{"gene":"SNX3","run_date":"2026-04-28T20:42:08","timeline":{"discoveries":[{"year":2001,"finding":"SNX3 is associated with early endosomes through its PX domain, which directly binds phosphatidylinositol-3-phosphate (PtdIns(3)P). Overexpression of SNX3 alters endosomal morphology and delays transport to the lysosome; microinjection of SNX3 antibodies impairs transport from the early to the recycling endosome.","method":"PX domain-PtdIns(3)P binding assay, overexpression studies, antibody microinjection, endosomal morphology analysis","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — direct lipid-binding assay combined with functional overexpression and antibody perturbation experiments, replicated across multiple approaches in a high-impact journal","pmids":["11433298"],"is_preprint":false},{"year":2007,"finding":"Yeast Grd19/Snx3p functions as a cargo-specific adapter for the retromer complex by directly binding a recycling signal in the iron transporter Ftr1p cytosolic tail. Snx3p and retromer partially colocalize on tubular endosomes and are physically associated; this complex mediates endosome-to-plasma membrane recycling of Fet3p-Ftr1p.","method":"Direct binding assay (recycling signal in Ftr1p binds Grd19/Snx3p), co-immunoprecipitation, colocalization microscopy, genetic epistasis with retromer mutants and Ypt6p Golgi Rab GTPase module","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — direct binding of cargo signal to SNX3, physical association with retromer, colocalization, and genetic epistasis, replicated in multiple experiments","pmids":["17420293"],"is_preprint":false},{"year":2008,"finding":"SNX3 is required for multivesicular body (MVB) formation but not for EGF receptor degradation, whereas Hrs is essential for lysosomal targeting but dispensable for MVB biogenesis. PtdIns(3)P thus controls complementary functions of Hrs and SNX3 in sorting and MVB biogenesis.","method":"RNAi knockdown of SNX3 and Hrs with electron microscopy of MVB morphology, EGF receptor degradation assays, epistasis analysis","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 2 — clean loss-of-function with defined cellular phenotype (MVB biogenesis defect) and genetic epistasis distinguishing SNX3 from Hrs function","pmids":["18767904"],"is_preprint":false},{"year":2008,"finding":"In yeast, Snx3/Grd19 and retromer sort Fet3-Ftr1 into a recycling pathway at a common endosome where Vps27 (ESCRT component) also localizes; the recycling (Snx3-retromer) and degradative (ESCRT/MVB) pathways diverge at this compartment. Iron-induced degradation requires ESCRT machinery and Rsp5 ubiquitin ligase-mediated ubiquitylation, while Snx3-retromer-dependent recycling is constitutive when ESCRT or ubiquitylation is absent.","method":"Genetic epistasis (ESCRT and Rsp5 mutants), fluorescence microscopy colocalization, ubiquitylation site mutagenesis of Fet3-Ftr1","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal genetic and cell biological approaches establishing pathway position and molecular mechanism","pmids":["18768754"],"is_preprint":false},{"year":2011,"finding":"SNX3 interacts directly with the cargo-selective subcomplex (VPS26/VPS29/VPS35) of the retromer to sort Wntless (Wls) into a morphologically distinct endosome-to-Golgi retrieval pathway that is independent of SNX1-SNX2 and SNX5-SNX6. This SNX3-retromer pathway is evolutionarily conserved and required for Wls recycling and Wnt secretion.","method":"Direct protein interaction assays (pulldown of SNX3 with retromer cargo-selective subcomplex), C. elegans genetic epistasis, Drosophila and mammalian cell knockdown with Wls trafficking readout","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — direct binding demonstrated, multiple organisms and orthogonal methods, replicated across labs","pmids":["21725319"],"is_preprint":false},{"year":2011,"finding":"Drosophila SNX3 (DSNX3) colocalizes with the retromer component Vps35 in early endosomes and interacts with Vps35. Loss of DSNX3 causes reduction of Wls levels and impairs Wingless secretion; overexpression of Wls rescues the Wg secretion defect, placing SNX3 upstream of Wls in the Wnt secretion pathway.","method":"Co-immunoprecipitation (DSNX3-Vps35), colocalization microscopy, Drosophila loss-of-function clonal analysis, dsRNA knockdown in S2 cells, genetic rescue by Wls overexpression","journal":"Cell research","confidence":"High","confidence_rationale":"Tier 2 — reciprocal interaction, colocalization, genetic rescue, and loss-of-function phenotype in multiple systems","pmids":["22041890"],"is_preprint":false},{"year":2013,"finding":"Snx3 and Vps35 (retromer component) interact with the transferrin receptor (Tfrc) to sort it to recycling endosomes. Loss of Snx3 in vertebrates causes Tfrc accumulation in early endosomes, impaired transferrin-mediated iron uptake, and anemia/hemoglobin defects in erythroid progenitors.","method":"Co-immunoprecipitation (Snx3, Vps35, and Tfrc), Snx3 knockdown/knockout in zebrafish and mouse with iron uptake assays, rescue with non-Tf iron chelates","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 2 — physical interaction demonstrated, in vivo loss-of-function with defined physiological phenotype, rescue experiment, multiple organisms","pmids":["23416069"],"is_preprint":false},{"year":2013,"finding":"SNX3 recruits to nascent phagosomes via its PI3P-binding PX domain and negatively regulates phagocytic uptake of bacteria by dendritic cells. SNX3 competes with EEA1 for binding to PI3P on phagosomal membranes, reducing EEA1 recruitment and thereby dampening phagocytosis.","method":"Live cell imaging of SNX3-phagosome recruitment, siRNA silencing with phagocytosis uptake assay, competition assay between SNX3 and EEA1 for PI3P binding","journal":"Immunology","confidence":"Medium","confidence_rationale":"Tier 2-3 — direct localization to phagosomes with functional consequence, competition mechanism supported but not fully reconstituted in vitro","pmids":["23237080"],"is_preprint":false},{"year":2018,"finding":"SNX3-retromer assembly is essential for Wntless endosome-to-Golgi transport, and SNX3 associates with an evolutionarily conserved endosomal membrane-remodeling complex composed of MON2, DOPEY2, and the putative aminophospholipid translocase ATP9A. In vivo suppression of MON2, DOPEY2, or ATP9A orthologues in C. elegans phenocopies loss of SNX3-retromer, leading to lysosomal degradation of Wntless and Wnt phenotype.","method":"Co-immunoprecipitation (SNX3 with MON2/DOPEY2/ATP9A), C. elegans genetic knockdown epistasis, dominant-negative ATPase mutant (TAT-5 E246Q) expression","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — reciprocal interaction demonstrated, in vivo genetic epistasis, mechanistic validation with ATPase-dead mutant, multiple organisms","pmids":["30213940"],"is_preprint":false},{"year":2018,"finding":"Alpha-synuclein inhibits Snx3-retromer-mediated recycling of iron transporters (Fet3/Ftr1) in yeast by blocking the association of Snx3 with endocytic vesicles, possibly by interfering with Snx3 binding to PI3P on endosomal