The EBNA-2 arginine-glycine domain is critical but not essential for B-lymphocyte growth transformation; the rest of region 3 lacks essential interactive domains

A global phylogenetic analysis of Japanese tonsil-derived Epstein-Barr virus strains using viral whole-genome cloning and long-read sequencing

Epstein-Barr virus (EBV) establishes lifelong latent infection in the majority of healthy individuals, while it is a causative agent for various diseases, including some malignancies. Recent high-throughput sequencing results indicate that there are substantial levels of viral genome heterogeneity among different EBV strains. However, the extent of EBV strain variation among asymptomatically infected individuals remains elusive. Here, we present a streamlined experimental strategy to clone and sequence EBV genomes derived from human tonsillar tissues, which are the reservoirs of asymptomatic EBV infection. Complete EBV genome sequences, including those of repetitive regions, were determined for seven tonsil-derived EBV strains. Phylogenetic analyses based on the whole viral genome sequences of worldwide non-tumour-derived EBV strains revealed that Asian EBV strains could be divided into several distinct subgroups. EBV strains derived from nasopharyngeal carcinoma-endemic areas constitute different subgroups from a subgroup of EBV strains from non-endemic areas, including Japan. The results could be consistent with biased regional distribution of EBV-associated diseases depending on the different EBV strains colonizing different regions in Asian countries.

Species-specific functions of Epstein-Barr virus nuclear antigen 2 (EBNA2) reveal dual roles for initiation and maintenance of B cell immortalization

Epstein-Barr virus (EBV) and related lymphocryptoviruses (LCV) from non-human primates infect B cells, transform their growth to facilitate life-long viral persistence in the host, and contribute to B cell oncogenesis. Co-evolution of LCV with their primate hosts has led to species-specificity so that LCVs preferentially immortalize B cells from their natural host in vitro. We investigated whether the master regulator of transcription, EBV nuclear antigen 2 (EBNA2), is involved in LCV species-specificity. Using recombinant EBVs, we show that EBNA2 orthologues of LCV isolated from chimpanzees, baboons, cynomolgus or rhesus macaques cannot replace EBV EBNA2 for the immortalization of human B cells. Thus, LCV species-specificity is functionally linked to viral proteins expressed during latent, growth-transforming infection. In addition, we identified three independent domains within EBNA2 that act through species-specific mechanisms. Importantly, the EBNA2 orthologues and species-specific EBNA2 domains separate unique roles for EBNA2 in the initiation of B cell immortalization from those responsible for maintaining the immortalized state. Investigating LCV species-specificity provides a novel approach to identify critical steps underlying EBV-induced B cell growth transformation, persistent infection, and oncogenesis.

Epstein-Barr virus super-enhancer eRNAs are essential for MYC oncogene expression and lymphoblast proliferation

Epstein-Barr virus (EBV) super-enhancers (ESEs) are essential for lymphoblastoid cell (LCL) growth and survival. Reanalyses of LCL global run-on sequencing (Gro-seq) data found abundant enhancer RNAs (eRNAs) being transcribed at ESEs. Inactivation of ESE components, EBV nuclear antigen 2 (EBNA2) and bromodomain-containing protein 4 (BRD4), significantly decreased eRNAs at ESEs -428 and -525 kb upstream of the MYC oncogene transcription start site (TSS). shRNA knockdown of the MYC -428 and -525 ESE eRNA caused LCL growth arrest and reduced cell growth. Furthermore, MYC ESE eRNA knockdown also significantly reduced MYC expression, ESE H3K27ac signals, and MYC ESEs looping to MYC TSS. These data indicate that ESE eRNAs strongly affect cell gene expression and enable LCL growth.

Ribosome Protein L4 is essential for Epstein-Barr Virus Nuclear Antigen 1 function

Epstein-Barr Virus (EBV) Nuclear Antigen 1 (EBNA1)-mediated origin of plasmid replication (oriP) DNA episome maintenance is essential for EBV-mediated tumorigenesis. We have now found that EBNA1 binds to Ribosome Protein L4 (RPL4). RPL4 shRNA knockdown decreased EBNA1 activation of an oriP luciferase reporter, EBNA1 DNA binding in lymphoblastoid cell lines, and EBV genome number per lymphoblastoid cell line. EBV infection increased RPL4 expression and redistributed RPL4 to cell nuclei. RPL4 and Nucleolin (NCL) were a scaffold for an EBNA1-induced oriP complex. The RPL4 N terminus cooperated with NCL-K429 to support EBNA1 and oriP-mediated episome binding and maintenance, whereas the NCL C-terminal K380 and K393 induced oriP DNA H3K4me2 modification and promoted EBNA1 activation of oriP-dependent transcription. These observations provide new insights into the mechanisms by which EBV uses NCL and RPL4 to establish persistent B-lymphoblastoid cell infection.

