EBV BART MicroRNAs Target Multiple Pro-apoptotic Cellular Genes to Promote Epithelial Cell Survival

Latent Epstein-Barr virus infection collaborates with Myc over-expression in normal human B cells to induce Burkitt-like Lymphomas in mice

Epstein-Barr virus (EBV) is an important cause of human lymphomas, including Burkitt lymphoma (BL). EBV+ BLs are driven by Myc translocation and have stringent forms of viral latency that do not express either of the two major EBV oncoproteins, EBNA2 (which mimics Notch signaling) and LMP1 (which activates NF-κB signaling). Suppression of Myc-induced apoptosis, often through mutation of the TP53 (p53) gene or inhibition of pro-apoptotic BCL2L11 (BIM) gene expression, is required for development of Myc-driven BLs. EBV+ BLs contain fewer cellular mutations in apoptotic pathways compared to EBV-negative BLs, suggesting that latent EBV infection inhibits Myc-induced apoptosis. Here we use an EBNA2-deleted EBV virus (ΔEBNA2 EBV) to create the first in vivo model for EBV+ BL-like lymphomas derived from primary human B cells. We show that cord blood B cells infected with both ΔEBNA2 EBV and a Myc-expressing vector proliferate indefinitely on a CD40L/IL21 expressing feeder layer in vitro and cause rapid onset EBV+ BL-like tumors in NSG mice. These LMP1/EBNA2-negative Myc-driven lymphomas have wild type p53 and very low BIM, and express numerous germinal center B cell proteins (including TCF3, BACH2, Myb, CD10, CCDN3, and GCSAM) in the absence of BCL6 expression. Myc-induced activation of Myb mediates expression of many of these BL-associated proteins. We demonstrate that Myc blocks LMP1 expression both by inhibiting expression of cellular factors (STAT3 and Src) that activate LMP1 transcription and by increasing expression of proteins (DNMT3B and UHRF1) known to enhance DNA methylation of the LMP1 promoters in human BLs. These results show that latent EBV infection collaborates with Myc over-expression to induce BL-like human B-cell lymphomas in mice. As NF-κB signaling retards the growth of EBV-negative BLs, Myc-mediated repression of LMP1 may be essential for latent EBV infection and Myc translocation to collaboratively induce human BLs.

The viral etiology of EBV-associated gastric cancers contributes to their unique pathology, clinical outcomes, treatment responses and immune landscape

Epstein-Barr virus (EBV) is a pathogen known to cause a number of malignancies, often taking years for them to develop after primary infection. EBV-associated gastric cancer (EBVaGC) is one such malignancy, and is an immunologically, molecularly and pathologically distinct entity from EBV-negative gastric cancer (EBVnGC). In comparison with EBVnGCs, EBVaGCs overexpress a number of immune regulatory genes to help form an immunosuppressive tumor microenvironment (TME), have improved prognosis, and overall have an "immune-hot" phenotype. This review provides an overview of the histopathology, clinical features and clinical outcomes of EBVaGCs. We also summarize the differences between the TMEs of EBVaGCs and EBVnGCs, which includes significant differences in cell composition and immune infiltration. A list of available EBVaGC and EBVnGC gene expression datasets and computational tools are also provided within this review. Finally, an overview is provided of the various chemo- and immuno-therapeutics available in treating gastric cancers (GCs), with a focus on EBVaGCs.

Recent Advances in Assessing the Clinical Implications of Epstein-Barr Virus Infection and Their Application to the Diagnosis and Treatment of Nasopharyngeal Carcinoma

Reports about the oncogenic mechanisms underlying nasopharyngeal carcinoma (NPC) have been accumulating since the discovery of Epstein-Barr virus (EBV) in NPC cells. EBV is the primary causative agent of NPC. EBV-host and tumor-immune system interactions underlie the unique representative pathology of NPC, which is an undifferentiated cancer cell with extensive lymphocyte infiltration. Recent advances in the understanding of immune evasion and checkpoints have changed the treatment of NPC in clinical settings. The main EBV genes involved in NPC are LMP1, which is the primary EBV oncogene, and BZLF1, which induces the lytic phase of EBV. These two multifunctional genes affect host cell behavior, including the tumor-immune microenvironment and EBV behavior. Latent infections, elevated concentrations of the anti-EBV antibody and plasma EBV DNA have been used as biomarkers of EBV-associated NPC. The massive infiltration of lymphocytes in the stroma suggests the immunogenic characteristics of NPC as a virus-infected tumor and, at the same time, also indicates the presence of a sophisticated immunosuppressive system within NPC tumors. In fact, immune checkpoint inhibitors have shown promise in improving the prognosis of NPC patients with recurrent and metastatic disease. However, patients with advanced NPC still require invasive treatments. Therefore, there is a pressing need to develop an effective screening system for early-stage detection of NPC in patients. Various modalities, such as nasopharyngeal cytology, cell-free DNA methylation, and deep learning-assisted nasopharyngeal endoscopy for screening and diagnosis, have been introduced. Each modality has its advantages and disadvantages. A reciprocal combination of these modalities will improve screening and early diagnosis of NPC.

Downregulation of MUS81 expression inhibits cell migration and maintains EBV latent infection through miR-BART9-5p in EBV-associated gastric cancer

Epstein-Barr virus (EBV) infection is associated with the occurrence and development of gastric cancer (GC). Methyl methanesulfonate and ultraviolet-sensitive gene 81 (MUS81) is the catalytic component of a structure-specific endonuclease and plays an important role in chromosomal stability. However, the link between EBV infection and MUS81 remains unclear. In the present study, we found that MUS81 expression was much lower in EBV-associated GC cells than in EBV-negative GC. MUS81 acts as an oncogene in GC by inducing the cell migration and proliferation. Western blot and luciferase reporter assays revealed that miR-BART9-5p directly targeted MUS81 and downregulated its expression. Additionally, overexpression of MUS81 in EBV-positive GC cells inhibited the expression of EBV nuclear antigen 1 (EBNA1). EBNA1 is critical for the pathogenesis of EBV-associated tumors and the maintenance of a stable copy number of the viral genomes. Altogether, these results indicated that the lowering MUS81 expression might be a mechanism by EBV to maintain its latent infection.

Human microbiomes in cancer development and therapy

Colonies formed by bacteria, archaea, fungi, and viral groups and their genomes, metabolites, and expressed proteins constitute complex human microbiomes. An increasing evidences showed that carcinogenesis and disease progression were link to microbiomes. Different organ sources, their microbial species, and their metabolites are different; the mechanisms of carcinogenic or procancerous are also different. Here, we summarize how microbiomes contribute to carcinogenesis and disease progression in cancers of the skin, mouth, esophagus, lung, gastrointestinal, genital, blood, and lymph malignancy. We also insight into the molecular mechanisms of triggering, promoting, or inhibiting carcinogenesis and disease progress induced by microbiomes or/and their secretions of bioactive metabolites. And then, the strategies of application of microorganisms in cancer treatment were discussed in detail. However, the mechanisms by which human microbiomes function are still poorly understood. The bidirectional interactions between microbiotas and endocrine systems need to be clarified. Probiotics and prebiotics are believed to benefit human health via a variety of mechanisms, in particular, in tumor inhibition. It is largely unknown how microbial agents cause cancer or how cancer progresses. We expect this review may open new perspectives on possible therapeutic approaches of patients with cancer.

