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Yang JJ, Ann DK, Kannan R, Lee VHL. Multidrug resistance protein 1 (MRP1) in rabbit conjunctival epithelial cells: its effect on drug efflux and its regulation by adenoviral infection. Pharm Res 2007; 24:1490-500. [PMID: 17404811 DOI: 10.1007/s11095-007-9267-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2006] [Accepted: 02/08/2007] [Indexed: 01/02/2023]
Abstract
PURPOSE To evaluate the expression, localization, function, and regulation of multidrug resistance protein (MRP1) in rabbit conjunctival epithelial cells (RCEC). MATERIALS AND METHODS MRP1 gene expression in RCEC was determined by reverse transcription-polymerase chain reaction (RT-PCR), and MRP1 protein expression and its localization were determined by Western blot analysis and immunofluorescence using an anti-MRP1 monoclonal antibody, MRPr1. The effect of MRP1 on the transport and uptake of fluorescein was evaluated in RCEC grown on Transwell filters. Moreover, the effect of adenovirus type 5 (Ad5)-infected RCEC, and cytokines (Interleukin 1 (IL-1), IL-6, and tumor necrosis factor alpha (TNFalpha)) on MRP1 expression and leukotriene C4 (LTC4) uptake were investigated. RESULTS A 652 bp RT-PCR product from rabbit conjunctiva showed a 87% homology to human MRP1. Immunostaining with MRPr1 revealed a predominant basolateral localization of MRP1 in RCEC. Uptake of fluorescein, a MRP1 substrate, was increased (203-290%) in the presence of uricosuric drug probenecid at 100 microM, anti-inflammatory drug indomethacin at 10 microM and diclofenac, flurbiprofen, and ofloxacin at 1 mM, and by ATP depletion, but not influenced by the depletion of GSH, and the presence of antiviral cidofovir and anti-inflammatory drug cromolyn and prednisolone. Apical-to-basolateral facilitated transport of LTC4 was abolished in the presence of probenecid. Western blot analysis with MRPr1 revealed a distinct band at approximately 190 kDa for freshly isolated and cultured RCEC. Both Ad5 and cytokines (IL-1, IL-6, and TNF-alpha) up-regulated MRP1 expression, thereby reducing LTC4 uptake. CONCLUSIONS MRP1 appears to be primarily localized in the basolateral membrane of RCEC and function in the efflux of certain organic anions and inflammatory factors out of cells from the basolateral membrane. The upregulation in the expression of MRP1 by Ad5-infection and cytokines suggests a role of MRP1 in the transport of inflammatory factors during ocular inflammation. Supported by NIH grants EY12578, EY10421, and EY12356.
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Shilling AD, Azam F, Kao J, Leung L. Use of canalicular membrane vesicles (CMVs) from rats, dogs, monkeys and humans to assess drug transport across the canalicular membrane. J Pharmacol Toxicol Methods 2006; 53:186-97. [PMID: 16176877 DOI: 10.1016/j.vascn.2005.08.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2004] [Accepted: 08/09/2005] [Indexed: 11/15/2022]
Abstract
INTRODUCTION A novel application of a Ultrafree filter cartridge/centrifugation method was evaluated to determine uptake in canalicular membrane vesicles (CMVs) from SD rats, beagle dogs, cynomolgus monkeys (common safety species in the pharmaceutical industry) and humans to assess biliary transport. METHODS CMVs prepared from fresh livers of rats, dogs, monkeys and humans (four donors) were characterized for enrichment, basolateral and Golgi contamination and orientation. The presence of MRP2 and p-glycoprotein (P-gp) were confirmed by Western blots. Uptake of [3H]-leukotriene C4 (LTC4) and [3H]-estradiol-17beta-d-glucuronide (E2-Gluc) was determined at a low substrate concentration and/or by kinetic measurements (K(m) and V(max)). Correlation of in vitro data with in vivo findings was achieved by determining the biliary clearance of E2-Gluc in rats after a single i.v. dose and with literature in vivo data for LTC4. RESULTS CMVs were highly enriched and minimally contaminated based on marker enzyme activities. Uptake clearance among different species varied by approximately ten-fold (rat > dog = human > monkey) for LTC4 and less than two-fold for E2-Gluc. The lower uptake of LTC4 by human than rat CMVs may be attributed to a higher Km value for human than rat CMVs. Uptake of LTC4 or E2-Gluc by human CMVs showed little inter-subject variability (2-5-fold). Differences in in vitro uptake clearance (10-fold) between LTC4 and E2-Gluc in rat CMVs seemed to correlate with differences in their biliary clearance (4-fold) in rats, consistent with LTC4 and E2-Gluc being a high and a low clearance substrate, respectively. DISCUSSION A novel application of a Ultrafree filter cartridge/centrifugation method was developed to determine uptake in CMVs from different preclinical animal safety species and humans, and may represent a useful approach to study the mechanism of biliary excretion during drug discovery and development.
