Jedlitschky G, Leier I, Buchholz U, Barnouin K, Kurz G, Keppler D
Division of Tumor Biochemistry, Deutsches Krebsforschungszentrum, Heidelberg, Germany.
Cancer Res. 1996 Mar 1;56(5):988-94.
Previous studies have identified the ATP-dependent export of glutathione conjugates as a physiological function of the multidrug resistance protein (MRP). The involvement of MRP in the transport of endogenous and xenobiotic conjugates was investigated further using membrane vesicles from MRP-transfected HeLa cells. The ATP-dependent transport of the glutathione conjugates [(3)H]leukotriene C(4), S-(2,4-dinitrophenyl)-[(3)H]glutathione, and (3)H- labeled oxidized glutathione was characterized by determination of the transport efficiency V(max):K(m) amounting to 1031, 114, and 7.1 ml multiplied by min(-1), respectively. Additional endogenous substrates for MRP-mediated transport included the steroid conjugate 17 beta- glucuronosyl [(3)H]estradiol and the bile salt conjugates [6 alpha-(14)C]glucuronosylhyodeoxycholate and 3 alpha-sulfatolithocholyl [(3)H]taurine. The K(m) value of MRP for 17-beta-glucuronosyl [(3)H]estradiol was 1.5 +/- 0.3 microM, with a V(max):K(m) ratio of 42 ml multiplied by mg protein(-1) multiplied by min(-1), and a K(i) value of 0.7 microM for the leukotriene receptor antagonist MK 571. MRP-mediated ATP-dependent transport was observed for the anticancer drug conjugates glucuronosyl [(3)H]etoposide and monocholoro-mono[(3)H]glutathionyl melphalan, but not for unmodified [(14)C]doxorubicin, [(3)H]daunorubicin, or [(3)H]vinblastine. Our results establish that MRP functions as an ATP-dependent export pump not only for glutathione conjugates but also for glucuronidated and sulfated endogenous as well as exogenous compounds.
以往的研究已确定谷胱甘肽偶联物的ATP依赖性外排是多药耐药蛋白（MRP）的一种生理功能。利用转染了MRP的HeLa细胞的膜囊泡，进一步研究了MRP在内源性和外源性偶联物转运中的作用。通过测定转运效率V(max):K(m)来表征谷胱甘肽偶联物[³H]白三烯C₄、S-(2,4-二硝基苯基)-[³H]谷胱甘肽和³H标记的氧化型谷胱甘肽的ATP依赖性转运，其V(max):K(m)值分别为1031、114和7.1 ml·min⁻¹。MRP介导转运的其他内源性底物包括类固醇偶联物17β-葡萄糖醛酸基[³H]雌二醇以及胆汁盐偶联物[6α-(¹⁴C)]葡萄糖醛酸基猪去氧胆酸和3α-硫酸石胆酰[³H]牛磺酸。MRP对17-β-葡萄糖醛酸基[³H]雌二醇的K(m)值为1.5±0.3 μM，V(max):K(m)比值为42 ml·mg蛋白⁻¹·min⁻¹，对白三烯受体拮抗剂MK 571的K(i)值为0.7 μM。观察到MRP介导的ATP依赖性转运作用于抗癌药物偶联物葡萄糖醛酸基[³H]依托泊苷和单氯-单[³H]谷胱甘肽基美法仑，但对未修饰的[¹⁴C]阿霉素、[³H]柔红霉素或[³H]长春碱则无此作用。我们的结果表明，MRP不仅作为一种ATP依赖性外排泵作用于谷胱甘肽偶联物，还作用于葡萄糖醛酸化和硫酸化的内源性以及外源性化合物。