EBNA2 and Its Coactivator EBNA-LP

While all herpesviruses can switch between lytic and latent life cycle, which are both driven by specific transcription programs, a unique feature of latent EBV infection is the expression of several distinct and well-defined viral latent transcription programs called latency I, II, and III. Growth transformation of B-cells by EBV in vitro is based on the concerted action of Epstein-Barr virus nuclear antigens (EBNAs) and latent membrane proteins(LMPs). EBV growth-transformed B-cells express a viral transcriptional program, termed latency III, which is characterized by the coexpression of EBNA2 and EBNA-LP with EBNA1, EBNA3A, -3B, and -3C as well as LMP1, LMP2A, and LMP2B. The focus of this review will be to discuss the current understanding of how two of these proteins, EBNA2 and EBNA-LP, contribute to EBV-mediated B-cell growth transformation.

Modulation of Epstein-Barr virus nuclear antigen 2-dependent transcription by protein arginine methyltransferase 5

Epstein-Barr Virus Nuclear Antigen (EBNA) 2 features an Arginine-Glycine repeat (RG) domain at amino acid positions 335-360, which is a known target for protein arginine methyltransferaser 5 (PRMT5). In this study, we performed protein affinity pull-down assays to demonstrate that endogenous PRMT5 derived from lymphoblastoid cells specifically associated with the protein bait GST-E2 RG. Transfection of a plasmid expressing PRMT5 induced a 2.5- to 3-fold increase in EBNA2-dependent transcription of both the LMP1 promoter in AKATA cells, which contain the EBV genome endogenously, and a Cp-Luc reporter plasmid in BJAB cells, which are EBV negative. Furthermore, we showed that there was a 2-fold enrichment of EBNA2 occupancy in target promoters in the presence of exogenous PRMT5. Taken together, we show that PRMT5 triggers the symmetric dimethylation of EBNA2 RG domain to coordinate with EBNA2-mediated transcription. This modulation suggests that PRMT5 may play a role in latent EBV infection.

Binding of the heterogeneous ribonucleoprotein K (hnRNP K) to the Epstein-Barr virus nuclear antigen 2 (EBNA2) enhances viral LMP2A expression

The Epstein-Barr Virus (EBV) -encoded EBNA2 protein, which is essential for the in vitro transformation of B-lymphocytes, interferes with cellular processes by binding to proteins via conserved sequence motifs. Its Arginine-Glycine (RG) repeat element contains either symmetrically or asymmetrically di-methylated arginine residues (SDMA and ADMA, respectively). EBNA2 binds via its SDMA-modified RG-repeat to the survival motor neurons protein (SMN) and via the ADMA-RG-repeat to the NP9 protein of the human endogenous retrovirus K (HERV-K (HML-2) Type 1). The hypothesis of this work was that the methylated RG-repeat mimics an epitope shared with cellular proteins that is used for interaction with target structures. With monoclonal antibodies against the modified RG-repeat, we indeed identified cellular homologues that apparently have the same surface structure as methylated EBNA2. With the SDMA-specific antibodies, we precipitated the Sm protein D3 (SmD3) which, like EBNA2, binds via its SDMA-modified RG-repeat to SMN. With the ADMA-specific antibodies, we precipitated the heterogeneous ribonucleoprotein K (hnRNP K). Specific binding of the ADMA- antibody to hnRNP K was demonstrated using E. coli expressed/ADMA-methylated hnRNP K. In addition, we show that EBNA2 and hnRNP K form a complex in EBV- infected B-cells. Finally, hnRNP K, when co-expressed with EBNA2, strongly enhances viral latent membrane protein 2A (LMP2A) expression by an unknown mechanism as we did not detect a direct association of hnRNP K with DNA-bound EBNA2 in gel shift experiments. Our data support the notion that the methylated surface of EBNA2 mimics the surface structure of cellular proteins to interfere with or co-opt their functional properties.

