HIF1α stability in hypoxia is not oxidant-initiated but can be tuned by redox regulation of the proteasome

Hypoxic adaptation mediated by HIF transcription factors requires mitochondria, which can increase peroxide to regulate HIF1α stability in hypoxia. Here, we use state-of-the-art tools to evaluate the role of peroxide and other reactive oxygen species (ROS) in regulating HIF1α stability. We show that antioxidant enzymes are neither homeostatically induced nor are peroxide levels increased in hypoxia. Forced expression of diverse antioxidant enzymes, all of which diminish peroxide, had disparate effects on HIF1α protein stability. Reduction of lipid peroxides by glutathione peroxidase-4 or superoxide by mitochondrial SOD, failed to influence HIF1α protein stability. These data showed that mitochondrial, cytosolic or lipid ROS were not necessary for HIF1α stability. In contrast, altering the cellular redox state to favor oxidized glutathione (GSSG) enhanced HIF1α stability via enhanced and selective S-glutathionlylation of proteasomal subunits. These data suggest that hypoxia-specific signals that drive HIF1α stability can be tuned by redox regulation of the proteasome.