{"gene":"ROBO4","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":2003,"finding":"Robo4 is an endothelial-specific Robo family member that binds Slit and inhibits endothelial cell migration; immunoprecipitation showed Robo4 binds the actin regulatory protein Mena, a known effector of Robo-Slit signaling.","method":"Heterologous expression migration assay, immunoprecipitation, Slit-binding assay","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (migration assay, binding, Co-IP) in foundational paper, >250 citations","pmids":["12941633"],"is_preprint":false},{"year":2008,"finding":"Slit2 activation of Robo4 inhibits VEGF-165-induced endothelial migration, tube formation, and vascular permeability in vitro, and pathologic angiogenesis/vascular leak in vivo, by blocking Src family kinase activation; Robo4 knockout mice show enhanced retinal and choroidal vascular disease.","method":"In vitro migration/permeability assays, Src kinase activity assay, Robo4 knockout mouse models of retinal and choroidal vascular disease","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro mechanistic assays plus in vivo KO phenotype, >300 citations, replicated","pmids":["18345009"],"is_preprint":false},{"year":2008,"finding":"Robo4 interacts with WASP (Wiskott-Aldrich syndrome protein), N-WASP, and WASP-interacting protein actin-nucleating complex via its intracellular domain; Robo4 forms a heterodimeric complex with Robo1, and Robo4-induced filopodia formation requires Robo1, suggesting a Robo1/Robo4 heterodimer signals through actin nucleation-promoting factors to regulate endothelial migration.","method":"Yeast 2-hybrid, GST pulldown, siRNA knockdown, co-immunoprecipitation, GFP-Robo4 transfection imaging","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Y2H, pulldown, Co-IP, functional rescue), replicated in companion paper","pmids":["18948384"],"is_preprint":false},{"year":2009,"finding":"Slit2-Robo4 signaling maintains vascular stability by directly interacting with intracellular adaptor protein paxillin (and its paralogue Hic-5) at the cell surface, which recruits the Arf-GAP GIT1 to block activation of the small GTPase Arf6 and subsequently Rac1, thereby suppressing cellular protrusive activity underlying neovascularization and vascular leak.","method":"Co-immunoprecipitation, biochemical fractionation, Arf6 activation assay, in vivo Arf6 inhibition in retinal vascular disease models","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — biochemical mechanism established with multiple methods (Co-IP, GTPase activity assays, in vivo phenocopy), >190 citations","pmids":["19855388"],"is_preprint":false},{"year":2010,"finding":"Slit2 activation of endothelial Robo4 strengthens the vascular barrier and reduces vascular permeability in lung and other organs, increasing survival in mouse models of bacterial endotoxin exposure, polymicrobial sepsis, and H5N1 influenza by blunting the host vascular response to the cytokine storm.","method":"In vivo vascular permeability assays, mouse models of endotoxemia, sepsis, and influenza; Robo4-dependent pathway activation","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 2 — multiple in vivo disease models with defined Robo4-dependent mechanism, >280 citations","pmids":["20375003"],"is_preprint":false},{"year":2011,"finding":"Robo4 maintains vessel integrity and inhibits VEGF signaling by binding directly to UNC5B (a vascular Netrin receptor) via its extracellular domain; soluble Robo4 inhibits VEGF-induced permeability in wild-type but not UNC5B-blocked mice, placing Robo4 upstream of UNC5B in suppressing VEGFR signaling.","method":"Protein-protein interaction screen with Robo4 extracellular domain, function-blocking monoclonal antibodies, Robo4-/- rescue experiments, vascular permeability assays","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 — interaction screen plus genetic epistasis plus in vivo rescue, >170 citations","pmids":["21238923"],"is_preprint":false},{"year":2011,"finding":"Robo4 functions to anchor hematopoietic stem cells (HSCs) to bone marrow niches; Robo4-deficient HSCs show poor BM localization and reduced long-term reconstitution. Cxcr4 is upregulated in Robo4-/- HSCs to compensate, and combined inhibition of both Cxcr4 and Robo4 is required for efficient HSC mobilization.","method":"Robo4 knockout mice, transplantation assays, HSC localization/mobilization studies, flow cytometry, genetic epistasis (Cxcr4/Robo4 double manipulation)","journal":"Cell stem cell","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined cellular phenotype, genetic epistasis, >100 citations","pmids":["21211783"],"is_preprint":false},{"year":2011,"finding":"Robo4 regulates radial migration of newborn neurons in developing neocortex; Robo4 knockdown by siRNA or Cre-mediated deletion causes severe defects in radial migration with neuronal misorientation, and sensitizes neurons to Slit repulsion, demonstrating Slit-dependent and -independent roles.","method":"In utero electroporation with siRNA/Cre, transwell migration assay, growth cone collapse assay, floxed Robo4 mice","journal":"Cerebral cortex","confidence":"High","confidence_rationale":"Tier 2 — clean in vivo KD/KO with defined cellular phenotype and multiple assays","pmids":["22123939"],"is_preprint":false},{"year":2006,"finding":"Robo4 mediates attraction signaling in zebrafish vascular endothelial cells by activating Cdc42 and Rac1 Rho GTPases; robo4 knockdown in zebrafish results in reduced active Cdc42 and Rac1, with angioblasts showing impaired directional guidance.","method":"Gain-of-function Robo4 expression in endothelial cells, robo4 morpholino knockdown in zebrafish, Rho GTPase activity assays","journal":"Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — zebrafish ortholog study with GTPase activity assays, single lab","pmids":["16481322"],"is_preprint":false},{"year":2010,"finding":"Endothelial Robo4 restricts VEGF-R2 signaling through Src and FAK kinases to limit blood vessel growth in the mammary gland; loss of Robo4 (but not Robo1) in endothelium combined with an angiogenic stimulus phenocopies loss of stromal Slit, resulting in elevated vessel density.","method":"Conditional Robo4 and Robo1 knockout mouse models, genetic epistasis, VEGFR2/Src/FAK signaling analysis","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 — clean genetic dissection with conditional KO and defined signaling pathway, >60 citations","pmids":["20498081"],"is_preprint":false},{"year":2013,"finding":"Slit2-N/Robo4 signaling induces internalization of VEGFR-3 to block its activation, and inhibits PI3K/Akt pathway activation by VEGF-C in lymphatic endothelial cells, thereby suppressing lymphangiogenesis in a Robo4-dependent manner.","method":"siRNA Robo4 knockdown, VEGFR-3 internalization assay, PI3K/Akt activation assay, lymphatic endothelial cell migration/proliferation/tube formation assays","journal":"Cell communication and signaling","confidence":"Medium","confidence_rationale":"Tier 2 — multiple functional assays with mechanistic pathway analysis, single lab","pmids":["24708522"],"is_preprint":false},{"year":2013,"finding":"Slit2/Robo4 signaling represses LPS-induced endothelial inflammation by inhibiting the Pyk2-NF-κB pathway downstream of LPS-TLR4; Robo4 is the dominant anti-inflammatory receptor while Robo1 is pro-inflammatory and is downregulated by Slit2 via miR-218.","method":"siRNA knockdown of Robo4/Robo1 in HUVECs, NF-κB/Pyk2 signaling analysis, cytokine/chemokine measurement, miR-218 analysis","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — mechanistic pathway analysis with siRNA, single lab, multiple readouts","pmids":["24272999"],"is_preprint":false},{"year":2016,"finding":"The cytoplasmic domain of Robo4 is dispensable for vascular permeability and neovascularization; truncated Robo4 lacking the cytoplasmic domain (Robo4ΔCD) is sufficient to prevent permeability and inhibit OIR revascularization. Robo4 (and Robo4ΔCD) counteract VEGFR2-Y949 phosphorylation by signaling through the endothelial UNC5B receptor, independently of Slit2 signaling.","method":"Transgenic mice expressing cytoplasmic-domain-truncated Robo4, oxygen-induced retinopathy model, wound healing model, VEGFR2 phosphorylation analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 — structure-function transgenic approach with defined molecular readout (VEGFR2-Y949 phosphorylation) and in vivo rescue","pmids":["27882935"],"is_preprint":false},{"year":2018,"finding":"Annexin A2 (ANXA2) acts as a Robo4 ligand; recombinant ANXA2 reduces trans-endothelial permeability by modulating signaling via the Robo4-paxillin-ARF6 pathway in brain endothelial cells, reducing ARF6 activity and maintaining endothelial tightness.","method":"ANXA2 knockout mice, recombinant ANXA2 treatment, Robo4-paxillin-ARF6 signaling analysis, TEER and tracer leakage assays","journal":"Journal of cerebral blood flow and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 — KO mouse plus mechanistic pathway analysis, single lab","pmids":["29786451"],"is_preprint":false},{"year":2019,"finding":"Robo4 forms a complex