Proceedings of the National Academy of Sciences · 1998 · 1.9K citations · 44 references
Life SciencesCell BiologyPhysiologyCellular MetabolismMetabolismMitochondrial BiologyCellular Responses To HypoxiaHypoxia AdaptationHypoxia PhysiologyOxidative StressReactive Oxygen SpeciesRedox SignalingCellular Hypoxia SignalingErythropoietic Response To HypoxiaHypoxiaHypoxia Response In MitochondriaReactive Oxygen Species GenerationRedox Signaling In HypoxiaTranscriptional Regulation Of Glycolytic EnzymesVascular Endothelial Growth Factor
Transcriptional activation of erythropoietin, glycolytic enzymes, and vascular endothelial growth factor occurs during hypoxia or in response to cobalt chloride (CoCl₂) in Hep3B cells, yet the mechanisms of cellular O₂ sensing and cobalt activation remain unclear. The study tested whether mitochondria act as O₂ sensors during hypoxia and whether hypoxia and cobalt activate transcription by increasing reactive oxygen species (ROS). Wild‑type Hep3B cells increase ROS during hypoxia or CoCl₂, whereas mitochondrial‑DNA‑depleted cells fail to respire and activate these genes during hypoxia but still respond to CoCl₂; antioxidants block transcriptional activation in both conditions, indicating that hypoxia signals via mitochondria‑dependent ROS while CoCl₂ signals via a mitochondria‑independent ROS pathway.
Transcriptional activation of erythropoietin, glycolytic enzymes, and vascular endothelial growth factor occurs during hypoxia or in response to cobalt chloride (CoCl 2 ) in Hep3B cells. However, neither the mechanism of cellular O 2 sensing nor that of cobalt is fully understood. We tested whether mitochondria act as O 2 sensors during hypoxia and whether hypoxia and cobalt activate transcription by increasing generation of reactive oxygen species (ROS). Results show ( i ) wild-type Hep3B cells increase ROS generation during hypoxia (1.5% O 2 ) or CoCl 2 incubation, ( ii ) Hep3B cells depleted of mitochondrial DNA (ρ 0 cells) fail to respire, fail to activate mRNA for erythropoietin, glycolytic enzymes, or vascular endothelial growth factor during hypoxia, and fail to increase ROS generation during hypoxia; ( iii ) ρ 0 cells increase ROS generation in response to CoCl 2 and retain the ability to induce expression of these genes; and ( iv ) the antioxidants pyrrolidine dithiocarbamate and ebselen abolish transcriptional activation of these genes during hypoxia or CoCl 2 in wild-type cells, and abolish the response to CoCl 2 in ρ° cells. Thus, hypoxia activates transcription via a mitochondria-dependent signaling process involving increased ROS, whereas CoCl 2 activates transcription by stimulating ROS generation via a mitochondria-independent mechanism.
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