Epstein-Barr virus infection in immortalized nasopharyngeal epithelial cells: regulation of infection and phenotypic characterization

Targeted eradication of EBV-positive cancer cells by CRISPR/dCas9-mediated EBV reactivation in combination with ganciclovir

Epstein-Barr virus (EBV) is a ubiquitous human tumor virus that establishes lifelong, persistent infections in B cells. The presence of EBV in cancer cells presents an opportunity to target these cells by reactivating the virus from latency. In this study, we developed a novel approach for EBV reactivation termed clustered regularly interspaced short palindromic repeats (CRISPR)/dCas9-mediated EBV reactivation (CMER) strategy. Using modified CRISPR-associated protein 9 (dCas9) fused with VP64, we designed 10 single guide RNAs (sgRNAs) to target and activate the EBV immediate-early gene promoter. In Akata Burkitt lymphoma cells, 9 out of 10 CMER sgRNAs effectively reactivated EBV. Among these, CMER sgRNA-5 triggered robust reactivation across various cell types, including lymphoma, gastric cancer, and nasopharyngeal carcinoma cells. Importantly, the combination of CMER and ganciclovir selectively eliminated EBV-positive cells, regardless of their cell origin. These findings indicate that targeted virus reactivation by CMER, combined with nucleoside analog therapy, holds promise for EBV-associated cancer treatment.

IMPORTANCE

This study explores a novel strategy called clustered regularly interspaced short palindromic repeats (CRISPR)/dCas9-mediated Epstein-Barr virus (EBV) reactivation (CMER) to reactivate the Epstein-Barr virus in cancer cells. EBV is associated with various cancers, and reactivating EBV from latency offers a potential therapeutic strategy. We utilized an enzymatically inactive CRISPR-associated protein 9 (dCas9) fused with VP64 and designed 10 single guide RNAs to target the EBV immediate-early gene promoter. Nine of these sgRNAs effectively reactivated EBV in Burkitt lymphoma cells, with CMER sgRNA-5 demonstrating strong reactivation across different cancer cell types. Combining CMER with ganciclovir selectively eliminated EBV-positive cells, showing promise for EBV-associated cancer treatment.

Interferon-induced transmembrane protein-1 competitively blocks Ephrin receptor A2-mediated Epstein-Barr virus entry into epithelial cells

Epstein-Barr virus (EBV) can infect both B cells and epithelial cells (ECs), causing diseases such as mononucleosis and cancer. It enters ECs via Ephrin receptor A2 (EphA2). The function of interferon-induced transmembrane protein-1 (IFITM1) in EBV infection of ECs remains elusive. Here we report that IFITM1 inhibits EphA2-mediated EBV entry into ECs. RNA-sequencing and clinical sample analysis show reduced IFITM1 in EBV-positive ECs and a negative correlation between IFITM1 level and EBV copy number. IFITM1 depletion increases EBV infection and vice versa. Exogenous soluble IFITM1 effectively prevents EBV infection in vitro and in vivo. Furthermore, three-dimensional structure prediction and site-directed mutagenesis demonstrate that IFITM1 interacts with EphA2 via its two specific residues, competitively blocking EphA2 binding to EBV glycoproteins. Finally, YTHDF3, an m6A reader, suppresses IFITM1 via degradation-related DEAD-box protein 5 (DDX5). Thus, this study underscores IFITM1's crucial role in blocking EphA2-mediated EBV entry into ECs, indicating its potential in preventing EBV infection.

EBV-induced T-cell responses in EBV-specific and nonspecific cancers

Epstein-Barr virus (EBV) is a ubiquitous human tumor virus associated with various malignancies, including B-lymphoma, NK and T-lymphoma, and epithelial carcinoma. It infects B lymphocytes and epithelial cells within the oropharynx and establishes persistent infection in memory B cells. With a balanced virus-host interaction, most individuals carry EBV asymptomatically because of the lifelong surveillance by T cell immunity against EBV. A stable anti-EBV T cell repertoire is maintained in memory at high frequency in the blood throughout persistent EBV infection. Patients with impaired T cell immunity are more likely to develop life-threatening lymphoproliferative disorders, highlighting the critical role of T cells in achieving the EBV-host balance. Recent studies reveal that the EBV protein, LMP1, triggers robust T-cell responses against multiple tumor-associated antigens (TAAs) in B cells. Additionally, EBV-specific T cells have been identified in EBV-unrelated cancers, raising questions about their role in antitumor immunity. Herein, we summarize T-cell responses in EBV-related cancers, considering latency patterns, host immune status, and factors like human leukocyte antigen (HLA) susceptibility, which may affect immune outcomes. We discuss EBV-induced TAA-specific T cell responses and explore the potential roles of EBV-specific T cell subsets in tumor microenvironments. We also describe T-cell immunotherapy strategies that harness EBV antigens, ranging from EBV-specific T cells to T cell receptor-engineered T cells. Lastly, we discuss the involvement of γδ T-cells in EBV infection and associated diseases, aiming to elucidate the comprehensive interplay between EBV and T-cell immunity.

[Epstein-Barr virus (Herpesviridae: Lymphocryptovirus) types 1 and 2 and other viral markers in patients with nasopharyngeal carcinoma in two geographically and ethnically distinct regions of Russia]

INTRODUCTION

The discovery of two types of Epstein-Barr virus (EBV) (EBV-1 and EBV-2) that have different biological properties stimulated the search for neoplasms associated with each type of the virus. The aim of the work is to study the nature of the association of nasopharyngeal cancer (NPC) with EBV-1 and EBV-2, serological activity for each viral type and the concentration of EBV DNA in the blood plasma of two gender, age and ethnic groups of NPC patients that represent geographically and climatically different regions of Russia,.

MATERIALS AND METHODS

In the blood plasma of patients with NPC and other non- EBV associated tumors of oral cavity (OTOCEBV-) from the North Caucasian (NCFD) and Central (CFD) Federal Districts of Russia, the types of EBV and the concentration of viral DNA were determined using respectively «nested» and real time PCR; titers of IgG and IgA antibodies to viral capsid antigen (VCA) were measured in indirect immunofluorescence assay.

RESULTS

The blood plasma samples testing showed that NPC and OTOCEBV- patients were infected with both types of EBV in approximately equal proportions. In two groups of NPC patients infected with one of the virus types only, EBV-1 or EBV-2, respectively, no statistically significant differences were found between the geometric mean values of IgG and IgA anti-EBV antibody titers and viral DNA concentrations in blood plasma. The distribution of virus types was not affected by either patient gender or ethnogeographic origin. The difference was found only between age groups: EBV-2 dominated in NPC patients up to 60 years, and EBV-1 was prevalent in patients over 60 years.

CONCLUSION

The lack of the predominance of one of EBV types in NPC patients that are the representatives of different ethnic groups from geographically and climatically different regions, suggests that none of these factors play an important role in the NPC carcinogenesis. Evidently, each type of EBV, EBV-1 or EBV-2, if the necessary conditions arise, are able to exhibit its oncogenic potential to initiate tumor development.

Therapeutic strategy for oncovirus-mediated oral cancer: A comprehensive review

Oral cancer is a neoplastic disorder of the oral cavities, including the lips, tongue, buccal mucosa, and lower and upper gums. Oral cancer assessment entails a multistep process that requires deep knowledge of the molecular networks involved in its progression and development. Preventive measures including public awareness of risk factors and improving public behaviors are necessary, and screening techniques should be encouraged to enable early detection of malignant lesions. Herpes simplex virus (HSV), human papillomavirus (HPV), Epstein-Barr virus (EBV), and Kaposi sarcoma-associated herpesvirus (KSHV) are associated with other premalignant and carcinogenic conditions leading to oral cancer. Oncogenic viruses induce chromosomal rearrangements; activate signal transduction pathways via growth factor receptors, cytoplasmic protein kinases, and DNA binding transcription factors; modulate cell cycle proteins, and inhibit apoptotic pathways. In this review, we present an up-to-date overview on the use of nanomaterials for regulating viral proteins and oral cancer as well as the role of phytocompounds on oral cancer. The targets linking oncoviral proteins and oral carcinogenesis were also discussed.