with TRAF7 (TNF receptor-associated factor 7, a ubiquitin E3 ligase) via the C-terminus of Robo4; this Robo4-TRAF7 complex suppresses TNFα-induced endothelial hyperpermeability by stabilizing VE-cadherin at cell junctions.","method":"Co-IP/binding assays, deletion assays mapping C-terminus interaction, TRAF7 gain/loss-of-function, VE-cadherin localization assay, Robo4-/- endotoxemia mouse model","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, domain mapping, functional rescue, in vivo validation","pmids":["30510113"],"is_preprint":false},{"year":2018,"finding":"ETV2 directly interacts with TET1 and TET2 methylcytosine-converting enzymes; ETV2-TET1/TET2 complexes demethylate the Robo4 proximal promoter to induce endothelial-specific Robo4 expression during differentiation from iPSCs to endothelial cells.","method":"Co-immunoprecipitation (ETV2-TET1/TET2 interaction), reporter assays, adenoviral ETV2-TET1/TET2 overexpression in non-ECs, bisulfite sequencing for promoter methylation","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP plus functional demethylation assay, single lab","pmids":["29618782"],"is_preprint":false},{"year":2004,"finding":"Soluble Robo4 extracellular domain (Robo4Fc) inhibits angiogenesis in vivo and endothelial migration/proliferation/tube formation in vitro; however, Slit1, Slit2, and Slit3 bind Robo1 but not Robo4 by immunoprecipitation and BiaCore analysis, suggesting Robo4 uses a different ligand mechanism.","method":"In vivo sponge angiogenesis model, rat aortic ring assay, VEGF/bFGF migration assay, immunoprecipitation, BiaCore binding analysis","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — multiple in vitro/in vivo functional assays plus direct binding analysis, single lab","pmids":["15486058"],"is_preprint":false},{"year":2015,"finding":"ROBO4 signaling in endothelial cells suppresses breast cancer growth and metastasis by regulating tumor angiogenesis, endothelial leakage, and tight junction protein ZO-1 levels; pharmacological activation of ARF6 inhibition downstream of Robo4 (using SecinH3) mimics Robo4 activation and reduces tumor angiogenesis.","method":"Robo4 knockout immunocompetent mouse breast cancer model, tumor angiogenesis quantification, SecinH3 pharmacological treatment, ZO-1 expression analysis","journal":"Molecular oncology","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo KO model with defined pathway (ARF6) and pharmacological rescue, single lab","pmids":["26778715"],"is_preprint":false},{"year":2015,"finding":"Vascular endothelial ROBO4 actively promotes HSC extravasation from blood into bone marrow (trans-endothelial migration), while simultaneously maintaining vascular barrier function to prevent BM-to-blood escape, thereby regulating directionality of HSC trafficking.","method":"ROBO4 knockout mice, induced vascular permeability experiments, HSC tracking/engraftment assays","journal":"Stem cell reports","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with defined directional trafficking phenotype, single lab","pmids":["25640759"],"is_preprint":false},{"year":2012,"finding":"Robo4 knockdown in retinal endothelial cells increases permeability, reduces tight junction proteins ZO-1 and occludin, causes F-actin rearrangement, and activates the LIMK/cofilin pathway, revealing a signaling cascade mediating barrier function.","method":"siRNA knockdown, RITC-dextran permeability assay, Western blotting for TJ proteins and LIMK/cofilin, immunofluorescence for F-actin","journal":"Current eye research","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA KD with multiple mechanistic readouts, single lab","pmids":["23163536"],"is_preprint":false},{"year":2022,"finding":"Soluble Robo4 is generated by constitutive ectodomain shedding by ADAM10 and ADAM17 (disintegrin metalloproteinases); Slit3 induces cell-surface Robo4 endocytosis, thereby shielding Robo4 from shedding by ADAMs and enhancing Robo4 signaling. Shed soluble Robo4 inhibits Slit3-induced angiogenesis.","method":"ADAM10/ADAM17 inhibitor and siRNA studies, Robo4 shedding assays, endocytosis assays with Slit3 treatment, angiogenesis functional assays","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — identification of sheddases with siRNA validation and functional consequence, single lab","pmids":["35288626"],"is_preprint":false},{"year":2023,"finding":"ALK5-SMAD2/3 and ALK1-SMAD1/5 signaling pathways positively and negatively regulate Robo4 expression, respectively; endothelial-specific Robo4 overexpression suppresses vascular permeability and reduces mortality in LPS-treated and SARS-CoV-2-infected mice.","method":"ALK1 inhibitor screening, SMAD pathway analysis, endothelial-specific Robo4 transgenic overexpression mice, LPS endotoxemia and SARS-CoV-2 infection models, vascular permeability assays","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal approaches (inhibitor screening, transgenic overexpression, in vivo disease models), single lab with strong methods","pmids":["36634143"],"is_preprint":false},{"year":2024,"finding":"ROBO4 interacts with IQGAP1 and TRAF7; in this complex, ROBO4 enhances IQGAP1 ubiquitination through the E3 ligase TRAF7, inhibits prolonged RAC1 activation, and decreases PTGS2/COX-2 expression in inflammatory endothelial cells, thereby suppressing prostaglandin-mediated vascular inflammation.","method":"RNA-seq, Co-IP (ROBO4-IQGAP1-TRAF7 complex), ubiquitination assay, RAC1 activation assay, Robo4-/- mouse models of arthritis/edema/pain","journal":"Communications biology","confidence":"High","confidence_rationale":"Tier 2 — Co-IP for complex identification, ubiquitination assay, RAC1 activity assay, in vivo KO phenotype","pmids":["38762541"],"is_preprint":false},{"year":2024,"finding":"USP5 stabilizes ROBO4 protein through deubiquitination; USP5 overexpression increases ROBO4 levels and aggravates high-glucose-induced retinal pigment epithelial cell damage, while USP5 knockdown decreases ROBO4 and mitigates this damage.","method":"Co-immunoprecipitation, deubiquitination assay, USP5 and ROBO4 overexpression/knockdown, cell damage assays in high-glucose conditions","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP and direct deubiquitination assay, single lab","pmids":["38735506"],"is_preprint":false},{"year":2017,"finding":"Recombinant Slit2 reduces surgical brain injury-induced BBB disruption via Robo4 and paxillin; Robo4 and paxillin siRNA knockdown reverses Slit2-mediated Rac1 activation, placing Robo4 upstream of a paxillin-Rac1 signaling axis in BBB protection.","method":"Robo4 and paxillin siRNA knockdown, Rac1 activity assay, recombinant Slit2 treatment, BBB permeability assays in SBI rat model","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA epistasis with pathway activity assay and in vivo model, single lab","pmids":["28389649"],"is_preprint":false},{"year":2018,"finding":"ROBO4 variants (missense and rare) segregate with bicuspid aortic valve and thoracic aortic aneurysm; silencing ROBO4 or expressing mutant ROBO4 in endothelial cell lines impairs barrier function and induces a gene expression repertoire consistent with endothelial-to-mesenchymal transition.","method":"Targeted sequencing in families, siRNA knockdown and mutant ROBO4 expression in endothelial lines, barrier function assays, EMT gene expression profiling","journal":"Nature genetics","confidence":"Medium","confidence_rationale":"Tier 2 — human genetics plus in vitro functional validation, single study","pmids":["30455415"],"is_preprint":false},{"year":2019,"finding":"Robo4 deletion in mice ameliorates platelet-activating factor (PAF)-mediated skin inflammation by reducing LPCAT1/LPCAT2 mRNA translation efficiency (via reduced ribosome and ATP levels), decreasing PAF receptor expression in macrophages, and suppressing LPS-induced IL-6 and p44/42/p65 phosphorylation while enhancing AKT phosphorylation.","method":"Robo4 KO mouse model, polyribosome assay for LPCAT1/LPCAT2 mRNA, HPLC for ATP, Western blot for signaling proteins, immunohistochemistry","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 2 — KO mouse with polyribosome assay and multiple signaling readouts, single lab","pmids":["32140075"],"is_preprint":false},{"year":2024,"finding":"Robo4 depletion in bone marrow endothelial cells promotes endothelial-to-mesenchymal transition (EndMT) by increasing endoglin (CD105) expression and activating both canonical (Smad) and non-canonical (AKT/NF-κB) TGF-β signaling, leading to Snail1 nuclear translocation; Robo4 overexpression stimulates ICAM-1 and VCAM-1 expression and suppresses EndMT and irradiation-induced permeability.","method":"Lentiviral RNAi and overexpression in endothelial cells, γ-radiation injury model, Western blot for Smad/AKT/NF-κB/Snail1, co-culture with HSPCs","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — gene manipulation with defined signaling pathway readouts, single lab","pmids":["38383474"],"is_preprint":false},{"year":2021,"finding":"HDAC3 (but not HDAC1 or HDAC2) maintains Robo4 expression in endothelial cells by sustaining GABP transcription factor expression; HDAC3-specific