{"gene":"NKD2","run_date":"2026-04-29T11:37:56","timeline":{"discoveries":[{"year":2004,"finding":"NKD2, but not NKD1, binds to basolateral sorting motifs in the cytoplasmic tail of TGF-alpha and escorts TGF-alpha-containing exocytic vesicles to the basolateral plasma membrane of polarized epithelial cells in a myristoylation-dependent manner; myristoylation-deficient G2A NKD2 fails to localize to the basolateral membrane and prevents TGF-alpha delivery there.","method":"Co-IP/pulldown, overexpression and dominant-negative (G2A mutant) in polarized MDCK cells, confocal microscopy, siRNA knockdown","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (binding assay, myristoylation-deficient mutant, rescue by siRNA silencing), replicated across follow-up papers","pmids":["15064403"],"is_preprint":false},{"year":2007,"finding":"NKD2 acts as a cargo recognition and targeting (CaRT) protein; Naked2-associated vesicles fuse at the lower lateral membrane of polarized MDCK cells independent of mu1B adaptin, a basolateral targeting segment within residues 1-173 is required, and shRNA knockdown of Naked2 dramatically reduces the 16-kDa cell-surface isoform of TGF-alpha.","method":"High-resolution microscopy, internal deletion mutagenesis, shRNA knockdown, domain-swap experiments in MDCK cells","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1-2 — reconstitution of vesicle targeting with mutagenesis and KD phenotype, orthogonal to PMID 15064403","pmids":["17553928"],"is_preprint":false},{"year":2008,"finding":"Naked2 is a short-lived protein (half-life ~60 min) degraded via ubiquitin-mediated proteasomal degradation; the RING finger E3 ubiquitin ligase AO7/RNF25 ubiquitylates NKD2, while TGF-alpha binding to the cytoplasmic tail of NKD2 (EGFR-independently) displaces AO7 and stabilizes NKD2, ensuring its delivery to the basolateral surface.","method":"Protein half-life assays, Co-IP, ubiquitylation assays, overexpression of TGF-alpha and EGFR-null conditions, identification of AO7/RNF25 as E3 ligase","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — identified specific E3 ligase, multiple orthogonal biochemical methods including ubiquitylation assays and co-IP, strong mechanistic resolution","pmids":["18757723"],"is_preprint":false},{"year":2008,"finding":"NKD2-associated basolaterally targeted exocytic vesicles contain Rab10 and myosin IIA as core trafficking machinery and Na+/K+-ATPase alpha1 as additional cargo, identified by fluorescence-activated vesicle sorting of myristoylation-deficient G2A NKD2 vesicles followed by LC/LC-MS/MS proteomics.","method":"Fluorescence-activated vesicle sorting, LC/LC-MS/MS proteomics, biochemical fractionation, validation by Western blot","journal":"Molecular & cellular proteomics : MCP","confidence":"Medium","confidence_rationale":"Tier 2 — large-scale proteomics with triple-replicate validation, but functional confirmation of Rab10/myosin IIA roles is partial","pmids":["18504258"],"is_preprint":false},{"year":2010,"finding":"Myristoylated NKD2 interacts with Dishevelled-1 (Dvl-1) at the plasma membrane, and this interaction promotes mutual polyubiquitylation and proteasomal degradation of both proteins, thereby antagonizing Wnt-beta-catenin signaling; this mechanism is myristoylation-dependent, as cytoplasmic G2A NKD2 does not degrade Dvl-1.","method":"Reciprocal co-IP, siRNA knockdown, overexpression, cell fractionation, ubiquitylation assays in HEK293 cells, zebrafish embryonic development assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal biochemical assays plus in vivo zebrafish validation, myristoylation-deficient mutant controls","pmids":["20177058"],"is_preprint":false},{"year":2006,"finding":"The N-terminal half of human Naked2 (residues 1-217, containing the Dishevelled-binding region, EF-hand, vesicle recognition, and membrane targeting motifs) behaves as an intrinsically unstructured protein; it lacks secondary/tertiary structure by CD and NMR and does not bind calcium or zinc.","method":"Circular dichroism, NMR spectroscopy, recombinant protein expression and purification","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 — direct structural analysis with two orthogonal biophysical methods, single study","pmids":["17045239"],"is_preprint":false},{"year":2001,"finding":"Human NKD1 and NKD2 were cloned; both encode proteins with conserved domain architecture including an EF-hand motif in the NH2 domain, organized across 10 exons, and function as homologs of Drosophila Nkd that negatively regulates the WNT-beta-catenin-TCF signaling pathway by binding Dishevelled.","method":"Molecular cloning, gene structure analysis, expression profiling in cancer cell lines and primary tumors","journal":"International journal of oncology","confidence":"Medium","confidence_rationale":"Tier 3 — cloning and domain characterization supported by conserved ortholog function, no direct functional assay in this paper","pmids":["11604995"],"is_preprint":false},{"year":2007,"finding":"Zebrafish Nkd2 (and Nkd1) antagonizes both canonical Wnt/beta-catenin signaling and non-canonical Wnt/PCP signaling; overexpression suppresses canonical Wnt at multiple developmental stages and exacerbates the convergence-and-extension defect in wnt11 (silberblick) mutants, while morpholino knockdown of Nkd1 suppresses the same C&E defect.","method":"Overexpression in zebrafish embryos, morpholino knockdown, genetic epistasis with slb/wnt11 mutant, canonical Wnt target gene assay","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with defined mutant background plus gain- and loss-of-function, ortholog confirmed by domain conservation","pmids":["17689523"],"is_preprint":false},{"year":2007,"finding":"Mouse nkd1 and nkd2 proteins bind Dvl (Dishevelled) proteins and inhibit Wnt signaling; double knockout mice are viable with subtle cranial bone morphology alterations reminiscent of axin2 mutation, indicating nkd1/nkd2 function is dispensable for murine embryonic development but places them in the Wnt/Dvl pathway in vivo.","method":"Targeted gene knockout (replacement of Dvl-binding exons with IRES-lacZ/neomycin), double-knockout mouse generation, skeletal phenotype analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — clean genetic knockout with pathway-consistent phenotype, genetic epistasis with known Wnt antagonist axin2","pmids":["17438140"],"is_preprint":false},{"year":2021,"finding":"NKD2 is an essential component of ORAI1-containing intracellular vesicles in effector T cells; downstream of TCR signaling, NKD2 orchestrates trafficking and plasma membrane insertion of ORAI1+ vesicles to sustain Ca2+-release-activated Ca2+ (CRAC) channel activity, Ca2+ entry, and cytokine production.","method":"Targeted screen, vesicle fractionation, co-localization, loss-of-function in T cells, Ca2+ imaging, cytokine assays","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 — targeted screen plus functional readout (Ca2+ entry, cytokine production), single study","pmids":["34433025"],"is_preprint":false},{"year":2015,"finding":"NKD2 overexpression in osteosarcoma cells decreases proliferation, migration, and invasion in vitro and reduces tumor growth and metastasis in vivo; downregulation of NKD2 enhances migratory and invasive potential, placing NKD2 as a negative regulator of Wnt signaling-driven OS metastasis.","method":"Overexpression and knockdown