Identification of EBV transforming genes by recombinant EBV technology

Epstein-Barr virus-encoded LMP2A stimulates migration of nasopharyngeal carcinoma cells via the EGFR/Ca2+/calpain/ITGβ4 axis

Epstein-Barr virus (EBV)-encoded latent membrane protein 2A (LMP2A) promotes the motility of nasopharyngeal carcinoma (NPC) cells. Previously, we have shown that the localization of integrin β4 (ITGβ4) is regulated by LMP2A, with ITGβ4 concentrated at the cellular protrusions in LMP2A-expressing NPC cells. In the present study, we aim to further investigate mechanisms involved in this process and its contribution to cell motility. We show that expression of LMP2A was correlated with increased epidermal growth factor receptor (EGFR) activation, elevated levels of intracellular Ca²⁺, calpain activation and accelerated cleavage of ITGβ4. Activation of EGFR and calpain activity was responsible for a redistribution of ITGβ4 from the basal layer of NPC cells to peripheral membrane structures, which correlated with an increased migratory capacity of NPC cells. Furthermore, we demonstrated that the calpain inhibitor calpastatin was downregulated in NPC primary tumors. In conclusion, our results point to LMP2A-mediated targeting of the EGFR/Ca²⁺/calpain/ITGβ4 signaling system as a mechanism underlying the increased motility of NPC cells. We suggest that calpain-facilitated cleavage of ITGβ4 contributes to the malignant phenotype of NPC cells.

Summary: LMP2A expression in nasopharyngeal carcinoma cells increases EGFR activation and cytosolic Ca²⁺, subsequently stimulates calpain-dependent cleavage of ITGβ4 and enhances cell motility.

Overexpression of MYC and BCL2 Predicts Poor Prognosis in Patients with Extranodal NK/T-cell Lymphoma, Nasal Type

Background: Recently double-hit lymphoma or double protein expressor lymphoma has been identified as a distinct group of diffuse large B cell lymphoma with poor prognosis. However, the expression status, clinical and prognostic effect of combined overexpression of MYC and BCL2 in extranodal NK/T-cell lymphoma, nasal type (ENKTL) are not known.

Materials and methods: Paraffin-embedded lymphoma samples from 53 patients with newly diagnosed ENKTL were studied using immunohistochemistry for MYC and BCL2, and fluorescent in situ hybridization (FISH) for MYC and BCL2 were done on 5 tissue sections with highest percentages of both MYC and BCL2 positive lymphoma cells.

Results: The median percentage of MYC-positive lymphoma cells and BCL2-positive lymphoma cells were 20% (range, 5%-45%) and 70% (10%-95%), respectively. Using median scores as cutoffs, we assigned each patient an IHC double-hit score (DHS) that ranged from 0 to 2. Using this DHS, 15 patients (28.3%) had a DHS of 0, 24 patients (45.3%) had a DHS of 1, and the remaining 14 patients (26.4%) had a DHS of 2. FISH analysis was performed on 5 tissue sections with DHS of 2, and none of them had MYC or BCL2 rearrangement. The DHS was not associated with patients' age, gender, disease stage, LDH level, B symptoms, performance status, or local tumor invasiveness. However, patients with tumor localized in extranasal sites seemed to have higher expression of BCL2 and higher DHS than nasal lesions (p=0.014 and 0.042, respectively). In univariate survival analysis, either high expression of MYC or BCL2 was significantly correlated with inferior PFS and OS (p<0.05). According to the DHS, patients with ENKTL could be divided into three significantly different risk groups for PFS and OS (3-year PFS rate for DHS of 0, 1, and 2 was 60%, 41%, and 21%, respectively, p=0.008; 3-year OS rate for DHS of 0, 1, and 2 was 79%, 49%, and 33%, respectively, p=0.015). In multivariate survival analysis, it was found that DHS was an independent prognostic factor for both PFS and OS (p=0.006 and 0.011, respectively).

Conclusions: Our study demonstrated that DHS can help identify patients with newly diagnosed ENKTL who are at a high risk for a poor clinical outcome, which needs to be validated in prospective clinical trials with patients treated uniformly.

