HIF-2α regulates glyceraldehyde-3-phosphate dehydrogenase expression in endothelial cells

Abstract

Endothelial cells (EC) express both hypoxia inducible factor-1α (HIF-1α) and -2α (HIF-2α), yet their roles in the EC hypoxic response are unclear. Hypoxia upregulates the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in EC through a 5′ hypoxic regulatory element (HRE). We compared the upregulation of GAPDH in human lung microvascular EC to that in hep3B cells, another cell type known to express both HIF-1α and HIF-2α. GAPDH mRNA increased to a lesser extent in hypoxic hep3B cells than in EC, yet upregulation occurred through the same HRE that was active in EC. HIF-1α protein induction in response to hypoxia was similar in both cell types. In contrast, HIF-2α protein levels were upregulated to a greater extent and for a longer period of time by hypoxia in EC than in hep3B cells. Correspondingly, electrophoretic mobility supershift assays showed that, in EC, there was preferential binding of HIF-2α to the GAPDH HRE while, in hep3B cells, there was binding of both HIF-1α and HIF-2α. The preferential binding of HIF-2α to the GAPDH HRE in EC may account for their higher level of induction of GAPDH. These findings suggest that cell-specific patterns of HIF-1α and HIF-2α expression lead to cell-specific gene upregulation during hypoxia.