membranes.","method":"Fluorescence microscopy of Snx3-mCherry vesicle association, yeast genetic model of Parkinson's disease, C. elegans dopaminergic neuron degeneration assay, iron chelator rescue","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 3 — mechanistic inference from imaging and genetic data; PI3P competition proposed but not directly demonstrated in vitro","pmids":["29452354"],"is_preprint":false},{"year":2019,"finding":"SNX3's PX domain binds PI(3)P in the phagosomal coat of Borrelia-containing phagosomes, enabling vesicle-phagosome contact via Rab5a vesicles. The C-terminal region of SNX3 recruits galectin-9, making SNX3 a hub for two distinct vesicle populations that contribute to phagosome compaction and maturation.","method":"Live cell imaging of SNX3 and Rab5a vesicle trafficking, PI(3)P binding assay (PX domain), co-immunoprecipitation/interaction assay of SNX3 with galectin-9, phagosome compaction assay","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — direct domain-lipid binding, protein-protein interaction, live imaging with functional readout (phagosome compaction), multiple orthogonal approaches","pmids":["31337623"],"is_preprint":false},{"year":2020,"finding":"Snx3 is required for neural tube closure in mice via its role in recycling WLS (Wnt ligand-binding protein) to support WNT secretion. Loss of Snx3 causes mis-trafficking of WLS to the lysosome. A human NTD-associated point mutation in SNX3 results in functionally impaired SNX3 that fails to colocalize with WLS and leads to WLS degradation.","method":"Mouse knockout (fully penetrant cranial NTD), live cell imaging of WLS recycling, WNT agonist rescue of NT closure, human variant functional assay","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 — in vivo loss-of-function with defined phenotype, live imaging of cargo mis-trafficking, genetic rescue, and human variant functional validation","pmids":["33214242"],"is_preprint":false},{"year":2021,"finding":"SNX3 interacts with EGFR upon EGF stimulation (detected by proximity labeling) and colocalizes with early endosomes and endocytosed EGF. SNX3 loss affects EGFR protein levels; long-term SNX3 silencing leads to compensatory EGFR overexpression, increased proliferation, migration, invasion, and tumor metastasis in TNBC models.","method":"Proximity labeling (BioID), colocalization microscopy, RNAi knockdown (transient and long-term), EGFR protein level assay, syngeneic mouse tumor model","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 3 — proximity labeling interaction and colocalization, functional KD phenotype, but mechanism linking SNX3 to EGFR stability not fully reconstituted","pmids":["34718348"],"is_preprint":false},{"year":2021,"finding":"In C. elegans, SNX-3 is essential for generation of ARF-6-associated recycling endosomal tubules and retrieval of clathrin-independent endocytic (CIE) cargoes back to the plasma membrane. This function is independent of the retromer trimer (VPS-26/-29/-35). SNX3 and EEA1 compete for binding to PI3P on early endosomes, and loss of SNX-3 allows increased EEA1 recruitment and ESCRT-mediated lysosomal degradation of CIE cargo.","method":"C. elegans genetic screen and loss-of-function, fluorescence microscopy of tubule formation, hTAC CIE cargo trafficking assay, competition assay between SNX3 and EEA1 for PI3P in HeLa cells, retromer component epistasis","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 — genetic screen, loss-of-function with defined cargo trafficking phenotype, competition assay in mammalian cells, epistasis ruling out retromer trimer dependence","pmids":["34081703"],"is_preprint":false},{"year":2022,"finding":"Alpha-synuclein disrupts Snx3-retromer retrograde trafficking of the proprotein convertase Kex2 and dipeptidyl aminopeptidase Ste13 from late endosomes to the trans-Golgi network in yeast, causing their default transit to the vacuole. The membrane-binding ability of α-syn is necessary for this inhibition, as the A30P membrane-binding-defective variant does not inhibit Snx3-retromer recycling.","method":"Fluorescence microscopy of Kex2-GFP/GFP-Ste13 trafficking, western blotting, yeast mating assay (α-factor processing), α-syn variant analysis (A53T, A30P, αsynΔC)","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple approaches in yeast model, α-syn variant mechanistic dissection, but specific molecular contact between α-syn and Snx3 not fully defined","pmids":["34570221"],"is_preprint":false},{"year":2025,"finding":"SNX3-retromer mediates retrograde trafficking of the AAV receptor AAVR; in vitro reconstitution demonstrates that AAVR's cytosolic tail directly engages the SNX3-retromer complex and drives membrane tubulation, a hallmark of retrograde trafficking.","method":"In vitro reconstitution assay (AAVR cytosolic tail with SNX3-retromer), membrane tubulation assay, AAVR-knockout cell trafficking studies","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 — in vitro reconstitution and tubulation assay, but preprint and not yet peer-reviewed","pmids":["bio_10.1101_2025.11.22.689972"],"is_preprint":true},{"year":2025,"finding":"SNX3 directly interacts with HMGB1 (identified by immunoprecipitation-mass spectrometry and localized surface plasmon resonance), and the SNX3-retromer complex mediates the efflux of nuclear HMGB1 to the cytoplasm, promoting pathological cardiac hypertrophy and heart failure.","method":"Immunoprecipitation-mass spectrometry, localized surface plasmon resonance (direct binding), cardiac-specific SNX3 knockout (TAC mouse), adenoviral overexpression (Ad-SNX3), AAC rat model, HMGB1 overexpression/knockdown epistasis","journal":"Acta pharmacologica Sinica","confidence":"Medium","confidence_rationale":"Tier 2 — direct binding confirmed by SPR, in vivo KO and OE with defined cardiac phenotype, epistasis with HMGB1; single lab","pmids":["39753981"],"is_preprint":false},{"year":2025,"finding":"Snx3 and SNX-BAR proteins (Vps5-Vps17) can form hybrid endosomal coats at variable subunit ratios, assembled on tubular carriers with greater membrane scaffolding activity than homogeneous coats. In vivo, Snx3 and SNX-BARs colocalize and mutually impact sorting of their respective cargos, linked through retromer oligomerization rather than simultaneous direct retromer binding.","method":"In vitro reconstitution with purified SNX-BARs and Snx3, membrane scaffolding assay, in vivo colocalization, cargo sorting epistasis","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 — in vitro reconstitution with purified components and in vivo validation; preprint, not yet peer-reviewed","pmids":["bio_10.1101_2025.07.29.667382"],"is_preprint":true}],"current_model":"SNX3 is a PI(3)P-binding sorting nexin whose PX domain anchors it to early endosomes, where it acts as a cargo-specific adapter for the retromer complex (directly engaging the VPS26/VPS29/VPS35 cargo-selective subcomplex) to drive tubular endosome-to-Golgi and endosome-to-plasma membrane retrograde recycling of defined cargos including Wntless (enabling Wnt secretion), the transferrin receptor (enabling iron uptake), and iron transporters; it also competes with EEA1 for PI(3)P binding to organize recycling tubules, contributes to multivesicular body biogenesis, regulates phagosome maturation by recruiting Rab5a vesicles and galectin-9 via its C-terminal region, and is inhibited by alpha-synuclein through interference with its endosomal membrane association."