TRANSCRIPTIONAL REGULATION OF THE RAT VASCULAR ENDOTHELIAL GROWTH-FACTOR GENE BY HYPOXIA

Vascular endothelial growth factor (VEGF), a potent angiogenic factor and endothelial cell-specific mitogen, is up-regulated by hypoxia. How ever, the mechanism(s) responsible for hypoxic induction of VEGF has n ot been clearly delineated. We report that the steady state VEGF mRNA levels are increased 12 +/- 0.6-fold, but the transcriptional rate for VEGF is increased only 3.1 +/- O.6-fold by hypoxia in PC12 cells. In order to investigate cis-regulatory sequences which mediate this respo nse to hypoxia, we cloned the rat genomic sequences encoding VEGF and identified a 28-base pair element in the 5' promoter that mediates hyp oxia-inducible transcription in transient expression assays. This elem ent has sequence and protein binding similarities to the hypoxia-induc ible factor 1 binding site within the erythropoietin 3' enhancer. Post -transcriptional mechanisms have also been suggested to play a role in the hypoxic induction of VEGF. Evidence is provided that a frequently used polyadenylation site is 1.9 kilobases downstream from the transl ation termination codon for rat VEGF. This site is 1.5 kilobases furth er downstream from the polyadenylation site previously reported for VE GF. This new finding reveals sequence motifs in the 3'-untranslated re gion that may mediate VEGF mRNA stability.