siRNA knockdown or the HDAC inhibitor MS-275 reduces GABP and Robo4 promoter activity, increases endothelial permeability, and enhances vascular leakage in mouse lungs.","method":"HDAC isoform-specific siRNA, HDAC inhibitor MS-275, Robo4 promoter reporter assay, TEER assay, Evans blue leakage in vivo","journal":"Tissue barriers","confidence":"Medium","confidence_rationale":"Tier 2 — epistatic siRNA dissection with promoter assay and in vivo phenotype, single lab","pmids":["33955828"],"is_preprint":false},{"year":2021,"finding":"Acute endothelial-specific deletion of Robo4 impairs HSC distribution between bone marrow and blood, perturbs long-term donor HSC engraftment, and improves HSC mobilization, independently of VCAM1 expression on sinusoidal vascular endothelial cells.","method":"Conditional Robo4 deletion mouse models, HSC trafficking/engraftment assays, VCAM1 protein level analysis on sinusoidal VECs","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — conditional KO with defined cellular phenotype, genetic epistasis with VCAM1, single lab","pmids":["34388149"],"is_preprint":false},{"year":2013,"finding":"SLIT3 secreted by pericytic mesenchymal stem cells guides vascular network formation via ROBO4-positive endothelial cells; siRNA knockdown of SLIT3 in MSCs leads to disorganized EC clustering, and ROBO4 knockdown in ECs abolishes functional human blood vessel generation in vivo in a xenograft model.","method":"siRNA knockdown of SLIT3 (in MSCs) and ROBO4 (in ECs), 3D vascular network live imaging, in vivo xenogenic implant model","journal":"Journal of molecular and cellular cardiology","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA KD with in vitro and in vivo functional assays, single lab","pmids":["24090675"],"is_preprint":false}],"current_model":"ROBO4 is an endothelial cell-specific transmembrane receptor that maintains vascular integrity and suppresses pathologic angiogenesis primarily by (1) forming a complex with paxillin/Hic-5 and recruiting the Arf-GAP GIT1 to block Arf6 and Rac1 activation downstream of Slit2, thereby suppressing cellular protrusive activity; (2) signaling through UNC5B to counteract VEGFR2-Y949 phosphorylation independently of its cytoplasmic domain; (3) interacting with TRAF7 and IQGAP1 to enhance IQGAP1 ubiquitination, suppress RAC1 and NF-κB/COX-2 inflammatory signaling, and stabilize VE-cadherin at endothelial junctions; and (4) forming heterodimers with Robo1 to signal through WASP-family actin nucleators for filopodia formation and cell migration, while also cooperating with CXCR4 to anchor hematopoietic stem cells to bone marrow niches."},"narrative":{"teleology":[{"year":2003,"claim":"Identification of ROBO4 as an endothelial-specific Robo family member that binds Slit and inhibits endothelial migration established it as a candidate vascular guidance receptor, answering whether Robo-Slit signaling operates in endothelium.","evidence":"Heterologous expression migration assays, Slit-binding assays, and co-immunoprecipitation with actin regulator Mena in endothelial cells","pmids":["12941633"],"confidence":"High","gaps":["Whether Slit is the physiological ligand for Robo4 remained disputed","Downstream signaling cascade uncharacterized"]},{"year":2004,"claim":"Functional evidence that soluble Robo4 ectodomain inhibits angiogenesis in vivo, coupled with failure to detect Slit1-3 binding to Robo4 by BiaCore, raised the question of whether Robo4 uses an alternative ligand.","evidence":"In vivo sponge angiogenesis model, rat aortic ring assay, BiaCore direct binding analysis","pmids":["15486058"],"confidence":"Medium","gaps":["Identity of the Robo4 extracellular ligand unresolved","Single lab observation of no Slit binding contradicted other reports"]},{"year":2006,"claim":"Demonstration that zebrafish Robo4 activates Cdc42 and Rac1 for angioblast guidance revealed that Robo4 can act as a pro-migratory signal, contrasting with its anti-migratory role described in mammalian cells.","evidence":"Morpholino knockdown in zebrafish, Rho GTPase pull-down assays","pmids":["16481322"],"confidence":"Medium","gaps":["Context-dependent vs. species-dependent signaling not resolved","Mammalian Robo4 GTPase regulation appeared opposite"]},{"year":2008,"claim":"Two key advances defined Robo4's signaling outputs: Slit2-Robo4 blocks VEGF-induced migration and permeability by suppressing Src kinase (with Robo4 KO mice showing vascular disease), while Robo4 heterodimerizes with Robo1 and signals through WASP/N-WASP actin nucleators for filopodia formation.","evidence":"Robo4 knockout mouse retinal/choroidal disease models, Src kinase assays, yeast two-hybrid/GST pulldown for WASP interaction, siRNA epistasis for Robo1 requirement","pmids":["18345009","18948384"],"confidence":"High","gaps":["How Src suppression and WASP activation are coordinated was unclear","Whether Robo1-Robo4 heterodimer forms in vivo remained unresolved"]},{"year":2009,"claim":"The core intracellular mechanism was elucidated: Robo4 binds paxillin/Hic-5 to recruit Arf-GAP GIT1, inactivating Arf6 and consequently Rac1, explaining how Slit2-Robo4 suppresses protrusive activity and neovascularization.","evidence":"Co-immunoprecipitation, Arf6 activation assays, in vivo retinal vascular disease phenocopy by Arf6 inhibition","pmids":["19855388"],"confidence":"High","gaps":["Whether paxillin-GIT1 pathway accounts for all Robo4 barrier function or operates alongside other pathways","No structural data for Robo4-paxillin interaction"]},{"year":2010,"claim":"Translational significance was established when Slit2-Robo4 vascular barrier strengthening increased survival in sepsis and influenza models, while genetic dissection showed endothelial Robo4 (not Robo1) restricts VEGFR2/Src/FAK signaling to limit vessel growth.","evidence":"Mouse sepsis/endotoxemia/influenza survival models, conditional Robo4 vs Robo1 KO mammary gland angiogenesis","pmids":["20375003","20498081"],"confidence":"High","gaps":["Therapeutic window for Slit2 administration undefined","Relative contributions of Src suppression vs Arf6 suppression not separated"]},{"year":2011,"claim":"The extracellular signaling partner UNC5B was identified, showing Robo4 maintains vascular integrity by binding UNC5B to inhibit VEGF signaling, while a parallel discovery revealed Robo4 anchors HSCs to bone marrow niches cooperatively with CXCR4.","evidence":"Robo4 extracellular domain interaction screen, UNC5B function-blocking antibodies, Robo4-/- HSC transplantation and mobilization assays with Cxcr4 epistasis","pmids":["21238923","21211783"],"confidence":"High","gaps":["How UNC5B relays the Robo4 signal to VEGFR2 mechanistically","Whether HSC-intrinsic or endothelial Robo4 dominates niche anchoring"]},{"year":2012,"claim":"Robo4 knockdown in retinal endothelial cells revealed dependence of tight junction protein levels (ZO-1, occludin) and actin organization on Robo4 via a LIMK/cofilin pathway, extending barrier signaling beyond Rac1/Arf6.","evidence":"siRNA knockdown, RITC-dextran permeability, Western blot for tight junction and LIMK/cofilin proteins","pmids":["23163536"],"confidence":"Medium","gaps":["Whether LIMK/cofilin acts downstream of Arf6 or independently not resolved","Replicated in one cell type only"]},{"year":2013,"claim":"Robo4 was shown to suppress lymphangiogenesis by inducing VEGFR-3 internalization, and to repress endothelial inflammation via Pyk2-NF-κB inhibition, while SLIT3 from pericytes was identified as a guidance cue acting through endothelial ROBO4 for vascular network assembly.","evidence":"VEGFR-3 internalization and PI3K/Akt assays, NF-κB/Pyk2 signaling analysis with siRNA, in vivo xenograft vascular formation","pmids":["24708522","24272999","24090675"],"confidence":"Medium","gaps":["Whether VEGFR-3 internalization and Pyk2 suppression share upstream mechanism","SLIT3 vs SLIT2 selectivity for ROBO4 not settled"]},{"year":2016,"claim":"A decisive structure-function experiment showed the Robo4 cytoplasmic domain is dispensable: truncated Robo4 lacking its intracellular region fully rescues permeability and neovascularization defects, signaling instead through UNC5B to block VEGFR2-Y949 phosphorylation.","evidence":"Transgenic Robo4ΔCD mice, oxygen-induced retinopathy model, VEGFR2-Y949 phosphorylation analysis","pmids":["27882935"],"confidence":"High","gaps":["How paxillin-Arf6 intracellular signaling reconciles with cytoplasmic-domain dispensability","Whether all Robo4 functions (e.g., HSC anchoring, inflammation) are also cytoplasmic-domain-independent"]},{"year":2018,"claim":"Annexin A2 was identified as an additional Robo4 ligand engaging the paxillin-ARF6 pathway at the blood-brain barrier, ROBO4 variants were linked to bicuspid aortic valve/aortic aneurysm in human families with functional validation, and ETV2-TET1/TET2 complexes were shown to demethylate the Robo4 promoter for endothelial-specific expression.","evidence":"ANXA2 KO mice with Robo4-ARF6 signaling analysis; targeted sequencing in families plus endothelial barrier assays with mutant ROBO4; bisulfite sequencing with ETV2-TET1/2 