The Epstein-Barr virus-encoded LMP2A and LMP2B proteins promote epithelial cell spreading and motility

Epstein-Barr Viruses: Their Immune Evasion Strategies and Implications for Autoimmune Diseases

Epstein-Barr virus (EBV), a member of the γ-herpesvirus family, is one of the most prevalent and persistent human viruses, infecting up to 90% of the adult population globally. EBV's life cycle includes primary infection, latency, and lytic reactivation, with the virus primarily infecting B cells and epithelial cells. This virus has evolved sophisticated strategies to evade both innate and adaptive immune responses, thereby maintaining a lifelong presence within the host. This persistence is facilitated by the expression of latent genes such as EBV nuclear antigens (EBNAs) and latent membrane proteins (LMPs), which play crucial roles in viral latency and oncogenesis. In addition to their well-known roles in several types of cancer, including nasopharyngeal carcinoma and B-cell lymphomas, recent studies have identified the pathogenic roles of EBV in autoimmune diseases such as multiple sclerosis, rheumatoid arthritis, and systemic lupus erythematosus. This review highlights the intricate interactions between EBV and the host immune system, underscoring the need for further research to develop effective therapeutic and preventive strategies against EBV-associated diseases.

Carcinogenic mechanisms of virus-associated lymphoma

The development of lymphoma is a complex multistep process that integrates numerous experimental findings and clinical data that have not yet yielded a definitive explanation. Studies of oncogenic viruses can help to deepen insight into the pathogenesis of lymphoma, and identifying associations between lymphoma and viruses that are established and unidentified should lead to cellular and pharmacologically targeted antiviral strategies for treating malignant lymphoma. This review focuses on the pathogenesis of lymphomas associated with hepatitis B and C, Epstein-Barr, and human immunodeficiency viruses as well as Kaposi sarcoma-associated herpesvirus to clarify the current status of basic information and recent advances in the development of virus-associated lymphomas.

EBV promotes vascular mimicry of dormant cancer cells by potentiating stemness and EMT

Vascular mimicry (VM) is defined as a vascular channel-like structure composed of tumor cells that correlates with the growth of cancer cells by providing blood circulation. However, whether VM can be formed in dormant cancer cells remains unclear. Our previous research revealed that polyploid giant cancer cells (PGCCs) are specific dormant cells related to the poor prognosis of head and neck cancer. Here, we demonstrated that EBV could promote VM formation by PGCCs in vivo and in vitro. Furthermore, we revealed that the activation of the ERK pathway partly mediated by LMP2A is responsible for stemness, and the acquisition of the stemness phenotype is crucial to the malignant biological behavior of PGCCs. The epithelial-to-mesenchymal transition (EMT) process plays a considerable role in PGCCs, and EMT progression is vital for EBV-positive PGCCs to form VM. This is the first study to reveal that EBV creates plasticity in PGCC-VM and provide a new strategy for targeted anti-tumor therapy.

Epstein-Barr Virus (EBV) Epithelial Associated Malignancies: Exploring Pathologies and Current Treatments

Epstein-Barr virus (EBV) is one of eight known herpesviruses with the potential to infect humans. Globally, it is estimated that between 90-95% of the population has been infected with EBV. EBV is an oncogenic virus that has been strongly linked to various epithelial malignancies such as nasopharyngeal and gastric cancer. Recent evidence suggests a link between EBV and breast cancer. Additionally, there are other, rarer cancers with weaker evidence linking them to EBV. In this review, we discuss the currently known epithelial malignancies associated with EBV. Additionally, we discuss and establish which treatments and therapies are most recommended for each cancer associated with EBV.

Epstein-Barr Virus Mediated Signaling in Nasopharyngeal Carcinoma Carcinogenesis

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

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.

EBV down-regulates COX-2 expression via TRAF2 and ERK signal pathway in EBV-associated gastric cancer

Epstein-Barr virus-associated gastric cancer (EBVaGC) accounts for nearly 10% of gastric cancer. Cyclooxygenase-2 (COX-2) plays a crucial role in cancer progression. However, there is no experimental study on the regulation mechanism of EBV on COX-2 in EBVaGC. To understand more about the tumorigenic mechanism of EBVaGC, the study investigated the role of EBV encode latent membrane protein LMP1 and LMP2A in the regulation of COX-2. The expression of COX-2 was examined in EBVaGC and EBV negative gastric cancer (EBVnGC) cell lines. The plasmids were transfected in SGC7901 to overexpress LMP1/2A. Small interfering RNA (si-RNA) targeting LMP1/2A in GT38 and targeting TRAF2 in SGC7901 were used to detect the expression of COX-2. Furthermore, si-ERK1/2 and the MEK inhibitor PD0325901 were used to investigate whether p-ERK participate in the regulation of COX-2 in SGC7901. The overexpression of LMP1 or LMP2A in SGC7901 down-regulates both COX-2 and TRAF2 expression, and knockdown of LMP1 or LMP2A in GT38 resulted in a certain recovery of COX-2 and TRAF2 expression. Moreover, si-TRAF2 indicated that a sharp down-regulation of COX-2. And the decrease of p-ERK also mediates the inhibitory effect of LMP1 on COX-2. In summary, overexpression of LMP1 and LMP2A inhibits COX-2, which is mediated by a decrease of TRAF2, and p-ERK is involved in the inhibition of COX-2 by LMP1 in gastric cancer.

