{"gene":"KREMEN1","run_date":"2026-04-28T18:30:27","timeline":{"discoveries":[{"year":2002,"finding":"KREMEN1 and KREMEN2 are high-affinity receptors for the Wnt antagonist DKK1. KREMEN2 forms a ternary complex with DKK1 and LRP6, inducing rapid endocytosis and removal of the Wnt co-receptor LRP6 from the plasma membrane, thereby blocking Wnt/beta-catenin signaling.","method":"Co-immunoprecipitation, cell surface binding assays, endocytosis assays, functional Wnt reporter assays, Xenopus embryo overexpression","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1-2 — foundational study with multiple orthogonal methods (Co-IP, binding assays, endocytosis, in vivo), 883 citations, replicated by multiple subsequent labs","pmids":["12050670"],"is_preprint":false},{"year":2002,"finding":"Kremen1 and Kremen2 functionally interact with DKK1 to regulate anteroposterior patterning of the CNS in Xenopus; morpholino knockdown of Krm1/2 leads to anterior neural defects, and Krm2 synergizes with dkk1 in inhibiting Wnt/LRP6 signaling in axis duplication assays.","method":"Antisense morpholino knockdown, axis duplication assays, rescue experiments with inhibitory anti-Dkk1 antibodies, Xenopus embryo overexpression","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis via morpholino knockdown with multiple functional readouts, replicated findings consistent with PMID:12050670","pmids":["12421700"],"is_preprint":false},{"year":2001,"finding":"KREMEN1 (Kremen) is a type-I transmembrane protein containing a kringle domain, a WSC domain, and CUB domains in the extracellular region, with no conserved intracellular signaling motif; its mRNA increases during embryonic development and cellular differentiation.","method":"Molecular cloning, domain analysis, in situ hybridization, northern blot","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 — original cloning and characterization by molecular biology, single lab","pmids":["11267660"],"is_preprint":false},{"year":2007,"finding":"In the absence of DKK proteins, Kremen2 promotes LRP6 cell-surface localization and stimulates LRP6-mediated Wnt/beta-catenin signaling; Krm2 knockdown specifically reduces LRP6 protein levels in neural crest explants, indicating a positive role for Kremens in Wnt signaling when Dkks are absent.","method":"Morpholino knockdown, overexpression, cell surface LRP6 localization assays, Wnt reporter assays, Xenopus neural crest induction","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (KD, OE, surface localization, reporter assays), strong mechanistic finding replicated with different approaches in same study","pmids":["17978005"],"is_preprint":false},{"year":2008,"finding":"DKK1 residues Arg197, Ser198, and Lys232 are specifically required for binding to Kremen (but not LRP6); these Kremen-binding residues lie on the opposite face of DKK1 from the LRP6-binding surface. Kremen is dispensable for DKK1-mediated Wnt antagonism unless cells express high levels of LRP5/6.","method":"Site-directed mutagenesis of DKK1, binding assays, Wnt reporter assays, co-expression experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis combined with binding and functional assays; identifies specific interaction residues","pmids":["18502762"],"is_preprint":false},{"year":2006,"finding":"Kremen1 knockout mice exhibit severe defects in thymic cortical architecture, with loss of defined cortical and medullary regions and failure of thymic epithelial cells to mature beyond the immature K5+K8+ stage; krm1-/- TEC lines show a 2-fold increase in canonical Wnt signaling by TOPFlash assay.","method":"Krm1 knockout mouse, histology, immunofluorescence, FACS, TOPFlash Wnt reporter assay","journal":"Clinical & developmental immunology","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined cellular phenotype and molecular readout (TOPFlash), multiple methods","pmids":["17162372"],"is_preprint":false},{"year":2012,"finding":"KREMEN1 is internalized from the cell surface via clathrin-mediated endocytosis, dependent on an atypical dileucine motif (DXXXLV) in its cytoplasmic tail; mutation of LV to AA blocked internalization, and inhibition of AP-2 or clathrin also blocked Kremen1 internalization.","method":"Internalization assays, site-directed mutagenesis of dileucine motif, AP-2 siRNA knockdown, clathrin inhibitor (pitstop 2), cell surface assays","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis plus pharmacological and genetic inhibition confirming clathrin-dependent mechanism","pmids":["23251700"],"is_preprint":false},{"year":2015,"finding":"Kremen1 functions as a dependence receptor, triggering cell death (apoptosis) in the absence of its ligand DKK1; a specific motif in the cytoplasmic tail of Kremen1, conserved only in placental mammals, is required for apoptosis induction and is distinct from the Wnt-inhibitory function. Cancer-associated somatic mutations in Kremen1 can impair its pro-apoptotic activity.","method":"Whole embryo culture, Wnt activity assays, mutagenesis of cytoplasmic tail, phylogenetic analysis, apoptosis assays","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis plus functional apoptosis assays with multiple orthogonal approaches demonstrating Wnt-independent function","pmids":["26206087"],"is_preprint":false},{"year":2016,"finding":"Crystal structures of the ectodomain of human KREMEN1 at 1.9–3.2 Å resolution reveal a rigid triangular arrangement of Kringle, WSC, and CUB domains; the WSC domain is homologous to hepatocyte growth factor. A low-resolution ternary complex structure shows DKK1-CRD2 sandwiched between LRP6PE3 and KRM1-Kringle-WSC; surface plasmon resonance and modeling suggest a direct interaction between Krm1-CUB and Lrp6-PE2.","method":"X-ray crystallography, surface plasmon resonance, complex crystal structure","journal":"Structure (London, England : 1993)","confidence":"High","confidence_rationale":"Tier 1 — crystal structures with SPR validation; provides atomic-level mechanism of ternary complex formation","pmids":["27524201"],"is_preprint":false},{"year":2016,"finding":"KREMEN1 mutation p.F209S (in the WSC domain) causes autosomal recessive ectodermal dysplasia with oligodontia in humans, implicating Kremen1-mediated Wnt signaling regulation in ectodermal and dental development.","method":"Exome sequencing, genotyping of 56 relatives in 4 consanguineous families, mutation mapping to conserved WSC domain","journal":"European journal of human genetics : EJHG","confidence":"Medium","confidence_rationale":"Tier 2 — human genetics with segregation analysis; mechanism inferred from known domain function but no direct functional assay in this paper","pmids":["27049303"],"is_preprint":false},{"year":2016,"finding":"Kremen1 is expressed in cochlear prosensory cells during development and in supporting cells of the adult mouse cochlea; gain- and loss-of-function experiments show Kremen1 biases cells toward supporting cell fate and suppresses hair cell formation via Wnt pathway modulation.","method":"Immunofluorescence/localization, gain-of-function overexpression, loss-of-function, zebrafish lateral line hair cell counting","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization with functional consequence, loss/gain of function in two model systems","pmids":["27550540"],"is_preprint":false},{"year":2018,"finding":"KREMEN1 is the entry receptor for Coxsackievirus A10 (CV-A10) and related group of EV-A enteroviruses; loss of KREMEN1 renders cells resistant to infection, and the extracellular domain of KREMEN1 binds CV-A10 directly and acts as a neutralizing agent; Kremen-deficient mice are resistant to CV-A10-induced lethal paralysis.","method":"Haploid genetic screen, KREMEN1 KO, overexpression, cell surface binding assay, soluble ectodomain neutralization, mouse infection model","journal":"Cell host & microbe","confidence":"High","confidence_rationale":"Tier 1-2 — genome-wide screen plus KO, OE, in vitro binding, and in vivo mouse model; multiple orthogonal methods","pmids":["29681460"],"is_preprint":false},{"year":2018,"finding":"miR-431 silences Kremen1 expression by targeting its 3'UTR, preventing amyloid-beta-mediated synapse loss in cortico-hippocampal neuronal cultures from 3xTg-AD mice; Kremen1 knockdown similarly prevents DKK1-induced synapse loss, placing Kremen1 downstream in DKK1-mediated