Epigenetic changes induced by pathogenic Chlamydia spp

Chlamydia trachomatis, C. pneumoniae, and C. psittaci, the three Chlamydia species known to cause human disease, have been collectively linked to several pathologies, including conjunctivitis, trachoma, respiratory disease, acute and chronic urogenital infections and their complications, and psittacosis. In vitro, animal, and human studies also established additional correlations, such as between C. pneumoniae and atherosclerosis and between C. trachomatis and ovarian cancer. As part of their survival and pathogenesis strategies as obligate intracellular bacteria, Chlamydia spp. modulate all three major types of epigenetic changes, which include deoxyribonucleic acid (DNA) methylation, histone post-translational modifications, and microRNA-mediated gene silencing. Some of these epigenetic changes may be implicated in key aspects of pathogenesis, such as the ability of the Chlamydia spp. to induce epithelial-to-mesenchymal transition, interfere with DNA damage repair, suppress cholesterol efflux from infected macrophages, act as a co-factor in human papillomavirus (HPV)-mediated cervical cancer, prevent apoptosis, and preserve the integrity of mitochondrial networks in infected host cells. A better understanding of the individual and collective contribution of epigenetic changes to pathogenesis will enhance our knowledge about the biology of Chlamydia spp. and facilitate the development of novel therapies and biomarkers. Pathogenic Chlamydia spp. contribute to epigenetically-mediated gene expression changes in host cells by multiple mechanisms.

MicroRNA-mediated control of Epstein-Barr virus infection and potential diagnostic and therapeutic implications

Herpesviruses, such as Epstein-Barr virus (EBV), encode multiple viral microRNAs that are expressed throughout various infection stages. While much progress has been made in evaluating both the viral and host microRNAs (miRNAs) that are detected during infection as well as elucidating their molecular targets in vitro, our understanding of their contributions to pathogenesis in vivo, viral oncogenesis, and clinical implications for these small molecules remains limited. miRNAs are widely recognized as key regulators of global cellular processes, including apoptosis, cell differentiation, and development of immune responses. This review discusses the roles of miRNAs in EBV infection and current advances in miRNA-based diagnostic and therapeutic strategies potentially applicable toward EBV-associated diseases.

Epstein-Barr virus miR-BHRF1-3 targets the BZLF1 3'UTR and regulates the lytic cycle

Suppression of lytic viral gene expression is a key aspect of the Epstein-Barr virus (EBV) life cycle to facilitate the establishment of latent infection. Molecular mechanisms regulating transitions between EBV lytic replication and latency are not fully understood. Here, we investigated the impact of viral microRNAs on the EBV lytic cycle. Through functional assays, we found that miR-BHRF1-3 attenuates EBV lytic gene expression following reactivation. To understand the miRNA targets contributing to this activity, we performed Ago PAR-CLIP analysis on EBV-positive, reactivated Burkitt's lymphoma cells and identified multiple miR-BHRF1-3 interactions with viral transcripts. Using luciferase reporter assays, we confirmed a miRNA interaction site within the 3'UTR of BZLF1 which encodes the essential immediate early (IE) transactivator Zta. Comparison of >850 published EBV genomes identified sequence polymorphisms within the miR-BHRF1-3 locus that deleteriously affect miRNA expression and function. Molecular interactions between the homologous viral miRNA, miR-rL1-17, and IE transcripts encoded by rhesus lymphocryptovirus were further identified. Our data demonstrate that regulation of IE gene expression by a BHRF1 miRNA is conserved amongst lymphocryptoviruses, and further reveal virally-encoded genetic elements that orchestrate viral antigen expression during the lytic cycle. Importance Epstein-Barr virus infection is predominantly latent in healthy individuals, while periodic cycles of reactivation are thought to facilitate persistent lifelong infection. Lytic infection has been linked to development of certain EBV-associated diseases. Here, we demonstrate that EBV miR-BHRF1-3 can suppress lytic replication by directly inhibiting Zta expression. Moreover, we identify nucleotide variants that impact the function of miR-BHRF1-3, which may contribute to specific EBV pathologies.

Association of Epstein–Barr Virus and Cytomegalovirus Infections with Esophageal Carcinoma

Background: Given the fact that viral infections play an important role, either directly or indirectly, in around 20 percent of human cancers, this study aimed at investigating the potential association of Epstein–Barr virus (EBV) and cytomegalovirus (CMV) infections in esophageal cancer that is the sixth most common cause of cancer-related deaths. Methods: In this case-control study, a total of 200 paraffin-embedded biopsies of cancerous and benign esophageal tissues were gathered from the biopsy bank of Imam Reza Hospital, Tabriz, Iran in 2017. All samples were first deparaffinized, and then subjected to commercial DNA extraction. The quality of extracted DNA was evaluated by amplification of the beta globulin gene. Identification of EBV and CMV DNA was performed using primers designed for the EBER region of EBV and the immediate early (IE) region of the CMV genome, respectively. Results: The mean age of the subjects in the test and control groups was 52.2 (17.1) and 59.9 (18.9), respectively. The distribution of gender (male/female) in patient and control groups was 54/46 and 53/47, respectively. Our results showed that the frequency of EBV (P < 0.001) and CMV (P < 0.001) in cancerous samples was statistically higher than control group. Moreover, in the cancerous group the rate of EBV was significantly higher in the esophageal adenocarcinomas (EAC) sample (12 out of 70) than esophageal squamous cell carcinomas (ESCC) (0 out of 30) (P = 0.016) but, in the ESCC group, 17 out of 30 subjects were positive for CMV which was significantly higher in comparison with EAC patients (1 out of 70) (P < 0.001). Conclusions: Findings indicated that EBV and CMV might be contributed to the pathogenesis of EAC and ESCC types of esophageal carcinoma, respectively, although further studies are warranted.

SSTR2 in Nasopharyngeal Carcinoma: Relationship with Latent EBV Infection and Potential as a Therapeutic Target

Nasopharyngeal carcinoma (NPC) is a malignant epithelial tumor, most commonly located in the pharyngeal recess and endemic to parts of Asia. It is often detected at a late stage which is associated with poor prognosis (5-year survival rate of 63%). Treatment for this malignancy relies predominantly on radiotherapy and/or systemic chemotherapy, which can be associated with significant morbidity and impaired quality of life. In endemic regions NPC is associated with infection by Epstein-Barr virus (EBV) which was shown to upregulate the somatostatin receptor 2 (SSTR2) cell surface receptor. With recent advances in molecular techniques allowing for an improved understanding of the molecular aetiology of this disease and its relation to SSTR2 expression, we provide a comprehensive and up-to-date overview of this disease and highlight the emergence of SSTR2 as a key tumor biomarker and promising target for imaging and therapy.

Stress-Induced Epstein-Barr Virus Reactivation

Epstein-Barr virus (EBV) is typically found in a latent, asymptomatic state in immunocompetent individuals. Perturbations of the host immune system can stimulate viral reactivation. Furthermore, there are a myriad of EBV-associated illnesses including various cancers, post-transplant lymphoproliferative disease, and autoimmune conditions. A thorough understanding of this virus, and the interplay between stress and the immune system, is essential to establish effective treatment. This review will provide a summary of the interaction between both psychological and cellular stressors resulting in EBV reactivation. It will examine mechanisms by which EBV establishes and maintains latency and will conclude with a brief overview of treatments targeting EBV.

Human herpesvirus-encoded MicroRNA in host-pathogen interaction

Human herpesviruses (HHV) are ubiquitous, linear dsDNA viruses that establish lifelong latency, disrupted by sporadic reactivation. HHV have evolved diverse ingenious mechanisms to evade robust host defenses. Incorporation of unique stem loop sequences that generate viral microRNAs (v-miRs) exemplifies one such evolutionary adaptation in HHV. These noncoding RNAs can control cellular and viral transcriptomes highlighting their ability in shaping host-HHV interactions. We summarize recent developments in functional characterization of HHV-encoded miRNAs in shaping the outcome of host-pathogen interaction. Non-immunogenic dissemination of v-miRs through exosomes confer added advantage to HHV in incessant modulation of host microenvironment. This review delineates the mechanistic role of v-miRs in facilitating viral persistence and tropism by targeting genes associated with cellular (apoptosis, angiogenesis, cell migration, etc.) and viral life cycle (latency, lytic and reactivation). Burgeoning evidences indicate plausible association of v-miRs in various immune-mediated diseases (nasopharyngeal carcinoma, neurological disorders, periodontal diseases, etc.) and herpesvirus-related malignancies indicating their broad-spectrum impact on host cellular pathways. We propose to exploit tisssue and systemic levels of v-miRs as diagnostic and prognostic markers for cancers and immune-mediated diseases. Therapeutic targeting of v-miRs will advance the promising outcomes of preclinical discoveries to bedside application.

