Epstein-Barr virus (EBV), a human gammaherpesvirus, is associated with a series of malignant tumors. These include lymphomas (Burkitt’s lymphoma, Hodgkin’s disease, T/NK-cell lymphoma, post-transplant lymphoproliferative disease, AIDS-associated lymphoma, X-linked lymphoproliferative syndrome), carcinomas (nasopharyngeal carcinoma, gastric carcinoma, carcinomas of major salivary glands, thymic carcinoma, mammary carcinoma) and a sarcoma (leiomyosarcoma). The latent EBV genomes persist in the tumor cells as circular episomes, co-replicating with the cellular DNA once per cell cycle. The expression of latent EBV genes is cell type specific due to the strict epigenetic control of their promoters. DNA methylation, histone modifications and binding of key cellular regulatory proteins contribute to the regulation of alternative promoters for transcripts encoding the nuclear antigens EBNA1 to 6 and affect the activity of promoters for transcripts encoding transmembrane proteins (LMP1, LMP2A, LMP2B). In addition to genes transcribed by RNA polymerase II, there are also two RNA polymerase III transcribed genes in the EBV genome (EBER 1 and 2). The 5′ and internal regulatory sequences of EBER 1 and 2 transcription units are invariably unmethylated. The highly abundant EBER 1 and 2 RNAs are not translated to protein. Based on the cell type specific epigenetic marks associated with latent EBV genomes one can distinguish between viral epigenotypes that differ in transcriptional activity in spite of having an identical (or nearly identical) DNA sequence. Whereas latent EBV genomes are regularly targeted by epigenetic control mechanisms in different cell types, EBV encoded proteins may, in turn, affect the activity of a set of cellular promoters by interacting with the very same epigenetic regulatory machinery. There are EBNA1 binding sites in the human genome. Because high affinity binding of EBNA1 to its recognition sites is known to specify sites of DNA demethylation, we suggest that binding of EBNA1 to its cellular target sites may elicit local demethylation and contribute thereby to the activation of silent cellular promoters. EBNA2 interacts with histone acetyltransferases, and EBNALP (EBNA5) coactivates transcription by displacing histone deacetylase 4 from EBNA2-bound promoter sites. EBNA3C (EBNA6) seems to be associated both with histone acetylases and deacetylases, although in separate complexes. LMP1, a transmembrane protein involved in malignant transformation, can affect both alternative systems of epigenetic memory, DNA methylation and the Polycomb-trithorax group of protein complexes. In epithelial cells LMP1 can up-regulate DNA methyltransferases and, in Hodgkin lymphoma cells, induce the Polycomb group protein Bmi-1. In addition, LMP1 can also modulate cellular gene expression programs by affecting, via the NF-κB pathway, levels of cellular microRNAs miR-146a and miR-155. These interactions may result in epigenetic dysregulation and subsequent cellular dysfunctions that may manifest in or contribute to the development of pathological changes (e.g. initiation and progression of malignant neoplasms, autoimmune phenomena, immunodeficiency). Thus, Epstein-Barr virus, similarly to other viruses and certain bacteria, may induce pathological changes by epigenetic reprogramming of host cells. Elucidation of the epigenetic consequences of EBV-host interactions (within the framework of the emerging new field of patho-epigenetics) may have important implications for therapy and disease prevention, because epigenetic processes are reversible and continuous silencing of EBV genes contributing to patho-epigenetic changes may prevent disease development.
Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus linked to a number of B cell cancers and lymphoproliferative disorders. During latent infection, EBV expresses 25 viral pre-microRNAs (miRNAs) and induces the expression of specific host miRNAs, such as miR-155 and miR-21, which potentially play a role in viral oncogenesis. To date, only a limited number of EBV miRNA targets have been identified; thus, the role of EBV miRNAs in viral pathogenesis and/or lymphomagenesis is not well defined. Here, we used photoactivatable ribonucleoside-enhanced crosslinking and immunoprecipitation (PAR-CLIP) combined with deep sequencing and computational analysis to comprehensively examine the viral and cellular miRNA targetome in EBV strain B95-8-infected lymphoblastoid cell lines (LCLs). We identified 7,827 miRNA-interaction sites in 3,492 cellular 3′UTRs. 531 of these sites contained seed matches to viral miRNAs. 24 PAR-CLIP-identified miRNA:3′UTR interactions were confirmed by reporter assays. Our results reveal that EBV miRNAs predominantly target cellular transcripts during latent infection, thereby manipulating the host environment. Furthermore, targets of EBV miRNAs are involved in multiple cellular processes that are directly relevant to viral infection, including innate immunity, cell survival, and cell proliferation. Finally, we present evidence that myc-regulated host miRNAs from the miR-17/92 cluster can regulate latent viral gene expression. This comprehensive survey of the miRNA targetome in EBV-infected B cells represents a key step towards defining the functions of EBV-encoded miRNAs, and potentially, identifying novel therapeutic targets for EBV-associated malignancies.
Over 90% of adults worldwide are infected with Epstein-Barr virus (EBV). While EBV infection is normally controlled by a healthy immune system, in immuno-compromised individuals, EBV can cause serious disease and/or cancer. During infection, EBV expresses viral microRNAs (miRNAs) and induces the expression of specific cellular miRNAs. In general, miRNAs inhibit target gene expression by binding to complementary regions on target messenger RNAs (mRNA). While cellular miRNAs regulate important biological processes such as cell growth and differentiation, and many miRNAs have been linked to cancer progression, the functions of EBV miRNAs are largely unknown. To identify targets of EBV miRNAs and cellular miRNAs in EBV-infected cells, we used a high-throughput method based on next-generation sequencing technology to give a global picture of miRNA-regulated gene expression. Our analysis showed that over 500 mRNAs can be regulated by viral miRNAs, many of which are directly relevant to EBV infection. This study provides a comprehensive survey of viral and cellular miRNA targets in B cells, which is a positive step towards identifying novel therapeutic targets for EBV-associated cancers.
Epstein-Barr virus (EBV) is a human lymphocryptovirus that is associated with several malignancies. Elevated EBV DNA in the blood is observed in transplant recipients prior to, and at the time of post-transplant lymphoproliferative disease; thus, a vaccine that either prevents EBV infection or lowers the viral load might reduce certain EBV malignancies. Two major approaches have been suggested for an EBV vaccine- immunization with either EBV glycoprotein 350 (gp350) or EBV latency proteins (e.g. EBV nuclear antigens [EBNAs]). No comparative trials, however, have been performed. Rhesus lymphocryptovirus (LCV) encodes a homolog for each gene in EBV and infection of monkeys reproduces the clinical, immunologic, and virologic features of both acute and latent EBV infection. We vaccinated rhesus monkeys at 0, 4 and 12 weeks with (a) soluble rhesus LCV gp350, (b) virus-like replicon particles (VRPs) expressing rhesus LCV gp350, (c) VRPs expressing rhesus LCV gp350, EBNA-3A, and EBNA-3B, or (d) PBS. Animals vaccinated with soluble gp350 produced higher levels of antibody to the glycoprotein than those vaccinated with VRPs expressing gp350. Animals vaccinated with VRPs expressing EBNA-3A and EBNA-3B developed LCV-specific CD4 and CD8 T cell immunity to these proteins, while VRPs expressing gp350 did not induce detectable T cell immunity to gp350. After challenge with rhesus LCV, animals vaccinated with soluble rhesus LCV gp350 had the best level of protection against infection based on seroconversion, viral DNA, and viral RNA in the blood after challenge. Surprisingly, animals vaccinated with gp350 that became infected had the lowest LCV DNA loads in the blood at 23 months after challenge. These studies indicate that gp350 is critical for both protection against infection with rhesus LCV and for reducing the viral load in animals that become infected after challenge. Our results suggest that additional trials with soluble EBV gp350 alone, or in combination with other EBV proteins, should be considered to reduce EBV infection or virus-associated malignancies in humans.
