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Brouillard P, Murtomäki A, Leppänen VM, Hyytiäinen M, Mestre S, Potier L, Boon LM, Revencu N, Greene A, Anisimov A, Salo MH, Hinttala R, Eklund L, Quéré I, Alitalo K, Vikkula M. Loss-of-function mutations of the TIE1 receptor tyrosine kinase cause late-onset primary lymphedema. J Clin Invest 2024; 134:e173586. [PMID: 38820174 PMCID: PMC11245153 DOI: 10.1172/jci173586] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2023] [Accepted: 05/24/2024] [Indexed: 06/02/2024] Open
Abstract
Primary lymphedema (PL), characterized by tissue swelling, fat accumulation, and fibrosis, results from defects in lymphatic vessels or valves caused by mutations in genes involved in development, maturation, and function of the lymphatic vascular system. Pathogenic variants in various genes have been identified in about 30% of PL cases. By screening of a cohort of 755 individuals with PL, we identified two TIE1 (tyrosine kinase with immunoglobulin- and epidermal growth factor-like domains 1) missense variants and one truncating variant, all predicted to be pathogenic by bioinformatic algorithms. The TIE1 receptor, in complex with TIE2, binds angiopoietins to regulate the formation and remodeling of blood and lymphatic vessels. The premature stop codon mutant encoded an inactive truncated extracellular TIE1 fragment with decreased mRNA stability, and the amino acid substitutions led to decreased TIE1 signaling activity. By reproducing the two missense variants in mouse Tie1 via CRISPR/Cas9, we showed that both cause edema and are lethal in homozygous mice. Thus, our results indicate that TIE1 loss-of-function variants can cause lymphatic dysfunction in patients. Together with our earlier demonstration that ANGPT2 loss-of-function mutations can also cause PL, our results emphasize the important role of the ANGPT2/TIE1 pathway in lymphatic function.
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Affiliation(s)
- Pascal Brouillard
- Human Molecular Genetics, de Duve Institute, University of Louvain, Brussels, Belgium
| | - Aino Murtomäki
- Wihuri Research Institute, Biomedicum Helsinki, Helsinki, Finland
- Translational Cancer Medicine Program, Faculty of Medicine, University of Helsinki, Helsinki, Finland
| | - Veli-Matti Leppänen
- Wihuri Research Institute, Biomedicum Helsinki, Helsinki, Finland
- Translational Cancer Medicine Program, Faculty of Medicine, University of Helsinki, Helsinki, Finland
| | - Marko Hyytiäinen
- Wihuri Research Institute, Biomedicum Helsinki, Helsinki, Finland
- Translational Cancer Medicine Program, Faculty of Medicine, University of Helsinki, Helsinki, Finland
| | - Sandrine Mestre
- Department of Vascular Medicine, Centre de Référence des Maladies Lymphatiques et Vasculaires Rares, Inserm IDESP, CHU Montpellier, Université de Montpellier, Montpellier, France
| | - Lucas Potier
- Human Molecular Genetics, de Duve Institute, University of Louvain, Brussels, Belgium
| | - Laurence M. Boon
- Human Molecular Genetics, de Duve Institute, University of Louvain, Brussels, Belgium
- Center for Vascular Anomalies, Division of Plastic Surgery, Cliniques Universitaires Saint-Luc, University of Louvain, VASCERN-VASCA Reference Centre, Brussels, Belgium
| | - Nicole Revencu
- Center for Human Genetics, Cliniques Universitaires Saint-Luc, University of Louvain, Brussels, Belgium
| | - Arin Greene
- Department of Plastic and Oral Surgery, Lymphedema Program, Boston Children’s Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Andrey Anisimov
- Wihuri Research Institute, Biomedicum Helsinki, Helsinki, Finland
- Translational Cancer Medicine Program, Faculty of Medicine, University of Helsinki, Helsinki, Finland
| | - Miia H. Salo
- Biocenter Oulu, Research Unit of Clinical Medicine and Medical Research Center Oulu, University of Oulu and Oulu University Hospital, Oulu, Finland
| | - Reetta Hinttala
- Biocenter Oulu, Research Unit of Clinical Medicine and Medical Research Center Oulu, University of Oulu and Oulu University Hospital, Oulu, Finland
| | - Lauri Eklund
- Oulu Center for Cell-Matrix Research, Faculty of Biochemistry and Molecular Medicine, Biocenter Oulu, University of Oulu, Oulu, Finland
| | - Isabelle Quéré
- Department of Vascular Medicine, Centre de Référence des Maladies Lymphatiques et Vasculaires Rares, Inserm IDESP, CHU Montpellier, Université de Montpellier, Montpellier, France
| | - Kari Alitalo
- Wihuri Research Institute, Biomedicum Helsinki, Helsinki, Finland
- Translational Cancer Medicine Program, Faculty of Medicine, University of Helsinki, Helsinki, Finland
| | - Miikka Vikkula
- Human Molecular Genetics, de Duve Institute, University of Louvain, Brussels, Belgium
- WELBIO department, WEL Research Institute, Wavre, Belgium
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2
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Akwii RG, Mikelis CM. Targeting the Angiopoietin/Tie Pathway: Prospects for Treatment of Retinal and Respiratory Disorders. Drugs 2021; 81:1731-1749. [PMID: 34586603 PMCID: PMC8479497 DOI: 10.1007/s40265-021-01605-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/06/2021] [Indexed: 12/21/2022]
Abstract
Anti-angiogenic approaches have significantly advanced the treatment of vascular-related pathologies. The ephemeral outcome and known side effects of the current vascular endothelial growth factor (VEGF)-based anti-angiogenic treatments have intensified research on other growth factors. The angiopoietin/Tie (Ang/Tie) family has an established role in vascular physiology and regulates angiogenesis, vascular permeability, and inflammatory responses. The Ang/Tie family consists of angiopoietins 1-4, their receptors, tie1 and 2 and the vascular endothelial-protein tyrosine phosphatase (VE-PTP). Modulation of Tie2 activation has provided a promising outcome in preclinical models and has led to clinical trials of Ang/Tie-targeting drug candidates for retinal disorders. Although less is known about the role of Ang/Tie in pulmonary disorders, several studies have revealed great potential of the Ang/Tie family members as drug targets for pulmonary vascular disorders as well. In this review, we summarize the functions of the Ang/Tie pathway in retinal and pulmonary vascular physiology and relevant disorders and highlight promising drug candidates targeting this pathway currently being or expected to be under clinical evaluation for retinal and pulmonary vascular disorders.
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Affiliation(s)
- Racheal Grace Akwii
- Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, 1406 S. Coulter St., Amarillo, TX, 79106, USA
| | - Constantinos M Mikelis
- Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, 1406 S. Coulter St., Amarillo, TX, 79106, USA.
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3
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Zhang Y, Kontos CD, Annex BH, Popel AS. Angiopoietin-Tie Signaling Pathway in Endothelial Cells: A Computational Model. iScience 2019; 20:497-511. [PMID: 31655061 PMCID: PMC6806670 DOI: 10.1016/j.isci.2019.10.006] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Revised: 09/21/2019] [Accepted: 09/30/2019] [Indexed: 12/13/2022] Open
Abstract
The angiopoietin-Tie signaling pathway is an important vascular signaling pathway involved in angiogenesis, vascular stability, and quiescence. Dysregulation in the pathway is linked to the impairments in vascular function associated with many diseases, including cancer, ocular diseases, systemic inflammation, and cardiovascular diseases. The present study uses a computational signaling pathway model validated against experimental data to quantitatively study various mechanistic aspects of the angiopoietin-Tie signaling pathway, including receptor activation, trafficking, turnover, and molecular mechanisms of its regulation. The model provides mechanistic insights into the controversial role of Ang2 and its regulators vascular endothelial protein tyrosine phosphatase (VE-PTP) and Tie1 and predicts synergistic effects of inhibition of VE-PTP, Tie1, and Tie2 cleavage on enhancing the vascular protective actions of Tie2.
