ROLE OF GLUCOSAMINE SYNTHESIS IN THE STIMULATION OF TGF-ALPHA GENE-TRANSCRIPTION BY GLUCOSE AND EGF

Transforming growth factor-alpha (TGF-alpha) gene transcription is reg ulated by both epidermal growth factor (EGF) and glucose. Previous stu dies have suggested that the metabolism of glucose to glucosamine thro ugh the enzyme L-glutamine: D-fructose-6-phosphate amidotransferase (G FAT) plays a critical role in the glucose signaling. In this paper, we compared the role of GFAT in the glucose and EGF signals. We found th at, although EGF stimulates GFAT mRNA accumulation in MDA-MB-468 cells , this effect of EGF occurred several hours after TGF-alpha transcript ion increased. MDA-MB-468 cells also exhibited a TGF-alpha transcripti onal response to low concentrations of glucose. The TGF-alpha response to glucose but not EGF could be inhibited by a blocker of GFAT activi ty. Blockade of GFAT was confirmed by using Western blotting with the RL2 antibody, which recognizes an epitope on proteins containing N-ace tylglucosamine. Exposure of cells to glucose increased the RL2 signal on several polypeptides, but this change could be blocked by inhibitio n of GFAT. These results support the notion that glucose stimulation o f TGF-alpha expression requires GFAT, but EGF stimulation does not.