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Cells exposed to oxygen deprivation in vitro have been shown to reduce proliferation and/or engage in programmed cell death. There is considerable controversy in the literature as to the role of hypoxia-inducible factor-1 (HIF-1) and HIF-1 target genes in initiating these responses. We therefore examined the oxygen dependence and the role of the hypoxia-responsive transcription factor HIF-1 in making the cellular death decision. Oxygen concentrations as low as 0.5% did not alter the growth of HIF-1-proficient or HIF-1-deficient murine fibroblasts, or human tumor cells, despite the appropriate induction of HIF-1 target genes. Severe hypoxia (<0.01% oxygen) did induced apoptosis, resulting in decreased colony formation, chromatin condensation, DNA fragmentation, and caspase activation but also independent of HIF1alpha status. Transcriptional induction of HIF-1-dependent genes putatively involved in cell death like BNip3 and BNip3L was therefore disassociated from hypoxia-dependent toxicity. Likewise, forced overexpression of a nondegradable form of HIF-1alpha in several human tumor cell lines was not sufficient to induce apoptosis under normoxic conditions. Taken together, these findings indicate that additional molecular events are triggered by anoxia in a HIF-1-independent manner, and these changes are necessary for cell death observed in low-oxygen environments.

Original publication




Journal article


Cancer Res

Publication Date





3171 - 3178


Animals, Apoptosis, Cell Hypoxia, DNA-Binding Proteins, Fibroblasts, HeLa Cells, Humans, Hypoxia-Inducible Factor 1, Hypoxia-Inducible Factor 1, alpha Subunit, Membrane Proteins, Mice, Mice, Knockout, Neoplasms, Nuclear Proteins, Oxygen, Proto-Oncogene Proteins, Transcription Factors, Tumor Suppressor Proteins