Mitochondrial reactive oxygen species activation of p38 mitogen-activated protein kinase is required for hypoxia signaling

Mammalian cells have the ability to sense low oxygen levels (hypoxia). An adaptive response to hypoxia involves the induction of the transcription factor hypoxia-inducible factor 1 (HIF-1). The intracellular signaling pathways that regulate HIF-1 activation during hypoxia remain unknown. Here, we demonstrate that p38α^-/- cells fail to activate HIF-1 under hypoxic conditions. Cells deficient in Mkk3 and Mkk6, the upstream regulators of p38α, also fail to activate HIF-1 under hypoxic conditions. The p38α^-/- cells are able to activate HIF-1 in response to anoxia or iron chelators during normoxia. Furthermore, the hypoxic activation of p38a and HIF-1 was abolished by myxothiazol, a mitochondrial complex III inhibitor, and glutathione peroxidase 1 (GPX1), a scavenger of hydrogen peroxide. Thus, the activation of p38a and HIF-1 is dependent on the generation of mitochondrial reactive oxygen species. These results provide genetic evidence that p38 mitogen-activated protein kinase signaling is essential for HIF-1 activation.