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Noguchi T, Ren XQ, Aoki S, Igarashi Y, Che XF, Nakajima Y, Takahashi H, Mitsuo R, Tsujikawa K, Sumizawa T, Haraguchi M, Kobayashi M, Goto S, Kanehisa M, Aikou T, Akiyama SI, Furukawa T. MRP1 mutated in the L0 region transports SN-38 but not leukotriene C4 or estradiol-17 (beta-D-glucuronate). Biochem Pharmacol 2005; 70:1056-65. [PMID: 16098482 DOI: 10.1016/j.bcp.2005.06.025] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2005] [Revised: 06/22/2005] [Accepted: 06/24/2005] [Indexed: 11/23/2022]
Abstract
Multidrug resistance protein 1 (MRP1) is an ATP-binding cassette transporter that confers multidrug resistance on tumor cells. Much convincing evidence has accumulated that MRP1 transports most substances in a GSH-dependent manner. On the other hand, several reports have revealed that MRP1 can transport some substrates independently of GSH; however, the importance of GSH-independent transport activity is not well established and the mechanistic differences between GSH-dependent and -independent transport by MRP1 are unclear. We previously demonstrated that the amino acids W261 and K267 in the L0 region of MRP1 were important for leukotriene C4 (LTC4) transport activity of MRP1 and for GSH-dependent photolabeling of MRP1 with azidophenyl agosterol-A (azidoAG-A). In this paper, we further tested the effect of W222L, W223L and R230A mutations in MRP1, designated dmL0MRP1, on MRP1 transport activity. SN-38 is an active metabolic form of CPT-11 that is one of the most promising anti-cancer drugs. Membrane vesicles prepared from cells expressing dmL0MRP1 could transport SN-38, but not LTC4 or estradiol-17 (beta-D-glucuronate), and could not be photolabeled with azidoAG-A. These data suggested that SN-38 was transported by a different mechanism than that of GSH-dependent transport. Understanding the GSH-independent transport mechanism of MRP1, and identification of drugs that are transported by this mechanism, will be critical for combating MRP1-mediated drug resistance. We performed a pairwise comparison of compounds that are transported by MRP1 in a GSH-dependent or -independent manner. These data indicated that it may be possible to predict compounds that are transported by MRP1 in a GSH-independent manner.
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Conseil G, Deeley RG, Cole SPC. Functional importance of three basic residues clustered at the cytosolic interface of transmembrane helix 15 in the multidrug and organic anion transporter MRP1 (ABCC1). J Biol Chem 2005; 281:43-50. [PMID: 16230346 DOI: 10.1074/jbc.m510143200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The multidrug resistance protein 1 (MRP1) mediates drug and organic anion efflux across the plasma membrane. The 17 transmembrane (TM) helices of MRP1 are linked by extracellular and cytoplasmic (CL) loops of various lengths and two cytoplasmic nucleotide binding domains. In this study, three basic residues clustered at the predicted TM15/CL7 interface were investigated for their role in MRP1 expression and activity. Thus, Arg1138, Lys1141, and Arg1142 were replaced with residues of the same or opposite charge, expressed in human embryonic kidney cells, and the properties of the mutant proteins were assessed. Neither Glu nor Lys substitutions of Arg1138 and Arg1142 affected MRP1 expression; however, all four mutants showed a decrease in organic anion transport with a relatively greater decrease in leukotriene C4 and glutathione transport. These mutations also modulated MRP1 ATPase activity as reflected by a decreased vanadate-induced trapping of 8-azido-[32P]ADP. Mutation of Lys1141 to either Glu or Arg reduced MRP1 expression, and routing to the plasma membrane was impaired. However, only the Glu-substituted Lys1141 mutant showed a decrease in organic anion transport, and this was associated with decreased substrate binding and vanadate-induced trapping of 8-azido-ADP. These studies identified a cluster of basic amino acids likely at the TM15/CL7 interface as a region important for both MRP1 expression and activity and demonstrated that each of the three residues plays a distinct role in the substrate specificity and catalytic activity of the transporter.
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Chen ZS, Hopper-Borge E, Belinsky MG, Shchaveleva I, Kotova E, Kruh GD. Characterization of the transport properties of human multidrug resistance protein 7 (MRP7, ABCC10). Mol Pharmacol 2003; 63:351-8. [PMID: 12527806 DOI: 10.1124/mol.63.2.351] [Citation(s) in RCA: 126] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Human multidrug resistance protein 7 (MRP7, ABCC10) is a recently described member of the C family of ATP binding cassette proteins (Cancer Lett 162:181-191, 2001). However, neither its biochemical activity nor physiological functions have been determined. Here we report the results of investigations of the in vitro transport properties of MRP7 using membrane vesicles prepared from human embryonic kidney 293 cells transfected with MRP7 expression vector. It is shown that expression of MRP7 is specifically associated with the MgATP-dependent transport of 17beta-estradiol-(17-beta-D-glucuronide) (E(2)17betaG). E(2)17betaG transport was saturable, with K(m) and V(max) values of 57.8 +/- 15 microM and 53.1 +/- 20 pmol/mg/min. By contrast, with E(2)17betaG, only modest enhancement of LTC(4) transport was observed and transport of several other established substrates of MRP family transporters was not detectable to any extent. In accord with the notion that MRP7 has a bipartite substrate binding pocket composed of sites for anionic and lipophilic moieties, transport of E(2)17betaG was susceptible to competitive inhibition by both amphiphiles, such as leukotriene C(4) (K(i(app)), 1.5 microM), glycolithocholate 3-sulfate (K(i(app)), 34.2 microM) and MK571 (K(i(app)), 28.5 microM), and lipophilic agents such as cyclosporine A (K(i(app)), 14.4 microM). Of the inhibitors tested, LTC(4) was the most potent, in agreement with the possibility that it is a substrate of the pump. The determination that MRP7 has the facility for mediating the transport of conjugates such as E(2)17betaG indicates that it is a lipophilic anion transporter involved in phase III (cellular extrusion) of detoxification.
