Induction of epidermal growth factor receptor expression by Epstein-Barr virus latent membrane protein 1 C-terminal-activating region 1 is mediated by NF-kappaB p50 homodimer/Bcl-3 complexes

Molecular determinants of the response of cancer cells towards geldanamycin and its derivatives

Geldanamycin is an ansamycin-derivative of a benzoquinone isolated from Streptomyces hygroscopicus. It inhibits tyrosine kinases and heat shock protein 90 (HSP90). Geldanamycin and 11 derivatives were subjected to molecular docking to HSP90, and 17-desmethoxy-17-N,N-dimethylamino-geldanamycin (17-DMAG) was the compound with the highest binding affinity (-7.73 ± 0.12 kcal/mol) and the lowest inhibition constant (2.16 ± 0.49 μM). Therefore, 17-DMAG was selected for further experiments in comparison to geldanamycin. Multidrug resistance (MDR) represents a major problem for successful cancer therapy. We tested geldanamycin and 17-DMAG against various drug-resistant cancer cell lines. Although geldanamycin and 17-DMAG inhibited the proliferation in all cell lines tested, multidrug-resistant P-glycoprotein-overexpressing CEM/ADR5000 cells were cross-resistant, ΔEGFR-overexpressing tumor cells and p53 knockout cells were sensitive to these two compounds. COMPARE and hierarchical cluster analyses were performed, and 60 genes were identified to predict the sensitivity or resistance of 59 NCI tumor cell lines towards geldanamycin and 17-DMAG. The distribution of cell lines according to their mRNA expression profiles indicated sensitivity or resistance to both compounds with statistical significance. Moreover, bioinformatic tools were used to study possible mechanisms of action of geldanamycin and 17-DMAG. Galaxy Cistrome analyses were carried out to predict transcription factor binding motifs in the promoter regions of the candidate genes. Interestingly, the NF-ĸB DNA binding motif (Rel) was identified as the top transcription factor. Furthermore, these 60 genes were subjected to Ingenuity Pathway Analysis (IPA) to study the signaling pathway interactions of these genes. Interestingly, IPA also revealed the NF-ĸB pathway as the top network among these genes. Finally, NF-ĸB reporter assays confirmed the bioinformatic prediction, and both geldanamycin and 17-DMAG significantly inhibited NF-κB activity after exposure for 24 h. In conclusion, geldanamycin and 17-DMAG exhibited cytotoxic activity against different tumor cell lines. Their activity was not restricted to HSP90 but indicated an involvement of the NF-KB pathway.

Epstein-Barr Virus Promotes Tumor Angiogenesis by Activating STIM1-Dependent Ca2+ Signaling in Nasopharyngeal Carcinoma

Epstein-Barr virus (EBV) promotes tumor angiogenesis in nasopharyngeal carcinoma (NPC) by activating store-operated Ca²⁺ entry. Since such entry has been linked to stromal interaction molecule 1 (STIM1), we examined whether the virus acts via STIM1-dependent Ca²⁺ signaling to promote tumor angiogenesis in NPC. STIM1 expression was detected in NPC cell lines HK1 and CNE2 that were negative or positive for EBV. STIM1 was knocked down in EBV-positive cells using recombinant lentivirus, then cytosolic Ca²⁺ levels were measured based on fluorescence resonance energy transfer. Cells were also exposed to epidermal growth factor (EGF), and secretion of vascular endothelial growth factor (VEGF) was measured using an enzyme-linked immunosorbent assay. Endothelial tube formation was quantified in an in vitro angiogenesis assay. Growth of CNE2-EBV xenografts was measured in mice, and angiogenesis was assessed based on immunohistochemical staining against CD31. Paraffin-embedded NPC tissues from patients were assayed for CD31 and STIM1. EGFR and ERK signaling pathways were assessed in NPC cell lines. STIM1 expression was higher in EBV-positive than in EBV-negative NPC cell lines. STIM1 knockdown in EBV-positive NPC cells significantly reduced Ca²⁺ influx and VEGF production after EGF treatment. STIM1 knockdown also inhibited xenograft growth and angiogenesis. Moreover, CD31 expression level was higher in EBV-positive than EBV-negative NPC tissues, and high expression of CD31 co-localized with high expression of STIM1 in EBV-positive tissues from NPC patients. Viral infection of NPC cells led to higher levels of phosphorylated ERK1/2 after EGF treatment, which STIM1 knockdown partially reversed. Our results suggest that EBV promotes EGF-induced ERK1/2 signaling by activating STIM1-dependent Ca²⁺ signaling, and that blocking such signaling may inhibit EBV-promoted angiogenesis in NPC.

Nasopharyngeal Carcinoma: The Role of the EGFR in Epstein-Barr Virus Infection

Epstein-Barr virus (EBV), a type 4 γ herpes virus, is recognized as a causative agent in nasopharyngeal carcinoma (NPC). Incidence of EBV-positive NPC have grown in recent decades along with worse outcomes compared with their EBV-negative counterparts. Latent membrane protein 1 (LMP1), encoded by EBV, induces NPC progression. The epidermal growth factor receptor (EGFR), a member of the ErbB family of receptor tyrosine kinases (RTK), is a driver of tumorigenesis, including for NPC. Little data exist on the relationship between EGFR and EBV-induced NPC. In our initial review, we found that LMP1 promoted the expression of EGFR in NPC in two main ways: the NF-κB pathway and STAT3 activation. On the other hand, EGFR also enhances EBV infection in NPC cells. Moreover, activation of EGFR signalling affects NPC cell proliferation, cell cycle progression, angiogenesis, invasion, and metastasis. Since EGFR promotes tumorigenesis and progression by downstream signalling pathways, causing poor outcomes in NPC patients, EGFR-targeted drugs could be considered a newly developed anti-tumor drug. Here, we summarize the major studies on EBV, EGFR, and LMP1-regulatory EGFR expression and nucleus location in NPC and discuss the clinical efficacy of EGFR-targeted agents in locally advanced NPC (LA NPC) and recurrent or metastatic NPC (R/M NPC) patients.

Tumor suppressor DRD2 facilitates M1 macrophages and restricts NF-κB signaling to trigger pyroptosis in breast cancer

Rationale: Breast cancer (BrCa) is the most common cancer worldwide, and the 5-year relative survival rate has declined in patients diagnosed at stage IV. Advanced BrCa is considered as incurable, which still lack effective treatment strategies. Identifying and characterizing new tumor suppression genes is important to establish effective prognostic biomarkers or therapeutic targets for late-stage BrCa.

Methods: RNA-seq was applied in BrCa tissues and normal breast tissues. Through analyzing differentially expressed genes, DRD2 was selected for further analysis. And expression and promoter methylation status of DRD2 were also determined. DRD2 functions were analyzed by various cell biology assays in vitro. Subcutaneous tumor model was used to explore DRD2 effects in vivo. A co-cultivated system was constructed to investigate interactions of DRD2 and macrophages in vitro. WB, IHC, IF, TUNEL, qRT-PCR, Co-IP, Antibody Array, and Mass Spectrum analysis were further applied to determine the detailed mechanism.

