Epstein-Barr virus encoded BALF1 gene is transcribed in Burkitt's lymphoma cell lines and in nasopharyngeal carcinoma's biopsies

The role of microbiota in nasopharyngeal cancer: Where do we stand?

Nasopharyngeal carcinoma (NPC) is a common head and neck cancer with a poor prognosis. One of the crucial challenges regarding NPC is its pathogenesis. Recent findings highlight the significance of host microbiota in the development of NPC, affected locally by nasopharyngeal microbiota or remotely by oral microbiota. The oral microbiota can migrate to the nasopharyngeal space, thereby impacting the composition of the nasopharyngeal microbiota. Specific bacterial strains have been linked to the development of nasopharyngeal cancer, including Neisseria, Staphylococcus, Leptotrichia, Staphylococcaceae, Granulicatella, Corynebacterium, Fusobacterium, and Prevotella. Several mechanisms have been proposed to elucidate how microbiota dysbiosis contributes to the development of NPC, including triggering tumor-promoting inflammation, reactivating the Epstein-Barr virus (EBV), inducing oxidative stress, weakening the immune system, and worsening tumor hypoxia. In addition, the composition of nasopharyngeal microbiota and the number of tumor-infiltrating microbiota can influence the prognosis and treatment response in patients with NPC. To the best of our knowledge, this is the first review discussing the impacts of the host microbiota on nasopharyngeal cancer pathogenesis, progression, and treatment response.

OTUD1 enhances gastric cancer aggressiveness by deubiquitinating EBV-encoded protein BALF1 to stabilize the apoptosis inhibitor Bcl-2

The Epstein-Barr virus (EBV) is implicated in several cancers, including EBV-associated gastric cancer (EBVaGC). This study focuses on EBV-encoded BALF1 (BamH1 A fragment leftward reading frame 1), a key apoptosis regulator in EBV-related cancers, whose specific impact on EBVaGC was previously unknown. Our findings indicate that BALF1 overexpression in gastric cancer cells significantly enhances their proliferation, migration, and resistance to chemotherapy-induced apoptosis, confirming BALF1's oncogenic potential. A novel discovery is that BALF1 undergoes degradation via the ubiquitin-proteasome pathway. Through analysis of 69 deubiquitinating enzymes (DUBs), ovarian tumor protease (OTU) domain-containing protein 1 (OTUD1) emerged as a vital regulator for maintaining BALF1 protein stability. Furthermore, BALF1 was found to play a role in regulating the stability of the B-cell lymphoma-2 (Bcl-2) protein, increasing its levels through deubiquitination. This mechanism reveals BALF1's multifaceted oncogenic role in gastric cancer, as it contributes both directly and indirectly to cancer progression, particularly by stabilizing Bcl-2, known for its anti-apoptotic characteristics. These insights significantly deepen our understanding of EBV's involvement in the pathogenesis of gastric cancer. The elucidation of OTUD1's role in BALF1 regulation and its influence on Bcl-2 stabilization provide new avenues for therapeutic intervention in EBVaGC, bridging the gap between viral oncogenesis and cellular protein regulation and offering a more holistic view of gastric cancer development under the influence of EBV.

Functional Implications of Epstein-Barr Virus Lytic Genes in Carcinogenesis

Epstein-Barr virus (EBV) is associated with a diverse range of tumors of both lymphoid and epithelial origin. Similar to other herpesviruses, EBV displays a bipartite life cycle consisting of latent and lytic phases. Current dogma indicates that the latent genes are key drivers in the pathogenesis of EBV-associated cancers, while the lytic genes are primarily responsible for viral transmission. In recent years, evidence has emerged to show that the EBV lytic phase also plays an important role in EBV tumorigenesis, and the expression of EBV lytic genes is frequently detected in tumor tissues and cell lines. The advent of next generation sequencing has allowed the comprehensive profiling of EBV gene expression, and this has revealed the consistent expression of several lytic genes across various types of EBV-associated cancers. In this review, we provide an overview of the functional implications of EBV lytic gene expression to the oncogenic process and discuss possible avenues for future investigations.

