Altered expression of the human base excision repair gene NTH1 in gastric cancer
Altered expression of the human base excision repair gene NTH1 in gastric cancer
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DOI：
10.1093/carcin/bgp108
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发表时间：
2009-08-01
期刊：
影响因子：
4.7
通讯作者：
Sugimura, Haruhiko
中科院分区：
文献类型：
--
作者：
Goto, Masanori;Shinmura, Kazuya;Sugimura, Haruhiko
碱基切除修复酶NTH1具有清除DNA中氧化嘧啶（如胸腺嘧啶乙二醇）的活性。为了明确NTH1基因是否参与胃癌发生，我们首先检测了8种胃癌细胞系中NTH1的表达水平，结果显示，包括AGS细胞系在内的8种胃癌细胞系中NTH1的表达均下调。接下来，空载体转染的AGS克隆和表达flag -NTH1的AGS克隆对Tg的切除修复活性的比较表明，低NTH1表达水平导致胃上皮细胞修复受损碱基的能力较低。36%（18/50）的原发性胃癌患者也检测到NTH1信使RNA表达降低。此外，免疫组织化学分析显示，24%（12/50）的原发性胃癌中NTH1主要定位于细胞质中，而非癌组织中NTH1主要定位于核，这表明核DNA的切除修复能力受损。临床病理因素与NTH1在胃癌组织中的表达水平及定位模式无相关性。接下来，我们在NTH1启动子区域发现了两个新的遗传多态性，即c - 163c >g和c - 241_1 -221del，荧光素酶测定显示两者都与启动子活性降低有关。然而，在胃癌病例对照研究中，没有发现多态性与胃癌风险之间的关联。这些发现提示NTH1表达下调和NTH1的异常定位可能参与了一部分胃癌的发病机制。
A base excision repair enzyme, NTH1, has activity that is capable of removing oxidized pyrimidines, such as thymine glycol (Tg), from DNA. To clarify whether the NTH1 gene is involved in gastric carcinogenesis, we first examined the NTH1 expression level in eight gastric cancer cell lines, and the results showed that NTH1 expression was downregulated in all of them, including cell line AGS. Next, a comparison of excisional repair activity against Tg by empty vector-transfected AGS clones and FLAG-NTH1-expressing AGS clones showed that a low NTH1 expression level led to low capacity to repair the damaged base in the gastric epithelial cells. Reduced messenger RNA expression of NTH1 was also detected in 36% (18/50) of primary gastric cancers. Moreover, immunohistochemical analysis revealed that NTH1 was predominantly localized in the cytoplasm in 24% (12/50) of the primary gastric cancers in contrast to the nuclear localization in non-cancerous tissue, suggesting impaired excisional repair ability for nuclear DNA. No associations between clinicopathological factors and NTH1 expression level or localization pattern were detected in the gastric cancers. Next, we found two novel genetic polymorphisms, i.e. c.-163C > G and c.-241_-221del, in the NTH1 promoter region, and a luciferase assay showed that both were associated with reduced promoter activity. However, there were no associations between the polymorphisms and risk of gastric cancer in a gastric cancer case-control study. These findings suggested that downregulation of NTH1 expression and abnormal localization of NTH1 may be involved in the pathogenesis of a subset of gastric cancers.