Results: In BrCa, DRD2 was found to be downregulated due to promoter methylation. Higher expression of DRD2 positively correlated with longer survival times especially in HER2-positive patients. DRD2 also promoted BrCa cells sensitivity to Paclitaxel. Ectopic expression of DRD2 significantly inhibited BrCa tumorigenesis. DRD2 also induced apoptosis as well as necroptosis in vitro and in vivo. DRD2 restricted NF-κB signaling pathway activation through interacting with β-arrestin2, DDX5 and eEF1A2. Interestingly, DRD2 also regulated microenvironment as it facilitated M1 polarization of macrophages, and triggered GSDME-executed pyroptosis.

Conclusion: Collectively, this study novelly manifests the role of DRD2 in suppressing BrCa tumorigenesis, predicting prognosis and treatment response. And this study further reveals the critical role of DRD2 in educating M1 macrophages, restricting NF-κB signaling pathway and triggering different processes of programmed cell death in BrCa. Taking together, those findings represent a predictive and therapeutic target for BrCa.

Co-expression of Epstein-Barr virus-encoded RNA1 and viral latent membrane protein 1 in osteosarcoma: A novel insight of predictive markers

Epstein-Barr virus is an etiologic agent of several malignancies. In this study, we explored the association of Epstein-Barr virus-encoded RNA1 and Epstein-Barr virus latent membrane protein 1 co-expression with osteosarcoma. Epstein-Barr virus-encoded RNA1 expression in tumor cells was quantified using reverse transcriptase polymerase chain reaction and in situ hybridization and Epstein-Barr virus latent membrane protein 1 expression was measured using immunohistochemistry staining. There was a statistically significant association between Epstein-Barr virus latent membrane protein 1 and Epstein-Barr virus-encoded RNA1 co-expression and characteristics of osteosarcoma such as nodal stage (p < 0.04), metastasis (p < 0.04), Ki67 index (p < 0.03), and tumor stage (p < 0.05). Co-expression of Epstein-Barr virus-encoded RNA1 and Epstein-Barr virus latent membrane protein 1 in tumors correlated with advanced osteosarcoma and indicated the aggressiveness of bone sarcoma.

Epstein-Barr Virus Mediated Signaling in Nasopharyngeal Carcinoma Carcinogenesis

Simple Summary

Epstein-Barr virus (EBV) infection is known to contribute in nasopharyngeal carcinoma (NPC) carcinogenesis. The oncogenic roles of the EBV proteins and non-coding RNAs in NPC are becoming evident with the aid of current advances in genome-wide and in-depth molecular analyses. This current work provides a comprehensive overview, which covers recent understandings of the pathogenic role of EBV infection in NPC. Perspectives on molecular mechanisms, which are involved in the pathogenesis of NPC, focusing on the connection between EBV and NPC cells and the corresponding signaling pathways are highlighted. Cancer hallmarks associated with EBV in NPC development are also discussed herein.

Abstract

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.

Differential behavior of NF-κB, IκBα and EGFR during the renal carcinogenic process in an experimental model in vivo

Renal cell carcinoma (RCC) is the most common type of cancer of the adult kidney. It is generally asymptomatic even at advanced stages, so opportune diagnosis is rare, making it almost impossible to study this cancer at its early stages. RCC tumors induced by ferric nitrilotriacetate (FeNTA) in rats histologically correspond to the human clear cell RCC subtype (ccRCC) and the exposure to this carcinogen during either one or two months leads to different early stages of neoplastic development. High levels of nuclear factor kappa B (NF-κB) and epidermal growth factor receptor (EGFR) as well as low levels of NF-κB inhibitor alpha (IκBα) are frequent in human RCC, but their status in FeNTA-induced tumors and their evolution along renal carcinogenesis is unclear. On this basis, in the present study NF-κB, IκBα and EGFR behavior was analyzed at different stages of the experimental renal carcinogenesis model. Similar to patients with RCC, neoplastic tissue showed high levels of p65, one of the predominant subunits of NF-κB in ccRCC and of EGFR (protein and mRNA), as well as a decrease in the levels of NF-κB's main inhibitor, IκBα, resulting in a classic oncogenic combination. Conversely, different responses were observed at early stages of carcinogenesis. After one month of FeNTA-exposure, NF-κB activity and EGFR levels augmented; but unexpectedly, IκBα also did. While after two months, NF-κB activity diminished, but EGFR and IκBα levels remained elevated. In conclusion, FeNTA-induced tumors and RCC human neoplasms are analogues regarding to the classic NF-κB, IκBα and EGFR behavior, and distinctive non-conventional combination of changes is developed at each early stage studied. The results obtained suggest that the dysregulation of the analyzed molecules could be related to different signaling pathways and therefore, to particular effects depending on the phase of the carcinogenic process.

Emerging therapeutic targets for nasopharyngeal carcinoma: opportunities and challenges

Introduction: Nasopharyngeal carcinoma (NPC) is a major public health problem in several countries, especially those in Southeast Asia and North Africa. In its typical poorly differentiated form, the Epstein-Barr virus (EBV) genome is present in the nuclei of all malignant cells with restricted expression of a few viral genes. The malignant phenotype of NPC cells results from the influence of these viral products in combination with cellular genetic, epigenetic and functional alterations. With regard to host/tumor interactions, NPC is a remarkable example of immune escape in the context of a hot tumor.Areas covered: This article has an emphasis on emerging therapeutic targets that are considered upstream or at an early stage of clinical application. It examines targets related to cellular oncogenic alterations, latent EBV infection and tumor interactions with the immune system.Expert opinion: There is a remarkable emergence of new agents that target EBV products. The clinical application of these agents would benefit from a systematic and comprehensive molecular classification of NPCs and from easy access to pre-clinical models in public repositories. There is a strong rationale for more investigations on the potential of immune modulators, especially those related to NK cells.

3D-QSAR and docking studies on ursolic acid derivatives for anticancer activity based on bladder cell line T24 targeting NF-kB pathway inhibition

Bladder cancer is the common reason for mortality worldwide, and its increasing rate announces as a significant area of research in drug designing. The side effects and toxicity of existing drugs and the consequence of gradual cancer cell resistance against the available therapy make the treatment poor. Globally, there is a continuous high demand to develop new, more potent, and easily affordable drugs against cancer. The current research article illustrates the application of developed three-dimensional quantitative structure-activity relationship (3D-QSAR) based on human bladder cancer cell line T24 in vitro anticancer activity. The derived QSAR model has been used for prediction of natural compounds and analogs with 80% similarity of the most active compound of the dataset. The developed model describes the structure-activity relationship for terpenes and their derivatives at the molecular level. The developed comparative molecular field analysis (CoMFA) model shows a satisfactory cross-validation correlation coefficient (q2) of 0.54 and a regression correlation coefficient (r2) of 0.86. In order to evaluate the compliance with electronic pharmacokinetic parameters, Lipinski's rule of five filter, absorption, distribution, metabolism, and excretion (ADME) and toxicity of predicted compounds have been calculated. Furthermore, molecular-docking study has been performed to prioritize these predicted compounds based on their docking score and binding pocket similarity through the identified potential anticancer targets. Finally, two compounds T9 and B42 have been identified as the best hit because these two fall within the standard limits of all filters and show a good binding affinity. Conclusively, all satisfactory results strongly suggest that the derived 3D-QSAR model and obtained candidate's binding structures are reasonable in the prediction of a new antagonist's activity. The strategy adopted in the present research is expected to be of immense importance and a great support in the identification and optimization of lead in the early and advance drug discovery.

