Feed-forward Signaling by Membrane-bound Ligand Receptor Circuit THE CASE OF NOTCH DELTA-LIKE 4 LIGAND IN ENDOTHELIAL CELLS
Feed-forward Signaling by Membrane-bound Ligand Receptor Circuit THE CASE OF NOTCH DELTA-LIKE 4 LIGAND IN ENDOTHELIAL CELLS
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DOI：
10.1074/jbc.m110.176065
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发表时间：
2010-12-24
影响因子：
4.8
通讯作者：
Molin, Daniel G. M.
中科院分区：
文献类型：
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作者：
Caolo, Vincenza;van den Akker, Nynke M. S.;Molin, Daniel G. M.
Delta like-4配体(DLL4)属于高度保守的缺口家族，在内皮细胞中特异表达。DLL4调控血管生长中的关键过程，包括内皮细胞(EC)的萌发和动脉的规范。血管内皮细胞生长因子-A促进其表达。在本研究中，我们证明了血管内皮生长因子诱导的DLL4的表达依赖于缺口的激活。血管内皮生长因子诱导的DLL4表达可被伽玛分泌酶或ADAM抑制剂阻断人心脏微血管内皮细胞的Noch信号通路所阻止。与血管内皮细胞生长因子-A类似，重组DLL4本身刺激Notch信号转导并导致DLL4表达上调，提示存在正前馈机制。这些作用可被Notch抑制剂消除，但不能被抑制血管内皮生长因子信号。Notch激活本身就足以诱导DLL4的表达，Notch胞内域(NICD)-1或-4过表达的积极作用说明了这一点。为了区分NICD/RBP-J kappa和FOXC2调控的DLL4表达，在启动子缺失实验中评估了DLL4启动子的活性。NiCd诱导的启动子活性依赖于RBP-J kappa位点，而不依赖于FOXC2结合位点。因此，结构活性FOXC2不影响DLL4的表达。我们观察到DLL4-EGFP转染的ECs在其附近的未转染细胞中诱导了DLL4的表达，这支持了正前馈机制可能将缺口激活传播到邻近内皮细胞的观点。总之，我们的数据为血管内皮生长因子或配体诱导的缺口信号通过正前馈机制上调DLL4的机制提供了证据。通过这种机制，DLL4可以繁殖自己的表达，并使内皮细胞之间的Notch表达和信号转导同步。
The DELTA like-4 ligand (DLL4) belongs to the highly conserved NOTCH family and is specifically expressed in the endothelium. DLL4 regulates crucial processes in vascular growth, including endothelial cell (EC) sprouting and arterial specification. Its expression is increased by VEGF-A. In the present study, we show that VEGF-induced DLL4 expression depends on NOTCH activation. VEGF-induced DLL4 expression was prevented by the blockage of NOTCH signaling with gamma-secretase or ADAM inhibitors in human cardiac microvascular ECs. Similar to VEGF-A, recombinant DLL4 itself stimulated NOTCH signaling and resulted in up-regulation of DLL4, suggesting a positive feed-forward mechanism. These effects were abrogated by NOTCH inhibitors but not by inhibition of VEGF signaling. NOTCH activation alone suffices to induce DLL4 expression as illustrated by the positive effect of NOTCH intracellular domain (NICD)-1 or -4 overexpression. To discriminate between NICD/RBP-J kappa and FOXC2-regulated DLL4 expression, DLL4 promoter activity was assessed in promoter deletion experiments. NICD induced promoter activity was dependent on RBP-J kappa site but independent of the FOXC2 binding site. Accordingly, constitutively active FOXC2 did not affect DLL4 expression. The notion that the positive feed-forward mechanism might propagate NOTCH activation to neighboring ECs was supported by our observation that DLL4-eGFP-transfected ECs induced DLL4 expression in nontransfected cells in their vicinity. In summary, our data provide evidence for a mechanism by which VEGF or ligand-induced NOTCH signaling up-regulates DLL4 through a positive feed-forward mechanism. By this mechanism, DLL4 could propagate its own expression and enable synchronization of NOTCH expression and signaling between ECs.