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（由适用提供）：长期暴露于无机砷是一个全球公共卫生问题，与增加肺，皮肤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。砷的确切致癌机制尚未完全阐明多年的研究以及与其暴露相关的健康影响的严重性。我们先前已经报道说，与环境相关的低剂量砷块自噬，这导致了NRF2的长时间激活，NRF2是自适应抗氧化剂和促寿命反应的主要编排者。具体而言，砷诱导的NRF2激活不是通过规范，活性氧（ROS）传感机理而是通过自噬依赖性的非规范机制而发生的。自噬是一种散装降解途径，可降解受损的细胞器和蛋白质聚集体。自噬的阻塞会导致线粒体有缺陷和ROS产生过量的积累，从而导致DNA突变。 NRF2激活以其针对ROS应激的细胞保护而闻名，这可以使砷暴露的细胞能够生存和维持驱动恶性转化的基因突变。因此，我们假设由砷诱导的自噬阻滞引起的NRF2的延长激活对于砷介导的恶性转化至关重要。我们的假设得到了最近的几本出版物的支持，表明延长NRF2激活在自噬缺陷小鼠中的致瘤作用被同时发生的NRF2敲除。此外，较早的研究发现，许多癌细胞中NRF2的高构水平高，有利于它们的增殖和化学耐药性，这种效果称为NRF2的“黑暗侧”。我们已经产生了大量的数据，表明砷通过抑制自噬体 - 散肌体融合步骤来自噬。三个小网介导自噬体外膜上的融合：STX17通过SNAP29与位于溶酶体膜上的VAMP8相互作用。我们认为，这些蛋白质中任何一种的遗传消融都应防止自噬体与溶酶体融合，并且这种消融的作用应模仿砷介导的p62依赖性NRF2 UP调节的影响。为了更好地理解砷致癌性，我们提出：目标1：阐明砷可以阻止自噬体 - 溶酶体融合的详细分子机制。 AIM 2：确定自噬失调和延长NRF2激活是否对于恶性转化至关重要。 AIM 3：测试细胞系的致瘤性，并将其与长时间的NRF2激活相关。影响：对导致砷诱导的癌变延长NRF2激活的分子事件的详细和彻底理解将证明在预防和治疗策略的产生中以及对生物标志物的识别，对处于风险的人群中非常有价值。