Na+-dependent neutral amino acid transporter ATB0 is a rabbit epithelial cell brush-border protein

Abstract

System B0 activity accounts for the majority of intestinal and kidney luminal neutral amino acid absorption. An amino acid transport system, called ATB0 (also known as ASCT2), with functional characteristics similar to those of system B0, has been recently cloned. We generated polyclonal antibodies to human and rabbit ATB0 COOH-terminal peptides and used Western blot analysis to detect ATB0 protein in rabbit tissues, rabbit ileal brush-border membrane vesicles (BBMV), and HeLa cells transfected with plasmids containing ATB0 cDNAs. Immunohistochemistry was used to localize ATB0 in rabbit kidney and intestine. In Western blots of rabbit tissues, ATB0 was a broad smear of 78- to 85-kDa proteins. In transfected HeLa cells, ATB0 appeared as a smear consisting of 57- to 65-kDa proteins. The highest expression was found in the kidney. ATB0 was enriched in rabbit ileal BBMV and in HeLa cells transfected with ATB0 cDNAs. In the kidney and in the intestine, ATB0 was confined to the brush-border membrane (BBM) of the proximal tubular cell and of the enterocyte, respectively. Tissue and intracellular distribution of ATB0 protein parallels that of system B0 activity. ATB0protein could be the transporter responsible for system B0in the BBM of epithelial cells.