Rappa G, Lorico A, Flavell R A, Sartorelli A C
Department of Pharmacology, Cancer Center, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
Cancer Res. 1997 Dec 1;57(23):5232-7.
The MRP (multidrug resistance protein) gene, a member of the ubiquitous superfamily of ATP-binding cassette transporters, is associated with the multidrug resistance of mammalian cells to natural product anticancer agents. We have previously shown that abrogation of MRP expression by gene targeting leads to hypersensitivity to several drugs. In two independently produced MRP double knockout clones, the baseline export of glutathione (GSH) was one-half that of wild-type embryonic stem (ES) cells. The export of GSH from wild-type ES cells, but not from the MRP double knockout clones, increased in the presence of etoposide (VP-16) and sodium arsenite, accompanied by equivalent decreases in intracellular levels of GSH. In the two MRP double knockout clones, the intracellular steady-state concentration of etoposide was twofold greater than that in wild-type cells. Depletion of intracellular GSH by D,L-buthionine sulfoximine increased the intracellular accumulation of radiolabeled etoposide in parental ES cells up to the level present in the two MRP knockout clones but did not change etoposide levels in the MRP knockout clones. These observations provide evidence that: (a) MRP exports GSH physiologically, presumably in association with an endogenous compound(s); (b) baseline MRP expression protects cells from the toxic effects of xenobiotics by effluxing the xenobiotics and GSH from the intracellular compartment into the extracellular medium by a co-transport mechanism; and (c) disruption of the gene encoding MRP abrogates the cotransport of xenobiotics and GSH.
多药耐药蛋白（MRP）基因是ATP结合盒转运体普遍存在的超家族成员之一，与哺乳动物细胞对天然产物抗癌药物的多药耐药性相关。我们之前已经表明，通过基因靶向消除MRP表达会导致对几种药物的超敏反应。在两个独立产生的MRP双敲除克隆中，谷胱甘肽（GSH）的基线输出量是野生型胚胎干细胞（ES）的一半。在存在依托泊苷（VP - 16）和亚砷酸钠的情况下，野生型ES细胞中GSH的输出增加，但MRP双敲除克隆中没有增加，同时细胞内GSH水平相应降低。在这两个MRP双敲除克隆中，依托泊苷的细胞内稳态浓度比野生型细胞高两倍。用D，L - 丁硫氨酸亚砜亚胺耗尽细胞内GSH会使亲代ES细胞中放射性标记的依托泊苷的细胞内积累增加到两个MRP敲除克隆中的水平，但不会改变MRP敲除克隆中依托泊苷的水平。这些观察结果提供了以下证据：（a）MRP在生理上输出GSH，推测与一种内源性化合物相关；（b）基线MRP表达通过将异生物素和GSH通过共转运机制从细胞内区室排出到细胞外培养基中，保护细胞免受异生物素的毒性作用；（c）编码MRP的基因的破坏消除了异生物素和GSH的共转运。
