{"gene":"MGAT5","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":2001,"finding":"MGAT5 initiates GlcNAc β1,6 branching on N-glycans, increasing N-acetyllactosamine that serves as ligand for galectins; galectin-3 was shown to associate with the TCR complex at the cell surface in an MGAT5-dependent manner, forming a galectin-glycoprotein lattice that restricts TCR recruitment to the site of antigen presentation and raises the T-cell activation threshold. Lactose competition for galectin binding phenocopied Mgat5-/- TCR clustering. Mgat5-deficient mice showed enhanced TCR clustering, actin microfilament re-organization, and downstream signaling.","method":"Mgat5 knockout mice, lactose competition assay, co-immunoprecipitation of galectin-3 with TCR complex, TCR clustering assay with agonist-coated beads, proliferation assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal functional assays, genetic KO model, galectin-TCR co-IP, chemical competition experiment, multiple orthogonal methods in a single rigorous study","pmids":["11217864"],"is_preprint":false},{"year":2000,"finding":"MGAT5-produced β1,6GlcNAc-branched N-glycans stimulate membrane ruffling and PI3K-PKB (Akt) activation, fueling a positive feedback loop that amplifies oncogene signaling. Loss of Mgat5 in mice markedly reduced mammary tumor growth and metastasis driven by the polyomavirus middle T oncogene, demonstrating that tumor progression depends on Mgat5 glycan-mediated focal adhesion signaling.","method":"Mgat5 knockout mice crossed with polyomavirus middle T oncogene transgenics; in vivo tumor growth and metastasis assays; PI3K-PKB signaling assays; membrane ruffling assays","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO in vivo tumor model, signaling biochemistry, multiple phenotypic readouts, replicated across labs","pmids":["10700233"],"is_preprint":false},{"year":2006,"finding":"Galectin-3 binding to Mgat5-modified β1,6GlcNAc N-glycans on fibronectin receptors regulates fibronectin fibrillogenesis and tumor cell motility. At optimal doses, exogenous galectin-3 activates FAK and PI3K, recruits conformationally active α5β1-integrin to fibrillar adhesions, and increases F-actin turnover. These effects are dependent on galectin-glycan binding and are absent in Mgat5-/- cells.","method":"Mgat5-/- mammary tumor cells, exogenous galectin-3 rescue, swainsonine inhibition, RGD peptide inhibition, anti-galectin-3 domain antibodies, FAK/PI3K biochemical assays, α5β1-integrin localization","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic KO cells, chemical inhibitors, antibody perturbation, multiple signaling readouts, single lab with multiple orthogonal methods","pmids":["16581792"],"is_preprint":false},{"year":2004,"finding":"β1,6GlcNAc N-glycans produced by Mgat5 on the TCR negatively regulate TCR signaling to promote Th2 over Th1 differentiation. Mgat5-/- T cells and swainsonine-treated T cells produce more IFN-γ and less IL-4; swainsonine had no additional effect in Mgat5-/- cells, confirming specificity. Mgat5 deficiency caused ~10-fold increase in IFN-γ production by polarized Th2 cells.","method":"Mgat5 knockout mice, swainsonine (Golgi α-mannosidase II inhibitor), cytokine ELISA, T-cell polarization assays","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO confirmed with chemical inhibitor showing no additive effect, multiple cytokine readouts, replicated in human and mouse T cells","pmids":["15585841"],"is_preprint":false},{"year":2002,"finding":"A secreted form of GnT-V promotes angiogenesis in vitro and in vivo independently of its glycosyltransferase activity. The highly basic domain of secreted GnT-V induces release of FGF-2 from heparan sulfate proteoglycans on the cell surface/extracellular matrix.","method":"In vitro angiogenesis assays, in vivo angiogenesis assays, addition of purified secreted GnT-V protein, domain analysis with basic domain","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and in vivo functional assays with purified protein, domain mapping, single lab","pmids":["11872751"],"is_preprint":false},{"year":2006,"finding":"Golgi-resident GnT-V is cleaved at its transmembrane region by γ-secretase (containing presenilin-1) to generate a soluble secreted form (~100 kDa) starting at His31. The cleavage was specifically inhibited by γ-secretase inhibitor DFK-167 and was completely abolished in presenilin-1/2 double-deficient cells. Overexpression of FAD-linked presenilin-1 increased GnT-V secretion rate.","method":"N-terminal protein sequencing of purified soluble GnT-V, γ-secretase inhibitor DFK-167, presenilin-1/2 double-knockout cells, presenilin-1 overexpression, site-directed mutagenesis of cleavage site","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — N-terminal sequencing of purified protein, genetic KO of protease, chemical inhibitor, mutagenesis; single lab but multiple orthogonal approaches","pmids":["17142794"],"is_preprint":false},{"year":1999,"finding":"Transcription factor Ets-1 regulates expression of the GnT-V (MGAT5) gene. GnT-V mRNA levels correlated with Ets-1 expression across 16 cancer cell lines (r=0.97). Transfection of Ets-1 cDNA enhanced GnT-V expression in low-Ets-1 cells; dominant-negative Ets-1 reduced GnT-V expression in high-Ets-1 cells.","method":"mRNA correlation across cell lines, Ets-1 cDNA transfection, dominant-negative Ets-1 transfection","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — gain-of-function and dominant-negative approaches, correlative data across 16 cell lines, single lab","pmids":["10438459"],"is_preprint":false},{"year":2007,"finding":"Mgat5 and Pten interact functionally in opposing directions to regulate PI3K/Akt signaling, cell spreading, and proliferation. Pten heterozygosity enhances cell adhesion-dependent PI3K/Akt signaling and is associated with increased surface β1,6GlcNAc-branched N-glycans; Mgat5/Pten double-mutant cells normalize these effects, indicating positive feedback from PI3K signaling to N-glycan branching.","method":"Mgat5/Pten double-mutant mouse embryonic fibroblasts, PI3K/Akt signaling assays, cell spreading and proliferation assays, flow cytometric lectin binding for N-glycan quantification, in vivo longevity analysis","journal":"Glycobiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — double-mutant genetic epistasis, biochemical signaling assays, in vivo survival data; single lab","pmids":["17400585"],"is_preprint":false},{"year":2009,"finding":"GnT-V (MGAT5) and its paralog GnT-Vb have distinct catalytic properties: GnT-V is active without exogenous cations and inhibited by EDTA, has a pH optimum of 6.5–7.0, and shows poor activity toward O-mannose-linked glycopeptides. Both enzymes transfer GlcNAcβ1,6 to Man residues of N-glycan substrates, but GnT-Vb shows ~2.5-fold higher Km for the biantennary N-glycan acceptor and much higher activity toward O-mannose glycopeptides.","method":"In vitro enzyme kinetics assays with purified truncated enzymes, synthetic trisaccharide and glycopeptide acceptors, HPLC product analysis","journal":"Glycobiology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with purified enzymes, kinetic characterization with multiple substrates, single lab with rigorous biochemistry","pmids":["19846580"],"is_preprint":false},{"year":2012,"finding":"In vivo, GnT-V (MGAT5) is responsible for synthesizing N-linked β1,6-branched glycans; GnT-V null brains lacked N-linked β1,6-glycans but had normal O-mannose β1,6-branched structures, showing GnT-Vb cannot compensate for GnT-V loss for N-glycan branching. Double knockout of GnT-V and GnT-Vb eliminated both N-linked and O-mannose β1,6-branched glycans in brain.","method":"GnT-V knockout mice, GnT-Vb knockout mice, GnT-V/GnT-Vb double knockout mice, glycan structural analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple genetic KO models, direct glycan structural analysis, defines in vivo substrate selectivity","pmids":["22715095"],"is_preprint":false},{"year":2011,"finding":"Mgat5 N-glycan branching regulates CTLA-4 endocytosis; deficiency promotes T-cell hyperactivity. Adoptive transfer of myelin-reactive Mgat5-/- T cells into Mgat5+/+ versus Mgat5-/- recipients caused more severe EAE in Mgat5-/- recipients, indicating that Mgat5 branching deficiency in recipient naive T cells and/or non-T cells also contributes to autoimmune disease pathogenesis.","method":"Mgat5 knockout mice, adoptive T-cell transfer, EAE model of autoimmune encephalomyelitis","journal":"ISRN neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO, adoptive transfer epistasis experiment, EAE disease readout; single lab","pmids":["22389815"],"is_preprint":false},{"year":2013,"finding":"RUNX2 transcription factor directly binds to the MGAT5 promoter and activates MGAT5 transcription in gastric cancer cells, as confirmed by ChIP-PCR. RUNX2 silencing reduced MGAT5 expression and suppressed tumor proliferation, invasion, migration, and metastasis in vivo.","method":"ChIP-PCR, JASPAR promoter binding prediction, RUNX2 siRNA knockdown, qRT-PCR, Western blot, in vivo xenograft","journal":"Frontiers in oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct ChIP evidence for promoter binding, functional KD phenotype; single lab","pmids":["37256183"],"is_preprint":false},{"year":2018,"finding":"GnT-V modifies human equilibrative nucleoside transporter 1 (hENT1) with β1,6-GlcNAc branched N-glycans; silencing GnT-V dramatically decreased β1,6-GlcNAc structure on hENT1, reduced hENT1 accumulation at the plasma membrane, and decreased gemcitabine uptake and chemosensitivity in bladder cancer cells.","method":"GnT-V shRNA knockdown, lectin blot for β1,6-GlcNAc on hENT1, cell surface fractionation, gemcitabine uptake assay, cell