De Greef C, Sehrer J, Viana F, van Acker K, Eggermont J, Mertens L, Raeymaekers L, Droogmans G, Nilius B
Laboratory of Physiology, K.U. Leuven, Belgium.
Biochem J. 1995 May 1;307 ( Pt 3)(Pt 3):713-8. doi: 10.1042/bj3070713.
It has been proposed that P-glycoprotein, the product of the human MDR1 gene, may function not only as a drug transporter but, depending on the conditions, as a volume-activated Cl- channel [Valverde, Diaz, Sepúlveda, Gill, Hyde and Higgins (1992) Nature (London) 355, 830-833; Gill, Hyde, Higgins, Valverde, Mintenig and Sepúlveda (1992) Cell 71, 23-32]. To verify this hypothesis, we have compared volume-activated Cl- currents with the level of MDR1 mRNA and its protein product in the human KB3 (epitheloid lung cancer) and HeLa cell lines. The related MDR2 was also included to find out whether it could account for observed discrepancies between Cl- current and MDR1 expression. A 40% decrease in osmolarity evoked a Cl- current in both cell types (at +80 mV: 50.3 +/- 4.3 pA/pF in KB3, n = 13; 28.2 +/- 3.3 pA/pF in HeLa, n = 16). The blocking of this current in both cell types by 5-nitro-2-(3-phenylpropylamino)-benzoic acid and by 1,9-dideoxyforskolin is similar to that of the presumed P-glycoprotein associated Cl- channel. As measured by reverse-transcriptase polymerase chain reaction, KB3 cells expressed only an extremely small amount of the messengers for MDR1 and MDR2. The signal observed for MDR1 in HeLa cells was at least an order of magnitude more intense than in KB3 cells, while MDR2 mRNA was undetectable. A clear difference in MDR1 expression between KB3 and HeLa was also observed at the protein level. These data are difficult to reconcile with the hypothesis that in HeLa and KB3 cells MDR1- or MDR2- encoded P-glycoproteins are associated with volume-activated Cl- channels.
有人提出，人类多药耐药基因1（MDR1）的产物P-糖蛋白不仅可能作为药物转运体发挥作用，而且根据具体情况，还可能作为容积激活的氯离子通道发挥作用[瓦尔韦德、迪亚兹、塞普尔韦达、吉尔、海德和希金斯（1992年），《自然》（伦敦）355卷，830 - 833页；吉尔、海德、希金斯、瓦尔韦德、明滕宁和塞普尔韦达（1992年），《细胞》71卷，23 - 32页]。为了验证这一假设，我们比较了容积激活的氯离子电流与人类KB3（上皮样肺癌）和HeLa细胞系中MDR1 mRNA及其蛋白质产物的水平。还纳入了相关的MDR2，以查明它是否能解释观察到的氯离子电流与MDR1表达之间的差异。渗透压降低40%会在两种细胞类型中诱发氯离子电流（在+80 mV时：KB3细胞中为50.3±4.3 pA/pF，n = 13；HeLa细胞中为28.2±3.3 pA/pF，n = 16）。5-硝基-2-（3-苯丙基氨基）苯甲酸和1,9-二脱氧佛司可林对两种细胞类型中这种电流的阻断作用，与推测的与P-糖蛋白相关的氯离子通道的阻断作用相似。通过逆转录聚合酶链反应测量，KB3细胞仅表达极少量的MDR1和MDR2信使RNA。HeLa细胞中观察到的MDR1信号强度至少比KB3细胞高一个数量级，而MDR2 mRNA则无法检测到。在蛋白质水平上，KB3和HeLa细胞之间的MDR1表达也存在明显差异。这些数据难以与以下假设相协调，即在HeLa和KB3细胞中，MDR1或MDR2编码的P-糖蛋白与容积激活的氯离子通道相关。