Epstein-Barr virus (EBV) is the primary cause of infectious mononucleosis and is associated with several cancers. Presently there is no licensed vaccine to prevent EBV diseases. Two types of candidate vaccines are under development; one involves immunization with the major glycoprotein (gp350) on the outside of the virus, while the other involves vaccination with EBV proteins expressed during latency. We compared these two types of candidate vaccines in a rhesus monkey model of EBV and found that the gp350 vaccine induced better protection from infection. In addition, animals that received the rhesus EBV glycoprotein and became infected had a lower level of rhesus EBV DNA in the blood at 23 months after challenge than animals that received the rhesus EBV latency protein vaccine that subsequently were infected. Since levels of EBV DNA in the blood have been predictive for EBV lymphomas in transplant patients, the ability of rhesus EBV gp350 to reduce levels of rhesus EBV in the blood after infection suggests the EBV gp350 could have a role in reducing certain EBV-associated cancers. This is the first test of candidate vaccines in the rhesus monkey model of EBV and shows that this model should be useful in further evaluation of EBV vaccines.
In human B cells infected with Epstein-Barr virus (EBV), latency-associated virus gene products inhibit expression of the pro-apoptotic Bcl-2-family member Bim and enhance cell survival. This involves the activities of the EBV nuclear proteins EBNA3A and EBNA3C and appears to be predominantly directed at regulating Bim mRNA synthesis, although post-transcriptional regulation of Bim has been reported. Here we show that protein and RNA stability make little or no contribution to the EBV-associated repression of Bim in latently infected B cells. However, treatment of cells with inhibitors of histone deacetylase (HDAC) and DNA methyltransferase (DNMT) enzymes indicated that epigenetic mechanisms are involved in the down-regulation of Bim. This was initially confirmed by chromatin immunoprecipitation analysis of histone acetylation levels on the Bim promoter. Consistent with this, methylation-specific PCR (MSP) and bisulphite sequencing of regions within the large CpG island located at the 5′ end of Bim revealed significant methylation of CpG dinucleotides in all EBV-positive, but not EBV-negative B cells examined. Genomic DNA samples exhibiting methylation of the Bim promoter included extracts from a series of explanted EBV-positive Burkitt's lymphoma (BL) biopsies. Subsequent analyses of the histone modification H3K27-Me3 (trimethylation of histone H3 lysine 27) and CpG methylation at loci throughout the Bim promoter suggest that in EBV-positive B cells repression of Bim is initially associated with this repressive epigenetic histone mark gradually followed by DNA methylation at CpG dinucleotides. We conclude that latent EBV initiates a chain of events that leads to epigenetic repression of the tumour suppressor gene Bim in infected B cells and their progeny. This reprogramming of B cells could have important implications for our understanding of EBV persistence and the pathogenesis of EBV-associated disease, in particular BL.
Bim is a cellular inducer of programmed cell death (pcd), so the level of Bim is a critical regulator of lymphocyte survival and reduced expression enhances lymphomagenesis in mice and humans. Regulation of Bim is uniquely important in the pathogenesis of Burkitt's lymphoma (BL), since in this human childhood cancer the Myc gene is deregulated by chromosomal translocation and Myc can induce pcd via Bim. Latent EBV represses Bim expression, and here we have discovered that this involves mechanisms that reprogramme B cells and their progeny. EBV does not significantly alter Bim protein or RNA stability, but relief of EBV-mediated repression by specific inhibitors suggested it involves modifications to chromatin. Consistent with this, reduced histone acetylation and increased levels of DNA methylation on the Bim promoter were found after latent EBV infection. Further analysis suggested that the DNA methylation is preceded by repression mediated via a polycomb protein repressive complex targeting the Bim gene. By initiating the heritable suppression of Bim, EBV increases the likelihood of B lymphomagenesis in general and BL in particular. This reprogramming of B cells by EBV may also play a role in the development of other chronic disorders such as autoimmune disease and suggests a general mechanism that could contribute to the pathogenesis associated with other microorganisms.
Epstein-Barr virus (EBV) is associated with a number of different human tumors and appears to play different pathogenetic roles in each case. Thus, immunoblastic B cell lymphomas of the immunosuppressed display the full pattern of EBV latent gene expression (expressing Epstein-Barr nuclear antigen [EBNA]1, 2, 3A, 3B, 3C, and -LP, and latent membrane protein [LMP]1, 2A, and 2B), just as do B lymphoblastoid cell lines transformed by the virus in vitro. In contrast, those EBV-associated tumors with a more complex, multistep pathogenesis show more restricted patterns of viral gene expression, limited in Burkitt's lymphoma to EBNA1 only and in nasopharyngeal carcinoma (NPC) to EBNA1 and LMP1, 2A, and 2B. Recent evidence has implicated EBV in the pathogenesis of another lymphoid tumor, Hodgkin's disease (HD), where the malignant Hodgkin's and Reed-Sternberg (HRS) cells are EBV genome positive in up to 50% of cases. Here we extend preliminary results on viral gene expression in HRS cells by adopting polymerase chain reaction-based and in situ hybridization assays capable of detecting specific EBV latent transcripts diagnostic of the different possible forms of EBV latency. We show that the transcriptional program of the virus in HRS cells is similar to that seen in NPC in several respects: (a) selective expression of EBNA1 mRNA from the BamHI F promoter; (b) downregulation of the BamHI C and W promoters and their associated EBNA mRNAs; (c) expression of LMP1 and, in most cases, LMP2A and 2B transcripts; and (d) expression of the "rightward-running" BamHI A transcripts once thought to be unique to NPC. This form of latency, consistently detected in EBV-positive HD irrespective of histological subtype, implies an active role for the virus in the pathogenesis of HD and also suggests that the tumor may remain sensitive to at least certain facets of the EBV-induced cytotoxic T cell response.
MicroRNAs (miRNAs) are a family of small RNA molecules that negatively regulate the expression of protein-coding genes and play critical roles in orchestrating diverse cellular processes. This regulatory mechanism is also exploited by viruses to direct their life cycle and evade the host immune system. Epstein-Barr virus (EBV) is an oncogenic virus that is closely associated with multiple human diseases, including nasopharyngeal carcinoma (NPC), which is a highly metastatic type of tumor and is frequently reported in South Asia. Several viral proteins have been found to promote the migration and invasiveness of NPC cells. However, not all tumor tissues express these viral oncoproteins, suggesting that other mechanisms may contribute to the aggressive behavior of NPC tumor cells. A previous sequencing study by our group revealed that the EBV miRNA miR-BART9 was expressed at high levels in all EBV-positive NPC tissues. In the present study, we used gain- and loss-of-function approaches to investigate the effect of miR-BART9 in EBV-negative and EBV-positive NPC cells. We discovered that miR-BART9 promotes the migration and invasiveness of cultured NPC cells. The promigratory activity observed in vitro was manifested as an enhanced metastatic ability in vivo. Computational analysis revealed that miR-BART9 may target E-cadherin, a membrane protein that is pivotal in preserving cell-cell junctions and the epithelial phenotype. Through biochemical assays and functional rescue analysis, we confirmed that miR-BART9 specifically inhibits E-cadherin to induce a mesenchymal-like phenotype and promote the migration of NPC cells. These results indicated that miR-BART9 is a prometastatic viral miRNA and suggested that high levels of miR-BART9 in EBV-positive NPC cells may contribute to the aggressiveness of tumor cells.
