The Synergistic effect and Mechanism of Arsenic on Chromium (VI) Carcinogenesis

描述(申请人提供)：六价铬(六价铬)和砷都是主要的环境问题，因为它们是已知的人类肺癌致癌物质，暴露在环境中非常普遍。同时接触铬(VI)和砷的人患肺癌的风险可能更大。这项研究侧重于金属致癌的机制，并探讨了砷通过干扰DNA双链断裂修复而协同增强铬(VI)致癌作用的假说。我们的数据显示，砷协同增加了铬(VI)诱导的人肺细胞染色体损伤和DNA双链断裂。砷抑制这种DNA损伤的修复和Mre11的表达，Mre11是一种在双链断裂修复中发挥关键作用的蛋白质。我们的研究还表明，Mre11缺乏会导致铬(VI)诱导的肿瘤转化。我们将通过三个相互关联的具体目标来验证我们的假设：1)表征砷对铬(VI)诱导的染色体畸变、DNA双链断裂及其修复的影响；2)确定砷如何抑制DNA双链断裂修复；3)确定砷诱导的MRN的调节是否有助于铬(VI)和砷诱导的肿瘤转化。这三个目标将结合现有的和最先进的毒理学、细胞遗传学和分子生物学技术，并采用下列方法：1)通过细胞遗传学分析和彗星试验分别检测铬(VI)诱导的染色体损伤和DNA双链断裂以及γ-H2A.X焦点的产生；2)基因表达、免疫定位、蛋白质表达研究和基因沉默将确定砷的协同作用机制；以及3)DNA双链和断裂修复将如何保护细胞免受砷和铬(VI)诱导的肿瘤转化的影响。这是唯一一项调查铬(VI)和砷联合暴露致癌作用的研究，这是 学习，因为人们在大多数情况下都同时接触到这些金属。我们的结果将导致关于砷对DNA双链断裂修复机制影响的详细信息的首次报道，以及首次发现以砷为靶标的DNA双链断裂修复蛋白。这项研究具有重要意义，因为它将提供：1)了解铬(VI)和砷的致癌机制；2)更好地评估接触这些金属的风险；以及3)进一步研究砷、铬(VI)、其他金属和一般肺癌的机制。 公共卫生相关性：六价铬(六价铬)和砷都是主要的环境危害，与人类肺癌有关。尽管人们在大多数情况下都同时接触到这些金属，但人们对共同暴露的潜在影响知之甚少。这项研究将探讨砷是如何破坏DNA损伤修复的，从而导致铬(VI)诱导的肺癌的增强。

DESCRIPTION (provided by applicant): Hexavalent chromium (Cr(VI)) and arsenic are both major environmental concern, because they are known human lung carcinogens and exposure is widespread. It is likely that humans with co- exposure to Cr(VI) and arsenic could have even greater risks of lung cancers. The proposed research focuses on mechanisms of metal-induced carcinogenesis and investigates the hypothesis that arsenic synergistically increases Cr(VI) carcinogenicity as a consequence of interference with the repair of DNA double strand breaks. Our data show that arsenic synergistically increases Cr(VI)-induced chromosome damage and DNA double strand breaks in human lung cells. Arsenic inhibits the repair of this DNA damage and the expression of Mre11, a protein which plays an essential role in the repair of double strand breaks. Our studies also show that Mre11 deficiency leads to Cr(VI)-induced neoplastic transformation. We will test our hypothesis through three interrelated specific aims: 1) characterize the effect of arsenic on Cr(VI)-induced chromosome aberration, DNA double strand breaks and their repair; 2) determine how arsenic inhibits DNA double strand break repair; 3) determine if arsenic-induced modulation of MRN contribute to Cr(VI) and arsenic-induced neoplastic transformation. These three aims will use a combination of established and state-of-the-art toxicological, cytogenetic, and molecular biological techniques and with the following approach: 1) Cr(VI)-induced chromosome damage and DNA double strand breaks will be measured by cytogenetic assay and comet assay as well as the production of gamma-H2A.X foci, respectively; 2) Gene expression, immune-localization, protein expression studies and gene silencing will determine the mechanisms of arsenic synergistic effect; and 3) DNA transfection and transformation assays will determine how double strand break repair protects cells from arsenic and Cr(VI)-induced neoplastic transformation. This is the only study investigating the carcinogenicity of co-exposure of Cr(VI) and arsenic, which is a critical area of study as people are exposed to these metals simultaneously under most conditions. Our results will lead to the first reports of detailed information on the effect of arsenic on DNA double stran break repair machinery and the first identification of DNA double strand break repair proteins targeted by arsenic. This research is significant because it will provide: 1) An understanding of Cr(VI) and arsenic's carcinogenic mechanism; 2) Essential information to better assess the risk of exposure to these metals; and 3) A mechanistic approach for further study of arsenic, Cr(VI), other metals, and lung cancer in general. PUBLIC HEALTH RELEVANCE: Both Hexavalent chromium (Cr(VI)) and arsenic are major environmental hazards and are associated with human lung cancer. Despite that people are exposed to these metals simultaneously under most conditions, little is known about the potential co- exposure impact. This research will investigate how arsenic disrupts DNA damage repair which results in enhancement of Cr(VI)-induced lung cancer.