title: Ligand-independent Tie2 dimers mediate kinase activity stimulated by high dose angiopoietin-1.
abstract: Tie2 is a receptor tyrosine kinase expressed on vascular endothelial cells (ECs). It has dual roles in promoting angiogenesis and stabilizing blood vessels, and it has been suggested that Tie2 forms dimers and/or oligomers in the absence of angiopoietin-1 (Ang1); however, the mechanism of ligand-independent dimerization of Tie2 and its biological significance have not been clarified. Using a bimolecular fluorescence complementation assay and a kinase-inactive Tie2 mutant, we show here that ligand-independent Tie2 dimerization is induced without Tie2 phosphorylation. Moreover, based on the fact that Tie1 never forms heterodimers with Tie2 in the absence of Ang1 despite having high amino acid sequence homology with Tie2, we searched for ligand-independent dimerization domains of Tie2 by reference to the difference with Tie1. We found that the YIA sequence of the intracellular domain of Tie2 corresponding to the LAS sequence in Tie1 is essential for this dimerization. When the YIA sequence was replaced by LAS in Tie2 (Tie2YIA/LAS), ligand-independent dimer was not formed in the absence of Ang1. When activation of Tie2YIA/LAS was induced by a high dose of Ang1, phosphorylation of Tie2 was limited compared with wild-type Tie2, resulting in retardation of activation of Erk downstream of Tie2. Therefore, these data suggest that ligand-independent dimerization of Tie2 is essential for a strong response upon stimulation with high dose Ang1.
authors.affiliation: Department of Signal Transduction, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamada-oka, Suita-shi, Osaka 565-0871, Japan.
authors.forename: Daishi
authors.initials: D
authors.lastname: Yamakawa
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Kidoya
authors.forename: Susumu
authors.initials: S
authors.lastname: Sakimoto
authors.forename: Weizhen
authors.initials: W
authors.lastname: Jia
authors.forename: Hisamichi
authors.initials: H
authors.lastname: Naito
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Takakura
mesh_terms: D020816:Amino Acid Motifs; D042683:Angiopoietin-1 / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects / Q000235:genetics; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D041681:NIH 3T3 Cells; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D055503:Protein Multimerization / Q000187:drug effects*; D017434:Protein Structure, Tertiary; D042810:Receptor, TIE-1 / Q000235:genetics / Q000378:metabolism; D042787:Receptor, TIE-2 / Q000235:genetics / Q000378:metabolism*
chemical_list: C467630:ANGPT1 protein, human; D042683:Angiopoietin-1; C467628:Angpt1 protein, mouse; D042810:Receptor, TIE-1; D042787:Receptor, TIE-2; D048049:Extracellular Signal-Regulated MAP Kinases
keywords: Angiogenesis; Angiopoietin; Endothelial Cell; Imaging; Tyrosine Protein Kinase (Tyrosine Kinase); Vascular Biology