Epstein-Barr viral miRNAs inhibit antiviral CD4+ T cell responses targeting IL-12 and peptide processing

A Critical Role for Epstein-Barr Virus in Primary Effusion Lymphoma

Some human cancers are caused by coinfections with two viruses. Here we focus on primary effusion lymphomas (PEL), which arise from coinfection of B cells with Kaposi's Sarcoma-associated herpesvirus (KSHV) and Epstein-Barr virus (EBV) and often are accompanied by systemic infections with human immunodeficiency virus (HIV). Both KSHV and EBV contribute to this oncogenesis of a rare B cell subset and HIV, by limiting the host immune response to coinfected cells, can too. Some of the mechanisms underlying the lymphomagenesis mediated by two tumor viruses are clear; some remain to be elucidated.

Epstein-Barr virus-mediated immune evasion in tumor promotion

Epstein-Barr virus (EBV) was the first DNA virus identified to be tightly associated with multiple human tumors. It promotes malignant progression of tumors - including related lymphomas, nasopharyngeal carcinoma, and gastric adenocarcinoma - in part by evading surveillance and attack by the host immune system. In this article we review the main molecular mechanisms by which EBV-encoded proteins and RNAs interact with key molecules of the host immune system to inhibit Toll-like receptor (TLR)-nuclear factor κB (NF-κB), retinoic acid-inducible gene I (RIG-I), and interferon (IFN) signaling pathways, affect antigen presentation, prevent the cytotoxic effects of CD8+ effector cells, regulate the tumor microenvironment (TME) and cell metastasis and invasion, and inhibit cell apoptosis. These interactions not only contribute to the persistence of the virus but also provide potential targets for developing new immunotherapy strategies.

Epstein-Barr Infection, Hodgkin's Lymphoma, and the Immune System: Insights into the Molecular Mechanisms Facilitating Immune Evasion

Epstein-Barr virus (EBV) constitutes a very common pathogen and a well-characterized carcinogen. EBV has the ability to establish a chronic latent infection, during which only a subset of the viral genes is expressed. EBV is implicated in multiple malignancies, including Hodgkin's lymphoma (HL). HL mainly affects adolescents and young adults and has an overall favorable prognosis. However, relapsed or refractory disease still poses a therapeutic challenge. EBV does not only induce malignant transformation but also hinders the detection and clearance of the neoplastic cells by the immune system. The proteins and non-coding RNAs expressed in latency IIa, which is associated with HL, employ a variety of mechanisms to target different steps of innate and adaptive immunity, to take advantage of the immunosuppressant effect of immune checkpoints, and to shape the microenvironment to support the survival and proliferation of malignant cells. They suppress the expression or promote the degradation of pattern-recognition receptors, interfere with type I interferon and proinflammatory cytokine mediated signaling, and hinder the effector function of natural killer cells. The processing and presentation of peptides to CD4 and CD8 T cells are also hampered. EBV induces the expression of immune checkpoints, the secretion of immunosuppressive cytokines, and the efflux of regulatory T cells in the tumor microenvironment. The current review provides a comprehensive overview of the molecular mechanisms underlying this complex interplay between EBV and the immune system in HL with focus on clinical data from the pediatric population, which is the key for developing novel, effective therapeutic interventions.

Multiple sclerosis and infection: history, EBV, and the search for mechanism

SUMMARYInfection has long been hypothesized as the cause of multiple sclerosis (MS), and recent evidence for Epstein-Barr virus (EBV) as the trigger of MS is clear and compelling. This clarity contrasts with yet uncertain viral mechanisms and their relation to MS neuroinflammation and demyelination. As long as this disparity persists, it will invigorate virologists, molecular biologists, immunologists, and clinicians to ascertain how EBV potentiates MS onset, and possibly the disease's chronic activity and progression. Such efforts should take advantage of the diverse body of basic and clinical research conducted over nearly two centuries since the first clinical descriptions of MS plaques. Defining the contribution of EBV to the complex and multifactorial pathology of MS will also require suitable experimental models and techniques. Such efforts will broaden our understanding of virus-driven neuroinflammation and specifically inform the development of EBV-targeted therapies for MS management and, ultimately, prevention.

Cutting-Edge Therapy and Immune Escape Mechanisms in EBV-Associated Tumors

Epstein-Barr virus (EBV), the first identified human tumor virus, significantly influences the immune microenvironment of associated cancers. EBV-induced expression of viral antigens by tumor cells triggers immune recognition and elicits a pro-inflammatory response. While mild inflammation may help eliminate malignant cells, intense inflammation can accelerate tumor progression. Moreover, EBV can establish lifelong latency in human hosts, characterized by low immunogenicity of its proteins and noncoding RNAs. This enables tumor cells to evade immune detection and impair immune cell function, disrupting immune homeostasis. Consequently, EBV-associated malignancies pose a considerable public health challenge globally, often complicating the prognosis of cancer patients under conventional treatment. With deeper research into the oncogenic expressions and mechanisms of EBV, novel targeted therapies against EBV are gaining prominence. This review discusses recent advancements in understanding how EBV helps tumor cells evade immune surveillance and induce immune dysfunction. It also examines the clinical potential of targeting EBV-associated tumors, providing fresh perspectives on the mechanisms and therapeutic strategies for these cancers.

Research landmarks on the 60th anniversary of Epstein-Barr virus

Epstein-Barr virus (EBV), the first human oncovirus discovered in 1964, has become a focal point in virology, immunology, and oncology because of its unique biological characteristics and significant role in human diseases. As we commemorate the 60th anniversary of EBV's discovery, it is an opportune moment to reflect on the major advancements in our understanding of this complex virus. In this review, we highlight key milestones in EBV research, including its virion structure and life cycle, interactions with the host immune system, association with EBV-associated diseases, and targeted intervention strategies.

