Identification of human multidrug resistance protein 1 (MRP1) mutations and characterization of a G671V substitution

The multidrug resistance protein 1 (MRP1) belonging to the ATP-binding cass ette (ABC) superfamily of transport proteins can confer resistance to multi ple natural product drugs and methotrexate in human tumor cells. In additio n, MRP1 is expressed in normal tissues acting as an efflux pump for glutath ione, glucuronate, and sulfate conjugates and may thus influence the pharma cokinetic properties of many drugs. Using polymerase chain reaction-single- strand conformation polymorphism analysis, we screened 36 Caucasian volunte ers for mutations in the coding exons of the MRP1 gene, including the adjac ent intron sequences. Among several mutations found. two are expected to ca use amino acid substitutions. One of these mutations (G671V) was of special interest because it is located near the first nucleotide binding domain. T o determine whether this mutation caused a change in the MRP1 phenotype, a mutant MRP1 expression vector was constructed and transfected into SV40-tra nsformed human embryonic kidney cells (HEKSV293T) and the transport propert ies of the mutant protein were examined. Transport of the MRP1 substrates l eukotriene C-4, 17 beta -estradiol 17 beta-(D)-glucuronide, and estrone sul fate by membrane vesicles prepared from transiently transfected HEKSV293T c ells was comparable to that of wild-type MRP1.