Epstein-Barr virus: Current questions and challenges

Epstein-Barr virus (EBV) infects most people worldwide and persists for life due to complicated interplay between lytic infection and multiple types of latent infections. While usually asymptomatic, EBV is a causative agent in several types of cancer and has a strong association with multiple sclerosis. Exactly how EBV promotes these diseases and why they are rare consequences of infection are incompletely understood. Here I will discuss current ideas on disease induction by EBV, including the importance of lytic protein expression in the context of latent infection as well as the possible importance of specific EBV variants in disease induction.

Expression of PD-L1 in EBV-associated malignancies

Epstein-Barr virus infection is closely related to the occurrence and development of a variety of malignant tumors. Tumor immunotherapy has been combined with modern biological high-tech technology, and has become the fourth cancer treatment mode after surgery, chemotherapy and radiotherapy. In 2013, immunotherapy was named the first of ten scientific breakthroughs by science. It aims to control and destroy tumor cells by stimulating and enhancing autoimmune function. In recent years, immune checkpoint inhibitors (ICIs) targeting PD-L1 have become a research hotspot in the field of cancer. Recent studies have shown that EBV infection can upregulate PD-L1 through complex mechanisms. Further understanding of these mechanisms and prevention of hyperprogressive disease (HPD) can make PD-L1 immune checkpoint inhibitors an effective way of immunotherapy for EBV related malignant tumors.

Epstein-Barr Virus BALF0 and BALF1 Modulate Autophagy

Autophagy is an essential catabolic process that degrades cytoplasmic components within the lysosome, therefore ensuring cell survival and homeostasis. A growing number of viruses, including members of the Herpesviridae family, have been shown to manipulate autophagy to facilitate their persistence or optimize their replication. Previous works showed that the Epstein–Barr virus (EBV), a human transforming gammaherpesvirus, hijacked autophagy during the lytic phase of its cycle, possibly to favor the formation of viral particles. However, the viral proteins that are responsible for an EBV-mediated subversion of the autophagy pathways remain to be characterized. Here we provide the first evidence that the BALF0/1 open reading frame encodes for two conserved proteins of the Bcl-2 family, BALF0 and BALF1, that are expressed during the early phase of the lytic cycle and can modulate autophagy. A putative LC3-interacting region (LIR) has been identified that is required both for BALF1 colocalization with autophagosomes and for its ability to stimulate autophagy.

Emodin Inhibits EBV Reactivation and Represses NPC Tumorigenesis

Nasopharyngeal carcinoma (NPC) is a unique malignancy derived from the epithelium of the nasopharynx. Despite great advances in the development of radiotherapy and chemotherapy, relapse and metastasis in NPC patients remain major causes of mortality. Evidence accumulated over recent years indicates that Epstein-Barr virus (EBV) lytic replication plays an important role in the pathogenesis of NPC and inhibition of EBV reactivation is now being considered as a goal for the therapy of EBV-associated cancers. With this in mind, a panel of dietary compounds was screened and emodin was found to have potential anti-EBV activity. Through Western blotting, immunofluorescence, and flow cytometric analysis, we show that emodin inhibits the expression of EBV lytic proteins and blocks virion production in EBV- positive epithelial cell lines. In investigating the underlying mechanism, reporter assays indicated that emodin represses Zta promoter (Zp) and Rta promoter (Rp) activities, triggered by various inducers. Mapping of the Zp construct reveals that the SP1 binding region is important for emodin-triggered repression and emodin is shown to be able to inhibit SP1 expression, suggesting that it likely inhibits EBV reactivation by suppression of SP1 expression. Moreover, we also show that emodin inhibits the tumorigenic properties induced by repeated EBV reactivation, including micronucleus formation, cell proliferation, migration, and matrigel invasiveness. Emodin administration also represses the tumor growth in mice which is induced by EBV activation. Taken together, our results provide a potential chemopreventive agent in restricting EBV reactivation and NPC recurrence.