viability assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — loss-of-function with defined substrate glycosylation and functional readout (transporter localization and drug uptake); single lab","pmids":["30143259"],"is_preprint":false},{"year":2021,"finding":"IGF2BP1 binds to MGAT5 mRNA through m6A modification and stabilizes it, promoting MGAT5 expression and liver cancer stem cell phenotypes (self-renewal, chemoresistance). MeRIP-qPCR confirmed direct IGF2BP1 binding to MGAT5 mRNA via m6A.","method":"IGF2BP1 shRNA knockdown, MeRIP-qPCR, mRNA stability assay (qRT-PCR), cancer stem cell phenotype assays, in vivo tumorigenesis","journal":"Stem cells and development","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — MeRIP-qPCR for direct m6A binding, mRNA stability measurement, functional rescue; single lab","pmids":["34514861"],"is_preprint":false},{"year":2022,"finding":"GnT-V (MGAT5) is selectively enriched in small extracellular vesicles (sEVs) among glycosyltransferases. GnT-V in sEVs exists as a cleaved form, and cleavage by SPPL3 protease is required for its loading into sEVs. Enzymatically active GnT-V in sEVs transfers to recipient cells and remodels their N-glycan structures to express GnT-V-produced glycans.","method":"Fractionation of sEV subtypes, single-particle imaging, SPPL3 protease involvement (knockdown), enzyme activity assays in sEVs, N-glycan profiling of recipient cells","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — fractionation, single-particle imaging, enzyme activity assays, glycan profiling; single lab with multiple complementary methods","pmids":["36590176"],"is_preprint":false},{"year":2022,"finding":"Structure-based design identified UDP-GlcNAc analogs with increased hydrophobicity (phosphate group replacement) as selective inhibitors of GnT-V activity. GnT-V is relatively tolerant of donor substrate hydrophobicity compared with other GlcNAc transferases (GnT-I–IV), suggesting unique catalytic pocket properties.","method":"In vitro HPLC-based enzyme assay with purified truncated GnT-V and other GlcNAc transferases, synthetic UDP-GlcNAc analog compounds, docking models","journal":"Biochimica et biophysica acta. General subjects","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro enzyme inhibition assay with purified enzyme, structure-based docking, single lab","pmids":["35248671"],"is_preprint":false},{"year":2023,"finding":"Molecular dynamics simulations and biochemical experiments revealed that residues outside the catalytic pocket of GnT-V are involved in recognition of the core part of the N-glycan acceptor. UDP binding was found to affect the orientation of the acceptor substrate via conformational change at the Manα1,6-Man linkage.","method":"Molecular dynamics simulation, biochemical mutagenesis and enzyme activity assays","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — computational simulation supported by biochemical experiments; single lab","pmids":["37974463"],"is_preprint":false},{"year":2021,"finding":"MGAT5-catalyzed N-glycan branching is a critical regulator of stiffness-dependent invasion in glioblastoma stem-like cells (GSCs). CRISPR-Cas9 deletion of MGAT5 in GSCs suppressed β1,6-branched N-glycan expression, abolished stiffness-dependent migration at 166 kPa, and reduced focal adhesion and EMT protein expression, linking MGAT5 N-glycosylation to mechanosensing via the galectin-3/integrin axis.","method":"CRISPR-Cas9 MGAT5 knockout, 3D nanofiber scaffold with adjustable stiffness, cell migration assay, focal adhesion protein expression, galectin-3 lectin binding","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with CRISPR, defined mechanical substrate, functional and molecular readouts; single lab","pmids":["33894774"],"is_preprint":false},{"year":2024,"finding":"Mgat5-deficient pancreatic ductal adenocarcinoma cells show increased sensitivity to TNF superfamily-mediated cell death pathways, and Mgat5 loss leads to tumor clearance that is dependent on T cells and dendritic cells (with early NK cell involvement) in vivo. Mgat5 knockout in an immunotherapy-resistant PDAC line significantly decreased tumor growth and increased survival upon immune checkpoint blockade.","method":"Mgat5 knockout clonal PDAC cell lines, in vivo syngeneic tumor models, T-cell/NK-cell depletion experiments, TNF superfamily cell death pathway analysis, immune checkpoint blockade treatment","journal":"JCI insight","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO in multiple cell lines, in vivo immune depletion epistasis, mechanistic cell death pathway analysis; single lab","pmids":["38912584"],"is_preprint":false},{"year":2023,"finding":"Loss of MGAT5 in neural stem/progenitor cells (NSPCs) shifts differentiation toward neurons and away from astrocytes in vitro, and causes accelerated neuronal differentiation and depletion of the NSPC niche in vivo, resulting in a shift in cortical neuron layers in Mgat5 null mice.","method":"Mgat5 null mice, in vitro NSPC differentiation assays, in vivo cortical layering analysis","journal":"Stem cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with in vitro and in vivo differentiation phenotypes; single lab","pmids":["37172586"],"is_preprint":false},{"year":2024,"finding":"GnT-V catalyzes β1,6-GlcNAc branching at N121 and N336 of PSMA; non-N-glycosylated PSMA is degraded via the autophagy-lysosome pathway. PSMA directly interacts with JAK2 (confirmed by co-immunoprecipitation), facilitating STAT3 activation, which in turn drives overexpression of both PSMA and GnT-V, forming a JAK2/STAT3/GnT-V/PSMA positive feedback loop.","method":"Site-specific N-glycosylation mapping, PSMA mutants, co-immunoprecipitation of PSMA-JAK2, autophagy-lysosome pathway inhibition, STAT3 transcription factor assays","journal":"International journal of biological macromolecules","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — site-specific glycosylation mapping, co-IP, mutant analysis, transcriptional circuit validated; single lab","pmids":["40112979"],"is_preprint":false},{"year":2025,"finding":"In mouse kidney, GnT-V selectively modifies two metalloproteases on the apical surface of tubules — ANPEP (alanyl aminopeptidase) and MEP1A (meprin α) — as its major in vivo substrates, at highly accessible glycosites clustered in C-terminal domains. Upon epithelial cell polarization, GnT-V products accumulate at the apical side, implicating polarized subcellular trafficking in substrate-selective glycosylation.","method":"Lectin-assisted proteomics (identification of GnT-V substrates), glycosite mapping, single-cell transcriptomics, epithelial cell polarization assay","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — lectin proteomics with glycosite mapping, cell polarization experiment; single lab with two complementary methods","pmids":["41323266"],"is_preprint":false},{"year":2024,"finding":"GnT-V binds to TIMP-1 (confirmed by GST pull-down) and promotes N-glycosylation of TIMP-1. GnT-V-mediated TIMP-1 N-glycosylation activates the VEGF signaling pathway, promoting retinal microvascular endothelial cell angiogenesis and ARPE-19 cell injury in diabetic retinopathy.","method":"GST pull-down, Western blot/Lectin blot, TIMP-1 mutation, GnT-V overexpression/knockdown, angiogenesis assay, in vivo DR model","journal":"Molecular biology reports","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — GST pull-down for GnT-V/TIMP-1 interaction, functional rescue with TIMP-1 mutant, in vivo model; single lab","pmids":["38499842"],"is_preprint":false},{"year":2023,"finding":"ISLR interacts directly with MGAT5 in gastric cancer cells, confirmed by co-immunoprecipitation. MGAT5 overexpression partially rescues the inhibitory effects of ISLR knockdown on cancer cell viability, proliferation, migration, invasion, and EMT.","method":"Co-immunoprecipitation, ISLR knockdown, MGAT5 overexpression rescue, proliferation/migration/invasion assays","journal":"Iranian journal of basic medical sciences","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single co-IP, genetic rescue experiment; single lab, single method for interaction","pmids":["37427332"],"is_preprint":false},{"year":1987,"finding":"GnT-V (MGAT5) enzymatic activity was directly measured in cell-line extracts using UDP-[3H]-GlcNAc and a synthetic trisaccharide acceptor, demonstrating the enzyme transfers GlcNAc to form the β1,6 branch product. The PHAR 2.1 variant of BW5147 cells expressed no detectable activity.","method":"In vitro enzyme activity assay with synthetic trisaccharide acceptor, reverse-phase chromatography product separation","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — direct in vitro enzyme activity assay with defined substrate and product characterization; early foundational biochemistry, single lab","pmids":["2956949"],"is_preprint":false},{"year":2016,"finding":"Loss of mgat5a in zebrafish enhances hair cell regeneration and regeneration of lateral line axons and caudal fins. Pharmacological inhibition of N-glycosylation with swainsonine phenocopied the mgat5a mutant. Overexpression analysis showed that N-glycosylation alters the responsiveness of TGF-β signaling, positioning MGAT5 as a negative regulator of tissue regeneration through modulation of TGF-β signaling.","method":"mgat5a insertional and CRISPR/Cas9 mutant zebrafish, hair cell regeneration assay, swainsonine pharmacological inhibition, mRNA overexpression, TGF-β signaling assay","journal":"Cell regeneration","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two independent mutant alleles plus pharmacological phenocopy, signaling pathway assay; single lab in zebrafish ortholog","pmids":["27795824"],"is_preprint":false}],"current_model":"MGAT5 encodes a Golgi-resident glycosyltransferase (GnT-V) that catalyzes the addition of GlcNAc in β1,6 linkage onto N-glycan branches, generating poly-N-acetyllactosamine-bearing glycans that serve as high-avidity ligands for galectins; these galectin-glycoprotein lattices restrain TCR and integrin clustering at the cell surface to set signaling thresholds, while MGAT5-modified glycans on specific substrates (hENT1, PSMA, TIMP-1, ANPEP, MEP1A) control their plasma membrane residency, stability, and function. MGAT5 expression is transcriptionally regulated by Ets-1 and RUNX2 and its mRNA is stabilized by IGF2BP1 via m6A modification; the membrane-bound enzyme is shed by γ-secretase cleavage at His31 to generate a soluble form that independently promotes angiogenesis by releasing FGF-2 from heparan sulfate proteoglycans, and active GnT-V can also be transferred between cells via small extracellular vesicles to remodel recipient-cell glycans."