Identification and characterization of a novel Epstein-Barr Virus-encoded circular RNA from LMP-2 Gene

Epstein-Barr virus (EBV) has been recently found to generate novel circular RNAs (circRNAs) through backsplicing. However, comprehensive catalogs of EBV circRNAs in other cell lines and their functional characterization are still lacking. In this study, we have identified a list of putative EBV circRNAs in GM12878, an EBV-transformed lymphoblastoid cell line, with a significant majority encoded from the EBV latent genes. A novel EBV circRNA derived from the exon 5 of LMP-2 gene which exhibited highest prevalence, was further validated using RNase R assay and Sanger sequencing. This circRNA, which we term circLMP-2_e5, can be universally detected in a panel of EBV-positive cell lines modelling different latency programs. It ranges from lower expression in nasopharyngeal carcinoma (NPC) cells to higher expression in B cells, and is localized to both the cytoplasm and the nucleus. We provide evidence that circLMP-2_e5 is expressed concomitantly with its cognate linear LMP-2 RNA upon EBV lytic reactivation, and may be produced as a result of exon skipping, with its circularization possibly occurring without the involvement of cis elements in the short flanking introns. Furthermore, we show that circLMP-2_e5 is not involved in regulating cell proliferation, host innate immune response, its linear parental transcripts, or EBV lytic reactivation. Taken together, our study expands the current repertoire of putative EBV circRNAs, broadens our understanding of the biology of EBV circRNAs, and lays the foundation for further investigation of their function in the EBV life cycle and disease development.

Nasopharyngeal Carcinoma and Its Association with Epstein-Barr Virus

Nasopharyngeal carcinoma (NPC) is caused by Epstein-Barr virus (EBV) infection, yet incorporating measurement of EBV DNA levels into clinical practice remains a challenge. Here, we summarize the relationship between NPC and EBV infection before describing the use of cell-free DNA as a plasma biomarker in cancer. We then compare conventional polymerase chain reaction methods and emerging next-generation sequencing approaches for EBV viral load detection emphasizing their prognostic and predictive utility. We conclude by considering how assay standardization, novel molecular approaches, and alternative clinical specimens may be leveraged to bring EBV testing into the routine care of patients with NPC.

miR-105-5p regulates PD-L1 expression and tumor immunogenicity in gastric cancer

Cancer immunotherapies targeting the interaction between Programmed death 1 (PD-1) and Programmed death ligand 1 (PD-L1) have recently been approved for the treatment of multiple cancer types, including gastric cancer. However, not all patients respond to these therapies, while some eventually acquire resistance. A partial predictive biomarker for positive response to PD-1/PD-L1 therapy is PD-L1 expression, which has been shown to be under strict post-transcriptional control in cancer. By fractionating the PD-L1 3' untranslated region (3'UTR) into multiple overlapping fragments, we identified a small 100-nucleotide-long cis-acting region as being necessary and sufficient for post-transcriptional repression of PD-L1 expression in gastric cancer. In parallel, we performed a correlation analysis between PD-L1 expression and all host miRNAs in stomach cancer patient samples. A single miRNA, miR-105-5p, was predicted to bind to the identified cis-acting 3'UTR region and to negatively correlate with PD-L1 expression. Overexpression of miR-105-5p in gastric cancer cell lines resulted in decreased expression of PD-L1, both at the total protein and surface expression levels, and induced CD8⁺ T cell activation in co-culture assays. Finally, we show that expression of miR-105-5p in gastric cancer is partly controlled by DNA methylation of a cancer- and germline-specific promoter of its host gene, GABRA3. Dysregulation of miR-105-5p is observed in many cancer types and this study shows the importance of this miRNA in controlling the immunogenicity of cancer cells, thus highlighting it as a potential biomarker for PD-1/PD-L1 therapy and target for combinatorial immunotherapy.

EBV miRNAs are potent effectors of tumor cell transcriptome remodeling in promoting immune escape

The Epstein Barr virus (EBV) contributes to the tumor phenotype through a limited set of primarily non-coding viral RNAs, including 31 mature miRNAs. Here we investigated the impact of EBV miRNAs on remodeling the tumor cell transcriptome. Strikingly, EBV miRNAs displayed exceptionally abundant expression in primary EBV-associated Burkitt’s Lymphomas (BLs) and Gastric Carcinomas (GCs). To investigate viral miRNA targeting, we used the high-resolution approach, CLASH in GC and BL cell models. Affinity constant calculations of targeting efficacies for CLASH hits showed that viral miRNAs bind their targets more effectively than their host counterparts, as did Kaposi’s sarcoma-associated herpesvirus (KSHV) and murine gammaherpesvirus 68 (MHV68) miRNAs. Using public BL and GC RNA-seq datasets, we found that high EBV miRNA targeting efficacies translates to enhanced reduction of target expression. Pathway analysis of high efficacy EBV miRNA targets showed enrichment for innate and adaptive immune responses. Inhibition of the immune response by EBV miRNAs was functionally validated in vivo through the finding of inverse correlations between EBV miRNAs and immune cell infiltration and T-cell diversity in BL and GC datasets. Together, this study demonstrates that EBV miRNAs are potent effectors of the tumor transcriptome that play a role in suppressing host immune response.

Burkitt’s Lymphoma and gastric cancer are both associated with EBV, a prolific DNA tumor virus that latently resides in nearly all human beings. Despite mostly restricting viral gene expression to noncoding RNAs, EBV has important influences on the fitness of infected tumor cells. Here, we show that the miRNA class of viral noncoding RNAs are a major viral contributor to remodeling the tumor cell regulatory machinery in patient tumor samples. First, an assessment of miRNA expression in clinical tumor samples showed that EBV miRNAs are expressed at unexpectedly high levels relative to cell miRNAs. Using a highly specific miRNA target identification approach, CLASH, we comprehensively identified both viral and cellular miRNA targets and the relative abundance of each miRNA-mRNA interaction. We also show that viral miRNAs bind to and alter the expression of their mRNA targets more effectively than their cellular miRNA counterparts. Pathway analysis of the most effectively targeted mRNAs revealed enrichment of immune signaling pathways and we show a corresponding inverse correlation between EBV miRNA expression and infiltrating immune cells in EBV positive primary tumors. Altogether, this study shows that EBV miRNAs are key regulators of the tumor cell phenotype and the immune cell microenvironment.

EBV miRNAs are potent effectors of tumor cell transcriptome remodeling in promoting immune escape

The Epstein Barr virus (EBV) contributes to the tumor phenotype through a limited set of primarily non-coding viral RNAs, including 31 mature miRNAs. Here we investigated the impact of EBV miRNAs on remodeling the tumor cell transcriptome. Strikingly, EBV miRNAs displayed exceptionally abundant expression in primary EBV-associated Burkitt's Lymphomas (BLs) and Gastric Carcinomas (GCs). To investigate viral miRNA targeting, we used the high-resolution approach, CLASH in GC and BL cell models. Affinity constant calculations of targeting efficacies for CLASH hits showed that viral miRNAs bind their targets more effectively than their host counterparts, as did Kaposi's sarcoma-associated herpesvirus (KSHV) and murine gammaherpesvirus 68 (MHV68) miRNAs. Using public BL and GC RNA-seq datasets, we found that high EBV miRNA targeting efficacies translates to enhanced reduction of target expression. Pathway analysis of high efficacy EBV miRNA targets showed enrichment for innate and adaptive immune responses. Inhibition of the immune response by EBV miRNAs was functionally validated in vivo through the finding of inverse correlations between EBV miRNAs and immune cell infiltration and T-cell diversity in BL and GC datasets. Together, this study demonstrates that EBV miRNAs are potent effectors of the tumor transcriptome that play a role in suppressing host immune response.