Contribution of the KSHV and EBV lytic cycles to tumourigenesis

Kaposi's Sarcoma-associated herpesvirus (KSHV) and Epstein Barr virus (EBV) are the causative agents of several malignancies. Like all herpesviruses, KSHV and EBV undergo distinct latent and lytic replication programmes. The transition between these states allows the establishment of a lifelong persistent infection, dissemination to sites of disease and the spread to new hosts. Latency-associated viral proteins have been well characterised in transformation and tumourigenesis pathways; however, a number of studies have shown that abrogation of KSHV and EBV lytic gene expression impairs the oncogenesis of several cancers. Furthermore, several lytically expressed proteins have been functionally tethered to the angioproliferative and anti-apoptotic phenotypes of virus-infected cells. As a result, the investigation and therapeutic targeting of KSHV and EBV lytic cycles may be essential for the treatment of their associated malignancies.

Therapies based on targeting Epstein-Barr virus lytic replication for EBV-associated malignancies

In recent years, Epstein‐Barr virus (EBV) lytic infection has been shown to significantly contribute to carcinogenesis. Thus, therapies aimed at targeting the EBV lytic cycle have been developed as novel strategies for treatment of EBV‐associated malignancies. In this review, focusing on the viral lytic proteins, we describe recent advances regarding the involvement of the EBV lytic cycle in carcinogenesis. Moreover, we further discuss 2 distinct EBV lytic cycle‐targeted therapeutic strategies against EBV‐induced malignancies. One of the strategies involves inhibition of the EBV lytic cycle by natural compounds known to have anti‐EBV properties; another is to intentionally induce EBV lytic replication in combination with nucleotide analogues. Recent advances in EBV lytic‐based strategies are beginning to show promise in the treatment and/or prevention of EBV‐related tumors.

Interaction of Epstein-Barr virus genes with human gastric carcinoma transcriptome

Gastric carcinoma (GC) is a leading cause of mortality. 10% of GC cases are related with EBV (Epstein-Barr virus) infection. The detailed mechanistic roles EBV genes play and especially the interaction between the viral genes and human genes in GC remain unclear. In this study, raw fastq data from 285 GC samples were downloaded from TCGA (The Cancer Genome Atlas), including 25 EBV positive (EBV+) GC samples and 260 EBV negative (EBV−) GC samples. RNA-seq based expression data were generated for both human genes (among all the samples) and for the EBV genes (among the 25 EBV+ samples). Bioinformatics analyses were performed to identify differentially expressed (DEx) human genes and DEx KEGG pathways in EBV+ vs. EBV− samples and co-expressed human gene modules and hub genes among the DEx genes. Within the EBV+ samples, analyses were conducted to find correlation between EBV gene expression and the human gene expression modules, between EBV gene expression and the human hub genes, and between EBV gene expression and the DEx human pathways. EBV genes LMP-1, BALF1 and BALF2 were found to have significant correlation with human hub genes, CNTD2 and VANGL2. EBV genes BALF4 and BALF5 were found to correlate with human pathways, including Jak-STAT signaling and Phosphatidylinositol Signaling System. Our study has revealed the coordinated expression patterns between EBV and human GC transcriptome and identified several key EBV genes that may play an important role in EBV+ GC pathogenesis through their interactions with human genes and pathways.

Analysis of Epstein-Barr Virus Genomes and Expression Profiles in Gastric Adenocarcinoma

