Liu J, Chen H, Miller D S, Saavedra J E, Keefer L K, Johnson D R, Klaassen C D, Waalkes M P
Laboratory of Comparative Carcinogenesis, National Cancer Institute at National Institute for Environmental Health Sciences, Research Triangle Park, North Carolina, USA.
Mol Pharmacol. 2001 Aug;60(2):302-9. doi: 10.1124/mol.60.2.302.
Recent work shows that long-term exposure to low levels of arsenite induces malignant transformation in a rat liver epithelial cell line. Importantly, these chronic arsenic-exposed (CAsE) cells also develop self-tolerance to acute arsenic exposure. Tolerance is accompanied by reduced cellular arsenic accumulation, suggesting a mechanistic basis for reduced arsenic sensitivity. The present study examined the role of xenobiotic export pumps in acquired arsenic tolerance. Microarray analysis of CAsE cells showed increased expression of the genes encoding for glutathione S-transferase Pi (GST-Pi), multidrug resistance-associated protein genes (MRP1/MRP2, which encode for the efflux transporter Mrp1/Mrp2) and the multidrug resistance gene (MDR1, which encodes for the efflux transporter P-glycoprotein). These findings were confirmed at the transcription level by reverse transcription-polymerase chain reaction and at the translation level by Western-blot analysis. Acquired arsenic tolerance was abolished when cells were exposed to ethacrynic acid (an inhibitor of GST-Pi), buthionine sulfoximine (a glutathione synthesis inhibitor), MK571 (a specific inhibitor for Mrps), and PSC833 (a specific inhibitor for P-glycoprotein) in dose-dependent fashions. MK571, PSC833, and buthionine sulfoximine markedly increased cellular arsenic accumulation. Consistent with a role for multidrug resistance efflux pumps in arsenic resistance, CAsE cells were found to be cross-resistant to cytotoxicity of several anticancer drugs, such as vinblastine, doxorubicin, actinomycin-D, and cisplatin, that are also substrates for Mrps and P-glycoprotein. Thus, acquired tolerance to arsenic is associated with increased expression GST-Pi, Mrp1/Mrp2 and P-glycoprotein, which function together to reduce cellular arsenic accumulation.
近期研究表明，长期暴露于低水平亚砷酸盐会诱导大鼠肝上皮细胞系发生恶性转化。重要的是，这些慢性砷暴露（CAsE）细胞对急性砷暴露也产生了自我耐受性。耐受性伴随着细胞内砷积累的减少，这表明砷敏感性降低存在机制基础。本研究探讨了外源性转运泵在获得性砷耐受性中的作用。对CAsE细胞进行微阵列分析显示，编码谷胱甘肽S-转移酶Pi（GST-Pi）、多药耐药相关蛋白基因（MRP1/MRP2，编码外排转运蛋白Mrp1/Mrp2）和多药耐药基因（MDR1，编码外排转运蛋白P-糖蛋白）的基因表达增加。这些发现通过逆转录-聚合酶链反应在转录水平以及通过蛋白质印迹分析在翻译水平得到了证实。当细胞以剂量依赖性方式暴露于依他尼酸（GST-Pi抑制剂）、丁硫氨酸亚砜胺（谷胱甘肽合成抑制剂）、MK571（Mrps特异性抑制剂）和PSC833（P-糖蛋白特异性抑制剂）时，获得性砷耐受性被消除。MK571、PSC833和丁硫氨酸亚砜胺显著增加了细胞内砷的积累。与多药耐药外排泵在砷抗性中的作用一致，发现CAsE细胞对几种抗癌药物（如长春碱、阿霉素、放线菌素-D和顺铂）的细胞毒性具有交叉抗性，这些抗癌药物也是Mrps和P-糖蛋白的底物。因此，对砷的获得性耐受性与GST-Pi、Mrp1/Mrp2和P-糖蛋白表达增加有关，它们共同作用以减少细胞内砷的积累。
