Epstein-Barr virus-encoded poly(A)- RNA confers resistance to apoptosis mediated through Fas by blocking the PKR pathway in human epithelial intestine 407 cells

The efficacy of natural products for the treatment of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a malignant tumor originating in the nasopharyngeal epithelium with a high incidence in southern China and parts of Southeast Asia. The current treatment methods are mainly radiotherapy and chemotherapy. However, they often have side effects and are not suitable for long-term exposure. Natural products have received more and more attention in cancer prevention and treatment because of their its high efficiency, low toxic side effects, and low toxicity. Natural products can serve as a viable alternative, and this study aimed to review the efficacy and mechanisms of natural products in the treatment of NPC by examining previous literature. Most natural products act by inhibiting cell proliferation, metastasis, inducing cell cycle arrest, and apoptosis. Although further research is needed to verify their effectiveness and safety, natural products can significantly improve the treatment of NPC.

Non-Response of Epstein-Barr Virus-Associated Breast Cancer after Primary Chemotherapy: Report of Two Cases

Based on epidemiological evidence and molecular findings, a possible association of Epstein-Barr virus (EBV) with the carcinogenesis of breast cancer has been described. However, the frequency of EBV in breast cancer and the role of EBV regarding tumor progression or therapeutic results is largely unexplored. Here, we report on two cases of advanced, lymph node-positive invasive breast cancer of no special type (NST), histologically showing no clinical or histological evidence of tumor regression as an equivalent of a lack of response to primary systemic therapy. Both tumors were considered to be EBV-associated due to their positivity in EBV-encoded RNA (EBER) in situ hybridization (ISH) and their immunoreactivity against EBV Epstein-Barr nuclear antigen 1 (EBNA1). We hypothesize that the unusual non-response to chemotherapy in these cases of breast cancer classified as triple-negative and HER2-positive may be linked to the EBV co-infection of tumor cells. Therefore, EBV tumor testing should be considered in patients with breast cancer presenting with resistance to chemotherapy. This hypothesis may provide a new aspect in the context of EBV-associated mechanisms of tumor progression.

Functional analysis and expression profile of human platelets infected by EBV in vitro

Platelet activation is commonly detected after infection by multiple viruses such as human immunodeficiency virus (HIV), H1N1 influenza, Hepatitis C virus (HCV), Ebola virus (EBV), and Dengue virus (DENV). Non-coding RNAs (ncRNAs) constitute the majority of the human transcribed genome, but the biology of platelet ncRNAs is largely unexplored. In this study, we performed microarray profiling to characterize the expression profile of human platelets infected with EBV in vitro after 2 h. A total of 187 long non-coding RNAs (lncRNAs) displayed differences, of which 114 were upregulated and 73 were downregulated; 78 microRNAs (miRNAs) showed differences, including 73 upregulated and 5 downregulated; 808 mRNAs displayed differences, among which 367 were upregulated and 441 were downregulated. Gene ontology (GO) analysis mostly related to G protein-coupled receptor signaling pathway, detection of chemical stimulus involved in sensory perception of smell and regulation of transcription by RNA polymerase II. Pathway analysis showed that the differentially expressed genes were mainly enriched in cell metabolism and immune-related response. A ceRNA network was established based on predicting regulatory pairs in differentially expressed genes, in which hsa-miR-6877-3p had the highest regulatory capability (degree = 31), FAM230A was the lncRNA with the highest regulatory capability (degree = 28). According to the EBV related miRNA regulation network, it revealed that ebv-miR-BART19-3p had the most target genes and BRWD1, FAM126B, TFRC and JMY were the genes most regulated by EBV-related miRNAs. After overlapping the three networks, we found that the EIFAK2 gene was strongly correlated with autologous ncRNAs, including hsa-miR-1972, hsa-miR-504-3p and hsa-miR-6825-5p, as well as with EBV ncRNAs, including EBER1, EBER2, miR-BART7-3p and miR-BART16. The present study contributes to a better understanding of the expression profiling of ncRNAs and their functions in platelets activated by EBV in vitro, and paves the way to further study on platelet function.

Oncogenic viruses and chemoresistance: What do we know?

Chemoresistance is often referred to as a major leading reason for cancer therapy failure, causing cancer relapse and further metastasis. As a result, an urgent need has been raised to reach a full comprehension of chemoresistance-associated molecular pathways, thereby designing new therapy methods. Many of metastatic tumor masses are found to be related with a viral cause. Although combined therapy is perceived as the model role therapy in such cases, chemoresistant features, which is more common in viral carcinogenesis, often get into way of this kind of therapy, minimizing the chance of survival. Some investigations indicate that the infecting virus dominates other leading factors, i.e., genetic alternations and tumor microenvironment, in development of cancer cell chemoresistance. Herein, we have gathered the available evidence on the mechanisms under which oncogenic viruses cause drug-resistance in chemotherapy.

Exosomes-carrying Epstein-Barr virus-encoded small RNA-1 induces indoleamine 2, 3-dioxygenase expression in tumor-infiltrating macrophages of oral squamous-cell carcinomas and suppresses T-cell activity by activating RIG-I/IL-6/TNF-α pathway

OBJECTIVES

Although exosomes carrying Epstein-Barr virus-encoded small RNA-1 (EBER-1) are involved in the immunosuppressive tumor microenvironments of EBV-associated head and neck carcinomas, the effects of EBER-1-associated exosomes on tumor-infiltrating macrophages are poorly understood.

MATERIALS AND METHODS

The association between EBV infection and expression of indoleamine 2,3-dioxygenase (IDO) was assessed in 165 paraffin-embedded oral squamous cell carcinoma (OSCC) tissue samples. Using in vitro techniques, we investigated whether stimulation of the RIG-I/IL-6/TNF-α pathway by exosomes carrying EBER-1 is critical for IDO induction in macrophages. We performed a thymidine incorporation and a cell cytolytic assay to test for up-regulated IDO in macrophages that can block the proliferation and function of effector T cells.

RESULTS

Some infiltrated macrophages expressed levels of IDO higher than OSCC cells which was significantly associated with presence of EBV. The production of IDO, tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) in human monocyte-derived macrophages (MDMs) was induced by EBV-associated exosomes in vitro. Mechanistically, the retinoic acid-inducible gene I (RIG-I) pathway in MDMs was stimulated by EBV-encoded small RNA-1 (EBER-1) whereas the inhibition of these pathways by BX-795 almost abolished the production of these two cytokines and IDO induction. Also, the EBER-1-activated IDO in MDMs suppressed the proliferation of T lymphocytes and diminished the cytolytic activity of CD8+ T cells.

CONCLUSION

Exosomes carrying EBER-1 could induce IDO expression in MDMs, considerably aided by an IL-6 and TNF-α-dependent mechanism via the RIG-I signaling pathway, which might create an immunosuppressive microenvironment affecting T-cell immune responses.