},"narrative":{"mechanistic_narrative":"MGAT5 encodes GnT-V, a Golgi glycosyltransferase that adds GlcNAc in β1,6 linkage to N-glycans, generating poly-N-acetyllactosamine branches that act as high-avidity galectin ligands and set surface signaling thresholds across immune, adhesion, and oncogenic programs [PMID:11217864, PMID:2956949, PMID:22715095]. The resulting galectin-glycoprotein lattice restrains TCR clustering to raise the T-cell activation threshold and biases differentiation toward Th2, while also gating CTLA-4 endocytosis, such that Mgat5 loss produces T-cell hyperactivity [PMID:11217864, PMID:15585841, PMID:22389815]. The same branched glycans on fibronectin receptors and integrins recruit galectin-3 to focal adhesions, activate FAK and PI3K-PKB(Akt) signaling, and amplify a positive feedback loop with N-glycan branching that drives membrane ruffling, cell motility, mechanosensitive invasion, and tumor progression; this circuit is reciprocally tuned by PTEN [PMID:10700233, PMID:16581792, PMID:17400585, PMID:33894774]. In vivo, GnT-V is the exclusive source of N-linked β1,6 branches and cannot be substituted by its paralog GnT-Vb, and its catalytic specificity is governed by metal-independence, acidic pH optimum, donor-pocket hydrophobicity, and acceptor recognition by residues outside the catalytic site [PMID:22715095, PMID:19846580, PMID:35248671, PMID:37974463]. GnT-V branches specific substrates to control their fate: it stabilizes the surface transporter hENT1 to set gemcitabine sensitivity, protects PSMA from autophagy-lysosomal degradation within a JAK2/STAT3 feedback loop, glycosylates TIMP-1 to activate VEGF signaling, and modifies apical kidney metalloproteases ANPEP and MEP1A [PMID:30143259, PMID:40112979, PMID:38499842, PMID:41323266]. MGAT5 transcription is driven by Ets-1 and by RUNX2 binding the promoter, and its mRNA is stabilized by IGF2BP1 through m6A modification [PMID:10438459, PMID:37256183, PMID:34514861]. The membrane enzyme is cleaved at His31 by γ-secretase to release a soluble form whose basic domain promotes angiogenesis by liberating FGF-2 from heparan sulfate proteoglycans independently of catalytic activity, and a SPPL3-cleaved active form is loaded into small extracellular vesicles that remodel recipient-cell glycans [PMID:17142794, PMID:11872751, PMID:36590176].","teleology":[{"year":1987,"claim":"Establishing that GnT-V is a discrete enzymatic activity required directly measuring transfer of GlcNAc to a defined acceptor, providing the biochemical foundation for all downstream work.","evidence":"In vitro enzyme assay with UDP-[3H]-GlcNAc and synthetic trisaccharide acceptor in cell-line extracts, including an activity-null variant","pmids":["2956949"],"confidence":"Medium","gaps":["Did not identify the gene/protein","No in vivo substrate identified","No structural basis for activity"]},{"year":2000,"claim":"It was unknown whether β1,6 branching contributed causally to malignancy; crossing Mgat5 knockout with an oncogene-driven tumor model showed branched glycans feed PI3K-PKB signaling and are required for tumor growth and metastasis.","evidence":"Mgat5 KO × polyomavirus middle T transgenic mice, in vivo tumor/metastasis assays, PI3K-PKB and membrane ruffling biochemistry","pmids":["10700233"],"confidence":"High","gaps":["Specific glycoprotein substrates mediating the effect not defined","Mechanism linking branching to PI3K not resolved at this stage"]},{"year":2001,"claim":"How branched N-glycans regulate cell signaling was unclear; the discovery that galectin-3 forms an Mgat5-dependent lattice on the TCR established the galectin-glycoprotein lattice as the mechanistic principle setting activation thresholds.","evidence":"Mgat5 KO mice, galectin-3/TCR co-IP, lactose competition, TCR clustering and proliferation assays","pmids":["11217864"],"confidence":"High","gaps":["Stoichiometry and structure of the lattice unresolved","Generality across other surface receptors not yet tested"]},{"year":2002,"claim":"A secreted GnT-V form was found to have a function independent of glycosyltransferase activity, revealing a moonlighting role in angiogenesis via FGF-2 release.","evidence":"In vitro/in vivo angiogenesis assays with purified secreted GnT-V, basic-domain mapping","pmids":["11872751"],"confidence":"Medium","gaps":["Protease generating the secreted form not identified here","Physiological relevance versus catalytic role unclear"]},{"year":2004,"claim":"Whether branching shapes T-cell fate was open; Mgat5 loss biased cytokine output toward Th1, defining branching as a negative regulator of TCR signaling controlling Th1/Th2 balance.","evidence":"Mgat5 KO mice and swainsonine (no additive effect), cytokine ELISA, polarization assays","pmids":["15585841"],"confidence":"High","gaps":["Receptor substrates beyond the TCR not enumerated","Transcriptional consequences downstream not mapped"]},{"year":2006,"claim":"Linking the lattice to motility, galectin-3 binding to Mgat5 glycans on fibronectin receptors was shown to activate FAK/PI3K and recruit active integrin to adhesions.","evidence":"Mgat5-/- tumor cells, exogenous galectin-3 rescue, swainsonine/RGP inhibition, FAK/PI3K and integrin localization assays","pmids":["16581792"],"confidence":"High","gaps":["Dose-dependence of galectin effects not fully resolved","Specific integrin glycosites not mapped"]},{"year":2006,"claim":"The origin of soluble GnT-V was unknown; γ-secretase was identified as the protease cleaving the enzyme at His31, mechanistically connecting presenilin activity to GnT-V shedding.","evidence":"N-terminal sequencing of soluble GnT-V, DFK-167 inhibitor, presenilin-1/2 double-KO cells, cleavage-site mutagenesis","pmids":["17142794"],"confidence":"High","gaps":["Regulation of cleavage in physiological contexts unclear","Relationship to SPPL3-mediated cleavage not addressed"]},{"year":2007,"claim":"The directionality of the branching/PI3K relationship was tested using Mgat5/Pten epistasis, establishing positive feedback from PI3K signaling back to N-glycan branching.","evidence":"Mgat5/Pten double-mutant MEFs, PI3K/Akt and spreading assays, lectin flow cytometry, longevity analysis","pmids":["17400585"],"confidence":"Medium","gaps":["Molecular mechanism coupling PI3K to MGAT5 expression/activity not defined","Single-lab epistasis"]},{"year":1999,"claim":"How MGAT5 is transcriptionally controlled was unknown; Ets-1 was identified as a regulator whose level correlates with and drives GnT-V expression.","evidence":"mRNA correlation across 16 cancer lines, Ets-1 and dominant-negative Ets-1 transfection","pmids":["10438459"],"confidence":"Medium","gaps":["Direct promoter binding not shown here","Correlative across-line data"]},{"year":2009,"claim":"Distinguishing GnT-V from paralog GnT-Vb required kinetic characterization, defining GnT-V's metal-independence, pH optimum, and preference for N-glycan over O-mannose acceptors.","evidence":"In vitro kinetics with purified truncated enzymes, synthetic acceptors, HPLC product analysis","pmids":["19846580"],"confidence":"High","gaps":["In vivo substrate preference not yet demonstrated","Structural basis of substrate discrimination unresolved"]},{"year":2011,"claim":"Branching was shown to control CTLA-4 endocytosis and contribute to autoimmunity, extending the lattice model to inhibitory receptor regulation and disease.","evidence":"Mgat5 KO mice, adoptive T-cell transfer, EAE model","pmids":["22389815"],"confidence":"Medium","gaps":["Direct CTLA-4 glycosite mapping not shown","Non-T-cell contributions not dissected"]},{"year":2012,"claim":"Genetic dissection in brain established GnT-V as the sole in vivo source of N-linked β1,6 branches, non-redundant with GnT-Vb.","evidence":"GnT-V, GnT-Vb, and double-KO mice with glycan structural analysis","pmids":["22715095"],"confidence":"High","gaps":["Tissue-specific substrate identities not addressed","Functional consequences in brain not characterized here"]},{"year":2013,"claim":"A direct transcriptional activator was confirmed when RUNX2 was shown to bind the MGAT5 promoter and drive expression in gastric cancer.","evidence":"ChIP-PCR, RUNX2 siRNA, qRT-PCR/Western, in vivo xenograft","pmids":["37256183"],"confidence":"Medium","gaps":["Relationship to Ets-1 regulation not integrated","Single-lab cancer context"]},{"year":2018,"claim":"The first defined functional substrate emerged: GnT-V branching of hENT1 controls its surface accumulation and thereby gemcitabine uptake and chemosensitivity.","evidence":"GnT-V shRNA, hENT1 lectin blot, surface fractionation, gemcitabine uptake/viability assays","pmids":["30143259"],"confidence":"Medium","gaps":["hENT1 glycosites not mapped","Single cancer-cell context"]},{"year":2021,"claim":"Post-transcriptional control