{"gene":"NECTIN3","run_date":"2026-04-29T11:37:56","timeline":{"discoveries":[{"year":2000,"finding":"Nectin-3 (nectin-3alpha) forms cis-homodimers and shows Ca2+-independent trans-homo-interaction causing homophilic cell-cell adhesion; it also shows trans-hetero-interaction with nectin-1 and nectin-2 (but not cis-heterodimerization). Nectin-3alpha interacts with afadin (an actin filament-binding protein) via its C-terminal PDZ-binding motif and co-localizes with nectin-2 at cadherin-based adherens junctions.","method":"Cell-based adhesion assays, co-immunoprecipitation, immunofluorescence colocalization","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (adhesion assays, Co-IP, localization), foundational discovery paper with 247 citations","pmids":["10744716"],"is_preprint":false},{"year":2000,"finding":"Human nectin-3/PRR3 carries the C-terminal A/EXYV consensus motif and interacts in vivo with both long and short isoforms of afadin, identifying it as an afadin-associated adhesion molecule at intercellular junctions.","method":"Co-immunoprecipitation (in vivo interaction assay), SDS-PAGE, expression analysis","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal Co-IP demonstrating afadin binding, single study","pmids":["11024295"],"is_preprint":false},{"year":2002,"finding":"Nectin-3 trans-hetero-interacts with nectin-1 through V-domain to V-domain contacts (KD ~1 nM), with the C-C'-C\"-D beta-strands of the nectin-1 V domain constituting the minimal binding region; C domains contribute to increased binding affinity.","method":"Surface plasmon resonance (affinity measurements), competition binding assays with monoclonal antibodies, chimeric receptor mapping (nectin1/PVR chimeras)","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — quantitative binding assays with mutagenesis/chimeric constructs, replicated across multiple approaches, 118 citations","pmids":["12011057"],"is_preprint":false},{"year":2003,"finding":"Nectin-3 heterophilically trans-interacts with Necl-5/Tage4/CD155 (but not homophilically); this interaction recruits nectin-3 to cell-cell contact sites and promotes cell motility of Ras-transformed cells. CD155 was found to co-distribute with αv integrin microdomains.","method":"Cell-based ligand binding assays, heterologous co-culture, immunofluorescence colocalization, co-immunoprecipitation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — two independent labs (PMID 12740392 and 12759359) demonstrated nectin-3/Necl-5 trans-interaction with functional consequences","pmids":["12740392","12759359"],"is_preprint":false},{"year":2004,"finding":"Upon cell-cell contact, Necl-5 trans-interaction with nectin-3 recruits afadin, E-cadherin, and catenins to the nectin-3 side of contact sites (not the Necl-5 side), and blocking this interaction inhibits E-cadherin-based adherens junction formation.","method":"Stable cell line expression of Necl-5/nectin-3/E-cadherin in L cells, anti-Necl-5 blocking antibody, immunofluorescence","journal":"Genes to cells","confidence":"Medium","confidence_rationale":"Tier 2 — defined pathway placement with blocking antibody and clean cell-line reconstitution","pmids":["15330856"],"is_preprint":false},{"year":2005,"finding":"Nectin-1 and nectin-3 localize at apex-apex junctions between pigment and non-pigment cell layers of the ciliary epithelia; heterophilic trans-interaction between nectin-1 and nectin-3 is required for formation of these junctions and for normal ciliary body morphogenesis, as demonstrated by microphthalmia and junction separation in nectin-3-/- mice.","method":"Genetic knockout (nectin-3-/- mice), immunofluorescence, immunoelectron microscopy","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined cellular phenotype and direct localization, 99 citations","pmids":["15728677"],"is_preprint":false},{"year":2005,"finding":"Necl-5 interaction with nectin-3 upon cell-cell contact triggers clathrin-dependent endocytosis of Necl-5, leading to its downregulation from the cell surface, which in turn reduces cell movement and proliferation — a mechanism underlying contact inhibition.","method":"Immunofluorescence, clathrin inhibition, cell migration and proliferation assays in NIH3T3 cells","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — defined molecular mechanism with pharmacological inhibition and functional readouts, 90 citations","pmids":["16216929"],"is_preprint":false},{"year":2006,"finding":"Nectin-3 localizes asymmetrically to the spermatid side of Sertoli-spermatid junctions and its heterophilic trans-interaction with nectin-2 (on the Sertoli cell side) is essential for Sertoli-spermatid junction formation and spermatid development; nectin-3-/- mice show male-specific infertility, distorted sperm nuclei, abnormal mitochondrial distribution, and mislocalization of nectin-2. Spermatogenic stem cell transplantation partially rescues the defects.","method":"Genetic knockout (nectin-3-/- mice), spermatogenic stem cell transplantation, immunohistochemistry","journal":"Genes to cells","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined cellular phenotype, rescue experiment, 82 citations","pmids":["16923130"],"is_preprint":false},{"year":2010,"finding":"Heterophilic interaction between nectin-1 (in ameloblasts) and nectin-3 (in stratum intermedium cells) recruits desmosomal junctions between these cell types, which are required for proper enamel formation and crown shape development in mouse teeth.","method":"Double knockout mice (nectin-1;nectin-3 compound mutants), immunohistochemistry, electron microscopy","journal":"Developmental dynamics","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with compound mutants, ultrastructural analysis, defined junctional phenotype","pmids":["21038445"],"is_preprint":false},{"year":2012,"finding":"CADM1 on mast cells binds heterophilically to nectin-3 expressed on dorsal root ganglion (DRG) neurons; this heterophilic interaction mediates mast cell attachment to DRG neurites and the subsequent calcium responses, as shown by neutralizing antibody blockade of nectin-3.","method":"Neutralizing antibody blockade, calcium imaging, cell attachment assay","journal":"Journal of neuroimmunology","confidence":"Medium","confidence_rationale":"Tier 2 — functional neutralization with defined molecular partner and two distinct readouts","pmids":["22703826"],"is_preprint":false},{"year":2012,"finding":"sFRP1 regulates spermatid adhesion at the apical ectoplasmic specialization by controlling FAK-Tyr397 phosphorylation; dephosphorylation of FAK by sFRP1 leads to retention of nectin-3 at the apical ES and delayed spermiation. Overexpression of sFRP1 in Sertoli-germ cell coculture confirmed that sFRP1 controls nectin-3 phosphorylation and localization downstream of FAK signaling.","method":"In vivo sFRP1 recombinant protein administration, lentiviral overexpression in Sertoli-germ cell coculture, Western blotting for phospho-FAK, immunolocalization of nectin-3","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo and in vitro corroboration with defined signaling pathway","pmids":["23073828"],"is_preprint":false},{"year":2013,"finding":"Hippocampal nectin-3 is required for stress-induced structural plasticity and memory: suppression of hippocampal nectin-3 causes spatial memory deficits and dendritic spine loss, while enhancing nectin-3 rescues early-life stress-induced