EBV-encoded Latent Membrane Protein Research Articles

Down‐regulation of miRNA‐204 by LMP‐1 enhances CDC42 activity and facilitates invasion of EBV‐associated nasopharyngeal carcinoma cells

Nasopharayngeal carcinoma (NPC) is an Epstein-Barr virus (EBV)-associated malignancy. It is known that microRNAs are implicated in the progression of NPC. However, the role of miR-204 in NPC is poorly understood. In this study, we found that miR-204 was down-regulated in NPC cells and tissues. Low-level expression of miR-204 was significantly associated with a more aggressive and poor prognostic phenotype of NPC. We further found that EBV-encoded latent membrane protein 1 (LMP-1) suppressed miR-204 expression by activating Stat-3. Cdc42 was identified as a direct target of miR-204. Mir-204 inhibited EBV positive C666-1 cell invasion and metastasis partly through targeting cdc42.

Therapeutic Evaluation of Epstein-Barr Virus-encoded Latent Membrane Protein-1 Targeted DNAzyme for Treating of Nasopharyngeal Carcinomas

The ability of the 10–23 DNAzyme to specifically cleave RNA with high efficiency has fuelled expectation that this agent may have useful applications for targeted therapy. Here, we, for the first time, investigated the antitumor and radiosensitizing effects of a DNAzyme (DZ1) targeted to the Epstein-Barr virus (EBV)-LMP1 mRNA of nasopharyngeal carcinoma (NPC) in patients. Preclinical studies indicated that the DNAzyme was safe and well tolerated. A randomized and double-blind clinical study was conducted in 40 NPC patients who received DZ1 or saline intratumorally, in conjunction with radiation therapy. Tumor regression, patient survival, EBV DNA copy number and tumor microvascular permeability were assessed in a 3-month follow-up. The mean tumor regression rate at week 12 was significantly higher in DZ1 treated group than in the saline control group. Molecular imaging analysis showed that DZ1 impacted on tumor microvascular permeability as evidenced by a faster decline of the Ktrans in DZ1-treated patients. The percentage of the samples with undetectable level of EBV DNA copy in the DZ1 group was significantly higher than that in the control group. No adverse events that could be attributed to the DZ1 injection were observed in patients.

Aggressive Mature Natural Killer Cell Neoplasms: From EBV-Infection to Disease Etiopathogeny

Mature Natural Killer (NK) cell neoplasms are rare tumors with higher prevalence in Asia, Central and South America, which are related to Epstein Barr Virus (EBV) infection. Nature killer /T cell lymphoma, nasal type, presents as a localized or generalized destructive tumor, affecting the nose, the upper aero digestive tract or any organ or tissue, whereas aggressive NK-cell leukemia manifests as a systemic disease that preferentially affects the bone marrow, the spleen and the liver, and rapidly evolve to multiorgan failure resulting in death. Both NK-cell neoplasms arise as a consequence of the inability of the immune system to control EBV infection and of the transforming potential of multiple EBV gene products. Chronic active EBV infection and EBV-related lymphoproliferative disorders of NK-cells are predisposing conditions. The tumor NK-cells do express an EBV infection type II latency pattern, specific EBV-encoded latent membrane proteins and early region EBV RNAs being detected on lymphoma cells. The EBV encoded proteins and non-coding EBV RNAs and micro-RNAs expressed on the infected cells are involved in immune deregulation and play a crucial role in cell transformation and oncogenesis. This review addresses the mechanisms used by EBV to infect the cells and to evade the immune-surveillance as well as to induce cell survival and transformation, and characterizes the spectrum of the clinical manifestations associated with chronic EBV-infection and related T-and NK-lymphoproliferative disorders. Improving the knowledge in this subject will help to develop new therapeutic approaches for chronic EBV-infection and even prevention strategies for the aggressive NK-cell malignancies.

