Bosch I, Jackson G R, Croop J M, Cantiello H F
Division of Pediatric Hematology/Oncology, Dana Farber Cancer Institute, Boston, Massachusetts, USA.
Am J Physiol. 1996 Nov;271(5 Pt 1):C1527-38. doi: 10.1152/ajpcell.1996.271.5.C1527.
Two distinct Drosophila melanogaster P-glycoprotein (Pgp) gene homologues of different chromosomal origin, MDR49 and MDR65, have been previously identified (38). Most Pgps are implicated in the development of the multidrug-resistance phenotype. Despite intense efforts to identify the molecular mechanism(s) associated with Pgp function, the endogenous substrate(s) of these transport molecules is largely unknown. Recent studies from our laboratory indicate that a murine Pgp homologue (E. H. Abraham, A. G. Prat, L. Gerweck, T. Seneveratne, R. J. Arceci, R. Kramer, G. Guidotti, and H. F. Cantiello. Proc. Natl. Acad. Sci. USA 90: 312-316, 1993) and a related protein, the cystic fibrosis transmembrane conductance regulator (CFTR; I. L. Reisin, A. Prat, E. H. Abraham, J. F. Amara, R. J. Gregory, D. A. Ausiello, and H. F. Cantiello. J. Biol. Chem. 269: 20584-20591, 1994), are novel ATP-permeable ion channels. The common feature of these two proteins is the conserved ATP-binding cassettes (ABC); thus molecules structurally linked to the ABC transporter family may be also functionally associated with ATP channel activity. In this study, MDR65 and MDR49 Pgps were functionally expressed in Sf9 cells, and patch-clamp techniques were applied to assess the role of these proteins in the electrodiffusional movement of ATP. In the presence of intracellular ATP and external NaCl, expression of MDR65 was associated with a linear electrodiffusional pathway that was permeable to both ATP and Cl-. Under symmetrical ATP conditions, only voltage depolarization activated a MDR65-mediated ATP-conductive pathway. Expression of MDR49 was also associated with a voltage-activated ATP conductance in symmetrical ATP, but no apparent permeability to either Cl- or ATP was observed under asymmetrical conditions. The different functional properties of MDR65 and MDR49 may be indicative of distinct physiological roles in this organism. The study indicates, however, that the two Drosophila Pgp homologues share strong functional similarities with their mammalian relatives Pgp and CFTR.
先前已鉴定出两个不同染色体来源的黑腹果蝇P-糖蛋白（Pgp）基因同源物，即MDR49和MDR65（38）。大多数Pgp与多药耐药表型的发展有关。尽管人们为确定与Pgp功能相关的分子机制付出了巨大努力，但这些转运分子的内源性底物在很大程度上仍不清楚。我们实验室最近的研究表明，一种小鼠Pgp同源物（E.H.亚伯拉罕、A.G.普拉特、L.格韦克、T.塞纳韦拉特内、R.J.阿尔塞西、R.克莱默、G.吉多蒂和H.F.坎蒂埃洛。美国国家科学院院刊90:312 - 316，1993）和一种相关蛋白，囊性纤维化跨膜电导调节因子（CFTR；I.L.雷辛、A.普拉特、E.H.亚伯拉罕、J.F.阿马拉、R.J.格雷戈里、D.A.奥西埃洛和H.F.坎蒂埃洛。生物化学杂志269:20584 - 20591，1994），是新型的ATP可渗透离子通道。这两种蛋白的共同特征是保守的ATP结合盒（ABC）；因此，在结构上与ABC转运蛋白家族相关的分子在功能上也可能与ATP通道活性有关。在本研究中，MDR65和MDR49 Pgp在Sf9细胞中功能性表达，并应用膜片钳技术评估这些蛋白在ATP电扩散运动中的作用。在细胞内存在ATP和细胞外存在NaCl的情况下，MDR65的表达与一条对ATP和Cl-都可渗透的线性电扩散途径相关。在对称ATP条件下，只有电压去极化激活了MDR65介导的ATP传导途径。MDR49的表达在对称ATP中也与电压激活的ATP电导相关，但在不对称条件下未观察到对Cl-或ATP有明显的通透性。MDR65和MDR49不同的功能特性可能表明它们在该生物体中有不同的生理作用。然而，该研究表明，这两个果蝇Pgp同源物与其哺乳动物亲属Pgp和CFTR具有很强的功能相似性。
