title: Functional analysis of the human variants of breast cancer resistance protein: I206L, N590Y, and D620N.
abstract: Previous studies have shown that the V12M and Q141K variants of breast cancer resistance protein (BCRP) can affect expression and function of the transporter. In this study, the effects of the I206L, N590Y, and D620N variants on protein expression, plasma membrane localization, and transport activity of BCRP were investigated. Wild-type BCRP and the three variants were stably expressed in human embryonic kidney (HEK) cells. Confocal microscopy analysis showed that the three variants were predominantly routed to the plasma membrane of HEK cells. The expression level of I206L in the plasma membrane was approximately 45% of that of wild-type protein, whereas the N590Y and D620N levels were increased approximately 3.6-fold and 2.4-fold, respectively, as determined by immunoblotting. All three variants transported mitoxantrone, pheophorbide a, and BODIPY FL-prazosin. After normalization for differences in BCRP expression, I206L, N590Y, and D620N exhibited approximately 2-fold, 0.3-fold, and 0.5-fold wild-type efflux activities, respectively. The variants also conferred resistance to mitoxantrone and topotecan. Mitoxantrone and topotecan resistance by I206L and N590Y was approximately 2-fold and 0.3-fold of the wild-type BCRP resistance levels, respectively. Although D620N conferred a topotecan resistance similar to that of the wild-type protein, its level of mitoxantrone resistance was decreased by 50%. After normalization to BCRP expression levels, ATPase activities of I206L were not significantly different from those of wild-type protein, whereas N590Y and D620N exhibited approximately 30% and 50% of wild-type ATPase activities, respectively. These results suggest that I206L has the lowest protein expression and the highest activity, whereas N590Y and D620N display higher expression and lower activity, relative to wild-type BCRP.
authors.affiliation: Department of Pharmaceutics, School of Pharmacy, University of Washington, Box 357610, Seattle, WA 98195-7610, USA.
authors.forename: R Robert
authors.initials: RR
authors.lastname: Vethanayagam
authors.forename: Honggang
authors.initials: H
authors.lastname: Wang
authors.forename: Anshul
authors.initials: A
authors.lastname: Gupta
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.forename: Fred
authors.initials: F
authors.lastname: Lewis
authors.forename: Jashvant D
authors.initials: JD
authors.lastname: Unadkat
authors.forename: Qingcheng
authors.initials: Q
authors.lastname: Mao
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D000483:Alleles; D019943:Amino Acid Substitution / Q000235:genetics*; D000970:Antineoplastic Agents / Q000494:pharmacology; D001216:Asparagine / Q000235:genetics; D001224:Aspartic Acid / Q000235:genetics; D002460:Cell Line; D019008:Drug Resistance, Neoplasm / Q000187:drug effects / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D014644:Genetic Variation / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D006801:Humans; D007532:Isoleucine / Q000235:genetics; D007930:Leucine / Q000235:genetics; D009363:Neoplasm Proteins / Q000235:genetics*; D020641:Polymorphism, Single Nucleotide; D014162:Transfection / Q000379:methods; D014443:Tyrosine / Q000235:genetics
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D009363:Neoplasm Proteins; D007532:Isoleucine; D001224:Aspartic Acid; D014443:Tyrosine; D001216:Asparagine; D007930:Leucine