Xie Jianxun, Shaikh Zahir A
Department of Biomedical and Pharmaceutical Sciences and Center for Molecular Toxicology, College of Pharmacy, University of Rhode Island, Kingston, RI 02881, USA.
Toxicology. 2006 Jul 5;224(1-2):56-65. doi: 10.1016/j.tox.2006.04.026. Epub 2006 Apr 27.
Cadmium (Cd) has been reported to cause cell cycle arrest in various cell types by p53-dependent and -independent mechanisms. This study was designed to investigate cell cycle progression in kidney cells that are the target of chronic Cd toxicity. Rat renal proximal tubular epithelial cells, NRK-52E, were treated with up to 20 microM CdCl2 in DMEM containing 10% calf serum for up to 24 h. Flow cytometric analysis revealed time- and concentration-dependent increases in cells in G2/M phase of the cell cycle. As compared to the control cells, the cells exposed to 20 microM Cd showed a doubling of the number of cells in this phase after 24 h. The cell cycle arrest was associated with a decrease in protein levels of both cyclins A and B. Further investigation into the mechanism revealed that Cd treatment led to down-modulation of cyclin-dependent kinases, Cdk1 and Cdk2, apparently by elevating the expression of cyclin kinase inhibitors, KIP1/p27 and WAF1/p21. Furthermore, the wild-type p53 DNA-binding activity was up-regulated. Based on these observations, it appears that Cd causes G2/M phase arrest in NRK-52E cells via elevation of p53 activity, increasing the expression of cyclin kinase inhibitors p27 and p21, and decreasing the expression of cyclin-dependent kinases Cdk1 and 2, and of cyclins A and B.
据报道，镉（Cd）可通过p53依赖性和非依赖性机制导致多种细胞类型的细胞周期停滞。本研究旨在调查作为慢性镉毒性靶标的肾细胞中的细胞周期进程。将大鼠肾近端小管上皮细胞NRK-52E在含有10%小牛血清的DMEM中用高达20微摩尔的CdCl2处理长达24小时。流式细胞术分析显示，细胞周期G2/M期的细胞数量呈时间和浓度依赖性增加。与对照细胞相比，暴露于20微摩尔镉的细胞在24小时后此期细胞数量增加了一倍。细胞周期停滞与细胞周期蛋白A和B的蛋白质水平降低有关。对机制的进一步研究表明，镉处理导致细胞周期蛋白依赖性激酶Cdk1和Cdk2的下调，显然是通过提高细胞周期蛋白激酶抑制剂KIP1/p27和WAF1/p21的表达来实现的。此外，野生型p53的DNA结合活性上调。基于这些观察结果，镉似乎通过提高p53活性、增加细胞周期蛋白激酶抑制剂p27和p21的表达以及降低细胞周期蛋白依赖性激酶Cdk1和2以及细胞周期蛋白A和B的表达，导致NRK-52E细胞的G2/M期停滞。
