Epstein-barr virus latent membrane protein 2B (LMP2B) modulates LMP2A activity

Raman spectroscopy of lymphocytes from patients with the Epstein-Barr virus infection

In this study, Raman spectroscopy is applied to trace lymphocytes activation following contact with the Epstein-Barr virus (EBV) of the herpesvirus family. The biomarker of cell activation is found to be the 520 cm-1 band, indicating formation of immunoglobulins. The blood samples are obtained from patients diagnosed with infectious mononucleosis and treated at the University Hospital in Kraków. The lymphocytes' Raman spectra are collected using a mapping technique, exciting samples with a 514.5 nm line of Ar + laser. Measurements are performed on the 1st, 4th, 6th, 12th and 30th day of hospitalization, until the patient has recovered. The highest intensity of the immunoglobulin marker is observed on the 4th day of hospitalization, while the results of the blood count of patients show the greatest increase in the number of lymphocytes at the beginning of hospitalization. No activated lymphocytes were observed in the blood of healthy volunteers. Some information is provided by the evaluation of B-cell activation by estimating the activated areas in the cells, which are determined by the presence of the Ig marker. The 900 cm-1 band and band around 1450 cm-1 are also analyzed as markers of the presence of the latent membrane protein, LMP2A (and 2B), of the EBV viral protein. The anomalous degree of depolarization observed in B-cells in the course of EBV infection appears to be due to the influence of a virus protein, disrupting BCR signal transduction.

Mechanisms of T cell evasion by Epstein-Barr virus and implications for tumor survival

Epstein-Barr virus (EBV) is a prevalent oncogenic virus estimated to infect greater than 90% of the world's population. Following initial infection, it establishes latency in host B cells. EBV has developed a multitude of techniques to avoid detection by the host immune system and establish lifelong infection. T cells, as important contributors to cell-mediated immunity, make an attractive target for these immunoevasive strategies. Indeed, EBV has evolved numerous mechanisms to modulate T cell responses. For example, it can augment expression of programmed cell death ligand-1 (PD-L1), which inhibits T cell function, and downregulates the interferon response, which has a strong impact on T cell regulation. It also modulates interleukin secretion and can influence major histocompatibility complex (MHC) expression and presentation. In addition to facilitating persistent EBV infection, these immunoregulatory mechanisms have significant implications for evasion of the immune response by tumor cells. This review dissects the mechanisms through which EBV avoids detection by host T cells and discusses how these mechanisms play into tumor survival. It concludes with an overview of cancer treatments targeting T cells in the setting of EBV-associated malignancy.

Epstein-Barr Virus History and Pathogenesis

Epstein-Barr virus (EBV) is the first identified human oncogenic virus that can establish asymptomatic life-long persistence. It is associated with a large spectrum of diseases, including benign diseases, a number of lymphoid malignancies, and epithelial cancers. EBV can also transform quiescent B lymphocytes into lymphoblastoid cell lines (LCLs) in vitro. Although EBV molecular biology and EBV-related diseases have been continuously investigated for nearly 60 years, the mechanism of viral-mediated transformation, as well as the precise role of EBV in promoting these diseases, remain a major challenge yet to be completely explored. This review will highlight the history of EBV and current advances in EBV-associated diseases, focusing on how this virus provides a paradigm for exploiting the many insights identified through interplay between EBV and its host during oncogenesis, and other related non-malignant disorders.

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

Stress-Induced Epstein-Barr Virus Reactivation

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

Role of Virally Encoded Circular RNAs in the Pathogenicity of Human Oncogenic Viruses

Human oncogenic viruses are a group of important pathogens that etiologically contribute to at least 12% of total cancer cases in the world. As an emerging class of non-linear regulatory RNA molecules, circular RNAs (circRNAs) have gained increasing attention as a crucial player in the regulation of signaling pathways involved in viral infection and oncogenesis. With the assistance of current circRNA enrichment and detection technologies, numerous novel virally-encoded circRNAs (vcircRNAs) have been identified in the human oncogenic viruses, initiating an exciting new era of vcircRNA research. In this review, we discuss the current understanding of the roles of vcircRNAs in the respective viral infection cycles and in virus-associated pathogenesis.

The role of EBV in haematolymphoid proliferations: emerging concepts relevant to diagnosis and treatment

Epstein-Barr virus (EBV) is a ubiquitous gammaherpesvirus with >90% of the adult population worldwide harbouring latent infection. A small subset of those infected develop EBV-associated neoplasms, including a range of lymphoproliferative disorders (LPD). The diagnostic distinction of these entities appears increasingly relevant as our understanding of EBV-host interactions and mechanisms of EBV-driven lymphomagenesis improves. EBV may lower the mutational threshold for malignant transformation, create potential vulnerabilities related to viral alteration of cell metabolism and allow for improved immune targeting. However, these tumours may escape immune surveillance by affecting their immune microenvironment, limiting viral gene expression or potential loss of the viral episome. Methods to manipulate the latency state of the virus to enhance immunogenicity are emerging as well as the potential to detect so-called 'hit and run' cases where EBV has been lost. Finally, measurement of EBV DNA remains an important biomarker for screening and monitoring of LPD. Methods to distinguish EBV DNA derived from virions during lytic activation from latent, methylated EBV DNA present in EBV-associated neoplasms may broaden the utility of this testing, particularly in patients with compromised immune function. We highlight some of these emerging areas relevant to the diagnosis and treatment of EBV-associated LPD with potential applicability to other EBV-associated neoplasms.

