Reactive oxygen species generated at mitochondrial complex III stabilize hypoxia-inducible factor-1 alpha during hypoxia - A mechanism of O-2 sensing

During hypoxia, hypoxia-inducible factor-1 alpha (HIF-1 alpha) is required for induction of a variety of genes including erythropoietin and vascular e ndothelial growth factor. Hypoxia increases mitochondrial reactive oxygen s pecies (ROS) generation at Complex III, which causes accumulation of HIF-1 alpha protein responsible for initiating expression of a luciferase reporte r construct under the control of a hypoxic response element. This response is lost in cells depleted of mitochondrial DNA (rho degrees cells). Overexp ression of catalase abolishes hypoxic response element-luciferase expressio n during hypoxia. Exogenous H2O2 stabilizes HIF-1 alpha protein during norm oxia and activates luciferase expression in wild-type and rho degrees cells . Isolated mitochondria increase ROS generation during hypoxia, as does the bacterium Paracoccus denitrificans. These findings reveal that mitochondri a-derived ROS are both required and sufficient to initiate HIF-1 alpha stab ilization during hypoxia.