Normoxic stabilization of hypoxia-inducible factor-1 expression and activity: Redox-dependent effect of nitrogen oxides

Hypoxia-inducible factor-1 (HIF-1) is an essential transcription factor inv olved in the oxygen-dependent regulation of gene expression. Thiol groups i n HIF-1 or in proteins that modify HIF-1 are conventional targets for regul ation by nitric oxide (NO). Moreover, NO delivery to tissue by hemoglobin a ppears to be oxygen dependent. Therefore, the role NO plays in regulating H IF-1 activity and expression was examined. The 1-substituted diazen-1-ium-1 ,2-diolate NOC-18 induced HIF-1 DNA-binding activity in normoxic bovine pul monary artery endothelial cells and rat aortic smooth muscle cells in a tim e- and dose-dependent manner. Induction of HIF-1-binding activity was consi stent with an increased expression of HIF-1 subunit proteins HIF-1 alpha an d HIF-1 beta. The effect of NOC-18 on HIF-1 activity was blocked by cyclohe ximide, consistent with a posttranscriptional effect. NOC-18 induction of H IF-1 DNA-binding activity was not blocked with oxyhemoglobin, nor was it re lated to the rate of NO evolution, arguing against NO-mediation of the effe ct. Additionally, the effect of NOC-18 could not be mimicked by Angeli's sa lt, arguing against nitroxyl mediation. However, the NOC-18 effect could be reproduced by S-nitrosoglutathione (GSNO), an endogenous nitrosonium donor formed in the presence of deoxyhemoglobin. Furthermore, the GSNO effect co uld be reversed by dithiothreitol as well as acivicin, an inhibitor of GSNO bioactivation. Taken together, these results suggest that an S-nitrosylati on reaction stabilizes HIF-1 protein expression and activity. We speculate that one signaling mechanism by which deoxyhemoglobin may activate HIF-1 in volves NO.