Nrf2, autophagy, and arsenic carcinogenesis

Nrf2、自噬和砷致癌

• 批准号: 9115334
• 负责人: Donna D Zhang
• 金额: $ 34.01万
• 依托单位: UNIVERSITY OF ARIZONA
• 依托单位国家: 美国
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-07-01 至 2021-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9115334
• 关键词: Ablation; Affinity; Antioxidants; Arsenic; Autophagocytosis; Autophagosome; Binding; Biochemical; Biological Markers; Bladder; CRISPR/Cas technology; Carcinogenicity Tests; Cell Line; Cells; Chimeric Proteins; Chronic; DNA Sequence Alteration; Data; Degradation Pathway; Disease; Dose; Epithelial Cells; Event; Exposure to; Fluorescence Resonance Energy Transfer; Food; Gene Deletion; Gene Mutation; Generations; Genetic; Genomics; Health; Human; Immunoprecipitation; In Vitro; Individual; Kinetics; Knock-out; Lysosomes; Malignant - descriptor; Malignant Neoplasms; Malignant neoplasm of lung; Mediating; Membrane; Mitochondria; Molecular; Mus; Nude Mice; Oncogenes; Organelles; Populations at Risk; Preventive; Production; Proteins; Proteomics; Public Health; Publications; Reactive Oxygen Species; Reporting; Research; Resistance; Risk; SNAP receptor; Severities; Side; Site; Skin; Stress; Technology; Testing; Therapeutic; Transformed Cell Line; Up-Regulation; Xenograft Model; arsenic-induced carcinogenesis; biomarker identification; cancer cell; carcinogenesis; carcinogenicity; cell transformation; drinking water; in vivo; lysosome membrane; metabolomics; mortality; prevent; protein aggregate; public health relevance; response; subcutaneous; transcriptomics; tumor growth; tumorigenic

 DESCRIPTION (provided by applicant): Chronic exposure to inorganic arsenic is a worldwide public health problem that has been associated to increased risks of developing cancers of the lung, skin, and bladder. Among these malignancies, arsenic- induced lung cancer presents with the highest mortality rate. The precise carcinogenic mechanism of arsenic has not yet been fully elucidated despite many years of research and the severity of the health effects associated to its exposure. We have previously reported that environmentally relevant, low doses of arsenic block autophagy, which resulted in prolonged activation of Nrf2, the main orchestrator of the adaptive antioxidant and pro-survival response. Specifically, arsenic-induced Nrf2 activation does not occur through the canonical, reactive oxygen species (ROS)-sensing mechanism but through the autophagy-dependent, non- canonical mechanism. Autophagy is a bulk degradation pathway that degrades damaged organelles and protein aggregates. Autophagy blockage can result in accumulation of defective mitochondria and excessive ROS production, which cause DNA mutations. Nrf2 activation is well known for its cellular protection against ROS stress, which can enable arsenic-exposed cells to survive and sustain gene mutations that drive malignant transformation. Therefore, we hypothesize that prolonged activation of Nrf2 resulting from arsenic-induced autophagy blockage is essential for the arsenic-mediated malignant transformation. Our hypothesis is supported by several recent publications demonstrating that the tumorigenic effect of prolonged Nrf2 activation in autophagy-deficient mice was abolished by concurrent Nrf2 knockout. Moreover, earlier studies have found high constitutive levels of Nrf2 in many cancer cells, which favor their proliferation and chemo resistance, an effect known as the "dark side" of Nrf2. We have generated substantial amounts of data indicating that arsenic blocks autophagy by inhibiting the autophagosome-lysosome fusion step. Three SNAREs mediate the fusion: Stx17 on the outer membrane of the autophagosome interacts through SNAP29 with VAMP8 that resides on the lysosome membrane. We believe that genetic ablation of any of these proteins should prevent the fusion of the autophagosome with the lysosome, and the effects of this ablation should mimic the effects of arsenic- mediated p62-dependent Nrf2 up regulation. To better understand arsenic carcinogenicity, we propose: Aim 1: Elucidate the detailed molecular mechanism by which arsenic blocks autophagosome- lysosome fusion. Aim 2: Determine if autophagy dysregulation and prolonged Nrf2 activation are essential for malignant transformation. Aim 3: Test the tumorigenicity of cell lines and correlate it with prolonged Nrf2 activation. Impact: A detailed and thorough understanding of the molecular events leading to the prolonged Nrf2 activation in arsenic-induced carcinogenesis will prove extremely valuable in the generation of preventive and therapeutic strategies, as well as in the identification of biomarkers, for the populations at risk.

 描述(由申请人提供)：长期接触无机砷是一个世界性的公共卫生问题，与肺癌、皮肤癌和膀胱癌的风险增加有关。在这些恶性肿瘤中，砷引起的肺癌的死亡率最高。尽管多年来的研究和接触砷对健康的严重影响，但砷的确切致癌机制尚未完全阐明。我们之前已经报道过，与环境相关的低剂量砷阻止自噬，导致Nrf2的长时间激活，Nrf2是适应性抗氧化剂和有利于生存的反应的主要协调者。具体地说，砷诱导的Nrf2激活不是通过典型的活性氧物种(ROS)感知机制发生的，而是通过自噬依赖的非典型机制发生的。自噬是一种大量降解受损细胞器和蛋白质聚集体的途径。自噬阻断会导致有缺陷的线粒体积累和过量的ROS产生，从而导致DNA突变。众所周知，NRF2的激活对ROS应激具有细胞保护作用，ROS应激可以使砷暴露的细胞存活并维持驱动恶性转化的基因突变。因此，我们推测，由砷诱导的自噬阻断导致的Nrf2的长期激活是砷介导的恶性转化所必需的。我们的假设得到了最近发表的几篇文章的支持，这些文章表明，在自噬缺陷小鼠中，延长Nrf2激活的致瘤效应被同时存在的Nrf2基因敲除。此外，早期的研究发现，在许多癌细胞中，Nrf2的组成水平很高，这有利于它们的增殖和化疗耐药，这一效应被称为Nrf2的“黑暗面”。我们已经产生了大量的数据表明，砷通过抑制自噬小体-溶酶体融合步骤来阻止自噬。自噬体膜上的Stx17通过SNAP29与位于溶酶体膜上的VAMP8相互作用。我们认为，这些蛋白中的任何一种的基因消融都应该阻止自噬小体与溶酶体的融合，这种消融的效果应该模仿砷介导的p62依赖的Nrf2上调调控的效果。为了更好地了解砷的致癌性，我们提出：目的1：阐明砷阻止自噬小体-溶酶体融合的详细分子机制。目的2：确定自噬功能失调和Nrf2激活时间延长是否是恶性转化所必需的。目的3：检测细胞系的致瘤性，并将其与Nrf2的激活时间相关联。影响：详细和彻底地了解在砷诱导的致癌过程中导致Nrf2长时间激活的分子事件将被证明在制定预防和治疗策略以及识别高危人群的生物标记物方面非常有价值。