Characterization of l-glutamine transport by a human neuroblastoma cell line

This study characterized the Na+-dependent transport of l-glutamine by a human neuroblastoma cell line, SK-N-SH. The Na+-dependent component represented >95% of the total glutamine uptake. Kinetic studies showed a single saturable high-affinity carrier with a Michaelis constant ( K m) of 163 ± 23 μM and a maximum transport velocity ( V max) of 13,713 ± 803 pmol · mg protein−1 · min−1. Glutamine uptake was markedly inhibited in the presence of l-alanine,l-asparagine, and l-serine. Li+ did not substitute for Na+. These data show thatl-glutamine is predominantly taken up through system ASC. Glutamine deprivation resulted in the decrease of glutamine transport by a mechanism that decreased V max without affecting K m. The expression of the system ASC subtype ASCT2 decreased in the glutamine-deprived group, whereas glutamine deprivation did not induce changes in system ASC subtype ASCT1 mRNA expression. Adaptive increases in Na+-dependent glutamate, Na+-dependent 2-(methylamino)isobutyric acid, and Na+-independent leucine transport were observed under glutamine-deprived conditions, which were completely blocked by actinomycin D and cycloheximide. These mechanisms may allow cells to survive and even grow under nutrient-deprived conditions.