Contribution of Epstein–Barr Virus Lytic Proteins to Cancer Hallmarks and Implications from Other Oncoviruses

Epstein–Barr virus (EBV) is a prevalent human gamma-herpesvirus that infects the majority of the adult population worldwide and is associated with several lymphoid and epithelial malignancies. EBV displays a biphasic life cycle, namely, latent and lytic replication cycles, expressing a diversity of viral proteins. Among the EBV proteins being expressed during both latent and lytic cycles, the oncogenic roles of EBV lytic proteins are largely uncharacterized. In this review, the established contributions of EBV lytic proteins in tumorigenesis are summarized according to the cancer hallmarks displayed. We further postulate the oncogenic properties of several EBV lytic proteins by comparing the evolutionary conserved oncogenic mechanisms in other herpesviruses and oncoviruses.

Latent membrane protein 1 and macrophage-derived TNFα synergistically activate and mobilize invadopodia to drive invasion of nasopharyngeal carcinoma

Invadopodia are actin-rich membrane protrusions that digest the matrix barrier during cancer metastasis. Since the discovery of invadopodia, they have been visualized as localized and dot-like structures in different types of cancer cells on top of a 2D matrix. In this investigation of Epstein-Barr virus (EBV)-associated nasopharyngeal carcinoma (NPC), a highly invasive cancer frequently accompanied by neck lymph node and distal organ metastases, we revealed a new form of invadopodium with mobilizing features. Integration of live-cell imaging and molecular assays revealed the interaction of macrophage-released TNFα and EBV-encoded latent membrane protein 1 (LMP1) in co-activating the EGFR/Src/ERK/cortactin and Cdc42/N-WASP signaling axes for mobilizing the invadopodia with lateral movements. This phenomenon endows the invadopodia with massive degradative power, visualized as a shift of focal dot-like digestion patterns on a 2D gelatin to a dendrite-like digestion pattern. Notably, single stimulation of either LMP1 or TNFα could only enhance the number of ordinary dot-like invadopodia, suggesting that the EBV infection sensitizes the NPC cells to form mobilizing invadopodia when encountering a TNFα-rich tumor microenvironment. This study unveils the interplay of EBV and stromal components in driving the invasive potential of NPC via unleashing the propulsion of invadopodia in overcoming matrix hurdles. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

EBV miRNAs BART11 and BART17-3p promote immune escape through the enhancer-mediated transcription of PD-L1

Epstein-Barr virus (EBV) is reportedly the first identified human tumor virus, and is closely related to the occurrence and development of nasopharyngeal carcinoma (NPC), gastric carcinoma (GC), and several lymphomas. PD-L1 expression is elevated in EBV-positive NPC and GC tissues; however, the specific mechanisms underlying the EBV-dependent promotion of PD-L1 expression to induce immune escape warrant clarification. EBV encodes 44 mature miRNAs. In this study, we find that EBV-miR-BART11 and EBV-miR-BART17-3p upregulate the expression of PD-L1 in EBV-associated NPC and GC. Furthermore, EBV-miR-BART11 targets FOXP1, EBV-miR-BART17-3p targets PBRM1, and FOXP1 and PBRM1 bind to the enhancer region of PD-L1 to inhibit its expression. Therefore, EBV-miR-BART11 and EBV-miR-BART17-3p inhibit FOXP1 and PBRM1, respectively, and enhance the transcription of PD-L1 (CD274, http://www.ncbi.nlm.nih.gov/gene/29126), resulting in the promotion of tumor immune escape, which provides insights into potential targets for EBV-related tumor immunotherapy.

Epstein-Barr virus (EBV)-encoded latent genes are reported to regulate PD-L1 expression to promote immune escape. Here, the authors show that EBV-encoded miRNAs EBV-miR-BART11 and EBV-miR-BART17-3p upregulate PD-L1 expression in nasopharyngeal carcinoma and gastric cancer by targeting FOXP1 and PBRM1.

Downregulation of SLC27A6 by DNA Hypermethylation Promotes Proliferation but Suppresses Metastasis of Nasopharyngeal Carcinoma Through Modulating Lipid Metabolism

Lipid is the building block and an important source of energy, contributing to the malignant behavior of tumor cells. Recent studies suggested that lipid droplets (LDs) accumulations were associated with nasopharyngeal carcinoma (NPC) progression. Solute carrier family 27 member 6 (SLC27A6) mediates the cellular uptake of long-chain fatty acid (LCFA), a necessary lipid component. However, the functions of SLC27A6 in NPC remain unknown. Here, we found a significant reduction of SLC27A6 mRNA in NPC tissues compared with normal nasopharyngeal epithelia (NNE). The promoter methylation ratio of SLC27A6 was greater in NPC than in non-cancerous tissues. The demethylation reagent 5-aza-2'-deoxycytidine (5-aza-dC) remarkably restored the mRNA expression of SLC27A6, suggesting that this gene was downregulated in NPC owing to DNA promoter hypermethylation. Furthermore, SLC27A6 overexpression level in NPC cell lines led to significant suppression of cell proliferation, clonogenicity in vitro, and tumorigenesis in vivo. Higher SLC27A6 expression, on the other hand, promoted NPC cell migration and invasion. In particular, re-expression of SLC27A6 faciliated epithelial-mesenchymal transition (EMT) signals in xenograft tumors. Furthermore, we observed that SLC27A6 enhanced the intracellular amount of triglyceride (TG) and total cholesterol (T-CHO) in NPC cells, contributing to lipid biosynthesis and increasing metastatic potential. Notably, the mRNA level of SLC27A6 was positively correlated with cancer stem cell (CSC) markers, CD24 and CD44. In summary, DNA promoter hypermethylation downregulated the expression of SLC27A6. Furthermore, re-expression of SLC27A6 inhibited the growth capacity of NPC cells but strengthened the CSC markers. Our findings revealed the dual role of SLC27A6 in NPC and shed novel light on the link between lipid metabolism and CSC maintenance.

Epstein-Barr Virus-Associated Gastric Cancer: Old Entity with New Relevance

Gastric cancer (GC) represents a major public health issue worldwide, being the fifth most common cancer and one of the leading causes of death by cancer. In 2014, The Cancer Genome Atlas (TCGA) established that tumors positive for Epstein-Barr virus (EBV) are considered a specific subtype of GC (EBVaGC). Several meta-analyses have shown that EBVaGC represents almost 10% of all gastric cancer worldwide, with small differences in the geographic distribution. This tumor subtype has a high potential of being clinically relevant and studies have shown that it has specific features, a better prognosis, and increased overall survival. In this review, we summarize some of the most frequent aspects of EBVaGC, including the specific features of this GC subtype, data regarding the potential steps of EBVaGC carcinogenesis, and perspectives on treatment opportunities.

