title: Regulation of breast cancer resistant protein by peroxisome proliferator-activated receptor α in human brain microvessel endothelial cells.
abstract: Breast cancer resistance protein (BCRP/ABCG2), an ATP-binding cassette (ABC) membrane-associated drug efflux transporter, is known to localize at the blood-brain barrier (BBB) and can significantly restrict xenobiotic permeability in the brain. The objective of this study is to investigate the regulation of BCRP functional expression by peroxisome proliferator-activated receptor alpha (PPARα), a ligand-activated transcription factor primarily involved in lipid metabolism, in a cerebral microvascular endothelial cell culture system (hCMEC/D3), representative of human BBB. We demonstrate that PPARα-selective ligands (i.e., clofibrate, GW7647) significantly induce BCRP mRNA and protein expression in a time- and concentration-dependent manner, whereas pharmacological inhibitors (i.e., MK886, GW6471) prevent this induction. Using [(3)H]mitoxantrone, an established BCRP substrate, we observe a significant reduction in its cellular accumulation by monolayer cells treated with clofibrate, suggesting increased BCRP efflux activity. In addition, we show a significant decrease in BCRP protein expression and function when PPARα is down-regulated by small interfering RNA. Applying chromatin immunoprecipitation and quantitative real-time polymerase chain reaction, we observe that clofibrate treatment increases PPARα binding to the peroxisome proliferator response element within the ABCG2 gene promoter. This study provides the first evidence of direct BCRP regulation by PPARα in a human in vitro BBB model and suggests new targeting strategies for either improving drug brain bioavailability or increasing neuroprotection.
authors.affiliation: Graduate Department of Pharmaceutical Sciences, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Md Tozammel
authors.initials: MT
authors.lastname: Hoque
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Robillard
authors.forename: Reina
authors.initials: R
authors.lastname: Bendayan
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000502:physiology*; D001483:Base Sequence; D001682:Biological Availability; D001812:Blood-Brain Barrier; D001921:Brain / Q000098:blood supply*; D002461:Cell Line, Transformed; D047369:Chromatin Immunoprecipitation; D017931:DNA Primers; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006801:Humans; D055806:Microvessels / Q000166:cytology / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000502:physiology*; D047493:PPAR alpha / Q000502:physiology*; D060888:Real-Time Polymerase Chain Reaction
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D017931:DNA Primers; D009363:Neoplasm Proteins; D047493:PPAR alpha