Identification of a novel gene family encoding human liver-specific organic anion transporter LST-1

We have isolated a novel liver-specific organic anion transporter, LST-1, t hat is expressed exclusively in the human, rat, and mouse liver. LST-1 is a new gene family located between the organic anion transporter family and p rostaglandin transporter. LST-1 transports taurocholate (K-m = 13.6 mu M) i n a sodium-independent manner. LST-1 also shows broad substrate specificity . It transports conjugated steroids (dehydroepiandrosterone sulfate, estrad iol-17 beta-glucuronide, and estrone-3-sulfate), eicosanoids (prostaglandin E-2, thromboxane B-2, leukotriene C-4, leukotriene E-4), and thyroid hormo nes (thyroxine, K-m = 3.0 mu M and triiodothyronine, K-m = 2.7 mu M), refle cting hepatic multispecificity. LST-1 is probably the most important transporter in human Liver for clearan ce of bile acids and organic anions because hepatic levels of another organ ic anion transporter, OATP, is very low. This is also the first report of t he human molecule that transports thyroid hormones.