Epstein-Barr virus (EBV) is a causative agent of a variety of lymphomas, nasopharyngeal carcinoma (NPC), and ∼9% of gastric carcinomas (GCs). An important question is whether particular EBV variants are more oncogenic than others, but conclusions are currently hampered by the lack of sequenced EBV genomes. Here, we contribute to this question by mining whole-genome sequences of 201 GCs to identify 13 EBV-positive GCs and by assembling 13 new EBV genome sequences, almost doubling the number of available GC-derived EBV genome sequences and providing the first non-Asian EBV genome sequences from GC. Whole-genome sequence comparisons of all EBV isolates sequenced to date (85 from tumors and 57 from healthy individuals) showed that most GC and NPC EBV isolates were closely related although American Caucasian GC samples were more distant, suggesting a geographical component. However, EBV GC isolates were found to contain some consistent changes in protein sequences regardless of geographical origin. In addition, transcriptome data available for eight of the EBV-positive GCs were analyzed to determine which EBV genes are expressed in GC. In addition to the expected latency proteins (EBNA1, LMP1, and LMP2A), specific subsets of lytic genes were consistently expressed that did not reflect a typical lytic or abortive lytic infection, suggesting a novel mechanism of EBV gene regulation in the context of GC. These results are consistent with a model in which a combination of specific latent and lytic EBV proteins promotes tumorigenesis.IMPORTANCE Epstein-Barr virus (EBV) is a widespread virus that causes cancer, including gastric carcinoma (GC), in a small subset of individuals. An important question is whether particular EBV variants are more cancer associated than others, but more EBV sequences are required to address this question. Here, we have generated 13 new EBV genome sequences from GC, almost doubling the number of EBV sequences from GC isolates and providing the first EBV sequences from non-Asian GC. We further identify sequence changes in some EBV proteins common to GC isolates. In addition, gene expression analysis of eight of the EBV-positive GCs showed consistent expression of both the expected latency proteins and a subset of lytic proteins that was not consistent with typical lytic or abortive lytic expression. These results suggest that novel mechanisms activate expression of some EBV lytic proteins and that their expression may contribute to oncogenesis.

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.

Epstein-Barr virus BRLF1 induces genomic instability and progressive malignancy in nasopharyngeal carcinoma cells

Nasopharyngeal carcinoma (NPC) is a serious health problem in China and Southeast Asia. Relapse is the major cause of mortality, but mechanisms of relapse are mysterious. Epstein-Barr virus (EBV) reactivation and host genomic instability (GI) have correlated with NPC development. Previously, we reported that lytic early genes DNase and BALF3 induce genetic alterations and progressive malignancy in NPC cells, implying lytic proteins may be required for NPC relapse. In this study, we show that immediate early gene BRLF1 induces chromosome mis-segregation and genomic instability in the NPC cells. Similar phenomenon was also demonstrated in 293 and zebrafish embryonic cells. BRLF1 nuclear localization signal (NLS) mutant still induced genomic instability and inhibitor experiments revealed that BRLF1 interferes with chromosome segregation and induces genomic instability by activating Erk signaling. Furthermore, the chromosome aberrations and tumorigenic features of NPC cells were significantly increased with the rounds of BRLF1 expression, and these cells developed into larger tumor nodules in mice. Therefore, BRLF1 may be the important factor contributing to NPC relapse and targeting BRLF1 may benefit patients.

Characterization of the subcellular localization of Epstein-Barr virus encoded proteins in live cells

Epstein-Barr virus (EBV) is the pathogenic factor of numerous human tumors, yet certain of its encoded proteins have not been studied. As a first step for functional identification, we presented the construction of a library of expression constructs for most of the EBV encoded proteins and an explicit subcellular localization map of 81 proteins encoded by EBV in mammalian cells. Viral open reading frames were fused with enhanced yellow fluorescent protein (EYFP) tag in eukaryotic expression plasmid then expressed in COS-7 live cells, and protein localizations were observed by fluorescence microscopy. As results, 34.57% (28 proteins) of all proteins showed pan-nuclear or subnuclear localization, 39.51% (32 proteins) exhibitted pan-cytoplasmic or subcytoplasmic localization, and 25.93% (21 proteins) were found in both the nucleus and cytoplasm. Interestingly, most envelope proteins presented pan-cytoplasmic or membranous localization, and most capsid proteins displayed enriched or complete localization in the nucleus, indicating that the subcellular localization of specific proteins are associated with their roles during viral replication. Taken together, the subcellular localization map of EBV proteins in live cells may lay the foundation for further illustrating the functions of EBV-encoded genes in human diseases especially in its relevant tumors.

