title: Estrogen receptor beta signaling through phosphatase and tensin homolog/phosphoinositide 3-kinase/Akt/glycogen synthase kinase 3 down-regulates blood-brain barrier breast cancer resistance protein.
abstract: Breast cancer resistance protein (BCRP) is an ATP-driven efflux pump at the blood-brain barrier that limits central nervous system pharmacotherapy. Our previous studies showed rapid loss of BCRP transport activity in rat brain capillaries exposed to low concentrations of 17-beta-estradiol (E2); this occurred without acute change in BCRP protein expression. Here, we describe a pathway through which sustained, extended exposure to E2 signals down-regulation of BCRP at the blood-brain barrier. Six-hour exposure of isolated rat and mouse brain capillaries to E2 reduced BCRP transport activity and BCRP monomer and dimer expression. Experiments with brain capillaries from estrogen receptor (ER)alpha and ERbeta knockout mice and with ER agonists and antagonists showed that E2 signaled through ERbeta to down-regulate BCRP expression. In rat brain capillaries, E2 increased unphosphorylated, active phosphatase and tensin homolog (PTEN); decreased phosphorylated, active Akt; and increased phosphorylated, active glycogen synthase kinase (GSK)3. Consistent with this, inhibition of phosphoinositide 3-kinase (PI3K) or Akt decreased BCRP activity and protein expression, and inhibition of PTEN or GSK3 reversed the E2 effect on BCRP. Lactacystin, a proteasome inhibitor, abolished E2-mediated BCRP down-regulation, suggesting internalization followed by transporter degradation. Dosing mice with E2 reduced BCRP activity in brain capillaries within 1 h; this reduction persisted for 24 h. BCRP protein expression in brain capillaries was unchanged 1 h after E2 dosing but was substantially reduced 6 and 24 h after dosing. Thus, E2 signals through ERbeta, PTEN/PI3K/Akt/GSK3 to stimulate proteasomal degradation of BCRP. These in vitro and in vivo findings imply that E2-mediated down-regulation of blood-brain barrier BCRP has the potential to increase brain uptake of chemotherapeutics that are BCRP substrates.
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical School Duluth, University of Minnesota, Duluth, Minnesota 55812, USA.
authors.forename: A M S
authors.initials: AM
authors.lastname: Hartz
authors.forename: E K
authors.initials: EK
authors.lastname: Madole
authors.forename: D S
authors.initials: DS
authors.lastname: Miller
authors.forename: B
authors.initials: B
authors.lastname: Bauer
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis*; D000818:Animals; D001812:Blood-Brain Barrier / Q000378:metabolism*; D002196:Capillaries / Q000378:metabolism; D015536:Down-Regulation; D004958:Estradiol / Q000494:pharmacology; D047628:Estrogen Receptor alpha / Q000235:genetics; D047629:Estrogen Receptor beta / Q000819:agonists / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D005260:Female; D038362:Glycogen Synthase Kinase 3 / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D051059:PTEN Phosphohydrolase / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D010744:Phosphoric Monoester Hydrolases / Q000502:physiology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction
chemical_list: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; C501412:Abcg2 protein, mouse; C489249:Abcg2 protein, rat; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D004958:Estradiol; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3; D010744:Phosphoric Monoester Hydrolases; D051059:PTEN Phosphohydrolase; C487757:Pten protein, mouse; C487216:Pten protein, rat; D046988:Proteasome Endopeptidase Complex
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