MGMT DOWN-REGULATION IN THE CARCINOGENICITY OF HEXAVALENT CHROMIUM

六价铬致癌性中的 MGMT 下调

• 批准号: 10480080
• 负责人: Zhishan Wang
• 金额: $ 33.35万
• 依托单位: CASE WESTERN RESERVE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-09-12 至 2023-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/10480080
• 关键词: Affect; Alkylating Agents; Animal Model; Cadmium; Carcinogens; Cells; Chromosome abnormality; Chronic; Country; Cultured Cells; DNA Methylation; DNA Modification Methylases; DNA Repair; DNA Repair Disorder; DNA Repair Gene; DNA lesion; Development; Down-Regulation; EZH2 gene; Environmental Health; Epigenetic Process; Exhibits; Exposure to; Frequencies; G9a histone methyltransferase; Genes; Genetic; Genome Stability; Genomic Instability; Goals; Histone H3; Histones; Human; Hypersensitivity; Impairment; Inflammation Process; Lesion; Literature; Liver neoplasms; Lung; MGMT gene; Malignant Neoplasms; Malignant neoplasm of lung; Mediating; Metabolism; Metal Carcinogenesis; Metals; Methylation; Modification; Mus; Nickel; Occupational; Persons; Phenotype; Play; Post-Translational Protein Processing; Prevention; Promoter Regions; Property; Reporting; Role; Sister Chromatid Exchange; Structure of parenchyma of lung; Testing; Toxic effect; Transgenic Animals; Transgenic Mice; United States; Up-Regulation; base; cancer cell; cancer risk; cancer stem cell; carcinogenesis; carcinogenicity; cell transformation; chromium hexavalent ion; cytotoxicity; genotoxicity; histone methyltransferase; insight; knock-down; lung tumorigenesis; mouse model; novel; overexpression; pollutant; prevent; protective effect; recruit; repaired; stem-like cell; transition mutation; tumorigenesis

PROJECT SUMMARY/ABSTRACT Hexavalent chromium [Cr(VI)] exposure causes multiple toxic effects in humans. The main concern of Cr(VI) toxicity is its carcinogenicity as Cr(VI) is one of the most well-recognized environmental and occupational carcinogens causing lung and other cancer in humans. While it is under active study, the mechanism of Cr(VI) carcinogenicity remains elusive. Previous studies showed that Cr(VI) exposure causes genotoxic effects, which are thought to play important roles in Cr(VI) carcinogenicity. On the other hand, studies also showed that Cr(VI) exposure dysregulates epigenetics such as increased DNA methylation and abnormal histone posttranslational modifications. However, it remains to be determined how dysregulated epigenetics contributes to Cr(VI) carcinogenicity and if Cr(VI)-caused epigenetic changes play a role in its genotoxic effect. Our preliminary studies showed: (i) Chronic Cr(VI) exposure increases the levels of histone H3 repressive methylation marks (H3K9me2 and H3K27me3) and their related histone methyltransferases (HMTases) (G9a, SUV39H1, and EZH2). (ii) Up- regulation of HMTases play a causal role in Cr(VI)-induced cancer stem cell (CSC)-like property and cell malignant transformation. (iii) Chronic Cr(VI) exposure down-regulates the expression of O6-methylguanine DNA methyltransferase (MGMT), a key gene in DNA repair network; and MGMT down-regulation plays a causal role in Cr(VI)-induced cell transformation. (iv) The level of O6-methylguanine (O6-MeG), a highly mutagenic DNA lesion, is significantly increased in Cr(VI)-transformed cells; but stably expressing MGMT greatly reduces Cr(VI) exposure-induced O6-MeG. (v) Cr(VI) exposure also significantly decreases the level of MGMT but increases O6-MeG level in mouse and human lung tissues. (vi) Stably knocking down HMTases G9a or SUV39H1 significantly increases MGMT level but reduces O6-MeG level in Cr(VI)-exposed cells. (vii) Cr(VI)- transformed cells display impaired DNA damage repair capacity but stably expressing MGMT significantly reduces chronic Cr(VI) exposure-caused DNA damage repair deficiency. And (viii) Treatment with a natural compound dihydromethysticin (DHM) is capable of increasing MGMT level and reducing O6-MeG level in Cr(VI)- transformed cells. (viii) We generated a conditional and lung specific MGMT expression transgenic mouse model. Based on these findings from our preliminary studies and that from literature reports, our central hypothesis is that up-regulation of HMTases by chronic Cr(VI) exposure down-regulates the expression of MGMT leading to increased level of highly mutagenic DNA lesion O6-MeG and promoting Cr(VI) carcinogenesis. Three aims are proposed: Aim 1 will determine the mechanism by which chronic Cr(VI) exposure causes MGMT down- regulation. Aim 2 will determine the role of MGMT in C(VI)-induced lung tumorigenesis using a conditional and lung specific MGMT expression transgenic mouse model. And Aim 3 will determine the protective effect of the natural compound DHM treatment on Cr(VI)-induced cell transformation and tumorigenesis in mice.