The molecular march of primary and recurrent nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) results from the aberrant and uncontrolled growth of the nasopharyngeal epithelium. It is highly associated with the Epstein-Barr virus, especially in regions where it is endemic. In the last decade, significant advances in genetic sequencing techniques have allowed the discovery of many new abnormal molecular processes that undoubtedly contribute to the establishment, growth and spread of this deadly disease. In this review, we consider NPC as EBV induced. We summarise the recent discoveries and how they add to our understanding of the pathophysiology of NPC in the context of genomics first in primary and then in recurrent disease. Overall, we find key early events lead to p16 inactivation and cyclin D1 expression, allowing latent viral infection. Host and viral factors work together to affect a variety of molecular pathways, the most fundamental being activation of NF-κB. Nonetheless, much still yearns to be discovered, especially in recurrent NPC.

Epstein Barr Virus Associated Lymphomas and Epithelia Cancers in Humans

Epstein Barr virus (EBV) is a cosmopolitan oncogenic virus, infecting about 90% of the world's population and it is associated to tumors originating from both epithelia and hematopoietic cells. Transmission of the virus is mainly through oral secretions; however, transmission through organ transplantation and blood transfusion has been reported. In order to evade immune recognition, EBV establishes latent infection in B lymphocytes where it expresses limited sets of proteins called EBV transcription programs (ETPs), including six nuclear antigens (EBNAs), three latent membrane proteins (LMP), and untranslated RNA called EBV encoded RNA (EBER), shown to efficiently transform B cells into lymphoblastic cells. These programs undergo different patterns of expression which determine the occurrence of distinct types of latency in the pathogenesis of a particular tumor. Hematopoietic cell derived tumors include but not limited to Burkitt's lymphoma, Hodgkin lymphoma, post-transplant lymphoproliferative disorders, and natural killer (NK)/T cell lymphoma. EBV undergoes lytic infection in epithelia cells for amplification of the viral particle for transmission where it expresses lytic stage genes. However, for reasons yet to be unveiled, EBV switches from the expression of lytic stage genes to the expression of ETPs in epithelia cells. The expression of the ETPs lead to the transformation of epithelia cells into permanently proliferating cells, resulting in epithelia cell derived malignancies such as nasopharyngeal cancer, gastric cancer, and breast cancer. In this review, we have summarized the current updates on EBV associated epithelial and B cell-derived malignancies, and the role of EBV latency gene products in the pathogenesis of the cancers, and have suggested areas for future studies when considering therapeutic measures.

Novel EBV LMP-2-affibody and affitoxin in molecular imaging and targeted therapy of nasopharyngeal carcinoma

Epstein-Barr virus (EBV) infection is closely linked to several human malignancies including endemic Burkitt’s lymphoma, Hodgkin’s lymphoma and nasopharyngeal carcinomas (NPC). Latent membrane protein 2 (LMP-2) of EBV plays a pivotal role in pathogenesis of EBV-related tumors and thus, is a potential target for diagnosis and targeted therapy of EBV LMP-2⁺ malignant cancers. Affibody molecules are developing as imaging probes and tumor-targeted delivery of small molecules. In this study, four EBV LMP-2-binding affibodies (Z_{EBV LMP-2}12, Z_{EBV LMP-2}132, Z_{EBV LMP-2}137, and Z_{EBV LMP-2}142) were identified by screening a phage-displayed LMP-2 peptide library for molecular imaging and targeted therapy in EBV xenograft mice model. Z_{EBV LMP-2} affibody has high binding affinity for EBV LMP-2 and accumulates in mouse tumor derived from EBV LMP-2⁺ xenografts for 24 h after intravenous (IV) injection. Subsequent fusion of Pseudomonas exotoxin PE38KDEL to the Z_{EBV LMP-2} 142 affibody led to production of Z142X affitoxin. This fused Z142X affitoxin exhibits high cytotoxicity specific for EBV⁺ cells in vitro and significant antitumor effect in mice bearing EBV⁺ tumor xenografts by IV injection. The data provide the proof of principle that EBV LMP-2-speicifc affibody molecules are useful for molecular imaging diagnosis and have potentials for targeted therapy of LMP-2-expressing EBV malignancies.

Molecular imaging diagnosis and targeted therapy have been successfully used for several types of tumors, but not yet applied to diagnose or treat EBV-associated NPC. Affibody molecules are small proteins engineered to bind to a large number of target proteins with high affinity, and therefore, can be developed as potential biopharmaceutical drugs for molecular diagnosis and therapeutic applications. In the present study, we screened and characterized EBV LMP-2-specific affibodies and evaluated their usage in molecular imaging of LMP-2 expressing cells and EBV LMP-2 tumor-bearing mice. Subsequently, we engineered and obtained an EBV LMP-2 affitoxin based on EBV LMP-2-binding affibodies and demonstrated its targeted cytotoxicity for EBV⁺ cell lines in vitro and in vivo. Our data indicate that the EBV LMP-2-specific affibody and its derived affitoxin are useful for diagnosis of LMP-2 expressing cells and targeted therapy of EBV-derived, LMP-2⁺ malignancies.

