Functional Reconstitution of Substrate Transport by Purified Multidrug Resistance Protein MRP1 (ABCC1) in Phospholipid Vesicles

Abstract The 190-kDa multidrug resistance protein MRP1 (ABCC1) is a polytopic transmembrane protein belonging to the ATP-binding cassette transporter superfamily. In addition to conferring resistance to various antineoplastic agents, MRP1 is a transporter of conjugated organic anions, including the cysteinyl leukotriene C4 (LTC4). We previously characterized the ATPase activity of reconstituted immunoaffinity-purified native MRP1 and showed it could be stimulated by its organic anion substrates (Mao, Q., Leslie, E. M., Deeley, R. G., and Cole, S. P. C. (1999) Biochim. Biophys. Acta 1461, 69–82). Here we show that purified reconstituted MRP1 is also capable of active transport of its substrates. Thus LTC4 uptake by MRP1 proteoliposomes was osmotically sensitive and could be inhibited by two MRP1-specific monoclonal antibodies. LTC4 uptake was also markedly reduced by the competitive inhibitor,S-decyl-glutathione, as well as by the MRP1 substrates 17β-estradiol 17-β-(d-glucuronide), oxidized glutathione, and vincristine in the presence of reduced glutathione. The K m for ATP and LTC4 were 357 ± 184 μm and 366 ± 38 nm, respectively, and 2.14 ± 0.75 μm for 17β-estradiol 17-β-(d-glucuronide). Transport of vincristine required the presence of both ATP and GSH. Conversely, GSH transport was stimulated by vincristine and verapamil. Our data represent the first reconstitution of transport competent purified native MRP1 and confirm that MRP1 is an efflux pump, which can transport conjugated organic anions and co-transport vincristine together with GSH.