Estrogen Receptor β 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-␤-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)␣ and ER␤ knockout mice and with ER agonists and antagonists showed that E2 signaled through ER␤ 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 ER␤, PTEN/PI3K/Akt/GSK3 to stimulate proteasomal degradation of BCRP. These in vitro and in vivo findings imply that E2-mediated down-regulation of bloodbrain barrier BCRP has the potential to increase brain uptake of chemotherapeutics that are BCRP substrates.

Identification of Estrogen Receptor β as a SUMO-1 Target Reveals a Novel Phosphorylated Sumoylation Motif and Regulation by Glycogen Synthase Kinase 3β

“…GSK3␤ is active in resting cells through constitutive Tyr-216 phosphorylation, and PI3K/Akt-activating stimuli such as insulin can cause phosphorylation at Ser-9 and inactivation of GSK3␤ (8). The mechanism by which nongenomic activation of ER␤ might contribute to Ser-9 dephosphorylation and GSK3␤ activation in our study is still uncertain, but recent findings in rodent brain capillaries and breast cancer cells have shown that sustained ER␤ activation by extended exposure to estradiol resulted in PTEN activation and decreased GSK3 phosphorylation (19,27). Interestingly, part of the mechanism involved might also refer to the ER␤ response to Akt activation, as we demonstrated that activation of the PI3K/Akt pathway downregulated ER␤ degradation and activity in breast cancer cells (38).…”

Protein repertoire impact of Ubiquitin–Proteasome System impairment: Insight into the protective role of beta-estradiol

“…To evaluate the effect of estradiol [34][35][36] on low-dose Epoxomicin treatment of NB cells we treated SH-SY5Y cells with betaestradiol for 24 h before exposing them to Epoxomicin for 24 and 48 h. Our results show that while estradiol treatment has a modest effect on cell cycle distribution of Epoxomicin treated cells for both 24 and 48 h (Fig. 4A).…”

Regulation of ABC Transporters Blood–Brain Barrier

“…Rodent brain capillaries (from females and males) express both ERα and ERβ, with expression of the latter dominating at both the mRNA and proteins levels (Hartz, Madole, Miller, & Bauer, 2010;Hartz, Mahringer, Miller, & Bauer, 2010). Exposing rat and mouse brain capillaries to subnanomolar to nanomolar concentrations of estradiol (E2) rapidly (minutes) and reversibly reduces BCRP-mediated transport activity without altering protein expression (Fig.…”

“…Exposing rat and mouse brain capillaries to subnanomolar to nanomolar concentrations of estradiol (E2) rapidly (minutes) and reversibly reduces BCRP-mediated transport activity without altering protein expression (Fig. 6) Hartz, Madole, et al, 2010). The reduction in activity is not altered by inhibitors of transcription and translation, but is blocked by Brefeldin A, an inhibitor of intracellular vesicle trafficking.…”

“…Note that extending the time of exposure to E2 reduces BCRP mRNA and protein expression (Hartz, Madole, et al, 2010;Mahringer & Fricker, 2010). These effects are mediated by ERβ, which signals though phosphatase and tensin homolog (PTEN), phosphatidylinositide 3-kinase (PI3-K), Akt, and glycogen synthase kinase 3 beta (GSK-3β) (Fig.…”