than did sequences within the dyad symmetry region. Though negative supercoiling was found to stabilize the single-stranded structures, they showed significant stability even after linearization of the oriP plasmids. Two major single-stranded structures detected involved approximately 12 bp of DNA. These loci could be transiently unwound regions that form because of negative supercoiling and the high A + T content of this region of DNA, or they could be cruciform structures extruded within the palindromic sequences of oriP that may be important sites for protein-DNA interactions in the EBV oriP.
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Affiliation(s)
- R Orlowski
- Department Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, Connecticut 06510-8064
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29
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Orlowski R, Polvino-Bodnar M, Hearing J, Miller G. Inhibition of specific binding of EBNA 1 to DNA by murine monoclonal and certain human polyclonal antibodies. Virology 1990; 176:638-42. [PMID: 2161154 DOI: 10.1016/0042-6822(90)90036-q] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
EBNA 1 was expressed as a nonfusion protein in Escherichia coli under control of the lac promoter. The major immunoreactive EBNA 1 proteins migrated as two doublets with molecular masses of about 39/41 and 49/51 kDa. Gel mobility shift experiments showed that these products exhibit the sequence-specific DNA binding on ori P previously characterized for a 28-kDa lambda N-fusion protein encompassing the carboxy third of the EBNA 1 protein. Three monoclonal antibodies previously found to react with EBNA 1 were shown to block binding of DNA by the EBNA 1 products expressed in bacteria. The same monoclonal antibodies also blocked specific DNA binding by EBNA 1 produced in Burkitt lymphoma cells infected by EB virus. Fab fragments of two monoclonal antibodies inhibited DNA binding by EBNA 1, indicating that the antibodies recognize an epitope of the protein that is involved in the recognition of DNA, or another domain crucial for DNA binding such as a dimerization site. Some but not all human antisera with antibody to EBNA 1 neutralized specific binding of EBNA 1 to DNA. These findings will help to map the residues of the EBNA 1 protein which are essential for specific binding of DNA.
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Affiliation(s)
- R Orlowski
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, Connecticut 06510
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30
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Sternås L, Middleton T, Sugden B. The average number of molecules of Epstein-Barr nuclear antigen 1 per cell does not correlate with the average number of Epstein-Barr virus (EBV) DNA molecules per cell among different clones of EBV-immortalized cells. J Virol 1990; 64:2407-10. [PMID: 2157896 PMCID: PMC249405 DOI: 10.1128/jvi.64.5.2407-2410.1990] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Epstein-Barr nuclear antigen 1 (EBNA-1) is the only viral protein required to support latent replication of Epstein-Barr virus (EBV). To assess the likelihood that EBNA-1 regulates the amount of EBV DNA in a cell, we measured the average numbers of EBNA-1 molecules and EBV DNA molecules per cell in different clones of cells. The amount of EBNA-1 protein present in recently established lymphoblastoid cell lines was measured with affinity-purified anti-EBNA-1 antibodies, and viral DNA was measured by nucleic acid hybridization. The average levels of EBNA-1 protein varied little between these cell lines, whereas the average amount of viral DNA present varied substantially; consequently, these numbers were not correlated. There is no apparent relationship between amounts of EBNA-1 and viral DNA.