},"narrative":{"teleology":[{"year":2001,"claim":"Establishing SNX3 as a PI3P-binding early endosomal protein resolved how a minimal PX-domain-only sorting nexin achieves membrane targeting and revealed its requirement for endosomal sorting and morphology.","evidence":"PX domain–PI3P binding assay, overexpression morphology analysis, and antibody microinjection blocking recycling endosome transport in mammalian cells","pmids":["11433298"],"confidence":"High","gaps":["No cargo identified at this stage","Mechanism of endosomal morphology alteration undefined","Relationship to retromer unknown"]},{"year":2007,"claim":"Identification of yeast Snx3/Grd19 as a cargo-specific adapter for retromer answered how retromer recognizes cargo lacking canonical sorting signals, establishing a new mode of retromer engagement distinct from SNX-BAR-dependent sorting.","evidence":"Direct binding of Snx3 to the Ftr1p recycling signal, co-IP with retromer, colocalization on tubular endosomes, and genetic epistasis with retromer mutants in S. cerevisiae","pmids":["17420293"],"confidence":"High","gaps":["Adapter function not yet confirmed in metazoans","Structural basis of SNX3–retromer–cargo ternary complex unknown"]},{"year":2008,"claim":"Demonstrating that SNX3 is required for MVB biogenesis independently of Hrs-mediated cargo sorting revealed that PI3P effectors partition complementary endosomal functions—SNX3 for intraluminal vesicle formation, Hrs for receptor degradation.","evidence":"RNAi knockdown with electron microscopy of MVB morphology and EGF receptor degradation assays in mammalian cells; parallel epistasis in yeast showing recycling–degradation pathway divergence at a common endosome","pmids":["18767904","18768754"],"confidence":"High","gaps":["Molecular mechanism by which SNX3 promotes MVB biogenesis unresolved","Whether SNX3's MVB role is retromer-dependent or independent unclear"]},{"year":2011,"claim":"Showing that SNX3 directly binds the VPS26/VPS29/VPS35 cargo-selective subcomplex to sort Wntless into a morphologically distinct retrieval pathway—independent of SNX1/SNX2/SNX5/SNX6—established SNX3-retromer as a dedicated Wnt-secretion-enabling sorting machine conserved across metazoa.","evidence":"Direct pulldown of SNX3 with retromer subcomplex, C. elegans and Drosophila genetic epistasis, mammalian cell knockdown with Wntless trafficking readout, Drosophila co-IP of DSNX3–Vps35 with genetic rescue by Wls overexpression","pmids":["21725319","22041890"],"confidence":"High","gaps":["How membrane curvature is generated without SNX-BAR proteins remained unclear","Identity of the membrane-remodeling machinery cooperating with SNX3-retromer unknown"]},{"year":2013,"claim":"Extension of SNX3-retromer cargo repertoire to the transferrin receptor linked endosomal sorting to systemic iron homeostasis, explaining how Snx3 loss causes anemia, and revealed SNX3's competition with EEA1 for PI3P on phagosomes as a mechanism regulating phagocytic uptake.","evidence":"Co-IP of Snx3/Vps35/Tfrc, zebrafish and mouse knockout with iron uptake assays and hemoglobin defects; live imaging and siRNA in dendritic cells showing SNX3–EEA1 competition on phagosomes","pmids":["23416069","23237080"],"confidence":"High","gaps":["Competition mechanism not reconstituted with purified components","Whether SNX3 directly contacts Tfrc cytosolic tail or requires VPS26 adaptations unresolved"]},{"year":2018,"claim":"Discovery that SNX3 associates with a MON2–DOPEY2–ATP9A membrane-remodeling complex resolved the long-standing question of how SNX3-retromer generates membrane tubules without SNX-BAR proteins, linking aminophospholipid flipping to retrograde carrier formation.","evidence":"Co-IP of SNX3 with MON2/DOPEY2/ATP9A, C. elegans genetic epistasis phenocopying SNX3-retromer loss, dominant-negative ATPase mutant validation","pmids":["30213940"],"confidence":"High","gaps":["Direct reconstitution of tubule formation by SNX3–MON2–DOPEY2–ATP9A not achieved","Structural organization of the complex undefined"]},{"year":2018,"claim":"Demonstration that alpha-synuclein inhibits SNX3 endosomal membrane association provided a mechanistic link between Parkinson's disease-associated protein aggregation and defective retromer-mediated iron transporter recycling.","evidence":"Fluorescence microscopy of Snx3-mCherry vesicle association in yeast α-synuclein model, C. elegans dopaminergic neuron degeneration assay, iron chelator rescue","pmids":["29452354"],"confidence":"Medium","gaps":["Direct α-synuclein–SNX3 molecular contact not demonstrated","PI3P competition between α-synuclein and SNX3 inferred but not reconstituted in vitro","Relevance to mammalian dopaminergic neurons not established"]},{"year":2019,"claim":"Identification of SNX3 as a bifunctional hub on phagosomes—recruiting Rab5a vesicles via its PX domain and galectin-9 via its C-terminal region—revealed how a minimal sorting nexin coordinates two distinct vesicle populations to drive phagosome compaction and maturation.","evidence":"Live cell imaging of SNX3/Rab5a vesicle trafficking to Borrelia-containing phagosomes, co-IP of SNX3 with galectin-9, phagosome compaction assay","pmids":["31337623"],"confidence":"High","gaps":["Whether galectin-9 recruitment is retromer-dependent or independent unclear","Structural basis of C-terminal region–galectin-9 interaction unknown"]},{"year":2020,"claim":"Mouse knockout establishing that Snx3 loss causes fully penetrant cranial neural tube defects through failed Wntless recycling and impaired Wnt secretion provided the first in vivo mammalian demonstration that SNX3-retromer is essential for embryonic development, with a human NTD-associated SNX3 variant shown to be functionally impaired.","evidence":"Mouse Snx3 knockout with NTD phenotype, live cell imaging of WLS mis-trafficking to lysosomes, WNT agonist rescue, human variant functional assay","pmids":["33214242"],"confidence":"High","gaps":["Whether other SNX3-retromer cargos contribute to the NTD phenotype unknown","Penetrance and spectrum of human SNX3 mutations in NTD populations not established"]},{"year":2021,"claim":"Discovery that SNX3 generates ARF-6-associated recycling tubules for clathrin-independent endocytic cargos independently of retromer expanded SNX3 function beyond retromer-dependent sorting and formalized the SNX3–EEA1 competition model as a general endosomal fate-determination mechanism.","evidence":"C. elegans genetic screen and loss-of-function, CIE cargo (hTAC) trafficking assays, SNX3–EEA1 PI3P competition in HeLa cells, retromer epistasis showing independence","pmids":["34081703"],"confidence":"High","gaps":["Molecular mechanism of SNX3-driven tubule formation without retromer not defined","Whether ARF-6-dependent and retromer-dependent functions of SNX3 occur on distinct membrane domains unknown"]},{"year":2022,"claim":"Demonstration that alpha-synuclein's membrane-binding activity is specifically required to disrupt SNX3-retromer trafficking of Kex2 and Ste13 cargos refined the pathological mechanism, distinguishing it from aggregation-dependent toxicity.","evidence":"Fluorescence microscopy and western blotting of Kex2/Ste13 trafficking in yeast expressing α-syn variants (A53T, A30P, ΔC), yeast mating assay for α-factor processing","pmids":["34570221"],"confidence":"Medium","gaps":["Direct molecular contact between membrane-bound α-synuclein and SNX3 or retromer not identified","Validation in mammalian neuronal cells lacking"]},{"year":null,"claim":"Key unresolved questions include the structural basis of the SNX3–retromer–cargo ternary complex at atomic resolution, how SNX3 generates membrane tubules in retromer-independent contexts, whether hybrid SNX3/SNX-BAR coats operate in vivo in mammalian cells, and the full spectrum of human disease caused by SNX3 mutations.