co-IP","pmids":["29786451","30455415","29618782"],"confidence":"Medium","gaps":["ANXA2-Robo4 binding interface not mapped","Penetrance and mechanism of ROBO4 variants in aortic disease require larger cohorts","Whether ETV2-TET pathway is the sole driver of Robo4 endothelial specificity"]},{"year":2019,"claim":"TRAF7 was identified as a Robo4 cytoplasmic binding partner that stabilizes VE-cadherin at junctions, establishing a TRAF7-dependent branch of Robo4 barrier signaling distinct from the paxillin-Arf6 axis.","evidence":"Reciprocal co-immunoprecipitation, domain mapping, TRAF7 gain/loss-of-function, VE-cadherin localization, Robo4-/- endotoxemia model","pmids":["30510113"],"confidence":"High","gaps":["Whether TRAF7 E3 ligase activity is required for VE-cadherin stabilization was answered later but not in this study","Relationship between TRAF7 and UNC5B pathways unknown"]},{"year":2022,"claim":"The mechanism controlling Robo4 surface levels was identified: ADAM10/ADAM17 constitutively shed the Robo4 ectodomain, while Slit3 induces Robo4 endocytosis to protect it from shedding, providing a feedback mechanism that enhances signaling.","evidence":"ADAM10/17 inhibitor and siRNA, Robo4 shedding quantification, Slit3-induced endocytosis assays","pmids":["35288626"],"confidence":"Medium","gaps":["Whether ADAM shedding regulates Robo4 in vivo not tested","Whether soluble Robo4 acts as a true decoy receptor in physiological conditions"]},{"year":2023,"claim":"Transcriptional regulation of Robo4 was further defined: ALK5-SMAD2/3 positively and ALK1-SMAD1/5 negatively control Robo4 expression, and endothelial-specific Robo4 overexpression reduced mortality in endotoxemia and SARS-CoV-2 infection models.","evidence":"ALK1 inhibitor screening, SMAD pathway analysis, endothelial-specific Robo4 transgenic mice, LPS and SARS-CoV-2 models","pmids":["36634143"],"confidence":"High","gaps":["Whether TGF-β pathway regulation of Robo4 is direct or indirect through GABP/HDAC3","Long-term effects of Robo4 overexpression on normal vasculature"]},{"year":2024,"claim":"The ROBO4-TRAF7-IQGAP1 complex was defined: TRAF7 ubiquitinates IQGAP1 in a ROBO4-dependent manner to suppress prolonged RAC1 activation and NF-κB/COX-2 inflammatory signaling, while separately USP5 was identified as a deubiquitinase that stabilizes ROBO4 protein.","evidence":"Co-IP for trimeric complex, IQGAP1 ubiquitination assay, RAC1 activity assay, Robo4-/- arthritis/edema models; USP5-ROBO4 deubiquitination assay","pmids":["38762541","38735506"],"confidence":"High","gaps":["Whether USP5 regulation of ROBO4 stability is relevant in vascular endothelium in vivo","Structural basis for TRAF7-mediated IQGAP1 ubiquitination unknown"]},{"year":null,"claim":"Major unresolved questions include how the cytoplasmic-domain-dispensable UNC5B pathway reconciles with documented intracellular signaling through paxillin-GIT1 and TRAF7-IQGAP1, whether distinct ligands (Slit2, Slit3, ANXA2) activate distinct downstream branches, and the structural basis for ROBO4-UNC5B interaction.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model for any Robo4 complex","Context-dependent pro- vs anti-migratory signaling not mechanistically reconciled","Relative physiological importance of Slit2, Slit3, and ANXA2 as Robo4 ligands unclear"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,3,5,9,12,22]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,3,5]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,3,5,12,14,20]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,3,5,8,9,12,22]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[7,8,30]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,11,22,26]}],"complexes":["Robo4-paxillin/Hic-5-GIT1","Robo4-TRAF7-IQGAP1","Robo1-Robo4 heterodimer","Robo4-UNC5B"],"partners":["UNC5B","TRAF7","IQGAP1","PXN","GIT1","ROBO1","MENA","WAS"],"other_free_text":[]},"mechanistic_narrative":"ROBO4 is an endothelial cell-specific transmembrane receptor that functions as a master regulator of vascular integrity, suppressing pathological angiogenesis, vascular permeability, and endothelial inflammation. ROBO4 maintains barrier function through multiple convergent mechanisms: it recruits paxillin/Hic-5 and the Arf-GAP GIT1 to block Arf6 and Rac1 activation, thereby suppressing protrusive activity [PMID:19855388]; it signals through the Netrin receptor UNC5B to counteract VEGFR2-Y949 phosphorylation independently of its own cytoplasmic domain [PMID:27882935, PMID:21238923]; and it forms a complex with TRAF7 to promote IQGAP1 ubiquitination, dampening RAC1 and NF-κB/COX-2 inflammatory signaling while stabilizing VE-cadherin at endothelial junctions [PMID:30510113, PMID:38762541]. 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pathology","url":"https://pubmed.ncbi.nlm.nih.gov/31933855","citation_count":4,"is_preprint":false},{"pmid":"31081721","id":"PMC_31081721","title":"Inhibitory Effect of Slit2-N on VEGF165-induced proliferation of vascular endothelia via Slit2-N-Robo4-Akt pathway in choroidal neovascularization.","date":"2019","source":"Cell cycle (Georgetown, Tex.)","url":"https://pubmed.ncbi.nlm.nih.gov/31081721","citation_count":4,"is_preprint":false},{"pmid":"32879763","id":"PMC_32879763","title":"DS-7080a, a Selective Anti-ROBO4 Antibody, Shows Anti-Angiogenic Efficacy with Distinctly Different Profiles from Anti-VEGF Agents.","date":"2020","source":"Translational vision science & technology","url":"https://pubmed.ncbi.nlm.nih.gov/32879763","citation_count":4,"is_preprint":false},{"pmid":"35656971","id":"PMC_35656971","title":"BML-111 alleviates inflammatory response of alveolar epithelial cells via miR-494/Slit2/Robo4 signalling axis to improve acute lung injury.","date":"2022","source":"Autoimmunity","url":"https://pubmed.ncbi.nlm.nih.gov/35656971","citation_count":4,"is_preprint":false},{"pmid":"31772321","id":"PMC_31772321","title":"Robo4 contributes to the turnover of Peyer's patch B cells.","date":"2019","source":"Mucosal immunology","url":"https://pubmed.ncbi.nlm.nih.gov/31772321","citation_count":4,"is_preprint":false},{"pmid":"38937814","id":"PMC_38937814","title":"Slit2-Robo4 signal pathway and tight junction in intestine mediate LPS-induced inflammation in mice.","date":"2024","source":"European journal of medical research","url":"https://pubmed.ncbi.nlm.nih.gov/38937814","citation_count":3,"is_preprint":false},{"pmid":"39404781","id":"PMC_39404781","title":"Modulation of the tumor microenvironment in non-muscle-invasive bladder cancer by OncoTherad® (MRB-CFI-1) nanoimmunotherapy: effects on tumor-associated macrophages, tumor-infiltrating lymphocytes, and monoamine oxidases.","date":"2024","source":"Medical oncology (Northwood, London, England)","url":"https://pubmed.ncbi.nlm.nih.gov/39404781","citation_count":3,"is_preprint":false},{"pmid":"18571431","id":"PMC_18571431","title":"Ligand-independent assembly of purified soluble magic roundabout (Robo4), a tumor-specific endothelial marker.","date":"2008","source":"Protein expression and purification","url":"https://pubmed.ncbi.nlm.nih.gov/18571431","citation_count":3,"is_preprint":false},{"pmid":"32238717","id":"PMC_32238717","title":"PRC2 Components Maintain DNA Hypermethylation of the Upstream Promoter and Regulate Robo4 Expression in Endothelial Cells.","date":"2020","source":"Biological & pharmaceutical bulletin","url":"https://pubmed.ncbi.nlm.nih.gov/32238717","citation_count":3,"is_preprint":false},{"pmid":"24524607","id":"PMC_24524607","title":"[Myocardial Slit2/Robo4 expression and impact of exogenous Slit2 on proliferation and migration of cardiac microvascular endothelial cells].","date":"2013","source":"Zhonghua xin xue guan bing za zhi","url":"https://pubmed.ncbi.nlm.nih.gov/24524607","citation_count":3,"is_preprint":false},{"pmid":"33030140","id":"PMC_33030140","title":"Withdrawal Notice: Molecular Mechanism of TLR4 Mediated T Cell Immune Effect in Transfusion-induced Acute Lung Injury based on Slit2/Robo4 Signaling Pathway.","date":"2020","source":"Current molecular pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/33030140","citation_count":1,"is_preprint":false},{"pmid":"35740295","id":"PMC_35740295","title":"Binding and Efficacy of Anti-Robo4 CAR-T Cells against Solid Tumors.","date":"2022","source":"Biomedicines","url":"https://pubmed.ncbi.nlm.nih.gov/35740295","citation_count":1,"is_preprint":false},{"pmid":"39938427","id":"PMC_39938427","title":"Clinical and immunohistochemical effects of OncoTherad (MRB-CFI-1) nanoimmunotherapy on SERBP1, HABP4, CD44 and Ki-67 in BCG-unresponsive non-muscle invasive bladder cancer.","date":"2025","source":"Tissue & cell","url":"https://pubmed.ncbi.nlm.nih.gov/39938427","citation_count":1,"is_preprint":false},{"pmid":"39693910","id":"PMC_39693910","title":"A novel serous ovarian carcinoma model induced by DMBA: Results from OncoTherad® (MRB-CFI-1) immunotherapy preclinical testing.","date":"2024","source":"Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie","url":"https://pubmed.ncbi.nlm.nih.gov/39693910","citation_count":1,"is_preprint":false},{"pmid":"40778968","id":"PMC_40778968","title":"Robo4 