Clément Geneviève, Bosman Fred T, Fontolliet Charlotte, Benhattar Jean
Institut de Pathologie, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland.
Cancer Res. 2004 Oct 1;64(19):6867-73. doi: 10.1158/0008-5472.CAN-03-2503.
Adenomatous polyposis coli (APC) promoter hypermethylation has been reported frequently in normal gastric mucosa, but it remained to be clarified whether this occurs in every individual. In this study, methylation of the APC promoter was analyzed in histologically normal-appearing gastric mucosa samples by methylation-sensitive single-strand conformation analysis and by a methylation-sensitive dot blot assay. Epithelial cell samples were collected by microdissection from tissue sections. Equal amounts of methylated and unmethylated APC alleles were found in all gastric mucosa samples from patients without any gastric lesions (20 samples). Allele-specific methylation analysis showed that the methylation of the APC promoter was monoallelic; however, which allele was methylated depended on the cell type. Increased or decreased methylation was found in 10 of 36 (28%) normal gastric mucosa samples adjacent to a gastric or esophageal adenocarcinoma. No allelic loss was found at the APC locus. Modification of the methylation status was also found in 3 of 21 (14%) normal-appearing gastric mucosa samples adjacent to intestinal metaplasia. In contrast, all normal mucosa samples in cases with chronic gastritis but without metaplasia or dysplasia showed a monoallelic methylation pattern. Our results indicate the following: (a) In normal gastric mucosa, the APC promoter shows monoallelic methylation, which is not due to imprinting but most likely due to allelic exclusion; (b) the excluded allele differs between foveolar and glandular epithelial cells; (c) the APC methylation pattern is frequently altered in normal-appearing gastric mucosa of gastric or esophageal adenocarcinoma patients; and (d) such alterations also occur in normal gastric mucosa adjacent to intestinal metaplasia.
在正常胃黏膜中，常报道有腺瘤性息肉病基因（APC）启动子高甲基化现象，但这种现象是否在每个个体中都会发生仍有待阐明。在本研究中，通过甲基化敏感的单链构象分析和甲基化敏感的斑点印迹分析，对组织学外观正常的胃黏膜样本中的APC启动子甲基化进行了分析。上皮细胞样本通过显微切割从组织切片中采集。在无任何胃部病变患者的所有胃黏膜样本（20个样本）中，均发现等量的甲基化和未甲基化APC等位基因。等位基因特异性甲基化分析表明，APC启动子的甲基化是单等位基因的；然而，哪个等位基因发生甲基化取决于细胞类型。在36个（28%）与胃或食管腺癌相邻的正常胃黏膜样本中，有10个样本的甲基化增加或减少。在APC基因座未发现等位基因缺失。在21个（14%）与肠化生相邻的外观正常的胃黏膜样本中，也发现了甲基化状态的改变。相比之下，所有患有慢性胃炎但无化生或发育异常的病例中的正常黏膜样本均显示单等位基因甲基化模式。我们的结果表明：（a）在正常胃黏膜中，APC启动子表现为单等位基因甲基化，这不是由于印记，而很可能是由于等位基因排斥；（b）在小凹上皮细胞和腺上皮细胞中，被排斥的等位基因不同；（c）在胃或食管腺癌患者外观正常的胃黏膜中，APC甲基化模式经常改变；（d）这种改变也发生在与肠化生相邻的正常胃黏膜中。
