CLONING OF THE SODIUM-DEPENDENT, BROAD-SCOPE, NEUTRAL AMINO-ACID TRANSPORTER B-O FROM A HUMAN PLACENTAL CHORIOCARCINOMA CELL-LINE

We have isolated a cDNA from a human placental choriocarcinoma cell cD NA library which, when expressed in HeLa cells, induces a Na+-dependen t amino acid transport system with preference for zwitterionic amino a cids, Anionic amino acids, cationic amino acids, imino acids, and N-me thylated amino acids are excluded by this system, These characteristic s are identical to those described for the amino acid transporter B-o. When expressed in Xenopus laevis oocytes that do not have detectable endogenous activity of the amino acid transporter B-o, the cloned tran sporter increases alanine transport in the oocytes severalfold and ind uces alanine-evoked inward currents in the presence of Na+. The cDNA c odes for a polypeptide containing 541 amino acids with 10 putative tra nsmembrane domains, Amino acid sequence homology predicts this transpo rter (hATB(o)) to be a member of a superfamily consisting of the gluta mate transporters, the neutral amino acid transport system ASCT, and t he insulin-activable neutral/anionic amino acid transporter, Chromosom al assignment studies with somatic cell hybrid analysis and fluorescen t in situ hybridization have located the ATB(o) gene to human chromoso me 19q13.3.