Characterization of the rapamycin-inducible EBV LMP1 activation system

Epstein-Barr virus (EBV) latent infection membrane protein 1 (LMP1) is required for EBV-mediated B lymphocyte transformation into proliferating lymphoblastoid cell lines (LCL). LMP1 oligomerizes spontaneously in membrane lipid rafts via its transmembrane domain and constitutively activates signal transduction pathways, including NF-κB, p38 Mitogen-Activated Protein Kinase (MAPK), and c-Jun N-terminal Kinase (JNK). Since LMP1 mimics the tumor necrosis factor receptor (TNFR), CD40, it may be effectively utilized to study the effects of constitutive activation of signal transduction pathways on cellular physiology. On the other hand, LMP1 presents a disadvantage in terms of determining the sequential events and factors involved in signaling pathways. A CD40-LMP1 chimeric molecule has been generated to overcome this limitation but does not represent the authentic and physiological nature of LMP1. In the current study, a ligand-dependent activation system for LMP1 using rapamycin-inducible dimerization was generated to delineate the LMP1 signaling pathway.

The Epstein-Barr virus latent membrane protein-1 (LMP1) 30-bp deletion and XhoI-polymorphism in nasopharyngeal carcinoma: a meta-analysis of observational studies

BACKGROUND

Epstein-Barr virus (EBV) is considered to be closely associated with nasopharyngeal carcinoma (NPC), in which EBV-encoded latent membrane protein 1 (LMP1) was found to have an oncogenic role. However, the results published on the LMP1 polymorphism are inconsistent. In the present study, we performed a meta-analysis to determine the frequency of the associations and a more precise association between NPC and EBV LMP1 gene variants (30-bp deletion (del)/XhoI-loss).

METHODS

Eligible articles met the inclusion/exclusion criteria and were identified in the following electronic databases: PubMed, ScienceDirect, and SciELO. Consequently, the data of interest were extracted and plotted in a table to calculate the frequency and odds ratio (OR) of the outcomes of interest (30-bp del-LMP1/XhoI-loss) in patients with NPC. Study quality (Newcastle-Ottawa Scale (NOS)), publication bias, and heterogeneity were assessed.

RESULTS

Thirty-one observational studies were included with a total of 2,846 individuals (NPC, n = 1,855; control, n = 991). The risk of bias in relation to study quality evaluated by NOS was considered low. The pooled estimate of the frequency of 30-bp del-LMP1 and XhoI-loss in patients with NPC was 77% (95% confidence interval (CI): 72 to 82) and 82% (95% CI: 71 to 92), respectively. There was an association between 30-bp del-LMP1 and NPC susceptibility (OR = 2.86, 95% CI: 1.35 to 6.07, P = 0.00). Similarly, there was an association between XhoI-loss and NPC (OR = 8.5, 95% CI: 1.7 to 41, P = 0.00). However, when we analyze the co-existence of the 30-bp del-LMP1 and XhoI-loss in patients with NPC, there was no association (OR = 1.09, 95% CI: 0.06 to 18.79, P = 0.002).

CONCLUSIONS

Our results suggest an association between the 30-bp del-LMP1 and XhoI-loss with NPC susceptibility. However, our data should be interpreted with caution because the sample size was small, and there was heterogeneity between the studies. Thus, future studies are needed with adjusted estimates to simultaneously evaluate multiple factors involved in the development of NPC.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42014013496 .

Epstein-Barr virus genetics: talking about the BAC generation

Genetic mutant organisms pervade all areas of Biology. Early on, herpesviruses (HV) were found to be amenable to genetic analysis using homologous recombination techniques in eukaryotic cells. More recently, HV genomes cloned onto a bacterial artificial chromosome (BAC) have become available. HV BACs can be easily modified in E.coli and reintroduced in eukaryotic cells to produce infectious viruses. Mutants derived from HV BACs have been used both to understand the functions of all types of genetic elements present on the virus genome, but also to generate mutants with potentially medically relevant properties such as preventative vaccines. Here we retrace the development of the BAC technology applied to the Epstein-Barr virus (EBV) and review the strategies available for the construction of mutants. We expand on the appropriate controls required for proper use of the EBV BACs, and on the technical hurdles researchers face in working with these recombinants. We then discuss how further technological developments might successfully overcome these difficulties. Finally, we catalog the EBV BAC mutants that are currently available and illustrate their contributions to the field using a few representative examples.

