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 cDNA library which, when expressed in HeLa cells, induces a Na+-dependent amino acid transport system with preference for zwitterionic amino acids, Anionic amino acids, cationic amino acids, imino acids, and N-methylated amino acids are excluded by this system, These characteristics 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 transporter increases alanine transport in the oocytes severalfold and induces alanine-evoked inward currents in the presence of Na+. The cDNA codes for a polypeptide containing 541 amino acids with 10 putative transmembrane domains, Amino acid sequence homology predicts this transporter (hATB(o)) to be a member of a superfamily consisting of the glutamate transporters, the neutral amino acid transport system ASCT, and the insulin-activable neutral/anionic amino acid transporter, Chromosomal assignment studies with somatic cell hybrid analysis and fluorescent in situ hybridization have located the ATB(o) gene to human chromosome 19q13.3.