{"gene":"TEK","run_date":"2026-06-10T10:51:54","timeline":{"discoveries":[{"year":1995,"finding":"The autophosphorylated TEK/TIE2 kinase domain associates with GRB2 and SH-PTP2 (PTPN11) from endothelial cell lysates in a manner highly dependent on specific tyrosine residues in the TEK C-tail; PI3-kinase and PLCγ were NOT detected as binding partners in this assay.","method":"Radiolabeled soluble TEK kinase domain used to probe mouse embryo expression library and pull down from endothelial lysates; site-directed mutagenesis of C-tail tyrosines","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro kinase domain pulldown with mutagenesis, single lab, two orthogonal methods (library screen + endothelial lysate pulldown)","pmids":["7478529"],"is_preprint":false},{"year":1997,"finding":"Tie2 protein is tyrosine-phosphorylated (actively signaling) in endothelial cells of both angiogenic tissues (healing wounds, ovary, uterus) and quiescent adult vasculature, indicating dual roles in angiogenesis and vascular maintenance.","method":"Immunoprecipitation of Tie2 from rat/mouse tissues followed by anti-phosphotyrosine blotting; RNase protection assay for mRNA; immunohistochemistry","journal":"Circulation research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal IP/phospho-blot in multiple tissue types, single lab with multiple orthogonal methods (IP, RPA, IHC)","pmids":["9314838"],"is_preprint":false},{"year":1998,"finding":"TEK/Tie2 signals through a novel docking protein Dok-R (now DOKR/DOK4): activated TEK phosphorylates Dok-R via a PTB domain interaction; phosphorylated Dok-R co-immunoprecipitates rasGAP and Nck, and Dok-R is constitutively bound to Crk through its proline-rich tail.","method":"Yeast two-hybrid screen with activated Tek; co-immunoprecipitation; co-expression in cells; domain-mapping","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid plus co-IP validation, single lab, multiple orthogonal methods","pmids":["9764820"],"is_preprint":false},{"year":1998,"finding":"The murine Tie2/Tek proximal promoter drives endothelial cell-specific transcription through two positive regulatory elements (U and A) and one inhibitory region (I); element U functions in an endothelial-cell-selective manner and binds distinct protein factors.","method":"Reporter transfection experiments in endothelial vs. non-endothelial cells; electrophoretic mobility-shift assays (EMSA); deletion mutagenesis","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional reporter assays with EMSA, single lab, two orthogonal methods","pmids":["9461528"],"is_preprint":false},{"year":1999,"finding":"Angiopoietin-1 stimulation of TEK recruits five SH2-domain proteins (Grb2, Grb7, Grb14, Shp2, and p85 of PI3K) to a multifunctional docking site at Tyr1100 in the Tek C-tail; mutation of Tyr1100 abolishes Grb2/Grb7 binding and p85/Grb7 phosphorylation in vivo; Ang1-induced Tek signaling activates both cell survival (PI3K-dependent) and migration pathways.","method":"Yeast two-hybrid; in vivo co-immunoprecipitation; site-directed mutagenesis of Tyr1100; cell migration and survival assays with PI3K inhibitors","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — yeast two-hybrid validated by in vivo co-IP plus mutagenesis plus functional assays, multiple orthogonal methods in single rigorous study","pmids":["10521483"],"is_preprint":false},{"year":1999,"finding":"Genetic ablation of both TEK and TIE in mice demonstrates that TEK is absolutely required cell-autonomously for endocardial integrity at E10.5, whereas TEK and TIE are dispensable for initial vasculogenesis but redundantly required for microvasculature maintenance during late organogenesis and in the adult.","method":"Double-knockout mouse genetics; mosaic analysis in chimeric embryos","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis via double-KO and mosaic analysis, replicated developmental phenotypes, rigorous in vivo approach","pmids":["10498691"],"is_preprint":false},{"year":2003,"finding":"Tyr1106 on Tie2 is an Ang1-dependent autophosphorylation site that mediates binding and phosphorylation of Dok-R via its PTB domain; the Dok-R PH domain further contributes to Tie2 binding in a PI3K-dependent manner; Tie2 mutant lacking Tyr1106 fails to restore endothelial cell migration in Tie2-null cells, establishing Tyr1106 as critical for coupling cell migration signaling to Ang1.","method":"Site-directed mutagenesis; phosphorylation state-specific antibody; co-immunoprecipitation; migration rescue assay in Tie2-null endothelial cells","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — mutagenesis + phospho-specific antibody + functional rescue in null cells; multiple rigorous orthogonal methods","pmids":["12665569"],"is_preprint":false},{"year":2005,"finding":"Angiopoietin-2 acts as a rapidly acting autocrine destabilizer of quiescent endothelium via Tie2; exogenous Ang1, soluble Tie2, and VEGF rescue Ang2-induced endothelial detachment, but soluble Tie2 cannot block autocrine (endogenous) Ang2-mediated detachment, demonstrating an internal autocrine loop mechanism distinct from paracrine Ang2 signaling.","method":"3D endothelial/smooth-muscle co-culture spheroid model; umbilical-vein explant model; Tie2 small-molecule inhibitor; soluble Tie2 blocking; overexpression and stimulated release of Ang2","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — two independent model systems with multiple pharmacologic and genetic interventions, single lab but rigorously controlled","pmids":["15687104"],"is_preprint":false},{"year":2005,"finding":"Ang1 oligomerization state is critical for Tie2 binding and activation: at least tetrameric (≥4 subunit) multimers mediated by intermolecular disulfide bonds involving Cys41 and Cys54 are required; dimeric and monomeric Ang1 variants lose binding and activation capacity for Tie2.","method":"Generation of Ang1/Ang2 variants; SDS-PAGE; rotary metal-shadowing transmission electron microscopy; Tie2 phosphorylation assays; binding assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution with defined mutant ligands, structural visualization by EM, and functional binding/phosphorylation assays; multiple orthogonal methods","pmids":["15769741"],"is_preprint":false},{"year":2006,"finding":"Crystal structures of the Tie2 receptor ectodomain (alone and in complex with Ang2) reveal that Tie2 contains three (not two) Ig domains folded with three EGF domains into an arrowhead shape; Ang2 binds at the tip via a lock-and-key mechanism with minimal conformational change in either molecule, similar to antibody-antigen recognition; structure-based mutagenesis validated the binding interface.","method":"X-ray crystallography; structure-based mutagenesis","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure at atomic resolution validated by mutagenesis; definitive structural determination","pmids":["16732286"],"is_preprint":false},{"year":2006,"finding":"Activation of Tie2 by either Ang1 or Ang2 leads to ligand release from the endothelial cell surface and receptor internalization/degradation; Ang2 is a considerably weaker Tie2 activator than Ang1 and behaves as a partial agonist; Ang1-induced internalization is faster and more pronounced than Ang2-induced internalization.","method":"Concentration-response phosphorylation assays; receptor internalization assays; ligand binding and accumulation assays in endothelial cells","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple cellular assays (phosphorylation, internalization, ligand release), single lab","pmids":["16895971"],"is_preprint":false},{"year":2008,"finding":"Ang1 bridges Tie2 molecules at cell-cell contacts to form trans-Tie2 complexes, preferentially activating Akt; in isolated cells, ECM-bound Ang1 anchors Tie2 at cell-substratum contacts, preferentially activating Erk; these spatially distinct Tie2 complexes produce differential downstream gene expression profiles linked to vascular quiescence vs. angiogenesis respectively.","method":"Fluorescence microscopy of Tie2 localization; Akt and Erk phosphorylation assays; microarray gene expression with real-time PCR validation; endothelial cell-cell contact manipulation","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (localization, signaling, transcriptomics) with rigorous spatial manipulation; replicated by Alitalo group (cited in same corpus)","pmids":["18425120"],"is_preprint":false},{"year":2008,"finding":"Somatic TEK mutations (including the frequent L914F substitution and several double mutations in cis) cause ligand-independent TIE2 hyperphosphorylation in vitro; the L914F mutant shows abnormal subcellular localization and retains ligand responsiveness, in contrast to the inherited R849W mutant, indicating mechanistically distinct pathogenic pathways for inherited vs. sporadic venous malformations.","method":"Sequencing of lesion vs. blood DNA; in vitro TIE2 phosphorylation assays; overexpression of mutant TIE2 in HUVECs with immunofluorescence localization","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro kinase assays with multiple defined mutants plus cellular localization studies, replicated across multiple patient samples","pmids":["19079259"],"is_preprint":false},{"year":2008,"finding":"Pericytes express a functionally active Tie2 receptor; Ang1 promotes pericyte survival and migration via Tie2, and Ang2 increases pericyte apoptosis; Tie2 antisense confirmed angiopoietin effects are Tie2-dependent in pericytes.","method":"ELISA, Western blot, flow cytometry for Tie2 on pericytes; apoptosis assays (Annexin V); migration assay; Tie2 antisense knockdown","journal":"Investigative ophthalmology & visual science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple methods with antisense knockdown confirmation, single lab","pmids":["18436850"],"is_preprint":false},{"year":2012,"finding":"ANG-2 binds integrins (not Tie2) on TIE2-low angiogenic endothelial cells, inducing FAK phosphorylation (integrin adaptor), RAC1 activation, migration, and sprouting angiogenesis in a TIE2-independent