Functional characterization of Clonorchis sinensis sodium-bile acid co-transporter (CsSBAT) as a steroid sulfate transporter.

Clonorchis sinensis (Cs) is a common trematode in Asian countries. Infection by Cs can result in many clinical symptoms. Here, a cDNA encoding a Cs apical sodium-dependent bile acid transporter (CsSBAT) was isolated from a Cs cDNA library, and functional characterization was performed using Xenopus laevis oocyte expression system. When expressed in Xenopus laevis oocytes, CsSBAT mediated the transport of radiolabeled estrone sulfate and dehydroepiandrosterone sulfate. No trans-uptake of carnitine, estradiol 17 ß-D glucuronide, prostaglandin E2, p-aminohippuric acid, α-ketoglutaric acid, and tetraethylammonium was observed. CsSBAT-mediated estrone sulfate uptake was in a time- and sodium-dependent manner. CsSBAT showed no exchange properties in efflux experiments. Concentration-dependent results showed saturable kinetics consistent with the Michaelis-Menten equation. Nonlinear regression analyses yielded a Km value of 0.3 ± 0.04 µM for [3H]estrone sulfate. CsSBAT-mediated estrone sulfate uptake was strongly inhibited by sulfate conjugates but not glucuronide conjugates. These findings contribute to our understanding of CsSBAT transport properties and the cascade of estrogen metabolite movement in Cs.