Affinage

NKD2

Protein naked cuticle homolog 2 · UniProt Q969F2

Length
451 aa
Mass
50.1 kDa
Annotated
2026-04-29
32 papers in source corpus 21 papers cited in narrative 21 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

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).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 2001 Medium

    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

    PMID:11604995

    Open questions at the time
    • No direct functional assay for human NKD2 Wnt antagonism in this study
    • Binding to human Dvl not demonstrated
  2. 2004 High

    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

    PMID:15064403

    Open questions at the time
    • Identity of vesicle machinery components unknown at this point
    • Mechanism by which NKD2 recognizes membrane target site unresolved
  3. 2006 Medium

    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

    PMID:17045239

    Open questions at the time
    • Structure of the C-terminal half uncharacterized
    • Whether disorder is functionally required for partner binding unknown
  4. 2007 High

    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

    PMID:17438140 PMID:17689523

    Open questions at the time
    • Redundancy with Nkd1 obscures Nkd2-specific roles
    • Mechanism of PCP pathway antagonism not defined at molecular level
  5. 2007 High

    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

    PMID:17553928

    Open questions at the time
    • Direct receptor for vesicle docking at basolateral membrane not identified
    • Structural basis of the targeting segment unknown
  6. 2008 High

    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

    PMID:18504258 PMID:18757723

    Open questions at the time
    • Functional validation of Rab10 and myosin IIA in NKD2-dependent trafficking incomplete
    • Whether AO7 regulation is tissue-specific unknown
  7. 2010 High

    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

    PMID:20177058

    Open questions at the time
    • E3 ligase responsible for Dvl-1 ubiquitylation in this context not identified
    • Whether NKD2 also targets Dvl-2/3 not tested
  8. 2015 Medium

    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

    PMID:25579177 PMID:26124080 PMID:26396173

    Open questions at the time
    • Upstream signals initiating methylation not fully defined
    • Whether methylation is a driver or passenger event in tumorigenesis unclear
  9. 2016 Medium

    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

    PMID:26902120 PMID:27246976 PMID:27496341

    Open questions at the time
    • Relative contribution of each silencing mechanism in a given tumor type unknown
    • Whether these regulatory inputs operate in normal tissues unaddressed
  10. 2021 Medium

    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

    PMID:34433025

    Open questions at the time
    • 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
  11. 2022 Medium

    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

    PMID:35988461

    Open questions at the time
    • 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

Open questions

Synthesis pass · forward-looking unresolved questions
  • 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.
  • 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

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 3 GO:0098772 molecular function regulator activity 3
Localization
GO:0031410 cytoplasmic vesicle 4 GO:0005886 plasma membrane 3 GO:0005829 cytosol 2
Pathway
R-HSA-162582 Signal Transduction 5 R-HSA-5653656 Vesicle-mediated transport 4 R-HSA-392499 Metabolism of proteins 2
Partners
DVL1ORAI1RAB10RNF25TGFA

