胃癌组织中相关肿瘤抑制基因启动子区甲基化状态

目的分析胃癌组织中肿瘤抑制基因启动子区甲基化状态及其与临床分期、分型的关系。方法采用甲基化特异性聚合酶链反应方法,检测106例胃癌及其邻近胃小凹上皮、16例慢性胃炎小凹上皮石蜡标本中E钙黏素（E—CD）、错配修复酶hMLH1、APC和6-氧-甲基鸟嘌呤-DNA甲基转移酶（MGMT）基因启动子区甲基化状态,并对其中46例胃癌采用免疫组化方法检测E—CD蛋白表达情况。结果在胃癌、胃癌邻近小凹上皮及慢性胃炎小凹上皮中,基因甲基化频率分别为72．6％（77／106）、44．3％（47／106）和12．5％（2／16）,三者问差异有统计学意义（P〈0．01）。Laurén弥漫型胃癌甲基化（80．6％,50／62）明显高于肠型胃癌甲基化（61．4％,27／44）,两者间差异有统计学意义（P〈0．01）。甲基化与患者的年龄、性别、Ming分型及区域淋巴结转移无关（均P〉0．05）,甲基化与胃癌的浸润深度、pTNM分期和分化程度有关（均P〈0．05）。行E—CD蛋白检测的46例胃癌中,22例有E—CD基因甲基化,其中20例（90．9％）E—CD蛋白呈异质性减弱或基本消失表达;24例无E—CD基因甲基化,其中9例（37．5％）E—CD蛋白呈异质性减弱或基本消失表达,两者间差异有统计学意义（P〈0．01）。结论上述肿瘤抑制基因启动了区甲基化可能是胃癌发生的早期事件。胃癌E—CD基因甲基化与E—CD蛋白异质性减弱或消失表达密切相关。

Promoter methylation of several tumor suppressor genes in human gastric adenocarcinoma

OBJECTIVE: To study the promoter methylation of several tumor suppressor genes in human gastric foveolar epithelia (GFE) of chronic gastritis, adjacent GFE of gastric adenocarcinoma (GAC) and GAC. METHODS: Methylation specific PCR (MSP) technique was used to examine the promoter methylation of 4 tumor suppressor genes (E-cadherin, hMLH1, APC, and MGMT) in 106 paraffin-embedded specimens of GAC, including tumor tissues and adjacent GFE, and 16 paraffin-embedded specimens of GFE of chronic gastritis. Immunohistochemistry was used to detect the protein expression of E-cadherin (E-CD) in 46 out of the 106 cases of GAC. RESULTS: The promoter methylation rates of tumor suppressor genes in the GAC tissue were 72.6% (77/106), significantly higher than that in the adjacent GFE (44.3%, 47/106) and the GFE of chronic gastritis (12.5%, 2/16, P < 0.01). The promote methylation rate of tumor suppressor genes in the GAC Laurén diffuse type was 80.6% (50/62), significantly higher than that of the GAC of intestinal type (61.4%, 27/44, P < 0.01). The rates of promoter methylation was significantly associated with depth of penetration, pTNM staging and degree of differentiation in GAC (all P < 0.05), but was no significantly associated with age, gender, Ming's classification and local lymph node metastasis (all P > 0.05). The rate of loss of E-CD protein expression or heterogeneously reduction of E-CD protein expression in the specimens of GAC with promoter methylation was 90.9% (20/22), significantly higher than that in the specimens of GAC without promoter methylation (9/24, 37.5%, P < 0.01). CONCLUSION: Promoter methylation of above tumor suppressor genes is seldom found in the GFE of chronic gastritis, frequently found in the adjacent GFE of GAC, but very commonly in GAC. Promoter methylation may be an early event in the carcinogensis of GAC. E-CD gene promoter methylation is closely related to loss or heterogeneously reduction of E-CD protein expression.