Epstein-Barr virus small RNAs potentiate tumorigenicity of Burkitt lymphoma cells independently of an effect on apoptosis

Regulation mechanism of EBV-encoded EBER1 and LMP2A on YAP1 and the impact of YAP1 on the EBV infection status in EBV-associated gastric carcinoma

This study aims to explore the role and regulatory mechanism of Yes-associated protein 1 (YAP1) in the development of Epstein-Barr virus-associated gastric cancer (EBVaGC). Here we showed that EBV can upregulate the expression and activity of YAP1 protein through its encoded latent products EBV-encoded small RNA 1 (EBER1) and latent membrane protein 2A (LMP2A), enhancing the malignant characteristics of EBVaGC cells. In addition, we also showed that overexpression of YAP1 induced the expression of EBV encoding latent and lytic phase genes and proteins in the epithelial cell line AGS-EBV infected with EBV, and increased the copy number of the EBV genome, while loss of YAP1 expression reduced the aforementioned indicators. Moreover, we found that YAP1 enhanced EBV lytic reactivation induced by two known activators, 12-O-tetradecanoylhorbol-13-acetate (TPA) and sodium butyrate (NaB). These results indicated a bidirectional regulatory mechanism between EBV and YAP1 proteins, providing new experimental evidence for further understanding the regulation of EBV infection patterns and carcinogenic mechanisms in gastric cancer.

Epstein-Barr Virus History and Pathogenesis

Epstein-Barr virus (EBV) is the first identified human oncogenic virus that can establish asymptomatic life-long persistence. It is associated with a large spectrum of diseases, including benign diseases, a number of lymphoid malignancies, and epithelial cancers. EBV can also transform quiescent B lymphocytes into lymphoblastoid cell lines (LCLs) in vitro. Although EBV molecular biology and EBV-related diseases have been continuously investigated for nearly 60 years, the mechanism of viral-mediated transformation, as well as the precise role of EBV in promoting these diseases, remain a major challenge yet to be completely explored. This review will highlight the history of EBV and current advances in EBV-associated diseases, focusing on how this virus provides a paradigm for exploiting the many insights identified through interplay between EBV and its host during oncogenesis, and other related non-malignant disorders.

Novel approach to identify putative Epstein-Barr-virus microRNAs regulating host cell genes with relevance in tumor biology and immunology

The human Epstein-Barr virus is associated with several human solid and hematopoietic malignancies. However, the underlying molecular mechanisms including virus-encoded microRNAs (miRs), which lead to the malignant transformation of infected cells and immune evasion of EBV-associated tumors, have not yet been characterized. The expression levels of numerous known EBV-specific miRs and their suitability as diagnostic and/or prognostic markers were determined in different human EBV-positive tissues followed by in silico analyses to identify putative EBV-miR-regulated target genes, thereby offering a suitable screening strategy to overcome the limited available data sets of EBV-miRs and their targeted gene networks. Analysis of microarray data sets from healthy human B cells and malignant-transformed EBV-positive B cells of patients with Burkitt's lymphoma revealed statistically significant (p < 0.05) deregulated genes with known functions in oncogenic properties, immune escape and anti-tumoral immune responses. Alignments of in vivo and in silico data resulted in the prediction of putative candidate EBV-miRs and their target genes. Thus, a combinatorial approach of bioinformatics, transcriptomics and in situ expression analyses is a promising tool for the identification of EBV-miRs and their potential targets as well as their eligibility as markers for EBV detection in different EBV-associated human tissue.

MicroRNA and Other Non-Coding RNAs in Epstein-Barr Virus-Associated Cancers

EBV is a direct causative agent in around 1.5% of all cancers. The oncogenic properties of EBV are related to its ability to activate processes needed for cellular proliferation, survival, migration, and immune evasion. The EBV latency program is required for the immortalization of infected B cells and involves the expression of non-coding RNAs (ncRNAs), including viral microRNAs. These ncRNAs have different functions that contribute to virus persistence in the asymptomatic host and to the development of EBV-associated cancers. In this review, we discuss the function and potential clinical utility of EBV microRNAs and other ncRNAs in EBV-associated malignancies. This review is not intended to be comprehensive, but rather to provide examples of the importance of ncRNAs.

Connivance, Complicity, or Collusion? The Role of Noncoding RNAs in Promoting Gammaherpesvirus Tumorigenesis

EBV and KSHV are etiologic agents of multiple types of lymphomas and carcinomas. The frequency of EBV⁺ or KSHV⁺ malignancies arising in immunocompromised individuals reflects the intricate evolutionary balance established between these viruses and their immunocompetent hosts. However, the specific mechanisms by which these pathogens drive tumorigenesis remain poorly understood. In recent years an enormous array of cellular and viral noncoding RNAs (ncRNAs) have been discovered, and host ncRNAs have been revealed as contributory factors to every single cancer hallmark cellular process. As new evidence emerges that gammaherpesvirus ncRNAs also alter host processes and viral factors dysregulate host ncRNA expression, and as novel viral ncRNAs continue to be discovered, we examine the contribution of small, non-miRNA ncRNAs and long ncRNAs to gammaherpesvirus tumorigenesis.

Coordinated repression of BIM and PUMA by Epstein-Barr virus latent genes maintains the survival of Burkitt lymphoma cells

While the association of Epstein-Barr virus (EBV) with Burkitt lymphoma (BL) has long been recognised, the precise role of the virus in BL pathogenesis is not fully resolved. EBV can be lost spontaneously from some BL cell lines, and these EBV-loss lymphoma cells reportedly have a survival disadvantage. Here we have generated an extensive panel of EBV-loss clones from multiple BL backgrounds and examined their phenotype comparing them to their isogenic EBV-positive counterparts. We report that, while loss of EBV from BL cells is rare, it is consistently associated with an enhanced predisposition to undergo apoptosis and reduced tumorigenicity in vivo. Importantly, reinfection of EBV-loss clones with EBV, but surprisingly not transduction with individual BL-associated latent viral genes, restored protection from apoptosis. Expression profiling and functional analysis of apoptosis-related proteins and transcripts in BL cells revealed that EBV inhibits the upregulation of the proapoptotic BH3-only proteins, BIM and PUMA. We conclude that latent EBV genes cooperatively enhance the survival of BL cells by suppression of the intrinsic apoptosis pathway signalling via inhibition of the potent apoptosis initiators, BIM and PUMA.

EBV and Apoptosis: The Viral Master Regulator of Cell Fate?

Epstein-Barr virus (EBV) was first discovered in cells from a patient with Burkitt lymphoma (BL), and is now known to be a contributory factor in 1-2% of all cancers, for which there are as yet, no EBV-targeted therapies available. Like other herpesviruses, EBV adopts a persistent latent infection in vivo and only rarely reactivates into replicative lytic cycle. Although latency is associated with restricted patterns of gene expression, genes are never expressed in isolation; always in groups. Here, we discuss (1) the ways in which the latent genes of EBV are known to modulate cell death, (2) how these mechanisms relate to growth transformation and lymphomagenesis, and (3) how EBV genes cooperate to coordinately regulate key cell death pathways in BL and lymphoblastoid cell lines (LCLs). Since manipulation of the cell death machinery is critical in EBV pathogenesis, understanding the mechanisms that underpin EBV regulation of apoptosis therefore provides opportunities for novel therapeutic interventions.

Arsenic trioxide inhibits EBV reactivation and promotes cell death in EBV-positive lymphoma cells

Background

Epstein-Barr Virus (EBV) is associated with hematopoietic malignancies, such as Burkitt’s lymphoma, post-transplantation lymphoproliferative disorder, and diffuse large B-cell lymphoma. The current approach for EBV-associated lymphoma involves chemotherapy to eradicate cancer cells, however, normal cells may be injured and organ dysfunction may occur with currently employed regimens. This research is focused on employing arsenic trioxide (ATO) as EBV-specific cancer therapy takes advantage of the fact the EBV resides within the malignant cells.