in human/mouse OS cells, in vitro proliferation/migration/invasion assays, xenograft mouse model, microarray analysis","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — multiple in vitro and in vivo functional assays, pathway validation, single study","pmids":["25579177"],"is_preprint":false},{"year":2016,"finding":"miR-130b directly targets NKD2 (validated by target analysis and functional rescue), reducing NKD2 protein levels in osteosarcoma cells and thereby activating Wnt signaling to promote proliferation and inhibit apoptosis.","method":"miRNA target prediction, qRT-PCR, Western blot, MTT assay, flow cytometry, miR-130b inhibitor experiments with NKD2 rescue","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2-3 — direct target validation with functional rescue, but luciferase reporter confirmation not explicitly stated in abstract","pmids":["26902120"],"is_preprint":false},{"year":2015,"finding":"NKD2 expression is silenced by promoter region hypermethylation in breast cancer; restoration of NKD2 suppresses cell proliferation in vitro and in vivo, induces G1/S arrest, and inhibits Wnt signaling; NKD2 promoter methylation is regulated by DNA methylation (reversed by 5-aza-2'-deoxycytidine).","method":"Methylation-specific PCR, 5-aza-2'-deoxycytidine demethylation, Western blot, flow cytometry, xenograft mouse model","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 — epigenetic mechanism established with demethylation rescue and multiple functional readouts","pmids":["26124080"],"is_preprint":false},{"year":2015,"finding":"NKD2 promoter hypermethylation silences NKD2 in gastric cancer; restored NKD2 suppresses SOX18 and MMP-2/7/9 expression, inhibits cell invasion/migration, induces G2/M arrest, and suppresses xenograft tumor growth, placing NKD2 upstream of SOX18 in a metastasis-regulatory axis.","method":"Methylation-specific PCR, gene expression array, flow cytometry, transwell invasion assay, xenograft mouse model, Western blot","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 — pathway placement via KO/KD with defined downstream targets and in vivo validation","pmids":["26396173"],"is_preprint":false},{"year":2017,"finding":"The lncRNA ZFAS1 simultaneously binds EZH2 and LSD1/CoREST (shown by RNA immunoprecipitation and RNA pull-down) to epigenetically repress NKD2 (and KLF2) transcription; rescue experiments confirmed that ZFAS1's oncogenic function is partly dependent on repressing NKD2.","method":"RNA immunoprecipitation (RIP), RNA pull-down, rescue experiments, knockdown in gastric cancer cells","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2-3 — RIP and pull-down identify the epigenetic complex; functional rescue links NKD2 repression to phenotype","pmids":["27246976"],"is_preprint":false},{"year":2016,"finding":"The lncRNA HULC interacts with EZH2 (by RIP and RNA pull-down) to epigenetically repress NKD2 transcription in colorectal carcinoma; rescue experiments show HULC's oncogenic function partly depends on NKD2 repression.","method":"RNA immunoprecipitation (RIP), RNA pull-down, rescue experiments, knockdown/overexpression in CRC cells","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 3 — RIP/pull-down with functional rescue, single study","pmids":["27496341"],"is_preprint":false},{"year":2018,"finding":"NKD2 expression is upregulated during osteoblast differentiation of dental follicle stem/progenitor cells; siRNA silencing of Nkd2 significantly decreases osteoblast differentiation ability and reduces Wnt/beta-catenin pathway activity as measured by TCF luciferase reporter assay.","method":"siRNA knockdown, beta-catenin/TCF luciferase activity assay, Western blot, RT-qPCR in rat DFSCs","journal":"International journal of molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2-3 — luciferase reporter plus loss-of-function with differentiation phenotype, single study","pmids":["30106129"],"is_preprint":false},{"year":2020,"finding":"LINC00922 recruits DNMT1, DNMT3A, and DNMT3B to the NKD2 promoter (shown by RIP and ChIP assay) to promote NKD2 promoter methylation, thereby reducing NKD2 expression and activating Wnt signaling to promote breast cancer EMT and metastasis.","method":"RIP, ChIP assay, overexpression/knockdown experiments, in vivo xenograft","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2-3 — ChIP identifies specific methyltransferases at NKD2 promoter with functional rescue, single study","pmids":["33045317"],"is_preprint":false},{"year":2025,"finding":"In oral squamous cell carcinoma cells, IFIX overexpression upregulates NKD2 expression; NKD2 silencing mimics IFIX knockdown (inducing EMT), while NKD2 silencing restores the pro-invasive phenotype in IFIX-overexpressing cells, placing NKD2 downstream of IFIX as a mediator of Wnt signaling inhibition and EMT suppression.","method":"Overexpression/knockdown of IFIX and NKD2 in CAL-27 and SCC-25 OSCC cells, qRT-PCR, Western blot, proliferation/invasion/migration assays","journal":"Journal of cellular and molecular medicine","confidence":"Low","confidence_rationale":"Tier 3 — genetic epistasis by co-expression experiments but no direct binding or pathway reconstitution, single study","pmids":["39833105"],"is_preprint":false},{"year":2023,"finding":"NKD2 activates NF-κB transcriptional activity in thyroid cancer cells; ectopic NKD2 expression increases NF-κB activity and cell proliferation, while NKD2 knockdown reduces NF-κB activity, identifying a pro-oncogenic NKD2/NF-κB axis in thyroid cancer.","method":"Overexpression and knockdown in THCA cells, NF-κB transcriptional activity assay, proliferation assays","journal":"Molecular biotechnology","confidence":"Low","confidence_rationale":"Tier 3 — reporter assay links NKD2 to NF-κB, but mechanism is unclear and contradicts the predominant tumor-suppressive role; single study, no mechanistic detail","pmids":["36820951"],"is_preprint":false},{"year":2022,"finding":"Chrysophanol directly binds NKD2 (confirmed by molecular docking and microscale thermophoresis), suppresses NKD2 expression, and thereby inhibits NF-κB activation; NKD2 overexpression in HK-2 cells compromises the anti-fibrotic effects of chrysophanol, placing NKD2 upstream of NF-κB in renal fibrosis.","method":"Molecular docking, microscale thermophoresis (MST) binding assay, NKD2 overexpression in HK-2 cells, UUO mouse model, Western blot","journal":"Phytomedicine","confidence":"Medium","confidence_rationale":"Tier 1-2 — direct binding confirmed by MST plus genetic rescue experiments in vitro and in vivo, single study","pmids":["35988461"],"is_preprint":false}],"current_model":"NKD2 is a myristoylated, intrinsically disordered adaptor protein with at least two distinct mechanistic roles: (1) as an inducible Wnt antagonist, it localizes to the plasma membrane where it interacts with Dishevelled-1, promoting mutual polyubiquitylation and proteasomal degradation to attenuate Wnt/β-catenin signaling; and (2) as a cargo recognition and targeting protein, it binds the cytoplasmic tail of TGF-alpha and directs TGF-alpha-containing exocytic vesicles to the basolateral membrane of polarized epithelial cells via a myristoylation-dependent mechanism, with its stability protected from AO7/RNF25-mediated ubiquitylation by TGF-alpha interaction; additionally, NKD2 orchestrates TCR-stimulation-dependent trafficking of ORAI1+ vesicles to the plasma membrane to sustain CRAC channel Ca2+ entry in T cells, and its expression is frequently silenced by EZH2-dependent promoter hypermethylation in multiple cancers."