Chen Jun, Shaikh Zahir A
Department of Biomedical and Pharmaceutical Science, and Center for Molecular Toxicology, College of Pharmacy, University of Rhode Island, Kingston, RI 02881, USA.
Toxicol Appl Pharmacol. 2009 Nov 15;241(1):81-9. doi: 10.1016/j.taap.2009.07.038. Epub 2009 Aug 12.
Kidney is the primary target organ in chronic cadmium (Cd) toxicity, and oxidative stress plays an important role in this process. The nuclear transcription factor Nrf2 binds to antioxidant response elements (AREs) and regulates genes involved in protecting cells from oxidative damage. Whether kidney cells respond to Cd by activating Nrf2 is unknown. This study was designed to examine the Cd-induced activation of Nrf2 transcriptional activity in a stable rat kidney cell line, NRK-52E, and to investigate the protection this might offer against apoptosis. The cells were treated with 5-20 microM CdCl(2) for 5 h, followed by a recovery period of up to 24 h. A concentration-dependent increase (up to 2.9-fold) in the level of reactive oxygen species was noted upon termination of 5-h Cd treatment. The Nrf2-ARE binding activity also increased and peaked (6.1-fold) at 10 microM Cd concentration. Time-course study revealed that the binding activity increased at 1 h of Cd treatment and peaked 2 h post Cd treatment. Apoptosis was detected 6 h post treatment with Cd and a concentration- and time-dependent increase in the apoptotic cell population occurred during the next 18 h. Over-expression of Nrf2 by transient transfection conferred resistance against Cd-induced apoptosis. Conversely, suppression of Nrf2 expression by specific siRNA resulted in greater sensitivity of the cells to Cd by decreasing the levels of two antioxidant enzymes, hemeoxygenase-1 and glutamate-cysteine ligase. Taken together, these results suggest that in kidney cells the activation of Nrf2 is an adaptive intracellular response to Cd-induced oxidative stress, and that Nrf2 is protective against Cd-induced apoptosis.
肾脏是慢性镉（Cd）毒性作用的主要靶器官，氧化应激在此过程中起重要作用。核转录因子Nrf2与抗氧化反应元件（AREs）结合，并调节参与保护细胞免受氧化损伤的基因。肾细胞是否通过激活Nrf2来响应镉尚不清楚。本研究旨在检测稳定的大鼠肾细胞系NRK-52E中镉诱导的Nrf2转录活性激活情况，并研究其对细胞凋亡的保护作用。细胞用5-20 microM CdCl₂处理5小时，随后恢复期长达24小时。在5小时镉处理结束时，观察到活性氧水平呈浓度依赖性增加（高达2.9倍）。Nrf2-ARE结合活性也增加，并在10 microM镉浓度时达到峰值（6.1倍）。时间进程研究表明，结合活性在镉处理1小时时增加，并在镉处理后2小时达到峰值。镉处理6小时后检测到细胞凋亡，在接下来的18小时内，凋亡细胞群体呈浓度和时间依赖性增加。通过瞬时转染过表达Nrf2可赋予细胞对镉诱导凋亡的抗性。相反，通过特异性siRNA抑制Nrf2表达会导致细胞对镉的敏感性增加，这是通过降低两种抗氧化酶血红素加氧酶-1和谷氨酸-半胱氨酸连接酶的水平实现的。综上所述，这些结果表明，在肾细胞中，Nrf2的激活是对镉诱导的氧化应激的一种适应性细胞内反应，并且Nrf2对镉诱导的细胞凋亡具有保护作用。