Modulation of Angiogenic Processes by the Human Gammaherpesviruses, Epstein-Barr Virus and Kaposi's Sarcoma-Associated Herpesvirus

Angiogenesis is the biological process by which new blood vessels are formed from pre-existing vessels. It is considered one of the classic hallmarks of cancer, as pathological angiogenesis provides oxygen and essential nutrients to growing tumors. Two of the seven known human oncoviruses, Epstein–Barr virus (EBV) and Kaposi’s sarcoma-associated herpesvirus (KSHV), belong to the Gammaherpesvirinae subfamily. Both viruses are associated with several malignancies including lymphomas, nasopharyngeal carcinomas, and Kaposi’s sarcoma. The viral genomes code for a plethora of viral factors, including proteins and non-coding RNAs, some of which have been shown to deregulate angiogenic pathways and promote tumor growth. In this review, we discuss the ability of both viruses to modulate the pro-angiogenic process.

Cell Type-Specific Roles of NF-κB Linking Inflammation and Thrombosis

The transcription factor NF-κB is a central mediator of inflammation with multiple links to thrombotic processes. In this review, we focus on the role of NF-κB signaling in cell types within the vasculature and the circulation that are involved in thrombo-inflammatory processes. All these cells express NF-κB, which mediates important functions in cellular interactions, cell survival and differentiation, as well as expression of cytokines, chemokines, and coagulation factors. Even platelets, as anucleated cells, contain NF-κB family members and their corresponding signaling molecules, which are involved in platelet activation, as well as secondary feedback circuits. The response of endothelial cells to inflammation and NF-κB activation is characterized by the induction of adhesion molecules promoting binding and transmigration of leukocytes, while simultaneously increasing their thrombogenic potential. Paracrine signaling from endothelial cells activates NF-κB in vascular smooth muscle cells and causes a phenotypic switch to a “synthetic” state associated with a decrease in contractile proteins. Monocytes react to inflammatory situations with enforced expression of tissue factor and after differentiation to macrophages with altered polarization. Neutrophils respond with an extension of their life span—and upon full activation they can expel their DNA thereby forming so-called neutrophil extracellular traps (NETs), which exert antibacterial functions, but also induce a strong coagulatory response. This may cause formation of microthrombi that are important for the immobilization of pathogens, a process designated as immunothrombosis. However, deregulation of the complex cellular links between inflammation and thrombosis by unrestrained NET formation or the loss of the endothelial layer due to mechanical rupture or erosion can result in rapid activation and aggregation of platelets and the manifestation of thrombo-inflammatory diseases. Sepsis is an important example of such a disorder caused by a dysregulated host response to infection finally leading to severe coagulopathies. NF-κB is critically involved in these pathophysiological processes as it induces both inflammatory and thrombotic responses.

Blockage of store-operated Ca2+ entry antagonizes Epstein-Barr virus-promoted angiogenesis by inhibiting Ca2+ signaling-regulated VEGF production in nasopharyngeal carcinoma

Background

Epstein-Barr virus (EBV) actively contributes to the pathological process of nasopharyngeal carcinoma (NPC) by enabling NPC cells to acquire various capacities required for their malignant biological actions. Our earlier works demonstrated that EBV-encoded latent membrane protein 1 (LMP1) enhanced vascular endothelial growth factor (VEGF)-mediated angiogenesis by boosting store-operated Ca²⁺ entry (SOCE) upon extracellular epidermal growth factor (EGF) stimulation. However, the antagonistic effects of SOCE blockage on EBV-promoted angiogenesis must be appropriately evaluated in vivo, and the global effect of EBV infection on the EGF-elicited cytosolic Ca²⁺ signaling, which regulates VEGF-mediated angiogenesis remains to be further clarified.

Materials and methods

Two EBV-infected NPC cell lines, CNE2-EBV and HK1-EBV, along with their parental cell lines were employed in the present study. Dynamic cytosolic Ca²⁺ changes were measured in individual fluorescent Ca²⁺ indicator-loaded cells. Amounts of VEGF production were determined by enzyme-linked immunosorbent assay (ELISA). Human umbilical vein endothelial cells (HUVECs)-formed tube networks were quantitatively evaluated as an in vitro angiogenesis assay. A mouse model concurrently bearing EBV-positive/negative xenografts was utilized to evaluate the tumor growth and angiogenesis in vivo.

Results

EBV infection reliably promoted transplanted tumor growth while enhancing angiogenesis. Introduction of EBV into EBV-negative NPC cells increased the EGF-stimulated VEGF production while amplifying the EGF-evoked Ca²⁺ responses. Inhibition of the EBV-boosted Ca²⁺ signaling using 2-aminoethyl diphenylborinate (2-APB), a specific SOCE inhibitor, effectively antagonized the EBV-promoted VEGF production and endothelial tube formation in vitro. Pharmacological blockage of SOCE exhibited anti-angiogenic effect in the EBV-positive xenografts.

Conclusion

SOCE can serve as a candidate pharmacological target for treating NPC, as blockage of the Ca²⁺ signaling via SOCE is a feasible strategy to suppress the EBV-driven malignant profiles in NPC cells.

Rediscovery of NF-κB signaling in nasopharyngeal carcinoma: How genetic defects of NF-κB pathway interplay with EBV in driving oncogenesis?

Nasopharyngeal carcinoma (NPC) is a unique EBV-associated subtype of head and neck cancer, which has the highest incidence in Southern China and eastern South Asia. The interaction between genetic risk factors and environmental challenge, have been considered to contribute to the development of nasopharyngeal carcinogenesis. Constitutive activation of NF-κB signaling has been seen in NPC tissues and is associated with unfavorable prognosis. Recently, several whole exome sequencing study consistently revealed that high frequency mutations of NF-κB pathway negative regulators is common in nasopharyngeal carcinoma, which reinforce the importance of NF-κB driving oncogenesis. This review focuses on the current state of research in role of NF-κB in NPC carcinogenesis. We summarized the newly identified loss of function (LOF) mutations on NF-κB negative regulators leading to it's activation bypass LMP-1 stimulation. We discussed the critical role of NF-κB activation in immortalization and transformation of nasopharygeal epithelium. We also depicted how NF-κB signaling mediated chronic inflammation contribute to persistent EBV infection, immune evasion of EBV infected cells, metabolic reprogramming, and cancer stem cells (CSCs) formation in NPC. Lastly, we discussed the clinical resonance of targeting NF-κB for NPC precise therapy.