Epstein-Barr virus strains defined by the latent membrane protein 1 sequence characterize Thai ethnic groups

Epstein-Barr virus (EBV) is ubiquitous in the human population and seroepidemiological studies have revealed that more than 90% of adults are infected with the virus in Thailand. It has been suggested that latent membrane protein 1 (LMP1) variants may differ in their tumorigenicity and geographical localization. The distribution of LMP1 variants of EBV in the Thai population was studied. A total of 259 LMP1 sequences from ten Thai ethnic groups (Lahu, Lisu, Shan, Red Karen, White Karen, Hmong, Akha, Mlabri, Moken and Urak Lawoi) were studied using direct PCR sequencing. Nucleotide sequences corresponding to the C terminus of the LMP1, including previously published sequences from central and southern Thais, were used in the phylogenetic analysis. Five strains--the B95-8 prototype, China 1, China 2, Mediterranean (Med) and SEA 2--were identified in ethnic groups in Thailand. The major strain and the distribution pattern differed by group and location. When the ethnic groups were classified by linguistic group, the prevalence of the SEA 2 strain was significantly different between Austro-Thais and other linguistic groups (P=0.0001), whereas, among Tibeto-Burman linguistic groups, the prevalence of the Med strain was different between matrilocal and patrilocal groups (P=0.0245). The distribution of LMP1 strains in ethnic minorities in Thailand is associated with ethnogeographical factors and the social/marriage system. This study thus provides evidence for the importance of interactions between populations in virus diversity.

A functional insertion/deletion polymorphism in the promoter region of NFKB1 gene increases susceptibility for nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a common malignancy in southern China and Southeast Asia. Nuclear factor-kappaB (NF-kappaB)-activation plays critical roles in Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) mediated tumorigenesis in NPC. A functional insertion/deletion polymorphism (-94 insertion/deletion ATTG) in the promoter of NFKB1 gene, which encodes the p50 subunit of NF-kappaB protein complex, was recently identified. This study found that the frequency of ATTG(2) allele in NPC patients was significantly higher than that in control subjects (66% vs. 57.1%, p=0.015, OR=1.453), suggesting that the functional NFKB1 promoter polymorphism is associated with increased risk for NPC.

Epstein-Barr virus nuclear antigen 2 trans-activates the cellular antiapoptotic bfl-1 gene by a CBF1/RBPJ kappa-dependent pathway

The human herpesvirus Epstein-Barr virus (EBV) establishes latency and promotes the long-term survival of its host B cell by targeting the molecular machinery controlling cell fate decisions. The cellular antiapoptotic bfl-1 gene confers protection from apoptosis under conditions of growth factor deprivation when expressed ectopically in an EBV-negative Burkitt's lymphoma-derived cell line (B. D'Souza, M. Rowe, and D. Walls, J. Virol. 74:6652-6658, 2000), and the EBV latent membrane protein 1 (LMP1) and its cellular functional homologue CD40 can both drive bfl-1 via an NF-kappaB-dependent enhancer element in the bfl-1 promoter (B. N. D'Souza, L. C. Edelstein, P. M. Pegman, S. M. Smith, S. T. Loughran, A. Clarke, A. Mehl, M. Rowe, C. Gélinas, and D. Walls, J. Virol. 78:1800-1816, 2004). Here we show that the EBV nuclear antigen 2 (EBNA2) also upregulates bfl-1. EBNA2 trans-activation of bfl-1 requires CBF1 (or RBP-J kappa), a nuclear component of the Notch signaling pathway, and there is an essential role for a core consensus CBF1-binding site on the bfl-1 promoter. trans-activation is dependent on the EBNA2-CBF1 interaction, is modulated by other EBV gene products known to interact with the CBF1 corepressor complex, and does not involve activation of NF-kappaB. bfl-1 expression is induced and maintained at high levels by the EBV growth program in a lymphoblastoid cell line, and withdrawal of either EBNA2 or LMP1 does not lead to a reduction in bfl-1 mRNA levels in this context, whereas the simultaneous loss of both EBV proteins results in a major decrease in bfl-1 expression. These findings are relevant to our understanding of EBV persistence, its role in malignant disease, and the B-cell developmental process.