Methods and results

Our research reveals that low ATO inhibits EBV gene expression and genome replication. EBV spontaneous reactivation starts as early as 6 h after re-suspending EBV-positive Mutu cells in RPMI media in the absence of ATO, however this does not occur in Mutu cells cultured with ATO. ATO’s inhibition of EBV spontaneous reactivation is dose dependent. The expression of the EBV immediate early gene Zta and early gene BMRF1 is blocked with low concentrations of ATO (0.5 nM – 2 nM) in EBV latency type I cells and EBV-infected PBMC cells. The combination of ATO and ganciclovir further diminishes EBV gene expression. ATO-mediated reduction of EBV gene expression can be rescued by co-treatment with the proteasome inhibitor MG132, indicating that ATO promotes ubiquitin conjugation and proteasomal degradation of EBV genes. Co-immunoprecipitation assays with antibodies against Zta pulls down more ubiquitin in ATO treated cell lysates. Furthermore, MG132 reverses the inhibitory effect of ATO on anti-IgM-, PMA- and TGF-β-mediated EBV reactivation. Thus, mechanistically ATO’s inhibition of EBV gene expression occurs via the ubiquitin pathway. Moreover, ATO treatment results in increased cell death in EBV-positive cells compared to EBV-negative cells, as demonstrated by both MTT and trypan blue assays. ATO-induced cell death in EBV-positive cells is dose dependent. ATO and ganciclovir in combination further enhances cell death specifically in EBV-positive cells.

Conclusion

ATO-mediated inhibition of EBV lytic gene expression results in cell death selectively in EBV-positive lymphocytes, suggesting that ATO may potentially serve as a drug to treat EBV-related lymphomas in the clinical setting.

Characterization of Epstein-Barr virus-encoded small RNA gene variations in virus associated lymphomas in Northern China

Epstein-Barr virus (EBV)-encoded small RNAs (EBER1 and EBER2) are highly expressed in all forms of EBV latency in EBV-associated malignancies. EBER gene variations and their association with EBV-associated disease still remain poorly characterized. To investigate the patterns of EBER gene variations and their roles in tumorigenesis, EBER gene sequences were analyzed by nested-PCR and DNA sequencing in 101 lymphomas from Northern China, a non-nasopharyngeal carcinoma (NPC) endemic area. In addition, EBV type 1 and type 2 classifications were made by using nested-PCR assays across type-specific regions in the EBNA2 gene. EB-6m was the dominant subtype (95.0%, 96/101) in lymphoma. The distribution of the EBER subtypes in the four lymphoma groups was not significantly different (p > 0.05), neither was that of the EBNA2 type (p > 0.05). Compared with previous data in the same area, the distribution of EBER subtypes in lymphoma was similar to that in EBV-associated gastric carcinoma (EBVaGC) and throat washing (TW) from healthy donors (p > 0.05), but was significantly different from that of NPC. The EBNA2 type distribution between lymphoma and the other three groups was significantly different (p < 0.05). The proportion of type 1 and type 2 dual infections was higher in lymphoma than that in GC, NPC and TW. The mutation 7123nt A → T was identified in 11 of 101 (10.9%, 11/101) lymphomas, significantly more than that in EBV-associated gastric carcinomas (EBVaGC) (0%, 0/50) and throat washings (TWs) from healthy donors (3.3%, 3/92) (p < 0.05). These findings indicate that EBER subtypes may not be associated with pathogenesis of lymphoma, but that a point mutation at position 7123nt (A → T) provides a new area for further exploration. Furthermore it is necessary to investigate the role of EBNA2-subtype mixed infections in the establishment of lymphoma.

Consideration of Epstein-Barr Virus-Encoded Noncoding RNAs EBER1 and EBER2 as a Functional Backup of Viral Oncoprotein Latent Membrane Protein 1

The Epstein-Barr virus (EBV)-encoded noncoding RNAs EBER1 and EBER2 are highly abundant through all four latency stages of EBV infection (III-II-I-0) and have been associated with an oncogenic phenotype when expressed in cell lines cultured in vitro. In vivo, EBV-infected B cells derived from freshly isolated lymphocytes show that EBER1/2 deletion does not impair viral latency. Based on published quantitative proteomics data from BJAB cells expressing EBER1 and EBER2, we propose that the EBERs, through their activation of AKT in a B-cell-specific manner, are a functionally redundant backup of latent membrane protein 1 (LMP1)-an essential oncoprotein in EBV-associated malignancies, with a main role in AKT activation. Our proposed model may explain the lack of effect on viral latency establishment in EBER-minus EBV infection.

Multifunctional non-coding Epstein-Barr virus encoded RNAs (EBERs) contribute to viral pathogenesis

Epstein-Barr Virus (EBV) is known as an oncogenic herpesvirus implicated in the pathogenesis of various malignancies. It has been reported that EBV non-coding RNAs (ncRNAs) including EBV-encoded small RNAs (EBERs) and EBV-miRNAs contribute to viral pathogenesis. EBERs that are expressed abundantly in latently EBV-infected cells have been reported to play significant roles in tumorigenesis by EBV. Furthermore, it was demonstrated that the modulation of host innate immune signals by EBERs contributes to EBV-mediated pathogenesis including oncogenesis. Recently it was demonstrated that EBERs are secreted via exosomes by EBV-infected cells. It was also demonstrated that exosomes contain a number of EBV-encoded miRNAs. Various mRNAs have been identified as targets for regulation by EBV-miRNAs in host cells, therefore, EBERs and EBV-miRNAs might function through the transfer of exosomes.

Proteomics and Transcriptomics of BJAB Cells Expressing the Epstein-Barr Virus Noncoding RNAs EBER1 and EBER2

In Epstein-Barr virus (EBV) latent infection, the EBV-encoded RNAs EBER1 and EBER2 accumulate in the host cell nucleus to ~10⁶ copies. While the expression of EBERs in cell lines is associated with transformation, a mechanistic explanation of their roles in EBV latency remains elusive. To identify EBER-specific gene expression features, we compared the proteome and mRNA transcriptome from BJAB cells (an EBV-negative B lymphoma cell line) stably transfected with an empty plasmid or with one carrying both EBER genes. We identified ~1800 proteins with at least 2 SILAC pair measurements, of which only 8 and 12 were up- and downregulated ≥ 2-fold, respectively. One upregulated protein was PIK3AP1, a B-cell specific protein adapter known to activate the PI3K-AKT signaling pathway, which regulates alternative splicing and translation in addition to its pro-survival effects. In the mRNA-seq data, the mRNA levels for some of the proteins changing in the SILAC data did not change. We instead observed isoform switch events. We validated the most relevant findings with biochemical assays. These corroborated the upregulation of PIK3AP1 and AKT activation in BJAB cells expressing high levels of both EBERs and EBNA1 (a surrogate of Burkitt’s lymphoma EBV latency I) relative to those expressing only EBNA1. The mRNA-seq data in these cells showed multiple upregulated oncogenes whose mRNAs are enriched for 3´-UTR AU-rich elements (AREs), such as ccl3, ccr7, il10, vegfa and zeb1. The CCL3, CCR7, IL10 and VEGFA proteins promote cell proliferation and are associated with EBV-mediated lymphomas. In EBV latency, ZEB1 represses the transcription of ZEBRA, an EBV lytic phase activation factor. We previously found that EBER1 interacts with AUF1 in vivo and proposed stabilization of ARE-containing mRNAs. Thus, the ~10⁶ copies of EBER1 may promote not only cell proliferation due to an increase in the levels of ARE-containing genes like ccl3, ccr7, il10, and vegfa, but also the maintenance of latency, through higher levels of zeb1.

