The hypoxia-inducible factor 1/NOR-1 axis regulates the survival response of endothelial cells to hypoxia.
Hypoxia induces apoptosis but also triggers adaptive mechanisms to ensure cell survival. Here we show that the prosurvival effects of hypoxia-inducible factor 1 (HIF-1) in endothelial cells are mediated by neuron-derived orphan receptor 1 (NOR-1). The overexpression of NOR-1 decreased the rate of endothelial cells undergoing apoptosis in cultures exposed to hypoxia, while the inhibition of NOR-1 increased cell apoptosis. Hypoxia upregulated NOR-1 mRNA levels in a time- and dose-dependent manner. Blocking antibodies against VEGF or SU5614 (a VEGF receptor 2 inhibitor) did not prevent hypoxia-induced NOR-1 expression, suggesting that NOR-1 is not induced by the autocrine secretion of VEGF in response to hypoxia. The reduction of HIF-1 alpha protein levels by small interfering RNAs, or by inhibitors of the phosphatidylinositol-3 kinase (PI3K)/Akt pathway or mTOR, significantly counteracted hypoxia-induced NOR-1 upregulation. Intracellular Ca(2+) was involved in hypoxia-induced PI3K/Akt activation and in the downstream NOR-1 upregulation. A hypoxia response element mediated the transcriptional activation of NOR-1 induced by hypoxia as we show by transient transfection and chromatin immunoprecipitation assays. Finally, the attenuation of NOR-1 expression reduced both basal and hypoxia-induced cIAP2 (cellular inhibitor of apoptosis protein 2) mRNA levels, while NOR-1 overexpression upregulated cIAP2. Therefore, NOR-1 is a downstream effector of HIF-1 signaling involved in the survival response of endothelial cells to hypoxia.
Martorell
Lluis
L
Cardiovascular Research Center (CSIC-ICCC), Hospital de la Santa Creu i Sant Pau, c/Sant Antoni Maria Claret #167, 08025 Barcelona, Spain.
Gentile
Maurizio
M
Rius
Jordi
J
Rodríguez
Cristina
C
Crespo
Javier
J
Badimon
Lina
L
Martínez-González
José
J
D017209:Apoptosis; D019898:Autocrine Communication; D000075747:Baculoviral IAP Repeat-Containing 3 Protein; D015687:Cell Hypoxia; D002470:Cell Survival; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D020405:Dermis / Q000166:cytology; D042783:Endothelial Cells / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D051034:Inhibitor of Apoptosis Proteins / Q000378:metabolism; D055806:Microvessels / Q000166:cytology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011485:Protein Binding; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011987:Receptors, Steroid / Q000378:metabolism*; D011988:Receptors, Thyroid Hormone / Q000378:metabolism*; D020218:Response Elements / Q000235:genetics; D015398:Signal Transduction; D044767:Ubiquitin-Protein Ligases; D014471:Umbilical Veins / Q000166:cytology; D015854:Up-Regulation / Q000235:genetics; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
C115163:CREB1 protein, human; D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D051034:Inhibitor of Apoptosis Proteins; C490412:NR4A3 protein, human; D011987:Receptors, Steroid; D011988:Receptors, Thyroid Hormone; D042461:Vascular Endothelial Growth Factor A; C494832:BIRC3 protein, human; D000075747:Baculoviral IAP Repeat-Containing 3 Protein; D044767:Ubiquitin-Protein Ligases; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt