Multiple pathways for Epstein-Barr virus episome loss from nasopharyngeal carcinoma. Int J Cancer

Lineberger Comprehensive Cancer Center, Center for AIDS Research and Department of Microbiology and Immunology, University of North Carolina, Chapel Hill, NC, USA.
International Journal of Cancer (Impact Factor: 5.09). 11/2008; 123(9):2105-12. DOI: 10.1002/ijc.23685
Source: PubMed


Epstein-Barr virus (EBV) is the prototypical example for episomal persistence of genetic information. Yet, little is known about how this viral episome is lost. Episome loss occurs naturally in nasopharyngeal carcinoma (NPC) upon explantation into culture. Using whole-genome profiling, we found evidence for 2 different pathways of episome loss: (i) rapid loss of the entire episome or (ii) successive mutation/deletion of the episome until at least 1 essential cis-element is destroyed. This second phenotype was seen in a clone of HONE-1 NPC cells that maintains the EBV episome for prolonged time in culture. The conceptual insights provided by our quantitative analysis should aid our understanding of mammalian episomes, as well as lead to designs to cure latent viral infection.

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Available from: Dirk P Dittmer
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    • "EBNAl is a unique viral protein that is found in the four forms of latent infection by EBV. It provides a distinct episome maintenance function by binding to oriP, which is the latent origin of DNA replication (17,18). Therefore, the expression level of EBNA1 is a key factor that episomes maintain in a steady state in vitro. "
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    ABSTRACT: The present study aimed to identify the molecular pathological changes of the nasopharyngeal carcinoma (NPC) epithelial CNE3 cell line, which has been used in experimental studies for 20 years in a culture environment. The pathological type of NPC and the presence of the Epstein-Barr virus (EBV) were identified. CNE3 short tandem repeats (STRs) were amplified, analyzed and compared using metastatic carcinoma tissue from primary NPC. Immunohistochemistry (IHC) and in situ hybridization (ISH) were used to identify the immunophenotype and EBV-encoded small RNA (EBER) expression in nude mice transplanted CNE3 tumor cells. Polymerase chain reaction (PCR) and DNA sequencing were used to identify the EBV oncogene, BamH1-A right frame 1 (BARF1) and electron microscopy was used to analyze the organization of the ultrastructure. CNE3 was not cross-contaminated by other human cell lines and the EBV was no longer present in the CNE3 cells. The pathological type of CNE3 was transformed from an undifferentiated non-keratinizing carcinoma with focal adenocarcinoma differentiation into a poorly-differentiated adenocarcinoma. In conclusion, this knowledge on the molecular pathological changes of CNE3 may aid in the development of new research approaches for NPC.
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    • "Instead, it is necessary to track prospectively the fate of viral genomes in transformed cells. In vitro, B-cell cancers tend to maintain gammaherpesvirus genomes, whereas Kaposi's sarcoma and nasopharyngeal carcinoma tend to lose them (Ganem, 2006; Dittmer et al., 2008). In vivo, murid herpesvirus-4 (MuHV-4) infection increases the incidence of virus-negative cancers (Sunil-Chandra et al., 1994; Tarakanova et al., 2005). "
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    ABSTRACT: Cancers with viral aetiologies can potentially be prevented by antiviral vaccines. Therefore, it is important to understand how viral infections and cancers might be linked. Some cancers frequently carry gammaherpesvirus genomes. However, they generally express the same viral genes as non-transformed cells, and differ mainly in also carrying oncogenic host mutations. Infection, therefore, seems to play a triggering or accessory role in disease. The hit-and-run hypothesis proposes that cumulative host mutations can allow viral genomes to be lost entirely, such that cancers remaining virus-positive represent only a fraction of those to which infection contributes. This would have considerable implications for disease control. However, the hit-and-run hypothesis has so far lacked experimental support. Here, we tested it by using Cre-lox recombination to trigger transforming mutations in virus-infected cells. Thus, 'floxed' oncogene mice were infected with Cre recombinase-positive murid herpesvirus-4 (MuHV-4). The emerging cancers showed the expected genetic changes but, by the time of presentation, almost all lacked viral genomes. Vaccination with a non-persistent MuHV-4 mutant nonetheless conferred complete protection. Equivalent human gammaherpesvirus vaccines could therefore potentially prevent not only viral genome-positive cancers, but possibly also some cancers less suspected of a viral origin because of viral genome loss.
    Full-text · Article · Sep 2010 · Journal of General Virology
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    • "NPC is a multi-factorial disease. Genetic predisposition (Dittmer et al. 2008) and epigenetic alterations (Wong et al. 2004) are significant in the initiation and progression of NPC. In addition, the pathogenesis of NPC is closely linked to Epstein–Barr virus infection. "
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    ABSTRACT: This study aimed at evaluating the potential anti-proliferative effects of the microRNA let-7 family in nasopharyngeal carcinoma (NPC) cells. In addition, the association between let-7 suppression and DNA hypermethylation is examined. Levels of mature let-7 family members (-a, -b, -d, -e, -g, and -i) in normal nasopharyngeal cells (NP69 and NP460) and nasopharyngeal carcinoma cells (HK1 and HONE1) were measured by real-time quantitative PCR. Cell-proliferation assay and c-Myc immunohistochemical staining were performed on NPC cells transfected with let-7 precursor molecules. In addition, expression changes in let-7 family members in response to demethylating agents (5-azacytidine and zebularine) were also examined. In comparison with the normal nasopharyngeal cells, let-7 (-a, -b, -d, -e, -g, and -i) levels were reduced in nasopharyngeal carcinoma cells. Ectopic expression of the let-7 family in nasopharyngeal carcinoma cells resulted in inhibition of cell proliferation through downregulation of c-Myc expression. Demethylation treatment of nasopharyngeal carcinoma cells caused activation of let-7 expression in poorly differentiated nasopharyngeal carcinoma cells only. Our results suggested that miRNA let-7 might play a role in the proliferation of NPC. DNA methylation is a potential regulatory pathway, which is affected when let-7 is suppressed in NPC cells. However, the extent of DNA hypermethylation/hypomethylation in regulating let-7 expression requires further elucidation.
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