Inhibition of Epstein-Barr virus reactivation by the flavonoid apigenin

Background

Lytic reactivation of EBV has been reported to play an important role in human diseases, including NPC carcinogenesis. Inhibition of EBV reactivation is considered to be of great benefit in the treatment of virus-associated diseases. For this purpose, we screened for inhibitory compounds and found that apigenin, a flavonoid, seemed to have the ability to inhibit EBV reactivation.

Methods

We performed western blotting, immunofluorescence and luciferase analyses to determine whether apigenin has anti-EBV activity.

Results

Apigenin inhibited expression of the EBV lytic proteins, Zta, Rta, EAD and DNase in epithelial and B cells. It also reduced the number of EBV-reactivating cells detectable by immunofluorescence analysis. In addition, apigenin has been found to reduce dramatically the production of EBV virions. Luciferase reporter analysis was performed to determine the mechanism by which apigenin inhibits EBV reactivation: apigenin suppressed the activity of the immediate-early (IE) gene Zta and Rta promoters, suggesting it can block initiation of the EBV lytic cycle.

Conclusion

Taken together, apigenin inhibits EBV reactivation by suppressing the promoter activities of two viral IE genes, suggesting apigenin is a potential dietary compound for prevention of EBV reactivation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-016-0313-9) contains supplementary material, which is available to authorized users.

Viral Carcinogenesis Beyond Malignant Transformation: EBV in the Progression of Human Cancers

Cancer progression begins when malignant cells colonize adjacent sites, and it is characterized by increasing tumor heterogeneity, invasion and dissemination of cancer cells. Clinically, progression is the most relevant stage in the natural history of cancers. A given virus is usually regarded as oncogenic because of its ability to induce malignant transformation of cells. Nonetheless, oncogenic viruses may also be important for the progression of infection-associated cancers. Recently this hypothesis has been addressed because of studies on the contribution of the Epstein-Barr virus (EBV) to the aggressiveness of nasopharyngeal carcinoma (NPC). Several EBV products modulate cancer progression phenomena, such as the epithelial-mesenchymal transition, cell motility, invasiveness, angiogenesis, and metastasis. In this regard, there are compelling data about the effects of EBV latent membrane proteins (LMPs) and EBV nuclear antigens (EBNAs), as well as nontranslated viral RNAs, such as the EBV-encoded small nonpolyadenylated RNAs (EBERs) and viral microRNAs, notably EBV miR-BARTs. The available data on the mechanisms and players involved in the contribution of EBV infection to the aggressiveness of NPC are discussed in this review. Overall, this conceptual framework may be valuable for the understanding of the contribution of some infectious agents in the progression of cancers.

Epstein-Barr virus BALF3 mediates genomic instability and progressive malignancy in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a head and neck cancer prevalent throughout Southern China and Southeast Asia. Patient death following relapse after primary treatment remains all too common but the cause of NPC relapse is unclear. Clinical and epidemiological studies have revealed the high correlation among NPC development, Epstein-Barr virus (EBV) reactivation and host genomic instability. Previously, recurrent EBV reactivation was shown to cause massive genetic alterations and enhancement of tumor progression in NPC cells and these may be required for NPC relapse. Here, EBV BALF3 has the ability to induce micronuclei and DNA strand breaks. After recurrent expression of BALF3 in NPC cells, genomic copy number aberrations, determined by array-based comparative genomic hybridization, had accumulated to a significant extent and tumorigenic features, such as cell migration, cell invasion and spheroid formation, increased with the rounds of induction. In parallel experiments, cells after highly recurrent induction developed into larger tumor nodules than control cells when inoculated into NOD/SCID mice. Furthermore, RNA microarrays showed that differential expression of multiple cancer capability-related genes and oncogenes increased with recurrent BALF3 expression and these changes correlated with genetic aberrations. Therefore, EBV BALF3 is a potential factor that mediates the impact of EBV on NPC relapse.

Human papillomavirus and Epstein-Barr virus co-infection in cervical carcinoma in Algerian women

Background

Despite the fact that the implication of human papillomavirus (HPV) in the carcinogenesis and prognosis of cervical cancer is well established, the impact of a co-infection with high risk HPV (HR-HPV) and Epstein-Barr virus (EBV) is still not fully understood.

