Original ArticlesA naturally occurring mutation in MRP1 results in a selective decrease in organic anion transport and in increased doxorubicin resistanceConrad, Silkea; Kauffmann, Hans-Martina; Ito, Ken-ichib; Leslie, Elaine M.b; Deeley, Roger G.b; Schrenk, Dietera; Cole, Susan P. C.bAuthor Information aFood Chemistry and Environmental Toxicology, University of Kaiserslautern, Kaiserslautern, Germany and bCancer Research Laboratories, Queen′s University, Kingston, Ontario, Canada Correspondence to Susan P.C. Cole, Canada Research Chair in Cancer Biology and Senior Scientist of Cancer Care Ontario, Cancer Research Laboratories, Room 328 Botterell Hall, Queen's University, Kingston, Ontario K7L 3N6, Canada Tel: +1 613 533 6507; fax: +1 613 533 6830; e-mail: [email protected] Received 23 January 2002 Accepted 9 March 2002 Pharmacogenetics: June 2002 - Volume 12 - Issue 4 - p 321-330 Buy Abstract The human 190 kDa multidrug resistance protein, MRP1, is a polytopic membrane glycoprotein that confers resistance to a wide range of chemotherapeutic agents. It also transports structurally diverse conjugated organic anions, as well as certain unconjugated and conjugated compounds, in a reduced glutathione-stimulated manner. In this study, we characterized a low-frequency (< 1%) naturally occurring mutation in MRP1 expected to cause the substitution of a conserved arginine with serine at position 433 in a predicted cytoplasmic loop of the protein. Transport experiments with membrane vesicles prepared from transfected human embryonic kidney cells and HeLa cells revealed a two-fold reduction in the ATP-dependent transport of the MRP1 substrates, leukotriene C4 (LTC4) and oestrone sulphate. Kinetic analysis showed that this reduction was due to a decrease in Vmax for both substrates but Km was unchanged. In contrast, 17β-oestradiol-17β-(D-glucuronide) transport by the Arg433Ser mutant MRP1 was similar to that by wild-type MRP1. Fluorescence confocal microscopy showed that the mutant MRP1 was routed correctly to the plasma membrane. In contrast to the reduced LTC4 and oestrone sulphate transport, stably transfected HeLa cells expressing Arg433Ser mutant MRP1 were 2.1-fold more resistant to doxorubicin than cells expressing wild-type MRP1, while resistance to VP-16 and vincristine was unchanged. These results provide the first example of a naturally occurring mutation predicted to result in an amino acid substitution in a cytoplasmic region of MRP1 that shows an altered phenotype with respect to both conjugated organic anion transport and drug resistance. © 2002 Lippincott Williams & Wilkins, Inc.