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Affiliation(s)
- L Sternås
- McArdle Laboratory for Cancer Research, University of Wisconsin-Madison 53706
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31
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Spector DH, Klucher KM, Rabert DK, Wright DA. Human cytomegalovirus early gene expression. Curr Top Microbiol Immunol 1990; 154:21-45. [PMID: 2161321 DOI: 10.1007/978-3-642-74980-3_2] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- D H Spector
- Department of Biology and Center for Molecular Genetics, University of California, San Diego, La Jolla 92093
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32
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Dillner J, Wendel-Hansen V, Kjellström G, Kallin B, Rosén A. Purification and characterization of the Epstein-Barr virus nuclear antigen 2 using monoclonal antipeptide antibodies. Int J Cancer 1988; 42:721-7. [PMID: 2846447 DOI: 10.1002/ijc.2910420516] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The Epstein-Barr virus (EBV) nuclear antigen 2 (EBNA-2) is the only one of the EBNA proteins to have been implicated as an EBV-encoded transforming protein. More detailed studies of this protein have been hampered by the lack of EBNA-2-specific monoclonal antibodies (MAbs) and of purified protein. To overcome these problems, we isolated 5 hybridomas producing MAbs reactive with an 18 residue synthetic peptide corresponding to the carboxyterminus of EBNA-2. Four of the 5 MAbs were specifically reactive with EBNA-2 in its denatured form on immunoblots. The 5th antibody (115E) was reactive with the native form of EBNA-2. By using a one-step immunoaffinity purification method with 115E cross-linked to protein-A-Sepharose, we purified EBNA-2 to homogeneity, i.e., more than 1,200-fold, from Burkitt lymphoma cell extracts. A major 32-kDa associated protein and a less abundant 17-kDa protein were co-purified with EBNA-2. Immunoprecipitation with 115E from 35S-methionine-labelled cell extracts showed that the 32-kDa protein co-precipitated with EBNA-2 from EBV-positive cells, but was not detectable in immunoprecipitates of EBV-negative cells. When the immunoprecipitates or the purified proteins were immunoblotted with EBV-immune sera, only EBNA-2 was reactive, indicating that the associated proteins are of cellular origin. Immunoprecipitation of cells labelled with 32P-orthophosphate showed that EBNA-2, but not the associated proteins, is a phosphoprotein. The expression level of EBNA-2 varied between different EBV-carrying cell lines, as measured by a 2-site ELISA based on antibody 115E. In indirect immunofluorescence, the 115E MAb gave an EBNA-2-specific characteristic granular staining pattern. These characteristics of EBNA-2 resemble those of other viral transforming proteins.
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Affiliation(s)
- J Dillner
- Department of Medical Cell Genetics, Karolinska Institute, Stockholm, Sweden
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33
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Polvino-Bodnar M, Kiso J, Schaffer PA. Mutational analysis of Epstein-Barr virus nuclear antigen 1 (EBNA 1). Nucleic Acids Res 1988; 16:3415-35. [PMID: 2836795 PMCID: PMC336503 DOI: 10.1093/nar/16.8.3415] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
We have constructed a set of nonsense mutants in the EBNA 1 gene of Epstein-Barr virus by inserting a synthetic oligonucleotide, which has translational termination codons in all three reading frames, at various positions in a cloned copy of the EBNA 1 gene. The EBNA 1 proteins encoded by these mutants and three deletion mutants were analyzed using several functional assays. It was determined that there are two separable phosphorylation domains in the carboxy half of the molecule. The carboxy half of the molecule was also found to contain a region between the unique Sac I and Sac II sites that is required for transactivation of the EBNA 1-specific enhancer element found within ori P. The mutants also served to identify a 248 bp region that affects the pattern of intranuclear localization of the protein. Correlations between the functional domains established by these studies and other properties of EBNA 1 are discussed.
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Affiliation(s)
- M Polvino-Bodnar
- Laboratory of Tumor Virus Genetics, Dana-Farber Cancer Institute, Boston, MA 02115
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34
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Affiliation(s)
- J Dillner
- Department of Tumor Biology, Karolinska Institute, Stockholm, Sweden
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35
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Smotkin D, Wettstein FO. The major human papillomavirus protein in cervical cancers is a cytoplasmic phosphoprotein. J Virol 1987; 61:1686-9. [PMID: 3033296 PMCID: PMC254156 DOI: 10.1128/jvi.61.5.1686-1689.1987] [Citation(s) in RCA: 150] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
In a previous study, the most abundant viral transcript in a human papillomavirus type 16-associated cervical cancer and in a cancer-derived cell line was characterized, and its translation product, the E7 protein, was identified (D. Smotkin and F. O. Wettstein, Proc. Natl. Acad. Sci. USA 68:4680-4684, 1986). Here we show that the E7 protein had a half life of about 1 h and was located in the soluble cytoplasmic fraction. The protein was phosphorylated at serine residues and exhibited a high heterogeneous sedimentation rate in nondenaturing glycerol gradients, suggesting an oligomer formation or association with cellular protein.
