Characterization of macromolecular lignins as Epstein-Barr virus inducer in foodstuff associated with nasopharyngeal carcinoma risk

Novel Therapies Boosting T Cell Immunity in Epstein Barr Virus-Associated Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma (NPC) is a malignant tumour of the head and neck affecting localised regions of the world, with the highest rates described in Southeast Asia, Northern Africa, and Greenland. Its high morbidity rate is linked to both late-stage diagnosis and unresponsiveness to conventional anti-cancer treatments. Multiple aetiological factors have been described including environmental factors, genetics, and viral factors (Epstein Barr Virus, EBV), making NPC treatment that much more complex. The most common forms of NPCs are those that originate from the epithelial tissue lining the nasopharynx and are often linked to EBV infection. Indeed, they represent 75–95% of NPCs in the low-risk populations and almost 100% of NPCs in high-risk populations. Although conventional surgery has been improved with nasopharyngectomy’s being carried out using more sophisticated surgical equipment for better tumour resection, recent findings in the tumour microenvironment have led to novel treatment options including immunotherapies and photodynamic therapy, able to target the tumour and improve the immune system. This review provides an update on the disease’s aetiology and the future of NPC treatments with a focus on therapies activating T cell immunity.

Chromatin Structure of Epstein-Barr Virus Latent Episomes

EBV latent infection is characterized by a highly restricted pattern of viral gene expression. EBV can establish latent infections in multiple different tissue types with remarkable variation and plasticity in viral transcription and replication. During latency, the viral genome persists as a multi-copy episome, a non-integrated-closed circular DNA with nucleosome structure similar to cellular chromosomes. Chromatin assembly and histone modifications contribute to the regulation of viral gene expression, DNA replication, and episome persistence during latency. This review focuses on how EBV latency is regulated by chromatin and its associated processes.

Epstein-Barr virus Zta upregulates matrix metalloproteinases 3 and 9 that synergistically promote cell invasion in vitro

Zta is a lytic transactivator of Epstein-Barr virus (EBV) and has been shown to promote migration and invasion of epithelial cells. Although previous studies indicate that Zta induces expression of matrix metalloproteinase (MMP) 9 and MMP1, direct evidence linking the MMPs to Zta-induced cell migration and invasion is still lacking. Here we performed a series of in vitro studies to re-examine the expression profile and biologic functions of Zta-induced MMPs in epithelial cells derived from nasopharyngeal carcinoma. We found that, in addition to MMP9, MMP3 was a new target gene upregulated by Zta. Ectopic Zta expression in EBV-negative cells increased both mRNA and protein production of MMP3. Endogenous Zta also contributed to induction of MMP3 expression, migration and invasion of EBV-infected cells. Zta activated the MMP3 promoter through three AP-1 elements, and its DNA-binding domain was required for the promoter binding and MMP3 induction. We further tested the effects of MMP3 and MMP9 on cell motility and invasiveness in vitro. Zta-promoted cell migration required MMP3 but not MMP9. On the other hand, both MMP3 and MMP9 were essential for Zta-induced cell invasion, and co-expression of the two MMPs synergistically increased cell invasiveness. Therefore, this study provides integrated evidence demonstrating that, at least in the in vitro cell models, Zta drives cell migration and invasion through MMPs.

Non-viral environmental risk factors for nasopharyngeal carcinoma: a systematic review

This review aims to systematically summarize the epidemiological studies on nasopharyngeal carcinoma (NPC) conducted over the past half century, covering descriptive epidemiological studies and reports on non-viral risk factors. Multiple lines of epidemiologic evidence for established risk factors are systematically presented in comprehensive tables. The potential interactions among environmental factors and genetic components, and also the impacts of parallel sequencing technology on the aetiology of NPC are discussed. Finally, we propose a modified model for the pathogenesis of nasopharyngeal carcinoma based on the current knowledge.

Epstein-Barr virus lytic transactivator Zta enhances chemotactic activity through induction of interleukin-8 in nasopharyngeal carcinoma cells

Epstein-Barr virus (EBV)-associated, undifferentiated type of nasopharyngeal carcinoma (NPC) is characterized by intensive leukocyte infiltration. Interaction between the infiltrating cells and the tumor cells has been considered crucial for NPC development. Recruitment of the infiltrates can be directed by certain chemokines present in the NPC tissues. It is unknown whether and how EBV lytic infection regulates expression of the chemokines. Using an antibody array, we first found that several chemokines secreted from EBV-infected NPC cells are increased upon EBV reactivation into the lytic cycle, and interleukin-8 (IL-8) is the chemokine upregulated most significantly and consistently. Further studies showed that the EBV lytic transactivator Zta is a potent inducer of IL-8 in NPC cells, augmenting secreted and intracellular IL-8 proteins, as well as IL-8 RNA. Zta upregulates Egr-1, a cellular transcription factor that has been involved in upregulation of IL-8, but the Zta-induced IL-8 expression is independent of Egr-1. The ability of Zta to transactivate the IL-8 promoter is important for the induction of IL-8, and we have identified two Zta-responsive elements in the promoter. Zta can bind to these two elements in vitro and can also be recruited to the IL-8 promoter in vivo. DNA-binding-defective Zta mutants can neither activate the IL-8 promoter nor induce IL-8 production. In addition, Zta-expressing NPC cells exert enhanced chemotactic activity that is mainly mediated by IL-8. Since IL-8 may contribute to not only leukocyte infiltration but also multiple oncogenic processes, the present study provides a potential link between EBV lytic infection and pathogenesis of NPC.