The interactome of EBV LMP1 evaluated by proximity-based BioID approach

Epstein-Barr virus LMP1 is an oncoprotein required for immortalizing B lymphocytes and also plays important roles in transforming non-lymphoid tissue. The discovery of LMP1 protein interactions will likely generate targets to treat EBV-associated cancers. Here, we define the broader LMP1 interactome using the recently developed BioID method. Combined with mass spectrometry, we identified over 1000 proteins across seven independent experiments with direct or indirect relationships to LMP1. Pathway analysis suggests that a significant number of the proteins identified are involved in signal transduction and protein or vesicle trafficking. Interestingly, a large number of proteins thought to be important in the formation of exosomes and protein targeting were recognized as probable LMP1 interacting partners, including CD63, syntenin-1, ALIX, TSG101, HRS, CHMPs, and sorting nexins. Therefore, it is likely that LMP1 modifies protein trafficking and exosome biogenesis pathways. In support of this, knock-down of syntenin-1 and ALIX resulted in reduced exosomal LMP1.

Cytomegalovirus, Macrophages and Breast Cancer

The human cytomegalovirus (HCMV) is a betaherpesvirus that is highly host specific, infects among others epithelial cells and macrophages, and has been recently mentioned as having oncomodulatory properties. HCMV is detected in the breast tumor tissue where macrophages, especially tumor associated macrophages, are associated with a poor prognosis. In this review, we will discuss the potential implication of HCMV in breast cancer with emphasis on the role played by macrophages.

Regulation of EBV LMP1-triggered EphA4 downregulation in EBV-associated B lymphoma and its impact on patients' survival

Epstein-Barr virus (EBV), an oncogenic human virus, is associated with several lymphoproliferative disorders, including Burkitt lymphoma, Hodgkin disease, diffuse large B-cell lymphoma (DLBCL), and posttransplant lymphoproliferative disorder (PTLD). In vitro, EBV transforms primary B cells into lymphoblastoid cell lines (LCLs). Recently, several studies have shown that receptor tyrosine kinases (RTKs) play important roles in EBV-associated neoplasia. However, details of the involvement of RTKs in EBV-regulated B-cell neoplasia and malignancies remain largely unclear. Here, we found that erythropoietin-producing hepatocellular receptor A4 (EphA4), which belongs to the largest RTK Eph family, was downregulated in primary B cells post-EBV infection at the transcriptional and translational levels. Overexpression and knockdown experiments confirmed that EBV-encoded latent membrane protein 1 (LMP1) was responsible for this EphA4 suppression. Mechanistically, LMP1 triggered the extracellular signal-regulated kinase (ERK) pathway and promoted Sp1 to suppress EphA4 promoter activity. Functionally, overexpression of EphA4 prevented LCLs from proliferation. Pathologically, the expression of EphA4 was detected in EBV(-) tonsils but not in EBV(+) PTLD. In addition, an inverse correlation of EphA4 expression and EBV presence was verified by immunochemical staining of EBV(+) and EBV(-) DLBCL, suggesting EBV infection was associated with reduced EphA4 expression. Analysis of a public data set showed that lower EphA4 expression was correlated with a poor survival rate of DLBCL patients. Our findings provide a novel mechanism by which EphA4 can be regulated by an oncogenic LMP1 protein and explore its possible function in B cells. The results provide new insights into the role of EphA4 in EBV(+) PTLD and DLBCL.

The Latent Membrane Protein 1 (LMP1)

Almost exactly twenty years after the discovery of Epstein-Barr virus (EBV), the latent membrane protein 1 (LMP1) entered the EBV stage, and soon thereafter, it was recognized as the primary transforming gene product of the virus. LMP1 is expressed in most EBV-associated lymphoproliferative diseases and malignancies, and it critically contributes to pathogenesis and disease phenotypes. Thirty years of LMP1 research revealed its high potential as a deregulator of cellular signal transduction pathways leading to target cell proliferation and the simultaneous subversion of cell death programs. However, LMP1 has multiple roles beyond cell transformation and immortalization, ranging from cytokine and chemokine induction, immune modulation, the global alteration of gene and microRNA expression patterns to the regulation of tumor angiogenesis, cell-cell contact, cell migration, and invasive growth of tumor cells. By acting like a constitutively active receptor, LMP1 recruits cellular signaling molecules associated with tumor necrosis factor receptors such as tumor necrosis factor receptor-associated factor (TRAF) proteins and TRADD to mimic signals of the costimulatory CD40 receptor in the EBV-infected B lymphocyte. LMP1 activates NF-κB, mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3-K), IRF7, and STAT pathways. Here, we review LMP1's molecular and biological functions, highlighting the interface between LMP1 and the cellular signal transduction network as an important factor of virus-host interaction and a potential therapeutic target.

SKF95365 induces apoptosis and cell-cycle arrest by disturbing oncogenic Ca(2+) signaling in nasopharyngeal carcinoma cells

Background

Aberrant modulation of store-operated calcium ions (Ca²⁺) entry promotes the progression of human malignancies. Previously, we reported that the blockage of store-operated Ca²⁺ entry inhibited epidermal growth factor (EGF)-stimulated migration and distant metastasis in nasopharyngeal carcinoma (NPC) cells. However, the effects of pharmacological blocker on other Ca²⁺ signaling-regulated malignant characteristics in NPC cells remained poorly understood.

Methods

We examined the effects of SKF96365, an inhibitor of store-operated Ca²⁺ channel, on EGF-launched Ca²⁺ signaling in two NPC cell lines. We determined the effects of SKF96365 on cell proliferation, colony formation, apoptosis, and cell-cycle status in vitro. We further elucidated the antitumor activity of SKF96365 in xenograft-bearing mice.

Results

It was found that SKF96365 disturbed the thapsigargin (TG)-stimulated Ca²⁺ release from endoplasmic reticulum and the subsequent Ca²⁺ influx. SKF96365 alone stimulated Ca²⁺ responses merely due to endoplasmic reticulum-released Ca²⁺. SKF96365 promoted cell mortality, inhibited colony formation, and induced apoptosis and cell-cycle arrest, while blunting the EGF-evoked Ca²⁺ signaling. Furthermore, we confirmed that SKF96365 reduced NPC xenograft growth while activating caspase-7-related apoptotic pathway.

Conclusion

SKF96365 exerts multiple antitumor activities through the distraction on the oncogenic Ca²⁺ signaling transduction in NPC cells.