},"narrative":{"teleology":[{"year":2001,"claim":"Cloning of human NKD1 and NKD2 established them as vertebrate homologs of Drosophila naked cuticle, predicted to antagonize Wnt/β-catenin signaling via a conserved EF-hand-containing domain architecture.","evidence":"Molecular cloning, gene structure analysis, and expression profiling in human cancer cell lines","pmids":["11604995"],"confidence":"Medium","gaps":["No direct functional assay for human NKD2 Wnt antagonism in this study","Binding to human Dvl not demonstrated"]},{"year":2004,"claim":"NKD2 was revealed to have an unexpected second function as a cargo recognition and targeting protein, directly binding basolateral sorting motifs in TGF-α and escorting TGF-α vesicles to the basolateral membrane in a myristoylation-dependent manner.","evidence":"Co-IP/pulldown, myristoylation-deficient G2A mutant, confocal microscopy, and siRNA knockdown in polarized MDCK cells","pmids":["15064403"],"confidence":"High","gaps":["Identity of vesicle machinery components unknown at this point","Mechanism by which NKD2 recognizes membrane target site unresolved"]},{"year":2006,"claim":"Biophysical characterization showed the N-terminal half of NKD2 (residues 1–217) is intrinsically disordered and does not bind calcium or zinc, indicating the EF-hand motif is non-functional for metal coordination.","evidence":"Circular dichroism and NMR spectroscopy on recombinant NKD2 fragment","pmids":["17045239"],"confidence":"Medium","gaps":["Structure of the C-terminal half uncharacterized","Whether disorder is functionally required for partner binding unknown"]},{"year":2007,"claim":"Genetic studies in mouse and zebrafish established NKD2 as a bona fide in vivo Wnt antagonist: Nkd1/Nkd2 double-knockout mice showed Wnt-pathway-consistent cranial bone defects, and zebrafish Nkd2 overexpression suppressed canonical Wnt signaling and modulated non-canonical Wnt/PCP signaling.","evidence":"Targeted gene knockout in mice with skeletal phenotyping; gain- and loss-of-function in zebrafish embryos with genetic epistasis against wnt11/slb","pmids":["17438140","17689523"],"confidence":"High","gaps":["Redundancy with Nkd1 obscures Nkd2-specific roles","Mechanism of PCP pathway antagonism not defined at molecular level"]},{"year":2007,"claim":"Domain mapping identified a basolateral targeting segment within NKD2 residues 1–173 that operates independently of the mu1B adaptin pathway, refining the CaRT mechanism.","evidence":"Internal deletion mutagenesis, domain-swap experiments, and shRNA knockdown in MDCK cells","pmids":["17553928"],"confidence":"High","gaps":["Direct receptor for vesicle docking at basolateral membrane not identified","Structural basis of the targeting segment unknown"]},{"year":2008,"claim":"Two discoveries clarified NKD2 regulation and vesicle composition: AO7/RNF25 was identified as the E3 ligase mediating NKD2 ubiquitylation and degradation, with TGF-α binding displacing AO7 to stabilize NKD2; proteomics of NKD2-associated vesicles identified Rab10 and myosin IIA as trafficking machinery.","evidence":"Ubiquitylation assays, half-life measurements, and co-IP for AO7/RNF25; fluorescence-activated vesicle sorting and LC/LC-MS/MS proteomics","pmids":["18757723","18504258"],"confidence":"High","gaps":["Functional validation of Rab10 and myosin IIA in NKD2-dependent trafficking incomplete","Whether AO7 regulation is tissue-specific unknown"]},{"year":2010,"claim":"The Wnt-antagonist mechanism was molecularly defined: myristoylated NKD2 interacts with Dvl-1 at the plasma membrane, triggering mutual polyubiquitylation and proteasomal degradation of both proteins, directly linking NKD2's membrane association to Wnt pathway attenuation.","evidence":"Reciprocal co-IP, ubiquitylation assays, cell fractionation in HEK293 cells, and zebrafish developmental assay with G2A mutant","pmids":["20177058"],"confidence":"High","gaps":["E3 ligase responsible for Dvl-1 ubiquitylation in this context not identified","Whether NKD2 also targets Dvl-2/3 not tested"]},{"year":2015,"claim":"Epigenetic silencing of NKD2 by promoter hypermethylation was established as a recurrent event across multiple cancers, with demethylation or re-expression restoring Wnt inhibition, cell cycle arrest, and tumor suppression.","evidence":"Methylation-specific PCR, 5-aza-2'-deoxycytidine treatment, xenograft models in breast and gastric cancer cells","pmids":["26124080","26396173","25579177"],"confidence":"Medium","gaps":["Upstream signals initiating methylation not fully defined","Whether methylation is a driver or passenger event in tumorigenesis unclear"]},{"year":2016,"claim":"Multiple lncRNAs (HULC, ZFAS1) and miRNAs (miR-130b) were shown to repress NKD2 through distinct mechanisms—EZH2 recruitment to the promoter or direct mRNA targeting—establishing NKD2 as a convergent node of epigenetic and post-transcriptional silencing in cancer.","evidence":"RIP, RNA pull-down, ChIP, miRNA target validation, and rescue experiments in CRC, gastric cancer, and osteosarcoma cells","pmids":["27496341","27246976","26902120"],"confidence":"Medium","gaps":["Relative contribution of each silencing mechanism in a given tumor type unknown","Whether these regulatory inputs operate in normal tissues unaddressed"]},{"year":2021,"claim":"A new trafficking role was uncovered in immune cells: NKD2 was identified as essential for TCR-stimulation-dependent delivery of ORAI1-containing vesicles to the plasma membrane, sustaining CRAC channel Ca²⁺ entry and cytokine production in effector T cells.","evidence":"Targeted screen, vesicle fractionation, co-localization, loss-of-function Ca²⁺ imaging and cytokine assays in T cells","pmids":["34433025"],"confidence":"Medium","gaps":["Whether NKD2 acts via the same myristoylation-dependent CaRT mechanism as in epithelial cells not tested","Adaptor partners in T cell vesicle trafficking not identified","Single study awaiting independent replication"]},{"year":2022,"claim":"NKD2 was linked to NF-κB pathway activation in the context of renal fibrosis; direct binding of the small molecule chrysophanol to NKD2 suppressed NKD2-dependent NF-κB activation.","evidence":"Molecular docking, microscale thermophoresis binding assay, NKD2 overexpression/rescue in HK-2 cells, UUO mouse model","pmids":["35988461"],"confidence":"Medium","gaps":["Molecular mechanism linking NKD2 to NF-κB activation undefined","Whether NF-κB regulation is independent of Wnt antagonism not resolved","Chrysophanol specificity for NKD2 over other targets not comprehensively assessed"]},{"year":null,"claim":"Key unresolved questions include: the structural basis for NKD2's multivalent interactions, the E3 ligase mediating Dvl-1 co-degradation, the molecular mechanism connecting NKD2 to NF-κB signaling, and whether NKD2's CaRT function in T cell ORAI1 trafficking shares the same myristoylation-dependent mechanism as epithelial TGF-α sorting.