Down-regulation of EBV-LMP1 radio-sensitizes nasal pharyngeal carcinoma cells via NF-κB regulated ATM expression

Deciphering the Role of Epstein-Barr Virus Latent Membrane Protein 1 in Immune Modulation: A Multifaced Signalling Perspective

The disruption of antiviral sensors and the evasion of immune defences by various tactics are hallmarks of EBV infection. One of the EBV latent gene products, LMP1, was shown to induce the activation of signalling pathways, such as NF-κB, MAPK (JNK, ERK1/2, p38), JAK/STAT and PI3K/Akt, via three subdomains of its C-terminal domain, regulating the expression of several cytokines responsible for modulation of the immune response and therefore promoting viral persistence. The aim of this review is to summarise the current knowledge on the EBV-mediated induction of immunomodulatory molecules by the activation of signal transduction pathways with a particular focus on LMP1-mediated mechanisms. A more detailed understanding of the cytokine biology molecular landscape in EBV infections could contribute to the more complete understanding of diseases associated with this virus.

The Dual Functions of Andrographolide in the Epstein-Barr Virus-Positive Head-and-Neck Cancer Cells: The Inhibition of Lytic Reactivation of the Epstein-Barr Virus and the Induction of Cell Death

Andrographolide, a medicinal compound, exhibits several pharmacological activities, including antiviral and anticancer properties. Previously, we reported that andrographolide inhibits Epstein-Barr virus (EBV) lytic reactivation, which is associated with viral transmission and oncogenesis in epithelial cancers, including head-and-neck cancer (HNC) cells. However, the underlying mechanism through which andrographolide inhibits EBV lytic reactivation and affects HNC cells is poorly understood. Therefore, we investigated these mechanisms using EBV-positive HNC cells and the molecular modeling and docking simulation of protein. Based on the results, the expression of EBV lytic genes and viral production were significantly inhibited in andrographolide-treated EBV-positive HNC cells. Concurrently, there was a reduction in transcription factors (TFs), myocyte enhancer factor-2D (MEF2D), specificity protein (SP) 1, and SP3, which was significantly associated with a combination of andrographolide and sodium butyrate (NaB) treatment. Surprisingly, andrographolide treatment also significantly induced the expression of DNA Methyltransferase (DNMT) 1, DNMT3B, and histone deacetylase (HDAC) 5 in EBV-positive cells. Molecular modeling and docking simulation suggested that HDAC5 could directly interact with MEF2D, SP1, and SP3. In our in vitro study, andrographolide exhibited a stronger cytotoxic effect on EBV-positive cells than EBV-negative cells by inducing cell death. Interestingly, the proteome analysis revealed that the expression of RIPK1, RIPK3, and MLKL, the key molecules for necroptosis, was significantly greater in andrographolide-treated cells. Taken together, it seems that andrographolide exhibits concurrent activities in HNC cells; it inhibits EBV lytic reactivation by interrupting the expression of TFs and induces cell death, probably via necroptosis.

Insights into intricacies of the Latent Membrane Protein-1 (LMP-1) in EBV-associated cancers

Numerous lymphomas, carcinomas, and other disorders have been associated with Epstein-Barr Virus (EBV) infection. EBV's carcinogenic potential can be correlated to latent membrane protein 1 (LMP1), which is essential for fibroblast and primary lymphocyte transformation. LMP1, a transmembrane protein with constitutive activity, belongs to the tumour necrosis factor receptor (TNFR) superfamily. LMP1 performs number of role in the life cycle of EBV and the pathogenesis by interfering with, reprogramming, and influencing a vast range of host cellular activities and functions that are getting well-known but still poorly understood. LMP1, pleiotropically perturbs, reprograms and balances a wide range of various processes of cell such as extracellular vesicles, epigenetics, ubiquitin machinery, metabolism, cell proliferation and survival, and also promotes oncogenic transformation, angiogenesis, anchorage-independent cell growth, metastasis and invasion, tumour microenvironment. By the help of various experiments, it is proven that EBV-encoded LMP1 activates multiple cell signalling pathways which affect antigen presentation, cell-cell interactions, chemokine and cytokine production. Therefore, it is assumed that LMP1 may perform majorly in EBV associated malignancies. For the development of novel techniques toward targeted therapeutic applications, it is essential to have a complete understanding of the LMP1 signalling landscape in order to identify potential targets. The focus of this review is on LMP1-interacting proteins and related signalling processes. We further discuss tactics for using the LMP1 protein as a potential therapeutic for cancers caused by the EBV.

Radio-Susceptibility of Nasopharyngeal Carcinoma: Focus on Epstein- Barr Virus, MicroRNAs, Long Non-Coding RNAs and Circular RNAs

Nasopharyngeal carcinoma (NPC) is a type of head and neck cancer. As a neoplastic disorder, NPC is a highly malignant squamous cell carcinoma that is derived from the nasopharyngeal epithelium. NPC is radiosensitive; radiotherapy or radiotherapy combining with chemotherapy are the main treatment strategies. However, both modalities are usually accompanied by complications and acquired resistance to radiotherapy is a significant impediment to effective NPC therapy. Therefore, there is an urgent need to discover effective radio-sensitization and radio-resistance biomarkers for NPC. Recent studies have shown that Epstein-Barr virus (EBV)-encoded products, microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs), which share several common signaling pathways, can function in radio-related NPC cells or tissues. Understanding these interconnected regulatory networks will reveal the details of NPC radiation sensitivity and resistance. In this review, we discuss and summarize the specific molecular mechanisms of NPC radio-sensitization and radio-resistance, focusing on EBV-encoded products, miRNAs, lncRNAs and circRNAs. This will provide a foundation for the discovery of more accurate, effective and specific markers related to NPC radiotherapy. EBVencoded products, miRNAs, lncRNAs and circRNAs have emerged as crucial molecules mediating the radio-susceptibility of NPC. This understanding will improve the clinical application of markers and inform the development of novel therapeutics for NPC.