Targeting Epstein-Barr Virus in Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma (NPC) is consistently associated with Epstein-Barr virus (EBV) infection in regions in which it is endemic, including Southern China and Southeast Asia. The high mortality rates of NPC patients with advanced and recurrent disease highlight the urgent need for effective treatments. While recent genomic studies have revealed few druggable targets, the unique interaction between the EBV infection and host cells in NPC strongly implies that targeting EBV may be an efficient approach to cure this virus-associated cancer. Key features of EBV-associated NPC are the persistence of an episomal EBV genome and the requirement for multiple viral latent gene products to enable malignant transformation. Many translational studies have been conducted to exploit these unique features to develop pharmaceutical agents and therapeutic strategies that target EBV latent proteins and induce lytic reactivation in NPC. In particular, inhibitors of the EBV latent protein EBNA1 have been intensively explored, because of this protein's essential roles in maintaining EBV latency and viral genome replication in NPC cells. In addition, recent advances in chemical bioengineering are driving the development of therapeutic agents targeting the critical functional regions of EBNA1. Promising therapeutic effects of the resulting EBNA1-specific inhibitors have been shown in EBV-positive NPC tumors. The efficacy of multiple classes of EBV lytic inducers for NPC cytolytic therapy has also been long investigated. However, the lytic-induction efficiency of these compounds varies among different EBV-positive NPC models in a cell-context-dependent manner. In each tumor, NPC cells can evolve and acquire somatic changes to maintain EBV latency during cancer progression. Unfortunately, the poor understanding of the cellular mechanisms regulating EBV latency-to-lytic switching in NPC cells limits the clinical application of EBV cytolytic treatment. In this review, we discuss the potential approaches for improvement of the above-mentioned EBV-targeting strategies.

Regulation of Protein Kinase R by Epstein-Barr Virus EBER1 RNA

Protein kinase R (PKR) is a key antiviral component of the innate immune pathway and is activated by viral double-stranded RNAs (dsRNAs). Adenovirus-associated RNA 1 (VAI) is an abundant, noncoding viral RNA that functions as a decoy by binding PKR but not inducing activation, thereby inhibiting the antiviral response. In VAI, coaxial stacking produces an extended helix that mediates high-affinity PKR binding but is too short to result in activation. Like adenovirus, Epstein-Barr virus produces high concentrations of a noncoding RNA, EBER1. Here, we compare interactions of PKR with VAI and EBER1 and present a structural model of EBER1. Both RNAs function as inhibitors of dsRNA-mediated PKR activation. However, EBER1 weakly activates PKR whereas VAI does not. PKR binds EBER1 more weakly than VAI. Assays at physiological ion concentrations indicate that both RNAs can accommodate two PKR monomers and induce PKR dimerization. A structural model of EBER1 was obtained using constraints derived from chemical structure probing and small-angle X-ray scattering experiments. The central stem of EBER1 coaxially stacks with stem loop 4 and stem loop 1 to form an extended RNA duplex of ∼32 bp that binds PKR and promotes activation. Our observations that EBER1 binds PKR much more weakly than VAI and exhibits weak PKR activation suggest that EBER1 is less well suited to function as an RNA decoy.

Translational genomics of nasopharyngeal cancer

Nasopharyngeal carcinoma (NPC), also named the Cantonese cancer, is a unique cancer with strong etiological association with infection of the Epstein-Barr virus (EBV). With particularly high prevalence in Southeast Asia, the involvement of EBV and genetic aberrations contributive to NPC tumorigenesis have remained unclear for decades. Recently, genomic analysis of NPC has defined it as a genetically homogeneous cancer, driven largely by NF-κB signaling caused by either somatic aberrations of NF-κB negative regulators or by overexpression of the latent membrane protein 1 (LMP1), an EBV viral oncoprotein. This represents a landmark finding of the NPC genome. Exome and RNA sequencing data from new EBV-positive NPC models also highlight the importance of PI3K pathway aberrations in NPC. We also realize for the first time that NPC mutational burden, mutational signatures, MAPK/PI3K aberrations, and MHC Class I gene aberrations, are prognostic for patient outcome. Together, these multiple genomic discoveries begin to shape the focus of NPC therapy development. Given the challenge of NF-κB targeting in human cancers, more innovative drug discovery approaches should be explored to target the unique atypical NF-κB activation feature of NPC. Our next decade of NPC research should focus on further identification of the -omic landscapes of recurrent and metastatic NPC, development of gene-based precision medicines, as well as large-scale drug screening with the newly developed and well-characterized EBV-positive NPC models. Focused preclinical and clinical investigations on these major directions may identify new and effective targeting strategies to further improve survival of NPC patients.

Epstein-Barr virus noncoding RNAs from the extracellular vesicles of nasopharyngeal carcinoma (NPC) cells promote angiogenesis via TLR3/RIG-I-mediated VCAM-1 expression

Viral noncoding RNAs (Epstein-Barr virus-encoded RNAs, EBERs) are believed to play a critical role in the progression of lymphoma and nasopharyngeal carcinoma (NPC). However, the accurate mechanisms accounting for their oncogenic function have not been elucidated, especially in terms of interaction between tumor cells and mesenchymal cells. Here, we report that, in addition to NPC cells, EBERs are also found in endothelial cells in Epstein-Barr virus (EBV)-infected NPC parenchymal tissues, which implicates NPC-derived extracellular vesicles (EVs) in transmitting EBERs to endothelial cells. In support of this hypothesis, we first ascertained if EBERs could be transferred to endothelial cells via EVs isolated from NPC culture supernatant. Then, we clarified that EVs-derived EBERs could promote angiogenesis through stimulation of VCAM-1 expression. Finally, we explored the involvement of EBER recognition by TLR3 and RIG-I in NPC angiogenesis. Our observations collectively illustrate the significance and mechanism of EVs-derived EBERs in angiogenesis and underlie the interaction mechanisms between EBV-infected NPC cells and the tumor microenvironment.

Long Non-Coding RNAs: Novel Players in Regulation of Immune Response Upon Herpesvirus Infection

Herpesviruses have developed a variety of sophisticated immune evasion strategies to establish lifelong latent infection, including the use of long non-coding RNAs (lncRNAs). In this review, we summarize the lncRNA action modes, i.e., RNA-protein, RNA-RNA, and RNA-DNA interactions, involved in regulating important aspects of immunity by controlling gene expression at various stages. Upon herpesvirus infection, host lncRNAs, such as nuclear paraspeckle assembly transcript 1, negative regulator of antiviral, and B-cell integration cluster have been functionally characterized as negative or positive antiviral regulators in the immune response. Herpesviruses have also evolved multiple strategies to modulate the host immune response using lncRNAs, such as latency-associated transcript, β 2.7 RNA, 5 kb and 7.2 kb lncRNAs, Epstein-Barr virus-encoded non-coding RNA, BamH I-A rightward transcripts, polyadenylated nuclear, and herpesvirus saimiri U-rich RNAs. We discuss the various mechanisms of immune-related lncRNAs, and their diversified and important functions in the modulation of innate and adaptive immunity upon herpesvirus infection as well as in host-pathogen interactions, which will facilitate our understanding of rational design of novel strategies to combat herpesvirus infection.