GDF10 inhibits cell proliferation and epithelial-mesenchymal transition in nasopharyngeal carcinoma by the transforming growth factor-β/Smad and NF-κB pathways

Growth differentiation factor-10 (GDF10) belongs to a member of the transforming growth factor-β (TGF-β) superfamily. Dysfunction of the TGF-β pathway can lead to carcinoma progression. Previous studies have shown that GDF10 acts as a tumor suppressor gene in some cancers. However, the molecular mechanisms of the association between GDF10 and cell functions in nasopharyngeal carcinoma (NPC) remain unclear. In this study, the expression and methylation levels of GDF10 were studied in human subjects and cell lines. Furthermore, overexpression of GDF10 was used to explore its biological function and potential mechanism in NPC cell lines. GDF10 was downregulated in NPC owing to its aberrant promoter methylation. After treatment with 5-aza-2'-deoxycytidine, the expression of GDF10 in NPC cells was reversed. We also confirmed that the overexpression of GDF10 significantly inhibited cell proliferation and tumor growth both in vitro and in vivo, respectively. Additionally, GDF10 overexpression in NPC cells attenuated migration and invasion and inhibited epithelial-to-mesenchymal transition with a decrease in nuclear Smad2 and NF-κB protein accumulation. GDF10 was silenced owing to its promoter hypermethylation, and it might originally act as a functional tumor suppressor via TGF-β/Smad and NF-κB signaling pathways in NPC.

High-Risk Human Papillomavirus and Epstein-Barr Virus Coinfection: A Potential Role in Head and Neck Carcinogenesis

Simple Summary

A subset of carcinomas that arise in the head and neck region show a viral etiology. In fact, a subgroup of oropharyngeal cancers are caused by some types of human papillomavirus (HPV), so-called high-risk (HR)-HPVs, whereas undifferentiated nasopharyngeal carcinomas are etiologically related to Epstein–Barr virus (EBV). However, studies have reported the presence of both HR-HPV and EBV in some types of head and neck cancers. In this review, we discuss the potential contribution and role of HR-HPV/EBV coinfection in head and neck carcinogenesis, as well as the mechanisms that are potentially involved. In addition, HR-HPV/EBV interaction models are proposed.

Abstract

High-risk human papillomaviruses (HR-HPVs) and Epstein–Barr virus (EBV) are recognized oncogenic viruses involved in the development of a subset of head and neck cancers (HNCs). HR-HPVs are etiologically associated with a subset of oropharyngeal carcinomas (OPCs), whereas EBV is a recognized etiological agent of undifferentiated nasopharyngeal carcinomas (NPCs). In this review, we address epidemiological and mechanistic evidence regarding a potential cooperation between HR-HPV and EBV for HNC development. Considering that: (1) both HR-HPV and EBV infections require cofactors for carcinogenesis; and (2) both oropharyngeal and oral epithelium can be directly exposed to carcinogens, such as alcohol or tobacco smoke, we hypothesize possible interaction mechanisms. The epidemiological and experimental evidence suggests that HR-HPV/EBV cooperation for developing a subset of HNCs is plausible and warrants further investigation.

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.

Nondestructive quantification of single-cell nuclear and cytoplasmic mechanical properties based on large whole-cell deformation

The mechanical properties of cell nuclei have been recognized to reflect and modulate important cell behaviors such as migration and cancer cell malignant tendency. However, these nuclear properties are difficult to characterize accurately using conventional measurement methods, which are often based on probing or deforming local sites over a nuclear region. The corresponding results are sensitive to the measurement position, and they are not decoupled from the cytoplasmic properties. Microfluidics is widely recognized as a promising technique for bioassay and phenotyping. In this report, we develop a simple and nondestructive approach for the single-cell quantification of nuclear elasticity based on microfluidics by considering different deformation levels of a live cell captured along a confining microchannel. We apply two inlet pressure levels to drive the flow of human nasopharyngeal epithelial cells (NP460) and human nasopharyngeal cancerous cells (NPC43) into the microchannels. A model considering the essential intracellular components (cytoplasm and nucleus) for describing the mechanics of a cell deforming along the confining microchannel is used to back-calculate the cytoplasmic and nuclear properties. On the other hand, we also apply a widely used chemical nucleus extraction technique to examine its possible effects (e.g., reduced nuclear modulus and reduced lamin A/C expression). To determine if the decoupled nuclear properties are representative of cancer-related attributes, we classify the NP460 and NPC43 cells using the decoupled physical properties as classification factors, resulting in an accuracy of 79.1% and a cell-type specificity exceeding 74%. It should be mentioned that the cells can be recollected at the device outlet after the nondestructive measurement. Hence, the reported cell elasticity measurement can be combined with downstream genetic and biochemical assays for general cell research and cancer diagnostic applications.

The Role of EBV-Induced Hypermethylation in Gastric Cancer Tumorigenesis

Epstein–Barr-virus-associated Gastric Cancer (EBVaGC) comprises approximately 10% of global gastric cancers and is known to be the most hypermethylated of all tumor types. EBV infection has been shown to directly induce the hypermethylation of both the host and viral genome following initial infection of gastric epithelial cells. Many studies have been completed in an attempt to identify genes that frequently become hypermethylated and therefore significant pathways that become silenced to promote tumorigenesis. It is clear that EBV-induced hypermethylation silences key tumor suppressor genes, cell cycle genes and cellular differentiation factors to promote a highly proliferative and poorly differentiated cell population. EBV infection has been shown to induce methylation in additional malignancies including Nasopharyngeal Carcinoma and Burkitt’s Lymphoma though not to the same level as in EBVaGC. Lastly, some genes silenced in EBVaGC are common to other heavily methylated tumors such as colorectal and breast tumors; however, some genes are unique to EBVaGC and can provide insights into the major pathways involved in tumorigenesis.

Epithelial cell infection by Epstein-Barr virus

Epstein-Barr Virus (EBV) is etiologically associated with multiple human malignancies including Burkitt lymphoma and Hodgkin disease as well as nasopharyngeal and gastric carcinoma. Entry of EBV into target cells is essential for virus to cause disease and is mediated by multiple viral envelope glycoproteins and cell surface associated receptors. The target cells of EBV include B cells and epithelial cells. The nature and mechanism of EBV entry into these cell types are different, requiring different glycoprotein complexes to bind to specific receptors on the target cells. Compared to the B cell entry mechanism, the overall mechanism of EBV entry into epithelial cells is less well known. Numerous receptors have been implicated in this process and may also be involved in additional processes of EBV entry, transport, and replication. This review summarizes EBV glycoproteins, host receptors, signal molecules and transport machinery that are being used in the epithelial cell entry process and also provides a broad view for related herpesvirus entry mechanisms.

Epstein-Barr virus is absent in gastric superficial neoplastic lesions

Epstein-Barr virus (EBV) has been associated with about 9% of all gastric carcinomas, but its role in gastric carcinogenesis remains unclear since there is lack of evidence of EBV presence in pre-neoplastic lesions of gastric mucosa. This study intends to determine the prevalence of EBV in gastric dysplasia and superficial neoplasia to clarify whether EBV infection is an early or late event in gastric cancer development. This retrospective study included a total of 242 gastric lesions from 199 consecutive patients who were referred for endoscopic resection. The histological classification of lesions includes 137 low- and high-grade dysplasia and 105 superficial carcinomas. EBV infection was investigated by EBER-ISH. Results showed that EBV was not detected in any epithelial cells of any case with dysplasia or superficial carcinomas, although we observed the presence of a small number of EBV-infected lymphocytes in 2.1% of all lesions. These results showed that EBV is not present in gastric dysplasia neither in superficial carcinomas suggesting that EBV carcinogenesis is a late event in well/moderately differentiated gastric carcinogenesis.

F factor plasmid-mediated Epstein-Barr virus genome introduction establishes an EBV positive NPC cell model

Background

Most Epstein-Barr virus (EBV)-positive cells lose the EBV episomes upon prolonged propagation.