synaptic degeneration.","method":"miRNA transfection, 3'UTR luciferase reporter, immunofluorescence of synaptic puncta, neuronal culture","journal":"Frontiers in cellular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2-3 — luciferase reporter validation plus functional synapse loss assay; single lab","pmids":["29643768"],"is_preprint":false},{"year":2019,"finding":"Kremen1-induced apoptotic signaling requires homodimerization of the receptor; DKK1 binding inhibits Kremen1 multimerization and alleviates cell death; Kremen2, which has no intrinsic apoptotic activity, heterodimerizes with Kremen1 and inhibits Kremen1-induced cell death.","method":"Co-immunoprecipitation, forced dimerization constructs, apoptosis assays, Wnt reporter assays","journal":"Cell death discovery","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP plus forced dimerization plus functional apoptosis assays, mechanistically resolving prior findings","pmids":["31069116"],"is_preprint":false},{"year":2020,"finding":"Crystal structures of CV-A10 mature virus alone and in complex with KRM1 show that KRM1 spans the viral canyon with a large footprint on VP1; receptor binding induces release of a pocket factor and initiates conformational changes (expanded A-particles) primed for viral uncoating.","method":"Cryo-EM and X-ray crystallography of virus-receptor complex","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — atomic-resolution structures of native and receptor-bound virus; mechanistically explains receptor-triggered uncoating","pmids":["31911601"],"is_preprint":false},{"year":2020,"finding":"Atomic structures of CV-A10 in complex with KRM1 under neutral and acidic conditions reveal KRM1 binds the mature viral particle above the canyon of VP1 across two adjacent asymmetric units; KRM1 binding induces pocket factor release (accelerated at acidic pH), and biochemical studies show receptor binding at acidic pH enables virion uncoating in vitro, identifying KRM1 as a two-in-one attachment and uncoating receptor.","method":"Cryo-EM structural determination, in vitro uncoating assay, biochemical binding studies under pH variation","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — atomic structures plus in vitro functional uncoating assay; orthogonal to PMID:31911601","pmids":["32690697"],"is_preprint":false},{"year":2020,"finding":"DKK3 signals through Kremen-1 and DVL-1 to reduce JNK/AP-1-mediated neuroinflammation after intracerebral hemorrhage; Kremen-1 siRNA knockdown abrogates DKK3's neuroprotective effects, placing Kremen-1 as a necessary downstream mediator of DKK3 anti-inflammatory signaling.","method":"siRNA in vivo knockdown, Western blot, immunofluorescence, neurobehavioral assays in mouse ICH model","journal":"Journal of neuroinflammation","confidence":"Medium","confidence_rationale":"Tier 2-3 — in vivo siRNA epistasis with multiple readouts; single lab, no direct binding confirmed here","pmids":["32331523"],"is_preprint":false},{"year":2014,"finding":"In the zebrafish posterior lateral line primordium, Kremen1 restricts the spatial range of secreted DKK proteins; loss of Kremen1 results in increased spread of DKK1b protein and a decrease (not increase) in Wnt signaling, revealing a non-cell-autonomous mechanism whereby Kremen1 limits DKK diffusion to control Wnt activity.","method":"Zebrafish krm1 mutant, cell transplantation, DKK1b-mTangerine fusion protein visualization, Wnt reporter assays","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 — genetic mutant, transplantation epistasis, and direct protein spread visualization; multiple orthogonal methods","pmids":["25038040"],"is_preprint":false},{"year":2021,"finding":"KREMEN1 is a functional entry receptor for SARS-CoV-2; KREMEN1 alone is sufficient to mediate SARS-CoV-2 spike-dependent cell entry in vitro and in vivo; KREMEN1 was identified by screening 5054 human membrane proteins for interaction with the SARS-CoV-2 spike protein.","method":"Genome-wide receptome screen, cell infection assay, in vivo mouse model, neutralizing antibody blockade","journal":"Cell research","confidence":"High","confidence_rationale":"Tier 2 — large-scale screen plus in vitro and in vivo functional validation of receptor sufficiency","pmids":["34837059"],"is_preprint":false},{"year":2018,"finding":"DKK4-CRD2 mediates high-affinity binding to both the E1E2 region of LRP6 and the Kremen1 extracellular domain; DKK4 and Krm family proteins function synergistically to inhibit Wnt signaling, and a diverse range of ternary complexes comprising Dkk, Krm, and LRP5/6 proteins can form.","method":"NMR structure determination, surface plasmon resonance, Wnt reporter assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — NMR structure plus SPR binding data plus functional assay; rigorous multi-method study","pmids":["29925589"],"is_preprint":false},{"year":2026,"finding":"Kremen1 induces cell death with autophagic (rather than apoptotic) features; protein proximity (BioID) assays identified SEC24C (a COP-II complex component) as a critical effector; Kremen1 is in proximity with SEC24C and ATG9A after vesicular trafficking, and this fosters SEC24C proximity with ATG8, ERGIC, and ATG9A, increasing autophagosome numbers and driving cell death. Pharmacological autophagy inhibition or genetic silencing of SEC24C or ATG9A suppresses this cell death.","method":"BioID proximity labeling, pharmacological autophagy inhibition, siRNA knockdown of autophagy effectors, cell death assays","journal":"Cell communication and signaling : CCS","confidence":"High","confidence_rationale":"Tier 2 — proximity proteomics plus genetic and pharmacological validation identifying specific effectors of a novel cell death mechanism","pmids":["41807954"],"is_preprint":false},{"year":2025,"finding":"Disease-associated KREMEN1 variants (Cys111Ser, Gly166Asp, Phe209Ser, Phe258_Pro259del) show significantly reduced N- and O-glycosylation and impaired ternary complex formation with DKK1 and LRP6 compared to wild-type; patient fibroblasts exhibit higher basal WNT pathway activity followed by attenuated WNT3A response, demonstrating that these ectodermal dysplasia mutations broadly dysregulate WNT signaling.","method":"Ectopic expression in HEK293T cells, glycosylation analysis, co-immunoprecipitation for complex formation, TOPFlash WNT reporter in patient fibroblasts","journal":"The Journal of investigative dermatology","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis with glycosylation, complex formation, and functional WNT assays, plus patient cell validation","pmids":["40553753"],"is_preprint":false},{"year":2023,"finding":"VP2 residue N142 of CVA10 is critical for binding to KREMEN1; mutation of N142 drastically reduces KREMEN1 receptor-binding activity, viral attachment, cell infection, and in vivo pathogenicity in mice.","method":"Neutralization-resistant mutant screening, soluble KREMEN1 binding assay, cell infection assay, mouse pathogenicity model","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis plus binding, infection, and in vivo assays identifying specific virus-receptor contact residue","pmids":["37788227"],"is_preprint":false},{"year":2025,"finding":"VP2 residue K140 (K2140) is completely conserved among all KRM1-dependent enteroviruses (CVA2-CVA6, CVA10, CVA12) and is essential for receptor binding and infection; KRM1 residue D90 engages K2140 directly. CVA8 was experimentally demonstrated to use KRM1 as its receptor through this same interaction.","method":"Mutational analysis, binding assays, infection assays in vitro and in vivo, receptor identification for CVA8","journal":"mBio","confidence":"High","confidence_rationale":"Tier 1-2 — systematic mutagenesis across multiple viruses, direct binding assay identifying receptor contact residue, in vivo validation","pmids":["39817751"],"is_preprint":false}],"current_model":"KREMEN1 is a multifunctional type-I transmembrane protein (with extracellular Kringle, WSC, and CUB domains) that serves as a high-affinity receptor for DKK family proteins: in the presence of DKK1, KREMEN1 forms a ternary complex with DKK1 and LRP5/6 and drives clathrin-mediated endocytosis of LRP6 to inhibit canonical Wnt/beta-catenin signaling; in the absence of DKK1, KREMEN1 can promote LRP6 surface retention and Wnt signaling, restrict DKK diffusion to spatially pattern Wnt activity, or act as a dependence receptor triggering autophagic cell death via SEC24C/ATG9A — an apoptotic activity requiring homodimerization and a placental-mammal-specific cytoplasmic motif that is antagonized by heterodimerization with KREMEN2; additionally, KREMEN1 functions as a cell-surface entry receptor for multiple EV-A enteroviruses (including CVA2–A6, A8, A10, A12) and SARS-CoV-2, binding viral capsid proteins in the canyon region."