Oshimo Yasuhiro, Oue Naohide, Mitani Yoshitsugu, Nakayama Hirofumi, Kitadai Yasuhiko, Yoshida Kazuhiro, Chayama Kazuaki, Yasui Wataru
Department of Molecular Pathology, Hiroshima University Graduate School of Biomedical Sciences, Hiroshima, Japan.
Int J Cancer. 2004 Jun 10;110(2):212-8. doi: 10.1002/ijc.20090.
The retinoblastoma protein-interacting zinc finger gene, RIZ1 (GenBank accession number U17838), is involved in chromatin-mediated gene expression and is also a target for frameshift mutation in microsatellite-unstable cancers. Methylation of the RIZ1 promoter CpG island has been shown to be a common mechanism in inactivating the RIZ1 gene in human liver and breast cancers. We investigated levels of RIZ1 mRNA in 45 gastric carcinoma tissues by quantitative RT-PCR and in gastric carcinoma cell lines by RT-PCR. In addition, we examined CpG island methylator phenotype (CIMP) status, p53 mutation status, and the correlation between promoter methylation status and RIZ1 mRNA expression. CIMP status was investigated by examining the methylation status of MINT1, MINT2, MINT12, MINT25 and MINT31. p53 mutation status was examined by PCR-single strand conformation polymorphism and promoter methylation status was examined by methylation-specific PCR. Promoter hypermethylation of the RIZ1 gene was found in 31 (69%) of 45 gastric carcinoma tissues and in 3 (21%) of 14 corresponding non-neoplastic mucosae, the incidence being significantly different (p = 0.002). None of the 12 normal gastric tissues from young non-cancer individuals showed hypermethylation. Promoter hypermethylation was associated with reduced RIZ1 expression in gastric carcinoma tissues (p = 0.029). Promoter hypermethylation of the RIZ1 gene was significantly associated with CIMP (p = 0.002). Mutation status of the p53 gene was not associated with methylation status or RIZ1 expression in gastric carcinoma. In gastric carcinoma cell lines MKN-28 and KATO-III, the RIZ1 promoter was hypermethylated and RIZ1 transcription was inactive. Treatment of these cells with demethylating agent 5-aza-2'-deoxycytidine restored RIZ1 transcription. Our results suggest that transcriptional inactivation of the RIZ1 gene by promoter hypermethylation may participate in stomach carcinogenesis.
视网膜母细胞瘤蛋白相互作用锌指基因RIZ1（GenBank登录号U17838）参与染色质介导的基因表达，也是微卫星不稳定癌症中移码突变的靶点。RIZ1启动子CpG岛的甲基化已被证明是人类肝癌和乳腺癌中RIZ1基因失活的常见机制。我们通过定量RT-PCR检测了45例胃癌组织中RIZ1 mRNA的水平，并通过RT-PCR检测了胃癌细胞系中RIZ1 mRNA的水平。此外，我们还检测了CpG岛甲基化表型（CIMP）状态、p53突变状态以及启动子甲基化状态与RIZ1 mRNA表达之间的相关性。通过检测MINT1、MINT2、MINT12、MINT25和MINT31的甲基化状态来研究CIMP状态。通过PCR-单链构象多态性检测p53突变状态，通过甲基化特异性PCR检测启动子甲基化状态。在45例胃癌组织中的31例（69%）以及14例相应的非肿瘤黏膜中的3例（21%）发现了RIZ1基因启动子高甲基化，其发生率有显著差异（p = 0.002）。来自年轻非癌症个体的12例正常胃组织中均未显示高甲基化。启动子高甲基化与胃癌组织中RIZ1表达降低相关（p = 0.029）。RIZ1基因启动子高甲基化与CIMP显著相关（p = 0.002）。胃癌中p53基因的突变状态与甲基化状态或RIZ1表达无关。在胃癌细胞系MKN-28和KATO-III中，RIZ1启动子发生高甲基化，RIZ1转录失活。用去甲基化剂5-氮杂-2'-脱氧胞苷处理这些细胞可恢复RIZ1转录。我们的结果表明，启动子高甲基化导致的RIZ1基因转录失活可能参与胃癌的发生。
