Lee Jae-Hyuk, Park Seun-Ja, Abraham Susan C, Seo Jae-Sung, Nam Jong-Hee, Choi Chan, Juhng Sang-Woo, Rashid Asif, Hamilton Stanley R, Wu Tsung-Teh
Department of Pathology, MD Anderson Cancer Center, Houston, TX 77030, USA.
Oncogene. 2004 Jun 3;23(26):4646-54. doi: 10.1038/sj.onc.1207588.
Gastric carcinogenesis involves multiple genetic and epigenetic alterations. Epigenetic silencing of tumor-related genes due to CpG island methylation (CIM) has been recently reported in gastric cancer, but the role in precursor lesions is not well understood. We analysed the methylation status of the tumor suppressor gene p16, the DNA mismatch repair gene hMLH1, and four CpG islands (MINT1, MINT2, MINT25, and MINT31) using methylation-specific polymerase chain reaction in 35 polypoid adenomas and 46 flat dysplasias unassociated with carcinoma, 34 early adenocarcinomas (T1N0M0) and associated adenomas/dysplasias, and corresponding adjacent non-neoplastic mucosa. The extent of CIM was defined by the fraction of methylated loci (methylation index), and compared with previously characterized genetic alterations (microsatellite instability (MSI) and APC gene mutation). We found that methylation of p16 was more frequent in adenocarcinoma-associated dysplasias/adenomas (29%) and adenocarcinomas (44%) as compared to flat dysplasias (4%) and adenomas (18%) unassociated with adenocarcinoma (P=0.001). The mean methylation index increased from normal/chronic gastritis (CG) mucosa (0.09) to intestinal metaplasia (IM) (0.16), flat dysplasias (0.40) or polypoid adenomas (0.41) unassociated with carcinoma, dysplasias/adenomas associated with carcinoma (0.44), and adenocarcinomas (0.44). There was no difference in frequencies of high-level CpG island methylation (CIM-H, methylation index > or =0.5) among flat dysplasias (50%) and polypoid adenomas (51%) unassociated with carcinoma, dysplasias/adenomas associated with adenocarcinoma (47%), and adenocarcinoma (47%). CIM-H was present in 15% of IM, but not in normal/CG mucosa. There was a significant correlation between methylation of hMLH1 and high-level of microsatellite instability (MSI-H): methylation of hMLH1 was present in 71% of MSI-H tumors, but only 8% of MSI-low tumors and 13% of microsatellite-stable tumors (P=0.0001). There was no statistical difference between methylation index and APC mutation. Our results indicate that concurrent promoter methylation is an early and frequent event in gastric tumorigenesis, including both MSI-H and microsatellite-stable neoplasms. Methylation of the p16 gene may contribute to the malignant transformation of gastric precursor lesions.
胃癌发生涉及多种基因和表观遗传改变。最近报道了胃癌中因CpG岛甲基化（CIM）导致的肿瘤相关基因的表观遗传沉默，但在癌前病变中的作用尚不清楚。我们使用甲基化特异性聚合酶链反应分析了35例息肉状腺瘤和46例与癌无关的扁平发育异常、34例早期腺癌（T1N0M0）及相关腺瘤/发育异常以及相应的相邻非肿瘤性黏膜中肿瘤抑制基因p16、DNA错配修复基因hMLH1和四个CpG岛（MINT1、MINT2、MINT25和MINT31）的甲基化状态。CIM的程度由甲基化位点的比例（甲基化指数）定义，并与先前特征化的基因改变（微卫星不稳定性（MSI）和APC基因突变）进行比较。我们发现，与扁平发育异常（4%）和与腺癌无关的腺瘤（18%）相比，腺癌相关发育异常/腺瘤（29%）和腺癌（44%）中p16的甲基化更常见（P = 0.001）。甲基化指数从正常/慢性胃炎（CG）黏膜（0.09）增加到肠化生（IM）（0.16）、与癌无关的扁平发育异常（0.40）或息肉状腺瘤（0.41）、癌相关发育异常/腺瘤（0.44）以及腺癌（0.44）。在与癌无关的扁平发育异常（50%）和息肉状腺瘤（51%）、癌相关发育异常/腺瘤（47%）以及腺癌（47%）中，高水平CpG岛甲基化（CIM-H，甲基化指数≥0.5）的频率没有差异。CIM-H存在于15%的IM中，但不存在于正常/CG黏膜中。hMLH1的甲基化与高水平微卫星不稳定性（MSI-H）之间存在显著相关性：hMLH1的甲基化存在于71%的MSI-H肿瘤中，但仅存在于8%的MSI低肿瘤和13%的微卫星稳定肿瘤中（P = 0.0001）。甲基化指数与APC突变之间没有统计学差异。我们的结果表明，同时发生的启动子甲基化是胃癌发生中的一个早期且常见的事件，包括MSI-H和微卫星稳定的肿瘤。p16基因的甲基化可能有助于胃前体病变的恶性转化。