},"narrative":{"teleology":[{"year":2001,"claim":"Identification of KREMEN1 as a novel transmembrane protein with Kringle, WSC, and CUB ectodomains established the molecular architecture of this receptor family before any function was known.","evidence":"Molecular cloning, domain analysis, and expression profiling during embryonic development","pmids":["11267660"],"confidence":"Medium","gaps":["No ligand or signaling pathway identified","No functional assays performed","Intracellular signaling mechanism unknown"]},{"year":2002,"claim":"The discovery that KREMEN1/2 are high-affinity DKK1 receptors that form a ternary complex with DKK1 and LRP6 to drive LRP6 endocytosis established the core mechanism of KREMEN-mediated Wnt inhibition and its role in anteroposterior CNS patterning.","evidence":"Co-IP, binding assays, endocytosis assays, Wnt reporters, and Xenopus morpholino knockdown with axis duplication assays","pmids":["12050670","12421700"],"confidence":"High","gaps":["Endocytic machinery mediating LRP6 internalization not defined","Structural basis of ternary complex unknown","Whether KREMEN has DKK-independent functions unresolved"]},{"year":2006,"claim":"Kremen1 knockout mice revealed its requirement for thymic epithelial architecture and confirmed that endogenous KREMEN1 restrains canonical Wnt signaling in vivo.","evidence":"Krm1 knockout mouse with histology, FACS, and TOPFlash Wnt reporter assay in KO-derived TECs","pmids":["17162372"],"confidence":"High","gaps":["Whether thymic phenotype is Wnt-dependent or reflects other KREMEN1 functions not resolved","Redundancy with KREMEN2 in other tissues not addressed"]},{"year":2007,"claim":"The finding that KREMEN2 promotes LRP6 surface retention and Wnt signaling in the absence of DKK proteins overturned the view that Kremens are purely Wnt-inhibitory and revealed a context-dependent positive role.","evidence":"Morpholino knockdown, overexpression, surface LRP6 localization assays, and Wnt reporter in Xenopus neural crest","pmids":["17978005"],"confidence":"High","gaps":["Whether KREMEN1 has the same DKK-independent positive role as KREMEN2 not directly tested","Molecular basis of DKK-dependent vs. DKK-independent switching unknown"]},{"year":2008,"claim":"Mapping of DKK1 residues required for KREMEN binding (distinct from LRP6-binding surface) showed that the ternary complex involves bipartite DKK1 contacts, and revealed KREMEN is dispensable for Wnt antagonism at low LRP5/6 levels.","evidence":"Site-directed mutagenesis of DKK1 with binding and Wnt reporter assays","pmids":["18502762"],"confidence":"High","gaps":["Atomic structure of ternary complex not yet available","Physiological LRP6 expression levels determining KREMEN requirement not defined"]},{"year":2012,"claim":"Identification of the cytoplasmic dileucine motif (DXXXLV) required for clathrin/AP-2-mediated KREMEN1 endocytosis provided the mechanistic basis for how KREMEN1 internalizes LRP6.","evidence":"Mutagenesis of dileucine motif, AP-2 siRNA, and clathrin inhibitor pitstop 2 with internalization assays","pmids":["23251700"],"confidence":"High","gaps":["Whether the same motif mediates DKK1/LRP6-dependent co-endocytosis not directly shown","Adaptor protein interacting with the motif not identified"]},{"year":2014,"claim":"Discovery that KREMEN1 restricts the spatial diffusion range of secreted DKK proteins revealed a non-cell-autonomous mechanism distinct from ternary complex endocytosis, showing that KREMEN1 loss paradoxically decreases Wnt signaling by allowing DKK to spread further.","evidence":"Zebrafish krm1 mutant, cell transplantation, DKK1b-mTangerine fusion protein visualization, Wnt reporter","pmids":["25038040"],"confidence":"High","gaps":["Whether this DKK-sequestration function operates in mammalian tissues not tested","Quantitative parameters of DKK diffusion restriction not modeled"]},{"year":2015,"claim":"KREMEN1 was established as a dependence receptor that triggers cell death in the absence of DKK1 ligand, via a placental-mammal-specific cytoplasmic motif separate from the Wnt-regulatory domain, linking KREMEN1 to cancer biology.","evidence":"Mutagenesis of cytoplasmic tail, apoptosis assays, phylogenetic analysis, analysis of cancer-associated mutations","pmids":["26206087"],"confidence":"High","gaps":["Downstream death effectors not identified","Whether cell death is apoptotic, autophagic, or mixed not resolved","In vivo relevance of dependence receptor activity not demonstrated"]},{"year":2016,"claim":"Crystal structures of the KREMEN1 ectodomain and its ternary complex with DKK1-CRD2 and LRP6 provided atomic-level understanding of how the three proteins assemble, with DKK1 sandwiched between LRP6 and KRM1.","evidence":"X-ray crystallography at 1.9–3.2 Å resolution with SPR validation","pmids":["27524201"],"confidence":"High","gaps":["Full-length ternary complex structure at high resolution not obtained","Conformational changes upon complex formation and endocytosis trigger not resolved"]},{"year":2016,"claim":"Human genetic evidence linked KREMEN1 loss-of-function (F209S in WSC domain) to autosomal recessive ectodermal dysplasia, establishing KREMEN1 as a Mendelian disease gene for ectodermal/dental development.","evidence":"Exome sequencing and segregation analysis in 4 consanguineous families","pmids":["27049303"],"confidence":"Medium","gaps":["No direct functional assay of the F209S mutation in this study","Whether disease mechanism is purely Wnt-dependent or involves dependence receptor activity unknown"]},{"year":2018,"claim":"Genome-wide haploid genetic screening identified KREMEN1 as the essential entry receptor for CV-A10 and related EV-A enteroviruses, opening an entirely new functional dimension for this Wnt-pathway receptor.","evidence":"Haploid screen, KREMEN1 KO, overexpression, soluble ectodomain neutralization, mouse infection model","pmids":["29681460"],"confidence":"High","gaps":["Structural basis of virus-receptor interaction not yet resolved","Which KREMEN1 domains mediate viral attachment unknown"]},{"year":2019,"claim":"Demonstration that KREMEN1 homodimerization is required for dependence receptor-mediated cell death — inhibited by DKK1 binding or KREMEN2 heterodimerization — resolved the molecular logic of how ligand availability switches KREMEN1 between survival and death signaling.","evidence":"Reciprocal co-immunoprecipitation, forced dimerization constructs, apoptosis assays","pmids":["31069116"],"confidence":"High","gaps":["Downstream signaling cascade from the homodimer not identified","Structural basis of homo- vs. heterodimerization unknown"]},{"year":2020,"claim":"Cryo-EM and crystal structures of CV-A10 bound to KREMEN1 revealed the receptor spans the viral canyon of VP1 across adjacent protomers, triggering pocket factor release and conformational changes for uncoating — establishing KREMEN1 as a combined attachment and uncoating receptor.","evidence":"Cryo-EM structures at neutral and acidic pH, X-ray crystallography, in vitro uncoating assays","pmids":["31911601","32690697"],"confidence":"High","gaps":["How receptor binding is coordinated with endosomal trafficking for genome release not defined","Whether the same structural mechanism applies to all KRM1-dependent enteroviruses not confirmed"]},{"year":2021,"claim":"Identification of KREMEN1 as a functional entry receptor for SARS-CoV-2, independent of ACE2, extended its viral receptor role to coronaviruses.","evidence":"Genome-wide receptome screen of 5054 membrane proteins, cell infection, in vivo mouse model","pmids":["34837059"],"confidence":"High","gaps":["Structural basis of spike-KREMEN1 interaction not resolved","Relative physiological contribution vs. ACE2 in human tissues unclear","Whether KREMEN1 mediates uncoating for SARS-CoV-2 unknown"]},{"year":2023,"claim":"Identification of VP2 residue N142 as