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- Chen, Han, et al.
(författare)
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LTBP-2 confers pleiotropic suppression and promotes dormancy in a growth factor permissive microenvironment in nasopharyngeal carcinoma
- 2012
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Ingår i: Cancer Letters. - : Elsevier. - 0304-3835 .- 1872-7980. ; 325:1, s. 89-98
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Tidskriftsartikel (refereegranskat)abstract
- This study identified LTBP-2 as a pleiotropic tumor suppressor in nasopharyngeal carcinoma, which safeguards against critical malignant behaviors of tumor cells. LTBP-2 expression was significantly decreased or lost in up to 100% of NPC cell lines (7/7) and 80% of biopsies (24/30). Promoter hypermethylation was found to be involved in LTBP-2 silencing. Using a tetracycline-regulated inducible expression system, we unveiled functional roles of LTBP-2 in suppressing colony formation, anchorage-independent growth, cell migration, angiogenesis, VEGF secretion, and tumorigenicity. Three-dimensional culture studies suggested the involvement of LTBP-2 in maintenance of tumor cell dormancy in a growth factor favorable microenvironment.
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| 4. |
- Yip, Yim Ling, et al.
(författare)
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Efficient Immortalization of Primary Nasopharyngeal Epithelial Cells for EBV Infection Study
- 2013
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:10
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Tidskriftsartikel (refereegranskat)abstract
- Nasopharyngeal carcinoma (NPC) is common among southern Chinese including the ethnic Cantonese population living in Hong Kong. Epstein-Barr virus (EBV) infection is detected in all undifferentiated type of NPC in this endemic region. Establishment of stable and latent EBV infection in premalignant nasopharyngeal epithelial cells is an early event in NPC development and may contribute to its pathogenesis. Immortalized primary nasopharyngeal epithelial cells represent an important tool for investigation of EBV infection and its tumorigenic potential in this special type of epithelial cells. However, the limited availability and small sizes of nasopharyngeal biopsies have seriously restricted the establishment of primary nasopharyngeal epithelial cells for immortalization. A reliable and effective method to immortalize primary nasopharyngeal epithelial cells will provide unrestricted materials for EBV infection studies. An earlier study has reported that Bmi-1 expression could immortalize primary nasopharyngeal epithelial cells. However, its efficiency and actions in immortalization have not been fully characterized. Our studies showed that Bmi-1 expression alone has limited ability to immortalize primary nasopharyngeal epithelial cells and additional events are often required for its immortalization action. We have identified some of the key events associated with the immortalization of primary nasopharyngeal epithelial cells. Efficient immortalization of nasopharyngeal epithelial cells could be reproducibly and efficiently achieved by the combined actions of Bmi-1 expression, activation of telomerase and silencing of p16 gene. Activation of MAPK signaling and gene expression downstream of Bmi-1 were detected in the immortalized nasopharyngeal epithelial cells and may play a role in immortalization. Furthermore, these newly immortalized nasopharyngeal epithelial cells are susceptible to EBV infection and supported a type II latent EBV infection program characteristic of EBV-infected nasopharyngeal carcinoma. The establishment of an efficient method to immortalize primary nasopharyngeal epithelial cells will facilitate the investigation into the role of EBV infection in pathogenesis of nasopharyngeal carcinoma.
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| 5. |
- Yip, Yim-Ling, et al.
(författare)
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Expression of Epstein-Barr Virus-Encoded LMP1 and hTERT Extends the Life Span and Immortalizes Primary Cultures of Nasopharyngeal Epithelial Cells
- 2010
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Ingår i: Journal of Medical Virology. - : Wiley. - 1096-9071 .- 0146-6615. ; 82:10, s. 1711-1723
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Tidskriftsartikel (refereegranskat)abstract
- Cell immortalization is regarded as an early and pre-requisite step in tumor development. Defining the specific genetic events involved in cell immortalization may provide insights into the early events of carcinogenesis. Nasopharyngeal carcinoma is common among the Southern Chinese population. Epstein-Barr virus (EBV) infection is associated closely with nasopharyngeal carcinoma. The involvement of LMP1(an EBV-encoded oncogene) has been implicated in the pathogenesis of nasopharyngeal carcinoma. In this study, LMP1 expression, in combination with ectopic expression of hTERT (catalytic unit of human telomerase), was shown to extend the life span of primary cultures of nasopharyngeal epithelial cells and facilitate the immortalization of one of the cell lines (NP446). This is the first report on the successful immortalization of nasopharyngeal epithelial cells involving LMP1. The events associated with the immortalization of nasopharyngeal epithelial cells by LMP1/hTERT were characterized. Expression of c-Myc, Bmi-1, and Id-1 were upregulated at an early stage of immortalization. At a later stage of immortalization, downregulation of p21 and p16 expression were observed. Upregulation of EGFR expression and activation of MAPK signaling pathway were observed in LMP1/hTERT-immortalized nasopharyngeal epithelial cells. The LMP1/hTERT-immortalized NP446 cells were non-tumorigenic in immunosuppressed nude mice and retained anchorage-dependent growth, suggesting that additional events are required for tumorigenic transformation. The ability of the EBV-encoded LMP1, in the presence of hTERT expression, to extend the life span and immortalize primary cultures of nasopharyngeal epithelial cells supports the involvement of EBV infection and its viral products in the early stage of pathogenesis of nasopharyngeal carcinoma. J. Med. Virol. 82:1711-1723, 2010. (C) 2010 Wiley-Liss, Inc.
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| 6. |
- Zhang, Hao, et al.
(författare)
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Papillomavirus type 16 E6/E7 and human telomerase reverse transcriptase in esophageal cell immortalization and early transformation
- 2007
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Ingår i: Cancer Letters. - : Elsevier BV. - 1872-7980 .- 0304-3835. ; 245:1-2, s. 184-194
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Tidskriftsartikel (refereegranskat)abstract
- Infection with high-risk human papillomavirus (HPV) has been implicated in the pathogenesis of esophageal squamous cell carcinoma, and up-regulation of telomerase in esophageal adenocarcinoma. We immortalized normal esophageal epithelial cells by over-expression of the HPV16 E6/E7 and human telomerase reverse transcriptase (hTERT) genes. HPV16 E6/E7-induced immortalization was accompanied by reduced RB and p53, but increased p16 and p21, protein expression. hTERT-immortalized cells had unaffected RB and p53, but significantly decreased p16 and p21, protein expression. Aurora-A protein was also upregulated in E6E7 immortalized cells, and to a less extent in hTERT immortalized cells. Fluorescence in situ hybridization showed that the Aurora-A gene locus was amplified in E6E7 immortalized cells, which might account in part for the Aurora-A overexpression. These molecular changes led to an abrogation of the G2 checkpoint. E6E7 and hTERT immortalized esophageal cells recapitulated many of the molecular changes observed in esophageal carcinomas, where RB and p53 are frequently downregulated. However, down-regulation of p16 and p21 occurred frequently in esophageal cancer, owing to aberrant gene promoter methylation. We showed in the immortalized cells that aberrant methylation had not yet set in, suggesting that promoter methylation might not be necessary for cellular immortalization. In addition to supporting the role of HPV and telomerase in esophageal carcinogenesis, our cell lines may also be useful in vitro models for further studies of esophageal carcinogenesis.
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