Purpose

The purposes of this study were to establish a simple cell model for nasopharyngeal carcinoma (NPC) research by introducing a plasmid with the EBV genome into NPC cells and then to investigate the resulting changes in malignant biological behaviour and NPC-associated signalling pathways.

Methods

HONE1 NPC cells were transfected with F-factor plasmids including the EBV genome (HONE1-EBV cells). Then cell proliferation, migration, cell cycle distribution and apoptosis were evaluated in vitro by using CCK8, transwell and flow cytometry assays respectively. EBV-encoded proteins and cell signal tranducting proteins were detected by western blot assays. EBV-encoded RNAs were detected by in situ hybridization. EBV particles were assayed by transmission electron microscope (TEM). The morphology of cells were detected by immunofluorescence assays for alpha-tubulin.

Results

Latent membrane protein 1 (LMP1), latent membrane protein 2A (LMP2A), Epstein-Barr nuclear antigen 1 (EBNA1) and EBV-encoded small RNAs (EBERs) were successfully expressed in HONE1-EBV cells. No EBV particles were founded by TEM. Introduction of the EBV genome significantly promoted proliferation, cell cycle progression and migration and inhibited apoptosis in HONE1 cells. Immunofluorescence assays showed that the morphology of HONE1-EBV cells changed into spindle. Furthermore, EBV genome introduction significantly inhibited the JAK/STAT signalling pathway, while it activated the PI3K-AKT and NF-κB signalling pathways in HONE1 cells.

Conclusion

These findings suggest that F-factor plasmid-mediated EBV genome introduction was successful in constructing an EBV positive cell model, which showed deteriorated biological behavior and activated NPC-associated signalling pathways. This model can serve as a good tool for studying EBV in NPC, but the subtle differences in cancer-associated pathways must be considered.

EBV infection is associated with histone bivalent switch modifications in squamous epithelial cells

Epstein-Barr virus (EBV) induces histone modifications to regulate signaling pathways involved in EBV-driven tumorigenesis. To date, the regulatory mechanisms involved are poorly understood. In this study, we show that EBV infection of epithelial cells is associated with aberrant histone modification; specifically, aberrant histone bivalent switches by reducing the transcriptional activation histone mark (H3K4me3) and enhancing the suppressive mark (H3K27me3) at the promoter regions of a panel of DNA damage repair members in immortalized nasopharyngeal epithelial (NPE) cells. Sixteen DNA damage repair family members in base excision repair (BER), homologous recombination, nonhomologous end-joining, and mismatch repair (MMR) pathways showed aberrant histone bivalent switches. Among this panel of DNA repair members, MLH1, involved in MMR, was significantly down-regulated in EBV-infected NPE cells through aberrant histone bivalent switches in a promoter hypermethylation-independent manner. Functionally, expression of MLH1 correlated closely with cisplatin sensitivity both in vitro and in vivo. Moreover, seven BER members with aberrant histone bivalent switches in the EBV-positive NPE cell lines were significantly enriched in pathway analysis in a promoter hypermethylation-independent manner. This observation is further validated by their down-regulation in EBV-infected NPE cells. The in vitro comet and apurinic/apyrimidinic site assays further confirmed that EBV-infected NPE cells showed reduced DNA damage repair responsiveness. These findings suggest the importance of EBV-associated aberrant histone bivalent switch in host cells in subsequent suppression of DNA damage repair genes in a methylation-independent manner.

EBV(LMP1)-induced metabolic reprogramming inhibits necroptosis through the hypermethylation of the RIP3 promoter

EBV infection is a recognized epigenetic driver of carcinogenesis. We previously showed that EBV could protect cancer cells from TNF-induced necroptosis. This study aims to explore the epigenetic mechanisms allowing cancer cells with EBV infection to escape from RIP3-dependent necroptosis.

Methods: Data from the TCGA database were used to evaluate the prognostic value of RIP3 promoter methylation and its expression. Western blotting, real-time PCR, and immunochemistry were conducted to investigate the relationship between LMP1 and RIP3 in cell lines and NPC tissues. BSP, MSP and hMeDIP assays were used to examine the methylation level. Induction of necroptosis was detected by cell viability assay, p-MLKL, and Sytox Green staining.

Results: RIP3 promoter hypermethylation is an independent prognostic factor of poorer disease-free and overall survival in HNSCC patients, respectively. RIP3 is down-regulated in NPC (a subtype of HNSCC). EBV(LMP1) suppresses RIP3 expression by hypermethylation of the RIP3 promoter. RIP3 protein expression was inversely correlated with LMP1 expression in NPC tissues. Restoring RIP3 expression in EBV(LMP1)-positive cells inhibits xenograft tumor growth. The accumulation of fumarate and reduction of α-KG in EBV(LMP1)-positive cells led to RIP3 silencing due to the inactivation of TETs. Decreased FH activity caused fumarate accumulation, which might be associated with its acetylation. Incubating cells with fumarate protected NPC cells from TNF-induced necroptosis.

Conclusion: These results demonstrate a pathway by which EBV(LMP1)-associated metabolite changes inhibited necroptosis signaling by DNA methylation, and shed light on the mechanism underlying EBV-related carcinogenesis, which may provide new options for cancer diagnosis and therapy.

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.

mTORC2-mediated PDHE1α nuclear translocation links EBV-LMP1 reprogrammed glucose metabolism to cancer metastasis in nasopharyngeal carcinoma

EBV infection of preinvasive nasopharyngeal epithelium is believed to be an initiation step during pathogenesis of nasopharyngeal carcinoma (NPC), but the mechanisms remain poorly understood. Here we report a novel mechanism driving NPC metastasis through the EBV-encoded LMP1-mediated metabolic reprogramming, via activation of IGF1-mTORC2 signaling and nuclear acetylation of the Snail promoter by the PDHE1α, an enzyme involved in glucose metabolism. Mechanistically, EBV-LMP1 increases the cellular secretion of IGF1 which promotes phosphorylation of IGF1R to activate mTORC2/AKT signaling linking glucose metabolism to cell motility. LMP1 expression facilitates translocation of mitochondrial PDHE1α into the nucleus in a phosphorylation-dependent manner at Ser²⁹³ residue. Functionally, nuclear PDHE1α promotes H3K9 acetylation on the Snail promoter to enhance cell motility, thereby driving cancer metastasis. Importantly, the IGF1/mTORC2/PDHE1α/Snail axis correlates significantly with disease progression and poor prognosis in NPC patients. This study highlights the functional importance of IGF1-mTORC2-PDHE1α signaling mediated by EBV-LMP1 in NPC pathogenesis.