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Affiliation(s)
- Yu Zhang
- Department of Biomedical Engineering, School of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA.
| | - Christopher D Kontos
- Department of Medicine, Division of Cardiology, Duke University Medical Center, Durham, NC 27710, USA
| | - Brian H Annex
- Department of Medicine and the Vascular Biology Center, Medical College of Georgia at Augusta University, Augusta, GA 30912, USA
| | - Aleksander S Popel
- Department of Biomedical Engineering, School of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA
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4
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Sialic acid as a target for the development of novel antiangiogenic strategies. Future Med Chem 2018; 10:2835-2854. [PMID: 30539670 DOI: 10.4155/fmc-2018-0298] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Sialic acid is associated with glycoproteins and gangliosides of eukaryotic cells. It regulates various molecular interactions, being implicated in inflammation and cancer, where its expression is regulated by sialyltransferases and sialidases. Angiogenesis, the formation of new capillaries, takes place during inflammation and cancer, and represents the outcome of several interactions occurring at the endothelial surface among angiogenic growth factors, inhibitors, receptors, gangliosides and cell-adhesion molecules. Here, we elaborate on the evidences that many structures involved in angiogenesis are sialylated and that their interactions depend on sialic acid with implications in angiogenesis itself, inflammation and cancer. We also discuss the possibility to exploit sialic acid as a target for the development of novel antiangiogenic drugs.
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Kreitman M, Noronha A, Yarden Y. Irreversible modifications of receptor tyrosine kinases. FEBS Lett 2018; 592:2199-2212. [PMID: 29790151 DOI: 10.1002/1873-3468.13095] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Revised: 04/12/2018] [Accepted: 05/08/2018] [Indexed: 01/18/2023]
Abstract
Each group of the 56 receptor tyrosine kinases (RTK) binds with one or more soluble growth factors and coordinates a vast array of cellular functions. These outcomes are tightly regulated by inducible post-translational events, such as tyrosine phosphorylation, ubiquitination, ectodomain shedding, and regulated intramembrane proteolysis. Because of the delicate balance required for appropriate RTK function, cells may become pathogenic upon dysregulation of RTKs themselves or their post-translational covalent modifications. For example, reduced ectodomain shedding and decreased ubiquitination of the cytoplasmic region, both of which enhance growth factor signals, characterize malignant cells. Whereas receptor phosphorylation and ubiquitination are reversible, proteolytic cleavage events are irreversible, and either modification might alter the subcellular localization of RTKs. Herein, we focus on ectodomain shedding by metalloproteinases (including ADAM family proteases), cleavage within the membrane or cytoplasmic regions of RTKs (by gamma-secretases and caspases, respectively), and complete receptor proteolysis in lysosomes and proteasomes. Roles of irreversible modifications in RTK signaling, pathogenesis, and pharmacology are highlighted.
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Affiliation(s)
- Matthew Kreitman
- Department of Biological Regulation, Weizmann Institute of Science, Rehovot, Israel
| | - Ashish Noronha
- Department of Biological Regulation, Weizmann Institute of Science, Rehovot, Israel
| | - Yosef Yarden
- Department of Biological Regulation, Weizmann Institute of Science, Rehovot, Israel
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Duran CL, Howell DW, Dave JM, Smith RL, Torrie ME, Essner JJ, Bayless KJ. Molecular Regulation of Sprouting Angiogenesis. Compr Physiol 2017; 8:153-235. [PMID: 29357127 DOI: 10.1002/cphy.c160048] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The term angiogenesis arose in the 18th century. Several studies over the next 100 years laid the groundwork for initial studies performed by the Folkman laboratory, which were at first met with some opposition. Once overcome, the angiogenesis field has flourished due to studies on tumor angiogenesis and various developmental models that can be genetically manipulated, including mice and zebrafish. In addition, new discoveries have been aided by the ability to isolate primary endothelial cells, which has allowed dissection of various steps within angiogenesis. This review will summarize the molecular events that control angiogenesis downstream of biochemical factors such as growth factors, cytokines, chemokines, hypoxia-inducible factors (HIFs), and lipids. These and other stimuli have been linked to regulation of junctional molecules and cell surface receptors. In addition, the contribution of cytoskeletal elements and regulatory proteins has revealed an intricate role for mobilization of actin, microtubules, and intermediate filaments in response to cues that activate the endothelium. Activating stimuli also affect various focal adhesion proteins, scaffold proteins, intracellular kinases, and second messengers. Finally, metalloproteinases, which facilitate matrix degradation and the formation of new blood vessels, are discussed, along with our knowledge of crosstalk between the various subclasses of these molecules throughout the text. Compr Physiol 8:153-235, 2018.
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Affiliation(s)
- Camille L Duran
- Department of Molecular and Cellular Medicine, Texas A&M Health Science Center, College Station, Texas, USA
| | - David W Howell
- Department of Molecular and Cellular Medicine, Texas A&M Health Science Center, College Station, Texas, USA
| | - Jui M Dave
- Department of Molecular and Cellular Medicine, Texas A&M Health Science Center, College Station, Texas, USA
| | - Rebecca L Smith
- Department of Molecular and Cellular Medicine, Texas A&M Health Science Center, College Station, Texas, USA
| | - Melanie E Torrie
- Department of Genetics, Development and Cell Biology, Iowa State University, Ames, Iowa, USA
| | - Jeffrey J Essner
- Department of Genetics, Development and Cell Biology, Iowa State University, Ames, Iowa, USA
| | - Kayla J Bayless
- Department of Molecular and Cellular Medicine, Texas A&M Health Science Center, College Station, Texas, USA
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Yang P, Chen N, Jia JH, Gao XJ, Li SH, Cai J, Wang Z. Tie-1: A potential target for anti-angiogenesis therapy. ACTA ACUST UNITED AC 2015; 35:615-622. [PMID: 26489611 DOI: 10.1007/s11596-015-1479-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2015] [Revised: 06/19/2015] [Indexed: 01/30/2023]
Abstract
The tyrosine kinase system angiopoietin (Ang)/Tie interacts with vascular endothelial growth factor pathway and regulates vessel quiescence in adults as well as later steps of the angiogenic cascade related to vessel maturation. Since all Angs are able to bind to Tie-2 but none binds to Tie-1, the function of Tie-2 and its ligands have captured attention. However, emerging evidence indicates unique roles of the orphan receptor Tie-1 in angiogenesis under physiological and pathological conditions. It is required for maintaining vascular endothelial cell integrity and survival during murine embryo development and in adult and may be involved in modulating differentiation of hematopoietic cells in adult. Tie-1 exhibits poor tyrosine kinase activity and signals via forming heterodimers with Tie-2, inhibiting Tie-2 signaling mediated by Angs. This inhibition can be relieved by Tie-1 ectodomain cleavage mediated by tumor- and inflammatory-related factors, which causes destabilization of vessels and initiates vessel remodeling. Up-regulated Tie-1 expression has been found not only in some leukemia cells and tumor related endothelial cells but also in cytoplasm of carcinoma cells of a variety of human solid tumors, which is associated with tumor progression. In addition, it has pro-inflammatory functions in endothelial cells and is involved in some inflammatory diseases associated with angiogenesis. Recent research indicated that Tie-1 gene ablation exhibited significant effects on tumor blood- and lymph-angiogenesis and improved anti-Ang therapy, suggesting Tie-1 may be a potential target for tumor anti-angiogenesis treatment.
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MESH Headings
- Angiogenesis Inhibitors/therapeutic use
- Angiopoietins/genetics
- Angiopoietins/metabolism
- Animals
- Embryo, Mammalian
- Embryonic Development/genetics
- Endothelial Cells/drug effects
- Endothelial Cells/metabolism
- Endothelial Cells/pathology
- Gene Expression Regulation, Developmental
- Gene Expression Regulation, Neoplastic
- Humans
- Mice
- Neoplasms/drug therapy
- Neoplasms/genetics
- Neoplasms/metabolism
- Neoplasms/pathology
- Neovascularization, Pathologic/drug therapy
- Neovascularization, Pathologic/genetics
- Neovascularization, Pathologic/metabolism
- Neovascularization, Pathologic/pathology
- Protein Binding
- Receptor, TIE-1/antagonists & inhibitors
- Receptor, TIE-1/genetics
- Receptor, TIE-1/metabolism
- Receptor, TIE-2/genetics
- Receptor, TIE-2/metabolism
- Signal Transduction
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Affiliation(s)
- Ping Yang
- Department of Obstetrics and Gynecology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
- Department of Obstetrics and Gynecology, First Affiliated Hospital, School of Medicine, Shihezi University, Shihezi, 832008, China
| | - Na Chen
- Department of Obstetrics and Gynecology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Jing-Hui Jia
- Department of Obstetrics and Gynecology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Xue-Jiao Gao
- Department of Obstetrics and Gynecology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Shi-Han Li
- Department of Obstetrics and Gynecology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Jing Cai
- Department of Obstetrics and Gynecology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China.
| | - Zehua Wang
- Department of Obstetrics and Gynecology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China.
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Wang X, Zhao R, Liu C, Qiao T. Abnormal expression of Tie1 on the valves of great saphenous varicose vein. Phlebology 2012; 28:93-100. [PMID: 22987233 DOI: 10.1258/phleb.2012.012018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
OBJECTIVE To investigate the abnormal expressions of Tie1 on the valves of great saphenous varicose vein, and to discuss the relationship between the phenomenon and pathogenesis of varicose vein of lower extremity. METHODS Varicose veins group 18 samples, normal control group 14 samples. Immunohistochemistry staining has investigated the expression of CD31 and Tie1 in the first valves of great saphenous veins. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) has checked mRNA expression of Tie1. Western blot has checked the expression of Tie1 protein in venous valves. RESULTS In normal control group valves, there was no difference between proximal and distal sides endothelium, which expressing CD31 in both valvar basement and valve cusp (positive endothelial cells [ECs] percentage: P > 0.05, P > 0.05). However, the endothelium of the proximal side demonstrates Tie1 stronger than distal side in valvar basement (positive ECs percentage: P < 0.05), which was not found at valve cusp (positive ECs percentage: P > 0.05). In varicose veins group, the endothelium of proximal side cells expresses CD31 weaker than distal side at both valvar basement and valve cusp (positive ECs percentage: P < 0.05, P < 0.05) besides the morphological alteration of valves. Moreover, it expresses Tie1 much weaker than diatal side (positive ECs percentage: P < 0.01). Semi-quantitative RT-PCR showed that valves of varicose veins group expressed Tie1 much weaker than the normal control group (P < 0.01). Western blot could not detect the expression of Tie1 in venous valves. CONCLUSION The decreasing expression of Tie1 may play an important role in the pathogenesis of primary lower extremity varicose veins.
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Affiliation(s)
- Xin Wang
- Department of Vascular Surgery, Affiliated Drum Tower Hospital, Medical College of Nanjing University
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9
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English WR, Corvol P, Murphy G. LPS activates ADAM9 dependent shedding of ACE from endothelial cells. Biochem Biophys Res Commun 2012; 421:70-5. [PMID: 22480688 DOI: 10.1016/j.bbrc.2012.03.113] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Accepted: 03/21/2012] [Indexed: 02/08/2023]
Abstract
Angiotensin-I converting enzyme (ACE) is a zinc dependent peptidase with a major role in regulating vasoactive peptide metabolism. ACE, a transmembrane protein, undergoes proteolysis, or shedding, by an as yet unidentified proteinase to release a catalytically active soluble form of the enzyme. Physiologically, soluble ACE in plasma is derived primarily from endothelial cells. We demonstrate that ACE shedding from confluent endothelial cells is increased in response to bacterial lipopolysaccharide, but not phorbol esters. Characterisation of lipopolysaccharide stimulated shedding showed that there is a lag phase before soluble ACE can be detected which is sensitive to inhibitors of translation, NF-κB, TNFα and TNFR-I/II. The shedding phase is less sensitive to these inhibitors, but is ablated by BB-94, a Matrix Metalloproteinase (MMP)/A Disintegrin and Metalloproteinase (ADAM) inhibitor. Tissue Inhibitor of Metalloproteinase (TIMP) profiling suggested a requirement for ADAM9 in lipopolysaccharide induced ACE shedding, which was confirmed by depletion with siRNA. Transient transfection of ADAM9 and ACE cDNAs into HEK293 cells demonstrated that ADAM9 requires both membrane anchorage and its catalytic domain to shed ACE.
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Affiliation(s)
- William R English
- Department of Oncology, University of Cambridge, Cancer Research UK Cambridge Research Institute, The Li Ka Shing Centre, Robinson Way CB2 0RE, UK.
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Abstract
The angiopoietins act through the endothelial receptor tyrosine kinase Tie2 to regulate vessel maturation in angiogenesis and control quiescence and stability of established vessels. The activating ligand, Ang1 (angiopoietin-1), is constitutively expressed by perivascular cells, and the ability of endothelial cells to respond to the ligand is controlled at the level of the Ang1 receptor. This receptor interacts with the related protein Tie1 on the cell surface, and Tie1 inhibits Ang1 signalling through Tie2. The responsiveness of endothelium to Ang1 is determined by the relative levels of Tie2 and the inhibitory co-receptor Tie1 in the cells. Tie1 undergoes regulated ectodomain cleavage which is stimulated by a range of factors including VEGF (vascular endothelial growth factor), inflammatory cytokines and changes in shear stress. Ectodomain cleavage of Tie1 relieves inhibition of Tie2 and enhances Ang1 signalling. This mechanism regulates Ang1 signalling without requiring changes in the level of the ligand and allows Ang1 signalling to be co-ordinated with other signals in the cellular environment. Regulation of signalling at the level of receptor responsiveness may be an important adaptation in systems in which an activating ligand is normally present in excess or where the ligand provides a constitutive maintenance signal.
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11
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Singh H, Hansen TM, Patel N, Brindle NPJ. The molecular balance between receptor tyrosine kinases Tie1 and Tie2 is dynamically controlled by VEGF and TNFα and regulates angiopoietin signalling. PLoS One 2012; 7:e29319. [PMID: 22235284 PMCID: PMC3250418 DOI: 10.1371/journal.pone.0029319] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2011] [Accepted: 11/24/2011] [Indexed: 11/18/2022] Open
Abstract
Angiopoietin-1 (Ang1) signals via the receptor tyrosine kinase Tie2 which exists in complex with the related protein Tie1 at the endothelial cell surface. Tie1 undergoes regulated ectodomain cleavage in response to phorbol esters, vascular endothelial growth factor (VEGF) and tumour necrosis factor-α (TNFα). Recently phorbol esters and VEGF were found also to stimulate ectodomain cleavage of Tie2. Here we investigate for the first time the effects of factors activating ectodomain cleavage on both Tie1 and Tie2 within the same population of cells, and their impact on angiopoietin signalling. We find that phorbol ester and VEGF activated Tie1 cleavage within minutes followed by restoration to control levels by 24 h. However, several hours of PMA and VEGF treatment were needed to elicit a detectable decrease in cellular Tie2, with complete loss seen at 24 h of PMA treatment. TNFα stimulated Tie1 cleavage, and induced a sustained decrease in cellular Tie1 over 24 h whilst increasing cellular Tie2. These differential effects of agonists on Tie1 and Tie2 result in dynamic modulation of the cellular Tie2∶Tie1 ratio. To assess the impact of this on Ang1 signalling cells were stimulated with VEGF and TNFα for differing times and Ang1-induced Tie2 phosphorylation examined. Elevated Tie2∶Tie1, in response to acute VEGF treatment or chronic TNFα, was associated with increased Ang1-activated Tie2 in cells. These data demonstrate cellular levels of Tie1 and Tie2 are differentially regulated by pathophysiologically relevant agonists resulting in dynamic control of the cellular Tie2∶Tie1 balance and modulation of Ang1 signalling. These findings highlight the importance of regulation of signalling at the level of the receptor. Such control may be an important adaptation to allow modulation of cellular signalling responses in systems in which the activating ligand is normally present in excess or where the ligand provides a constitutive maintenance signal.