MicroRNAs (miRNAs) are a family of small RNA molecules that negatively regulate the expression of protein-coding genes and orchestrate diverse cellular processes. This regulatory mechanism is also exploited by viruses to manage their life cycle and to evade the host immune system. Epstein-Barr virus (EBV) is closely associated with nasopharyngeal carcinoma (NPC), which is a highly metastatic type of tumor. A previous by our group study discovered that the EBV miRNA miR-BART9 is expressed at high levels in all EBV-positive NPC tissues. In the present study, we used gain- and loss-of-function approaches to investigate the function of miR-BART9 in EBV-negative and EBV-positive NPC cells. We showed that miR-BART9 promotes the migration and invasiveness of cultured NPC cells and enhances the metastatic ability of NPC tumors in vivo. Through computational analysis, we discovered that E-cadherin, a membrane protein that is critical for maintaining cell-cell contact and suppressing tumor metastasis, is a potential target for miR-BART9. Through biochemical assays and a functional rescue analysis, we confirmed that miR-BART9 specifically inhibits E-cadherin to enhance the motility of NPC cells. Our results show that miR-BART9 is a prometastatic viral miRNA and suggest that miR-BART9 may contribute to the aggressiveness of EBV-positive NPC tumors.
Latent Epstein-Barr virus (EBV) infection and growth transformation of B lymphocytes is characterized by EBV nuclear and membrane protein expression (EBV nuclear antigen [EBNA] and latent membrane protein [LMP], respectively). LMP1 is known to be an oncogene in rodent fibroblasts and to induce B-lymphocyte activation and cellular adhesion molecules in the EBV-negative Burkitt's lymphoma cell line Louckes. EBNA-2 is required for EBV-induced growth transformation; it lowers rodent fibroblast serum dependence and specifically induces the B-lymphocyte activation antigen CD23 in Louckes cells. These initial observations are now extended through an expanded study of EBNA- and LMP1-induced phenotypic effects in a different EBV-negative B-lymphoma cell line, BJAB. LMP1 effects were also evaluated in the EBV-negative B-lymphoma cell line BL41 and the EBV-positive Burkitt's lymphoma cell line, Daudi (Daudi is deleted for EBNA-2 and does not express LMP). Previously described EBNA-2- and LMP1-transfected Louckes cells were studied in parallel. EBNA-2, from EBV-1 strains but not EBV-2, induced CD23 and CD21 expression in transfected BJAB cells. In contrast, EBNA-3C induced CD21 but not CD23, while no changes were evident in vector control-, EBNA-1-, or EBNA-LP-transfected clones. EBNAs did not affect CD10, CD30, CD39, CD40, CD44, or cellular adhesion molecules. LMP1 expression in all cell lines induced growth in large clumps and expression of the cellular adhesion molecules ICAM-1, LFA-1, and LFA-3 in those cell lines which constitutively express low levels. LMP1 expression induced marked homotypic adhesion in the BJAB cell line, despite the fact that there was no significant increase in the high constitutive BJAB LFA-1 and ICAM-1 levels, suggesting that LMP1 also induces an associated functional change in these molecules. LMP1 induction of these cellular adhesion molecules was also associated with increased heterotypic adhesion to T lymphocytes. The Burkitt's lymphoma marker, CALLA (CD10), was uniformly down regulated by LMP1 in all cell lines. In contrast, LMP1 induced unique profiles of B-lymphocyte activation antigens in the various cell lines. LMP1 induced CD23 and CD39 in BJAB; CD23 in Louckes; CD39 and CD40 in BL41; and CD21, CD40, and CD44 in Daudi. In BJAB, CD23 surface and mRNA expression were markedly increased by EBNA-2 and LMP1 coexpression, compared with EBNA-2 or LMP1 alone. This cooperative effect was CD23 specific, since no such effect was observed on another marker, CD21.(ABSTRACT TRUNCATED AT 400 WORDS)
Epstein-Barr virus (EBV), an oncogenic human herpesvirus, induces cell proliferation after infection of resting B lymphocytes, its reservoir in vivo. The viral latent proteins are necessary for permanent B cell growth, but it is unknown whether they are sufficient. EBV was recently found to encode microRNAs (miRNAs) that are expressed in infected B cells and in some EBV-associated lymphomas. EBV miRNAs are grouped into two clusters located either adjacent to the BHRF1 gene or in introns contained within the viral BART transcripts. To understand the role of the BHRF1 miRNA cluster, we have constructed a virus mutant that lacks all its three members (Δ123) and a revertant virus. Here we show that the B cell transforming capacity of the Δ123 EBV mutant is reduced by more than 20-fold, relative to wild type or revertant viruses. B cells exposed to the knock-out virus displayed slower growth, and exhibited a two-fold reduction in the percentage of cells entering the cell cycle S phase. Furthermore, they displayed higher latent gene expression levels and latent protein production than their wild type counterparts. Therefore, the BHRF1 miRNAs accelerate B cell expansion at lower latent gene expression levels. Thus, this miRNA cluster simultaneously enhances expansion of the virus reservoir and reduces the viral antigenic load, two features that have the potential to facilitate persistence of the virus in the infected host. Thus, the EBV BHRF1 miRNAs may represent new therapeutic targets for the treatment of some EBV-associated lymphomas.
To persist in their hosts, herpes viruses must avoid recognition by the host's immune system. Down-regulation of viral antigen production through expression of viral miRNAs is a particularly elegant mechanism as these genetic elements do not encode proteins and remain therefore invisible to the immune system. Upon primary infection, Epstein-Barr virus (EBV) colonizes B cells and, through expression of its latent proteins, induces their continuous proliferation. The resulting expansion of infected B cells elicits a T cell response directed against the latent proteins that results in their elimination. Therefore, rapid proliferation of infected B cells, combined with reduced latent protein production, would facilitate establishment of EBV's viral reservoir before mounting of the immune response. Here, we find that a cluster of three microRNAs encoded near the EBV BHRF1 gene is crucial for efficient B cell transformation. In the absence of these genetic elements, infected B cells grow markedly more slowly. Furthermore, B cells exposed to an EBV mutant that lacks the BHRF1 microRNA cluster produced more latent proteins. Thus, the BHRF1 microRNA cluster possesses properties that potentiate EBV's oncogenic properties and therefore facilitate expansion of the EBV B cell reservoir.