The EBV oncogene LMP1 protects lymphoma cells from cell death through the collagen-mediated activation of DDR1

AbstractThe malignant Hodgkin and Reed-Sternberg (HRS) cells of Hodgkin lymphoma are surrounded by a tumor microenvironment that is composed of a variety of cell types, as well as noncellular components such as collagen. Although HRS cells harbor oncogenic Epstein-Barr virus (EBV) in approximately 50% of cases, it is not known if the tumor microenvironment contributes to EBV-driven lymphomagenesis. We show that expression of the EBV-encoded latent membrane protein-1 (LMP1) in primary human germinal center B cells, the presumed progenitors of HRS cells, upregulates discoidin domain receptor 1 (DDR1), a receptor tyrosine kinase activated by collagen. We also show that HRS cells intimately associated with collagen frequently overexpress DDR1 and that short-term exposure to collagen is sufficient to activate DDR1 in Hodgkin lymphoma-derived cell lines. The ectopic expression of DDR1 significantly increased the survival of collagen-treated DG75 Burkitt lymphoma cells, following etoposide treatment. Conversely, knockdown of DDR1 significantly decreased the survival of collagen-treated L428 Hodgkin lymphoma cells in the absence of specific apoptotic stimulus, suggesting that DDR1 also influences baseline survival. Our results identify a hitherto unknown function for collagen in protecting Hodgkin lymphoma cells from apoptosis and suggest an important contribution of the tumor microenvironment in promoting the oncogenic effects of EBV.

Leukemia inhibitory factor promotes nasopharyngeal carcinoma progression and radioresistance

Radioresistance of EBV-associated nasopharyngeal carcinoma (NPC) is associated with poor prognosis for patients with this form of cancer. Here, we found that NPC patients had increased serum levels of leukemia inhibitory factor (LIF) and that higher LIF levels correlated with local tumor recurrence. Furthermore, in vitro studies with NPC cells and in vivo xenograft mouse studies demonstrated that LIF critically contributes to NPC tumor growth and radioresistance. Using these model systems, we found that LIF treatment activated the mTORC1/p70S6K signaling pathway, enhanced tumor growth, inhibited DNA damage responses, and enhanced radioresistance. Treatment with either soluble LIF receptor (sLIFR), a LIF antagonist, or the mTOR inhibitor rapamycin reversed LIF-mediated effects, resulting in growth arrest and increased sensitivity to γ irradiation. Immunohistochemical (IHC) analyses of human NPC biopsies revealed that LIF and LIFR were overexpressed in tumor cells and that LIF expression correlated with the presence of the activated p-p70S6K. Finally, we found that the EBV-encoded protein latent membrane protein 1 (LMP1) enhances LIF production. Together, our findings indicate that LIF promotes NPC tumorigenesis and suggest that serum LIF levels may predict local recurrence and radiosensitivity in NPC patients.

Cancer stem-like cell characteristics induced by EB virus-encoded LMP1 contribute to radioresistance in nasopharyngeal carcinoma by suppressing the p53-mediated apoptosis pathway

Emerging evidence confirms that cancer stem cells (CSCs) are responsible for the chemoradioresistance of malignancies. EBV-encoded latent membrane protein 1 (LMP1) is associated with tumor relapse and poor prognosis of nasopharyngeal carcinoma (NPC). However, whether LMP1 induces the development of CSCs and the mechanism by which this rare cell subpopulation leads to radioresistance in NPC remain unclear. In the present study, LMP1-transformed NPC cells showed significant radioresistance compared to the empty vector control. We found that LMP1 up-regulated the expression of several stemness-related genes, increased the cell number of side population (SP) by flow cytometry analysis, enhanced the self-renewal properties of the cells in a spherical culture and enhanced the in vivo tumor initiation ability. We also found that LMP1 positively regulated the expression of the CSC marker CD44. The CD44+/High subpopulation of the LMP1-transformed NPC cells displayed more significant CSC characteristics than the CD44−/Low subpopulation of the LMP1-transformed NPC cells; these characteristics included the upregulation of stemness-related genes, in vitro self-renewal and in vivo tumor initiation ability. Importantly, the CD44+/High subpopulation displayed more radioresistance than the CD44−/Low subpopulation. Our results also demonstrated that phosphorylation of the DNA damage response (DDR) proteins, ATM, Chk1, Chk2 and p53, was inactivated in the LMP1-induced CD44+/High cells in response to DNA damage, and this was accompanied by a downregulation of the p53-targeted proapoptotic genes, which suggested that the inactivation of the p53-mediated apoptosis pathway was responsible for the radioresistance in the CD44+/High cells. Taken together, we found that LMP1 induced an increase in CSC-like CD44+/High cells, and we determined the molecular mechanism underlying the radioresistance of the LMP1-activated CSCs, highlighting the need of CSC-targeted radiotherapy in EBV-positive NPC.

