Expression of the Epstein-Barr virus genome in a nasopharyngeal carcinoma epithelial tumor cell line

m6A-enriched lncRNA LINC00839 promotes tumor progression by enhancing TAF15-mediated transcription of amine oxidase AOC1 in nasopharyngeal carcinoma

Dysregulation of long non-coding RNAs (lncRNAs) contributes to tumorigenesis by modulating specific cancer-related pathways, but the roles of m6A-enriched lncRNAs and underlying mechanisms remain elusive in nasopharyngeal carcinoma (NPC). Here, we reanalyzed the previous genome-wide analysis of lncRNA profiles in 18 pairs of NPC and normal tissues, as well as in 10 paired samples from NPC with or without posttreatment metastases. We discerned that an oncogenic m6A-enriched lncRNA, LINC00839, which was substantially upregulated in NPC and correlated with poor clinical prognosis, promoted NPC growth and metastasis both in vitro and in vivo. Mechanistically, by using RNA pulldown assay combined with mass spectrometry, we found that LINC00839 interacted directly with the transcription factor, TATA-box binding protein associated factor (TAF15). Besides, ChIP and dual-luciferase report assays demonstrated that LINC00839 coordinated the recruitment of TAF15 to the promoter region of amine oxidase copper-containing 1 (AOC1), which encodes a secreted glycoprotein playing vital roles in various cancers, thereby activating AOC1 transcription in trans. In this study, potential effects of AOC1 in NPC progression were first proposed. Moreover, ectopic expression of AOC1 partially rescued the inhibitory effect of downregulation of LINC00839 in NPC. Furthermore, we showed that silencing vir-like m6A methyltransferase-associated (VIRMA) and insulin-like growth factor 2 mRNA-binding proteins 1 (IGF2BP1) attenuated the expression level and RNA stability of LINC00839 in an m6A-dependent manner. Taken together, our study unveils a novel oncogenic VIRMA/IGF2BP1-LINC00839-TAF15-AOC1 axis, and highlights the significance and prognostic value of LINC00839 expression in NPC carcinogenesis.

Multiple pathways for Epstein-Barr virus episome loss from nasopharyngeal carcinoma

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.

Association of Epstein-Barr Virus with Nasopharyngeal Carcinoma and Current Status of Development of Cancer-derived Cell Lines

It is well known that the Epstein-Barr virus (EBV) contributes directly to tumourigenesis in nasopharyngeal carcinoma (NPC), primarily in the undifferentiated form of NPC (WHO type III; UNPC or UC), which is commonly found in South East Asia. Unfortunately, research in NPC has been severely hampered by the lack of authentic EBV-positive (EBV+) human NPC cell lines for study. Since 1975, there have been more than 20 reported NPC cell lines. However, many of these NPC-derived cell lines do not express EBV transcripts in long-term culture, and therefore that finding may dispute the fundamental theory of NPC carcinogenesis. In fact, currently only one EBV+ human NPC cell line (C-666) in long-term culture has been reported. Hence, most of the NPC cell lines may not be representative of the disease itself. In order to better understand and treat NPC, there is an urgent need to develop more EBV+ human NPC cell lines. In this review, we discuss the authenticity of existing NPC cell lines and the impact of our understanding of NPC biology on the treatment of the disease and the relationship of EBV to NPC in the context of cell lines. Key words: Carcinogenesis, Cell culture, Epstein-Barr virus, Hayflick’s limit

Norepinephrine up-regulates the expression of vascular endothelial growth factor, matrix metalloproteinase (MMP)-2, and MMP-9 in nasopharyngeal carcinoma tumor cells

Recent studies using ovarian cancer cells have shown that the catecholamine hormones norepinephrine (norepi) and epinephrine (epi) may influence cancer progression by modulating the expression of matrix metalloproteinases (MMP) and vascular endothelial growth factor (VEGF). The purpose of this study is to determine if the stress hormone norepi can influence the expression of MMP-2, MMP-9, and VEGF in nasopharyngeal carcinoma (NPC) tumors by using three NPC tumor cell lines. The NPC cell lines HONE-1, HNE-1, and CNE-1 were treated with norepi. The effects of norepi on MMP-2, MMP-9, and VEGF synthesis were measured by ELISA; functional MMP activity was measured by the invasive potential of the cells using a membrane invasion culture system whereas functional activity of VEGF was analyzed using a human umbilical vein endothelial cell tube formation assay. Norepi treatment increased MMP-2, MMP-9, and VEGF levels in culture supernatants of HONE-1 cells, which could be inhibited by the beta-blocker propranolol. Norepi induced the invasiveness of all NPC cell lines in a dose-dependent manner, which was blocked by CMT-3, an MMP inhibitor, and propranolol. Norepi stimulated the release of functional angiogenic VEGF by HONE-1 cells as well. Finally, HONE-1 cells were shown to express beta-adrenergic receptors as did seven of seven NPC biopsies examined. The data suggest that catecholamine hormones produced by the sympathetic-adrenal medullary axis may affect NPC tumor progression, in part, through modulation of key angiogenic cytokines.