critical for KREMEN1 binding defined a specific virus-side contact point and validated the structural model across in vitro and in vivo systems.","evidence":"Neutralization-resistant mutant screening, soluble KREMEN1 binding, cell infection, and mouse pathogenicity assays","pmids":["37788227"],"confidence":"High","gaps":["Atomic-level structure of VP2 N142 contact with KREMEN1 not directly resolved"]},{"year":2025,"claim":"Systematic mutagenesis across all KRM1-dependent enteroviruses identified VP2 K140 as a universally conserved contact engaged by KRM1 residue D90, unifying the receptor-binding mechanism and extending KRM1 usage to CVA8.","evidence":"Mutational analysis across CVA2–A6, A8, A10, A12 with binding, infection, and in vivo assays","pmids":["39817751"],"confidence":"High","gaps":["Whether additional KREMEN1 residues contribute to serotype-specific binding not fully mapped"]},{"year":2025,"claim":"Functional characterization of ectodermal dysplasia-associated KREMEN1 variants showed that disease mutations impair N/O-glycosylation and ternary complex formation with DKK1-LRP6, causing WNT pathway dysregulation in patient fibroblasts.","evidence":"Glycosylation analysis, co-IP for complex formation, TOPFlash WNT reporter in patient fibroblasts","pmids":["40553753"],"confidence":"High","gaps":["Whether glycosylation defects also impair viral receptor or dependence receptor functions not tested","Animal model rescue of ectodermal dysplasia not performed"]},{"year":2026,"claim":"Resolution of the downstream cell death pathway showed KREMEN1 triggers autophagic (not apoptotic) cell death via proximity interactions with SEC24C and ATG9A after vesicular trafficking, identifying the effector machinery of its dependence receptor activity.","evidence":"BioID proximity labeling, pharmacological autophagy inhibition, siRNA knockdown of SEC24C and ATG9A, cell death assays","pmids":["41807954"],"confidence":"High","gaps":["How KREMEN1 homodimerization connects to SEC24C engagement not established","Whether SEC24C-dependent autophagy operates in vivo not shown","Structural basis of KREMEN1-SEC24C interaction not defined"]},{"year":null,"claim":"Key unresolved questions include: how KREMEN1 switches between Wnt-inhibitory, Wnt-promoting, DKK-sequestering, and cell-death modes in different cellular contexts; the structural basis of KREMEN1 homodimerization and its coupling to SEC24C/ATG9A-mediated autophagy; and whether its Wnt-modulatory and viral receptor functions are physiologically interrelated.","evidence":"","pmids":[],"confidence":"Low","gaps":["No integrated structural model of full-length KREMEN1 in different signaling states","In vivo validation of SEC24C-dependent autophagic cell death pathway lacking","Functional crosstalk between viral entry and Wnt signaling through KREMEN1 not investigated"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,11,18]},{"term_id":"GO:0001618","term_label":"virus receptor activity","supporting_discovery_ids":[11,14,15,22,23]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,3,5,17]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,3,6,11]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[6,20]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[6,20]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,3,4,5,17,19]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[7,13,20]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[20]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[1,9,10]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[5]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[11,18]}],"complexes":["DKK1-KREMEN1-LRP6 ternary complex","KREMEN1 homodimer"],"partners":["DKK1","LRP6","LRP5","KREMEN2","DKK4","SEC24C","ATG9A","DKK3"],"other_free_text":[]},"mechanistic_narrative":"KREMEN1 is a type-I transmembrane receptor that functions as a central modulator of Wnt/β-catenin signaling and as a dependence receptor coupling ligand availability to cell death, while also serving as an entry receptor for multiple enteroviruses and SARS-CoV-2. Its ectodomain, composed of Kringle, WSC, and CUB domains arranged in a rigid triangular architecture, forms a ternary complex with DKK1/DKK4 and LRP5/6, triggering clathrin-mediated endocytosis of LRP6 via a cytoplasmic dileucine motif to inhibit Wnt signaling; in the absence of DKK proteins, KREMEN1 instead promotes LRP6 surface retention and Wnt pathway activation, and restricts diffusion of secreted DKK to spatially pattern Wnt activity [PMID:12050670, PMID:17978005, PMID:25038040, PMID:23251700, PMID:27524201]. Independent of its Wnt-modulatory role, KREMEN1 functions as a dependence receptor: in the absence of DKK1, homodimerization of KREMEN1 triggers autophagic cell death mediated by SEC24C and ATG9A through a placental-mammal-specific cytoplasmic motif, and this activity is antagonized by DKK1 binding or heterodimerization with KREMEN2 [PMID:26206087, PMID:31069116, PMID:41807954]. Loss-of-function mutations in KREMEN1 (e.g., F209S in the WSC domain) cause autosomal recessive ectodermal dysplasia with oligodontia, associated with impaired glycosylation and defective ternary complex formation [PMID:27049303, PMID:40553753]. KREMEN1 also serves as the essential cell-surface entry receptor for EV-A enteroviruses (CVA2–A6, A8, A10, A12), binding viral capsid VP1/VP2 in the canyon region to trigger pocket factor release and uncoating, and mediates SARS-CoV-2 spike-dependent cell entry [PMID:29681460, PMID:31911601, PMID:34837059]."},"prefetch_data":{"uniprot":{"accession":"Q96MU8","full_name":"Kremen protein 1","aliases":["Dickkopf receptor","Kringle domain-containing transmembrane protein 1","Kringle-containing protein marking the eye and the nose"],"length_aa":473,"mass_kda":51.7,"function":"Receptor for Dickkopf proteins. Cooperates with DKK1/2 to inhibit Wnt/beta-catenin signaling by promoting the endocytosis of Wnt receptors LRP5 and LRP6. In the absence of DKK1, potentiates Wnt-beta-catenin signaling by maintaining LRP5 or LRP6 at the cell membrane. Can trigger apoptosis in a Wnt-independent manner and this apoptotic activity is inhibited upon binding of the ligand DKK1. Plays a role in limb development; attenuates Wnt signaling in the developing limb to allow normal limb patterning and can also negatively regulate bone formation. Modulates cell fate decisions in the developing cochlea with an inhibitory role in hair cell fate specification","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q96MU8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KREMEN1","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/KREMEN1","total_profiled":1310},"omim":[{"mim_id":"618428","title":"POPOV-CHANG SYNDROME; POPCHAS","url":"https://www.omim.org/entry/618428"},{"mim_id":"617392","title":"ECTODERMAL DYSPLASIA 13, HAIR/TOOTH TYPE; ECTD13","url":"https://www.omim.org/entry/617392"},{"mim_id":"609898","title":"KRINGLE DOMAIN-CONTAINING TRANSMEMBRANE PROTEIN 1; KREMEN1","url":"https://www.omim.org/entry/609898"},{"mim_id":"601288","title":"TYROSINE 3-MONOOXYGENASE/TRYPTOPHAN 5-MONOOXYGENASE ACTIVATION PROTEIN, ZETA ISOFORM; YWHAZ","url":"https://www.omim.org/entry/601288"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/KREMEN1"},"hgnc":{"alias_symbol":["KRM1"],"prev_symbol":["KREMEN"]},"alphafold":{"accession":"Q96MU8","domains":[{"cath_id":"2.40.20.10","chopping":"29-116","consensus_level":"medium","plddt":96.1325,"start":29,"end":116},{"cath_id":"2.60.120.290","chopping":"215-321","consensus_level":"high","plddt":97.0598,"start":215,"end":321},{"cath_id":"3.50.4","chopping":"118-207","consensus_level":"high","plddt":98.0414,"start":118,"end":207}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96MU8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96MU8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96MU8-F1-predicted_aligned_error_v6.png","plddt_mean":78.