Epstein-Barr virus infection and nasopharyngeal carcinoma

Epstein-Barr virus (EBV) is associated with multiple types of human cancer, including lymphoid and epithelial cancers. The closest association with EBV infection is seen in undifferentiated nasopharyngeal carcinoma (NPC), which is endemic in the southern Chinese population. A strong association between NPC risk and the HLA locus at chromosome 6p has been identified, indicating a link between the presentation of EBV antigens to host immune cells and NPC risk. EBV infection in NPC is clonal in origin, strongly suggesting that NPC develops from the clonal expansion of a single EBV-infected cell. In epithelial cells, the default program of EBV infection is lytic replication. However, latent infection is the predominant mode of EBV infection in NPC. The establishment of latent EBV infection in pre-invasive nasopharyngeal epithelium is believed to be an early stage of NPC pathogenesis. Recent genomic study of NPC has identified multiple somatic mutations in the upstream negative regulators of NF-κB signalling. Dysregulated NF-κB signalling may contribute to the establishment of latent EBV infection in NPC. Stable EBV infection and the expression of latent EBV genes are postulated to drive the transformation of pre-invasive nasopharyngeal epithelial cells to cancer cells through multiple pathways.This article is part of the themed issue 'Human oncogenic viruses'.

Gene Analysis of Epstein-Barr Virus-Associated Lymphomas in Hu-PBL/SCID Chimeras

Aims and background

The mechanisms of Epstein-Barr virus (EBV)-associated tumor development are incompletely understood. The aim of this study was to investigate the gene expression of EBV-associated lymphomas in hu-PBL/SCID mice.

Methods

Human peripheral blood lymphocytes (hu-PBL) from EBV-seropositive donors were transplanted into severe combined immunodeficiency (SCID) mice. In situ hybridization was used to detect EBV-encoded small RNA-1 (EBER1) in tumor tissues. Mutation of TP53 exons 5–8 in EBV-induced lymphomas was analyzed by PCR-SSCP. Immunohistochemical staining was used to examine EBV gene products and cellular oncoproteins.

Results

Twenty-one of 29 mice developed tumors. EBER1 was positive in the nuclei of almost all tumor cells. Immunohistochemistry showed positive staining of LMP1, EBNA2 and ZEBRA in a small number of tumor cells. Immunohistochemically detectable p53 protein expression was common (85.7%), but TP53 gene mutations were identified in only four cases (19.1%) of EBV-associated lymphomas. Positivity rates of C-myc, Bcl-2 and Bax expression were 100%, 95.2%, and 90.5%, respectively, in the 21 cases of EBV-associated lymphomas.

Conclusions

Our preliminary findings suggest that EBV-associated lymphomas in hu-PBL/SCID chimeras show EBV infection, expression of oncogenic viral genes, and overexpression of cellular oncogenes. TP53 gene mutations are rare but p53 protein is commonly expressed in EBV-associated lymphomas.

Virus Infection and Death Receptor-Mediated Apoptosis

Virus infection can trigger extrinsic apoptosis. Cell-surface death receptors of the tumor necrosis factor family mediate this process. They either assist persistent viral infection or elicit the elimination of infected cells by the host. Death receptor-mediated apoptosis plays an important role in viral pathogenesis and the host antiviral response. Many viruses have acquired the capability to subvert death receptor-mediated apoptosis and evade the host immune response, mainly by virally encoded gene products that suppress death receptor-mediated apoptosis. In this review, we summarize the current information on virus infection and death receptor-mediated apoptosis, particularly focusing on the viral proteins that modulate death receptor-mediated apoptosis.

Viral lncRNA: A regulatory molecule for controlling virus life cycle

Long non-coding RNAs (lncRNAs) are found not only in mammals but also in other organisms, including viruses. Recent findings suggest that lncRNAs play various regulatory roles in multiple major biological and pathological processes. During viral life cycles, lncRNAs are involved in a series of steps, including enhancing viral gene expression, promoting viral replication and genome packaging, boosting virion release, maintaining viral latency and assisting viral transformation; additionally, lncRNAs antagonize host antiviral innate immune responses. In contrast to proteins that function in viral infection, lncRNAs are expected to be novel targets for the modulation of all types of biochemical processes due to their broad characteristics and profound influence. This review highlights our current understanding of the regulatory roles of lncRNAs during viral infection processes with an emphasis on the potential usefulness of lncRNAs as a target for viral intervention strategies, which could have therapeutic implications for the application of a clinical approach for the treatment of viral diseases.

High Levels of EBV-Encoded RNA 1 (EBER1) Trigger Interferon and Inflammation-Related Genes in Keratinocytes Expressing HPV16 E6/E7

Different types of cells infected with Epstein-Barr virus (EBV) can release exosomes containing viral components that functionally affect neighboring cells. Previously, we found that EBV was localized mostly in infiltrating lymphocytes within the stromal layer of cervical lesions. In this study, we aimed to determine effects of exosome-transferred EBV-encoded RNAs (EBERs) on keratinocytes expressing human papillomavirus (HPV) 16 E6/E7 (DonorI-HPV16 HFKs). Lipid transfection of in vitro-transcribed EBER1 molecules (ivt EBER1) into DonorI-HPV16 HFKs caused strong induction of interferon (IFN)-related genes and interleukin 6 (IL-6). To gain insights into the physiological situation, monocyte-derived dendritic cells (moDCs), low passage DonorI-HPV16 HFKs and primary keratinocytes were used as recipient cells for internalization of exosomes from wild-type EBV (wt EBV) or B95-8 EBV-infected lymphoblastoid cell lines (LCLs). qRT-PCR was used to determine the expression of EBER1, HPV16 E6/E7, IFN-related genes and IL-6 in recipient cells. The secretion of inflammatory cytokines was investigated using cytometric bead array. Wt EBV-modified exosomes induced both IFN-related genes and IL-6 upon uptake into moDCs, while exosomes from B95-8 EBV LCLs induced only IL-6 in moDCs. Internalization of EBV-modified exosomes was demonstrated in DonorI-HPV16 HFKs, yielding only EBER1 but not EBER2. However, EBER1 transferred by exosomes did not induce IFN-related genes or IL-6 expression and inflammatory cytokine secretion in DonorI-HPV16 HFKs and primary keratinocytes. EBER1 copy numbers in exosomes from wt EBV-infected LCLs were 10-fold higher than in exosomes from B95-8 LCLs (equal cell equivalent), whereas ivt EBER1 was used at approximately 100-fold higher concentration than in exosomes. These results demonstrated that the induction of IFN-related genes and IL-6 by EBER1 depends on quantity of EBER1 and type of recipient cells. High levels of EBER1 in cervical cells or infiltrating dendritic cells may play a role in the inflammation-to-oncogenesis transition of HPV-associated cervical cancer through modulation of innate immune signals.