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Milman G, Hwang ES. Epstein-Barr virus nuclear antigen forms a complex that binds with high concentration dependence to a single DNA-binding site. J Virol 1987; 61:465-71. [PMID: 3027376 PMCID: PMC253970 DOI: 10.1128/jvi.61.2.465-471.1987] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
A bacterially synthesized 28-kilodalton carboxyl-terminal fragment (28K-EBNA of Epstein-Barr virus nuclear antigen shows highly concentration dependent binding to monomer, dimer, and trimer copies of synthetic DNA-binding site 5' GATCTAGGATAGCATATGCTACCCCGGGG 3' 3' ATCCTATCGTATACGATGGGGCCCCCTAG 5' in bacterial plasmids. The rate of the binding reaction is independent of the number of sites, but dependent upon the length of the DNA containing the sites. These data are consistent with 28K-EBNA locating its binding sites by a process of facilitated transfer or sliding along the DNA. The highly concentration dependent binding suggests that multiple 28K-EBNA monomer polypeptides form a complex before or during binding. Binding occurs equally well at 24 and 37 degrees C, but not at 0 degrees C. A 28K-EBNA complex bound to a single site has unoccupied binding sites capable of interacting with additional DNA molecules. Such interaction is confirmed by agarose gel electrophoresis of protein-DNA complexes which indicate that a 28K-EBNA complex forms bridges between two DNA molecules. A bridge between the two binding regions in the Epstein-Barr virus origin of plasmid replication (oriP) would form a loop structure which could be an important feature for the regulatory function of authentic Epstein-Barr virus nuclear antigen.
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Wang SC, Hammarskjöld ML, Klein G. Immunoprecipitation of Epstein-Barr virus EBNA1 protein using human polyclonal serum. J Virol Methods 1986; 13:323-32. [PMID: 3018021 DOI: 10.1016/0166-0934(86)90057-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
We have developed a method that permits the use of human polyclonal serum to immunoprecipitate BamH1-K EBNA(EBNA1) from EBV transformed cell lines and from cells transfected with an expression vector containing the Bam K region of EBV. Serum from healthy seropositive donors is preabsorbed once with lysate of EBV-negative Burkitt lymphoma cells, then fractionated by gel filtration. The main IgG fraction is then used for the immunoprecipitations. Immunoprecipitated material is visualized by immunoblotting using the same serum. Two proteins with apparent molecular weights of 74 and 62 kD are specifically precipitated from extracts of B95-8 cells. Several proteins are immunoprecipitated from cells transfected with the Bam K containing vector, the apparent molecular weights of the 4 major bands are 74, 68, 62 and 57 kD. Labelling of transfected cells with [3H]glycine and [32P]orthophosphate shows that the 74 and 62 kD proteins can be labelled with both isotopes.
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Hammarskjöld ML, Wang SC, Klein G. High-level expression of the Epstein-Barr virus EBNA1 protein in CV1 cells and human lymphoid cells using a SV40 late replacement vector. Gene 1986; 43:41-50. [PMID: 3019836 DOI: 10.1016/0378-1119(86)90006-5] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
To construct a recombinant plasmid designed to yield large amounts of the Epstein-Barr virus (EBV) nuclear antigen, EBNA1, the EBV BamHI-K fragment (B95-8 strain) was inserted into an expression vector composed of SV40 and pBR322 DNA. The vector replicates in both Escherichia coli and eukaryotic cells. Introduction of such a BamHI-K-containing vector into CV1 monkey cells (using DEAE-dextran, glycerol and chloroquine diphosphate) gave high yields of the correct size EBNA1 protein in 40-50% of the transfected cells. Maximal amounts of EBNA1 could be extracted from the cells at 65-72 h post transfection. Using a quantitative ELISA assay, it was estimated that transfected cells express 500-1000 times more EBNA1 than lymphoid cells, latently infected with EBV. A monoclonal antibody directed against EBNA1 immunoprecipitated two proteins of 74 and 62 kDa from transfected cells. These same two proteins were detected in immunoprecipitation and immunoblot experiments using human EBV-positive polyclonal serum, although this serum also detected several other protein products in transfected cells. In vivo labelling of transfected cells with [32P]orthophosphate showed that the 74- and 62-kDa proteins are modified by phosphorylation. The same vector construction was also used to transfect an EBV-negative human lymphoblastoid cell line (Ramos). Expression of the EBNA1 protein was obtained in up to 20% of the cells.
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