memory deficits and spine loss. The CRH-CRHR1 signaling pathway (but not glucocorticoid receptors) regulates nectin-3 levels, acting via the nectin-afadin complex.","method":"AAV-mediated knockdown/overexpression in mice, CRHR1 genetic inactivation, CRH overexpression in forebrain neurons, behavioral testing, spine density analysis","journal":"Nature neuroscience","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic tools (KO, OE, rescue), defined pathway (CRHR1→nectin-3), and structural/behavioral readouts; 108 citations","pmids":["23644483"],"is_preprint":false},{"year":2013,"finding":"Nectin-3 expressed on T lymphocytes trans-interacts with nectin-2 expressed on endothelial cells (particularly at high endothelial venules); blocking either nectin-3 on lymphocytes or nectin-2 on endothelial cells with monoclonal antibodies inhibits lymphocyte transendothelial migration in vitro.","method":"Blocking monoclonal antibodies, soluble nectin-3 binding assay, transendothelial migration assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — functional blockade with defined molecular interaction and migration readout","pmids":["24116228"],"is_preprint":false},{"year":2014,"finding":"MMP-9 proteolytically cleaves nectin-3 in the hippocampal CA1 perisynaptic compartment following chronic restraint stress; this cleavage requires NMDA receptor activity. Loss of nectin-3 in CA1 (but not CA3) mediates stress-induced social and cognitive behavioral alterations.","method":"Gelatinase activity assay, NMDA receptor inhibition, MMP-9 knockout/inhibition, behavioral testing, western blotting","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — defined enzymatic cleavage mechanism with genetic/pharmacological dissection and behavioral readouts, 106 citations","pmids":["25232752"],"is_preprint":false},{"year":2014,"finding":"Nectin-3 deficiency in cochlear hair cells causes aberrant HC-HC contacts instead of normal HC-SC contacts, leading to disturbances in hair bundle orientation and morphology, kinocilium positioning, and abnormal localization of cadherin-catenin complexes and polarity proteins Pals1 and Par-3.","method":"Nectin-3-deficient mice, immunofluorescence, confocal microscopy","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 — clean genetic KO with defined cellular and molecular phenotype at multiple levels","pmids":["24381198"],"is_preprint":false},{"year":2015,"finding":"Crystal structure of the afadin PDZ domain (AFPDZ) in complex with the nectin-3 C-terminal peptide reveals that: the last three amino acids of the nectin-3 C-terminus (class II PDZ-binding motif, X-Φ-X-Φ) are sufficient for binding; the AFPDZ undergoes a conformational change (~2.5 Å wider ligand-binding groove in α2 helix) compared to unbound structures; the complex crystallizes as a dimer via antiparallel β-sheet between β2 strands.","method":"X-ray crystallography (crystal structure of AFPDZ-nectin-3 fusion protein complex)","journal":"Protein science","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with functional domain validation","pmids":["25534554"],"is_preprint":false},{"year":2016,"finding":"In rat uterine epithelial cells, nectin-3 redistributes from basal cytoplasm to cell junctions at the time of implantation (day 6 of pregnancy), a process likely controlled by progesterone. At this junctional location, nectin-3 does not interact with occludin or l-afadin, suggesting a protein complex independent of canonical AJ components.","method":"Immunofluorescence, Western blotting, coimmunoprecipitation","journal":"Reproductive sciences","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP with negative result for occludin/afadin interaction, localization tied to functional state","pmids":["27217376"],"is_preprint":false},{"year":2017,"finding":"Nectin-3 knockdown in all dentate gyrus (DG) neuron populations impairs long-term spatial memory and temporal order memory, and modulates differentiation/maturation of adult-born DG granule cells; selective knockdown in new DG neurons reduces dendritic spine density (especially thin spines) and impairs long-term spatial memory.","method":"AAV-mediated and retroviral nectin-3 knockdown in DG neurons, behavioral testing, dendritic spine analysis, immunofluorescence for neurogenesis markers","journal":"Translational psychiatry","confidence":"High","confidence_rationale":"Tier 2 — cell-type-specific KD with two viral systems, multiple behavioral and structural readouts","pmids":["28872640"],"is_preprint":false},{"year":2017,"finding":"Nectin-3 (an adhesion junction protein from the spermatid plasma membrane) is internalized via tubulobulbar complexes in the testis; immunoelectron microscopy localizes nectin-3 labeling at junctions, at tubulobulbar complex bulbs (identified by dual plasma membrane and ER association), and in associated double-membrane vesicles, indicating clathrin/actin-mediated endocytic internalization of junction proteins.","method":"Pre-embedding immunoelectron microscopy","journal":"Anatomical record","confidence":"Medium","confidence_rationale":"Tier 2 — high-resolution ultrastructural localization with functional contextual inference","pmids":["28176461"],"is_preprint":false},{"year":2020,"finding":"ZNF582 directly regulates the transcription and expression of nectin-3; ZNF582 binds the nectin-3 promoter (ChIP-seq/ChIP-qPCR/luciferase assay), and ZNF582 restoration suppresses NPC migration/invasion while knockdown of nectin-3 reverses this tumor-suppressive effect.","method":"ChIP-seq, ChIP-qPCR, luciferase reporter assay, siRNA knockdown, in vitro migration/invasion assays, in vivo xenograft","journal":"Cancer communications","confidence":"Medium","confidence_rationale":"Tier 2 — direct promoter binding validated by multiple ChIP methods with functional rescue experiment","pmids":["33038291"],"is_preprint":false},{"year":2020,"finding":"Nectin-3 knockdown in the medial prefrontal cortex (mPFC) of adolescent mice reproduces stress-induced impairments in social recognition memory, spatial working memory, dendritic simplification, and reduced spine density; membrane localization of nectin-3 in mPFC correlates with behavioral performance.","method":"AAV-mediated nectin-3 knockdown, behavioral testing, dendritic morphology analysis, subcellular fractionation/western blotting","journal":"Neuroscience bulletin","confidence":"Medium","confidence_rationale":"Tier 2 — AAV-mediated region-specific KD with defined structural and behavioral phenotypes","pmids":["32385776"],"is_preprint":false},{"year":2023,"finding":"Nectin-3, in addition to its adherens junction localization, localizes to the brush border of colonocytes and can function as a cell-surface receptor for Clostridioides difficile toxin B (TcdB), allowing toxin access to colonic epithelial cells.","method":"Immunofluorescence microscopy on colonic tissue, receptor localization studies","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 — direct tissue localization demonstrating unexpected brush-border distribution linked to toxin receptor function","pmids":["37747247"],"is_preprint":false},{"year":2025,"finding":"Nectin-3 in cochlear supporting cells (SCs) is regulated by PCP signaling (via Vangl2) and is required for proper type II spiral ganglion neuron (SGNII) peripheral afferent turning; loss of Nectin-3 partially phenocopies Vangl2 mutant turning defects, and