High prevalence of the EBER variant EB-8m in endemic nasopharyngeal carcinomas

Epstein-Barr virus (EBV)-encoded small RNAs (EBERs) are the most highly expressed transcripts in all EBV-associated tumors and are involved in both lymphoid and epithelioid carcinogenesis. Our previous study on Chinese isolates from non-endemic area of nasopharyngeal carcinoma (NPC) identified new EBER variants (EB-8m and EB-10m) which were less common but relatively more frequent in NPC cases than healthy donors. In the present study, we determined the EBER variants in NPC cases and healthy donors from endemic and non-endemic areas of NPC within China and compared the EBER variants, in relation to the genotypes at BamHI F region (prototype F and f variant), between population groups and between two areas. According to the phylogenetic tree, four EBER variants (EB-6m, EB-8m, EB-10m and B95-8) were identified. EB-6m was dominant in all population groups except for endemic NPC group, in which EB-8m was dominant. EB-8m was more common in endemic NPC cases (82.0%, 41/50) than non-endemic NPC cases (33.7%, 32/95) (p<0.0001), and it was also more frequent in healthy donors from endemic area (32.4%, 24/74) than healthy donors from non-endemic area (1.1%, 1/92) (p<0.0001). More importantly, the EB-8m was more prevalent in NPC cases than healthy donors in both areas (p<0.0001). The f variant, which has been suggested to associate with endemic NPC, demonstrated preferential linkage with EB-8m in endemic isolates, however, the EB-8m variant seemed to be more specific to NPC isolates than f variant. These results reveal high prevalence of EBER EB-8m variant in endemic NPC cases, suggesting an association between NPC development and EBV isolates carrying EB-8m variant. Our finding identified a small healthy population group that shares the same viral strain which predominates in NPC cases. It could be interesting to carry extensive cohort studies following these individuals to evaluate the risk to develop NPC.

Pan-viral-microRNA screening identifies interferon inhibition as a common function of diverse viruses

Diverse viruses encode regulatory RNAs called microRNAs (miRNAs). Despite much progress, the functions of the majority of viral miRNAs remain unknown. Most previous studies have used biochemical methods to uncover targets of viral miRNAs, but it is unclear what fraction of these targets is functionally important. Here, we apply an alternative strategy based on the premise that assorted viral miRNAs will share functionality. Screening a library of >70 human viral miRNAs showed that three unrelated miRNAs from distantly related herpesviruses significantly inhibited IFN signaling. Strikingly, each of these miRNAs directly reduced expression of the cyclic AMP-responsive element-binding protein (CBP), which as part of the p300-CBP complex, mediates IFN signaling. We show that both 5' and 3' derivatives from Epstein-Barr virus (EBV) encoded miR-BART-18 precursor miRNA (pre-miRNA) and the orthologous pre-miRNA from Rhesus lymphocryptovirus contribute to reducing IFN signaling. Thus, through both convergent and divergent evolutionary mechanisms, varied herpesviral miRNAs share the ability to decrease IFN signaling. Restoring miR-BART-18 to cells infected with an EBV miRNA mutant conveyed a cellular growth advantage upon IFN treatment, and relevant miRNAs from other herpesviruses were able to complement this activity. Blocking miR-BART-18 function in an EBV(+) tumor cell line renders cells more susceptible to IFN-mediated effects. These findings provide a mechanism that can at least partially explain the resistance of some EBV-associated tumors to IFN therapy. Our work suggests that similar pan-viral-miRNA functional-based screening strategies are warranted for determining relevant activities of other viral miRNAs.

Epstein-Barr virus latent genes

Latent Epstein–Barr virus (EBV) infection has a substantial role in causing many human disorders. The persistence of these viral genomes in all malignant cells, yet with the expression of limited latent genes, is consistent with the notion that EBV latent genes are important for malignant cell growth. While the EBV-encoded nuclear antigen-1 (EBNA-1) and latent membrane protein-2A (LMP-2A) are critical, the EBNA-leader proteins, EBNA-2, EBNA-3A, EBNA-3C and LMP-1, are individually essential for in vitro transformation of primary B cells to lymphoblastoid cell lines. EBV-encoded RNAs and EBNA-3Bs are dispensable. In this review, the roles of EBV latent genes are summarized.

Virus and noncoding RNAs: stars in the host–virus interaction game

ABSTRACT: 

In the past few years, noncoding RNAs (ncRNAs) have emerged as key modulators of the transcriptional and post-transcriptional control of a variety of cellular processes such as development, signaling, homeostasis and oncogenesis. Like their host cells, many viruses produce ncRNAs. During viral infection, and in order to establish persistent life-long infection of the host, viruses express both protein-coding and noncoding genes, modulating the cellular environment to favor infection. Given their limited genomic capacity, viruses evolved or acquired ncRNAs only if advantageous, either by enhancing the viral life cycle or assisting the virus in immune evasion of the host's response to infection. With variable length, structure, number, abundance and protein-binding partners, viral ncRNAs show specificity and diversity with respect to time of expression during the different stages of the virus life cycle and viral infection. Here, we review our current knowledge on the RNA-based mechanisms that regulate host–virus interaction focusing on viral ncRNAs and cellular ncRNAs modulated by viruses upon infection.

Epstein-Barr virus and Burkitt lymphoma

In 1964, a new herpesvirus, Epstein-Barr virus (EBV), was discovered in cultured tumor cells derived from a Burkitt lymphoma (BL) biopsy taken from an African patient. This was a momentous event that reinvigorated research into viruses as a possible cause of human cancers. Subsequent studies demonstrated that EBV was a potent growth-transforming agent for primary B cells, and that all cases of BL carried characteristic chromosomal translocations resulting in constitutive activation of the c-MYC oncogene. These results hinted at simple oncogenic mechanisms that would make Burkitt lymphoma paradigmatic for cancers with viral etiology. In reality, the pathogenesis of this tumor is rather complicated with regard to both the contribution of the virus and the involvement of cellular oncogenes. Here, we review the current understanding of the roles of EBV and c-MYC in the pathogenesis of BL and the implications for new therapeutic strategies to treat this lymphoma.

Differential proteomic analysis of endemic and sporadic Epstein-Barr virus-positive and negative Burkitt lymphoma

BACKGROUND

Burkitt lymphoma (BL) is the most common non-Hodgkin lymphoma in children worldwide and the most common paediatric malignancy in sub-Saharan Africa. The endemic (eBL) and sporadic (sBL) variants have distinct epidemiologic and virologic characteristics. Although gene expression studies have defined the transcriptional profiles of both, their proteomic signatures have not been studied.

METHODS

We compared the proteomic expression profiles using differential mass spectrometry-based isotope tag for relative and absolute quantitation (iTRAQ) analysis of a cell line representing Epstein-Barr virus (EBV)+ eBL, EBV+ and EBV- sBL, and EBV+/- normal B cells from healthy donors.

RESULTS

In total, there were 144 differentially expressed proteins with a statistically significant false discovery rate (FDR) of ⩽0.2. Results revealed over-expression of specific proteins with well-established links to lymphomagenesis such as TUBB2C (FDR 0.05), UCHL1 (FDR 0.05) and HSP90AB1 (FDR 0.1). Distinct characteristics based upon the epidemiologic and virologic subtypes of BL were also identified. In sBL, PCNA (FDR 0.05) and SLC3A2 (FDR 0.1) were significantly over-expressed. In eBL, C1QBP (FDR 0.1) and ENO1 (FDR 0.25) were significantly over-expressed. Comparison of EBV+ to EBV- BL cell lines and B cells revealed significant over-expression of DDX3X (FDR 0.1). Proteins were validated using Western blot analysis.

CONCLUSION

Our results suggest unique signal transduction pathways associated with EBV infection and epidemiological subtype of BL that may contribute to lymphomagenesis. These proteomic findings provide potential diagnostic, prognostic and therapeutic links to BL.

Epstein-Barr Virus-Encoded RNAs: Key Molecules in Viral Pathogenesis

The Epstein-Barr virus (EBV) is known as an oncogenic herpesvirus that has been implicated in the pathogenesis of various malignancies. EBV-encoded RNAs (EBERs) are non-coding RNAs expressed abundantly in latently EBV-infected cells. Herein, I summarize the current understanding of the functions of EBERs, including the interactions with cellular factors through which EBERs contribute to EBV-mediated pathogenesis. Previous studies have demonstrated that EBERs are responsible for malignant phenotypes in lymphoid cells, and can induce several cytokines that can promote the growth of various EBV-infected cancer cells. EBERs were also found to bind retinoic acid-inducible gene I (RIG-I) and thus activate its downstream signaling. Furthermore, EBERs induce interleukin-10, an autocrine growth factor for Burkitt’s lymphoma cells, by activating RIG-I/interferon regulatory factor 3 pathway, suggesting that EBER-mediated innate immune signaling modulation contributes to EBV-mediated oncogenesis. Recently, EBV-infected cells were reported to secret EBERs, which were then recognized by toll-like receptor 3 (TLR3), leading to the induction of type I interferon and inflammatory cytokines, and subsequent immune activation. Furthermore, EBER1 was detected in the sera of patients with active EBV-infectious diseases, suggesting that EBER1-meidated TLR3 signaling activation could account for the pathogenesis of active EBV-infectious diseases.

The labyrinth of interactions of Epstein-Barr virus-encoded small RNAs

Epstein-Barr Virus (EBV) is an oncogenic herpesvirus implicated in the pathogenesis of a number of human malignancies. However, the mechanism by which EBV leads to malignant transformation is not clear. A number of viral latent gene products, including non-protein coding small RNAs, are believed to be involved. Epstein-Barr virus-encoded RNA 1 (EBER1) and EBER2 are two such RNA molecules that are abundantly expressed (up to 10(7) copies) in all EBV-infected cells, but their function remains poorly understood. These polymerase III transcripts have extensive secondary structure and exist as ribonucleoproteins. An accumulating body of evidence suggests that EBERs play an important role, directly or indirectly, in EBV-induced oncogenesis. Here, we summarize the current understanding of the complex interactions of EBERs with various cellular factors and the potential pathways by which these small RNAs are able to influence EBV-infected cells to proliferate and to induce tumorigenesis. The exosome pathway is probably involved in the cellular excretion of EBERs and facilitating some of their biological effects.

Downregulation of the polyamine regulator spermidine/spermine N(1)-acetyltransferase by Epstein-Barr virus in a Burkitt's lymphoma cell line

Transition of Akata Burkitt's lymphoma (BL) from a malignant to nonmalignant phenotype upon loss of Epstein-Barr virus (EBV) is evidence for a viral contribution to tumorigenesis despite the tight restriction of EBV gene expression in BL. Examination of global cellular gene expression in Akata subclones that retained or lost EBV identified spermidine/spermine N(1)-acetyltransferase (SAT1), an inducible enzyme whose catabolism of polyamines affects both apoptosis and cell growth, as one of a limited number of cellular genes downregulated by EBV. Re-infection of the EBV-negative Akata clone reduced SAT1 mRNA to a level comparable with the parental EBV-positive Akata. EBV-positive Akata cells demonstrated decreased SAT1 enzyme activity concomitant with altered intracellular polyamine constituents. Reduction of SAT1 in EBV-positive BL was a transcriptional effect. Forced expression of the viral BCL2 homologue, BHRF1, in an EBV-negative Akata clone reduced SAT1 mRNA. Thus, EBV repression of polyamine catabolism becomes a complementary alteration to dysregulated c-myc enhancement of polyamine synthesis in BL and favorable to BL lymphomagenesis.

AUF1/hnRNP D is a novel protein partner of the EBER1 noncoding RNA of Epstein-Barr virus

Epstein-Barr virus (EBV)-infected cells express two noncoding RNAs called EBV-encoded RNA (EBER) 1 and EBER2. Despite their high abundance in the nucleus (about 10(6) copies), the molecular function of these noncoding RNAs has remained elusive. Here, we report that the insertion into EBER1 of an RNA aptamer that binds the bacteriophage MS2 coat protein allows the isolation of EBER1 and associated protein partners. By combining MS2-mediated selection with stable isotope labeling of amino acids in cell culture (SILAC) and analysis by mass spectrometry, we identified AUF1 (AU-rich element binding factor 1)/hnRNP D (heterogeneous nuclear ribonucleoprotein D) as an interacting protein of EBER1. AUF1 exists as four isoforms generated by alternative splicing and is best known for its role in destabilizing mRNAs upon binding to AU-rich elements (AREs) in their 3' untranslated region (UTR). Using UV crosslinking, we demonstrate that predominantly the p40 isoform of AUF1 interacts with EBER1 in vivo. Electrophoretic mobility shift assays show that EBER1 can compete for the binding of the AUF1 p40 isoform to ARE-containing RNA. Given the high abundance of EBER1 in EBV-positive cells, EBER1 may disturb the normal homeostasis between AUF1 and ARE-containing mRNAs or compete with other AUF1-interacting targets in cells latently infected by EBV.

Gammaherpesvirus and lymphoproliferative disorders in immunocompromised patients

Two lymphotropic human gamma herpesviruses can cause lymphoproliferative disorders: Epstein Barr virus (EBV, formally designated as human herpesvirus 4) and Kaposi sarcoma herpesvirus (KSHV, also called human herpesvirus 8). Individuals with inherited or acquired immunodeficiency have a greatly increased risk of developing a malignancy caused by one of these two viruses. Specific types of lymphoproliferations, including malignant lymphomas, occur in individuals with HIV infection, transplant recipients and children with primary immunodeficiency. Some of these diseases, such as Hodgkin's and non-Hodgkin lymphoma resemble those occurring in immunocompetent patients, but the proportion of tumors in which EBV is present is increased. Others, like primary effusion lymphoma and polymorphic post-transplant lymphoproliferative disorder are rarely seen outside the context of a specific immunodeficient state. Understanding the specific viral associations in selected lymphoproliferative disorders, and the insights into the molecular mechanisms of viral oncogenesis, will lead to better treatments for these frequently devastating diseases.

Epigenetic dysregulation of epstein-barr virus latency and development of autoimmune disease

Epstein-Barr virus (EBV) is ahumanherpesvirus thatpersists in the memory B-cells of the majority of the world population in a latent form. Primary EBV infection is asymptomatic or causes a self-limiting disease, infectious mononucleosis. Virus latency is associated with a wide variety of neoplasms whereof some occur in immune suppressed individuals. Virus production does not occur in strict latency. The expression of latent viral oncoproteins and nontranslated RNAs is under epigenetic control via DNA methylation and histone modifications that results either in a complete silencing of the EBV genome in memory B cells, or in a cell-type dependent usage of a couple of latency promoters in tumor cells, germinal center B cells and lymphoblastoid cells (LCL, transformed by EBV in vitro). Both, latent and lytic EBV proteins elicit a strong immune response. In immune suppressed and infectious mononucleosis patients, an increased viral load can be detected in the blood. Enhanced lytic replication may result in new infection- and transformation-events and thus is a risk factor both for malignant transformation and the development of autoimmune diseases. An increased viral load or a changed presentation of a subset of lytic or latent EBV proteins that cross-react with cellular antigens may trigger pathogenic processes through molecular mimicry that result in multiple sclerosis (MS), systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA).

Noncoding RNPs of viral origin

Like their host cells, many viruses produce noncoding (nc)RNAs. These show diversity with respect to time of expression during viral infection, length and structure, protein-binding partners and relative abundance compared with their host-cell counterparts. Viruses, with their limited genomic capacity, presumably evolve or acquire ncRNAs only if they selectively enhance the viral life cycle or assist the virus in combating the host's response to infection. Despite much effort, identifying the functions of viral ncRNAs has been extremely challenging. Recent technical advances and enhanced understanding of host-cell ncRNAs promise accelerated insights into the RNA warfare mounted by this fascinating class of RNPs.

