Transcriptional regulation of the human asparagine synthetase gene by carbohydrate availability

Transcription of the asparagine synthetase (AS) gene is induced by amino ac id deprivation. The present data illustrate that this gene is also under tr anscriptional control by carbohydrate availability. Incubation of human Hep G2 hepatoma cells in glucose-free medium resulted in an increased AS mRNA c ontent, reaching a maximum of about 14-fold over control cells after approx . 12 h. Extracellular glucose caused the repression of the content of AS mR NA in a concentration-dependent manner, with a k(1/2) (concentration causin g a half-maximal repression) of 1 mM. Fructose, galactose, mannose, 2-deoxy glucose and xylitol were found to maintain the mRNA content of both AS and the glucose-regulated protein GRP78 in a state of repression, whereas 3-O-m ethylglucose did not. Incubation in either histidine-free glucose-free medi um also resulted in adaptive regulation of the AS gene in BNL-CL.2 mouse he patocytes, rat C6 glioma cells and human MOLT4 lymphocytes, in addition to HepG2 cells. In contrast, the steady-state mRNA content of GRP78 was unaffe cted by amino acid availability. Transient transfection assays using a repo rter gene construct documented that glucose deprivation increases AS gene t ranscription via elements within the proximal 3 kbp of the AS promoter. The se results illustrate that human AS gene transcription is induced following glucose limitation of the cells.