HYPOXIA REGULATES VASCULAR ENDOTHELIAL GROWTH-FACTOR GENE-EXPRESSION IN ENDOTHELIAL-CELLS - IDENTIFICATION OF A 5'-ENHANCER

Vascular endothelial growth factor (VEGF) is a potent mitogen specific for endothelial cells. Its expression is dramatically induced by low oxygen tension in a variety of cell types, and it has been suggested t o be a key mediator of hypoxia-induced angiogenesis. Although VEGF act ion is targeted to endothelial cells, it is generally believed that th ese cells do not express VEGF. In addition, the mechanisms by which hy poxia regulates VEGF production remain unclear. We report in the prese nt study that pulmonary artery endothelial cells do not express VEGF u nder basal conditions; however, significant VEGF mRNA levels accumulat e when these cells are exposed to hypoda. Using a DNA fragment contain ing human VEGF promoter sequence, we identified a 28-bp element that i s necessary and sufficient to upregulate transcription in response to hypoxia. This element can act as a hypoxia-specific enhancer when plac ed upstream or downstream from a heterologous promoter. The enhancer i ncludes, in addition to an octamer homologous to the hypoxia-inducible factor-1 (HIF-1) consensus, a sequence that resides 3' to the consens us. Although this sequence may not be involved in the binding of HIF-1 , it is absolutely required for the enhancer activity and may be the b inding site for certain constitutive binding proteins. The expression of VEGF by endothelial cells in response to hypoxia. may provide an im portant mechanism by which endothelial cell permeability and prolifera tion is regulated in an autocrine manner.