Folate concentration dependent transport activity of the Multidrug Resistance Protein 1 (ABCC1)

Jan Hendrik Hooijberg, Gerrit Jansen, Yehuda G Assaraf, Ietje Kathmann, Rob Pieters, Adrie C Laan, Anjo J P Veerman, Gertjan J L Kaspers, Godefridus J Peters

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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.

Original languageEnglish
Pages (from-to)1541-8
Number of pages8
JournalBiochemical Pharmacology
Issue number8
Publication statusPublished - 15 Apr 2004


  • ATP Binding Cassette Transporter, Subfamily B, Member 1/genetics
  • Antibiotics, Antineoplastic/pharmacokinetics
  • Biological Transport
  • Daunorubicin/pharmacokinetics
  • Female
  • Folic Acid Deficiency/metabolism
  • Folic Acid/metabolism
  • Gene Expression
  • Humans
  • Nucleotides/metabolism
  • Ovarian Neoplasms
  • Time Factors
  • Tumor Cells, Cultured

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