Inhibition of Epstein-Barr Virus Replication in Human Papillomavirus-Immortalized Keratinocytes

Epstein-Barr virus (EBV) is implicated in the pathogenesis of human papillomavirus (HPV)-associated oropharyngeal squamous cell carcinoma (OSCC). EBV-associated cancers harbor a latent EBV infection characterized by a lack of viral replication and the expression of viral oncogenes. Cellular changes promoted by HPV are comparable to those shown to facilitate EBV latency, though whether HPV-positive cells support a latent EBV infection has not been demonstrated. Using a model of direct EBV infection into HPV16-immortalized tonsillar cells grown in organotypic raft culture, we showed robust EBV replication in HPV-negative rafts but little to no replication in HPV-immortalized rafts. The reduced EBV replication was independent of immortalization, as human telomerase-immortalized normal oral keratinocytes supported robust EBV replication. Furthermore, we observed reduced EBV lytic gene expression and increased expression of EBER1, a noncoding RNA highly expressed in latently infected cells, in the presence of HPV. The use of human foreskin keratinocyte rafts expressing the HPV16 E6 and/or E7 oncogene(s) (HPV E6 and E7 rafts) showed that E7 was sufficient to reduce EBV replication. EBV replication is dependent upon epithelial differentiation and the differentiation-dependent expression of the transcription factors KLF4 and PRDM1. While KLF4 and PRDM1 levels were unaltered, the expression levels of KLF4 transcriptional targets, including late differentiation markers, were reduced in HPV E6 and E7 rafts compared to their levels in parental rafts. However, the HPV E7-mediated block in EBV replication correlated with delayed expression of early differentiation markers. Overall, this study reveals an HPV16-mediated block in EBV replication, through E7, that may facilitate EBV latency and long-term persistence in the tumor context.IMPORTANCE Using a model examining the establishment of EBV infection in HPV-immortalized tissues, we showed an HPV-induced interruption of the normal EBV life cycle reminiscent of a latent EBV infection. Our data support the notion that a persistent EBV epithelial infection depends upon preexisting cellular alterations and suggest the ability of HPV to promote such changes. More importantly, these findings introduce a model for how EBV coinfection may influence HPV-positive (HPV-pos) OSCC pathogenesis. Latently EBV-infected epithelial cells, as well as other EBV-associated head-and-neck carcinomas, exhibit oncogenic phenotypes commonly seen in HPV-pos OSCC. Therefore, an HPV-induced shift in the EBV life cycle toward latency would not only facilitate EBV persistence but also provide additional viral oncogene expression, which can contribute to the rapid progression of HPV-pos OSCC. These findings provide a step toward defining a role for EBV as a cofactor in HPV-positive oropharyngeal tumors.

Molecular features and translational outlook for Epstein-Barr virus-associated gastric cancer

Epstein-Barr Virus (EBV) was the first discovered human tumor virus and is the etiological agent of B cell lymphomas and also epithelial cancers. Indeed, nearly 10% of gastric cancers worldwide are EBV-positive and display unique molecular, epigenetic, and clinicopathological features. EBV-positive gastric cancers display the highest rate of host genome methylation of all tumor types studied and harbor recurrent mutations activating PI3Kα, silencing ARID1A, and amplifying PD-L1. While EBV infection of B cells can be studied efficiently, de novo epithelial cell infection is much more difficult. We propose that new culture models including 3D-based gastric organoids and xenografts can bring new insight into EBV-induced gastric carcinogenesis and will lead to improved precision medicine-based therapies for patients with EBV-positive gastric cancer.

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

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

Taurine exhibits an apoptosis-inducing effect on human nasopharyngeal carcinoma cells through PTEN/Akt pathways in vitro

Nasopharyngeal carcinoma (NPC) is a distinctive type of head and neck malignancy with a high incidence in southern China. Previous studies have confirmed that taurine shows an anti-cancer effect on a variety of human tumors by inhibiting cell proliferation and inducing apoptosis. However, the underlying molecular mechanism of its anti-cancer effect on NPC is not well understood. To clarify these anti-cancer mechanisms, we performed cell viability and colony formation assays. Apoptotic cells were quantified by flow cytometry. The expression levels of apoptosis-related proteins were evaluated by Western blot. The results showed that taurine markedly inhibited cell proliferation in NPC cells, but only slightly in an immortalized normal nasopharyngeal cell line. Taurine suppressed colony formation and induced apoptosis of NPC cell lines in a dose-dependent manner. Furthermore, taurine increased the active form of caspase-9/3 in a dose-dependent manner. Taurine down-regulated the anti-apoptotic protein Bcl-xL and up-regulated the pro-apoptotic protein Bax and GRP78, a major endoplasmic reticulum (ER) chaperone. These results suggest the involvement of mitochondrial and ER stress signaling in apoptosis. In addition, taurine increased the levels of PTEN (phosphatase and tensin homolog deleted on chromosome 10) and p53, and reduced phosphorylated Akt (protein kinase B). In conclusion, taurine may inhibit cell proliferation and induce apoptosis in NPC through PTEN activation with concomitant Akt inactivation.

The Dynamic Roles of TGF-β Signalling in EBV-Associated Cancers

The transforming growth factor-β (TGF-β) signalling pathway plays a critical role in carcinogenesis. It has a biphasic action by initially suppressing tumorigenesis but promoting tumour progression in the later stages of disease. Consequently, the functional outcome of TGF-β signalling is strongly context-dependent and is influenced by various factors including cell, tissue and cancer type. Disruption of this pathway can be caused by various means, including genetic and environmental factors. A number of human viruses have been shown to modulate TGF-β signalling during tumorigenesis. In this review, we describe how this pathway is perturbed in Epstein-Barr virus (EBV)-associated cancers and how EBV interferes with TGF-β signal transduction. The role of TGF-β in regulating the EBV life cycle in tumour cells is also discussed.

Air-Liquid Interface Method To Study Epstein-Barr Virus Pathogenesis in Nasopharyngeal Epithelial Cells

Epstein-Barr virus (EBV) is a ubiquitous gammaherpesvirus that establishes a latent reservoir in peripheral B-lymphocytes with sporadic reactivation. EBV also infects epithelial cells, predominantly resulting in a lytic infection, which may contribute to EBV transmission from saliva. In the nasopharynx, EBV infection can lead to the clonal expansion of a latently infected cell and the development of nasopharyngeal carcinoma (NPC). The mechanisms governing EBV pathogenesis in nasopharyngeal epithelium are largely unknown. An advanced understanding would depend on a physiologically relevant culture model of polarized airway epithelium. The recent application of the organotypic raft culture in keratinocytes has demonstrated great promise for the use of polarized cultures in the study of EBV permissive replication. In this study, the adaptation of an air-liquid interface (ALI) culture method using transwell membranes was explored in an EBV-infected NPC cell line. In the EBV-infected NPC HK1 cell line, ALI culture resulted in the completion of EBV reactivation, with global induction of the lytic cascade, replication of EBV genomes, and production of infectious progeny virus. We propose that the ALI culture method can be widely adopted as a physiologically relevant model to study EBV pathogenesis in polarized nasal epithelial cells.

IMPORTANCE

Lifting adherent cells to the air-liquid interface (ALI) is a method conventionally used to culture airway epithelial cells into polarized apical and basolateral surfaces. Reactivation of Epstein-Barr virus (EBV) from monolayer epithelial cultures is sometimes abortive, which may be attributed to the lack of authentic reactivation triggers that occur in stratified epithelium in vivo In the present work, the ALI culture method was applied to study EBV reactivation in nasopharyngeal epithelial cells. The ALI culture of an EBV-infected cell line yielded high titers and can be dissected by a variety of molecular virology assays that measure induction of the EBV lytic cascade and EBV genome replication and assembly. EBV infection of polarized cultures of primary epithelial cells can be challenging and can have variable efficiencies. However, the use of the ALI method with established EBV-infected cell lines offers a readily available and reproducible approach for the study of EBV permissive replication in polarized epithelia.

Role of Epstein-Barr Virus in the Pathogenesis of Head and Neck Cancers and Its Potential as an Immunotherapeutic Target

The role of Epstein-Barr virus (EBV) infection in the development and progression of tumor cells has been described in various cancers. Etiologically, EBV is a causative agent in certain variants of head and neck cancers such as nasopharyngeal cancer. Proteins expressed by the EVB genome are involved in invoking and perpetuating the oncogenic properties of the virus. However, these protein products were also identified as important targets for therapeutic research in the past decades, particularly within the context of immunotherapy. The adoptive transfer of EBV-targeted T-cells as well as the development of EBV vaccines has opened newer lines of research to conceptualize novel therapeutic approaches toward the disease. This review addresses the most important aspects of the association of EBV with head and neck cancers from an immunological perspective. It also aims to highlight the current and future prospects of enhanced EBV-targeted immunotherapies.

