Martorell Lluis, Gentile Maurizio, Rius Jordi, Rodríguez Cristina, Crespo Javier, Badimon Lina, Martínez-González José
Cardiovascular Research Center (CSIC-ICCC), Hospital de la Santa Creu i Sant Pau, c/Sant Antoni Maria Claret #167, 08025 Barcelona, Spain.
Mol Cell Biol. 2009 Nov;29(21):5828-42. doi: 10.1128/MCB.00945-09. Epub 2009 Aug 31.
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.
缺氧可诱导细胞凋亡，但也会触发适应性机制以确保细胞存活。在此我们表明，缺氧诱导因子1（HIF-1）在内皮细胞中的促生存作用是由神经源性孤儿受体1（NOR-1）介导的。NOR-1的过表达降低了暴露于缺氧环境的培养物中内皮细胞的凋亡率，而抑制NOR-1则增加了细胞凋亡。缺氧以时间和剂量依赖的方式上调NOR-1的mRNA水平。针对血管内皮生长因子（VEGF）的阻断抗体或SU5614（一种VEGF受体2抑制剂）并不能阻止缺氧诱导的NOR-1表达，这表明NOR-1不是由VEGF对缺氧的自分泌反应所诱导的。小干扰RNA或磷脂酰肌醇-3激酶（PI3K）/蛋白激酶B（Akt）途径或雷帕霉素靶蛋白（mTOR）抑制剂降低HIF-1α蛋白水平，显著抵消了缺氧诱导的NOR-1上调。细胞内钙离子（Ca²⁺）参与了缺氧诱导的PI3K/Akt激活以及下游的NOR-1上调。如我们通过瞬时转染和染色质免疫沉淀试验所示，一个缺氧反应元件介导了缺氧诱导的NOR-1转录激活。最后，NOR-1表达的减弱降低了基础和缺氧诱导的细胞凋亡抑制蛋白2（cIAP2）的mRNA水平，而NOR-1的过表达上调了cIAP2。因此，NOR-1是HIF-1信号传导的下游效应器，参与内皮细胞对缺氧的存活反应。