EBV-LMP1 promotes radioresistance by inducing protective autophagy through BNIP3 in nasopharyngeal carcinoma

Studies have indicated that dysfunction of autophagy is involved in the initiation and progression of multiple tumors and their chemoradiotherapy. Epstein–Barr virus (EBV) is a lymphotropic human gamma herpes virus that has been implicated in the pathogenesis of nasopharyngeal carcinoma (NPC). EBV encoded latent membrane protein1 (LMP1) exhibits the properties of a classical oncoprotein. In previous studies, we experimentally demonstrated that LMP1 could increase the radioresistance of NPC. However, how LMP1 contributes to the radioresistance in NPC is still not clear. In the present study, we found that LMP1 could enhance autophagy by upregulating the expression of BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3). Knockdown of BNIP3 could increase the apoptosis and decrease the radioresistance mediated by protective autophagy in LMP1-positive NPC cells. The data showed that increased BNIP3 expression is mediated by LMP1 through the ERK/HIF1α signaling axis, and LMP1 promotes the binding of BNIP3 to Beclin1 and competitively reduces the binding of Bcl-2 to Beclin1, thus upregulating autophagy. Furthermore, knockdown of BNIP3 can reduce the radioresistance promoted by protective autophagy in vivo. These data clearly indicated that, through BNIP3, LMP1 induced autophagy, which has a crucial role in the protection of LMP1-positive NPC cells against irradiation. It provides a new basis and potential target for elucidating LMP1-mediated radioresistance.

(-)-Epigallocatechin-3-gallate inhibits EBV lytic replication via targeting LMP1-mediated MAPK signal axes

Epstein–Barr virus (EBV)-encoded latent membrane protein 1 (LMP1) plays an important oncogenic role in the viral latent infection. Recently, increasing evidence indicates that the high expression of LMP1 during EBV lytic cycle is related to the viral lytic replication. However, the mechanism by which LMP1 regulates EBV lytic replication remains unclear. (−)-Epigallocatechin-3-gallate (EGCG) prevents carcinogenesis by directly targeting numerous membrane proteins and effectively inhibits EBV lytic cascade. Here, we demonstrated that LMP1 promotes EBV lytic replication through the downstream signal molecules MAPKs, including ERKs, p38, and JNKs. LMP1 induces the phosphorylation of p53 through MAPKs to enhance the ability of wild-type p53 (wt-p53) to activate expression of BZLF1 gene, while the JNKs/c-Jun signal axis appears to be involved in EBV lytic replication induced by LMP1 in p53 mutant manner. We provided the first evidence that EGCG directly targets the viral membrane LMP1 (K_d = 0.36 μM, n = 1) using fluorescence quenching, isothermal titration calorimetry (ITC) assay, and CNBR-activated Sepharose 4B pull-down affinity chromatography. Furthermore, we revealed that EGCG inhibits EBV lytic replication via suppressing LMP1 and thus blocking the downstream MAPKs/wt-p53 signal axis in AGS-EBV cells and JNKs/c-Jun signal axis in p53 mutant B95.8 cells. Our study, for the first time, reports the binding and inhibitory efficacy of EGCG to the LMP1, which is a key oncoprotein encoded by EBV. These findings suggest the novel function of LMP1 in the regulation of EBV lytic cycle and reveal the new role of EGCG in EBV-associated malignancies through suppressing viral reactivation.

Targeting the signaling in Epstein-Barr virus-associated diseases: mechanism, regulation, and clinical study

Epstein–Barr virus-associated diseases are important global health concerns. As a group I carcinogen, EBV accounts for 1.5% of human malignances, including both epithelial- and lymphatic-originated tumors. Moreover, EBV plays an etiological and pathogenic role in a number of non-neoplastic diseases, and is even involved in multiple autoimmune diseases (SADs). In this review, we summarize and discuss some recent exciting discoveries in EBV research area, which including DNA methylation alterations, metabolic reprogramming, the changes of mitochondria and ubiquitin-proteasome system (UPS), oxidative stress and EBV lytic reactivation, variations in non-coding RNA (ncRNA), radiochemotherapy and immunotherapy. Understanding and learning from this advancement will further confirm the far-reaching and future value of therapeutic strategies in EBV-associated diseases.

Targeting Epstein-Barr virus oncoprotein LMP1-mediated high oxidative stress suppresses EBV lytic reactivation and sensitizes tumors to radiation therapy

Generating oxidative stress is a critical mechanism by which host cells defend against infection by pathogenic microorganisms. Radiation resistance is a critical problem in radiotherapy against cancer. Epstein-Barr virus (EBV) is a cancer-causing virus and its reactivation plays an important role in the development of EBV-related tumors. This study aimed to explore the inner relationship and regulatory mechanism among oxidative stress, EBV reactivation, and radioresistance and to identify new molecular subtyping models and treatment strategies to improve the therapeutic effects of radiotherapy.

Methods: ROS, NADP⁺/NADPH, and GSSG/GSH were detected to evaluate the oxidative stress of cells. 8-OHdG is a reliable oxidative stress marker to evaluate the oxidative stress in patients. Its concentration in serum was detected using an ELISA method and in biopsies was detected using IHC. qPCR array was performed to evaluate the expression of essential oxidative stress genes. qPCR, Western blot, and IHC were used to measure the level of EBV reactivation in vitro and in vivo. A Rta-IgG ELISA kit and EBV DNA detection kit were used to analyze the reactivation of EBV in serum from NPC patients. NPC tumor tissue microarrays was used to investigate the prognostic role of oxidative stress and EBV reactivation. Radiation resistance was evaluated by a colony formation assay. Xenografts were treated with NAC, radiation, or a combination of NAC and radiation. EBV DNA load of tumor tissue was evaluated using an EBV DNA detection kit. Oxidative stress, EBV reactivation, and the apoptosis rate in tumor tissues were detected by using 8-OHdG, EAD, and TUNEL assays, respectively.

Results: We found that EBV can induce high oxidative stress, which promotes its reactivation and thus leads to radioresistance. Basically, EBV caused NPC cells to undergo a process of 'Redox Resetting' to acquire a new redox status with higher levels of ROS accumulation and stronger antioxidant systems by increasing the expression of the ROS-producing enzyme, NOX2, and the cellular master antioxidant regulator, Nrf2. Also, EBV encoded driving protein LMP1 promotes EBV reactivation through production of ROS. Furthermore, high oxidative stress and EBV reactivation were positively associated with poor overall survival of patients following radiation therapy and were significant related to NPC patients' recurrence and clinical stage. By decreasing oxidative stress using an FDA approved antioxidant drug, NAC, sensitivity of tumors to radiation was increased. Additionally, 8-OHdG and EBV DNA could be dual prognostic markers for NPC patients.

Conclusions: Oxidative stress mediates EBV reactivation and leads to radioresistance. Targeting oxidative stress can provide therapeutic benefits to cancer patients with radiation resistance. Clinically, we, for the first time, generated a molecular subtyping model for NPC relying on 8-OHdG and EBV DNA level. These dual markers could identify patients who are at a high risk of poor outcomes but who might benefit from the sequential therapy of reactive oxygen blockade followed by radiation therapy, which provides novel perspectives for the precise treatment of NPC.

