The epigenetic mechanism of hexavalent chromium carcinogenesis

项目概要/摘要 六价铬[Cr（VI）]是最常见的环境污染物之一，可引起肺和其他 癌Cr（VI）致癌的机制尚未阐明。这项研究的长期目标是 确定Cr（VI）致癌性的机制，并确定更好的治疗和预防的目标， 铬（VI）暴露导致的肺癌。表观遗传学是指基因模式的可遗传变化， 表达不是由DNA序列的变化引起的，而是由DNA甲基化、组蛋白 翻译后修饰，microRNA和长非编码RNA。癌症干细胞（CSC）是癌症 具有正常干细胞特征的细胞。CSC或CSC样细胞被认为是癌症起始细胞。 细胞基因组印记是指一种表观遗传机制，通过这种机制，某些基因在亲本中表达- 的起源特异性的方式，限制他们的表达从两个亲本染色体之一。许多 研究表明，表观遗传学和基因组印记的失调在癌症发生中起关键作用。 越来越多的证据表明，Cr（VI）也会引起表观遗传效应，如改变DNA甲基化， 组蛋白翻译后修饰。然而，Cr（VI）触发这些表观遗传的机制 修饰仍然在很大程度上是未知的，这些表观遗传修饰是否在Cr（VI）中起因果作用 致癌作用尚不清楚。我们的初步研究发现：（i）慢性Cr（VI）暴露诱导CSC样 性质和细胞恶性转化;（ii）慢性Cr（VI）暴露增加了几种HMT酶的水平， 其在Cr（VI）诱导的CSC样性质和细胞转化中起因果作用;（iii）较高水平的H3 在人的肺癌组织中也检测到抑制性甲基化标记及其相关的HMT酶 （iv）HMTases的上调在慢性Cr（VI）暴露引起的 Dlk 1-Dio 3基因组印记簇的失调;（v）miR-494下调在Cr（VI）- 诱导的细胞转化;和（vi）氧化应激增加HMT酶的水平。基于文献和 根据我们的初步数据，我们假设：（i）铬（VI）暴露会产生氧化应激，从而增加水平 （ii）HMTases的上调使Dlk 1-Dio 3基因组印迹簇失调， 降低miR-494的水平;和（iii）miR-494的下调增加其靶标和关键蛋白的水平。 CSC因子c-Myc和BMI 1，其产生促进Cr（VI）诱导的细胞转化的CSC样性质， 肿瘤发生这项拟议的研究不仅填补了表观遗传学和Cr（VI）致癌作用的知识空白， 而且为氧化应激在Cr（VI）致癌中的关键作用提供了新的机制见解。三 目的1：通过下调Dlk 1-Dio 3印迹的miR-494诱导CSC样性质 簇及其在Cr（VI）诱导的细胞转化和肿瘤发生中的作用。目的2：下调miR-494 慢性Cr（VI）胁迫诱导的HMTases通过去调节Dlk 1-Dio 3基因组印迹簇。目标3： 慢性Cr（VI）暴露通过氧化应激上调HMTases。

PROJECT SUMMARY/ABSTRACT Hexavalent chromium [Cr(VI)] is one of the most common environmental pollutants causing lung and other cancer. The mechanism of Cr(VI) carcinogenesis has not been elucidated. The long-term goal of this study is to determine the mechanism of Cr(VI) carcinogenicity and identify targets for better treatment and prevention of lung cancer resulting from Cr(VI) exposure. Epigenetics refers to heritable changes in the pattern of gene expression that are not caused by changes in DNA sequence, but are mediated by DNA methylation, histone posttranslational modifications, microRNAs and long noncoding RNAs. Cancer stem cells (CSCs) are cancer cells possessing characteristics of normal stem cells. CSCs or CSC-like cells are considered as cancer initiating cells. Genomic imprinting refers to an epigenetic mechanism by which certain genes are expressed in a parent- of-origin-specific manner, restricting their expression from only one of the two parental chromosomes. Many studies demonstrated that deregulation of epigenetics and genomic imprinting plays key roles in carcinogenesis. Accumulating evidence shows that Cr(VI) also causes epigenetic effects such as changing DNA methylation and histone posttranslational modifications. However, the mechanisms by which Cr(VI) triggers these epigenetic modifications remain largely unknown and whether these epigenetic modifications play a causal role in Cr(VI) carcinogenesis are not clear. Our preliminary studies found: (i) Chronic Cr(VI) exposure induces CSC-like property and cell malignant transformation; (ii) Chronic Cr(VI) exposure increases the levels of several HMTases, which play a causal role in Cr(VI)-induced CSC-like property and cell transformation; (iii) Higher levels of H3 repressive methylation marks and their related HMTases are also detected in lung cancer tissues of humans exposed to chromium; (iv) Up-regulation of HMTases plays a crucial role in chronic Cr(VI) exposure-caused deregulation of Dlk1-Dio3 genomic imprinting cluster; (v) miR-494 down-regulation plays a causal role in Cr(VI)- induced cell transformation; and (vi) Oxidative stress increases the levels of HMTases. Based on literature and our preliminary data, we hypothesize: (i) Cr(VI) exposure generates oxidative stress, which increases the levels of HMTases; (ii) Up-regulation of HMTases deregulates the Dlk1-Dio3 genomic imprinting cluster, which decreases the level of miR-494; and (iii) Down-regulation of miR-494 increases the levels of its targets and key CSC factors c-Myc and BMI1, which produce CSC-like property promoting Cr(VI)-induced cell transformation and tumorigenesis. This proposed study not only fills the knowledge gap of epigenetics and Cr(VI) carcinogenesis, but also provides novel mechanistic insights for the crucial role of oxidative stress in Cr(VI) carcinogenesis. Three aims are proposed: Aim 1: Induction of CSC-like property by down-regulating miR-494 of Dlk1-Dio3 imprinting cluster and its role in Cr(VI)-induced cell transformation and tumorigenesis. Aim 2: Down-regulation of miR-494 by chronic Cr(VI) exposure-induced HMTases through deregulating Dlk1-Dio3 genomic imprinting cluster. Aim 3: Up-regulation of HMTases by chronic Cr(VI) exposure through oxidative stress.