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Keitel V, Nies AT, Brom M, Hummel-Eisenbeiss J, Spring H, Keppler D. A common Dubin-Johnson syndrome mutation impairs protein maturation and transport activity of MRP2 (ABCC2). Am J Physiol Gastrointest Liver Physiol 2003; 284:G165-74. [PMID: 12388192 DOI: 10.1152/ajpgi.00362.2002] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Absence of a functional multidrug resistance protein 2 (MRP2; symbol ABCC2) from the hepatocyte canalicular membrane is the molecular basis of Dubin- Johnson syndrome, an inherited disorder associated with conjugated hyperbilirubinemia in humans. In this work, we analyzed a relatively frequent Dubin-Johnson syndrome mutation that leads to an exchange of two hydrophobic amino acids, isoleucine 1173 to phenylalanine (MRP2I1173F), in a predicted extracellular loop of MRP2. HEK-293 cells stably transfected with MRP2I1173F cDNA synthesized a mutant protein that was mainly core-glycosylated, predominantly retained in the endoplasmic reticulum, and degraded by proteasomes. MRP2I1173F did not mediate ATP-dependent transport of leukotriene C(4) (LTC(4)) into vesicles from plasma membrane and endoplasmic reticulum preparations while normal MRP2 was functionally active. Human HepG2 cells were used to study localization of MRP2I1173F in a polarized cell system. Quantitative analysis showed that GFP-tagged MRP2I1173F was localized to the apical membrane in only 5% of transfected, polarized HepG2 cells compared with 80% for normal MRP2-GFP. Impaired protein maturation followed by proteasomal degradation of inactive MRP2I1173F explain the deficient hepatobiliary elimination observed in this group of Dubin-Johnson syndrome patients.
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Tabas LB, Dantzig AH. A high-throughput assay for measurement of multidrug resistance protein-mediated transport of leukotriene C4 into membrane vesicles. Anal Biochem 2002; 310:61-6. [PMID: 12413474 DOI: 10.1016/s0003-2697(02)00282-8] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
This study investigated a high-throughput assay to measure multidrug resistance-associated protein (MRP1)-mediated uptake into membrane vesicles. Typically, a rapid filtration technique using a 12-filter vacuum manifold is used. We report here the development of a 96-well microtiter dish assay. MRP1-transfected HeLa cells (HeLa-T5) were used for the membrane vesicle preparations. The uptake of 50nM [3H]leukotriene C(4) (LTC(4)) was measured in a 96-well microtiter dish with rapid filtration onto a Perkin Elmer unifilter GF/B plate using a Perkin Elmer Filtermate 196. Counting of the isotype was conducted with a Perkin Elmer Top Count NXT. Uptake was adenosine 5'-triphosphate-dependent and linear over a 120-s time course. Uptake was inhibited by the leukotriene D(4) antagonist, MK 571, with a k(i) of 0.67 microM, and by the anti-MRP1 monoclonal antibody QCRL-3 but not by QCRL-1. Inhibition by estradiol-17-beta-glucuronide was 35-fold greater than inhibition by estradiol-3-beta-glucuronide. The kinetic parameters for LTC(4) uptake were determined to be a K(m) of 157nM with a V(max) of 344pmol/min/mg protein. The properties of MRP1-mediated transport of LTC(4) are consistent with those previously reported. The microtiter dish assay is a more expedient method for measuring transport into membrane vesicles and will have applications to other transporters.
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Belinsky MG, Chen ZS, Shchaveleva I, Zeng H, Kruh GD. Characterization of the drug resistance and transport properties of multidrug resistance protein 6 (MRP6, ABCC6). Cancer Res 2002; 62:6172-7. [PMID: 12414644] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/27/2023]
Abstract
Mutations in human multidrug resistance protein 6 (MRP6, ABCC6), a member of the MRP family of drug efflux pumps, are the genetic basis of Pseudoxanthoma elasticum, a disease that affects elastin fibers in the skin, retina, and blood vessels. However, little is known about the functional characteristics of the protein, including its potential activity as a resistance factor for anticancer agents. Here, we report the results of investigations of the in vitro transport properties and drug resistance activity of MRP6. Using membrane vesicles prepared from Chinese hamster ovary cells transfected with MRP6 expression vector, it is shown that expression of MRP6 is specifically associated with the MgATP-dependent transport of the glutathione S-conjugates leukotriene C(4) and S-(2, 4-dinitrophenyl)glutathione and the cyclopentapeptide BQ123 but not glucuronate conjugates such as 17beta-estradiol 17-(beta-D-glucuronide). Analysis of the drug sensitivity of MRP6-transfected cells revealed low levels of resistance to several natural product agents, including etoposide, teniposide, doxorubicin, and daunorubicin. These results indicate that MRP6 is a glutathione conjugate pump that is able to confer low levels of resistance to certain anticancer agents.
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9
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Terlouw SA, Masereeuw R, van den Broek PHH, Notenboom S, Russel FGM. Role of multidrug resistance protein 2 (MRP2) in glutathione-bimane efflux from Caco-2 and rat renal proximal tubule cells. Br J Pharmacol 2001; 134:931-8. [PMID: 11682439 PMCID: PMC1573022 DOI: 10.1038/sj.bjp.0704284] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. The multidrug resistance protein 2 (MRP2) has been shown to play an important role in the transport of glutathione conjugates in the liver. Its importance in renal excretion, however, is still uncertain and other organic anion transporters may be involved. The objective of the present study was to characterize glutathione conjugate efflux from rat kidney proximal tubule cells (PTC), and to determine the contribution of Mrp2. 2. We used isolated PTC in suspension, as well as grown to monolayer density. For comparison, transport characteristics were also determined in the human intestinal epithelial cell line Caco-2, an established model to study MRP2-mediated transport. The cells were loaded with monochlorobimane (MCB) at 10 degrees C. MCB enters the cells by simple diffusion and is conjugated with glutathione to form the fluorescent glutathione-bimane (GS-B). 3. In primary cultures of rat PTC, no indications for a transporter-mediated mechanism were found. The efflux of GS-B from Caco-2 cells and freshly isolated PTC was time- and temperature-dependent. Furthermore, GS-B transport in both models was inhibited by chlorodinitrobenzene (CDNB), with an inhibitory constant of 46.8+/-0.9 microM in freshly isolated PTC. In Caco-2 cells, the inhibitory potency of CDNB was approximately 20 fold higher. Finally, efflux of GS-B from freshly isolated PTC from Mrp2-deficient (TR(-)) rats was studied. As compared to normal rat PTC, transport characteristics were not different. 4. We conclude that in freshly isolated rat PTC glutathione conjugate excretion is mediated by other organic anion transporters rather than by Mrp2.