EpsteinBarr virusencoded microRNAs involve in tumorigenesis and development

Epstein-Barr virus (EBV), a definite tumorigenic virus, is closely related to the development of nasopharyngeal cancer, gastric cancer, lymphoma and other tumors. EBV encodes a total of 44 mature microRNAs, which can regulate the expression of virus and host genes. EBV-encoded microRNAs and their regulated target molecules participate in the biological functions of tumor apoptosis, proliferation, invasion, and metastasis during tumorigenesis and development, and play an important role in the development of tumor.

EBV-miR-BART12 inhibits cell migration and proliferation by targeting Snail expression in EBV-associated gastric cancer

Epstein-Barr virus (EBV) was the first oncovirus found to encode microRNAs. In EBV-associated gastric cancer (EBVaGC), EBV-encoded BamHI-A rightward transcript microRNAs (BARTs) are highly expressed. However, the role of BARTs in EBVaGC remains obscure. In this study, we found that EBV-miR-BART12 (miR-BART12) inhibits cell proliferation and migration. Zinc finger protein SNAI1 (Snail) is an important epithelial-mesenchymal transition (EMT) inducer, and overexpression of Snail is closely associated with cancer metastasis. Here, we report that Snail expression in EBVaGC cells is lower than in EBV-negative gastric cancer (EBVnGC) cells. A dual luciferase reporter assay showed that miR-BART12 targets Snail directly by interacting with its 3'-UTR. A CHX chase assay revealed that miR-BART12 accelerates the degradation of Snail. Furthermore, we found that miR-BART12 can regulate the expression of EMT-related genes. Flow cytometry analysis showed that transfection with miR-BART12 induced G2/M phase arrest and promoted cell apoptosis. In summary, the results of our study have suggested a new mechanism by which BARTs can repress cell proliferation and migration in gastric cancer.

Epstein-Barr Virus Limits the Accumulation of IPO7, an Essential Gene Product

Epstein-Barr virus (EBV) encodes more than 40 miRNAs that target cellular mRNAs to aid its infection, replication, and maintenance in individual cells and in its human host. Importin-7 (IPO7), also termed Imp7 or RanBPM7, is a nucleocytoplasmic transport protein that has been frequently identified as a target for two of these viral miRNAs. How the viral life cycle might benefit from regulating IPO7 has been unclear, though. We demonstrate with CRISPR-Cas9 mutagenesis that IPO7 is essential in at least three cells lines and that increasing its levels of expression inhibits growth of infected cells. EBV thus regulates the level of IPO7 to limit its accumulation consistent with its being required for survival of its host cell.

The many ways Epstein-Barr virus takes advantage of the RNA tool kit

Epstein-Barr virus (EBV) was the first human cancer-causing virus to be discovered over fifty years ago. Given its relatively large genome size for a virus and hence the capacity to store more than mere protein-coding information, EBV also harbours genetic material for producing an array of distinct noncoding (nc)RNAs. The double-stranded nature of its DNA genome allows the utilization of the whole gamut of ncRNA types, including both RNA polymerase II and III transcripts, in devising a sophisticated strategy to ensure its replication upon infection in host cells and evasion of host immune responses. Owing to the development of sensitive technologies in recent years, mostly entailing next-generation sequencing, the list of ncRNA types generated by EBV has expanded now to include two RNAs (EBER1 and EBER2) best categorized as long ncRNAs, dozens of microRNAs, one small nucleolar RNA, stable intronic sequence RNAs, and the most recently discovered circular RNAs. With the application of cutting-edge technology, the molecular mechanisms of some of these noncoding transcripts are beginning to emerge, while others remain yet to be elucidated. As viruses often take advantage of existing molecular pathways established by the host, it is likely that further novel concepts of the greatly unexplored noncoding world can be learned from studying the many EBV ncRNAs.

Identification and validation of methylated differentially expressed miRNAs and immune infiltrate profile in EBV-associated gastric cancer

BACKGROUND

The recent discovery of cancer/tissue specificity of miRNA has indicated its great potential as a therapeutic target. In Epstein-Barr virus-associated gastric cancer (EBVaGC), host genes are affected by extensive DNA methylation, including miRNAs. However, the role of methylated miRNA in the development of EBVaGC and immune cell infiltration has largely remained elusive.

RESULTS

After crossmatching the DNA methylation and expression profile of miRNA and mRNA in the Gene Expression Omnibus (GEO) and the Cancer Genome Atlas Research Network (TCGA), we discovered that miR-129-2-3p was significantly suppressed due to hypermethylation on its enhancer in EBVaGC. The differentially expressed genes (DEGs) added up to 30, among which AKAP12 and LARP6 were predicted to be the target genes of miR-129-2-3p and negatively correlated with patients' survival. Accordingly, miR-129-2-3p was significantly down-regulated in tumor samples in 26 (65%) out of 40 cases in our cohort (P < 0.0001). The proliferation, migration and invasion functions of GC cells were significantly promoted when transfected with miR-129-2-3p inhibitor and suppressed when transfected with mimics or treated with 5-aza-2'-deoxycytidine. Moreover, a comprehensive regulation network was established by combining the putative transcription factors, miRNA-mRNA and protein-protein interaction (PPI) analysis. Pathway enrichment analysis showed that cytokine activity, especially CCL20, was the most prominent biological process in EBVaGC development. Immune cell infiltration analysis demonstrated CD4+ T cell, macrophage and dendritic cell infiltrates were significantly enriched for the prognostic-indicated hub genes.

CONCLUSION

This study has provided a comprehensive analysis of differentially expressed miRNAs and mRNAs associated with genome-wide DNA methylation by integrating multi-source data including transcriptome, methylome and clinical data from GEO and TCGA, QPCR of tumor samples and cell function assays. It also gives a hint on the relationships between methylated miRNA, DEGs and the immune infiltration. Further experimental and clinical investigations are warranted to explore the underlying mechanism and validate our findings.

Critical review of Epstein-Barr virus microRNAs relation with EBV-associated gastric cancer

Epstein-Barr virus (EBV)-associated gastric cancer (EBVaGC) is regarded as the most prevalent malignant tumor triggered by EBV infection. In recent years, increasing attention has been considered to recognize more about the disease process's exact mechanisms. There is accumulating evidence that showing epigenetic modifications play critical roles in the EBVaGC pathogenesis. MicroRNAs (miRNAs), as critical epigenetic modulators, are single-strand short noncoding RNA (length ~ <200 bp), which regulate gene expression through binding to the 3'-untranslated region (3'-UTR) of target RNA transcripts and either degrade or repress their activities. In the latest research on EBV, it was found that this virus could encode miRNAs. Mechanistically, EBV-encoded miRNAs are involved in carcinogenesis and the progression of EBV-associated malignancies. Moreover, these miRNAs implicated in immune evasion, identification of pattern recognition receptors, regulation of lymphocyte activation and lethality, modulation of infected host cell antigen, maintain of EBV infection status, promotion of cell proliferation, invasion and migration, and reduction of apoptosis. As good news, not only has recent data demonstrated the crucial function of EBV-encoded miRNAs in the pathogenesis of EBVaGC, but it has also been revealed that aberrant expression of exosomal miRNAs in EBVaGC has made them biomarkers for detection of EBVaGC. Regarding these substantial characterizes, the critical role of EBV-encoded miRNAs has been a hot topic in research. In this review, we will focus on the multiple mechanisms involved in EBVaGC caused by EBV-encoded miRNAs and briefly discuss their potential application in the clinic as a diagnostic biomarker.

