title: Acquired mutations in the MXR/BCRP/ABCP gene alter substrate specificity in MXR/BCRP/ABCP-overexpressing cells.
abstract: A disparity was noted in the transport of rhodamine 123 among nine MXR/BCRP/ABCP-overexpressing cells studied; all demonstrated mitoxantrone transport, whereas only two effluxed rhodamine 123. When the MXR/BCRP/ABCP gene was sequenced in the cell lines studied, differences were noted at amino acid 482, predicted to be at the start of the third transmembrane domain. Sequencing genomic DNA revealed wild-type MXR/BCRP/ABCP to have an arginine at position 482. Cells having a threonine or glycine at position 482 were able to efflux rhodamine 123, whereas cells having an arginine were not. A vaccinia virus expression system confirmed that rhodamine as well as doxorubicin efflux is observed with R482T or R482G but not with the wild-type R482; all three MXR/BCRP/ABCP forms transported mitoxantrone. Cross-resistance studies suggest that, compared with wild-type MXR/BCRP/ABCP, cells having an R482T mutation have higher anthracycline resistance, whereas an R482G mutation seems to confer relatively less resistance to SN-38 and topotecan. These results suggest that amino acid 482 has a crucial role in MXR/BCRP/ABCP function and that mutation of a single amino acid residue significantly changes substrate specificity, thus altering the drug resistance phenotype.
authors.affiliation: Cancer Therapeutics Branch, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland 20892, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Honjo
authors.forename: C A
authors.initials: CA
authors.lastname: Hrycyna
authors.forename: Q W
authors.initials: QW
authors.lastname: Yan
authors.forename: W Y
authors.initials: WY
authors.lastname: Medina-Pérez
authors.forename: R W
authors.initials: RW
authors.lastname: Robey
authors.forename: A
authors.initials: A
authors.lastname: van de Laar
authors.forename: T
authors.initials: T
authors.lastname: Litman
authors.forename: M
authors.initials: M
authors.lastname: Dean
authors.forename: S E
authors.initials: SE
authors.lastname: Bates
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism; D002166:Camptothecin / Q000031:analogs & derivatives / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology; D018432:Drug Resistance, Multiple / Q000235:genetics; D019008:Drug Resistance, Neoplasm; D019450:Genes, MDR / Q000235:genetics; D005822:Genetic Vectors / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D000077146:Irinotecan; D008942:Mitoxantrone / Q000493:pharmacokinetics / Q000494:pharmacology; D009154:Mutation; D009363:Neoplasm Proteins; D012333:RNA, Messenger / Q000235:genetics; D020112:Rhodamine 123 / Q000493:pharmacokinetics; D013379:Substrate Specificity; D019772:Topotecan / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured; D014616:Vaccinia virus / Q000235:genetics
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D020112:Rhodamine 123; D000077146:Irinotecan; D019772:Topotecan; D004317:Doxorubicin; D008942:Mitoxantrone; D002166:Camptothecin