title: Folate concentration dependent transport activity of the Multidrug Resistance Protein 1 (ABCC1).
abstract: The Multidrug Resistance Protein MRP1 (ABCC1) can confer resistance to a variety of therapeutic drugs. In addition, MRP1/ABCC1 mediates cellular export of natural folates, such as folic acid and l-leucovorin. In this study we determined whether cellular folate status affected the functional activity of MRP1/ABCC1 mediated efflux of an established substrate, the anthracycline daunorubicin (DNR). As a model system we used the human ovarian carcinoma cell line 2008wt, and its MRP1/ABCC1 transfected subline 2008/MRP1. Both types of these moderate- and high-MRP1/ABCC1 expressing cells displayed efflux of DNR when maintained in standard culture media (2.3microM folic acid). The initial total cellular DNR efflux rate in 2008/MRP1 cells was approximately 2-fold higher compared to 2008wt cells. This efflux consisted of MRP1/ABCC1 mediated transport, possibly non-MRP1 mediated transport, as well as passive diffusion. Benzbromarone, a specific MRP1 inhibitor, decreased the initial efflux rate in 2008/MRP1 cells (4-fold) and in 2008wt cells (2-fold). When 2008/MRP1 cells were challenged for 2 days in folate-free medium, total cellular DNR efflux was decreased to 43% of the initial efflux rate under folate-rich conditions. In 2008wt cells DNR efflux was decreased to 84% of the folate-rich conditions. Benzbromarone did not inhibit DNR efflux after the folate-free period in both cell lines. Repletion of folate by a 2-24hr exposure to 2.5microM l-leucovorin or folic acid resulted in a complete restoration of DNR efflux. In contrast, expression of MRP1/ABCC1 protein was not changed significantly during the folate-free period or the repletion-period, nor were cellular ATP or ADP pools. In conclusion, this study demonstrates that the cellular folate status can influence the transport activity of MRP1/ABCC1. These results have potentially important implications in the understanding of the (patho-)physiological roles of MRP1/ABCC1, and possibly other ABC transporter proteins in cellular folate homeostasis and drug resistance.
authors.affiliation: Department of Pediatric Hematology/Oncology, VU University Medical Center (VUMC), De Boelelaan 1117, 1007 MB, Amsterdam, The Netherlands. jh.hooijberg@vumc.nl
authors.forename: Jan Hendrik
authors.initials: JH
authors.lastname: Hooijberg
authors.forename: Gerrit
authors.initials: G
authors.lastname: Jansen
authors.forename: Yehuda G
authors.initials: YG
authors.lastname: Assaraf
authors.forename: Ietje
authors.initials: I
authors.lastname: Kathmann
authors.forename: Rob
authors.initials: R
authors.lastname: Pieters
authors.forename: Adrie C
authors.initials: AC
authors.lastname: Laan
authors.forename: Anjo J P
authors.initials: AJ
authors.lastname: Veerman
authors.forename: Gertjan J L
authors.initials: GJ
authors.lastname: Kaspers
authors.forename: Godefridus J
authors.initials: GJ
authors.lastname: Peters
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism*; D000903:Antibiotics, Antineoplastic / Q000493:pharmacokinetics; D001692:Biological Transport; D003630:Daunorubicin / Q000493:pharmacokinetics; D005260:Female; D005492:Folic Acid / Q000378:metabolism*; D005494:Folic Acid Deficiency / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D009711:Nucleotides / Q000378:metabolism; D010051:Ovarian Neoplasms; D013997:Time Factors; D014407:Tumor Cells, Cultured
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000903:Antibiotics, Antineoplastic; D009711:Nucleotides; D005492:Folic Acid; D003630:Daunorubicin