项目概要/摘要 六价铬 [Cr(VI)] 暴露会对人体造成多种毒性作用。 Cr(VI)的主要关注点 毒性在于其致癌性，因为 Cr(VI) 是最受认可的环境和职业危害之一 导致人类肺癌和其他癌症的致癌物质。 Cr(VI) 的机理正在积极研究中。 致癌性仍然难以捉摸。先前的研究表明，六价铬暴露会导致基因毒性效应， 被认为在 Cr(VI) 致癌性中发挥重要作用。另一方面，研究还表明Cr(VI) 暴露会导致表观遗传学失调，例如 DNA 甲基化增加和组蛋白翻译后异常 修改。然而，表观遗传学失调如何影响 Cr(VI) 仍有待确定 致癌性以及 Cr(VI) 引起的表观遗传变化是否在其遗传毒性作用中发挥作用。我们的初步研究 结果表明：(i) 慢性 Cr(VI) 暴露会增加组蛋白 H3 抑制性甲基化标记 (H3K9me2) 的水平 和 H3K27me3) 及其相关的组蛋白甲基转移酶 (HMTase)（G9a、SUV39H1 和 EZH2）。 (ii) 向上- HMTase 的调节在 Cr(VI) 诱导的癌症干细胞 (CSC) 样特性和细胞恶性中起因果作用 转变。 (iii) 慢性 Cr(VI) 暴露会下调 O6-甲基鸟嘌呤 DNA 的表达 甲基转移酶（MGMT），DNA修复网络中的关键基因； MGMT 下调起着因果作用 Cr(VI) 诱导的细胞转化。 (iv) O6-甲基鸟嘌呤 (O6-MeG) 的水平，这是一种高度诱变 DNA Cr(VI) 转化细胞中的病变显着增加；但稳定表达 MGMT 大大降低了 Cr(VI) 暴露诱导的 O6-MeG。 (v) Cr(VI) 暴露也会显着降低 MGMT 水平，但 增加小鼠和人类肺组织中的 O6-MeG 水平。 (vi) 稳定地敲低 HMTase G9a 或 SUV39H1 显着增加 MGMT 水平，但降低 Cr(VI) 暴露细胞中的 O6-MeG 水平。 (vii) Cr(VI)- 转化细胞表现出受损的 DNA 损伤修复能力，但稳定表达 MGMT 显着 减少慢性 Cr(VI) 暴露引起的 DNA 损伤修复缺陷。 (viii) 用自然疗法治疗 化合物二氢迷幻素 (DHM) 能够提高 Cr(VI)- 中的 MGMT 水平并降低 O6-MeG 水平 转化的细胞。 (viii)我们生成了条件性和肺特异性MGMT表达转基因小鼠模型。 根据我们的初步研究结果和文献报道，我们的中心假设是 慢性 Cr(VI) 暴露上调 HMTase 会下调 MGMT 的表达，从而导致 高诱变 DNA 损伤 O6-MeG 水平增加并促进 Cr(VI) 致癌。三个目标是 建议：目标 1 将确定慢性 Cr(VI) 暴露导致 MGMT 下降的机制 规定。目标 2 将使用条件和条件确定 MGMT 在 C(VI) 诱导的肺肿瘤发生中的作用 肺特异性MGMT表达转基因小鼠模型。而目标3将决定该装置的保护效果 天然化合物 DHM 治疗对 Cr(VI) 诱导的小鼠细胞转化和肿瘤发生。