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Ohno N, Tani A, Chen ZS, Uozumi K, Hanada S, Akiba S, Ren XQ, Furukawa T, Sumizawa T, Arima T, Akiyama SI. Prognostic significance of multidrug resistance protein in adult T-cell leukemia. Clin Cancer Res 2001; 7:3120-6. [PMID: 11595704] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Abstract
The response of adult T-cell leukemia (ATL) to chemotherapy is poor, and a major obstacle to successful treatment is intrinsic or acquired drug resistance. To determine the clinical significance of multidrug resistance protein (MRP) 1 in ATL, we studied MRP1 expression and its association with clinical outcome. The expression of MRP1 mRNA in leukemia cells from 48 ATL patients was studied by slot blot analysis. The expression level of MRP1 mRNA in chronic-type ATL was significantly higher than that in lymphoma-type ATL (P = 0.033). There was no correlation between MRP1 expression and age, gender, WBC count, LDH, hypercalcemia, blood urea nitrogen, or performance status. However, the expression of MRP1 mRNA correlated only with peripheral blood abnormal lymphocyte counts (P = 0.008). The transporting activity of MRP1 was assessed using membrane vesicles. Membrane vesicles prepared from ATL cells with high expression of MRP1 mRNA showed a higher ATP-dependent leukotriene C(4) uptake than did those with low expression of MRP1 mRNA. This uptake was almost completely inhibited by LTD(4) antagonists ONO-1078 and MK571. In acute- and lymphoma-type ATL, high expression of MRP1 mRNA at diagnosis correlated with shorter survival, and Cox regression analysis revealed that MRP1 expression was an independent prognostic factor. These findings suggest that functionally active MRP1 is expressed in some ATL cells and that it is involved in drug resistance and has a possible causal relationship with poor prognosis in ATL. Multidrug resistance-reversing agents, such as ONO-1078 and MK571, that directly interact and inhibit the transporting activity of MRP1 may be useful for treating ATL patients.
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MESH Headings
- ATP Binding Cassette Transporter, Subfamily B, Member 1/genetics
- ATP Binding Cassette Transporter, Subfamily B, Member 1/metabolism
- Adult
- Aged
- Aged, 80 and over
- Female
- Gene Expression Regulation, Neoplastic
- Humans
- Leukemia-Lymphoma, Adult T-Cell/genetics
- Leukemia-Lymphoma, Adult T-Cell/metabolism
- Leukemia-Lymphoma, Adult T-Cell/pathology
- Leukotriene C4/pharmacokinetics
- Male
- Membranes/metabolism
- Middle Aged
- Multivariate Analysis
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Survival Analysis
- Tritium
- Tumor Cells, Cultured
- Vincristine/metabolism
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Zhang DW, Cole SP, Deeley RG. Identification of an amino acid residue in multidrug resistance protein 1 critical for conferring resistance to anthracyclines. J Biol Chem 2001; 276:13231-9. [PMID: 11278596 DOI: 10.1074/jbc.m010008200] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Murine multidrug resistance protein 1 (mrp1), unlike human MRP1, does not confer resistance to anthracyclines. Previously, we have shown that a human/murine hybrid protein containing amino acids 959-1187 of MRP1 can confer resistance to these drugs. We have now examined the functional characteristics of mutant proteins in which we have converted individual amino acids in the comparable region of mrp1 to those present at the respective locations in MRP1. These mutations had no effect on the drug resistance profile conferred by mrp1 with the exception of converting glutamine 1086 to glutamate, as it is in the corresponding position (1089) in MRP1. This mutation created a protein that conferred resistance to doxorubicin without affecting vincristine resistance, or the ability of mrp1 to transport leukotriene C(4) (LTC(4)) and 17beta-estradiol 17-(beta-d-glucuronide) (E(2)17betaG). Furthermore, mutation Q1086D conferred the same phenotype as mutation Q1086E while the mutation Q1086N did not detectably alter the drug resistance profile of mrp1, suggesting that an anionic side chain was required for anthracycline resistance. To confirm the importance of MRP1 E1089 for conferring resistance to anthracyclines, we mutated this residue to Gln, Asp, Ala, Leu, and Lys in the human protein. The mutation E1089D showed the same phenotype as MRP1, while the E1089Q substitution markedly decreased resistance to anthracyclines without affecting LTC(4) and E(2)17betaG transport. Conversion of Glu-1089 to Asn, Ala, or Leu had a similar effect on resistance to anthracyclines, while conversion to a positive amino acid, Lys, completely eliminated resistance to anthracyclines and vincristine without affecting transport of LTC(4), E(2)17betaG, and the GSH-dependent substrate, estrone-3-sulfate. These results demonstrate that an acidic amino acid residue at position 1089 in predicted TM14 of MRP1 is critical for the ability of the protein to confer drug resistance particularly to the anthracyclines, but is not essential for its ability to transport conjugated organic anions such as LTC(4) and E(2)17betaG.
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MESH Headings
- ATP Binding Cassette Transporter, Subfamily B, Member 1/chemistry
- ATP Binding Cassette Transporter, Subfamily B, Member 1/genetics
- ATP Binding Cassette Transporter, Subfamily B, Member 1/metabolism
- Amino Acid Sequence
- Amino Acid Substitution
- Animals
- Antibiotics, Antineoplastic/toxicity
- Antineoplastic Agents/toxicity
- Binding Sites
- Biological Transport
- Cell Line
- Cell Membrane/metabolism
- Cell Survival/drug effects
- Doxorubicin/toxicity
- Drug Resistance, Multiple
- Estradiol/analogs & derivatives
- Estradiol/pharmacokinetics
- Estrone/analogs & derivatives
- Estrone/pharmacokinetics
- Etoposide/toxicity
- Humans
- Kinetics
- Leukotriene C4/pharmacokinetics
- Mice
- Models, Molecular
- Molecular Sequence Data
- Mutagenesis, Site-Directed
- Protein Structure, Secondary
- Recombinant Proteins/chemistry
- Recombinant Proteins/metabolism
- Transfection
- Vincristine/toxicity
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Zeng H, Liu G, Rea PA, Kruh GD. Transport of amphipathic anions by human multidrug resistance protein 3. Cancer Res 2000; 60:4779-84. [PMID: 10987286] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
Abstract
The multidrug resistance-associated protein 1 (MRP1) and the canalicular multispecific organic anion transporter (cMOAT or MRP2) are ATP-binding cassette transporters that confer resistance to some anticancer drugs and efflux glutathione and glucuronate conjugates from the cell. The MRP subfamily of ABC transporters, however, contains at least four other members of which MRP3 (MOAT-D) bears the closest structural resemblance to MRP1. Although transfection studies have established that human MRP3 confers increased resistance to several anticancer agents, neither the substrate selectivity nor physiological functions of this transporter have been determined. Here we report the results of investigations of the in vitro transport properties of cloned human MRP3 using membrane vesicles prepared from MRP3-transfected HEK293 cells. It is shown that the expression of MRP3 is specifically associated with enhancement of the MgATP-dependent transport into membrane vesicles of the glucuronide estradiol 17-beta-D-glucuronide (E(2)17betaG), the glutathione conjugates 2,4-dinitrophenyl S-glutathione (DNP-SG) and leukotriene C4 (LTC4), the antimetabolite methotrexate, and the bile acid glycocholate. DNP-SG, LTC4, and E(2)17betaG are transported at moderate affinity and low capacity with Km and Vmax values of 5.7 +/- 1.7 microM and 3.8 +/- 0.1 pmol/mg/min, 5.3 +/- 2.6 microM and 20.2 +/- 5.9 pmol/mg/min, and 25.6 +/- 5.4 microM and 75.6 +/- 5.9 pmol/mg/min, respectively. Methotrexate and glycocholate are transported at low affinity and high capacity with Km and Vmax values of 776 +/- 319 microM and 288 +/- 54 pmol/mg/min and 248 +/- 113 microM and 183 +/- 34 pmol/mg/min, respectively. On the basis of these findings, the osmotic dependence of the transport measured and its inability to transport taurocholate, MRP3, like MRP1 and cMOAT, is concluded to be competent in the transport of glutathione S-conjugates, glucuronides, and methotrexate, albeit at low to moderate affinity. In contrast to MRP1, cMOAT, and all other characterized mammalian ABC transporters, however, MRP3 is active in the transport of the monoanionic human bile constituent glycocholate.
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Gao M, Cui HR, Loe DW, Grant CE, Almquist KC, Cole SP, Deeley RG. Comparison of the functional characteristics of the nucleotide binding domains of multidrug resistance protein 1. J Biol Chem 2000; 275:13098-108. [PMID: 10777615 DOI: 10.1074/jbc.275.17.13098] [Citation(s) in RCA: 148] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Multidrug Resistance Protein 1 (MRP1) transports diverse organic anionic conjugates and confers resistance to cytotoxic xenobiotics. The protein contains two nucleotide binding domains (NBDs) with features characteristic of members of the ATP-binding cassette superfamily and exhibits basal ATPase activity that can be stimulated by certain substrates. It is not known whether the two NBDs of MRP1 are functionally equivalent. To investigate this question, we have used a baculovirus dual expression vector encoding both halves of MRP1 to reconstitute an active transporter and have compared the ability of each NBD to be photoaffinity-labeled with 8-azido-[(32)P]ATP and to trap 8-azido-[(32)P]ADP in the presence of orthovanadate. We found that NBD1 was preferentially labeled with 8-azido-[(32)P]ATP, while trapping of 8-azido-[(32)P]ADP occurred predominantly at NBD2. Although trapping at NBD2 was dependent on co-expression of both halves of MRP1, binding of 8-azido-ATP by NBD1 remained detectable when the NH(2)-proximal half of MRP1 was expressed alone and when NBD1 was expressed as a soluble polypeptide. Mutation of the conserved Walker A lysine 684 or creation of an insertion mutation between Walker A and B motifs eliminated binding by NBD1 and all detectable trapping of 8-azido-ADP at NBD2. Both mutations decreased leukotriene C(4) (LTC(4)) transport by approximately 70%. Mutation of the NBD2 Walker A lysine 1333 eliminated trapping of 8-azido-ADP by NBD2 but, in contrast to the mutations in NBD1, essentially eliminated LTC(4) transport activity without affecting labeling of NBD1 with 8-azido-[(32)P]ATP.