Triptolide suppresses the proliferation and induces the apoptosis of nasopharyngeal carcinoma cells via the PI3K/Akt pathway

Nasopharyngeal carcinoma (NPC) is an endothelium-associated malignancy that is heavily influenced by Epstein Barr virus infection. Triptolide, extracted from Tripterygium wilfordii, has been proven to possess anti-inflammatory, immunosuppressive and anti-cancerous activity. Although the effect of triptolide on numerous cancer cell types has been outlined, its effect in NPC remained unclear. The present study investigated the effects and underlying mechanisms of triptolide in C666-1 and NP69 cells. It was revealed that triptolide significantly inhibited proliferation and induced apoptosis in C666-1 cells. Increased levels of cleaved-caspase-3 and apoptosis regulator BAX, decreased expression of apoptosis regulator Bcl-2, and reduced phosphorylation of RAC-α serine/threonine-protein kinase (Akt), were responsible for this induction of apoptosis. Notably, pretreating C666-1 cells with the phosphatidylinositol 3-kinase (PI3K)/Akt inhibitor LY294002 suggested that with increasing concentrations of LY294002, triptolide exhibited decreasing ability to suppress proliferation and induce apoptosis in these cells. In conclusion, the results demonstrated that triptolide suppressed the proliferation and induced the apoptosis of C666-1 cells in a PI3K/Akt-dependent manner and therefore, may serve as a promising therapeutic candidate for NPC.

Pathogenic Role of Exosomes in Epstein-Barr Virus (EBV)-Associated Cancers

Exosomes are 40- to 100-nm membrane-bound small vesicles that carry a great variety of cellular cargoes including proteins, DNA, messenger RNAs (mRNAs), and microRNAs (miRNAs). These nanovesicles are detected in various biological fluids such as serum, urine, saliva, and seminal fluids. Exosomes serve as key mediators in intercellular communication by facilitating the transfer and exchange of cellular components from cells to cells. They contain various pathogenic factors whereby their adverse effects have been implicated in multiple viral infections and cancers. Interestingly, accumulating evidences showed that exosomes derived from tumour viruses or oncoviruses, exacerbate virus-associated cancers by remodelling the tumour microenvironment. In this review, we summarize the contributing factors of Epstein-Barr virus (EBV) products-containing exosomes in viral pathogenesis and their potential implications in EBV-driven malignancies. Understanding the biological role of these exosomes in the disease would undoubtedly boost the development of a more comprehensive strategy to combat EBV-associated cancers and to better predict the therapeutic outcomes. Furthermore, we also highlight the potentials and challenges of EBV products-containing exosomes being employed as diagnostic markers and therapeutic targets for EBV-related cancers. Since these aspects are rather underexplored, we attempt to underline interesting areas that warrant further investigations in the future.

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.

Lentivirus-mediated RNAi knockdown of LMP2A inhibits the growth of the Epstein-Barr-associated gastric carcinoma cell line GT38 in vitro

In this study, lentivirus-mediated RNA interference (RNAi) was applied to inhibit latent membrane protein 2A (LMP2A) gene expression, in order to explore the effects of LMP2A silencing on the growth of an Epstein-Barr virus-associated gastric carcinoma (EBVaGC) cell line in vitro. Lentivirus-mediated RNAi technology was employed to specifically knock down the LMP2A gene in the EBV-positive gastric carcinoma cell line GT38. After infection, reverse transcription-quantitative polymerase chain reaction, western blotting, flow cytometry and colony formation assays were conducted to evaluate the expression of LMP2A and the biological behavior of the GT38 cell line in vitro. The results showed that the expression of the LMP2A gene was clearly downregulated in the infected cells, which indicated that a highly efficient and stable lentivirus vector was successfully constructed. In the GT38 cells in which the expression of LMP2A was downregulated, the proliferation and colony formation of the cells was significantly inhibited. In addition, it was found that the cell cycle of the GT38 cells was arrested in the G0/G1 phase and the apoptosis rate was increased. These results indicate that lentivirus-mediated RNAi knockdown of LMP2A inhibits the growth of the EBVaGC cell line GT38 in vitro, and suggests that LMP2A is a potential target for gene therapy in the treatment of EBVaGC.

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.

Nasopharyngeal Cancer: Molecular Landscape

Nasopharyngeal carcinoma (NPC) is a unique epithelial malignancy arising from the superior aspect of the pharyngeal mucosal space, associated with latent Epstein-Barr virus infection in most cases. The capacity to characterize cancer genomes in unprecedented detail is now providing insights into the genesis and molecular underpinnings of this disease. Herein, we provide an overview of the molecular aberrations that likely drive nasopharyngeal tumor development and progression. The contributions of major Epstein-Barr virus–encoded factors, including proteins, small RNAs, and microRNAs, along with their interactions with pathways regulating cell proliferation and survival are highlighted. We review recent analyses that clearly define the role of genetic and epigenetic variations affecting the human genome in NPC. These findings point to the impact of DNA methylation and histone modifications on gene expression programs that promote this malignancy. The molecular interactions that allow NPC cells to evade immune recognition and elimination, which is crucial for the survival of cells expressing potentially immunogenic viral proteins, are also described. Finally, the potential utility of detecting host and viral factors for the diagnosis and prognosis of NPC is discussed. Altogether, the studies summarized herein have greatly expanded our knowledge of the molecular biology of NPC, yet much remains to be uncovered. Emerging techniques for using and analyzing well-annotated biospecimens from patients with NPC will ultimately lead to a greater level of understanding, and enable improvements in precision therapies and clinical outcomes.

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.