of MGAT5 was established when IGF2BP1 was shown to stabilize MGAT5 mRNA via m6A, linking branching to liver cancer stemness.","evidence":"IGF2BP1 shRNA, MeRIP-qPCR, mRNA stability assay, stemness and in vivo tumorigenesis assays","pmids":["34514861"],"confidence":"Medium","gaps":["m6A site on MGAT5 not pinpointed","Generality beyond liver cancer stem cells unknown"]},{"year":2021,"claim":"Branching was connected to mechanosensing when CRISPR deletion of MGAT5 abolished stiffness-dependent glioblastoma invasion via the galectin-3/integrin axis.","evidence":"CRISPR MGAT5 KO in GSCs, tunable-stiffness scaffolds, migration, focal adhesion/EMT readouts, galectin-3 binding","pmids":["33894774"],"confidence":"Medium","gaps":["Specific mechanoreceptor substrates not identified","Single-lab GSC system"]},{"year":2022,"claim":"Selective inhibitor design and computational/biochemical analysis revealed GnT-V's unusual donor-pocket hydrophobicity tolerance and acceptor recognition by residues outside the catalytic site.","evidence":"In vitro inhibition with UDP-GlcNAc analogs across GnT-I–V, docking; MD simulations with mutagenesis","pmids":["35248671","37974463"],"confidence":"Medium","gaps":["No experimental high-resolution structure","Inhibitor selectivity in cells not demonstrated"]},{"year":2022,"claim":"An intercellular dimension of GnT-V was revealed: SPPL3-cleaved active enzyme is loaded into small EVs that transfer to recipient cells and remodel their glycans.","evidence":"sEV fractionation, single-particle imaging, SPPL3 knockdown, sEV enzyme activity, recipient N-glycan profiling","pmids":["36590176"],"confidence":"Medium","gaps":["Physiological relevance of glycan transfer in vivo unclear","Relationship of SPPL3 to γ-secretase cleavage not reconciled"]},{"year":2023,"claim":"A developmental role emerged: MGAT5 loss in neural stem/progenitor cells shifts differentiation toward neurons and depletes the niche, altering cortical layering.","evidence":"Mgat5 null mice, in vitro NSPC differentiation, in vivo cortical layering analysis","pmids":["37172586"],"confidence":"Medium","gaps":["Substrate(s) governing NSPC fate not identified","Signaling pathway downstream not mapped"]},{"year":2024,"claim":"MGAT5 was implicated in immune evasion when its loss sensitized PDAC to TNF-superfamily death and enabled T/DC/NK-dependent tumor clearance with checkpoint blockade.","evidence":"Mgat5 KO PDAC lines, syngeneic in vivo models, immune-cell depletion, cell death pathway analysis, checkpoint blockade","pmids":["38912584"],"confidence":"Medium","gaps":["Specific glycoprotein substrates controlling death sensitivity not defined","Single-lab models"]},{"year":2024,"claim":"Substrate-specific control of protein fate was extended to PSMA, whose GnT-V branching prevents autophagic degradation within a JAK2/STAT3/GnT-V/PSMA feedback loop, and to TIMP-1, whose glycosylation activates VEGF signaling.","evidence":"PSMA glycosite mapping, PSMA-JAK2 co-IP, autophagy inhibition, STAT3 assays; GnT-V/TIMP-1 GST pull-down, TIMP-1 mutant, angiogenesis and in vivo DR model","pmids":["40112979","38499842"],"confidence":"Medium","gaps":["Mechanism of glycan-dependent degradation protection not fully resolved","Single-lab disease contexts"]},{"year":2025,"claim":"Unbiased in vivo substrate profiling identified ANPEP and MEP1A as major kidney GnT-V substrates and linked polarized trafficking to substrate-selective glycosylation.","evidence":"Lectin-assisted proteomics, glycosite mapping, single-cell transcriptomics, epithelial polarization assay","pmids":["41323266"],"confidence":"Medium","gaps":["Functional consequences of ANPEP/MEP1A branching not established","Trafficking machinery directing apical accumulation unknown"]},{"year":null,"claim":"A high-resolution structure and unified mechanistic account of how subcellular trafficking and substrate accessibility dictate which proteins GnT-V branches in a given tissue remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No experimental enzyme structure in the corpus","Rules governing tissue/substrate selectivity incomplete","Reconciliation of multiple cleaved/secreted/EV forms not unified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,24,8,9]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[12,20,22,21]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[5,9]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[14]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[4,5]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,9,24]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,3,10,18]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,2,7,20]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[1,11,12,18,22]}],"complexes":[],"partners":["LGALS3","TIMP-1","PSMA","JAK2","ISLR","PSEN1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q09328","full_name":"Alpha-1,6-mannosylglycoprotein 6-beta-N-acetylglucosaminyltransferase A","aliases":["Alpha-mannoside beta-1,6-N-acetylglucosaminyltransferase V","GlcNAc-T V","GNT-V","Mannoside acetylglucosaminyltransferase 5","N-acetylglucosaminyl-transferase V"],"length_aa":741,"mass_kda":84.5,"function":"Catalyzes the addition of N-acetylglucosamine (GlcNAc) in beta 1-6 linkage to the alpha-linked mannose of biantennary N-linked oligosaccharides (PubMed:10395745, PubMed:30140003). Catalyzes an important step in the biosynthesis of branched, complex-type N-glycans, such as those found on EGFR, TGFR (TGF-beta receptor) and CDH2 (PubMed:10395745, PubMed:22614033, PubMed:30140003). Via its role in the biosynthesis of complex N-glycans, plays an important role in the activation of cellular signaling pathways, reorganization of the actin cytoskeleton, cell-cell adhesion and cell migration. MGAT5-dependent EGFR N-glycosylation enhances the interaction between EGFR and LGALS3 and thereby prevents rapid EGFR endocytosis and prolongs EGFR signaling. Required for efficient interaction between TGFB1 and its receptor. Enhances activation of intracellular signaling pathways by several types of growth factors, including FGF2, PDGF, IGF, TGFB1 and EGF. MGAT5-dependent CDH2 N-glycosylation inhibits CDH2-mediated homotypic cell-cell adhesion and contributes to the regulation of downstream signaling pathways. Promotes cell migration. Contributes to the regulation of the inflammatory response. MGAT5-dependent TCR N-glycosylation enhances the interaction between TCR and LGALS3, limits agonist-induced TCR clustering, and thereby dampens TCR-mediated responses to antigens. Required for normal leukocyte evasation and accumulation at sites of inflammation (By similarity). Inhibits attachment of monocytes to the vascular endothelium and subsequent monocyte diapedesis (PubMed:22614033) Promotes proliferation of umbilical vein endothelial cells and angiogenesis, at least in part by promoting the release of the growth factor FGF2 from the extracellular matrix","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q09328/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MGAT5","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MGAT5","total_profiled":1310},"omim":[{"mim_id":"615553","title":"ARTHROGRYPOSIS, IMPAIRED INTELLECTUAL DEVELOPMENT, AND SEIZURES; AMRS","url":"https://www.omim.org/entry/615553"},{"mim_id":"612441","title":"ALPHA-1,6-@MANNOSYL-GLYCOPROTEIN BETA-1,6-N-ACETYLGLUCOSAMINYLTRANSFERASE, ISOZYME B; MGAT5B","url":"https://www.omim.org/entry/612441"},{"mim_id":"606822","title":"PROTEIN O-MANNOSE BETA-1,2-N-ACETYLGLUCOSAMINYLTRANSFERASE; POMGNT1","url":"https://www.omim.org/entry/606822"},{"mim_id":"605632","title":"SOLUTE CARRIER FAMILY 35 (UDP-N-ACETYLGLUCOSAMINE TRANSPORTER), MEMBER 3; SLC35A3","url":"https://www.omim.org/entry/605632"},{"mim_id":"604621","title":"BETA-1,4-@MANNOSYL-GLYCOPROTEIN BETA-1,4-N-ACETYLGLUCOSAMINYLTRANSFERASE; MGAT3","url":"https://www.omim.org/entry/604621"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MGAT5"},"hgnc":{"alias_symbol":["GNT-V","MGAT5A"],"prev_symbol":[]},"alphafold":{"accession":"Q09328","domains":[{"cath_id":"-","chopping":"154-207","consensus_level":"high","plddt":84.6309,"start":154,"end":207},{"cath_id":"-","chopping":"221-378","consensus_level":"high","plddt":89.6456,"start":221,"end":378},{"cath_id":"3.40.50.2000","chopping":"433-602","consensus_level":"high","plddt":91.2704,"start":433,"end":602},{"cath_id":"-","chopping":"631-726","consensus_level":"high","plddt":94.0986,"start":631,"end":726}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q09328","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q09328-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q09328-F1-predicted_aligned_error_v6.png","plddt_mean":83.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MGAT5","jax_strain_url":"https://www.jax.org/strain/search?query=MGAT5"},"sequence":{"accession":"Q09328","fasta_url":"https://rest.uniprot.org/uniprotkb/Q09328.