Fleisher A S, Esteller M, Tamura G, Rashid A, Stine O C, Yin J, Zou T T, Abraham J M, Kong D, Nishizuka S, James S P, Wilson K T, Herman J G, Meltzer S J
Department of Medicine, Gastroenterology Division, University of Maryland School of Medicine and Baltimore VA Hospital, Baltimore, Maryland, MD 21201, USA.
Oncogene. 2001 Jan 18;20(3):329-35. doi: 10.1038/sj.onc.1204104.
A significant portion of gastric cancers exhibit defective DNA mismatch repair, manifested as microsatellite instability (MSI). High-frequency MSI (MSI-H) is associated with hypermethylation of the human mut-L homologue 1 (hMLH1) mismatch repair gene promoter and diminished hMLH1 expression in advanced gastric cancers. However, the relationship between MSI and hMLH1 hypermethylation has not been studied in early gastric neoplasms. We therefore investigated hMLH1 hypermethylation, hMLH1 expression and MSI in a group of early gastric cancers and gastric adenomas. Sixty-four early gastric neoplasms were evaluated, comprising 28 adenomas, 18 mucosal carcinomas, and 18 carcinomas with superficial submucosal invasion but clear margins. MSI was evaluated using multiplex fluorescent PCR to amplify loci D2S123, D5S346, D17S250, BAT 25 and BAT 26. Methylation-specific PCR was performed to determine the methylation status of hMLH1. In two hypermethylated MSI-H cancers, hMLH1 protein expression was also evaluated by immunohistochemistry. Six of sixty-four early gastric lesions were MSI-H, comprising 1 adenoma, 4 mucosal carcinomas, and 1 carcinoma with superficial submucosal invasion. Two lesions (one adenoma and one mucosal carcinoma) demonstrated low-frequency MSI (MSI-L). The remaining 56 neoplasms were MSI-stable (MSI-S). Six of six MSI-H, one of two MSI-L, and none of thirty MSI-S lesions showed hMLH1 hypermethylation (P<0.001). Diminished hMLH1 protein expression was demonstrated by immunohistochemistry in two of two MSI-H hypermethylated lesions. hMLH1 promoter hypermethylation is significantly associated with MSI and diminished hMLH1 expression in early gastric neoplasms. MSI and hypermethylation-associated inactivation of hMLH1 are more prevalent in early gastric cancers than in gastric adenomas. Thus, hypermethylation-associated inactivation of the hMLH1 gene can occur early in gastric carcinogenesis.
相当一部分胃癌存在DNA错配修复缺陷，表现为微卫星不稳定（MSI）。高频MSI（MSI-H）与人类错配修复基因mut-L同源物1（hMLH1）启动子的高甲基化以及晚期胃癌中hMLH1表达降低有关。然而，在早期胃肿瘤中，MSI与hMLH1高甲基化之间的关系尚未得到研究。因此，我们对一组早期胃癌和胃腺瘤中的hMLH1高甲基化、hMLH1表达及MSI进行了研究。评估了64例早期胃肿瘤，包括28例腺瘤、18例黏膜癌和18例伴有浅表黏膜下浸润但切缘清晰的癌。采用多重荧光PCR扩增位点D2S123、D5S346、D17S250、BAT 25和BAT 26来评估MSI。进行甲基化特异性PCR以确定hMLH1的甲基化状态。在两例高甲基化的MSI-H癌症中，还通过免疫组织化学评估了hMLH1蛋白表达。64例早期胃病变中有6例为MSI-H，包括1例腺瘤、4例黏膜癌和1例伴有浅表黏膜下浸润的癌。2个病变（1例腺瘤和1例黏膜癌）表现为低频MSI（MSI-L）。其余56个肿瘤为MSI稳定（MSI-S）。6例MSI-H病变中有6例、2例MSI-L病变中有1例、30例MSI-S病变中无一例显示hMLH1高甲基化（P<0.001）。免疫组织化学显示，2例MSI-H高甲基化病变中有2例hMLH1蛋白表达降低。hMLH1启动子高甲基化与早期胃肿瘤中的MSI及hMLH1表达降低显著相关。MSI及hMLH1高甲基化相关失活在早期胃癌中比在胃腺瘤中更常见。因此，hMLH1基因的高甲基化相关失活可在胃癌发生早期出现。