epistasis analysis places Nectin-3 and Rac1 in the same genetic pathway controlling SGNII axon guidance.","method":"Mouse genetics (conditional KO), genetic epistasis analysis, in vivo afferent turning phenotype quantification","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 — clean genetic KO with epistasis analysis placing Nectin-3 in PCP pathway, defined axon guidance phenotype","pmids":["40207531"],"is_preprint":false}],"current_model":"NECTIN3 is a Ca2+-independent immunoglobulin-like cell adhesion molecule that forms cis-homodimers and engages in trans-homo- and trans-hetero-interactions (with nectin-1, nectin-2, and Necl-5/CD155) via its V domain; its cytoplasmic C-terminal class II PDZ-binding motif directly binds afadin (structure solved by crystallography), linking it to the actin cytoskeleton and cadherin-based adherens junctions; in the testis, nectin-3 (spermatid side) heterophilically trans-interacts with nectin-2 (Sertoli side) to maintain Sertoli-spermatid junctions essential for spermatogenesis; in the brain, hippocampal nectin-3 is proteolytically cleaved by MMP-9 (NMDA receptor-dependent) downstream of CRH-CRHR1 signaling during stress, causing dendritic spine loss and memory deficits; and in the cochlea, Nectin-3 acts downstream of PCP/Vangl2 signaling to mediate cell adhesion guiding spiral ganglion neuron axon turning."},"narrative":{"teleology":[{"year":2000,"claim":"Establishing that nectin-3 is a homophilic and heterophilic adhesion molecule that links to afadin and cadherin-based junctions resolved the question of whether nectin-3 could function as a Ca²⁺-independent cell adhesion receptor integrated into adherens junctions.","evidence":"Cell-based adhesion assays, co-immunoprecipitation, and immunofluorescence colocalization in transfected cells","pmids":["10744716","11024295"],"confidence":"High","gaps":["Structural basis of nectin-3 cis-dimerization and trans-interactions not resolved","In vivo function of nectin-3 not yet tested with genetic models"]},{"year":2002,"claim":"Mapping the nectin-1/nectin-3 heterophilic interface to V-domain beta-strands with nanomolar affinity established the molecular basis for their preferential trans-interaction over homophilic binding.","evidence":"Surface plasmon resonance and competition binding with chimeric receptors and monoclonal antibodies","pmids":["12011057"],"confidence":"High","gaps":["Atomic-resolution crystal structure of the nectin-1/nectin-3 trans-dimer not yet available","Relative contribution of C domains to in vivo function unknown"]},{"year":2003,"claim":"Identification of Necl-5/CD155 as a heterophilic trans-partner for nectin-3 expanded the nectin interactome beyond the nectin family and linked nectin-3 to cell motility regulation in Ras-transformed cells.","evidence":"Cell-based ligand binding assays, heterologous co-culture, and immunofluorescence in multiple independent studies","pmids":["12740392","12759359"],"confidence":"High","gaps":["Structural basis of the nectin-3/Necl-5 interaction undetermined","Relevance of this interaction to normal (non-transformed) physiology unclear"]},{"year":2005,"claim":"Demonstration that nectin-3/Necl-5 trans-interaction triggers clathrin-dependent endocytosis of Necl-5, reducing proliferation and migration, established nectin-3 as a mediator of contact inhibition of cell growth.","evidence":"Clathrin inhibition, cell migration and proliferation assays in NIH3T3 cells","pmids":["16216929"],"confidence":"High","gaps":["Signaling intermediates between nectin-3 engagement and clathrin recruitment not identified","Whether this mechanism operates in epithelial tissues in vivo not tested"]},{"year":2005,"claim":"Nectin-3 knockout mice revealed that heterophilic nectin-1/nectin-3 trans-interaction is required for junction formation in the ciliary epithelium, providing the first in vivo genetic evidence for nectin-3 function in tissue morphogenesis.","evidence":"Nectin-3−/− mice with microphthalmia, immunofluorescence and immunoelectron microscopy","pmids":["15728677"],"confidence":"High","gaps":["Molecular mechanism linking nectin-3 loss to junction disassembly not dissected","Whether redundancy with other nectins limits phenotypic severity unknown"]},{"year":2006,"claim":"Discovery that nectin-3 on spermatids trans-interacts with nectin-2 on Sertoli cells, and that nectin-3−/− mice are male-infertile, established nectin-3 as essential for spermatid adhesion and maturation.","evidence":"Nectin-3−/− mice, spermatogenic stem cell transplantation rescue, immunohistochemistry","pmids":["16923130"],"confidence":"High","gaps":["How nectin-3 loss leads to mitochondrial mislocalization and nuclear distortion mechanistically unresolved","Identity of downstream signaling pathways at the apical ectoplasmic specialization not fully defined"]},{"year":2010,"claim":"Compound nectin-1;nectin-3 mutant mice showed that heterophilic nectin-1/nectin-3 interaction recruits desmosomes to ameloblast–stratum intermedium junctions, broadening nectin-3's role from adherens to desmosomal junction assembly.","evidence":"Compound knockout mice, immunohistochemistry, electron microscopy of tooth enamel organ","pmids":["21038445"],"confidence":"High","gaps":["Mechanism by which nectin trans-interaction nucleates desmosome assembly not identified","Whether other tooth developmental pathways are affected independently of desmosomes unknown"]},{"year":2013,"claim":"Placing nectin-3 downstream of CRH–CRHR1 signaling in the hippocampus, and showing that nectin-3 manipulation bidirectionally controls stress-induced spine loss and memory deficits, identified nectin-3 as a synaptic effector of stress.","evidence":"AAV-mediated knockdown/overexpression in mice, CRHR1 genetic inactivation, CRH overexpression, behavioral and spine analysis","pmids":["23644483"],"confidence":"High","gaps":["Intracellular signaling cascade from CRHR1 activation to nectin-3 downregulation not fully delineated","Whether afadin is co-regulated with nectin-3 in this context not established"]},{"year":2014,"claim":"Identification of MMP-9 as the protease that cleaves nectin-3 in hippocampal CA1 in an NMDA receptor–dependent manner explained how chronic stress removes nectin-3 from perisynaptic sites to impair cognition.","evidence":"MMP-9 knockout/pharmacological inhibition, NMDA receptor blockade, gelatinase activity assay, behavioral testing","pmids":["25232752"],"confidence":"High","gaps":["Exact cleavage site on nectin-3 not mapped","Fate of the cleaved ectodomain (shed fragment signaling) not investigated"]},{"year":2014,"claim":"Nectin-3 deficiency in cochlear hair cells caused aberrant hair cell–hair cell contacts, disrupted hair bundle orientation, and mislocalized polarity proteins, revealing nectin-3 as a determinant of planar cell polarity in the inner ear.","evidence":"Nectin-3-deficient mice, immunofluorescence and confocal microscopy of cochlear epithelium","pmids":["24381198"],"confidence":"High","gaps":["Upstream signals controlling nectin-3 expression in hair cells not identified at this point","Whether nectin-3 directly interacts with polarity proteins or acts indirectly unknown"]},{"year":2015,"claim":"The crystal structure of the afadin PDZ domain bound to the nectin-3 C-terminal peptide revealed the atomic basis for their interaction, including a conformational widening of the binding