inhibits neovascularization in oxygen-induced retinopathy by regulating ARF6 and VEGF.","date":"2025","source":"Human cell","url":"https://pubmed.ncbi.nlm.nih.gov/40778968","citation_count":0,"is_preprint":false},{"pmid":"41639767","id":"PMC_41639767","title":"Leveraging in-silico deep learning and computational analyses to predict the pathogenicity of ROBO4 variants of uncertain significance in aortic aneurysm and dissection patients.","date":"2026","source":"BMC cardiovascular disorders","url":"https://pubmed.ncbi.nlm.nih.gov/41639767","citation_count":0,"is_preprint":false},{"pmid":"35993202","id":"PMC_35993202","title":"[The destructive role of soluble Robo4 secreted by the M1-polarized-microglia during cerebral ischemia-reperfusion in blood-brain barrier integrity].","date":"2022","source":"Sheng li xue bao : [Acta physiologica Sinica]","url":"https://pubmed.ncbi.nlm.nih.gov/35993202","citation_count":0,"is_preprint":false},{"pmid":"39181524","id":"PMC_39181524","title":"A great diversity of ROBO4 expression and regulations identified by data mining and transgene mice.","date":"2024","source":"Gene expression patterns : GEP","url":"https://pubmed.ncbi.nlm.nih.gov/39181524","citation_count":0,"is_preprint":false},{"pmid":"41613935","id":"PMC_41613935","title":"Congenital Coarctation of the Aorta in a Patient With ROBO4 c.695C>T (p.Thr232Met) Germline Variant.","date":"2026","source":"Annals of internal medicine. Clinical cases","url":"https://pubmed.ncbi.nlm.nih.gov/41613935","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.08.28.672833","title":"Towards active vaccination against tumour endothelial marker Robo4","date":"2025-09-02","source":"bioRxiv","url":"https://doi.org/10.1101/2025.08.28.672833","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":47976,"output_tokens":7588,"usd":0.128874},"stage2":{"model":"claude-opus-4-6","input_tokens":11302,"output_tokens":4293,"usd":0.245753},"total_usd":0.374627,"stage1_batch_id":"msgbatch_01SUR8NDzVrNmyszWyJeCct7","stage2_batch_id":"msgbatch_01G7Yfutko3cDWzejrwH5AMx","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2003,\n      \"finding\": \"Robo4 is an endothelial-specific Robo family member that binds Slit and inhibits endothelial cell migration; immunoprecipitation showed Robo4 binds the actin regulatory protein Mena, a known effector of Robo-Slit signaling.\",\n      \"method\": \"Heterologous expression migration assay, immunoprecipitation, Slit-binding assay\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (migration assay, binding, Co-IP) in foundational paper, >250 citations\",\n      \"pmids\": [\"12941633\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Slit2 activation of Robo4 inhibits VEGF-165-induced endothelial migration, tube formation, and vascular permeability in vitro, and pathologic angiogenesis/vascular leak in vivo, by blocking Src family kinase activation; Robo4 knockout mice show enhanced retinal and choroidal vascular disease.\",\n      \"method\": \"In vitro migration/permeability assays, Src kinase activity assay, Robo4 knockout mouse models of retinal and choroidal vascular disease\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro mechanistic assays plus in vivo KO phenotype, >300 citations, replicated\",\n      \"pmids\": [\"18345009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Robo4 interacts with WASP (Wiskott-Aldrich syndrome protein), N-WASP, and WASP-interacting protein actin-nucleating complex via its intracellular domain; Robo4 forms a heterodimeric complex with Robo1, and Robo4-induced filopodia formation requires Robo1, suggesting a Robo1/Robo4 heterodimer signals through actin nucleation-promoting factors to regulate endothelial migration.\",\n      \"method\": \"Yeast 2-hybrid, GST pulldown, siRNA knockdown, co-immunoprecipitation, GFP-Robo4 transfection imaging\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Y2H, pulldown, Co-IP, functional rescue), replicated in companion paper\",\n      \"pmids\": [\"18948384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Slit2-Robo4 signaling maintains vascular stability by directly interacting with intracellular adaptor protein paxillin (and its paralogue Hic-5) at the cell surface, which recruits the Arf-GAP GIT1 to block activation of the small GTPase Arf6 and subsequently Rac1, thereby suppressing cellular protrusive activity underlying neovascularization and vascular leak.\",\n      \"method\": \"Co-immunoprecipitation, biochemical fractionation, Arf6 activation assay, in vivo Arf6 inhibition in retinal vascular disease models\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — biochemical mechanism established with multiple methods (Co-IP, GTPase activity assays, in vivo phenocopy), >190 citations\",\n      \"pmids\": [\"19855388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Slit2 activation of endothelial Robo4 strengthens the vascular barrier and reduces vascular permeability in lung and other organs, increasing survival in mouse models of bacterial endotoxin exposure, polymicrobial sepsis, and H5N1 influenza by blunting the host vascular response to the cytokine storm.\",\n      \"method\": \"In vivo vascular permeability assays, mouse models of endotoxemia, sepsis, and influenza; Robo4-dependent pathway activation\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple in vivo disease models with defined Robo4-dependent mechanism, >280 citations\",\n      \"pmids\": [\"20375003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Robo4 maintains vessel integrity and inhibits VEGF signaling by binding directly to UNC5B (a vascular Netrin receptor) via its extracellular domain; soluble Robo4 inhibits VEGF-induced permeability in wild-type but not UNC5B-blocked mice, placing Robo4 upstream of UNC5B in suppressing VEGFR signaling.\",\n      \"method\": \"Protein-protein interaction screen with Robo4 extracellular domain, function-blocking monoclonal antibodies, Robo4-/- rescue experiments, vascular permeability assays\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — interaction screen plus genetic epistasis plus in vivo rescue, >170 citations\",\n      \"pmids\": [\"21238923\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Robo4 functions to anchor hematopoietic stem cells (HSCs) to bone marrow niches; Robo4-deficient HSCs show poor BM localization and reduced long-term reconstitution. Cxcr4 is upregulated in Robo4-/- HSCs to compensate, and combined inhibition of both Cxcr4 and Robo4 is required for efficient HSC mobilization.\",\n      \"method\": \"Robo4 knockout mice, transplantation assays, HSC localization/mobilization studies, flow cytometry, genetic epistasis (Cxcr4/Robo4 double manipulation)\",\n      \"journal\": \"Cell stem cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular phenotype, genetic epistasis, >100 citations\",\n      \"pmids\": [\"21211783\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Robo4 regulates radial migration of newborn neurons in developing neocortex; Robo4 knockdown by siRNA or Cre-mediated deletion causes severe defects in radial migration with neuronal misorientation, and sensitizes neurons to Slit repulsion, demonstrating Slit-dependent and -independent roles.\",\n      \"method\": \"In utero electroporation with siRNA/Cre, transwell migration assay, growth cone collapse assay, floxed Robo4 mice\",\n      \"journal\": \"Cerebral cortex\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean in vivo KD/KO with defined cellular phenotype and multiple assays\",\n      \"pmids\": [\"22123939\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Robo4 mediates attraction signaling in zebrafish vascular endothelial cells by activating Cdc42 and Rac1 Rho GTPases; robo4 knockdown in zebrafish results in reduced active Cdc42 and Rac1, with angioblasts showing impaired directional guidance.\",\n      \"method\": \"Gain-of-function Robo4 expression in endothelial cells, robo4 morpholino knockdown in zebrafish, Rho GTPase activity assays\",\n      \"journal\": \"Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — zebrafish ortholog study with GTPase activity assays, single lab\",\n      \"pmids\": [\"16481322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Endothelial Robo4 restricts VEGF-R2 signaling through Src and FAK kinases to limit blood vessel growth in the mammary gland; loss of Robo4 (but not Robo1) in endothelium combined with an angiogenic stimulus phenocopies loss of stromal Slit, resulting in elevated vessel density.\",\n      \"method\": \"Conditional Robo4 and Robo1 knockout mouse models, genetic epistasis, VEGFR2/Src/FAK signaling analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic dissection with conditional KO and defined signaling pathway, >60 citations\",\n      \"pmids\": [\"20498081\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Slit2-N/Robo4 signaling induces internalization of VEGFR-3 to block its activation, and inhibits PI3K/Akt pathway activation by VEGF-C in lymphatic endothelial cells, thereby suppressing lymphangiogenesis in a Robo4-dependent manner.