Serum long non-coding RNAs MALAT1, AFAP1-AS1 and AL359062 as diagnostic and prognostic biomarkers for nasopharyngeal carcinoma

Circulating RNAs in serum, plasma or other body liquid have emerged as useful and highly promising biomarkers for noninvasive diagnostic application. Herein, we aimed to establish a serum long non-coding RNAs (lncRNAs) signature for diagnosing nasopharyngeal carcinoma (NPC). In this study, we recruited a cohort of 101 NPC patients, 20 patients with chronic nasopharyngitis (CN), 20 EBV carriers (EC) and 101 healthy controls. qRT-PCR was performed with NPC cells and serum samples to screen a pool of 38 NPC-related lncRNAs obtained from the LncRNADisease database. A profile of three circulating lncRNAs (MALAT1, AFAP1-AS1 and AL359062) was established for NPC diagnosis. By Receiver Operating Characteristic (ROC) curve analysis, this three-lncRNA signature showed high accuracy in discriminating NPC from healthy controls (AUC = 0.918), CN (AUC = 0.893) or EC (AUC = 0.877). Furthermore, high levels of these three lncRNAs were closely related to advanced NPC tumor node metastasis stages and EBV infection. Serum levels of these three lncRNAs declined significantly in patients after therapy. Our present study indicates that circulating MALAT1, AFAP1-AS1 and AL359062 may represent novel serum biomarkers for NPC diagnosis and prognostic prediction after treatment.

Epstein-Barr virus infection and nasopharyngeal carcinoma

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

The Immunomodulatory Capacity of an Epstein-Barr Virus Abortive Lytic Cycle: Potential Contribution to Viral Tumorigenesis

Epstein-Barr virus (EBV) is characterized by a bipartite life cycle in which latent and lytic stages are alternated. Latency is compatible with long-lasting persistency within the infected host, while lytic expression, preferentially found in oropharyngeal epithelial tissue, is thought to favor host-to-host viral dissemination. The clinical importance of EBV relates to its association with cancer, which we think is mainly a consequence of the latency/persistency mechanisms. However, studies in murine models of tumorigenesis/lymphomagenesis indicate that the lytic cycle also contributes to cancer formation. Indeed, EBV lytic expression is often observed in established cell lines and tumor biopsies. Within the lytic cycle EBV expresses a handful of immunomodulatory (BCRF1, BARF1, BNLF2A, BGLF5 & BILF1) and anti-apoptotic (BHRF1 & BALF1) proteins. In this review, we discuss the evidence supporting an abortive lytic cycle in which these lytic genes are expressed, and how the immunomodulatory mechanisms of EBV and related herpesviruses Kaposi Sarcoma herpesvirus (KSHV) and human cytomegalovirus (HCMV) result in paracrine signals that feed tumor cells. An abortive lytic cycle would reconcile the need of lytic expression for viral tumorigenesis without relaying in a complete cycle that would induce cell lysis to release the newly formed infective viral particles.

New Insights from Elucidating the Role of LMP1 in Nasopharyngeal Carcinoma

Latent membrane protein 1 (LMP1) is an Epstein-Barr virus (EBV) oncogenic protein that has no intrinsic enzymatic activity or sequence homology to cellular or viral proteins. The oncogenic potential of LMP1 has been ascribed to pleiotropic signaling properties initiated through protein-protein interactions in cytosolic membrane compartments, but the effects of LMP1 extend to nuclear and extracellular processes. Although LMP1 is one of the latent genes required for EBV-immortalization of B cells, the biology of LMP1 in the pathogenesis of the epithelial cancer nasopharyngeal carcinoma (NPC) is more complex. NPC is prevalent in specific regions of the world with high incidence in southeast China. The epidemiology and time interval from seroconversion to NPC onset in adults would suggest the involvement of multiple risk factors that complement the establishment of a latent and persistent EBV infection. The contribution of LMP1 to EBV pathogenesis in polarized epithelia has only recently begun to be elucidated. Furthermore, the LMP1 gene has emerged as one of the most divergent sequences in the EBV genome. This review will discuss the significance of recent advances in NPC research from elucidating LMP1 function in epithelial cells and lessons that could be learned from mining LMP1 sequence diversity.

Modulation of the tumor microenvironment by Epstein-Barr virus latent membrane protein 1 in nasopharyngeal carcinoma

Latent membrane protein 1 (LMP1) is a primary oncogene encoded by the Epstein‐Barr virus, and various portions of LMP1 are detected in nasopharyngeal carcinoma (NPC) tumor cells. LMP1 has been extensively studied since the discovery of its transforming property in 1985. LMP1 promotes cancer cell growth during NPC development and facilitates the interaction of cancer cells with surrounding stromal cells for invasion, angiogenesis, and immune modulation. LMP1 is detected in 100% of pre‐invasive NPC tumors and in approximately 50% of advanced NPC tumors. Moreover, a small population of LMP1‐expressing cells in advanced NPC tumor tissue is proposed to orchestrate NPC tumor tissue maintenance and development through cancer stem cells and progenitor cells. Recent studies suggest that LMP1 activity shifts according to tumor development stage, but it still has a pivotal role during all stages of NPC development.

Latent Membrane Protein 1 Is a Novel Determinant of Epstein-Barr Virus Genome Persistence and Reactivation

Latent membrane protein 1 (LMP1) is a constitutively active oncogenic signaling protein encoded by Epstein-Barr virus (EBV). Despite monoclonal infection in cases of nasopharyngeal carcinoma (NPC), it has been difficult to reconcile the heterogeneous LMP1 protein levels detected in tumor cells. The LMP1 protein is a pleiotropic signaling protein with oncogenic potential. Findings from this study are consistent with the hypothesis that LMP1 has a role distinct from that of oncogenesis that facilitates the viral life cycle by promoting an unstable but productive infection in differentiating epithelia.

Epstein-Barr virus (EBV) is a ubiquitous gammaherpesvirus that persistently infects humans, with nearly 95% seropositivity in adults. Infection in differentiating epithelia is permissive, but EBV-associated nasopharyngeal carcinoma (NPC) tumors harbor a clonal and nonproductive latent infection. However, in explanted NPC cultures and epithelial cell lines, episomal EBV genomes are frequently lost. The resulting unstable infection has hampered efforts to study the determinants of EBV persistence and latency in epithelial oncogenesis. The EBV nuclear antigen 1 (EBNA1) protein is required for tethering EBV episomes to cellular DNA and for mitotic segregation to daughter cells. Expression of EBNA1 does not ensure faithful partitioning of EBV episomes or replicons, suggesting that additional regulatory mechanisms have yet to be elucidated. The EBV latent membrane protein 1 (LMP1) is an oncogenic signaling protein expressed in latent and lytic cycles. This study identified that LMP1 contributes to the loss of EBV genomes in latently infected cells and promotes differentiation-induced lytic replication in a polarized air-liquid interface (ALI) culture model. Deletion of LMP1 in recombinantly infected 293 cells promoted the retention of EBV genomes in passaged cells, which was in part localized to a conserved PXQXT motif in the C-terminal signaling domain (CTAR1). Additionally, knockdown of LMP1 in the recombinantly infected NPC cell line HK1 resulted in decreased induction of lytic proteins and infectious EBV titers. These findings are consistent with the hypothesis that in epithelial infections, regulation of LMP1 mechanisms may be a determinant of infection outcome and a potential risk factor for EBV persistence in preneoplastic cells.