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q09328/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q09328"}},"corpus_meta":[{"pmid":"11217864","id":"PMC_11217864","title":"Negative 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research","url":"https://pubmed.ncbi.nlm.nih.gov/25524127","citation_count":6,"is_preprint":false},{"pmid":"18097551","id":"PMC_18097551","title":"Positive expressions of N-acetylglucosaminyltransferase-V (GnT-V) and beta1-6 branching N-linked oligosaccharides in human testicular germ cells diminish during malignant transformation and progression.","date":"2008","source":"International journal of oncology","url":"https://pubmed.ncbi.nlm.nih.gov/18097551","citation_count":6,"is_preprint":false},{"pmid":"39233219","id":"PMC_39233219","title":"Structure and function of N-acetylglucosaminyltransferase V (GnT-V).","date":"2024","source":"Biochimica et biophysica acta. General subjects","url":"https://pubmed.ncbi.nlm.nih.gov/39233219","citation_count":5,"is_preprint":false},{"pmid":"40112979","id":"PMC_40112979","title":"Increased N-glycosylation of PSMA by GnT-V enhances tumor malignancy through interacting with JAK2 and the subsequent STAT3-mediated transcriptional activation in prostate cancer.","date":"2025","source":"International journal of biological macromolecules","url":"https://pubmed.ncbi.nlm.nih.gov/40112979","citation_count":4,"is_preprint":false},{"pmid":"38499842","id":"PMC_38499842","title":"GnT-V-mediated aberrant N-glycosylation of TIMP-1 promotes diabetic retinopathy progression.","date":"2024","source":"Molecular biology reports","url":"https://pubmed.ncbi.nlm.nih.gov/38499842","citation_count":2,"is_preprint":false},{"pmid":"12122020","id":"PMC_12122020","title":"Sequences of the mouse N-acetylglucosaminyltransferase V (Mgat5) mRNA and an mRNA expressed by an Mgat5-deficient cell line.","date":"2002","source":"Glycobiology","url":"https://pubmed.ncbi.nlm.nih.gov/12122020","citation_count":2,"is_preprint":false},{"pmid":"37427332","id":"PMC_37427332","title":"ISLR interacts with MGAT5 to promote the malignant progression of human gastric cancer AGS cells.","date":"2023","source":"Iranian journal of basic medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/37427332","citation_count":2,"is_preprint":false},{"pmid":"12549224","id":"PMC_12549224","title":"[GnT-V overexpression in human hepatocarcinoma cells affects its migration and expression of cell adhesion molecules].","date":"2001","source":"Shi yan sheng wu xue bao","url":"https://pubmed.ncbi.nlm.nih.gov/12549224","citation_count":2,"is_preprint":false},{"pmid":"41323266","id":"PMC_41323266","title":"Selective modification of glycoprotein substrates by GnT-V in mouse kidney.","date":"2025","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/41323266","citation_count":1,"is_preprint":false},{"pmid":"40199132","id":"PMC_40199132","title":"MGAT3 and MGAT5 overexpression alters the protein cargo of extracellular vesicles released by metastatic melanoma cells.","date":"2025","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/40199132","citation_count":0,"is_preprint":false},{"pmid":"18655794","id":"PMC_18655794","title":"Evidence for tyrosinase as a beta1,6 branch containing glycoprotein: substrate of GnT-V.","date":"2008","source":"Life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/18655794","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":30781,"output_tokens":7174,"usd":0.099976,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":16294,"output_tokens":6307,"usd":0.119572,"stage2_stop_reason":"end_turn"},"total_usd":0.219548,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2001,\n      \"finding\": \"MGAT5 initiates GlcNAc β1,6 branching on N-glycans, increasing N-acetyllactosamine that serves as ligand for galectins; galectin-3 was shown to associate with the TCR complex at the cell surface in an MGAT5-dependent manner, forming a galectin-glycoprotein lattice that restricts TCR recruitment to the site of antigen presentation and raises the T-cell activation threshold. Lactose competition for galectin binding phenocopied Mgat5-/- TCR clustering. Mgat5-deficient mice showed enhanced TCR clustering, actin microfilament re-organization, and downstream signaling.\",\n      \"method\": \"Mgat5 knockout mice, lactose competition assay, co-immunoprecipitation of galectin-3 with TCR complex, TCR clustering assay with agonist-coated beads, proliferation assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal functional assays, genetic KO model, galectin-TCR co-IP, chemical competition experiment, multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"11217864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"MGAT5-produced β1,6GlcNAc-branched N-glycans stimulate membrane ruffling and PI3K-PKB (Akt) activation, fueling a positive feedback loop that amplifies oncogene signaling. Loss of Mgat5 in mice markedly reduced mammary tumor growth and metastasis driven by the polyomavirus middle T oncogene, demonstrating that tumor progression depends on Mgat5 glycan-mediated focal adhesion signaling.\",\n      \"method\": \"Mgat5 knockout mice crossed with polyomavirus middle T oncogene transgenics; in vivo tumor growth and metastasis assays; PI3K-PKB signaling assays; membrane ruffling assays\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO in vivo tumor model, signaling biochemistry, multiple phenotypic readouts, replicated across labs\",\n      \"pmids\": [\"10700233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Galectin-3 binding to Mgat5-modified β1,6GlcNAc N-glycans on fibronectin receptors regulates fibronectin fibrillogenesis and tumor cell motility. At optimal doses, exogenous galectin-3 activates FAK and PI3K, recruits conformationally active α5β1-integrin to fibrillar adhesions, and increases F-actin turnover. These effects are dependent on galectin-glycan binding and are absent in Mgat5-/- cells.\",\n      \"method\": \"Mgat5-/- mammary tumor cells, exogenous galectin-3 rescue, swainsonine inhibition, RGD peptide inhibition, anti-galectin-3 domain antibodies, FAK/PI3K biochemical assays, α5β1-integrin localization\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO cells, chemical inhibitors, antibody perturbation, multiple signaling readouts, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"16581792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"β1,6GlcNAc N-glycans produced by Mgat5 on the TCR negatively regulate TCR signaling to promote Th2 over Th1 differentiation. Mgat5-/- T cells and swainsonine-treated T cells produce more IFN-γ and less IL-4; swainsonine had no additional effect in Mgat5-/- cells, confirming specificity. Mgat5 deficiency caused ~10-fold increase in IFN-γ production by polarized Th2 cells.\",\n      \"method\": \"Mgat5 knockout mice, swainsonine (Golgi α-mannosidase II inhibitor), cytokine ELISA, T-cell polarization assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO confirmed with chemical inhibitor showing no additive effect, multiple cytokine readouts, replicated in human and mouse T cells\",\n      \"pmids\": [\"15585841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"A secreted form of GnT-V promotes angiogenesis in vitro and in vivo independently of its glycosyltransferase activity. The highly basic domain of secreted GnT-V induces release of FGF-2 from heparan sulfate proteoglycans on the cell surface/extracellular matrix.\",\n      \"method\": \"In vitro angiogenesis assays, in vivo angiogenesis assays, addition of purified secreted GnT-V protein, domain analysis with basic domain\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and in vivo functional assays with purified protein, domain mapping, single lab\",\n      \"pmids\": [\"11872751\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Golgi-resident GnT-V is cleaved at its transmembrane region by γ-secretase (containing presenilin-1) to generate a soluble secreted form (~100 kDa) starting at His31. The cleavage was specifically inhibited by γ-secretase inhibitor DFK-167 and was completely abolished in presenilin-1/2 double-deficient cells. Overexpression of FAD-linked presenilin-1 increased GnT-V secretion rate.\",\n      \"method\": \"N-terminal protein sequencing of purified soluble GnT-V, γ-secretase inhibitor DFK-167, presenilin-1/2 double-knockout cells, presenilin-1 overexpression, site-directed mutagenesis of cleavage site\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — N-terminal sequencing of purified protein, genetic KO of protease, chemical inhibitor, mutagenesis; single lab but multiple orthogonal approaches\",\n      \"pmids\": [\"17142794\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Transcription factor Ets-1 regulates expression of the GnT-V (MGAT5) gene. GnT-V mRNA levels correlated with Ets-1 expression across 16 cancer cell lines (r=0.97). Transfection of Ets-1 cDNA enhanced GnT-V expression in low-Ets-1 cells; dominant-negative Ets-1 reduced GnT-V expression in high-Ets-1 cells.\",\n      \"method\": \"mRNA correlation across cell lines, Ets-1 cDNA transfection, dominant-negative Ets-1 transfection\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — gain-of-function and dominant-negative approaches, correlative data across 16 cell lines, single lab\",\n      \"pmids\": [\"10438459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Mgat5 and Pten interact functionally in opposing directions to regulate PI3K/Akt signaling, cell spreading, and proliferation. Pten heterozygosity enhances cell adhesion-dependent PI3K/Akt signaling and is associated with increased surface β1,6GlcNAc-branched N-glycans; Mgat5/Pten double-mutant cells normalize these effects, indicating positive feedback from PI3K signaling to N-glycan branching.\",\n      \"method\": \"Mgat5/Pten double-mutant mouse embryonic fibroblasts, PI3K/Akt signaling assays, cell spreading and proliferation assays, flow cytometric lectin binding for N-glycan quantification, in vivo longevity analysis\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — double-mutant genetic epistasis, biochemical signaling assays, in vivo survival data; single lab\",\n      \"pmids\": [\"17400585\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"GnT-V (MGAT5) and its paralog GnT-Vb have distinct catalytic properties: GnT-V is active without exogenous cations and inhibited by EDTA, has a pH optimum of 6.5–7.0, and shows poor activity toward O-mannose-linked glycopeptides. Both enzymes transfer GlcNAcβ1,6 to Man residues of N-glycan substrates, but GnT-Vb shows ~2.5-fold higher Km for the biantennary N-glycan acceptor and much higher activity toward O-mannose glycopeptides.