Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, PA, USA.
Cell Cycle. 2010 Feb 1;9(3):570-79. doi: 10.4161/cc.9.3.10591.
The Hedgehog (Hh) pathway orchestrates developmental and homeostatic angiogenesis. the three Hh isoforms--Sonic Hedgehog (Shh), Indian Hedgehog (Ihh) and Desert Hedgehog (Dhh)--signal through patched-1 (ptCH1) and Smoothened (SMo), to activate the Gli transcription factors with a characteristic rank of potency (Shh >> Ihh > Dhh). To dissect the mechanisms through which Hh proteins promote angiogenesis, we analyzed processes inherent to vessel formation in endothelial cells. We found that none of the Hh ligands were able to induce Gli-target genes in human umbilical vein (HUVeC) or human cardiac microvascular endothelial cells (HMVeC), suggesting that endothelial cells do not respond to Hh through the canonical pathway. However, our results show that the three Hh proteins promote endothelial cell tubulogenesis in 3D cultures in a SMo- and Gi protein-dependent manner. Consistent with the required cytoskeletal re-arrangement for tubulogenesis, Shh, Ihh and Dhh all stimulated the small GTPase RhoA and the formation of actin stress fibers. This effect, which was mediated by SMO, Gi proteins and Rac1, defines a new non-canonical Hh pathway. In addition to regulating the actin cytoskeleton, the Hh ligands promoted survival through inhibition of the pro-apoptotic effect of PTCH1 in a SMO-independent manner. Altogether, our results support the existence of Gli-independent Hh responses in endothelial cells that regulate tubulogenesis and apoptosis. The identification of novel non-canonical responses elicited by Hh proteins in endothelial cells highlights the complexity of the Hh signaling pathway and reveals striking differences in ligand strength for transcriptional and non-transcriptional responses
刺猬(Hh)途径协调发育和动态血管生成。三种 Hh 同种型 - Sonic Hedgehog(Shh),Indian Hedgehog(Ihh)和 Desert Hedgehog(Dhh) - 通过 patched-1(ptCH1)和 Smoothened(SMo)发出信号,以激活Gli 转录因子,其特征为效力等级(Shh>>Ihh>Dhh)。为了解剖 Hh 蛋白促进血管生成的机制,我们分析了内皮细胞中固有血管形成过程。我们发现,Hh 配体都不能在人脐静脉(HUVeC)或人心血管微血管内皮细胞(HMVeC)中诱导 Gli 靶基因,这表明内皮细胞不通过经典途径对 Hh 作出反应。然而,我们的结果表明,三种 Hh 蛋白以 SMo 和 Gi 蛋白依赖性方式促进内皮细胞在 3D 培养中的管状形成。与管状形成所需的细胞骨架重新排列一致,Shh,Ihh 和 Dhh 均刺激小 GTPase RhoA 和肌动蛋白应力纤维的形成。这种效应由 SMO、Gi 蛋白和 Rac1 介导,定义了一种新的非经典 Hh 途径。除了调节肌动球蛋白细胞骨架外,Hh 配体还通过 SMo 独立的方式抑制 PTCH1 的促凋亡作用来促进存活。总之,我们的研究结果支持内皮细胞中存在调节管状形成和凋亡的 Gli 非依赖性 Hh 反应。鉴定内皮细胞中由 Hh 蛋白引发的新的非经典反应突显了 Hh 信号通路的复杂性,并揭示了配体在转录和非转录反应中的强度差异。
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