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Affiliation(s)
- Harprit Singh
- Department of Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom
| | - Tania M. Hansen
- Department of Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom
| | - Nisha Patel
- Department of Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom
| | - Nicholas P. J. Brindle
- Department of Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom
- * E-mail:
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12
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Hansen TM, Singh H, Tahir TA, Brindle NPJ. Effects of angiopoietins-1 and -2 on the receptor tyrosine kinase Tie2 are differentially regulated at the endothelial cell surface. Cell Signal 2010; 22:527-32. [PMID: 19922791 PMCID: PMC2807028 DOI: 10.1016/j.cellsig.2009.11.007] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2009] [Revised: 10/22/2009] [Accepted: 11/10/2009] [Indexed: 11/01/2022]
Abstract
Angiopoietin-1 (Ang1) and Ang2 are ligands for the receptor tyrosine kinase Tie2. Structural data suggest that the two ligands bind Tie2 similarly. However, in endothelial cells Ang1 activates Tie2 whereas Ang2 can act as an apparent antagonist. In addition, each ligand exhibits distinct kinetics of release following binding. These observations suggest that additional factors influence function and binding of angiopoietins with receptors in the cellular context. Previous work has shown that Ang1 binding and activation of Tie2 are inhibited by Tie1, a related receptor that complexes with Tie2 in cells. In this study we have investigated binding of Ang1 and Ang2 to Tie2 in endothelial cells. In contrast to Ang1, binding of Ang2 to Tie2 was found to be not affected by Tie1. Neither PMA-induced Tie1 ectodomain cleavage nor suppression of Tie1 expression by siRNA affected the ability of Ang2 to bind Tie2. Analysis of the level of Tie1 co-immunoprecipitating with angiopoietin-bound Tie2 demonstrated that Ang2 can bind Tie2 in Tie2:Tie1 complexes whereas Ang1 preferentially binds non-complexed Tie2. Stimulation of Tie1 ectodomain cleavage did not increase the agonist activity of Ang2 for Tie2. Similarly, the Tie2-agonist activity of Ang2 was not affected by siRNA suppression of Tie1 expression. Consistent with previous reports, loss of Tie1 ectodomain enhanced the agonist activity of Ang1 for Tie2. Importantly, Ang2 was still able to antagonize the elevated Ang1-activation of Tie2 that occurs on Tie1 ectodomain loss. Together these data demonstrate that Ang1 and Ang2 bind differently to Tie2 at the cell surface and this is controlled by Tie1. This differential regulation of angiopoietin binding allows control of Tie2 activation response to Ang1 without affecting Ang2 agonist activity and maintains the ability of Ang2 to antagonize even the enhanced Ang1 activation of Tie2 that occurs on loss of Tie1 ectodomain. This provides a mechanism by which signalling through Tie2 can be modified by stimuli in the cellular microenvironment.
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Affiliation(s)
- Tania M Hansen
- University of Leicester, Department of Cardiovascular Sciences, RKCSB, PO Box 65, Leicester LE2 7LX, UK
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13
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Angiopoietin-1-induced ubiquitylation of Tie2 by c-Cbl is required for internalization and degradation. Biochem J 2009; 423:375-80. [DOI: 10.1042/bj20091010] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Tie2 [where ‘Tie’ is an acronym from tyrosine kinase with Ig and EGF (epidermal growth factor) homology domains] is a receptor tyrosine kinase expressed predominantly on the surface of endothelial cells. Activated by its ligands, the angiopoietins, Tie2 initiates signalling pathways that modulate vascular stability and angiogenesis. Deletion of either the Tie2 or Ang1 (angiopoietin-1) gene in mice results in lethal vascular defects, signifying their importance in vascular development. The mechanism employed by the Tie2 signalling machinery to attenuate or cause receptor trafficking is not well defined. Stimulation of Tie2-expressing cells with Ang1 results in its ubiquitylation, suggesting that this may provide the necessary signal for receptor turnover. Using a candidate molecule approach, we demonstrate that Tie2 co-immunoprecipitates with c-Cbl in an Ang1-dependent manner and its ubiquitylation can be inhibited by the dominant-interfering molecule v-Cbl (a viral form of c-Cbl that contains only the tyrosine kinase-binding domain region). Inhibition of the Tie2–Cbl interaction by overexpression of v-Cbl blocks ligand-induced Tie2 internalization and degradation. In summary, our results illustrate that c-Cbl interacts with the Tie2 signalling complex in a stimulation-dependent manner, and that this interaction is required for Tie2 ubiquitylation, internalization and degradation.
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14
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15
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Thomas M, Augustin HG. The role of the Angiopoietins in vascular morphogenesis. Angiogenesis 2009; 12:125-37. [PMID: 19449109 DOI: 10.1007/s10456-009-9147-3] [Citation(s) in RCA: 278] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2009] [Accepted: 04/24/2009] [Indexed: 01/20/2023]
Abstract
The Angiopoietin/Tie system acts as a vascular specific ligand/receptor system to control endothelial cell survival and vascular maturation. The Angiopoietin family includes four ligands (Angiopoietin-1, Angiopoietin-2 and Angiopoietin-3/4) and two corresponding tyrosine kinase receptors (Tie1 and Tie2). Ang-1 and Ang-2 are specific ligands of Tie2 binding the receptor with similar affinity. Tie2 activation promotes vessel assembly and maturation by mediating survival signals for endothelial cells and regulating the recruitment of mural cells. Ang-1 acts in a paracrine agonistic manner inducing Tie2 phosphorylation and subsequent vessel stabilization. In contrast, Ang-2 is produced by endothelial cells and acts as an autocrine antagonist of Ang-1-mediated Tie2 activation. Ang-2 thereby primes the vascular endothelium to exogenous cytokines and induces vascular destabilization at higher concentrations. Ang-2 is strongly expressed in the vasculature of many tumors and it has been suggested that Ang-2 may act synergistically with other cytokines such as vascular endothelial growth factor to promote tumor-associated angiogenesis and tumor progression. The better mechanistic understanding of the Ang/Tie system is gradually paving the way toward the rationale exploitation of this vascular signaling system as a therapeutic target for neoplastic and non-neoplastic diseases.
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Affiliation(s)
- Markus Thomas
- Joint Research Division Vascular Biology, Medical Faculty Mannheim (CBTM), University of Heidelberg, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany
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16
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Singh H, Milner CS, Aguilar Hernandez MM, Patel N, Brindle NPJ. Vascular endothelial growth factor activates the Tie family of receptor tyrosine kinases. Cell Signal 2009; 21:1346-50. [PMID: 19376222 DOI: 10.1016/j.cellsig.2009.04.002] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2009] [Revised: 04/09/2009] [Accepted: 04/11/2009] [Indexed: 12/17/2022]
Abstract
The ability of cells to respond appropriately to changes in their environment requires integration and cross-talk between relevant signalling pathways. The vascular endothelial growth factor (VEGF) and angiopoietin families of ligands are key regulators of blood vessel formation. VEGF binds to receptor tyrosine kinases of the VEGF-receptor family to activate signalling pathways leading to endothelial migration, proliferation and survival whereas the angiopoietins interact with the Tie receptor tyrosine kinases to control vessel stability, survival and maturation. Here we show that VEGF can also activate the angiopoietin receptor Tie2. Activation of human endothelial cells with VEGF caused a four-fold stimulation of tyrosine phosphorylation of Tie2. This stimulation was not due to VEGF-induction of Tie2 ligands as soluble ligand binding domain of Tie2 failed to inhibit VEGF activation of the receptor. Immunoprecipitation analysis demonstrated no physical interaction between VEGF receptors and Tie2. However Tie2 does interact with the related receptor tyrosine kinase Tie1 and this receptor was found to be essential for VEGF activation of Tie2. VEGF stimulated proteolytic cleavage of Tie1 generating a truncated Tie1 intracellular domain. Similarly, phorbol ester also both stimulated Tie1 truncation and activated Tie2 phosphorylation. Inhibition of Tie1 cleavage with the metalloprotease inhibitor TAPI-2 suppressed VEGF- and phorbol ester-induced phosphorylation of Tie2. Truncated Tie1 formed in response to VEGF was also found to be tyrosine phosphorylated and this was independent of Tie2, though Tie2 could enhance Tie1 intracellular domain phosphorylation. Together these data demonstrate that VEGF activates Tie2 via a mechanism involving proteolytic cleavage of the associated tyrosine kinase Tie1 leading to trans-phosphorylation of Tie2. This novel mechanism of receptor tyrosine kinase activation is likely to be important in integrating signalling between two of the key receptor groups regulating angiogenesis.
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Affiliation(s)
- Harprit Singh
- University of Leicester, Department of Cardiovascular Sciences, RKCSB, PO Box 65, Leicester LE27LX, UK
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17
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Control of vascular morphogenesis and homeostasis through the angiopoietin-Tie system. Nat Rev Mol Cell Biol 2009; 10:165-77. [PMID: 19234476 DOI: 10.1038/nrm2639] [Citation(s) in RCA: 1005] [Impact Index Per Article: 67.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Angiogenesis, the growth of blood vessels, is a fundamental biological process that controls embryonic development and is also involved in numerous life-threatening human diseases. Much work in the field of angiogenesis research has centred on the vascular endothelial growth factor (VEGF)-VEGF receptor system. The Tie receptors and their angiopoietin (Ang) ligands have been identified as the second vascular tissue-specific receptor Tyr kinase system. Ang-Tie signalling is essential during embryonic vessel assembly and maturation, and functions as a key regulator of adult vascular homeostasis. The structural characteristics and the spatio-temporal regulation of the expression of receptors and ligands provide unique insights into the functions of this vascular signalling system.
