Hypoxia up-regulates hypoxia-inducible factor-1alpha transcription by involving phosphatidylinositol 3-kinase and nuclear factor kappaB in pulmonary artery smooth muscle cells.
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.
Belaiba
Rachida S
RS
Experimental Pediatric Cardiology, Department of Pediatric Cardiology and Congenital Heart Disease, German Heart Center Munich at the Technical University Munich, D-80636 Munich, Germany.
Bonello
Steve
S
Zähringer
Christian
C
Schmidt
Stefanie
S
Hess
John
J
Kietzmann
Thomas
T
Görlach
Agnes
A
D000818:Animals; D001158:Arteries / Q000378:metabolism; D001483:Base Sequence; D002478:Cells, Cultured; D006801:Humans; D000860:Hypoxia / Q000235:genetics / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000235:genetics; D015398:Signal Transduction; D014158:Transcription, Genetic / Q000235:genetics*; D015854:Up-Regulation / Q000235:genetics*
D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D016328:NF-kappa B; D012333:RNA, Messenger; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt