Identification of an oxygen responsive enhancer element in the glyceraldehyde-3-phosphate dehydrogenase gene

The glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is induced by hypoxia in endothelial cells (EC). Upregulation occurs primarily at the level of transcription and occurs to a much greater extent in EC than in other cell types. To characterize EC specific hypoxia response elements within the GAPDH gene, we performed transient transfection studies in EC, fibroblasts and smooth muscle cells using portions of the GAPDH promoter linked to a CAT reporter gene. These initial studies identified an EC specific hypoxia responsive region that was further characterized (using SV40-promoter-CAT reporter constructs) as a 19-nucleotide sequence (-130 to -112) containing both an hypoxia inducible factor-1 (HIF-1)-binding site and a novel flanking sequence. Electrophoretic mobility shift assays confirmed inducible EC protein binding to this fragment. Mutation of either the HIF-1-binding site or the flanking sequence resulted in complete loss of function and loss of inducible protein binding. Thus, a single HIF-1-binding site is necessary, but not sufficient, for hypoxic regulation of GAPDH in EC. Furthermore, the novel HIF-1 flanking sequence required for GAPDH upregulation and the protein(s) that bind to it may be EC specific.