Yashiro Masakazu, Yasuda Koichi, Nishii Takafumi, Kaizaki Ryoji, Sawada Tetsuji, Ohira Masaichi, Hirakawa Kosei
Department of Surgical Oncology, Osaka City University Graduate School of Medicine, Abeno-ku, Osaka 545-8585, Japan.
Int J Oncol. 2009 Nov;35(5):997-1003. doi: 10.3892/ijo_00000414.
ERas is a recently identified oncogene that supports the tumorigenic growth of embryonic stem cells, it is constitutively active in the absence of mutation. ERas oncogene is expressed only in viviparity phase cells, but not in somatic cells because of epigenetic transcriptional silencing in the somatic phase. The aim of this study was to clarify the ERas expression and its epigenetic regulation in gastric cancer of somatic phase. Fifteen gastric cancer cell lines were used. ERas mRNA expression and its epigenetic regulation were examined by reverse transcription-polymerase chain reaction and bisulfite sequencing analysis. To identify a subset of cancer stem cells, termed 'side population' (SP) cells, flow cytometry analysis was performed. ERas is expressed in 8 of the 15 gastric cancer cell lines, but is silenced in the remaining 7 cancer cell lines and normal cell lines. Six of 7 cancer cell lines without ERas expression had promoter methylation, which correlated with silencing of ERas expression. ERas expression is re-activated following treatment with the DNA methyltransferase inhibitor 5-aza-CdR. The percentage of SP fraction of ERas-positive gastric cancer cells was significantly (p=0.024) higher (3.4+/-1.8%), in comparison to that of ERas-negative cells (1.6+/-0.4%). These findings suggested that the activating ERas oncogene might be associated with tumorigenic growth of somatic cells, and might be a putative molecule responsible for cancer stem cell-like characteristics in gastric cancer. Loss of methylation in the promoter of ERas might be one of mechanisms responsible for the re-expression of an embryonic oncogene in gastric cancer.
ERas是一种最近发现的致癌基因，它支持胚胎干细胞的致瘤性生长，在没有突变的情况下呈组成性激活。ERas致癌基因仅在胎生期细胞中表达，而在体细胞中不表达，因为在体细胞期存在表观遗传转录沉默。本研究的目的是阐明ERas在体细胞期胃癌中的表达及其表观遗传调控。使用了15种胃癌细胞系。通过逆转录-聚合酶链反应和亚硫酸氢盐测序分析检测ERas mRNA表达及其表观遗传调控。为了鉴定称为“侧群”（SP）细胞的癌症干细胞亚群，进行了流式细胞术分析。15种胃癌细胞系中有8种表达ERas，但其余7种癌细胞系和正常细胞系中ERas沉默。7种无ERas表达的癌细胞系中有6种具有启动子甲基化，这与ERas表达的沉默相关。用DNA甲基转移酶抑制剂5-氮杂-2'-脱氧胞苷（5-aza-CdR）处理后，ERas表达重新激活。与ERas阴性细胞（1.6±0.4%）相比，ERas阳性胃癌细胞的SP分数百分比显著更高（3.4±1.8%，p=0.024）。这些发现表明，激活的ERas致癌基因可能与体细胞的致瘤性生长相关，可能是胃癌中具有癌症干细胞样特征的一个推定分子。ERas启动子甲基化的缺失可能是胃癌中胚胎致癌基因重新表达的机制之一。