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14
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Van Aubel RA, Koenderink JB, Peters JG, Van Os CH, Russel FG. Mechanisms and interaction of vinblastine and reduced glutathione transport in membrane vesicles by the rabbit multidrug resistance protein Mrp2 expressed in insect cells. Mol Pharmacol 1999; 56:714-9. [PMID: 10496953] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/14/2023] Open
Abstract
The present study examined how the multidrug resistance protein (MRP) 2, which is an ATP-dependent anionic conjugate transporter, also mediates transport of the chemotherapeutic cationic drug vinblastine (VBL). We show that ATP-dependent [(3)H]VBL (0.2 microM) uptake into membrane vesicles from Sf9 cells infected with a baculovirus encoding rabbit Mrp2 (Sf9-Mrp2) was similar to vesicles from mock-infected Sf9 cells (Sf9-mock) but could be stimulated by reduced glutathione (GSH) with a half-maximum stimulation of 1.9 +/- 0.1 mM. At 5 mM GSH, initial ATP-dependent [(3)H]VBL uptake rates were saturable with an apparent K(m) of 1.5 +/- 0.3 microM. The inhibitory effect of VBL on Mrp2-mediated ATP-dependent transport of the anionic conjugate [(3)H]leukotriene C(4) was potentiated by increasing GSH concentrations. Membrane vesicles from Sf9-Mrp2 cells exhibited a approximately 7-fold increase in initial GSH uptake rates compared with membrane vesicles from Sf9-mock cells. Uptake of [(3)H]GSH was osmotically sensitive, independent of ATP, and was trans-inhibited by GSH. The anionic conjugates estradiol-17beta-D-glucuronide and leukotriene C(4) cis-inhibited [(3)H]GSH uptake but only in the presence of ATP. Whereas ATP-dependent [(3)H]VBL uptake was stimulated by GSH, VBL did not affect [(3)H]GSH uptake. Our results show that GSH is required for Mrp2-mediated ATP-dependent VBL transport and that Mrp2 transports GSH independent of VBL.
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Kawabe T, Chen ZS, Wada M, Uchiumi T, Ono M, Akiyama S, Kuwano M. Enhanced transport of anticancer agents and leukotriene C4 by the human canalicular multispecific organic anion transporter (cMOAT/MRP2). FEBS Lett 1999; 456:327-31. [PMID: 10456333 DOI: 10.1016/s0014-5793(99)00979-5] [Citation(s) in RCA: 125] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We established stable human canalicular multispecific organic anion transporter (cMOAT/MRP2) cDNA transfectants, CHO/cMOAT from non-polarized Chinese hamster ovary (CHO)-K1 and LLC/cMOAT from polarized pig kidney epithelial LLC-PK1. Human cMOAT was mainly localized in the plasma membrane of CHO/cMOAT and in the apical membrane of LLC/cMOAT. The ATP-dependent uptake of leukotriene C4 (LTC4) into CHO/cMOAT membrane vesicles was enhanced compared with empty vector transfectants. Km values in CHO/cMOAT membrane vesicles were 0.24 microM for LTC4 and 175 microM for ATP. Drug sensitivity to vincristine and cisplatin in human cMOAT cDNA transfectants decreased, but not to etoposide. Cellular accumulation of vincristine and cisplatin in human cMOAT cDNA transfectants decreased, but not of etoposide. The uptake of LTC4 into CHO/cMOAT membrane vesicles was inhibited by exogenous administration of vincristine or cisplatin, but not that of etoposide. Moreover, this inhibition was more enhanced in the presence of glutathione. These consequences indicate that drug resistance to vincristine or cisplatin appears to be modulated by human cMOAT through transport of the agents, possibly in direct or indirect association with glutathione.
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Chen ZS, Sumizawa T, Furukawa T, Ono K, Tani A, Komatsu M, Akiyama S. An enhanced active efflux of CPT-11 and SN-38 in cisplatin-resistant human KB carcinoma cells. Cancer Lett 1999; 138:13-22. [PMID: 10378768 DOI: 10.1016/s0304-3835(98)00367-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Cisplatin-resistant KCP-4 cells were 12.4- and 31.6-fold more resistant to CPT-11 and SN-38 than parental KB-3-1 cells, respectively. We studied the mechanism of cross-resistance to CPT-11 and SN-38. Our previous study showed that multidrug resistance protein (MRP), canalicular multispecific organic anion transporter (cMOAT) and P-glycoprotein (P-gp) were not expressed in KCP-4 cells (Chen, Z.-S. et al., Exp. Cell Res., 240 (1998) 312-320, and Chuman, Y. et al., Biochem. Biophys. Res. Commun., 226 (1996) 158-165). The accumulation of both CPT-11 and SN-38 in KCP-4 cells was lower than that in KB-3-1 cells. The ATP-dependent efflux of CPT-11 and SN-38 from KCP-4 cells was enhanced compared with that from KB-3-1 cells. DNA topoisomerase (topo) I expression, topo I activity, topo I-mediated cleavable complex, and the sensitivity to SN-38 of DNA topo I in KCP-4 were similar to those in KB-3-1 cells. Furthermore, the conversion of CPT-11 to SN-38 in the two cell lines was also similar. The transport of LTC4 in KCP-4 membrane vesicles was competitively inhibited by bis-(glutathionato)-platinum (II) (GS-Pt), CPT-11 and SN-38. These findings suggested that an unknown transporter distinct from P-gp, MRP or cMOAT is expressed in KCP-4 cells and transports CPT-11 and SN-38.
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Sjölinder M, Tornhamre S, Claesson HE, Hydman J, Lindgren J. Characterization of a leukotriene C4 export mechanism in human platelets: possible involvement of multidrug resistance-associated protein 1. J Lipid Res 1999; 40:439-46. [PMID: 10064732] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/11/2023] Open
Abstract
Platelets express leukotriene (LT) C4 synthase and can thus participate in the formation of bioactive LTC4. To further elucidate the relevance of this capability, we have now determined the capacity of human platelets to export LTC4. Endogenously formed LTC4 was efficiently released from human platelets after incubation with LTA4 at 37 degrees C, whereas only 15% of produced LTC4 was exported when the cells were incubated at 0 degrees C. The activation energy of the process was calculated to 49.9 +/- 7.7 kJ/mol, indicating carrier-mediated LTC4 export. This was also supported by the finding that the transport was saturable, reaching a maximal export rate of 470 +/- 147 pmol LTC4/min x 10(9) platelets. Furthermore, markedly suppressed LTC4 transport was induced by a combination of the metabolic inhibitors antimycin A and 2-deoxyglucose, suggesting energy-dependent export. The presence in platelets of multidrug resistance-associated protein 1 (MRP1), a protein described to be an energy-dependent LTC4 transporter in various cell types, was demonstrated at the mRNA and protein level. Additional support for a role of MRP1 in platelet LTC4 export was obtained by the findings that the process was inhibited by probenecid and the 5-lipoxygenase-activating protein (FLAP) inhibitor, MK-886. The present findings further support the physiological relevance of platelet LTC4 production.