The Role of Gammaherpesviruses in Cancer Pathogenesis

Worldwide, one fifth of cancers in the population are associated with viral infections. Among them, gammaherpesvirus, specifically HHV4 (EBV) and HHV8 (KSHV), are two oncogenic viral agents associated with a large number of human malignancies. In this review, we summarize the current understanding of the molecular mechanisms related to EBV and KSHV infection and their ability to induce cellular transformation. We describe their strategies for manipulating major cellular systems through the utilization of cell cycle, apoptosis, immune modulation, epigenetic modification, and altered signal transduction pathways, including NF-kB, Notch, Wnt, MAPK, TLR, etc. We also discuss the important EBV latent antigens, namely EBNA1, EBNA2, EBNA3’s and LMP’s, which are important for targeting these major cellular pathways. KSHV infection progresses through the engagement of the activities of the major latent proteins LANA, v-FLIP and v-Cyclin, and the lytic replication and transcription activator (RTA). This review is a current, comprehensive approach that describes an in-depth understanding of gammaherpes viral encoded gene manipulation of the host system through targeting important biological processes in viral-associated cancers.

The role of Epstein-Barr virus infection in the pathogenesis of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is closely associated with Epstein-Barr virus (EBV) infection. EBV episomes are detected in almost all NPC cells. The role of EBV in NPC pathogenesis has long been postulated but remains enigmatic. In contrast to infection of B lymphocytes, EBV infection does not directly transform nasopharyngeal epithelial cells into proliferative clones with malignant potential. EBV infection of normal pharyngeal epithelial cells is predominantly lytic in nature. Genetic alterations in premalignant nasopharyngeal epithelium, in combination with inflammatory stimulation in the nasopharyngeal mucosa, presumably play essential roles in the establishment of a latent EBV infection in infected nasopharyngeal epithelial cells during the early development of NPC. Establishment of latent EBV infection in premalignant nasopharyngeal epithelial cells and expression of latent viral genes, including the BART transcripts and BART-encoded microRNAs, are crucial features of NPC. Expression of EBV genes may drive further malignant transformation of premalignant nasopharyngeal epithelial cells into cancer cells. The difficulties involved in the establishment of NPC cell lines and the progressive loss of EBV epsiomes in NPC cells propagated in culture strongly implicate the contribution of host stromal components to the growth of NPC cells in vivo and maintenance of EBV in infected NPC cells. Defining the growth advantages of EBV-infected NPC cells in vivo will lead to a better understanding of the contribution of EBV infection in NPC pathogenesis, and may lead to the identification of novel therapeutic targets for NPC treatment.

The role of Epstein-Barr virus in epithelial malignancies

The close association of Epstein–Barr virus (EBV) infection with non-keratinizing nasopharyngeal carcinomas and a subset of gastric carcinomas suggests that EBV infection is a crucial event in these cancers. The difficulties encountered in infecting and transforming primary epithelial cells in experimental systems suggest that the role of EBV in epithelial malignancies is complex and multifactorial in nature. Genetic alterations in the premalignant epithelium may support the establishment of latent EBV infection, which is believed to be an initiation event. Oncogenic properties have been reported in multiple EBV latent genes. The BamH1 A rightwards transcripts (BARTs) and the BART-encoded microRNAs (miR-BARTs) are highly expressed in EBV-associated epithelial malignancies and may induce malignant transformation. However, enhanced proliferation may not be the crucial function of EBV infection in epithelial malignancies, at least in the early stages of cancer development. EBV-encoded gene products may confer anti-apoptotic properties and promote the survival of infected premalignant epithelial cells harbouring genetic alterations. Multiple EBV-encoded microRNAs have been reported to have immune evasion functions. Genetic alterations in host cells, as well as inflammatory stroma, could modulate the expression of EBV genes and alter the growth properties of infected premalignant epithelial cells, encouraging their selection during carcinogenesis.

Immune Evasion by Epstein-Barr Virus

Epstein-Bar virus (EBV) is widespread within the human population with over 90% of adults being infected. In response to primary EBV infection, the host mounts an antiviral immune response comprising both innate and adaptive effector functions. Although the immune system can control EBV infection to a large extent, the virus is not cleared. Instead, EBV establishes a latent infection in B lymphocytes characterized by limited viral gene expression. For the production of new viral progeny, EBV reactivates from these latently infected cells. During the productive phase of infection, a repertoire of over 80 EBV gene products is expressed, presenting a vast number of viral antigens to the primed immune system. In particular the EBV-specific CD4+ and CD8+ memory T lymphocytes can respond within hours, potentially destroying the virus-producing cells before viral replication is completed and viral particles have been released. Preceding the adaptive immune response, potent innate immune mechanisms provide a first line of defense during primary and recurrent infections. In spite of this broad range of antiviral immune effector mechanisms, EBV persists for life and continues to replicate. Studies performed over the past decades have revealed a wide array of viral gene products interfering with both innate and adaptive immunity. These include EBV-encoded proteins as well as small noncoding RNAs with immune-evasive properties. The current review presents an overview of the evasion strategies that are employed by EBV to facilitate immune escape during latency and productive infection. These evasion mechanisms may also compromise the elimination of EBV-transformed cells, and thus contribute to malignancies associated with EBV infection.

Epstein-barr virus in gastric carcinoma

The Epstein-Barr virus (EBV) is detected in about 10% of gastric carcinoma cases throughout the world. In EBV-associated gastric carcinoma, all tumor cells harbor the clonal EBV genome. Gastric carcinoma associated with EBV has distinct clinicopathological features, occurs predominately in men and in younger-aged individuals, and presents a generally diffuse histological type. Most cases of EBV-associated gastric carcinoma exhibit a histology rich in lymphocyte infiltration. The immunological reactiveness in the host may represent a relatively preferable prognosis in EBV-positive cases. This fact highlights the important role of EBV in the development of EBV-associated gastric carcinoma. We have clearly proved direct infection of human gastric epithelialcells by EBV. The infection was achieved by using a recombinant EBV. Promotion of growth by EBV infection was observed in the cells. Considerable data suggest that EBV may directly contribute to the development of EBV-associated GC. This tumor-promoting effect seems to involve multiple mechanisms, because EBV affects several host proteins and pathways that normally promote apoptosis and regulate cell proliferation.

