The protective role of Nrf2 against arsenic-induced toxicity and carcinogenicity

描述(由申请人提供)：转录因子Nrf2通过上调携带抗氧化剂反应元件(ARE)的基因，编码抗氧化酶、解毒酶、异物转运体和应激反应蛋白，成为细胞保护机制的主要调节因子。最近，越来越多的证据表明Nrf2在癌症中具有双重功能。(I)在正常细胞中，当Nrf2-Keap1轴完整且Nrf2基础水平较低时，化学预防化合物瞬时激活Nrf2可提供对环境毒素和致癌物的保护。(Ii)在某些癌细胞系中，Nrf2的结构性激活为癌细胞的生存创造了有利的环境。此外，Nrf2有助于化疗耐药，抑制Nrf2途径可提高癌症治疗的疗效。砷(As)是一种人类致癌物，会导致皮肤、肺和膀胱癌。世界各地的大量人口通过受污染的饮用水接触到砷，这对人类健康构成了重大挑战。然而，仍然缺乏足够的啮齿动物模型来研究砷的致癌作用。NIH ES015010的这一竞争性更新利用了砷在自噬中以前未被认识到的作用，导致Nrf2的长期激活，这是在上一次资助期间发现的。我们假设，砷介导的致癌作用与其解除自噬途径调控的能力有关。我们认为，经典的Nrf2诱导剂可以减轻这种影响，因此，可以作为化学预防药物来对抗砷的损害效应。目的1(体外)：通过解除对自噬的调控(延长Nrf2的激活)，阐明砷诱导Nrf2的新机制。目的2(体外)：利用可移植的同基因小鼠肺癌模型，确定Nrf2在砷介导的自噬小体形成和致癌性中的作用。目标3(体内)：验证这项工作的生物学和药理学相关性。通过这一提议，我们将(I)获得关于砷如何解除对自噬的调控的新的机制洞察力，(Ii)证实放松对自噬的调控与砷的致瘤性之间的联系，(Iii)为砷的致癌性研究提供新的生物标志物和敏感的动物模型，以及(Iv)展示使用经典的Nrf2激活剂靶向Nrf2途径以对抗砷诱导的毒性和致癌性的潜在翻译影响。此外，开发的同基因小鼠肺癌模型将对研究其他致癌物质的科学界具有无价的价值。

DESCRIPTION (provided by applicant): The transcription factor, Nrf2, has emerged as the master regulator of a cellular protective mechanism by upregulating antioxidant response element (ARE)- bearing genes encoding antioxidant enzymes, detoxifying enzymes, xenobiotic transporters, and stress response proteins. Very recently, mounting evidence points to the dual function of Nrf2 in cancer. (i) In normal cells when the Nrf2- Keap1 axis is intact and basal level of Nrf2 are low, transient activation of Nrf2 by chemopreventive compounds confers protection against environmental toxins and carcinogens. (ii) In certain cancer cell lines, constitutive activation of Nrf2 creates an environment conducive for cancer cell survival. Moreover, Nrf2 contributes to chemoresistance and inhibition of the Nrf2 pathway enhances the efficacy of cancer treatments. Arsenic (As) is a human carcinogen, which causes tumors in the skin, lung and bladder. Large populations around the world are exposed to arsenic through contaminated drinking water, which imposes a major challenge to human health. However, a sufficient rodent model to study arsenic-carcinogenicity is still lacking. This competing renewal of NIH ES015010 takes advantage of a previously unrecognized role of arsenic in autophagy leading to prolonged activation of Nrf2, which was uncovered during the last funding period. We hypothesize that arsenic-mediated carcinogenicity is associated with its ability to deregulate the autophagic pathway. We believe that canonical Nrf2 inducers can alleviate this effect and thus, can be used as chemopreventive agents to counteract the damaging effects of arsenic. The following three aims are proposed: Aim 1 (in vitro): Elucidate a novel mechanism of Nrf2 induction by arsenic through deregulation of autophagy (prolonged activation of Nrf2). Aim 2 (ex vivo): Determine the role of Nrf2 in arsenic-mediated autophagosome formation and carcinogenicity using a transplantable syngeneic mouse lung cancer model. Aim 3 (in vivo): Validate the biological and pharmacological relevancy of this work. From this proposal we will (i) gain novel mechanistic insight of how arsenic deregulates autophagy, (ii) confirm the association between deregulation of autophagy and tumorigenicity of arsenic, (iii) provide new biomarkers and a sensitive animal model for arsenic carcinogenicity studies and (iv) demonstrate the potential translational impact of targeting the Nrf2 pathway using canonical Nrf2 activators to combat arsenic-induced toxicity and carcinogenicity. In addition, the syngeneic mouse lung cancer model developed will be invaluable for scientific communities studying other carcinogens.