manner; in vivo ANG-2 blockade inhibits FAK phosphorylation in TIE2-low ECs.","method":"Identification of TIE2-low subpopulation in tumor vasculature; co-IP/binding assays of ANG-2 with integrins; phosphorylation assays for FAK; RAC1 activity assay; in vivo ANG-2 neutralization","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal binding assays, phosphorylation, Rac1 GEF assay, and in vivo validation; multiple orthogonal methods in single study","pmids":["22585576"],"is_preprint":false},{"year":2014,"finding":"VE-PTP (PTPRB) negatively regulates TIE2 by dephosphorylation; inhibition of VE-PTP catalytic activity with AKB-9778 activates TIE2, enhances Ang1-induced TIE2 activation, and stimulates phosphorylation of AKT, eNOS, and ERK in the TIE2 pathway; this is effective even in the presence of high ANG2.","method":"Anti-VE-PTP antibody and small-molecule VE-PTP inhibitor (AKB-9778); TIE2 and downstream signaling phosphorylation assays; mouse models of ocular NV and vascular leakage","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — pharmacological and antibody-based inhibition with multiple downstream signaling readouts and in vivo confirmation; multiple orthogonal methods","pmids":["25180601"],"is_preprint":false},{"year":2015,"finding":"Analysis of 22 TIE2 patient mutations reveals that VM-causing mutations cause defective receptor trafficking and subcellular localization by multiple distinct mechanisms, leading to attenuated ligand response; TIE2 mutations cause chronic MAPK pathway activation, loss of endothelial monolayer integrity due to fibronectin ECM deficiency, and upregulation of the plasminogen/plasmin proteolytic pathway.","method":"Endothelial cell cultures with 22 TIE2 mutants; mouse models; ultrastructural analysis of patient biopsies; Western blotting for MAPK; ECM fibronectin quantification","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — comprehensive panel of 22 mutations with multiple orthogonal cellular and in vivo methods, validated in patient tissue","pmids":["26319232"],"is_preprint":false},{"year":2016,"finding":"TEK mutations in primary congenital glaucoma (PCG) cause haploinsufficiency through multiple protein loss-of-function mechanisms including absence of protein production, aggregate formation, enhanced proteasomal degradation, altered subcellular localization, and reduced ligand responsiveness; hemizygosity for Tek in mice leads to hypomorphic Schlemm's canal and elevated intraocular pressure, demonstrating dose-sensitivity of angiopoietin-TEK signaling in anterior chamber vascular development.","method":"Cellular assays in transfected cells for each TEK variant; immunofluorescence for localization; proteasome inhibition assays; mouse hemizygous Tek model with IOP measurement","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple patient variants functionally characterized by multiple orthogonal cellular mechanisms plus in vivo mouse model validation","pmids":["27270174"],"is_preprint":false},{"year":2016,"finding":"ANG2 acts as a Tie2 antagonist during infection/inflammation (when Tie1 is cleaved by ectodomain shedding), suppressing p-Tie2, activating FOXO1, increasing ANG2 expression (positive feedback), and promoting vascular leakage; under pathogen-free conditions, ANG2 acts as a Tie2 agonist promoting high p-Tie2, low FOXO1, and stable vessel enlargement. Tie1 ectodomain cleavage (induced by infection or TNF-α) switches ANG2 from agonist to antagonist.","method":"Mouse models of Mycoplasma pulmonis infection vs. pathogen-free conditions; anti-Tie2 antibody; PI3K inhibition; ANG2 overexpression/neutralization; ANG1 administration; FOXO1 activity measurement; Tie1 cleavage analysis","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple in vivo and pharmacological interventions with mechanistic signaling readouts; context-dependent agonist/antagonist switch mechanistically established","pmids":["27548529"],"is_preprint":false},{"year":2016,"finding":"Tie2 insufficiency in endothelial cells decreases COUP-TFII protein levels (a key venous identity regulator); Ang1 stimulation increases COUP-TFII in cultured ECs; Tie2 knockdown or blockade of the downstream PI3K/Akt pathway reduces COUP-TFII, which can be reversed by proteasome inhibition, establishing that Tie2 maintains venous EC identity via Akt-mediated proteasomal stabilization of COUP-TFII.","method":"Endothelial-specific Tek deletion in mice (Tie2-Cre); Ang1 stimulation of cultured ECs; PI3K/Akt inhibition; proteasome inhibition; Western blot for COUP-TFII","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo knockout plus multiple pharmacological interventions with molecular mechanism (proteasomal degradation), multiple orthogonal methods","pmids":["28005008"],"is_preprint":false},{"year":2017,"finding":"Ang1 induces Tie2 dimerization and activation via intermolecular β-sheet formation between membrane-proximal Fibronectin type III domain 3 (Fn3) of Tie2; Tie1 Fn3 is structurally similar and compatible with Tie2/Tie1 heterodimerization by the same mechanism; mutagenesis of key Fn3 residues decreases Ang1-induced Tie2 phosphorylation; Fn2–Fn2 interactions maintain preformed Tie2 oligomerization (mutation increases basal phosphorylation); one PCG-associated Tie2 mutation maps to the Fn2–Fn2 interface and disrupts Tie2 clustering/junctional localization.","method":"X-ray crystallography of Tie2 and Tie1 Fn3 domains; mutagenesis of dimerization interfaces; Tie2 phosphorylation assays; structural analysis of disease mutations","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus functional mutagenesis validation across multiple interface residues; disease mutation structural interpretation","pmids":["28396439"],"is_preprint":false},{"year":2017,"finding":"Tie2 ECR forms strong dimers in the absence of ligand through membrane-proximal FNIII domains (FNIIIc primarily); two dimer modes are structurally defined; mutagenesis implicates dimer-1 in solution-phase sTie2 dimerization; modeling suggests Ang1 may cross-link Tie2 dimers into higher-order oligomers to explain context-dependent clustering.","method":"2.5-Å resolution X-ray crystal structure of Tie2(FNIIIa-c); small-angle X-ray scattering (SAXS) of sTie2 in solution; mutagenesis of dimer interfaces","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — atomic-resolution crystal structure plus SAXS plus mutagenesis; two orthogonal structural methods","pmids":["28396397"],"is_preprint":false},{"year":2017,"finding":"Pericyte-expressed Tie2 is functional: silencing Tie2 in pericytes produces a pro-migratory phenotype and controls sprouting angiogenesis; Tie2 downstream signaling in pericytes involves Calpain, Akt, and FOXO3A; pericyte-specific Tie2 deletion (Ng2-Cre) transiently delays retinal angiogenesis but leads to a pro-angiogenic phenotype promoting tumor growth.","method":"Pericyte Tie2 siRNA knockdown; in vitro sprouting assay; in vivo spheroid assay; Ng2-Cre-driven conditional Tie2 deletion in mice; retinal angiogenesis and tumor growth assays; signaling pathway analysis (Calpain, Akt, FOXO3A)","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vitro siRNA with defined signaling readouts plus genetic in vivo validation; multiple orthogonal methods","pmids":["28719590"],"is_preprint":false},{"year":2018,"finding":"In sepsis, Tie2 protein is suppressed at two levels: (1) MMP14 (MT1-MMP) cleaves the Tie2 N-terminal ectodomain, generating a soluble fragment (mechanistically demonstrated by MMP14 necessity and sufficiency); (2) at the transcriptional level, laminar flow induces Tie2 mRNA via GATA3, and loss of flow/GATA3 in sepsis reduces Tie2 mRNA; both mechanisms operate in vitro, in mice, and in septic human tissues.","method":"Western blot and qPCR in TNF-α-treated HUVECs; cecal ligation and puncture mouse model; MMP14 knockdown/overexpression; shear flow experiments; GATA3 knockdown; postmortem kidney biopsies from septic patients","journal":"Critical care medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal mechanistic approaches (MMP14 necessity/sufficiency, transcription factor knockdown, flow experiments) validated in three species","pmids":["29979219"],"is_preprint":false},{"year":2019,"finding":"Endocardial-specific loss of Tie2 causes mid-gestation lethality with hyperplastic but simplified trabeculae due to reduced endocardial cell proliferation/sprouting; hyperplastic trabeculae result from enhanced cardiomyocyte proliferation associated with upregulation of Bmp10, increased retinoic acid (RA) signaling, and Erk1/2 hyperphosphorylation; inhibition of RA signaling in utero partially rescues the myocardial phenotype.","method":"Endocardial-specific Tie2 conditional knockout mice; histology and proliferation assays; Bmp10 and RA signaling pathway analysis; pharmacological RA receptor antagonist (BMS493) in utero treatment","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional knockout with defined molecular pathway (Bmp10/RA/Erk) and pharmacological rescue; multiple orthogonal methods","pmids":["31112136"],"is_preprint":false},{"year":2020,"finding":"EphA4 is a negative regulator of Tie2 signaling in vascular endothelial cells: endothelial EphA4 deletion (EphA4fl/fl/Tie2-Cre mice) enhances pial collateral remodeling, cerebral blood flow, and functional recovery after stroke; EphA4-Tie2 crosstalk is mediated through p-Akt regulation.","method":"Endothelial-specific EphA4 knockout using Tie2-Cre; vessel painting for collateral assessment; CBF measurement; peptide inhibition of EphA4; p-Akt signaling assays","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis via conditional knockout plus pharmacological inhibition with mechanistic signaling readout (p-Akt), multiple orthogonal in vivo approaches","pmids":["31689239"],"is_preprint":false},{"year":2020,"finding":"SVEP1 stimulates TEK expression in HUVECs (measured by qPCR); the PCG-associated SVEP1:p.R997C variant abrogates this stimulation, establishing SVEP1 as a transcriptional modifier of TEK expression that contributes to