{"gene":"ZNRF3","run_date":"2026-06-11T09:02:07","timeline":{"discoveries":[{"year":2012,"finding":"ZNRF3 is a cell-surface transmembrane E3 ubiquitin ligase that promotes turnover of Frizzled and LRP6 Wnt receptors, thereby inhibiting Wnt signaling. R-spondin inhibits ZNRF3 by directly binding to its extracellular domain and inducing association between ZNRF3 and LGR4, which results in membrane clearance of ZNRF3.","method":"Co-immunoprecipitation, cell surface receptor turnover assays, in vivo Wnt/PCP signaling assays, functional epistasis","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, functional rescue, in vivo assays, replicated across multiple labs","pmids":["22575959"],"is_preprint":false},{"year":2013,"finding":"Crystal structures of the ZNRF3 ectodomain alone and in complex with R-spondin 2 (Rspo2 Fu1-Fu2) and with RNF43 ectodomain reveal that a prominent loop in Rspo Fu1 clamps into a groove on the ZNRF3 ectodomain surface. Rspo binding enhances dimerization of ZNRF3 ectodomain. Signaling potency of Rspo depends on ability to recruit ZNRF3 or RNF43 via Fu1 into a complex with LGR receptors (which bind Rspo via Fu2).","method":"X-ray crystallography, biophysical binding assays, cell-based signaling assays, mutagenesis of Rspo chimeras","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures with functional validation and mutagenesis, replicated by multiple structural studies","pmids":["24225776"],"is_preprint":false},{"year":2013,"finding":"Crystal structures of the ZNRF3 ectodomain and its complex with R-spondin 1 (RSPO1) show that ZNRF3 binds RSPO1 via the RSPO1 furin-like 1 (Fu1) domain with micromolar affinity. The ZNRF3-binding site overlaps with trans-interactions seen in 2:2 LGR5-RSPO1 complexes, suggesting that ZNRF3/RNF43 binding disrupts such arrangements.","method":"X-ray crystallography, SPR/binding affinity measurements","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with binding measurements, corroborated by multiple independent structural studies","pmids":["24349440"],"is_preprint":false},{"year":2013,"finding":"Both LGR4 and ZNRF3 binding motifs of R-spondin are required for R-spondin-induced LGR4/ZNRF3 interaction, membrane clearance of ZNRF3, and activation of Wnt signaling. A ZNRF3 mutant with reduced affinity to R-spondin cannot be suppressed by R-spondin, supporting a dual receptor model where LGR4/5 is the engagement receptor and ZNRF3/RNF43 is the effector receptor.","method":"Mutagenesis of R-spondin binding interfaces, co-immunoprecipitation, membrane clearance assays, Wnt signaling reporter assays","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, mutagenesis, functional assays in multiple cell lines, corroborated by structural studies","pmids":["24165923"],"is_preprint":false},{"year":2013,"finding":"Recombinant ZNRF3 ectodomain and LGR4 LRR1-14 fragment can be reconstituted in vitro from bacterially expressed proteins. ZNRF3 ECD inhibits RSPO-enhanced Wnt3a signaling, and ternary RSPO:LGR4:ZNRF3 complexes were detected for RSPO2 and RSPO3. RSPO proteins bind ZNRF3 weakly compared to LGR4.","method":"Bacterial protein reconstitution, TR-FRET binding assay, native gel electrophoretic mobility shift assay, cell-based signaling assay","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with multiple orthogonal biochemical methods, single lab","pmids":["24050775"],"is_preprint":false},{"year":2015,"finding":"Dishevelled (DVL) is required for ZNRF3/RNF43-mediated ubiquitination and degradation of Frizzled. DVL physically interacts with ZNRF3, and this interaction is essential for ZNRF3 Wnt-inhibitory activity. Binding of Frizzled through the DEP domain of DVL is required for DVL-mediated FZD downregulation. Fusion of the DEP domain to ZNRF3 overcomes DVL dependency for