HPV-driven oncogenesis-much more than the E6 and E7 oncoproteins

High-risk human papillomaviruses are well-established drivers of several cancer types including cervical, head and neck, penile as well as anal cancers. While the E6 and E7 viral oncoproteins have proven to be critical for malignant transformation, evidence is also beginning to emerge suggesting that both host pathways and additional viral genes may also be pivotal for malignant transformation. Here, we focus on the role of host APOBEC genes, which have an important role in molecular editing including in the response to the viral DNA and their role in HPV-driven carcinogenesis. Further, we also discuss data developed suggesting the existence of HPV-derived miRNAs in HPV + tumors and their potential role in regulating the host transcriptome. Collectively, while recent advances in these two areas have added complexity to the working model of papillomavirus-induced oncogenesis, these discoveries have also shed a light onto new areas of research that will be required to fully understand the process.

Unveiling the nexus: The tumor microenvironment as a strategic frontier in viral cancers

Viral infections are a significant factor in the etiology of various cancers, with the tumor microenvironment (TME) playing a crucial role in disease progression. This review delves into the complex interactions between viruses and the TME, highlighting how these interactions shape the course of viral cancers. We explore the distinct roles of immune cells, including T-cells, B-cells, macrophages, and dendritic cells, within the TME and their influence on cancer progression. The review also examines how viral oncoproteins manipulate the TME to promote immune evasion and tumor survival. Unraveling these mechanisms highlights the emerging paradigm of targeting the TME as a novel approach to cancer treatment. Our analysis provides insights into the dynamic interplay between viruses and the TME, offering a roadmap for innovative treatments that leverage the unique characteristics of viral cancers.

How Epstein Barr Virus Causes Lymphomas

Since Epstein-Barr Virus (EBV) was isolated 60 years ago, it has been studied clinically, epidemiologically, immunologically, and molecularly in the ensuing years. These combined studies allow a broad mechanistic understanding of how this ubiquitous human pathogen which infects more than 90% of adults can rarely cause multiple types of lymphomas. We survey these findings to provide a coherent description of its oncogenesis.

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.

Epstein-Barr virus: the mastermind of immune chaos

The Epstein-Barr virus (EBV) is a ubiquitous human pathogen linked to various diseases, including infectious mononucleosis and multiple types of cancer. To control and eliminate EBV, the host's immune system deploys its most potent defenses, including pattern recognition receptors, Natural Killer cells, CD8+ and CD4+ T cells, among others. The interaction between EBV and the human immune system is complex and multifaceted. EBV employs a variety of strategies to evade detection and elimination by both the innate and adaptive immune systems. This demonstrates EBV's mastery of navigating the complexities of the immunological landscape. Further investigation into these complex mechanisms is imperative to advance the development of enhanced therapeutic approaches with heightened efficacy. This review provides a comprehensive overview of various mechanisms known to date, employed by the EBV to elude the immune response, while establishing enduring latent infections or instigate its lytic replication.

Epstein-Barr virus-associated lymphomas decoded

Epstein-Barr virus (EBV)-associated lymphomas cover a range of histological B- and T-cell non-Hodgkin and Hodgkin lymphoma subtypes. The role of EBV on B-cell malignant pathogenesis and its impact on the tumour microenvironment are intriguing but incompletely understood. Both the International Consensus Classification (ICC) and 5th Edition of the World Health Organization (WHO-HAEM5) proposals give prominence to the distinct clinical, prognostic, genetic and tumour microenvironmental features of EBV in lymphoproliferative disorders. There have been major advances in our biological understanding, in how to harness features of EBV and its host immune response for targeted therapy, and in using EBV as a method to monitor disease response. In this article, we showcase the latest developments and how they may be integrated to stimulate new and innovative approaches for further lines of investigation and therapy.

Understanding the Mode of Action of a Micro-Immunotherapy Formulation: Pre-Clinical Evidence from the Study of 2LEBV® Active Ingredients

BACKGROUND

Epstein-Barr virus (EBV) is often kept silent and asymptomatic; however, its reactivation induces a chronic and/or recurrent infection that is associated with numerous diseases, including cancer and inflammation-related disorders. As no specific treatment is currently available, the immune factors-based micro-immunotherapy (MI) medicine 2LEBV® could be considered a valuable therapeutic option to sustain the immune system in EBV reactivation.

METHODS

The present work aimed to investigate, for the first time, the effect of 2LEBV® in several in vitro models of uninfected immune-related cells.

RESULTS

2LEBV® displayed phagocytosis-enhancing capabilities in granulocytes. In human peripheral blood mononuclear cells (PBMCs), it increased the intra- and extra-cellular expression of interleukin (IL)-2. Moreover, it modulated the secretion of other cytokines, increasing IL-4, IL-6, and tumor necrosis factor-α levels or lowering other cytokines levels such as IL-9. Finally, 2LEBV® reduced the expression of human leukocyte antigen (HLA)-II in endothelial cells and macrophages.

CONCLUSIONS

Although these data are still preliminary and the chosen models do not consider the underlying EBV-reactivation mechanisms, they still provide a better understanding of the mechanisms of action of 2LEBV®, both at functional and molecular levels. Furthermore, they open perspectives regarding the potential targets of 2LEBV® in its employment as a therapeutic intervention for EBV-associated diseases.