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18
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Makinde T, Agrawal DK. Intra and extravascular transmembrane signalling of angiopoietin-1-Tie2 receptor in health and disease. J Cell Mol Med 2008; 12:810-28. [PMID: 18266978 PMCID: PMC4401129 DOI: 10.1111/j.1582-4934.2008.00254.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Angiopoietin-1 (Ang-1) is the primary agonist for Tie2 tyrosine kinase receptor (Tie2), and the effect of Ang-1-Tie2 signalling is context-dependent. Deficiency in either Ang-1 or Tie2 protein leads to severe microvascular defects and subsequent embryonic lethality in murine model. Tie2 receptors are expressed in several cell types, including endothelial cells, smooth muscle cells, fibroblasts, epithelial cells, monocytes, neutrophils, eosinophils and glial cells. Ang-1-Tie2 signalling induces a chemotactic effect in smooth muscle cells, neutrophils and eosinophils, and induces differentiation of mesenchymal cells to smooth muscle cells. Additionally, this signalling pathway induces the secretion of serotonin, matrix metalloproteinases (MMPs) and plasmin. Ang-1 inhibits the secretion of tissue inhibitor of matrix metalloproteinase (TIMPs). Aberrant expression and activity of Tie2 in vascular and non-vascular cells may result in the development of rheumatoid arthritis, cancer, hypertension and psoriasis. Ang-1 has an anti-inflammatory effect, when co-localized with vascular endothelial growth factor (VEGF) in the vasculature. Thus, Ang-1 could be potentially important in the therapy of various pathological conditions such as pulmonary hypertension, arteriosclerosis and diabetic retinopathy. In this article, we have summarized and critically reviewed the pathophysiological role of Ang-1-Tie2 signalling pathway.
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Affiliation(s)
- T Makinde
- Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, NE 68178, USA
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19
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Saharinen P, Eklund L, Alitalo K. Angiopoietins and Tie Receptors. Angiogenesis 2008. [DOI: 10.1007/978-0-387-71518-6_10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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20
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Findley CM, Cudmore MJ, Ahmed A, Kontos CD. VEGF induces Tie2 shedding via a phosphoinositide 3-kinase/Akt dependent pathway to modulate Tie2 signaling. Arterioscler Thromb Vasc Biol 2007; 27:2619-26. [PMID: 17901375 DOI: 10.1161/atvbaha.107.150482] [Citation(s) in RCA: 130] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE Tie2 and its ligands, the angiopoietins (Ang), are required for embryonic and postnatal angiogenesis. Previous studies have demonstrated that Tie2 is proteolytically cleaved, resulting in the production of a 75-kDa soluble receptor fragment (sTie2). We investigated mechanisms responsible for Tie2 shedding and its effects on Tie2 signaling and endothelial cellular responses. METHODS AND RESULTS sTie2 bound both Ang1 and Ang2 and inhibited angiopoietin-mediated Tie2 phosphorylation and antiapoptosis. In human umbilical vein endothelial cells, Tie2 shedding was both constitutive and induced by treatment with PMA or vascular endothelial growth factor (VEGF). Constitutive and VEGF-inducible Tie2 shedding were mediated by PI3K/Akt and p38 MAPK. Tie2 shedding was blocked by pharmacological inhibitors of either PI3K or Akt as well as by overexpression of the lipid phosphatase PTEN. In contrast, sTie2 shedding was enhanced by overexpression of either dominant negative PTEN, which increased Akt phosphorylation, or constitutively active, myristoylated Akt. CONCLUSIONS These findings demonstrate that VEGF regulates angiopoietin-Tie2 signaling by inducing proteolytic cleavage and shedding of Tie2 via a novel PI3K/Akt-dependent pathway. These results suggest a previously unrecognized mechanism by which VEGF may inhibit vascular stabilization to promote angiogenesis and vascular remodeling.
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Affiliation(s)
- Clarence M Findley
- Department of Pharmacology and Cancer Biology, Duke University Medical Center and the Duke University School of Medicine, Durham, NC, Durham, NC 27710, USA
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21
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Marron MB, Singh H, Tahir TA, Kavumkal J, Kim HZ, Koh GY, Brindle NPJ. Regulated proteolytic processing of Tie1 modulates ligand responsiveness of the receptor-tyrosine kinase Tie2. J Biol Chem 2007; 282:30509-17. [PMID: 17728252 PMCID: PMC2270410 DOI: 10.1074/jbc.m702535200] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Regulated ectodomain shedding followed by intramembrane proteolysis has recently been recognized as important in cell signaling and for degradation of several type I transmembrane proteins. The receptor-tyrosine kinase Tie1 is known to undergo ectodomain cleavage generating a membrane-tethered endodomain. Here we show Tie1 is a substrate for regulated intramembrane proteolysis. After Tie1 ectodomain cleavage the newly formed 45-kDa endodomain undergoes additional proteolytic processing mediated by gamma-secretase to generate an amino-terminal-truncated 42-kDa fragment that is subsequently degraded by proteasomal activity. This sequential processing occurs constitutively and is stimulated by phorbol ester and vascular endothelial growth factor. To assess the biological significance of regulated Tie1 processing, we analyzed its effects on angiopoietin signaling. Activation of ectodomain cleavage causes loss of phosphorylated Tie1 holoreceptor and generation of phosphorylated receptor fragments in the presence of cartilage oligomeric protein angiopoietin 1. A key function of gamma-secretase is in preventing accumulation of these phosphorylated fragments. We also find that regulated Tie1 processing modulates ligand responsiveness of the Tie-1-associated receptor Tie2. Activation of Tie1 ectodomain cleavage increases cartilage oligomeric protein angiopoietin 1 activation of Tie2. This correlates with increased ability of Tie2 to bind ligand after shedding of the Tie1 extracellular domain. A similar enhancement of ligand activation of Tie2 is seen when Tie1 expression is suppressed by RNA interference. Together these data indicate that Tie1, via its extracellular domain, limits the ability of ligand to bind and activate Tie2. Furthermore the data suggest that regulated processing of Tie1 may be an important mechanism for controlling signaling by Tie2.
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Affiliation(s)
| | | | | | | | - Hak-Zoo Kim
- Department of Cardiovascular Sciences, University of Leicester, RKCSB, PO Box 65, Leicester, LE2 7LX UK
| | - Gou Young Koh
- Department of Cardiovascular Sciences, University of Leicester, RKCSB, PO Box 65, Leicester, LE2 7LX UK
| | - Nicholas PJ Brindle
- Address correspondence to: Nicholas PJ Brindle, Dept Cardiovascular Sciences, University of Leicester, RKCSB, PO Box 65, Leicester, LE2 7LX UK, Tel: +44 116 252 5802, Fax: +44 116 252 3179,
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22
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Yuan HT, Venkatesha S, Chan B, Deutsch U, Mammoto T, Sukhatme VP, Woolf AS, Karumanchi SA. Activation of the orphan endothelial receptor Tie1 modifies Tie2-mediated intracellular signaling and cell survival. FASEB J 2007; 21:3171-83. [PMID: 17504972 DOI: 10.1096/fj.07-8487com] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
A critical role for Tie1, an orphan endothelial receptor, in blood vessel morphogenesis has emerged from mutant mouse studies. Moreover, it was recently demonstrated that certain angiopoietin (Ang) family members can activate Tie1. We report here that Ang1 induces Tie1 phosphorylation in endothelial cells. Tie1 phosphorylation was, however, Tie2 dependent because 1) Ang1 failed to induce Tie1 phosphorylation when Tie2 was down-regulated in endothelial cells; 2) Tie1 phosphorylation was induced in the absence of Ang1 by either a constitutively active form of Tie2 or a Tie2 agonistic antibody; 3) in HEK 293 cells Ang1 phosphorylated a form of Tie1 without kinase activity when coexpressed with Tie2, and Ang1 failed to phosphorylate Tie1 when coexpressed with kinase-defective Tie2. Ang1-mediated AKT and 42/44MAPK phosphorylation is predominantly Tie2 mediated, and Tie1 down-regulates this pathway. Finally, based on a battery of in vitro and in vivo data, we show that a main role for Tie1 is to modulate blood vessel morphogenesis by virtue of its ability to down-regulate Tie2-driven signaling and endothelial survival. Our new observations help to explain why Tie1 null embryos have increased capillary densities in several organ systems. The experiments also constitute a paradigm for how endothelial integrity is fine-tuned by the interplay between closely related receptors by a single growth factor.
