title: The hypoxia-inducible factor 1/NOR-1 axis regulates the survival response of endothelial cells to hypoxia.
abstract: 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.
authors.affiliation: Cardiovascular Research Center (CSIC-ICCC), Hospital de la Santa Creu i Sant Pau, c/Sant Antoni Maria Claret #167, 08025 Barcelona, Spain.
authors.forename: Lluis
authors.initials: L
authors.lastname: Martorell
authors.forename: Maurizio
authors.initials: M
authors.lastname: Gentile
authors.forename: Jordi
authors.initials: J
authors.lastname: Rius
authors.forename: Cristina
authors.initials: C
authors.lastname: Rodríguez
authors.forename: Javier
authors.initials: J
authors.lastname: Crespo
authors.forename: Lina
authors.initials: L
authors.lastname: Badimon
authors.forename: José
authors.initials: J
authors.lastname: Martínez-González
mesh_terms: 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
chemical_list: 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