Yang Bin, House Michael G, Guo Mingzhou, Herman James G, Clark Douglas P
Department of Pathology, The Johns Hopkins Medical Institutions, Baltimore, MD, USA.
Mod Pathol. 2005 Mar;18(3):412-20. doi: 10.1038/modpathol.3800287.
Recent studies indicate that tumor suppressor genes can be epigenetically silenced through promoter hypermethylation. To further understand epigenetic alterations in cholangiocarcinoma, we have studied the methylation profiles of 12 candidate tumor suppressor genes (APC, E-cadherin/CDH1, MGMT, RASSF1A, GSTP, RAR-beta, p14ARF, p15INK4b, p16INK4a, p73, hMLH1 and DAPK) in 72 cases of cholangiocarcinoma, including equal number cases of intrahepatic cholangiocarcinoma and extrahepatic cholangiocarcinoma. A total of 10 cases of benign biliary epithelia were included as controls. The methylation status of tumor suppressor genes was analyzed using methylation-specific PCR. We found that 85% of all cholangiocarcinomas had methylation of at least one tumor suppressor gene. The frequency of tumor suppressor gene methylation in cholangiocarcinoma was: RASSF1A (65%), p15INK4b (50%), p16INK4a (50%), APC (46%), E-cadherin/CDH1 (43%), p14(ARF) (38%), p73 (36%), MGMT (33%), hMHL1 (25%), GSTP (14%), RAR-beta (14%) and DAPK (3%). Although single tumor suppressor gene methylation can be seen in benign biliary epithelium, methylation of multiple tumor suppressor genes is only seen in cholangiocarcinoma. About 70% (50/72) of the cholangiocarcinomas had three or more tumor suppressor genes methylated and 52% (38/72) of cases had four or more tumor suppressor genes methylated. Concerted methylation of multiple tumor suppressor genes was closely associated with methylation of RASSF1A, p16 and/or hMHL1. Methylation of RASSF1A was more common in extrahepatic cholangiocarcinoma than intrahepatic cholangiocarcinoma (83 vs 47%, P=0.003) while GSTP was more frequently seen in intrahepatic compared to extrahepatic cholangiocarcinoma (31 vs 6%, P=0.012). Our study indicates that methylation of promoter CpG islands of tumor suppressor genes is a common epigenetic event in cholangiocarcinoma. Based on distinct methylation profiles, intrahepatic cholangiocarcinoma and extrahepatic cholangiocarcinoma are two closely related but biologically unique neoplastic processes. Taking advantage of the unique concurrent methylation profile of multiple genes in cholangiocarcinoma may facilitate the distinction of cholangiocarcinoma from benign biliary epithelium in clinical settings.
近期研究表明，肿瘤抑制基因可通过启动子高甲基化在表观遗传层面发生沉默。为进一步了解胆管癌中的表观遗传改变，我们研究了72例胆管癌中12个候选肿瘤抑制基因（APC、E-钙黏蛋白/CDH1、MGMT、RASSF1A、GSTP、RAR-β、p14ARF、p15INK4b、p16INK4a、p73、hMLH1和DAPK）的甲基化谱，其中肝内胆管癌和肝外胆管癌病例数相等。共纳入10例良性胆管上皮作为对照。采用甲基化特异性PCR分析肿瘤抑制基因的甲基化状态。我们发现，所有胆管癌中有85%至少有一个肿瘤抑制基因发生甲基化。胆管癌中肿瘤抑制基因甲基化的频率依次为：RASSF1A（65%）、p15INK4b（50%）、p16INK4a（50%）、APC（46%）、E-钙黏蛋白/CDH1（43%）、p14(ARF)（38%）、p73（36%）、MGMT（33%）、hMHL1（25%）、GSTP（14%）、RAR-β（14%）和DAPK（3%）。虽然在良性胆管上皮中可见单个肿瘤抑制基因甲基化，但多个肿瘤抑制基因甲基化仅见于胆管癌。约70%（50/72）的胆管癌有三个或更多肿瘤抑制基因发生甲基化，52%（38/72）的病例有四个或更多肿瘤抑制基因发生甲基化。多个肿瘤抑制基因的协同甲基化与RASSF1A、p16和/或hMHL1的甲基化密切相关。RASSF1A甲基化在肝外胆管癌中比肝内胆管癌更常见（83%对47%，P=0.003），而GSTP甲基化在肝内胆管癌中比肝外胆管癌更常见（31%对6%，P=0.012）。我们的研究表明，肿瘤抑制基因启动子CpG岛的甲基化是胆管癌中常见的表观遗传事件。基于不同的甲基化谱，肝内胆管癌和肝外胆管癌是两个密切相关但生物学特性独特的肿瘤形成过程。利用胆管癌中多个基因独特的同时甲基化谱可能有助于在临床环境中将胆管癌与良性胆管上皮区分开来。