Regulation of intracellular signalling by the terminal membrane proteins of members of the Gammaherpesvirinae

The human gamma(1)-herpesvirus Epstein-Barr virus (EBV) and the gamma(2)-herpesviruses Kaposi's sarcoma-associated herpesvirus (KSHV), rhesus rhadinovirus (RRV), herpesvirus saimiri (HVS) and herpesvirus ateles (HVA) all contain genes located adjacent to the terminal-repeat region of their genomes, encoding membrane proteins involved in signal transduction. Designated 'terminal membrane proteins' (TMPs) because of their localization in the viral genome, they interact with a variety of cellular signalling molecules, such as non-receptor protein tyrosine kinases, tumour-necrosis factor receptor-associated factors, Ras and Janus kinase (JAK), thereby initiating further downstream signalling cascades, such as the MAPK, PI3K/Akt, NF-kappaB and JAK/STAT pathways. In the case of TMPs expressed during latent persistence of EBV and HVS (LMP1, LMP2A, Stp and Tip), their modulation of intracellular signalling pathways has been linked to the provision of survival signals to latently infected cells and, hence, a contribution to occasional cellular transformation. In contrast, activation of similar pathways by TMPs of KSHV (K1 and K15) and RRV (R1), expressed during lytic replication, may extend the lifespan of virus-producing cells, alter their migration and/or modulate antiviral immune responses. Whether R1 and K1 contribute to the oncogenic properties of KSHV and RRV has not been established satisfactorily, despite their transforming qualities in experimental settings.

Dynamic chromatin boundaries delineate a latency control region of Epstein-Barr virus

The oncogenic potential of latent Epstein-Barr virus (EBV) can be regulated by epigenetic factors controlling LMP1 and EBNA2 gene transcription. The EBV latency control region (LCR) constitutes approximately 12 kb of viral sequence spanning the divergent promoters of LMP1 and EBNA2 and encompasses the EBV latent replication origin OriP and RNA polymerase III-transcribed EBV-encoded RNA genes. We have used the chromatin immunoprecipitation assay to examine the chromatin architecture of the LCR in different types of EBV latency programs. We have found that histone H3 K4 methylation (H3mK4) was enriched throughout a large domain that extended from internal repeat 1 (IR1) to the terminal repeat in type III latency where EBNA2 and LMP1 genes are expressed. In type I latency where EBNA2 and LMP1 genes are transcriptionally silent, the H3mK4 domain contracts and does not enter the EBNA2 or LMP1 promoters. In contrast, histone H3 K9 methylation (H3mK9), associated with silent heterochromatin, was enriched in the EBNA2 and LMP1 upstream control regions in type I but not type III cells. MTA [5'-deoxy-5'(methylthio)adenosine], a pharmacological inhibitor of protein methylation, globally reduced histone H3mK4 and inhibited EBNA2 transcription in type III cells. 5'-Azacytidine, an inhibitor of DNA methylation that derepresses EBNA2 transcription in type I latency, caused H3mK4 expansion and a corresponding loss of H3mK9 at IR1. The chromatin boundary protein and transcription repressor CCCTC-binding factor was enriched at the EBNA2 transcription control region in type I but not type III cells. We also present evidence that OriP binding factors EBNA1 and ORC2 can interact with sequences outside of OriP including a region within IR1 that may influence EBNA2 transcription status. These results indicate that types I and III latency programs have distinct histone methylation patterns in the LCR and suggest that chromatin architecture coordinates gene expression of LMP1 and EBNA2.

Production of high-titer Epstein-Barr virus recombinants derived from Akata cells by using a bacterial artificial chromosome system

An Epstein-Barr virus (EBV) genome in Burkitt's lymphoma-derived cell line Akata was cloned into a bacterial artificial chromosome (BAC) vector. The BAC clone, designated AK-BAC, was rapidly and precisely modified by means of efficient homologous recombination in Escherichia coli. This system was used to produce recombinant EBVs with transgenes. An expression cassette of green fluorescent protein (GFP) was inserted into AK-BAC, and the resultant BAC clone, AK-BAC-GFP, was transfected into Akata cells. We found that transfected BAC plasmids efficiently formed episomes in EBV-positive Akata cells. Mixtures of wild-type and AK-BAC-GFP viruses were then produced and used to infect EBV-negative Akata cells. We obtained cell clones that harbored only AK-BAC-GFP but no wild-type episome. These cell clones produced infectious viruses after stimulating virus production, and the recombinant viruses of AK-BAC-GFP efficiently immortalized primary B lymphocytes. We further revised the method so that any kind of cDNA could be rapidly inserted into the unique I-PpoI site that had been artificially introduced into AK-BAC. The AK-BAC system will have a broad range of applications, such as genetic analyses of various viral gene products and development of viral vectors for human gene therapy.