Flaviviral RNAs: weapons and targets in the war between virus and host

Flaviviruses are a genus of (+)ssRNA (positive ssRNA) enveloped viruses that replicate in the cytoplasm of cells of diverse species from arthropods to mammals. Many are important human pathogens such as DENV-1-4 (dengue virus types 1-4), WNV (West Nile virus), YFV (yellow fever virus), JEV (Japanese encephalitis virus) and TBEV (tick-borne encephalitis). Given their RNA genomes it is not surprising that flaviviral life cycles revolve around critical RNA transactions. It is these we highlight in the present article. First, we summarize the mechanisms governing flaviviral replication and the central role of conserved RNA elements and viral protein-RNA interactions in RNA synthesis, translation and packaging. Secondly, we focus on how host RNA-binding proteins both benefit and inhibit flaviviral replication at different stages of their life cycle in mammalian hosts. Thirdly, we cover recent studies on viral non-coding RNAs produced in flavivirus-infected cells and how these RNAs affect various aspects of cellular RNA metabolism. Together, the article puts into perspective the central role of flaviviral RNAs in modulating both viral and cellular functions.

Molecular approaches towards characterization, monitoring and targeting of viral-associated hematological malignancies

Viral-associated malignancies usually arise in the setting of altered immunity or with declines in immune function associated with aging. The main culprits are the lymphotropic herpesvirus, including Epstein-Barr virus (EBV) and human herpesvirus-8, which are the focus of this review. Chronic persistent infection and viral reactivation are the main risk factors for development of herpesvirus-associated malignancies and have provided the rationale for intensive monitoring of viral loads in some clinical contexts. Quantitative detection of EBV levels in the post-transplant period and following treatment of EBV-associated malignancies now have a proven role in outcome prediction. Both T-cell immunotherapy and humoral immunotherapies directed against latent viral antigens represent promising interventional approaches to treatment of viral-associated malignancies.

RNA families in Epstein-Barr virus

Epstein-Barr virus (EBV) is a tumorigenic human γ-herpesvirus, which produces several known structured RNAs with functional importance: two are implicated in latency maintenance and tumorigenic phenotypes, EBER1 and EBER2; a viral small nucleolar RNA (v-snoRNA1) that may generate a small regulatory RNA; and an internal ribosomal entry site in the EBNA1 mRNA. A recent bioinformatics and RNA-Seq study of EBV identified two novel EBV non-coding (nc)RNAs with evolutionary conservation in lymphocryptoviruses and likely functional importance. Both RNAs are transcribed from a repetitive region of the EBV genome (the W repeats) during a highly oncogenic type of viral latency. One novel ncRNA can form a massive (586 nt) hairpin, while the other RNA is generated from a short (81 nt) intron and is found in high abundance in EBV-infected cells.

Non-coding RNAs in homeostasis, disease and stress responses: an evolutionary perspective

Cells and organisms are subject to challenges and perturbations in their environment and physiology in all stages of life. The molecular response to such changes, including insulting conditions such as pathogen infections, involves coordinated modulation of gene expression programmes and has not only homeostatic but also ecological and evolutionary importance. Although attention has been primarily focused on signalling pathways and protein networks, non-coding RNAs (ncRNAs), which comprise a significant output of the genomes of prokaryotes and especially eukaryotes, are increasingly implicated in the molecular mechanisms of these responses. Long and short ncRNAs not only regulate development and cell physiology, they are also involved in disease states, including cancers, in host-pathogen interactions, and in a variety of stress responses. Indeed, regulatory RNAs are part of genetically encoded response networks and also underpin epigenetic processes, which are emerging as key mechanisms of adaptation and transgenerational inheritance. Here we present the growing evidence that ncRNAs are intrinsically involved in cellular and organismal adaptation processes, in both robustness and protection to stresses, as well as in mechanisms generating evolutionary change.

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.

Epstein-Barr virus-encoded small non-coding RNAs induce cancer cell chemoresistance and migration

Epstein-Barr virus (EBV) encoded small, non-coding, non-polyadenylated RNAs, known as EBERs are the most abundantly expressed viral transcripts in latently EBV infected cells. We found the specific role of EBERs in cell cycle progression, resistance against chemotherapeutic drug and cellular invasion in gastric cancer cells in vitro. Ectopic expression of EBERs upregulates the expression of IL-6 and activate its downstream STAT3, which is significantly involved in downregulating the expression of cell cycle inhibitor genes p21 and p27. Stable expression of EBERs regulates the activation of pFAK and pPAK1 and the expression of anti-metastatic genes RhoGDI and KAI-1 in gastric cancer cells. In addition, administration of neu-IL-6 antibody and dominant negative STAT3β reduces chemoresistance and inhibits invasion of EBERs-expressing gastric cancer cells. Our results thus revealed a novel role of EBERs in the coordination of IL-6-STAT3 signaling pathway to chemoresistance and cellular migration.

Epstein-Barr Virus (EBV)-associated gastric carcinoma

The ubiquitous Epstein-Barr virus (EBV) is associated with several human tumors, which include lymphoid and epithelial malignancies. It is known that EBV persistently infects the memory B cell pool of healthy individuals by activating growth and survival signaling pathways that can contribute to B cell lymphomagenesis. Although the monoclonal proliferation of EBV-infected cells can be observed in epithelial tumors, such as nasopharyngeal carcinoma and EBV-associated gastric carcinoma, the precise role of EBV in the carcinogenic progress is not fully understood. This review features characteristics and current understanding of EBV-associated gastric carcinoma. EBV-associated gastric carcinoma comprises almost 10% of all gastric carcinoma cases and expresses restricted EBV latent genes (Latency I). Firstly, definition, epidemiology, and clinical features are discussed. Then, the route of infection and carcinogenic role of viral genes are presented. Of particular interest, the association with frequent genomic CpG methylation and role of miRNA for carcinogenesis are topically discussed. Finally, the possibility of therapies targeting EBV-associated gastric carcinoma is proposed.

Expression of LINC00312, a long intergenic non-coding RNA, is negatively correlated with tumor size but positively correlated with lymph node metastasis in nasopharyngeal carcinoma

The long intergenic non-coding RNA LINC00312, also called NAG7, was first cloned by our group. Our previous studies have found that LINC00312 could inhibit proliferation and induce apoptosis in nasopharyngeal carcinoma (NPC) cells but also stimulate NPC cell invasion. However, the relevance of LINC00312 in NPC progression or in patient outcomes has not been reported. This study aims to assess the possible correlations of LINC00312 expression with NPC progression and its potential prognostic predictive ability in NPC outcomes. A NPC tissue microarray, which included 561 normal and NPC tissue cores, was used to detect LINC00312 expression, and we found that LINC00312 was significantly down-regulated in NPC tissues compared with non-cancerous nasopharyngeal epithelium tissues. Positive expression of LINC00312 was negatively correlated with tumor size (P < 0.001) but positively correlated with lymph node metastasis (P = 0.002). A receiver operating characteristic (ROC) analysis revealed that LINC00312 expression could distinguish non-cancerous patients from NPC patients (P < 0.001, sensitivity: 72.1 %, specificity: 87.7 %). We also found that LINC00312 was strongly negatively correlated with EBER-1, a non-coding RNA transcribed by Epstein-Barr Virus, in NPC (r = -0.384, P < 0.001). In the final logistic regression analysis model, the abnormal expression of LINC00312 and EBER-1 were found to be independent contributors to nasopharyngeal carcinogenesis (P < 0.001, P < 0.001, respectively). A survival analysis revealed that LINC00312 could predict a good prognosis of no lymph node metastasis (Disease Free Survival (DFS): P = 0.005, Overall Survival (OS): P = 0.001) and a poor prognosis of lymph node metastasis (DFS: P = 0.011, OS: P = 0.001) in NPC patients. Low expression of LINC00312 was an independent risk factor for OS in multivariate analyses (P = 0.017). These observations indicated that LINC00312 could represent a potential biomarker for metastasis, progression and prognosis in NPC.