NF-κB p65 Subunit Is Modulated by Latent Transforming Growth Factor-β Binding Protein 2 (LTBP2) in Nasopharyngeal Carcinoma HONE1 and HK1 Cells

NF-κB is a well-characterized transcription factor, widely known as a key player in tumor-derived inflammation and cancer development. Herein, we present the functional and molecular relevance of the canonical NF-κB p65 subunit in nasopharyngeal carcinoma (NPC). Loss- and gain-of-function approaches were utilized to reveal the functional characteristics of p65 in propagating tumor growth, tumor-associated angiogenesis, and epithelial-to-mesenchymal transition in NPC cells. Extracellular inflammatory stimuli are critical factors that trigger the NF-κB p65 signaling; hence, we investigated the components of the tumor microenvironment that might potentially influence the p65 signaling pathway. This led to the identification of an extracellular matrix (ECM) protein that was previously reported as a candidate tumor suppressor in NPC. Our studies on the Latent Transforming Growth Factor-β Binding Protein 2 (LTBP2) protein provides substantial evidence that it can modulate the p65 transcriptional activity. Re-expression of LTBP2 elicits tumor suppressive effects that parallel the inactivation of p65 in NPC cells. LTBP2 was able to reduce phosphorylation of p65 at Serine 536, inhibit nuclear localization of active phosphorylated p65, and impair the p65 DNA-binding ability. This results in a consequential down-regulation of p65-related gene expression. Therefore, the data suggest that the overall up-regulation of p65 expression and the loss of this candidate ECM tumor suppressor are milestone events contributing to NPC development.

Changes in expression induced by Epstein-Barr Virus LMP1-CTAR1: potential role of bcl3

The Epstein-Barr virus protein latent membrane protein 1 (LMP1) has two NF-κB activating domains within its intracellular carboxy terminus (carboxy-terminal activating region 1 [CTAR1] and CTAR2). LMP1-CTAR1 is required for B-lymphocyte transformation, is capable of transforming rodent fibroblasts, and uniquely activates phosphoinositol (PI3) kinase, the noncanonical NF-κB pathway, and expression of the epidermal growth factor receptor (EGFR). In this study, the effects of LMP1-CTAR1 on cellular gene expression were determined by high-throughput sequencing. Additionally, the binding of bcl3 was determined using chromatin immunoprecipitation (ChIP) and sequencing. LMP1-CTAR1 induced few changes in transcription with more genes showing decreased expression. Ingenuity pathway analysis indicated significant enrichment for genes involved in cancer and cellular movement, survival, growth, and proliferation pathways. ChIP in combination with high-throughput sequencing (ChIP-Seq) identified bcl3 binding for more than 2,000 genes in LMP1-CTAR1-expressing cells with more than 90% of the peaks at genes detected within the probable promoter region. Only a small subset of the genes with significant changes in expression had corresponding peaks in the bcl3 ChIP. However, both NFKB2 and PI3 kinase were identified in the bcl3 ChIP. Additionally, many of the predicted upstream regulators for the changes in expression were identified in the bcl3 ChIP. Analysis of the proteins in the NF-κB pathway revealed many changes identified by the high-throughput RNA sequencing (RNA-Seq) and bcl3 ChIP that would likely activate noncanonical NF-κB signaling and possibly inhibit canonical NF-κB signaling. These findings suggest that the two LMP1 signaling domains modulate their combined activity and that the bcl3 transcription factor is likely responsible for some of the unique effects of CTAR1 on cellular expression.

The Epstein-Barr virus protein latent membrane protein 1 (LMP1) has potent effects on cell growth. LMP1 has two regions, carboxy-terminal activating region 1 (CTAR1) and CTAR2, that distinctly activate NF-κB, a transcription factor complex involved in activation of important host genes. In this study, analysis of the effects on cellular gene expression revealed that CTAR1 significantly affected cellular expression in part through effects on a specific form of NF-κB. The data suggest that LMP1 can activate a distinct subset of host gene expression through its CTAR1 domain which in combination with other signaling effects induced by the CTAR2 domain likely affects cell movement, survival, and growth.

Blockage of LMP1-modulated store-operated Ca(2+) entry reduces metastatic potential in nasopharyngeal carcinoma cell

Epstein-Barr virus (EBV)-encoded latent membrane proteins (LMPs) expedite progression of EBV-relevant cancers. Of the full set of LMPs, latent membrane protein 1 (LMP1) was identified to uniquely augment store-operated Ca(2+) entry (SOCE). Previously, we reported that the suppression of SOCE exhibited inhibitory effects on cell migration and the extravasation from vasculature in EBV-negative nasopharyngeal carcinoma (NPC) cells. In this follow-up study, we aimed to expand our understanding of the modulation of SOCE by LMP1 and test the possibility that blockage of LMP1-modulated SOCE affects the LMP1-promoted metastatic potential. Here we showed that suppressions of the LMP1-boosted SOCE blunted the LMP1-promoted cell migration, VEGF-mediated angiogenesis and permeabilization in vitro. Blockage of SOCE inhibited vasculature-invasion of circulating cells and distant metastatic colonization in vivo. Notably, utilizing VEGFR2-EGFP-tag zebrafish we revealed that the LMP1-expressing cells arrested in a small-caliber vessel mobilized surrounding endothelial cells to facilitate vasculature-invasion. Thus, the LMP1-boosted SOCE promotes metastatic potential of NPC cells by solidifying their collaborations with the nearby non-cancer cells through the manipulation of oncogenic Ca(2+) signaling. Our study highlights the advantage of using both conventional mammal and transgenic zebrafish for developing a novel therapeutic strategy targeting the multiple steps of invasion-metastasis cascade.

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.

LMP1 promotes expression of insulin-like growth factor 1 (IGF1) to selectively activate IGF1 receptor and drive cell proliferation

Epstein-Barr Virus (EBV) is a gammaherpesvirus that infects the majority of the human population and is linked to the development of multiple cancers, including nasopharyngeal carcinoma. Latent membrane protein 1 (LMP1) is considered the primary oncoprotein of EBV, and in epithelial cells it induces the expression and activation, or phosphorylation, of the epidermal growth factor receptor kinase. To identify effects on additional kinases, an unbiased screen of receptor tyrosine kinases potentially activated by LMP1 was performed. Using a protein array, it was determined that LMP1 selectively activates insulin-like growth factor 1 receptor (IGF1R). This activation takes place in fibroblast, epithelial, and nasopharyngeal cell lines that express LMP1 stably and transiently. Of note, LMP1 altered the phosphorylation, but not the expression, of IGF1R. The use of LMP1 mutants with defective signaling domains revealed that the C-terminal activating region 2 domain of LMP1 increased the mRNA expression and the secretion of the ligand IGF1, which promoted phosphorylation of IGF1R. IGF1R phosphorylation was dependent upon activation of canonical NF-κB signaling and was suppressed by IκBα and a dominant negative form of TRAF6. Inhibition of IGF1R activation with two small-molecule inhibitors, AG1024 and picropodophyllin (PPP), or with short hairpin RNA (shRNA) directed against IGF1R selectively reduced proliferation, focus formation, and Akt activation in LMP1-positive cells but did not impair LMP1-induced cell migration. Expression of constitutively active Akt rescued cell proliferation in the presence of IGF1R inhibitors. These findings suggest that LMP1-mediated activation of IGF1R contributes to the ability of LMP1 to transform epithelial cells.