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of NKD2 or its complexes","E3 ligase for mutual Dvl/NKD2 degradation not identified","CaRT mechanism in T cells not molecularly characterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,9]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[4,7,8]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,4]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[0,1,3,9]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[4,5]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[4,7,8,10,12]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,1,3,9]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[2,4]}],"complexes":[],"partners":["DVL1","TGFA","RNF25","RAB10","ORAI1"],"other_free_text":[]},"mechanistic_narrative":"NKD2 is a myristoylated, intrinsically disordered adaptor protein that functions both as a Wnt/β-catenin signaling antagonist and as a cargo recognition and targeting (CaRT) protein for vesicle trafficking. In polarized epithelial cells, NKD2 binds the cytoplasmic tail of TGF-α and escorts TGF-α–containing exocytic vesicles to the basolateral plasma membrane in a myristoylation-dependent manner, with its stability regulated by AO7/RNF25-mediated ubiquitylation that is antagonized by TGF-α binding [PMID:15064403, PMID:18757723]. At the plasma membrane, myristoylated NKD2 interacts with Dishevelled-1, promoting mutual polyubiquitylation and proteasomal degradation of both proteins to attenuate canonical Wnt signaling, a function conserved from zebrafish to mammals [PMID:20177058, PMID:17438140]. NKD2 also orchestrates TCR-stimulated trafficking of ORAI1-containing vesicles to the plasma membrane to sustain CRAC channel Ca²⁺ entry in effector T cells [PMID:34433025], and its expression is frequently silenced by EZH2- and DNMT-dependent promoter hypermethylation in multiple cancer types [PMID:26124080, PMID:27496341]."},"prefetch_data":{"uniprot":{"accession":"Q969F2","full_name":"Protein naked cuticle homolog 2","aliases":[],"length_aa":451,"mass_kda":50.1,"function":"Cell autonomous antagonist of the canonical Wnt signaling pathway. May activate a second Wnt signaling pathway that controls planar cell polarity (By similarity). Required for processing of TGFA and for targeting of TGFA to the basolateral membrane of polarized epithelial cells","subcellular_location":"Cell membrane; Cytoplasm; Cytoplasmic vesicle","url":"https://www.uniprot.org/uniprotkb/Q969F2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/NKD2","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/NKD2","total_profiled":1310},"omim":[{"mim_id":"607852","title":"NKD INHIBITOR OF WNT SIGNALING PATHWAY 2; NKD2","url":"https://www.omim.org/entry/607852"},{"mim_id":"607851","title":"NKD INHIBITOR OF WNT SIGNALING PATHWAY 1; NKD1","url":"https://www.omim.org/entry/607851"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"lung","ntpm":40.8}],"url":"https://www.proteinatlas.org/search/NKD2"},"hgnc":{"alias_symbol":["Naked2"],"prev_symbol":[]},"alphafold":{"accession":"Q969F2","domains":[{"cath_id":"-","chopping":"123-154","consensus_level":"medium","plddt":84.7363,"start":123,"end":154}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q969F2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q969F2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q969F2-F1-predicted_aligned_error_v6.png","plddt_mean":55.47},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NKD2","jax_strain_url":"https://www.jax.org/strain/search?query=NKD2"},"sequence":{"accession":"Q969F2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q969F2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q969F2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q969F2"}},"corpus_meta":[{"pmid":"27246976","id":"PMC_27246976","title":"Long noncoding RNA ZFAS1 promotes gastric cancer cells proliferation by epigenetically repressing KLF2 and NKD2 expression.","date":"2017","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/27246976","citation_count":139,"is_preprint":false},{"pmid":"11604995","id":"PMC_11604995","title":"Molecular cloning, gene structure, and expression analyses of NKD1 and NKD2.","date":"2001","source":"International journal of oncology","url":"https://pubmed.ncbi.nlm.nih.gov/11604995","citation_count":115,"is_preprint":false},{"pmid":"25579177","id":"PMC_25579177","title":"NKD2, a negative regulator of Wnt signaling, suppresses tumor growth and metastasis in osteosarcoma.","date":"2015","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/25579177","citation_count":108,"is_preprint":false},{"pmid":"26985708","id":"PMC_26985708","title":"Curcumin inhibits tumor epithelial‑mesenchymal transition by downregulating the Wnt signaling pathway and upregulating NKD2 expression in colon cancer cells.","date":"2016","source":"Oncology reports","url":"https://pubmed.ncbi.nlm.nih.gov/26985708","citation_count":76,"is_preprint":false},{"pmid":"27496341","id":"PMC_27496341","title":"Long noncoding RNA HULC promotes colorectal carcinoma progression through epigenetically repressing NKD2 expression.","date":"2016","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/27496341","citation_count":62,"is_preprint":false},{"pmid":"15064403","id":"PMC_15064403","title":"Myristoylated Naked2 escorts transforming growth factor alpha to the basolateral plasma membrane of polarized epithelial cells.","date":"2004","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/15064403","citation_count":55,"is_preprint":false},{"pmid":"17689523","id":"PMC_17689523","title":"Zebrafish Naked1 and Naked2 antagonize both canonical and non-canonical Wnt signaling.","date":"2007","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/17689523","citation_count":51,"is_preprint":false},{"pmid":"20177058","id":"PMC_20177058","title":"Myristoylated Naked2 antagonizes Wnt-beta-catenin activity by degrading Dishevelled-1 at the plasma membrane.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20177058","citation_count":49,"is_preprint":false},{"pmid":"16752383","id":"PMC_16752383","title":"Frequent amplifications and abundant expression of TRIO, NKD2, and IRX2 in soft tissue sarcomas.","date":"2006","source":"Genes, chromosomes & cancer","url":"https://pubmed.ncbi.nlm.nih.gov/16752383","citation_count":44,"is_preprint":false},{"pmid":"18504258","id":"PMC_18504258","title":"Use of fluorescence-activated vesicle sorting for isolation of Naked2-associated, basolaterally targeted exocytic vesicles for proteomics analysis.","date":"2008","source":"Molecular & cellular proteomics : MCP","url":"https://pubmed.ncbi.nlm.nih.gov/18504258","citation_count":36,"is_preprint":false},{"pmid":"17553928","id":"PMC_17553928","title":"Naked2 acts as a cargo recognition and targeting protein to ensure proper delivery and fusion of TGF-alpha containing exocytic vesicles at the lower lateral membrane of polarized MDCK cells.","date":"2007","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/17553928","citation_count":34,"is_preprint":false},{"pmid":"27374455","id":"PMC_27374455","title":"Silencing NKD2 by Promoter Region Hypermethylation Promotes Esophageal Cancer Progression by Activating Wnt Signaling.","date":"2016","source":"Journal of thoracic oncology : official publication of the International Association for the Study of Lung Cancer","url":"https://pubmed.ncbi.nlm.nih.gov/27374455","citation_count":34,"is_preprint":false},{"pmid":"35988461","id":"PMC_35988461","title":"Chrysophanol, a main anthraquinone from Rheum palmatum L. (rhubarb), protects against renal fibrosis by suppressing NKD2/NF-κB pathway.","date":"2022","source":"Phytomedicine : international journal of phytotherapy and phytopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/35988461","citation_count":33,"is_preprint":false},{"pmid":"26124080","id":"PMC_26124080","title":"Epigenetic silencing of NKD2, a major component of Wnt signaling, promotes breast cancer growth.","date":"2015","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/26124080","citation_count":32,"is_preprint":false},{"pmid":"17438140","id":"PMC_17438140","title":"Viable mice with compound mutations in the Wnt/Dvl pathway antagonists nkd1 and nkd2.","date":"2007","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/17438140","citation_count":31,"is_preprint":false},{"pmid":"26902120","id":"PMC_26902120","title":"miR-130b targets NKD2 and regulates the Wnt signaling to promote proliferation and inhibit apoptosis in osteosarcoma 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Facial Nerve Regeneration via circRNA_Nkd2/miR-214-3p/MED19 Axis.","date":"2024","source":"International journal of nanomedicine","url":"https://pubmed.ncbi.nlm.nih.gov/38371458","citation_count":21,"is_preprint":false},{"pmid":"18757723","id":"PMC_18757723","title":"EGF receptor-independent action of TGF-alpha protects Naked2 from AO7-mediated ubiquitylation and proteasomal degradation.","date":"2008","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/18757723","citation_count":16,"is_preprint":false},{"pmid":"17045239","id":"PMC_17045239","title":"Structural studies of human Naked2: a biologically active intrinsically unstructured protein.","date":"2006","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/17045239","citation_count":12,"is_preprint":false},{"pmid":"28261348","id":"PMC_28261348","title":"Epigenetic dysregulation of NKD2 is a valuable predictor assessing treatment outcome in acute myeloid leukemia.","date":"2017","source":"Journal of Cancer","url":"https://pubmed.ncbi.nlm.nih.gov/28261348","citation_count":10,"is_preprint":false},{"pmid":"30106129","id":"PMC_30106129","title":"Nkd2 promotes the differentiation of dental follicle stem/progenitor cells into osteoblasts.","date":"2018","source":"International journal of molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/30106129","citation_count":9,"is_preprint":false},{"pmid":"38010861","id":"PMC_38010861","title":"Curcumin suppresses the Wnt/β-catenin signaling pathway by inhibiting NKD2 methylation to ameliorate intestinal ischemia/reperfusion injury.","date":"2023","source":"The Kaohsiung journal of medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/38010861","citation_count":5,"is_preprint":false},{"pmid":"26084600","id":"PMC_26084600","title":"Up-Regulation of Corticocerebral NKD2 in Lipopolysaccharide-Induced Neuroinflammation.","date":"2015","source":"Cellular and molecular neurobiology","url":"https://pubmed.ncbi.nlm.nih.gov/26084600","citation_count":4,"is_preprint":false},{"pmid":"33455110","id":"PMC_33455110","title":"LINC00538 promotes the progression of colon cancer through inhibiting NKD2 expression.","date":"2020","source":"Journal of B.U.ON. : official journal of the Balkan Union of Oncology","url":"https://pubmed.ncbi.nlm.nih.gov/33455110","citation_count":4,"is_preprint":false},{"pmid":"39833105","id":"PMC_39833105","title":"NKD2 as a Mediator of IFIX Antioncogene-Induced Wnt Signalling and Epithelial-Mesenchymal Transition in Human OSCC.","date":"2025","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/39833105","citation_count":4,"is_preprint":false},{"pmid":"36820951","id":"PMC_36820951","title":"NKD2 Trigger NF-κB Signaling Pathway and Facilitates Thyroid Cancer Cell Proliferation.","date":"2023","source":"Molecular 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the nkd2 promoter contributed to allelic diversity of the r1 gene in maize (Zea mays).","date":"2022","source":"The Plant journal : for cell and molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/35876146","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.09.05.674475","title":"Interactions Between Dietary Metabolites and Regulatory Risk Variants for Human Colon Cancer","date":"2025-09-08","source":"bioRxiv","url":"https://doi.org/10.1101/2025.09.05.674475","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":17808,"output_tokens":5215,"usd":0.065824},"stage2":{"model":"claude-opus-4-6","input_tokens":8748,"output_tokens":3076,"usd":0.18096},"total_usd":0.246784,"stage1_batch_id":"msgbatch_012ZiiCUBfB62NCTQd4Bk1Jo","stage2_batch_id":"msgbatch_01Xuqq9aUHoQouS7UVGZNStZ","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2004,\n      \"finding\": \"NKD2, but not NKD1, binds to basolateral sorting motifs in the cytoplasmic tail of TGF-alpha and escorts TGF-alpha-containing exocytic vesicles to the basolateral plasma membrane of polarized epithelial cells in a myristoylation-dependent manner; myristoylation-deficient G2A NKD2 fails to localize to the basolateral membrane and prevents TGF-alpha delivery there.\",\n      \"method\": \"Co-IP/pulldown, overexpression and dominant-negative (G2A mutant) in polarized MDCK cells, confocal microscopy, siRNA knockdown\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (binding assay, myristoylation-deficient mutant, rescue by siRNA silencing), replicated across follow-up papers\",\n      \"pmids\": [\"15064403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"NKD2 acts as a cargo recognition and targeting (CaRT) protein; Naked2-associated vesicles fuse at the lower lateral membrane of polarized MDCK cells independent of mu1B adaptin, a basolateral targeting segment within residues 1-173 is required, and shRNA knockdown of Naked2 dramatically reduces the 16-kDa cell-surface isoform of TGF-alpha.\",\n      \"method\": \"High-resolution microscopy, internal deletion mutagenesis, shRNA knockdown, domain-swap experiments in MDCK cells\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution of vesicle targeting with mutagenesis and KD phenotype, orthogonal to PMID 15064403\",\n      \"pmids\": [\"17553928\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Naked2 is a short-lived protein (half-life ~60 min) degraded via ubiquitin-mediated proteasomal degradation; the RING finger E3 ubiquitin ligase AO7/RNF25 ubiquitylates NKD2, while TGF-alpha binding to the cytoplasmic tail of NKD2 (EGFR-independently) displaces AO7 and stabilizes NKD2, ensuring its delivery to the basolateral surface.\",\n      \"method\": \"Protein half-life assays, Co-IP, ubiquitylation assays, overexpression of TGF-alpha and EGFR-null conditions, identification of AO7/RNF25 as E3 ligase\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — identified specific E3 ligase, multiple orthogonal biochemical methods including ubiquitylation assays and co-IP, strong mechanistic resolution\",\n      \"pmids\": [\"18757723\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"NKD2-associated basolaterally targeted exocytic vesicles contain Rab10 and myosin IIA as core trafficking machinery and Na+/K+-ATPase alpha1 as additional cargo, identified by fluorescence-activated vesicle sorting of myristoylation-deficient G2A NKD2 vesicles followed by LC/LC-MS/MS proteomics.