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KREMEN1","jax_strain_url":"https://www.jax.org/strain/search?query=KREMEN1"},"sequence":{"accession":"Q96MU8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96MU8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96MU8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96MU8"}},"corpus_meta":[{"pmid":"12050670","id":"PMC_12050670","title":"Kremen 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embryonic implantation in mice.","date":"2008","source":"Fertility and sterility","url":"https://pubmed.ncbi.nlm.nih.gov/18068158","citation_count":15,"is_preprint":false},{"pmid":"25038040","id":"PMC_25038040","title":"Kremen1 restricts Dkk activity during posterior lateral line development in zebrafish.","date":"2014","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/25038040","citation_count":11,"is_preprint":false},{"pmid":"38945954","id":"PMC_38945954","title":"Noncoding RNA regulates the expression of Krm1 and Dkk2 to synergistically affect aortic valve lesions.","date":"2024","source":"Experimental & molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/38945954","citation_count":10,"is_preprint":false},{"pmid":"20933216","id":"PMC_20933216","title":"Embryonic expression and evolutionary analysis of the amphioxus Dickkopf and Kremen family genes.","date":"2010","source":"Journal of genetics and genomics = Yi chuan xue 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KREMEN2 forms a ternary complex with DKK1 and LRP6, inducing rapid endocytosis and removal of the Wnt co-receptor LRP6 from the plasma membrane, thereby blocking Wnt/beta-catenin signaling.\",\n      \"method\": \"Co-immunoprecipitation, cell surface binding assays, endocytosis assays, functional Wnt reporter assays, Xenopus embryo overexpression\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — foundational study with multiple orthogonal methods (Co-IP, binding assays, endocytosis, in vivo), 883 citations, replicated by multiple subsequent labs\",\n      \"pmids\": [\"12050670\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Kremen1 and Kremen2 functionally interact with DKK1 to regulate anteroposterior patterning of the CNS in Xenopus; morpholino knockdown of Krm1/2 leads to anterior neural defects, and Krm2 synergizes with dkk1 in inhibiting Wnt/LRP6 signaling in axis duplication assays.\",\n      \"method\": \"Antisense morpholino knockdown, axis duplication assays, rescue experiments with inhibitory anti-Dkk1 antibodies, Xenopus embryo overexpression\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis via morpholino knockdown with multiple functional readouts, replicated findings consistent with PMID:12050670\",\n      \"pmids\": [\"12421700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"KREMEN1 (Kremen) is a type-I transmembrane protein containing a kringle domain, a WSC domain, and CUB domains in the extracellular region, with no conserved intracellular signaling motif; its mRNA increases during embryonic development and cellular differentiation.\",\n      \"method\": \"Molecular cloning, domain analysis, in situ hybridization, northern blot\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — original cloning and characterization by molecular biology, single lab\",\n      \"pmids\": [\"11267660\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In the absence of DKK proteins, Kremen2 promotes LRP6 cell-surface localization and stimulates LRP6-mediated Wnt/beta-catenin signaling; Krm2 knockdown specifically reduces LRP6 protein levels in neural crest explants, indicating a positive role for Kremens in Wnt signaling when Dkks are absent.\",\n      \"method\": \"Morpholino knockdown, overexpression, cell surface LRP6 localization assays, Wnt reporter assays, Xenopus neural crest induction\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (KD, OE, surface localization, reporter assays), strong mechanistic finding replicated with different approaches in same study\",\n      \"pmids\": [\"17978005\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"DKK1 residues Arg197, Ser198, and Lys232 are specifically required for binding to Kremen (but not LRP6); these Kremen-binding residues lie on the opposite face of DKK1 from the LRP6-binding surface. Kremen is dispensable for DKK1-mediated Wnt antagonism unless cells express high levels of LRP5/6.\",\n      \"method\": \"Site-directed mutagenesis of DKK1, binding assays, Wnt reporter assays, co-expression experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis combined with binding and functional assays; identifies specific interaction residues\",\n      \"pmids\": [\"18502762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Kremen1 knockout mice exhibit severe defects in thymic cortical architecture, with loss of defined cortical and medullary regions and failure of thymic epithelial cells to mature beyond the immature K5+K8+ stage; krm1-/- TEC lines show a 2-fold increase in canonical Wnt signaling by TOPFlash assay.\",\n      \"method\": \"Krm1 knockout mouse, histology, immunofluorescence, FACS, TOPFlash Wnt reporter assay\",\n      \"journal\": \"Clinical & developmental immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular phenotype and molecular readout (TOPFlash), multiple methods\",\n      \"pmids\": [\"17162372\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"KREMEN1 is internalized from the cell surface via clathrin-mediated endocytosis, dependent on an atypical dileucine motif (DXXXLV) in its cytoplasmic tail; mutation of LV to AA blocked internalization, and inhibition of AP-2 or clathrin also blocked Kremen1 internalization.\",\n      \"method\": \"Internalization assays, site-directed mutagenesis of dileucine motif, AP-2 siRNA knockdown, clathrin inhibitor (pitstop 2), cell surface assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis plus pharmacological and genetic inhibition confirming clathrin-dependent mechanism\",\n      \"pmids\": [\"23251700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Kremen1 functions as a dependence receptor, triggering cell death (apoptosis) in the absence of its ligand DKK1; a specific motif in the cytoplasmic tail of Kremen1, conserved only in placental mammals, is required for apoptosis induction and is distinct from the Wnt-inhibitory function. Cancer-associated somatic mutations in Kremen1 can impair its pro-apoptotic activity.\",\n      \"method\": \"Whole embryo culture, Wnt activity assays, mutagenesis of cytoplasmic tail, phylogenetic analysis, apoptosis assays\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis plus functional apoptosis assays with multiple orthogonal approaches demonstrating Wnt-independent function\",\n      \"pmids\": [\"26206087\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Crystal structures of the ectodomain of human KREMEN1 at 1.9–3.2 Å resolution reveal a rigid triangular arrangement of Kringle, WSC, and CUB domains; the WSC domain is homologous to hepatocyte growth factor. A low-resolution ternary complex structure shows DKK1-CRD2 sandwiched between LRP6PE3 and KRM1-Kringle-WSC; surface plasmon resonance and modeling suggest a direct interaction between Krm1-CUB and Lrp6-PE2.\",\n      \"method\": \"X-ray crystallography, surface plasmon resonance, complex crystal structure\",\n      \"journal\": \"Structure (London, England : 1993)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures with SPR validation; provides atomic-level mechanism of ternary complex formation\",\n      \"pmids\": [\"27524201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"KREMEN1 mutation p.F209S (in the WSC domain) causes autosomal recessive ectodermal dysplasia with oligodontia in humans, implicating Kremen1-mediated Wnt signaling regulation in ectodermal and dental development.\",\n      \"method\": \"Exome sequencing, genotyping of 56 relatives in 4 consanguineous families, mutation mapping to conserved WSC domain\",\n      \"journal\": \"European journal of human genetics : EJHG\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — human genetics with segregation analysis; mechanism inferred from known domain function but no direct functional assay in this paper\",\n      \"pmids\": [\"27049303\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Kremen1 is expressed in cochlear prosensory cells during development and in supporting cells of the adult mouse cochlea; gain- and loss-of-function experiments show Kremen1 biases cells toward supporting cell fate and suppresses hair cell formation via Wnt pathway modulation.