Environmental Epigenetics and Stem/Progenitor Cell Injury

描述(由申请人提供)： 在环境中暴露于内分泌干扰剂或异种雌激素会增加患乳腺癌的风险。动物和种群研究表明，一种印记现象，即早期接触异种雌激素可能会导致晚年发生肿瘤。这些环境应激源改变乳腺基因组的分子机制还不是很清楚。我们的初步数据提示我们假设，表观遗传改变，以CpG岛超甲基化的形式，将这种印记信息传递给预先暴露于异种雌激素的未分化细胞的后代。具体地说，我们认为，位于人类乳房干/祖细胞隔间的未成熟细胞是这种环境侮辱的主要目标。在具体目标1中，原代乳房干/祖细胞将暴露于异种雌激素--己烯雌酚、双酚A或17(3-雌二醇)，在体外系统中。全球分析预计将在所分析的约29,000个CpG岛中确定1-2%的甲基化状态改变。这些表观遗传事件可能是干细胞/祖细胞暴露于异种雌激素的直接结果。这种损伤的表观遗传记忆然后被传递到分化的上皮细胞，进而在异种移植模型中导致乳腺肿瘤的发生。在具体目标2中，我们将从功能上确定这些内分泌化学物质长期暴露于干/祖细胞是否扰乱了雌激素信号的动态平衡，并在其下游靶点触发了表观遗传级联反应。多梳阻遏子可以被招募到启动子CpG岛上，然后在这些启动子上添加DNA甲基转移酶。获得性DNA甲基化是局部甲基转移酶活性增强的结果，标志着可遗传的基因沉默。在特定的目标3中，我们将证明在临床样本中也观察到由异种雌激素暴露引起的CpG岛超甲基化。在原发性乳腺肿瘤中，这些分子改变的存在可能构成异种雌激素表型(S)。在这方面，表现出这种表观类型的患者很可能在他们的早期生活中接触到异种雌激素。此外，这些低水平的甲基化变化可能存在于外观正常的乳腺上皮中，在人类乳房中留下了一个癌变的领域。利用我们实验室开发的数学模型方法，这种类型的CpG岛超甲基化可以作为分子遗迹来追踪。我们将进一步开发该模型，以重现异种雌激素诱导的乳腺肿瘤发生的历史，从癌前病变到增生，再到原位癌到浸润性癌。确定异种雌激素表型的潜在CpG岛基因座的临床敏感性和特异性将作为该U01项目的一个定量里程碑。这些基因座是未来乳腺癌早期检测的生物标志物，可能是环境雌激素的生物传感器。

DESCRIPTION (provided by applicant): Environmental exposure to endocrine-disrupting agents, or xenoestrogens, can increase the risk of developing breast cancer. Animal and population studies suggest an imprinting phenomenon whereby early exposure of xenoestrogen can lead to tumorigenesis later in life. The molecular mechanism by which these environmental stressors can transform breast genomes is not well understood. Our preliminary data prompt us to hypothesize that epigenetic alteration, in the form of CpG island hypermethylation, transmits this imprinted information to the progeny of undifferentiated cells pre-exposed to xenoestrogens. Specifically, we propose that immature cells located in the stem/progenitor compartment of the human breast are prime targets of this environmental insult. In Specific Aim 1, primary breast stem/progenitor cells will be exposed to xenoestrogens - diethylstilbestrol, bisphenol A, or 17(3-estradiol in an in vitro system. 'Global analysis is expected to identify altered methylation status in 1-2% of ~29,000 CpG islands analyzed. These epigenetic events can be the direct results of exposing stem/progenitor cells to xenoestrogens. The epigenetic memory of this injury is then transmitted to differentiated epithelial cells and in turn leads to breast tumorigenesis in a xenograft model. In Specific Aim 2, we will functionally determine whether the prolonged exposure of these endocrine chemicals to stem/progenitor cells disrupt the homeostasis of estrogen signaling and triggers an epigenetic cascade in its downstream targets. Polycomb repressors can be recruited to promoter CpG islands followed by the addition of DNA methyltransferases at these promoters. Acquired DMA methylation, as a result of increased local methyltransferase activities, marks the heritable gene silencing. In Specific Aim 3, we will demonstrate that CpG island hypermethylation induced by xenoestrogen exposure is also observed in clinical samples. The presence of these molecular alterations in primary breast tumors may constitute a xenoestrogen epigenotype(s). In this regard, patients exhibiting this epigenotype are likely exposed to xenoestrogens in their early lives. In addition, low levels of these methylation changes may exist in normal looking mammary epithelial, leaving a field of cancerization in the human breast. This type of CpG island hypermethylation can be tracked as molecular relics using a mathematical modeling approach developed in our laboratory. We will develop the model further to recreate the history of xenoestrogen- induced breast tumorigenesis, from pre-neoplastic lesions to hyperplasia to carcinoma in situ to invasive carcinoma. Clinical sensitivity and specificity of potential CpG island loci pinpointing the xenoestrogen epigenotype will be provided as a quantitative milestone for this U01 project. These loci are future biomarkers for early breast cancer detection and are putative biosensors to environmental estrogens.