\",\n      \"method\": \"In vitro enzyme kinetics assays with purified truncated enzymes, synthetic trisaccharide and glycopeptide acceptors, HPLC product analysis\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with purified enzymes, kinetic characterization with multiple substrates, single lab with rigorous biochemistry\",\n      \"pmids\": [\"19846580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In vivo, GnT-V (MGAT5) is responsible for synthesizing N-linked β1,6-branched glycans; GnT-V null brains lacked N-linked β1,6-glycans but had normal O-mannose β1,6-branched structures, showing GnT-Vb cannot compensate for GnT-V loss for N-glycan branching. Double knockout of GnT-V and GnT-Vb eliminated both N-linked and O-mannose β1,6-branched glycans in brain.\",\n      \"method\": \"GnT-V knockout mice, GnT-Vb knockout mice, GnT-V/GnT-Vb double knockout mice, glycan structural analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple genetic KO models, direct glycan structural analysis, defines in vivo substrate selectivity\",\n      \"pmids\": [\"22715095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Mgat5 N-glycan branching regulates CTLA-4 endocytosis; deficiency promotes T-cell hyperactivity. Adoptive transfer of myelin-reactive Mgat5-/- T cells into Mgat5+/+ versus Mgat5-/- recipients caused more severe EAE in Mgat5-/- recipients, indicating that Mgat5 branching deficiency in recipient naive T cells and/or non-T cells also contributes to autoimmune disease pathogenesis.\",\n      \"method\": \"Mgat5 knockout mice, adoptive T-cell transfer, EAE model of autoimmune encephalomyelitis\",\n      \"journal\": \"ISRN neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO, adoptive transfer epistasis experiment, EAE disease readout; single lab\",\n      \"pmids\": [\"22389815\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"RUNX2 transcription factor directly binds to the MGAT5 promoter and activates MGAT5 transcription in gastric cancer cells, as confirmed by ChIP-PCR. RUNX2 silencing reduced MGAT5 expression and suppressed tumor proliferation, invasion, migration, and metastasis in vivo.\",\n      \"method\": \"ChIP-PCR, JASPAR promoter binding prediction, RUNX2 siRNA knockdown, qRT-PCR, Western blot, in vivo xenograft\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct ChIP evidence for promoter binding, functional KD phenotype; single lab\",\n      \"pmids\": [\"37256183\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"GnT-V modifies human equilibrative nucleoside transporter 1 (hENT1) with β1,6-GlcNAc branched N-glycans; silencing GnT-V dramatically decreased β1,6-GlcNAc structure on hENT1, reduced hENT1 accumulation at the plasma membrane, and decreased gemcitabine uptake and chemosensitivity in bladder cancer cells.\",\n      \"method\": \"GnT-V shRNA knockdown, lectin blot for β1,6-GlcNAc on hENT1, cell surface fractionation, gemcitabine uptake assay, cell viability assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — loss-of-function with defined substrate glycosylation and functional readout (transporter localization and drug uptake); single lab\",\n      \"pmids\": [\"30143259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"IGF2BP1 binds to MGAT5 mRNA through m6A modification and stabilizes it, promoting MGAT5 expression and liver cancer stem cell phenotypes (self-renewal, chemoresistance). MeRIP-qPCR confirmed direct IGF2BP1 binding to MGAT5 mRNA via m6A.\",\n      \"method\": \"IGF2BP1 shRNA knockdown, MeRIP-qPCR, mRNA stability assay (qRT-PCR), cancer stem cell phenotype assays, in vivo tumorigenesis\",\n      \"journal\": \"Stem cells and development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — MeRIP-qPCR for direct m6A binding, mRNA stability measurement, functional rescue; single lab\",\n      \"pmids\": [\"34514861\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GnT-V (MGAT5) is selectively enriched in small extracellular vesicles (sEVs) among glycosyltransferases. GnT-V in sEVs exists as a cleaved form, and cleavage by SPPL3 protease is required for its loading into sEVs. Enzymatically active GnT-V in sEVs transfers to recipient cells and remodels their N-glycan structures to express GnT-V-produced glycans.\",\n      \"method\": \"Fractionation of sEV subtypes, single-particle imaging, SPPL3 protease involvement (knockdown), enzyme activity assays in sEVs, N-glycan profiling of recipient cells\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — fractionation, single-particle imaging, enzyme activity assays, glycan profiling; single lab with multiple complementary methods\",\n      \"pmids\": [\"36590176\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Structure-based design identified UDP-GlcNAc analogs with increased hydrophobicity (phosphate group replacement) as selective inhibitors of GnT-V activity. GnT-V is relatively tolerant of donor substrate hydrophobicity compared with other GlcNAc transferases (GnT-I–IV), suggesting unique catalytic pocket properties.\",\n      \"method\": \"In vitro HPLC-based enzyme assay with purified truncated GnT-V and other GlcNAc transferases, synthetic UDP-GlcNAc analog compounds, docking models\",\n      \"journal\": \"Biochimica et biophysica acta. General subjects\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzyme inhibition assay with purified enzyme, structure-based docking, single lab\",\n      \"pmids\": [\"35248671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Molecular dynamics simulations and biochemical experiments revealed that residues outside the catalytic pocket of GnT-V are involved in recognition of the core part of the N-glycan acceptor. UDP binding was found to affect the orientation of the acceptor substrate via conformational change at the Manα1,6-Man linkage.\",\n      \"method\": \"Molecular dynamics simulation, biochemical mutagenesis and enzyme activity assays\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — computational simulation supported by biochemical experiments; single lab\",\n      \"pmids\": [\"37974463\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MGAT5-catalyzed N-glycan branching is a critical regulator of stiffness-dependent invasion in glioblastoma stem-like cells (GSCs). CRISPR-Cas9 deletion of MGAT5 in GSCs suppressed β1,6-branched N-glycan expression, abolished stiffness-dependent migration at 166 kPa, and reduced focal adhesion and EMT protein expression, linking MGAT5 N-glycosylation to mechanosensing via the galectin-3/integrin axis.\",\n      \"method\": \"CRISPR-Cas9 MGAT5 knockout, 3D nanofiber scaffold with adjustable stiffness, cell migration assay, focal adhesion protein expression, galectin-3 lectin binding\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with CRISPR, defined mechanical substrate, functional and molecular readouts; single lab\",\n      \"pmids\": [\"33894774\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Mgat5-deficient pancreatic ductal adenocarcinoma cells show increased sensitivity to TNF superfamily-mediated cell death pathways, and Mgat5 loss leads to tumor clearance that is dependent on T cells and dendritic cells (with early NK cell involvement) in vivo. Mgat5 knockout in an immunotherapy-resistant PDAC line significantly decreased tumor growth and increased survival upon immune checkpoint blockade.\",\n      \"method\": \"Mgat5 knockout clonal PDAC cell lines, in vivo syngeneic tumor models, T-cell/NK-cell depletion experiments, TNF superfamily cell death pathway analysis, immune checkpoint blockade treatment\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO in multiple cell lines, in vivo immune depletion epistasis, mechanistic cell death pathway analysis; single lab\",\n      \"pmids\": [\"38912584\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Loss of MGAT5 in neural stem/progenitor cells (NSPCs) shifts differentiation toward neurons and away from astrocytes in vitro, and causes accelerated neuronal differentiation and depletion of the NSPC niche in vivo, resulting in a shift in cortical neuron layers in Mgat5 null mice.\",\n      \"method\": \"Mgat5 null mice, in vitro NSPC differentiation assays, in vivo cortical layering analysis\",\n      \"journal\": \"Stem cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with in vitro and in vivo differentiation phenotypes; single lab\",\n      \"pmids\": [\"37172586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GnT-V catalyzes β1,6-GlcNAc branching at N121 and N336 of PSMA; non-N-glycosylated PSMA is degraded via the autophagy-lysosome pathway. PSMA directly interacts with JAK2 (confirmed by co-immunoprecipitation), facilitating STAT3 activation, which in turn drives overexpression of both PSMA and GnT-V, forming a JAK2/STAT3/GnT-V/PSMA positive feedback loop.\",\n      \"method\": \"Site-specific N-glycosylation mapping, PSMA mutants, co-immunoprecipitation of PSMA-JAK2, autophagy-lysosome pathway inhibition, STAT3 transcription factor assays\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — site-specific glycosylation mapping, co-IP, mutant analysis, transcriptional circuit validated; single lab\",\n      \"pmids\": [\"40112979\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In mouse kidney, GnT-V selectively modifies two metalloproteases on the apical surface of tubules — ANPEP (alanyl aminopeptidase) and MEP1A (meprin α) — as its major in vivo substrates, at highly accessible glycosites clustered in C-terminal domains. Upon epithelial cell polarization, GnT-V products accumulate at the apical side, implicating polarized subcellular trafficking in substrate-selective glycosylation.