Chimerically fused antigen rich of overlapped epitopes from latent membrane protein 2 (LMP2) of Epstein-Barr virus as a potential vaccine and diagnostic agent

Epstein-Barr virus (EBV) is prevalent throughout the world and is associated with several malignant diseases in humans. Latent membrane protein 2 (LMP2) of EBV plays a crucial role in the pathogenesis of EBV-associated tumors; therefore, LMP2 has been considered to be a potential immunodiagnostic and immunotherapeutic target. A multi-epitope-based antigen is a promising option for therapeutic vaccines and diagnoses of such malignancies. In this study, we systematically screened cytotoxic T lymphocyte (CTL), helper T cell (Th) and B-cell epitopes within EBV-LMP2 using bioinformatics. Based on the screen, two peptides rich in overlapping epitopes of both T cells and B cells were selected to construct a plasmid containing the sequence for a chimeric multi-epitope protein referred to as EBV-LMP2m, which is composed of LMP2aa195∼232 and LMP2aa419∼436. The EBV-LMP2m protein was expressed in E. coli BL21 (DE3) after prokaryotic codon optimization. Inoculation of the purified chimeric antigen in BALB/c mice induced not only high levels of specific IgG in the serum and secretory IgA in the vaginal mucus but also a specific CTL response. By using purified EBV-LMP2m as an antigen, the presence of specific IgG in the serum specimens of 202 nasopharyngeal carcinoma (NPC) patients was effectively detected with 52.84% sensitivity and 95.40% specificity, which represents an improvement over the traditional detection method based on VCA-IgA (60.53% sensitivity and 76.86% specificity). The above results indicate that EBV-LMP2m may be used not only as a potential target antigen for EBV-associated tumors but also a diagnostic agent for NPC patients.

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.

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.

SYK interaction with ITGβ4 suppressed by Epstein-Barr virus LMP2A modulates migration and invasion of nasopharyngeal carcinoma cells

Epstein-Barr virus (EBV)-encoded Latent Membrane Protein 2A (LMP2A) is an EBV latency-associated protein regularly expressed in nasopharyngeal carcinoma (NPC). In B cells, LMP2A activity resembles that of a constitutively activated antigen receptor, which recruits the Syk tyrosine kinase to activate a set of downstream signaling pathways. LMP2A also downregulates cellular Syk levels. In the present study, we demonstrate that Syk interacts with the integrin β4 subunit (ITGβ4) of integrin α6β4 in epithelial cells and that concurrent LMP2A expression interferes with this interaction by competitive binding to Syk. We find that both Syk and LMP2A have an effect on ITGβ4 cell surface expression. However, in LMP2A expressing cells, ITGβ4 remains concentrated at the cellular protrusions, an expression pattern characteristic of motile cells, including NPC-derived epithelial cells. This effect of LMP2A on ITGβ4 localization is associated with a greater propensity for migration and invasion in-vitro, and may contribute to the invasive property of LMP2A-expressing NPC.

Epstein-Barr virus and nasopharyngeal carcinoma

Since its discovery 50 years ago, Epstein-Barr virus (EBV) has been linked to the development of cancers originating from both lymphoid and epithelial cells. Approximately 95% of the world's population sustains an asymptomatic, life-long infection with EBV. The virus persists in the memory B-cell pool of normal healthy individuals, and any disruption of this interaction results in virus-associated B-cell tumors. The association of EBV with epithelial cell tumors, specifically nasopharyngeal carcinoma (NPC) and EBV-positive gastric carcinoma (EBV-GC), is less clear and is currently thought to be caused by the aberrant establishment of virus latency in epithelial cells that display premalignant genetic changes. Although the precise role of EBV in the carcinogenic process is currently poorly understood, the presence of the virus in all tumor cells provides opportunities for developing novel therapeutic and diagnostic approaches. The study of EBV and its role in carcinomas continues to provide insight into the carcinogenic process that is relevant to a broader understanding of tumor pathogenesis and to the development of targeted cancer therapies.

Oncogenic effects of WNT5A in Epstein-Barr virus‑associated nasopharyngeal carcinoma

The molecular events that drive the progression of Epstein-Barr virus (EBV)-associated nasopharyngeal carcinoma (NPC) are still to be elucidated. Here, we report for the first time the pathogenic significance of an NPC-associated gene, wingless-type MMTV integration site family, member 5A (WNT5A) and the contribution of EBV to its expression. WNT5A is a representative Wnt protein that activates non-canonical Wnt signalling. With regard to its role in carcinogenesis, there is conflicting evidence as to whether WNT5A has a tumour-promoting or tumour-suppressive role. We show that WNT5A is upregulated in primary NPC tissue samples. We also demonstrate that WNT5A expression was dramatically increased in NPC cell lines expressing the EBV-encoded LMP2A gene, suggesting that this EBV-encoded latent gene is responsible for upregulating WNT5A in NPC. In addition, in vitro WNT5A overexpression promotes the proliferation, migration and invasion of NPC cells. Our results not only reveal pro-tumorigenic effects of WNT5A in NPC but also suggest that WNT5A could be an important therapeutic target in patients with EBV-associated disease.