IMPORTANCE

EBV is linked to the development of multiple cancers in both lymphoid and epithelial cells, including nasopharyngeal carcinoma. Nasopharyngeal carcinoma is a major cancer that develops in specific populations, with nearly 80,000 new cases reported annually. LMP1 is consistently expressed in early lesions and continues to be detected within 50 to 80% of these cancers at later stages. It is therefore of paramount importance to understand the mechanisms through which LMP1 alters cell growth and contributes to tumorigenesis. This study is the first to determine that LMP1 activates the IGF1R tyrosine kinase by regulating expression of the ligand IGF1. Additionally, the data in this paper reveal that specific targeting of IGF1R selectively impacts LMP1-positive cells. These findings suggest that therapies directed against IGF1R may specifically impair the growth of EBV-infected cells.

Viruses exploit the function of epidermal growth factor receptor

Epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that regulates cellular homeostatic processes. Following ligand binding, EGFR activates different downstream signalling cascades that promote cell survival, proliferation, motility, and angiogenesis and induces F-actin-dependent EGFR endocytosis, which relocalises the activated receptors for degradation or recycling. The responses that are induced by ligand binding to EGFR, including cell signalling activation, protein kinase phosphorylation and cytoskeletal network rearrangement, resemble those induced by virus infection. Increasing evidence demonstrates that many viruses usurp EGFR endocytosis or EGFR-mediated signalling for entry, replication, inflammation, and viral antagonism to the host antiviral system. In addition, viruses have acquired sophisticated mechanisms to regulate EGFR functions by interrupting the EGFR-recycling process and modulating EGFR expression. In this review, we provide an overview of the mechanisms by which viruses alter EGFR signalling in favour of their continued survival.

Novel mechanisms of EBV-induced oncogenesis

Epstein-Barr virus is an etiologic factor in multiple types of cancer that primarily develop in lymphocytes and epithelial cells. The tumors are latently infected yet express distinct subsets of viral proteins that are essential for transformation. The viral oncogenes may be expressed in a subset of cells and are transferred through exosomes to many cells to induce growth and alter the tumor environment. In some of the viral cancers, viral proteins are not expressed, however, the viral miRNAs can alter growth by decreasing expression of negative regulators of cell growth such as tumor suppressors and cellular proteins that induce apoptosis.

Dynamic activation of the key pathways: linking colitis to colorectal cancer in a mouse model

An association between carcinogenesis and inflammation has long been appreciated. Chemically induced colitis-associated cancer (CAC) is a classical mouse model for investigating 'inflammation-cancer link' in the intestine. Diverse mechanisms behind this non-resolving inflammation model have been reported before, most of them were emphasized on key cancer genes, cytokines, and signal transduction abnormality based on prior knowledge. In this study, we dynamically and globally dissect the alteration of key pathways in the development from colitis to colorectal cancer. Striking evidence from gene expression profiling, serum cytokines detection, and immunohistochemistry analysis all reveals that different key pathways [NF-κB, STAT3, p38 mitogen-activated protein kinase (MAPK), and Wnt/β-catenin signaling] and their target genes are hyperactive in different phases of the inflammation-cancer link. Nuclear factor-κB (NF-κB) and STAT3 signaling are hyperactive in the whole process, while p38 MAPK and Wnt/β-catenin signaling are only hyperactive in the beginning and ending, respectively. Through this unbiased system biological approach, we provide strong evidence that different key pathways are specifically involved in different phases, which bridge the gap between inflammation and cancer.

Quantitative study of cytotoxic T-lymphocyte immunotherapy for nasopharyngeal carcinoma

BACKGROUND

In clinical practice, the common strategy for immunotherapy of nasopharyngeal carcinoma (NPC) is to infuse cytotoxic T-lymphocyte (CTL) lines several times by intravenous injection, but it is difficult by laboratory research to investigate the relationship between treatment time-point, the amount of CTL added and the therapeutic effect. The objective of this study is to establish a mathematical model to study the therapeutic effect of different treatment time-points and amounts of CTL, and to predict the change in therapeutic effect when the percentage of EBV LMP2-specific CTL is increased from 10% to 20%.

RESULTS

The concentration of epidermal growth factor receptor (EGFR) in the tumor cell cytomembranes increases after CTL is added. Concurrently, there is a marked downward trend of the phosphorylated transforming growth factor-α (TGFα)-EGFR complex in the tumor cell cytomembranes, which indicates restriction of tumor growth after CTL immunotherapy. The relationships among the time of addition of CTL, the amount of CTL added, different CTL specificities for LMP2 and the increment rate k of the total number of tumor cells were evaluated.

CONCLUSIONS

The simulation results quantify the relationships among treatment time-points, amount of CTL added, and the corresponding therapeutic effect of immunotherapy for NPC.

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′E_κ) is active in Igκ-expressing NPC cells and LMP1 upregulates the activity of 3′E_κ in NPC cells. Moreover, mutation analysis of the PU binding site in 3′E_κ and inhibition of the MEK/ERKs pathway by PD98059 indicate that the PU site is functional and LMP1-enhanced 3′E_κ 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′E_κin vitro. ChIP assays further demonstrate Ets-1 binding to the PU motif of 3′E_κ in cells. These results suggest that LMP1 upregulates 3′E_κ 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.

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.

Activation of oxidative stress-regulated Bcl-3 suppresses CTCF in corneal epithelial cells

Epigenetic factor CTCF (CCCTC binding factor) plays important roles in genetic controls of the cell fate. Previous studies found in corneal epithelial cells that CTCF is regulated by epidermal growth factor (EGF) through activation of NF-κB p65/p50. It also found that CTCF is suppressed in ultraviolet (UV) stress-induced corneal epithelial cells. However, it is still unknown how UV stress down-regulates CTCF affecting the cell fate. In the present study, we report that regulation of CTCF by extracellular stress signals is dependent upon activations of an oxidative stress-regulated protein Bcl-3. We found that activated Bcl-3 was able to bind to the κB sites identified in the CTCF promoter region. Bcl-3 was activated by UV irradiation to interact with NF-κB p50 by forming a Bcl-3/p50 heterodimer complex. The Bcl-3/p50 complex suppressed CTCF promoter activity to down-regulate CTCF transcription. Unlike the effect of EGF, UV stress-induced Bcl-3 activation suppressed CTCF activity without involving the IκBα and p65 pathway. Thus, results of the study reveal a novel mechanism for regulatory control of CTCF in UV stress-induced human corneal epithelial cells, which requires activation and formation of Bcl-3/p50 complex through a noncanonical NF-κB pathway.