\",\n      \"method\": \"siRNA Robo4 knockdown, VEGFR-3 internalization assay, PI3K/Akt activation assay, lymphatic endothelial cell migration/proliferation/tube formation assays\",\n      \"journal\": \"Cell communication and signaling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays with mechanistic pathway analysis, single lab\",\n      \"pmids\": [\"24708522\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Slit2/Robo4 signaling represses LPS-induced endothelial inflammation by inhibiting the Pyk2-NF-κB pathway downstream of LPS-TLR4; Robo4 is the dominant anti-inflammatory receptor while Robo1 is pro-inflammatory and is downregulated by Slit2 via miR-218.\",\n      \"method\": \"siRNA knockdown of Robo4/Robo1 in HUVECs, NF-κB/Pyk2 signaling analysis, cytokine/chemokine measurement, miR-218 analysis\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic pathway analysis with siRNA, single lab, multiple readouts\",\n      \"pmids\": [\"24272999\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The cytoplasmic domain of Robo4 is dispensable for vascular permeability and neovascularization; truncated Robo4 lacking the cytoplasmic domain (Robo4ΔCD) is sufficient to prevent permeability and inhibit OIR revascularization. Robo4 (and Robo4ΔCD) counteract VEGFR2-Y949 phosphorylation by signaling through the endothelial UNC5B receptor, independently of Slit2 signaling.\",\n      \"method\": \"Transgenic mice expressing cytoplasmic-domain-truncated Robo4, oxygen-induced retinopathy model, wound healing model, VEGFR2 phosphorylation analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — structure-function transgenic approach with defined molecular readout (VEGFR2-Y949 phosphorylation) and in vivo rescue\",\n      \"pmids\": [\"27882935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Annexin A2 (ANXA2) acts as a Robo4 ligand; recombinant ANXA2 reduces trans-endothelial permeability by modulating signaling via the Robo4-paxillin-ARF6 pathway in brain endothelial cells, reducing ARF6 activity and maintaining endothelial tightness.\",\n      \"method\": \"ANXA2 knockout mice, recombinant ANXA2 treatment, Robo4-paxillin-ARF6 signaling analysis, TEER and tracer leakage assays\",\n      \"journal\": \"Journal of cerebral blood flow and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse plus mechanistic pathway analysis, single lab\",\n      \"pmids\": [\"29786451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Robo4 forms a complex with TRAF7 (TNF receptor-associated factor 7, a ubiquitin E3 ligase) via the C-terminus of Robo4; this Robo4-TRAF7 complex suppresses TNFα-induced endothelial hyperpermeability by stabilizing VE-cadherin at cell junctions.\",\n      \"method\": \"Co-IP/binding assays, deletion assays mapping C-terminus interaction, TRAF7 gain/loss-of-function, VE-cadherin localization assay, Robo4-/- endotoxemia mouse model\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, domain mapping, functional rescue, in vivo validation\",\n      \"pmids\": [\"30510113\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ETV2 directly interacts with TET1 and TET2 methylcytosine-converting enzymes; ETV2-TET1/TET2 complexes demethylate the Robo4 proximal promoter to induce endothelial-specific Robo4 expression during differentiation from iPSCs to endothelial cells.\",\n      \"method\": \"Co-immunoprecipitation (ETV2-TET1/TET2 interaction), reporter assays, adenoviral ETV2-TET1/TET2 overexpression in non-ECs, bisulfite sequencing for promoter methylation\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus functional demethylation assay, single lab\",\n      \"pmids\": [\"29618782\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Soluble Robo4 extracellular domain (Robo4Fc) inhibits angiogenesis in vivo and endothelial migration/proliferation/tube formation in vitro; however, Slit1, Slit2, and Slit3 bind Robo1 but not Robo4 by immunoprecipitation and BiaCore analysis, suggesting Robo4 uses a different ligand mechanism.\",\n      \"method\": \"In vivo sponge angiogenesis model, rat aortic ring assay, VEGF/bFGF migration assay, immunoprecipitation, BiaCore binding analysis\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple in vitro/in vivo functional assays plus direct binding analysis, single lab\",\n      \"pmids\": [\"15486058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"ROBO4 signaling in endothelial cells suppresses breast cancer growth and metastasis by regulating tumor angiogenesis, endothelial leakage, and tight junction protein ZO-1 levels; pharmacological activation of ARF6 inhibition downstream of Robo4 (using SecinH3) mimics Robo4 activation and reduces tumor angiogenesis.\",\n      \"method\": \"Robo4 knockout immunocompetent mouse breast cancer model, tumor angiogenesis quantification, SecinH3 pharmacological treatment, ZO-1 expression analysis\",\n      \"journal\": \"Molecular oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO model with defined pathway (ARF6) and pharmacological rescue, single lab\",\n      \"pmids\": [\"26778715\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Vascular endothelial ROBO4 actively promotes HSC extravasation from blood into bone marrow (trans-endothelial migration), while simultaneously maintaining vascular barrier function to prevent BM-to-blood escape, thereby regulating directionality of HSC trafficking.\",\n      \"method\": \"ROBO4 knockout mice, induced vascular permeability experiments, HSC tracking/engraftment assays\",\n      \"journal\": \"Stem cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined directional trafficking phenotype, single lab\",\n      \"pmids\": [\"25640759\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Robo4 knockdown in retinal endothelial cells increases permeability, reduces tight junction proteins ZO-1 and occludin, causes F-actin rearrangement, and activates the LIMK/cofilin pathway, revealing a signaling cascade mediating barrier function.\",\n      \"method\": \"siRNA knockdown, RITC-dextran permeability assay, Western blotting for TJ proteins and LIMK/cofilin, immunofluorescence for F-actin\",\n      \"journal\": \"Current eye research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA KD with multiple mechanistic readouts, single lab\",\n      \"pmids\": [\"23163536\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Soluble Robo4 is generated by constitutive ectodomain shedding by ADAM10 and ADAM17 (disintegrin metalloproteinases); Slit3 induces cell-surface Robo4 endocytosis, thereby shielding Robo4 from shedding by ADAMs and enhancing Robo4 signaling. Shed soluble Robo4 inhibits Slit3-induced angiogenesis.\",\n      \"method\": \"ADAM10/ADAM17 inhibitor and siRNA studies, Robo4 shedding assays, endocytosis assays with Slit3 treatment, angiogenesis functional assays\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — identification of sheddases with siRNA validation and functional consequence, single lab\",\n      \"pmids\": [\"35288626\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ALK5-SMAD2/3 and ALK1-SMAD1/5 signaling pathways positively and negatively regulate Robo4 expression, respectively; endothelial-specific Robo4 overexpression suppresses vascular permeability and reduces mortality in LPS-treated and SARS-CoV-2-infected mice.\",\n      \"method\": \"ALK1 inhibitor screening, SMAD pathway analysis, endothelial-specific Robo4 transgenic overexpression mice, LPS endotoxemia and SARS-CoV-2 infection models, vascular permeability assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal approaches (inhibitor screening, transgenic overexpression, in vivo disease models), single lab with strong methods\",\n      \"pmids\": [\"36634143\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ROBO4 interacts with IQGAP1 and TRAF7; in this complex, ROBO4 enhances IQGAP1 ubiquitination through the E3 ligase TRAF7, inhibits prolonged RAC1 activation, and decreases PTGS2/COX-2 expression in inflammatory endothelial cells, thereby suppressing prostaglandin-mediated vascular inflammation.\",\n      \"method\": \"RNA-seq, Co-IP (ROBO4-IQGAP1-TRAF7 complex), ubiquitination assay, RAC1 activation assay, Robo4-/- mouse models of arthritis/edema/pain\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP for complex identification, ubiquitination assay, RAC1 activity assay, in vivo KO phenotype\",\n      \"pmids\": [\"38762541\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"USP5 stabilizes ROBO4 protein through deubiquitination; USP5 overexpression increases ROBO4 levels and aggravates high-glucose-induced retinal pigment epithelial cell damage, while USP5 knockdown decreases ROBO4 and mitigates this damage.\",\n      \"method\": \"Co-immunoprecipitation, deubiquitination assay, USP5 and ROBO4 overexpression/knockdown, cell damage assays in high-glucose conditions\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP and direct deubiquitination assay, single lab\",\n      \"pmids\": [\"38735506\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Recombinant Slit2 reduces surgical brain injury-induced BBB disruption via Robo4 and paxillin; Robo4 and paxillin siRNA knockdown reverses Slit2-mediated Rac1 activation, placing Robo4 upstream of a paxillin-Rac1 signaling axis in BBB protection.\",\n      \"method\": \"Robo4 and paxillin siRNA knockdown, Rac1 activity assay, recombinant Slit2 treatment, BBB permeability assays in SBI rat model\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA epistasis with pathway activity assay and in vivo model, single lab\",\n      \"pmids\": [\"28389649\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ROBO4 variants (missense and rare) segregate with bicuspid aortic valve and thoracic aortic aneurysm; silencing ROBO4 or expressing mutant ROBO4 in endothelial cell lines impairs barrier function and induces a gene expression repertoire consistent with endothelial-to-mesenchymal transition.\",\n      \"method\": \"Targeted sequencing in families, siRNA knockdown and mutant ROBO4 expression in endothelial lines, barrier function assays, EMT gene expression profiling\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — human genetics plus in vitro functional validation, single study\",\n      \"pmids\": [\"30455415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Robo4 deletion in mice ameliorates platelet-activating factor (PAF)-mediated skin inflammation by reducing LPCAT1/LPCAT2 mRNA translation efficiency (via reduced ribosome and ATP levels), decreasing PAF receptor expression in macrophages, and suppressing LPS-induced IL-6 and p44/42/p65 phosphorylation while enhancing AKT phosphorylation.\",\n      \"method\": \"Robo4 KO mouse model, polyribosome assay for LPCAT1/LPCAT2 mRNA, HPLC for ATP, Western blot for signaling proteins, immunohistochemistry\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse with polyribosome assay and multiple signaling readouts, single lab\",\n      \"pmids\": [\"32140075\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Robo4 depletion in bone marrow endothelial cells promotes endothelial-to-mesenchymal transition (EndMT) by increasing endoglin (CD105) expression and activating both canonical (Smad) and non-canonical (AKT/NF-κB) TGF-β signaling, leading to Snail1 nuclear translocation; Robo4 overexpression stimulates ICAM-1 and VCAM-1 expression and suppresses EndMT and irradiation-induced permeability.\",\n      \"method\": \"Lentiviral RNAi and overexpression in endothelial cells, γ-radiation injury model, Western blot for Smad/AKT/NF-κB/Snail1, co-culture with HSPCs\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gene manipulation with defined signaling pathway readouts, single lab\",\n      \"pmids\": [\"38383474\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"HDAC3 (but not HDAC1 or HDAC2) maintains Robo4 expression in endothelial cells by sustaining GABP transcription factor expression; HDAC3-specific siRNA knockdown or the HDAC inhibitor MS-275 reduces GABP and Robo4 promoter activity, increases endothelial permeability, and enhances vascular leakage in mouse lungs.\",\n      \"method\": \"HDAC isoform-specific siRNA, HDAC inhibitor MS-275, Robo4 promoter reporter assay, TEER assay, Evans blue leakage in vivo\",\n      \"journal\": \"Tissue barriers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistatic siRNA dissection with promoter assay and in vivo phenotype, single lab\",\n      \"pmids\": [\"33955828\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Acute endothelial-specific deletion of Robo4 impairs HSC distribution between bone marrow and blood, perturbs long-term donor HSC engraftment, and improves HSC mobilization, independently of VCAM1 expression on sinusoidal vascular endothelial cells.\",\n      \"method\": \"Conditional Robo4 deletion mouse models, HSC trafficking/engraftment assays, VCAM1 protein level analysis on sinusoidal VECs\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with defined cellular phenotype, genetic epistasis with VCAM1, single lab\",\n      \"pmids\": [\"34388149\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SLIT3 secreted by pericytic mesenchymal stem cells guides vascular network formation via ROBO4-positive endothelial cells; siRNA knockdown of SLIT3 in MSCs leads to disorganized EC clustering, and ROBO4 knockdown in ECs abolishes functional human blood vessel generation in vivo in a xenograft model.\",\n      \"method\": \"siRNA knockdown of SLIT3 (in MSCs) and ROBO4 (in ECs), 3D vascular network live imaging, in vivo xenogenic implant model\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA KD with in vitro and in vivo functional assays, single lab\",\n      \"pmids\": [\"24090675\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ROBO4 is an endothelial cell-specific transmembrane receptor that maintains vascular integrity and suppresses pathologic angiogenesis primarily by (1) forming a complex with paxillin/Hic-5 and recruiting the Arf-GAP GIT1 to block Arf6 and Rac1 activation downstream of Slit2, thereby suppressing cellular protrusive activity; (2) signaling through UNC5B to counteract VEGFR2-Y949 phosphorylation independently of its cytoplasmic domain; (3) interacting with TRAF7 and IQGAP1 to enhance IQGAP1 ubiquitination, suppress RAC1 and NF-κB/COX-2 inflammatory signaling, and stabilize VE-cadherin at endothelial junctions; and (4) forming heterodimers with Robo1 to signal through WASP-family actin nucleators for filopodia formation and cell migration, while also cooperating with CXCR4 to anchor hematopoietic stem cells to bone marrow niches.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ROBO4 is an endothelial cell-specific transmembrane receptor that functions as a master regulator of vascular integrity, suppressing pathological angiogenesis, vascular permeability, and endothelial inflammation. ROBO4 maintains barrier function through multiple convergent mechanisms: it recruits paxillin/Hic-5 and the Arf-GAP GIT1 to block Arf6 and Rac1 activation, thereby suppressing protrusive activity [PMID:19855388]; it signals through the Netrin receptor UNC5B to counteract VEGFR2-Y949 phosphorylation independently of its own cytoplasmic domain [PMID:27882935, PMID:21238923]; and it forms a complex with TRAF7 to promote IQGAP1 ubiquitination, dampening RAC1 and NF-κB/COX-2 inflammatory signaling while stabilizing VE-cadherin at endothelial junctions [PMID:30510113, PMID:38762541]. Beyond its vascular roles, ROBO4 anchors hematopoietic stem cells to bone marrow niches cooperatively with CXCR4 [PMID:21211783], and loss-of-function ROBO4 variants segregate with bicuspid aortic valve and thoracic aortic aneurysm in human families [PMID:30455415].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Identification of ROBO4 as an endothelial-specific Robo family member that binds Slit and inhibits endothelial migration established it as a candidate vascular guidance receptor, answering whether Robo-Slit signaling operates in endothelium.\",\n      \"evidence\": \"Heterologous expression migration assays, Slit-binding assays, and co-immunoprecipitation with actin regulator Mena in endothelial cells\",\n      \"pmids\": [\"12941633\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Slit is the physiological ligand for Robo4 remained disputed\", \"Downstream signaling cascade uncharacterized\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Functional evidence that soluble Robo4 ectodomain inhibits angiogenesis in vivo, coupled with failure to detect Slit1-3 binding to Robo4 by BiaCore, raised the question of whether Robo4 uses an alternative ligand.\",\n      \"evidence\": \"In vivo sponge angiogenesis model, rat aortic ring assay, BiaCore direct binding analysis\",\n      \"pmids\": [\"15486058\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the Robo4 extracellular ligand unresolved\", \"Single lab observation of no Slit binding contradicted other reports\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstration that zebrafish Robo4 activates Cdc42 and Rac1 for angioblast guidance revealed that Robo4 can act as a pro-migratory signal, contrasting with its anti-migratory role described in mammalian cells.\",\n      \"evidence\": \"Morpholino knockdown in zebrafish, Rho GTPase pull-down assays\",\n      \"pmids\": [\"16481322\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Context-dependent vs. species-dependent signaling not resolved\", \"Mammalian Robo4 GTPase regulation appeared opposite\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Two key advances defined Robo4's signaling outputs: Slit2-Robo4 blocks VEGF-induced migration and permeability by suppressing Src kinase (with Robo4 KO mice showing vascular disease), while Robo4 heterodimerizes with Robo1 and signals through WASP/N-WASP actin nucleators for filopodia formation.\",\n      \"evidence\": \"Robo4 knockout mouse retinal/choroidal disease models, Src kinase assays, yeast two-hybrid/GST pulldown for WASP interaction, siRNA epistasis for Robo1 requirement\",\n      \"pmids\": [\"18345009\", \"18948384\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Src suppression and WASP activation are coordinated was unclear\", \"Whether Robo1-Robo4 heterodimer forms in vivo remained unresolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"The core intracellular mechanism was elucidated: Robo4 binds paxillin/Hic-5 to recruit Arf-GAP GIT1, inactivating Arf6 and consequently Rac1, explaining how Slit2-Robo4 suppresses protrusive activity and neovascularization.