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Nakamura T, Oka M, Aizawa K, Soda H, Fukuda M, Terashi K, Ikeda K, Mizuta Y, Noguchi Y, Kimura Y, Tsuruo T, Kohno S. Direct interaction between a quinoline derivative, MS-209, and multidrug resistance protein (MRP) in human gastric cancer cells. Biochem Biophys Res Commun 1999; 255:618-24. [PMID: 10049760 DOI: 10.1006/bbrc.1999.0245] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
MS-209 is a novel quinoline derivative reversing P-glycoprotein-mediated multidrug resistance (MDR). We investigated the interaction between MS-209 and multidrug resistance protein (MRP) in MRP-overexpressing human gastric cancer cells. We measured [3H]leukotriene C4 uptake into the membrane vesicles of the cells and intracellular calcein and [3H]vincristine accumulation with or without MS-209. In multi-drug-resistant MKN45R0.8 cells selected by doxorubicin, MS-209 dose dependently reduced MRP-mediated [3H]leukotriene C4 uptake and increased calcein accumulation. In both resistant and unselected cell lines expressing the MRP gene, MS-209 increased [3H]vincristine accumulation in proportion with the level of MRP mRNA expression and enhanced the cytotoxicity of etoposide, doxorubicin, and vincristine. The reversal effects correlated with the level of MRP mRNA expression in these cells. Our results indicate that MS-209 effectively reverses intrinsic and acquired MRP-mediated MDR of gastric cancer cells by interacting directly with MRP.
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Renes J, de Vries EG, Nienhuis EF, Jansen PL, Müller M. ATP- and glutathione-dependent transport of chemotherapeutic drugs by the multidrug resistance protein MRP1. Br J Pharmacol 1999; 126:681-8. [PMID: 10188979 PMCID: PMC1565864 DOI: 10.1038/sj.bjp.0702360] [Citation(s) in RCA: 197] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The present study was performed to investigate the ability of the multidrug resistance protein (MRPI) to transport different cationic substrates in comparison with MDR1-P-glycoprotein (MDR1). Transport studies were performed with isolated membrane vesicles from in vitro selected multidrug resistant cell lines overexpressing MDR1 (A2780AD) or MRP1 (GLC4/Adr) and a MRP1-transfected cell line (S1(MRP)). As substrates we used 3H-labelled derivatives of the hydrophilic monoquaternary cation N-(4',4'-azo-in-pentyl)-21-deoxy-ajmalinium (APDA), the basic drug vincristine and the more hydrophobic basic drug daunorubicin. All three are known MDR1-substrates. MRP1 did not mediate transport of these substrates per se. In the presence of reduced glutathione (GSH), there was an ATP-dependent uptake of vincristine and daunorubicin, but not of APDA, into GLC4/Adr and S1(MRP) membrane vesicles which could be inhibited by the MRP1-inhibitor MK571. ATP- and GSH-dependent transport of daunorubicin and vincristine into GLC4/Adr membrane vesicles was inhibited by the MRP1-specific monoclonal antibody QCRL-3. MRP1-mediated daunorubicin transport rates were dependent on the concentration of GSH and were maximal at concentrations > or = 10 mM. The apparent KM value for GSH was 2.7 mM. Transport of daunorubicin in the presence of 10 mM GSH was inhibited by MK571 with an IC50 of 0.4 microM. In conclusion, these results demonstrate that MRP1 transports vincristine and daunorubicin in an ATP- and GSH-dependent manner. APDA is not a substrate for MRP1.
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Bakos E, Evers R, Szakács G, Tusnády GE, Welker E, Szabó K, de Haas M, van Deemter L, Borst P, Váradi A, Sarkadi B. Functional multidrug resistance protein (MRP1) lacking the N-terminal transmembrane domain. J Biol Chem 1998; 273:32167-75. [PMID: 9822694 DOI: 10.1074/jbc.273.48.32167] [Citation(s) in RCA: 243] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human multidrug resistance protein (MRP1) causes drug resistance by extruding drugs from tumor cells. In addition to an MDR-like core, MRP1 contains an N-terminal membrane-bound region (TMD0) connected to the core by a cytoplasmic linker (L0). We have studied truncated MRP1 versions containing either the MDR-like core alone or the core plus linker L0, produced in the baculovirus-insect (Sf9) cell system. Their function was examined in isolated membrane vesicles. Full-length MRP1 showed ATP-dependent, vanadate-sensitive accumulation of leukotriene C4 and N-ethylmaleimide glutathione. In addition, leukotriene C4-stimulated, vanadate-dependent nucleotide occlusion was detected. The MDR-like core was virtually inactive. Co-expression of the core with the N-terminal region including L0 fully restored MRP1 function. Unexpectedly, a truncated MRP1 mutant lacking the entire TMD0 region but still containing L0 behaved like wild-type MRP1 in vesicle uptake and nucleotide trapping experiments. We also expressed the MRP1 constructs in polarized canine kidney derived MDCKII cells. Like wild-type MRP1, the MRP1 protein without the TMD0 region was routed to the lateral plasma membrane and transported dinitrophenyl glutathione and daunorubicin. The TMD0L0 and the MRP1 minus TMD0L0 remained in an intracellular compartment. Taken together, these experiments strongly suggest that the TMD0 region is neither required for the transport function of MRP1 nor for its proper routing to the plasma membrane.