FZD downregulation.","method":"DVL knockout cells, co-immunoprecipitation, ubiquitination assay, domain fusion rescue experiments, cell surface receptor quantification","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, domain fusion rescue, KO phenotype, multiple orthogonal methods","pmids":["25891077"],"is_preprint":false},{"year":2015,"finding":"Crystal structure of the ternary hLGR5-mRspo2Fu1-Fu2-mZNRF3ecto complex at low resolution confirms that Rspo proteins cross-link LGRs and ZNRF3 into a 2:2:2 complex (vs. 1:1:1 complex with RNF43).","method":"X-ray crystallography","journal":"Journal of structural biology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — crystal structure but low resolution, single lab","pmids":["26123262"],"is_preprint":false},{"year":2018,"finding":"SCFβ-TRCP E3 ubiquitin ligase directly interacts with and ubiquitinates ZNRF3, regulating its protein stability via proteasomal degradation. ZNRF3 ubiquitination by β-TRCP is both CKI-phosphorylation- and degron-dependent, analogous to β-catenin degradation.","method":"Co-immunoprecipitation, ubiquitination assay, proteasome inhibitor treatment, phosphorylation-dependent degron analysis","journal":"Protein & cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and ubiquitination assay with degron analysis, single lab, two orthogonal approaches","pmids":["29497989"],"is_preprint":false},{"year":2020,"finding":"PTPRK (protein tyrosine phosphatase receptor-type kappa) promotes ZNRF3 internalization and Wnt receptor degradation by dephosphorylating a '4Y' endocytic tyrosine motif in ZNRF3. Phosphorylation of this motif inhibits ZNRF3 internalization and reduces Wnt receptor turnover; dephosphorylation by PTPRK promotes ZNRF3 internalization. Xenopus Ptprk deficiency increases Wnt signaling with organizer defects.","method":"Identification of 4Y endocytic signal by mutagenesis, Xenopus loss-of-function, cell-based Wnt reporter assays, ZNRF3 internalization assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — mutagenesis of endocytic signal, in vivo epistasis, multiple orthogonal methods in two systems","pmids":["31934854"],"is_preprint":false},{"year":2021,"finding":"MET proto-oncogene phosphorylates the '4Y' endocytic motif of ZNRF3 in response to HGF stimulation, thereby inhibiting ZNRF3 internalization and reducing Wnt receptor degradation, thus enhancing Wnt/β-catenin signaling. PTPRK dephosphorylates the same motif to promote ZNRF3 internalization. MET inhibition promotes ZNRF3 internalization and Wnt receptor degradation.","method":"Co-immunoprecipitation of MET-ZNRF3, phosphorylation assays, pharmacological MET inhibition, ZNRF3 internalization assays, Wnt reporter assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP, phosphorylation assay, pharmacological and genetic perturbation, multiple orthogonal methods","pmids":["34590584"],"is_preprint":false},{"year":2021,"finding":"USP42 deubiquitinase binds to the Dishevelled-interacting region (DIR) of ZNRF3 and deubiquitinates ZNRF3, protecting it from R-spondin-induced ubiquitin-dependent membrane clearance. USP42 thereby stabilizes ZNRF3 at the plasma membrane, increases FZD/LRP6 turnover, and inhibits Wnt signaling.","method":"Co-immunoprecipitation, deubiquitination assay, membrane clearance assay, Wnt signaling reporter, organoid assays","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP, in vitro deubiquitination assay, multiple cell-based functional assays including organoids","pmids":["33786993"],"is_preprint":false},{"year":2021,"finding":"ZNRF3 deletion in hepatocytes promotes hepatocyte proliferation; RNF43 is upregulated as a compensatory response. Concomitant deletion of both RNF43 and ZNRF3 results in metabolic reprogramming of periportal hepatocytes, clonal expansion, and