Methods

Fifty eight randomly selected cases of squamous cell carcinomas (SCC) of the uterine cervix, 14 normal cervices specimens, 21 CIN-2/3 and 16 CIN-1 cases were examined for EBV and HPV infections. Detection of HR-HPV specific sequences was carried out by PCR amplification using consensus primers of Manos and by Digene Hybrid Capture. The presence of EBV was revealed by amplifying a 660 bp specific EBV sequence of BALF1. mRNA expression of LMP-1 in one hand and protein levels of BARF-1, LMP-1 and EBNA-1 in the other hand were assessed by RT-PCR and immunoblotting and/or immunohischemistry respectively.

Results

HR-HPV infection was found in patients with SCC (88%), low-grade (75%) and high grade (95%) lesions compared to only 14% of normal cervix cases. However, 69%, 12.5%, 38.1%, and 14% of SCC, CIN-1, CIN-2/3 and normal cervix tissues, respectively, were EBV infected. The highest co-infection (HR-HPV and EBV) was found in squamous cell carcinoma cases (67%). The latter cases showed 27% and 29% expression of EBV BARF-1 and LMP-1 oncogenes respectively.

Conclusion

The high rate of HR-HPV and EBV co-infection in SCC suggests that EBV infection is incriminated in cervical cancer progression. This could be taken into account as bad prognosis in this type of cancer. However, the mode of action in dual infection in cervical oncogenesis needs further investigation.

Role of the Crosstalk between Autophagy and Apoptosis in Cancer

Autophagy and apoptosis are catabolic pathways essential for organismal homeostasis. Autophagy is normally a cell-survival pathway involving the degradation and recycling of obsolete, damaged, or harmful macromolecular assemblies; however, excess autophagy has been implicated in type II cell death. Apoptosis is the canonical programmed cell death pathway. Autophagy and apoptosis have now been shown to be interconnected by several molecular nodes of crosstalk, enabling the coordinate regulation of degradation by these pathways. Normally, autophagy and apoptosis are both tumor suppressor pathways. Autophagy fulfils this role as it facilitates the degradation of oncogenic molecules, preventing development of cancers, while apoptosis prevents the survival of cancer cells. Consequently, defective or inadequate levels of either autophagy or apoptosis can lead to cancer. However, autophagy appears to have a dual role in cancer, as it has now been shown that autophagy also facilitates the survival of tumor cells in stress conditions such as hypoxic or low-nutrition environments. Here we review the multiple molecular mechanisms of coordination of autophagy and apoptosis and the role of the proteins involved in this crosstalk in cancer. A comprehensive understanding of the interconnectivity of autophagy and apoptosis is essential for the development of effective cancer therapeutics.

A role for Epstein-Barr viral BALF1 in facilitating tumor formation and metastasis potential

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus that triggers transformation and tumorigenesis of latently infected B cells in vitro. BALF1, a Bcl-2-like EBV gene expressed in both latent and lytic stages, was recently characterized in EBV-infected cells; however, the role and function of BALF1 has remained elusive. Here, we demonstrate that BALF1 expression alters cellular morphology. Importantly, BALF1 promotes cellular transformation, with tumorigenicity assays showing larger and substantially greater numbers of tumors in BALF1 transfectant-injected mice compared to mice injected with pcDNA control transfectants. In addition, BALF1 expression increases cell survival under low-serum conditions, an effect that is attributable to suppression of apoptosis, not to promotion of cell-cycle progression. Furthermore, BALF1 transfectants exhibit markedly increased tumor metastasis in vitro and in vivo. Taken together, these findings suggest that BALF1 may be a new tumor marker for EBV diagnosis and provide a new direction for research on treatments of EBV-associated tumors.

