Although circulating
estrone-3-sulfate is a major precursor of biologically active
estrogen, permeation across the plasma membrane is unlikely to occur by diffusion because of the high hydrophilicity of the molecule. The object of this study was to clarify the involvement of specific transporter(s) in the supply of
estrone-3-sulfate to human
breast cancer-derived T-47D cells, which grow in an
estrogen-dependent manner. The proliferation of T-47D cells was increased by the addition of
estrone-3-sulfate, or
estradiol, to the cultivation medium. The initial uptake rate of
estrone-3-sulfate kinetically exhibited a single saturable component, with Km and Vmax values of 7.6 microM and 172 pmol/mg of
protein/min, respectively. The replacement of extracellular Na+ with Li+, K+, or N-methylglucamine+ had no effect on the uptake of [3H]
estrone-3-
sulfate. The uptake was strongly inhibited by
sulfate conjugates of
steroid hormones, but not by
estradiol-17beta-glucuronide.
Taurocholate and
sulfobromophthalein inhibited the uptake, whereas other tested anionic and cationic compounds did not. The expression of organic
anion transporting
polypeptides, OATP-D and OATP-E, which are candidate transporters of
estrone-3-sulfate, was detected by reverse transcription-polymerase chain reaction analysis, although their actual involvement in the uptake of
estrogen remains to be clarified. In conclusion, the uptake of
estrone-3-sulfate by T-47D cells was mediated by a carrier-mediated transport mechanism, suggesting that the
estrogen precursor is actively imported by
estrogen-dependent
breast cancer cells.