Epstein-Barr virus-encoded latent membrane protein 1 promotes extracellular vesicle secretion through syndecan-2 and synaptotagmin-like-4 in nasopharyngeal carcinoma cells

Increasing evidence indicates that extracellular vesicles (EVs) play an important role in cancer cell-to-cell communication. The Epstein-Barr virus (EBV)-encoded latent membrane protein 1 (LMP1), which is closely associated with nasopharyngeal carcinoma (NPC) pathogenesis, can trigger multiple cell signaling pathways that affect cell progression. Several reports have shown that LMP1 promotes EV secretion, and LMP1 trafficking by EVs can enhances cancer progression and metastasis. However, the molecular mechanism by which LMP1 promotes EV secretion is not well understood. In the present study, we found that LMP1 promotes EV secretion by upregulated syndecan-2 (SDC2) and synaptotagmin-like-4 (SYTL4) through nuclear factor (NF)-κB signaling in NPC cells. Further study indicated that SDC2 interacted with syntenin, which promoted the formation of the EVs, and SYTL4 is associated with the release of EVs. Moreover, we found that stimulation of EV secretion by LMP1 can enhance the proliferation and invasion ability of recipient NPC cells and tumor growth in vivo. In summary, we found a new mechanism by which LMP1 upregulates SDC2 and SYTL4 through NF-κB signaling to promote EV secretion, and further enhance cancer progression of NPC.

LMP1-positive extracellular vesicles promote radioresistance in nasopharyngeal carcinoma cells through P38 MAPK signaling

Radioresistance has been one of the impediments to effective nasopharyngeal carcinoma (NPC) therapy in clinical settings. Epstein‐Barr virus (EBV) encoded latent membrane protein 1 (LMP1) is expressed in NPC and has potent effects on radioresistance. It has been detected in extracellular vesicles (EVs) or exosomes and shown to promote tumor proliferation and invasive potential. However, whether LMP1‐positive EVs can confer radioresistance to cancer cells and the mechanism used to promote radioresistance need to be elucidated. In this study, the data showed that EVs derived from LMP1‐positive NPC cells could induce recipient NPC cell proliferation and invasion and suppress apoptosis, especially promoting radioresistance. In addition, LMP1 could increase the secretion of LMP1‐positive EVs. Furthermore, transmitted LMP1 subsequently performed its oncogenic functions through activating P38 MAPK signaling in recipient cells, and inhibiting P38 activity could efficaciously restore the sensitivity of NPC cells to ionizing radiation (IR). Finally, we found that LMP1‐positive EVs could promote tumor growth and P38 inhibition eliminates this promoting effect in vivo, and EV formation is associated with a poor prognosis in NPC patients. These results showed that a few cells expressing LMP1 could enhance the radioresistance of NPC cells through potentially impacting the infected host and also modulating the tumor microenvironment.

Epstein–Barr virus: overcoming the DNA damage response

Infections by DNA viruses including, Epstein–Barr virus (EBV), typically induce cellular DNA damage responses (DDR), in particular double-stranded break signaling. To avoid apoptosis associated with constitutive DDR signaling, downstream steps of this pathway must be inactivated. EBV has developed multiple ways of disabling the DDR using several different viral proteins expressed at various stages of EBV infection. Here the interplay between EBV and host DDRs is discussed at each stage of EBV infection, along with the EBV proteins and miRNAs that are known to interfere with DDR signaling. The newly discovered APOBEC editing of EBV DNA and protection from this mutation is also discussed.

Epstein-Barr Virus (EBV)-Related Lymphoproliferative Disorders in Ataxia Telangiectasia: Does ATM Regulate EBV Life Cycle?

Epstein-Barr virus (EBV) is an ubiquitous herpesvirus with a tropism for epithelial cells (where lytic replication occurs) and B-cells (where latency is maintained). EBV persists throughout life and chronic infection is asymptomatic in most individuals. However, immunocompromised patients may be unable to control EBV infection and are at increased risk of EBV-related malignancies, such as diffuse large B-cell lymphomas or Hodgkin's lymphomas. Ataxia telangiectasia (AT) is a primary immunodeficiency caused by mutations in the ATM gene and associated with an increased incidence of cancers, particularly EBV-associated lymphomas. However, the immune deficiency present in AT patients is often too modest to explain the increased incidence of EBV-related malignancies. The ATM defect in these patients could therefore impair the normal regulation of EBV latency in B-cells, thus promoting lymphomagenesis. This suggests that ATM plays a role in the normal regulation of EBV latency. ATM is a serine/threonine kinase involved in multiple cell functions such as DNA damage repair, cell cycle regulation, oxidative stress, and gene expression. ATM is implicated in the lytic cycle of EBV, where EBV uses the activation of DNA damage repair pathway to promote its own replication. ATM regulates the latent cycle of the EBV-related herpesvirus KSHV and MHV68. However, the contribution of ATM in the control of the latent cycle of EBV is not yet known. A better understanding of the regulation of EBV latency could be harnessed in the conception of novel therapeutic strategies in AT and more generally in all ATM deficient EBV-related malignancies.

Modulation of radiation sensitivity and antitumor immunity by viral pathogenic factors: Implications for radio-immunotherapy

Several DNA viruses including Human Papillomavirus (HPV), Epstein-Barr virus (EBV), and Human cytomegalovirus (HCMV) are mechanistically associated with the development of human cancers (HPV, EBV) and/or modulation of the immune system (HCMV). Moreover, a number of distinct mechanisms have been described regarding the modulation of tumor cell response to ionizing radiation and evasion from the host immune system by viral factors. There is further accumulating interest in the treatment with immune-modulatory therapies such as immune checkpoint inhibitors for malignancies with a viral etiology. Also, patients with HPV-positive tumors have a significantly improved prognosis that is attributable to increased intrinsic radiation sensitivity and may also arise from modulation of a cytotoxic T cell response in the tumor microenvironment (TME). In this review, we will highlight recent advances in the understanding of the biological basis of radiation response mediated by viral pathogenic factors and evasion from and modulation of the immune system by viruses.