EBV miR-BARTs and human lncRNAs: Shifting the balance in competing endogenous RNA networks in EBV-associated gastric cancer

Non-coding RNAs (ncRNAs) contribute to the regulation of gene expression. By acting as competing endogenous RNA (ceRNA), long non-coding RNAs (lncRNAs) hijack microRNAs (miRNAs) and inhibit their ability to bind their coding targets. Viral miRNAs can compete with and target the same transcripts as human miRNAs, shifting the balance in networks associated with multiple cellular processes and diseases. Epstein-Barr virus (EBV) is an example of how a subset of viral coding RNA and non-coding RNAs can cause deregulation of human transcripts and contribute to the development of EBV-associated malignancies. EBV non-coding transforming genes include lncRNAs (i.e circular RNAs), and small ncRNAs (i.e. miRNAs). Among the latter, most ongoing research has focused on miR-BARTs whereas target many genes associated with apoptosis and epithelial-mesenchymal transition, in EBV-associated gastric cancer (GC). In this review, we propose to include the interactions between EBV ncRNAs human transcripts in the hypothesis known as "competitive viral and host RNAs". These interactions may shift the balance in biological pathways such as apoptosis and epithelial-mesenchymal transition in EBV-associated gastric cancer.

Circulating Epstein-Barr virus microRNA profile reveals novel biomarker for nasopharyngeal carcinoma diagnosis

Nasopharyngeal carcinoma (NPC), a tumor quite prevalent in Asia, is closely associated with Epstein-Barr virus (EBV) infection status. Many NPC patients are not able to be treated in time when being diagnosed at an advanced stage. EBV-encoded microRNAs are reliable sources of biomarkers for NPC diagnosis. In this study, we conducted circulating EBV microRNAs profiling by quantitative reverse transcription polymerase chain reaction (qRT-PCR) among plasma samples of 159 NPC patients versus 145 normal controls (NCs) and serum samples of 60 NPC patients versus 60 NCs. Among the 44 mature EBV-encoded miRNAs, only miR-BART19-3p in plasma was proved to be significantly up-regulated in NPC patients (P< 0.05; fold change (FC) > 2.0). The area under the receiver operating characteristic curve (AUC) for the signature to discriminate NPC patients from NCs was 0.848 with the sensitivity and specificity being 71.7% and 72.3%, respectively. The identified biomarker was analyzed in tissue specimens (44 NPC VS. 32 NCs) and proved to be consistently up-regulated in NPC tumor tissues. Bioinformatics analysis was further conducted to predict the potential targets of miR-BART-19-3p, which provided some hints to its close relationship with NPC development. In conclusion, we identified a novel biomarker - plasma miR-BART19-3p for the detection of NPC.

The roles of miRNAs and lncRNAs in Epstein-Barr virus associated epithelial cell tumors

Epstein-Barr virus (EBV) infection is highly prevalent in the population and is known to be associated with a variety of human tumors, such as nasopharyngeal carcinoma, gastric cancer, and lymphoma; however, the mechanisms of EBV carcinogenesis remain unclear. Recent studies have revealed that many non-coding RNAs participate in the regulation of proliferation, migration, invasion, and other processes in EBV-associated tumor, and the interaction between ncRNAs and the potential target genes has gradually become a research hotspot. Therefore, here, we discuss the expression and roles of ncRNAs in EBV-associated epithelial tumors.

PTSelect™: A post-transcriptional technology that enables rapid establishment of stable CHO cell lines and surveillance of clonal variation

Currently, stable Chinese hamster ovary cell lines producing therapeutic, recombinant proteins are established either by antibiotic and/or metabolic selection. Here, we report a novel technology, PTSelect™ that utilizes an siRNA cloned upstream of the gene of interest (GOI) that is processed to produce functional PTSelect™-siRNAs, which enable cell enrichment. Cells with stably integrated GOI are selected and separated from cells without GOI by transfecting CD4/siRNA mRNA regulated by PTSelect™-siRNAs and exploiting the variable expression of CD4 on the cell surface. This study describes the PTSelect™ principle and compares the productivity, doubling time and stability of clones developed by PTSelect™ with conventionally developed clones. PTSelect™ rapidly established a pool population with comparable stability and productivity to pools generated by traditional methods and can further be used to easily monitor productivity changes due to clonal drift, identifying individual cells with reduced productivity.

EBV-encoded miRNAs can sensitize nasopharyngeal carcinoma to chemotherapeutic drugs by targeting BRCA1

Nasopharyngeal carcinoma (NPC) is an Epstein‐Barr virus (EBV)‐associated epithelial malignancy. The high expression of BART‐miRNAs (miR‐BARTs) during latent EBV infection in NPC strongly supports their pathological importance in cancer progression. Recently, we found that several BART‐miRNAs work co‐operatively to modulate the DNA damage response (DDR) by reducing Ataxia‐telangiectasia‐mutated (ATM) activity. In this study, we further investigated the role of miR‐BARTs on DDR. The immunohistochemical study showed that the DNA repair gene, BRCA1, is consistently down‐regulated in primary NPCs. Using computer prediction programs and a series of reporter assays, we subsequently identified the negative regulatory role of BART2‐3p, BART12, BART17‐5p and BART19‐3p in BRCA1 expression. The ectopic expression of these four miR‐BARTs suppressed endogenous BRCA1 expression in EBV‐negative epithelial cell lines, whereas BRCA1 expression was enhanced by repressing endogenous miR‐BARTs activities in C666‐1 cells. More importantly, suppressing BRCA1 expression in nasopharyngeal epithelial cell lines using miR‐BART17‐5p and miR‐BART19‐3p mimics reduced the DNA repair capability and increased the cell sensitivity to the DNA‐damaging chemotherapeutic drugs, cisplatin and doxorubicin. Our findings suggest that miR‐BARTs play a novel role in DDR and may facilitate the development of effective NPC therapies.

tRFTar: Prediction of tRF-target gene interactions via systemic re-analysis of Argonaute CLIP-seq datasets

tRNA-derived fragments (tRFs), which by definition are cleaved from tRNAs, comprise a novel class of regulatory small non-coding RNAs. Recent evidence has revealed that tRFs can be loaded onto Argonaute (AGO) family proteins to perform post-transcriptional regulations via substantial tRF-target gene interactions (TGIs). However, there is no resource that systematically profiles potential AGO-mediated TGIs. To this end, we performed a systemic computational screening of potential AGO-mediated TGIs by a re-analysis of 146 crosslinking-immunoprecipitation and high-throughput sequencing (CLIP-seq) datasets in which 920,690 TGIs between 12,102 tRFs and 5,688 target genes were identified. The predicted TGIs have superior signal-to-noise ratio and good consistency with TGIs identified from an orthogonal technique. AGO-bound tRFs are not evenly distributed, where the 5'-tRF and 3'-tRF are enriched and some commonly expressed tRFs are also overrepresented. The tRFs tend to target conserved regions of transcripts and co-express with their target genes. Filtering TGIs with consistent co-expression with target genes results in a set of regulatory TGIs that contains 25,281 tRF-target pairs. Together, our results unveiled the extensive regulatory interactions between tRFs and target genes. Finally, the CLIP-derived TGIs were incorporated in a user-friendly online platform termed as tRFTar, where various functions like custom searching, co-expressed TGI filtering, genome browser and TGI-based tRF functional enrichment analysis are enabled to help users to investigate the functions of tRFs. The tRFTar is freely available at http://www.rnanut.net/tRFTar/.

Epstein-Barr virus-encoded miR-BART5-5p upregulates PD-L1 through PIAS3/pSTAT3 modulation, worsening clinical outcomes of PD-L1-positive gastric carcinomas

BACKGROUND

Epstein-Barr virus (EBV) is etiologically associated with ~ 10% of all gastric carcinomas. However, the molecular mechanisms and roles of EBV miRNAs in gastric carcinoma oncogenesis are yet to be elucidated.