MicroRNAs (miRNA) have emerged as an important new class of modulators of gene expression. In this study we investigated miRNA that are differentially expressed in lupus nephritis. Microarray technology was used to investigate differentially expressed miRNA in peripheral blood mononuclear cells (PBMCs) and Epstein-Barr Virus (EBV)-transformed cell lines obtained from lupus nephritis affected patients and unaffected controls. TaqMan-based stem-loop real-time polymerase chain reaction was used for validation. Microarray analysis of miRNA expressed in both African American (AA) and European American (EA) derived lupus nephritis samples revealed 29 and 50 differentially expressed miRNA, respectively, of 850 tested. There were 18 miRNA that were differentially expressed in both racial groups. When samples from both racial groups and different specimen types were considered, there were 5 primary miRNA that were differentially expressed. We have identified 5 miRNA; hsa-miR-371-5P, hsa-miR-423-5P, hsa-miR-638, hsa-miR-1224-3P and hsa-miR-663 that were differentially expressed in lupus nephritis across different racial groups and all specimen types tested. Hsa-miR-371-5P, hsa-miR-1224-3P and hsa-miR-423-5P, are reported here for the first time to be associated with lupus nephritis. Our work establishes EBV-transformed B cell lines as a useful model for the discovery of miRNA as biomarkers for SLE. Based on these findings, we postulate that these differentially expressed miRNA may be potential novel biomarkers for SLE as well as help elucidate pathogenic mechanisms of lupus nephritis. The investigation of miRNA profiles in SLE may lead to the discovery and development of novel methods to diagnosis, treat and prevent SLE.
Infection with the Epstein-Barr virus (EBV) is a strong predisposing factor in the development of nasopharyngeal carcinoma (NPC). Many viral gene products including EBNA1, LMP1, and LMP2 have been implicated in NPC tumorigenesis, although the de novo control of these viral oncoproteins remains largely unclear. The recent discovery of EBV-encoded viral microRNA (miRNA) in lymphoid malignancies has prompted us to examine the NPC-associated EBV miRNA. Using large-scale cloning analysis on EBV-positive NPC cells, two novel EBV miRNA, now named miR-BART21 and miR-BART22, were identified. These two EBV-encoded miRNA are abundantly expressed in most NPC samples. We found two nucleotide variations in the primary transcript of miR-BART22, which we experimentally confirmed to augment its biogenesis in vitro and thus may underline the high and consistent expression of miR-BART22 in NPC tumors. More importantly, we determined that the EBV latent membrane protein 2A (LMP2A) is the putative target of miR-BART22. LMP2A is a potent immunogenic viral antigen that is recognized by the cytotoxic T cells; down-modulation of LMP2A expression by miR-BART22 may permit escape of EBV-infected cells from host immune surveillance. Taken together, we demonstrated that two newly identified EBV-encoded miRNA are highly expressed in NPC. Specific sequence variations on the prevalent EBV strain in our locality might contribute to the higher miR-BART22 expression level in our NPC samples. Our findings emphasize the role of miR-BART22 in modulating LMP2A expression, which may facilitate NPC carcinogenesis by evading the host immune response.
The Epstein-Barr virus (EBV) is an oncogenic human Herpes virus involved in the pathogenesis of nasal NK/T-cell lymphoma. EBV encodes microRNAs (miRNAs) and induces changes in the host cellular miRNA profile. MiRNAs are short non-coding RNAs of about 19–25 nt length that regulate gene expression by post-transcriptional mechanisms and are frequently deregulated in human malignancies including cancer. The microRNA profiles of EBV-positive NK/T-cell lymphoma, non-infected T-cell lymphoma and normal thymus were established by deep sequencing of small RNA libraries. The comparison of the EBV-positive NK/T-cell vs. EBV-negative T-cell lymphoma revealed 15 up- und 16 down-regulated miRNAs. In contrast, the majority of miRNAs was repressed in the lymphomas compared to normal tissue. We also identified 10 novel miRNAs from known precursors and two so far unknown miRNAs. The sequencing results were confirmed for selected miRNAs by quantitative Real-Time PCR (qRT-PCR). We show that the proinflammatory cytokine interleukin 1 alpha (IL1A) is a target for miR-142-3p and the oncogenic BCL6 for miR-205. MiR-142-3p is down-regulated in the EBV-positive vs. EBV-negative lymphomas. MiR-205 was undetectable in EBV-negative lymphoma and strongly down-regulated in EBV-positive NK/T-cell lymphoma as compared to thymus. The targets were confirmed by reporter assays and by down-regulation of the proteins by ectopic expression of the cognate miRNAs. Taken together, our findings demonstrate the relevance of deregulated miRNAs for the post-transcriptional gene regulation in nasal NK/T-cell lymphomas.
The reports on the origin of human CD8+ Vα24+ T-cell receptor (TCR) natural killer T (NKT) cells are controversial. The underlying mechanism that controls human CD4 versus CD8 NKT cell development is not well-characterized. In the present study, we have studied total 177 eligible patients and subjects including 128 healthy latent Epstein-Barr-virus(EBV)-infected subjects, 17 newly-onset acute infectious mononucleosis patients, 16 newly-diagnosed EBV-associated Hodgkin lymphoma patients, and 16 EBV-negative normal control subjects. We have established human-thymus/liver-SCID chimera, reaggregated thymic organ culture, and fetal thymic organ culture. We here show that the average frequency of total and CD8+ NKT cells in PBMCs from 128 healthy latent EBV-infected subjects is significantly higher than in 17 acute EBV infectious mononucleosis patients, 16 EBV-associated Hodgkin lymphoma patients, and 16 EBV-negative normal control subjects. However, the frequency of total and CD8+ NKT cells is remarkably increased in the acute EBV infectious mononucleosis patients at year 1 post-onset. EBV-challenge promotes CD8+ NKT cell development in the thymus of human-thymus/liver-SCID chimeras. The frequency of total (3% of thymic cells) and CD8+ NKT cells (∼25% of NKT cells) is significantly increased in EBV-challenged chimeras, compared to those in the unchallenged chimeras (<0.01% of thymic cells, CD8+ NKT cells undetectable, respectively). The EBV-induced increase in thymic NKT cells is also reflected in the periphery, where there is an increase in total and CD8+ NKT cells in liver and peripheral blood in EBV-challenged chimeras. EBV-induced thymic CD8+ NKT cells display an activated memory phenotype (CD69+CD45ROhiCD161+CD62Llo). After EBV-challenge, a proportion of NKT precursors diverges from DP thymocytes, develops and differentiates into mature CD8+ NKT cells in thymus in EBV-challenged human-thymus/liver-SCID chimeras or reaggregated thymic organ cultures. Thymic antigen-presenting EBV-infected dendritic cells are required for this process. IL-7, produced mainly by thymic dendritic cells, is a major and essential factor for CD8+ NKT cell differentiation in EBV-challenged human-thymus/liver-SCID chimeras and fetal thymic organ cultures. Additionally, these EBV-induced CD8+ NKT cells produce remarkably more perforin than that in counterpart CD4+ NKT cells, and predominately express CD8αα homodimer in their co-receptor. Thus, upon interaction with certain viruses, CD8 lineage-specific NKT cells are developed, differentiated and matured intrathymically, a finding with potential therapeutic importance against viral infections and tumors.
We show that the average frequency of total and CD8+ NKT cells in PBMCs from 128 healthy latent EBV-infected subjects is significantly higher than in 17 patients with acute lytic EBV infection, 16 EBV-associated HL patients, and 16 EBV-negative normal subjects. The frequency of total and CD8+ NKT cells is remarkably increased in the lytic EBV-infected patients at year 1 post-onset. EBV-challenge promotes total and CD8+ NKT cell development in the thymus and liver of human-thymus/liver-SCID chimeras, compared to those in the unchallenged chimeras. After EBV-challenge, a proportion of NKT precursors diverges from DP thymocytes, develops and differentiates into mature CD8+ NKT cells in thymus in EBV-challenged human-thymus/liver-SCID chimeras or reaggregated thymic organ cultures. Thymic EBV-infected dendritic cells are required for this process. IL-7 is an essential factor for CD8+ NKT cell differentiation. EBV-induced CD8+ NKT cells produce remarkably more perforin, and predominately express CD8αα homodimer. CD8 lineage-specific NKT cells are developed and differentiated intrathymically upon EBV-exposure, a finding with potential therapeutic importance against viral infections and tumors.
