A Switch in Akt Isoforms Is Required for Notch-Induced Snail1 Expression and Protection from Cell Death
A Switch in Akt Isoforms Is Required for Notch-Induced Snail1 Expression and Protection from Cell Death
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DOI：
10.1128/mcb.01074-15
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发表时间：
2016-03-01
影响因子：
5.3
通讯作者：
Diaz, Victor M.
中科院分区：
文献类型：
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作者：
Fras, Alex;Lambies, Guillem;Diaz, Victor M.
主动脉内皮细胞（EC）中的Notch激活发生在心脏瓣膜形成过程中的胚胎阶段，并诱导内皮-间质转化（EndMT）。使用主动脉 EC，我们在此表明活跃的 Notch 表达会促进 EndMT，从而导致血管内皮钙粘蛋白 (VE-cadherin) 的下调和间充质基因（例如纤连蛋白和 Snail1/2 的基因）的上调。在这些细胞中，转化生长因子β1通过增加Snail1和纤连蛋白的激活而加剧Notch效应。当分析Notch下游通路时，我们检测到糖原合酶激酶3β（GSK-3β）磷酸化和失活的增加，这有利于Snail1核保留和蛋白质稳定。然而，Akt 的总活性下调。 Akt 活性和 GSK-3 β 磷酸化之间的差异可以通过 Notch 诱导的 Akt 同工型转换来解释，即 EC 中表达的主要同工型 Akt1 减少，而 Akt2 转录上调。从机制上讲，Akt2 诱导需要刺激 β-catenin/TCF4 转录复合物，从而激活 Akt2 启动子。活性磷酸化 Akt2 易位至表达 Notch 的细胞中的细胞核，导致该区室中的 GSK-3 β 失活。 Akt2（而非 Akt1）与核膜中的核纤层蛋白 B 共定位于细胞核中。除了促进 GSK-3 beta 失活之外，Notch 还能下调另一种 Akt2 核底物 Forkhead box O1 (FoxO1)。此外，Notch 通过 Akt2 和 Snail1 依赖性机制保护 EC 免受氧化应激诱导的细胞凋亡。
Notch activation in aortic endothelial cells (ECs) takes place at embryonic stages during cardiac valve formation and induces endothelial-to-mesenchymal transition (EndMT). Using aortic ECs, we show here that active Notch expression promotes EndMT, resulting in downregulation of vascular endothelial cadherin (VE-cadherin) and upregulation of mesenchymal genes such as those for fibronectin and Snail1/2. In these cells, transforming growth factor beta 1 exacerbates Notch effects by increasing Snail1 and fibronectin activation. When Notch-downstream pathways were analyzed, we detected an increase in glycogen synthase kinase 3 beta (GSK-3 beta) phosphorylation and inactivation that facilitates Snail1 nuclear retention and protein stabilization. However, the total activity of Akt was downregulated. The discrepancy between Akt activity and GSK-3 beta phosphorylation is explained by a Notch-induced switch in the Akt isoforms, whereby Akt1, the predominant isoform expressed in ECs, is decreased and Akt2 transcription is upregulated. Mechanistically, Akt2 induction requires the stimulation of the beta-catenin/TCF4 transcriptional complex, which activates the Akt2 promoter. Active, phosphorylated Akt2 translocates to the nucleus in Notch-expressing cells, resulting in GSK-3 beta inactivation in this compartment. Akt2, but not Akt1, colocalizes in the nucleus with lamin B in the nuclear envelope. In addition to promoting GSK-3 beta inactivation, Notch downregulates Forkhead box O1 (FoxO1), another Akt2 nuclear substrate. Moreover, Notch protects ECs from oxidative stress-induced apoptosis through an Akt2- and Snail1-dependent mechanism.