RT Journal Article
SR Electronic
T1 Breast Cancer Resistance Protein Exports Sulfated Estrogens but Not Free Estrogens
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 610
OP 618
DO 10.1124/mol.64.3.610
VO 64
IS 3
A1 Yasuo Imai
A1 Sakiyo Asada
A1 Satomi Tsukahara
A1 Etsuko Ishikawa
A1 Takashi Tsuruo
A1 Yoshikazu Sugimoto
YR 2003
UL http://molpharm.aspetjournals.org/content/64/3/610.abstract
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.