EBV-microRNAs as Potential Biomarkers in EBV-related Fever: A Narrative Review

At present, timely and accurate diagnosis and effective treatment of Epstein- Barr Virus (EBV) infection-associated fever remain a difficult challenge. EBV encodes 44 mature microRNAs (miRNAs) that inhibit viral lysis, adjust inflammatory response, regulate cellular apoptosis, promote tumor genesis and metastasis, and regulate tumor cell metabolism. Herein, we have collected the specific expression data of EBV-miRNAs in EBV-related fevers, including infectious mononucleosis (IM), EBVassociated hemophagocytic lymphohistiocytosis (EBV-HLH), chronic active EBV infection (CAEBV), and EBV-related tumors, and proposed the potential value of EBVmiRNAs as biomarkers to assist in the identification, diagnosis, and prognosis of EBVrelated fever, as well as therapeutic targets for drug development.

MicroRNAs in infectious diseases: potential diagnostic biomarkers and therapeutic targets

MicroRNAs (miRNAs) are conserved, short, non-coding RNAs that play a crucial role in the post-transcriptional regulation of gene expression. They have been implicated in the pathogenesis of cancer and neurological, cardiovascular, and autoimmune diseases. Several recent studies have suggested that miRNAs are key players in regulating the differentiation, maturation, and activation of immune cells, thereby influencing the host immune response to infection. The resultant upregulation or downregulation of miRNAs from infection influences the protein expression of genes responsible for the immune response and can determine the risk of disease progression. Recently, miRNAs have been explored as diagnostic biomarkers and therapeutic targets in various infectious diseases. This review summarizes our current understanding of the role of miRNAs during viral, fungal, bacterial, and parasitic infections from a clinical perspective, including critical functional mechanisms and implications for their potential use as biomarkers and therapeutic targets.

Global and cell type-specific immunological hallmarks of severe dengue progression identified via a systems immunology approach

Severe dengue (SD) is a major cause of morbidity and mortality. To define dengue virus (DENV) target cells and immunological hallmarks of SD progression in children's blood, we integrated two single-cell approaches capturing cellular and viral elements: virus-inclusive single-cell RNA sequencing (viscRNA-Seq 2) and targeted proteomics with secretome analysis and functional assays. Beyond myeloid cells, in natural infection, B cells harbor replicating DENV capable of infecting permissive cells. Alterations in cell type abundance, gene and protein expression and secretion as well as cell-cell communications point towards increased immune cell migration and inflammation in SD progressors. Concurrently, antigen-presenting cells from SD progressors demonstrate intact uptake yet impaired interferon response and antigen processing and presentation signatures, which are partly modulated by DENV. Increased activation, regulation and exhaustion of effector responses and expansion of HLA-DR-expressing adaptive-like NK cells also characterize SD progressors. These findings reveal DENV target cells in human blood and provide insight into SD pathogenesis beyond antibody-mediated enhancement.

Precision medicine in nasopharyngeal carcinoma: comprehensive review of past, present, and future prospect

Nasopharyngeal carcinoma (NPC) is an aggressive malignancy with high propensity for lymphatic spread and distant metastasis. It is prominent as an endemic malignancy in Southern China and Southeast Asia regions. Studies on NPC pathogenesis mechanism in the past decades such as through Epstein Barr Virus (EBV) infection and oncogenic molecular aberrations have explored several potential targets for therapy and diagnosis. The EBV infection introduces oncoviral proteins that consequently hyperactivate many promitotic pathways and block cell-death inducers. EBV infection is so prevalent in NPC patients such that EBV serological tests were used to diagnose and screen NPC patients. On the other hand, as the downstream effectors of oncogenic mechanisms, the promitotic pathways can potentially be exploited therapeutically. With the apparent heterogeneity and distinct molecular aberrations of NPC tumor, the focus has turned into a more personalized treatment in NPC. Herein in this comprehensive review, we depict the current status of screening, diagnosis, treatment, and prevention in NPC. Subsequently, based on the limitations on those aspects, we look at their potential improvements in moving towards the path of precision medicine. The importance of recent advances on the key molecular aberration involved in pathogenesis of NPC for precision medicine progression has also been reported in the present review. Besides, the challenge and future outlook of NPC management will also be highlighted.

Viral miRNA regulation of host gene expression

Viruses have evolved a multitude of mechanisms to combat barriers to productive infection in the host cell. Virally-encoded miRNAs are one such means to regulate host gene expression in ways that benefit the virus lifecycle. miRNAs are small non-coding RNAs that regulate protein expression but do not trigger the adaptive immune response, making them powerful tools encoded by viruses to regulate cellular processes. Diverse viruses encode for miRNAs but little sequence homology exists between miRNAs of different viral species. Despite this, common cellular pathways are targeted for regulation, including apoptosis, immune evasion, cell growth and differentiation. Herein we will highlight the viruses that encode miRNAs and provide mechanistic insight into how viral miRNAs aid in lytic and latent infection by targeting common cellular processes. We also highlight how viral miRNAs can mimic host cell miRNAs as well as how viral miRNAs have evolved to regulate host miRNA expression. These studies dispel the myth that viral miRNAs are subtle regulators of gene expression, and highlight the critical importance of viral miRNAs to the virus lifecycle.

A virus-induced circular RNA maintains latent infection of Kaposi's sarcoma herpesvirus

Non-coding RNAs (ncRNAs) play important roles in host-pathogen interactions; oncogenic viruses like Kaposi's sarcoma herpesvirus (KSHV) employ ncRNAs to establish a latent reservoir and persist for the life of the host. We previously reported that KSHV infection alters a novel class of RNA, circular RNAs (circRNAs). CircRNAs are alternative splicing isoforms and regulate gene expression, but their importance in infection is largely unknown. Here, we showed that a human circRNA, hsa_circ_0001400, is induced by various pathogenic viruses, namely KSHV, Epstein-Barr virus, and human cytomegalovirus. The induction of circRNAs including circ_0001400 by KSHV is co-transcriptionally regulated, likely at splicing. Consistently, screening for circ_0001400-interacting proteins identified a splicing factor, PNISR. Functional studies using infected primary endothelial cells revealed that circ_0001400 inhibits KSHV lytic transcription and virus production. Simultaneously, the circRNA promoted cell cycle, inhibited apoptosis, and induced immune genes. RNA-pull down assays identified transcripts interacting with circ_0001400, including TTI1, which is a component of the pro-growth mTOR complexes. We thus identified a circRNA that is pro-growth and anti-lytic replication. These results support a model in which KSHV induces circ_0001400 expression to maintain latency. Since circ_0001400 is induced by multiple viruses, this novel viral strategy may be widely employed by other viruses.