The Epstein-Barr virus (EBV) latent-lytic switch is mediated by the BZLF1 immediate-early protein. EBV is normally latent in memory B cells, but cellular factors which promote viral latency specifically in B cells have not been identified. In this report, we demonstrate that the B-cell specific transcription factor, Oct-2, inhibits the function of the viral immediate-early protein, BZLF1, and prevents lytic viral reactivation. Co-transfected Oct-2 reduces the ability of BZLF1 to activate lytic gene expression in two different latently infected nasopharyngeal carcinoma cell lines. Furthermore, Oct-2 inhibits BZLF1 activation of lytic EBV promoters in reporter gene assays, and attenuates BZLF1 binding to lytic viral promoters in vivo. Oct-2 interacts directly with BZLF1, and this interaction requires the DNA-binding/dimerization domain of BZLF1 and the POU domain of Oct-2. An Oct-2 mutant (Δ262–302) deficient for interaction with BZLF1 is unable to inhibit BZLF1-mediated lytic reactivation. However, an Oct-2 mutant defective for DNA-binding (Q221A) retains the ability to inhibit BZLF1 transcriptional effects and DNA-binding. Importantly, shRNA-mediated knockdown of endogenous Oct-2 expression in several EBV-positive Burkitt lymphoma and lymphoblastoid cell lines increases the level of lytic EBV gene expression, while decreasing EBNA1 expression. Moreover, treatments which induce EBV lytic reactivation, such as anti-IgG cross-linking and chemical inducers, also decrease the level of Oct-2 protein expression at the transcriptional level. We conclude that Oct-2 potentiates establishment of EBV latency in B cells.
Epstein-Barr virus (EBV) is a human herpesvirus associated with B-cell malignancies. EBV infection of cells can result in either lytic replication or latency. Memory B cells are the primary site of EBV latency within the human host, while oropharyngeal epithelial cells support the lytic form of infection. However, the cellular mechanism(s) that enable EBV to establish viral latency in a B-cell specific manner are not currently understood. In this report, we show that the B-cell specific cellular transcription factor, Oct-2, promotes viral latency by inhibiting the lytic form of infection. We find that Oct-2 interacts directly with the EBV immediate-early protein, BZLF1, and abrogates its ability to activate lytic viral gene transcription through protein-protein interactions off the DNA. Furthermore, knockdown of endogenous Oct-2 expression in several latently-infected Burkitt lymphoma B-cell lines increases EBV lytic protein expression. In addition, we show that certain stimuli which can prompt lytic EBV reactivation in B cells also decrease expression of endogenous Oct-2. Our results suggest that the cellular transcription factor, Oct-2, promotes EBV latency in a B-cell dependent manner.
Over 90% of the adult human population is chronically infected with the Epstein-Barr virus (EBV), an oncogenic herpesvirus. EBV primarily infects naive human B cells and persists latently in memory B cells. Most individuals experience an asymptomatic infection that is effectively controlled by the adaptive immune response. However, EBV-associated lymphomas can develop in immunocompromised individuals. These tumors typically express all nine EBV latent proteins (latency III). Latency III is also associated with the expression of three precursor microRNAs (miRNAs) located within the EBV BHRF1 gene locus. The role of these BHRF1 miRNAs was unclear until recent in vitro studies demonstrated that they cooperate to enhance virus-induced B cell transformation and decrease the antigenic load of virus-infected cells, indicating that the BHRF1 miRNA cluster may serve as a novel therapeutic target for the treatment of latency III EBV-associated malignancies. However, to date, it is not known if BHRF1 miRNAs enhance virus-induced oncogenesis and/or immune evasion of EBV in vivo. To understand the in vivo contribution of the BHRF1 miRNA cluster to EBV infection and EBV-associated tumorigenesis, we monitored EBV infection and assessed tumor formation in humanized mice exposed to wild-type virus and a viral mutant (Δ123) that lacks all three BHRF1 miRNAs. Our results demonstrate that while the BHRF1 miRNAs facilitate the development of acute systemic EBV infection, they do not enhance the overall oncogenic potential of EBV in vivo.
Infection with Epstein-Barr virus (EBV) is highly prevalent worldwide, and it has been associated with infectious mononucleosis and severe diseases including Burkitt lymphoma, Hodgkin lymphoma, nasopharyngeal lymphoma, and lymphoproliferative disorders. Although EBV has been the focus of extensive research, much still remains unknown concerning what makes some individuals more sensitive to infection and to adverse outcomes as a result of infection. Here we use an integrative genomics approach in order to localize genetic factors influencing levels of Epstein Barr virus (EBV) nuclear antigen-1 (EBNA-1) IgG antibodies, as a measure of history of infection with this pathogen, in large Mexican American families. Genome-wide evidence of both significant linkage and association was obtained on chromosome 6 in the human leukocyte antigen (HLA) region and replicated in an independent Mexican American sample of large families (minimum p-value in combined analysis of both datasets is 1.4×10−15 for SNPs rs477515 and rs2516049). Conditional association analyses indicate the presence of at least two separate loci within MHC class II, and along with lymphocyte expression data suggest genes HLA-DRB1 and HLA-DQB1 as the best candidates. The association signals are specific to EBV and are not found with IgG antibodies to 12 other pathogens examined, and therefore do not simply reveal a general HLA effect. We investigated whether SNPs significantly associated with diseases in which EBV is known or suspected to play a role (namely nasopharyngeal lymphoma, Hodgkin lymphoma, systemic lupus erythematosus, and multiple sclerosis) also show evidence of associated with EBNA-1 antibody levels, finding an overlap only for the HLA locus, but none elsewhere in the genome. The significance of this work is that a major locus related to EBV infection has been identified, which may ultimately reveal the underlying mechanisms by which the immune system regulates infection with this pathogen.
Many factors influence individual differences in susceptibility to infectious disease, including genetic factors of the host. Here we use several genome-wide investigative tools (linkage, association, joint linkage and association, and the analysis of gene expression data) to search for host genetic factors influencing Epstein-Barr virus (EBV) infection. EBV is a human herpes virus that infects up to 90% of adults worldwide, infection with which has been associated with severe complications including malignancies and autoimmune disorders. In a sample of >1,300 Mexican American family members, we found significant evidence of association of anti–EBV antibody levels with loci on chromosome 6 in the human leukocyte antigen region, which contains genes related to immune function. The top two independent loci in this region were HLA-DRB1 and HLA-DQB1, both of which are involved in the presentation of foreign antigens to T cells. This finding was specific to EBV and not to 12 other pathogens we examined. We also report an overlap of genetic factors influencing both EBV antibody level and EBV–related cancers and autoimmune disorders. This work demonstrates the presence of EBV susceptibility loci and provides impetus for further investigation to better understand the underlying mechanisms related to differences in disease progression among individuals infected with this pathogen.