C-terminal region of EBNA-2 determines the superior transforming ability of type 1 Epstein-Barr virus by enhanced gene regulation of LMP-1 and CXCR7

Type 1 Epstein-Barr virus (EBV) strains immortalize B lymphocytes in vitro much more efficiently than type 2 EBV, a difference previously mapped to the EBNA-2 locus. Here we demonstrate that the greater transforming activity of type 1 EBV correlates with a stronger and more rapid induction of the viral oncogene LMP-1 and the cell gene CXCR7 (which are both required for proliferation of EBV-LCLs) during infection of primary B cells with recombinant viruses. Surprisingly, although the major sequence differences between type 1 and type 2 EBNA-2 lie in N-terminal parts of the protein, the superior ability of type 1 EBNA-2 to induce proliferation of EBV-infected lymphoblasts is mostly determined by the C-terminus of EBNA-2. Substitution of the C-terminus of type 1 EBNA-2 into the type 2 protein is sufficient to confer a type 1 growth phenotype and type 1 expression levels of LMP-1 and CXCR7 in an EREB2.5 cell growth assay. Within this region, the RG, CR7 and TAD domains are the minimum type 1 sequences required. Sequencing the C-terminus of EBNA-2 from additional EBV isolates showed high sequence identity within type 1 isolates or within type 2 isolates, indicating that the functional differences mapped are typical of EBV type sequences. The results indicate that the C-terminus of EBNA-2 accounts for the greater ability of type 1 EBV to promote B cell proliferation, through mechanisms that include higher induction of genes (LMP-1 and CXCR7) required for proliferation and survival of EBV-LCLs.

Epstein-Barr virus (EBV) is a common human virus that is involved in several types of cancer and directly causes human B lymphocytes to proliferate when they become infected. EBV occurs naturally as two different viral types (type 1 and type 2). The genomes of these viruses are mostly very similar but they differ in a few genes, particularly the EBNA-2 gene. For many years it has been known that type 1 EBV is much more effective than type 2 EBV at causing B lymphocyte proliferation and this difference is mediated by the EBNA-2 gene. Here we have shown that the greater ability of type 1 EBNA-2 to cause B cell proliferation is due to superior induction of the EBV LMP-1 and the cell CXCR7 genes, both of which are required for growth of EBV-infected lymphocytes. We mapped the section of type 1 EBNA-2 responsible for this to the C-terminus of the protein, including the transactivation and EBNA-LP interaction domains. The results provide a mechanism for the long-standing question of the functional difference between these two major types of EBV and will be important in understanding the significance of the EBV types in human infection.

The NP9 protein encoded by the human endogenous retrovirus HERV-K(HML-2) negatively regulates gene activation of the Epstein-Barr virus nuclear antigen 2 (EBNA2)

Epstein-Barr virus (EBV) is a human tumour virus that efficiently growth-transforms primary human B-lymphocytes in vitro. The viral nuclear antigen 2 (EBNA2) is essential for immortalisation of B-cells and stimulates viral and cellular gene expression through interaction with DNA-bound transcription factors. Like its cellular homologue Notch, it associates with the DNA-bound repressor RBPJκ (CSL/CBF1) thereby converting RBPJκ into the active state. For instance, both EBNA2 and Notch activate the cellular HES1 promoter. In EBV-transformed lymphocytes, the RNA of the NP9 protein encoded by human endogenous retrovirus HERV-K(HML-2) Type 1 is strongly up-regulated. The NP9 protein is detectable both in EBV-positive Raji cells, a Burkitt's lymphoma cell line, and in IB4, an EBV-transformed human lymphoblastoid cell line. NP9 binds to LNX that forms a complex with the Notch regulator Numb. Therefore, the function of NP9 vis-à-vis Notch and EBNA2 was analysed. Here, we show that NP9 binds to EBNA2 and negatively affects the EBNA2-mediated activation of the viral C- and LMP2A promoters. In contrast, NP9 did neither interfere in the activation of the HES1 promoter by Notch nor the induction of the viral LMP1 promoter by EBNA2. In an electrophoretic mobility shift analysis, NP9 reduced the binding of EBNA2 to DNA-bound RBPJκ by about 50%. The down-regulation of EBNA2-activity by NP9 might represent a cellular defence mechanism against viral infection or could, alternatively, represent an adaptation of the virus to prevent excessive viral protein production that might otherwise be harmful for the infected cell.

Asymmetric Arginine dimethylation of Epstein-Barr virus nuclear antigen 2 promotes DNA targeting

The Epstein-Barr virus (EBV) growth-transforms B-lymphocytes. The virus-encoded nuclear antigen 2 (EBNA2) is essential for transformation and activates gene expression by association with DNA-bound transcription factors such as RBPJkappa (CSL/CBF1). We have previously shown that EBNA2 contains symmetrically dimethylated Arginine (sDMA) residues. Deletion of the RG-repeat results in a reduced ability of the virus to immortalise B-cells. We now show that the RG repeat also contains asymmetrically dimethylated Arginines (aDMA) but neither non-methylated (NMA) Arginines nor citrulline residues. We demonstrate that only aDMA-containing EBNA2 is found in a complex with DNA-bound RBPJkappa in vitro and preferentially associates with the EBNA2-responsive EBV C, LMP1 and LMP2A promoters in vivo. Inhibition of methylation in EBV-infected cells results in reduced expression of the EBNA2-regulated viral gene LMP1, providing additional evidence that methylation is a prerequisite for DNA-binding by EBNA2 via association with the transcription factor RBPJkappa.

