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• The MRP gene encodes an ATP-dependent export pump for leukotriene C4 and structurally related conjugates.

  Leier I., Jedlitschky G., Buchholz U., Cole S.P., Deeley R.G., Keppler D.

  The multidrug resistance-associated protein (MRP) is the product of an ATP-binding cassette transporter gene overexpressed in some tumor cells resistant to antineoplastic agents. We studied the transport function of MRP in membrane vesicles prepared from HeLa cells transfected with an MRP expressi ... >> More

  The multidrug resistance-associated protein (MRP) is the product of an ATP-binding cassette transporter gene overexpressed in some tumor cells resistant to antineoplastic agents. We studied the transport function of MRP in membrane vesicles prepared from HeLa cells transfected with an MRP expression vector and overexpressing this 190-kDa membrane glycoprotein. ATP-dependent primary-active transport into the vesicles was demonstrated for leukotriene C4 (LTC4), LTD4, LTE4, and S-(2,4-dinitrophenyl)glutathione with relative rates, at a substrate concentration of 50 nM, of 1.0, 0.27, 0.14, and 0.16, respectively. The endogenous glutathione conjugate LTC4 had the highest affinity for this transporter with a Km of 97 nM. The Km for ATP was 19 microM. Direct photoaffinity labeling with [3H]LTC4 labeled a 190-kDa membrane protein predominantly in the MRP-transfected HeLa cells. ATP-dependent LTC4 transport was effectively inhibited by the LTD4 receptor antagonist MK 571, whereas cyclosporin A and, particularly, its analog PSC 833 were much less potent. The respective Ki values were 0.6, 5, and 27 microM, respectively. In addition, MK 571 preferentially inhibited photoaffinity labeling of the 190-kDa protein in the MRP transfectants. Our results provide direct evidence that the MRP gene encodes a primary-active ATP-dependent export pump for conjugates of lipophilic compounds with glutathione and several other anionic residues. We conclude that the biosynthetic release of LTC4 from cells is mediated by the 190-kDa product of the MRP gene. << Less

  J. Biol. Chem. 269:27807-27810(1994) [PubMed] [EuropePMC]

• Pharmacological characterization of the murine and human orthologs of multidrug-resistance protein in transfected human embryonic kidney cells.

  Stride B.D., Grant C.E., Loe D.W., Hipfner D.R., Cole S.P.C., Deeley R.G.

  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 ... >> More

  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. << Less

  Mol. Pharmacol. 52:344-353(1997) [PubMed] [EuropePMC]

  This publication is cited by 3 other entries.

• Increased sensitivity to anticancer drugs and decreased inflammatory response in mice lacking the multidrug resistance-associated protein.

  Wijnholds J., Evers R., van Leusden M.R., Mol C.A., Zaman G.J., Mayer U., Beijnen J.H., van der Valk M., Krimpenfort P., Borst P.

  The multidrug resistance-associated protein (MRP) mediates the cellular excretion of many drugs, glutathione S-conjugates (GS-X) of lipophilic xenobiotics and endogenous cysteinyl leukotrienes. Increased MRP levels in tumor cells can cause multidrug resistance (MDR) by decreasing the intracellular ... >> More

  The multidrug resistance-associated protein (MRP) mediates the cellular excretion of many drugs, glutathione S-conjugates (GS-X) of lipophilic xenobiotics and endogenous cysteinyl leukotrienes. Increased MRP levels in tumor cells can cause multidrug resistance (MDR) by decreasing the intracellular drug concentration. The physiological role or roles of MRP remain ill-defined, however. We have generated MRP-deficient mice by using embryonic stem cell technology. Mice homozygous for the mrp mutant allele, mrp-/-, are viable and fertile, but their response to an inflammatory stimulus is impaired. We attribute this defect to a decreased secretion of leukotriene C4 (LTC4) from leukotriene-synthesizing cells. Moreover, the mrp-/-mice are hypersensitive to the anticancer drug etoposide. The phenotype of mrp-/-mice is consistent with a role for MRP as the main LTC4-exporter in leukotriene-synthesizing cells, and as an important drug exporter in drug-sensitive cells. Our results suggest that this ubiquitous GS-X pump is dispensable in mice, making treatment of MDR with MRP-specific reversal agents potentially feasible. << Less

  Nat. Med. 3:1275-1279(1997) [PubMed] [EuropePMC]