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of SNX3–retromer–cargo complex published in the timeline","Retromer-independent tubulation mechanism undefined","In vivo relevance of hybrid SNX3/SNX-BAR coats in mammals not tested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,7,10]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1,4,6]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[7,13]}],"localization":[{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[0,1,4,5,6,10,13]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[0,10,13]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[1,4,6,8,13]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[1,4,6,8]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[4,5,11]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[11]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[7,10]}],"complexes":["SNX3-retromer (VPS26/VPS29/VPS35)","SNX3-MON2-DOPEY2-ATP9A"],"partners":["VPS35","VPS26","VPS29","WLS","TFRC","LGALS9","MON2","ATP9A"],"other_free_text":[]},"mechanistic_narrative":"SNX3 is a phosphatidylinositol-3-phosphate (PI3P)-binding sorting nexin that functions as a cargo-specific adapter on early endosomes, directing retrograde recycling of transmembrane cargos through the retromer pathway and organizing endosomal membrane identity. Its PX domain anchors it to PI3P-enriched endosomal membranes, where it directly engages the VPS26/VPS29/VPS35 cargo-selective retromer subcomplex—independently of SNX-BAR proteins—to sort Wntless (required for Wnt secretion), the transferrin receptor (required for iron uptake), and yeast iron transporters (Fet3–Ftr1) into tubular retrieval carriers destined for the Golgi or plasma membrane [PMID:21725319, PMID:23416069, PMID:17420293]. SNX3 also competes with EEA1 for PI3P binding, thereby controlling the balance between recycling and ESCRT-mediated lysosomal degradation of clathrin-independent endocytic cargos, contributes to multivesicular body biogenesis, and promotes phagosome maturation by recruiting Rab5a vesicles and galectin-9 via its C-terminal region [PMID:34081703, PMID:18767904, PMID:31337623]. Loss of SNX3 in mice causes fully penetrant cranial neural tube defects due to failed Wntless recycling and impaired Wnt signaling, and a human SNX3 variant associated with neural tube defects is functionally impaired [PMID:33214242]."},"prefetch_data":{"uniprot":{"accession":"O60493","full_name":"Sorting nexin-3","aliases":["Protein SDP3"],"length_aa":162,"mass_kda":18.8,"function":"Phosphoinositide-binding protein required for multivesicular body formation. Specifically binds phosphatidylinositol 3-phosphate (PtdIns(P3)). Can also bind phosphatidylinositol 4-phosphate (PtdIns(P4)), phosphatidylinositol 5-phosphate (PtdIns(P5)) and phosphatidylinositol 3,5-biphosphate (PtdIns(3,5)P2) (By similarity). Plays a role in protein transport between cellular compartments. Together with RAB7A facilitates endosome membrane association of the retromer cargo-selective subcomplex (CSC/VPS). May in part act as component of the SNX3-retromer complex which mediates the retrograde endosome-to-TGN transport of WLS distinct from the SNX-BAR retromer pathway (PubMed:21725319, PubMed:24344282, PubMed:30213940). Promotes stability and cell surface expression of epithelial sodium channel (ENAC) subunits SCNN1A and SCNN1G (By similarity). Not involved in EGFR degradation. Involved in the regulation of phagocytosis in dendritic cells possibly by regulating EEA1 recruitment to the nascent phagosomes (PubMed:23237080). Involved in iron homeostasis through regulation of endocytic recycling of the transferrin receptor TFRC presumably by delivering the transferrin:transferrin receptor complex to recycling endosomes; the function may involve the CSC retromer subcomplex (By similarity). Involved in regulation of neurite outgrowth in primary neurons (By similarity). Required for trafficking of WLS to the early endosome for recycling which promotes both canonical and non-canonical WNT signaling and is essential for neural tube closure (By similarity) (Microbial infection) In the case of Salmonella enterica infection, plays a role in maturation of the Salmonella-containing vacuole (SCV) and promotes recruitment of LAMP1 to SCVs","subcellular_location":"Early endosome; Cytoplasmic vesicle, phagosome","url":"https://www.uniprot.org/uniprotkb/O60493/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SNX3","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000112335","cell_line_id":"CID000680","localizations":[{"compartment":"vesicles","grade":3}],"interactors":[{"gene":"POLR1C","stoichiometry":0.2},{"gene":"RAB7A","stoichiometry":0.2},{"gene":"VPS29","stoichiometry":0.2},{"gene":"VPS35","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000680","total_profiled":1310},"omim":[{"mim_id":"605931","title":"SORTING NEXIN 4; SNX4","url":"https://www.omim.org/entry/605931"},{"mim_id":"605930","title":"SORTING NEXIN 3; SNX3","url":"https://www.omim.org/entry/605930"},{"mim_id":"605929","title":"SORTING NEXIN 2; SNX2","url":"https://www.omim.org/entry/605929"},{"mim_id":"601349","title":"MICROPHTHALMIA, SYNDROMIC 8; MCOPS8","url":"https://www.omim.org/entry/601349"},{"mim_id":"601272","title":"SORTING NEXIN 1; SNX1","url":"https://www.omim.org/entry/601272"}],"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/SNX3"},"hgnc":{"alias_symbol":["Grd19"],"prev_symbol":[]},"alphafold":{"accession":"O60493","domains":[{"cath_id":"3.30.1520.10","chopping":"23-145","consensus_level":"high","plddt":93.365,"start":23,"end":145}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O60493","model_url":"https://alphafold.ebi.ac.uk/files/AF-O60493-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O60493-F1-predicted_aligned_error_v6.png","plddt_mean":88.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SNX3","jax_strain_url":"https://www.jax.org/strain/search?query=SNX3"},"sequence":{"accession":"O60493","fasta_url":"https://rest.uniprot.org/uniprotkb/O60493.