liver tumor formation, showing that ZNRF3 and RNF43 cooperate to restrict WNT/β-catenin activity and balance metabolic function and proliferation in the liver.","method":"Conditional knockout mice (liver-specific), scRNA-seq, chromatin accessibility assays, histology, proliferation assays","journal":"Cell stem cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with defined phenotypic readout in multiple genetic combinations, multi-method","pmids":["34129813"],"is_preprint":false},{"year":2018,"finding":"ZNRF3 is required for mammalian testis sex determination. XY mice lacking ZNRF3 show gonadal sex reversal associated with ectopic WNT/β-catenin activity and reduced Sox9 expression. Two human ZNRF3 missense variants identified in 46,XY DSD patients disrupt ZNRF3 activity in cell lines and zebrafish embryo assays.","method":"Conditional KO mice, exome sequencing, functional assays in human cell lines and zebrafish embryos","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo KO phenotype with pathway epistasis, functional variant validation in two orthogonal model systems","pmids":["29735715"],"is_preprint":false},{"year":2019,"finding":"Adrenocortical-specific loss of ZNRF3 (but not RNF43) results in adrenal hyperplasia dependent on Porcupine-mediated Wnt ligand secretion. ZNRF3 loss triggers moderate-level Wnt/β-catenin activation expanding only the inner cortex, and genetic reduction of β-catenin dosage reverses the ZNRF3-deficient phenotype.","method":"Conditional KO mice, Porcupine inhibitor treatment, genetic β-catenin dosage reduction, histology, signaling analysis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with genetic epistasis, pharmacological validation, multiple orthogonal methods","pmids":["30692207"],"is_preprint":false},{"year":2023,"finding":"LGR4 (but not LGR5) forms a 2:2 complex with RNF43/ZNRF3 that provides high-affinity bivalent binding of R-spondin. Co-expression of ZNRF3 with LGR4 dramatically increases binding affinity of monovalent RSPO2 furin domain, whereas co-expression of ZNRF3 with LGR5 has no effect, indicating LGR4 and RNF43/ZNRF3 cooperate for high-affinity R-spondin engagement.","method":"Whole-cell binding affinity measurements with monovalent and bivalent RSPO ligands, co-expression studies","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional binding assays in whole cells, single lab, two ligand formats tested","pmids":["37402772"],"is_preprint":false},{"year":2024,"finding":"RNF43 preferentially down-regulates FZD1/FZD5/FZD7 while ZNRF3 preferentially targets FZD6 for endocytosis. The transmembrane domain (TMD) of RNF43 is a key molecular determinant for inducing FZD5 endocytosis; TMD swap between RNF43 and ZNRF3 redirects their FZD substrate preference.","method":"FZD endocytosis assays, TMD swap mutagenesis, flow cytometry, cell surface receptor quantification","journal":"Life science alliance","confidence":"High","confidence_rationale":"Tier 2 / Moderate — domain-swap mutagenesis with functional readout, multiple FZD substrates tested, mechanistic insight into TMD specificity","pmids":["38969364"],"is_preprint":false},{"year":2024,"finding":"ZNRF3 and RNF43 interact with EGFR via their extracellular domains, leading to EGFR ubiquitination and subsequent degradation facilitated by the E3 ligase RING domain. ZNRF3 overexpression reduces EGFR levels; ZNRF3/RNF43 knockout increases EGFR signaling and promotes cancer cell growth.","method":"Co-immunoprecipitation of ZNRF3-EGFR, ubiquitination assays, ZNRF3 overexpression/KO cell growth assays, proteogenomics correlation","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ubiquitination assay, KO phenotype; single lab, peer-reviewed version","pmids":["41960900"],"is_preprint":false},{"year":2024,"finding":"Deletions