The Epstein-Barr virus LMP1 interactome: biological implications and therapeutic targets

The oncogenic potential of Epstein-Barr virus (EBV) is mostly attributed to latent membrane protein 1 (LMP1), which is essential and sufficient for transformation of fibroblast and primary lymphocytes. LMP1 expression results in the activation of multiple signaling cascades like NF-ΚB and MAP kinases that trigger cell survival and proliferative pathways. LMP1 specific signaling events are mediated through the recruitment of a number of interacting proteins to various signaling domains. Based on these properties, LMP1 is an attractive target to develop effective therapeutics to treat EBV-related malignancies. In this review, we focus on LMP1 interacting proteins, associated signaling events, and potential targets that could be exploited for therapeutic strategies.

Contribution of the KSHV and EBV lytic cycles to tumourigenesis

Kaposi's Sarcoma-associated herpesvirus (KSHV) and Epstein Barr virus (EBV) are the causative agents of several malignancies. Like all herpesviruses, KSHV and EBV undergo distinct latent and lytic replication programmes. The transition between these states allows the establishment of a lifelong persistent infection, dissemination to sites of disease and the spread to new hosts. Latency-associated viral proteins have been well characterised in transformation and tumourigenesis pathways; however, a number of studies have shown that abrogation of KSHV and EBV lytic gene expression impairs the oncogenesis of several cancers. Furthermore, several lytically expressed proteins have been functionally tethered to the angioproliferative and anti-apoptotic phenotypes of virus-infected cells. As a result, the investigation and therapeutic targeting of KSHV and EBV lytic cycles may be essential for the treatment of their associated malignancies.

Epstein-Barr Virus Hijacks DNA Damage Response Transducers to Orchestrate Its Life Cycle

The Epstein–Barr virus (EBV) is a ubiquitous virus that infects most of the human population. EBV infection is associated with multiple human cancers, including Burkitt’s lymphoma, Hodgkin’s lymphoma, a subset of gastric carcinomas, and almost all undifferentiated non-keratinizing nasopharyngeal carcinoma. Intensive research has shown that EBV triggers a DNA damage response (DDR) during primary infection and lytic reactivation. The EBV-encoded viral proteins have been implicated in deregulating the DDR signaling pathways. The consequences of DDR inactivation lead to genomic instability and promote cellular transformation. This review summarizes the current understanding of the relationship between EBV infection and the DDR transducers, including ATM (ataxia telangiectasia mutated), ATR (ATM and Rad3-related), and DNA-PK (DNA-dependent protein kinase), and discusses how EBV manipulates the DDR signaling pathways to complete the replication process of viral DNA during lytic reactivation.

(-)-Epigallocatechin-3-gallate inhibition of Epstein-Barr virus spontaneous lytic infection involves downregulation of latent membrane protein 1

The Epstein-Barr virus (EBV) lytic cycle contributes to the development of EBV-associated diseases. EBV-encoded latent membrane protein 1 (LMP1) is key to EBV lytic replication, and our previous work indicated that epigallocatechin-3-gallate (EGCG) inhibited constitutive EBV lytic infection through the suppression of LMP1-activated phosphoinositide 3-kinase/Akt and mitogen-activated protein kinase kinase/extracellular signal-related protein kinase 1/2 signaling. The present study demonstrated that LMP1 in CNE-LMP1 constructed cells significantly induced the expression of the EBV lytic proteins BZLF1 (P<0.001) and BMRF1 (P<0.05) compared with CNE1 cells. Following treatment with a specific DNAzyme that targets LMP1, significantly reduced protein expression levels of BZLF1 and BMRF1 in EBV-associated epithelial carcinoma CNE1-LMP1 cells (P<0.001 and P<0.01, respectively) and lymphoma B95.8 cells (both P<0.01) were observed. Furthermore, EGCG significantly inhibited the mRNA and protein expression levels of LMP1 (P<0.05) in an apparent dose-dependent manner in CNE1-LMP1 and B95.8 cells. Thus, the present findings indicated that the molecular mechanism underlying EGCG inhibition of EBV lytic infection involves downregulation of LMP1.

Silencing of ATM expression by siRNA technique contributes to glioma stem cell radiosensitivity in vitro and in vivo

Evidence has shown that both high expression of the ataxia-telangiectasia mutated (ATM) gene and glioma stem cells (GSCs) are responsible for radioresistance in glioma. Thus, we hypothesized that brain tumor radiosensitivity may be enhanced via silencing of the ATM gene in GSCs. In the present study we successfully induced GSCs from two cell lines and used CD133 and nestin to identify GSCs. A lentivirus was used to deliver siRNA-ATMPuro (A group) to GSCs prior to radiation, while siRNA-HKPuro (N group) and GSCs (C group) were used as negative and blank controls, respectively. RT-qPCR and western blotting were performed to verify the efficiency of the siRNA-ATM technique. The expression of the ATM gene and ATM protein were significantly downregulated post-transfection. Cell Counting Kit-8 (CCK-8) and colony formation assays revealed that the A group demonstrated weak cell proliferation and lower survival fractions post-irradiation compared to the C/N groups. Flow cytometry was used to examine the percentage of cell apoptosis and G2 phase arrest, which were both higher in the A group than in the C/N groups. We found that the comet tail percentage evaluated by comet assay was higher in the A group than in the C/N groups. After radiation treatment, three radiosensitive genes [p53, proliferating cell nuclear antigen (PCNA), survivin] exhibited a decreasing tendency as determined by RT-qPCR. Mice underwent subcutaneous implantation, followed by radiation, and the resulting necrosis and hemorrhage were more obvious in the A group than in the N groups. In conclusion, silencing of ATM via the siRNA technique improved radiosensitivity of GSCs both in vitro and in vivo.

Chicken gga-miR-19a Targets ZMYND11 and Plays an Important Role in Host Defense against Mycoplasma gallisepticum (HS Strain) Infection

