Tahara Tomomitsu, Arisawa Tomiyasu, Shibata Tomoyuki, Wang Fang Yu, Nakamura Masakatsu, Sakata Mikijyu, Nagasaka Mitsuo, Takagi Tamaki, Kamiya Yoshio, Fujita Hiroshi, Nakamura Masahiko, Hasegawa Shin, Iwata Masami, Takahama Kazuya, Watanabe Makoto, Hirata Ichiro, Nakano Hiroshi
Department of Gastroenterology, Fujita Health University School of Medicine, Dengakugakubo, Kutsukake-cho, Toyoake, Aichi, Japan.
Digestion. 2007;75(1):54-61. doi: 10.1159/000101775. Epub 2007 Apr 16.
Aberrant DNA methylation is one of the major events in carcinogenesis. Promoter DNA methylation is also present in various non-neoplastic tissues including gastric epithelium as age-related phenomenon, suggesting that it occurs early in the process of tumorigenesis.
We aimed to clarify the relationship of aberrant DNA methylation in non-neoplastic gastric epithelia with the risk of gastric cancer, Helicobactor pylori infection, and the degree of H. pylori-induced gastritis.
89 patients enrolled in this study. The status of aberrant DNA methylation was compared in two groups of patients: 43 cases with gastric cancer (mean age 65.9 years [29-91], F:M = 0.30, intestinal type [n = 25], diffuse type [n = 18]) and 46 age- and sex-matched patients without gastric cancer (peptic ulcer diseases [n = 11], gastritis [n = 35]) as a control group. Genomic DNA was extracted directly from non-neoplastic epithelia of antral biopsies obtained by endoscopy. The promoter methylation status of the p14 and p21 genes was determined by methylation-specific-polymerase chain reaction (MSP). The promoter methylation status of the p16 gene was quantified by digital densitographic analysis following MSP. The degree of gastritis in the antrum was assessed according to the updated Sydney system. The PG I/II ratio was calculated based on the data of serum PG I and PG II levels measured by radioimmunoassay.
In all 89 subjects, CpG island methylation was found in 25.8% for p14, 52.8% for p16, 1.1% for p21. Among non-cancer patients, the methylation frequency of the p14 gene was significantly higher in H. pylori-positive than in H. pylori-negative patients (38.5 vs. 10.0%, p = 0.03). The mean (+/- SD) methylation levels of the p16 gene in non-neoplastic gastric epithelium was significantly higher in gastric cancer cases both in all patients and in H. pylori-positive patients (0.45 +/- 0.31 vs. 0.20 +/- 0.17; p = 0.019, 0.45 +/- 0.31 vs. 0.20 +/- 0.17; p = 0.016, respectively). The methylation level of the p16 gene was also associated with the presence of intestinal-type gastric cancer (p = 0.017). The methylation level of the p16 gene was significantly higher in patients with intestinal metaplasia (IM) than those without (p = 0.04). Furthermore, the methylation level of the p16 gene was correlated with lower PG l/ll ratio (p = 0.04). The methylation of the p21gene was found in only 1 patient with gastric cancer.
Our data suggest that promoter of the p14 gene may be one of the specific regions whose methylation is closely associated with H. pylori infection. Methylation levels of the p16 gene seem to be accumulated in the progression of gastric mucosal atrophy and IM, and thus may be associated with the presence of gastric cancer especially for intestinal-type histopathology.
异常DNA甲基化是致癌过程中的主要事件之一。启动子DNA甲基化也存在于包括胃上皮在内的各种非肿瘤组织中，作为与年龄相关的现象，这表明它在肿瘤发生过程中早期就会出现。
我们旨在阐明非肿瘤性胃上皮中异常DNA甲基化与胃癌风险、幽门螺杆菌感染以及幽门螺杆菌诱导的胃炎程度之间的关系。
本研究纳入89例患者。比较两组患者的异常DNA甲基化状态：43例胃癌患者（平均年龄65.9岁[29 - 91岁]，女性与男性比例为0.30，肠型[n = 25]，弥漫型[n = 18]）和46例年龄和性别匹配的无胃癌患者（消化性溃疡疾病[n = 11]，胃炎[n = 35]）作为对照组。通过内镜检查从胃窦活检的非肿瘤上皮中直接提取基因组DNA。通过甲基化特异性聚合酶链反应（MSP）确定p14和p21基因的启动子甲基化状态。在MSP后通过数字密度分析对p16基因的启动子甲基化状态进行定量。根据更新的悉尼系统评估胃窦炎的程度。基于放射免疫测定法测量的血清PG I和PG II水平的数据计算PG I/II比值。
在所有89名受试者中，p14的CpG岛甲基化发生率为25.8%，p16为52.8%，p21为1.1%。在非癌症患者中，幽门螺杆菌阳性患者的p14基因甲基化频率显著高于幽门螺杆菌阴性患者（38.5%对10.0%，p = 0.03）。在所有患者以及幽门螺杆菌阳性患者中，胃癌病例中非肿瘤性胃上皮中p16基因的平均（±标准差）甲基化水平显著高于非胃癌病例（分别为0.45±0.31对0.20±0.17；p = 0.019，0.45±0.31对0.20±0.17；p = 0.016）。p16基因的甲基化水平也与肠型胃癌的存在相关（p = 0.017）。肠化生（IM）患者的p16基因甲基化水平显著高于无肠化生患者（p = 0.04）。此外，p16基因的甲基化水平与较低的PG I/II比值相关（p = 0.04）。仅在1例胃癌患者中发现p21基因的甲基化。
我们的数据表明，p14基因的启动子可能是其甲基化与幽门螺杆菌感染密切相关的特定区域之一。p16基因的甲基化水平似乎在胃黏膜萎缩和IM的进展过程中积累，因此可能与胃癌的存在相关，尤其是对于肠型组织病理学。
