A Study of Gene Methylation in Head and Neck Cancer

This dissertation, "A Study of Gene Methylation in Head and Neck Cancer" by Thian-sze, Stanley, Wong, 黃天仕, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled "A study of gene methylation in head and neck cancer" Submitted by Wong Thian Sze, Stanley for the degree of Doctor of Philosophy at The University of Hong Kong in January 2005 Head and neck cancers are common worldwide. We aimed to evaluate the clinical value of novel molecular biomarkers, methylated genes, in screening of head and neck cancers. In the first part of this study, we first demonstrated that methylation of a tumor suppressor gene, such as p16, is a common event in head and neck cancer cell lines. CpG methylation is directly associated with transcription silencing of p16 in head and neck cancer cell lines. Furthermore, transcription of p16 could be restored by treatment with a demethylating agent. In order to select suitable methylated genes for the screening of head and neck cancers, we used a candidate gene approach to evaluate the methylation profiles of head and neck cancers. From the methylation profiles of head and neck cancers, we observed that SCGB3A1 was a sensitive marker for nasopharyngel carcinoma (NPC). Methylation of ivSCGB3A1 was detected in more than 70% NPC tissues. Methylation analysis in the normal head and neck tissues suggested that SCGB3A1 was specifically methylated in the cancerous nasopharygeal tissues. Methylated SCGB3A1 could also be detected in the body fluids of NPC patients suggesting that methylated SCGB3A1 may be employed as biomarker in the non-invasive screening of NPC. Another application of the methylated gene was the monitoring of the metastatic lymph node of head and neck squamous cell carcinoma (HNSCC) patients. The presence of methylated p16 and p15 in the metastatic lymph node prompted us to suggest the use of methylated markers in combination with conventional cytology examination in lymph node monitoring. Furthermore, the association between gene methylation in normal head and neck tissues and the smoking habits of patients suggesting that CpG methylation is an early event and could be attributed to exogenous factors. To improve the sensitivity of the methylation markers, we advanced our test by using a more sensitive method, real-time methylation-specific polymerase chain reaction (real- time MSP), and employing the multiple markers approach. Our results suggested that real-time MSP has a higher detection rate in comparison with the conventional methylation-specific polymerase chain reaction (MSP). Moreover, the use of multiple methylation markers in conjunction with EBV antibody titer was the most effective approach in NPC screening. CpG methylation is commonly identified in tumor suppressor genes. From our methylation profile, however, we observed that the oncogene TERT was also susceptible vto CpG methylation. We, therefore, were interested to examine the effect of CpG methylation in transcription regulation of TERT. Our results suggested that CpG methylation would also have a negative regulatory effect on TERT transcription in head and neck cancer cell lines. Our results indicated that oncogene is also prone to CpG methylation. Taken together, our results suggested that CpG methylation is a common epigenetic alteration in head and neck cancer. Genes which are highly susceptible to CpG methylation may be employed as molecular biomarkers in the screening of head and neck cancers. vi DOI: 10.5353/th_b3131872 Subjects: