title: The human multidrug resistance protein MRP5 transports folates and can mediate cellular resistance against antifolates.
abstract: Members of the multidrug resistance protein family, notably MRP1-4/ABCC1-4, and the breast cancer resistance protein BCRP/ABCG2 have been recognized as cellular exporters for the folate antagonist methotrexate (MTX). Here we show that MRP5/ABCC5 is also an antifolate and folate exporter based on the following evidence: (a) Using membrane vesicles from HEK293 cells, we show that MRP5 transports both MTX (KM = 1.3 mmol/L and VMAX = 780 pmol per mg protein per minute) and folic acid (KM = 1.0 mmol/L and VMAX = 875 pmol per mg protein per minute). MRP5 also transports MTX-glu2 (KM = 0.7 mmol/L and VMAX = 450 pmol per mg protein per minute) but not MTX-glu3. (b) Both accumulation of total [3H]MTX and of MTX polyglutamates were significantly reduced in MRP5 overexpressing cells. (c) Cell growth inhibition studies with MRP5 transfected HEK293 cells showed that MRP5 conferred high-level resistance (>160-fold) against the antifolates MTX, GW1843, and ZD1694 (raltitrexed) in short-term (4 hours) incubations with high drug concentrations; this resistance was proportional to the MRP5 level. (d) MRP5-mediated resistance (8.5- and 2.1-fold) was also found in standard long-term incubations (72 hours) at low concentrations of ZD1694 and GW1843. These results show the potential of MRP5 to mediate transport of (anti)folates and contribute to resistance against antifolate drugs.
authors.affiliation: Division of Molecular Biology and Center of Biomedical Genetics, The Netherlands Cancer Institute, Amsterdam.
authors.forename: Peter
authors.initials: P
authors.lastname: Wielinga
authors.forename: Jan Hendrik
authors.initials: JH
authors.lastname: Hooijberg
authors.forename: Sjofn
authors.initials: S
authors.lastname: Gunnarsdottir
authors.forename: Ietje
authors.initials: I
authors.lastname: Kathmann
authors.forename: Glen
authors.initials: G
authors.lastname: Reid
authors.forename: Noam
authors.initials: N
authors.lastname: Zelcer
authors.forename: Kasper
authors.initials: K
authors.lastname: van der Born
authors.forename: Marcel
authors.initials: M
authors.lastname: de Haas
authors.forename: Ingrid
authors.initials: I
authors.lastname: van der Heijden
authors.forename: Gertjan
authors.initials: G
authors.lastname: Kaspers
authors.forename: Jan
authors.initials: J
authors.lastname: Wijnholds
authors.forename: Gerrit
authors.initials: G
authors.lastname: Jansen
authors.forename: Godefridus
authors.initials: G
authors.lastname: Peters
authors.forename: Piet
authors.initials: P
authors.lastname: Borst
mesh_terms: D001692:Biological Transport; D002460:Cell Line; D005492:Folic Acid / Q000493:pharmacokinetics*; D005493:Folic Acid Antagonists / Q000493:pharmacokinetics*; D006801:Humans; D008727:Methotrexate / Q000031:analogs & derivatives* / Q000493:pharmacokinetics*; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism*; D011099:Polyglutamic Acid / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D013379:Substrate Specificity
chemical_list: D005492:Folic Acid; D005493:Folic Acid Antagonists; D008727:Methotrexate; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D011099:Polyglutamic Acid; C120809:ABCC5 protein, human; C014085:methotrexate polyglutamate