The objective of these experiments was to develop strategies for creation and identification of recombinant mutant Epstein-Barr viruses (EBV). EBV recombinant molecular genetics has been limited to mutations within a short DNA segment deleted from a nontransforming EBV and an underlying strategy which relies on growth transformation of primary B lymphocytes for identification of recombinants. Thus, mutations outside the deletion or mutations which affect transformation cannot be easily recovered. In these experiments we investigated whether a toxic drug resistance gene, guanine phosphoribosyltransferase or hygromycin phosphotransferase, driven by the simian virus 40 promoter can be recombined into the EBV genome and can function to identify B-lymphoma cells infected with recombinant virus. Two different strategies were used to recombine the drug resistance marker into the EBV genome. Both utilized transfection of partially permissive, EBV-infected B95-8 cells and positive selection for cells which had incorporated a functional drug resistance gene. In the first series of experiments, B95-8 clones were screened for transfected DNA that had recombined into the EBV genome. In the second series of experiments, the transfected drug resistance marker was linked to the plasmid and lytic EBV origins so that it was maintained as an episome and could recombine with the B95-8 EBV genome during virus replication. The recombinant EBV from either experiment could be recovered by infection and toxic drug selection of EBV-negative B-lymphoma cells. The EBV genome in these B-lymphoma cells is frequently an episome. Virus genes associated with latent infection of primary B lymphocytes are expressed. Expression of Epstein-Barr virus nuclear antigen 2 (EBNA-2) and the EBNA-3 genes is variable relative to that of EBNA-1, as is characteristic of some naturally infected Burkitt tumor cells. Moreover, the EBV-infected B-lymphoma cells are often partially permissive for early replicative cycle gene expression and virus replication can be induced, in contrast to previously reported in vitro infected B-lymphoma cells. These studies demonstrate that dominant selectable markers can be inserted into the EBV genome, are active in the context of the EBV genome, and can be used to recover recombinant EBV in B-lymphoma cells. This system should be particularly useful for recovering EBV genomes with mutations in essential transforming genes.
Epstein-Barr virus (EBV) causes a persistent infection in human B cells by establishing specific transcription programs to control B cell activation and differentiation. Transcriptional reprogramming of EBV infected B cells is predominantly driven by the action of EBV nuclear antigens, among them the transcriptional repressor EBNA3A. By comparing gene expression profiles of wt and EBNA3A negative EBV infected B cells, we have previously identified a broad array of cellular genes controlled by EBNA3A. We now find that genes repressed by EBNA3A in these cells are significantly enriched for the repressive histone mark H3K27me3, which is installed by Polycomb group (PcG) proteins. This PcG-controlled subset of genes also carries H3K27me3 marks in a variety of other tissues, suggesting that the commitment to PcG silencing is an intrinsic feature of these gene loci that can be used by EBNA3A. In addition, EBNA3A targets frequently reside in co-regulated gene clusters. To study the mechanism of gene repression by EBNA3A and to evaluate the relative contribution of PcG proteins during this process, we have selected the genomic neighbors CXCL10 and CXCL9 as a model for co-repressed and PcG-controlled genes. We show that EBNA3A binds to CBF1 occupied intergenic enhancers located between CXCL10 and CXCL9 and displaces the transactivator EBNA2. This impairs enhancer activity, resulting in a rapid transcriptional shut-down of both genes in a CBF1-dependent manner and initiation of a delayed gain of H3K27me3 marks covering an extended chromatin domain. H3K27me3 marks increase gradually and are maintained by EBNA3A. Our study provides direct evidence that repression by EBNA3A requires CBF1 and that EBNA3A and EBNA2 compete for access to CBF1 at identical genomic sites. Most importantly, our results demonstrate that transcriptional silencing by EBNA3A precedes the appearance of repressive PcG marks and indicate that both events are triggered by loss of enhancer activity.
Epstein-Barr virus (EBV) is a γ-herpesvirus which establishes a latent infection in human B cells and is associated with the pathogenesis of several types of cancer. Here, we report that cellular genes repressed by the EBV nuclear antigen 3A (EBNA3A) in EBV infected B cells frequently form contiguous clusters in the human genome and are committed to epigenetic silencing by Polycomb group (PcG) proteins. The chemokine genes CXCL10 and CXCL9 and their receptors on NK and T cells are critical weapons of the infected host to control herpesvirus infections. CXCL10 and CXCL9 are close neighbors within an extended PcG-controlled domain. We show that EBNA3A binds to intergenic enhancers located between CXCL10 and CXCL9 and displaces the transactivator EBNA2. This process impairs enhancer activity, resulting in a rapid transcriptional shut-down of both genes followed by a delayed gain of PcG histone marks. These PcG marks increase within the following weeks and are maintained by EBNA3A. Our results show that rapid transcriptional shut-down of distal genes and domain-wide PcG silencing is triggered by loss of enhancer activity and suggest that EBNA3A can reprogram the cellular genome in order to escape the immune surveillance of the host.
Epstein-Barr virus (EBV), a ubiquitous B-lymphotropic herpesvirus, ectopically infects T or NK cells to cause severe diseases of unknown pathogenesis, including chronic active EBV infection (CAEBV) and EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH). We developed xenograft models of CAEBV and EBV-HLH by transplanting patients' PBMC to immunodeficient mice of the NOD/Shi-scid/IL-2Rγnull strain. In these models, EBV-infected T, NK, or B cells proliferated systemically and reproduced histological characteristics of the two diseases. Analysis of the TCR repertoire expression revealed that identical predominant EBV-infected T-cell clones proliferated in patients and corresponding mice transplanted with their PBMC. Expression of the EBV nuclear antigen 1 (EBNA1), the latent membrane protein 1 (LMP1), and LMP2, but not EBNA2, in the engrafted cells is consistent with the latency II program of EBV gene expression known in CAEBV. High levels of human cytokines, including IL-8, IFN-γ, and RANTES, were detected in the peripheral blood of the model mice, mirroring hypercytokinemia characteristic to both CAEBV and EBV-HLH. Transplantation of individual immunophenotypic subsets isolated from patients' PBMC as well as that of various combinations of these subsets revealed a critical role of CD4+ T cells in the engraftment of EBV-infected T and NK cells. In accordance with this finding, in vivo depletion of CD4+ T cells by the administration of the OKT4 antibody following transplantation of PBMC prevented the engraftment of EBV-infected T and NK cells. This is the first report of animal models of CAEBV and EBV-HLH that are expected to be useful tools in the development of novel therapeutic strategies for the treatment of the diseases.
Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus that infects more than 90% of the adult human population in the world. EBV usually infects B lymphocytes and does not produce symptoms in infected individuals, but in rare occasions it infects T or NK lymphocytes and causes severe diseases such as chronic active EBV infection (CAEBV) and EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH). We developed mouse models of these two human diseases in which EBV-infected T or NK lymphocytes proliferate in mouse tissues and reproduce human pathologic conditions such as overproduction of small proteins called “cytokines” that produce inflammatory responses in the body. These mouse models are thought to be very useful for the elucidation of the pathogenesis of CAEBV and EBV-HLH as well as for the development of therapeutic strategies for the treatment of these diseases. Experiments with the models demonstrated that a subset of lymphocytes called CD4-positive lymphocytes are essential for the proliferation of EBV-infected T and NK cells. This result implies that removal of CD4-positive lymphocytes or suppression of their functions may be an effective strategy for the treatment of CAEBV and EBV-HLH.