METHODS

MicroRNA microarray and TaqMan quantitative real-time RT-PCR were conducted. RT-PCR and luciferase reporter assay for PIAS3, western blotting for 20 proteins, immunofluorescence for STAT3, transfection with miRBART5-5p-plasmid, STAT3-plasmid, miRBART5-5p mimic, or PIAS3-siRNA, and in vitro assays for biological effects of PD-L1 were implemented. In situ hybridization for EBV-encoded small RNAs and immunohistochemistry were performed on gastric carcinoma tissues.

RESULTS

Transfecting miR-BART5-5p into EBV(-) gastric carcinoma cell lines caused a decrease in PIAS3 3'-UTR reporter activity, PIAS3 downregulation, and subsequent STAT3 activation followed by PIAS3/pSTAT3-dependent PD-L1 upregulation. Interestingly, due to PD-L1 knockdown, apoptosis was increased, while the rate of cell proliferation, invasion capacity, and migration were decreased in miR-BART5-5p-transfected cells. In EBV(+) gastric carcinoma cells, anti-miR-BART5-5p reduced PD-L1 levels through PIAS3/pSTAT3 control. Among 103 patients with EBV-associated gastric carcinomas, overall survival was significantly shortened for those with PD-L1(+) tumors compared to those with PD-L1(-) tumors (P = 0.049).

CONCLUSIONS

Our findings imply that miR-BART5-5p directly targets PIAS3 and augments PD-L1 through miR-BART5/PIAS3/pSTAT3/PD-L1 axis control. This contributes to antiapoptosis, tumor cell proliferation, invasion and migration, as well as immune escape, furthering gastric carcinoma progression and worsening the clinical outcome, especially in the PD-L1(+) group of patients with EBV-associated gastric carcinomas. miR-BART5-5p may, therefore, be amenable to PD-1/PD-L1 immune checkpoint inhibitor therapy.

miRNAs: EBV Mechanism for Escaping Host's Immune Response and Supporting Tumorigenesis

Epstein-Barr virus (EBV) or human herpesvirus 4 (HHV-4) is a ubiquitous human oncogenic virus, and the first human virus found to express microRNAs (miRNAs). Its genome contains two regions encoding more than 40 miRNAs that regulate expression of both viral and human genes. There are numerous evidences that EBV miRNAs impact immune response, affect antigen presentation and recognition, change T- and B-cell communication, drive antibody production during infection, and have a role in cell apoptosis. Moreover, the ability of EBV to induce B-cell transformation and take part in mechanisms of oncogenesis in humans is well known. Although EBV infection is associated with development of various diseases, the role of its miRNAs is still not understood. There is abundant data describing EBV miRNAs in nasopharyngeal carcinoma and several studies that have tried to evaluate their role in gastric carcinoma and lymphoma. This review aims to summarize so far known data about the role of EBV miRNAs in altered regulation of gene expression in human cells in EBV-associated diseases.

CRISPR/Cas9 gene editing: A new therapeutic approach in the treatment of infection and autoimmunity

CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein9) may be viewed as an adaptive bacterial immune system. When a virus infects a bacterium, a fragment of the virus genome is inserted into the CRISPR sequence of the bacterial genome as a memory. When the bacterium becomes infected again with the same virus, an RNA molecule that is a transcript of the memory sequence, directs Cas9, an endonuclease, to the complementary region of the virus genome, and Cas9 disables the virus by a double-strand break. In recent years, studies have shown that by designing synthetic RNA molecules and delivering them along with Cas9 into eukaryotic cells, different regions of the cell's genome can be targeted and manipulated. These findings have drawn much attention to this new technology and it has been shown that CRISPR/Cas9 gene editing can be used to treat some human diseases. These include infectious diseases and autoimmune diseases. In this review article, in addition to a brief overview of the biology of the CRISPR/Cas9 system, we collected the most recent findings on the applications of CRISPR/Cas9 technology for better investigation of the pathogenesis and treatment of viral infections (human immunodeficiency virus infection, hepatitis virus infections, and onco-virus infections), non-viral infections (parasitic, fungal, and bacterial infections), and autoimmune diseases.

Epstein-Barr virus-encoded miR-BART6-3p inhibits cancer cell proliferation through the LOC553103-STMN1 axis

Epstein-Barr virus (EBV) is a tumorigenic virus that can cause various human malignancies such as nasopharyngeal carcinoma (NPC) and gastric cancer (GC). EBV encodes 44 mature micro (mi)RNAs, mostly exhibiting oncogenic properties and promoting cancer progression. However, we have previously found that one EBV-encoded miRNA, namely EBV-miR-BART6-3p, acts as a tumor suppressor by inhibiting metastasis and invasion. Here, we report that EBV-miR-BART6-3p inhibits the proliferation of EBV-associated cancers, NPC, and GC, by targeting and downregulating a long non-coding RNA (lncRNA), LOC553103. Through proteomics analysis, we determined that stathmin (STMN1) is affected by EBV-miR-BART6-3p and LOC553103. Further, via RNA immunoprecipitation and luciferase reporter assay, we confirmed that LOC553103 directly binds and stabilizes the 3'UTR region of STMN1 mRNA. These results indicate that the EBV-miR-BART6-3p/LOC553103/STMN1 axis regulates the expression of cell cycle-associated proteins, which then inhibit EBV-associated tumor cell proliferation. These findings provide potential targets or strategies for novel EBV-related cancer treatments, as well as contributes new insights into the understanding of EBV infection-related carcinogenesis.

Functional analysis of prv-miR-LLT11a encoded by pseudorabies virus

Viral-encoded microRNAs (miRNAs) have vital roles in the regulation of virus replications and host immune responses. The results of previous studies have indicated that miRNA clusters are involved in the replication and virulence of the pseudorabies virus (PRV), which may potentially lead to immune escape or facilitation of PRV replication. This study's previous research revealed that prv-miR-LLT11a was differentially expressed during PRV infection. The present study's results have demonstrated that prv-miR-LLT11a could significantly inhibit PRV replication. It was further determined that SLA-1 was the target gene of prv-miR-LLT11a, and simultaneously, that overexpression of prv-miR-LLT11a could downregulate the mRNA and protein levels of SLA-1 in a dose-independent manner. Furthermore, the present study also observed that prv-miR-LLT11a can downregulate TAP1 expression. Our findings provide a better understanding of the molecular mechanism involved in the effects of prv-miR-LLT11a on SLA-1 and TAP1 as well as its involvement in immune system evasion of PRV.

Epstein-Barr Virus Infection of Oral Squamous Cells

The Epstein-Barr virus (EBV) is a human herpesvirus associated with various cancers. The number of reports that describe infection of EBV in oral squamous carcinoma cells is increasing. However, there is no available in vitro model to study the possible role of EBV in the development of oral squamous cell carcinoma. Herein, we report establishment of a latent EBV infection of well-differentiated HSC1 cells and poorly differentiated SCC25 cells. Viral copy numbers per cell in EBV-infected HSC1 and SCC25 cells are 2 and 5, respectively. Although the EBV copy number was small, spontaneous viral replication was observed in EBV-infected HSC1 cells. Contrarily, infectious viral production was not observed in EBV-infected SCC25 cells, despite containing larger number of EBV genomes. Chemical activation of cells induced expression of viral lytic BZLF1 gene in EBV-infected HSC1 cells, but not in EBV-infected SCC25 cells. EBV infection activated proliferation and migration of HSC1 cells. However, EBV-infection activated migration but not proliferation in SCC25 cells. In conclusion, EBV can infect squamous cells and establish latent infection, but promotion of cell proliferation and of lytic EBV replication may vary depending on stages of cell differentiation. Our model can be used to study the role of EBV in the development of EBV-associated oral squamous cell carcinoma.