The EBV Oncogene LMP1 Protects Lymphoma Cells From Cell Death Through The Collagen-Mediated Activation Of Discoidin Domain Receptor 1

The malignant Hodgkin/Reed-Sternberg (HRS) cells of Hodgkin lymphoma are surrounded by a tumour microenvironment which is composed of a variety of cell types, as well as non-cellular components such as collagen. Although HRS cells harbour oncogenic Epstein-Barr virus (EBV) in approximately 50% of cases, it is not known if the tumour microenvironment contributes to EBV-driven lymphomagenesis. We show that expression of the EBV-encoded latent membrane protein-1 (LMP1) in primary human germinal centre B cells, the presumed progenitors of HRS cells, up-regulates discoidin domain receptor 1 (DDR1), a receptor tyrosine kinase activated by collagen. We show that HRS cells intimately associated with collagen frequently over-express DDR1 and that short-term exposure to collagen is sufficient to activate DDR1 in Hodgkin lymphoma-derived cell lines. We also show that ectopic expression of DDR1 significantly increased the survival of collagen-treated DG75, Burkitt lymphoma cells, following etoposide treatment. Conversely, inhibition of DDR1, by RNA interference, significantly decreased the survival of collagen-treated L428 Hodgkin lymphoma cells in the absence of specific apoptotic stimulus suggesting that DDR1 also influences baseline survival. Our results identify a hitherto unknown function for collagen in protecting Hodgkin lymphoma from apoptosis and suggest an important contribution of the tumour microenvironment in promoting the oncogenic effects of EBV. Disclosures:No relevant conflicts of interest to declare.

TRAF6 is a critical regulator of LMP1 functionsin vivo

EBV-encoded latent membrane protein 1 (LMP1) is critical for EBV-driven B-cell transformation and most EBV-associated malignancies and is also implicated in exacerbation of autoimmunity. LMP1 functionally mimics the TNFR superfamily member CD40, but LMP1-induced signals and downstream B-cell functions are amplified and sustained compared with those mediated by CD40. CD40 and LMP1 both depend upon TNFR-associated factor (TRAF) adaptor molecules to mediate signaling but use them differently. LMP1 is dependent upon TRAFs 3 and 5 to deliver B-cell activation signals, while CD40 predominantly uses TRAFs 2 and 6 for this purpose. Both LMP1 and CD40 functions in B cells require TRAF6, which physically associates with both receptors but via different binding sites. In B-cell CD40 signaling, TRAF6 is required for a particular subset of CD40-dependent immune functions in vivo. Inasmuch as CD40 and LMP1 use other TRAFs differentially, we predicted that TRAF6 is critical for a specific subset of LMP1 functions in vivo and that this subset will be overlapping but distinct from the TRAF6-requiring functions of CD40. This study tests this prediction using a B-cell-specific TRAF6-deficient mouse model. We found that B-cell TRAF6 is important for LMP1-mediated antibody and autoantibody production in mice, as well as germinal center formation, but not the secondary lymphoid organ enlargement that results from LMP1 transgenic expression. Results highlight differential TRAF6 requirements for specific B-cell functions by LMP1 versus CD40. These differences may make important contributions to the contrasts between normally regulated CD40 versus pathogenic LMP1-mediated signals.

Downregulation of miR‐15a due to LMP1 promotes cell proliferation and predicts poor prognosis in nasal NK/T‐cell lymphoma

Nasal NK/T-cell lymphoma (NNKTL) is an Epstein-Barr virus (EBV)-associated malignancy and has distinct clinical and histological features. However, its genetic features are hitherto unclear. MicroRNAs (miRNAs) play a crucial role in the pathogenesis of several malignancies via regulating gene expression. In this study, we investigated whether the specific microRNAs were related to the tumor behaviors in NNKTL. MiRNA array and Quantitative RT-PCR analyses revealed that miR-15a was expressed at a much lower level in NNKTL cells (SNK-1, SNK-6, and SNT-8) than in normal peripheral NK cells and EBV-negative NK cell line KHYG-1. Quantitative PCR and western blot analyses showed that the expression of MYB and cyclin D1, which are validated targets of miR-15a, was higher in NNKTL cells. Transfection of NNKTL cells (SNK-6 and SNT-8) with a miR-15a precursor decreased MYB and cyclin D1 levels, thereby blocking G1/S transition and cell proliferation. Knockdown of EBV-encoded latent membrane protein 1 (LMP1) significantly increased miR-15a expression in SNK-6 cells. In NNKTL tissues, we found that reduced miR-15a expression, which correlated with MYB and cyclin D1 expression, was associated with poor prognosis of NNKTL patients. These data suggest that downregulation of miR-15a, possibly due to LMP1, implicates in the pathogenesis of NNKTL by inducing cell proliferation via MYB and cyclin D1. Thus, miR-15a could be a potential target for antitumor therapy and a prognostic predictor for NNKTL.