Four EBNA2 domains are important for EBNALP coactivation

EBNA2 transcriptional activation and regulated EBNALP coactivation are critical for Epstein-Barr virus-infected primary B-lymphocyte growth transformation. EBNALP coactivation requires the EBNA2 acidic activation domain (E2AD); EBNALP can bind to E2AD. EBNALP has now been found to bind less well to EBNA2 amino acids 1 to 58, which has been identified to be a second transcriptional activation domain, E2AD2. E2AD2 was specifically coactivated by EBNALP. Moreover, E2AD, E2AD2, EBNA2 RG domain, and the intermediate domain between RG and E2AD had significant roles in EBNA2-mediated activation and EBNALP coactivation.

Epstein-Barr virus nuclear antigen 2 binds via its methylated arginine-glycine repeat to the survival motor neuron protein

Here we provide evidence that EBNA2 is methylated in vivo and that methylation of EBNA2 is a prerequisite for binding to SMN. We present SMN as a novel binding partner of EBNA2 by showing that EBNA2 colocalizes with SMN in nuclear gems and that both proteins can be coimmunoprecipitated from cellular extract. Furthermore, in vitro methylation of either wild-type EBNA2 or a glutathione S-transferase-EBNA2 fusion protein encompassing the arginine-glycine (RG) repeat element is necessary for in vitro binding to the Tudor domain of SMN. The recently shown functional cooperation of SMN and EBNA2 in transcriptional activation and the previous observation of a severely reduced transformation potential yet strongly enhanced transcriptional activity of an EBNA2 mutant lacking the RG repeat indicate that binding of SMN to EBNA2 is a critical step in B-cell transformation by Epstein-Barr virus.

Lysine residues of Epstein-Barr virus-encoded nuclear antigen 2 do not confer secondary modifications via ubiquitin or SUMO-like proteins but modulate transcriptional activation

Epstein-Barr virus nuclear antigen 2 (EBNA2) is essential for transformation through activation of viral and cellular genes. Within 487 residues, EBNA2 contains six lysine (K) residues (positions 335, 357, 359, 363, 366 and 480), which were mutated to arginine (R) residues, either individually or in combination, and tested for subcellular localization, mobility by SDS-PAGE and transactivation of three promoters. All mutants featuring the K(480)R mutation within the nuclear localization signal were partially cytoplasmic with a reduced level of transactivation of the latent membrane protein 1 (LMP1) promoter (-327 to +40). The K(366)R mutation also showed a decrease in transactivation of a promoter consisting only of 12 recombination signal-binding protein-Jkappa-binding sites, while all mutants with the K(335)R exchange showed a markedly elevated transactivation with the -327 to +40 construct and all mutants showed slightly reduced transactivation with a -634 to +40 LMP1 promoter. None of the mutants exhibited altered migration in SDS-PAGE, excluding secondary modification, i.e. through SUMO-like proteins.

Functional cooperation of Epstein-Barr virus nuclear antigen 2 and the survival motor neuron protein in transactivation of the viral LMP1 promoter

Epstein-Barr virus nuclear antigen 2 (EBNA2) is essential for viral transformation of B cells and transactivates cellular and viral target genes by binding RBPJkappa tethered to cognate promoter elements. EBNA2 interacts with the DEAD-box protein DP103 (DDX20/Gemin3), which in turn is complexed to the survival motor neuron (SMN) protein. SMN is implicated in RNA processing, but a role in transcriptional regulation has also been suggested. Here, we show that DP103 and SMN are complexed in B cells and that SMN coactivates the viral LMP promoter in the presence of EBNA2 in reporter gene assays and in vivo. Subcellular localization studies revealed that nuclear gems and/or coiled bodies containing DP103 and SMN are targeted by EBNA2. Protein-protein interaction experiments demonstrated that DP103 binds to SMN exon 6 and that both EBNA2 and SMN interact with the C terminus of DP103. Furthermore, a DP103 binding-deficient SMN mutant was released from nuclear gems and/or coiled bodies and further enhanced coactivation. In addition, impaired transactivation of a DP103 binding-deficient EBNA2 mutant was rescued by overexpression of SMN. Testing different promoter constructs in luciferase assays showed that RBPJkappa is required but not sufficient for coactivation by EBNA2 and SMN. Overall, our data suggest that EBNA2 might target spliceosomal complexes by binding to DP103, thereby releasing SMN which subsequently exerts a coactivational function within the RNA-polymerase II transcription complex on the LMP1 promoter.