The Epstein-Barr virus-encoded microRNA MiR-BART9 promotes tumor metastasis by targeting E-cadherin in nasopharyngeal carcinoma

MicroRNAs (miRNAs) are a family of small RNA molecules that negatively regulate the expression of protein-coding genes and play critical roles in orchestrating diverse cellular processes. This regulatory mechanism is also exploited by viruses to direct their life cycle and evade the host immune system. Epstein-Barr virus (EBV) is an oncogenic virus that is closely associated with multiple human diseases, including nasopharyngeal carcinoma (NPC), which is a highly metastatic type of tumor and is frequently reported in South Asia. Several viral proteins have been found to promote the migration and invasiveness of NPC cells. However, not all tumor tissues express these viral oncoproteins, suggesting that other mechanisms may contribute to the aggressive behavior of NPC tumor cells. A previous sequencing study by our group revealed that the EBV miRNA miR-BART9 was expressed at high levels in all EBV-positive NPC tissues. In the present study, we used gain- and loss-of-function approaches to investigate the effect of miR-BART9 in EBV-negative and EBV-positive NPC cells. We discovered that miR-BART9 promotes the migration and invasiveness of cultured NPC cells. The promigratory activity observed in vitro was manifested as an enhanced metastatic ability in vivo. Computational analysis revealed that miR-BART9 may target E-cadherin, a membrane protein that is pivotal in preserving cell-cell junctions and the epithelial phenotype. Through biochemical assays and functional rescue analysis, we confirmed that miR-BART9 specifically inhibits E-cadherin to induce a mesenchymal-like phenotype and promote the migration of NPC cells. These results indicated that miR-BART9 is a prometastatic viral miRNA and suggested that high levels of miR-BART9 in EBV-positive NPC cells may contribute to the aggressiveness of tumor cells.

MicroRNAs (miRNAs) are a family of small RNA molecules that negatively regulate the expression of protein-coding genes and orchestrate diverse cellular processes. This regulatory mechanism is also exploited by viruses to manage their life cycle and to evade the host immune system. Epstein-Barr virus (EBV) is closely associated with nasopharyngeal carcinoma (NPC), which is a highly metastatic type of tumor. A previous by our group study discovered that the EBV miRNA miR-BART9 is expressed at high levels in all EBV-positive NPC tissues. In the present study, we used gain- and loss-of-function approaches to investigate the function of miR-BART9 in EBV-negative and EBV-positive NPC cells. We showed that miR-BART9 promotes the migration and invasiveness of cultured NPC cells and enhances the metastatic ability of NPC tumors in vivo. Through computational analysis, we discovered that E-cadherin, a membrane protein that is critical for maintaining cell-cell contact and suppressing tumor metastasis, is a potential target for miR-BART9. Through biochemical assays and a functional rescue analysis, we confirmed that miR-BART9 specifically inhibits E-cadherin to enhance the motility of NPC cells. Our results show that miR-BART9 is a prometastatic viral miRNA and suggest that miR-BART9 may contribute to the aggressiveness of EBV-positive NPC tumors.

Epstein-Barr virus as a paradigm in nasopharyngeal cancer: from lab to clinic

Nasopharyngeal carcinoma (NPC) of the undifferentiated subtype remains endemic in southern China, with a peak incidence in this region approaching 30 cases per 100,000 population per year. Despite advances in chemotherapy and radiation delivery techniques in localized disease, distant metastasis is still common and NPC remains the seventh leading cause of cancer death in the region. There is great need for early diagnosis, developing novel therapies, and identifying patients with localized disease at higher risk of future recurrence or metastasis to appropriately tailor their treatment and improve outcomes. Knowledge of the integral involvement of Epstein-Barr virus (EBV) in the pathogenesis of undifferentiated NPC has been of seminal importance in developing strategies to optimize disease management. The close association with EBV is being evaluated in multiple settings including screening of at-risk populations, disease prognostication, development of targeted therapies, optimizing adjuvant treatment, and early recurrence detection. These translational studies are likely to have an enormous effect on management of undifferentiated NPC and significantly improve the landscape of the disease in years to come.

Epstein-Barr virus latent membrane protein 2A contributes to anoikis resistance through ERK activation

Epstein-Barr virus (EBV) is associated with various malignancies, including epithelial cancers. In this study, we analyzed the effect of EBV infection on epithelial cells by using EBV-converted epithelial cells. In EBV-positive cells, the extracellular signal-regulated kinase (ERK) pathway is constitutively activated. Inhibition of ERK activity leads to reduced anoikis resistance; therefore, EBV-positive cells are more resistant to anoikis, a type of apoptosis induced by cell detachment, than are EBV-negative cells. Among the viral genes expressed in EBV-positive cells, the latent membrane protein 2A (LMP2A) is responsible for induction of ERK-mediated anoikis resistance, although the expression level of LMP2A is much lower in EBV-positive cells than in EBV-transformed B cells. Further analysis demonstrated that LMP2A downregulation of the proanoikis mediator Bim through proteasomal degradation is dependent on the immunoreceptor tyrosine-based activation motif (ITAM). These findings suggest that LMP2A-mediated ERK activation is involved in the generation of EBV-associated epithelial malignancies.

Inhibition of store-operated Ca2+ entry suppresses EGF-induced migration and eliminates extravasation from vasculature in nasopharyngeal carcinoma cell

Store-operated Ca(2+) entry (SOCE) mediates Ca(2+) responses evoked by extracellular signaling molecules to promote increases in cytosolic Ca(2+), thereby triggering downstream signal transduction. Here we demonstrated that either the pharmacological blockage of Ca(2+) influx through SOCE or the knockdown of Orai1, a key molecule of SOCE, suppressed the epidermal growth factor-induced migration by disturbing Ca(2+) signaling in nasopharyngeal carcinoma (NPC) cell. Furthermore, Orai1 depletion led to a delayed cell attachment to the extracellular matrix surface in vitro and eliminated the extravasation of microinjected cells from vasculature in a zebrafish hematogenous metastasis model. Our findings thus indicate that SOCE acts as a predominant Ca(2+) signaling involved in NPC cell metastasis, and may serve as a candidate target for anti-metastasis therapy in NPC.