Mycoplasma gallisepticum (MG), one of the most pathogenic Mycoplasmas, can cause chronic respiratory disease (CRD) in chickens. It has been suggested that micro-ribonucleic acids (miRNAs) are involved in microbial pathogenesis. However, little is known about the roles of miRNAs in MG infection. Previously, we found by deep sequencing that gga-miR-19a was significantly up-regulated in the lungs of MG-infected chicken embryos. In this work, we confirmed that gga-miR-19a was up-regulated in both MG-infected chicken embryonic lungs and MG-infected DF-1 (chicken embryo fibroblast) cells. At 72 h post-transfection, we found that the over-expression of gga-miR-19a significantly enhanced the proliferation of MG-infected DF-1 cells by promoting the transition from the G1 phase to the S and G2 phases, while a gga-miR-19a inhibitor repressed the proliferation of MG-infected DF-1 cells by arresting the cell cycle in the G1 phase. Moreover, we found that gga-miR-19a regulated the expression of the host zinc-finger protein, MYND-type containing 11 (ZMYND11), through binding to its 3′ untranslated region (3′-UTR). DAVID analysis revealed that ZMYND11 could negatively regulate the NF-kappaB (NF-κB) signaling pathway in chickens (Gallus gallus). Upon MG infection, gga-miR-19a, NF-κB, MyD88, and TNF-α were all up-regulated, whereas ZMYND11 was down-regulated. The over-expression of gga-miR-19a in the DF-1 cells did not affect the above gene expression patterns, and gga-miR-19a inhibitor repressed the expression of NF-κB, MyD88, and TNF-α, but enhanced the expression of ZMYND11. In conclusion, gga-miR-19a might suppress the expression of ZMYND11 in MG-infected chicken embryonic lungs and DF-1 cells, activate the NF-κB signaling pathway, and promote pro-inflammatory cytokines expression, the cell cycle progression and cell proliferation to defend against MG infection.

EBV-LMP1 targeted DNAzyme enhances radiosensitivity by inhibiting tumor angiogenesis via the JNKs/HIF-1 pathway in nasopharyngeal carcinoma

LMP1, which is encoded by the Epstein-Barr virus, is proposed to be one of the major oncogenic factors involved in nasopharyngeal carcinoma (NPC). Previous studies demonstrated that down-regulation of LMP1 by LMP1-targeted DNAzyme (DZ1) increases the radiosensitivity of NPC. However, the mechanism by which DZ1 contributes to this radiosensitivity remains unclear. In this study, we determined whether a DZ1 blockade of LMP1 expression has an overall positive effect on the radiotherapy of NPCs by repressing HIF-1/VEGF activity and to investigate the mechanisms underlying LMP1-induced HIF-1 activation in NPC cells. The results showed that DZ1 inhibited the microtubule-forming ability of HUVECs co-cultured with NPC cells, which occurs with the down-regulation of VEGF expression and secretion. Moreover, LMP1 increases phosphorylated JNKs/c-Jun signaling, which is involved in the regulation of HIF-1/VEGF activity. After silencing LMP1 and decreasing phosphorylation of JNKs, NPC cells exhibited an enhanced radiosensitivity. Furthermore, in vivo experiments revealed a significant inhibition of tumor growth and a marked reduction of the Ktrans parameter, which reflects the condition of tumor micro-vascular permeability. Taken together, our data suggested that VEGF expression is increased by LMP1 through the JNKs/c-Jun signaling pathway and indicated that DZ1 enhances the radiosensitivity of NPC cells by inhibiting HIF-1/VEGF activity.

Co-infection of Epstein-Barr virus and human papillomavirus in human tumorigenesis

Viral infections contribute to approximately 12% of cancers worldwide, with the vast majority occurring in developing countries and areas. Two DNA viruses, Epstein-Barr virus (EBV) and human papillomavirus (HPV), are associated with 38% of all virus-associated cancers. The probability of one patient infected with these two distinct types of viruses is increasing. Here, we summarize the co-infection of EBV and HPV in human malignancies and address the possible mechanisms for the co-infection of EBV and HPV during tumorigenesis.

Repression of Hox genes by LMP1 in nasopharyngeal carcinoma and modulation of glycolytic pathway genes by HoxC8

Epstein-Barr virus (EBV) causes human lymphoid malignancies, and the EBV product latent membrane protein 1 (LMP1) has been identified as an oncogene in epithelial carcinomas such as nasopharyngeal carcinoma (NPC). EBV can epigenetically reprogram lymphocyte-specific processes and induce cell immortalization. However, the interplay between LMP1 and the NPC host cell remains largely unknown. Here, we report that LMP1 is important to establish the Hox gene expression signature in NPC cell lines and tumor biopsies. LMP1 induces repression of several Hox genes in part via stalling of RNA polymerase II (RNA Pol II). Pol II stalling can be overcome by irradiation involving the epigenetic regulator TET3. Furthermore, we report that HoxC8, one of the genes silenced by LMP1, has a role in tumor growth. Ectopic expression of HoxC8 inhibits NPC cell growth in vitro and in vivo, modulates glycolysis and regulates the expression of tricarboxylic acid (TCA) cycle-related genes. We propose that viral latency products may repress via stalling key mediators that in turn modulate glycolysis.

Immune control of oncogenic γ-herpesviruses

Human γ-herpesviruses contain Epstein Barr virus (EBV), the first human tumor virus that was identified in man, and Kaposi Sarcoma associated herpesvirus (KSHV), one of the most recently identified human oncogenic pathogens. Both of these have co-evolved with humans to cause tumors only in a minority of infected individuals, despite their exquisite ability to establish persistent infections. In this review we will summarize the fine-tuned balance between immune responses, immune escape and cellular transformation by these viruses, which results in life-long persistent, but asymptomatic infection with immune control in most virus carriers. A detailed understanding of this balance is required to immunotherapeutically reinstall it in patients that suffer from EBV and KSHV associated malignancies.

DNAzyme-based therapeutics for cancer treatment

Gene-silencing strategies based on catalytic nucleic acids have been rapidly developed in the past decades. Ribozymes, antisense oligonucleotides and RNA interference have been actively pursued for years due to their potential application in gene inactivation. Pioneered by Joyce et al., a new class of catalytic nucleic acid composed of deoxyribonucleotides has emerged via an in vitro selection system. The therapeutic potential of these RNA-cleaving DNAzymes have been shown both in vitro and in vivo. Although they rival the activity and stability of synthetic ribozymes, they are limited by inefficient delivery to the intracellular targets. Recent successes in clinical testing of the DNAzymes in cancer patients have revitalized the potential clinical utility of DNAzymes.

Novel roles and therapeutic targets of Epstein-Barr virus-encoded latent membrane protein 1-induced oncogenesis in nasopharyngeal carcinoma

Epstein-Barr virus (EBV) was first discovered 50 years ago as an oncogenic gamma-1 herpesvirus and infects more than 90% of the worldwide adult population. Nasopharyngeal carcinoma (NPC) poses a serious health problem in southern China and is one of the most common cancers among the Chinese. There is now strong evidence supporting a role for EBV in the pathogenesis of NPC. Latent membrane protein 1 (LMP1), a primary oncoprotein encoded by EBV, alters several functional and oncogenic properties, including transformation, cell death and survival in epithelial cells in NPC. LMP1 may increase protein modification, such as phosphorylation, and initiate aberrant signalling via derailed activation of host adaptor molecules and transcription factors. Here, we summarise the novel features of different domains of LMP1 and several new LMP1-mediated signalling pathways in NPC. When then focus on the potential roles of LMP1 in cancer stem cells, metabolism reprogramming, epigenetic modifications and therapy strategies in NPC.

