Estrogen regulation and ion dependence of taurine uptake by MCF-7 human breast cancer cells

It has been reported that estrogen receptor-positive MCF-7 cells express TauT, a Na(+)-dependent taurine transporter. However, there is a paucity of information relating to the characteristics of taurine transport in this human breast cancer cell line. Therefore, we have examined the characteristics and regulation of taurine uptake by MCF-7 cells. Taurine uptake by MCF-7 cells showed an absolute dependence upon extracellular Na(+). Although taurine uptake was reduced in Cl(-) free medium a significant portion of taurine uptake persisted in the presence of NO(3) (-). Taurine uptake by MCF-7 cells was inhibited by extracellular β-alanine but not by L-alanine or L-leucine. 17β-estadiol increased taurine uptake by MCF-7 cells: the V(max) of influx was increased without affecting the K(m). The effect of 17β-estradiol on taurine uptake by MCF-7 cells was dependent upon the presence of extracellular Na(+). In contrast, 17β-estradiol had no significant effect on the kinetic parameters of taurine uptake by estrogen receptor-negative MDA-MB-231 cells. It appears that estrogen regulates taurine uptake by MCF-7 cells via TauT. In addition, Na(+)-dependent taurine uptake may not be strictly dependent upon extracellular Cl(-).