The role of viruses in HIV-associated lymphomas

Lymphomas are among the most common cancers in people with HIV (PWH). The lymphoma subtypes and pathogenesis of lymphoma in PWH are different from the immunocompetent population. It is well-known that HIV causes severe CD4+ T cell lymphopenia in the absence of antiretroviral therapy (ART); however, the risk of developing certain subtypes of lymphoma remains elevated even in people receiving ART with preserved CD4+ T cells. HIV contributes to lymphomagenesis and causes decreased immune surveillance via T cell depletion and dysregulation, B cell dysregulation, and the potential contribution of HIV-encoded proteins. The oncogenic gammaherpesviruses, Epstein-Barr virus (EBV) and Kaposi sarcoma herpesvirus (KSHV, also known as human herpesvirus 8), are the causative agents in the majority of HIV-associated lymphomas. HIV-associated T cell depletion and dysregulation allows EBV and KSHV to proliferate in infected B cells. Specific EBV- and KSHV-encoded proteins participate in B cell activation, and proliferation leading to B cell transformation. Understanding the distinct pathogenesis of HIV-associated lymphomas affords opportunities to develop therapies that specifically target these unique aspects and improve lymphoma outcomes in PWH. Agents being studied that target the specific roles of HIV, EBV, and KSHV in lymphomagenesis include immunotherapies, targeted agents, and cellular therapies.

A brief overview of the Epstein Barr virus and its association with Burkitt's lymphoma

Epstein Barr virus (EBV) is known as an oncovirus and associates with several human malignancies such as Burkitt's lymphoma, other non-Hodgkin lymphomas, nasopharyngeal carcinoma, Hodgkin's disease, gastric adenocarcinoma, etc. in Burkitt's lymphoma, and the key event is the translocation of MYC gene, that increase of cell survival and aberrant expression of MYC gene. The biology of EBV and its function in the development of Burkitt's lymphoma are discussed in this review

Strategies of Epstein-Barr virus to evade innate antiviral immunity of its human host

Epstein-Barr virus (EBV) is a double-stranded DNA virus of the Herpesviridae family. This virus preferentially infects human primary B cells and persists in the human B cell compartment for a lifetime. Latent EBV infection can lead to the development of different types of lymphomas as well as carcinomas such as nasopharyngeal and gastric carcinoma in immunocompetent and immunocompromised patients. The early phase of viral infection is crucial for EBV to establish latency, but different viral components are sensed by cellular sensors called pattern recognition receptors (PRRs) as the first line of host defense. The efficacy of innate immunity, in particular the interferon-mediated response, is critical to control viral infection initially and to trigger a broad spectrum of specific adaptive immune responses against EBV later. Despite these restrictions, the virus has developed various strategies to evade the immune reaction of its host and to establish its lifelong latency. In its different phases of infection, EBV expresses up to 44 different viral miRNAs. Some act as viral immunoevasins because they have been shown to counteract innate as well as adaptive immune responses. Similarly, certain virally encoded proteins also control antiviral immunity. In this review, we discuss how the virus governs innate immune responses of its host and exploits them to its advantage.

Viral Encoded miRNAs in Tumorigenesis: Theranostic Opportunities in Precision Oncology

About 15% of all human cancers have a viral etiology. Although progress has been made, understanding the viral oncogenesis and associated molecular mechanisms remain complex. The discovery of cellular miRNAs has led to major breakthroughs. Interestingly, viruses have also been discovered to encode their own miRNAs. These viral, small, non-coding miRNAs are also known as viral-miRNAs (v-miRNAs). Although the function of v-miRNAs largely remains to be elucidated, their role in tumorigenesis cannot be ignored. V-miRNAs have also been shown to exploit the cellular machinery to benefit viral replication and survival. Although the discovery of Hepatitis C virus (HCV), and its viral miRNAs, is a work in progress, the existence of HPV-, EBV-, HBV-, MCPyV- and KSHV-encoded miRNA has been documented. V-miRNAs have been shown to target host factors to advance tumorigenesis, evade and suppress the immune system, and deregulate both the cell cycle and the apoptotic machinery. Although the exact mechanisms of v-miRNAs-induced tumorigenesis are still unclear, v-miRNAs are active role-players in tumorigenesis, viral latency and cell transformation. Furthermore, v-miRNAs can function as posttranscriptional gene regulators of both viral and host genes. Thus, it has been proposed that v-miRNAs may serve as diagnostic biomarkers and therapeutic targets for cancers with a viral etiology. Although significant challenges exist in their clinical application, emerging reports demonstrate their potent role in precision medicine. This review will focus on the roles of HPV-, HCV-, EBV-, HBV-, MCPyV-, and KSHV-produced v-miRNAs in tumorigenesis, as effectors in immune evasion, as diagnostic biomarkers and as novel anti-cancer therapeutic targets. Finally, it will discuss the challenges and opportunities associated with v-miRNAs theranostics in precision oncology.

