Changes in glucose levels are known to directly alter gene expression. A number of previous studies have found that these effects are in part mediated by modulating the levels and the activity of transcription factors. We have investigated an alternative mechanism by which glucose might regulate gene expression by modulating levels of a transcriptional repressor. We have focused on Id2, which is a protein that indirectly regulates gene expression by sequestering certain transcription factors and preventing them from forming functional dimers. Id2 targets include the class A basic helix-loop-helix transcription factors and the sterol regulatory element-binding protein (SREBP)-1. We demonstrate that increases in glucose levels cause a rapid increase in levels of Id2 in J774.2 macrophages, and a number of lines of evidence indicate that this is via the hexosamine pathway because 1) the effect of glucose requires glutamine; 2) the effect of glucose is mimicked by low levels of glucosamine; 3) the effect of glucose is inhibited by azaserine, an inhibitor of glutamine:fructose-6-phosphate amidotransferase (GFAT); and 4) adenoviral mediated overexpression of GFAT increases levels of Id2. We go on to show that increases in Id2 can have functional effects on metabolic genes, because Id2 blocked the SREBP-1-induced induction of hormone-sensitive lipase (HSL) promoter activity, whereas Id2 alone does not modulate activity of the HSL promoter. In summary, these studies define a new mechanism by which glucose uses the hexosamine pathway to regulate gene expression by increasing levels of a transcriptional repressor. E proteins; diabetes; atherosclerosis IT IS WELL RECOGNIZED that changes in glucose levels have direct effects of gene expression in a range of tissues (49). Gene expression events induced by normal physiological fluctuations in glucose levels play a critical role in the maintenance of proper glucose and lipid homeostasis. These effects have been thoroughly investigated mostly in liver, where changes in glucose levels play an important role in switching off gluconeogenesis and switching on glycolytic pathways (15, 17). Glucose also plays a key role in regulating the expression and release of insulin in the ␤-cells of the pancreas (45), and the insulin released subsequently plays an important role in the regulation of metabolic genes (17). However, persistent hyperglycemia associated with diabetes is known to contribute to a wide range of gene expression events associated with the development of diabetic complications (5). More recently, we and others (19,21,41,44) have shown that glucose has direct effects on genes controlling cholesterol ester metabolism in macrophages, and these findings have suggested a possible link between hyperglycemia and foam cell formation. The mechanisms by which glucose regulates gene expression in macrophages have not been characterized.A number of mechanisms have been implicated in glucosemediated regulation of gene expression (5). The hexosamine pathway has drawn particular attentio...