\",\n      \"method\": \"Fluorescence-activated vesicle sorting, LC/LC-MS/MS proteomics, biochemical fractionation, validation by Western blot\",\n      \"journal\": \"Molecular & cellular proteomics : MCP\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — large-scale proteomics with triple-replicate validation, but functional confirmation of Rab10/myosin IIA roles is partial\",\n      \"pmids\": [\"18504258\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Myristoylated NKD2 interacts with Dishevelled-1 (Dvl-1) at the plasma membrane, and this interaction promotes mutual polyubiquitylation and proteasomal degradation of both proteins, thereby antagonizing Wnt-beta-catenin signaling; this mechanism is myristoylation-dependent, as cytoplasmic G2A NKD2 does not degrade Dvl-1.\",\n      \"method\": \"Reciprocal co-IP, siRNA knockdown, overexpression, cell fractionation, ubiquitylation assays in HEK293 cells, zebrafish embryonic development assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal biochemical assays plus in vivo zebrafish validation, myristoylation-deficient mutant controls\",\n      \"pmids\": [\"20177058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The N-terminal half of human Naked2 (residues 1-217, containing the Dishevelled-binding region, EF-hand, vesicle recognition, and membrane targeting motifs) behaves as an intrinsically unstructured protein; it lacks secondary/tertiary structure by CD and NMR and does not bind calcium or zinc.\",\n      \"method\": \"Circular dichroism, NMR spectroscopy, recombinant protein expression and purification\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — direct structural analysis with two orthogonal biophysical methods, single study\",\n      \"pmids\": [\"17045239\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Human NKD1 and NKD2 were cloned; both encode proteins with conserved domain architecture including an EF-hand motif in the NH2 domain, organized across 10 exons, and function as homologs of Drosophila Nkd that negatively regulates the WNT-beta-catenin-TCF signaling pathway by binding Dishevelled.\",\n      \"method\": \"Molecular cloning, gene structure analysis, expression profiling in cancer cell lines and primary tumors\",\n      \"journal\": \"International journal of oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — cloning and domain characterization supported by conserved ortholog function, no direct functional assay in this paper\",\n      \"pmids\": [\"11604995\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Zebrafish Nkd2 (and Nkd1) antagonizes both canonical Wnt/beta-catenin signaling and non-canonical Wnt/PCP signaling; overexpression suppresses canonical Wnt at multiple developmental stages and exacerbates the convergence-and-extension defect in wnt11 (silberblick) mutants, while morpholino knockdown of Nkd1 suppresses the same C&E defect.\",\n      \"method\": \"Overexpression in zebrafish embryos, morpholino knockdown, genetic epistasis with slb/wnt11 mutant, canonical Wnt target gene assay\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with defined mutant background plus gain- and loss-of-function, ortholog confirmed by domain conservation\",\n      \"pmids\": [\"17689523\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Mouse nkd1 and nkd2 proteins bind Dvl (Dishevelled) proteins and inhibit Wnt signaling; double knockout mice are viable with subtle cranial bone morphology alterations reminiscent of axin2 mutation, indicating nkd1/nkd2 function is dispensable for murine embryonic development but places them in the Wnt/Dvl pathway in vivo.\",\n      \"method\": \"Targeted gene knockout (replacement of Dvl-binding exons with IRES-lacZ/neomycin), double-knockout mouse generation, skeletal phenotype analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic knockout with pathway-consistent phenotype, genetic epistasis with known Wnt antagonist axin2\",\n      \"pmids\": [\"17438140\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"NKD2 is an essential component of ORAI1-containing intracellular vesicles in effector T cells; downstream of TCR signaling, NKD2 orchestrates trafficking and plasma membrane insertion of ORAI1+ vesicles to sustain Ca2+-release-activated Ca2+ (CRAC) channel activity, Ca2+ entry, and cytokine production.\",\n      \"method\": \"Targeted screen, vesicle fractionation, co-localization, loss-of-function in T cells, Ca2+ imaging, cytokine assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — targeted screen plus functional readout (Ca2+ entry, cytokine production), single study\",\n      \"pmids\": [\"34433025\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"NKD2 overexpression in osteosarcoma cells decreases proliferation, migration, and invasion in vitro and reduces tumor growth and metastasis in vivo; downregulation of NKD2 enhances migratory and invasive potential, placing NKD2 as a negative regulator of Wnt signaling-driven OS metastasis.\",\n      \"method\": \"Overexpression and knockdown in human/mouse OS cells, in vitro proliferation/migration/invasion assays, xenograft mouse model, microarray analysis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple in vitro and in vivo functional assays, pathway validation, single study\",\n      \"pmids\": [\"25579177\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"miR-130b directly targets NKD2 (validated by target analysis and functional rescue), reducing NKD2 protein levels in osteosarcoma cells and thereby activating Wnt signaling to promote proliferation and inhibit apoptosis.\",\n      \"method\": \"miRNA target prediction, qRT-PCR, Western blot, MTT assay, flow cytometry, miR-130b inhibitor experiments with NKD2 rescue\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct target validation with functional rescue, but luciferase reporter confirmation not explicitly stated in abstract\",\n      \"pmids\": [\"26902120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"NKD2 expression is silenced by promoter region hypermethylation in breast cancer; restoration of NKD2 suppresses cell proliferation in vitro and in vivo, induces G1/S arrest, and inhibits Wnt signaling; NKD2 promoter methylation is regulated by DNA methylation (reversed by 5-aza-2'-deoxycytidine).\",\n      \"method\": \"Methylation-specific PCR, 5-aza-2'-deoxycytidine demethylation, Western blot, flow cytometry, xenograft mouse model\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epigenetic mechanism established with demethylation rescue and multiple functional readouts\",\n      \"pmids\": [\"26124080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"NKD2 promoter hypermethylation silences NKD2 in gastric cancer; restored NKD2 suppresses SOX18 and MMP-2/7/9 expression, inhibits cell invasion/migration, induces G2/M arrest, and suppresses xenograft tumor growth, placing NKD2 upstream of SOX18 in a metastasis-regulatory axis.\",\n      \"method\": \"Methylation-specific PCR, gene expression array, flow cytometry, transwell invasion assay, xenograft mouse model, Western blot\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pathway placement via KO/KD with defined downstream targets and in vivo validation\",\n      \"pmids\": [\"26396173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The lncRNA ZFAS1 simultaneously binds EZH2 and LSD1/CoREST (shown by RNA immunoprecipitation and RNA pull-down) to epigenetically repress NKD2 (and KLF2) transcription; rescue experiments confirmed that ZFAS1's oncogenic function is partly dependent on repressing NKD2.