Exosomes Derived from Epstein-Barr Virus-Infected Cells Are Internalized via Caveola-Dependent Endocytosis and Promote Phenotypic Modulation in Target Cells

Epstein-Barr virus (EBV), a human gammaherpesvirus, establishes a lifelong latent infection in B lymphocytes and epithelial cells following primary infection. Several lines of evidence suggest that exosomes derived from EBV-infected cells are internalized and transfer viral factors, including EBV-encoded latent membrane protein and microRNAs, to the recipient cells. However, the detailed mechanism by which exosomes are internalized and their physiological impact on the recipient cells are still poorly understood. In this study, we visualized the internalization of fluorescently labeled exosomes derived from EBV-uninfected and EBV-infected B cells of type I and type III latency into EBV-negative epithelial cells. In this way, we demonstrated that exosomes derived from all three cell types were internalized into the target cells in a similar fashion. Internalization of exosomes was significantly suppressed by treatment with an inhibitor of dynamin and also by the knockdown of caveolin-1. Labeled exosomes were colocalized with caveolae and subsequently trafficked through endocytic pathways. Moreover, we observed that exosomes derived from type III latency cells upregulated proliferation and expression of intercellular adhesion molecule 1 (ICAM-1) in the recipient cells more significantly than did those derived from EBV-negative and type I latency cells. We also identified the EBV latent membrane protein 1 (LMP1) gene as responsible for induction of ICAM-1 expression. Taken together, our data indicate that exosomes released from EBV-infected B cells are internalized via caveola-dependent endocytosis, which, in turn, contributes to phenotypic changes in the recipient cells through transferring one or more viral factors.

Exosomes released in vitro from Epstein–Barr virus (EBV)-infected cells contain EBV-encoded latent phase mRNAs

EBV is a human herpesvirus associated with a number of malignancies. Both lymphoblastoid cell lines (LCLs), and EBV-infected nasopharyngeal carcinoma (NPC) cells have been demonstrated to release exosomes containing the EBV-encoded latent membrane protein 1 (LMP1), and mature micro-RNAs (EBV-miRNAs). Here we analyze the EBV protein and nucleic acid content of exosomes from different EBV-infected cells (LCL, 721 and Daudi) and we show for the first time that exosomes released from LCLs and 721 also contain EBV-encoded latent phase mRNAs. This confirms and strengthens exosomes pathogenetic potential, and might provide insights for development of novel diagnostic and therapeutic strategies.

Herpesviruses and the microbiome

The focus of this article will be to examine the role of common herpesviruses as a component of the microbiome of atopic patients and to review clinical observations suggesting that atopic patients might be predisposed to more severe and atypical herpes-related illness because their immune response is biased toward a TH2 cytokine profile. Human populations are infected with 8 herpesviruses, including herpes simplex virus HSV1 and HSV2 (also termed HHV1 and HHV2), varicella zoster virus (VZV or HHV3), EBV (HHV4), cytomegalovirus (HHV5), HHV6, HHV7, and Kaposi sarcoma-associated herpesvirus (termed KSV or HHV8). Herpesviruses are highly adapted to lifelong infection of their human hosts and thus can be considered a component of the human "microbiome" in addition to their role in illness triggered by primary infection. HSV1 and HSV2 infection and reactivation can present with more severe cutaneous symptoms termed eczema herpeticum in the atopic population, similar to the more severe eczema vaccinatum, and drug reaction with eosinophilia and systemic symptoms syndrome (DRESS) is associated with reactivation of HSV6 and possibly other herpesviruses in both atopic and nonatopic patients. In this review evidence is reviewed that primary infection with herpesviruses may have an atypical presentation in the atopic patient and conversely that childhood infection might alter the atopic phenotype. Reactivation of latent herpesviruses can directly alter host cytokine profiles through viral expression of cytokine-like proteins, such as IL-10 (EBV) or IL-6 (cytomegalovirus and HHV8), viral encoded and secreted siRNA and microRNAs, and modulation of expression of host transcription pathways, such as nuclear factor κB. Physicians caring for allergic and atopic populations should be aware of common and uncommon presentations of herpes-related disease in atopic patients to provide accurate diagnosis and avoid unnecessary laboratory testing or incorrect diagnosis of other conditions, such as drug allergy or autoimmune disease. Antiviral therapy and vaccines should be administered promptly when indicated clinically.