of ZNRF3 exon 2 produce a 42-amino-acid deleted protein (ΔEx2-ZNRF3) that impairs R-spondin (RSPO1) binding and attenuates RSPO1-dependent activation of Wnt/β-catenin signaling in cell-based TCF-LEF reporter assays, causing congenital adrenal hypoplasia.","method":"RT-PCR, 3D structural modeling, cell-based TCF-LEF reporter assay with RSPO1 stimulation","journal":"The Journal of clinical endocrinology and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional assay with mutant protein, structural modeling, single lab","pmids":["37878959"],"is_preprint":false},{"year":2024,"finding":"ZNRF3 germline missense variants in the RING ligase domain cause macrocephalic NDD through dominant-negative hyperactivation of Wnt/β-catenin signaling (disrupting ubiquitin ligase function/Wnt receptor turnover), while a missense variant in the RSPO-binding domain causes microcephalic NDD by attenuating Wnt/β-catenin signaling through disrupted RSPO binding.","method":"Structural modeling, in vitro TCF/LEF transcriptional reporter assays with and without Wnt3a and RSPO stimulation, variant functional testing","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional reporter assays with domain-specific variants, structural modeling, single lab","pmids":["39168120"],"is_preprint":false},{"year":2024,"finding":"Tumor-associated ZNRF3 truncating mutations show loss-of-function at endogenous expression levels. Defective R-Spondin domain missense variants undergo ER-associated degradation due to protein misfolding, reducing protein levels and preventing correct membrane localization (partially restorable at 27°C). When representative RING and R-Spondin domain variants are heterozygously introduced at endogenous levels, their effect on β-catenin signaling mirrors heterozygous knockout, with no dominant-negative activity detected.","method":"Endogenous knock-in of variants, β-catenin signaling assays, protein stability assays, temperature rescue experiments","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 / Strong — endogenous knock-in mutagenesis, multiple orthogonal methods, rigorous controls distinguishing LOF from dominant-negative","pmids":["39674817"],"is_preprint":false},{"year":2025,"finding":"Cryo-EM structures of human LGR4, LGR4-RSPO2, and LGR4-RSPO2-ZNRF3 ternary complexes show that LGR4, RSPO2, and ZNRF3 assemble into a 2:2:2 complex with the ZNRF3 dimer at the center. Upon RSPO2 binding, LGR4 undergoes no significant conformational change. Forced ZNRF3 dimerization by the ternary complex likely underpins sequestration of ZNRF3 from Wnt receptors and facilitates ZNRF3 auto-inactivation.","method":"Cryo-electron microscopy structure determination","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — cryo-EM structure of ternary complex, single lab but high-resolution structural data","pmids":["41034211"],"is_preprint":false},{"year":2025,"finding":"ZNRF3-induced FZD degradation depends on endogenous Wnt stimulation; ZNRF3 selectively degrades Wnt-engaged FZD rather than constitutively degrading all FZD. Wnt enhances FZD-DVL association, and DVL then recruits ZNRF3 to FZD to promote its degradation. ZNRF3/RNF43 selectively target FZD5/8 for degradation upon Wnt stimulation, while DVL promotes ligand-independent FZD endocytosis but is dispensable for Wnt-induced FZD5/8 endocytosis.","method":"FZD endocytosis assays, co-immunoprecipitation, ZNRF3/RNF43 knockout cells, Wnt stimulation experiments","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods, KO cells, Co-IP, corroborated by independent concurrent study (eLife 2025)","pmids":["41086253","41070826"],"is_preprint":false},{"year":2023,"finding":"Disulfide-constrained peptides (DCPs) that bind ZNRF3 induce ZNRF3 ubiquitination and cell surface clearance, leading to FZD