title: The role of multidrug resistance proteins MRP1, MRP2 and MRP3 in cellular folate homeostasis.
abstract: Previously, we reported that the multidrug resistance proteins MRP1, MRP2 and MRP3 confer resistance to therapeutic antifolates by mediating their cellular extrusion. We now determined whether MRPs also play a role in controlling cellular homeostasis of natural folates. In MRP1, MRP2 and MRP3-transfected 2008 human ovarian carcinoma cells total cellular folate content was 32-38% lower than in 2008 cells (105+/-14pmolfolate/mgprotein) when grown in medium containing 2.3 microM folic acid (FA). Under these conditions cellular growth rates were not compromised. However, when cells were challenged under folate-depleted conditions with a short exposure (4 hr) to FA or leucovorin, MRP1 and MRP3 overexpressing cells were impaired in their growth. In contrast to wild-type cells, MRP1 transfected cells retained only 60% of the maximum growth when exposed to 500 nM leucovorin or 500 microM FA. For 2008/MRP1 and 2008/MRP3 cells FA growth stimulation capacity was dramatically decreased when, during a 4 hr exposure, metabolism into rapidly polyglutamatable and retainable dihydrofolate was blocked by the dihydrofolate reductase inhibitor trimetrexate. To retain growth under such conditions MRP1 overexpressing cells required much higher concentrations of FA (EC(50) > 500 microM) compared to 2008 cells (EC(50): 12 microM). These results suggest that down- and up-regulation of MRP1 (and MRP3) expression can influence cellular folate homeostasis, in particular when cellular retention by polyglutamylation of folates is attenuated.
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: Godefridus J
authors.initials: GJ
authors.lastname: Peters
authors.forename: Yehuda G
authors.initials: YG
authors.lastname: Assaraf
authors.forename: Ietje
authors.initials: I
authors.lastname: Kathmann
authors.forename: David G
authors.initials: DG
authors.lastname: Priest
authors.forename: Marlene A
authors.initials: MA
authors.lastname: Bunni
authors.forename: Anjo J P
authors.initials: AJ
authors.lastname: Veerman
authors.forename: George L
authors.initials: GL
authors.lastname: Scheffer
authors.forename: Gertjan J L
authors.initials: GJ
authors.lastname: Kaspers
authors.forename: Gerrit
authors.initials: G
authors.lastname: Jansen
mesh_terms: D002455:Cell Division / Q000502:physiology; D005492:Folic Acid / Q000378:metabolism / Q000502:physiology*; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D026901:Membrane Transport Proteins; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000502:physiology*; D014407:Tumor Cells, Cultured
chemical_list: D005492:Folic Acid; D026901:Membrane Transport Proteins; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; C000715087:ABCC2 protein, human; C114462:multidrug resistance-associated protein 3; C421109:multidrug resistance-associated protein 1