Delayed-type Hypersensitivity (DTH) Immune Response Related With EBV-DNA in Nasopharyngeal Carcinoma Treated With Autologous Dendritic Cell Vaccination After Radiotherapy

The aim of this work was to investigate the outcome of an autologous dendritic cell (DC) vaccination in patients with stage II/III nasopharyngeal carcinomas (NPC). From 38 patients with stage II/III Epstein-Barr virus (EBV)-associated NPCs after a radiotherapy, 16 human leukocyte antigen-A2 (HLA-A2)-positive patients were enrolled and medicated with autologous DCs, which were pulsed with HLA-A2-restricted EBV-encoded latent membrane protein 2A (LMP2A) peptides. The lymphocyte subsets, serum cytokines, and EBV-DNA levels as well as the delayed-type hypersensitivity (DTH) responses were determined after vaccination combined with a radiotherapy/chemotherapy. The serum levels of interleukin-2 and interferon-γ (P<0.05) as well as the percentage of natural killer and CD4+T cells increased significantly (P<0.05) after the vaccination. Nine of 16 (56.25%) patients showed a positive skin response to the HLA-A2 restricted EBV LMP2A peptides in a DTH test. The serum EBV-DNA level decreased significantly from 1519 ± 384 to 1214 ± 211 copies/mL in the 9 DTH-positive patients (P=0.0310). No unanticipated or serious toxicity was observed and the vaccine was well tolerated. In conclusion, in NPC patients vaccinated after radiotherapy with autologous DCs, which were pulsed with EBV LMP2A peptides, Th1-specific immune responses were elicited particularly in DTH test positive individuals. The clinical results obtained are encouraging and the EBV-specific HLA-A2-restricted DC vaccination is a promising treatment for EBV-related NPCs.

Enrichment of stem-like cell population comprises transformation ability of Epstein–Barr virus latent membrane protein 2A for non-transformed cells

Epstein–Barr virus (EBV) is a representative human oncogenic virus that causes malignancies of various cell lineages. LMP2A, an EBV-encoded latent membrane protein, is expressed in EBV-associated malignancies of various cell lineages. LMP2A caused visible tumor formation transplanted in nude mice when transferred to immortalized non-transformed fibroblasts, NIH3T3. LMP2A-expressing cells showed higher ability of colony formation in soft agar than empty vector-transfected control cells, although the expression of LMP2A did not cause focus transformation in low serum concentrations. LMP2A expression increased the size of Hoechst 33,342 dye excreting side population (SP), in which cancer-initiating cells or cancer stem-like cells were enriched. SP increase by LMP2A was also responsible for colony formation in soft agar. The LMP2A-mediated SP increase depended on the activations of Stat3, MEK/ERK, and PI3K pathways, and on upregulation of HMGA2. Enrichment of SP, stem-like cells, by LMP2A promoted the transformation capability of LMP2A from non-transformed cells. The enrichment of stem-like cell population by a virus-encoded factor might explain the oncogenic functions of oncogenic viruses.

Epstein-Barr virus-encoded latent membrane protein-1 upregulates 14-3-3σ and Reprimo to confer G2/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 G2/M progression was detected in all LMP-1 expressing cells. Therefore, we conclude that LMP-1 may induce cell cycle arrest at G2/M progression via upregulation of 14-3-3σ and Reprimo.

221P - Methylation Marker has a Complementary Value to Epstein-Barr Virus-Based Tests in Early Detection of Nasopharyngeal Carcinoma