Epstein-Barr virus infection and human malignancies

The Epstein-Barr virus (EBV) is a herpes virus which establishes a life-long persistent infection in over 90% of the human adult population world-wide. Based on its association with a variety of lymphoid and epithelial malignancies, EBV has been classified as a group 1 carcinogen by the International Agency for Research on Cancer. In this article we discuss the evidence supporting an aetiological role for EBV in the pathogenesis of human tumours. The biology of EBV infection will be described with special emphasis on viral transforming gene products. A brief survey of EBV-associated tumours is followed by a discussion of specific problems. Evidence is presented which suggests that failures of the EBV-specific immunity may play a role in the pathogenesis of EBV-associated tumours also in patients without clinically manifest immunodeficiencies. Finally, the timing of EBV infection in the pathogenesis of virus-associated malignancies is discussed. There is good evidence that EBV infection precedes expansion of the malignant cell populations in some virus-associated tumours. However, this is clearly not always the case and for some of these tumours there are indications that clonal genetic alterations may occur prior to EBV infection. Thus, whilst there is good evidence to suggest that EBV is a human carcinogen, its precise role(s) in the development of virus-associated human tumours requires clarification.

Epstein-Barr virus infection and human malignancies

The Epstein-Barr virus (EBV) is a herpes virus which establishes a life-long persistent infection in over 90% of the human adult population world-wide. Based on its association with a variety of lymphoid and epithelial malignancies, EBV has been classified as a group 1 carcinogen by the International Agency for Research on Cancer. In this article we discuss the evidence supporting an aetiological role for EBV in the pathogenesis of human tumours. The biology of EBV infection will be described with special emphasis on viral transforming gene products. A brief survey of EBV-associated tumours is followed by a discussion of specific problems. Evidence is presented which suggests that failures of the EBV-specific immunity may play a role in the pathogenesis of EBV-associated tumours also in patients without clinically manifest immunodeficiencies. Finally, the timing of EBV infection in the pathogenesis of virus-associated malignancies is discussed. There is good evidence that EBV infection precedes expansion of the malignant cell populations in some virus-associated tumours. However, this is clearly not always the case and for some of these tumours there are indications that clonal genetic alterations may occur prior to EBV infection. Thus, whilst there is good evidence to suggest that EBV is a human carcinogen, its precise role(s) in the development of virus-associated human tumours requires clarification.

Epstein-Barr virus infection and human malignancies

The Epstein-Barr virus (EBV) is a herpes virus which establishes a life-long persistent infection in over 90% of the human adult population world-wide. Based on its association with a variety of lymphoid and epithelial malignancies, EBV has been classified as a group 1 carcinogen by the International Agency for Research on Cancer. In this article we discuss the evidence supporting an aetiological role for EBV in the pathogenesis of human tumours. The biology of EBV infection will be described with special emphasis on viral transforming gene products. A brief survey of EBV-associated tumours is followed by a discussion of specific problems. Evidence is presented which suggests that failures of the EBV-specific immunity may play a role in the pathogenesis of EBV-associated tumours also in patients without clinically manifest immunodeficiencies. Finally, the timing of EBV infection in the pathogenesis of virus-associated malignancies is discussed. There is good evidence that EBV infection precedes expansion of the malignant cell populations in some virus-associated tumours. However, this is clearly not always the case and for some of these tumours there are indications that clonal genetic alterations may occur prior to EBV infection. Thus, whilst there is good evidence to suggest that EBV is a human carcinogen, its precise role(s) in the development of virus-associated human tumours requires clarification.

Molecular virology of Epstein-Barr virus

Epstein-Barr virus (EBV) interacts with its host in three distinct ways in a highly regulated fashion: (i) EBV infects human B lymphocytes and induces proliferation of the infected cells, (ii) it enters into a latent phase in vivo that follows the proliferative phase, and (iii) it can be reactivated giving rise to the production of infectious progeny for reinfection of cells of the same type or transmission of the virus to another individual. In healthy people, these processes take place simultaneously in different anatomical and functional compartments and are linked to each other in a highly dynamic steady-state equilibrium. The development of a genetic system has paved the way for the dissection of those processes at a molecular level that can be studied in vitro, i.e. B-cell immortalization and the lytic cycle leading to production of infectious progeny. Polymerase chain reaction analyses coupled to fluorescent-activated cell sorting has on the other hand allowed a descriptive analysis of the virus-host interaction in peripheral blood cells as well as in tonsillar B cells in vivo. This paper is aimed at compiling our present knowledge on the process of B-cell immortalization in vitro as well as in vivo latency, and attempts to integrate this knowledge into the framework of the viral life cycle in vivo.

