Activation of Nrf2 in defense against cadmium-induced oxidative stress
Activation of Nrf2 in defense against cadmium-induced oxidative stress
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DOI：
10.1021/tx800019a
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发表时间：
2008-07-01
影响因子：
4.1
通讯作者：
Ma, Qiang
中科院分区：
文献类型：
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作者：
He, Xiaoqing;Chen, Michael G.;Ma, Qiang
接触镉(Cd)会引起一系列不良反应，包括氧化损伤和癌症。CD的分子靶标在很大程度上仍未确定。在这里，我们分析了转录因子Nrf2在Cd诱导的氧化应激保护中的功能和信号转导。野生型(NRF2(+/+))小鼠胚胎成纤维细胞(MEF)产生低水平的活性氧(ROS)，而镉处理显著增加ROS的产生。另一方面，Nrf2基因敲除(Nrf2(-/-))的MEF细胞在基础条件下表现出较高的ROS水平，而Cd在低浓度时显著增加ROS的产生，从而增加了对Cd诱导的细胞死亡的敏感性。Cd可诱导WT MEF细胞基础和诱导性细胞保护酶NQO1和HO1的表达，但对Nrf2(-/-)MEF细胞无诱导作用。在小鼠Hepa1c1c7细胞中，当Cd驱动的ARE依赖的报告表达和Cd激活的Nrf2与内源性Ares结合时，所需的基因的诱导需要抗氧化反应元件(ARE)。CD对Nrf2的激活涉及到Nrf2蛋白的稳定、细胞质中Nrf2/Keap1复合体的形成、复合体移位到细胞核内，以及随后复合体的破坏。最后，发现Nrf2在细胞质中泛素化，而在细胞核中去泛素化。本研究提供了一个机制转录模型，在该模型中，Cd通过金属激活的信号通路激活Nrf2，该信号通路涉及泛素化/去泛素化和Nrf2与Keap1的复合体形成/解离之间的动态相互作用。
Exposure to cadmium (Cd) elicits a range of adverse responses including oxidative damage and cancer. The molecular targets of Cd remain largely unidentified. Here, we analyzed the function and signal transduction of transcription factor Nrf2 in protection against Cd-induced oxidative stress. Wild-type (Nrf2(+/+)) mouse embryonic fibroblasts (MEF) produced reactive oxygen species (ROS) at a low level, whereas treatment with Cd significantly increased the ROS production. On the other hand, Nrf2 knockout (Nrf2(-/-)) MEF cells exhibited an elevated level of ROS under a basal condition, and Cd dramatically increased the ROS production at concentrations as low as 2 mu M, resulting in increased sensitivity to Cd-induced cell death. Cd induced the basal and inducible expression of cytoprotective enzymes NQO1 and HO1 in WT MEF cells, but induction was lost in Nrf2(-/-) MEF cells. Induction of the genes required antioxidant response elements (ARE) as Cd drove ARE-dependent reporter expression and Cd-activated Nrf2 bound to endogenous AREs in mouse hepa1c1c7 cells. Activation of Nrf2 by Cd involved stabilization of the Nrf2 protein, increased formation of Nrf2/Keap1 complex in the cytoplasm, translocation of the complex into the nucleus, and subsequently disruption of the complex. Lastly, Nrf2 was found ubiquitinated in the cytoplasm but deubiquitinated in the nucleus. The study provided a mechanistic transcriptional model in which Cd activates Nrf2 through a metal-activated signaling pathway involving a dynamic interplay between ubiquitination/deubiquitination and complex formation/dissociation of Nrf2 and Keap1.