The impact of EBV on the epigenetics of gastric carcinoma

EBV is an important human tumor virus and is closely related to the occurrence of a variety of tumors, involving 10% of gastric cancer. In EBV-associated gastric carcinoma (EBVaGC), EBV expresses restrict viral genes including EBV nuclear antigen 1, EBV encoded small RNAs, Bam HI-A rightward transcripts, latent membrane protein 2A and miRNAs. The role of EBV in gastric carcinogenesis has received increasing attention and is considered to be another pathogenic factor in addition to Helicobacter pylori. A typical characteristic of EBVaGC is the extensive methylation of viral and host genome. Combined with other epigenetic mechanisms, EBV infection acts as an epigenetic driver of EBVaGC oncogenesis. In this review we discuss recent findings of EBV effect on host epigenetic alterations in EBVaGC and its role in oncogenic process.

MiR-BART1-5p targets core 2β-1,6-acetylglucosaminyltransferase GCNT3 to inhibit cell proliferation and migration in EBV-associated gastric cancer

GCNT3 (core 2β-1,6-acetylglucosaminyltransferase) is a novel core mucin synthase. It is known that abnormal expression of GCNT3 promotes the progression of several human cancers. However, its relationship with Epstein-Barr virus (EBV) has not been comprehensively studied. We found GCNT3 expression in EBV-associated gastric cancer cells and tissues to be lower than in EBV-negative gastric cancer cells and tissues, and high expression was significantly associated with advanced tumor-lymph node metastasis. Luciferase reporter assay revealed that miR-BART1-5p directly targeted GCNT3. In addition, miR-BART1-5p mimics transfection was observed to reduce cell proliferation and migration, while miR-BART1-5p inhibitor increased cell proliferation and migration following transfection. In conclusion, both miR-BART1-5p and knockdown of GCNT3 inhibited cell proliferation and migration. In addition, EBV may regulate GCNT3 by affecting the NF-kB signaling pathway. E-cadherin, N-cadherin, vimentin, and p-ERK were found to be downstream molecules of the miR-BART1-5p/GCNT3 pathway.

Small RNA analysis provides new insights into cytoplasmic incompatibility in Drosophila melanogaster induced by Wolbachia

Wolbachia is a genus of endosymbiotic bacteria that induce a wide range of effects on their insect hosts. Cytoplasmic incompatibility (CI) is the most common phenotype mediated by Wolbachia and results in embryonic lethality when Wolbachia-infected males mate with uninfected females. Studies have revealed that bacteria can regulate many cellular processes in their hosts using small non-coding RNAs, so we investigated the involvement of small RNAs (sRNAs) in CI. Comparison of sRNA libraries between Wolbachia-infected and uninfected Drosophila melanogaster testes revealed 18 novel microRNAs (miRNAs), of which 12 were expressed specifically in Wolbachia-infected flies and one specifically in Wolbachia-uninfected flies. Furthermore, ten miRNAs showed differential expression, with four upregulated and six downregulated in Wolbachia-infected flies. Of the upregulated miRNAs, nov-miR-12 exhibited the highest upregulation in the testes of D. melanogaster. We then identified pipsqueak (psq) as the target gene of nov-miR-12 with the greatest complementarity in its 3' untranslated region (UTR). Wolbachia infection was correlated with reduced psq expression in D. melanogaster, and luciferase assays demonstrated that nov-miR-12 could downregulate psq through binding to its 3'UTR region. Knockdown of psq in Wolbachia-free fly testes significantly reduced egg hatching rate and mimicked the cellular abnormalities of Wolbachia-induced CI in embryos, including asynchronous nuclear division, chromatin bridging, and chromatin fragmentation. These results suggest that Wolbachia may induce CI in insect hosts by miRNA-mediated changes in host gene expression. Moreover, these findings reveal a potential molecular strategy for elucidating the complex interactions between endosymbionts and their insect hosts, such as Wolbachia-driven CI.

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.

Implication of viral microRNAs in the genesis and diagnosis of Epstein-Barr virus-associated tumors

The Epstein-Barr virus (EBV) is tightly associated with a variety of human tumors, including Burkitt lymphoma and acquired immune deficiency syndrome-related lymphoma of B-cell origin, as well as nasopharyngeal carcinoma and gastric cancer of epithelial origin. The virus latently infects the host cells and expresses proteins and non-coding RNAs to achieve malignancy. MicroRNAs (miRNAs or miRs) are small RNAs consisting of 19-25 nucleotides, which directly bind to the 3'-untranslated region of mRNAs to promote degradation and inhibit translation of mRNAs. EBV-encoded miRs are generated from two regions of the viral genome, within the apoptosis regulator BHRF1 gene locus and near the BamHI A region in a latency type-dependent manner. In addition, EBV-encoded miRs epigenetically regulate the expression of molecules that are effectors of the cell cycle progression, migration, apoptosis and innate immunity, serving a vital role in supporting viral replication and occurrence of EBV-associated tumors. The feasibility of using such miRs as biomarkers for the diagnosis and prognosis of EBV-associated tumors is currently under investigation.

Epstein-Barr Virus and Innate Immunity: Friends or Foes?

Epstein–Barr virus (EBV) successfully persists in the vast majority of adults but causes lymphoid and epithelial malignancies in a small fraction of latently infected individuals. Innate immunity is the first-line antiviral defense, which EBV has to evade in favor of its own replication and infection. EBV uses multiple strategies to perturb innate immune signaling pathways activated by Toll-like, RIG-I-like, NOD-like, and AIM2-like receptors as well as cyclic GMP-AMP synthase. EBV also counteracts interferon production and signaling, including TBK1-IRF3 and JAK-STAT pathways. However, activation of innate immunity also triggers pro-inflammatory response and proteolytic cleavage of caspases, both of which exhibit proviral activity under some circumstances. Pathogenic inflammation also contributes to EBV oncogenesis. EBV activates NFκB signaling and induces pro-inflammatory cytokines. Through differential modulation of the proviral and antiviral roles of caspases and other host factors at different stages of infection, EBV usurps cellular programs for death and inflammation to its own benefits. The outcome of EBV infection is governed by a delicate interplay between innate immunity and EBV. A better understanding of this interplay will instruct prevention and intervention of EBV-associated cancers.

Mechanisms of B-Cell Oncogenesis Induced by Epstein-Barr Virus

Epstein-Barr virus (EBV) is a ubiquitous gammaherpesvirus which asymptomatically infects the majority of the world population. Under immunocompromised conditions, EBV can trigger human cancers of epithelial and lymphoid origin. The oncogenic potential of EBV is demonstrated by in vitro infection and transformation of quiescent B cells into lymphoblastoid cell lines (LCLs). These cell lines, along with primary infection using genetically engineered viral particles coupled with recent technological advancements, have elucidated the underlying mechanisms of EBV-induced B-cell lymphomagenesis.

Roles of Non-coding RNAs During Herpesvirus Infection

Non-coding RNAs (ncRNAs) play essential roles in multiple aspects of the life cycles of herpesviruses and contribute to lifelong persistence of herpesviruses within their respective hosts. In this chapter, we discuss the types of ncRNAs produced by the different herpesvirus families during infection, some of the cellular ncRNAs manipulated by these viruses, and the overall contributions of ncRNAs to the viral life cycle, influence on the host environment, and pathogenesis.

Defining early events of Epstein-Barr virus (EBV) infection in immortalized nasopharyngeal epithelial cells using cell-free EBV infection

Epstein-Barr virus (EBV) infection is strongly associated with nasopharyngeal carcinoma, a common cancer in Southeast Asia and certain regions of Africa. However, the dynamics of EBV episome maintenance in infected nasopharyngeal epithelial (NPE) cells remain largely undefined. Here, we report the establishment of a highly efficient cell-free EBV infection method for NPE cells. By using this method, we have defined some of the dynamic events involved in the early stage of EBV infection in NPE cells. We report, for the first time, a rapid loss of EBV copies from infected NPE cells during the first 12-72 h post-infection. The rate of EBV loss slowed at later stages of infection. Live cell imaging revealed that the freshly infected NPE cells were delayed in entry into mitosis compared with uninfected cells. Freshly infected NPE cells transcribed significantly higher levels of lytic EBV genes BZLF1 and BMRF1 yet significantly lower levels of EBER1/2 than stably infected NPE cells. Notably, there were very low or undetectable levels of protein expressions of EBNA1, LMP1, Zta and Rta in freshly infected NPE cells, whereas EBNA1 and LMP1 proteins were readily detected in stable EBV-infected NPE cells. The kinetics of EBV loss and the differential EBV gene expression profiles between freshly and stably infected NPE cells are in line with the suggestion of epigenetic changes in the EBV genome that affect viral gene expression and the adaptation of host cells to EBV infection to maintain persistent EBV infection in NPE cells.