\",\n      \"method\": \"Lectin-assisted proteomics (identification of GnT-V substrates), glycosite mapping, single-cell transcriptomics, epithelial cell polarization assay\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — lectin proteomics with glycosite mapping, cell polarization experiment; single lab with two complementary methods\",\n      \"pmids\": [\"41323266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GnT-V binds to TIMP-1 (confirmed by GST pull-down) and promotes N-glycosylation of TIMP-1. GnT-V-mediated TIMP-1 N-glycosylation activates the VEGF signaling pathway, promoting retinal microvascular endothelial cell angiogenesis and ARPE-19 cell injury in diabetic retinopathy.\",\n      \"method\": \"GST pull-down, Western blot/Lectin blot, TIMP-1 mutation, GnT-V overexpression/knockdown, angiogenesis assay, in vivo DR model\",\n      \"journal\": \"Molecular biology reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — GST pull-down for GnT-V/TIMP-1 interaction, functional rescue with TIMP-1 mutant, in vivo model; single lab\",\n      \"pmids\": [\"38499842\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ISLR interacts directly with MGAT5 in gastric cancer cells, confirmed by co-immunoprecipitation. MGAT5 overexpression partially rescues the inhibitory effects of ISLR knockdown on cancer cell viability, proliferation, migration, invasion, and EMT.\",\n      \"method\": \"Co-immunoprecipitation, ISLR knockdown, MGAT5 overexpression rescue, proliferation/migration/invasion assays\",\n      \"journal\": \"Iranian journal of basic medical sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single co-IP, genetic rescue experiment; single lab, single method for interaction\",\n      \"pmids\": [\"37427332\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"GnT-V (MGAT5) enzymatic activity was directly measured in cell-line extracts using UDP-[3H]-GlcNAc and a synthetic trisaccharide acceptor, demonstrating the enzyme transfers GlcNAc to form the β1,6 branch product. The PHAR 2.1 variant of BW5147 cells expressed no detectable activity.\",\n      \"method\": \"In vitro enzyme activity assay with synthetic trisaccharide acceptor, reverse-phase chromatography product separation\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro enzyme activity assay with defined substrate and product characterization; early foundational biochemistry, single lab\",\n      \"pmids\": [\"2956949\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Loss of mgat5a in zebrafish enhances hair cell regeneration and regeneration of lateral line axons and caudal fins. Pharmacological inhibition of N-glycosylation with swainsonine phenocopied the mgat5a mutant. Overexpression analysis showed that N-glycosylation alters the responsiveness of TGF-β signaling, positioning MGAT5 as a negative regulator of tissue regeneration through modulation of TGF-β signaling.\",\n      \"method\": \"mgat5a insertional and CRISPR/Cas9 mutant zebrafish, hair cell regeneration assay, swainsonine pharmacological inhibition, mRNA overexpression, TGF-β signaling assay\",\n      \"journal\": \"Cell regeneration\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two independent mutant alleles plus pharmacological phenocopy, signaling pathway assay; single lab in zebrafish ortholog\",\n      \"pmids\": [\"27795824\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MGAT5 encodes a Golgi-resident glycosyltransferase (GnT-V) that catalyzes the addition of GlcNAc in β1,6 linkage onto N-glycan branches, generating poly-N-acetyllactosamine-bearing glycans that serve as high-avidity ligands for galectins; these galectin-glycoprotein lattices restrain TCR and integrin clustering at the cell surface to set signaling thresholds, while MGAT5-modified glycans on specific substrates (hENT1, PSMA, TIMP-1, ANPEP, MEP1A) control their plasma membrane residency, stability, and function. MGAT5 expression is transcriptionally regulated by Ets-1 and RUNX2 and its mRNA is stabilized by IGF2BP1 via m6A modification; the membrane-bound enzyme is shed by γ-secretase cleavage at His31 to generate a soluble form that independently promotes angiogenesis by releasing FGF-2 from heparan sulfate proteoglycans, and active GnT-V can also be transferred between cells via small extracellular vesicles to remodel recipient-cell glycans.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MGAT5 encodes GnT-V, a Golgi glycosyltransferase that adds GlcNAc in β1,6 linkage to N-glycans, generating poly-N-acetyllactosamine branches that act as high-avidity galectin ligands and set surface signaling thresholds across immune, adhesion, and oncogenic programs [#0, #24, #9]. The resulting galectin-glycoprotein lattice restrains TCR clustering to raise the T-cell activation threshold and biases differentiation toward Th2, while also gating CTLA-4 endocytosis, such that Mgat5 loss produces T-cell hyperactivity [#0, #3, #10]. The same branched glycans on fibronectin receptors and integrins recruit galectin-3 to focal adhesions, activate FAK and PI3K-PKB(Akt) signaling, and amplify a positive feedback loop with N-glycan branching that drives membrane ruffling, cell motility, mechanosensitive invasion, and tumor progression; this circuit is reciprocally tuned by PTEN [#1, #2, #7, #17]. In vivo, GnT-V is the exclusive source of N-linked β1,6 branches and cannot be substituted by its paralog GnT-Vb, and its catalytic specificity is governed by metal-independence, acidic pH optimum, donor-pocket hydrophobicity, and acceptor recognition by residues outside the catalytic site [#9, #8, #15, #16]. GnT-V branches specific substrates to control their fate: it stabilizes the surface transporter hENT1 to set gemcitabine sensitivity, protects PSMA from autophagy-lysosomal degradation within a JAK2/STAT3 feedback loop, glycosylates TIMP-1 to activate VEGF signaling, and modifies apical kidney metalloproteases ANPEP and MEP1A [#12, #20, #22, #21]. MGAT5 transcription is driven by Ets-1 and by RUNX2 binding the promoter, and its mRNA is stabilized by IGF2BP1 through m6A modification [#6, #11, #13]. The membrane enzyme is cleaved at His31 by γ-secretase to release a soluble form whose basic domain promotes angiogenesis by liberating FGF-2 from heparan sulfate proteoglycans independently of catalytic activity, and a SPPL3-cleaved active form is loaded into small extracellular vesicles that remodel recipient-cell glycans [#5, #4, #14].\",\n  \"teleology\": [\n    {\n      \"year\": 1987,\n      \"claim\": \"Establishing that GnT-V is a discrete enzymatic activity required directly measuring transfer of GlcNAc to a defined acceptor, providing the biochemical foundation for all downstream work.\",\n      \"evidence\": \"In vitro enzyme assay with UDP-[3H]-GlcNAc and synthetic trisaccharide acceptor in cell-line extracts, including an activity-null variant\",\n      \"pmids\": [\"2956949\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not identify the gene/protein\", \"No in vivo substrate identified\", \"No structural basis for activity\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"It was unknown whether β1,6 branching contributed causally to malignancy; crossing Mgat5 knockout with an oncogene-driven tumor model showed branched glycans feed PI3K-PKB signaling and are required for tumor growth and metastasis.\",\n      \"evidence\": \"Mgat5 KO × polyomavirus middle T transgenic mice, in vivo tumor/metastasis assays, PI3K-PKB and membrane ruffling biochemistry\",\n      \"pmids\": [\"10700233\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific glycoprotein substrates mediating the effect not defined\", \"Mechanism linking branching to PI3K not resolved at this stage\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"How branched N-glycans regulate cell signaling was unclear; the discovery that galectin-3 forms an Mgat5-dependent lattice on the TCR established the galectin-glycoprotein lattice as the mechanistic principle setting activation thresholds.\",\n      \"evidence\": \"Mgat5 KO mice, galectin-3/TCR co-IP, lactose competition, TCR clustering and proliferation assays\",\n      \"pmids\": [\"11217864\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and structure of the lattice unresolved\", \"Generality across other surface receptors not yet tested\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"A secreted GnT-V form was found to have a function independent of glycosyltransferase activity, revealing a moonlighting role in angiogenesis via FGF-2 release.\",\n      \"evidence\": \"In vitro/in vivo angiogenesis assays with purified secreted GnT-V, basic-domain mapping\",\n      \"pmids\": [\"11872751\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Protease generating the secreted form not identified here\", \"Physiological relevance versus catalytic role unclear\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Whether branching shapes T-cell fate was open; Mgat5 loss biased cytokine output toward Th1, defining branching as a negative regulator of TCR signaling controlling Th1/Th2 balance.\",\n      \"evidence\": \"Mgat5 KO mice and swainsonine (no additive effect), cytokine ELISA, polarization assays\",\n      \"pmids\": [\"15585841\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor substrates beyond the TCR not enumerated\", \"Transcriptional consequences downstream not mapped\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Linking the lattice to motility, galectin-3 binding to Mgat5 glycans on fibronectin receptors was shown to activate FAK/PI3K and recruit active integrin to adhesions.