Epstein-Barr virus-encoded EBNA1 enhances RNA polymerase III-dependent EBER expression through induction of EBER-associated cellular transcription factors

BACKGROUND

Epstein-Barr Virus (EBV)-encoded RNAs (EBERs) are non-polyadenylated RNA molecules transcribed from the EBV genome by RNA polymerase III (pol III). EBERs are the most abundant viral latent gene products, although the precise mechanisms by which EBV is able to achieve such high levels of EBER expression are not fully understood. Previously EBV has been demonstrated to induce transcription factors associated with EBER expression, including pol III transcription factors and ATF-2. We have recently demonstrated that EBV-encoded nuclear antigen-1 (EBNA1) induces cellular transcription factors, and given these findings, we investigated the role of EBNA1 in induction of EBER-associated transcription factors.

RESULTS

Our data confirm that in epithelial cells EBNA1 can enhance cellular pol III transcription. Transient expression of EBNA1 in Ad/AH cells stably expressing the EBERs led to induction of both EBER1 and EBER2 and conversely, expression of a dominant negative EBNA1 led to reduced EBER expression in EBV-infected Ad/AH cells. EBNA1 can induce transcription factors used by EBER genes, including TFIIIC, ATF-2 and c-Myc. A variant chromatin precipitation procedure showed that EBNA1 is associated with the promoters of these genes but not with the promoters of pol III-transcribed genes, including the EBERs themselves. Using shRNA knock-down, we confirm the significance of both ATF-2 and c-Myc in EBER expression. Further, functional induction of a c-Myc fusion protein led to increased EBER expression, providing c-Myc binding sites upstream of EBER1 were intact. In vivo studies confirm elevated levels of the 102 kD subunit of TFIIIC in the tumour cells of EBV-positive nasopharyngeal carcinoma biopsies.

CONCLUSIONS

Our findings reveal that EBNA1 is able to enhance EBER expression through induction of cellular transcription factors and add to the repertoire of EBNA1's transcription-regulatory properties.

New variations of Epstein-Barr virus-encoded small RNA genes in nasopharyngeal carcinomas, gastric carcinomas, and healthy donors in northern China

It has been generally believed that the Epstein-Barr virus (EBV)-encoded small RNA 1 and 2 (EBER1 and EBER2) genes are conserved as two families that correlated with type 1 (B95-8) and type 2 (AG876 or P3HR-1) EBV strains. EBER polymorphism and its association with EBV-associated disease have not received much attention. To explore the variations of EBER genes in different malignancies and healthy donors, the sequences of EBER genes were analyzed in 154 EBV-positive samples, including 47 nasopharyngeal carcinoma (NPC), 50 EBV-associated gastric carcinoma (EBVaGC) biopsies and 57 throat washing (TW) samples from healthy donors in northern China, where NPC is non-endemic. Three main distinct variants of EBER genes, designated as EB-6m, EB-8m, and EB-10m, were identified. EB-6m had a previously identified EBER sequence identical to P3HR-1 and was found in 33/47 (70.2%) NPC, 48/50 (96.0%) EBVaGC, and 54/57 (94.7%) TW isolates. EB-8m and EB-10m were new EBER variants with more mutations in EBER2 genes. They were found in 13/47 (27.7%) NPC cases, whereas in only 1/50 (2.0%) EBVaGC cases and not found in TW cases. The distributions were significantly different (P < 0.05). Other five isolates (one NPC, one EBVaGC and three TW cases) showed different sequences and could not be assigned to any of the three groups. Type 1 EBV strains showed heterogeneous in terms of EBER variants. These results suggest that EBER locus can be useful to identify different EBV isolates, and it would be interesting to evaluate the association of EBER polymorphisms with EBV-associated tumors.

Viral response to chemotherapy in endemic burkitt lymphoma

PURPOSE

Some EBV-directed therapies are predicted to be effective only when lytic viral replication occurs. We studied whether cyclophosphamide chemotherapy induces EBV to switch from latent to lytic phases of infection in a series of EBV-associated Burkitt lymphomas.

EXPERIMENTAL DESIGN

Children with first presentation of an expanding, solid maxillary or mandibular mass consistent with Burkitt lymphoma underwent fine-needle aspiration just prior to the initiation of cyclophosphamide therapy and again 1 to 5 days later. Aspirated cells were examined for latent and lytic EBV infection using in situ hybridization to EBV-encoded RNA (EBER), immunohistochemical analysis of the lytic EBV proteins BZLF1 and BMRF1, reverse transcription PCR targeting BZLF1 transcripts, and EBV viral load measurement by quantitative PCR.

RESULTS

Among 21 lymphomas expressing EBER prior to chemotherapy, 9 of 10 still expressed EBER on day 1 after therapy whereas only 2 of 11 (18%) specimens still expressed EBER at days 3 to 5, implying that chemotherapy was fairly effective at eliminating latently infected cells. Neither of the lytic products, BZLF1 or BMRF1, were significantly upregulated at the posttherapy time points examined. However, EBV genomic copy number increased in 5 of 10 samples 1 day after treatment began, suggesting that viral replication occurs within the first 24 hours.

CONCLUSION

Cyclophosphamide may induce the lytic phase of EBV infection and is fairly effective in diminishing EBER-expressing tumor cells within 5 days. These findings provide the rationale for a trial testing synergistic tumor cell killing using cyclophosphamide with a drug like ganciclovir targeting lytically infected cells.

Lymphoid hyperplasia and lymphoma in transgenic mice expressing the small non-coding RNA, EBER1 of Epstein-Barr virus

Background

Non-coding RNAs have critical functions in diverse biological processes, particularly in gene regulation. Viruses, like their host cells, employ such functional RNAs and the human cancer associated Epstein-Barr virus (EBV) is no exception. Nearly all EBV associated tumours express the EBV small, non-coding RNAs (EBERs) 1 and 2, however their role in viral pathogenesis remains largely obscure.

Methodology/Principal Findings

To investigate the action of EBER1 in vivo, we produced ten transgenic mouse lines expressing EBER1 in the lymphoid compartment using the mouse immunoglobulin heavy chain intronic enhancer Eμ. Mice of several of these EμEBER1 lines developed lymphoid hyperplasia which in some cases proceeded to B cell malignancy. The hallmark of the transgenic phenotype is enlargement of the spleen and mesenteric lymph nodes and in some cases enlargement of the thymus, liver and peripheral lymph nodes. The tumours were found to be of B cell origin and showed clonal IgH rearrangements. In order to explore if EBER1 would cooperate with c-Myc (deregulated in Burkitt's lymphoma) to accelerate lymphomagenesis, a cross-breeding study was undertaken with EμEBER1 and EμMyc mice. While no significant reduction in latency to lymphoma onset was observed in bi-transgenic mice, c-Myc induction was detected in some EμEBER1 single transgenic tumours, indicative of a functional cooperation.

Conclusions/Significance

This study is the first to describe the in vivo expression of a polymerase III, non-coding viral gene and demonstrate its oncogenic potential. The data suggest that EBER1 plays an oncogenic role in EBV associated malignant disease.

Epstein-Barr virus-encoded EBNA1 inhibits the canonical NF-kappaB pathway in carcinoma cells by inhibiting IKK phosphorylation

BACKGROUND

The Epstein-Barr virus (EBV)-encoded EBNA1 protein is expressed in all EBV-associated tumours, including undifferentiated nasopharyngeal carcinoma (NPC), where it is indispensable for viral replication, genome maintenance and viral gene expression. EBNA1's transcription factor-like functions also extend to influencing the expression of cellular genes involved in pathways commonly dysregulated during oncogenesis, including elevation of AP-1 activity in NPC cell lines resulting in enhancement of angiogenesis in vitro. In this study we sought to extend these observations by examining the role of EBNA1 upon another pathway commonly deregulated during carcinogenesis; namely NF-kappaB.

