Oh Bong-Kyeong, Kim Haeryoung, Park Hye-Jung, Shim Yhong-Hee, Choi Jinsub, Park Chanil, Park Young Nyun
Cancer Metastasis Research Center, Yonsei University College of Medicine, Seoul, Korea.
Int J Mol Med. 2007 Jul;20(1):65-73.
Aberrant DNA methylation on CpG islands is one of the most consistent epigenetic changes in human cancers, and the methylation process is catalyzed by DNA methyltransferase (DNMT). We evaluated i) the mRNA levels of three DNMTs; DNMT1, DNMT3a and DNMT3b, in 25 hepatocellular carcinomas (HCCs), in their corresponding non-cancerous liver tissues and in 7 normal livers by using real-time reverse transcriptase-polymerase chain reaction; ii) nuclear expression of DNMT1 and DNMT3a proteins in the HCCs by immunohistochemistry, iii) the methylation status of 5 genes; p16, p15, E-cadherin, HIC-1 and RASSF1A in the same tissues, and iv) the relationships between the above results and the clinicopathological characteristics, including prognosis. The differences in mRNA expression levels for DNMT1, DNMT3a and DNMT3b were statistically significant between HCC and normal livers (p<0.001), HCC and chronic hepatitis (p<0.001) and HCC and cirrhosis (p<0.001). An increase in mRNA expression levels of >4-fold for DNMT3b in HCCs was significantly associated with a poorer overall survival (p=0.027) and shorter metastasis-free survival (p=0.0299). A poorer recurrence-free survival was noted in HCCs with a >4-fold increase in DNMT3a mRNA (p=0.0120). The average numbers of methylated genes were 0, 1.27, 1.38 and 2.72 for normal livers, chronic hepatitis, cirrhosis and HCCs, respectively, and this progressive increase from normal livers to chronic hepatitis/cirrhosis through HCC may suggest that tumor suppressor gene methylation is an early event in hepatocarcinogenesis. These results first suggest that hepatocarcinogenesis involves an increased expression of DNMT1, DNMT3a and DNMT3b mRNA and a progressive increase in the number of methylated genes from normal liver, chronic hepatitis/cirrhosis to HCC and secondly that an increase in the DNMT3a and DNMT3b mRNA levels in HCCs relative to their non-cancerous tissues may be a predictor of poor survival.
CpG岛的异常DNA甲基化是人类癌症中最常见的表观遗传变化之一，DNA甲基转移酶（DNMT）催化甲基化过程。我们通过实时逆转录聚合酶链反应评估了：i）25例肝细胞癌（HCC）、其相应的癌旁肝组织和7例正常肝脏中三种DNMT（DNMT1、DNMT3a和DNMT3b）的mRNA水平；ii）通过免疫组织化学检测HCC中DNMT1和DNMT3a蛋白的核表达；iii）相同组织中5个基因（p16、p15、E-钙黏蛋白、HIC-1和RASSF1A）的甲基化状态；iv）上述结果与包括预后在内的临床病理特征之间的关系。HCC与正常肝脏（p<0.001）、HCC与慢性肝炎（p<0.001）以及HCC与肝硬化（p<0.001）之间，DNMT1、DNMT3a和DNMT3b的mRNA表达水平差异具有统计学意义。HCC中DNMT3b的mRNA表达水平增加>4倍与较差的总生存期（p=0.027）和较短的无转移生存期（p=0.0299）显著相关。DNMT3a的mRNA增加>4倍的HCC中，无复发生存期较差（p=0.0120）。正常肝脏、慢性肝炎、肝硬化和HCC中甲基化基因的平均数量分别为0、1.27、1.38和2.72，从正常肝脏到慢性肝炎/肝硬化再到HCC的这种逐渐增加可能表明肿瘤抑制基因甲基化是肝癌发生的早期事件。这些结果首先表明，肝癌发生涉及DNMT1、DNMT3a和DNMT3b mRNA表达增加以及从正常肝脏、慢性肝炎/肝硬化到HCC甲基化基因数量的逐渐增加；其次，HCC中相对于其癌旁组织的DNMT3a和DNMT3b mRNA水平增加可能是生存不良的预测指标。