IMPORTANCE Latent membrane protein 1 (LMP1) is a constitutively active oncogenic signaling protein encoded by Epstein-Barr virus (EBV). Despite monoclonal infection in cases of nasopharyngeal carcinoma (NPC), it has been difficult to reconcile the heterogeneous LMP1 protein levels detected in tumor cells. The LMP1 protein is a pleiotropic signaling protein with oncogenic potential. Findings from this study are consistent with the hypothesis that LMP1 has a role distinct from that of oncogenesis that facilitates the viral life cycle by promoting an unstable but productive infection in differentiating epithelia.

RERG suppresses cell proliferation, migration and angiogenesis through ERK/NF-κB signaling pathway in nasopharyngeal carcinoma

Background

Nasopharyngeal carcinoma (NPC) is a malignancy of the head and neck that is prevalent in Southeast Asia and southern China. Recent studies in epigenetics suggest that DNA methylation plays a pivotal role in the onset and progression of cancer. Combining the methyl-DNA binding domain capture technique and cDNA microarray analysis, we identified a unique hypermethylated gene, RERG (Ras-like estrogen-regulated growth inhibitor), that was down-regulated in NPC tissues. RERG is a tumor suppressor gene that was first reported in breast cancer. However, the functions of RERG are largely unknown in other tumor types.

Methods

RERG expression was assessed in human subjects (NPC primary tissues and non-cancer tissues) and cell lines (NPC cell lines and an immortalized epithelial cell line NP460). Further, we investigated the methylation rate of RERG in both human subject and cell lines. 5-Aza-2’-deoxycytidine (Aza) or combined with trichostatin A (TSA) were treated to three NPC cell lines (HK1, C666-1 and HK1_EBV). In addition, the role of RERG in NPC cells and its underlying mechanisms were explored by overexpression of RERG in NPC cell lines.

Results

RERG was significantly down-regulated in NPC cancer nests compared to normal nasopharyngeal epithelium cells. Furthermore, the RERG promoter was frequently methylated in NPC tissues and cell lines. The RERG methylation rate yielded an area under the curve (AUC) of receiver operating characteristic (ROC) curve was 0.897 (95%CI: 0.818–0.976). The down-regulation of RERG was restored in NPC cells treated with Aza and TSA. In addition, ectopic expression of RERG in NPC cell lines resulted in a significant suppression of cell proliferation, clonogenicity, migration and invasion. RERG-overexpressing cells showed significantly slower growth and less angiogenesis in tumor xenografts in nude mice. RERG suppressed the ERK/NF-κB signaling pathway and inhibited tumor growth and angiogenesis with down-regulation of MMPs and IL8 in tumors of nude mouse xenografts.

Conclusions

Our results suggest that RERG is frequently silenced by promoter CpG methylation in NPC, and acts as a functional tumor suppressor by suppressing the ERK/NF-κB signaling pathway. These findings support the potential use of RERG as a novel molecular target in NPC therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-017-0554-9) contains supplementary material, which is available to authorized users.

Comprehensive genomic profiling of different subtypes of nasopharyngeal carcinoma reveals similarities and differences to guide targeted therapy

BACKGROUND

To date, no targeted therapy has been approved for nasopharyngeal carcinoma (NPC), and this underscores the need for an in-depth understanding of clinically relevant genomic alterations (CRGAs).

METHODS

Comprehensive genomic profiling was performed for 190 NPC patients, including 20 patients with nasopharyngeal adenocarcinoma (NPAC), 62 patients with nasopharyngeal squamous cell carcinoma (NPSCC), and 108 patients with nasopharyngeal undifferentiated carcinoma (NPUC). The associations of genes and pathways with subtypes, Epstein-Barr virus (EBV) infections, and the tumor mutation burden (TMB) were statistically evaluated.

RESULTS

Although the overall rates of genomic alterations were similar, the 3 NPC subtypes exhibited different mutational landscapes. Notably, mutations in a proven-treatable target gene, isocitrate dehydrogenase 2 (IDH2), were significantly associated with NPUC but not with NPAC or NPSCC. The top 5 ranked CRGAs included CDKN2A (29%), IDH2 (16%), SMARCB1 (7%), PIK3CA (6%), and NF1 (5%) in NPUC; CDKN2A (27%), PIK3CA (23%), FBXW7 (11%), PTEN (11%), and EGFR (8%) in NPSCC; and CDKN2A (20%), KRAS (15%), CCND1 (10%), MAP3K1 (10%), and NOTCH1 (10%) in NPAC. The incidence of EBV infections significantly correlated with the subtypes and with TP53, CDKN2A, and CDKN2B. The TMB status correlated with the subtypes and with LRP1B, FBXW7, and PIK3CA mutations as well as DNA repair, phosphoinositide 3-kinase/mammalian target of rapamycin, and mitogen-activated protein kinase pathways.

CONCLUSIONS

These results indicate that different NPC subtypes harbor different CRGAs. Both EBV infections and the TMB are associated with the NPC subtypes as well as the alterations of individual genes and pathways. The high frequency of IDH2 mutations in NPUC may facilitate potential targeted therapy and will ultimately point to new therapeutic strategies. Cancer 2017;123:3628-37. © 2017 American Cancer Society.

Epstein-Barr virus (EBV)-associated epithelial and non-epithelial lesions of the oral cavity

Epstein–Barr virus (EBV) is known to be associated with the development of malignant lymphoma and lymphoproliferative disorders (LPDs) in immunocompromised patients. EBV, a B-lymphotropic gamma-herpesvirus, causes infectious mononucleosis and oral hairy leukoplakia, as well as various pathological types of lymphoid malignancy. Furthermore, EBV is associated with epithelial malignancies such as nasopharyngeal carcinoma (NPC), salivary gland tumor, gastric carcinoma and breast carcinoma. In terms of oral disease, there have been several reports of EBV-related oral squamous cell carcinoma (OSCC) worldwide. However, the role of EBV in tumorigenesis of human oral epithelial or lymphoid tissue is unclear. This review summarizes EBV-related epithelial and non-epithelial tumors or tumor-like lesions of the oral cavity. In addition, we describe EBV latent genes and their expression in normal epithelium, inflamed gingiva, epithelial dysplasia and SCC, as well as considering LPDs (MTX- and age-related) and DLBCLs of the oral cavity.

The potent tumor suppressor miR-497 inhibits cancer phenotypes in nasopharyngeal carcinoma by targeting ANLN and HSPA4L

Nasopharyngeal carcinoma (NPC) is a malignancy with poor prognosis that is endemic to Southeast Asia. We profiled microRNAs (miRNAs) of NPCs using microarrays and confirmed the results by quantitative RT-PCR. The results revealed that seven miRNAs were significantly up-regulated, and six miRNAs were down-regulated, in NPC tissues relative to noncancerous nasopharyngeal epithelia (NNE). Expression of miR-497 was also significantly reduced in the plasma of NPC patients relative to the plasma of noncancerous control patients. The concordant down-regulation of miR-497 in tissues and plasma suggested that miR-497 could be used as a diagnostic biomarker for NPC. Functional analyses of the effect of miR-497 on cancer phenotypes revealed that transfection of miR-497 mimic into NPC cells suppressed cell growth and migration and induced apoptosis. Subcutaneous xenografts of transfected cells in nude mice demonstrated that miR-497 significantly inhibited tumor growth. Two potential targets of miR-497, ANLN (anillin, actin-binding protein) and HSPA4L (heat shock 70 kDa protein 4–like), both of which were overexpressed in NPC tissues, were negatively regulated by miR-497 mimic in NPC cell lines. Silencing of ANLN and HSPA4L suppressed cell proliferation and migration and induced apoptosis in NPC cells. Our findings indicate that miR-497 is a potent tumor suppressor that inhibits cancer phenotypes by targeting ANLN and HSPA4L in NPC.