ABSTRACT Undifferentiated nasopharyngeal carcinoma (NPC) is strongly linked to Epstein-Barr virus (EBV) infection. The presence of aberrant antibodies against EBV and high viral DNA load can be predictive for the disease and have been proposed for screening tools. Beside the EBV-based markers, analysis of aberrant methylation in gene promoter of tumor suppressor gene (TSG) may have potential value in identifying NPC at early stage. This study determined methylation status of multiple TSGs and evaluated whether it may improve NPC early detection using EBV-based assays. Association between EBV-encoded latent membrane protein 1 (LMP1) and methylation status was also tested. Nasopharyngeal brushings and sera were obtained from 53 NPC cases, 22 high risk individuals and 25 healthy EBV carriers. In all sera the detection of antibody against EBV was performed using EBV-IgA ELISA. EBV DNA load was measured by a quantitative light-cycler PCR on nasopharyngeal brushing samples. For methylation analysis, DNA was modified using bisulfite treatment and amplified by methylation-specific PCR (MSP) or quantitative MSP to target region within promoter of eleven TSGs. The expression of LMP1 was tested using immunohistochemistry. NPC samples demonstrated frequent methylation for individual TSGs (DAPK1 79%, CDH13 77%, DLC1 77%, RASSF1A 76%, CADM1 70%, p16 66%, WIF1 61%, CHFR 59%, RIZ1 57% and RASSF2A 29%). High risk individuals showed high frequency of four methylated genes, low methylation of two TSGs and undetectable methylation of another four TSGs. Healthy subjects had similar pattern as high risk individuals. Because not all of methylated genes allowed good discrimination between NPC and healthy individuals, a panel of markers (RASSF1A, p16, WIF1, CHFR and RIZ1) was determined and combined analysis revealed a detection rate of 98%. Quantitative analysis of MAL gene, TSG that has never been tested in NPC, showed promising result for NPC marker. The expression of LMP1 was observed to associate with methylated RASSF1A. In conclusion, methylation analysis has a complementary value to EBV-based assays for NPC risk assessment. The association of EBV oncogene to methylation status underlined the role of EBV in epigenetic event during oncogenesis. Disclosure All authors have declared no conflicts of interest.

Dasatinib therapy results in decreased B cell proliferation, splenomegaly, and tumor growth in a murine model of lymphoma expressing Myc and Epstein-Barr virus LMP2A

Epstein-Barr virus (EBV) infection and latency has been associated with malignant diseases including nasopharyngeal carcinoma, Hodgkin lymphoma, Burkitt lymphoma, and immune deficiency associated lymphoproliferative diseases. EBV-encoded latent membrane protein 2A (LMP2A) recruits Lyn and Syk kinases via its SH2-domain binding motifs, and modifies their signaling pathways. LMP2A transgenic mice develop hyperproliferative bone marrow B cells and immature peripheral B cells through modulation of Lyn kinase signaling. LMP2A/λ-MYC double transgenic mice develop splenomegaly and cervical lymphomas starting at 8weeks of age. We reasoned that targeting Lyn in LMP2A-expressing B cells with dasatinib would provide a therapeutic option for EBV-associated malignancies. Here, we show that dasatinib inhibits B cell colony formation by LMP2A transgenic bone marrow cells, and reverses splenomegaly and tumor growth in both a pre-tumor and a syngeneic tumor transfer model of EBV-associated Burkitt lymphoma. Our data support the idea that dasatinib may prove to be an effective therapeutic molecule for the treatment of EBV-associated malignancies.

Epstein-Barr Virus-Encoded LMP1 Interacts with FGD4 to Activate Cdc42 and Thereby Promote Migration of Nasopharyngeal Carcinoma Cells

Epstein-Barr virus (EBV) is closely associated with nasopharyngeal carcinoma (NPC), a human malignancy notorious for its highly metastatic nature. Among EBV-encoded genes, latent membrane protein 1 (LMP1) is expressed in most NPC tissues and exerts oncogenicity by engaging multiple signaling pathways in a ligand-independent manner. LMP1 expression also results in actin cytoskeleton reorganization, which modulates cell morphology and cell motility— cellular process regulated by RhoGTPases, such as Cdc42. Despite the prominent association of Cdc42 activation with tumorigenesis, the molecular basis of Cdc42 activation by LMP1 in NPC cells remains to be elucidated. Here using GST-CBD (active Cdc42-binding domain) as bait in GST pull-down assays to precipitate active Cdc42 from cell lysates, we demonstrated that LMP1 acts through its transmembrane domains to preferentially induce Cdc42 activation in various types of epithelial cells, including NPC cells. Using RNA interference combined with re-introduction experiments, we identified FGD4 (FYVE, RhoGEF and PH domain containing 4) as the GEF (guanine nucleotide exchange factor) responsible for the activation of Cdc42 by LMP1. Serial deletion experiments and co-immunoprecipitation assays further revealed that ectopically expressed FGD4 modulated LMP1-mediated Cdc42 activation by interacting with LMP1. Moreover, LMP1, through its transmembrane domains, directly bound FGD4 and enhanced FGD4 activity toward Cdc42, leading to actin cytoskeleton rearrangement and increased motility of NPC cells. Depletion of FGD4 or Cdc42 significantly reduced (∼50%) the LMP1-stimulated cell motility, an effect that was partially reversed by expression of a constitutively active mutant of Cdc42. Finally, quantitative RT-PCR and immunohistochemistry analyses showed that FGD4 and LMP1 were expressed in NPC tissues, supporting the potential physiologically relevance of this mechanism in NPC. Collectively, our results not only uncover a novel mechanism underlying LMP1-mediated Cdc42 activation, namely LMP1 interaction with FGD4, but also functionally link FGD4 to NPC tumorigenesis.