Nuclear factor kappa B-dependent activation of the antiapoptotic bfl-1 gene by the Epstein-Barr virus latent membrane protein 1 and activated CD40 receptor

Suppression of the cellular apoptotic program by the oncogenic herpesvirus Epstein-Barr virus (EBV) is central to both the establishment of latent infection and the development of EBV-associated malignancies. We have previously shown that expression of the EBV latent membrane protein 1 (LMP1) in Burkitt's lymphoma cell lines leads to increased mRNA levels from the cellular antiapoptotic bfl-1 gene (also known as A1). Furthermore, ectopic expression of Bfl-1 in an EBV-positive cell line exhibiting a latency type 1 infection protects against apoptosis induced by growth factor deprivation (B. N. D'Souza, M. Rowe, and D. Walls, J. Virol. 74:6652-6658, 2000). We now report that LMP1 drives bfl-1 promoter activity through interactions with components of the tumor necrosis factor receptor (TNFR)/CD40 signaling pathway. We present evidence that this process is NF-kappa B dependent, involves the recruitment of TNFR-associated factor 2, and is mediated to a greater extent by the carboxyl-terminal activating region 2 (CTAR2) relative to the CTAR1 domain of LMP1. Activation of CD40 receptor also led to increased bfl-1 mRNA levels and an NF-kappa B-dependent increase in bfl-1 promoter activity in Burkitt's lymphoma-derived cell lines. We have delineated a 95-bp region of the promoter that functions as an LMP1-dependent transcriptional enhancer in this cellular context. This sequence contains a novel NF-kappa B-like binding motif that is essential for transactivation of bfl-1 by LMP1, CD40, and the NF-kappa B subunit protein p65. These findings highlight the role of LMP1 as a mediator of EBV-host cell interactions and may indicate an important route by which it exerts its cellular growth transforming properties.

Epstein-Barr virus latent membrane protein 1: structure and functions

The Epstein-Barr virus latent membrane protein (LMP) 1 is a versatile protein that has profound effects on target cells through its effect on constitutive cellular proteins, e.g. TRAFs, TRADD, RIP, JAK3, BRAM1, and p85. LMP1 can stimulate or inhibit signaling pathways, resulting in transformation of rodent fibroblast cell lines, blockade of differentiation in epithelial cells, upregulation of anti-apoptotic proteins, production of cytokines, upregulation of cell surface markers, upregulation of DNA methyltransferase activity, and downregulation of cell adhesion molecules and cyclin-dependent kinases. Overall, this results in greater transformation and survival in LMP1-expressing cells. Within nasopharyngeal carcinoma biopsy tissues, a naturally occurring LMP1 variant has been identified as having a 10-amino acid deletion in the C-terminus that seems to confer greater transformation potential than non-deleted LMP1. The role of LMP1 as a viral oncogene and its interaction with cellular factors are discussed.

Epstein-Barr virus regulates STAT1 through latent membrane protein 1

This study shows a mechanism for the increase of signal transducer and activator of transcription 1 (STAT1) in Epstein-Barr virus-immortalized cells. Latent membrane protein 1 (LMP-1) expression was sufficient to induce STAT1 expression, DNA binding, and transcriptional activity. LMP-1-expressing cells can induce an increase in STAT1 expression in LMP-negative cells in the same culture, suggesting an indirect regulation of STAT1 expression. The increase in STAT1 expression is mediated by the C-terminal activating region 1 (CTAR-1) and/or CTAR-2 domains of LMP-1 and is inhibited by mutant IkappaB, demonstrating a role for NFkappaB in LMP-1-mediated STAT1 expression.