Anti-tumor immunity against nasopharyngeal carcinoma by means of LMP2A-specific cytotoxic T lymphocytes induced by dendritic cells

OBJECTIVE

Adoptive immunotherapy with specific cytotoxicity T lymphocytes (CTLs) induced by dendritic cells (DCs) pulsed with tumor antigens plays a crucial role in the immunity against tumor. The purpose of this study was to assess the feasibility and efficacy of latent membrane protein 2A (LMP2A)-specific CTLs immunity against nasopharyngeal carcinoma (NPC) in vitro and in vivo.

METHODS

DCs were generated by culturing the monocytes purified from human peripheral blood mononuclear cells (PBMCs) in cytokine cocktail containing granulocyte/macrophage colony-stimulating factor (GM-CSF), interleukin-4 (IL-4), and tumor necrosis factor-alpha (TNF-alpha). The phenotype of mature DCs was analyzed by fluorescence activated cell sorter (FACS). Mature DCs transfected with EBV-LMP2A recombinant adenovirus were co-cultured with autologous PBMCs to induce LMP2A-specific CTLs. The expression of the surface antigens such as CD3, CD4, CD8 and CD56 on CTLs were detected by FACS. The specific cytotoxicity of CTLs on target CNE cells expressing EBV-LMP2A was confirmed using cytotoxicity assay. The anti-tumor effect of LMP2A-specific CTLs in vivo was assessed in the mice tumor models implanted with CNE cells expressing EBV-LMP2A.

RESULTS

Mature DCs expressed typically morphologic characteristics and high level of surface markers (CD1a, CD83, CD86, CD80 and HLA-DR). LMP2A-transfected DCs could induce LMP2A-specific CTLs consisting of a majority of CD4+ and CD8+ T cells. Cytotoxicity assay confirmed that the LMP2A-specific CTLs displayed significant cytotoxicity on target CNE cells compared with the controls. The study in vivo demonstrated that the treatment using these specific CTLs retarded the growth of established tumor in the treated mice.

CONCLUSION

These findings suggest that DCs transfected with EBV-LMP2A recombinant adenovirus can elicit LMP2A-specific CTLs that have a specific killing effect on NPC in vitro and in vivo. The results provide experimental basis for the further immunotherapy of NPC in clinical trails.

An unbalanced translocation involving chromosome 14 is the probable cause for loss of potentially functional rearranged immunoglobulin heavy chain genes in the Epstein-Barr virus-positive Hodgkin's lymphoma-derived cell line L591

In the vast majority of cases, Hodgkin-Reed Sternberg (H-RS) cells, the malignant cells in Hodgkin's lymphoma (HL), are derived from germinal centre B cells. In some cases, somatic mutations within the rearranged immunoglobulin heavy (IgH) chain genes were detected, rendering potentially functional gene rearrangements non-functional. In these H-RS cells the expression of high-affinity B-cell receptors (BCR) was prevented. As in other cases only one non-productive IgH chain gene rearrangement was amplified from H-RS cells, it was speculated whether, in these cases, the functionally rearranged IgH chain genes were lost. An alternative explanation might be that the rearranged genes could not be amplified owing to a high load of somatic mutations within the primer binding sites. Here, we showed that, in the HL-derived Epstein-Barr virus (EBV)-positive cell line L591, only one non-functional somatically mutated IgH gene rearrangement could be detected. The other potentially functional IgH gene rearrangement was lost as a result of an unbalanced translocation affecting the long arm of chromosome 14. Moreover, L591 cells express the EBV latent membrane proteins LMP1 and LMP2A, which might have contributed to the 'escape' of these cells from apoptosis within the germinal centre. We conclude that, apart from the introduction of 'crippling mutations' into the rearranged VDJ genes rearrangement, deletions of the IGH locus may be regarded as another mechanism to prevent the expression of a BCR in H-RS cells.