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.

Transcriptome changes induced by Epstein-Barr virus LMP1 and LMP2A in transgenic lymphocytes and lymphoma

Latent membrane protein 1 (LMP1) and LMP2A affect cell growth in both epithelial cells and lymphocytes. In this study, the effects on cellular gene expression were determined by microarray analysis of transgenic mice expressing LMP1, LMP2A, or both using the immunoglobulin heavy chain promoter and enhancer. Large differential changes were detected, indicating that LMP1 and LMP2A can both potently affect host gene transcription, inducing distinct transcriptional profiles. Seventy percent of the changes detected in LMP1/2A doubly transgenic lymphocytes were also modulated by LMP1 or LMP2A alone. These common and unique expression changes indicate that the combined effects of LMP1 and LMP2A may be additive, synergistic, or inhibitory. Using significant pathway analysis, the expression changes detected in LMP1, LMP2A, and LMP1/2A transgenic B lymphocytes were predicted to commonly target cancer and inflammatory pathways. Additionally, using the correlation coefficient to calculate the regulation of known c-Rel and Stat3 transcriptional targets, both were found to be enhanced in LMP1 lymphocytes and lymphomas, and a selection of Stat3 targets was further evaluated and confirmed using quantitative reverse transcription-PCR (RT-PCR). Analyses of the effects on cell growth and viability revealed that LMP2A transgenic lymphocytes had the greatest enhanced viability in vitro; however, doubly transgenic lymphocytes (LMP1/2A) did not have enhanced survival in culture and these mice were similar to negative littermates. These findings indicate that the combined expression of LMP1 and LMP2A has potentially different biological outcomes than when the two proteins are expressed individually.

The Epstein-Barr virus proteins latent membrane protein 1 (LMP1) and LMP2A have potent effects on cell growth. In transgenic mice that express these proteins in B lymphocytes, the cell growth and survival properties are also affected. LMP1 transgenic mice have increased development of lymphoma, and the LMP1 lymphocytes have increased viability in culture. LMP2A transgenic lymphocytes have altered B cell development and enhanced survival. In this study, analysis of the cellular gene expression changes in transgenic LMP1 and LMP2A lymphocytes and LMP1 lymphomas revealed that both transgenes individually and in combination affected pathways important for the development of cancer and inflammation. Importantly, the combined expression of the two proteins had unique effects on cellular expression and cell viability. This is the first study to look at the combined effects of LMP1 and LMP2A on global changes in host gene expression.

Epstein-Barr virus latent membrane protein-2A induces ITAM/Syk- and Akt-dependent epithelial migration through αv-integrin membrane translocation

Epstein-Barr virus (EBV) is a highly prevalent herpesvirus associated with epithelial cancers, including nasopharyngeal carcinoma (NPC). The EBV protein latent membrane protein 2 (LMP2) is expressed in NPC tumor tissue and has been shown to induce transformation, inhibit differentiation, and promote migration of epithelial cells. In this study, the effect of LMP2A on migration of human epithelial cells was further analyzed. LMP2A expression induced migration in human foreskin keratinocytes (HFK) and HaCaT keratinocytes measured by wound healing scratch assay and chemoattractant-induced Transwell migration assay. The induction of migration by LMP2A required the ITAM signaling domain of LMP2A and activation of the Syk tyrosine kinase. LMP2A-induced Transwell migration required the Akt signaling pathway, and activation of Akt by LMP2A required the ITAM signaling domain of LMP2A. LMP2A also induced phosphorylation of the Akt target GSK3β, a Wnt signaling mediator that has been shown to regulate the activity of focal adhesion kinase (FAK), a tyrosine kinase activated by clustering and ligand interaction of integrins. Inhibition of either FAK or its signaling mediator Src kinase inhibited LMP2A-induced migration. Interestingly, αV-integrin was greatly increased in membrane-enriched fractions by LMP2A, and a neutralizing antibody to αV-integrin blocked migration, suggesting that the effects of LMP2A on membrane-localized αV-integrin promoted migration. The results of this study indicate that LMP2A expression in human epithelial cells induces αV-integrin-dependent migration through a mechanism requiring ITAM-mediated Syk and Akt activation and inducing membrane translocation or stabilization of αV-integrin and FAK activation. The specific effects of LMP2A on an integrin with a diverse repertoire of ligand specificities could promote migration of different cell types and be initiated by multiple chemoattractants.

Epstein-Barr virus latent membrane protein 2A promotes invasion of nasopharyngeal carcinoma cells through ERK/Fra-1-mediated induction of matrix metalloproteinase 9

Epstein-Barr virus (EBV)-associated nasopharyngeal carcinoma (NPC) is highly metastatic, and this malignant feature may be promoted by an EBV oncoprotein, latent membrane protein 2A (LMP2A). Acting as a signal regulator, LMP2A can enhance invasiveness and motility of epithelial cells. Downstream from the LMP2A-triggered signaling events, it is largely unknown what key effector proteins are induced and essentially promote cell invasion. In the present study, we found that in NPC cells, LMP2A upregulated matrix metalloproteinase 9 (MMP9), a metastasis-associated protease. LMP2A increased MMP9 expression at both the mRNA and protein levels. It also activated the MMP9 promoter, in which two AP-1 elements were required for the promoter activation. Among AP-1 transcription factors, Fra-1 was induced by LMP2A and is essential for LMP2A-triggered MMP9 expression. Induction of Fra-1 was dependent on the LMP2A-activated ERK1/2 pathway, and induction of the ERK1/2-Fra-1-MMP9 axis required PY motifs in the amino-terminal domain of LMP2A. Notably, LMP2A-promoted invasion of NPC cells was blocked when MMP9 expression, Fra-1 induction, or ERK1/2 activation was inhibited. In addition, we found an association of LMP2A with MMP9 expression in NPC tumor biopsy specimens, where Fra-1 was a major mediation factor. This study reveals an underlying mechanism of LMP2A-induced cell invasion, from signal transduction to upregulation of a critical protease. Considering that MMP9 can also be upregulated by another EBV oncoprotein, LMP1, this protease may be a pivotal effector at which the EBV-induced, invasion-promoting mechanisms converge, serving as an attractive therapeutic target for NPC treatment.