Nasopharyngeal carcinoma (NPC) is a prevalent malignancy in Southeast Asia and is strongly associated with Epstein-Barr virus (EBV). We investigated the primary diagnostic value of circulating EBV DNA and anti-EBV immunoglobulin G (IgG) and IgA levels in Indonesian NPC patients (n = 149). By a 213-bp Epstein-Barr virus nuclear antigen 1 (EBNA1)-based real-time LightCycler PCR, 72.5% of patients were positive for EBV DNA in whole blood, with 29.5% having levels above a previously determined clinical cutoff value (COV) of 2,000 EBV DNA copies/ml, the upper level in healthy carriers. In a 99-bp LightCycler PCR, 85.9% of patients were positive and 60.4% had levels above the COV. This assay quantified a significantly higher EBV load than the 213-bp PCR assay (P < 0.0001), suggesting that circulating EBV DNA is fragmented. Using data from 11 different studies, we showed a significant inverse correlation between PCR amplicon size and the percentage of patients positive for circulating EBV DNA (Spearman's rho = −0.91; P < 0.0001). EBV DNA loads were unrelated to anti-EBV IgG or IgA levels, as measured by VCA-p18 and EBNA1-specific synthetic peptide-based enzyme-linked immunosorbent assays. The presence of circulating tumor cells was assessed by amplification of BamHI-A rightward frame 1 (BARF1) mRNA, a viral oncogene abundantly expressed in EBV-carrying carcinomas but virtually absent from EBV-associated lymphomas. Despite high EBV DNA loads and the presence of EBNA1 and human U1A small nuclear ribonucleoprotein mRNA, BARF1 mRNA was never detected in blood. We conclude that amplicon size significantly influences EBV DNA load measurement in NPC patients. The circulating EBV DNA load is independent of serological parameters and does not reflect intact tumor cells. The primary diagnostic value of the EBV DNA load for the detection of NPC is limited.
We have performed the first extensive profiling of Epstein-Barr virus (EBV) miRNAs on in vivo derived normal and neoplastic infected tissues. We describe a unique pattern of viral miRNA expression by normal infected cells in vivo expressing restricted viral latency programs (germinal center: Latency II and memory B: Latency I/0). This includes the complete absence of 15 of the 34 miRNAs profiled. These consist of 12 BART miRNAs (including approximately half of Cluster 2) and 3 of the 4 BHRF1 miRNAs. All but 2 of these absent miRNAs become expressed during EBV driven growth (Latency III). Furthermore, EBV driven growth is accompanied by a 5–10 fold down regulation in the level of the BART miRNAs expressed in germinal center and memory B cells. Therefore, Latency III also expresses a unique pattern of viral miRNAs. We refer to the miRNAs that are specifically expressed in EBV driven growth as the Latency III associated miRNAs. In EBV associated tumors that employ Latency I or II (Burkitt's lymphoma, Hodgkin's disease, nasopharyngeal carcinoma and gastric carcinoma), the Latency III associated BART but not BHRF1 miRNAs are up regulated. Thus BART miRNA expression is deregulated in the EBV associated tumors. This is the first demonstration that Latency III specific genes (the Latency III associated BARTs) can be expressed in these tumors. The EBV associated tumors demonstrate very similar patterns of miRNA expression yet were readily distinguished when the expression data were analyzed either by heat-map/clustering or principal component analysis. Systematic analysis revealed that the information distinguishing the tumor types was redundant and distributed across all the miRNAs. This resembles “secret sharing” algorithms where information can be distributed among a large number of recipients in such a way that any combination of a small number of recipients is able to understand the message. Biologically, this may be a consequence of functional redundancy between the miRNAs.
miRNAs are small (∼22 bp) RNAs. They play central roles in many cellular processes. Epstein-Barr virus (EBV) is an important human pathogen that establishes persistent infection in nearly all humans and is associated with several common forms of cancer. To achieve persistent infection, the virus infects B cells and uses a series of discrete transcription programs to drive these B cells to become memory B cells – the site of long term persistent infection. It was the first human virus found to express miRNAs of which there are at least 40. The functions of a few of these miRNAs are known but their expression in latently infected normal and neoplastic tissues in vivo have not been described. Here we have profiled EBV miRNAs in a wide range of infected normal and neoplastic tissue. We demonstrate that there are indeed latency program specific patterns of viral miRNA expression and that these patterns are disrupted in EBV associated tumors implicating EBV miRNAs both in long term persistence and in oncogenesis.
The Epstein-Barr virus (EBV) genes expressed in B lymphocytes immortalized in vitro or in Burkitt's lymphoma (BL) cells infected in vivo have been characterized previously; however, the viral products which are essential for immortalization or for establishment of EBV latency are still not known. To approach this question, we compared the kinetics of expression of EBV nuclear antigens and the two EBV-encoded small RNAs, EBER1 and EBER2, after infection of primary B cells or EBV genome-negative BL cells with either an immortalizing EBV strain (B95-8) or the nonimmortalizing deletion mutant (HR-1). Following infection of primary cells with B95-8 virus, EBV nuclear antigen (EBNA)-2 was expressed first, followed by EBNA-1, -3, and -4 (also called leader protein [LP]) and the two small RNAs. Infection of EBV genome-negative BL cells with the same strain of virus resulted in a similar pattern of gene expression, except that the EBNAs appeared together and more rapidly. EBERs were not apparent in one BL cell line converted by B95-8. The only products detected after infection of primary B lymphocytes with the HR-1 deletion mutant were the EBNA-4 (LP) family and trace amounts of EBER1. Although HR-1 could express neither EBNA-1, EBNA-3, nor EBER2 in primary cells, all these products were expressed rapidly after HR-1 infection of EBV genome-negative BL cell lines. The results indicate that the mutation in HR-1 virus affects immortalization not only through failure to express EBNA-2, a gene which is deleted, but also indirectly by curtailing expression of several other EBV genes whose coding regions are intact in the HR-1 virus and normally expressed during latency. The pattern of latent EBV gene expression after HR-1 infection is dependent on the host cell, perhaps through products specific for the cell cycle or the state of B-cell differentiation.
Epstein-Barr Virus (EBV) is an oncogenic γ-herpesvirus that capably establishes both latent and lytic modes of infection in host cells and causes malignant diseases in humans. Nuclear antigen 2 (EBNA2)-mediated transcription of both cellular and viral genes is essential for the establishment and maintenance of the EBV latency program in B lymphocytes. Here, we employed a protein affinity pull-down and LC-MS/MS analysis to identify nucleophosmin (NPM1) as one of the cellular proteins bound to EBNA2. Additionally, the specific domains that are responsible for protein-protein interactions were characterized as EBNA2 residues 300 to 360 and the oligomerization domain (OD) of NPM1. As in c-MYC, dramatic NPM1 expression was induced in EBV positively infected B cells after three days of viral infection, and both EBNA2 and EBNALP were implicated in the transactivation of the NPM1 promoter. Depletion of NPM1 with the lentivirus-expressed short-hairpin RNAs (shRNAs) effectively abrogated EBNA2-dependent transcription and transformation outgrowth of lymphoblastoid cells. Notably, the ATP-bound state of NPM1 was required to induce assembly of a protein complex containing EBNA2, RBP-Jκ, and NPM1 by stabilizing the interaction of EBNA2 with RBP-Jκ. In a NPM1-knockdown cell line, we demonstrated that an EBNA2-mediated transcription defect was fully restored by the ectopic expression of NPM1. Our findings highlight the essential role of NPM1 in chaperoning EBNA2 onto the latency-associated membrane protein 1 (LMP1) promoters, which is coordinated with the subsequent activation of transcriptional cascades through RBP-Jκ during EBV infection. These data advance our understanding of EBV pathology and further imply that NPM1 can be exploited as a therapeutic target for EBV-associated diseases.