groove, resolving how nectin-3 is physically linked to the cytoskeleton.","evidence":"X-ray crystallography of AFPDZ–nectin-3 fusion protein complex","pmids":["25534554"],"confidence":"High","gaps":["Structure of full-length nectin-3 or the nectin-3/afadin complex beyond the PDZ interface not available","Regulation of the PDZ interaction (phosphorylation, competition) not structurally characterized"]},{"year":2023,"claim":"Discovery that nectin-3 localizes to the colonocyte brush border and serves as a receptor for C. difficile toxin B extended nectin-3 biology from developmental adhesion to pathogen entry.","evidence":"Immunofluorescence microscopy on colonic tissue, receptor localization studies","pmids":["37747247"],"confidence":"Medium","gaps":["Binding interface between TcdB and nectin-3 not structurally resolved","Whether other nectin family members can substitute as TcdB receptors not tested","Functional consequence of TcdB binding on nectin-3 adhesion function not examined"]},{"year":2025,"claim":"Placing nectin-3 downstream of PCP/Vangl2 signaling and in the same genetic pathway as Rac1 for spiral ganglion neuron axon turning unified nectin-3's adhesive role with planar polarity-guided axon guidance in the cochlea.","evidence":"Conditional knockout mice, genetic epistasis analysis, afferent turning phenotype quantification","pmids":["40207531"],"confidence":"Medium","gaps":["How Vangl2 transcriptionally or post-transcriptionally regulates nectin-3 expression not determined","Whether Rac1 acts upstream or downstream of nectin-3-mediated adhesion not resolved","Role of afadin in this cochlear guidance pathway not examined"]},{"year":null,"claim":"Key unresolved questions include the full-length structural basis of nectin-3 cis- and trans-dimeric assemblies, the intracellular signaling cascades immediately downstream of nectin-3 engagement, the MMP-9 cleavage site and function of the shed ectodomain, and whether nectin-3 plays roles in immune cell biology beyond lymphocyte transendothelial migration.","evidence":"","pmids":[],"confidence":"Low","gaps":["No full-length or trans-dimer crystal structure available","Downstream signaling immediately triggered by nectin-3 ligation largely undefined","Shed ectodomain biology unexplored"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[0,2,3,5,7,8]},{"term_id":"GO:0001618","term_label":"virus receptor activity","supporting_discovery_ids":[21]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,7,14,16,20,21]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[16]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[0,2,5,7,8,12]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[5,7,8,14,22]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[11,13,17,20]},{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[7,10,16]}],"complexes":["nectin-afadin complex"],"partners":["NECTIN1","NECTIN2","PVR","AFDN","CADM1","MMP9","VANGL2"],"other_free_text":[]},"mechanistic_narrative":"NECTIN3 is a Ca²⁺-independent immunoglobulin-like cell adhesion molecule that forms cis-homodimers and engages in heterophilic trans-interactions with nectin-1, nectin-2, and Necl-5/CD155 through its V domain, linking cell-cell contacts to the actin cytoskeleton and cadherin-based adherens junctions via its cytoplasmic PDZ-binding motif that directly binds afadin [PMID:10744716, PMID:25534554]. In the testis, nectin-3 on spermatids trans-interacts with nectin-2 on Sertoli cells to maintain Sertoli–spermatid junctions essential for spermatogenesis, and nectin-3-deficient mice are male-infertile with distorted sperm morphology [PMID:16923130]. In the hippocampus and prefrontal cortex, nectin-3 is required for dendritic spine maintenance and memory; chronic stress triggers NMDA receptor–dependent MMP-9 cleavage of nectin-3 downstream of CRH–CRHR1 signaling, causing spine loss and cognitive impairment [PMID:23644483, PMID:25232752]. Nectin-3 also mediates tissue-specific adhesion in the ciliary epithelium, cochlear organ of Corti (acting downstream of PCP/Vangl2 signaling to guide spiral ganglion neuron axon turning), and tooth enamel organ, and serves as a cell-surface receptor for Clostridioides difficile toxin B on colonocytes [PMID:15728677, PMID:24381198, PMID:40207531, PMID:37747247]."},"prefetch_data":{"uniprot":{"accession":"Q9NQS3","full_name":"Nectin-3","aliases":["CDw113","Nectin cell adhesion molecule 3","Poliovirus receptor-related protein 3"],"length_aa":549,"mass_kda":61.0,"function":"Cell adhesion molecule that promotes cell-cell adhesion through heterophilic trans-interactions with nectins-like or other nectins, such as trans-interaction with NECTIN2 at Sertoli-spermatid junctions (PubMed:16216929). Trans-interaction with PVR induces activation of CDC42 and RAC small G proteins through common signaling molecules such as SRC and RAP1 (PubMed:16216929). Induces endocytosis-mediated down-regulation of PVR from the cell surface, resulting in reduction of cell movement and proliferation (PubMed:16216929). Involved in axon guidance by promoting contacts between the commissural axons and the floor plate cells (By similarity). Also involved in the formation of cell-cell junctions, including adherens junctions and synapses (By similarity). Promotes formation of checkerboard-like cellular pattern of hair cells and supporting cells in the auditory epithelium via heterophilic interaction with NECTIN1: NECTIN1 is present in the membrane of hair cells and associates with NECTIN3 on supporting cells, thereby mediating heterotypic adhesion between these two cell types (By similarity). Plays a role in the morphology of the ciliary body (By similarity)","subcellular_location":"Cell membrane; Postsynaptic cell membrane; Cell junction, adherens junction","url":"https://www.uniprot.org/uniprotkb/Q9NQS3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/NECTIN3","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/NECTIN3","total_profiled":1310},"omim":[{"mim_id":"621139","title":"COILED-COIL DOMAIN-CONTAINING PROTEIN 178; CCDC178","url":"https://www.omim.org/entry/621139"},{"mim_id":"607147","title":"NECTIN CELL ADHESION MOLECULE 3; NECTIN3","url":"https://www.omim.org/entry/607147"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Uncertain","locations":[{"location":"Cell Junctions","reliability":"Uncertain"},{"location":"Cytosol","reliability":"Uncertain"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"testis","ntpm":51.0}],"url":"https://www.proteinatlas.org/search/NECTIN3"},"hgnc":{"alias_symbol":["nectin-3","PPR3","PVRR3","DKFZP566B0846","CDw113","CD113"],"prev_symbol":["PVRL3"]},"alphafold":{"accession":"Q9NQS3","domains":[{"cath_id":"2.60.40.10","chopping":"59-166","consensus_level":"high","plddt":93.3954,"start":59,"end":166},{"cath_id":"2.60.40.10","chopping":"170-265","consensus_level":"high","plddt":96.3629,"start":170,"end":265},{"cath_id":"2.60.40.10","chopping":"268-352","consensus_level":"high","plddt":94.4145,"start":268,"end":352}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NQS3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NQS3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NQS3-F1-predicted_aligned_error_v6.png","plddt_mean":73.