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O60493/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O60493"}},"corpus_meta":[{"pmid":"21725319","id":"PMC_21725319","title":"A SNX3-dependent retromer pathway mediates retrograde transport of the Wnt sorting receptor Wntless and is required for Wnt secretion.","date":"2011","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/21725319","citation_count":276,"is_preprint":false},{"pmid":"11433298","id":"PMC_11433298","title":"SNX3 regulates endosomal function through its PX-domain-mediated interaction with PtdIns(3)P.","date":"2001","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/11433298","citation_count":252,"is_preprint":false},{"pmid":"17420293","id":"PMC_17420293","title":"Grd19/Snx3p functions as a cargo-specific adapter for retromer-dependent endocytic recycling.","date":"2007","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/17420293","citation_count":144,"is_preprint":false},{"pmid":"22041890","id":"PMC_22041890","title":"SNX3 controls Wingless/Wnt secretion through regulating retromer-dependent recycling of Wntless.","date":"2011","source":"Cell 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of the Snx3-retromer complex and ESCRT proteins mediate regulated cargo sorting at a common endosome.","date":"2008","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/18768754","citation_count":57,"is_preprint":false},{"pmid":"34063020","id":"PMC_34063020","title":"Defect Study and Modelling of SnX3-Based Perovskite Solar Cells with SCAPS-1D.","date":"2021","source":"Nanomaterials (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/34063020","citation_count":37,"is_preprint":false},{"pmid":"29452354","id":"PMC_29452354","title":"Alpha-synuclein inhibits Snx3-retromer-mediated retrograde recycling of iron transporters in S. cerevisiae and C. elegans models of Parkinson's disease.","date":"2018","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/29452354","citation_count":31,"is_preprint":false},{"pmid":"12471201","id":"PMC_12471201","title":"Sorting nexin 3 (SNX3) is disrupted in a patient with a translocation 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activation","date":"2025-05-13","source":"bioRxiv","url":"https://doi.org/10.1101/2025.05.08.652881","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15457,"output_tokens":4974,"usd":0.060491},"stage2":{"model":"claude-opus-4-6","input_tokens":8450,"output_tokens":3439,"usd":0.192337},"total_usd":0.252828,"stage1_batch_id":"msgbatch_011rkcQdVV1RaFq9XhcG6df6","stage2_batch_id":"msgbatch_01RzgrJafdF4EWHhj5mNi6dh","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2001,\n      \"finding\": \"SNX3 is associated with early endosomes through its PX domain, which directly binds phosphatidylinositol-3-phosphate (PtdIns(3)P). Overexpression of SNX3 alters endosomal morphology and delays transport to the lysosome; microinjection of SNX3 antibodies impairs transport from the early to the recycling endosome.\",\n      \"method\": \"PX domain-PtdIns(3)P binding assay, overexpression studies, antibody microinjection, endosomal morphology analysis\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct lipid-binding assay combined with functional overexpression and antibody perturbation experiments, replicated across multiple approaches in a high-impact journal\",\n      \"pmids\": [\"11433298\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Yeast Grd19/Snx3p functions as a cargo-specific adapter for the retromer complex by directly binding a recycling signal in the iron transporter Ftr1p cytosolic tail. Snx3p and retromer partially colocalize on tubular endosomes and are physically associated; this complex mediates endosome-to-plasma membrane recycling of Fet3p-Ftr1p.\",\n      \"method\": \"Direct binding assay (recycling signal in Ftr1p binds Grd19/Snx3p), co-immunoprecipitation, colocalization microscopy, genetic epistasis with retromer mutants and Ypt6p Golgi Rab GTPase module\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct binding of cargo signal to SNX3, physical association with retromer, colocalization, and genetic epistasis, replicated in multiple experiments\",\n      \"pmids\": [\"17420293\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SNX3 is required for multivesicular body (MVB) formation but not for EGF receptor degradation, whereas Hrs is essential for lysosomal targeting but dispensable for MVB biogenesis. PtdIns(3)P thus controls complementary functions of Hrs and SNX3 in sorting and MVB biogenesis.\",\n      \"method\": \"RNAi knockdown of SNX3 and Hrs with electron microscopy of MVB morphology, EGF receptor degradation assays, epistasis analysis\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean loss-of-function with defined cellular phenotype (MVB biogenesis defect) and genetic epistasis distinguishing SNX3 from Hrs function\",\n      \"pmids\": [\"18767904\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"In yeast, Snx3/Grd19 and retromer sort Fet3-Ftr1 into a recycling pathway at a common endosome where Vps27 (ESCRT component) also localizes; the recycling (Snx3-retromer) and degradative (ESCRT/MVB) pathways diverge at this compartment. Iron-induced degradation requires ESCRT machinery and Rsp5 ubiquitin ligase-mediated ubiquitylation, while Snx3-retromer-dependent recycling is constitutive when ESCRT or ubiquitylation is absent.\",\n      \"method\": \"Genetic epistasis (ESCRT and Rsp5 mutants), fluorescence microscopy colocalization, ubiquitylation site mutagenesis of Fet3-Ftr1\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal genetic and cell biological approaches establishing pathway position and molecular mechanism\",\n      \"pmids\": [\"18768754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SNX3 interacts directly with the cargo-selective subcomplex (VPS26/VPS29/VPS35) of the retromer to sort Wntless (Wls) into a morphologically distinct endosome-to-Golgi retrieval pathway that is independent of SNX1-SNX2 and SNX5-SNX6. This SNX3-retromer pathway is evolutionarily conserved and required for Wls recycling and Wnt secretion.\",\n      \"method\": \"Direct protein interaction assays (pulldown of SNX3 with retromer cargo-selective subcomplex), C. elegans genetic epistasis, Drosophila and mammalian cell knockdown with Wls trafficking readout\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct binding demonstrated, multiple organisms and orthogonal methods, replicated across labs\",\n      \"pmids\": [\"21725319\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Drosophila SNX3 (DSNX3) colocalizes with the retromer component Vps35 in early endosomes and interacts with Vps35. Loss of DSNX3 causes reduction of Wls levels and impairs Wingless secretion; overexpression of Wls rescues the Wg secretion defect, placing SNX3 upstream of Wls in the Wnt secretion pathway.