Epstein–Barr virus‐encoded LMP1 triggers regulation of the ERK‐mediated Op18/stathmin signaling pathway in association with cell cycle

The MAPKs are activated by a variety of cellular stimuli to participate in a series of signaling cascades and mediate diverse intracellular responses. One potential target of the MAPKs is Op18/stathmin, a molecule that acts as an integrator of diverse cell signaling pathways and regulates the dynamics of microtubules, which are involved in modulating a variety of cellular processes, including cell cycle progression and cell growth. Our study focused on the regulation of the MAPK-mediated Op18/stathmin signaling pathway, which is triggered by the Epstein-Barr virus-encoded latent membrane protein 1 ( LMP1) oncogene in nasopharyngeal carcinoma cells. The results showed that the activity of MAPK, which was induced by LMP1, varied with cell cycle progression; LMP1 upregulated phosphorylation of ERK during the G(1)/S phase, but negatively regulated phosphorylation of ERK during the G(2)/M phase. We found that the regulation of Op18/stathmin signaling by LMP1 was mainly mediated through ERK. The inhibition of LMP1 expression attenuated the interaction of ERK with Op18/stathmin and promoted microtubule depolymerization. These findings indicate the existence of a new cell cycle-associated signaling pathway in which LMP1 regulates ERK-mediated Op18/stathmin signaling.

EBV-Encoded LMP1 Upregulates Igκ 3′Enhancer Activity and Igκ Expression in Nasopharyngeal Cancer Cells by Activating the Ets-1 through ERKs Signaling

Accumulating evidence indicates that epithelial cancer cells, including nasopharyngeal carcinoma (NPC) cells, express immunoglobulins (Igs). We previously found that the expression of the kappa light chain protein in NPC cells can be upregulated by the EBV-encoded latent membrane protein 1 (LMP1). In the present study, we used NPC cell lines as models and found that LMP1-augmented kappa production corresponds with elevations in ERKs phosphorylation. PD98059 attenuates LMP1-induced ERKs phosphorylation resulting in decreased expression of the kappa light chain. ERK-specific small interfering RNA blunts LMP1-induced kappa light chain gene expression. Luciferase reporter assays demonstrate that immunoglobulin κ 3′ enhancer (3′Eκ) is active in Igκ-expressing NPC cells and LMP1 upregulates the activity of 3′Eκ in NPC cells. Moreover, mutation analysis of the PU binding site in 3′Eκ and inhibition of the MEK/ERKs pathway by PD98059 indicate that the PU site is functional and LMP1-enhanced 3′Eκ activity is partly regulated by this site. PD98059 treatment also leads to a concentration-dependent inhibition of LMP1-induced Ets-1 expression and phosphorylation, which corresponds with a dose-dependent attenuation of LMP1-induced ERK phosphorylation and kappa light chain expression. Suppression of endogenous Ets-1 by small interfering RNA is accompanied by a decrease of Ig kappa light chain expression. Gel shift assays using nuclear extracts of NPC cells indicate that the transcription factor Ets-1 is recruited by LMP1 to the PU motif within 3′Eκ in vitro. ChIP assays further demonstrate Ets-1 binding to the PU motif of 3′Eκ in cells. These results suggest that LMP1 upregulates 3′Eκ activity and kappa gene expression by activating the Ets-1 transcription factor through the ERKs signaling pathway. Our studies provide evidence for a novel regulatory mechanism of kappa expression, by which virus-encoded proteins activate the kappa 3′ enhancer through activating transcription factors in non-B epithelial cancer cells.