RESULTS

In this report we demonstrate that EBNA1 inhibits the canonical NF-kappaB pathway in carcinoma lines by inhibiting the phosphorylation of IKKalpha/beta. In agreement with this observation we find a reduction in the phosphorylation of IkappaBalpha and reduced phosphorylation and nuclear translocation of p65, resulting in a reduction in the amount of p65 in nuclear NF-kappaB complexes. Similar effects were also found in carcinoma lines infected with recombinant EBV and in the EBV-positive NPC-derived cell line C666-1. Inhibition of NF-kappaB was dependent upon regions of EBNA1 essential for gene transactivation whilst the interaction with the deubiquitinating enzyme, USP7, was entirely dispensable. Furthermore, in agreement with EBNA1 inhibiting p65 NF-kappaB we demonstrate that p65 was exclusively cytoplasmic in 11 out of 11 NPC tumours studied.

CONCLUSIONS

Inhibition of p65 NF-kappaB in murine and human epidermis results in tissue hyperplasia and the development of squamous cell carcinoma. In line with this, p65 knockout fibroblasts have a transformed phenotype. Inhibition of p65 NF-kappaB by EBNA1 may therefore contribute to the development of NPC by inducing tissue hyperplasia. Furthermore, inhibition of NF-kappaB is employed by viruses as an immune evasion strategy which is also closely linked to oncogenesis during persistent viral infection. Our findings therefore further implicate EBNA1 in playing an important role in the pathogenesis of NPC.

Modulation of innate immunity system by Epstein-Barr virus-encoded non-coding RNA and oncogenesis

Epstein-Barr virus (EBV)-encoded small RNAs (EBERs) are polyA-, non-coding RNAs that are expressed abundantly in all forms of cells latently infected with EBV. EBERs (EBER1 and EBER2) contribute to the clonal proliferation of EBV-negative Burkitt's lymphoma (BL) cells in soft agar, tumorigenicity in SCID mice, up-regulation of the bcl-2 oncoprotein, resistance to apoptosis, and maintenance of malignant phenotypes in BL cells. EBERs induce the expression of interleukin (IL)-10 in BL cells, insulin-like growth factor 1 (IGF-I) in gastric and nasopharyngeal carcinoma cells, IL-9 in T cells, and IL-6 in lymphoblastoid cell lines. Additionally, each of these cytokines acts as an autocrine growth factor. In BL cells, EBERs bind the double-stranded RNA-activated protein kinase PKR, inhibit its phosphorylation, and thereby prevent IFN-alpha-mediated apoptosis. In epithelial cells, EBERs confer resistance to Fas-mediated apoptosis by blocking PKR activity. EBERs form complexes with PKR, ribosomal protein L22, lupus erythematosis-associated antigen (La), and retinoic acid-inducible gene I (RIG-I). In BL cells, EBERs activate RIG-I signaling and induce the expression of type-I IFNs and interferon stimulated genes (ISGs) through the activation of RIG-I substrates, nuclear factor-kappa B (NF-kappaB), and IFN regulatory factor 3 (IRF-3), and anti-inflamatory cytokine IL-10 through IRF-3 but not NF-kappaB signaling. EBERs also play critical roles in the growth transformation of B lymphocytes. Although EBER1 and EBER2 exhibit similarities in their primary (54%) and secondary structures, recent findings have shown that recombinant EBVs carrying only the EBER2 gene play a greater role in the growth transformation of B lymphocytes than EBVs carrying only the EBER1 gene. Thus, EBERs play multiple roles in various cell types, and we present a model that highlights the functions of EBERs in EBV-mediated oncogenesis in BL cells.

Role of EBERs in the pathogenesis of EBV infection

Epstein-Barr virus (EBV)-encoded small RNAs (EBERs) are noncoding RNAs that are expressed abundantly in latently EBV-infected cells. Previous studies demonstrated that EBERs (EBER1 and EBER2) play significant roles in various EBV-infected cancer cells. EBERs are responsible for malignant phenotypes of Burkitt's lymphoma (BL) cells including resistance to apoptosis. In addition, EBERs induce the expression of interleukin (IL)-10 in BL cells, insulin-like growth factor (IGF)-1 in gastric carcinoma and nasopharyngeal carcinoma cells, IL-9 in T cells that act as an autocrine growth factor. It was also reported that EBERs play critical roles in the B cell growth transformation including IL-6 induction by EBER2. EBERs have been discovered to interact with cellular proteins that play a key role in antiviral innate immunity. They bind the protein kinase RNA-dependent (PKR) and inhibit its activation, leading to resistance to PKR-mediated apoptosis. Recently, it was demonstrated that EBERs bind RIG-I and activate its downstream signaling, which induces expression of type-I interferon (IFN)s. Furthermore, EBERs induce IL-10 through IRF3 but not NF-kappaB activation in BL cells, suggesting that modulation of innate immune signaling by EBERs contribute to EBV-mediated oncogenesis. Most recently, it was reported that EBERs are secreted from EBV-infected cells and are recognized by toll-like receptor (TLR)3, leading to induction of type-I IFNs and inflammatory cytokines, and subsequent immune activation. Furthermore, EBER1 could be detected in the sera of patients with active EBV infectious diseases, suggesting that activation of TLR3 signaling by EBER1 would be account for the pathogenesis of active EBV infectious diseases.

Burkitt's lymphoma: the Rosetta Stone deciphering Epstein-Barr virus biology

Epstein-Barr virus was originally identified in the tumour cells of a Burkitt's lymphoma, and was the first virus to be associated with the pathogenesis of a human cancer. Studies on the relationship of EBV with Burkitt's lymphoma have revealed important general principles that are relevant to other virus-associated cancers. In addition, the impact of such studies on the knowledge of EBV biology has been enormous. Here, we review some of the key historical observations arising from studies on Burkitt's lymphoma that have informed our understanding of EBV, and we summarise the current hypotheses regarding the role of EBV in the pathogenesis of Burkitt's lymphoma.

Features distinguishing Epstein-Barr virus infections of epithelial cells and B cells: viral genome expression, genome maintenance, and genome amplification

Epstein-Barr virus (EBV) is associated with malignant diseases of lymphoid and epithelial cell origin. The tropism of EBV is due to B-cell-restricted expression of CD21, the major receptor molecule for the virus. However, efficient infection of CD21- epithelial cells can be achieved via transfer from EBV-coated B cells. We compare and contrast here the early events following in vitro infection of primary B cells and epithelial cells. Using sensitive, quantitative reverse transcription-PCR assays for several latent and lytic transcripts and two-color immunofluorescence staining to analyze expression at the single cell level, we confirmed and extended previous reports indicating that the two cell types support different patterns of transcription. Furthermore, whereas infection of B cells with one or two copies of EBV resulted in rapid amplification of the viral genome to >20 copies per cell, such amplification was not normally observed after infection of primary epithelial cells or undifferentiated epithelial lines. In epithelial cells, EBNA1 expression was detected in only ca. 40% of EBER+ cells, and the EBV genome was subsequently lost during prolonged culture. One exception was that infection of AGS, a gastric carcinoma line, resulted in maintenance of EBNA1 expression and amplification of the EBV episome. In contrast to B cells, where amplification of the EBV episome occurred even with a replication-defective BZLF1-knockout virus, amplification in AGS cells was dependent upon early lytic cycle gene expression. These data highlight the influence of the host cell on the outcome of EBV infection with regard to genome expression, amplification, and maintenance.