\",\n      \"method\": \"Co-immunoprecipitation (DSNX3-Vps35), colocalization microscopy, Drosophila loss-of-function clonal analysis, dsRNA knockdown in S2 cells, genetic rescue by Wls overexpression\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal interaction, colocalization, genetic rescue, and loss-of-function phenotype in multiple systems\",\n      \"pmids\": [\"22041890\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Snx3 and Vps35 (retromer component) interact with the transferrin receptor (Tfrc) to sort it to recycling endosomes. Loss of Snx3 in vertebrates causes Tfrc accumulation in early endosomes, impaired transferrin-mediated iron uptake, and anemia/hemoglobin defects in erythroid progenitors.\",\n      \"method\": \"Co-immunoprecipitation (Snx3, Vps35, and Tfrc), Snx3 knockdown/knockout in zebrafish and mouse with iron uptake assays, rescue with non-Tf iron chelates\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — physical interaction demonstrated, in vivo loss-of-function with defined physiological phenotype, rescue experiment, multiple organisms\",\n      \"pmids\": [\"23416069\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SNX3 recruits to nascent phagosomes via its PI3P-binding PX domain and negatively regulates phagocytic uptake of bacteria by dendritic cells. SNX3 competes with EEA1 for binding to PI3P on phagosomal membranes, reducing EEA1 recruitment and thereby dampening phagocytosis.\",\n      \"method\": \"Live cell imaging of SNX3-phagosome recruitment, siRNA silencing with phagocytosis uptake assay, competition assay between SNX3 and EEA1 for PI3P binding\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct localization to phagosomes with functional consequence, competition mechanism supported but not fully reconstituted in vitro\",\n      \"pmids\": [\"23237080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SNX3-retromer assembly is essential for Wntless endosome-to-Golgi transport, and SNX3 associates with an evolutionarily conserved endosomal membrane-remodeling complex composed of MON2, DOPEY2, and the putative aminophospholipid translocase ATP9A. In vivo suppression of MON2, DOPEY2, or ATP9A orthologues in C. elegans phenocopies loss of SNX3-retromer, leading to lysosomal degradation of Wntless and Wnt phenotype.\",\n      \"method\": \"Co-immunoprecipitation (SNX3 with MON2/DOPEY2/ATP9A), C. elegans genetic knockdown epistasis, dominant-negative ATPase mutant (TAT-5 E246Q) expression\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal interaction demonstrated, in vivo genetic epistasis, mechanistic validation with ATPase-dead mutant, multiple organisms\",\n      \"pmids\": [\"30213940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Alpha-synuclein inhibits Snx3-retromer-mediated recycling of iron transporters (Fet3/Ftr1) in yeast by blocking the association of Snx3 with endocytic vesicles, possibly by interfering with Snx3 binding to PI3P on endosomal membranes.\",\n      \"method\": \"Fluorescence microscopy of Snx3-mCherry vesicle association, yeast genetic model of Parkinson's disease, C. elegans dopaminergic neuron degeneration assay, iron chelator rescue\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — mechanistic inference from imaging and genetic data; PI3P competition proposed but not directly demonstrated in vitro\",\n      \"pmids\": [\"29452354\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SNX3's PX domain binds PI(3)P in the phagosomal coat of Borrelia-containing phagosomes, enabling vesicle-phagosome contact via Rab5a vesicles. The C-terminal region of SNX3 recruits galectin-9, making SNX3 a hub for two distinct vesicle populations that contribute to phagosome compaction and maturation.\",\n      \"method\": \"Live cell imaging of SNX3 and Rab5a vesicle trafficking, PI(3)P binding assay (PX domain), co-immunoprecipitation/interaction assay of SNX3 with galectin-9, phagosome compaction assay\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct domain-lipid binding, protein-protein interaction, live imaging with functional readout (phagosome compaction), multiple orthogonal approaches\",\n      \"pmids\": [\"31337623\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Snx3 is required for neural tube closure in mice via its role in recycling WLS (Wnt ligand-binding protein) to support WNT secretion. Loss of Snx3 causes mis-trafficking of WLS to the lysosome. A human NTD-associated point mutation in SNX3 results in functionally impaired SNX3 that fails to colocalize with WLS and leads to WLS degradation.\",\n      \"method\": \"Mouse knockout (fully penetrant cranial NTD), live cell imaging of WLS recycling, WNT agonist rescue of NT closure, human variant functional assay\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo loss-of-function with defined phenotype, live imaging of cargo mis-trafficking, genetic rescue, and human variant functional validation\",\n      \"pmids\": [\"33214242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SNX3 interacts with EGFR upon EGF stimulation (detected by proximity labeling) and colocalizes with early endosomes and endocytosed EGF. SNX3 loss affects EGFR protein levels; long-term SNX3 silencing leads to compensatory EGFR overexpression, increased proliferation, migration, invasion, and tumor metastasis in TNBC models.\",\n      \"method\": \"Proximity labeling (BioID), colocalization microscopy, RNAi knockdown (transient and long-term), EGFR protein level assay, syngeneic mouse tumor model\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — proximity labeling interaction and colocalization, functional KD phenotype, but mechanism linking SNX3 to EGFR stability not fully reconstituted\",\n      \"pmids\": [\"34718348\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In C. elegans, SNX-3 is essential for generation of ARF-6-associated recycling endosomal tubules and retrieval of clathrin-independent endocytic (CIE) cargoes back to the plasma membrane. This function is independent of the retromer trimer (VPS-26/-29/-35). SNX3 and EEA1 compete for binding to PI3P on early endosomes, and loss of SNX-3 allows increased EEA1 recruitment and ESCRT-mediated lysosomal degradation of CIE cargo.\",\n      \"method\": \"C. elegans genetic screen and loss-of-function, fluorescence microscopy of tubule formation, hTAC CIE cargo trafficking assay, competition assay between SNX3 and EEA1 for PI3P in HeLa cells, retromer component epistasis\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic screen, loss-of-function with defined cargo trafficking phenotype, competition assay in mammalian cells, epistasis ruling out retromer trimer dependence\",\n      \"pmids\": [\"34081703\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Alpha-synuclein disrupts Snx3-retromer retrograde trafficking of the proprotein convertase Kex2 and dipeptidyl aminopeptidase Ste13 from late endosomes to the trans-Golgi network in yeast, causing their default transit to the vacuole. The membrane-binding ability of α-syn is necessary for this inhibition, as the A30P membrane-binding-defective variant does not inhibit Snx3-retromer recycling.