TEK-related PCG penetrance.","method":"SVEP1 stimulation of HUVECs; TaqMan qPCR for TEK; transfection of mutant SVEP1 in HEK293 cells; immunofluorescence for SVEP1 in developing SC","journal":"Investigative ophthalmology & visual science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional cell-based assay with mutant vs. WT comparison, single lab, limited to transcriptional level readout","pmids":["33027505"],"is_preprint":false},{"year":2021,"finding":"SIRT7 negatively regulates TEK/TIE2 expression by binding the transcription factor EST-1 and inducing H3K18 deacetylation at the TEK promoter; Co-IP confirmed direct SIRT7-EST-1 interaction; knockdown of EST-1 removes SIRT7-mediated TEK transcriptional repression.","method":"CHIP-qPCR; electrophoretic mobility shift assay (EMSA); promoter reporter assay; Co-IP; siRNA knockdown; RNA-seq","journal":"Cellular oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CHIP-qPCR, EMSA, and Co-IP provide mechanistic evidence for epigenetic regulation; single lab, multiple complementary methods","pmids":["34797559"],"is_preprint":false},{"year":2023,"finding":"VE-PTP (PTPRB) is upregulated in kidney endothelial cells after ischemia-reperfusion injury, inactivating Tie2; genetic deletion of VE-PTP or injection of angiopoietin mimetic Hepta-ANG1 activates Tie2, protects kidneys from IR-AKI, promotes ENTPD1/CD39 expression, and suppresses FOXO1 target genes in the vasculature; a new glomerular endothelial subpopulation emerges with Tie2 activation.","method":"VE-PTP conditional knockout mice; Hepta-ANG1 injection; bilateral IR-AKI mouse model; single-cell RNAseq; histology; immunostaining; FOXO1 transcriptome comparison","journal":"Journal of the American Society of Nephrology : JASN","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO plus pharmacological activation plus scRNAseq mechanistic profiling; multiple orthogonal approaches in rigorous study","pmids":["36787763"],"is_preprint":false},{"year":2023,"finding":"Endothelial Tie2 (but not Tie1) is atheroprotective: deletion of Tie2 in arterial endothelium increases FOXO1 nuclear localization, endothelial adhesion molecule expression, and immune cell accumulation, promoting atherosclerosis; Tie2 is also expressed in aortic fibroblasts, and its silencing increases inflammation-related gene expression in these cells.","method":"Arterial endothelium-specific Tie2 deletion in atherosclerotic mouse model; FOXO1 nuclear localization assay; adhesion molecule expression; immune cell quantification; Tie2 silencing in isolated fibroblasts","journal":"Nature cardiovascular research","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific genetic deletion with multiple molecular readouts (FOXO1, adhesion molecules, inflammation) in disease model","pmids":["37476204"],"is_preprint":false},{"year":2017,"finding":"TEK/Tie2 (and angiopoietin-1/-2) signaling is required for formation of ascending vasa recta (AVR) in the renal medulla; late gestational deletion of Tie2 or both Ang1 and Ang2 prevents AVR formation, leading to medullary interstitial fluid accumulation, cyst formation, loss of medullary vascular bundles, and impaired urine concentrating ability.","method":"Conditional Tie2 deletion and Ang1/Ang2 double-knockout mice; histology; urine concentration measurements; transgenic reporter mice for AVR phenotype characterization","journal":"Journal of the American Society of Nephrology : JASN","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis via conditional KO with defined functional and structural phenotypes; multiple orthogonal methods","pmids":["29237738"],"is_preprint":false}],"current_model":"TEK/TIE2 is an endothelial (and pericyte/monocyte) receptor tyrosine kinase activated by multimeric Ang1 binding at its Ig-domain arrowhead tip, driving receptor dimerization via membrane-proximal FNIII domains and autophosphorylation at key sites (Tyr1100, Tyr1106) that recruit a multifunctional docking complex (p85/PI3K, Grb2, Grb7, Grb14, Shp2, Dok-R) to activate PI3K/Akt (survival, COUP-TFII stabilization, vascular quiescence) and Erk (migration, angiogenesis) pathways in a spatially regulated manner—trans-Tie2 complexes at cell-cell junctions favor Akt/quiescence while ECM-anchored Tie2 at cell-substratum contacts favors Erk/angiogenesis; Ang2 is a context-dependent partial agonist or antagonist whose switch is gated by Tie1 ectodomain integrity (MMP-mediated cleavage in inflammation converts Ang2 to antagonist); VE-PTP (PTPRB) dephosphorylates and inactivates TIE2, and MMP14 sheds its ectodomain in sepsis, while laminar flow and GATA3 sustain its transcription; gain-of-function somatic mutations (e.g., L914F) cause ligand-independent hyperphosphorylation and chronic MAPK activation underlying sporadic venous malformations, whereas loss-of-function alleles cause primary congenital glaucoma through haploinsufficiency of Schlemm's canal formation."},"narrative":{"mechanistic_narrative":"TEK/TIE2 is an endothelial receptor tyrosine kinase that governs vascular quiescence, maintenance, and angiogenic remodeling, and is also functionally expressed in pericytes and aortic fibroblasts [PMID:10498691, PMID:18425120, PMID:28719590, PMID:37476204]. The ligand angiopoietin-1 must assemble into at least tetrameric, disulfide-linked multimers to bind and activate TIE2 [PMID:15769741], engaging the receptor at the tip of an arrowhead-shaped ectodomain built from three Ig and three EGF domains through a lock-and-key interaction [PMID:16732286]; ligand-driven dimerization is executed by intermolecular β-sheet formation between membrane-proximal fibronectin type III (Fn3) domains, while Fn2–Fn2 contacts maintain preformed receptor oligomers [PMID:28396439, PMID:28396397]. Activated TIE2 autophosphorylates C-terminal tyrosines that nucleate a multifunctional docking complex: Tyr1100 recruits Grb2, Grb7, Grb14, Shp2 (PTPN11), and the p85 subunit of PI3K [PMID:7478529, PMID:10521483], and Tyr1106 binds the adaptor Dok-R to couple the receptor to migration signaling [PMID:9764820, PMID:12665569]. These inputs drive PI3K/Akt and Erk arms that are spatially partitioned—trans-TIE2 complexes bridged by Ang1 at cell-cell junctions favor Akt and quiescence, whereas ECM-anchored TIE2 at cell-substratum contacts favors Erk and angiogenesis [PMID:18425120]. Downstream, Akt sustains venous endothelial identity by proteasomal stabilization of COUP-TFII and restrains FOXO1 to enforce vascular stability and atheroprotection [PMID:28005008, PMID:37476204]. Angiopoietin-2 is a context-dependent partial agonist/antagonist whose switch is gated by Tie1 ectodomain shedding during inflammation [PMID:16895971, PMID:27548529], and in TIE2-low angiogenic endothelium ANG2 instead signals through integrins to activate FAK and RAC1 independently of TIE2 [PMID:22585576]. TIE2 activity is negatively set by the phosphatase VE-PTP (PTPRB), pharmacologic inhibition of which boosts TIE2/Akt/eNOS/Erk signaling and is protective in ocular neovascularization and ischemic kidney injury [PMID:25180601, PMID:36787763], and by EphA4-mediated suppression of Akt [PMID:31689239]; receptor levels are further controlled by GATA3/laminar-flow-driven transcription and MMP14 ectodomain shedding in sepsis [PMID:29979219]. TIE2 signaling is essential in vivo for endocardial integrity and trabeculation, microvascular maintenance, renal vasa recta formation, and Schlemm's canal development [PMID:10498691, PMID:31112136, PMID:29237738, PMID:27270174]. Gain-of-function somatic mutations such as L914F cause ligand-independent hyperphosphorylation and chronic MAPK activation underlying venous malformations [PMID:19079259, PMID:26319232], whereas loss-of-function TEK alleles cause primary congenital glaucoma through haploinsufficiency of angiopoietin-TEK signaling in anterior chamber vascular development [PMID:27270174].","teleology":[{"year":1995,"claim":"Established that the TIE2 cytoplasmic tail signals through specific phosphotyrosine-dependent SH2 adaptors, defining its earliest signaling partners.","evidence":"Soluble TEK kinase domain library screen and endothelial lysate pulldown with C-tail tyrosine mutagenesis","pmids":["7478529"],"confidence":"Medium","gaps":["PI3K and PLCγ not detected here, conflicting with later docking studies","in vitro kinase-domain assay rather than full-length receptor in cells"]},{"year":1997,"claim":"Showed TIE2 is actively phosphorylated in both angiogenic and quiescent adult vessels, framing its dual role in remodeling and maintenance.","evidence":"Tie2 IP/anti-phosphotyrosine blotting across rat/mouse tissues with RPA and IHC","pmids":["9314838"],"confidence":"Medium","gaps":["does not resolve which ligand or downstream pathway drives quiescence vs. angiogenesis"]},{"year":1998,"claim":"Identified the Dok-R adaptor and an endothelial-selective promoter, linking TIE2 to RasGAP/Nck/Crk effectors and explaining endothelial-restricted expression.","evidence":"Yeast two-hybrid and co-IP for Dok-R; reporter/EMSA dissection of the Tie2 promoter","pmids":["9764820","9461528"],"confidence":"Medium","gaps":["functional consequence of Dok-R/Crk/Nck assembly not yet tied to a phenotype","transcription factors binding promoter element U unidentified"]},{"year":1999,"claim":"Defined the Tyr1100 multifunctional docking site and demonstrated in vivo that TEK is cell-autonomously required for endocardial integrity and microvascular maintenance.","evidence":"Ang1-stimulated co-IP/mutagenesis of Tyr1100 with survival/migration assays; double-KO and chimeric mouse genetics","pmids":["10521483","10498691"],"confidence":"High","gaps":["spatial regulation of Akt vs. Erk outputs not yet addressed","redundancy with TIE not fully mechanistically resolved"]},{"year":2003,"claim":"Pinpointed Tyr1106 as the autophosphorylation site coupling TIE2 to Dok-R-driven endothelial migration, separating migration from survival signaling.","evidence":"Phospho-specific antibody, mutagenesis, and migration rescue in Tie2-null endothelial cells","pmids":["12665569"],"confidence":"High","gaps":["in