EBNA-LP associates with cellular proteins including DNA-PK and HA95

EBNA-LP-associated proteins were identified by sequencing proteins that immunoprecipitated with Flag epitope-tagged EBNA-LP (FLP) from lymphoblasts in which FLP was stably expressed. The association of EBNA-LP with Hsp70 (72/73) was confirmed, and sequences of DNA-PK catalytic subunit (DNA-PKcs), HA95, Hsp27, prolyl 4-hydroxylase alpha-1 subunit, alpha-tubulin, and beta-tubulin were identified. The fraction of total cellular HA95 that associated with FLP was very high, while progressively lower fractions of the total DNA-PKcs, Hsp70, Hsp 27, alpha-tubulin, and beta-tubulin specifically associated with EBNA-LP as determined by immunoblotting with antibodies to these proteins. EBNA-LP bound to two domains in the DNA-PKcs C terminus and DNA-PKcs associated with the EBNA-LP repeat domain. DNA-PKcs that was bound to EBNA-LP phosphorylated p53 or EBNA-LP in vitro, and the phosphorylation of EBNA-LP was inhibited by Wortmannin, a specific in vitro inhibitor of DNA-PKcs.

The genetic approach to the Epstein-Barr virus: from basic virology to gene therapy

The Epstein-Barr virus (EBV) infects humans and the genome of this infectious agent has been detected in several tumour types, ranging from lymphomas to carcinomas. The analysis of the functions of the numerous viral proteins encoded by EBV has been impeded by the large size of the viral genome, which renders the construction of viral mutants difficult. To overcome these limitations, several genetic systems have been developed that allow the modification of the viral genome. Two different approaches, depending on the host cell type in which the viral mutants are generated, have been used in the past. Traditionally, mutants were constructed in EBV infected eukaryotic cells, but more recently, approaches that make use of a recombinant EBV cloned in Escherichia coli have been proposed. The phenotype associated with the inactivation or modification of nearly 20 of the 100 EBV viral genes has been reported in the literature. In most of the reported cases, the EBV latent genes that mediate the ability of EBV to immortalize infected cells were the targets of the genetic analysis, but some virus mutants in which genes involved in DNA lytic replication or infection were disrupted have also been reported. The ability to modify the viral genome also opens the way to the construction of viral strains with medical relevance. A cell line infected by a virus that lacks the EBV packaging sequences can be used as a helper cell line for the encapsidation of EBV based viral vectors. This cell line will allow the evaluation of EBV as a gene transfer system with applications in gene therapy. Finally, genetically modified non-pathogenic strains will provide a basis for the design of an attenuated EBV live vaccine.

Epstein-Barr virus nuclear protein 2 interacts with p300, CBP, and PCAF histone acetyltransferases in activation of the LMP1 promoter

The Epstein-Barr virus (EBV) nuclear protein 2 (EBNA2) and herpes simplex virion protein 16 (VP16) acidic domains that mediate transcriptional activation now are found to have affinity for p300, CBP, and PCAF histone acetyltransferases (HATs). Transcriptionally inactive point mutations in these domains lack affinity for p300, CBP, or PCAF. P300 and CBP copurify with the principal HAT activities that bind to EBNA2 or VP16 acidic domains through velocity sedimentation and anion-exchange chromatography. EBNA2 binds to both the N- and C-terminal domains of p300 and coimmune-precipitates from transfected 293T cells with p300. In EBV-infected Akata Burkitt's tumor cells that do not express the EBV encoded oncoproteins EBNA2 or LMP1, p300 expression enhances the ability of EBNA2 to up-regulate LMP1 expression. Through its intrinsic HAT activity, PCAF can further potentiate the p300 effect. In 293 T cells, P300 and CBP (but not PCAF) can also coactivate transcription mediated by the EBNA2 or VP16 acidic domains and HAT-negative mutants of p300 have partial activity. Thus, the EBNA2 and VP16 acidic domains can utilize the intrinsic HAT or scaffolding properties of p300 to activate transcription.

