| Summary: | 碩士 === 國立中興大學 === 生物醫學研究所 === 92 === In Taiwan, hepatocellular carcinoma is the leading cause of cancer death. Hepatitis B virus and hepatitis C virus infections are the major contributing factors of hepatocarcinogenesis. Recent studies have reported that aberrant hypermethylation in the CpG-rich promoter regions of many tumor suppressor genes is associated with the lack of gene transcription and the development of hepatocellular carcinoma. Loss of heterozygosity on chromosome 16 is a common genetic alternation in human hepatocarcinomas, indicating the existence of tumor suppressor genes on this chromosome. In this study, we focus on the gene mehtylation studies of hundreds hepatoma biopsies in five selected potential tumor suppressor genes, named TSC2, SOCS1, E2F4, CDH1 and CDH13 genes, which located on human chromosome 16. Aberrant methylation frequencies of this 5 genes detected by MS-PCR in 155 hepatoma pairs were39.4% for CDH13, 20.6% for SOCS1 and CDH1, 0% for TSC2 and E2F4. In mRNA expression assay, CDH13 gene hypermethylated hepatoma cells exhibited higher CDH13 mRNA level than its normal tissue pairs. This phenomenon has been demonstrated in three hepatoma cell lines that HA22T cell line with CDH13 gene hypermethylation obtained highest CDH13 mRNA expression, while HepG2 and Hep3B cell lines with CDH13 gene unmethylation showed no detectable CDH13 mRNA expression. In protein expression assay, CDH13 proteins appeared three different isoforms located on cytosol and membrane and differential display in three hepatoma cell lines. In CDH13 protein immunohistochemistry staining, overexpressed CDH13 protein has been detected in tumor vessels and hepatocytes in different hepatitis viruses-infected hepatoma cells. Finally, we found several transcription regulation factors, such as AP2-α, MZF1-4, n-Myc, and c-ETS, which located on the CpG island of CDH13 promoter region, have been hypermethylated in all 20 CpG sites in HA22T cell line. It may alter the regulation of transcription factors in CDH13 gene expression.
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