vivo requirement of Tyr1106 not tested","interplay with Tyr1100 docking complex unclear"]},{"year":2005,"claim":"Resolved Ang1 multimerization requirements and the autocrine destabilizing action of Ang2, clarifying ligand-level control of receptor activation.","evidence":"Defined Ang variants with EM/SDS-PAGE and phosphorylation assays; 3D spheroid and explant models with soluble Tie2 blockade","pmids":["15769741","15687104"],"confidence":"High","gaps":["structural basis of how multimerization clusters receptors not yet defined","autocrine vs. paracrine Ang2 receptor topology unresolved"]},{"year":2006,"claim":"Provided the atomic structure of the TIE2 ectodomain and defined Ang2 as a weak partial agonist whose binding triggers receptor internalization.","evidence":"X-ray crystallography of Tie2/Ang2 with structure-based mutagenesis; concentration-response phosphorylation and internalization assays","pmids":["16732286","16895971"],"confidence":"High","gaps":["lock-and-key binding with minimal conformational change does not explain how activation signal is transmitted","molecular trigger distinguishing Ang1 vs Ang2 agonism unresolved"]},{"year":2008,"claim":"Established spatial signal partitioning (trans-junctional Akt vs. ECM-anchored Erk), pericyte TIE2 function, and the somatic gain-of-function basis of venous malformations.","evidence":"TIE2 localization imaging with Akt/Erk readouts and transcriptomics; pericyte assays with antisense; lesion sequencing and mutant phosphorylation/localization assays","pmids":["18425120","18436850","19079259"],"confidence":"High","gaps":["mechanism converting receptor location to differential effector choice not molecularly defined","L914F abnormal localization mechanism unresolved"]},{"year":2012,"claim":"Revealed a TIE2-independent ANG2-integrin axis in TIE2-low angiogenic endothelium, expanding angiopoietin signaling beyond the receptor.","evidence":"Integrin binding/co-IP, FAK phosphorylation, RAC1 activity assays, and in vivo ANG2 neutralization in tumor vasculature","pmids":["22585576"],"confidence":"High","gaps":["which integrin heterodimers mediate binding not fully specified","relationship to TIE2-dependent ANG2 effects in same vascular bed unclear"]},{"year":2015,"claim":"Defined the cellular pathology of VM-causing TIE2 mutations: trafficking defects, chronic MAPK activation, fibronectin ECM loss, and plasmin pathway upregulation.","evidence":"Panel of 22 TIE2 mutants in endothelial cells, mouse models, patient biopsy ultrastructure, and ECM/MAPK assays","pmids":["26319232"],"confidence":"High","gaps":["link between specific trafficking defects and downstream MAPK level not quantified per mutant"]},{"year":2014,"claim":"Identified VE-PTP (PTPRB) as the negative regulator dephosphorylating TIE2, providing a druggable node to activate the pathway even under high ANG2.","evidence":"VE-PTP antibody and small-molecule inhibitor AKB-9778 with TIE2/AKT/eNOS/ERK readouts and ocular vascular mouse models","pmids":["25180601"],"confidence":"High","gaps":["direct enzyme-substrate kinetics on specific TIE2 phosphosites not resolved"]},{"year":2016,"claim":"Established the Tie1-gated ANG2 agonist/antagonist switch, the Akt/COUP-TFII venous identity axis, and the TEK haploinsufficiency mechanism of primary congenital glaucoma.","evidence":"Infection vs. pathogen-free mouse models with FOXO1/Tie1-cleavage readouts; Tek deletion with PI3K/proteasome inhibition and COUP-TFII blots; functional characterization of PCG TEK variants with hemizygous mouse IOP","pmids":["27548529","28005008","27270174"],"confidence":"High","gaps":["protease responsible for Tie1 shedding in inflammation not pinned down here","dose threshold for Schlemm's canal phenotype not defined"]},{"year":2017,"claim":"Defined the structural mechanism of receptor dimerization (Fn3 β-sheet) and preformed oligomerization (Fn2–Fn2), established pericyte TIE2 signaling via Calpain/Akt/FOXO3A, and roles in renal vasa recta development.","evidence":"Crystal structures of Tie2/Tie1 Fn domains with interface mutagenesis; pericyte siRNA and Ng2-Cre deletion with signaling readouts; conditional Tie2 and Ang1/Ang2 KO renal phenotyping","pmids":["28396439","28396397","28719590","29237738"],"confidence":"High","gaps":["how Ang1 cross-links dimers into higher-order clusters remains a model, not directly observed","pericyte vs. endothelial TIE2 division of labor in vivo incompletely defined"]},{"year":2018,"claim":"Showed TIE2 levels are suppressed in sepsis at two levels—MMP14 ectodomain shedding and loss of laminar-flow/GATA3-driven transcription—linking hemodynamics and inflammation to receptor abundance.","evidence":"TNF-α HUVEC assays, cecal ligation/puncture mice, MMP14 and GATA3 manipulation, shear flow, and septic human kidney biopsies","pmids":["29979219"],"confidence":"High","gaps":["relative contribution of shedding vs. transcriptional loss to vascular leak not quantified"]},{"year":2019,"claim":"Defined endocardial TIE2 control of trabeculation via a Bmp10/retinoic-acid/Erk axis, with pharmacologic RA inhibition partially rescuing the phenotype.","evidence":"Endocardial-specific Tie2 conditional KO with proliferation, Bmp10/RA analysis, and in utero RA antagonist treatment","pmids":["31112136"],"confidence":"High","gaps":["how endocardial TIE2 loss non-cell-autonomously raises Bmp10/RA in myocardium not fully mechanistic"]},{"year":2020,"claim":"Identified EphA4 and SVEP1 as additional regulators—EphA4 suppresses TIE2/Akt in stroke remodeling, and SVEP1 transcriptionally drives TEK expression relevant to PCG penetrance.","evidence":"Endothelial EphA4 KO and peptide inhibition with p-Akt readout; SVEP1 stimulation of HUVECs with qPCR and PCG variant comparison","pmids":["31689239","33027505"],"confidence":"High","gaps":["direct biochemical EphA4-TIE2 interaction not shown","SVEP1 effect characterized only at transcriptional level"]},{"year":2021,"claim":"Defined epigenetic control of TEK transcription by SIRT7/EST-1-mediated H3K18 deacetylation at the promoter.","evidence":"ChIP-qPCR, EMSA, reporter assay, Co-IP, and siRNA knockdown","pmids":["34797559"],"confidence":"Medium","gaps":["single-lab mechanism; physiological context of SIRT7 repression of TEK not established in vivo"]},{"year":2023,"claim":"Extended VE-PTP/TIE2/FOXO1 biology to disease, showing TIE2 activation protects ischemic kidneys and that endothelial TIE2 is atheroprotective via FOXO1 restraint.","evidence":"VE-PTP conditional KO and Hepta-ANG1 in IR-AKI with scRNAseq; arterial endothelial Tie2 deletion in atherosclerosis with FOXO1/adhesion readouts","pmids":["36787763","37476204"],"confidence":"High","gaps":["how TIE2/Akt mechanistically excludes FOXO1 from the nucleus in these tissues not resolved","fibroblast TIE2 function only partially characterized"]},{"year":null,"claim":"How spatially distinct TIE2 complexes are molecularly decoded into Akt vs. Erk outputs, and how higher-order Ang1-driven clustering is physically organized at junctions vs. matrix, remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["no structural model of the active full-length clustered receptor","the switch coupling localization to effector selection is undefined","in vivo phosphosite-resolved signaling maps lacking"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,4,6,12]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,4,6]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[8,9,10]},{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[8,10]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[11,20,23]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,4]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[4,6,11,15]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[5,24,30,17]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[12,16,17,18]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[11,8]}],"complexes":[],"partners":["ANGPT1","ANGPT2","PTPN11","GRB2","GRB7","GRB14","DOK4","PTPRB"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q02763","full_name":"Angiopoietin-1 receptor","aliases":["Endothelial tyrosine kinase","Tunica interna endothelial cell kinase","Tyrosine kinase with Ig and EGF homology domains-2","Tyrosine-protein kinase receptor TEK","Tyrosine-protein kinase receptor TIE-2","hTIE2","p140 TEK"],"length_aa":1124,"mass_kda":125.8,"function":"Tyrosine-protein kinase that acts as a cell-surface receptor for ANGPT1, ANGPT2 and ANGPT4 and regulates angiogenesis, endothelial cell survival, proliferation, migration, adhesion and cell spreading, reorganization of the actin cytoskeleton, but also maintenance of vascular quiescence. Has anti-inflammatory effects by preventing the leakage of pro-inflammatory plasma proteins and leukocytes from blood vessels. Required for normal angiogenesis and heart development during embryogenesis. Required for post-natal hematopoiesis. After birth, activates or inhibits angiogenesis, depending on the context. Inhibits angiogenesis and promotes vascular stability in quiescent vessels, where endothelial cells have tight contacts. In quiescent vessels, ANGPT1 oligomers recruit TEK to cell-cell contacts, forming complexes with TEK molecules from adjoining cells, and this leads to preferential activation of phosphatidylinositol 3-kinase and the AKT1 signaling cascades. In migrating endothelial cells that lack cell-cell adhesions, ANGT1 recruits TEK to contacts with the extracellular matrix, leading to the formation of focal adhesion complexes, activation of PTK2/FAK and of the downstream kinases MAPK1/ERK2 and MAPK3/ERK1, and ultimately to the stimulation of sprouting angiogenesis. ANGPT1 signaling triggers receptor dimerization and autophosphorylation at specific tyrosine residues that then serve as binding sites for scaffold proteins and effectors. Signaling is modulated by ANGPT2 that has lower affinity for TEK, can promote TEK autophosphorylation in the absence of ANGPT1, but inhibits ANGPT1-mediated signaling by competing for the same binding site. Signaling is also modulated by formation of heterodimers with TIE1, and by proteolytic processing that gives rise to a soluble TEK extracellular domain. The soluble extracellular domain modulates signaling by functioning as decoy receptor for angiopoietins. 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expression library and pull down from endothelial lysates; site-directed mutagenesis of C-tail tyrosines\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro kinase domain pulldown with mutagenesis, single lab, two orthogonal methods (library screen + endothelial lysate pulldown)\",\n      \"pmids\": [\"7478529\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Tie2 protein is tyrosine-phosphorylated (actively signaling) in endothelial cells of both angiogenic tissues (healing wounds, ovary, uterus) and quiescent adult vasculature, indicating dual roles in angiogenesis and vascular maintenance.\",\n      \"method\": \"Immunoprecipitation of Tie2 from rat/mouse tissues followed by anti-phosphotyrosine blotting; RNase protection assay for mRNA; immunohistochemistry\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal IP/phospho-blot in multiple tissue types, single lab with multiple orthogonal methods (IP, RPA, IHC)\",\n      \"pmids\": [\"9314838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"TEK/Tie2 signals through a novel docking protein Dok-R (now DOKR/DOK4): activated TEK phosphorylates Dok-R via a PTB domain interaction; phosphorylated Dok-R co-immunoprecipitates rasGAP and Nck, and Dok-R is constitutively bound to Crk through its proline-rich tail.\",\n      \"method\": \"Yeast two-hybrid screen with activated Tek; co-immunoprecipitation; co-expression in cells; domain-mapping\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid plus co-IP validation, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"9764820\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The murine Tie2/Tek proximal promoter drives endothelial cell-specific transcription through two positive regulatory elements (U and A) and one inhibitory region (I); element U functions in an endothelial-cell-selective manner and binds distinct protein factors.\",\n      \"method\": \"Reporter transfection experiments in endothelial vs. non-endothelial cells; electrophoretic mobility-shift assays (EMSA); deletion mutagenesis\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional reporter assays with EMSA, single lab, two orthogonal methods\",\n      \"pmids\": [\"9461528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Angiopoietin-1 stimulation of TEK recruits five SH2-domain proteins (Grb2, Grb7, Grb14, Shp2, and p85 of PI3K) to a multifunctional docking site at Tyr1100 in the Tek C-tail; mutation of Tyr1100 abolishes Grb2/Grb7 binding and p85/Grb7 phosphorylation in vivo; Ang1-induced Tek signaling activates both cell survival (PI3K-dependent) and migration pathways.\",\n      \"method\": \"Yeast two-hybrid; in vivo co-immunoprecipitation; site-directed mutagenesis of Tyr1100; cell migration and survival assays with PI3K inhibitors\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — yeast two-hybrid validated by in vivo co-IP plus mutagenesis plus functional assays, multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"10521483\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Genetic ablation of both TEK and TIE in mice demonstrates that TEK is absolutely required cell-autonomously for endocardial integrity at E10.5, whereas TEK and TIE are dispensable for initial vasculogenesis but redundantly required for microvasculature maintenance during late organogenesis and in the adult.\",\n      \"method\": \"Double-knockout mouse genetics; mosaic analysis in chimeric embryos\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis via double-KO and mosaic analysis, replicated developmental phenotypes, rigorous in vivo approach\",\n      \"pmids\": [\"10498691\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Tyr1106 on Tie2 is an Ang1-dependent autophosphorylation site that mediates binding and phosphorylation of Dok-R via its PTB domain; the Dok-R PH domain further contributes to Tie2 binding in a PI3K-dependent manner; Tie2 mutant lacking Tyr1106 fails to restore endothelial cell migration in Tie2-null cells, establishing Tyr1106 as critical for coupling cell migration signaling to Ang1.\",\n      \"method\": \"Site-directed mutagenesis; phosphorylation state-specific antibody; co-immunoprecipitation; migration rescue assay in Tie2-null endothelial cells\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — mutagenesis + phospho-specific antibody + functional rescue in null cells; multiple rigorous orthogonal methods\",\n      \"pmids\": [\"12665569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Angiopoietin-2 acts as a rapidly acting autocrine destabilizer of quiescent endothelium via Tie2; exogenous Ang1, soluble Tie2, and VEGF rescue Ang2-induced endothelial detachment, but soluble Tie2 cannot block autocrine (endogenous) Ang2-mediated detachment, demonstrating an internal autocrine loop mechanism distinct from paracrine Ang2 signaling.\",\n      \"method\": \"3D endothelial/smooth-muscle co-culture spheroid model; umbilical-vein explant model; Tie2 small-molecule inhibitor; soluble Tie2 blocking; overexpression and stimulated release of Ang2\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — two independent model systems with multiple pharmacologic and genetic interventions, single lab but rigorously controlled\",\n      \"pmids\": [\"15687104\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Ang1 oligomerization state is critical for Tie2 binding and activation: at least tetrameric (≥4 subunit) multimers mediated by intermolecular disulfide bonds involving Cys41 and Cys54 are required; dimeric and monomeric Ang1 variants lose binding and activation capacity for Tie2.\",\n      \"method\": \"Generation of Ang1/Ang2 variants; SDS-PAGE; rotary metal-shadowing transmission electron microscopy; Tie2 phosphorylation assays; binding assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution with defined mutant ligands, structural visualization by EM, and functional binding/phosphorylation assays; multiple orthogonal methods\",\n      \"pmids\": [\"15769741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Crystal structures of the Tie2 receptor ectodomain (alone and in complex with Ang2) reveal that Tie2 contains three (not two) Ig domains folded with three EGF domains into an arrowhead shape; Ang2 binds at the tip via a lock-and-key mechanism with minimal conformational change in either molecule, similar to antibody-antigen recognition; structure-based mutagenesis validated the binding interface.\",\n      \"method\": \"X-ray crystallography; structure-based mutagenesis\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure at atomic resolution validated by mutagenesis; definitive structural determination\",\n      \"pmids\": [\"16732286\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Activation of Tie2 by either Ang1 or Ang2 leads to ligand release from the endothelial cell surface and receptor internalization/degradation; Ang2 is a considerably weaker Tie2 activator than Ang1 and behaves as a partial agonist; Ang1-induced internalization is faster and more pronounced than Ang2-induced internalization.\",\n      \"method\": \"Concentration-response phosphorylation assays; receptor internalization assays; ligand binding and accumulation assays in endothelial cells\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple cellular assays (phosphorylation, internalization, ligand release), single lab\",\n      \"pmids\": [\"16895971\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Ang1 bridges Tie2 molecules at cell-cell contacts to form trans-Tie2 complexes, preferentially activating Akt; in isolated cells, ECM-bound Ang1 anchors Tie2 at cell-substratum contacts, preferentially activating Erk; these spatially distinct Tie2 complexes produce differential downstream gene expression profiles linked to vascular quiescence vs. angiogenesis respectively.\",\n      \"method\": \"Fluorescence microscopy of Tie2 localization; Akt and Erk phosphorylation assays; microarray gene expression with real-time PCR validation; endothelial cell-cell contact manipulation\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (localization, signaling, transcriptomics) with rigorous spatial manipulation; replicated by Alitalo group (cited in same corpus)\",\n      \"pmids\": [\"18425120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Somatic TEK mutations (including the frequent L914F substitution and several double mutations in cis) cause ligand-independent TIE2 hyperphosphorylation in vitro; the L914F mutant shows abnormal subcellular localization and retains ligand responsiveness, in contrast to the inherited R849W mutant, indicating mechanistically distinct pathogenic pathways for inherited vs. sporadic venous malformations.\",\n      \"method\": \"Sequencing of lesion vs. blood DNA; in vitro TIE2 phosphorylation assays; overexpression of mutant TIE2 in HUVECs with immunofluorescence localization\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro kinase assays with multiple defined mutants plus cellular localization studies, replicated across multiple patient samples\",\n      \"pmids\": [\"19079259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Pericytes express a functionally active Tie2 receptor; Ang1 promotes pericyte survival and migration via Tie2, and Ang2 increases pericyte apoptosis; Tie2 antisense confirmed angiopoietin effects are Tie2-dependent in pericytes.\",\n      \"method\": \"ELISA, Western blot, flow cytometry for Tie2 on pericytes; apoptosis assays (Annexin V); migration assay; Tie2 antisense knockdown\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple methods with antisense knockdown confirmation, single lab\",\n      \"pmids\": [\"18436850\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ANG-2 binds integrins (not Tie2) on TIE2-low angiogenic endothelial cells, inducing FAK phosphorylation (integrin adaptor), RAC1 activation, migration, and sprouting angiogenesis in a TIE2-independent manner; in vivo ANG-2 blockade inhibits FAK phosphorylation in TIE2-low ECs.