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NECTIN3","jax_strain_url":"https://www.jax.org/strain/search?query=NECTIN3"},"sequence":{"accession":"Q9NQS3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NQS3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NQS3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NQS3"}},"corpus_meta":[{"pmid":"10744716","id":"PMC_10744716","title":"Nectin-3, a new member of immunoglobulin-like cell adhesion molecules that shows homophilic and heterophilic cell-cell adhesion activities.","date":"2000","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10744716","citation_count":247,"is_preprint":false},{"pmid":"12011057","id":"PMC_12011057","title":"Prominent role of the Ig-like V domain in trans-interactions of nectins. Nectin3 and nectin 4 bind to the predicted C-C'-C\"-D beta-strands of the nectin1 V domain.","date":"2002","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12011057","citation_count":118,"is_preprint":false},{"pmid":"12740392","id":"PMC_12740392","title":"Tage4/Nectin-like molecule-5 heterophilically trans-interacts with cell adhesion molecule Nectin-3 and enhances cell migration.","date":"2003","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12740392","citation_count":114,"is_preprint":false},{"pmid":"23644483","id":"PMC_23644483","title":"Nectin-3 links CRHR1 signaling to stress-induced memory deficits and spine loss.","date":"2013","source":"Nature neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/23644483","citation_count":108,"is_preprint":false},{"pmid":"25232752","id":"PMC_25232752","title":"Role for MMP-9 in stress-induced downregulation of nectin-3 in hippocampal CA1 and associated behavioural 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Nectin-3alpha interacts with afadin (an actin filament-binding protein) via its C-terminal PDZ-binding motif and co-localizes with nectin-2 at cadherin-based adherens junctions.\",\n      \"method\": \"Cell-based adhesion assays, co-immunoprecipitation, immunofluorescence colocalization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (adhesion assays, Co-IP, localization), foundational discovery paper with 247 citations\",\n      \"pmids\": [\"10744716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Human nectin-3/PRR3 carries the C-terminal A/EXYV consensus motif and interacts in vivo with both long and short isoforms of afadin, identifying it as an afadin-associated adhesion molecule at intercellular junctions.\",\n      \"method\": \"Co-immunoprecipitation (in vivo interaction assay), SDS-PAGE, expression analysis\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP demonstrating afadin binding, single study\",\n      \"pmids\": [\"11024295\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Nectin-3 trans-hetero-interacts with nectin-1 through V-domain to V-domain contacts (KD ~1 nM), with the C-C'-C\\\"-D beta-strands of the nectin-1 V domain constituting the minimal binding region; C domains contribute to increased binding affinity.\",\n      \"method\": \"Surface plasmon resonance (affinity measurements), competition binding assays with monoclonal antibodies, chimeric receptor mapping (nectin1/PVR chimeras)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative binding assays with mutagenesis/chimeric constructs, replicated across multiple approaches, 118 citations\",\n      \"pmids\": [\"12011057\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Nectin-3 heterophilically trans-interacts with Necl-5/Tage4/CD155 (but not homophilically); this interaction recruits nectin-3 to cell-cell contact sites and promotes cell motility of Ras-transformed cells. CD155 was found to co-distribute with αv integrin microdomains.\",\n      \"method\": \"Cell-based ligand binding assays, heterologous co-culture, immunofluorescence colocalization, co-immunoprecipitation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — two independent labs (PMID 12740392 and 12759359) demonstrated nectin-3/Necl-5 trans-interaction with functional consequences\",\n      \"pmids\": [\"12740392\", \"12759359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Upon cell-cell contact, Necl-5 trans-interaction with nectin-3 recruits afadin, E-cadherin, and catenins to the nectin-3 side of contact sites (not the Necl-5 side), and blocking this interaction inhibits E-cadherin-based adherens junction formation.\",\n      \"method\": \"Stable cell line expression of Necl-5/nectin-3/E-cadherin in L cells, anti-Necl-5 blocking antibody, immunofluorescence\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined pathway placement with blocking antibody and clean cell-line reconstitution\",\n      \"pmids\": [\"15330856\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Nectin-1 and nectin-3 localize at apex-apex junctions between pigment and non-pigment cell layers of the ciliary epithelia; heterophilic trans-interaction between nectin-1 and nectin-3 is required for formation of these junctions and for normal ciliary body morphogenesis, as demonstrated by microphthalmia and junction separation in nectin-3-/- mice.\",\n      \"method\": \"Genetic knockout (nectin-3-/- mice), immunofluorescence, immunoelectron microscopy\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular phenotype and direct localization, 99 citations\",\n      \"pmids\": [\"15728677\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Necl-5 interaction with nectin-3 upon cell-cell contact triggers clathrin-dependent endocytosis of Necl-5, leading to its downregulation from the cell surface, which in turn reduces cell movement and proliferation — a mechanism underlying contact inhibition.\",\n      \"method\": \"Immunofluorescence, clathrin inhibition, cell migration and proliferation assays in NIH3T3 cells\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — defined molecular mechanism with pharmacological inhibition and functional readouts, 90 citations\",\n      \"pmids\": [\"16216929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Nectin-3 localizes asymmetrically to the spermatid side of Sertoli-spermatid junctions and its heterophilic trans-interaction with nectin-2 (on the Sertoli cell side) is essential for Sertoli-spermatid junction formation and spermatid development; nectin-3-/- mice show male-specific infertility, distorted sperm nuclei, abnormal mitochondrial distribution, and mislocalization of nectin-2. Spermatogenic stem cell transplantation partially rescues the defects.\",\n      \"method\": \"Genetic knockout (nectin-3-/- mice), spermatogenic stem cell transplantation, immunohistochemistry\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular phenotype, rescue experiment, 82 citations\",\n      \"pmids\": [\"16923130\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Heterophilic interaction between nectin-1 (in ameloblasts) and nectin-3 (in stratum intermedium cells) recruits desmosomal junctions between these cell types, which are required for proper enamel formation and crown shape development in mouse teeth.\",\n      \"method\": \"Double knockout mice (nectin-1;nectin-3 compound mutants), immunohistochemistry, electron microscopy\",\n      \"journal\": \"Developmental dynamics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with compound mutants, ultrastructural analysis, defined junctional phenotype\",\n      \"pmids\": [\"21038445\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CADM1 on mast cells binds heterophilically to nectin-3 expressed on dorsal root ganglion (DRG) neurons; this heterophilic interaction mediates mast cell attachment to DRG neurites and the subsequent calcium responses, as shown by neutralizing antibody blockade of nectin-3.\",\n      \"method\": \"Neutralizing antibody blockade, calcium imaging, cell attachment assay\",\n      \"journal\": \"Journal of neuroimmunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional neutralization with defined molecular partner and two distinct readouts\",\n      \"pmids\": [\"22703826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"sFRP1 regulates spermatid adhesion at the apical ectoplasmic specialization by controlling FAK-Tyr397 phosphorylation; dephosphorylation of FAK by sFRP1 leads to retention of nectin-3 at the apical ES and delayed spermiation. Overexpression of sFRP1 in Sertoli-germ cell coculture confirmed that sFRP1 controls nectin-3 phosphorylation and localization downstream of FAK signaling.\",\n      \"method\": \"In vivo sFRP1 recombinant protein administration, lentiviral overexpression in Sertoli-germ cell coculture, Western blotting for phospho-FAK, immunolocalization of nectin-3\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo and in vitro corroboration with defined signaling pathway\",\n      \"pmids\": [\"23073828\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Hippocampal nectin-3 is required for stress-induced structural plasticity and memory: suppression of hippocampal nectin-3 causes spatial memory deficits and dendritic spine loss, while enhancing nectin-3 rescues early-life stress-induced memory deficits and spine loss. The CRH-CRHR1 signaling pathway (but not glucocorticoid receptors) regulates nectin-3 levels, acting via the nectin-afadin complex.\",\n      \"method\": \"AAV-mediated knockdown/overexpression in mice, CRHR1 genetic inactivation, CRH overexpression in forebrain neurons, behavioral testing, spine density analysis\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic tools (KO, OE, rescue), defined pathway (CRHR1→nectin-3), and structural/behavioral readouts; 108 citations\",\n      \"pmids\": [\"23644483\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Nectin-3 expressed on T lymphocytes trans-interacts with nectin-2 expressed on endothelial cells (particularly at high endothelial venules); blocking either nectin-3 on lymphocytes or nectin-2 on endothelial cells with monoclonal antibodies inhibits lymphocyte transendothelial migration in vitro.\",\n      \"method\": \"Blocking monoclonal antibodies, soluble nectin-3 binding assay, transendothelial migration assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional blockade with defined molecular interaction and migration readout\",\n      \"pmids\": [\"24116228\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"MMP-9 proteolytically cleaves nectin-3 in the hippocampal CA1 perisynaptic compartment following chronic restraint stress; this cleavage requires NMDA receptor activity. Loss of nectin-3 in CA1 (but not CA3) mediates stress-induced social and cognitive behavioral alterations.\",\n      \"method\": \"Gelatinase activity assay, NMDA receptor inhibition, MMP-9 knockout/inhibition, behavioral testing, western blotting\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — defined enzymatic cleavage mechanism with genetic/pharmacological dissection and behavioral readouts, 106 citations\",\n      \"pmids\": [\"25232752\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Nectin-3 deficiency in cochlear hair cells causes aberrant HC-HC contacts instead of normal HC-SC contacts, leading to disturbances in hair bundle orientation and morphology, kinocilium positioning, and abnormal localization of cadherin-catenin complexes and polarity proteins Pals1 and Par-3.\",\n      \"method\": \"Nectin-3-deficient mice, immunofluorescence, confocal microscopy\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with defined cellular and molecular phenotype at multiple levels\",\n      \"pmids\": [\"24381198\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Crystal structure of the afadin PDZ domain (AFPDZ) in complex with the nectin-3 C-terminal peptide reveals that: the last three amino acids of the nectin-3 C-terminus (class II PDZ-binding motif, X-Φ-X-Φ) are sufficient for binding; the AFPDZ undergoes a conformational change (~2.5 Å wider ligand-binding groove in α2 helix) compared to unbound structures; the complex crystallizes as a dimer via antiparallel β-sheet between β2 strands.\",\n      \"method\": \"X-ray crystallography (crystal structure of AFPDZ-nectin-3 fusion protein complex)\",\n      \"journal\": \"Protein science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional domain validation\",\n      \"pmids\": [\"25534554\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In rat uterine epithelial cells, nectin-3 redistributes from basal cytoplasm to cell junctions at the time of implantation (day 6 of pregnancy), a process likely controlled by progesterone. At this junctional location, nectin-3 does not interact with occludin or l-afadin, suggesting a protein complex independent of canonical AJ components.\",\n      \"method\": \"Immunofluorescence, Western blotting, coimmunoprecipitation\",\n      \"journal\": \"Reproductive sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP with negative result for occludin/afadin interaction, localization tied to functional state\",\n      \"pmids\": [\"27217376\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Nectin-3 knockdown in all dentate gyrus (DG) neuron populations impairs long-term spatial memory and temporal order memory, and modulates differentiation/maturation of adult-born DG granule cells; selective knockdown in new DG neurons reduces dendritic spine density (especially thin spines) and impairs long-term spatial memory.\",\n      \"method\": \"AAV-mediated and retroviral nectin-3 knockdown in DG neurons, behavioral testing, dendritic spine analysis, immunofluorescence for neurogenesis markers\",\n      \"journal\": \"Translational psychiatry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific KD with two viral systems, multiple behavioral and structural readouts\",\n      \"pmids\": [\"28872640\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Nectin-3 (an adhesion junction protein from the spermatid plasma membrane) is internalized via tubulobulbar complexes in the testis; immunoelectron microscopy localizes nectin-3 labeling at junctions, at tubulobulbar complex bulbs (identified by dual plasma membrane and ER association), and in associated double-membrane vesicles, indicating clathrin/actin-mediated endocytic internalization of junction proteins.\",\n      \"method\": \"Pre-embedding immunoelectron microscopy\",\n      \"journal\": \"Anatomical record\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — high-resolution ultrastructural localization with functional contextual inference\",\n      \"pmids\": [\"28176461\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ZNF582 directly regulates the transcription and expression of nectin-3; ZNF582 binds the nectin-3 promoter (ChIP-seq/ChIP-qPCR/luciferase assay), and ZNF582 restoration suppresses NPC migration/invasion while knockdown of nectin-3 reverses this tumor-suppressive effect.