The Qo site of the mitochondrial complex III is required for the transduction of hypoxic signaling via reactive oxygen species production

M ammalian cells increase transcription of genes for adaptation to hypoxia through the stabilization of hypoxia- inducible factor 1 alpha ( HIF-1 alpha) protein. How cells transduce hypoxic signals to stabilize the HIF-1 alpha protein remains unresolved. We demonstrate that cells de. cient in the complex III subunit cytochrome b, which are respiratory incompetent, increase ROS levels and stabilize the HIF-1 alpha protein during hypoxia. RNA interference of the complex III subunit Rieske iron sulfur protein in the cytochrome b-null cells and treatment of wild- type cells with stigmatellin abolished reactive oxygen species ( ROS) generation at the Qo site of complex III. These interventions maintained hydroxylation of HIF-1 alpha protein and prevented stabilization of HIF-1 alpha protein during hypoxia. Antioxidants maintained hydroxylation of HIF-1 alpha protein and prevented stabilization of HIF-1 alpha protein during hypoxia. Exogenous hydrogen peroxide under normoxia prevented hydroxylation of HIF-1 alpha protein and stabilized HIF-1 alpha protein. These results provide genetic and pharmacologic evidence that the Qo site of complex III is required for the transduction of hypoxic signal by releasing ROS to stabilize the HIF-1 alpha protein.