\",\n      \"method\": \"Identification of TIE2-low subpopulation in tumor vasculature; co-IP/binding assays of ANG-2 with integrins; phosphorylation assays for FAK; RAC1 activity assay; in vivo ANG-2 neutralization\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal binding assays, phosphorylation, Rac1 GEF assay, and in vivo validation; multiple orthogonal methods in single study\",\n      \"pmids\": [\"22585576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"VE-PTP (PTPRB) negatively regulates TIE2 by dephosphorylation; inhibition of VE-PTP catalytic activity with AKB-9778 activates TIE2, enhances Ang1-induced TIE2 activation, and stimulates phosphorylation of AKT, eNOS, and ERK in the TIE2 pathway; this is effective even in the presence of high ANG2.\",\n      \"method\": \"Anti-VE-PTP antibody and small-molecule VE-PTP inhibitor (AKB-9778); TIE2 and downstream signaling phosphorylation assays; mouse models of ocular NV and vascular leakage\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — pharmacological and antibody-based inhibition with multiple downstream signaling readouts and in vivo confirmation; multiple orthogonal methods\",\n      \"pmids\": [\"25180601\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Analysis of 22 TIE2 patient mutations reveals that VM-causing mutations cause defective receptor trafficking and subcellular localization by multiple distinct mechanisms, leading to attenuated ligand response; TIE2 mutations cause chronic MAPK pathway activation, loss of endothelial monolayer integrity due to fibronectin ECM deficiency, and upregulation of the plasminogen/plasmin proteolytic pathway.\",\n      \"method\": \"Endothelial cell cultures with 22 TIE2 mutants; mouse models; ultrastructural analysis of patient biopsies; Western blotting for MAPK; ECM fibronectin quantification\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — comprehensive panel of 22 mutations with multiple orthogonal cellular and in vivo methods, validated in patient tissue\",\n      \"pmids\": [\"26319232\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"TEK mutations in primary congenital glaucoma (PCG) cause haploinsufficiency through multiple protein loss-of-function mechanisms including absence of protein production, aggregate formation, enhanced proteasomal degradation, altered subcellular localization, and reduced ligand responsiveness; hemizygosity for Tek in mice leads to hypomorphic Schlemm's canal and elevated intraocular pressure, demonstrating dose-sensitivity of angiopoietin-TEK signaling in anterior chamber vascular development.\",\n      \"method\": \"Cellular assays in transfected cells for each TEK variant; immunofluorescence for localization; proteasome inhibition assays; mouse hemizygous Tek model with IOP measurement\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple patient variants functionally characterized by multiple orthogonal cellular mechanisms plus in vivo mouse model validation\",\n      \"pmids\": [\"27270174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ANG2 acts as a Tie2 antagonist during infection/inflammation (when Tie1 is cleaved by ectodomain shedding), suppressing p-Tie2, activating FOXO1, increasing ANG2 expression (positive feedback), and promoting vascular leakage; under pathogen-free conditions, ANG2 acts as a Tie2 agonist promoting high p-Tie2, low FOXO1, and stable vessel enlargement. Tie1 ectodomain cleavage (induced by infection or TNF-α) switches ANG2 from agonist to antagonist.\",\n      \"method\": \"Mouse models of Mycoplasma pulmonis infection vs. pathogen-free conditions; anti-Tie2 antibody; PI3K inhibition; ANG2 overexpression/neutralization; ANG1 administration; FOXO1 activity measurement; Tie1 cleavage analysis\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple in vivo and pharmacological interventions with mechanistic signaling readouts; context-dependent agonist/antagonist switch mechanistically established\",\n      \"pmids\": [\"27548529\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Tie2 insufficiency in endothelial cells decreases COUP-TFII protein levels (a key venous identity regulator); Ang1 stimulation increases COUP-TFII in cultured ECs; Tie2 knockdown or blockade of the downstream PI3K/Akt pathway reduces COUP-TFII, which can be reversed by proteasome inhibition, establishing that Tie2 maintains venous EC identity via Akt-mediated proteasomal stabilization of COUP-TFII.\",\n      \"method\": \"Endothelial-specific Tek deletion in mice (Tie2-Cre); Ang1 stimulation of cultured ECs; PI3K/Akt inhibition; proteasome inhibition; Western blot for COUP-TFII\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo knockout plus multiple pharmacological interventions with molecular mechanism (proteasomal degradation), multiple orthogonal methods\",\n      \"pmids\": [\"28005008\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Ang1 induces Tie2 dimerization and activation via intermolecular β-sheet formation between membrane-proximal Fibronectin type III domain 3 (Fn3) of Tie2; Tie1 Fn3 is structurally similar and compatible with Tie2/Tie1 heterodimerization by the same mechanism; mutagenesis of key Fn3 residues decreases Ang1-induced Tie2 phosphorylation; Fn2–Fn2 interactions maintain preformed Tie2 oligomerization (mutation increases basal phosphorylation); one PCG-associated Tie2 mutation maps to the Fn2–Fn2 interface and disrupts Tie2 clustering/junctional localization.\",\n      \"method\": \"X-ray crystallography of Tie2 and Tie1 Fn3 domains; mutagenesis of dimerization interfaces; Tie2 phosphorylation assays; structural analysis of disease mutations\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus functional mutagenesis validation across multiple interface residues; disease mutation structural interpretation\",\n      \"pmids\": [\"28396439\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Tie2 ECR forms strong dimers in the absence of ligand through membrane-proximal FNIII domains (FNIIIc primarily); two dimer modes are structurally defined; mutagenesis implicates dimer-1 in solution-phase sTie2 dimerization; modeling suggests Ang1 may cross-link Tie2 dimers into higher-order oligomers to explain context-dependent clustering.\",\n      \"method\": \"2.5-Å resolution X-ray crystal structure of Tie2(FNIIIa-c); small-angle X-ray scattering (SAXS) of sTie2 in solution; mutagenesis of dimer interfaces\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — atomic-resolution crystal structure plus SAXS plus mutagenesis; two orthogonal structural methods\",\n      \"pmids\": [\"28396397\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Pericyte-expressed Tie2 is functional: silencing Tie2 in pericytes produces a pro-migratory phenotype and controls sprouting angiogenesis; Tie2 downstream signaling in pericytes involves Calpain, Akt, and FOXO3A; pericyte-specific Tie2 deletion (Ng2-Cre) transiently delays retinal angiogenesis but leads to a pro-angiogenic phenotype promoting tumor growth.\",\n      \"method\": \"Pericyte Tie2 siRNA knockdown; in vitro sprouting assay; in vivo spheroid assay; Ng2-Cre-driven conditional Tie2 deletion in mice; retinal angiogenesis and tumor growth assays; signaling pathway analysis (Calpain, Akt, FOXO3A)\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vitro siRNA with defined signaling readouts plus genetic in vivo validation; multiple orthogonal methods\",\n      \"pmids\": [\"28719590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In sepsis, Tie2 protein is suppressed at two levels: (1) MMP14 (MT1-MMP) cleaves the Tie2 N-terminal ectodomain, generating a soluble fragment (mechanistically demonstrated by MMP14 necessity and sufficiency); (2) at the transcriptional level, laminar flow induces Tie2 mRNA via GATA3, and loss of flow/GATA3 in sepsis reduces Tie2 mRNA; both mechanisms operate in vitro, in mice, and in septic human tissues.\",\n      \"method\": \"Western blot and qPCR in TNF-α-treated HUVECs; cecal ligation and puncture mouse model; MMP14 knockdown/overexpression; shear flow experiments; GATA3 knockdown; postmortem kidney biopsies from septic patients\",\n      \"journal\": \"Critical care medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal mechanistic approaches (MMP14 necessity/sufficiency, transcription factor knockdown, flow experiments) validated in three species\",\n      \"pmids\": [\"29979219\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Endocardial-specific loss of Tie2 causes mid-gestation lethality with hyperplastic but simplified trabeculae due to reduced endocardial cell proliferation/sprouting; hyperplastic trabeculae result from enhanced cardiomyocyte proliferation associated with upregulation of Bmp10, increased retinoic acid (RA) signaling, and Erk1/2 hyperphosphorylation; inhibition of RA signaling in utero partially rescues the myocardial phenotype.\",\n      \"method\": \"Endocardial-specific Tie2 conditional knockout mice; histology and proliferation assays; Bmp10 and RA signaling pathway analysis; pharmacological RA receptor antagonist (BMS493) in utero treatment\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional knockout with defined molecular pathway (Bmp10/RA/Erk) and pharmacological rescue; multiple orthogonal methods\",\n      \"pmids\": [\"31112136\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"EphA4 is a negative regulator of Tie2 signaling in vascular endothelial cells: endothelial EphA4 deletion (EphA4fl/fl/Tie2-Cre mice) enhances pial collateral remodeling, cerebral blood flow, and functional recovery after stroke; EphA4-Tie2 crosstalk is mediated through p-Akt regulation.\",\n      \"method\": \"Endothelial-specific EphA4 knockout using Tie2-Cre; vessel painting for collateral assessment; CBF measurement; peptide inhibition of EphA4; p-Akt signaling assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis via conditional knockout plus pharmacological inhibition with mechanistic signaling readout (p-Akt), multiple orthogonal in vivo approaches\",\n      \"pmids\": [\"31689239\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SVEP1 stimulates TEK expression in HUVECs (measured by qPCR); the PCG-associated SVEP1:p.R997C variant abrogates this stimulation, establishing SVEP1 as a transcriptional modifier of TEK expression that contributes to TEK-related PCG penetrance.\",\n      \"method\": \"SVEP1 stimulation of HUVECs; TaqMan qPCR for TEK; transfection of mutant SVEP1 in HEK293 cells; immunofluorescence for SVEP1 in developing SC\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional cell-based assay with mutant vs. WT comparison, single lab, limited to transcriptional level readout\",\n      \"pmids\": [\"33027505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SIRT7 negatively regulates TEK/TIE2 expression by binding the transcription factor EST-1 and inducing H3K18 deacetylation at the TEK promoter; Co-IP confirmed direct SIRT7-EST-1 interaction; knockdown of EST-1 removes SIRT7-mediated TEK transcriptional repression.\",\n      \"method\": \"CHIP-qPCR; electrophoretic mobility shift assay (EMSA); promoter reporter assay; Co-IP; siRNA knockdown; RNA-seq\",\n      \"journal\": \"Cellular oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CHIP-qPCR, EMSA, and Co-IP provide mechanistic evidence for epigenetic regulation; single lab, multiple complementary methods\",\n      \"pmids\": [\"34797559\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"VE-PTP (PTPRB) is upregulated in kidney endothelial cells after ischemia-reperfusion injury, inactivating Tie2; genetic deletion of VE-PTP or injection of angiopoietin mimetic Hepta-ANG1 activates Tie2, protects kidneys from IR-AKI, promotes ENTPD1/CD39 expression, and suppresses FOXO1 target genes in the vasculature; a new glomerular endothelial subpopulation emerges with Tie2 activation.\",\n      \"method\": \"VE-PTP conditional knockout mice; Hepta-ANG1 injection; bilateral IR-AKI mouse model; single-cell RNAseq; histology; immunostaining; FOXO1 transcriptome comparison\",\n      \"journal\": \"Journal of the American Society of Nephrology : JASN\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO plus pharmacological activation plus scRNAseq mechanistic profiling; multiple orthogonal approaches in rigorous study\",\n      \"pmids\": [\"36787763\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Endothelial Tie2 (but not Tie1) is atheroprotective: deletion of Tie2 in arterial endothelium increases FOXO1 nuclear localization, endothelial adhesion molecule expression, and immune cell accumulation, promoting atherosclerosis; Tie2 is also expressed in aortic fibroblasts, and its silencing increases inflammation-related gene expression in these cells.\",\n      \"method\": \"Arterial endothelium-specific Tie2 deletion in atherosclerotic mouse model; FOXO1 nuclear localization assay; adhesion molecule expression; immune cell quantification; Tie2 silencing in isolated fibroblasts\",\n      \"journal\": \"Nature cardiovascular research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific genetic deletion with multiple molecular readouts (FOXO1, adhesion molecules, inflammation) in disease model\",\n      \"pmids\": [\"37476204\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"TEK/Tie2 (and angiopoietin-1/-2) signaling is required for formation of ascending vasa recta (AVR) in the renal medulla; late gestational deletion of Tie2 or both Ang1 and Ang2 prevents AVR formation, leading to medullary interstitial fluid accumulation, cyst formation, loss of medullary vascular bundles, and impaired urine concentrating ability.\",\n      \"method\": \"Conditional Tie2 deletion and Ang1/Ang2 double-knockout mice; histology; urine concentration measurements; transgenic reporter mice for AVR phenotype characterization\",\n      \"journal\": \"Journal of the American Society of Nephrology : JASN\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis via conditional KO with defined functional and structural phenotypes; multiple orthogonal methods\",\n      \"pmids\": [\"29237738\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TEK/TIE2 is an endothelial (and pericyte/monocyte) receptor tyrosine kinase activated by multimeric Ang1 binding at its Ig-domain arrowhead tip, driving receptor dimerization via membrane-proximal FNIII domains and autophosphorylation at key sites (Tyr1100, Tyr1106) that recruit a multifunctional docking complex (p85/PI3K, Grb2, Grb7, Grb14, Shp2, Dok-R) to activate PI3K/Akt (survival, COUP-TFII stabilization, vascular quiescence) and Erk (migration, angiogenesis) pathways in a spatially regulated manner—trans-Tie2 complexes at cell-cell junctions favor Akt/quiescence while ECM-anchored Tie2 at cell-substratum contacts favors Erk/angiogenesis; Ang2 is a context-dependent partial agonist or antagonist whose switch is gated by Tie1 ectodomain integrity (MMP-mediated cleavage in inflammation converts Ang2 to antagonist); VE-PTP (PTPRB) dephosphorylates and inactivates TIE2, and MMP14 sheds its ectodomain in sepsis, while laminar flow and GATA3 sustain its transcription; gain-of-function somatic mutations (e.g., L914F) cause ligand-independent hyperphosphorylation and chronic MAPK activation underlying sporadic venous malformations, whereas loss-of-function alleles cause primary congenital glaucoma through haploinsufficiency of Schlemm's canal formation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TEK/TIE2 is an endothelial receptor tyrosine kinase that governs vascular quiescence, maintenance, and angiogenic remodeling, and is also functionally expressed in pericytes and aortic fibroblasts [#5, #11, #22, #29]. The ligand angiopoietin-1 must assemble into at least tetrameric, disulfide-linked multimers to bind and activate TIE2 [#8], engaging the receptor at the tip of an arrowhead-shaped ectodomain built from three Ig and three EGF domains through a lock-and-key interaction [#9]; ligand-driven dimerization is executed by intermolecular \\u03b2-sheet formation between membrane-proximal fibronectin type III (Fn3) domains, while Fn2\\u2013Fn2 contacts maintain preformed receptor oligomers [#20, #21]. Activated TIE2 autophosphorylates C-terminal tyrosines that nucleate a multifunctional docking complex: Tyr1100 recruits Grb2, Grb7, Grb14, Shp2 (PTPN11), and the p85 subunit of PI3K [#0, #4], and Tyr1106 binds the adaptor Dok-R to couple the receptor to migration signaling [#2, #6]. These inputs drive PI3K/Akt and Erk arms that are spatially partitioned\\u2014trans-TIE2 complexes bridged by Ang1 at cell-cell junctions favor Akt and quiescence, whereas ECM-anchored TIE2 at cell-substratum contacts favors Erk and angiogenesis [#11]. Downstream, Akt sustains venous endothelial identity by proteasomal stabilization of COUP-TFII and restrains FOXO1 to enforce vascular stability and atheroprotection [#19, #29]. Angiopoietin-2 is a context-dependent partial agonist/antagonist whose switch is gated by Tie1 ectodomain shedding during inflammation [#10, #18], and in TIE2-low angiogenic endothelium ANG2 instead signals through integrins to activate FAK and RAC1 independently of TIE2 [#14]. TIE2 activity is negatively set by the phosphatase VE-PTP (PTPRB), pharmacologic inhibition of which boosts TIE2/Akt/eNOS/Erk signaling and is protective in ocular neovascularization and ischemic kidney injury [#15, #28], and by EphA4-mediated suppression of Akt [#25]; receptor levels are further controlled by GATA3/laminar-flow-driven transcription and MMP14 ectodomain shedding in sepsis [#23]. TIE2 signaling is essential in vivo for endocardial integrity and trabeculation, microvascular maintenance, renal vasa recta formation, and Schlemm's canal development [#5, #24, #30, #17]. Gain-of-function somatic mutations such as L914F cause ligand-independent hyperphosphorylation and chronic MAPK activation underlying venous malformations [#12, #16], whereas loss-of-function TEK alleles cause primary congenital glaucoma through haploinsufficiency of angiopoietin-TEK signaling in anterior chamber vascular development [#17].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Established that the TIE2 cytoplasmic tail signals through specific phosphotyrosine-dependent SH2 adaptors, defining its earliest signaling partners.\",\n      \"evidence\": \"Soluble TEK kinase domain library screen and endothelial lysate pulldown with C-tail tyrosine mutagenesis\",\n      \"pmids\": [\"7478529\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"PI3K and PLC\\u03b3 not detected here, conflicting with later docking studies\", \"in vitro kinase-domain assay rather than full-length receptor in cells\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Showed TIE2 is actively phosphorylated in both angiogenic and quiescent adult vessels, framing its dual role in remodeling and maintenance.\",\n      \"evidence\": \"Tie2 IP/anti-phosphotyrosine blotting across rat/mouse tissues with RPA and IHC\",\n      \"pmids\": [\"9314838\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"does not resolve which ligand or downstream pathway drives quiescence vs. angiogenesis\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Identified the Dok-R adaptor and an endothelial-selective promoter, linking TIE2 to RasGAP/Nck/Crk effectors and explaining endothelial-restricted expression.\",\n      \"evidence\": \"Yeast two-hybrid and co-IP for Dok-R; reporter/EMSA dissection of the Tie2 promoter\",\n      \"pmids\": [\"9764820\", \"9461528\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"functional consequence of Dok-R/Crk/Nck assembly not yet tied to a phenotype\", \"transcription factors binding promoter element U unidentified\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Defined the Tyr1100 multifunctional docking site and demonstrated in vivo that TEK is cell-autonomously required for endocardial integrity and microvascular maintenance.