\",\n      \"method\": \"Fluorescence microscopy of Kex2-GFP/GFP-Ste13 trafficking, western blotting, yeast mating assay (α-factor processing), α-syn variant analysis (A53T, A30P, αsynΔC)\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple approaches in yeast model, α-syn variant mechanistic dissection, but specific molecular contact between α-syn and Snx3 not fully defined\",\n      \"pmids\": [\"34570221\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SNX3-retromer mediates retrograde trafficking of the AAV receptor AAVR; in vitro reconstitution demonstrates that AAVR's cytosolic tail directly engages the SNX3-retromer complex and drives membrane tubulation, a hallmark of retrograde trafficking.\",\n      \"method\": \"In vitro reconstitution assay (AAVR cytosolic tail with SNX3-retromer), membrane tubulation assay, AAVR-knockout cell trafficking studies\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution and tubulation assay, but preprint and not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.11.22.689972\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SNX3 directly interacts with HMGB1 (identified by immunoprecipitation-mass spectrometry and localized surface plasmon resonance), and the SNX3-retromer complex mediates the efflux of nuclear HMGB1 to the cytoplasm, promoting pathological cardiac hypertrophy and heart failure.\",\n      \"method\": \"Immunoprecipitation-mass spectrometry, localized surface plasmon resonance (direct binding), cardiac-specific SNX3 knockout (TAC mouse), adenoviral overexpression (Ad-SNX3), AAC rat model, HMGB1 overexpression/knockdown epistasis\",\n      \"journal\": \"Acta pharmacologica Sinica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding confirmed by SPR, in vivo KO and OE with defined cardiac phenotype, epistasis with HMGB1; single lab\",\n      \"pmids\": [\"39753981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Snx3 and SNX-BAR proteins (Vps5-Vps17) can form hybrid endosomal coats at variable subunit ratios, assembled on tubular carriers with greater membrane scaffolding activity than homogeneous coats. In vivo, Snx3 and SNX-BARs colocalize and mutually impact sorting of their respective cargos, linked through retromer oligomerization rather than simultaneous direct retromer binding.\",\n      \"method\": \"In vitro reconstitution with purified SNX-BARs and Snx3, membrane scaffolding assay, in vivo colocalization, cargo sorting epistasis\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with purified components and in vivo validation; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.07.29.667382\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"SNX3 is a PI(3)P-binding sorting nexin whose PX domain anchors it to early endosomes, where it acts as a cargo-specific adapter for the retromer complex (directly engaging the VPS26/VPS29/VPS35 cargo-selective subcomplex) to drive tubular endosome-to-Golgi and endosome-to-plasma membrane retrograde recycling of defined cargos including Wntless (enabling Wnt secretion), the transferrin receptor (enabling iron uptake), and iron transporters; it also competes with EEA1 for PI(3)P binding to organize recycling tubules, contributes to multivesicular body biogenesis, regulates phagosome maturation by recruiting Rab5a vesicles and galectin-9 via its C-terminal region, and is inhibited by alpha-synuclein through interference with its endosomal membrane association.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SNX3 is a phosphatidylinositol-3-phosphate (PI3P)-binding sorting nexin that functions as a cargo-specific adapter on early endosomes, directing retrograde recycling of transmembrane cargos through the retromer pathway and organizing endosomal membrane identity. Its PX domain anchors it to PI3P-enriched endosomal membranes, where it directly engages the VPS26/VPS29/VPS35 cargo-selective retromer subcomplex—independently of SNX-BAR proteins—to sort Wntless (required for Wnt secretion), the transferrin receptor (required for iron uptake), and yeast iron transporters (Fet3–Ftr1) into tubular retrieval carriers destined for the Golgi or plasma membrane [PMID:21725319, PMID:23416069, PMID:17420293]. SNX3 also competes with EEA1 for PI3P binding, thereby controlling the balance between recycling and ESCRT-mediated lysosomal degradation of clathrin-independent endocytic cargos, contributes to multivesicular body biogenesis, and promotes phagosome maturation by recruiting Rab5a vesicles and galectin-9 via its C-terminal region [PMID:34081703, PMID:18767904, PMID:31337623]. Loss of SNX3 in mice causes fully penetrant cranial neural tube defects due to failed Wntless recycling and impaired Wnt signaling, and a human SNX3 variant associated with neural tube defects is functionally impaired [PMID:33214242].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Establishing SNX3 as a PI3P-binding early endosomal protein resolved how a minimal PX-domain-only sorting nexin achieves membrane targeting and revealed its requirement for endosomal sorting and morphology.\",\n      \"evidence\": \"PX domain–PI3P binding assay, overexpression morphology analysis, and antibody microinjection blocking recycling endosome transport in mammalian cells\",\n      \"pmids\": [\"11433298\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No cargo identified at this stage\", \"Mechanism of endosomal morphology alteration undefined\", \"Relationship to retromer unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identification of yeast Snx3/Grd19 as a cargo-specific adapter for retromer answered how retromer recognizes cargo lacking canonical sorting signals, establishing a new mode of retromer engagement distinct from SNX-BAR-dependent sorting.\",\n      \"evidence\": \"Direct binding of Snx3 to the Ftr1p recycling signal, co-IP with retromer, colocalization on tubular endosomes, and genetic epistasis with retromer mutants in S. cerevisiae\",\n      \"pmids\": [\"17420293\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Adapter function not yet confirmed in metazoans\", \"Structural basis of SNX3–retromer–cargo ternary complex unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Demonstrating that SNX3 is required for MVB biogenesis independently of Hrs-mediated cargo sorting revealed that PI3P effectors partition complementary endosomal functions—SNX3 for intraluminal vesicle formation, Hrs for receptor degradation.\",\n      \"evidence\": \"RNAi knockdown with electron microscopy of MVB morphology and EGF receptor degradation assays in mammalian cells; parallel epistasis in yeast showing recycling–degradation pathway divergence at a common endosome\",\n      \"pmids\": [\"18767904\", \"18768754\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which SNX3 promotes MVB biogenesis unresolved\", \"Whether SNX3's MVB role is retromer-dependent or independent unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Showing that SNX3 directly binds the VPS26/VPS29/VPS35 cargo-selective subcomplex to sort Wntless into a morphologically distinct retrieval pathway—independent of SNX1/SNX2/SNX5/SNX6—established SNX3-retromer as a dedicated Wnt-secretion-enabling sorting machine conserved across metazoa.