\",\n      \"evidence\": \"Mgat5-/- tumor cells, exogenous galectin-3 rescue, swainsonine/RGP inhibition, FAK/PI3K and integrin localization assays\",\n      \"pmids\": [\"16581792\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Dose-dependence of galectin effects not fully resolved\", \"Specific integrin glycosites not mapped\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"The origin of soluble GnT-V was unknown; γ-secretase was identified as the protease cleaving the enzyme at His31, mechanistically connecting presenilin activity to GnT-V shedding.\",\n      \"evidence\": \"N-terminal sequencing of soluble GnT-V, DFK-167 inhibitor, presenilin-1/2 double-KO cells, cleavage-site mutagenesis\",\n      \"pmids\": [\"17142794\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Regulation of cleavage in physiological contexts unclear\", \"Relationship to SPPL3-mediated cleavage not addressed\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"The directionality of the branching/PI3K relationship was tested using Mgat5/Pten epistasis, establishing positive feedback from PI3K signaling back to N-glycan branching.\",\n      \"evidence\": \"Mgat5/Pten double-mutant MEFs, PI3K/Akt and spreading assays, lectin flow cytometry, longevity analysis\",\n      \"pmids\": [\"17400585\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism coupling PI3K to MGAT5 expression/activity not defined\", \"Single-lab epistasis\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"How MGAT5 is transcriptionally controlled was unknown; Ets-1 was identified as a regulator whose level correlates with and drives GnT-V expression.\",\n      \"evidence\": \"mRNA correlation across 16 cancer lines, Ets-1 and dominant-negative Ets-1 transfection\",\n      \"pmids\": [\"10438459\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct promoter binding not shown here\", \"Correlative across-line data\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Distinguishing GnT-V from paralog GnT-Vb required kinetic characterization, defining GnT-V's metal-independence, pH optimum, and preference for N-glycan over O-mannose acceptors.\",\n      \"evidence\": \"In vitro kinetics with purified truncated enzymes, synthetic acceptors, HPLC product analysis\",\n      \"pmids\": [\"19846580\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo substrate preference not yet demonstrated\", \"Structural basis of substrate discrimination unresolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Branching was shown to control CTLA-4 endocytosis and contribute to autoimmunity, extending the lattice model to inhibitory receptor regulation and disease.\",\n      \"evidence\": \"Mgat5 KO mice, adoptive T-cell transfer, EAE model\",\n      \"pmids\": [\"22389815\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct CTLA-4 glycosite mapping not shown\", \"Non-T-cell contributions not dissected\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Genetic dissection in brain established GnT-V as the sole in vivo source of N-linked β1,6 branches, non-redundant with GnT-Vb.\",\n      \"evidence\": \"GnT-V, GnT-Vb, and double-KO mice with glycan structural analysis\",\n      \"pmids\": [\"22715095\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue-specific substrate identities not addressed\", \"Functional consequences in brain not characterized here\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"A direct transcriptional activator was confirmed when RUNX2 was shown to bind the MGAT5 promoter and drive expression in gastric cancer.\",\n      \"evidence\": \"ChIP-PCR, RUNX2 siRNA, qRT-PCR/Western, in vivo xenograft\",\n      \"pmids\": [\"37256183\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relationship to Ets-1 regulation not integrated\", \"Single-lab cancer context\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"The first defined functional substrate emerged: GnT-V branching of hENT1 controls its surface accumulation and thereby gemcitabine uptake and chemosensitivity.\",\n      \"evidence\": \"GnT-V shRNA, hENT1 lectin blot, surface fractionation, gemcitabine uptake/viability assays\",\n      \"pmids\": [\"30143259\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"hENT1 glycosites not mapped\", \"Single cancer-cell context\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Post-transcriptional control of MGAT5 was established when IGF2BP1 was shown to stabilize MGAT5 mRNA via m6A, linking branching to liver cancer stemness.\",\n      \"evidence\": \"IGF2BP1 shRNA, MeRIP-qPCR, mRNA stability assay, stemness and in vivo tumorigenesis assays\",\n      \"pmids\": [\"34514861\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"m6A site on MGAT5 not pinpointed\", \"Generality beyond liver cancer stem cells unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Branching was connected to mechanosensing when CRISPR deletion of MGAT5 abolished stiffness-dependent glioblastoma invasion via the galectin-3/integrin axis.\",\n      \"evidence\": \"CRISPR MGAT5 KO in GSCs, tunable-stiffness scaffolds, migration, focal adhesion/EMT readouts, galectin-3 binding\",\n      \"pmids\": [\"33894774\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific mechanoreceptor substrates not identified\", \"Single-lab GSC system\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Selective inhibitor design and computational/biochemical analysis revealed GnT-V's unusual donor-pocket hydrophobicity tolerance and acceptor recognition by residues outside the catalytic site.\",\n      \"evidence\": \"In vitro inhibition with UDP-GlcNAc analogs across GnT-I–V, docking; MD simulations with mutagenesis\",\n      \"pmids\": [\"35248671\", \"37974463\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No experimental high-resolution structure\", \"Inhibitor selectivity in cells not demonstrated\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"An intercellular dimension of GnT-V was revealed: SPPL3-cleaved active enzyme is loaded into small EVs that transfer to recipient cells and remodel their glycans.\",\n      \"evidence\": \"sEV fractionation, single-particle imaging, SPPL3 knockdown, sEV enzyme activity, recipient N-glycan profiling\",\n      \"pmids\": [\"36590176\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological relevance of glycan transfer in vivo unclear\", \"Relationship of SPPL3 to γ-secretase cleavage not reconciled\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A developmental role emerged: MGAT5 loss in neural stem/progenitor cells shifts differentiation toward neurons and depletes the niche, altering cortical layering.\",\n      \"evidence\": \"Mgat5 null mice, in vitro NSPC differentiation, in vivo cortical layering analysis\",\n      \"pmids\": [\"37172586\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Substrate(s) governing NSPC fate not identified\", \"Signaling pathway downstream not mapped\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"MGAT5 was implicated in immune evasion when its loss sensitized PDAC to TNF-superfamily death and enabled T/DC/NK-dependent tumor clearance with checkpoint blockade.\",\n      \"evidence\": \"Mgat5 KO PDAC lines, syngeneic in vivo models, immune-cell depletion, cell death pathway analysis, checkpoint blockade\",\n      \"pmids\": [\"38912584\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific glycoprotein substrates controlling death sensitivity not defined\", \"Single-lab models\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Substrate-specific control of protein fate was extended to PSMA, whose GnT-V branching prevents autophagic degradation within a JAK2/STAT3/GnT-V/PSMA feedback loop, and to TIMP-1, whose glycosylation activates VEGF signaling.\",\n      \"evidence\": \"PSMA glycosite mapping, PSMA-JAK2 co-IP, autophagy inhibition, STAT3 assays; GnT-V/TIMP-1 GST pull-down, TIMP-1 mutant, angiogenesis and in vivo DR model\",\n      \"pmids\": [\"40112979\", \"38499842\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of glycan-dependent degradation protection not fully resolved\", \"Single-lab disease contexts\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Unbiased in vivo substrate profiling identified ANPEP and MEP1A as major kidney GnT-V substrates and linked polarized trafficking to substrate-selective glycosylation.\",\n      \"evidence\": \"Lectin-assisted proteomics, glycosite mapping, single-cell transcriptomics, epithelial polarization assay\",\n      \"pmids\": [\"41323266\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequences of ANPEP/MEP1A branching not established\", \"Trafficking machinery directing apical accumulation unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A high-resolution structure and unified mechanistic account of how subcellular trafficking and substrate accessibility dictate which proteins GnT-V branches in a given tissue remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No experimental enzyme structure in the corpus\", \"Rules governing tissue/substrate selectivity incomplete\", \"Reconciliation of multiple cleaved/secreted/EV forms not unified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 24, 8, 9]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [12, 20, 22, 21]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [5, 9]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [14]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [4, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 9, 24]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 3, 10, 18]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 2, 7, 20]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [1, 11, 12, 18, 22]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"LGALS3\", \"TIMP-1\", \"PSMA\", \"JAK2\", \"ISLR\", \"PSEN1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}