\",\n      \"method\": \"Immunofluorescence/localization, gain-of-function overexpression, loss-of-function, zebrafish lateral line hair cell counting\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with functional consequence, loss/gain of function in two model systems\",\n      \"pmids\": [\"27550540\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"KREMEN1 is the entry receptor for Coxsackievirus A10 (CV-A10) and related group of EV-A enteroviruses; loss of KREMEN1 renders cells resistant to infection, and the extracellular domain of KREMEN1 binds CV-A10 directly and acts as a neutralizing agent; Kremen-deficient mice are resistant to CV-A10-induced lethal paralysis.\",\n      \"method\": \"Haploid genetic screen, KREMEN1 KO, overexpression, cell surface binding assay, soluble ectodomain neutralization, mouse infection model\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — genome-wide screen plus KO, OE, in vitro binding, and in vivo mouse model; multiple orthogonal methods\",\n      \"pmids\": [\"29681460\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"miR-431 silences Kremen1 expression by targeting its 3'UTR, preventing amyloid-beta-mediated synapse loss in cortico-hippocampal neuronal cultures from 3xTg-AD mice; Kremen1 knockdown similarly prevents DKK1-induced synapse loss, placing Kremen1 downstream in DKK1-mediated synaptic degeneration.\",\n      \"method\": \"miRNA transfection, 3'UTR luciferase reporter, immunofluorescence of synaptic puncta, neuronal culture\",\n      \"journal\": \"Frontiers in cellular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — luciferase reporter validation plus functional synapse loss assay; single lab\",\n      \"pmids\": [\"29643768\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Kremen1-induced apoptotic signaling requires homodimerization of the receptor; DKK1 binding inhibits Kremen1 multimerization and alleviates cell death; Kremen2, which has no intrinsic apoptotic activity, heterodimerizes with Kremen1 and inhibits Kremen1-induced cell death.\",\n      \"method\": \"Co-immunoprecipitation, forced dimerization constructs, apoptosis assays, Wnt reporter assays\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus forced dimerization plus functional apoptosis assays, mechanistically resolving prior findings\",\n      \"pmids\": [\"31069116\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Crystal structures of CV-A10 mature virus alone and in complex with KRM1 show that KRM1 spans the viral canyon with a large footprint on VP1; receptor binding induces release of a pocket factor and initiates conformational changes (expanded A-particles) primed for viral uncoating.\",\n      \"method\": \"Cryo-EM and X-ray crystallography of virus-receptor complex\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — atomic-resolution structures of native and receptor-bound virus; mechanistically explains receptor-triggered uncoating\",\n      \"pmids\": [\"31911601\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Atomic structures of CV-A10 in complex with KRM1 under neutral and acidic conditions reveal KRM1 binds the mature viral particle above the canyon of VP1 across two adjacent asymmetric units; KRM1 binding induces pocket factor release (accelerated at acidic pH), and biochemical studies show receptor binding at acidic pH enables virion uncoating in vitro, identifying KRM1 as a two-in-one attachment and uncoating receptor.\",\n      \"method\": \"Cryo-EM structural determination, in vitro uncoating assay, biochemical binding studies under pH variation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — atomic structures plus in vitro functional uncoating assay; orthogonal to PMID:31911601\",\n      \"pmids\": [\"32690697\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"DKK3 signals through Kremen-1 and DVL-1 to reduce JNK/AP-1-mediated neuroinflammation after intracerebral hemorrhage; Kremen-1 siRNA knockdown abrogates DKK3's neuroprotective effects, placing Kremen-1 as a necessary downstream mediator of DKK3 anti-inflammatory signaling.\",\n      \"method\": \"siRNA in vivo knockdown, Western blot, immunofluorescence, neurobehavioral assays in mouse ICH model\",\n      \"journal\": \"Journal of neuroinflammation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — in vivo siRNA epistasis with multiple readouts; single lab, no direct binding confirmed here\",\n      \"pmids\": [\"32331523\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In the zebrafish posterior lateral line primordium, Kremen1 restricts the spatial range of secreted DKK proteins; loss of Kremen1 results in increased spread of DKK1b protein and a decrease (not increase) in Wnt signaling, revealing a non-cell-autonomous mechanism whereby Kremen1 limits DKK diffusion to control Wnt activity.\",\n      \"method\": \"Zebrafish krm1 mutant, cell transplantation, DKK1b-mTangerine fusion protein visualization, Wnt reporter assays\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic mutant, transplantation epistasis, and direct protein spread visualization; multiple orthogonal methods\",\n      \"pmids\": [\"25038040\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"KREMEN1 is a functional entry receptor for SARS-CoV-2; KREMEN1 alone is sufficient to mediate SARS-CoV-2 spike-dependent cell entry in vitro and in vivo; KREMEN1 was identified by screening 5054 human membrane proteins for interaction with the SARS-CoV-2 spike protein.\",\n      \"method\": \"Genome-wide receptome screen, cell infection assay, in vivo mouse model, neutralizing antibody blockade\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — large-scale screen plus in vitro and in vivo functional validation of receptor sufficiency\",\n      \"pmids\": [\"34837059\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"DKK4-CRD2 mediates high-affinity binding to both the E1E2 region of LRP6 and the Kremen1 extracellular domain; DKK4 and Krm family proteins function synergistically to inhibit Wnt signaling, and a diverse range of ternary complexes comprising Dkk, Krm, and LRP5/6 proteins can form.\",\n      \"method\": \"NMR structure determination, surface plasmon resonance, Wnt reporter assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structure plus SPR binding data plus functional assay; rigorous multi-method study\",\n      \"pmids\": [\"29925589\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Kremen1 induces cell death with autophagic (rather than apoptotic) features; protein proximity (BioID) assays identified SEC24C (a COP-II complex component) as a critical effector; Kremen1 is in proximity with SEC24C and ATG9A after vesicular trafficking, and this fosters SEC24C proximity with ATG8, ERGIC, and ATG9A, increasing autophagosome numbers and driving cell death. Pharmacological autophagy inhibition or genetic silencing of SEC24C or ATG9A suppresses this cell death.\",\n      \"method\": \"BioID proximity labeling, pharmacological autophagy inhibition, siRNA knockdown of autophagy effectors, cell death assays\",\n      \"journal\": \"Cell communication and signaling : CCS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — proximity proteomics plus genetic and pharmacological validation identifying specific effectors of a novel cell death mechanism\",\n      \"pmids\": [\"41807954\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Disease-associated KREMEN1 variants (Cys111Ser, Gly166Asp, Phe209Ser, Phe258_Pro259del) show significantly reduced N- and O-glycosylation and impaired ternary complex formation with DKK1 and LRP6 compared to wild-type; patient fibroblasts exhibit higher basal WNT pathway activity followed by attenuated WNT3A response, demonstrating that these ectodermal dysplasia mutations broadly dysregulate WNT signaling.\",\n      \"method\": \"Ectopic expression in HEK293T cells, glycosylation analysis, co-immunoprecipitation for complex formation, TOPFlash WNT reporter in patient fibroblasts\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis with glycosylation, complex formation, and functional WNT assays, plus patient cell validation\",\n      \"pmids\": [\"40553753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"VP2 residue N142 of CVA10 is critical for binding to KREMEN1; mutation of N142 drastically reduces KREMEN1 receptor-binding activity, viral attachment, cell infection, and in vivo pathogenicity in mice.