The pathological roles of BART miRNAs in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a distinct type of head and neck cancer prevalent in south-east Asia and southern China, where it constitutes a significant health burden. Although the close association of NPC with Epstein-Barr virus (EBV) infection has been known for more than four decades, the exact role that EBV plays in the pathogenesis of this malignancy is still unclear. While NPC tumours are known to express a number of EBV-encoded proteins, they also express a large number of virus-encoded microRNAs (miRNAs), the most abundant of which are those encoded from the BamHI-A region of the viral genome: the so-called BART miRNAs. miRNAs are small non-coding mRNAs that negatively regulate the expression of various genes at the post-transcriptional level. Accumulating evidence suggests that miRNAs play important roles in tumourigenesis. Here, we review the role of EBV-encoded BART miRNAs in modulating apoptosis and host innate defence mechanisms and their contribution to NPC pathogenesis. The rationale and strategies for therapeutic targeting of BART miRNAs in EBV-infected NPC are also discussed.

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.

Identification and characterization of novel B-cell epitopes within EBV latent membrane protein 2 (LMP2)

The purpose of this study was to screen and identify the linear B-cell epitopes of Epstein-Barr virus (EBV) latent membrane protein 2 (LMP2). The secondary structure and surface properties of EBV LMP2A protein were analyzed. In combination with hydrophilicity, accessibility, flexibility, and antigenicity analysis, and average antigenicity index (AI) of epitope peptide investigation, three peptides were selected as potential candidates of linear B-cell epitopes. The peptides were 199-209 (RIEDPPFNSLL), 318-322 (TLNLT), and 381-391 (KSLSSTEFIPN). The fragments encoding potential B-cell epitopes were cloned and overexpressed in an E. coli system. The immune sera of these fusion proteins were collected from BALB/c mice by subcutaneously immunizing them three times. Western blotting results showed that these epitope recombinant proteins could be recognized by the serum antibodies against the whole LMP2 from nasopharyngeal carcinoma (NPC). Indirect ELISA measuring individual sera from 196 NPC patients, 44 infectious mononucleosis (IM) patients, 253 healthy adults, and 61 healthy children, indicated that NPC patients had significantly higher reactivity to these epitope-fused proteins compared with IM and healthy individuals (p < 0.05). In addition, all the immune sera of peptide-fused proteins responded to native LMP2A antigen obtained from the EBV prototype strain, B95-8 cells. IFA results confirmed that specific antibodies induced by epitope peptide-fused proteins recognized intracellular regions of LMP2A. These results demonstrated that these three predictive epitopes not only were immunodominant B-cell epitopes of LMP2A, but also may be potential targets for applications in the design of diagnostic tools.

Deciphering the role of Epstein-Barr virus in the pathogenesis of T and NK cell lymphoproliferations

Epstein-Barr virus (EBV) is a highly successful herpesvirus, colonizing more than 90% of the adult human population worldwide, although it is also associated with various malignant diseases. Primary infection is usually clinically silent, and subsequent establishment of latency in the memory B lymphocyte compartment allows persistence of the virus in the infected host for life. EBV is so markedly B-lymphotropic when exposed to human lymphocytes in vitro that the association of EBV with rare but distinct types of T and NK cell lymphoproliferations was quite unexpected. Whilst relatively rare, these EBV-associated T and NK lymphoproliferations can be therapeutically challenging and prognosis for the majority of patients is dismal. In this review, we summarize the current knowledge on the role of EBV in the pathogenesis of these tumours, and the implications for treatment.

Epstein-Barr virus-encoded LMP2A induces an epithelial-mesenchymal transition and increases the number of side population stem-like cancer cells in nasopharyngeal carcinoma

It has been recently reported that a side population of cells in nasopharyngeal carcinoma (NPC) displayed characteristics of stem-like cancer cells. However, the molecular mechanisms underlying the modulation of such stem-like cell populations in NPC remain unclear. Epstein-Barr virus was the first identified human tumor virus to be associated with various malignancies, most notably NPC. LMP2A, the Epstein-Barr virus encoded latent protein, has been reported to play roles in oncogenic processes. We report by immunostaining in our current study that LMP2A is overexpressed in 57.6% of the nasopharyngeal carcinoma tumors sampled and is mainly localized at the tumor invasive front. We found also in NPC cells that the exogenous expression of LMP2A greatly increases their invasive/migratory ability, induces epithelial-mesenchymal transition (EMT)-like cellular marker alterations, and stimulates stem cell side populations and the expression of stem cell markers. In addition, LMP2A enhances the transforming ability of cancer cells in both colony formation and soft agar assays, as well as the self-renewal ability of stem-like cancer cells in a spherical culture assay. Additionally, LMP2A increases the number of cancer initiating cells in a xenograft tumor formation assay. More importantly, the endogenous expression of LMP2A positively correlates with the expression of ABCG2 in NPC samples. Finally, we demonstrate that Akt inhibitor (V) greatly decreases the size of the stem cell side populations in LMP2A-expressing cells. Taken together, our data indicate that LMP2A induces EMT and stem-like cell self-renewal in NPC, suggesting a novel mechanism by which Epstein-Barr virus induces the initiation, metastasis and recurrence of NPC.