\",\n      \"evidence\": \"Direct pulldown of SNX3 with retromer subcomplex, C. elegans and Drosophila genetic epistasis, mammalian cell knockdown with Wntless trafficking readout, Drosophila co-IP of DSNX3–Vps35 with genetic rescue by Wls overexpression\",\n      \"pmids\": [\"21725319\", \"22041890\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How membrane curvature is generated without SNX-BAR proteins remained unclear\", \"Identity of the membrane-remodeling machinery cooperating with SNX3-retromer unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Extension of SNX3-retromer cargo repertoire to the transferrin receptor linked endosomal sorting to systemic iron homeostasis, explaining how Snx3 loss causes anemia, and revealed SNX3's competition with EEA1 for PI3P on phagosomes as a mechanism regulating phagocytic uptake.\",\n      \"evidence\": \"Co-IP of Snx3/Vps35/Tfrc, zebrafish and mouse knockout with iron uptake assays and hemoglobin defects; live imaging and siRNA in dendritic cells showing SNX3–EEA1 competition on phagosomes\",\n      \"pmids\": [\"23416069\", \"23237080\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Competition mechanism not reconstituted with purified components\", \"Whether SNX3 directly contacts Tfrc cytosolic tail or requires VPS26 adaptations unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Discovery that SNX3 associates with a MON2–DOPEY2–ATP9A membrane-remodeling complex resolved the long-standing question of how SNX3-retromer generates membrane tubules without SNX-BAR proteins, linking aminophospholipid flipping to retrograde carrier formation.\",\n      \"evidence\": \"Co-IP of SNX3 with MON2/DOPEY2/ATP9A, C. elegans genetic epistasis phenocopying SNX3-retromer loss, dominant-negative ATPase mutant validation\",\n      \"pmids\": [\"30213940\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct reconstitution of tubule formation by SNX3–MON2–DOPEY2–ATP9A not achieved\", \"Structural organization of the complex undefined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstration that alpha-synuclein inhibits SNX3 endosomal membrane association provided a mechanistic link between Parkinson's disease-associated protein aggregation and defective retromer-mediated iron transporter recycling.\",\n      \"evidence\": \"Fluorescence microscopy of Snx3-mCherry vesicle association in yeast α-synuclein model, C. elegans dopaminergic neuron degeneration assay, iron chelator rescue\",\n      \"pmids\": [\"29452354\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct α-synuclein–SNX3 molecular contact not demonstrated\", \"PI3P competition between α-synuclein and SNX3 inferred but not reconstituted in vitro\", \"Relevance to mammalian dopaminergic neurons not established\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identification of SNX3 as a bifunctional hub on phagosomes—recruiting Rab5a vesicles via its PX domain and galectin-9 via its C-terminal region—revealed how a minimal sorting nexin coordinates two distinct vesicle populations to drive phagosome compaction and maturation.\",\n      \"evidence\": \"Live cell imaging of SNX3/Rab5a vesicle trafficking to Borrelia-containing phagosomes, co-IP of SNX3 with galectin-9, phagosome compaction assay\",\n      \"pmids\": [\"31337623\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether galectin-9 recruitment is retromer-dependent or independent unclear\", \"Structural basis of C-terminal region–galectin-9 interaction unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Mouse knockout establishing that Snx3 loss causes fully penetrant cranial neural tube defects through failed Wntless recycling and impaired Wnt secretion provided the first in vivo mammalian demonstration that SNX3-retromer is essential for embryonic development, with a human NTD-associated SNX3 variant shown to be functionally impaired.\",\n      \"evidence\": \"Mouse Snx3 knockout with NTD phenotype, live cell imaging of WLS mis-trafficking to lysosomes, WNT agonist rescue, human variant functional assay\",\n      \"pmids\": [\"33214242\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other SNX3-retromer cargos contribute to the NTD phenotype unknown\", \"Penetrance and spectrum of human SNX3 mutations in NTD populations not established\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Discovery that SNX3 generates ARF-6-associated recycling tubules for clathrin-independent endocytic cargos independently of retromer expanded SNX3 function beyond retromer-dependent sorting and formalized the SNX3–EEA1 competition model as a general endosomal fate-determination mechanism.\",\n      \"evidence\": \"C. elegans genetic screen and loss-of-function, CIE cargo (hTAC) trafficking assays, SNX3–EEA1 PI3P competition in HeLa cells, retromer epistasis showing independence\",\n      \"pmids\": [\"34081703\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of SNX3-driven tubule formation without retromer not defined\", \"Whether ARF-6-dependent and retromer-dependent functions of SNX3 occur on distinct membrane domains unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstration that alpha-synuclein's membrane-binding activity is specifically required to disrupt SNX3-retromer trafficking of Kex2 and Ste13 cargos refined the pathological mechanism, distinguishing it from aggregation-dependent toxicity.\",\n      \"evidence\": \"Fluorescence microscopy and western blotting of Kex2/Ste13 trafficking in yeast expressing α-syn variants (A53T, A30P, ΔC), yeast mating assay for α-factor processing\",\n      \"pmids\": [\"34570221\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular contact between membrane-bound α-synuclein and SNX3 or retromer not identified\", \"Validation in mammalian neuronal cells lacking\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of the SNX3–retromer–cargo ternary complex at atomic resolution, how SNX3 generates membrane tubules in retromer-independent contexts, whether hybrid SNX3/SNX-BAR coats operate in vivo in mammalian cells, and the full spectrum of human disease caused by SNX3 mutations.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of SNX3–retromer–cargo complex published in the timeline\", \"Retromer-independent tubulation mechanism undefined\", \"In vivo relevance of hybrid SNX3/SNX-BAR coats in mammals not tested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 7, 10]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 4, 6]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [7, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [0, 1, 4, 5, 6, 10, 13]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0, 10, 13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [1, 4, 6, 8, 13]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [1, 4, 6, 8]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 5, 11]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [7, 10]}\n    ],\n    \"complexes\": [\n      \"SNX3-retromer (VPS26/VPS29/VPS35)\",\n      \"SNX3-MON2-DOPEY2-ATP9A\"\n    ],\n    \"partners\": [\n      \"VPS35\",\n      \"VPS26\",\n      \"VPS29\",\n      \"WLS\",\n      \"TFRC\",\n      \"LGALS9\",\n      \"MON2\",\n      \"ATP9A\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}