Contribution of Epstein-Barr virus infection to chemoresistance of gastric carcinoma cells to 5-fluorouracil

Although Epstein-Barr virus (EBV) is associated with 6-16% of the gastric carcinoma (GC) cases, the effect of EBV infection on the tumorigenesis process and the responsiveness to chemotherapy remain unclear. We compared chemosensitivity of the EBV-positive GC (AGSEBV) and EBV-negative GC (AGS) cells to 5-fluorouracil (5-FU). Although 5-FU inhibited the growth of both cell lines in a dose- and time-dependent manner, the sensitivity of EBV-positive GC cells to 5-FU was lower than that of EBV-negative GC cells. The cleavage of PARP and caspase-3 was also lower in AGS-EBV cells than in AGS cells following 5-FU treatment. Both the level of Bcl-2 expression and the ratio of Bcl-2/Bax were higher in AGS-EBV than in AGS cells not only at basal state but also following 5-FU treatment. Moreover, p53 and p21 expression was enhanced further by 5-FU in AGS than in AGS-EBV cells. Immunofluorescence assay and Western blot showed that 5-FU induced the expression of EBV-lytic genes including BZLF1, BRLF1, BMRF1 and BHRF1. Our results suggest that latent and lytic EBV infection contributes to the chemoresistance to 5-FU in gastric carcinoma by modulating apoptosis related cellular genes.

Mitochondrial localization of viral proteins as a means to subvert host defense

Viruses have developed a battery of distinct strategies to overcome the very sophisticated defense mechanisms of the infected host. Throughout the process of pathogen-host co-evolution, viruses have therefore acquired the capability to prevent host cell apoptosis because elimination of infected cells via apoptosis is one of the most ancestral defense mechanism against infection. Conversely, induction of apoptosis may favor viral dissemination as a result of the dismantlement of the infected cells. Mitochondria have been long recognized for their key role in the modulation of apoptosis but more recently, mitochondria have been shown to serve as a crucial platform for innate immune signaling as illustrated by the identification of MAVS. Thus, it is therefore not surprising that this organelle represents a recurrent target for viruses, aiming to manipulate the fate of the infected host cell or to inhibit innate immune response. In this review, we highlight the viral proteins that are specifically targeted to the mitochondria to subvert host defense. This article is part of a Special Issue entitled Mitochondria: the deadly organelle.

Recurrent chemical reactivations of EBV promotes genome instability and enhances tumor progression of nasopharyngeal carcinoma cells

Nasopharyngeal carcinoma (NPC) is an endemic malignancy prevalent in South East Asia. Epidemiological studies have associated this disease closely with Epstein-Barr virus (EBV) infection. Previous studies also showed that EBV reactivation is implicated in the progression of NPC. Thus, we proposed that recurrent reactivations of EBV may be important for its pathogenic role. In this study, NPC cell lines latently infected with EBV, NA and HA, and the corresponding EBV-negative NPC cell lines, NPC-TW01 (TW01) and HONE-1, were treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) and sodium n-butyrate (SB) for lytic cycle induction. A single treatment with TPA/SB revealed that DNA double-strand breaks and formation of micronuclei (a marker for genome instability) were associated with EBV reactivation in NA and HA cells. Examination of EBV early genes had identified several lytic proteins, particularly EBV DNase, as potent activators that induced DNA double-strand breaks and contribute to genome instability. Recurrent reactivations of EBV in NA and HA cells resulted in a marked increase of genome instability. In addition, the degree of chromosomal aberrations, as shown by chromosome structural variants and DNA copy-number alterations, is proportional to the frequency of TPA/SB-induced EBV reactivation. Whereas these DNA abnormalities were limited in EBV-negative TW01 cells with mock or TPA/SB treatment, and were few in mock-treated NA cells. The invasiveness and tumorigenesis assays also revealed a profound increase in both characteristics of the repeatedly reactivated NA cells. These results suggest that recurrent EBV reactivations may result in accumulation of genome instability and promote the tumor progression of NPC.