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Affiliation(s)
- Hai Tao Yuan
- Division of Molecular and Vascular Medicine, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Ave., RW663, Boston, MA 02215, USA.
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23
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Singh AJ, Meyer RD, Band H, Rahimi N. The carboxyl terminus of VEGFR-2 is required for PKC-mediated down-regulation. Mol Biol Cell 2005; 16:2106-18. [PMID: 15673613 PMCID: PMC1073687 DOI: 10.1091/mbc.e04-08-0749] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Vascular endothelial growth factor receptor-2 (VEGFR-2/Flk-1) is a receptor tyrosine kinase (RTK) whose activation regulates angiogenesis. The regulatory mechanisms that attenuate VEGFR-2 signal relay are largely unknown. Our study shows that VEGFR-2 promotes phosphorylation of c-Cbl, but activation, ubiquitylation, and down-regulation of VEGFR-2 are not influenced by c-Cbl activity. A structure-function analysis of VEGFR-2 and pharmacological approach revealed that down-regulation of VEGFR-2 is mediated by a distinct mechanism involving PKC. A tyrosine mutant VEGFR-2, defective in PLC-gamma1 activation underwent down-regulation efficiently in response to ligand stimulation, suggesting that activation of classical PKCs are not involved in VEGFR-2 down-regulation. Further studies showed that the ectodomain of VEGFR-2 is dispensable for PKC-dependent down-regulation. Progressive deletion of the carboxyl-terminal domain showed that at least 39 amino acids within the carboxyl-terminal domain, immediately C-terminal to the kinase domain, is required for efficient PKC-mediated down-regulation of VEGFR-2. Mutation of serine sites at 1188 and 1191, within this 39 amino acid region, compromised the ability of VEGFR-2 to undergo efficient ligand-dependent down-regulation. Altogether the results show that the regulatory mechanisms involved in the attenuation of VEGFR-2 activation is mediated by nonclassical PKCs and the presence of serine sites in the carboxyl terminal of VEGFR-2.
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Affiliation(s)
- Amrik J Singh
- Department of Ophthalmology, Boston University School of Medicine, MA 02118, USA
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24
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Affiliation(s)
- Ian Zachary
- Department of Medicine, University College London, 5 University Street, London WC1E 6JJ, UK.
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25
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26
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Porat RM, Grunewald M, Globerman A, Itin A, Barshtein G, Alhonen L, Alitalo K, Keshet E. Specific Induction oftie1Promoter by Disturbed Flow in Atherosclerosis-Prone Vascular Niches and Flow-Obstructing Pathologies. Circ Res 2004; 94:394-401. [PMID: 14670840 DOI: 10.1161/01.res.0000111803.92923.d6] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Nonlaminar flow is a major predisposing factor to atherosclerosis. Yet little is known regarding hemodynamic gene regulation in disease-prone areas of the vascular tree in vivo. We have determined spatial patterns of expression of endothelial cell receptors in the arterial tree and of reporter gene constructs in transgenic animals. In this study we show that the endothelial cell-specific receptor Tie1 is induced by disturbed flow in atherogenic vascular niches. Specifically, tie1 expression in the adult is upregulated in vascular bifurcations and branching points along the arterial tree. It is often confined to a single ring of endothelial cells functioning as sphincters and hence experiencing the steepest gradient in shear stress. In aortic valves, tie1 is asymmetrically induced only in endothelial cells encountering changes in flow direction. Disturbance of laminar flow by a surgical interposition of a vein into an artery led to induction of tie1, specifically in the region where the differently sized vessels adjoin. In pathological settings, tie1 expression is specifically induced in areas of disturbed flow because of the emergence of aneurysms and, importantly, in endothelial cells precisely overlying atherosclerotic plaques. Hemodynamic features of atherosclerotic lesion-prone regions, recreated in vitro with the aid of a flow chamber with a built-in step, corroborated an upregulated tie1 promoter activity only in cells residing where flow separation and recirculation take place. These defined promoter elements might be harnessed for targeting gene expression to atherosclerotic lesions.
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MESH Headings
- Animals
- Animals, Genetically Modified
- Aortic Aneurysm, Abdominal/genetics
- Aortic Valve/metabolism
- Arteriosclerosis/genetics
- Arteriosclerosis/pathology
- Arteriosclerosis/physiopathology
- Endothelial Cells/metabolism
- Female
- Gene Expression Regulation
- In Situ Hybridization
- Lac Operon/genetics
- Luciferases/genetics
- Luciferases/metabolism
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Promoter Regions, Genetic/genetics
- Pulmonary Valve/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Rats
- Rats, Wistar
- Receptor, TIE-1/genetics
- Receptor, TIE-1/physiology
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Regional Blood Flow
- Retina/metabolism
- Rheology
- Stress, Mechanical
- Veins/physiopathology
- Veins/transplantation
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Affiliation(s)
- Rinnat M Porat
- Department of Molecular Biology, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
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27
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Madri JA. The evolving roles of cell surface proteases in health and disease: implications for developmental, adaptive, inflammatory, and neoplastic processes. Curr Top Dev Biol 2003; 54:391-410. [PMID: 12696757 DOI: 10.1016/s0070-2153(03)54016-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- Joseph A Madri
- Department of Pathology, Yale University School of Medicine, New Haven, Connecticut 06510, USA
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28
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Chen-Konak L, Guetta-Shubin Y, Yahav H, Shay-Salit A, Zilberman M, Binah O, Resnick N. Transcriptional and post-translation regulation of the Tie1 receptor by fluid shear stress changes in vascular endothelial cells. FASEB J 2003; 17:2121-3. [PMID: 14500555 DOI: 10.1096/fj.02-1151fje] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The interaction between the vascular endothelium and hemodynamic forces (and more specifically, fluid shear stress), induced by the flow of blood, plays a major role in vascular remodeling and in new blood vessels formation via a process termed arteriogenesis. Tie1 is an orphan tyrosine kinase receptor expressed almost exclusively in endothelial cells and is required for normal vascular development and maintenance. The present study demonstrates that Tie1 expression is rapidly down-regulated in endothelial cells exposed to shear stress, and more so to shear stress changes. This down-regulation is accompanied by a rapid cleavage of Tie1 and binding of the cleaved Tie1 45 kDa endodomain to Tie2. The rapid cleavage of Tie1 is followed by a transcriptional down-regulation in response to shear stress. The activity of the Tie1 promoter is suppressed by shear stress and by tumor necrosis factor alpha. Shear stress-induced transcriptional suppression of Tie1 is mediated by a negative shear stress response element, localized in a region of 250 bp within the promoter. The rapid down-regulation of Tie1 by shear stress changes and its rapid binding to Tie2 may be required for destabilization of endothelial cells in order to initiate the process of vascular restructuring.
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MESH Headings
- Animals
- Antigens, CD
- Arteries/cytology
- Cadherins/metabolism
- Cattle
- Cells, Cultured
- Endothelium, Vascular/enzymology
- Gene Expression Regulation
- Models, Biological
- Protein Processing, Post-Translational
- Receptor, TIE-1/genetics
- Receptor, TIE-1/metabolism
- Receptor, TIE-2/metabolism
- Response Elements
- Stress, Mechanical
- Transcription, Genetic
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Affiliation(s)
- Limor Chen-Konak
- The Interdepartmental Program in Biotechnology, The Rappaport Family Institute for Research in the Medical Sciences and the Bruce Rappaport Faculty of Medicine, Technion, Haifa, Israel
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29
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Abstract
Tyrosine kinases are key regulators of breast cancer cell survival and proliferation. Ten years ago, we conducted a screen for protein kinases expressed in primary human breast tumors and cultured cancer cells. Here, we review the progress from the last ten years in understanding the functions of these kinases with a focus on breast cancer. Three themes emerge: (1). tyrosine kinases regulate proliferation through the MAP Kinase pathway, (2). tyrosine kinases regulate cellular survival through the PI3 Kinase-Akt pathway, and (3). the cell cycle is regulated through a complex series of serine-threonine kinases. Our improved understanding of these signaling cascades has led to novel strategies for therapeutic intervention in breast cancer.
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Affiliation(s)
- Rolf J Craven
- Department of Surgery, University of North Carolina at Chapel Hill, 21-237 Lineberger, Comprehensive Cancer Centre, Camous Box 7295, Chapel Hill, NC 27599, USA.
