Carbon Monoxide and Nitric Oxide Suppress the Hypoxic Induction of Vascular Endothelial Growth Factor Gene via the 5′ Enhancer*

Vascular endothelial growth factor (VEGF) plays an important role in angiogenesis and blood vessel remodeling. Its expression is up-regulated in vascular smooth muscle cells by a number of conditions, including hypoxia. Hypoxia increases the transcriptional rate of VEGF via a 28-base pair enhancer located in the 5′-upstream region of the gene. The gas molecules nitric oxide (NO) and carbon monoxide (CO) are important vasodilating agents. We report here that these biological molecules can suppress the hypoxia-induced production of VEGF mRNA and protein in smooth muscle cells. In transient expression studies, both NO and CO inhibited the ability of the hypoxic enhancer we have previously identified to activate gene transcription. Furthermore, electrophoretic mobility shift assays indicated decreased binding of hypoxia-inducible factor 1 (HIF-1) to this enhancer by nuclear proteins isolated from CO-treated cells, although HIF-1 protein levels were unaffected by CO. Given that both CO and NO activate guanylyl cyclase to produce cGMP and that a cGMP analog (8-Br-cGMP) showed a similar suppressive effect on the hypoxic induction of the VEGF enhancer, we speculate that the suppression of VEGF by these two gas molecules occurs via a cyclic GMP-mediated pathway.