Stress response, p97, and Nrf2 in arsenic-mediated toxicity

7.项目总结/摘要 据估计，砷及其砷衍生物对全世界2亿多人造成影响。 砷的暴露来自许多来源，如受污染的饮用水，土壤或作为 空气污染物各种流行病学研究已经将慢性砷暴露与一些 疾病状态，包括肺癌、膀胱癌或皮肤癌;代谢疾病，如糖尿病; 心血管和其他血管疾病;以及皮肤问题，如"黑脚病"。除了有 流行病学研究已经做了大量的努力来了解病理机制，但 迄今为止，这些方面的许多沿着问题仍然模糊不清。了解砷的部分问题是 毒性是砷改变的细胞系统的绝对数量。例如，砷导致氧化 应激、蛋白质质量控制的妥协、热休克反应和细胞周期改变等等。 我们实验室的工作已经确定了砷对细胞影响的关键环节。长期治疗， 亚砷酸盐（砷的氧化物之一）的水平导致自噬的妥协，一个主要的蛋白质质量 控制路径这种突破发生在自噬体/溶酶体融合的步骤中，导致细胞内的 自噬体和高水平的自噬特异性因子p62。关键的是，p62包含了一种认识， Keap1的元件，其是Cul3-Keap1-Rbx1 E3泛素连接酶复合物中的底物识别因子。 这种E3复合物通常维持低水平的氧化应激反应转录因子Nrf2。在 过量p62、Keap 1的存在被占据，允许Nrf2的组成型高水平表达， 随后激活抗氧化反应元件调节基因。这个高级表达式赋予一个 对细胞的生长有利，并可能导致疾病，如癌症。尽管有这些机械性的飞跃， 亚砷酸盐干扰自噬的机制仍然未知。目前研究中 程序中，我们提出了砷干扰AAA+蛋白质质量控制机器的假设， 第97页。这提供了砷和自噬以及其他蛋白质质量控制之间的关键联系 机制等为了探究这种砷介导的破坏的详细机制基础，我们将使用 一系列详细的机制酶学研究，加上细胞生物化学和体内研究。 这些努力将得到我们组建的多PI团队的极大帮助。

7. Project Summary/Abstract Arsenic and its arsenical derivatives are estimated to effect greater then 200 million people worldwide. Exposure to arsenicals comes from a number of sources such as contaminated drinking water, soil or as an airborne pollutant. Various epidemiological studies have linked chronic arsenic exposure to a number of disease states including cancer of the lungs, bladder, or skin; metabolic diseases such as diabetes; cardiovascular and other vascular diseases; and skin problems such as 'black foot disease'. In addition to the epidemiological studies there has been a great deal of effort to understand the mechanisms of pathology, but to date many questions along these lines remain obfuscated. Part of the problem with understanding arsenic toxicity is the sheer number of cellular systems that arsenic alters. For instance arsenic leads to oxidative stress, compromise of protein quality control, heat-shock response, and cell-cycle alterations to name a few. Work from our lab has identified a crucial link in the effects of arsenic on cells. Chronic treatment with low levels of arsenite (one of the oxides of arsenic) leads to a compromise of autophagy, a major protein quality control pathway. This breach comes at the step of autophagosome/lysosome fusion, leading to a build-up of autophagosomes and high levels of the autophagy specificity factor, p62. Critically, p62 contains a recognition element for Keap1, which is a substrate recognition factor in the Cul3-Keap1-Rbx1 E3 ubiquitin ligase complex. This E3 complex normally maintains a low level of the oxidative stress responsive transcription factor, Nrf2. In the presence of excess p62, Keap1 is occupied, allowing for constitutive, high level expression of Nrf2 and subsequent activation of antioxidant response element regulated genes. This high-level expression confers a growth advantage on the cells and can lead to diseases such as cancer. Despite these mechanistic leaps, it remains the mechanism by which arsenite interferes with autophagy is unknown. In the present research program we propose the hypothesis that arsenicals interfere with the AAA+ protein quality control machine, p97. This provides a critical link between arsenic and autophagy as well as other protein quality control mechanisms. To probe the detailed mechanistic underpinnings of this arsenic-mediated breach we will use an array of detailed mechanistic enzymology studies, coupled with cellular biochemistry, and in vivo studies. These efforts will be greatly aided by the multi-PI team we have assembled.