The interplay between Epstein-Bar virus (EBV) with the p53 and its homologs during EBV associated malignancies

p53, p63, and p73, the members of the p53 family of proteins, are structurally similar proteins that play central roles regulating cell cycle and apoptotic cell death. Alternative splicing at the carboxyl terminus and the utilization of different promoters further categorizes these proteins as having different isoforms for each. Among such isoforms, TA and ΔN versions of each protein serve as the pro and the anti-apoptotic proteins, respectively. Changes in the expression patterns of these isoforms are noted in many human cancers. Proteins of certain human herpesviruses, like Kaposi's sarcoma-associated herpesvirus (KSHV) and Epstein-Barr virus (EBV), interact with p53 family members and alter their expressions in many malignancies. Upon infections in the B cells and epithelial cells, EBV expresses different lytic or latent proteins during viral replication and latency respectively to preserve viral copy number, chromosomal integrity and viral persistence inside the host. In this review, we have surveyed and summarised the interactions of EBV gene products, known so far, with the p53 family proteins. The interactions between P53 and EBV oncoproteins are observed in stomach cancer, non-Hodgkin's lymphoma (NHL) of the head and neck, Nasopharyngeal Cancer (NPC), Gastric carcinoma (GC) and Burkitt's lymphoma (BL). EBV latent protein EBNA1, EBNA3C, LMP-1, and lytic proteins BZLF-1 can alter p53 expressions in many cancer cell lines. Interactions of p63 with EBNA-1, 2, 5, LMP-2A and BARF-1 have also been investigated in several cancers. Similarly, associations of p73 isoform with EBV latent proteins EBNA3C and LMP-1 have been reported. Methylation and single nucleotide polymorphisms in p53 have also been found to be correlated with EBV infection. Therefore, interactions and altered expression strategies of the isoforms of p53 family proteins in EBV associated cancers propose an important field for further molecular research.

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

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

Manipulation of Type I Interferon Signaling by HIV and AIDS-Associated Viruses

Type I Interferons were first described for their profound antiviral abilities in cell culture and animal models, and later, they were translated into potent antiviral therapeutics. However, as additional studies into the function of Type I Interferons progressed, it was also seen that pathogenic viruses have coevolved to encode potent mechanisms allowing them to evade or suppress the impact of Type I Interferons on their replication. For chronic viral infections, such as HIV and many of the AIDS-associated viruses, including HTLV, HCV, KSHV, and EBV, the clinical efficacy of Type I Interferons is limited by these mechanisms. Here, we review some of the ways that HIV and AIDS-associated viruses thrive in Type I Interferon-rich environments via mechanisms that block the function of this important antiviral cytokine. Overall, a better understanding of these mechanisms creates avenues to better understand the innate immune response to these viruses as well as plan the development of antivirals that would allow the natural antiviral effect of Type I Interferons to manifest during these infections.

Analysis of a structured intronic region of the LMP2 pre-mRNA from EBV reveals associations with human regulatory proteins and nuclear actin

Objective

The pre-mRNA of the Epstein–Barr virus LMP2 (latent membrane protein 2) has a region of unusual RNA structure that partially spans two consecutive exons and the entire intervening intron; suggesting RNA folding might affect splicing—particularly via interactions with human regulatory proteins. To better understand the roles of protein associations with this structured intronic region, we undertook a combined bioinformatics (motif searching) and experimental analysis (biotin pulldowns and RNA immunoprecipitations) of protein binding.

Result

Characterization of the ribonucleoprotein composition of this region revealed several human proteins as interactors: regulatory proteins hnRNP A1 (heterogeneous nuclear ribonucleoprotein A1), hnRNP U, HuR (human antigen R), and PSF (polypyrimidine tract-binding protein-associated splicing factor), as well as, unexpectedly, the cytoskeletal protein actin. Treatment of EBV-positive cells with drugs that alter actin polymerization specifically showed marked effects on splicing in this region. This suggests a potentially novel role for nuclear actin in regulation of viral RNA splicing.

Electronic supplementary material

The online version of this article (10.1186/s13104-019-4070-1) contains supplementary material, which is available to authorized users.

Molecular mechanisms of EBV-driven cell cycle progression and oncogenesis

The early stage of oncogenesis is linked to the disorder of the cell cycle. Abnormal gene expression often leads to cell cycle disorders, resulting in malignant transformation of human cells. Epstein–Barr virus (EBV) is associated with a diverse range of human neoplasms, such as malignant lymphoma, nasopharyngeal carcinoma and gastric cancer. EBV mainly infects human lymphocytes and oropharyngeal epithelial cells. EBV is latent in lymphocytes for a long period of time, is detached from the cytoplasm by circular DNA, and can integrate into the chromosome of cells. EBV expresses a variety of latent genes during latent infection. The interaction between EBV latent genes and oncogenes leads to host cell cycle disturbances, including the promotion of G₁/S phase transition and inhibition of cell apoptosis, thereby promoting the development of EBV-associated neoplasms. Molecular mechanisms of EBV-driven cell cycle progression and oncogenesis involve diverse genes and signal pathways. Here, we review the molecular mechanisms of EBV-driven cell cycle progression and promoting oncogenesis.