\",\n      \"method\": \"Neutralization-resistant mutant screening, soluble KREMEN1 binding assay, cell infection assay, mouse pathogenicity model\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis plus binding, infection, and in vivo assays identifying specific virus-receptor contact residue\",\n      \"pmids\": [\"37788227\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"VP2 residue K140 (K2140) is completely conserved among all KRM1-dependent enteroviruses (CVA2-CVA6, CVA10, CVA12) and is essential for receptor binding and infection; KRM1 residue D90 engages K2140 directly. CVA8 was experimentally demonstrated to use KRM1 as its receptor through this same interaction.\",\n      \"method\": \"Mutational analysis, binding assays, infection assays in vitro and in vivo, receptor identification for CVA8\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — systematic mutagenesis across multiple viruses, direct binding assay identifying receptor contact residue, in vivo validation\",\n      \"pmids\": [\"39817751\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"KREMEN1 is a multifunctional type-I transmembrane protein (with extracellular Kringle, WSC, and CUB domains) that serves as a high-affinity receptor for DKK family proteins: in the presence of DKK1, KREMEN1 forms a ternary complex with DKK1 and LRP5/6 and drives clathrin-mediated endocytosis of LRP6 to inhibit canonical Wnt/beta-catenin signaling; in the absence of DKK1, KREMEN1 can promote LRP6 surface retention and Wnt signaling, restrict DKK diffusion to spatially pattern Wnt activity, or act as a dependence receptor triggering autophagic cell death via SEC24C/ATG9A — an apoptotic activity requiring homodimerization and a placental-mammal-specific cytoplasmic motif that is antagonized by heterodimerization with KREMEN2; additionally, KREMEN1 functions as a cell-surface entry receptor for multiple EV-A enteroviruses (including CVA2–A6, A8, A10, A12) and SARS-CoV-2, binding viral capsid proteins in the canyon region.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"KREMEN1 is a type-I transmembrane receptor that functions as a central modulator of Wnt/β-catenin signaling and as a dependence receptor coupling ligand availability to cell death, while also serving as an entry receptor for multiple enteroviruses and SARS-CoV-2. Its ectodomain, composed of Kringle, WSC, and CUB domains arranged in a rigid triangular architecture, forms a ternary complex with DKK1/DKK4 and LRP5/6, triggering clathrin-mediated endocytosis of LRP6 via a cytoplasmic dileucine motif to inhibit Wnt signaling; in the absence of DKK proteins, KREMEN1 instead promotes LRP6 surface retention and Wnt pathway activation, and restricts diffusion of secreted DKK to spatially pattern Wnt activity [PMID:12050670, PMID:17978005, PMID:25038040, PMID:23251700, PMID:27524201]. Independent of its Wnt-modulatory role, KREMEN1 functions as a dependence receptor: in the absence of DKK1, homodimerization of KREMEN1 triggers autophagic cell death mediated by SEC24C and ATG9A through a placental-mammal-specific cytoplasmic motif, and this activity is antagonized by DKK1 binding or heterodimerization with KREMEN2 [PMID:26206087, PMID:31069116, PMID:41807954]. Loss-of-function mutations in KREMEN1 (e.g., F209S in the WSC domain) cause autosomal recessive ectodermal dysplasia with oligodontia, associated with impaired glycosylation and defective ternary complex formation [PMID:27049303, PMID:40553753]. KREMEN1 also serves as the essential cell-surface entry receptor for EV-A enteroviruses (CVA2–A6, A8, A10, A12), binding viral capsid VP1/VP2 in the canyon region to trigger pocket factor release and uncoating, and mediates SARS-CoV-2 spike-dependent cell entry [PMID:29681460, PMID:31911601, PMID:34837059].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Identification of KREMEN1 as a novel transmembrane protein with Kringle, WSC, and CUB ectodomains established the molecular architecture of this receptor family before any function was known.\",\n      \"evidence\": \"Molecular cloning, domain analysis, and expression profiling during embryonic development\",\n      \"pmids\": [\"11267660\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No ligand or signaling pathway identified\", \"No functional assays performed\", \"Intracellular signaling mechanism unknown\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"The discovery that KREMEN1/2 are high-affinity DKK1 receptors that form a ternary complex with DKK1 and LRP6 to drive LRP6 endocytosis established the core mechanism of KREMEN-mediated Wnt inhibition and its role in anteroposterior CNS patterning.\",\n      \"evidence\": \"Co-IP, binding assays, endocytosis assays, Wnt reporters, and Xenopus morpholino knockdown with axis duplication assays\",\n      \"pmids\": [\"12050670\", \"12421700\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endocytic machinery mediating LRP6 internalization not defined\", \"Structural basis of ternary complex unknown\", \"Whether KREMEN has DKK-independent functions unresolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Kremen1 knockout mice revealed its requirement for thymic epithelial architecture and confirmed that endogenous KREMEN1 restrains canonical Wnt signaling in vivo.\",\n      \"evidence\": \"Krm1 knockout mouse with histology, FACS, and TOPFlash Wnt reporter assay in KO-derived TECs\",\n      \"pmids\": [\"17162372\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether thymic phenotype is Wnt-dependent or reflects other KREMEN1 functions not resolved\", \"Redundancy with KREMEN2 in other tissues not addressed\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"The finding that KREMEN2 promotes LRP6 surface retention and Wnt signaling in the absence of DKK proteins overturned the view that Kremens are purely Wnt-inhibitory and revealed a context-dependent positive role.\",\n      \"evidence\": \"Morpholino knockdown, overexpression, surface LRP6 localization assays, and Wnt reporter in Xenopus neural crest\",\n      \"pmids\": [\"17978005\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether KREMEN1 has the same DKK-independent positive role as KREMEN2 not directly tested\", \"Molecular basis of DKK-dependent vs. DKK-independent switching unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Mapping of DKK1 residues required for KREMEN binding (distinct from LRP6-binding surface) showed that the ternary complex involves bipartite DKK1 contacts, and revealed KREMEN is dispensable for Wnt antagonism at low LRP5/6 levels.\",\n      \"evidence\": \"Site-directed mutagenesis of DKK1 with binding and Wnt reporter assays\",\n      \"pmids\": [\"18502762\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic structure of ternary complex not yet available\", \"Physiological LRP6 expression levels determining KREMEN requirement not defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identification of the cytoplasmic dileucine motif (DXXXLV) required for clathrin/AP-2-mediated KREMEN1 endocytosis provided the mechanistic basis for how KREMEN1 internalizes LRP6.\",\n      \"evidence\": \"Mutagenesis of dileucine motif, AP-2 siRNA, and clathrin inhibitor pitstop 2 with internalization assays\",\n      \"pmids\": [\"23251700\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the same motif mediates DKK1/LRP6-dependent co-endocytosis not directly shown\", \"Adaptor protein interacting with the motif not identified\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Discovery that KREMEN1 restricts the spatial diffusion range of secreted DKK proteins revealed a non-cell-autonomous mechanism distinct from ternary complex endocytosis, showing that KREMEN1 loss paradoxically decreases Wnt signaling by allowing DKK to spread further.\",\n      \"evidence\": \"Zebrafish krm1 mutant, cell transplantation, DKK1b-mTangerine fusion protein visualization, Wnt reporter\",\n      \"pmids\": [\"25038040\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this DKK-sequestration function operates in mammalian tissues not tested\", \"Quantitative parameters of DKK diffusion restriction not modeled\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"KREMEN1 was established as a dependence receptor that triggers cell death in the absence of DKK1 ligand, via a placental-mammal-specific cytoplasmic motif separate from the Wnt-regulatory domain, linking KREMEN1 to cancer biology.