Long Non-Coding RNAs in Infection Biology

Long non-coding RNA have emerged as an increasingly well studied subset of non-coding RNAs (ncRNAs) following their recent discovery in a number of organisms including humans and characterization of their functional and regulatory roles in variety of distinct cellular mechanisms. The recent annotations of long ncRNAs in humans peg their numbers as similar to protein-coding genes. However, despite the rapid advancements in the field the functional characterization and biological roles of most of the long ncRNAs still remain unidentified, although some candidate long ncRNAs have been extensively studied for their roles in cancers and biological phenomena such as X-inactivation and epigenetic regulation of genes. A number of recent reports suggest an exciting possibility of long ncRNAs mediating host response and immune function, suggesting an elaborate network of regulatory interactions mediated through ncRNAs in infection. The present role of long ncRNAs in host-pathogen cross talk is limited to a handful of mechanistically distinct examples. The current commentary chronicles the findings of these reports on the role of long ncRNAs in infection biology and further highlights the bottlenecks and future directions toward understanding the biological significance of the role of long ncRNAs in infection biology.

Cyclin D1 overexpression supports stable EBV infection in nasopharyngeal epithelial cells

Undifferentiated nasopharyngeal carcinomas (NPCs) are commonly present with latent EBV infection. However, events regulating EBV infection at early stages of the disease and the role of EBV in disease pathogenesis are largely undefined. Genetic alterations leading to activation of cyclin D1 signaling in premalignant nasopharyngeal epithelial (NPE) cells have been postulated to predispose cells to EBV infection. We previously reported that loss of p16, a negative regulator of cyclin D1 signaling, is a frequent feature of NPC tumors. Here, we report that early premalignant lesions of nasopharyngeal epithelium overexpress cyclin D1. Furthermore, overexpression of cyclin D1 is closely associated with EBV infection. Therefore we investigated the potential role of cyclin D1 overexpression in dysplastic NPE cells in vitro. In human telomerase reverse transcriptase-immortalized NPE cells, overexpression of cyclin D1 or a p16-resistant form of CDK4 (CDK4(R24C)) suppressed differentiation. This suppression may have implications for the close association of EBV infection with undifferentiated NPC. In these in vitro models, we found that cellular growth arrest and senescence occurred in EBV-infected cell populations immediately after infection. Nevertheless, overexpression of cyclin D1 or a p16-resistant form of CDK4 or knockdown of p16 in the human telomerase reverse transcriptase-immortalized NPE cell lines could counteract the EBV-induced growth arrest and senescence. We conclude that dysregulated expression of cyclin D1 in NPE cells may contribute to NPC pathogenesis by enabling persistent infection of EBV.

Roles of cell signaling pathways in cell-to-cell contact-mediated Epstein-Barr virus transmission

Epstein-Barr virus (EBV), a human gamma herpesvirus, establishes a life-long latent infection in B lymphocytes and epithelial cells following primary infection. Several lines of evidence indicate that the efficiency of EBV infection in epithelial cells is accelerated up to 10(4)-fold by coculturing with EBV-infected Burkitt's lymphoma (BL) cells compared to infection with cell-free virions, indicating that EBV infection into epithelial cells is mainly mediated via cell-to-cell contact. However, the molecular mechanisms involved in this pathway are poorly understood. Here, we establish a novel assay to assess cell-to-cell contact-mediated EBV transmission by coculturing an EBV-infected BL cell line with an EBV-negative epithelial cell line under stimulation for lytic cycle induction. By using this assay, we confirmed that EBV was transmitted from BL cells to epithelial cells via cell-to-cell contact but not via cell-to-cell fusion. The inhibitor treatments of extracellular signal-regulated kinase (ERK) and nuclear factor (NF)-κB pathways blocked EBV transmission in addition to lytic induction. The blockage of the phosphoinositide 3-kinase (PI3K) pathway impaired EBV transmission coupled with the inhibition of lytic induction. Knockdown of the RelA/p65 subunit of NF-κB reduced viral transmission. Moreover, these signaling pathways were activated in cocultured BL cells and in epithelial cells. Finally, we observed that viral replication was induced in cocultured BL cells. Taken together, our data suggest that cell-to-cell contact induces multiple cell signaling pathways in BL cells and epithelial cells, contributing to the induction of the viral lytic cycle in BL cells and the enhancement of viral transmission to epithelial cells.

Role of EBER and BARF1 in nasopharyngeal carcinoma (NPC) tumorigenesis

Epstein-Barr virus (EBV)-encoded small RNA (EBER) is the most abundant EBV viral transcript and is used as a target molecule to detect EBV-infected cells in tissues by in situ hybridization. EBER is expected to form double-stranded RNA-like structures. The results of the present study show that EBER contributes to oncogenesis by modulating innate immunity in patients with NPC and Burkett's lymphoma. BARF1 is a homolog of the human proto-oncogene c-fms and is expressed as a latent gene in NPC. Reconstitution of NPC-type EBV infection using NPC-derived cell lines shows that BARF1 contributes to the tumorigenicity of NPC cells.

Enhanced Autophagy and Reduced Expression of Cathepsin D Are Related to Autophagic Cell Death in Epstein-Barr Virus-Associated Nasal Natural Killer/T-Cell Lymphomas: An Immunohistochemical Analysis of Beclin-1, LC3, Mitochondria (AE-1), and Cathepsin D in Nasopharyngeal Lymphomas

This study investigated autophagy in 37 cases of nasopharyngeal lymphomas including 23 nasal natural killer (NK)/T-cell lymphomas (NKTCL), 3 cytotoxic T-cell lymphomas (cytotoxic-TML) and 9 B-cell lymphomas (BML) by means of antigen-retrieval immunohistochemistry of beclin-1, LC3, mitochondria (AE-1) and cathepsin D. Peculiar necrosis was noted in EBV⁺ lymphomas comprising 21 NKTCL, 2 cytotoxic-TML and 1 BML. Lymphomas without peculiar necrosis showed high expression of beclin-1, macrogranular cytoplasmal stain of LC3 with sporadic nuclear stain, a hallmark of autophagic cell death (ACD), some aggregated mitochondria and high expression of cathepsin D, suggesting a state of growth with enhanced autophagy with sporadic ACD. EBV⁺ NKTCL with the peculiar necrosis, showed significantly low level of macrogranular staining of LC3, aggregated mitochondria and low expression of cathepsin D in the cellular areas when degenerative lymphoma cells showed decreased beclin-1, significantly advanced LC3-labeled autophagy, residual aggregated mitochondria and significantly reduced expression of cathepsin D, suggesting advanced autophagy with regional ACD. Consequently it was suggested that enhanced autophagy and reduced expression of lysosomal enzymes induced regional ACD under EBV infection in NKTCL.