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30
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Iljin K, Petrova TV, Veikkola T, Kumar V, Poutanen M, Alitalo K. A fluorescent Tie1 reporter allows monitoring of vascular development and endothelial cell isolation from transgenic mouse embryos. FASEB J 2002; 16:1764-74. [PMID: 12409319 DOI: 10.1096/fj.01-1043com] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Tie1 is an endothelial receptor tyrosine kinase essential for development and maintenance of the vascular system. Here we report generation of transgenic mice expressing enhanced green fluorescent protein (EGFP) or a chimeric protein consisting of a Zeosin resistance marker and EGFP under the control of mouse Tie1 promoter. Intravital monitoring of fluorescence showed that the EGFP reporter recapitulates the Tie1 expression pattern in the developing vasculature, and flow cytometry using EGFP allowed the isolation of essentially pure Tie1-expressing endothelial cells from transgenic mouse embryos. However, EGFP and LacZ transgenic markers were strongly down-regulated in the adult vasculature; unlike the Tie1-LacZ knock-in locus, the promoter was not reactivated during tumor neovascularization, indicating the presence of additional regulatory elements in the Tie1 locus. Starting at midgestation, Tie1 promoter activity became stronger in the arterial than in the venous endothelium; in adult mice, promoter activity was observed in arterioles, capillaries, and lymphatic vessels, indicating a significant degree of specificity in different types of endothelial cells. Our results establish Tie1-Z/EGFP transgenic mice as a useful model to study embryonic vascular development and a convenient source for the isolation of primary endothelial cells.
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MESH Headings
- Animals
- Blood Vessels/embryology
- Blood Vessels/metabolism
- Cell Line
- Embryo, Mammalian/blood supply
- Embryo, Mammalian/cytology
- Embryo, Mammalian/metabolism
- Endothelium, Vascular/cytology
- Endothelium, Vascular/metabolism
- Female
- Green Fluorescent Proteins
- Humans
- Luminescent Proteins/genetics
- Luminescent Proteins/metabolism
- Male
- Mice
- Mice, Inbred Strains
- Mice, Transgenic
- Neoplasms, Experimental/blood supply
- Neoplasms, Experimental/genetics
- Neoplasms, Experimental/metabolism
- Neovascularization, Pathologic/genetics
- Neovascularization, Pathologic/metabolism
- Promoter Regions, Genetic/genetics
- Receptor Protein-Tyrosine Kinases/genetics
- Receptor Protein-Tyrosine Kinases/metabolism
- Receptor, TIE-1
- Receptors, Cell Surface/genetics
- Receptors, Cell Surface/metabolism
- Receptors, TIE
- Skin/metabolism
- Time Factors
- Transfection
- Tumor Cells, Cultured
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Affiliation(s)
- Kristina Iljin
- Molecular/Cancer Biology Laboratory, Haartman Institute and Helsinki University Central Hospital and Ludwig Institute for Cancer Research, Biomedicum Helsinki, 00014 Helsinki, Finland
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31
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Tsiamis AC, Morris PN, Marron MB, Brindle NPJ. Vascular endothelial growth factor modulates the Tie-2:Tie-1 receptor complex. Microvasc Res 2002; 63:149-58. [PMID: 11866538 DOI: 10.1006/mvre.2001.2377] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The receptor tyrosine kinase Tie-1 is expressed predominantly in endothelial cells where it physically associates with the related receptor Tie-2. Positive signalling through Tie-2 is associated with microvessel stability and suppression of this signal is thought to be required for vascular endothelial growth factor (VEGF)-induced microvessel remodelling or growth. Here we examine the effects of VEGF on Tie-1 and the Tie-2:Tie-1 complex. We show that VEGF induces generation of the Tie-1 endodomain and loss of the full-length receptor. The effects of VEGF on endodomain formation are not suppressed by inhibitors of protein kinase C and do not involve the nitric oxide signalling pathway. Tyrosine kinase inhibitors, in contrast, do abolish endodomain generation in response to the endothelial growth factor. VEGF stimulation of cells does not cause dissociation of the Tie-2:Tie-1 complex; rather the complex is converted to a form comprising the full-length-Tie-2 and Tie-1 endodomain. VEGF can therefore switch the Tie-2:Tie-1 complex between two different forms in endothelial cells. The ability of VEGF to modulate Tie-1 and the Tie-2:Tie-1 complex provides a mechanism whereby this initiator of vessel growth and remodelling can directly modulate receptors involved in vessel stabilization. Such cross-talk is likely to be important in the coordinate control of blood vessel formation during development and in postnatal angiogenesis.
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Affiliation(s)
- Achilleas C Tsiamis
- Department of Surgery, University of Leicester, RKCSB, Leicester, LE2 7LX, United Kingdom
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Kontos CD, Cha EH, York JD, Peters KG. The endothelial receptor tyrosine kinase Tie1 activates phosphatidylinositol 3-kinase and Akt to inhibit apoptosis. Mol Cell Biol 2002; 22:1704-13. [PMID: 11865050 PMCID: PMC135589 DOI: 10.1128/mcb.22.6.1704-1713.2002] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Tie1 is an orphan receptor tyrosine kinase that is expressed almost exclusively in endothelial cells and that is required for normal embryonic vascular development. Genetic studies suggest that Tie1 promotes endothelial cell survival, but other studies have suggested that the Tie1 kinase has little to no activity, and Tie1-mediated signaling pathways are unknown. To begin to study Tie1 signaling, a recombinant glutathione S-transferase (GST)-Tie1 kinase fusion protein was produced in insect cells and found to be autophosphorylated in vitro. GST-Tie1 but not a kinase-inactive mutant associated with a recombinant p85 SH2 domain protein in vitro, suggesting that Tie1 might signal through phosphatidylinositol (PI) 3-kinase. To study Tie1 signaling in a cellular context, a c-fms-Tie1 chimeric receptor (fTie1) was expressed in NIH 3T3 cells. Ligand stimulation of fTie1 resulted in Tie1 autophosphorylation and downstream activation of PI 3-kinase and Akt. Stimulation of fTie1-expressing cells potently inhibited UV irradiation-induced apoptosis in a PI 3-kinase-dependent manner. Moreover, both Akt phosphorylation and inhibition of apoptosis were abrogated by mutation of tyrosine 1113 to phenylalanine, suggesting that this residue is an important PI 3-kinase binding site. These findings are the first biochemical demonstration of a signal transduction pathway and corresponding cellular function for Tie1, and the antiapoptotic effect of Tie1 is consistent with the results of previous genetic studies.
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Affiliation(s)
- Christopher D Kontos
- Department of Medicine, Division of Cardiology, Duke University Medical Center, Durham, NC 27710, USA.
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Jones N, Iljin K, Dumont DJ, Alitalo K. Tie receptors: new modulators of angiogenic and lymphangiogenic responses. Nat Rev Mol Cell Biol 2001; 2:257-67. [PMID: 11283723 DOI: 10.1038/35067005] [Citation(s) in RCA: 276] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Angiogenesis is required for normal embryonic vascular development and aberrant angiogenesis contributes to several diseases, including cancer, diabetes and tissue ischaemia. What are the molecular mechanisms that regulate this important process? The Tie family of receptors and their ligands, the angiopoietins, are beginning to provide insight into how vessels make decisions such as whether to grow or regress--processes that are important not only during development but throughout an organism's life.
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Affiliation(s)
- N Jones
- Department of Medical Biophysics, University of Toronto, Sunnybrook and Women's College Health Sciences Centre, 2075 Bayview Avenue, S-227, Toronto, Ontario, Canada M4N 3M5
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Marron MB, Hughes DP, McCarthy MJ, Beaumont ER, Brindle NP. Tie-1 receptor tyrosine kinase endodomain interaction with SHP2: potential signalling mechanisms and roles in angiogenesis. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2001; 476:35-46. [PMID: 10949653 DOI: 10.1007/978-1-4615-4221-6_3] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The endothelial receptor tyrosine kinase plays an essential role in vascular development where it is thought to be required for vessel maturation and stabilization. The ligands responsible for activating Tie-1, its signalling pathways and specific cellular functions are however not known. As with some other receptor tyrosine kinases, Tie-1 is subject to extracellular proteolytic cleavage generating a membrane bound receptor fragment comprising the intracellular and transmembrane domains. Here we examine the signalling potential of this Tie-1 endodomain. We show that the Tie-1 endodomain has poor ability to induce tyrosine phosphorylation. However, on formation the endodomain physically associates with a number of tyrosine phosphorylated signalling intermediates including the tyrosine phosphatase and adaptor protein SHP2. The assembly of this multimolecular complex is consistent with the endodomain having a ligand-independent signalling role in the endothelial cell. The potential roles of ectodomain cleavage and cleavage activated signalling in regulating microvessel stability in angiogenesis, vessel remodelling and regression are considered.
