Reactive oxygen species generated at mitochondrial Complex III stabilize hypoxia-inducible factor-1α during hypoxia: A mechanism of O₂ sensing

During hypoxia, hypoxia-inducible factor-1α (HIF-1α) is required for induction of a variety of genes including erythropoietin and vascular endothelial growth factor. Hypoxia increases mitochondrial reactive oxygen species (ROS) generation at Complex III, which causes accumulation of HIF-1α protein responsible for initiating expression of a luciferase reporter construct under the control of a hypoxic response element. This response is lost in cells depleted of mitochondrial DNA (p⁰ cells). Overexpression of catalase abolishes hypoxic response element-luciferase expression during hypoxia. Exogenous H₂O₂ stabilizes HIF-1α protein during normoxia and activates luciferase expression in wild-type and p⁰ cells. Isolated mitochondria increase ROS generation during hypoxia, as does the bacterium Paracoccus denitrificans. These findings reveal that mitochondria-derived ROS are both required and sufficient to initiate HIF-1α stabilization during hypoxia.