HYPOXIA RESPONSE ELEMENTS IN THE ALDOLASE-A, ENOLASE-1, AND LACTATE-DEHYDROGENASE-A GENE PROMOTERS CONTAIN ESSENTIAL BINDING-SITES FOR HYPOXIA-INDUCIBLE FACTOR-1

Hypoxia-inducible factor 1 (HIF-1) is a basic helix-loop-helix transcr iption factor which is expressed when mammalian cells are subjected to hypoxia and which activates transcription of genes encoding erythropo ietin, vascular endothelial growth factor, and other pro teins that ar e important for maintaining oxygen homeostasis. Previous studies have provided indirect evidence that HIF-1 also regulates transcription of genes encoding glycolytic enzymes, In this paper we characterize hypox ia response elements in the promoters of the ALDA, ENO1, and Ldha gene s, We demonstrate that HIF-1 plays an essential role in activating tra nscription via these elements and show that although absolutely necess ary, the presence of a HIF-1 binding site alone is not sufficient to m ediate transcriptional responses to hypoxia, Analysis of hypoxia respo nse elements in the ENO1 and Ldha gene promoters revealed that each co ntains two functionally-essential HIF-1 sites arranged as direct and i nverted repeats, respectively. Our data establish that functional hypo xia-response elements consist of a pair of contiguous transcription fa ctor binding sites at least one of which contains the core sequence 5' -RCGTG-3' and is recognized by HIF-1. These results provide further ev idence that the coordinate transcriptional activation of genes encodin g glycolytic enzymes which occurs in hypoxic cells is mediated by HIF- 1.