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Affiliation(s)
- M B Marron
- University of Leicester Cardiovascular Research Institute, UK
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Marron MB, Hughes DP, Edge MD, Forder CL, Brindle NP. Evidence for heterotypic interaction between the receptor tyrosine kinases TIE-1 and TIE-2. J Biol Chem 2000; 275:39741-6. [PMID: 10995770 DOI: 10.1074/jbc.m007189200] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The orphan receptor tyrosine kinase Tie-1 is expressed in endothelial cells and is essential for vascular development. Nothing is known about the signaling pathways utilized by this receptor. In this study we have used chimeric receptors composed of the TrkA ectodomain fused to the transmembrane and intracellular domains of Tie-1, or the related receptor Tie-2, to examine Tie-1 signaling capacity. In contrast to TrkA/Tie-2, the Tie-1 chimera was unable to phosphorylate cellular proteins or undergo autophosphorylation. Consistent with this Tie-1 exhibited negligible kinase activity. Co-immunoprecipitation analysis revealed Tie-1 was present in endothelial cells bound to Tie-2. Full-length Tie-1 and truncated receptor, formed by regulated endoproteolytic cleavage, were found to complex with Tie-2. Association was mediated by the intracellular domains of the receptors and did not require Tie-1 to be membrane-localized. Tie-1 bound to Tie-2 was not tyrosine-phosphorylated under basal conditions or following Tie-2 stimulation. This study provides the first evidence for the existence of a pre-formed complex of Tie-1 and Tie-2 in endothelial cells. The data suggest Tie-1 does not signal via ligand-induced kinase activation involving homo-oligomerization. The physical association between Tie-1 and Tie-2 is consistent with Tie-1 having a role in modulating Tie-2 signaling.
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Affiliation(s)
- M B Marron
- Department of Surgery, University of Leicester, RKCSB, P. O. Box 65, Leicester LE2 7LX, United Kingdom
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Abstract
Heregulin was shown to promote the proteolytic cleavage of its receptor, ErbB-4, in several cell lines. The growth factor also rapidly promoted the transient translocation of ErbB-4 to a detergent-insoluble fraction, in which the receptor was hyper-tyrosine-phosphorylated compared with the receptor present in the detergent-soluble pool. However, an 80-kDa proteolytic fragment of ErbB-4 was found in the detergent-soluble fraction, but not in the detergent-insoluble fraction. Although the heregulin-induced cleavage of ErbB-4 produced a fragment of ErbB-4 very similar to that induced by 12-O-tetradecanoylphorbol-13-acetate or pervanadate (each of which is blocked by metalloprotease inhibitors), the growth factor-induced cleavage was not sensitive to these inhibitors under the same conditions. The heregulin-induced cleavage of ErbB-4 could be blocked by conditions that prevent clathrin-coated pit formation, suggesting that heregulin-mediated ErbB-4 cleavage occurs subsequent to internalization. When reagents that prevent acidification of endosomes were employed, heregulin-induced ErbB-4 cleavage was sensitive to metalloprotease inhibitors. The results imply that during ligand-dependent receptor trafficking, activated ErbB-4 receptors are subject to proteolytic cleavage involving an intracellular metalloprotease.
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Affiliation(s)
- W Zhou
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, USA
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Fujikawa K, de Aos Scherpenseel I, Jain SK, Presman E, Christensen RA, Varticovski L. Role of PI 3-kinase in angiopoietin-1-mediated migration and attachment-dependent survival of endothelial cells. Exp Cell Res 1999; 253:663-72. [PMID: 10585289 DOI: 10.1006/excr.1999.4693] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Angiopoietin-1 is a unique growth factor which induces Tie2 receptor autophosphorylation and interaction with signal transduction molecules, GRB2 and p85 subunit of PI 3-kinase, but no detectable mitogenic response. Here we show that PI 3-kinase-dependent activation of Akt and attachment to extracellular matrix are required for angiopoietin-1-mediated endothelial cell survival. Apoptosis of growth factor-deprived cells grown in monolayer was decreased by angiopoietin-1 and correlated with Akt activation. In contrast, angiopoietin-1, bFGF or VEGF failed to protect cells in suspension culture. Ceramide, an intermediate of several apoptotic pathways, interferes with growth factor-mediated Akt activation. Ceramide induced endothelial cell death and abolished angiopoietin-1-mediated activation of Akt and the effect on cell survival. In addition, we found that PI 3-kinase activity is necessary for migration of endothelial cells in response to Angiopoietin-1. A transient activation of MAPK/ERKs was also detected within 10 min after stimulation with angiopoietin-1. In contrast to VEGF-mediated biological effects, inhibition of MAPK/ERKs by PD98059 in endothelial cells did not affect angiopoietin-1 mediated survival or migration. These findings indicate significant differences in intracellular signaling between VEGF and angiopoietin-1 and that PI 3-kinase lipid products are key mediators of the biological effects of angiopoietin-1.
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Affiliation(s)
- K Fujikawa
- Department of Medicine, St. Elizabeth's Medical Center, Tufts University School of Medicine, 736 Cambridge Street, Boston, Massachusetts 02135, USA
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Abstract
As our understanding of the control of vasculogenesis and angiogenesis continues to grow, we will be confronted with an increasing number of interacting and intersecting receptor-mediated signaling pathways. If we are to be successful in developing new and novel effective therapeutic reagents that can function as stimulators or inhibitors of these critically important processes, we will have to develop a sophisticated, full understanding of the complex interactions associated with ephrin-based and metalloprotease-based signaling pathways.
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Affiliation(s)
- N Ilan
- Department of Pathology, Yale University School of Medicine, New Haven, CT 06510, USA
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Inflammatory Cytokines and Vascular Endothelial Growth Factor Stimulate the Release of Soluble Tie Receptor From Human Endothelial Cells Via Metalloprotease Activation. Blood 1999. [DOI: 10.1182/blood.v93.6.1969.406k14_1969_1979] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Activation of endothelial cells, important in processes such as angiogenesis, is regulated by cell surface receptors, including those in the tyrosine kinase (RTK) family. Receptor activity, in turn, can be modulated by phosphorylation, turnover, or proteolytic release of a soluble extracellular domain. Previously, we demonstrated that release of soluble tie-1 receptor from endothelial cells by phorbol myristate acetate (PMA) is mediated through protein kinase C and a Ca2+-dependent protease. In this study, the release of soluble tie-1 was shown to be stimulated by inflammatory cytokines and vascular endothelial growth factor (VEGF), but not by growth factors such as basic fibroblast growth factor (bFGF) or transforming growth factor (TGF). Release of soluble tie by tumor necrosis factor (TNF) or VEGF occurred within 10 minutes of stimulation and reached maximal levels within 60 minutes. Specificity was shown by fluorescence-activated cell sorting (FACS) analysis; endothelial cells exhibited a significant decrease in cell surface tie-1 expression in response to TNF, whereas expression of epidermal growth factor receptor (EGF-R) and CD31 was stable. In contrast, tie-1 expression on megakaryoblastic UT-7 cells was unaffected by PMA or TNF. Sequence analysis of the cleaved receptor indicated that tie-1 was proteolyzed at the E749/S750 peptide bond in the proximal transmembrane domain. Moreover, the hydroxamic acid derivative BB-24 demonstrated dose-dependent inhibition of cytokine-, PMA-, and VEGF-stimulated shedding, suggesting that the tie-1 protease was a metalloprotease. Protease activity in a tie-1 peptide cleavage assay was (1) associated with endothelial cell membranes, (2) specifically activated in TNF-treated cells, and (3) inhibited by BB-24. Additionally, proliferation of endothelial cells in response to VEGF, but not bFGF, was inhibited by BB-24, suggesting that the release of soluble tie-1 receptor plays a role in VEGF-mediated proliferation. This study demonstrated that the release of soluble tie-1 from endothelial cells is stimulated by inflammatory cytokines and VEGF through the activation of an endothelial membrane-associated metalloprotease.
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