Viral oncogenes, noncoding RNAs, and RNA splicing in human tumor viruses

Viral oncogenes are responsible for oncogenesis resulting from persistent virus infection. Although different human tumor viruses express different viral oncogenes and induce different tumors, their oncoproteins often target similar sets of cellular tumor suppressors or signal pathways to immortalize and/or transform infected cells. Expression of the viral E6 and E7 oncogenes in papillomavirus, E1A and E1B oncogenes in adenovirus, large T and small t antigen in polyomavirus, and Tax oncogene in HTLV-1 are regulated by alternative RNA splicing. However, this regulation is only partially understood. DNA tumor viruses also encode noncoding RNAs, including viral microRNAs, that disturb normal cell functions. Among the determined viral microRNA precursors, EBV encodes 25 from two major clusters (BART and BHRF1), KSHV encodes 12 from a latent region, human polyomavirus MCV produce only one microRNA from the late region antisense to early transcripts, but HPVs appears to produce no viral microRNAs.

Functional expression of double-stranded RNA-dependent protein kinase in rat intestinal epithelial cells

Intestinal epithelial cells (IECs) are exposed to external environment, microbial and viral products, and serve as essential barriers to antigens. Recent studies have shown that IECs express Toll-like receptors (TLRs) and respond to microbial components. The antimicrobial and antiviral barriers consist of many molecules including TLRs. To investigate the further component of this barrier in intestine, we examined the expression of double-stranded RNA-dependent protein kinase (PKR). PKR is a player in the cellular antiviral response and phosphorylates alpha-subunit of the eukaryotic translation initiation factor 2 (eIF-2alpha) to block protein synthesis and induces apoptosis. In this study, we showed that the expression of PKR was restricted to the cytoplasm of absorptive epithelial cells in the intestine of adult rat. We also demonstrated that PKR was expressed in the cultured rat intestinal epithelial cells (IEC-6). The level of PKR protein expression and the activity of alkaline phosphatase (ALP) increased in the cultured IEC-6 cells in a time-dependent manner. Inhibition of PKR by the 2-aminopurine treatment decreased ALP activity in the IEC-6 cells. Treatment of IEC-6 cells with synthetic double-stranded RNA (dsRNA) induced cell death in a dose-dependent manner. The addition of hydrocortisone also provoked suppression of PKR expression and ALP activity. This modulation might be mediated by signal transducers and activators of transcription-1 (STAT-1) protein. We concluded that PKR is expressed in IECs as potent barriers to antigens and is a possible modulator of the differentiation of rat IECs.

Downregulation of microRNA-200 in EBV-associated gastric carcinoma

EBV-associated gastric carcinoma is a distinct gastric carcinoma subtype with characteristic morphologic features similar to those of cells that undergo epithelial-to-mesenchymal transition. The effect of microRNA abnormalities in carcinogenesis was investigated by measuring the expression of the epithelial-to-mesenchymal transition-related microRNAs, miR-200a and miR-200b, in 36 surgically resected gastric carcinomas using quantitative reverse transcription-PCR analysis. MiR-200 family expression was decreased in EBV-associated gastric carcinoma, as compared with that in EBV-negative carcinoma. Downregulation of the miR-200 family was found in gastric carcinoma cell lines infected with recombinant EBV (MKN74-EBV, MKN7-EBV, and NUGC3-EBV), accompanied by the loss of cell adhesion, reduction of E-cadherin expression, and upregulation of ZEB1 and ZEB2. E-cadherin expression was partially restored by transfection of EBV-infected cells with miR-200 family precursors. Reverse transcription-PCR analysis of primary precursors of miR-200 (pri-miR-200) revealed that the transcription of pri-miR-200 was decreased in EBV-infected cells. Transfection of MKN74 cells with BARF0, EBNA1, and LMP2A resulted in a decrease of pri-miR-200, whereas transfection with EBV-encoded small RNA (EBER) did not. These four latent genes contributed to the downregulation of the mature miR-200 family and the subsequent upregulation of ZEB1/ZEB2, resulting in the reduction of E-cadherin expression. These findings indicate that all the latency type I genes have a synergetic effect on the downregulation of the miR-200 family that leads to reduced E-cadherin expression, which is a crucial step in the carcinogenesis of EBV-associated gastric carcinoma.

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.

Viral strategies to subvert the mammalian translation machinery

Viruses do not carry their own protein biosynthesis machinery and the translation of viral proteins therefore requires that the virus usurps the machinery of the host cell. To allow optimal translation of viral proteins at the expense of cellular proteins, virus families have evolved a variety of methods to repress the host translation machinery, while allowing effective viral protein synthesis. Many viruses use noncanonical mechanisms that permit translation of their own RNAs under these conditions. Viruses have also developed mechanisms to evade host innate immune responses that would repress translation under conditions of viral infection, in particular PKR activation in response to double-stranded RNA (dsRNA). Importantly, the study of viral translation mechanisms has enormously enhanced our understanding of many aspects of the cellular protein biosynthesis pathway and its components. A number of unusual mechanisms of translation initiation that were first discovered in viruses have since been observed in cellular mRNAs, and it has become apparent that a diverse range of translation mechanisms operates in eukaryotes, allowing subtle regulation of this essential process.

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.

Induction of sialyl-Lex expression by herpes simplex virus type 1 is dependent on viral immediate early RNA-activated transcription of host fucosyltransferase genes

We have previously shown that varicella-zoster virus (VZV) and cytomegalovirus (CMV) infection of diploid human fibroblasts (HEL) results in neo-expression of Lewis antigens sialyl Lewis x (sLe(x)) and Lewis y (Le(y)), respectively, after transcriptional activation of different combinations of dormant human fucosyltransferase genes (FUT1, FUT3, FUT5, and FUT6), whose gene products are responsible for the synthesis of Le antigens. Here, we show that herpes simplex virus type 1 (HSV-1) also induces sLe(x) expression dependent on induction of FUT3, FUT5, and FUT6 transcription in infected cells. HSV-1 induction of FUT5 was subsequently used as a model system for analyzing the mechanism of viral activation of dormant fucosyltransferase genes. We show that this is a rapid process, which gives rise to elevated FUT5 RNA levels already at 90 min postinfection. Augmented FUT5 transcription was found to be dependent on transcription of viral genes, but not dependent on the immediate early proteins ICP0 and ICP4, as demonstrated by experiments with HSV-1 mutants defective in expression of these genes. Augmented FUT5 transcription takes place in cycloheximide-treated HSV-1-infected cells, suggesting a more direct role for IE viral RNA during activation of cellular FUT5.