Cytotoxic CD4+ T cells driven by T-cell intrinsic IL-18R/MyD88 signaling predominantly infiltrate Trypanosoma cruzi-infected hearts

Increasing attention has been directed to cytotoxic CD4+ T cells (CD4CTLs) in different pathologies, both in humans and mice. The impact of CD4CTLs in immunity and the mechanisms controlling their generation, however, remain poorly understood. Here, we show that CD4CTLs abundantly differentiate during mouse infection with the intracellular parasite Trypanosoma cruzi. CD4CTLs display parallel kinetics to Th1 cells in the spleen, mediate specific cytotoxicity against cells presenting pathogen-derived antigens and express immunoregulatory and/or exhaustion markers. We demonstrate that CD4CTL absolute numbers and activity are severely reduced in both Myd88-/- and Il18ra-/- mice. Of note, the infection of mixed-bone marrow chimeras revealed that WT but not Myd88-/- cells transcribe the CD4CTL gene signature and that Il18ra-/- and Myd88-/- CD4+ T cells phenocopy each other. Moreover, adoptive transfer of WT CD4+GzB+ T cells to infected Il18ra-/- mice extended their survival. Importantly, cells expressing the CD4CTL phenotype predominate among CD4+ T cells infiltrating the infected mouse cardiac tissue and are increased in the blood of Chagas patients, in which the frequency of CD4CTLs correlates with the severity of cardiomyopathy. Our findings describe CD4CTLs as a major player in immunity to a relevant human pathogen and disclose T-cell intrinsic IL-18R/MyD88 signaling as a key pathway controlling the magnitude of the CD4CTL response.

MicroRNA Regulation of Human Herpesvirus Latency

Herpesviruses are ubiquitous human pathogens. After productive (lytic) infection, all human herpesviruses are able to establish life-long latent infection and reactivate from it. Latent infection entails suppression of viral replication, maintenance of the viral genome in infected cells, and the ability to reactivate. Most human herpesviruses encode microRNAs (miRNAs) that regulate these processes during latency. Meanwhile, cellular miRNAs are hijacked by herpesviruses to participate in these processes. The viral or cellular miRNAs either directly target viral transcripts or indirectly affect viral infection through host pathways. These findings shed light on the molecular determinants that control the lytic-latent switch and may lead to novel therapeutics targeting latent infection. We discuss the multiple mechanisms by which miRNAs regulate herpesvirus latency, focusing on the patterns in these mechanisms.

Immunosuppressive Tumor Microenvironment and Immunotherapy of Epstein–Barr Virus-Associated Malignancies

The Epstein–Barr virus (EBV) can cause different types of cancer in human beings when the virus infects different cell types with various latent patterns. EBV shapes a distinct and immunosuppressive tumor microenvironment (TME) to its benefit by influencing and interacting with different components in the TME. Different EBV-associated malignancies adopt similar but slightly specific immunosuppressive mechanisms by encoding different EBV products to escape both innate and adaptive immune responses. Strategies reversing the immunosuppressive TME of EBV-associated malignancies have been under evaluation in clinical practice. As the interactions among EBV, tumor cells, and TME are intricate, in this review, we mainly discuss the epidemiology of EBV, the life cycle of EBV, the cellular and molecular composition of TME, and a landscape of different EBV-associated malignancies and immunotherapy by targeting the TME.

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

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

Mono a Mano: ZBP1's Love-Hate Relationship with the Kissing Virus

Z-DNA binding protein (ZBP1) very much represents the nuclear option. By initiating inflammatory cell death (ICD), ZBP1 activates host defenses to destroy infectious threats. ZBP1 is also able to induce noninflammatory regulated cell death via apoptosis (RCD). ZBP1 senses the presence of left-handed Z-DNA and Z-RNA (ZNA), including that formed by expression of endogenous retroelements. Viruses such as the Epstein-Barr "kissing virus" inhibit ICD, RCD and other cell death signaling pathways to produce persistent infection. EBV undergoes lytic replication in plasma cells, which maintain detectable levels of basal ZBP1 expression, leading us to suggest a new role for ZBP1 in maintaining EBV latency, one of benefit for both host and virus. We provide an overview of the pathways that are involved in establishing latent infection, including those regulated by MYC and NF-κB. We describe and provide a synthesis of the evidence supporting a role for ZNA in these pathways, highlighting the positive and negative selection of ZNA forming sequences in the EBV genome that underscores the coadaptation of host and virus. Instead of a fight to the death, a state of détente now exists where persistent infection by the virus is tolerated by the host, while disease outcomes such as death, autoimmunity and cancer are minimized. Based on these new insights, we propose actionable therapeutic approaches to unhost EBV.

MicroRNAs are minor constituents of extracellular vesicles that are rarely delivered to target cells

Mammalian cells release different types of vesicles, collectively termed extracellular vesicles (EVs). EVs contain cellular microRNAs (miRNAs) with an apparent potential to deliver their miRNA cargo to recipient cells to affect the stability of individual mRNAs and the cells’ transcriptome. The extent to which miRNAs are exported via the EV route and whether they contribute to cell-cell communication are controversial. To address these issues, we defined multiple properties of EVs and analyzed their capacity to deliver packaged miRNAs into target cells to exert biological functions. We applied well-defined approaches to produce and characterize purified EVs with or without specific viral miRNAs. We found that only a small fraction of EVs carried miRNAs. EVs readily bound to different target cell types, but EVs did not fuse detectably with cellular membranes to deliver their cargo. We engineered EVs to be fusogenic and document their capacity to deliver functional messenger RNAs. Engineered fusogenic EVs, however, did not detectably alter the functionality of cells exposed to miRNA-carrying EVs. These results suggest that EV-borne miRNAs do not act as effectors of cell-to-cell communication.