stabilization and Wnt pathway activation. Multimeric DCPs were more effective than monomeric forms at inducing ZNRF3 clearance.","method":"Cell surface ZNRF3 clearance assay, ubiquitination assay, Wnt reporter assay, organoid growth assay, peptide valency comparison","journal":"Cell chemical biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional assays with mechanistic readout (ubiquitination, surface clearance), single lab","pmids":["38056465"],"is_preprint":false}],"current_model":"ZNRF3 is a cell-surface transmembrane RING-domain E3 ubiquitin ligase that constitutes a negative feedback regulator of Wnt signaling by ubiquitinating and promoting lysosomal/endosomal degradation of Frizzled (FZD) and LRP6 Wnt receptors; FZD degradation is selective for Wnt-engaged FZD and requires DVL as an adaptor to recruit ZNRF3 to the FZD-DVL complex; R-spondin proteins inhibit ZNRF3 by cross-linking it via their Fu1 domain with LGR4 into a 2:2:2 ternary complex (visualized by cryo-EM) that sequesters and auto-inactivates ZNRF3 through forced dimerization; ZNRF3 internalization and activity are post-translationally regulated by phosphorylation of a '4Y' endocytic motif—MET kinase phosphorylates this motif (inhibiting internalization) and PTPRK phosphatase dephosphorylates it (promoting internalization)—while the deubiquitinase USP42 stabilizes ZNRF3 at the membrane by antagonizing R-spondin-induced ubiquitination; additionally, SCFβ-TRCP ubiquitinates ZNRF3 itself in a phospho-degron-dependent manner to control its protein stability; beyond Wnt receptors, ZNRF3 also targets EGFR for ubiquitination and degradation via its extracellular domain; in vivo, ZNRF3 controls adrenal cortex homeostasis, liver metabolic zonation and hepatocyte proliferation, and mammalian gonadal sex determination through spatiotemporal regulation of Wnt/β-catenin signaling gradients."},"narrative":{"mechanistic_narrative":"ZNRF3 is a cell-surface transmembrane RING-domain E3 ubiquitin ligase that acts as a negative-feedback regulator of Wnt/β-catenin signaling by ubiquitinating Frizzled (FZD) and LRP6 Wnt receptors and driving their membrane clearance and degradation [PMID:22575959]. Receptor targeting is selective rather than constitutive: ZNRF3 degrades Wnt-engaged FZD, with Wnt stimulation enhancing the FZD–DVL association and DVL serving as the adaptor that recruits ZNRF3 to FZD; fusing the DVL DEP domain to ZNRF3 bypasses this dependency [PMID:25891077, PMID:41086253, PMID:41070826]. Substrate preference is encoded in part by the transmembrane domain, which directs ZNRF3 toward particular FZD subtypes [PMID:38969364], and the ligase additionally engages EGFR through its extracellular domain to drive EGFR ubiquitination and degradation [PMID:41960900]. ZNRF3 is itself the effector arm of the R-spondin/LGR axis: R-spondin binds the ZNRF3 ectodomain via its Fu1 domain and, together with LGR4 (bound through Fu2), cross-links the receptors into a 2:2:2 ternary complex centered on a ZNRF3 dimer, sequestering and auto-inactivating ZNRF3 through forced dimerization and membrane clearance [PMID:22575959, PMID:24225776, PMID:24165923, PMID:41034211]. ZNRF3 abundance and surface activity are further tuned post-translationally—phosphorylation of a '4Y' endocytic motif by MET inhibits internalization while PTPRK dephosphorylation promotes it [PMID:31934854, PMID:34590584], the deubiquitinase USP42 stabilizes ZNRF3 against R-spondin-induced clearance [PMID:33786993], and SCFβ-TRCP ubiquitinates ZNRF3 in a phospho-degron-dependent manner to control its stability [PMID:29497989]. In vivo, this regulatory output sets Wnt/β-catenin gradients that govern adrenal cortex homeostasis [PMID:30692207], hepatocyte proliferation and metabolic zonation [PMID:34129813], and mammalian