Biomarkers for enhancing the radiosensitivity of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a common head and neck malignancy. The incidence of NPC is higher in Southern China and Southeast Asia compared with Western countries. Given its high radiosensitivity, the standard treatment for NPC is radiotherapy. However, radioresistance remains a serious obstacle to successful treatment. Radioresistance can cause local recurrence and distant metastases in some patients after treatment by radiation. Thus, special emphasis has been given to the discovery of effective radiosensitizers. This review aims to discuss the biomarkers, classified according to the main mechanisms of radiosensitization, which can enhance the sensitivity of NPC cells to ionizing radiation.

LMP1 stimulates the transcription of eIF4E to promote the proliferation, migration and invasion of human nasopharyngeal carcinoma

Eukaryotic translation initiation factor 4E (eIF4E) is the rate-limiting translation initiation factor for many oncogenes. Previous studies have shown eIF4E overexpression in nasopharyngeal carcinoma (NPC). We aimed to study whether viral oncogene latent membrane protein 1 (LMP1) stimulates the transcription of eIF4E to promote NPC malignancy. In NPC cell lines (CNE1 and CNE2), ectopic LMP1 significantly increased the mRNA and protein levels of eIF4E and the transcriptional activity of the eIF4E promoter in a LMP1-plasmid-transfected dose-dependent manner. As a backward experiment, knocking down of LMP1 significantly reduced eIF4E mRNA in B95-8 cells. In the high LMP1 expression condition, knocking down of c-Myc significantly reduced eIF4E mRNA in both NPC and B95-8 cells, and knocking down of eIF4E significantly inhibited the tumor proliferation, migration and invasion promoted by LMP1. The results indicated that LMP1 stimulates the transcription of eIF4E via c-Myc to promote NPC. To the best of our knowledge, this is the first evidence that LMP1 stimulates the transcription of eIF4E. This might be an important cause of the overexpression of eIF4E in NPC and be the novel mechanism by which LMP1 initiates cancer. LMP1-stimulated eIF4E initiates the translation of those oncogenes transcriptionally activated by LMP1 to amplify and pass down the carcinogenesis signals launched by LMP1.

Targeting Epstein-Barr virus oncoprotein LMP1-mediated glycolysis sensitizes nasopharyngeal carcinoma to radiation therapy

Our goal in this work was to illustrate the Epstein-Barr virus (EBV)-modulated global biochemical profile and provide a novel metabolism-related target to improve the therapeutic regimen of nasopharyngeal carcinoma (NPC). We used a metabolomics approach to investigate EBV-modulated metabolic changes, and found that the exogenous overexpression of the EBV-encoded latent membrane protein 1 (LMP1) significantly increased glycolysis. The deregulation of several glycolytic genes, including hexokinase 2 (HK2), was determined to be responsible for the reprogramming of LMP1-mediated glucose metabolism in NPC cells. The upregulation of HK2 elevated aerobic glycolysis and facilitated proliferation by blocking apoptosis. More importantly, HK2 was positively correlated with LMP1 in NPC biopsies, and high HK2 levels were significantly associated with poor overall survival of NPC patients following radiation therapy. Knockdown of HK2 effectively enhanced the sensitivity of LMP1-overexpressing NPC cells to irradiation. Finally, c-Myc was demonstrated to be required for LMP1-induced upregulation of HK2. The LMP1-mediated attenuation of the PI3-K/Akt-GSK3beta-FBW7 signaling axis resulted in the stabilization of c-Myc. These findings indicate a close relationship between EBV and glycolysis in NPC. Notably, LMP1 is the key regulator of the reprogramming of EBV-mediated glycolysis in NPC cells. Given the importance of EBV-mediated deregulation of glycolysis, anti-glycolytic therapy might represent a worthwhile avenue of exploration in the treatment of EBV-related cancers.

Expression of Epstein-Barr virus-encoded latent membrane protein (LMP-1), p16 and p53 proteins in nonendemic nasopharyngeal carcinoma (NPC): a clinicopathological study

BACKGROUND AND AIMS

Although the latent membrane protein type 1 (LMP1) is frequently expressed in Epstein-Barr virus (EBV) malignancies, its contribution to the pathogenesis of nasopharyngeal carcinoma (NPC) is not fully defined. LMP1 functions as a viral mimic of the TNFR family member engaging a number of signaling pathways that induce morphological and phenotypic alterations. This study aimed to investigate the LMP1 expression and EBV infection in relation to clinical outcome and survival in a series of Mexican NPC patients. We also studied expression of p16 and p53 proteins.

METHODS

We analyzed in 25 tumor specimens the expression of LMP1, p16 and p53 by immunohistochemistry (IHC) and EBV presence by IHC/in situ hybridization. Differences in clinical outcome and survival in relation to protein expression were correlated through χ(2) statistics and Kaplan-Meier survival curves.

RESULTS

Our results showed a rate of 92% (23/25) of EBV infection. The expressions of LMP-1, p16 and p53 proteins were 40.0, 44.0 and 40.0%, respectively. LMP-1 immunoexpression was more common in older patients (>50 vs. <50 years old, p = 0.02) and with parapharyngeal space invasion (p = 0.02). The presence of metastatic disease at diagnosis (p = 0.03), distant recurrence disease (p = 0.006) and shorter distance recurrence-free survival (p = 0.05) was associated with lack of p16.

CONCLUSIONS

In our series, EBV infection rates are particularly high for nonendemic NPC, although without a statistically significant difference in overall survival, LMP1 and p16 expression was correlated with poorer clinical prognosis. Probably, LMP1 and p16 detection identify a worse clinical prognosis in NPC patient subgroup.

Integrated analysis of differential miRNA and mRNA expression profiles in human radioresistant and radiosensitive nasopharyngeal carcinoma cells

Background

The purpose of this study was to identify miRNAs and genes involved in nasopharyngeal carcinoma (NPC) radioresistance, and explore the underlying mechanisms in the development of radioresistance.