Growth-promoting properties of Epstein-Barr virus EBER-1 RNA correlate with ribosomal protein L22 binding

The Epstein-Barr virus (EBV)-encoded RNAs, EBER-1 and EBER-2, are highly abundant noncoding nuclear RNAs expressed during all forms of EBV latency. The EBERs have been shown to impart significant tumorigenic potential upon EBV-negative Burkitt lymphoma (BL) cells and to contribute to the growth potential of other B-cell lymphoma-, gastric carcinoma-, and nasopharyngeal carcinoma-derived cell lines. However, the mechanisms underlying this EBER-dependent enhancement of cell growth potential remain to be elucidated. Here we focused on the known interaction between EBER-1 and the cellular ribosomal protein L22 and the consequences of this interaction with respect to the growth-promoting properties of the EBERs. L22, a component of 60S ribosomal subunits, binds three sites on EBER-1, and a substantial fraction of available L22 is relocalized from nucleoli to the nucleoplasm in EBV-infected cells. To investigate the hypothesis that EBER-1-mediated relocalization of L22 in EBV-infected cells is critical for EBER-dependent functions, we investigated whether EBER-1 expression is necessary and sufficient for nucleoplasmic retention of L22. Following demonstration of this, we utilized RNA-protein binding assays and fluorescence localization studies to demonstrate that mutation of the L22 binding sites on EBER-1 prevents L22 binding and inhibits EBER-1-dependent L22 relocalization. Finally, the in vivo consequence of preventing L22 relocalization in EBER-expressing cells was examined in soft agar colony formation assays. We demonstrate that BL cells expressing mutated EBER-1 RNAs rendered incapable of binding L22 have significantly reduced capacity to enhance cell growth potential relative to BL cells expressing wild-type EBERs.

Epstein-Barr virus independent dysregulation of UBP43 expression alters interferon-stimulated gene expression in Burkitt lymphoma

Epstein-Barr virus (EBV) persists as a life-long latent infection within memory B cells, but how EBV may circumvent the innate immune response within this virus reservoir is unclear. Recent studies suggest that the latency-associated non-coding RNAs of EBV may actually induce type I (antiviral) interferon production, raising the question of how EBV counters the negative consequences this is likely to have on viral persistence. We addressed this by examining the type I interferon response in Burkitt lymphoma (BL) cell lines, the only in vitro model of the restricted program of EBV latency-gene expression in persistently infected B cells in vivo. Importantly, we observed no effect of EBV on interferon alpha-induced signaling or evidence of type I interferon production, suggesting that EBV in this latent state is silent to the cell's innate antiviral surveillance. We did uncover, however, a defect in the negative feedback control of interferon signaling in a subpopulation of BL lines as was revealed by prolonged interferon-stimulated gene transcription consistent with sustained tyrosine phosphorylation on STAT1 and STAT2. This was due to inadequate induction of expression of the ubiquitin-specific protease UBP43, which removes the ubiquitin-like ISG15 polypeptide conjugated to proteins (ISGylation) in response to type I interferons. Results here are consistent with previous findings in genetically engineered Ubp43^−/− murine cells that UBP43 down-regulates interferon signaling, independent of its ISG15 isopeptidase activity, by precluding the protein kinase JAK1 from the interferon receptor. This natural deficiency in UBP43 expression may therefore provide a useful model to further probe the biological roles of UBP43 and ISGylation.

Biomarkers for early detection of high risk cancers: from gliomas to nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NpC) is a malignant disease associated with Epstein-Barr virus infection, and often diagnosed at an advanced stage. This significantly curtails patient survival. We hypothesize that a panel of biomarkers can be assembled to assess NpC incidence, early detection, and tumor progression during therapeutic intervention. Our thesis rests on a model of successfully predicting high-risk gliomas by means of a carefully crafted panel of molecular mitotic biomarkers (i.e., securin, survivin and MCM2). The strategy we propose holds strong promise for prevention and cure of NpC. The approach we propose seeks to identify certain biomarkers from viral materials, patient tissues and assessment of related diseases, whose signatures, taken together, will be endowed with some degree of congruency, or sense of a coordinated language (i.e., "votes"). Biomarker "voting" will then permit to outline a broad coordinated molecular map for the molecular and epigenetic characterization of each individual patient's NpC tumor. We will draw on the process of contrasting biomarkers in health and disease, which rests on the auto-proteomic concept particularly relevant in high-risk cancer individuals, such as is the case for NpC. In brief we defend, current advances in human proteome profiling proffers the possibility of having individual baseline proteomic profiles using local body fluids (e.g., saliva, nasal secretions, sputum) or systemic fluids (e.g., plasma, serum, cerebrospinal fluid) to unravel a personalized molecular map for high-risk NpC individuals. Regular check-up will monitor for new or impending manifestations of NpC, and provide a secure assessment of incidence and early detection.

An Epstein-Barr virus anti-apoptotic protein constitutively expressed in transformed cells and implicated in burkitt lymphomagenesis: the Wp/BHRF1 link

Two factors contribute to Burkitt lymphoma (BL) pathogenesis, a chromosomal translocation leading to c-myc oncogene deregulation and infection with Epstein-Barr virus (EBV). Although the virus has B cell growth–transforming ability, this may not relate to its role in BL since many of the transforming proteins are not expressed in the tumor. Mounting evidence supports an alternative role, whereby EBV counteracts the high apoptotic sensitivity inherent to the c-myc–driven growth program. In that regard, a subset of BLs carry virus mutants in a novel form of latent infection that provides unusually strong resistance to apoptosis. Uniquely, these virus mutants use Wp (a viral promoter normally activated early in B cell transformation) and express a broader-than-usual range of latent antigens. Here, using an inducible system to express the candidate antigens, we show that this marked apoptosis resistance is mediated not by one of the extended range of EBNAs seen in Wp-restricted latency but by Wp-driven expression of the viral bcl2 homologue, BHRF1, a protein usually associated with the virus lytic cycle. Interestingly, this Wp/BHRF1 connection is not confined to Wp-restricted BLs but appears integral to normal B cell transformation by EBV. We find that the BHRF1 gene expression recently reported in newly infected B cells is temporally linked to Wp activation and the presence of W/BHRF1-spliced transcripts. Furthermore, just as Wp activity is never completely eclipsed in in vitro–transformed lines, low-level BHRF1 transcripts remain detectable in these cells long-term. Most importantly, recognition by BHRF1-specific T cells confirms that such lines continue to express the protein independently of any lytic cycle entry. This work therefore provides the first evidence that BHRF1, the EBV bcl2 homologue, is constitutively expressed as a latent protein in growth-transformed cells in vitro and, in the context of Wp-restricted BL, may contribute to virus-associated lymphomagenesis in vivo.

Cancer almost always develops through the cumulative effects of several independent changes in the target cell. For certain tumors, one step in the chain involves infection of the cell with a particular type of virus. The best example is Burkitt lymphoma (BL), a tumor of B lymphocytes which develops through the combined action of a genetic accident leading to uncontrolled expression of the c-myc oncogene and infection with a common herpesvirus, the Epstein-Barr virus (EBV). Recent evidence suggests that, although latent EBV infection can itself drive B cell growth, the virus plays a different role in the context of BL, namely to counteract the naturally poor survival ability of c-myc–expressing cells while leaving their c-myc–driven growth intact. Here we show that EBV achieves this by unexpectedly switching on a viral protein that was thought never to be seen in latent infection; this viral protein resembles one of the cell's own key survival proteins called bcl2. Furthermore, the work has led us to realise that this virally encoded bcl2-like protein is not only important in the context of BL but, contrary to conventional wisdom, is actually part of EBV's natural strategy for B cell growth transformation.

Epstein-Barr virus-encoded EBNA1 modulates the AP-1 transcription factor pathway in nasopharyngeal carcinoma cells and enhances angiogenesis in vitro

The Epstein-Barr virus (EBV)-encoded EBNA1 protein is expressed in all virus-associated tumours, including nasopharyngeal carcinoma (NPC), where it plays an essential role in EBV genome maintenance, replication and transcription. Previous studies suggest that EBNA1 may have additional effects relevant to oncogenesis, including enhancement of cell survival, raising the possibility that EBNA1 may influence cellular gene expression. We have recently demonstrated by gene expression microarray profiling in an NPC cell model that EBNA1 influences the expression of a range of cellular genes, including those involved in transcription, translation and cell signalling. Here, we report for the first time that EBNA1 enhances activity of the AP-1 transcription factor in NPC cells and demonstrate that this is achieved by EBNA1 binding to the promoters of c-Jun and ATF2, enhancing their expression. In addition, we demonstrate elevated expression of the AP-1 targets interleukin 8, vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1alpha in response to EBNA1 expression, which enhances microtubule formation in an in vitro angiogenesis assay. Furthermore, we confirm elevation of VEGF and the phosphorylated isoforms of c-Jun and ATF2 in NPC biopsies. These findings implicate EBNA1 in the angiogenic process and suggest that this viral protein might directly contribute to the development and aggressively metastatic nature of NPC.

