Determination of carcinogenic me chanisms in stem cells using ES/iPS cells

有几份报告表明，某些致癌物的靶标可能是组织干细胞。为了建立一个评估干细胞中化合物致癌活性的模型系统，我们测定了化学诱导的小鼠胚胎干细胞(MES)的DNA损伤以及外源代谢酶(Cyp1a1和CyP1B1)和未分化标志物(Sox2、Nanog、Oct3/4、Dppa5和碱性磷酸酶ALP)的表达。将这些模式与小鼠胚胎成纤维细胞(MEF)进行比较，MEF是一种典型的分化细胞，以了解干细胞特异性反应。在致癌物7，12-二甲基苯并(A)菲(DMBA)处理的细胞中检测到DNA加合物。与MES细胞相比，MEF中Cyp1a1的表达水平几乎高出两倍，表明与CyP1b1的表达水平有很好的相关性，而不是Cyp1a1的表达水平。在MES细胞中，DMBA处理抑制了已知的未分化标志物Sox2、Nanog、Oct3/4和Dppa5的表达，并减少了ALP阳性细胞。3-甲基胆蒽处理MES细胞诱导了细胞色素P450的表达，没有检测到DNA加合物的形成，也没有下调未分化标志物的表达，这表明DMBA诱导的DNA损伤可能是破坏茎的作用，从而破坏了受损的干细胞。

There are several reports suggesting that the target of certain carcinogens would be tissue stem cells. To develop a model system assessing carcinogenic activity of chemical compounds in stem cells, we determined chemical-induced DNA damage in murine embryonic stem (mES) cells as well as the expression of xenobiotics-metabolizing enzymes (Cyp1a1 and Cyp1b1) and undifferentiation markers (Sox2, Nanog, Oct3/4, Dppa5 and alkaline phosphatase ALP). These patterns were compared with murine embryonic fibroblast (MEF), a representative differentiated cell to understand stem cell-specific responses. DNA adducts were detected in a carcinogen 7,12-dimethylbenz(a)anthracene (DMBA)-treated cells. The level was almost two times higher in MEF as compared with mES cells, indicating a good correlation with the expression magnitude of Cyp1b1, not Cyp1a1. In mES cells, DMBA treatment suppressed the expression of well-known undifferentiation markers Sox2, Nanog, Oct3/4 and Dppa5, and decreased ALP-positive cells. 3-Methylcholanthrene-treatment in mES cells induced Cyps expression with no detectable DNA adduct formation and no down regulation of undifferentiation markers, indicating that DNA damage induced by DMBA would be responsible for disruption of stemness by which damaged stem cells are being eliminated.