We have investigated the regulation of the expression of two growth factors found in vascular smooth muscle, transforming growth factor α (TGFα) and basic fibroblast growth factor (bFGF). Cells cultured in medium containing 30 mM glucose exhibited a 2-fold increase in TGFα mRNA and a 3-fold increase in bFGF mRNA compared with cells grown in normal (5.5 mM) glucose. Glucosamine was more potent than glucose, leading to a 6-fold increase in TGFα mRNA. TGFα protein levels were also increased by glucosa-mine treatment, and the predominant species present was the membrane-bound precursor form of TGFα. To examine further the regulation of growth factors by sugars, cultured rat aortic smooth muscle cells were transfected with a plasmid construct consisting of a 1.2-kilobase-pair fragment of the TGFα promoter linked to a luciferase reporter gene. Increasing the concentration of glucose in the culture medium from 5.5 mM to 30 mM led to a rapid, 1.7-fold increase in the activity of the TGFα promoter. Glucosamine was much more potent than glucose in this stimulation, with 2 mM glucosamine causing a 12-fold increase in TGFα promoter activity. Insulin had no effect on luciferase activity in either the presence or the absence of added sugars. The glucose response element of the TGFα gene maps to a 130-base-pair segment that includes three potential binding sites for the transcription factor Sp1. We conclude that high glucose concentrations such as are reached in diabetes mellitus can stimulate the transcription of the genes for growth factors in vascular smooth muscle cells. This signaling pathway apparently involves the metabolism of glucose to glucosamine. This effect could be representative of nutritional regulation of a family of genes and could contribute to the toxicity of hyperglycemia and the vascular complications of diabetes.