PT  - JOURNAL ARTICLE
AU  - Imai, Yasuo
AU  - Asada, Sakiyo
AU  - Tsukahara, Satomi
AU  - Ishikawa, Etsuko
AU  - Tsuruo, Takashi
AU  - Sugimoto, Yoshikazu
TI  - Breast Cancer Resistance Protein Exports Sulfated Estrogens but Not Free Estrogens
AID  - 10.1124/mol.64.3.610
DP  - 2003 Sep 01
TA  - Molecular Pharmacology
PG  - 610--618
VI  - 64
IP  - 3
4099  - http://molpharm.aspetjournals.org/content/64/3/610.short
4100  - http://molpharm.aspetjournals.org/content/64/3/610.full
SO  - Mol Pharmacol2003 Sep 01; 64
AB  - Breast cancer resistance protein (BCRP), an ATP-binding cassette transporter, confers resistance to a series of anticancer reagents such as mitoxantrone, 7-ethyl-10-hydroxycamptothecin, and topotecan. We reported previously that estrone and 17β-estradiol reverse BCRP-mediated multidrug resistance. In the present study, we demonstrate that BCRP exports estrogen metabolites. First, we generated BCRP-transduced LLC-PK1 (LLC/BCRP) cells, in which exogenous BCRP is expressed in the apical membrane, and investigated transcellular transport of 3H-labeled compounds using cells plated on microporous filter membranes. The basal-to-apical transport (excretion) of mitoxantrone, estrone, and 17β-estradiol was greater in LLC/BCRP cells than in LLC-PK1 cells. Thin-layer chromatography of transported steroids revealed that the transport of estrone and 17β-estradiol was independent of BCRP expression. Alternatively, increased excretion of estrone sulfate and 17β-estradiol sulfate was observed in LLC/BCRP cells. BCRP inhibitors completely inhibited the increased excretion of sulfated estrogens across the apical membrane. Conversion of estrogens into their sulfate conjugates was similar between LLC/BCRP and LLC-PK1 cells, suggesting that the increased excretion of estrogen sulfates was attributable to BCRP-mediated transport. Next, the uptake of 3H-labeled compounds in membrane vesicles from BCRP-transduced K562 (K562/BCRP) cells was investigated. 3H-labeled estrone sulfate, but not 3H-labeled estrone or 17β-estradiol, was taken up by membrane vesicles from K562/BCRP cells, and this was ATP-dependent. Additionally, BCRP inhibitors suppressed the transport of estrone sulfate in membrane vesicles from K562/BCRP cells. These results suggest that BCRP does not transport either free estrone or 17β-estradiol but exports sulfate conjugates of these estrogens.