Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 114, Issue 17, Pages 4376-4381Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1616166114
Keywords
tyrosine kinase; angiopoietin; dimerization; homotypic interactions; crystallography
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Funding
- Jenny and Antti Wihuri Foundation
- Academy of Finland [307366, 292816, 273817]
- Sigrid Juselius Foundation
- Cancer Society of Finland
- Leducq Foundation [11CVD03]
- Helsinki University Hospital's Government Special State Subsidy for Health Sciences
- Novo Nordisk Foundation
- Jane and Aatos Erkko Foundation
- Academy of Finland (AKA) [292816, 307366, 307366, 292816] Funding Source: Academy of Finland (AKA)
- Cancer Foundation Finland sr [170102, 150065] Funding Source: researchfish
- Novo Nordisk Fonden [NNF16OC0023554] Funding Source: researchfish
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The endothelial cell (EC)-specific receptor tyrosine kinases Tie1 and Tie2 are necessary for the remodeling and maturation of blood and lymphatic vessels. Angiopoietin-1 (Ang1) growth factor is a Tie2 agonist, whereas Ang2 functions as a context-dependent agonist/antagonist. The orphan receptor Tie1 modulates Tie2 activation, which is induced by association of angiopoietins with Tie2 in cis and across EC-EC junctions in trans. Except for the binding of the C-terminal angiopoietin domains to the Tie2 ligand-binding domain, the mechanisms for Tie2 activation are poorly understood. We report here the structural basis of Ang1-induced Tie2 dimerization in cis and provide mechanistic insights on Ang2 antagonism, Tie1/Tie2 heterodimerization, and Tie2 clustering. We find that Ang1-induced Tie2 dimerization and activation occurs via the formation of an intermolecular beta-sheet between the membrane-proximal (third) Fibronectin type III domains (Fn3) of Tie2. The structures of Tie2 and Tie1 Fn3 domains are similar and compatible with Tie2/Tie1 heterodimerization by the same mechanism. Mutagenesis of the key interaction residues of Tie2 and Tie1 Fn3 domains decreased Ang1-induced Tie2 phosphorylation and increased the basal phosphorylation of Tie1, respectively. Furthermore, the Tie2 structures revealed additional interactions between the Fn 2 (Fn2) domains that coincide with a mutation of Tie2 in primary congenital glaucoma that leads to defective Tie2 clustering and junctional localization. Mutagenesis of the Fn2-Fn2 interface increased the basal phosphorylation of Tie2, suggesting that the Fn2 interactions are essential in preformed Tie2 oligomerization. The interactions of the membrane-proximal domains could provide new targets for modulation of Tie receptor activity.
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