\",\n      \"method\": \"RNA immunoprecipitation (RIP), RNA pull-down, rescue experiments, knockdown in gastric cancer cells\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — RIP and pull-down identify the epigenetic complex; functional rescue links NKD2 repression to phenotype\",\n      \"pmids\": [\"27246976\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The lncRNA HULC interacts with EZH2 (by RIP and RNA pull-down) to epigenetically repress NKD2 transcription in colorectal carcinoma; rescue experiments show HULC's oncogenic function partly depends on NKD2 repression.\",\n      \"method\": \"RNA immunoprecipitation (RIP), RNA pull-down, rescue experiments, knockdown/overexpression in CRC cells\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — RIP/pull-down with functional rescue, single study\",\n      \"pmids\": [\"27496341\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"NKD2 expression is upregulated during osteoblast differentiation of dental follicle stem/progenitor cells; siRNA silencing of Nkd2 significantly decreases osteoblast differentiation ability and reduces Wnt/beta-catenin pathway activity as measured by TCF luciferase reporter assay.\",\n      \"method\": \"siRNA knockdown, beta-catenin/TCF luciferase activity assay, Western blot, RT-qPCR in rat DFSCs\",\n      \"journal\": \"International journal of molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — luciferase reporter plus loss-of-function with differentiation phenotype, single study\",\n      \"pmids\": [\"30106129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"LINC00922 recruits DNMT1, DNMT3A, and DNMT3B to the NKD2 promoter (shown by RIP and ChIP assay) to promote NKD2 promoter methylation, thereby reducing NKD2 expression and activating Wnt signaling to promote breast cancer EMT and metastasis.\",\n      \"method\": \"RIP, ChIP assay, overexpression/knockdown experiments, in vivo xenograft\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — ChIP identifies specific methyltransferases at NKD2 promoter with functional rescue, single study\",\n      \"pmids\": [\"33045317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In oral squamous cell carcinoma cells, IFIX overexpression upregulates NKD2 expression; NKD2 silencing mimics IFIX knockdown (inducing EMT), while NKD2 silencing restores the pro-invasive phenotype in IFIX-overexpressing cells, placing NKD2 downstream of IFIX as a mediator of Wnt signaling inhibition and EMT suppression.\",\n      \"method\": \"Overexpression/knockdown of IFIX and NKD2 in CAL-27 and SCC-25 OSCC cells, qRT-PCR, Western blot, proliferation/invasion/migration assays\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — genetic epistasis by co-expression experiments but no direct binding or pathway reconstitution, single study\",\n      \"pmids\": [\"39833105\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"NKD2 activates NF-κB transcriptional activity in thyroid cancer cells; ectopic NKD2 expression increases NF-κB activity and cell proliferation, while NKD2 knockdown reduces NF-κB activity, identifying a pro-oncogenic NKD2/NF-κB axis in thyroid cancer.\",\n      \"method\": \"Overexpression and knockdown in THCA cells, NF-κB transcriptional activity assay, proliferation assays\",\n      \"journal\": \"Molecular biotechnology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — reporter assay links NKD2 to NF-κB, but mechanism is unclear and contradicts the predominant tumor-suppressive role; single study, no mechanistic detail\",\n      \"pmids\": [\"36820951\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Chrysophanol directly binds NKD2 (confirmed by molecular docking and microscale thermophoresis), suppresses NKD2 expression, and thereby inhibits NF-κB activation; NKD2 overexpression in HK-2 cells compromises the anti-fibrotic effects of chrysophanol, placing NKD2 upstream of NF-κB in renal fibrosis.\",\n      \"method\": \"Molecular docking, microscale thermophoresis (MST) binding assay, NKD2 overexpression in HK-2 cells, UUO mouse model, Western blot\",\n      \"journal\": \"Phytomedicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — direct binding confirmed by MST plus genetic rescue experiments in vitro and in vivo, single study\",\n      \"pmids\": [\"35988461\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NKD2 is a myristoylated, intrinsically disordered adaptor protein with at least two distinct mechanistic roles: (1) as an inducible Wnt antagonist, it localizes to the plasma membrane where it interacts with Dishevelled-1, promoting mutual polyubiquitylation and proteasomal degradation to attenuate Wnt/β-catenin signaling; and (2) as a cargo recognition and targeting protein, it binds the cytoplasmic tail of TGF-alpha and directs TGF-alpha-containing exocytic vesicles to the basolateral membrane of polarized epithelial cells via a myristoylation-dependent mechanism, with its stability protected from AO7/RNF25-mediated ubiquitylation by TGF-alpha interaction; additionally, NKD2 orchestrates TCR-stimulation-dependent trafficking of ORAI1+ vesicles to the plasma membrane to sustain CRAC channel Ca2+ entry in T cells, and its expression is frequently silenced by EZH2-dependent promoter hypermethylation in multiple cancers.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"NKD2 is a myristoylated, intrinsically disordered adaptor protein that functions both as a Wnt/β-catenin signaling antagonist and as a cargo recognition and targeting (CaRT) protein for vesicle trafficking. In polarized epithelial cells, NKD2 binds the cytoplasmic tail of TGF-α and escorts TGF-α–containing exocytic vesicles to the basolateral plasma membrane in a myristoylation-dependent manner, with its stability regulated by AO7/RNF25-mediated ubiquitylation that is antagonized by TGF-α binding [PMID:15064403, PMID:18757723]. At the plasma membrane, myristoylated NKD2 interacts with Dishevelled-1, promoting mutual polyubiquitylation and proteasomal degradation of both proteins to attenuate canonical Wnt signaling, a function conserved from zebrafish to mammals [PMID:20177058, PMID:17438140]. NKD2 also orchestrates TCR-stimulated trafficking of ORAI1-containing vesicles to the plasma membrane to sustain CRAC channel Ca²⁺ entry in effector T cells [PMID:34433025], and its expression is frequently silenced by EZH2- and DNMT-dependent promoter hypermethylation in multiple cancer types [PMID:26124080, PMID:27496341].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Cloning of human NKD1 and NKD2 established them as vertebrate homologs of Drosophila naked cuticle, predicted to antagonize Wnt/β-catenin signaling via a conserved EF-hand-containing domain architecture.\",\n      \"evidence\": \"Molecular cloning, gene structure analysis, and expression profiling in human cancer cell lines\",\n      \"pmids\": [\"11604995\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No direct functional assay for human NKD2 Wnt antagonism in this study\", \"Binding to human Dvl not demonstrated\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"NKD2 was revealed to have an unexpected second function as a cargo recognition and targeting protein, directly binding basolateral sorting motifs in TGF-α and escorting TGF-α vesicles to the basolateral membrane in a myristoylation-dependent manner.