Cloning and Functional Expression of a Human Na+and Cl−-dependent Neutral and Cationic Amino Acid Transporter B0+

Abstract

A Na؉ -dependent neutral and cationic amino acid transport system (B 0؉) plays an important role in many cells and tissues; however, the molecular basis for this transport system is still unknown. To identify new transporters, the expressed sequence tag database was queried, and cDNA fragments with sequence similarity to the Na ؉ /Cl ؊ -dependent neurotransmitter transporter family were identified. Based on these sequences, rapid amplification of cDNA ends of human mammary gland cDNA was used to obtain a cDNA of 4.5 kilobases (kb). The open reading frame encodes a 642-amino acid protein named amino acid transporter B 0؉ . Human ATB 0؉(hATB 0؉ ) is a novel member of the Na ؉ /Cl ؊ -dependent neurotransmitter transporter family with the highest sequence similarity to the glycine and proline transporters. Northern blot analysis identified transcripts of ϳ4.5 kb and ϳ2 kb in the lung. Another tissue survey suggests expression in the trachea, salivary gland, mammary gland, stomach, and pituitary gland. Electrophysiology and radiolabeled amino acid uptake measurements were used to functionally characterize the transporter expressed in Xenopus oocytes. hATB 0؉ was found to transport both neutral and cationic amino acids, with the highest affinity for hydrophobic amino acids and the lowest affinity for proline. Amino acid transport was Na ؉ and Cl ؊ -dependent and was attenuated in the presence of 2-aminobicyclo-[2.2.1]-heptane-2-carboxylic acid, a system B 0؉ inhibitor. These characteristics are consistent with system B 0؉ amino acid transport. Thus, hATB 0؉ is the first cloned B 0؉ amino acid transporter.

Relationship between [ 14 C]MeAIB uptake and amino acid transporter family gene expression levels or proliferative activity in a pilot study in human carcinoma cells: Comparison with [ 3 H]methionine uptake

“…Moreover, amino acids and amino acid transporters play important roles other than in energy metabolism, such as in macromolecular synthesis, mTOR activation, and ROS homeostasis beyond energy metabolism [49]. There are approximately fifty different types of amino acid transporters, but only LAT1 [50], LAT3 [51], ASCT2 [52], ATB 0, + [53] and xCT [54] have been reported to be expressed at high levels on the surface of cancer cells. Recently, there have been numerous reports in cancer cells related to glutamine transport via ASCT2 and LAT1 [55][56][57].…”

Collectrin and ACE2 in renal and intestinal amino acid transport

“…The mRNA is highly expressed in brain, salivary and mammary glands, lungs and large intestine. 34,35 A knockout mouse model is not available yet.…”

Cell volume regulation in mammalian oocytes and preimplantation embryos

“…Yet, it appears that post-compaction embryos may be able to utilize organic osmolytes, since alanine, glutamine, glycine, and b-alanine each rescued development of blastocysts from 8-cell embryos and supported greater cell numbers at increased osmolarities, while betaine and proline were not effective (Richards et al, 2010). Except for b-alanine, which is carried by TAUT as discussed above, the remaining of these putative organic osmolytes that can be used by post-compaction embryos are carried by the amino acid transport system designated B 0,þ (Richards et al, 2010), which is related to GLYT1 (Sloan and Mager, 1999) and becomes active in preimplantation embryos after compaction (Van Winkle et al, 1990a). Acute cell volume homeostasis by coupled Na þ /H þ and HCO 3 À /Cl À exchangers is likely present at least through the morula stage (Zhou and Baltz, 2012), and thus acute protection against cell volume regulation is functional through preimplantation embryo development.…”