Epithelial raft cultures for investigations of virus growth, pathogenesis and efficacy of antiviral agents

The organotypic epithelial raft cultures, originally developed to study keratinocytes differentiation, represent a novel approach to the study of viruses able to infect epithelial cells. Organotypic epithelial raft cultures accurately reproduce the process of epithelial differentiation in vitro and can be prepared from normal keratinocytes, explanted epithelial tissue, or established cell lines. This culture system permits cells to proliferate and fully differentiate at the air-liquid interface on a dermal-equivalent support. Normal primary human keratinocytes (PHKs) stratify and fully differentiate in a manner similar to the normal squamous epithelial tissues, while transformed cell lines exhibit dysplastic morphologies similar to the (pre)neoplastic lesions seen in vivo. This three-dimensional (3D) culture system provides an essential tool for investigations of virus growth, virus-host cell interactions, for the genetic analysis of viral proteins and regulatory sequences, and for the evaluation of antiviral agents. The 3D epithelial cultures have proven a breakthrough in the research on papillomaviruses, since their life cycle is strictly linked to the differentiation of the host epithelium. In the last years, several reports have shown the usefulness of the 3D epithelial cultures for the study of other viruses that target at least during a part of their life cycles epithelial cells. The 3D epithelial cultures allow the analysis of virus-host cell interactions in stratified epithelia that more closely resemble the in vivo situation. In this review we describe the advances on research on 3D epithelial cultures for the study of virus growth and pathogenesis of different families of viruses, including papilloma-, herpes-, pox-, adeno-, and parvoviruses.

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.

EBV latent membrane protein 1 effects on plakoglobin, cell growth, and migration

Latent membrane protein 1 (LMP1), the major oncoprotein of EBV, is likely responsible for many of the altered cellular growth properties in EBV-associated cancers, including nasopharyngeal carcinoma (NPC). In this study, the effects of LMP1 on cell growth and migration were studied in the context of the EBV-positive C666-1 NPC cell line. In the soft agar transformation and Transwell metastasis assays, LMP1 enhanced cell growth and migration through activation of phosphatidylinositol 3-kinase (PI3K)/Akt and nuclear factor-kappaB (NF-kappaB) signaling. Inhibitors of PI3K, Akt, and NF-kappaB signaling dramatically reduced these enhanced properties. An IkappaBalpha super-repressor also blocked these effects. However, constitutive activation of Akt alone did not alter cell growth, suggesting that both PI3K/Akt and NF-kappaB activation are required by LMP1. These enhanced effects required the full-length LMP1 encompassing both the PI3K/Akt-activating COOH-terminal activation region (CTAR) 1 and the nonredundant NF-kappaB-activating regions CTAR1 and CTAR2. LMP2A, a latent protein that is also frequently expressed in NPC, similarly activates the PI3K/Akt pathway; however, its overexpression in C666-1 cells did not affect cell growth or migration. LMP1 also decreased expression of the junctional protein plakoglobin, which was shown to be partially responsible for enhanced migration induced by LMP1. This study reveals that in epithelial cells the transforming properties of LMP1 require activation of both PI3K/Akt and NF-kappaB and shows that the loss of plakoglobin expression by LMP1 is a significant factor in the enhanced migration.

Epstein-Barr virus latent membrane protein 2A upregulates UDP-glucose dehydrogenase gene expression via ERK and PI3K/Akt pathway

The Epstein-Barr virus latent membrane protein 2A (LMP2A) is frequently detected in nasopharyngeal carcinoma (NPC), a tumour of high metastatic capacity. A recent microarray assay notes that expression of the UDP-glucose dehydrogenase (UGDH) gene, participating in glycosaminoglycan synthesis, shows high correlation with LMP2A levels in NPC biopsies. This study extends the finding and demonstrates that the UGDH transcript and protein quantities, the enzyme activity, and glycosaminoglycan contents increase in LMP2A overexpressed human embryonic kidney 293 (HEK293) cells. The luciferase reporter gene assay demarcates that a region from 630 to 486 bp upstream of the transcription start is critical for LMP2A-mediated gene expression. Moreover, a specificity protein 1 (Sp1) binding site mutation in this region reduces the LMP2A-responsive expression of the UGDH gene. Consistent with these findings, cell motility enhancement by LMP2A diminishes by treating the cells with Sp1-specific inhibitor and small interference RNA (siRNA). Using a signalling pathway-specific inhibitor, it is revealed that phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular signal-regulated kinase (ERK), not c-Jun N-terminal kinase (JNK) and p38, participate in LMP2A-induced UGDH expression. This study provides a model for molecular mechanism participating in LMP2A-mediated UGDH gene activation.

DNA tumour viruses promote tumour cell invasion and metastasis by deregulating the normal processes of cell adhesion and motility

Approximately 15-20% of global cancer incidence is causally linked to viral infection, yet the low incidence of cancers in healthy infected individuals suggests that malignant conversion of virus-infected cells occurs after a long period as a result of additional genetic modifications. There are four families of viruses that are now documented to be involved in the development of human cancers which include members of the polyomavirus, hepadnavirus, papillomavirus and herpesvirus families. Although a number of these viruses are implicated in the aetiology of lymphomas or leukaemias, the vast majority are associated with malignancies of epithelial cells. In epithelial tissues, several classes of proteins are involved in maintaining tissue architecture, including those that promote cell-cell adhesion, and others, which mediate cell-matrix interactions. Proteins representative of all classes are frequently altered in malignant tumour cells that possess invasive and metastatic properties. Malignant tumour cells acquire mechanisms to degrade basement membranes and invade the underlying tissue. Many viruses encode proteins which engage signalling pathways that affect one or more of these mechanisms. It is believed that activation of these processes by chronic viral infection can, under certain circumstances, promote tumour cell invasion and metastasis. This review will take a brief look at the current knowledge of viral-induced alterations in cell motility and invasiveness in the context of tumour invasion and metastasis.