\",\n      \"evidence\": \"Co-IP/pulldown, myristoylation-deficient G2A mutant, confocal microscopy, and siRNA knockdown in polarized MDCK cells\",\n      \"pmids\": [\"15064403\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of vesicle machinery components unknown at this point\", \"Mechanism by which NKD2 recognizes membrane target site unresolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Biophysical characterization showed the N-terminal half of NKD2 (residues 1–217) is intrinsically disordered and does not bind calcium or zinc, indicating the EF-hand motif is non-functional for metal coordination.\",\n      \"evidence\": \"Circular dichroism and NMR spectroscopy on recombinant NKD2 fragment\",\n      \"pmids\": [\"17045239\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structure of the C-terminal half uncharacterized\", \"Whether disorder is functionally required for partner binding unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Genetic studies in mouse and zebrafish established NKD2 as a bona fide in vivo Wnt antagonist: Nkd1/Nkd2 double-knockout mice showed Wnt-pathway-consistent cranial bone defects, and zebrafish Nkd2 overexpression suppressed canonical Wnt signaling and modulated non-canonical Wnt/PCP signaling.\",\n      \"evidence\": \"Targeted gene knockout in mice with skeletal phenotyping; gain- and loss-of-function in zebrafish embryos with genetic epistasis against wnt11/slb\",\n      \"pmids\": [\"17438140\", \"17689523\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Redundancy with Nkd1 obscures Nkd2-specific roles\", \"Mechanism of PCP pathway antagonism not defined at molecular level\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Domain mapping identified a basolateral targeting segment within NKD2 residues 1–173 that operates independently of the mu1B adaptin pathway, refining the CaRT mechanism.\",\n      \"evidence\": \"Internal deletion mutagenesis, domain-swap experiments, and shRNA knockdown in MDCK cells\",\n      \"pmids\": [\"17553928\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct receptor for vesicle docking at basolateral membrane not identified\", \"Structural basis of the targeting segment unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Two discoveries clarified NKD2 regulation and vesicle composition: AO7/RNF25 was identified as the E3 ligase mediating NKD2 ubiquitylation and degradation, with TGF-α binding displacing AO7 to stabilize NKD2; proteomics of NKD2-associated vesicles identified Rab10 and myosin IIA as trafficking machinery.\",\n      \"evidence\": \"Ubiquitylation assays, half-life measurements, and co-IP for AO7/RNF25; fluorescence-activated vesicle sorting and LC/LC-MS/MS proteomics\",\n      \"pmids\": [\"18757723\", \"18504258\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional validation of Rab10 and myosin IIA in NKD2-dependent trafficking incomplete\", \"Whether AO7 regulation is tissue-specific unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"The Wnt-antagonist mechanism was molecularly defined: myristoylated NKD2 interacts with Dvl-1 at the plasma membrane, triggering mutual polyubiquitylation and proteasomal degradation of both proteins, directly linking NKD2's membrane association to Wnt pathway attenuation.\",\n      \"evidence\": \"Reciprocal co-IP, ubiquitylation assays, cell fractionation in HEK293 cells, and zebrafish developmental assay with G2A mutant\",\n      \"pmids\": [\"20177058\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"E3 ligase responsible for Dvl-1 ubiquitylation in this context not identified\", \"Whether NKD2 also targets Dvl-2/3 not tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Epigenetic silencing of NKD2 by promoter hypermethylation was established as a recurrent event across multiple cancers, with demethylation or re-expression restoring Wnt inhibition, cell cycle arrest, and tumor suppression.\",\n      \"evidence\": \"Methylation-specific PCR, 5-aza-2'-deoxycytidine treatment, xenograft models in breast and gastric cancer cells\",\n      \"pmids\": [\"26124080\", \"26396173\", \"25579177\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Upstream signals initiating methylation not fully defined\", \"Whether methylation is a driver or passenger event in tumorigenesis unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Multiple lncRNAs (HULC, ZFAS1) and miRNAs (miR-130b) were shown to repress NKD2 through distinct mechanisms—EZH2 recruitment to the promoter or direct mRNA targeting—establishing NKD2 as a convergent node of epigenetic and post-transcriptional silencing in cancer.\",\n      \"evidence\": \"RIP, RNA pull-down, ChIP, miRNA target validation, and rescue experiments in CRC, gastric cancer, and osteosarcoma cells\",\n      \"pmids\": [\"27496341\", \"27246976\", \"26902120\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contribution of each silencing mechanism in a given tumor type unknown\", \"Whether these regulatory inputs operate in normal tissues unaddressed\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"A new trafficking role was uncovered in immune cells: NKD2 was identified as essential for TCR-stimulation-dependent delivery of ORAI1-containing vesicles to the plasma membrane, sustaining CRAC channel Ca²⁺ entry and cytokine production in effector T cells.\",\n      \"evidence\": \"Targeted screen, vesicle fractionation, co-localization, loss-of-function Ca²⁺ imaging and cytokine assays in T cells\",\n      \"pmids\": [\"34433025\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether NKD2 acts via the same myristoylation-dependent CaRT mechanism as in epithelial cells not tested\", \"Adaptor partners in T cell vesicle trafficking not identified\", \"Single study awaiting independent replication\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"NKD2 was linked to NF-κB pathway activation in the context of renal fibrosis; direct binding of the small molecule chrysophanol to NKD2 suppressed NKD2-dependent NF-κB activation.\",\n      \"evidence\": \"Molecular docking, microscale thermophoresis binding assay, NKD2 overexpression/rescue in HK-2 cells, UUO mouse model\",\n      \"pmids\": [\"35988461\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism linking NKD2 to NF-κB activation undefined\", \"Whether NF-κB regulation is independent of Wnt antagonism not resolved\", \"Chrysophanol specificity for NKD2 over other targets not comprehensively assessed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the structural basis for NKD2's multivalent interactions, the E3 ligase mediating Dvl-1 co-degradation, the molecular mechanism connecting NKD2 to NF-κB signaling, and whether NKD2's CaRT function in T cell ORAI1 trafficking shares the same myristoylation-dependent mechanism as epithelial TGF-α sorting.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of NKD2 or its complexes\", \"E3 ligase for mutual Dvl/NKD2 degradation not identified\", \"CaRT mechanism in T cells not molecularly characterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 9]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [4, 7, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 4]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0, 1, 3, 9]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [4, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 7, 8, 10, 12]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 1, 3, 9]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"DVL1\", \"TGFA\", \"RNF25\", \"RAB10\", \"ORAI1\"],\n    \"other_free_text\": []\n  }\n}\n```"}