Epstein-Barr virus LMP1 induces focal adhesions and epithelial cell migration through effects on integrin-α5 and N-cadherin

Epstein-Barr virus (EBV) is a γ-herpesvirus associated with human epithelial and B-cell malignancies. The EBV latent membrane protein (LMP) 1 is expressed in nasopharyngeal carcinoma (NPC) and promotes oncogenic intracellular signaling mechanisms. LMP1 also promotes a pro-migratory phenotype through potential effects on cell surface proteins, as expression of LMP1 induces an epithelial-mesenchymal transition (EMT) in epithelial cell lines. In this study, LMP1 was examined for potential effects on cadherin and integrin surface interactions, and assessed for biological effects on adhesion and motility to fibronectin. Expression of LMP1 in the non-tumorigenic epithelial cell line MCF10a induced an EMT-associated cadherin switch. The induced N-cadherin was ligated and localized to the cell surface as determined by triton-solubility and immunofluorescence assays. In addition, LMP1 induced the assembly of focal adhesions (FAs) with increased production of fibronectin in MCF10a and NP460hTERT-immortalized nasopharyngeal cells. Biochemical enrichment of fibronectin-associated proteins indicated that LMP1 selectively promoted the recruitment of integrin-α5 and Src family kinase proteins to FA complexes. Neutralizing antibodies to N-cadherin and integrin-α5, but not integrin-αV, blocked the adhesion and transwell motility of MCF10a cells to fibronectin induced by LMP1. LMP1-induced transwell motility was also decreased by Src inhibition with the PP2 kinase inhibitor and short hairpin RNAs. These studies reveal that LMP1 has multiple mechanisms to promote the adhesive and migratory properties of epithelial cells through induction of fibronectin and modulation of cell surface interactions involving integrin-α5 and N-cadherin, which may contribute to the metastatic potential of NPC.

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

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

Regulation of DNA Damage Signaling and Cell Death Responses by Epstein-Barr Virus Latent Membrane Protein 1 (LMP1) and LMP2A in Nasopharyngeal Carcinoma Cells

Nasopharyngeal carcinoma (NPC) is closely associated with latent Epstein-Barr virus (EBV) infection. Although EBV infection of preneoplastic epithelial cells is not immortalizing, EBV can modulate oncogenic and cell death mechanisms. The viral latent membrane proteins 1 (LMP1) and LMP2A are consistently expressed in NPC and can cooperate in bitransgenic mice expressed from the keratin-14 promoter to enhance carcinoma development in an epithelial chemical carcinogenesis model. In this study, LMP1 and LMP2A were coexpressed in the EBV-negative NPC cell line HK1 and examined for combined effects in response to genotoxic treatments. In response to DNA damage activation, LMP1 and LMP2A coexpression reduced γH2AX (S139) phosphorylation and caspase cleavage induced by a lower dose (5 μM) of the topoisomerase II inhibitor etoposide. Regulation of γH2AX occurred before the onset of caspase activation without modulation of other DNA damage signaling mediators, including ATM, Chk1, or Chk2, and additionally was suppressed by inducers of DNA single-strand breaks (SSBs) and replication stress. Despite reduced DNA damage repair signaling, LMP1-2A coexpressing cells recovered from cytotoxic doses of etoposide; however, LMP1 expression was sufficient for this effect. LMP1 and LMP2A coexpression did not enhance cell growth, with a moderate increase of cell motility to fibronectin. This study supports that LMP1 and LMP2A jointly regulate DNA repair signaling and cell death activation with no further enhancement in the growth properties of neoplastic cells.

IMPORTANCE

NPC is characterized by clonal EBV infection and accounts for >78,000 annual cancer cases with increased incidence in regions where EBV is endemic, such as southeast Asia. The latent proteins LMP1 and LMP2A coexpressed in NPC can individually enhance growth or survival properties in epithelial cells, but their combined effects and potential regulation of DNA repair and checkpoint mechanisms are relatively undetermined. In this study, LMP1-2A coexpression suppressed activation of the DNA damage response (DDR) protein γH2AX induced by selective genotoxins that promote DNA replication stress or SSBs. Expression of LMP1 was sufficient to recover cells, resulting in outgrowth of LMP1 and LMP1-2A-coexpressing cells and indicating distinct LMP1-dependent effects in the restoration of replicative potential. These findings demonstrate novel properties for LMP1 and LMP2A in the cooperative modulation of DDR and apoptotic signaling pathways, further implicating both proteins in the progression of NPC and epithelial malignancies.

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

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

Telomerase activity impacts on Epstein-Barr virus infection of AGS cells

The Epstein-Barr virus (EBV) is transmitted from host-to-host via saliva and is associated with epithelial malignancies including nasopharyngeal carcinoma (NPC) and some forms of gastric carcinoma (GC). Nevertheless, EBV does not transform epithelial cells in vitro where it is rapidly lost from infected primary epithelial cells or epithelial tumor cells. Long-term infection by EBV, however, can be established in hTERT-immortalized nasopharyngeal epithelial cells. Here, we hypothesized that increased telomerase activity in epithelial cells enhances their susceptibility to infection by EBV. Using HONE-1, AGS and HEK293 cells we generated epithelial model cell lines with increased or suppressed telomerase activity by stable ectopic expression of hTERT or of a catalytically inactive, dominant negative hTERT mutant. Infection experiments with recombinant prototypic EBV (rB95.8), recombinant NPC EBV (rM81) with increased epithelial cell tropism compared to B95.8, or recombinant B95.8 EBV with BZLF1-knockout that is not able to undergo lytic replication, revealed that infection frequencies positively correlate with telomerase activity in AGS cells but also partly depend on the cellular background. AGS cells with increased telomerase activity showed increased expression mainly of latent EBV genes, suggesting that increased telomerase activity directly acts on the EBV infection of epithelial cells by facilitating latent EBV gene expression early upon virus inoculation. Thus, our results indicate that infection of epithelial cells by EBV is a very selective process involving, among others, telomerase activity and cellular background to allow for optimized host-to-host transmission via saliva.

Epstein-Barr virus transcription factor Zta acts through distal regulatory elements to directly control cellular gene expression

Lytic replication of the human gamma herpes virus Epstein-Barr virus (EBV) is an essential prerequisite for the spread of the virus. Differential regulation of a limited number of cellular genes has been reported in B-cells during the viral lytic replication cycle. We asked whether a viral bZIP transcription factor, Zta (BZLF1, ZEBRA, EB1), drives some of these changes. Using genome-wide chromatin immunoprecipitation coupled to next-generation DNA sequencing (ChIP-seq) we established a map of Zta interactions across the human genome. Using sensitive transcriptome analyses we identified 2263 cellular genes whose expression is significantly changed during the EBV lytic replication cycle. Zta binds 278 of the regulated genes and the distribution of binding sites shows that Zta binds mostly to sites that are distal to transcription start sites. This differs from the prevailing view that Zta activates viral genes by binding exclusively at promoter elements. We show that a synthetic Zta binding element confers Zta regulation at a distance and that distal Zta binding sites from cellular genes can confer Zta-mediated regulation on a heterologous promoter. This leads us to propose that Zta directly reprograms the expression of cellular genes through distal elements.