Epstein-Barr virus BART gene expression

Introns from the Epstein-Barr virus (EBV) BART RNAs produce up to 20 micro RNAs (miRNAs) but the spliced exons of the BART RNAs have also been investigated as possible mRNAs, with the potential to express the RPMS1 and A73 proteins. Recombinant RPMS1 and A73 proteins were expressed in Escherichia coli and used to make new monoclonal antibodies that reacted specifically with artificially expressed RPMS1 and A73. These antibodies did not detect endogenous expression of A73 and RPMS1 proteins in a panel of EBV-infected cell lines representing the different known types of EBV infection. BART RNA could not be detected on Northern blots of cytoplasmic poly(A)(+) RNA from the C666.1 NPC cell line and BART RNA was found to be mainly in the nucleus of C666.1 cells, arguing against an mRNA role for BART RNAs. In contrast, some early lytic cycle EBV mRNAs were found to be expressed in C666.1 cells. Artificially expressed A73 protein was known to be able to bind to the cellular RACK1 protein and has now also been shown to be able to regulate calcium flux, presumably via RACK1. Overall, the results support the conclusion that the miRNAs are functionally important products of BART transcription in the cell lines studied because the A73 and RPMS1 proteins could not be detected in natural EBV infections. However, the possibility remains that A73 and RPMS1 might be expressed in some situations because of the clear potential relevance of their biochemical functions.

Blood diffusion and Th1-suppressive effects of galectin-9-containing exosomes released by Epstein-Barr virus-infected nasopharyngeal carcinoma cells

Epstein-Barr virus (EBV)-associated nasopharyngeal carcinoma (NPC) is the third most frequent virus-associated human malignancy. How this tumor escapes immune recognition despite the expression of several viral antigens has remained poorly understood. Our previous in vitro studies have shown that NPC cells release exosomes containing high amounts of galectin-9, a ligand of the membrane receptor Tim-3, which is able to induce apoptosis in mature Th1 lymphocytes. Here, we sought to determine whether galectin-9-carrying exosomes were produced in NPC patients and whether such exosomes might play a role in the immune evasion of NPC cells. We report that galectin-9-containing exosomes are selectively detected in plasma samples from NPC patients and mice xenografted with NPC tumors. The incorporation into exosomes protects galectin-9 against proteolytic cleavage but retains its Tim-3-binding capacity. Importantly, NPC exosomes induce massive apoptosis in EBV-specific CD4(+) cells used as a model of target T cells. This effect is inhibited by both anti-Tim-3 and antigalectin-9 blocking antibodies. These results indicate that blocking galectin-9/Tim-3 interaction in vivo might alleviate the Th1-suppressive effect of NPC exosomes and sustain antitumoral T-cell responses and thereby improve clinical efficacy of immunotherapeutic approaches against NPC.

Amplicons on chromosome 3 contain oncogenes induced by recurrent exposure to 12-O-tetradecanoylphorbol-13-acetate and sodium n-butyrate and Epstein-Barr virus reactivation in a nasopharyngeal carcinoma cell line

Nasopharyngeal carcinoma (NPC) is closely associated with Epstein-Barr virus (EBV) infection and exposure to environmental carcinogens. In this study, an inducible Epstein-Barr virus (EBV) reactivation NPC cell line, NA, was used to investigate the impact of recurrent 12-O-tetradecanoylphorbol-13-acetate-sodium n-butyrate (TPA/SB) treatment and EBV reactivation on chromosomal abnormalities utilizing array-based comparative genomic hybridization (CGH). It was observed that most copy-number aberrations (CNA) were progressively nonrandomly clustered on chromosomes 3, 8, and 9, as the frequency of TPA/SB treatment and EBV reactivation increased. All of the prominent amplicons detected (including 3p14.1, 3p13, 3p12.3, 3p12.2, 3q26.2, 3q26.31, and 3q26.32) were located on chromosome 3, with multiple oncogenes assigned to these sites. The amplification patterns of 3p12.3 and 3q26.2 were validated using fluorescence in situ hybridization (FISH) analysis. Subsequent quantitative real-time polymerase chain reaction detected increasing expression of ROBO1 and SKIL oncogenes in NA cells harboring higher frequency of TPA/SB treatment and EBV reactivation, consistent with copy-number amplification of these loci. These findings demonstrate that a high incidence of TPA/SB induced-EBV reactivation has a profound influence on the carcinogenesis of NPC through altered DNA copy number.