The Epstein Barr virus circRNAome

Our appreciation for the extent of Epstein Barr virus (EBV) transcriptome complexity continues to grow through findings of EBV encoded microRNAs, new long non-coding RNAs as well as the more recent discovery of over a hundred new polyadenylated lytic transcripts. Here we report an additional layer to the EBV transcriptome through the identification of a repertoire of latent and lytic viral circular RNAs. Utilizing RNase R-sequencing with cell models representing latency types I, II, and III, we identified EBV encoded circular RNAs expressed from the latency Cp promoter involving backsplicing from the W1 and W2 exons to the C1 exon, from the EBNA BamHI U fragment exon, and from the latency long non-coding RPMS1 locus. In addition, we identified circular RNAs expressed during reactivation including backsplicing from exon 8 to exon 2 of the LMP2 gene and a highly expressed circular RNA derived from intra-exonic backsplicing within the BHLF1 gene. While expression of most of these circular RNAs was found to depend on the EBV transcriptional program utilized and the transcription levels of the associated loci, expression of LMP2 exon 8 to exon 2 circular RNA was found to be cell model specific. Altogether we identified over 30 unique EBV circRNAs candidates and we validated and determined the structural features, expression profiles and nuclear/cytoplasmic distributions of several predominant and notable viral circRNAs. Further, we show that two of the EBV circular RNAs derived from the RPMS1 locus are detected in EBV positive clinical stomach cancer specimens. This study increases the known EBV latency and lytic transcriptome repertoires to include viral circular RNAs and it provides an essential foundation and resource for investigations into the functions and roles of this new class of EBV transcripts in EBV biology and diseases.

Our understanding of the extent of EBV transcriptome complexity has recently come to light with discoveries of viral microRNAs, snoRNAs, and a diverse set of transcript isoforms expressed during reactivation. While EBV utilizes distinct transcriptional programs during it’s normal infection cycle, the latency programs are critical drivers of EBV associated oncogenesis where they activate oncogenic pathways without killing the cell via lytic viral replication. Further, pathogenic latency programs typically express minimal levels of viral protein coding genes and instead rely on non-coding RNA mechanisms to alter the host cell environment. The utilization of non-coding RNAs in these settings is presumably an effort to minimize infected cell killing by the immune system through adaptive immune responses. Using tissue culture models representing the spectrum of EBV transcriptional states that occur in vivo, we report here that EBV expresses the circular class of predominantly non-coding RNAs. This stands to reveal a previously unknown set of players in EBV associated biology and disease. The findings reported here set a key platform from which future functional and potentially clinical related studies can be carried out to bring the initial findings from discovery to a new understanding of EBV biology and disease.

Contribution of Epstein⁻Barr Virus Latent Proteins to the Pathogenesis of Classical Hodgkin Lymphoma

Pathogenic viruses have evolved to manipulate the host cell utilising a variety of strategies including expression of viral proteins to hijack or mimic the activity of cellular functions. DNA tumour viruses often establish latent infection in which no new virions are produced, characterized by the expression of a restricted repertoire of so-called latent viral genes. These latent genes serve to remodel cellular functions to ensure survival of the virus within host cells, often for the lifetime of the infected individual. However, under certain circumstances, virus infection may contribute to transformation of the host cell; this event is not a usual outcome of infection. Here, we review how the Epstein–Barr virus (EBV), the prototypic oncogenic human virus, modulates host cell functions, with a focus on the role of the EBV latent genes in classical Hodgkin lymphoma.

Constructing TC-1-GLUC-LMP2 Model Tumor Cells to Evaluate the Anti-Tumor Effects of LMP2-Related Vaccines

Epstein-Barr virus (EBV) is related to a variety of malignant tumors, and its encoded protein, latent membrane protein 2 (LMP2), is an effective target antigen that is widely used to construct vector vaccines. However, the model cells carrying LMP2 have still not been established to assess the oncolytic effect of LMP2-related vaccines at present. In this study, TC-1-GLUC-LMP2 tumor cells were constructed as target cells to evaluate the anti-tumor effects of LMP2-assosiated vaccines. The results showed that both LMP2 and Gaussia luciferase (GLuc) genes could be detected by polymerase chain reaction (PCR) and reverse transcription-polymerase chain reaction (RT-PCR) in TC-1-GLUC-LMP2 cells. Western blot results showed that the LMP2 and Gaussia luciferase proteins were stably expressed in tumor cells for at least 30 generations. We mixed 5 × 10⁴ LMP2-specific mouse splenic lymphocytes with 5 × 10³ TC-1-GLUC-LMP2 target cells and found that the target cells were killed as the specific killing effect was obviously enhanced by the increased quantities of LMP2-peptide stimulated spleens. Furthermore, the tumor cells could not be observed in the mice inoculated TC-1-GLUC-LMP2 cells after being immunized with vaccine-LMP2, while the vaccine-NULL immunized mice showed that tumor volume gradually grew with increased inoculation time. These results indicated that the TC-1-GLUC-LMP2 cells stably expressing LMP2 and GLuc produced tumors in mice, and that the LMP2-specific cytotoxic T lymphocyte (CTL) effectively killed the cells in vitro and in vivo, suggesting that TC-1-GLUC-LMP2 cells can be used as model cells to assess the immune and antitumor effects of LMP2-related vaccines.

