Environmental Epigenetics and Stem/Progenitor Cell Injury

描述（由申请人提供）： 环境暴露于内分泌干扰剂，或异种雌激素，可增加患乳腺癌的风险。动物和人群研究表明，早期暴露于外源性雌激素可能导致生命后期的肿瘤发生的印记现象。这些环境压力因素改变乳腺基因组的分子机制还不清楚。我们的初步数据提示我们假设，表观遗传改变，在CpG岛超甲基化的形式，将这种印迹信息传递给未分化细胞的后代预暴露于异种雌激素。具体来说，我们建议，位于干/祖细胞室的人乳房的未成熟细胞是这种环境的侮辱的主要目标。在特定目标1中，原代乳腺干细胞/祖细胞将在体外系统中暴露于异种雌激素-己烯雌酚、双酚A或17 β-雌二醇。“全球分析预计将在分析的约29，000个CpG岛中的1-2%中鉴定出改变的甲基化状态。这些表观遗传事件可能是将干/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传递到分化的上皮细胞，进而导致异种移植模型中的乳腺肿瘤发生。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/祖细胞是否会破坏雌激素信号传导的稳态，并在其下游靶点中引发表观遗传级联反应。多梳阻遏物可以被募集到启动子CpG岛，然后在这些启动子处添加DNA甲基转移酶。由于局部甲基转移酶活性增加，获得性DMA甲基化标志着可遗传的基因沉默。在具体目标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诱导的CpG岛超甲基化。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观基因型。在这方面，表现出这种表观基因型的患者可能在其早期生活中暴露于异种雌激素。此外，低水平的这些甲基化变化可能存在于正常的乳腺上皮细胞中，在人类乳腺中留下癌变的区域。这种类型的CpG岛超甲基化可以使用我们实验室开发的数学建模方法作为分子遗迹进行跟踪。我们将进一步发展该模型，以重现异种雌激素诱导的乳腺肿瘤发生的历史，从肿瘤前病变到增生到原位癌再到浸润性癌。将提供潜在CpG岛位点的临床灵敏度和特异性，以确定异种雌激素表型，作为该U 01项目的定量里程碑。这些位点是未来早期乳腺癌检测的生物标志物，也是环境雌激素的推定生物传感器。

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.