| Budget Amount *help |
¥38,700,000 (Direct Cost: ¥38,700,000)
Fiscal Year 2004: ¥9,500,000 (Direct Cost: ¥9,500,000)
Fiscal Year 2003: ¥9,700,000 (Direct Cost: ¥9,700,000)
Fiscal Year 2002: ¥10,000,000 (Direct Cost: ¥10,000,000)
Fiscal Year 2001: ¥9,500,000 (Direct Cost: ¥9,500,000)
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| Research Abstract |
It has been suggested not only genetic changes but also epigenetic changes such as DNA methylation during tumorigenesis. Genome wide screening of DNA methylation changes in cancer revealed that hundreds of genes are inactivated by DNA methylation in human cancer. In the current study, we have investigated the role of DNA methylation in the tumorigenesis of gastrointestinal cancer. We also investigated the molecular mechanisms how DNA methylation leads to gene silencing. Tb this end, we examined the methylation status of genes involved in cell cycle regulation, apoptosis, signal pathway including Ras and Wnt CHFR expression was silenced by DNA methylation of the 5' region of the gene in 80% of colorectal and 20% of the gastric cancer cell lines tested and in 40% of primary colorectal and 39% of primary gastric cancers;, and expression could be restored by treatment with 5-aza-2'-deoxycytidine, a methyltransferase inhibitor. In addition, histones H3 and H4 were found to be deacetylated i
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n cell lines showing aberrant methylation, indicating a role for histone deacetylation in the methylation-dependent gene silencing. Cells not expressing CHFR showed impaired checkpoint function, which led to nuclear localization of cyclin B1 after treatment with docetaxel or paclitaxel, two microtubule inhibitors. By affecting mitotic checkpoint function, CHFR inactivation likely plays a key role in tumorigenesis in gastric cancer. We also identified frequent promoter hypermethylation and gene silencing of the genes encoding secreted frizzled-related proteins (STRPS) in colorectal cancer. SFRPS possess a domain similar to one in the WNT-receptor frizzled proteins and can inhibit WNT receptor binding to downregulate pathway signaling during development. Here we show that restoration of SFRP function in colorectal cancer cells attenuates WNT signaling even in the presence of downstream mutations. We also show that the epigenetic loss of SFRP function occurs early in colorectal cancer progression and may thus provide constitutive WNT signaling that is required to complement downstream mutations in the evolution of colorectal cancer. BNIP3 protein is a proapoptotic member of the Bcl-2 family that is expressed in hypoxic regions of tumors. BNIP3 was not expressed in 14 of the 24 cell lines tested, and its absence was not caused by gene mutation or by altered expression of hypoxia inducible factor-1, a key transcription factor that regulates BNIP3 expression. On the other hand, methylation of the 5' CpG island of BNIP3 was closely correlated with silencing the gene. Moreover, treating methylated cells with the methyltransferase inhibitor 5-aza-2'-deoxycytidine restored hypoxia-induced expression of BNIP3 mRNA and protein, which in turn led to cell death. Aberrant methylation of BNIP3 was also detected in 66% of primary colorectal and 49% of primary gastric cancers, but not in normal tissue samples collected from areas adjacent to the tumors. Apparently, epigenetic alteration of BNIP3 is a frequent and cancer-specific event; which suggests that inactivation of BNIP3 likely plays a key role in the progression of some gastrointestinal cancers and that it may be a useful molecular target for therapy. These results indicated that DNA methylation and histone deacetylation play critical roles in tumorigenesis of gastrointestinal cancer. The inhibitors of DNA methylation and histone deacetylation may be a potential anti-cancer drug that modulate gene expression. Less
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