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Priebe W, Krawczyk M, Kuo MT, Yamane Y, Savaraj N, Ishikawa T. Doxorubicin- and daunorubicin-glutathione conjugates, but not unconjugated drugs, competitively inhibit leukotriene C4 transport mediated by MRP/GS-X pump. Biochem Biophys Res Commun 1998; 247:859-63. [PMID: 9647783 DOI: 10.1006/bbrc.1998.8887] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Overexpression of the multidrug resistance-associated protein (MRP1) gene encoding a human GS-X pump in cultured cells resulted in increased cellular resistance to antitumor agents, including doxorubicin (Dox) and daunomycin (Dau), as well as certain heavy metals. However, studies with membrane vesicles prepared from the resistant cells revealed that Dox and Dau are poor substrates for the transport mediated by MRP/GS-X pump, suggesting that metabolic modifications of these drugs might be required for the transport. To test this hypothesis, we prepared four glutathione conjugates by linking the cysteine residue of GSH to Dox and Dau at eitehr the C-7 or C-14 position. The affinity of the synthesized conjugates toward MRP/GS-X pump was examined in the LTC4 transport assay using membrane vesicles prepared from an MRP1 gene-overexpressing cell line, SR3A. Unconjugated Dox and Dau failed to inhibit the transport of LTC4, whereas 30 microM GS-Dox or GS-Dau conjugates completely inhibited the transport. Kinetic analyses revealed that the inhibition by these GS-conjugates is competitive with Ki values ranging from 60 to 200 nM, suggesting that these compounds have high affinities toward MRP/GS-X pump and share the common binding site(s) with LTC4. Our present results support the hypothesis that glutathionation can facilitate the transport of anthracyclines by the MRP/GS-X pump.
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Stride BD, Grant CE, Loe DW, Hipfner DR, Cole SP, Deeley RG. Pharmacological characterization of the murine and human orthologs of multidrug-resistance protein in transfected human embryonic kidney cells. Mol Pharmacol 1997; 52:344-53. [PMID: 9281595 DOI: 10.1124/mol.52.3.344] [Citation(s) in RCA: 103] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Overexpression of the human multidrug-resistance protein (MRP) causes a form of multidrug resistance similar to that conferred by P-glycoprotein, although the two proteins are only distantly related. In contrast to P-glycoprotein, human MRP has also been shown to be a primary active transporter of a structurally diverse range of organic anionic conjugates, some of which may be physiological substrates. At present, the mechanism by which MRP transports these compounds and mediates multidrug resistance is not understood. With the objective of developing an animal model for studies on the normal functions of MRP and its ability to confer multidrug resistance in vivo, we recently cloned the murine ortholog of MRP (mrp). To assess the degree of functional conservation between mrp and MRP, we directly compared the drug cross-resistance profiles they confer when transfected into human embryonic kidney cells, as well as their ability to actively transport leukotriene C4, 17beta-Estradiol 17beta-(D-glucuronide), and vincristine; mrp and MRP conferred similar drug resistance profiles, with the exception that only MRP conferred resistance to the anthracyclines tested. Consistent with these findings, accumulation of [3H]vincristine and [3H]VP-16 was decreased, and efflux of [3H]vincristine was increased in both murine and human MRP-transfected cell populations, whereas only human MRP-transfected cells displayed decreased accumulation and increased efflux of [3H]daunorubicin. Membrane vesicles derived from both transfected cell populations transported leukotriene C4 in an ATP-dependent manner with comparable efficiency, although the efficiency of 17beta-estradiol 17beta-(D-glucuronide) transport was somewhat higher with MRP transfectants. ATP-dependent transport of vincristine was also observed with vesicles from mrp and MRP transfectants but only in the presence of glutathione. These studies reveal intrinsic differences between the murine and human MRP orthologs with respect to their ability to confer resistance to a major class of chemotherapeutic drugs.
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Böhme M, Müller M, Leier I, Jedlitschky G, Keppler D. Cholestasis caused by inhibition of the adenosine triphosphate-dependent bile salt transport in rat liver. Gastroenterology 1994; 107:255-65. [PMID: 8020669 DOI: 10.1016/0016-5085(94)90084-1] [Citation(s) in RCA: 107] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
BACKGROUND/AIMS Inhibition of bile salt transport across the hepatocyte during cholestasis induced by cyclosporin A has been shown. However, the contribution of the different bile salt transport systems in liver to cholestasis has remained controversial. METHODS The sensitivity of different bile salt transport systems in liver to cyclosporin-induced inhibition was determined by transport assays in plasma membrane vesicles and by in vivo studies in the rat. RESULTS Cyclosporin A--induced inhibition of sodium-dependent uptake of bile salts across the sinusoidal membrane, of potential-dependent, and of adenosine triphosphate (ATP)-dependent bile salt transport across the canalicular membrane exhibited inhibition constants (Ki) of 5, 70, and 0.2 mumol/L, respectively. The nonimmunosuppressive cyclosporin analogue PSC 833 also preferentially inhibited the ATP-dependent bile salt transport with an inhibition constant of 0.6 mumol/L. Cyclosporin A and its analogue PSC 833 [(3'-oxo-4-butenyl-4-methyl-Thr1)-(Val2)-cyclosporin] (25 mg/kg each) served as tools to interfere with [14C]taurocholate secretion into bile in vivo, causing an accumulation of [14C]-taurocholate in liver and reducing bile flow to 50%. In mutant rats deficient in the transport of leukotriene C4 and related conjugates across the canalicular membrane, bile flow was reduced to 14%. CONCLUSIONS The cyclosporins preferentially inhibit the ATP-dependent bile salt export carrier in the canalicular membrane. This inhibition reduces bile salt-dependent bile flow and causes intrahepatic cholestasis.
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