Dietary risk factors for nasopharyngeal carcinoma in Maghrebian countries

North Africa is one of the major Nasopharyngeal Carcinoma (NPC) endemic regions. Specific food items unique to this area were implicated to be associated with NPC risk, but results were inconsistent. Here we have performed a large-scale case-control study in the Maghrebian population from Tunisia, Algeria and Morocco. From 2002 to 2005, interviews were conducted on 636 cases and 615 controls. Controls were hospitalized individuals from 15 non-cancer hospital departments, or friends and family members of non-NPC cancer subjects, matched by center, childhood household type (rural or urban), age and sex. Conditional logistic regression is used to evaluate the risk of factors. In results, consumption of rancid butter, rancid sheep fat and preserved meat not spicy (mainly quaddid) were associated with significantly increased risk of NPC, while consumption of cooked vegetables and industrial preserved fish was associated with reduced risk. Other foods such as fresh citrus fruits and spicy preserved meat (mainly osban) in childhood, industrial made olive condiments in adulthood, were marginally associated. In multivariate analyses, only rancid butter, rancid sheep fat and cooked vegetables were significantly associated with NPC. In regard to possible causative substances, our results implicate the involvement of butyric acid, a potential Epstein-Barr virus (EBV) activator.

Epstein-Barr virus and cancer

EBV was the first human virus to be directly implicated in carcinogenesis. It infects >90% of the world's population. Although most humans coexist with the virus without serious sequelae, a small proportion will develop tumors. Normal host populations can have vastly different susceptibility to EBV-related tumors as demonstrated by geographical and immunological variations in the prevalence of these cancers. EBV has been implicated in the pathogenesis of Burkitt's lymphoma, Hodgkin's disease, non-Hodgkin's lymphoma, nasopharyngeal carcinoma, and lymphomas, as well as leiomyosarcomas arising in immunocompromised individuals. The presence of this virus has also been associated with epithelial malignancies arising in the gastric region and the breast, although some of this work remains in dispute. EBV uses its viral proteins, the actions of which mimic several growth factors, transcription factors, and antiapoptotic factors, to usurp control of the cellular pathways that regulate diverse homeostatic cellular functions. Recent advances in antiviral therapeutics, application of monoclonal antibodies, and generation of EBV-specific CTLs are beginning to show promise in the treatment of EBV-related disorders.

Inhibition of the Epstein–Barr virus lytic cycle by Zta-targeted RNA interference

Epstein–Barr virus (EBV) reactivation into the lytic cycle plays certain roles in the development of EBV-associated diseases, so an effective strategy to block the viral lytic cycle may be of value to reduce the disease risk or to improve the clinical outcome. This study examined whether the EBV lytic cycle could be inhibited using RNA interference (RNAi) directed against the essential viral gene Zta. In cases of EBV reactivation triggered by chemicals or by exogenous Rta, Zta-targeted RNAi prevented the induction of Zta and its downstream genes and further blocked the lytic replication of viral genomes. This antiviral effect of RNAi was not likely to be mediated by activation of the interferon pathway, as phosphorylation of STAT1 was not induced. In addition, novel EBV-infected epithelial cells showing constitutive activation of the lytic cycle were cloned; such established lytic infection was also suppressed by Zta-targeted RNAi. These results indicate that RNAi can be used to inhibit the EBV lytic cycle effectively in vitro and could also be of potential use to develop anti-EBV treatments.

Epidemiology of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a rare malignancy in most parts of the world, with an incidence well under 1 per 100,000 person-years. Exceptions are the Chinese, especially the Cantonese living in the central region of Guangdong Province in Southern China. Other populations with elevated rates include the natives of Southeast Asia, the natives of the Artic region, and the Arabs of North Africa and parts of the Middle East. Intake of preserved foods at an early age has been linked to NPC risk in all population groups with increased NPC rates. Other recognized risk factors for NPC are cigarette smoking, and occupational exposure to formaldehyde and wood dust.