\",\n      \"evidence\": \"Co-immunoprecipitation, Arf6 activation assays, in vivo retinal vascular disease phenocopy by Arf6 inhibition\",\n      \"pmids\": [\"19855388\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether paxillin-GIT1 pathway accounts for all Robo4 barrier function or operates alongside other pathways\", \"No structural data for Robo4-paxillin interaction\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Translational significance was established when Slit2-Robo4 vascular barrier strengthening increased survival in sepsis and influenza models, while genetic dissection showed endothelial Robo4 (not Robo1) restricts VEGFR2/Src/FAK signaling to limit vessel growth.\",\n      \"evidence\": \"Mouse sepsis/endotoxemia/influenza survival models, conditional Robo4 vs Robo1 KO mammary gland angiogenesis\",\n      \"pmids\": [\"20375003\", \"20498081\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Therapeutic window for Slit2 administration undefined\", \"Relative contributions of Src suppression vs Arf6 suppression not separated\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"The extracellular signaling partner UNC5B was identified, showing Robo4 maintains vascular integrity by binding UNC5B to inhibit VEGF signaling, while a parallel discovery revealed Robo4 anchors HSCs to bone marrow niches cooperatively with CXCR4.\",\n      \"evidence\": \"Robo4 extracellular domain interaction screen, UNC5B function-blocking antibodies, Robo4-/- HSC transplantation and mobilization assays with Cxcr4 epistasis\",\n      \"pmids\": [\"21238923\", \"21211783\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How UNC5B relays the Robo4 signal to VEGFR2 mechanistically\", \"Whether HSC-intrinsic or endothelial Robo4 dominates niche anchoring\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Robo4 knockdown in retinal endothelial cells revealed dependence of tight junction protein levels (ZO-1, occludin) and actin organization on Robo4 via a LIMK/cofilin pathway, extending barrier signaling beyond Rac1/Arf6.\",\n      \"evidence\": \"siRNA knockdown, RITC-dextran permeability, Western blot for tight junction and LIMK/cofilin proteins\",\n      \"pmids\": [\"23163536\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether LIMK/cofilin acts downstream of Arf6 or independently not resolved\", \"Replicated in one cell type only\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Robo4 was shown to suppress lymphangiogenesis by inducing VEGFR-3 internalization, and to repress endothelial inflammation via Pyk2-NF-κB inhibition, while SLIT3 from pericytes was identified as a guidance cue acting through endothelial ROBO4 for vascular network assembly.\",\n      \"evidence\": \"VEGFR-3 internalization and PI3K/Akt assays, NF-κB/Pyk2 signaling analysis with siRNA, in vivo xenograft vascular formation\",\n      \"pmids\": [\"24708522\", \"24272999\", \"24090675\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether VEGFR-3 internalization and Pyk2 suppression share upstream mechanism\", \"SLIT3 vs SLIT2 selectivity for ROBO4 not settled\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"A decisive structure-function experiment showed the Robo4 cytoplasmic domain is dispensable: truncated Robo4 lacking its intracellular region fully rescues permeability and neovascularization defects, signaling instead through UNC5B to block VEGFR2-Y949 phosphorylation.\",\n      \"evidence\": \"Transgenic Robo4ΔCD mice, oxygen-induced retinopathy model, VEGFR2-Y949 phosphorylation analysis\",\n      \"pmids\": [\"27882935\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How paxillin-Arf6 intracellular signaling reconciles with cytoplasmic-domain dispensability\", \"Whether all Robo4 functions (e.g., HSC anchoring, inflammation) are also cytoplasmic-domain-independent\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Annexin A2 was identified as an additional Robo4 ligand engaging the paxillin-ARF6 pathway at the blood-brain barrier, ROBO4 variants were linked to bicuspid aortic valve/aortic aneurysm in human families with functional validation, and ETV2-TET1/TET2 complexes were shown to demethylate the Robo4 promoter for endothelial-specific expression.\",\n      \"evidence\": \"ANXA2 KO mice with Robo4-ARF6 signaling analysis; targeted sequencing in families plus endothelial barrier assays with mutant ROBO4; bisulfite sequencing with ETV2-TET1/2 co-IP\",\n      \"pmids\": [\"29786451\", \"30455415\", \"29618782\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"ANXA2-Robo4 binding interface not mapped\", \"Penetrance and mechanism of ROBO4 variants in aortic disease require larger cohorts\", \"Whether ETV2-TET pathway is the sole driver of Robo4 endothelial specificity\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"TRAF7 was identified as a Robo4 cytoplasmic binding partner that stabilizes VE-cadherin at junctions, establishing a TRAF7-dependent branch of Robo4 barrier signaling distinct from the paxillin-Arf6 axis.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, domain mapping, TRAF7 gain/loss-of-function, VE-cadherin localization, Robo4-/- endotoxemia model\",\n      \"pmids\": [\"30510113\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TRAF7 E3 ligase activity is required for VE-cadherin stabilization was answered later but not in this study\", \"Relationship between TRAF7 and UNC5B pathways unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The mechanism controlling Robo4 surface levels was identified: ADAM10/ADAM17 constitutively shed the Robo4 ectodomain, while Slit3 induces Robo4 endocytosis to protect it from shedding, providing a feedback mechanism that enhances signaling.\",\n      \"evidence\": \"ADAM10/17 inhibitor and siRNA, Robo4 shedding quantification, Slit3-induced endocytosis assays\",\n      \"pmids\": [\"35288626\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether ADAM shedding regulates Robo4 in vivo not tested\", \"Whether soluble Robo4 acts as a true decoy receptor in physiological conditions\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Transcriptional regulation of Robo4 was further defined: ALK5-SMAD2/3 positively and ALK1-SMAD1/5 negatively control Robo4 expression, and endothelial-specific Robo4 overexpression reduced mortality in endotoxemia and SARS-CoV-2 infection models.\",\n      \"evidence\": \"ALK1 inhibitor screening, SMAD pathway analysis, endothelial-specific Robo4 transgenic mice, LPS and SARS-CoV-2 models\",\n      \"pmids\": [\"36634143\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TGF-β pathway regulation of Robo4 is direct or indirect through GABP/HDAC3\", \"Long-term effects of Robo4 overexpression on normal vasculature\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"The ROBO4-TRAF7-IQGAP1 complex was defined: TRAF7 ubiquitinates IQGAP1 in a ROBO4-dependent manner to suppress prolonged RAC1 activation and NF-κB/COX-2 inflammatory signaling, while separately USP5 was identified as a deubiquitinase that stabilizes ROBO4 protein.\",\n      \"evidence\": \"Co-IP for trimeric complex, IQGAP1 ubiquitination assay, RAC1 activity assay, Robo4-/- arthritis/edema models; USP5-ROBO4 deubiquitination assay\",\n      \"pmids\": [\"38762541\", \"38735506\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether USP5 regulation of ROBO4 stability is relevant in vascular endothelium in vivo\", \"Structural basis for TRAF7-mediated IQGAP1 ubiquitination unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major unresolved questions include how the cytoplasmic-domain-dispensable UNC5B pathway reconciles with documented intracellular signaling through paxillin-GIT1 and TRAF7-IQGAP1, whether distinct ligands (Slit2, Slit3, ANXA2) activate distinct downstream branches, and the structural basis for ROBO4-UNC5B interaction.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model for any Robo4 complex\", \"Context-dependent pro- vs anti-migratory signaling not mechanistically reconciled\", \"Relative physiological importance of Slit2, Slit3, and ANXA2 as Robo4 ligands unclear\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 3, 5, 9, 12, 22]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 3, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 3, 5, 12, 14, 20]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 3, 5, 8, 9, 12, 22]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [7, 8, 30]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 11, 22, 26]}\n    ],\n    \"complexes\": [\n      \"Robo4-paxillin/Hic-5-GIT1\",\n      \"Robo4-TRAF7-IQGAP1\",\n      \"Robo1-Robo4 heterodimer\",\n      \"Robo4-UNC5B\"\n    ],\n    \"partners\": [\n      \"UNC5B\",\n      \"TRAF7\",\n      \"IQGAP1\",\n      \"PXN\",\n      \"GIT1\",\n      \"ROBO1\",\n      \"MENA\",\n      \"WAS\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}