L -Type Amino Acid Transporter-1 Expressed in Human Astrocytomas, U343MGa

LAT1 (L-type amino acid transporter 1), one of the L-type amino acid transporters, transports the branched and aromatic amino acids. LAT1 requires the heavy chain of 4F2 antigen (4F2hc) for the functional expression as an amino acid transporter. The expression of this transporter is up-regulated in tumor cells and rapidly-growing cells to support their proliferation. Here, we studied the expression of LAT1 and 4F2hc in human cultured cells by real-time PCR and Western blot, and found that human brain astrocytomas, U343MGa, highly expressed LAT1 and 4F2hc mRNAs and proteins. The uptake of [14C]leucine by U343MGa cells is Na+-independent and inhibited by BCH (2-amino-2-norbornane carboxylic acid), and branched and aromatic amino acids, indicating that the LAT1 is expressed at the cell surface. Pulse chase labeling and surface labeling experiments of this cell line indicate that the protein synthesis of LAT1 and 4F2hc is slow, however, the heterodimeric complex assembled in the cells is very stable, and that the disulfide bond between the LAT1 and 4F2hc is not directly involved in the stability of the heterodimer.