Mechanisms involved in Burkitt's tumor formation

Burkitt's lymphoma is a rapidly fatal tumor if untreated, but it is curable with intensive polychemotherapy. Unfortunately, the toxicities reported for its treatment in adults are poorly tolerated. Novel therapies aimed at specific molecular targets might prove to be less toxic. A better knowledge of the mechanisms involved in the pathogenesis of Burkitt's lymphoma would facilitate the identification of such targets. This review explores the current knowledge on the alterations found in the three main Burkitt's lymphoma variants.

The B cell antigen receptor and overexpression of MYC can cooperate in the genesis of B cell lymphomas

A variety of circumstantial evidence from humans has implicated the B cell antigen receptor (BCR) in the genesis of B cell lymphomas. We generated mouse models designed to test this possibility directly, and we found that both the constitutive and antigen-stimulated state of a clonal BCR affected the rate and outcome of lymphomagenesis initiated by the proto-oncogene MYC. The tumors that arose in the presence of constitutive BCR differed from those initiated by MYC alone and resembled chronic B cell lymphocytic leukemia/lymphoma (B-CLL), whereas those that arose in response to antigen stimulation resembled large B-cell lymphomas, particularly Burkitt lymphoma (BL). We linked the genesis of the BL-like tumors to antigen stimulus in three ways. First, in reconstruction experiments, stimulation of B cells by an autoantigen in the presence of overexpressed MYC gave rise to BL-like tumors that were, in turn, dependent on both MYC and the antigen for survival and proliferation. Second, genetic disruption of the pathway that mediates signaling from the BCR promptly killed cells of the BL-like tumors as well as the tumors resembling B-CLL. And third, growth of the murine BL could be inhibited by any of three distinctive immunosuppressants, in accord with the dependence of the tumors on antigen-induced signaling. Together, our results provide direct evidence that antigenic stimulation can participate in lymphomagenesis, point to a potential role for the constitutive BCR as well, and sustain the view that the constitutive BCR gives rise to signals different from those elicited by antigen. The mouse models described here should be useful in exploring further the pathogenesis of lymphomas, and in preclinical testing of new therapeutics.

It has long been suspected that the malignant proliferation of B lymphocytes known as lymphomas might represent a perversion of how the cells normally respond to antigen. In particular, the molecular receptor on the surface of the cells that signals the presence of antigen might be abnormally active in lymphomas. We have tested this hypothesis by engineering the genome of mice so that virtually all of the B cells are commandeered by a single version of the surface receptor, then stimulated that receptor with the molecule it is designed to recognize. Our results indicate that both the unstimulated and stimulated states of the receptor can cooperate with an oncogene known as MYC in the genesis of lymphomas. But the two states of the receptor give rise to different forms of lymphoma. In particular, the stimulated form cooperates with MYC to produce a disease that closely resembles Burkitt lymphoma. These results illuminate the mechanisms that are responsible for lymphomas and could inform the development of new strategies to treat the disease.

A series of genetically engineered mice were used to substantiate a long-standing speculation that chronic immune-stimulus may be involved in the genesis of certain lymphomas, illuminating the pathogenesis of B cell lymphomas and suggesting new strategies to treat several forms of this malignancy, including Burkitt lymphoma.

Epstein-Barr virus-encoded small RNA induces IL-10 through RIG-I-mediated IRF-3 signaling

Epstein-Barr virus-encoded small RNA (EBER) is nonpolyadenylated, noncoding RNA, forms stem-loop structure by intermolecular base-pairing giving rise to double-stranded RNA (dsRNA)-like molecule and exists abundantly in EBV-infected cells. EBER induces IL-10 and thus supports the growth of Burkitt's lymphoma (BL) cells. In this study, the mechanism of IL-10 induction by EBER was analysed in the context of dsRNA signaling pathway. Knockdown of retinoic acid-inducible gene I (RIG-I) by small interfering RNA (siRNA), and expression of dominant-negative RIG-I downregulated IL-10 induction in EBER(+) EBV-infected and EBER plasmid-transfected BL cells. Transfection of EBER-expressing plasmid or in vitro synthesized EBER induced IL-10 in RIG-I-expressing cell clones, and activation of IL-10 promoter by EBER was blocked by dominant-negative RIG-I. Blocking of nuclear factor (NF)-kappaB by dominant-negative IkappaB-alpha plasmid did not block IL-10 expression, whereas knockdown of IRF-3 by siRNA resulted in downregulation of IL-10 in EBER(+) BL cells. NF-kappaB is reported to function downstream of RIG-I signaling pathway and is involved in the induction of proinflammatory cytokines. Our results indicate that EBER induces an anti-inflammatory cytokine IL-10 through RIG-I-mediated IRF-3 but not NF-kappaB signaling. These findings suggest a new mechanism of dsRNA signaling pathway that triggers the expression of IL-10, which acts as an autocrine growth factor in BL cells.

Noncoding RNAs produced by oncogenic human herpesviruses

The two human herpesviruses that are causally associated with cancer are Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus (KSHV). Both are lymphocryptoviruses that establish latency in B lymphocytes and persist for the lifetime of the host. EBV and KSHV are both linked to a variety of lymphomas. EBV is also a causative agent or cofactor in epithelial malignancies such as nasopharyngeal carcinoma whereas Kaposi's sarcoma is of endothelial cell origin. Both viruses encode a limited number of proteins during latent replication that are important for growth transformation and evasion of the immune system. In addition, they express noncoding RNAs during both latent and lytic infection. Many of these RNAs have been highly conserved during evolution and are expressed in a wide variety of clinical settings, suggesting their fundamental importance in the viral life cycle. The function of some of these RNAs such as the nuclear EBV EBER RNAs remains elusive although they are some of the most abundant transcripts produced by each virus. Both EBV and KSHV also have recently been shown to encode and express microRNAs. The study of these viral microRNAs is just beginning although several of their cellular and viral gene targets have been established. Viral microRNAs appear to be involved in both modulation of the immune response as well as oncogenesis. Because each target gene may have many microRNAs acting on its mRNA, and each microRNA may have more than one target, there are likely to be many new discoveries regarding the complex interactions of viral microRNAs and host cell genes.

Epstein-Barr virus nuclear antigen 1 does not cause lymphoma in C57BL/6J mice

To test whether transgenic Epstein-Barr virus nuclear antigen 1 (EBNA1) expression in C57BL/6 mouse lymphocytes causes lymphoma, EBNA1 expressed in three FVB lineages at two or three times the level of latent infection was crossed up to six successive times into C57BL/6J mice. After five or six crosses, 14/36, (38%) EBNA1 transgenic mice, 11/31 (36%) littermate EBNA1-negative controls, and 9/25 (36%) inbred C57BL/6J mice housed in the same facility had lymphoma. These data indicate that EBNA1 does not significantly increase lymphoma prevalence in C57BL/6J mice.

Epstein-Barr virus and Burkitt lymphoma

Burkitt lymphoma (BL) is an aggressive B-cell malignancy with endemic, sporadic and immunodeficiency-associated variants. It has been known for many years that the fundamental transforming event in BL is the translocation of the MYC gene, and the events that bring about this translocation and those that allow cells to survive with the constitutive expression of MYC have been the subject of intense investigation. Epstein-Barr virus (EBV) infection, malaria, immunodeficiency and spontaneous, somatic mutation can all contribute to the origin and maintenance of this cancer and their mechanisms are the subject of this review.