1. Hypoxia up-regulates hypoxia-inducible factor-1alpha transcription by involving phosphatidylinositol 3-kinase and nuclear factor kappaB in pulmonary artery smooth muscle cells.
- Author
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Belaiba RS, Bonello S, Zähringer C, Schmidt S, Hess J, Kietzmann T, and Görlach A
- Subjects
- Animals, Arteries metabolism, Base Sequence, Cells, Cultured, Humans, Hypoxia genetics, Hypoxia-Inducible Factor 1, alpha Subunit genetics, Mice, Mice, Inbred C57BL, Proto-Oncogene Proteins c-akt, RNA, Messenger genetics, Signal Transduction, Hypoxia metabolism, Hypoxia-Inducible Factor 1, alpha Subunit metabolism, Myocytes, Smooth Muscle metabolism, NF-kappa B metabolism, Phosphatidylinositol 3-Kinases metabolism, Transcription, Genetic genetics, Up-Regulation genetics
- Abstract
The oxygen sensitive alpha-subunit of the hypoxia-inducible factor-1 (HIF-1) is a major trigger of the cellular response to hypoxia. Although the posttranslational regulation of HIF-1alpha by hypoxia is well known, its transcriptional regulation by hypoxia is still under debate. We, therefore, investigated the regulation of HIF-1alpha mRNA in response to hypoxia in pulmonary artery smooth muscle cells. Hypoxia rapidly enhanced HIF-1alpha mRNA levels and HIF-1alpha promoter activity. Furthermore, inhibition of the phosphatidylinositol 3-kinase (PI3K)/AKT but not extracellular signal-regulated kinase 1/2 pathway blocked the hypoxia-dependent induction of HIF-1alpha mRNA and HIF-1alpha promoter activity, suggesting involvement of a PI3K/AKT-regulated transcription factor. Interestingly, hypoxia also induced nuclear factor-kappaB (NFkappaB) nuclear translocation and activity. In line, expression of the NFkappaB subunits p50 and p65 enhanced HIF-1alpha mRNA levels, whereas blocking of NFkappaB by an inhibitor of nuclear factor-kappaB attenuated HIF-1alpha mRNA induction by hypoxia. Reporter gene assays revealed the presence of an NFkappaB site within the HIF-1alpha promoter, and mutation of this site abolished induction by hypoxia. In line, gel shift analysis and chromatin immunoprecipitation confirmed binding of p50 and p65 NFkappaB subunits to the HIF-1alpha promoter under hypoxia. Together, these findings provide a novel mechanism in which hypoxia induces HIF-1alpha mRNA expression via the PI3K/AKT pathway and activation of NFkappaB.
- Published
- 2007
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