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.

Tonic B-cell and viral ITAM signaling: context is everything

The presence of an immunoreceptor tyrosine-based activation motif (ITAM) makes immunoreceptors different from other signaling receptors, like integrins, G-coupled protein receptors, chemokine receptors, and growth factor receptors. This unique motif has the canonical sequence D/Ex(0-2)YxxL/Ix(6-8)YxxL/I, where x represents any amino acid and is present at least once in all immunoreceptor complexes. Immunoreceptors can promote survival, activation, and differentiation by transducing signals through these highly conserved motifs. Traditionally, ITAM signaling is thought to occur in response to ligand-induced aggregation, although evidence indicates that ligand-independent tonic signaling also provides functionally relevant signals. The majority of proteins containing ITAMs are transmembrane proteins that exist as part of immunoreceptor complexes. However, oncogenic viruses also have ITAM-containing proteins. In this review, we discuss what is known about tonic signaling by both cellular and viral ITAM-containing proteins and speculate what we might learn from each context.

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.

IFN-alpha-stimulated genes and Epstein-Barr virus gene expression distinguish WHO type II and III nasopharyngeal carcinomas

Nonkeratinizing nasopharyngeal carcinoma (NPC) is 100% associated with Epstein-Barr Virus (EBV) and divided into two subtypes (WHO types II and III) based on histology. We tested whether these subtypes can be distinguished at the molecular genetic level using an algorithm that analyzes sets of related genes (gene set enrichment analysis). We found that a class of IFN-stimulated genes (ISG), frequently associated with the antiviral response, was significantly activated in type III versus type II NPC. Consistent with this, replication of the endogenous EBV was suppressed in type III. A strong association was also seen with a subset of ISGs previously identified in systemic lupus erythematosus, another disease in which 'normal' EBV biology is deregulated, suggesting that this pattern of ISG expression may be linked to the increased EBV activity in both diseases. In contrast, unsupervised hierarchical clustering of the complete expression profiles failed to distinguish the two subsets. These results suggest that type II and III NPC have not originated from obviously distinct epithelial precursors; rather, the histologic differences may be a consequence of a differential antiviral response, involving IFNs, to chronic EBV infection.

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

Latent membrane protein 2A (LMP2A) and LMP2B are viral proteins expressed during Epstein-Barr virus (EBV) latency in EBV-infected B cells both in cell culture and in vivo. LMP2A has important roles in modulating B-cell receptor (BCR) signal transduction by associating with the cellular tyrosine kinases Lyn and Syk via specific phosphotyrosine motifs found within the LMP2A N-terminal tail domain. LMP2A has been shown to alter normal BCR signal transduction in B cells by reducing levels of Lyn and by blocking tyrosine phosphorylation and calcium mobilization following BCR cross-linking. Although little is currently known about the function of LMP2B in B cells, the similarity in structure between LMP2A and LMP2B suggests that they may localize to the same cellular compartments. To investigate the function of LMP2B, B-cell lines expressing LMP2A, LMP2B, LMP2A/LMP2B, and the relevant vector controls were analyzed. As was previously shown, cells expressing LMP2A had a dramatic block in normal BCR signal transduction as measured by calcium mobilization and tyrosine phosphorylation. There was no effect on BCR signal transduction in cells expressing LMP2B. Interestingly, when LMP2B was expressed in conjunction with LMP2A, there was a restoration of normal BCR signal transduction upon BCR cross-linking. The expression of LMP2B did not alter the cellular localization of LMP2A but did bind to and prevent the phosphorylation of LMP2A. A restoration of Lyn levels, but not a change in LMP2A levels, was also observed in cells coexpressing LMP2B with LMP2A. From these results, we conclude that LMP2B modulates LMP2A activity.

EBV-associated diseases in the AIDS patient

EBV-associated malignancies remain a considerable problem in HIV-infected individuals, even in the era of HAART. Although EBV is a common factor, each disease has a unique pathogenesis. Study of these diseases reveals the viral proteins expressed in the malignancies that might contribute to the development of the disease as well as the molecular basis for pathogenesis. It is likely that this knowledge will contribute to the development of novel therapeutics that will result in more favorable outcomes in the future.

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.

Viral immunoreceptor-associated tyrosine-based activation motifs: potential players in oncogenesis

Cancer is thought to arise as a consequence of multiple insults to a cell. Mutations that lead to increased expression or activity of proto-oncogenes or decreased expression of tumor suppressors are common insults that have been identified to date. However, when considering tumor viruses, viral proteins that modify cellular gene expression, alter host immune surveillance, or affect signaling pathways are also common players. Notably, several of these tumor viruses encode proteins containing an immunoreceptor-associated tyrosine-based activation motif (ITAM), a signaling motif recently implicated in epithelial cell oncogenesis. As expression of proteins bearing this motif is normally restricted to hematopoietic cells, recent work highlighting the consequences of ITAM expression in epithelial cells suggests it may play a role in solid tumor formation.