Breast cancer resistance protein exports sulfated estrogens but not free estrogens.

Abstract

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 17beta-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 17beta-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 17beta-estradiol was independent of BCRP expression. Alternatively, increased excretion of estrone sulfate and 17beta-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 17beta-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 17beta-estradiol but exports sulfate conjugates of these estrogens.

• Authors: Yasuo Imai, Sakiyo Asada, Satomi Tsukahara, Etsuko Ishikawa, Takashi Tsuruo, Yoshikazu Sugimoto
• Journal: Molecular pharmacology (Mol Pharmacol) Vol. 64 Issue 3 Pg. 610-8 (Sep 2003) ISSN: 0026-895X [Print] United States
• PMID: 12920197 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• ABCG2 protein, human
• ATP Binding Cassette Transporter, Subfamily G, Member 2
• ATP-Binding Cassette Transporters
• Estrogens
• Estrogens, Conjugated (USP)
• Neoplasm Proteins
• Sulfates
• Estrone
• estrone sulfate

Topics

• ATP Binding Cassette Transporter, Subfamily G, Member 2
• ATP-Binding Cassette Transporters (metabolism)
• Animals
• Biological Transport
• Breast Neoplasms (metabolism)
• Cell Line
• Dose-Response Relationship, Drug
• Drug Resistance, Neoplasm
• Estrogens (metabolism)
• Estrogens, Conjugated (USP) (metabolism)
• Estrone (analogs & derivatives, metabolism)
• LLC-PK1 Cells
• Models, Molecular
• Neoplasm Proteins (metabolism)
• Sulfates (metabolism)
• Swine