The majority of metazoan cells release vesicles of different types and origins, such as exosomes and microvesicles, now collectively termed extracellular vesicles (EVs). EVs have gained much attention because they contain microRNAs (miRNAs) and thus could regulate their specific mRNA targets in recipient or acceptor cells that take up EVs. Using a novel fusion assay with superior sensitivity and specificity, we revisited this claim but found no convincing evidence for an efficient functional uptake of EVs in many different cell lines and primary human blood cells. Even EVs engineered to fuse and deliver their miRNA cargo to recipient cells had no measurable effect on target mRNAs in very carefully controlled, quantitative experiments. Our negative results clearly indicate that EVs do not act as vehicles for miRNA-based cell-to-cell communication.

CD4 + T cells are found within endemic Burkitt lymphoma and modulate Burkitt lymphoma precursor cell viability and expression of pathogenically relevant Epstein-Barr virus genes

Endemic Burkitt lymphoma (eBL) is an aggressive B cell cancer characterized by an IgH/c-myc translocation and the harboring of Epstein-Barr virus (EBV). Evidence accumulates that CD4 + T cells might contribute to eBL pathogenesis. Here, we investigate the presence of CD4 + T cells in primary eBL tissue and their potential dichotomous impact on an EBV-infected pre-eBL cell model using ex vivo material and in vitro co-cultures. In addition, we establish a novel method to study the effect of IgH/c-myc translocation in primary B cells by employing a CRISPR/Cas9 knock-in approach to introduce and tag de novo translocation. We unprecedently document that CD4 + T cells are present in primary eBL tumor tissue. Furthermore, we demonstrate that CD4 + T cells on the one hand suppress eBL development by killing pre-eBL cells lacking IgH/c-myc translocation in vitro and on the other hand indirectly promote eBL development by inducing crucial EBV Latency III to Latency I switching in pre-eBL cells. Finally, we show that while the mere presence of an IgH/c-myc translocation does not suffice to escape CD4 + T-cell-mediated killing in vitro, the CD4 + T-cell-mediated suppression of EBV's Latency III program in vivo may allow cells harboring an IgH/c-myc translocation and additional mutations to evade immune control and proliferate by means of deregulated c-myc activity, resulting in neoplasia. Thus, our study highlights the dichotomous effects of CD4 + T cells and the mechanisms involved in eBL pathogenesis, suggests mechanisms of their impact on eBL progression, and provides a novel in vitro model for further investigation of IgH/c-myc translocation.

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

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

Herpesvirus Epigenetic Reprogramming and Oncogenesis

Among all of the known biological carcinogens, Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV) are two of the classical oncogenic herpesviruses known to induce the oncogenic phenotype. Many studies have revealed important functions related to epigenetic alterations of the EBV and KSHV genomes that mediate oncogenesis, but the detailed mechanisms are not fully understood. It is also challenging to fully describe the critical cellular events that drive oncogenesis as well as a comprehensive map of the molecular contributors. This review introduces the roles of epigenetic modifications of these viral genomes, including DNA methylation, histone modification, chromatin remodeling, and noncoding RNA expression, and elucidates potential strategies utilized for inducing oncogenesis by these human gammaherpesviruses.

Deletion of Viral microRNAs in the Oncogenesis of Epstein-Barr Virus-Associated Lymphoma

Epstein–Barr virus (EBV), which encodes >80 genes and nearly 50 non-coding RNAs, is a double-stranded DNA virus. EBV is associated with various types of lymphomas and lymphoproliferative disorders not only of B-cell but also T/NK-cell origin. However, the oncogenic mechanism remains poorly understood, including the EBV receptors expressed on T/NK cells, relationship of EBV with host genes, and epigenetic regulation of EBV and host genes. The roles of host and viral non-coding RNAs during tumorigenesis have been elucidated. EBV encodes at least 49 mature microRNAs (miRNAs), of which 44 are located in BamHI-A rightward transcripts (BARTs) region, and the remaining five are located in BamHI-H rightward fragment 1. BART miRNAs modulate cell differentiation, proliferation, apoptosis, and the cell cycle, and they are considered positive regulators of oncogenesis. We and others have recently reported that EBV-positive lymphomas frequently possess large deletions in BART miRNA clusters, suggesting that some viral miRNAs have suppressive effects on oncogenesis, and that deletion of these miRNAs may aid lymphoma formation.

Immune Escape by Non-coding RNAs of the Epstein Barr Virus

Epstein Barr virus (EBV) is one of the most successful pathogens of humans, persistently colonizing more than 95% of the adult human population. At the same time EBV encodes oncogenes that can readily transform human B cells in culture and threaten healthy virus carriers with lymphomagenesis. Cytotoxic lymphocytes have been identified in experimental models and by primary immunodeficiencies as the main protective immune compartments controlling EBV. EBV has reached a stalemate with these cytotoxic T and innate lymphocytes to ensure persistence in most infected humans. Recent evidence suggests that the non-coding RNAs of the virus contribute to viral immune escape to prevent immune eradication. This knowledge might be used in the future to attenuate EBV for vaccine development against this human tumor virus that was discovered more than 55 years ago.

Bta-miR-101 suppresses BEFV replication via targeting NKRF

MicroRNAs (miRNAs), as a kind of small noncoding RNAs, have been proved to play a regulatory role in virus infection. However, the role and mechanism of cellular miRNAs in bovine transient fever virus (BEFV) infection are largely unknown. In the present study, we found that bta-miR-101 was significantly up-regulated in the Madin-Darby Bovine Kidney (MDBK) cells upon BEFV infection. Notably, bta-miR-101 mimic dramatically inhibited BEFV replication, while bta-miR-101 inhibitor facilitated BEFV replication, suggesting that bta-miR-101 acted as an anti-viral host factor restraining BEFV replication. Subsequently, NF-κB repressing factor (NKRF) was identified as a target gene of bta-miR-101 by dual luciferase reporter assay, and bta-miR-101 mimic significantly down-regulated expression of NKRF, while bta-miR-101 inhibitor up-regulated its expression, respectively. Furthermore, NKRF could induce apoptosis, and favored the replication of BEFV. Finally, bta-miR-101 inhibited BEFV-induced apoptosis via targeting NKRF to suppress virus replication. In general, our study provides a novel mechanism for bta-miR-101 to exert its antiviral function, which provides a theoretical basis for the development of antiviral strategy.