Cross-regulation between herpesviruses and the TNF superfamily members

Herpesviruses have evolved numerous strategies to subvert host immune responses so they can coexist with their host species. These viruses 'co-opt' host genes for entry into host cells and then express immunomodulatory genes, including mimics of members of the tumour-necrosis factor (TNF) superfamily, that initiate and alter host-cell signalling pathways. TNF superfamily members have crucial roles in controlling herpesvirus infection by mediating the direct killing of infected cells and by enhancing immune responses. Despite these strong immune responses, herpesviruses persist in a latent form, which suggests a dynamic relationship between the host immune system and the virus that results in a balance between host survival and viral control.

EBER2 RNA-induced transcriptome changes identify cellular processes likely targeted during Epstein Barr Virus infection

BACKGROUND

Little is known about the physiological role of the EBER1 and 2 nuclear RNAs during Epstein Barr viral infection. The EBERs are transcribed by cellular RNA Polymerase III and their strong expression results in 106 to 107 copies per EBV infected cell, making them reliable diagnostic markers for the presence of EBV. Although the functions of most of the proteins targeted by EBER RNAs have been studied, the role of EBERs themselves still remains elusive.

FINDINGS

The cellular transcription response to EBER2 expression using the wild-type and an internal deletion mutant was determined. Significant changes in gene expression patterns were observed. A functional meta-analysis of the regulated genes points to inhibition of stress and immune responses, as well as activation of cellular growth and cytoskeletal reorganization as potential targets for EBER2 RNA. Different functions can be assigned to different parts of the RNA.

CONCLUSION

These results provide new avenues to the understanding of EBER2 and EBV biology, and set the grounds for a more in depth functional analysis of EBER2 using transcriptome activity measurements.

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.

Epstein-Barr virus (EBV)-encoded RNA 2 (EBER2) but not EBER1 plays a critical role in EBV-induced B-cell growth transformation

Epstein-Barr virus (EBV)-encoded RNA 1 (EBER1) and EBER2 are untranslated RNAs and the most abundant viral transcripts in latently EBV-infected cells. We previously reported that EBERs play a critical role in efficient EBV-induced growth transformation of primary B cells. To investigate whether EBER1 and EBER2 have distinct roles in B-cell growth transformation, recombinant EBVs carrying either EBER1 or EBER2 were generated. The transforming ability of recombinant EBVs expressing EBER2 was as high as that of EBVs expressing both EBER1 and EBER2. In contrast, the transforming ability of recombinant EBVs carrying EBER1 was impaired and was similar to that of EBV lacking both EBER1 and EBER2. Lymphoblastoid cell lines (LCLs) established with EBVs carrying EBER2 proliferated at low cell densities, while LCLs established with EBVs carrying EBER1 did not. Interleukin 6 (IL-6) production in LCLs expressing EBER2 was more abundant than in those lacking EBER2. The growth of LCLs lacking EBER2 was enhanced by the addition of recombinant IL-6 to the cell culture, while the growth of EBER2-expressing LCLs was inhibited by a neutralizing anti-IL-6 antibody. These results demonstrate that EBER2, but not EBER1, contributes to efficient B-cell growth transformation. We conclude that EBER1 and EBER2, despite their structural similarity, have different functions in latently infected lymphoblastoid cells.

[Mechanisms of EBV-mediated oncogenesis]

Epstein-Barr virus (EBV) is the DNA tumor virus, which is known to be relevant to various cancers. EBV maintains latent infection in cancer cells, and there are three types of latent infection (type I-III) according to the patterns of viral latent genes expression. EBV has the ability to transform B cells into immortalized lymphoblastoid cell lines (LCL) showing type III latency, in which all latent genes are expressed. The mechanism of B-cell transformation has provided a model of EBV-associated lymphomas in immunosuppressed individuals. In type I and II latency, the limited numbers of latent genes are expressed. Previous studies have demonstrated the oncogenic functions of latent EBV genes including nuclear antigen EBNA1, membrane protein LMP1 and LMP2A. In addition, we have demonstrated that EBV-encoded small RNA EBERs play a significant role in oncogenesis. Here we summarize recent progresses in the studies on molecular mechanisms of EBV-mediated oncogenesis.

Oncogenic role of Epstein-Barr virus-encoded small RNAs (EBERs) in nasopharyngeal carcinoma

OBJECTIVE

Epstein-Barr virus (EBV) is a causative agent of nasopharyngeal carcinoma (NPC), and EBV gene expression is considered to be closely associated with the pathogenesis of NPC. Among EBV genes expressed in NPC, EBV-encoded non-polyadenylated RNAs, termed EBERs, are the most abundant transcripts of EBV in NPC. However, the role of EBERs still remains unclear. This study was designed to investigate the relevance of EBERs to the oncogenesis of NPC.

METHODS

Two types of EBERs expression vectors (EBERs-high-expression vector and EBERs-low-expression vector) were constructed and transfected into EBV-negative cells, MDCK or EBV-negative clones of NPC-KT cells. Then, malignant transformation, represented by anchor independent growth, was evaluated between the EBERs-transfected cells and EBERs-negative cells using a soft agar colony formation assay. Apoptosis was induced by serum deprivation (0.1% concentration of fetal bovine serum) and interferon-alpha (IFN-alpha) (500 U/ml) treatment. Cell viability was evaluated with a trypan blue exclusion test. The activation of cellular transcriptional factor NF-kappaB was studied with the IL-8 promoter sequence using a luciferase reporter assay.

RESULTS

EBERs-high-expression vector-transfected MDCK cells showed enhanced growth ability in soft agar compared with either EBERs-low-expression vector-transfected MDCK cells or EBERs-untransfected MDCK cells. However, they did not show the acquisition of any anti-apoptotic potential against either IFN-alpha or serum deprivation. Introduction of EBERs-low-expression vector into MDCK cells did not show anchor independent growth characteristics. Neither EBV-negative NPC-KT cells nor MDCK cells transfected with EBERs-high-expression vector showed any difference from EBERs-untransfected EBV-negative NPC-KT cells. Introduction of EBERs into MDCK cells did not transactivate the IL-8 promoter, indicating that neither NF-kappaB nor AP-1 was activated by EBERs.

CONCLUSION

EBERs are believed to induce the initial transformation of epithelial cells, thus contributing to the oncogenesis of NPC. Expression of abundant EBERs is considered to be critical for this transforming property of EBERs.