\",\n      \"evidence\": \"Mutagenesis of cytoplasmic tail, apoptosis assays, phylogenetic analysis, analysis of cancer-associated mutations\",\n      \"pmids\": [\"26206087\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream death effectors not identified\", \"Whether cell death is apoptotic, autophagic, or mixed not resolved\", \"In vivo relevance of dependence receptor activity not demonstrated\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Crystal structures of the KREMEN1 ectodomain and its ternary complex with DKK1-CRD2 and LRP6 provided atomic-level understanding of how the three proteins assemble, with DKK1 sandwiched between LRP6 and KRM1.\",\n      \"evidence\": \"X-ray crystallography at 1.9–3.2 Å resolution with SPR validation\",\n      \"pmids\": [\"27524201\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length ternary complex structure at high resolution not obtained\", \"Conformational changes upon complex formation and endocytosis trigger not resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Human genetic evidence linked KREMEN1 loss-of-function (F209S in WSC domain) to autosomal recessive ectodermal dysplasia, establishing KREMEN1 as a Mendelian disease gene for ectodermal/dental development.\",\n      \"evidence\": \"Exome sequencing and segregation analysis in 4 consanguineous families\",\n      \"pmids\": [\"27049303\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No direct functional assay of the F209S mutation in this study\", \"Whether disease mechanism is purely Wnt-dependent or involves dependence receptor activity unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Genome-wide haploid genetic screening identified KREMEN1 as the essential entry receptor for CV-A10 and related EV-A enteroviruses, opening an entirely new functional dimension for this Wnt-pathway receptor.\",\n      \"evidence\": \"Haploid screen, KREMEN1 KO, overexpression, soluble ectodomain neutralization, mouse infection model\",\n      \"pmids\": [\"29681460\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of virus-receptor interaction not yet resolved\", \"Which KREMEN1 domains mediate viral attachment unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstration that KREMEN1 homodimerization is required for dependence receptor-mediated cell death — inhibited by DKK1 binding or KREMEN2 heterodimerization — resolved the molecular logic of how ligand availability switches KREMEN1 between survival and death signaling.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, forced dimerization constructs, apoptosis assays\",\n      \"pmids\": [\"31069116\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling cascade from the homodimer not identified\", \"Structural basis of homo- vs. heterodimerization unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Cryo-EM and crystal structures of CV-A10 bound to KREMEN1 revealed the receptor spans the viral canyon of VP1 across adjacent protomers, triggering pocket factor release and conformational changes for uncoating — establishing KREMEN1 as a combined attachment and uncoating receptor.\",\n      \"evidence\": \"Cryo-EM structures at neutral and acidic pH, X-ray crystallography, in vitro uncoating assays\",\n      \"pmids\": [\"31911601\", \"32690697\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How receptor binding is coordinated with endosomal trafficking for genome release not defined\", \"Whether the same structural mechanism applies to all KRM1-dependent enteroviruses not confirmed\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identification of KREMEN1 as a functional entry receptor for SARS-CoV-2, independent of ACE2, extended its viral receptor role to coronaviruses.\",\n      \"evidence\": \"Genome-wide receptome screen of 5054 membrane proteins, cell infection, in vivo mouse model\",\n      \"pmids\": [\"34837059\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of spike-KREMEN1 interaction not resolved\", \"Relative physiological contribution vs. ACE2 in human tissues unclear\", \"Whether KREMEN1 mediates uncoating for SARS-CoV-2 unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identification of VP2 residue N142 as critical for KREMEN1 binding defined a specific virus-side contact point and validated the structural model across in vitro and in vivo systems.\",\n      \"evidence\": \"Neutralization-resistant mutant screening, soluble KREMEN1 binding, cell infection, and mouse pathogenicity assays\",\n      \"pmids\": [\"37788227\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-level structure of VP2 N142 contact with KREMEN1 not directly resolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Systematic mutagenesis across all KRM1-dependent enteroviruses identified VP2 K140 as a universally conserved contact engaged by KRM1 residue D90, unifying the receptor-binding mechanism and extending KRM1 usage to CVA8.\",\n      \"evidence\": \"Mutational analysis across CVA2–A6, A8, A10, A12 with binding, infection, and in vivo assays\",\n      \"pmids\": [\"39817751\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether additional KREMEN1 residues contribute to serotype-specific binding not fully mapped\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Functional characterization of ectodermal dysplasia-associated KREMEN1 variants showed that disease mutations impair N/O-glycosylation and ternary complex formation with DKK1-LRP6, causing WNT pathway dysregulation in patient fibroblasts.\",\n      \"evidence\": \"Glycosylation analysis, co-IP for complex formation, TOPFlash WNT reporter in patient fibroblasts\",\n      \"pmids\": [\"40553753\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether glycosylation defects also impair viral receptor or dependence receptor functions not tested\", \"Animal model rescue of ectodermal dysplasia not performed\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Resolution of the downstream cell death pathway showed KREMEN1 triggers autophagic (not apoptotic) cell death via proximity interactions with SEC24C and ATG9A after vesicular trafficking, identifying the effector machinery of its dependence receptor activity.\",\n      \"evidence\": \"BioID proximity labeling, pharmacological autophagy inhibition, siRNA knockdown of SEC24C and ATG9A, cell death assays\",\n      \"pmids\": [\"41807954\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How KREMEN1 homodimerization connects to SEC24C engagement not established\", \"Whether SEC24C-dependent autophagy operates in vivo not shown\", \"Structural basis of KREMEN1-SEC24C interaction not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: how KREMEN1 switches between Wnt-inhibitory, Wnt-promoting, DKK-sequestering, and cell-death modes in different cellular contexts; the structural basis of KREMEN1 homodimerization and its coupling to SEC24C/ATG9A-mediated autophagy; and whether its Wnt-modulatory and viral receptor functions are physiologically interrelated.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No integrated structural model of full-length KREMEN1 in different signaling states\", \"In vivo validation of SEC24C-dependent autophagic cell death pathway lacking\", \"Functional crosstalk between viral entry and Wnt signaling through KREMEN1 not investigated\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 11, 18]},\n      {\"term_id\": \"GO:0001618\", \"supporting_discovery_ids\": [11, 14, 15, 22, 23]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 3, 5, 17]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 3, 6, 11]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [6, 20]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [6, 20]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 3, 4, 5, 17, 19]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [7, 13, 20]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [20]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [1, 9, 10]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [11, 18]}\n    ],\n    \"complexes\": [\n      \"DKK1-KREMEN1-LRP6 ternary complex\",\n      \"KREMEN1 homodimer\"\n    ],\n    \"partners\": [\n      \"DKK1\",\n      \"LRP6\",\n      \"LRP5\",\n      \"KREMEN2\",\n      \"DKK4\",\n      \"SEC24C\",\n      \"ATG9A\",\n      \"DKK3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}