The roles of EBV-encoded microRNAs in EBV-associated tumors

Epstein-Barr virus (EBV) is believed to be a pathogen causing a number of human cancers, but the pathogenic mechanisms remain unclear. An increasing number of studies have indicated that EBV-encoded microRNAs (EBV miRNAs) are expressed in a latency type- and tumor type-dependent manner, playing important roles in the development and progression of EBV-associated tumors. By targeting one or more genes of the virus and the host, EBV miRNAs are responsible for the deregulation of a variety of viral and host cell biological processes, including viral replication, latency maintenance, immune evasion, cell apoptosis and metabolism, and tumor proliferation and metastasis. In addition, some EBV miRNAs can be used as excellent diagnostic, prognostic and treatment efficacy predictive biomarkers for EBV-associated tumors. More importantly, EBV miRNA-targeting therapeutics have emerged and have been developing rapidly, which may open a new era in the treatment of EBV-associated tumors in the near future.

EBV miR-BART10-3p Promotes Cell Proliferation and Migration by Targeting DKK1

In Epstein-Barr virus (EBV)-infected epithelial cancers, BamHI A rightward transcript (BART) miRNAs are highly expressed. However, only a few target genes of BART miRNAs have been investigated. Our mRNA microarray data showed that DKK1 was markedly down-regulated in EBV-associated gastric carcinoma (EBVaGC) cells. Using luciferase reporter assay we tested whether miR-BART10-3p regulates DKK1 by directly targeting the 3'-UTR of DKK1 mRNA. We observed that miR-BART10-3p transfection decreased DKK1 expression, while an LNA inhibitor of miR-BART10-3p (LNA-miR-BART10-3p(i)) increased DKK1 expression. Furthermore, miR-BART10-3p and siDKK1 promoted cell proliferation and migration. In contrast, transfecting GC cells with LNA-miR-BART10-3p(i) or DKK1 over expression vector suppressed cell proliferation and migration. Our results suggest that miR-BART10-3p may be involved in the tumor progression of EBVaGC by targeting DKK1.

Epstein–Barr Virus and Cancer

Epstein–Barr virus (EBV) contributes to about 1.5% of all cases of human cancer worldwide, and viral genes are expressed in the malignant cells. EBV also very efficiently causes the proliferation of infected human B lymphocytes. The functions of the viral proteins and small RNAs that may contribute to EBV-associated cancers are becoming increasingly clear, and a broader understanding of the sequence variation of the virus genome has helped to interpret their roles. The improved understanding of the mechanisms of these cancers means that there are great opportunities for the early diagnosis of treatable stages of EBV-associated cancers and the use of immunotherapy to target EBV-infected cells or overcome immune evasion. There is also scope for preventing disease by immunization and for developing therapeutic agents that target the EBV gene products expressed in the cancers.

Epstein-Barr virus miR-BART3-3p promotes tumorigenesis by regulating the senescence pathway in gastric cancer

Epstein-Barr virus-associated gastric cancer (EBVaGC) accounts for about 10% of all gastric cancer cases and has unique pathological and molecular characteristics. EBV encodes a large number of microRNAs, which actively participate in the development of EBV-related tumors. Here, we report that EBV-miR-BART3-3p (BART3-3p) promotes gastric cancer cell growth in vitro and in vivo Moreover, BART3-3p inhibits the senescence of gastric cancer cells induced by an oncogene (RAS^G12V) or chemotherapy (irinotecan). LMP1 and EBNA3C encoded by EBV have also been reported to have antisenescence effects; however, in EBVaGC specimens, LMP1 expression is very low, and EBNA3C is not expressed. BART3-3p inhibits senescence of gastric cancer cells in a nude mouse model and inhibits the infiltration of natural killer cells and macrophages in tumor by altering the senescence-associated secretory phenotype (SASP). Mechanistically, BART3-3p directly targeted the tumor suppressor gene TP53 and caused down-regulation of p53's downstream target, p21. Analysis from clinical EBVaGC samples also showed a negative correlation between BART3-3p and TP53 expression. It is well known that mutant oncogene RAS^G12V or chemotherapeutic drugs can induce senescence, and here we show that both RAS^G12V and a chemotherapy drug also can induce BART3-3p expression in EBV-positive gastric cancer cells, forming a feedback loop that keeps the EBVaGC senescence at a low level. Our results suggest that, although TP53 is seldom mutated in EBVaGC, its expression is finely regulated such that EBV-encoded BART3-3p may play an important role by inhibiting the senescence of gastric cancer cells.

Epstein-Barr virus microRNAs regulate B cell receptor signal transduction and lytic reactivation

MicroRNAs (miRNAs) are post-transcriptional regulatory RNAs that can modulate cell signaling and play key roles in cell state transitions. Epstein-Barr virus (EBV) expresses >40 viral miRNAs that manipulate both viral and cellular gene expression patterns and contribute to reprogramming of the host environment during infection. Here, we identified a subset of EBV miRNAs that desensitize cells to B cell receptor (BCR) stimuli, and attenuate the downstream activation of NF-kappaB or AP1-dependent transcription. Bioinformatics and pathway analysis of Ago PAR-CLIP datasets identified multiple EBV miRNA targets related to BCR signal transduction, including GRB2, SOS1, MALT1, RAC1, and INPP5D, which we validated in reporter assays. BCR signaling is critical for B cell activation, proliferation, and differentiation, and for EBV, is linked to reactivation. In functional assays, we demonstrate that EBV miR-BHRF1-2-5p contributes to the growth of latently infected B cells through GRB2 regulation. We further determined that activities of EBV miR-BHRF1-2-5p, EBV miR-BART2-5p, and a cellular miRNA, miR-17-5p, directly regulate virus reactivation triggered by BCR engagement. Our findings provide mechanistic insight into some of the key miRNA interactions impacting the proliferation of latently infected B cells and importantly, governing the latent to lytic switch.

Establishment and characterization of new tumor xenografts and cancer cell lines from EBV-positive nasopharyngeal carcinoma

The lack of representative nasopharyngeal carcinoma (NPC) models has seriously hampered research on EBV carcinogenesis and preclinical studies in NPC. Here we report the successful growth of five NPC patient-derived xenografts (PDXs) from fifty-eight attempts of transplantation of NPC specimens into NOD/SCID mice. The take rates for primary and recurrent NPC are 4.9% and 17.6%, respectively. Successful establishment of a new EBV-positive NPC cell line, NPC43, is achieved directly from patient NPC tissues by including Rho-associated coiled-coil containing kinases inhibitor (Y-27632) in culture medium. Spontaneous lytic reactivation of EBV can be observed in NPC43 upon withdrawal of Y-27632. Whole-exome sequencing (WES) reveals a close similarity in mutational profiles of these NPC PDXs with their corresponding patient NPC. Whole-genome sequencing (WGS) further delineates the genomic landscape and sequences of EBV genomes in these newly established NPC models, which supports their potential use in future studies of NPC.

The lack of appropriate models restricts pre-clinical research for nasopharyngeal carcinoma (NPC). Here the authors report the development and characterization of NPC patient-derived xenografts (PDXs), and EBV positive NPC cell line from patient tumor, and suggest their potential use in future NPC research.