Characterization of the latent membrane protein 1 signaling complex of Epstein-Barr virus in the membrane of mammalian cells with bimolecular fluorescence complementation

Background

Bimolecular fluorescence complementation (BiFC) is a novel technique to examine protein-protein interaction through the assembly of fluorescent proteins. In the present study, BiFC was used to study the assembly of the Epstein-Barr virus latent membrane protein 1 (LMP1) signaling complex within the membrane of mammalian cells. LMP1 signaling requires oligomerization, localization to lipid rafts, and association of the cytoplasmic domain to adaptor proteins, such as the tumor necrosis factor receptor associated factors (TRAFs).

Methods

LMP1-TRAF and LMP1-LMP1 interactions were assayed by BiFC using fluorescence microscopy and flow cytometry. Function of LMP1 BiFC contructs were confirmed by transformation assays and nuclear factor- κB (NF-κB) reporter assays.

Results

BiFC was observed between LMP1 and TRAF2 or TRAF3 and mutation of the LMP1 signaling domains reduced complementation. Fluorescence was observed in previously described LMP1 signaling locations. Oligomerization of LMP1 with itself induced complementation and BiFC. LMP1-BiFC constructs were fully functional in rodent fibroblast transformation assays and activation of NF-κB reporter activity. The BiFC domain partially suppressed some LMP1 mutant phenotypes.

Conclusions

Together these data suggest that BiFC is a unique and novel platform to identify and characterize proteins recruited to the LMP1-signaling complex.

Canonical NF-kappaB activation is essential for Epstein-Barr virus latent membrane protein 1 TES2/CTAR2 gene regulation

Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) transforms rodent fibroblasts and is expressed in most EBV-associated malignancies. LMP1 (transformation effector site 2 [TES2]/C-terminal activation region 2 [CTAR2]) activates NF-κB, p38, Jun N-terminal protein kinase (JNK), extracellular signal-regulated kinase (ERK), and interferon regulatory factor 7 (IRF7) pathways. We have investigated LMP1 TES2 genome-wide RNA effects at 4 time points after LMP1 TES2 expression in HEK-293 cells. By using a false discovery rate (FDR) of <0.001 after correction for multiple hypotheses, LMP1 TES2 caused >2-fold changes in 1,916 mRNAs; 1,479 RNAs were upregulated and 437 were downregulated. In contrast to tumor necrosis factor alpha (TNF-α) stimulation, which transiently upregulates many target genes, LMP1 TES2 maintained most RNA effects through the time course, despite robust and sustained induction of negative feedback regulators, such as IκBα and A20. LMP1 TES2-regulated RNAs encode many NF-κB signaling proteins and secondary interacting proteins. Consequently, many LMP1 TES2-regulated RNAs encode proteins that form an extensive interactome. Gene set enrichment analyses found LMP1 TES2-upregulated genes to be significantly enriched for pathways in cancer, B- and T-cell receptor signaling, and Toll-like receptor signaling. Surprisingly, LMP1 TES2 and IκBα superrepressor coexpression decreased LMP1 TES2 RNA effects to only 5 RNAs, with FDRs of <0.001-fold and >2-fold changes. Thus, canonical NF-κB activation is critical for almost all LMP1 TES2 RNA effects in HEK-293 cells and a more significant therapeutic target than previously appreciated.

Epstein-Barr virus LMP1 activates EGFR, STAT3, and ERK through effects on PKCdelta

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus that infects more than 90% of the world's adult population and is linked to multiple malignancies, including Burkitt lymphoma, Hodgkin disease, and nasopharyngeal carcinoma (NPC). The EBV oncoprotein LMP1 induces transcription of the epidermal growth factor receptor (EGFR), which is expressed at high levels in NPC. EGFR transcription is induced by LMP1 through a p50 NFκB1-Bcl-3 complex, and Bcl-3 is induced by LMP1-mediated activation of STAT3. This study reveals that LMP1, through its carboxyl-terminal activation domain 1 (LMP1-CTAR1), activates both STAT3 and EGFR in a serum-independent manner with constitutive serine phosphorylation of STAT3. Upon treatment with EGF, the LMP1-CTAR1-induced EGFR was additionally phosphorylated and STAT3 became phosphorylated on tyrosine, concomitant with upregulation of a subset of STAT3 target genes. The kinase responsible for LMP1-CTAR1-mediated serine phosphorylation of STAT3 was identified to be PKCδ using specific RNAi, a dominant negative PKCδ, and the PKCδ inhibitor rottlerin. Interestingly, inhibition of PKCδ also inhibited constitutive phosphorylation of EGFR and LMP1-CTAR1-induced phosphorylation of ERK. Inhibition of PKCδ blocked LMP1-CTAR1-mediated transformation of Rat-1 cells, likely through the inhibition of ERK activation. These findings indicate that LMP1 activates multiple distinct signaling pathways and suggest that PKCδ functions as a master regulator of EGFR, STAT3, and ERK activation by LMP1-CTAR1.

Epstein-Barr virus latent membrane protein 1 modulates distinctive NF- kappaB pathways through C-terminus-activating region 1 to regulate epidermal growth factor receptor expression

Epstein-Barr Virus (EBV) latent membrane protein 1 (LMP1) is required for EBV B-lymphocyte transformation, transforms rodent fibroblasts, and can induce lymphoma and epithelial hyperplasia in transgenic mice. Two domains have been identified within the intracellular carboxy terminus that can activate NF-kappaB, C-terminus-activating region 1 (CTAR1) and CTAR2, through interactions with tumor necrosis receptor-associated factors (TRAFs). CTAR1 can activate both the canonical and noncanonical NF-kappaB pathways and has unique effects on cellular gene expression. The epidermal growth factor receptor (EGFR) is highly induced by LMP1-CTAR1 in epithelial cells through activation of a novel NF-kappaB form containing p50 homodimers and Bcl-3. To further understand the regulation of NF-kappaB in CTAR1-induced EGFR expression, we evaluated the ability of CTAR1 to induce EGFR in mouse embryonic fibroblasts (MEFs) defective for different NF-kappaB effectors. CTAR1-mediated EGFR induction required the NF-kappaB-inducing kinase (NIK) but not the IkappaB kinase (IKK) complex components that regulate canonical or noncanonical NF-kappaB pathways. CTAR1-mediated induction of nuclear p50 occurred in IKKbeta-, IKKgamma-, and NIK-defective MEFs, indicating that this induction is not dependent on the canonical or noncanonical NF-kappaB pathways. EGFR and nuclear p50 were expressed at high levels in TRAF2(-/-) fibroblasts and were not induced by CTAR1. In TRAF3(-/-) MEFs, CTAR1 induced nuclear p50 but did not affect basal levels of STAT3 serine phosphorylation or induce EGFR expression. EGFR was induced by LMP1 in TRAF6(-/-) MEFs. These findings suggest that this novel NF-kappaB pathway is differentially regulated by TRAF2 and TRAF3, and that distinct interactions of LMP1 and its effectors regulate LMP1-mediated gene expression.

