Angiopoietin receptor Tie2 is required for vein specification and maintenance via regulating COUP-TFII (original) (raw)
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Circulation Research, 1998
Angiopoietin-1 (Ang1) has been recently identified as the major physiological ligand for the tyrosine kinase receptor Tie2 and assigned responsibility for recruiting and sustaining periendothelial support cells. Angiopoietin-2 (Ang2) was found to disrupt blood vessel formation in the developing embryo by antagonizing the effects of Ang1 and Tie2 and was thus considered to represent a natural Ang1/Tie2 inhibitor. In vivo effects of either angiopoietin on postnatal neovascularization, however, have not been previously described. Accordingly, we used the cornea micropocket assay of neovascularization to investigate the impact of angiopoietins on neovascularization in vivo. Neither Ang1 nor Ang2 alone promoted neovascularization. Pellets containing vascular endothelial growth factor (VEGF) alone induced corneal neovascularity extending from the limbus across the cornea. Addition of Ang1 to VEGF (Ang1ϩVEGF) produced an increase in macroscopically evident perfusion of the corneal neovasculature without affecting macroscopic measurements of length (0.58Ϯ0.03 mm) or circumferential neovascularity (136Ϯ10°). In contrast, pellets containing Ang2ϩVEGF promoted significantly longer (0.67Ϯ0.05 mm) and more circumferential (160Ϯ15°) neovascularity than VEGF alone or Ang1ϩVEGF (PϽ0.05). Excess soluble Tie2 receptor (sTie2-Fc) precluded modulation of VEGF-induced neovascularization by both Ang2 and Ang1. Fluorescent microscopic findings demonstrated enhanced capillary density (fluorescence intensity, 2.55Ϯ0.23 e ϩ9 versus 1.23Ϯ0.17 e ϩ9 , PϽ0.01) and increased luminal diameter of the basal limbus artery (39.0Ϯ2.8 versus 27.9Ϯ1.3 m, PϽ0.01) for Ang1ϩVEGF compared with VEGF alone. In contrast to Ang1ϩVEGF, Ang2ϩVEGF produced longer vessels and, at the tip of the developing capillaries, frequent isolated sprouting cells. In the case of Ang2ϩVEGF, however, luminal diameter of the basal limbus artery was not increased (26.7Ϯ1.9 versus 27.9Ϯ1.3, PϭNS). These findings constitute what is to our knowledge the first direct demonstration of postnatal bioactivity associated with either angiopoietin. In particular, these results indicate that angiopoietins may potentiate the effects of other angiogenic cytokines. Moreover, these findings provide in vivo evidence that Ang1 promotes vascular network maturation, whereas Ang2 works to initiate neovascularization.
Angiopoietin-2, a Natural Antagonist for Tie2 That Disrupts In Vivo Angiogenesis
Science, 1997
normal vascular development has been verified by examination of mice with inacti-~ntagonist f o r~i e 2 That vating mutations in the genes for these factors or their receptors, which can exhibit defects in the earliest stages of endothelial Disrupts i viva An 9 i og esis cell generation (5). Negative angiogenic regulators such as oroliferin-related ~r o t e i n (4, angiostatin (7), and endostaiin
Nature Genetics, 2008
Germline substitutions in the endothelial cell tyrosine kinase receptor TIE2/TEK cause a rare inherited form of venous anomalies, mucocutaneous venous malformations (VMCM)1 -4. We now identified a somatic 2 nd hit causing loss-of-function of the receptor in a resected VMCM. We assessed for whether such localized, tissue-specific events play a role in the etiology of the far more common sporadic VM. Eight somatic TIE2 mutations were identified in lesions from 28 out of 57 patients (49.1%), not detected in their blood or in control tissues. The somatic mutations included a frequent L914F change, and a series of double-mutations that occurred in cis, all of which show ligand-independent hyperphosphorylation in vitro. When overexpressed in HUVECs, L914F showed abnormal localization and response to ligand, differing from wild-type and the common inherited R849W mutant, suggesting they may have distinct effects. The presence of the same mutations in multifocal VMs in two patients, suggests a common origin for the abnormal endothelial cells in the distant sites. In conclusion, these data illustrate that a sporadic disease may be explained by somatic changes in a gene causing rare, inherited forms, and pinpoint TIE2 pathways as potential therapeutic targets for VM.
