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J. Biol. Chem., Vol. 282, Issue 27, 19728-19741, July 6, 2007

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Cloning and Functional Characterization of Human Sodium-dependent Organic Anion Transporter (SLC10A6)^*

Joachim Geyer¹, Barbara Döring, Kerstin Meerkamp, Bernhard Ugele, Nadiya Bakhiya^¶, Carla F. Fernandes, José R. Godoy, Hansruedi Glatt^¶, and Ernst Petzinger

From the Institute of Pharmacology and Toxicology, Justus-Liebig-University of Giessen, Frankfurter Strasse 107, 35392 Giessen, Germany, University Hospital, Ludwig-Maximilians-University of Munich, 80337 Munich, Germany, and the ^¶Department of Nutritional Toxicology, German Institute of Human Nutrition Potsdam-Rehbrücke, 14558 Nuthetal, Germany

We have cloned human sodium-dependent organic anion transporter (SOAT) cDNA, which consists of 1502 bp and encodes a 377-amino acid protein. SOAT shows 42% sequence identity to the ileal apical sodium-dependent bile acid transporter ASBT and 33% sequence identity to the hepatic Na⁺/taurocholate-cotransporting polypeptide NTCP. Immunoprecipitation of a SOAT-FLAG-tagged protein revealed a glycosylated form at 46 kDa that decreased to 42 kDa after PNGase F treatment. SOAT exhibits a seven-transmembrane domain topology with an outside-to-inside orientation of the N-terminal and C-terminal ends. SOAT mRNA is most highly expressed in testis. Relatively high SOAT expression was also detected in placenta and pancreas. We established a stable SOAT-HEK293 cell line that showed sodium-dependent transport of dehydroepiandrosterone sulfate, estrone-3-sulfate, and pregnenolone sulfate with apparent K_m values of 28.7, 12.0, and 11.3 µM, respectively. Although bile acids, such as taurocholic acid, cholic acid, and chenodeoxycholic acid, were not substrates of SOAT, the sulfoconjugated bile acid taurolithocholic acid-3-sulfate was transported by SOAT-HEK293 cells in a sodium-dependent manner and showed competitive inhibition of SOAT transport with an apparent K_i value of 0.24 µM. Several nonsteroidal organosulfates also strongly inhibited SOAT, including 1-(-sulfooxyethyl)pyrene, bromosulfophthalein, 2- and 4-sulfooxymethylpyrene, and -naphthylsulfate. Among these inhibitors, 2- and 4-sulfooxymethylpyrene were competitive inhibitors of SOAT, with apparent K_i values of 4.3 and 5.5 µM, respectively, and they were also transported by SOAT-HEK293 cells.

Received for publication, March 28, 2007

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank^TM/EBI Data Bank with accession number(s) AJ583502 [GenBank] and EF437223.

^* This study was supported by the German Research Foundation (Deutsche Forschungsgemeinschaft, Bonn, Germany) Grant GE1921/1-1 (to J. G. and K. M.) and Graduate Research Program 455 "Molecular Veterinary Medicine" (to B. D. and J. R. G.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed. Tel.: 49-641-9938404; Fax: 49-641-9938419; E-mail: joachim.m.geyer{at}vetmed.uni-giessen.de.

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