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

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

Frequency of Epstein Barr Virus Type 1 Among Nasopharyngeal Carcinomas in Iranian Patients

Background: Around 95% of the world’s population are infected with the Epstein-Barr virus (EBV), which can persist latent in B lymphocytes and epithelial cells life-long. EBV has been linked with lymphoid and epithelial cancers and persistence of EBV infection in lymphoid or epithelial cells may result in virus-associated B-cell tumors or nasopharyngeal carcinomas (NPC). This study was conducted to determine the frequency of EBV DNA in nasopharyngeal carcinoma tissue of Iranian patients. Materials and methods: A total of 50 blocks of formalin-fixed paraffin-embedded tissue of NPCs from 38 (76 %) male and 12 (24%) female patients were collected from archives of Ahvaz hospitals. Sections were cut at 5 μm and DNA was extracted for detection of EBV DNA and EBV typing by mested PCR. DNA sequencing was performed to confirm PCR results. The distribution of EBV DNA was compared among WHO histological subtypes of NPC. Results: Some 3 female and 11 (22%) male NPC samples showed positive for EBV DNA type 1, 2/14(22.2%)WHO histological type II and 12/41(29.3%) WHO histological type III. Conclusions: The frequency of EBV DNA among NPCs in Iranian patients was found to be 28%, EBV type I predominating. Both WHO histological type II and III NPC subtypes demonstrated approximately the same detection prevalence.

Methylation and expression of Epstein-Barr virus latent membrane protein 1, 2A and 2B in EBV-associated gastric carcinomas and cell lines

BACKGROUND

Promoter CpG methylation of Epstein-Barr virus (EBV) genome plays an essential role in maintaining viral latency. Latent membrane protein (LMP) 1, 2A and 2B of EBV exert multiple oncogenic properties by activating multiple signal pathways and modulating the expression of various oncogenes.

AIMS

To study the methylation and expression of LMP1, 2A and LMP2B in EBV-positive cell lines and EBV-associated tumors.

METHODS

The methylation profiles of LMP1p, LMP2Ap and LMP2Bp were evaluated by methylation-specific PCR (MSP) and bisulfite sequencing PCR (BSP), as well as their expression by quantitative real-time (qRT)-PCR in 41 EBV-associated carcinomas (EBVaGCs) and 5 EBV-positive cell lines.

RESULTS

All LMP promoters were methylated at different degrees in EBV-positive cell lines and hypermethylated in EBV-associated gastric carcinomas, while unmethylated LMP2Ap alleles were detected in B95-8 cell line. Following 5-aza-2'-deoxycytidine (5-aza) treatment, the LMP1 expression was restored along with concomitant promoter demethylation; changes of LMP2A and LMP2B expression were different in different cells.

CONCLUSION

Methylation of LMP1, 2A and 2B promoters mediates the silencing of LMP1, 2A and 2B in EBV-associated carcinomas and cell lines in varying degrees, and could be reactivated by demethylation agent and thus may contribute to the therapy of EBVaGCs.

Understanding the interplay between host immunity and Epstein-Barr virus in NPC patients

Epstein-Barr virus (EBV) has been used as a paradigm for studying host-virus interactions, not only because of its importance as a human oncogenic virus associated with several malignancies including nasopharyngeal carcinoma (NPC) but also owing to its sophisticated strategies to subvert the host antiviral responses. An understanding of the interplay between EBV and NPC is critical for the development of EBV-targeted immunotherapy. Here, we summarize the current knowledge regarding the host immune responses and EBV immune evasion mechanisms in the context of NPC.

EBV noncoding RNA binds nascent RNA to drive host PAX5 to viral DNA

EBER2 is an abundant nuclear noncoding RNA expressed by the Epstein-Barr virus (EBV). Probing its possible chromatin localization by CHART revealed EBER2's presence at the terminal repeats (TRs) of the latent EBV genome, overlapping previously identified binding sites for the B cell transcription factor PAX5. EBER2 interacts with PAX5 and is required for the localization of PAX5 to the TRs. EBER2 knockdown phenocopies PAX5 depletion in upregulating the expression of LMP2A/B and LMP1, genes nearest the TRs. Knockdown of EBER2 also decreases EBV lytic replication, underscoring the essential role of the TRs in viral replication. Recruitment of the EBER2-PAX5 complex is mediated by base-pairing between EBER2 and nascent transcripts from the TR locus. The interaction is evolutionarily conserved in the related primate herpesvirus CeHV15 despite great sequence divergence. Using base-pairing with nascent RNA to guide an interacting transcription factor to its DNA target site is a previously undescribed function for a trans-acting noncoding RNA.