\",\n      \"evidence\": \"Ang1-stimulated co-IP/mutagenesis of Tyr1100 with survival/migration assays; double-KO and chimeric mouse genetics\",\n      \"pmids\": [\"10521483\", \"10498691\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"spatial regulation of Akt vs. Erk outputs not yet addressed\", \"redundancy with TIE not fully mechanistically resolved\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Pinpointed Tyr1106 as the autophosphorylation site coupling TIE2 to Dok-R-driven endothelial migration, separating migration from survival signaling.\",\n      \"evidence\": \"Phospho-specific antibody, mutagenesis, and migration rescue in Tie2-null endothelial cells\",\n      \"pmids\": [\"12665569\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"in vivo requirement of Tyr1106 not tested\", \"interplay with Tyr1100 docking complex unclear\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Resolved Ang1 multimerization requirements and the autocrine destabilizing action of Ang2, clarifying ligand-level control of receptor activation.\",\n      \"evidence\": \"Defined Ang variants with EM/SDS-PAGE and phosphorylation assays; 3D spheroid and explant models with soluble Tie2 blockade\",\n      \"pmids\": [\"15769741\", \"15687104\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"structural basis of how multimerization clusters receptors not yet defined\", \"autocrine vs. paracrine Ang2 receptor topology unresolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Provided the atomic structure of the TIE2 ectodomain and defined Ang2 as a weak partial agonist whose binding triggers receptor internalization.\",\n      \"evidence\": \"X-ray crystallography of Tie2/Ang2 with structure-based mutagenesis; concentration-response phosphorylation and internalization assays\",\n      \"pmids\": [\"16732286\", \"16895971\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"lock-and-key binding with minimal conformational change does not explain how activation signal is transmitted\", \"molecular trigger distinguishing Ang1 vs Ang2 agonism unresolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Established spatial signal partitioning (trans-junctional Akt vs. ECM-anchored Erk), pericyte TIE2 function, and the somatic gain-of-function basis of venous malformations.\",\n      \"evidence\": \"TIE2 localization imaging with Akt/Erk readouts and transcriptomics; pericyte assays with antisense; lesion sequencing and mutant phosphorylation/localization assays\",\n      \"pmids\": [\"18425120\", \"18436850\", \"19079259\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"mechanism converting receptor location to differential effector choice not molecularly defined\", \"L914F abnormal localization mechanism unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Revealed a TIE2-independent ANG2-integrin axis in TIE2-low angiogenic endothelium, expanding angiopoietin signaling beyond the receptor.\",\n      \"evidence\": \"Integrin binding/co-IP, FAK phosphorylation, RAC1 activity assays, and in vivo ANG2 neutralization in tumor vasculature\",\n      \"pmids\": [\"22585576\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"which integrin heterodimers mediate binding not fully specified\", \"relationship to TIE2-dependent ANG2 effects in same vascular bed unclear\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined the cellular pathology of VM-causing TIE2 mutations: trafficking defects, chronic MAPK activation, fibronectin ECM loss, and plasmin pathway upregulation.\",\n      \"evidence\": \"Panel of 22 TIE2 mutants in endothelial cells, mouse models, patient biopsy ultrastructure, and ECM/MAPK assays\",\n      \"pmids\": [\"26319232\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"link between specific trafficking defects and downstream MAPK level not quantified per mutant\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identified VE-PTP (PTPRB) as the negative regulator dephosphorylating TIE2, providing a druggable node to activate the pathway even under high ANG2.\",\n      \"evidence\": \"VE-PTP antibody and small-molecule inhibitor AKB-9778 with TIE2/AKT/eNOS/ERK readouts and ocular vascular mouse models\",\n      \"pmids\": [\"25180601\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"direct enzyme-substrate kinetics on specific TIE2 phosphosites not resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Established the Tie1-gated ANG2 agonist/antagonist switch, the Akt/COUP-TFII venous identity axis, and the TEK haploinsufficiency mechanism of primary congenital glaucoma.\",\n      \"evidence\": \"Infection vs. pathogen-free mouse models with FOXO1/Tie1-cleavage readouts; Tek deletion with PI3K/proteasome inhibition and COUP-TFII blots; functional characterization of PCG TEK variants with hemizygous mouse IOP\",\n      \"pmids\": [\"27548529\", \"28005008\", \"27270174\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"protease responsible for Tie1 shedding in inflammation not pinned down here\", \"dose threshold for Schlemm's canal phenotype not defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined the structural mechanism of receptor dimerization (Fn3 \\u03b2-sheet) and preformed oligomerization (Fn2\\u2013Fn2), established pericyte TIE2 signaling via Calpain/Akt/FOXO3A, and roles in renal vasa recta development.\",\n      \"evidence\": \"Crystal structures of Tie2/Tie1 Fn domains with interface mutagenesis; pericyte siRNA and Ng2-Cre deletion with signaling readouts; conditional Tie2 and Ang1/Ang2 KO renal phenotyping\",\n      \"pmids\": [\"28396439\", \"28396397\", \"28719590\", \"29237738\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"how Ang1 cross-links dimers into higher-order clusters remains a model, not directly observed\", \"pericyte vs. endothelial TIE2 division of labor in vivo incompletely defined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showed TIE2 levels are suppressed in sepsis at two levels\\u2014MMP14 ectodomain shedding and loss of laminar-flow/GATA3-driven transcription\\u2014linking hemodynamics and inflammation to receptor abundance.\",\n      \"evidence\": \"TNF-\\u03b1 HUVEC assays, cecal ligation/puncture mice, MMP14 and GATA3 manipulation, shear flow, and septic human kidney biopsies\",\n      \"pmids\": [\"29979219\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"relative contribution of shedding vs. transcriptional loss to vascular leak not quantified\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined endocardial TIE2 control of trabeculation via a Bmp10/retinoic-acid/Erk axis, with pharmacologic RA inhibition partially rescuing the phenotype.\",\n      \"evidence\": \"Endocardial-specific Tie2 conditional KO with proliferation, Bmp10/RA analysis, and in utero RA antagonist treatment\",\n      \"pmids\": [\"31112136\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"how endocardial TIE2 loss non-cell-autonomously raises Bmp10/RA in myocardium not fully mechanistic\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identified EphA4 and SVEP1 as additional regulators\\u2014EphA4 suppresses TIE2/Akt in stroke remodeling, and SVEP1 transcriptionally drives TEK expression relevant to PCG penetrance.\",\n      \"evidence\": \"Endothelial EphA4 KO and peptide inhibition with p-Akt readout; SVEP1 stimulation of HUVECs with qPCR and PCG variant comparison\",\n      \"pmids\": [\"31689239\", \"33027505\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"direct biochemical EphA4-TIE2 interaction not shown\", \"SVEP1 effect characterized only at transcriptional level\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined epigenetic control of TEK transcription by SIRT7/EST-1-mediated H3K18 deacetylation at the promoter.\",\n      \"evidence\": \"ChIP-qPCR, EMSA, reporter assay, Co-IP, and siRNA knockdown\",\n      \"pmids\": [\"34797559\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"single-lab mechanism; physiological context of SIRT7 repression of TEK not established in vivo\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended VE-PTP/TIE2/FOXO1 biology to disease, showing TIE2 activation protects ischemic kidneys and that endothelial TIE2 is atheroprotective via FOXO1 restraint.\",\n      \"evidence\": \"VE-PTP conditional KO and Hepta-ANG1 in IR-AKI with scRNAseq; arterial endothelial Tie2 deletion in atherosclerosis with FOXO1/adhesion readouts\",\n      \"pmids\": [\"36787763\", \"37476204\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"how TIE2/Akt mechanistically excludes FOXO1 from the nucleus in these tissues not resolved\", \"fibroblast TIE2 function only partially characterized\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How spatially distinct TIE2 complexes are molecularly decoded into Akt vs. Erk outputs, and how higher-order Ang1-driven clustering is physically organized at junctions vs. matrix, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"no structural model of the active full-length clustered receptor\", \"the switch coupling localization to effector selection is undefined\", \"in vivo phosphosite-resolved signaling maps lacking\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 4, 6, 12]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 4, 6]},\n      {\"term_id\": \"GO:0004672\", \"supporting_discovery_ids\": [4, 6]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [8, 9, 10]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [8, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [11, 20, 23]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 6, 11, 15]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [5, 24, 30, 17]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [12, 16, 17, 18]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [11, 8]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"ANGPT1\", \"ANGPT2\", \"PTPN11\", \"GRB2\", \"GRB7\", \"GRB14\", \"DOK4\", \"PTPRB\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":9,"faith_total":9,"faith_pct":100.0}}