Epstein-Barr virus and gastric carcinoma

The Epstein-Barr virus (EBV) is detected in the tissue of about 10% of gastric carcinoma cases throughout the world. In each case, 100% of carcinoma cells are infected with EBV. Analysis of EBV in carcinoma biopsies indicates that carcinoma is formed by the proliferation of a single EBV infected cell. These findings suggest that EBV plays an important role in the development of EBV positive gastric carcinomas. The EBV genes expressed are EBV determined nuclear antigen 1 (EBNA1), two small non-polyadenylated RNAs known as EBER1 and EBER2, and the transcripts from the BamHI-A region (BARF0); in addition, some cases also express a small amount of latent membrane protein 2A (LMP2A). Epithelial cells are refractory to EBV infection in vitro. This has hampered the study of the role of EBV in epithelial malignancies. The use of recombinant EBV carrying a selectable marker has enabled this difficulty to be overcome. EBV infected cell clones can be obtained from most carcinoma cell lines examined, and it was found that cell to cell contact was an efficient mode of EBV infection. Furthermore, it was possible to immortalize primary gastric epithelial cells by EBV infection. The cells expressed identical EBV genes to those typically seen in EBV positive gastric carcinoma, and showed accelerated malignant properties, including growth in soft agarose and tumorigenicity in severe combined immunodeficient (SCID) mice. These results suggest that EBV contributes to the maintenance of the malignant phenotype of EBV positive gastric carcinoma.

Productive infection of Epstein-Barr virus (EBV) in EBV-genome-positive epithelial cell lines (GT38 and GT39) derived from gastric tissues

We characterized the expression of Epstein-Barr virus (EBV) on two epithelial cell lines, GT38 and GT39, derived from human gastric tissues. The EBV nuclear antigen (EBNA) was detected in all cells of both cell lines. The EBV immediate-early BZLF 1 protein (ZEBRA), the early antigen diffuse component (EA-D), and one of the EBV envelope proteins (gp350/220) were expressed spontaneously in small proportions in the cells. EBNA 1, EBNA2, latent membrane protein 1, ZEBRA, and EA-D molecules were then observed by Western blotting in the cells. The lytic cycle was enhanced with treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) or n-butyrate. The virus particles were observed in the TPA treated GT38 cells by electron microscopy. Infectious EBV was detected with the transformation of cord blood lymphocytes and also with the induction of early antigen to Raji cells by the supernatants of both cells lines. A major single and minor multiple fused terminal fragments and a ladder of smaller fragments of the EBV genome were detected with a Xhol probe in both cell lines. These epithelial cells lines and viruses will be useful in studying their association with EBV in gastric epithelial cells.

Chromosomal abnormalities of a new nasopharyngeal carcinoma cell line (NPC-BM1) derived from a bone marrow metastatic lesion

An epithelial cell line, NPC-BM1, was established from a bone marrow biopsy of a female Taiwanese patient with nasopharyngeal carcinoma (NPC). Histopathology of the bone marrow biopsy and xenografts grown in severe combined immunodeficiency mice showed that the tumor was a nonkeratinizing, poorly differentiated carcinoma. NPC-BM1 cells grown as monolayers had a doubling time of 28.5 hours. Chromosome analysis showed that NPC-BM1 had the following features: 1) hypotetraploidy with a modal chromosome number of 87 (84-90); 2) numerically and structurally normal chromosomes 18; 3) numerical abnormalities without apparent structural alterations on chromosomes 14, 16, 17, 19, and 20; 4) ten structural abnormalities, t(1;9)(p11;q11), t(3;?;4)(p13;?;q13), add(4p),del(6p), i(8) [corrected] (q10),der(?)t(?;12),(?;p12),[corrected] add(21)(p11), del(X)(q24), add(X)(q22), and marker 1 (M1), in all metaphases examined, which were found to be present in two to five cell lines from primary NPC tumors reported previously; and 5) four other abnormalities, t(2;?;2)(p11.2;?;q21),t(11;22)(q11;q11),i(22)(q10), and marker 2 (M2), unique to this metastatic cell line. To the best of our knowledge, NPC-BM1 is the first NPC cell line derived from a distant metastatic site. Further evaluation of this cell line and additional metastatic NPC cell lines as well as primary NPC cell lines with respect to relations between the timing, karyotypic anomalies, and immunobiological characteristics in NPC progression and metastasis is warranted.

Selective homing of phenotypically lytic cells within nasopharyngeal carcinoma biopsies: numerous CD8- and CD16-positive cells in the tumor

We present a comparative analysis of cell-mediated immunity between circulating lymphocytes and tumor-infiltrating lymphocytes (TIL) from patients with nasopharyngeal carcinoma (NPC). Phenotypic analysis using a panel of monoclonal antibodies (MAbs) to define lymphocytic subsets has revealed a selective homing of phenotypically lytic cells such as CD8- and CD16-positive cells, but a low percentage of macrophages when compared to PBL of NPC patients. Also, PBL and TIL contain an equivalent percentage of activated T-lymphocytes expressing HLA-DR molecules and IL-2 receptors. Functionally, TIL exhibit an abolished NK-cell activity and concomitant decrease of proliferative response to phytohemagglutinin (PHA) and concanavalin A (ConA) stimulation when compared with PBL.