Methods

We used microarrays to compare the differences of both miRNA and mRNA expression profiles in the radioresistant NPC CNE2-IR and radiosensitive NPC CNE2 cells, applied qRT-PCR to confirm the reliability of microarray data, adopted databases prediction and anticorrelated analysis of miRNA and mRNA expression to identify the miRNA target genes, and employed bioinformatics tools to examine the functions and pathways in which miRNA target genes are involved, and construct a miRNA-target gene regulatory network. We further investigated the roles of miRNA-23a and its target gene IL-8 in the NPC radioresistance.

Results

The main findings were fourfold: (1) fifteen differential miRNAs and 372 differential mRNAs were identified, and the reliability of microarray data was validated for randomly selected eight miRNAs and nine genes; (2) 174 miRNA target were identified, and most of their functions and regulating pathways were related to tumor therapeutic resistance; (3) a posttranscriptional regulatory network including 375 miRNA-target gene pairs was constructed, in which the ten genes were coregulated by the six miRNAs; (4) IL-8 was a direct target of miRNA-23a, the expression levels of IL-8 were elevated in the radioresistant NPC tissues and showed inverse correlation with miRNA-23a expression, and genetic upregulation of miRNA-23a and antibody neutralization of secretory IL-8 could reduce NPC cells radioresistance.

Conclusions

We identified fifteen differential miRNAs and 372 differential mRNAs in the radioresistant NPC cells, constructed a posttranscriptional regulatory network including 375 miRNA-target gene pairs, discovered the ten target genes coregulated by the six miRNAs, and validated that downregulated miRNA-23a was involved in NPC radioresistance through directly targeting IL-8. Our data form a basis for further investigating the mechanisms of NPC radioresistance.

Activation of H2AX and ATM in varicella-zoster virus (VZV)-infected cells is associated with expression of specific VZV genes

Mammalian cells activate DNA damage response pathways in response to virus infections. Activation of these pathways can enhance replication of many viruses, including herpesviruses. Activation of cellular ATM results in phosphorylation of H2AX and recruits proteins to sites of DNA damage. We found that varicella-zoster (VZV) infected cells had elevated levels of phosphorylated H2AX and phosphorylated ATM and that these levels increased in cells infected with VZV deleted for ORF61 or ORF63, but not deleted for ORF67. Expression of VZV ORF61, ORF62, or ORF63 alone did not result in phosphorylation of H2AX. While BGLF4, the Epstein-Barr virus homolog of VZV ORF47 protein kinase, phosphorylates H2AX and ATM, neither VZV ORF47 nor ORF66 protein kinase phosphorylated H2AX or ATM. Cells lacking ATM had no reduction in VZV replication. Thus, VZV induces phosphorylation of H2AX and ATM and this effect is associated with the presence of specific VZV genes in virus-infected cells.

Genome-wide analyses of radioresistance-associated miRNA expression profile in nasopharyngeal carcinoma using next generation deep sequencing

BACKGROUND

Rapidly growing evidence suggests that microRNAs (miRNAs) are involved in a wide range of cancer malignant behaviours including radioresistance. Therefore, the present study was designed to investigate miRNA expression patterns associated with radioresistance in NPC.

METHODS

The differential expression profiles of miRNAs and mRNAs associated with NPC radioresistance were constructed. The predicted target mRNAs of miRNAs and their enriched signaling pathways were analyzed via biological informatical algorithms. Finally, partial miRNAs and pathways-correlated target mRNAs were validated in two NPC radioreisitant cell models.

RESULTS

50 known and 9 novel miRNAs with significant difference were identified, and their target mRNAs were narrowed down to 53 nasopharyngeal-/NPC-specific mRNAs. Subsequent KEGG analyses demonstrated that the 53 mRNAs were enriched in 37 signaling pathways. Further qRT-PCR assays confirmed 3 down-regulated miRNAs (miR-324-3p, miR-93-3p and miR-4501), 3 up-regulated miRNAs (miR-371a-5p, miR-34c-5p and miR-1323) and 2 novel miRNAs. Additionally, corresponding alterations of pathways-correlated target mRNAs were observed including 5 up-regulated mRNAs (ICAM1, WNT2B, MYC, HLA-F and TGF-β1) and 3 down-regulated mRNAs (CDH1, PTENP1 and HSP90AA1).

CONCLUSIONS

Our study provides an overview of miRNA expression profile and the interactions between miRNA and their target mRNAs, which will deepen our understanding of the important roles of miRNAs in NPC radioresistance.

Epstein-Barr Virus encoded LMP1 regulates cyclin D1 promoter activity by nuclear EGFR and STAT3 in CNE1 cells

The principal Epstein–Barr virus (EBV) oncoprotein, latent membrane protein 1 (LMP1) is strongly associated with nasopharyngeal carcinoma (NPC), a prevalent cancer in China. The epidermal growth factor receptor (EGFR) is important in carcinogenesis, as it is a ubiquitously expressed receptor tyrosine kinase. Signal transducer and activator of transcription 3 (STAT3) is a master transcriptional regulator in proliferation and apoptosis. Our previous study demonstrated that the nuclear EGFR could bind to the cyclin D1 promoter directly in the presence of LMP1, and the correlation between EGFR and STAT3 in NPC remains to be further explored. Here, we have shown that the interaction of EGFR and STAT3 increased in the nucleus in the presence of LMP1. LMP1 promoted both EGFR and STAT3 binding to the promoter region of cyclin D1, in turn, enhancing the promoter activity of cyclin D1. Furthermore, we demonstrated that both transcriptional activity and mRNA levels of cyclin D1 were decreased by small molecule interference of EGFR and STAT3 activity. These findings may provide a novel linkage between the EGFR and STAT3 signaling pathways and the activation of cyclin D1 by LMP1 in the carcinogenesis of NPC.

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 K^trans 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.

Targeting EBV-LMP1 DNAzyme enhances radiosensitivity of nasopharyngeal carcinoma cells by inhibiting telomerase activity

The latent membrane protein 1 (LMP1), which is encoded by the Epstein-Barr virus (EBV), has been suggested to be one of the major oncogenic factors in nasopharyngeal carcinoma (NPC). In previous studies, we experimentally demonstrated that downregulation of LMP1 expression by targeting EBV-LMP1 DNAzyme (Dz1) could increase the radiosensitivity of NPC. However, how Dz1 contributes to the radiosensitivity in NPC is still not clear. In the present study, we confirmed that Dz1 decreases LMP1 expression and downregulates the expression of the catalytic subunit of telomerase (hTERT), both at the protein and mRNA levels (P<0.01), and therefore, consequently inhibits telomerase activity (P<0.05) in LMP1-positive NPC cells. We also observed that LMP1 mediated Akt phosphorylation is involved in the regulation of hTERT expression and phosphorylation. After LMP1 and hTERT expression was silenced by Dz1 and hTERT-targeted siRNA, respectively, the radiosensitivity increased in CNE1-LMP1 cells (P<0.05). The inhibition was more significant after Dz1 treatment was combined with siRNA (P<0.01). We concluded that hTERT expression and phosphorylation could be regulated by LMP1 through the Akt pathway, and Dz1 enhances radiosensitivity of LMP1-positive NPC cells by inhibiting telomerase activity.

