Transcriptional regulation of the human asparagine synthetase gene by carbohydrate availability

Transcription of the asparagine synthetase ( AS ) gene is induced by amino acid deprivation. The present data illustrate that this gene is also under transcriptional control by carbohydrate availability. Incubation of human HepG2 hepatoma cells in glucose-free medium resulted in an increased AS mRNA content, reaching a maximum of about 14-fold over control cells after approx. 12 h. Extracellular glucose caused the repression of the content of AS mRNA in a concentration-dependent manner, with a k 1/2 (concentration causing a half-maximal repression) of 1 mM. Fructose, galactose, mannose, 2-deoxyglucose 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 -methylglucose did not. Incubation in either histidine-free or glucose-free medium also resulted in adaptive regulation of the AS gene in BNL-CL.2 mouse hepatocytes, rat C6 glioma cells and human MOLT4 lymphocytes, in addition to HepG2 cells. In contrast, the steady-state mRNA content of GRP78 was unaffected by amino acid availability. Transient transfection assays using a reporter gene construct documented that glucose deprivation increases AS gene transcription via elements within the proximal 3 kbp of the AS promoter. These results illustrate that human AS gene transcription is induced following glucose limitation of the cells.