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

초록

Background/Aims: Clonorchis sinensis (Cs) is a common trematode in Asian countries. Cs lives in the bile duct of the host. The environment of the bile duct is very extreme to the worm’s tissues and cells by bile juice included bile acid. A report showed that sodium-bile acid co-transporter (CsSBAT) affects to the survival of Cs. The purpose of this study was an expansion of understanding of the CsSBAT function. Methods: The CsSBAT gene was cloned by the hybridization cloning method from the adult Cs cDNA library. For functional analysis of CsSBAT, Xenopus laevis oocyte expression system using various isotope-labeled substrates. Results: The open reading frame of CsSBAT cDNA consisted of 1641 bp encoding a 546-amino acid protein. When expressed in Xenopus oocytes, CsSBAT mediated the transport of radiolabeled estrone sulfate in a time- and sodium-dependent manner. CsSBAT showed no exchange properties in efflux experiments. No transuptake of carnitine, estradiol 17 β-D-glucuronide, prostaglandin E2, p-aminohippuric acid, a-ketoglutaric acid, and tetraethylammonium was observed. Concentration-dependent results showed saturable kinetics consistent with the Michaelis-Menten equation. Nonlinear regression analyses yielded a Km value of 0.3 ± 0.04 mM for [3H]estronesulfate. When an inhibition study was performed using several sulfate and glucuronide conjugates, sulfate conjugates showed a strong inhibitory effect but not glucuronide conjugates. Conclusions: From these results, CsSBAT trasnport estrone sulfate by a sodium-dependent manner, and the findings might contribute to our understanding of estrogen metabolism in Cs.