Evidence

Reading pass · 21 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2004 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. Co-IP/pulldown, overexpression and dominant-negative (G2A mutant) in polarized MDCK cells, confocal microscopy, siRNA knockdown Proceedings of the National Academy of Sciences of the United States of America High 15064403
2007 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. High-resolution microscopy, internal deletion mutagenesis, shRNA knockdown, domain-swap experiments in MDCK cells Molecular biology of the cell High 17553928
2008 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. Protein half-life assays, Co-IP, ubiquitylation assays, overexpression of TGF-alpha and EGFR-null conditions, identification of AO7/RNF25 as E3 ligase Proceedings of the National Academy of Sciences of the United States of America High 18757723
2008 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. Fluorescence-activated vesicle sorting, LC/LC-MS/MS proteomics, biochemical fractionation, validation by Western blot Molecular & cellular proteomics : MCP Medium 18504258
2010 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. Reciprocal co-IP, siRNA knockdown, overexpression, cell fractionation, ubiquitylation assays in HEK293 cells, zebrafish embryonic development assay The Journal of biological chemistry High 20177058
2006 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. Circular dichroism, NMR spectroscopy, recombinant protein expression and purification Biochemical and biophysical research communications Medium 17045239
2001 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. Molecular cloning, gene structure analysis, expression profiling in cancer cell lines and primary tumors International journal of oncology Medium 11604995
2007 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. Overexpression in zebrafish embryos, morpholino knockdown, genetic epistasis with slb/wnt11 mutant, canonical Wnt target gene assay Developmental biology High 17689523
2007 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. Targeted gene knockout (replacement of Dvl-binding exons with IRES-lacZ/neomycin), double-knockout mouse generation, skeletal phenotype analysis Molecular and cellular biology High 17438140
2021 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. Targeted screen, vesicle fractionation, co-localization, loss-of-function in T cells, Ca2+ imaging, cytokine assays Cell reports Medium 34433025
2015 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. Overexpression and knockdown in human/mouse OS cells, in vitro proliferation/migration/invasion assays, xenograft mouse model, microarray analysis Oncogene Medium 25579177
2016 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. miRNA target prediction, qRT-PCR, Western blot, MTT assay, flow cytometry, miR-130b inhibitor experiments with NKD2 rescue Biochemical and biophysical research communications Medium 26902120
2015 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). Methylation-specific PCR, 5-aza-2'-deoxycytidine demethylation, Western blot, flow cytometry, xenograft mouse model Oncotarget Medium 26124080
2015 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. Methylation-specific PCR, gene expression array, flow cytometry, transwell invasion assay, xenograft mouse model, Western blot Oncotarget Medium 26396173
2017 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. RNA immunoprecipitation (RIP), RNA pull-down, rescue experiments, knockdown in gastric cancer cells Oncotarget Medium 27246976
2016 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. RNA immunoprecipitation (RIP), RNA pull-down, rescue experiments, knockdown/overexpression in CRC cells Gene Medium 27496341
2018 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. siRNA knockdown, beta-catenin/TCF luciferase activity assay, Western blot, RT-qPCR in rat DFSCs International journal of molecular medicine Medium 30106129
2020 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. RIP, ChIP assay, overexpression/knockdown experiments, in vivo xenograft Cellular signalling Medium 33045317
2025 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. Overexpression/knockdown of IFIX and NKD2 in CAL-27 and SCC-25 OSCC cells, qRT-PCR, Western blot, proliferation/invasion/migration assays Journal of cellular and molecular medicine Low 39833105
2023 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. Overexpression and knockdown in THCA cells, NF-κB transcriptional activity assay, proliferation assays Molecular biotechnology Low 36820951
2022 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. Molecular docking, microscale thermophoresis (MST) binding assay, NKD2 overexpression in HK-2 cells, UUO mouse model, Western blot Phytomedicine Medium 35988461