The chemopreventive compound curcumin is an efficient inhibitor of Epstein-Barr virus BZLF1 transcription in Raji DR-LUC cells

To characterize the effects of inhibitors of Epstein-Barr virus (EBV) reactivation, we established Raji DR-LUC cells as a new test system. These cells contain the firefly luciferase (LUC) gene under the control of an immediate-early gene promoter (duplicated right region [DR]) of EBV on a self-replicating episome. Luciferase induction thus serves as an intrinsic marker indicative for EBV reactivation from latency. The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) induced the viral key activator BamH fragment Z left frame 1 (BZLF1) protein ("ZEBRA") in this system, as demonstrated by induction of the BZLF1 protein-responsive DR promoter upstream of the luciferase gene. Conversely, both BZLF1 protein and luciferase induction were inhibited effectively by the chemopreventive agent curcumin. Semiquantitative reverse transcriptase (RT)-polymerase chain reaction (PCR) further demonstrated that the EBV inducers TPA, sodium butyrate, and transforming growth factor-beta (TGF-beta) increased levels of the mRNA of BZLF1 mRNA at 12, 24, and 48 h after treatment in these cells. TPA treatment also induced luciferase mRNA with similar kinetics. Curcumin was found to be highly effective in decreasing TPA-, butyrate-, and TGF-beta-induced levels of BZLF1 mRNA, and of TPA-induced luciferase mRNA, indicating that three major pathways of EBV are inhibited by curcumin. Electrophoretic mobility shift assays (EMSA) showed that activator protein 1 (AP-1) binding to a cognate AP-1 sequence was detected at 6 h and could be blocked by curcumin. Protein binding to the complete BZLF1 promoter ZIII site (ZIIIA+ZIIIB) demonstrated several specific complexes that gave weak signals at 6 h and 12 h but strong signals at 24 h, all of which were reduced after application of curcumin. Autostimulation of BZLF1 mRNA induction through binding to the ZIII site at 24 h was confirmed by antibody-induced supershift analysis. The present results confirm our previous finding that curcumin is an effective agent for inhibition of EBV reactivation in Raji DR-CAT cells (carrying DR-dependent chloramphenicol acetyltransferase), and they show for the first time that curcumin inhibits EBV reactivation mainly through inhibition of BZLF1 gene transcription.

CYP2E1 genetic polymorphisms and risk of nasopharyngeal carcinoma in Taiwan

BACKGROUND

Nasopharyngeal carcinoma occurs disproportionately among individuals of Chinese descent. The cytochrome P450 2E1 enzyme (CYP2E1) is known to activate nitrosamines and other carcinogens that are possibly involved in the development of this disease. Certain alleles of the CYP2E1 gene are thought to be more highly expressed than others, and their distribution varies between Asian and Caucasian populations. We conducted a case-control study to investigate whether such variations affect the risk of developing nasopharyngeal cancer.

METHODS

Three hundred sixty-four patients with nasopharyngeal carcinoma (96% of 378 eligible patients) and 320 control subjects (86% of 374 eligible subjects) were studied. A risk factor questionnaire was administered to participants to assess factors postulated to be linked to nasopharyngeal carcinoma. Peripheral blood was obtained from all subjects and DNA was purified from nucleated cells. A polymerase chain reaction-based restriction fragment length polymorphism assay that used the restriction enzymes Rsa I and Dra I was used to detect wild-type and variant forms of the CYP2E1 gene.

RESULTS

Individuals homozygous for an allele of the CYP2E1 gene that is detected by Rsa I digestion (c2 allele) were found to have an increased risk of nasopharyngeal carcinoma (relative risk [RR] = 2.6; 95% confidence interval [CI] = 1.2-5.7); this effect was limited to nonsmokers (RR = 9.3; 95% CI = 2.7-32) and was not affected by alcohol consumption.

CONCLUSIONS

Our findings suggest that the CYP2E1 genotype is a determinant of nasopharyngeal carcinoma risk.

Nasopharyngeal carcinoma, with emphasis on its relationship to Epstein-Barr virus

Nasopharyngeal carcinoma (NPC) is an epithelial tumor with a distinct geographic distribution and characteristic histologic appearance. It is rare in Europe and North America, but it is among the most common cancers in southern China. Genetic predisposition, environmental factors, and Epstein-Barr virus (EBV) all have been associated with the pathogenesis of this tumor. There is an increasing body of evidence that among all these factors, EBV appears to be the strongest and most consistently related factor. According to the current sensitive in situ hybridization methods for the detection of EBV-encoded small RNAs (EBER), almost 100% of cases of NPC, irrespective of their histologic subtypes, have demonstrable EBERs in the nuclei of the tumor cells. In this review paper, we discuss the predisposing genetic and environmental factors and the role of EBV in the pathogenesis of this tumor with particular emphasis on the role of EBV.