The Thai Journal of Veterinary Medicine


Glutamine is known to modulate the expression of various genes and uptake activity of nutrient transportersin mammalian cells. The purpose of the study was to investigate the influence of intracellular glutamine status onamino acid transport system A in placental choriocarcinoma cells (BeWo). Intracellular glutamine was depleted byculturing the cells in regular medium without glutamine and by treating the cells for 16 hours with methioninesulfoximine (MSX), an inhibitor of glutamine synthetase. When cultured in the presence of glutamine, treatment withMSX had no effect on system A activity as monitored by MeAIB uptake. However, when cultured in the absence ofglutamine, treatment with MSX (2 mM) reduced system A activity by 70%. The decrease in system A activity inducedby MSX treatment was blocked by co-treatment with glutamine but not with glutathione, or diazooxonorleucine (aglutamine analog). The decrease in system A activity caused by MSX treatment was associated with a decrease in themaximal velocity of the transport system but without any significant change in substrate affinity. Northern analysesindicated that there was no change in steady-state levels of ATA1 and ATA2 mRNA, suggesting that the regulationwas not at the level of transcription. These data show that intracellular glutamine is obligatory for maintenance ofoptimal expression/activity of system A in BeWo cells.

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