\",\n      \"method\": \"ChIP-seq, ChIP-qPCR, luciferase reporter assay, siRNA knockdown, in vitro migration/invasion assays, in vivo xenograft\",\n      \"journal\": \"Cancer communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct promoter binding validated by multiple ChIP methods with functional rescue experiment\",\n      \"pmids\": [\"33038291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Nectin-3 knockdown in the medial prefrontal cortex (mPFC) of adolescent mice reproduces stress-induced impairments in social recognition memory, spatial working memory, dendritic simplification, and reduced spine density; membrane localization of nectin-3 in mPFC correlates with behavioral performance.\",\n      \"method\": \"AAV-mediated nectin-3 knockdown, behavioral testing, dendritic morphology analysis, subcellular fractionation/western blotting\",\n      \"journal\": \"Neuroscience bulletin\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — AAV-mediated region-specific KD with defined structural and behavioral phenotypes\",\n      \"pmids\": [\"32385776\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Nectin-3, in addition to its adherens junction localization, localizes to the brush border of colonocytes and can function as a cell-surface receptor for Clostridioides difficile toxin B (TcdB), allowing toxin access to colonic epithelial cells.\",\n      \"method\": \"Immunofluorescence microscopy on colonic tissue, receptor localization studies\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct tissue localization demonstrating unexpected brush-border distribution linked to toxin receptor function\",\n      \"pmids\": [\"37747247\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Nectin-3 in cochlear supporting cells (SCs) is regulated by PCP signaling (via Vangl2) and is required for proper type II spiral ganglion neuron (SGNII) peripheral afferent turning; loss of Nectin-3 partially phenocopies Vangl2 mutant turning defects, and epistasis analysis places Nectin-3 and Rac1 in the same genetic pathway controlling SGNII axon guidance.\",\n      \"method\": \"Mouse genetics (conditional KO), genetic epistasis analysis, in vivo afferent turning phenotype quantification\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with epistasis analysis placing Nectin-3 in PCP pathway, defined axon guidance phenotype\",\n      \"pmids\": [\"40207531\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NECTIN3 is a Ca2+-independent immunoglobulin-like cell adhesion molecule that forms cis-homodimers and engages in trans-homo- and trans-hetero-interactions (with nectin-1, nectin-2, and Necl-5/CD155) via its V domain; its cytoplasmic C-terminal class II PDZ-binding motif directly binds afadin (structure solved by crystallography), linking it to the actin cytoskeleton and cadherin-based adherens junctions; in the testis, nectin-3 (spermatid side) heterophilically trans-interacts with nectin-2 (Sertoli side) to maintain Sertoli-spermatid junctions essential for spermatogenesis; in the brain, hippocampal nectin-3 is proteolytically cleaved by MMP-9 (NMDA receptor-dependent) downstream of CRH-CRHR1 signaling during stress, causing dendritic spine loss and memory deficits; and in the cochlea, Nectin-3 acts downstream of PCP/Vangl2 signaling to mediate cell adhesion guiding spiral ganglion neuron axon turning.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"NECTIN3 is a Ca²⁺-independent immunoglobulin-like cell adhesion molecule that forms cis-homodimers and engages in heterophilic trans-interactions with nectin-1, nectin-2, and Necl-5/CD155 through its V domain, linking cell-cell contacts to the actin cytoskeleton and cadherin-based adherens junctions via its cytoplasmic PDZ-binding motif that directly binds afadin [PMID:10744716, PMID:25534554]. In the testis, nectin-3 on spermatids trans-interacts with nectin-2 on Sertoli cells to maintain Sertoli–spermatid junctions essential for spermatogenesis, and nectin-3-deficient mice are male-infertile with distorted sperm morphology [PMID:16923130]. In the hippocampus and prefrontal cortex, nectin-3 is required for dendritic spine maintenance and memory; chronic stress triggers NMDA receptor–dependent MMP-9 cleavage of nectin-3 downstream of CRH–CRHR1 signaling, causing spine loss and cognitive impairment [PMID:23644483, PMID:25232752]. Nectin-3 also mediates tissue-specific adhesion in the ciliary epithelium, cochlear organ of Corti (acting downstream of PCP/Vangl2 signaling to guide spiral ganglion neuron axon turning), and tooth enamel organ, and serves as a cell-surface receptor for Clostridioides difficile toxin B on colonocytes [PMID:15728677, PMID:24381198, PMID:40207531, PMID:37747247].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing that nectin-3 is a homophilic and heterophilic adhesion molecule that links to afadin and cadherin-based junctions resolved the question of whether nectin-3 could function as a Ca²⁺-independent cell adhesion receptor integrated into adherens junctions.\",\n      \"evidence\": \"Cell-based adhesion assays, co-immunoprecipitation, and immunofluorescence colocalization in transfected cells\",\n      \"pmids\": [\"10744716\", \"11024295\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of nectin-3 cis-dimerization and trans-interactions not resolved\",\n        \"In vivo function of nectin-3 not yet tested with genetic models\"\n      ]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Mapping the nectin-1/nectin-3 heterophilic interface to V-domain beta-strands with nanomolar affinity established the molecular basis for their preferential trans-interaction over homophilic binding.\",\n      \"evidence\": \"Surface plasmon resonance and competition binding with chimeric receptors and monoclonal antibodies\",\n      \"pmids\": [\"12011057\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Atomic-resolution crystal structure of the nectin-1/nectin-3 trans-dimer not yet available\",\n        \"Relative contribution of C domains to in vivo function unknown\"\n      ]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identification of Necl-5/CD155 as a heterophilic trans-partner for nectin-3 expanded the nectin interactome beyond the nectin family and linked nectin-3 to cell motility regulation in Ras-transformed cells.\",\n      \"evidence\": \"Cell-based ligand binding assays, heterologous co-culture, and immunofluorescence in multiple independent studies\",\n      \"pmids\": [\"12740392\", \"12759359\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of the nectin-3/Necl-5 interaction undetermined\",\n        \"Relevance of this interaction to normal (non-transformed) physiology unclear\"\n      ]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstration that nectin-3/Necl-5 trans-interaction triggers clathrin-dependent endocytosis of Necl-5, reducing proliferation and migration, established nectin-3 as a mediator of contact inhibition of cell growth.\",\n      \"evidence\": \"Clathrin inhibition, cell migration and proliferation assays in NIH3T3 cells\",\n      \"pmids\": [\"16216929\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Signaling intermediates between nectin-3 engagement and clathrin recruitment not identified\",\n        \"Whether this mechanism operates in epithelial tissues in vivo not tested\"\n      ]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Nectin-3 knockout mice revealed that heterophilic nectin-1/nectin-3 trans-interaction is required for junction formation in the ciliary epithelium, providing the first in vivo genetic evidence for nectin-3 function in tissue morphogenesis.