Mapping EBNA-1 domains involved in binding to metaphase chromosomes

The Epstein-Barr virus (EBV) genome can persist in dividing human B cells as multicopy circular episomes. Viral episomes replicate in synchrony with host cell DNA and are maintained at a relatively constant copy number for a long time. Only two viral elements, the replication origin OriP and the EBNA-1 protein, are required for the persistence of viral genomes during latency. EBNA-1 activates OriP during the S phase and may also contribute to the partition and/or retention of viral genomes during mitosis. Indeed, EBNA-1 has been shown to interact with mitotic chromatin. Moreover, viral genomes are noncovalently associated with metaphase chromosomes. This suggests that EBNA-1 may facilitate the anchorage of viral genomes on cellular chromosomes, thus ensuring proper partition and retention. In the present paper, we have investigated the chromosome-binding activity of EBV EBNA-1, herpesvirus papio (HVP) EBNA-1, and various derivatives of EBV EBNA-1, fused to a variant of the green fluorescent protein. The results show that binding to metaphase chromosomes is a common property of EBV and HVP EBNA-1. Further studies indicated that at least three independent domains (CBS-1, -2, and -3) mediate EBNA-1 binding to metaphase chromosomes. In agreement with the anchorage model, two of these domains mapped to a region that has been previously demonstrated to be required for the long-term persistence of OriP-containing plasmids.

Residues 231 to 280 of the Epstein-Barr virus nuclear protein 2 are not essential for primary B-lymphocyte growth transformation

Epstein-Barr virus (EBV) nuclear protein 2 (EBNA-2) is a transcriptional transactivator of cellular and viral gene expression and is essential for the transformation of resting human B lymphocytes into long-term lymphoblastoid cell lines (LCLs). Previous molecular genetic analyses identified three domains that are critical for transformation and showed that the rest of EBNA-2 is not critical. We now find that codons 231 to 280 that were part of one of the critical domains (J. I. Cohen, F. Wang, and E. Kieff, J. Virol. 65:2545-2554, 1991) can be deleted with only a small effect on the ability of EBNA-2 to transactivate gene expression. In transient transfection assays, EBNA-2 deleted for codons 231 to 280 accumulated to higher levels and was similar to wild-type EBNA-2 in activation of the BamC promoter and in association with RBPJk, a cellular transcription factor that is important for EBNA-2 interaction with promoter regulatory elements. However, EBNA-2 d231-280 activated the viral latent membrane protein 1 (LMP1) promoter with only 60% of wild-type efficiency. Recombinant EBVs specifically deleted for EBNA-2 codons 231 to 280 were efficient in initiating the transformation of resting primary human B lymphocytes into LCLs. However, these LCLs grew less well than wild-type EBV-transformed LCLs, and 4- to 10-fold more cells were required for outgrowth following limit dilution. EBNA-2 d231-280 accumulated to unusually high levels in the recombinant transformed LCLs, and this was associated with somewhat higher EBNA-1 and lower LMP1 expression, consistent with the near-wild-type activation of the BamC EBNA promoter and the abnormally low activation of the LMP1 promoter in transient transfection assays. Thus, EBNA-2 d231-280 modestly perturbed the regulation of viral gene expression and resulted in less LMP1, while having surprisingly subtle effects on LCL outgrowth. Deletion of EBNA-2 codons 292 to 310, which are closer to the site that specifies interaction with RBPJk, was more disruptive of RBPJk association and of the ability to transform B lymphocytes.

The 131-amino-acid repeat region of the essential 39-kilodalton core protein of fowlpox virus FP9, equivalent to vaccinia virus A4L protein, is nonessential and highly immunogenic

The immunodominant, 39,000-molecular weight core protein (39K protein) of fowlpox virus (FP9 strain), equivalent to the vaccinia virus A4L gene product, contains highly charged domains at each end of the protein and multiple copies of a 12-amino-acid serine-rich repeat sequence in the middle of the protein. Similar repeats were also detected in other fowlpox virus strains, suggesting that they might confer a selective advantage to the virus. The molloscum contagiosum virus homolog (MC107L) also contains repeats, unlike the vaccinia virus protein. The number of repeats in the fowlpox virus protein does not seem to be crucial, since some strains have a different number of repeats, as shown by the difference in the size of the protein in these strains. The repeat region could be deleted, indicating that it is not essential for replication in vitro. It was not possible to delete the entire 39K protein, indicating that it was essential (transcriptional control signals for the flanking genes were left intact). The repeat region is partly responsible for the immunodominance of the protein, but the C-terminal part of the protein also contains highly antigenic linear epitopes. A role for the 39K protein in immune system modulation is discussed.