Inhibitory effect of ARHI on pancreatic cancer cells and NF-κB activity

The aim of this study was to investigate the effect of aplasia ras homolog member I (ARHI) on proliferation, apoptosis and the cell cycle in the pancreatic cancer cell line PANC-1. The study also aimed to examine the effect of ARHI on the activity of the nuclear factor (NF)-κB and to determine whether ARHI acts as a tumor suppressor in the development of pancreatic cancer by inhibiting the activity of NF-κB. A pIRES2‑EGFP‑ARHI vector, constructed by reverse transcrition (RT)‑PCR, was transiently transfected into the PANC-1 cells and analyzed for the expression of the ARHI protein by western blotting. A MTT assay was used to quantify cell proliferation, and apoptosis was analyzed by flow cytometry. The NF‑κB signaling pathway, specifically the pathway using the nuclear phosphorylated p65 isoform, was analyzed by western blotting. Expression of the ARHI protein was detected by western blotting subsequent to the PANC-1 cells being transiently transfected with the pIRES2‑EGFP‑ARHI construct. Cell proliferation was strongly inhibited in the PANC-1 cells transfected with pIRES2‑EGFP‑ARHI. The cell cycle assays indicated an increase in the number of cells at the G0/G1 phase and a decrease in the cells at the S phase, but the difference was not significant (P>0.05). Time course studies also indicated a marked increase in the apoptotic index following transient transfection, as well as a gradual decrease in the expression of the nuclear phosphorylated p65 protein. ARHI acts as a tumor suppressor by downregulating the NF‑κB signaling pathway, which results in the inhibition of cell proliferation, apoptosis and the cell cycle in the pancreatic tumor PANC-1 cell line.

Identification of heat shock protein 27 as a radioresistance-related protein in nasopharyngeal carcinoma cells

PURPOSE

To identify the proteins involved in radioresistance in nasopharyngeal cancer (NPC) cells.

METHODS

Sublethal ionizing radiation was applied to establish a radioresistant NPC cell line from its parental NPC cell line CNE1. Clonogenic survival assay, cell growth assay and flow cytometry analysis were used to examine the difference of radiosensitivity in the radioresistant CNE1 cells (CNE1-IR) and control CNE1 cells. Comparative proteomics was performed to identify the differential proteins in the two cell lines. Association of HSP27, one of upregulated proteins in CNE1-IR cells, with NPC cell radioresistance was selected for further investigation using antisense oligonucleotides (ASOs), clonogenic survival assay, Hoechst 33258 staining of apoptotic cells and MTT assay of cell viability.

RESULTS

Radioresistant NPC cell line CNE1-IR derived from its parental cell line CNE1 was established. Thirteen differential proteins in the CNE1-IR and CNE1 cells were identified by proteomics, and differential expression of HSP27, one of identified proteins, was selectively confirmed by western blot. Inhibition of HSP27 expression by HSP27 ASOs decreased clonogenic survival and cell viability and increased cell apoptosis of CNE1-IR cells after irradiation, that is, enhanced radiosensitivity of CNE1-IR cells.

CONCLUSION

The data suggest that HSP27 is a radioresistant protein in NPC cells, and its upregulation may be involved in the NPC radioresistance.

Regulatory mechanisms and clinical perspectives of miRNA in tumor radiosensitivity

MicroRNA (miRNA) influences carcinogenesis at multiple stages and it can effectively control tumor radiosensitivity by affecting DNA damage repair, cell cycle checkpoint, apoptosis, radio-related signal transduction pathways and tumor microenvironment. MiRNA also efficiently modulates tumor radiosensitivity at multiple levels by blocking the two essential non-homologous end-joining repair and homologous recombination repair pathways in the DNA damage response. It interferes with four radio-related pathways in ionizing radiation, including the PI3-K/Akt, NF-κB, MAPK and TGFβ signaling pathways. Moreover, the regulatory effect of miRNA in radiosensitivity can be enhanced when interacting with various key molecules, including H2AX, BRCA1, ATM, DNA-PK, RAD51, Chk1, Cdc25A, p53, PLK1, HIF-1 and VEGF, which are involved in these processes. Therefore, thoroughly understanding the mechanism of miRNA in tumor radiosensitivity could assist in finding novel targets to improve the radiotherapeutic effects and provide new clinical perspectives and insights for developing effective cancer treatments.

Epstein-Barr virus-encoded latent membrane protein 1 impairs G2 checkpoint in human nasopharyngeal epithelial cells through defective Chk1 activation

Nasopharyngeal carcinoma (NPC) is a common cancer in Southeast Asia, particularly in southern regions of China. EBV infection is closely associated with NPC and has long been postulated to play an etiological role in the development of NPC. However, the role of EBV in malignant transformation of nasopharyngeal epithelial cells remains enigmatic. The current hypothesis of NPC development is that premalignant nasopharyngeal epithelial cells harboring genetic alterations support EBV infection and expression of EBV genes induces further genomic instability to facilitate the development of NPC. The latent membrane protein 1 (LMP1) is a well-documented EBV-encoded oncogene. The involvement of LMP1 in human epithelial malignancies has been implicated, but the mechanisms of oncogenic actions of LMP1, particularly in nasopharyngeal cells, are unclear. Here we observed that LMP1 expression in nasopharyngeal epithelial cells impaired G2 checkpoint, leading to formation of unrepaired chromatid breaks in metaphases after γ-ray irradiation. We further found that defective Chk1 activation was involved in the induction of G2 checkpoint defect in LMP1-expressing nasopharyngeal epithelial cells. Impairment of G2 checkpoint could result in loss of the acentrically broken chromatids and propagation of broken centric chromatids in daughter cells exiting mitosis, which facilitates chromosome instability. Our findings suggest that LMP1 expression facilitates genomic instability in cells under genotoxic stress. Elucidation of the mechanisms involved in LMP1-induced genomic instability in nasopharyngeal epithelial cells will shed lights on the understanding of role of EBV infection in NPC development.