Epstein-Barr Virus (EBV) infects human B cells to establish a permanent infection in hosts, which can cause diseases ranging from infectious mononucleosis to a broad spectrum of human malignancies. The conversion of human primary B cells into indefinitely proliferating lymphoblastoid cell lines (LCLs) by in vitro EBV infection provides a suitable model for virus-mediated cellular transformation. Epstein-Barr nuclear antigen (EBNA) 2-mediated transcription is essential for the establishment and maintenance of EBV latent infection. In this report, we have extensively explored the mechanism by which EBNA2 activates the latency-specific LMP1 promoter to establish a permanent infection in B cells. We have identified and characterized the protein-protein interaction of EBNA2 with the nuclear shuttle protein nucleophosmin (NPM1) in vivo and in vitro. In particular, we have determined that the expression of NPM1 is promptly induced upon EBV infection and that EBNA2 has a role in activating NPM1 gene expression. Furthermore, we have shown that oligomerized NPM1 is charged by ATP and binds to EBNA2, which is crucial for its ability to stabilize its interaction with the DNA binding protein RBP-Jκ, which is in turn essential for supporting the transcriptional cascades of EBV latent infection. Our findings provide striking evidence to illustrate a new model for understanding EBV pathology.
Epstein-Barr Nuclear Antigen 1 (EBNA1) is essential for Epstein-Barr virus to immortalize naïve B-cells. Upon binding a cluster of 20 cognate binding-sites termed the family of repeats, EBNA1 transactivates promoters for EBV genes that are required for immortalization. A small domain, termed UR1, that is 25 amino-acids in length, has been identified previously as essential for EBNA1 to activate transcription. In this study, we have elucidated how UR1 contributes to EBNA1's ability to transactivate. We show that zinc is necessary for EBNA1 to activate transcription, and that UR1 coordinates zinc through a pair of essential cysteines contained within it. UR1 dimerizes upon coordinating zinc, indicating that EBNA1 contains a second dimerization interface in its amino-terminus. There is a strong correlation between UR1-mediated dimerization and EBNA1's ability to transactivate cooperatively. Point mutants of EBNA1 that disrupt zinc coordination also prevent self-association, and do not activate transcription cooperatively. Further, we demonstrate that UR1 acts as a molecular sensor that regulates the ability of EBNA1 to activate transcription in response to changes in redox and oxygen partial pressure (pO2). Mild oxidative stress mimicking such environmental changes decreases EBNA1-dependent transcription in a lymphoblastoid cell-line. Coincident with a reduction in EBNA1-dependent transcription, reductions are observed in EBNA2 and LMP1 protein levels. Although these changes do not affect LCL survival, treated cells accumulate in G0/G1. These findings are discussed in the context of EBV latency in body compartments that differ strikingly in their pO2 and redox potential.
Epstein-Barr virus (EBV) infects human B-cells and immortalizes them. Immortalization results in diseases that range from infectious mononucleosis to malignancies such as lymphomas. During immortalization, EBV expresses a small number of viral genes that modulate cellular proliferation and differentiation. One of the genes expressed by EBV, Epstein-Barr nuclear antigen 1 (EBNA1), activates the expression of the other viral genes required for immortalization. In this report, we have explored the mechanism by which EBNA1 activates gene expression. We have determined that EBNA1 uses the micronutrient zinc to self-associate, and that self-association is necessary for it to activate gene expression. Further, we have determined that environmental conditions such as oxygen tension and oxidative stress modulate EBNA1's capacity to self-associate, and therefore to activate gene expression. The gene expression profile and proliferative phenotype of EBV-infected cells is known to vary in differing environmental niches in the human body, such as lymph nodes and in peripheral circulation. We interpret our results to postulate that these differences arise as a consequence of varying oxygen tension in these microenvironments on EBNA1's capacity to activate viral gene expression. Our findings can be exploited to devise novel therapeutics against EBV-associated diseases that target EBNA1 through oxidative stress.
Virus-encoded microRNAs (miRNAs) have been shown to regulate a variety of biological processes involved in viral infection and viral-associated pathogenesis. Epstein-Barr virus (EBV) is a herpesvirus implicated in nasopharyngeal carcinoma (NPC) and other human malignancies. EBV-encoded miRNAs were among the first group of viral miRNAs identified. To understand the roles of EBV miRNAs in the pathogenesis of NPC, we utilized deep sequencing technology to characterize the EBV miRNA transcriptome in clinical NPC tissues. We obtained more than 110,000 sequence reads in NPC samples and identified 44 EBV BART miRNAs, including four new mature miRNAs derived from previously identified BART miRNA precursor hairpins. Further analysis revealed extensive sequence variations (isomiRs) of EBV miRNAs, including terminal isomiRs at both the 5′ and 3′ ends and nucleotide variants. Analysis of EBV genomic sequences indicated that the majority of EBV miRNA nucleotide variants resulted from post-transcriptional modifications. Read counts of individual EBV miRNA in NPC tissue spanned from a few reads to approximately 18,000 reads, confirming the wide expression range of EBV miRNAs. Several EBV miRNAs were expressed at levels similar to highly abundant human miRNAs. Sequence analysis revealed that most of the highly abundant EBV miRNAs share their seed sequences (nucleotides 2–7) with human miRNAs, suggesting that seed sequence content may be an important factor underlying the differential accumulation of BART miRNAs. Interestingly, many of these human miRNAs have been found to be dysregulated in human malignancies, including NPC. These observations not only provide a potential linkage between EBV miRNAs and human malignancy but also suggest a highly coordinated mechanism through which EBV miRNAs may mimic or compete with human miRNAs to affect cellular functions.
Although case-oriented evidence for an association of Epstein-Barr virus (EBV) with gastric carcinoma has been accumulating recently, the interaction(s) between EBV and gastric epithelial cells is/are largely unknown. In this study, we examined seven EBV-positive gastric carcinoma tissues for viral gene expression at the mRNA level, from which studies on the EBV oncogenicity in human epithelial cells will benefit. Reverse transcription-PCR analysis showed that all seven EBV-positive tumour tissues constitutively expressed EBV nuclear antigen (EBNA) 1 mRNA, but not EBNA2 mRNA. The EBNA transcription was initiated from one of three EBNA promoters, Qp: by contrast, both Cp and Wp were silent, thus resulting in the lack of EBNA2 mRNA. Latent membrane protein (LMP) 2A mRNA was detected in three of seven cases; however, neither LMP1 nor LMP2B mRNA was detected in any of the tumours tested. Transcripts from the BamHI-A region of the viral genome were detectable in all cases. BZLF1 mRNA and the product, an immediate-early gene for EBV replication, was not expressed in any of them, thereby suggesting that the tumour cells carried EBV genomes in a tightly latent form. These findings further extended our previous data regarding EBV latency in gastric carcinoma cells at the protein level, and have affirmed that the programme of viral gene expression in the tumour more closely resembles 'latency I' represented by Burkitt's lymphoma than 'latency II' represented by the majority of nasopharyngeal carcinomas.