Rzymski T, Paantjens A, Bod J, Harris A L
Molecular Oncology Laboratories, Cancer Research UK, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, UK.
Oncogene. 2008 Jul 31;27(33):4532-43. doi: 10.1038/onc.2008.100. Epub 2008 Apr 14.
Under anoxia a coordinated, cytoprotective program is induced, called the unfolded protein response (UPR). Activating transcription factor 4 (ATF4) is a mediator of the UPR and activates a gene expression program, promoting tumour growth and survival under anoxia. A key gene induced by ATF4 under normoxic conditions is SKIP3. We characterized the induction of SKIP3 during anoxic exposure to determine whether UPR alone was sufficient or there was a more complex regulatory response to anoxia. There was temporal separation of acute hypoxia-inducible factor (HIF)-1alpha- and chronic ATF4-dependent gene expression programs. SKIP3 was regulated by chronic (48 h) rather than acute anoxia (<24 h) by a complex set of pathways and mechanisms, besides ATF4 induced by the classical UPR, there was transcriptional regulation by nuclear factor-kappa B (NF-kappaB) and RNA stabilization by HuR. Temporal activation of the NF-kappaB pathway under anoxia protected cells from negative consequences of the oxygen stress and involved the canonical signalling pathways that promote IkappaBA phosphorylation and degradation, and reduced mRNA level of the inhibitory protein IkappaBA followed by the translational repression of IkappaBA. We also show that SKIP3 acts as an inhibitor of NF-kappaB and ATF4-dependent transcription under anoxia and provides a regulatory feedback loop. Repression of the survival pathway NF-kappaB by SKIP3 sensitized cells to metabolic consequences of the anoxic stress. Thus, the response to anoxia is mediated by three pathways independently of HIF, suggesting that combined therapeutic approaches would be needed to maximize effects against this pathway.
在缺氧条件下，会诱导一种协调的细胞保护程序，称为未折叠蛋白反应（UPR）。激活转录因子4（ATF4）是UPR的介导因子，可激活基因表达程序，促进缺氧条件下的肿瘤生长和存活。ATF4在常氧条件下诱导的一个关键基因是SKIP3。我们对缺氧暴露期间SKIP3的诱导进行了表征，以确定单独的UPR是否足够，或者对缺氧是否存在更复杂的调节反应。急性缺氧诱导因子（HIF）-1α和慢性ATF4依赖性基因表达程序存在时间上的分离。SKIP3受慢性（48小时）而非急性缺氧（<24小时）的调控，涉及一组复杂的途径和机制，除了经典UPR诱导的ATF4外，还有核因子-κB（NF-κB）的转录调控和HuR的RNA稳定作用。缺氧条件下NF-κB途径的时间激活保护细胞免受氧应激的负面影响，涉及促进IκBα磷酸化和降解的经典信号通路，降低抑制蛋白IκBα的mRNA水平，随后对IκBα进行翻译抑制。我们还表明，SKIP3在缺氧条件下作为NF-κB和ATF4依赖性转录的抑制剂，并提供一个调节反馈环。SKIP3对存活途径NF-κB的抑制使细胞对缺氧应激的代谢后果敏感。因此，对缺氧的反应由三条独立于HIF的途径介导，这表明需要联合治疗方法来最大化针对该途径的效果。