Epstein-Barr virus latent genes

Latent Epstein–Barr virus (EBV) infection has a substantial role in causing many human disorders. The persistence of these viral genomes in all malignant cells, yet with the expression of limited latent genes, is consistent with the notion that EBV latent genes are important for malignant cell growth. While the EBV-encoded nuclear antigen-1 (EBNA-1) and latent membrane protein-2A (LMP-2A) are critical, the EBNA-leader proteins, EBNA-2, EBNA-3A, EBNA-3C and LMP-1, are individually essential for in vitro transformation of primary B cells to lymphoblastoid cell lines. EBV-encoded RNAs and EBNA-3Bs are dispensable. In this review, the roles of EBV latent genes are summarized.

Latent Membrane Protein 2 (LMP2)

LMP2A is an EBV-encoded protein with three domains: (a) an N-terminal cytoplasmic domain, which has PY motifs that bind to WW domain-containing E3 ubiquitin ligases and an ITAM that binds to SH2 domain-containing proteins, (b) a transmembrane domain with 12 transmembrane segments that localizes LMP2A in cellular membranes, and (c) a 27-amino acid C-terminal domain which mediates homodimerization and heterodimerization of LMP2 protein isoforms. The most prominent two isoforms of the protein are LMP2A and LMP2B. The LMP2B isoform lacks the 19-amino acid N-terminal domain found in LMP2A, which modulates cellular signaling resulting in a baseline activation of B cells and degradation of cellular kinases leading to the downregulation of normal B cell signaling pathways. These two seemingly contradictory processes allow EBV to establish and maintain latency. LMP2 is expressed in many EBV-associated malignancies. While its antigenic properties may be useful in developing LMP2-specific immunity, the LMP2A N-terminal motifs also provide a basis to target LMP2A-modulated cellular kinases for the development of treatment strategies.

Molecular signature of Epstein Barr virus-positive Burkitt lymphoma and post-transplant lymphoproliferative disorder suggest different roles for Epstein Barr virus

Epstein Barr virus (EBV) infection is commonly associated with human cancer and, in particular, with lymphoid malignancies. Although the precise role of the virus in the pathogenesis of different lymphomas is largely unknown, it is well recognized that the expression of viral latent proteins and miRNA can contribute to its pathogenetic role. In this study, we compared the gene and miRNA expression profile of two EBV-associated aggressive B non-Hodgkin lymphomas known to be characterized by differential expression of the viral latent proteins aiming to dissect the possible different contribution of such proteins and EBV-encoded miRNAs. By applying extensive bioinformatic inferring and an experimental model, we found that EBV+ Burkitt lymphoma presented with significant over-expression of EBV-encoded miRNAs that were likely to contribute to its global molecular profile. On the other hand, EBV+ post-transplant diffuse large B-cell lymphomas presented a significant enrichment in genes regulated by the viral latent proteins. Based on these different viral and cellular gene expression patterns, a clear distinction between EBV+ Burkitt lymphoma and post-transplant diffuse large B-cell lymphomas was made. In this regard, the different viral and cellular expression patterns seemed to depend on each other, at least partially, and the latency type most probably played a significant role in their regulation. In conclusion, our data indicate that EBV influence over B-cell malignant clones may act through different mechanisms of transcriptional regulation and suggest that potentially different pathogenetic mechanisms may depend upon the conditions of the interaction between EBV and the host that finally determine the latency pattern.

The effect of Epstein-Barr virus Latent Membrane Protein 2 expression on the kinetics of early B cell infection

Infection of human B cells with wild-type Epstein-Barr virus (EBV) in vitro leads to activation and proliferation that result in efficient production of lymphoblastoid cell lines (LCLs). Latent Membrane Protein 2 (LMP2) is expressed early after infection and previous research has suggested a possible role in this process. Therefore, we generated recombinant EBV with knockouts of either or both protein isoforms, LMP2A and LMP2B (Δ2A, Δ2B, Δ2A/Δ2B) to study the effect of LMP2 in early B cell infection. Infection of B cells with Δ2A and Δ2A/Δ2B viruses led to a marked decrease in activation and proliferation relative to wild-type (wt) viruses, and resulted in higher percentages of apoptotic B cells. Δ2B virus infection showed activation levels comparable to wt, but fewer numbers of proliferating B cells. Early B cell infection with wt, Δ2A and Δ2B viruses did not result in changes in latent gene expression, with the exception of elevated LMP2B transcript in Δ2A virus infection. Infection with Δ2A and Δ2B viruses did not affect viral latency, determined by changes in LMP1/Zebra expression following BCR stimulation. However, BCR stimulation of Δ2A/Δ2B cells resulted in decreased LMP1 expression, which suggests loss of stability in viral latency. Long-term outgrowth assays revealed that LMP2A, but not LMP2B, is critical for efficient long-term growth of B cells in vitro. The lowest levels of activation, proliferation, and LCL formation were observed when both isoforms were deleted. These results suggest that LMP2A appears to be critical for efficient activation, proliferation and survival of EBV-infected B cells at early times after infection, which impacts the efficient long-term growth of B cells in culture. In contrast, LMP2B did not appear to play a significant role in these processes, and long-term growth of infected B cells was not affected by the absence of this protein.

Epstein-Barr virus-encoded latent membrane protein-1 upregulates 14-3-3σ and Reprimo to confer G(2)/M phase cell cycle arrest

Epstein-Barr virus (EBV) is a ubiquitous tumor-causing virus which infects more than 90% of the world population asymptomatically. Recent studies suggest that LMP-1, -2A and -2B cooperate in the tumorigenesis of EBV-associated epithelial cancers such as nasopharygeal carcinoma, oral and gastric cancer. In this study, LMPs were expressed in the HEK293T cell line to reveal their oncogenic mechanism via investigation on their involvement in the regulation of the cell cycle and genes that are involved. LMPs were expressed in HEK293T in single and co-expression manner. The transcription of cell cycle arrest genes were examined via real-time PCR. Cell cycle progression was examined via flow cytometry. 14-3-3σ and Reprimo were upregulated in all LMP-1 expressing cells. Moreover, cell cycle arrest at G(2)/M progression was detected in all LMP-1 expressing cells. Therefore, we conclude that LMP-1 may induce cell cycle arrest at G(2)/M progression via upregulation of 14-3-3σ and Reprimo.

The role of the EBV-encoded latent membrane proteins LMP1 and LMP2 in the pathogenesis of nasopharyngeal carcinoma (NPC)

Although frequently expressed in EBV-positive malignancies, the contribution of the oncogenic latent membrane proteins, LMP1 and LMP2, to the pathogenesis of nasopharyngeal carcinoma (NPC) is not fully defined. As a key effector in EBV-driven B cell transformation and an established "transforming" gene, LMP1 displays oncogenic properties in rodent fibroblasts and induces profound morphological and phenotypic effects in epithelial cells. LMP1 functions as a viral mimic of the TNFR family member, CD40, engaging a number of signalling pathways that induce morphological and phenotypic alterations in epithelial cells. Although LMP2A plays an essential role in maintaining viral latency in EBV infected B cells, its role in epithelial cells is less clear. Unlike LMP1, LMP2A does not display "classical" transforming functions in rodent fibroblasts but its ability to engage a number of potentially oncogenic cell signalling pathways suggests that LMP2A can also participate in EBV-induced epithelial cell growth transformation. Here we review the effects of LMP1 and LMP2 on various aspects of epithelial cell behaviour highlighting key aspects that may contribute to the pathogenesis of NPC.

A novel latent membrane 2 transcript expressed in Epstein-Barr virus-positive NK- and T-cell lymphoproliferative disease encodes a target for cellular immunotherapy

Therapeutic targeting of virus-encoded proteins using cellular immunotherapy has proved successful for Epstein-Barr virus (EBV)-associated posttransplant lymphoproliferative disease. However, the more limited repertoire and immunogenicity of EBV-encoded proteins in other malignancies such as Hodgkin lymphoma and extranodal natural killer (NK)/T lymphoma has been more challenging to target. The immunosubdominant latent membrane protein 2 (LMP2) is considered the optimal target in such Latency II tumors, although data relating to its expression in T/NK malignancies are limited. In addressing the validity of LMP2 as an immunotherapeutic target we found that LMP2-specific effector CD8(+) T cells recognized and killed EBV-positive NK- and T-cell tumor lines, despite an apparent absence of LMP2A protein and barely detectable levels of LMP2 transcripts from the conventional LMP2A and LMP2B promoters. We resolved this paradox by identifying in these lines a novel LMP2 mRNA, initiated from within the EBV terminal repeats and containing downstream, epitope-encoding exons. This same mRNA was also highly expressed in primary (extra-nodal) NK/T lymphoma tissue, with virtually undetectable levels of conventional LMP2A/B transcripts. Expression of this novel transcript in T/NK-cell lymphoproliferative diseases validates LMP2 as an attractive target for cellular immunotherapy and implicates this truncated LMP2 protein in NK- and T-cell lymphomagenesis. This study is registered at clinicaltrials.gov as NCT00062868.

The EBV-encoded latent membrane proteins, LMP2A and LMP2B, limit the actions of interferon by targeting interferon receptors for degradation

Although frequently expressed in Epstein-Barr virus (EBV)-positive malignancies, the role that latent membrane protein 2A and 2B (LMP2A and LMP2B) have in the oncogenic process remains obscure. Here we show a novel function for these proteins in epithelial cells, namely, their ability to modulate signalling from type I/II interferon receptors (IFNRs). We show that LMP2A- and LMP2B-expressing epithelial cells show decreased responsiveness to interferon (IFN)alpha and IFNgamma, as assessed by STAT1 phosphorylation, ISGF3 and GAF-mediated binding to IFN-stimulated response element and IFNgamma-activated factor sequence elements and luciferase reporter activation. Transcriptional profiling highlighted the extent of this modulation, with both viral proteins impacting 'globally' on IFN-stimulated gene expression. Although not affecting the levels of cell-surface IFNRs, LMP2A and LMP2B accelerated the turnover of IFNRs through processes requiring endosome acidification. This function may form part of EBV's strategy to limit anti-viral responses and define a novel function for LMP2A and LMP2B in modulating signalling from receptors that participate in innate immune responses.

Role of latent membrane protein 2 isoforms in Epstein-Barr virus latency

The oncogenic Epstein-Barr virus (EBV) infects the majority of the human population without doing harm and establishes a latent infection in the memory B-cell compartment. To accomplish this, EBV hijacks B-cell differentiation pathways and uses its own viral genes to interfere with B-cell signalling to achieve life-long persistence. EBV latent membrane protein 2A (LMP2A) provides a surrogate B-cell receptor signal essential for cell survival and is believed to have a crucial role in the maintenance of latency by blocking B-cell activation which would otherwise lead to lytic EBV infection. These two functions demand tight control of LMP2A activity and expression levels. Based on recent insights in the function of LMP2B, an isoform of LMP2A, we propose a model for how LMP2B modulates the activity of LMP2A contributing to maintenance of EBV latency.

Latent membrane protein 2B regulates susceptibility to induction of lytic Epstein-Barr virus infection

The B-lymphotropic Epstein-Barr virus (EBV) encodes two isoforms of latent membrane protein 2 (LMP2), LMP2A and LMP2B, which are expressed during latency in B cells. The function of LMP2B is largely unknown, whereas LMP2A blocks B-cell receptor (BCR) signaling transduction and induction of lytic EBV infection, thereby promoting B-cell survival. Transfection experiments on LMP2B in EBV-negative B cells and the silencing of LMP2B in EBV-harboring Burkitt's lymphoma-derived Akata cells suggest that LMP2B interferes with the function of LMP2A, but the role of LMP2B in the presence of functional EBV has not been established. Here, LMP2B, LMP2A, or both were overexpressed in EBV-harboring Akata cells to study the function of LMP2B. The overexpression of LMP2B increased the magnitude of EBV switching from its latent to its lytic form upon BCR cross-linking, as indicated by a more-enhanced upregulation and expression of EBV lytic genes and significantly increased production of transforming EBV compared to Akata vector control cells or LMP2A-overexpressing cells. Moreover, LMP2B lowered the degree of BCR cross-linking required to induce lytic EBV infection. Finally, LMP2B colocalized with LMP2A as demonstrated by immunoprecipitation and immunofluorescence and restored calcium mobilization upon BCR cross-linking, a signaling process inhibited by LMP2A. Thus, our findings suggest that LMP2B negatively regulates the function of LMP2A in preventing the switch from latent to lytic EBV replication.

Minimal protein domain requirements for the intracellular localization and self-aggregation of Epstein-Barr Virus Latent Membrane Protein 2

The EBV Latent Membrane Protein 2 (LMP2) may have a role in the establishment and maintenance of in vivo latency. The gene is transcribed into two mRNAs that produce two LMP2 protein isoforms. The LMP2a protein isoform has 12 transmembrane segments (TMs) and an amino terminal cytoplasmic signaling domain (CSD) while the LMP2b isoform is identical but lacks the CSD. There has not been a consensus on the cellular membrane localization being sometimes ascribed to either a plasma membrane or an intracellular location [M. Rovedo, R. Longnecker, J. Virol. 81:89-94, 2007; D. Lynch, J. Zimmerman, D.T. Rowe, J. Gen. Virol. 83:1025-1035, 2002; C. Dawson, J. George, S. Blake, R. Longnecker, L.S. Young, Virology 289:192-207, 2001]. Fluorescent marker and epitope tagged LMP2b truncation mutants progressively removing TMs from the N and C termini were used to assess the localization and aggregation properties of LMP2b. wtLMP2b had an exclusively intracellular perinuclear localization, while all truncations of the protein resulted in localization to the cell surface. By epitope loop-tagging, all the truncated LMP2b proteins were verified to be in the predicted membrane orientation. In co-transfection experiments, the C-terminal region was implicated in the self-aggregation properties of LMP2b. Thus, an intact 12 TM domain was required for intracellular localization and protein-protein interaction while a C-terminal region was responsible for auto-aggregative properties.

Silencing of latent membrane protein 2B reduces susceptibility to activation of lytic Epstein-Barr virus in Burkitt's lymphoma Akata cells

Epstein-Barr virus (EBV) latent membrane protein 2A (LMP2A) blocks B-cell receptor (BCR) signalling after BCR cross-linking to inhibit activation of lytic EBV, and ectopically expressed LMP2B negatively regulates LMP2A. Here, it is demonstrated that silencing of LMP2B in EBV-harbouring Burkitt's lymphoma Akata cells results in reduced expression of EBV immediate-early lytic BZLF1 gene mRNA and late lytic gp350/220 protein upon BCR cross-linking. Similarly, reduction of lytic EBV activation was observed in Akata cells overexpressing LMP2A. In contrast, silencing of LMP2A expression resulted in higher lytic EBV mRNA and protein expression in BCR cross-linked Akata cells. These observations indicate a role for LMP2B distinct from that of LMP2A in regulation of lytic EBV activation in the host cell and support the hypothesis that LMP2B exhibits a negative-regulatory effect on the ability of LMP2A to maintain EBV latency by preventing the switch to lytic replication.