The N-terminal half of EBNA2, except for seven prolines, is not essential for primary B-lymphocyte growth transformation

Previous molecular genetic analyses of Epstein-Barr virus nuclear protein 2 (EBNA2) identified a negative effect of deletion of codons 19 to 33 on transformation and gene transactivation, while deletion of codons 19 to 110 was a null mutation for transformation and gene transactivation. We here report the surprising finding that codons 2 to 88, which encode the highly conserved unique N terminus (amino acids 1 to 58) and most of the polyproline repeat (amino acids 59 to 95), can be deleted with only minimal effects on transformation. Codons 97 to 122 can also be deleted with only minimal effects on transformation. However, deletion of 35 of the 37 prolines (amino acids 59 to 93) or deletion of codons 2 to 95 results in a null transforming phenotype. Although EBNA2 from which codons 59 to 93 were deleted was a null mutation for transformation, it was similar to some transforming mutants of EBNA2 in abundance, in interaction with RBPJK, and in transactivation of the LMP1 promoter in transient transfection assays. These data indicate that between three and seven prolines are critical for EBNA2 structure or for intermolecular interaction. Aside from these seven prolines, codons encoding the rest of the N-terminal half (amino acids 2 to 230) of EBNA2 are nonessential for primary B-lymphocyte growth transformation.

The Epstein-Barr virus nuclear protein 2 acidic domain forms a complex with a novel cellular coactivator that can interact with TFIIE

Epstein-Barr virus nuclear antigen 2 (EBNA 2) activates transcription of specific genes and is essential for B-lymphocyte transformation. EBNA 2 has an acidic activation domain which interacts with general transcription factors TFIIB, TFIIH, and TAF40. We now show that EBNA 2 is specifically bound to a novel nuclear protein, p100, and that p100 can coactivate gene expression mediated by the EBNA 2 acidic domain. The EBNA 2 acidic domain was used to affinity purify p100. cDNA clones encoding the p100 open reading frame were identified on the basis of peptide sequences of the purified protein. Antibody against p100 coimmunoprecipitated p100 and EBNA 2 from Epstein-Barr virus-transformed lymphocyte extracts, indicating that EBNA 2 and p100 are complexed in vivo. p100 overexpression in cells specifically augmented EBNA 2 acidic domain-mediated activation. The coactivating effect is probably mediated by p100 interaction with TFIIE. Bacterially expressed p100 specifically adsorbs TFIIE from nuclear extracts, and in vitro-translated p56 or p34 TFIIE subunit can independently bind to p100. p100 also appears to be essential for normal cell growth, since cell viability was reduced by antisense p100 RNA and restored by sense p100 RNA expression.

Epstein-Barr virus nuclear protein 3C modulates transcription through interaction with the sequence-specific DNA-binding protein J kappa

The Epstein-Barr virus (EBV) nuclear protein 3C (EBNA 3C) is essential for EBV-mediated transformation of primary B lymphocytes, is turned on by EBNA 2, and regulates transcription of some of the viral and cellular genes which are regulated by EBNA 2. EBNA 2 is targeted to response elements by binding to the DNA sequence-specific, transcriptional repressor protein J kappa. We now show that EBNA 3C also binds to J kappa. EBNA 3C causes J kappa to not bind DNA or EBNA 2. J kappa DNA binding activity in EBV-transformed lymphoblastoid cells is consequently reduced. More than 10% of the EBNA 3C coimmunoprecipitated with J kappa from extracts of non-EBV-infected B lymphoblasts that had been stably converted to EBNA 3C expression. EBNA 3C in nuclear extracts from these cells (or in vitro-translated EBNA 3C) prevented J kappa from interacting with a high-affinity DNA binding site. Under conditions of transient overexpression in B lymphoblasts, EBNA 2 and EBNA 3C associated with J kappa and less EBNA 2 associated with J kappa when EBNA 3C was coexpressed in the same cell. EBNA 3C had no effect on the activity of a -512/+40 LMP1 promoter-CAT reporter construct that has two upstream J kappa sites, but it did inhibit EBNA 2 transactivation of this promoter. These data are compatible with a role for EBNA 3C as a "feedback" down modulator of EBNA 2-mediated transactivation. EBNA 3C could, in theory, also activate transcription by inhibiting the interaction of the J kappa repressor with its cognate DNA. The interaction of two viral transcriptional regulators with the same cell protein may reflect an unusually high level of complexity or stringency in target gene regulation.

The Epstein-Barr virus nuclear protein 2 acidic domain can interact with TFIIB, TAF40, and RPA70 but not with TATA-binding protein

The Epstein-Barr virus nuclear antigen 2 (EBNA-2) acidic domain is essential for B-lymphocyte growth transformation and can activate transcription when brought to a promoter by a sequence-specific DNA-binding domain. We now show that the EBNA-2 acidic domain has slightly less activity than the proteotypic acidic transactivator VP16 in depleting nuclear extracts of basal transcription activity. Like VP16, EBNA-2 associates with TFIIB, TAF40, and RPA70. However, EBNA-2 has much less avidity for TATA-binding protein. A Trp-to-Thr mutation within the acidic domain abolishes EBNA-2 transactivating activity and greatly compromises the association with TFIIB, TAF40, and RPA70, establishing a genetic linkage between transactivating activity and these associations.