Source papers

Stage 0 corpus · 32 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2017 Long noncoding RNA ZFAS1 promotes gastric cancer cells proliferation by epigenetically repressing KLF2 and NKD2 expression. Oncotarget 139 27246976
2001 Molecular cloning, gene structure, and expression analyses of NKD1 and NKD2. International journal of oncology 115 11604995
2015 NKD2, a negative regulator of Wnt signaling, suppresses tumor growth and metastasis in osteosarcoma. Oncogene 108 25579177
2016 Curcumin inhibits tumor epithelial‑mesenchymal transition by downregulating the Wnt signaling pathway and upregulating NKD2 expression in colon cancer cells. Oncology reports 76 26985708
2016 Long noncoding RNA HULC promotes colorectal carcinoma progression through epigenetically repressing NKD2 expression. Gene 62 27496341
2004 Myristoylated Naked2 escorts transforming growth factor alpha to the basolateral plasma membrane of polarized epithelial cells. Proceedings of the National Academy of Sciences of the United States of America 55 15064403
2007 Zebrafish Naked1 and Naked2 antagonize both canonical and non-canonical Wnt signaling. Developmental biology 51 17689523
2010 Myristoylated Naked2 antagonizes Wnt-beta-catenin activity by degrading Dishevelled-1 at the plasma membrane. The Journal of biological chemistry 49 20177058
2006 Frequent amplifications and abundant expression of TRIO, NKD2, and IRX2 in soft tissue sarcomas. Genes, chromosomes & cancer 44 16752383
2008 Use of fluorescence-activated vesicle sorting for isolation of Naked2-associated, basolaterally targeted exocytic vesicles for proteomics analysis. Molecular & cellular proteomics : MCP 36 18504258
2016 Silencing NKD2 by Promoter Region Hypermethylation Promotes Esophageal Cancer Progression by Activating Wnt Signaling. Journal of thoracic oncology : official publication of the International Association for the Study of Lung Cancer 34 27374455
2007 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. Molecular biology of the cell 34 17553928
2022 Chrysophanol, a main anthraquinone from Rheum palmatum L. (rhubarb), protects against renal fibrosis by suppressing NKD2/NF-κB pathway. Phytomedicine : international journal of phytotherapy and phytopharmacology 33 35988461
2015 Epigenetic silencing of NKD2, a major component of Wnt signaling, promotes breast cancer growth. Oncotarget 32 26124080
2007 Viable mice with compound mutations in the Wnt/Dvl pathway antagonists nkd1 and nkd2. Molecular and cellular biology 31 17438140
2016 miR-130b targets NKD2 and regulates the Wnt signaling to promote proliferation and inhibit apoptosis in osteosarcoma cells. Biochemical and biophysical research communications 30 26902120
2015 Silencing NKD2 by promoter region hypermethylation promotes gastric cancer invasion and metastasis by up-regulating SOX18 in human gastric cancer. Oncotarget 29 26396173
2020 LINC00922 regulates epithelial-mesenchymal transition, invasive and migratory capacities in breast cancer through promoting NKD2 methylation. Cellular signalling 27 33045317
2024 Hypoxic Bone Mesenchymal Stem Cell-Derived Exosomes Direct Schwann Cells Proliferation, Migration, and Paracrine to Accelerate Facial Nerve Regeneration via circRNA_Nkd2/miR-214-3p/MED19 Axis. International journal of nanomedicine 21 38371458
2008 EGF receptor-independent action of TGF-alpha protects Naked2 from AO7-mediated ubiquitylation and proteasomal degradation. Proceedings of the National Academy of Sciences of the United States of America 16 18757723
2006 Structural studies of human Naked2: a biologically active intrinsically unstructured protein. Biochemical and biophysical research communications 12 17045239
2017 Epigenetic dysregulation of NKD2 is a valuable predictor assessing treatment outcome in acute myeloid leukemia. Journal of Cancer 10 28261348
2018 Nkd2 promotes the differentiation of dental follicle stem/progenitor cells into osteoblasts. International journal of molecular medicine 9 30106129
2023 Curcumin suppresses the Wnt/β-catenin signaling pathway by inhibiting NKD2 methylation to ameliorate intestinal ischemia/reperfusion injury. The Kaohsiung journal of medical sciences 5 38010861
2025 NKD2 as a Mediator of IFIX Antioncogene-Induced Wnt Signalling and Epithelial-Mesenchymal Transition in Human OSCC. Journal of cellular and molecular medicine 4 39833105
2023 NKD2 Trigger NF-κB Signaling Pathway and Facilitates Thyroid Cancer Cell Proliferation. Molecular biotechnology 4 36820951
2020 LINC00538 promotes the progression of colon cancer through inhibiting NKD2 expression. Journal of B.U.ON. : official journal of the Balkan Union of Oncology 4 33455110
2016 NKD2 a novel marker to study the progression of osteosarcoma development. European review for medical and pharmacological sciences 4 27424978
2015 Up-Regulation of Corticocerebral NKD2 in Lipopolysaccharide-Induced Neuroinflammation. Cellular and molecular neurobiology 4 26084600
2021 NKD2 mediates stimulation-dependent ORAI1 trafficking to augment Ca2+ entry in T cells. Cell reports 3 34433025
2013 A monoclonal antibody produced against Naked2. Monoclonal antibodies in immunodiagnosis and immunotherapy 1 23909424
2022 Rearrangement with the nkd2 promoter contributed to allelic diversity of the r1 gene in maize (Zea mays). The Plant journal : for cell and molecular biology 0 35876146