Regulation of the Macroautophagic Machinery, Cellular Differentiation, and Immune Responses by Human Oncogenic γ-Herpesviruses

The human γ-herpesviruses Epstein-Barr virus (EBV) and Kaposi sarcoma-associated herpesvirus (KSHV) encode oncogenes for B cell transformation but are carried by most infected individuals without symptoms. For this purpose, they manipulate the anti-apoptotic pathway macroautophagy, cellular proliferation and apoptosis, as well as immune recognition. The mechanisms and functional relevance of these manipulations are discussed in this review. They allow both viruses to strike the balance between efficient persistence and dissemination in their human hosts without ever being cleared after infection and avoiding pathologies in most of their carriers.

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.

Multiple Viral microRNAs Regulate Interferon Release and Signaling Early during Infection with Epstein-Barr Virus

Epstein-Barr virus (EBV), a human herpesvirus, encodes 44 microRNAs (miRNAs), which regulate many genes with various functions in EBV-infected cells. Multiple target genes of the EBV miRNAs have been identified, some of which play important roles in adaptive antiviral immune responses. Using EBV mutant derivatives, we identified additional roles of viral miRNAs in governing versatile type I interferon (IFN) responses upon infection of human primary mature B cells. We also found that Epstein-Barr virus-encoded small RNAs (EBERs) and LF2, viral genes with previously reported functions in inducing or regulating IFN-I pathways, had negligible or even contrary effects on secreted IFN-α in our model. Data mining and Ago PAR-CLIP experiments uncovered more than a dozen previously uncharacterized, direct cellular targets of EBV miRNA associated with type I IFN pathways. We also identified indirect targets of EBV miRNAs in B cells, such as TRL7 and TLR9, in the prelatent phase of infection. The presence of epigenetically naive, non-CpG methylated viral DNA was essential to induce IFN-α secretion during EBV infection in a TLR9-dependent manner. In a newly established fusion assay, we verified that EBV virions enter a subset of plasmacytoid dendritic cells (pDCs) and determined that these infected pDCs are the primary producers of IFN-α in EBV-infected peripheral blood mononuclear cells. Our findings document that many EBV-encoded miRNAs regulate type I IFN response in newly EBV infected primary human B cells in the prelatent phase of infection and dampen the acute release of IFN-α in pDCs upon their encounter with EBV.IMPORTANCE Acute antiviral functions of all nucleated cells rely on type I interferon (IFN-I) pathways triggered upon viral infection. Host responses encompass the sensing of incoming viruses, the activation of specific transcription factors that induce the transcription of IFN-I genes, the secretion of different IFN-I types and their recognition by the heterodimeric IFN-α/β receptor, the subsequent activation of JAK/STAT signaling pathways, and, finally, the transcription of many IFN-stimulated genes (ISGs). In sum, these cellular functions establish a so-called antiviral state in infected and neighboring cells. To counteract these cellular defense mechanisms, viruses have evolved diverse strategies and encode gene products that target antiviral responses. Among such immune-evasive factors are viral microRNAs (miRNAs) that can interfere with host gene expression. We discovered that multiple miRNAs of Epstein-Barr virus (EBV) control over a dozen cellular genes that contribute to the antiviral states of immune cells, specifically B cells and plasmacytoid dendritic cells (pDCs). We identified the viral DNA genome as the activator of IFN-α and question the role of abundant EBV EBERs, that, contrary to previous reports, do not have an apparent inducing function in the IFN-I pathway early after infection.

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.

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 Role of NK Cells in EBV Infection and EBV-Associated NPC

A vast majority of the population worldwide are asymptomatic carriers of Epstein-Barr Virus (EBV). However, some infected individuals eventually develop EBV-related cancers, including Nasopharyngeal Carcinoma (NPC). NPC is one of the most common EBV-associated epithelial cancers, and is highly prevalent in Southern China and Southeast Asia. While NPC is highly sensitive to radiotherapy and chemotherapy, there is a lack of effective and durable treatment among the 15%–30% of patients who subsequently develop recurrent disease. Natural Killer (NK) cells are natural immune lymphocytes that are innately primed against virus-infected cells and nascent aberrant transformed cells. As EBV is found in both virally infected and cancer cells, it is of interest to examine the NK cells’ role in both EBV infection and EBV-associated NPC. Herein, we review the current understanding of how EBV-infected cells are cleared by NK cells, and how EBV can evade NK cell-mediated elimination in the context of type II latency in NPC. Next, we summarize the current literature about NPC and NK cell biology. Finally, we discuss the translational potential of NK cells in NPC. This information will deepen our understanding of host immune interactions with EBV-associated NPC and facilitate development of more effective NK-mediated therapies for NPC treatment.

Herpesvirus latency

Herpesviruses infect virtually all humans and establish lifelong latency and reactivate to infect other humans. Latency requires multiple functions: maintaining the herpesvirus genome in the nuclei of cells; partitioning the viral genome to daughter cells in dividing cells; avoiding recognition by the immune system by limiting protein expression; producing noncoding viral RNAs (including microRNAs) to suppress lytic gene expression or regulate cellular protein expression that could otherwise eliminate virus-infected cells; modulating the epigenetic state of the viral genome to regulate viral gene expression; and reactivating to infect other hosts. Licensed antivirals inhibit virus replication, but do not affect latency. Understanding of the mechanisms of latency is leading to novel approaches to destroy latently infected cells or inhibit reactivation from latency.