\",\n      \"evidence\": \"Nectin-3−/− mice with microphthalmia, immunofluorescence and immunoelectron microscopy\",\n      \"pmids\": [\"15728677\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular mechanism linking nectin-3 loss to junction disassembly not dissected\",\n        \"Whether redundancy with other nectins limits phenotypic severity unknown\"\n      ]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Discovery that nectin-3 on spermatids trans-interacts with nectin-2 on Sertoli cells, and that nectin-3−/− mice are male-infertile, established nectin-3 as essential for spermatid adhesion and maturation.\",\n      \"evidence\": \"Nectin-3−/− mice, spermatogenic stem cell transplantation rescue, immunohistochemistry\",\n      \"pmids\": [\"16923130\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"How nectin-3 loss leads to mitochondrial mislocalization and nuclear distortion mechanistically unresolved\",\n        \"Identity of downstream signaling pathways at the apical ectoplasmic specialization not fully defined\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Compound nectin-1;nectin-3 mutant mice showed that heterophilic nectin-1/nectin-3 interaction recruits desmosomes to ameloblast–stratum intermedium junctions, broadening nectin-3's role from adherens to desmosomal junction assembly.\",\n      \"evidence\": \"Compound knockout mice, immunohistochemistry, electron microscopy of tooth enamel organ\",\n      \"pmids\": [\"21038445\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism by which nectin trans-interaction nucleates desmosome assembly not identified\",\n        \"Whether other tooth developmental pathways are affected independently of desmosomes unknown\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Placing nectin-3 downstream of CRH–CRHR1 signaling in the hippocampus, and showing that nectin-3 manipulation bidirectionally controls stress-induced spine loss and memory deficits, identified nectin-3 as a synaptic effector of stress.\",\n      \"evidence\": \"AAV-mediated knockdown/overexpression in mice, CRHR1 genetic inactivation, CRH overexpression, behavioral and spine analysis\",\n      \"pmids\": [\"23644483\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Intracellular signaling cascade from CRHR1 activation to nectin-3 downregulation not fully delineated\",\n        \"Whether afadin is co-regulated with nectin-3 in this context not established\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identification of MMP-9 as the protease that cleaves nectin-3 in hippocampal CA1 in an NMDA receptor–dependent manner explained how chronic stress removes nectin-3 from perisynaptic sites to impair cognition.\",\n      \"evidence\": \"MMP-9 knockout/pharmacological inhibition, NMDA receptor blockade, gelatinase activity assay, behavioral testing\",\n      \"pmids\": [\"25232752\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Exact cleavage site on nectin-3 not mapped\",\n        \"Fate of the cleaved ectodomain (shed fragment signaling) not investigated\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Nectin-3 deficiency in cochlear hair cells caused aberrant hair cell–hair cell contacts, disrupted hair bundle orientation, and mislocalized polarity proteins, revealing nectin-3 as a determinant of planar cell polarity in the inner ear.\",\n      \"evidence\": \"Nectin-3-deficient mice, immunofluorescence and confocal microscopy of cochlear epithelium\",\n      \"pmids\": [\"24381198\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Upstream signals controlling nectin-3 expression in hair cells not identified at this point\",\n        \"Whether nectin-3 directly interacts with polarity proteins or acts indirectly unknown\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The crystal structure of the afadin PDZ domain bound to the nectin-3 C-terminal peptide revealed the atomic basis for their interaction, including a conformational widening of the binding groove, resolving how nectin-3 is physically linked to the cytoskeleton.\",\n      \"evidence\": \"X-ray crystallography of AFPDZ–nectin-3 fusion protein complex\",\n      \"pmids\": [\"25534554\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structure of full-length nectin-3 or the nectin-3/afadin complex beyond the PDZ interface not available\",\n        \"Regulation of the PDZ interaction (phosphorylation, competition) not structurally characterized\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Discovery that nectin-3 localizes to the colonocyte brush border and serves as a receptor for C. difficile toxin B extended nectin-3 biology from developmental adhesion to pathogen entry.\",\n      \"evidence\": \"Immunofluorescence microscopy on colonic tissue, receptor localization studies\",\n      \"pmids\": [\"37747247\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Binding interface between TcdB and nectin-3 not structurally resolved\",\n        \"Whether other nectin family members can substitute as TcdB receptors not tested\",\n        \"Functional consequence of TcdB binding on nectin-3 adhesion function not examined\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Placing nectin-3 downstream of PCP/Vangl2 signaling and in the same genetic pathway as Rac1 for spiral ganglion neuron axon turning unified nectin-3's adhesive role with planar polarity-guided axon guidance in the cochlea.\",\n      \"evidence\": \"Conditional knockout mice, genetic epistasis analysis, afferent turning phenotype quantification\",\n      \"pmids\": [\"40207531\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"How Vangl2 transcriptionally or post-transcriptionally regulates nectin-3 expression not determined\",\n        \"Whether Rac1 acts upstream or downstream of nectin-3-mediated adhesion not resolved\",\n        \"Role of afadin in this cochlear guidance pathway not examined\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the full-length structural basis of nectin-3 cis- and trans-dimeric assemblies, the intracellular signaling cascades immediately downstream of nectin-3 engagement, the MMP-9 cleavage site and function of the shed ectodomain, and whether nectin-3 plays roles in immune cell biology beyond lymphocyte transendothelial migration.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No full-length or trans-dimer crystal structure available\",\n        \"Downstream signaling immediately triggered by nectin-3 ligation largely undefined\",\n        \"Shed ectodomain biology unexplored\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [0, 2, 3, 5, 7, 8]},\n      {\"term_id\": \"GO:0001618\", \"supporting_discovery_ids\": [21]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 7, 14, 16, 20, 21]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [16]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [0, 2, 5, 7, 8, 12]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [5, 7, 8, 14, 22]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [11, 13, 17, 20]},\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [7, 10, 16]}\n    ],\n    \"complexes\": [\n      \"nectin-afadin complex\"\n    ],\n    \"partners\": [\n      \"NECTIN1\",\n      \"NECTIN2\",\n      \"PVR\",\n      \"AFDN\",\n      \"CADM1\",\n      \"MMP9\",\n      \"VANGL2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}