Apical sodium-dependent bile acid transporter of Clonorchis sinensis acts as steroid hormone transporter

초록

The main habitat of Clonorchis sinensis (Cs) is bile duct. Because of bile acid toxicity, their living environment may be extreme condition. Thus, to maintain their life they have to control the bile acid with influx and efflux system. We, therefore, try to isolate and characterize the apical sodium-dependent bile acid transporter of Cs. From NCBI database, apical sodium-dependent bile acid transporter (ARO50445.1, CsASBAT) was selected. The selected gene was isolated using from cDNA library screening. The CsASBAT cDNA consists of 2031 base pairs which encoded a 546-amino acid residue protein. Hydropathy analysis showed 10 putative transmembrane-spanning domains with 4 N-glycosylation and 3 protein kinase C motifs. When expressed in Xenopus oocytes, radiolabeled estrone sulfate in a time- and sodium-dependent manner. The CsASBAT showed no exchange mode of estrone sulfate by efflux experiments. Concentration-dependency results showed saturable kinetics following Michaelis-Menten equation. Nonlinear regression analyses yielded a Km value of 0.3 ± 0.03 ?M for [3H]estrone sulfate. These results suggest that this transporter may acts as eliminatory system of freely entered estrogen by forming sulfate conjugate with estrogen sulfotransferase.