Immunology of EBV-Related Lymphoproliferative Disease in HIV-Positive Individuals

Epstein-Bar virus (EBV) can directly cause lymphoproliferative disease (LPD), including AIDS-defining lymphomas such as Burkitt’s lymphoma and other non-Hodgkin lymphomas (NHL), as well as human immunodeficiency virus (HIV)-related Hodgkin lymphoma (HL). The prevalence of EBV in HL and NHL is elevated in HIV-positive individuals compared with the general population. Rates of incidence of AIDS-defining cancers have been declining in HIV-infected individuals since initiation of combination anti-retroviral therapy (cART) use in 1996. However, HIV-infected persons remain at an increased risk of cancers related to infections with oncogenic viruses. Proposed pathogenic mechanisms of HIV-related cancers include decreased immune surveillance, decreased ability to suppress infection-related oncogenic processes and a state of chronic inflammation marked by alteration of the cytokine profile and expanded numbers of cytotoxic T lymphocytes with down-regulated co-stimulatory molecules and increased expression of markers of senescence in the setting of treated HIV infection. Here we discuss the cooperation of EBV-infected B cell- and environment-associated factors that may contribute to EBV-related lymphomagenesis in HIV-infected individuals. Environment-derived lymphomagenic factors include impaired host adaptive and innate immune surveillance, cytokine dysregulation and a pro-inflammatory state observed in the setting of chronic, cART-treated HIV infection. B cell factors include distinctive EBV latency patterns and host protein expression in HIV-associated LPD, as well as B cell-stimulating factors derived from HIV infection. We review the future directions for expanding therapeutic approaches in targeting the viral and immune components of EBV LPD pathogenesis.

Non-Coding RNAs: Strategy for Viruses' Offensive

The awareness of viruses as a constant threat for human public health is a matter of fact and in this resides the need of understanding the mechanisms they use to trick the host. Viral non-coding RNAs are gaining much value and interest for the potential impact played in host gene regulation, acting as fine tuners of host cellular defense mechanisms. The implicit importance of v-ncRNAs resides first in the limited genomes size of viruses carrying only strictly necessary genomic sequences. The other crucial and appealing characteristic of v-ncRNAs is the non-immunogenicity, making them the perfect expedient to be used in the never-ending virus-host war. In this review, we wish to examine how DNA and RNA viruses have evolved a common strategy and which the crucial host pathways are targeted through v-ncRNAs in order to grant and facilitate their life cycle.

Epstein-Barr Virus Mediated Signaling in Nasopharyngeal Carcinoma Carcinogenesis

Nasopharyngeal carcinoma (NPC) is one of the most common tumors occurring in China and Southeast Asia. Etiology of NPC seems to be complex and involves many determinants, one of which is Epstein-Barr virus (EBV) infection. Although evidence demonstrates that EBV infection plays a key role in NPC carcinogenesis, the exact relationship between EBV and dysregulation of signaling pathways in NPC needs to be clarified. This review focuses on the interplay between EBV and NPC cells and the corresponding signaling pathways, which are modulated by EBV oncoproteins and non-coding RNAs. These altered signaling pathways could be critical for the initiation and progression of NPC.

Viral non-coding RNAs: Stealth strategies in the tug-of-war between humans and herpesviruses

Oncogenic DNA viruses establish lifelong infections in humans, and they cause cancers, often in immunocompromised patients, despite anti-viral immune surveillance targeted against viral antigens. High-throughput sequencing techniques allowed the field to identify novel viral non-coding RNAs (ncRNAs). ncRNAs are ideal factors for DNA viruses to exploit; they are non-immunogenic to T cells, thus viral ncRNAs can manipulate host cells without evoking adaptive immune responses. Viral ncRNAs may still trigger the host innate immune response, but many viruses encode decoys/inhibitors to counter-act and evade recognition. In addition, ncRNAs can be secreted to the extracellular space and influence adjacent cells to create a pro-viral microenvironment. In this review, we present recent progress in understanding interactions between oncoviruses and ncRNAs including small and long ncRNAs, microRNAs, and recently identified viral circular RNAs. In addition, potential clinical applications for ncRNA will be discussed. Extracellular ncRNAs are suggested to be diagnostic and prognostic biomarkers and, with the realization of the importance of viral ncRNAs in tumorigenesis, approaches to target critical viral ncRNAs are emerging. Further understanding of viral utilization of ncRNAs will advance anti-viral therapeutics beyond conventional medication and vaccination.

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.

Role of Viral and Host microRNAs in Immune Regulation of Epstein-Barr Virus-Associated Diseases

Epstein-Barr virus (EBV) is an oncogenic human herpes virus that was discovered in 1964. Viral non-coding RNAs, such as BamHI-A rightward fragment-derived microRNAs (BART miRNAs) or BamHI-H rightward fragment 1-derived miRNAs (BHRF1 miRNA) in EBV-infected cells have been recently reported. Host miRNAs are also upregulated upon EBV infection. Viral and host miRNAs are important in maintaining viral infection and evasion of host immunity. Although miRNAs in EBV-infected cells often promote cell proliferation by targeting apoptosis or cell cycle, this review focuses on the regulation of the recognition of the host immune system. This review firstly describes the location and organization of two clusters of viral miRNAs, then describes evasion from host immune surveillance systems by modulating viral gene expression or inhibiting innate and acquired immunity by viral miRNAs as well as host miRNAs. Another topic is the enigmatic depletion of viral miRNAs in several types of EBV-infected tumor cells. Finally, this review introduces the strong correlation of nasopharyngeal cancer cases with a newly identified single nucleotide polymorphism that enhances BART miRNA promoter activity.