Nasopharyngeal carcinoma: the next challenges

Nasopharyngeal carcinoma (NPC) differs from other head and neck cancers in its aetiology, epidemiology and potential therapeutic options. Despite cure for the majority of the patients, challenges still exist in the prevention of disease relapse, treatment of patients with refractory or metastatic NPC and the management of long-term toxicities. This article discusses the specific challenges in pushing the boundaries of NPC treatments further, with an emphasis on prognostic/predictive markers, molecularly targeted therapies, immunotherapies and the areas of interest with regard to long-term toxicities arising from therapeutic interventions.

Transcriptional downregulation of p27KIP1 through regulation of E2F function during LMP1-mediated transformation

LMP1 induces the phenotypic transformation of fibroblasts and affects regulators of the cell cycle during this process. LMP1 decreases expression of the cyclin-dependent kinase inhibitor p27 and increases the levels and phosphorylation of cyclin-dependent kinase 2 and the retinoblastoma protein. In the present study, the effects of LMP1 on cell cycle progression and the mechanism of p27 downregulation by LMP1 were determined. Although p27 is frequently regulated at the posttranscriptional level during cell cycle progression and in cancer, LMP1 did not decrease ectopically expressed p27. However, LMP1 did decrease p27 RNA levels and inhibited the activity of p27 promoter reporters. The LMP1-regulated promoter element was mapped to a region containing two E2F sites. Electrophoretic mobility shift assays determined that the regulated cis element bound an inhibitory E2F complex containing E2F4 and p130. These findings indicate that LMP1 decreases p27 transcription through effects on E2F family transcription factors. This property likely contributes to the ability of LMP1 to stimulate cell cycle progression.

Bcl-3-regulated transcription from major immediate-early promoter of human cytomegalovirus in monocyte-derived macrophages

Monocytes/macrophages are key cells in the pathogenesis of human CMV (HCMV) infection, but the in vitro rate of viral production in primary human monocyte-derived macrophages (MDM) is considerably lower than in fibroblasts. Considering that the NF-kappaB signaling pathway is potentially involved in the replication strategy of HCMV through efficient transactivation of the major immediate-early promoter (MIEP), efficient viral replication, and late gene expression, we investigated the composition of the NF-kappaB complex in HCMV-infected MDMs and fibroblasts. Preliminary studies showed that HCMV could grow in primary MDM culture but that the viral titer in culture supernatants was lower than that observed in the supernatants of more permissive MRC5 fibroblasts. EMSA and microwell colorimetric NF-kappaB assay demonstrated that HCMV infection of MDMs increased p52 binding activity without activating the canonical p50/p65 complex. Moreover, Bcl-3 was up-regulated and was demonstrated to associate with p52, indicating p52/Bcl-3 complexes as the major component of the NF-kappaB complex in MDMs. Luciferase assays in promonocytic U937 cells transfected with an MIEP-luciferase reporter construct demonstrated MIEP activation in response to p52 and Bcl-3 overexpression. Chromatin immunoprecipitation assay demonstrated that p52 and Bcl-3 bind the MIEP in acutely HCMV-infected MDMs. In contrast, HCMV infection of MRC5 fibroblasts resulted in activation of p50/p65 heterodimers. Thus, activation of p52/Bcl-3 complexes in MDMs and p50/p65 heterodimers in fibroblasts in response to HCMV infection might explain the low-level growth of the virus in MDMs vs efficient growth in fibroblasts.

Nuclear factor-kappaB binds to the Epstein-Barr Virus LMP1 promoter and upregulates its expression

The latent membrane protein 1 (LMP1) oncogene carried by Epstein-Barr virus (EBV) is essential for transformation and maintenance of EBV-immortalized B cells in vitro, and it is expressed in most EBV-associated tumor types. The activation of the NF-kappaB pathway by LMP1 plays a critical role in the upregulation of antiapoptotic proteins. The EBV-encoded EBNA2 transactivator is required for LMP1 activation in latency III, while LMP1 itself appears to be critical for its activation in the latency II gene expression program. In both cases, additional viral and cellular transcription factors are required in mediating transcription activation of the LMP1 promoter. Using DNA affinity purification and chromatin immunoprecipitation assay, we showed here that members of the NF-kappaB transcription factor family bound to the LMP1 promoter in vitro and in vivo. Electrophoretic mobility shift assay analyses indicated the binding of the p50-p50 homodimer and the p65-p50 heterodimer to an NF-kappaB site in the LMP1 promoter. Transient transfections and reporter assays showed that the LMP1 promoter is activated by exogenous expression of NF-kappaB factors in both B cells and epithelial cells. Exogenous expression of NF-kappaB factors in the EBNA2-deficient P3HR1 cell line induced LMP1 protein expression. Overall, our data are consistent with the presence of a positive regulatory circuit between NF-kappaB activation and LMP1 expression.

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 1 induces expression of the epidermal growth factor receptor through effects on Bcl-3 and STAT3

Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) activates multiple signaling pathways. Two regions, C-terminal-activating region 1 (CTAR1) and CTAR2, have been identified within the cytoplasmic carboxy terminal domain that activates NF-kappaB. CTAR2 activates the canonical NF-kappaB pathway, which includes p50/p65 complexes. CTAR1 can activate both the canonical and noncanonical pathways to produce multiple distinct NF-kappaB dimers, including p52/p50, p52/p65, and p50/p50. CTAR1 also uniquely upregulates the epidermal growth factor receptor (EGFR) in epithelial cells. Increased p50-Bcl-3 complexes have been detected by chromatin precipitation on the NF-kappaB consensus motifs within the egfr promoter in CTAR1-expressing epithelial cells and nasopharyngeal carcinoma cells. In this study, the mechanism responsible for the increase in Bcl-3 has been further investigated. The data indicate that LMP1-CTAR1 induces Bcl-3 mRNA and increases the nuclear translocation of both Bcl-3 and p50. LMP1-CTAR1 constitutively activates STAT3, and this activation was not due to the induction of interleukin 6 (IL-6). In LMP1-CTAR1-expressing cells, increased levels of activated STAT3 were detected by chromatin immunoprecipitation on STAT-binding sites located within both the promoter and the second intron of Bcl-3. A STAT3 inhibitor significantly reduced the activation of STAT3, as well as the CTAR1-mediated upregulation of Bcl-3 and EGFR. These data suggest that LMP1 activates distinct forms of NF-kappaB through multiple pathways. In addition to activating the canonical and noncanonical pathways, LMP1-CTAR1 constitutively activates STAT3 and increases Bcl-3. The increased nuclear Bcl-3 and p50 homodimer complexes positively regulate EGFR expression. These results indicate that LMP1 likely regulates distinct cellular genes by activating specific NF-kappaB pathways.