Angiopoietin-1 Induces Kruppel-like Factor 2 Expression through a Phosphoinositide 3-Kinase/AKT-dependent Activation of Myocyte Enhancer Factor 2
Angiopoietin-1 Induces Kruppel-like Factor 2 Expression through a Phosphoinositide 3-Kinase/AKT-dependent Activation of Myocyte Enhancer Factor 2
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DOI：
10.1074/jbc.m806928200
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发表时间：
2009-02-27
影响因子：
4.8
通讯作者：
Mochizuki, Naoki
中科院分区：
文献类型：
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作者：
Sako, Keisuke;Fukuhara, Shigetomo;Mochizuki, Naoki
血管生成素-1（Ang 1）通过受体酪氨酸激酶Tie 2调节血管静止和血管生成。我们和另一个小组最近表明，Ang 1和Tie 2在细胞-细胞和细胞-基质接触时形成不同的信号复合物，并进一步证明前者选择性诱导Kruppel样因子2（KLF 2）的表达，KLF 2是一种参与血管静止的转录因子。在此，我们研究了Ang 1/Tie 2信号如何诱导KLF 2表达的机制，以阐明KLF 2在Ang 1/Tie 2信号介导的血管静止中的作用。Ang 1刺激KLF 2启动子驱动的报告基因在内皮细胞中表达，而当KLF 2启动子的肌细胞增强因子2（MEF 2）结合位点发生突变时，Ang 1则失败。siRNA对MEF 2的消耗消除了Ang 1诱导的KLF 2表达，表明Ang 1诱导KLF 2需要MEF 2。组成型活性磷脂酰肌醇3-激酶（PI 3 K）和AKT通过增强MEF 2的转录活性增加MEF 2依赖的报告基因的表达，并协同MEF 2刺激KLF 2启动子活性。一致地，抑制PI 3 K或AKT以及耗尽AKT废除Ang 1诱导的KLF 2表达。此外，我们证实了细胞外信号调节激酶5（ERK 5）的可分配性为Ang 1诱导KLF 2的表达。此外，KLF 2的耗竭导致Ang 1对血管内皮生长因子（VEGF）介导的内皮细胞中血管细胞粘附分子-1的表达和VEGF介导的单核细胞粘附至内皮细胞的抑制作用丧失。总之，这些发现表明Ang 1/Tie 2信号通过PI 3 K/AKT通路刺激MEF 2的转录活性，诱导KLF 2表达，这可能抵消VEGF介导的炎症反应。
Angiopoietin-1 (Ang1) regulates both vascular quiescence and angiogenesis through the receptor tyrosine kinase Tie2. We and another group have recently shown that Ang1 and Tie2 form distinct signaling complexes at cell-cell and cell-matrix contacts and further demonstrated that the former selectively induces expression of Kruppel-like factor 2 (KLF2), a transcription factor involved in vascular quiescence. Here, we investigated the mechanism of how Ang1/Tie2 signal induces KLF2 expression to clarify the role of KLF2 in Ang1/Tie2 signal-mediated vascular quiescence. Ang1 stimulated KLF2 promoter driven reporter gene expression in endothelial cells, whereas it failed when a myocyte enhancer factor 2 (MEF2)-binding site of KLF2 promoter was mutated. Depletion of MEF2 by siRNAs abolished Ang1-induced KLF2 expression, indicating the requirement of MEF2 in KLF2 induction by Ang1. Constitutive active phosphoinositide 3-kinase (PI3K)and AKT increased the MEF2-dependent reporter gene expression by enhancing its transcriptional activity and stimulated the KLF2 promoter activity cooperatively with MEF2. Consistently, inhibition of either PI3K or AKT and depletion of AKT abrogated Ang1-induced KLF2 expression. In addition, we confirmed the dispensability of extracellular signal-regulated kinase 5 (ERK5) for Ang1-induced KLF2 expression. Furthermore, depletion of KLF2 resulted in the loss of the inhibitory effect of Ang1 on vascular endothelial growth factor (VEGF)-mediated expression of vascular cell adhesion molecule-1 in endothelial cells and VEGF-mediated monocyte adhesion to endothelial cells. Collectively, these findings indicate that Ang1/Tie2 signal stimulates transcriptional activity of MEF2 through a PI3K/AKT pathway to induce KLF2 expression, which may counteract VEGF-mediated inflammatory responses.