Functional Significance of Tie2 Signaling in the Adult Vasculature
2010
Abundant data now demonstrate that the growth of new blood vessels, termed angiogenesis, plays both pathological and beneficial roles in human disease. Based on these data, a tremendous effort has been undertaken to understand the molecular mechanisms that drive blood vessel growth in adult tissues. Tie2 recently was identified as a receptor tyrosine kinase expressed principally on vascular endothelium. Disrupting Tie2 function in mice resulted in embryonic lethality with defects in embryonic vasculature, suggesting a role in blood vessel maturation and maintenance. Based on these studies, we undertook a series of studies to probe the function of Tie2 in adult vasculature that will form the focus of this chapter. Consistent with a role in blood vessel growth in adult vasculature, Tie2 was upregulated and activated in the endothelium of rat ovary and in healing rat skin wounds, both areas of active angiogenesis. Moreover, Tie2 was upregulated in the endothelium of vascular "hot spots" in human breast cancer specimens. Surprisingly, Tie2 also was expressed and activated in the endothelium of all normal rat tissues examined, suggesting a role in maintenance of adult vasculature. To determine the functional role of Tie2 in tumor vasculature, a soluble Tie2 extracellular domain (ExTek) was designed that blocked the activation of Tie2 by its activating ligand, angiopoietin 1 (Ang1). Administration of recombinant ExTek protein or an ExTek adenovirus inhibited tumor growth and metastasis in rodent tumor models, demonstrating a functional role for Tie2 in pathological angiogenesis in adult tissues. To begin to understand the endothelial signaling pathways and cellular responses that mediate Tie2 function, we identified signaling molecules that are recruited to the activated, autophosphorylated Tie2 kinase domain. Two of these molecules, SHP2 and GRB2, are part of the pathway upstream of mitogen-activated protein kinase (MAPK) activation, a pathway that may be responsible for morphogenetic effects of Tie2 on endothelial cells. Another signaling molecule, p85, is responsible for recruitment of phosphatidylinositol 3 kinase (PI3-K) and activation of the Akt/PI3-K pathway. Akt/PI3-K has emerged as a critical pathway downstream of Tie2 that is necessary for cell survival effects as well as for chemotaxis, activation of endothelial nitric oxide synthase, and perhaps for anti-inflammatory effects of Tie2 activation. together, 51 Downloaded from SA, Pasyk KA, Speer MC, Peters KG, Marchuk DA 1999 Allelic and locus heterogeneity in inherited venous malformations. Hum Mol Genet 8:1279 -1289 Chae JK, Kim I, Lim ST, Chung MJ, Kim WH, Kim HG, Ko JK, Koh GY 2000 Coadministration of angiopoietin-1 and vascular endothelial growth factor enhances collateral vascularization. Arterioscler Thromb Vasc Biol 20:2573-2578 Conway EM, Collen D, Carmeliet P 2001 Molecular mechanisms of blood vessel growth. Cardiovasc Res 49:507-521 Davis S, Aldrich TH, Jones PF, Acheson A, Compton DL, Jain V, Ryan TE, Bruno J, Radziejewski C, Maisonpierre PC, Yancopoulos GD 1996 Isolation of angiopoietin-1, a ligand for the TIE2 receptor, by secretion-trap expression cloning. Cell
Common and specific effects of TIE2 mutations causing venous malformations
Human Molecular Genetics, 2015
Venous malformations (VMs) are localized defects in vascular morphogenesis frequently caused by mutations in the gene for the endothelial tyrosine kinase receptor TIE2. Here, we report the analysis of a comprehensive collection of 22 TIE2 mutations identified in patients with VM, either as single amino acid substitutions or as double-mutations on the same allele. Using endothelial cell (EC) cultures, mouse models and ultrastructural analysis of tissue biopsies from patients, we demonstrate common as well as mutation-specific cellular and molecular features, on the basis of which mutations cluster into categories that correlate with data from genetic studies. Comparisons of double-mutants with their constituent single-mutant forms identified the pathogenic contributions of individual changes, and their compound effects. We find that defective receptor trafficking and subcellular localization of different TIE2 mutant forms occur via a variety of mechanisms, resulting in attenuated response to ligand. We also demonstrate, for the first time, that TIE2 mutations cause chronic activation of the MAPK pathway resulting in loss of normal EC monolayer due to extracellular matrix (ECM) fibronectin deficiency and leading to upregulation of plasminogen/plasmin proteolytic pathway. Corresponding EC and ECM irregularities are observed in affected tissues from mouse models and patients. Importantly, an imbalance between plasminogen activators versus inhibitors would also account for high -dimer levels, a major feature of unknown cause that distinguishes VMs from other vascular anomalies.
Angiopoietin-2 differentially regulates angiogenesis through TIE2 and integrin signaling
Journal of Clinical Investigation, 2012
Angiopoietin-2 (ANG-2) is a key regulator of angiogenesis that exerts context-dependent effects on ECs. ANG-2 binds the endothelial-specific receptor tyrosine kinase 2 (TIE2) and acts as a negative regulator of ANG-1/TIE2 signaling during angiogenesis, thereby controlling the responsiveness of ECs to exogenous cytokines. Recent data from tumors indicate that under certain conditions ANG-2 can also promote angiogenesis. However, the molecular mechanisms of dual ANG-2 functions are poorly understood. Here, we identify a model for the opposing roles of ANG-2 in angiogenesis. We found that angiogenesis-activated endothelium harbored a subpopulation of TIE2-negative ECs (TIE2 lo). TIE2 expression was downregulated in angiogenic ECs, which abundantly expressed several integrins. ANG-2 bound to these integrins in TIE2 lo ECs, subsequently inducing, in a TIE2-independent manner, phosphorylation of the integrin adaptor protein FAK, resulting in RAC1 activation, migration, and sprouting angiogenesis. Correspondingly, in vivo ANG-2 blockade interfered with integrin signaling and inhibited FAK phosphorylation and sprouting angiogenesis of TIE2 lo ECs. These data establish a contextual model whereby differential TIE2 and integrin expression, binding, and activation control the role of ANG-2 in angiogenesis. The results of this study have immediate translational implications for the therapeutic exploitation of angiopoietin signaling.
Angiopoietin-Tie signalling in the cardiovascular and lymphatic systems
Clinical science (London, England : 1979), 2017
Endothelial cells that form the inner layer of blood and lymphatic vessels are important regulators of vascular functions and centrally involved in the pathogenesis of vascular diseases. In addition to the vascular endothelial growth factor (VEGF) receptor pathway, the angiopoietin (Ang)-Tie system is a second endothelial cell specific ligand-receptor signalling system necessary for embryonic cardiovascular and lymphatic development. The Ang-Tie system also regulates postnatal angiogenesis, vessel remodelling, vascular permeability and inflammation to maintain vascular homoeostasis in adult physiology. This system is implicated in numerous diseases where the vasculature has an important contribution, such as cancer, sepsis, diabetes, atherosclerosis and ocular diseases. Furthermore, mutations in the TIE2 signalling pathway cause defects in vascular morphogenesis, resulting in venous malformations and primary congenital glaucoma. Here, we review recent advances in the understanding o...