testis sex determination [PMID:29735715]. Germline ZNRF3 variants cause human disease: RING-domain and RSPO-binding-domain variants produce neurodevelopmental disorders with macrocephaly or microcephaly respectively [PMID:39168120], and exon-2/RSPO-binding-domain lesions cause congenital adrenal hypoplasia [PMID:37878959], while 46,XY DSD-associated missense variants disrupt ZNRF3 activity [PMID:29735715].","teleology":[{"year":2012,"claim":"Established ZNRF3 as the molecular identity of a membrane E3 ligase that limits Wnt signaling and the target of R-spondin, answering how R-spondin potentiates Wnt at the receptor level.","evidence":"Co-IP, surface receptor turnover, and in vivo Wnt/PCP assays defining FZD/LRP6 turnover and R-spondin/LGR4-induced ZNRF3 clearance","pmids":["22575959"],"confidence":"High","gaps":["Structural basis of R-spondin/LGR4/ZNRF3 assembly not resolved","Adaptor coupling ZNRF3 to FZD unknown"]},{"year":2013,"claim":"Resolved the structural logic of the dual-receptor model, showing R-spondin Fu1 clamps the ZNRF3 ectodomain while Fu2 engages LGR receptors and that binding enhances ZNRF3 ectodomain dimerization.","evidence":"X-ray crystallography of ZNRF3 ectodomain alone and bound to Rspo, SPR/binding measurements, Rspo chimera mutagenesis, and in vitro reconstitution of ternary complexes","pmids":["24225776","24349440","24165923","24050775"],"confidence":"High","gaps":["Stoichiometry of the full ternary complex not definitively established at this stage","How ectodomain dimerization translates to catalytic auto-inactivation unresolved"]},{"year":2015,"claim":"Identified DVL as the obligate adaptor recruiting ZNRF3 to FZD, explaining how a RING ligase reaches its receptor substrate.","evidence":"DVL knockout cells, reciprocal Co-IP, ubiquitination assays, and DEP-domain fusion rescue","pmids":["25891077"],"confidence":"High","gaps":["Whether DVL recruitment selects specific FZD subtypes not addressed","Dependence on Wnt ligand engagement not yet defined"]},{"year":2015,"claim":"Confirmed that R-spondin cross-links LGR and ZNRF3 into a 2:2:2 assembly (versus 1:1:1 with RNF43), distinguishing the architectures of the two paralogs.","evidence":"Low-resolution X-ray crystallography of the ternary hLGR5–Rspo2–ZNRF3 complex","pmids":["26123262"],"confidence":"Medium","gaps":["Low resolution limits interface detail","Functional consequence of differing stoichiometry untested"]},{"year":2018,"claim":"Showed ZNRF3 stability is itself regulated by a phospho-degron, placing ZNRF3 protein levels under SCFβ-TRCP control analogous to β-catenin.","evidence":"Co-IP, ubiquitination assays, proteasome inhibition, and CKI-phosphorylation/degron analysis","pmids":["29497989"],"confidence":"Medium","gaps":["Single lab","Physiological/in vivo relevance of β-TRCP-mediated turnover not established"]},{"year":2018,"claim":"Demonstrated ZNRF3 is required for mammalian testis sex determination and linked human ZNRF3 variants to 46,XY DSD via ectopic Wnt/β-catenin activity.","evidence":"Conditional KO mice with pathway epistasis, exome sequencing, and variant functional testing in human cells and zebrafish","pmids":["29735715"],"confidence":"High","gaps":["Cell-type-specific substrates in the gonad not defined","Mechanism connecting ZNRF3 loss to Sox9 repression incompletely mapped"]},{"year":2019,"claim":"Defined an in vivo, dosage-sensitive role for ZNRF3 in adrenal cortex homeostasis dependent on Porcupine-secreted Wnt and β-catenin.","evidence":"Adrenocortical conditional KO, Porcupine inhibitor treatment, and genetic β-catenin dosage reduction","pmids":["30692207"],"confidence":"High","gaps":["Why ZNRF3 loss expands only the inner cortex unexplained","Non-redundancy with RNF43 in adrenal context not mechanistically resolved"]},{"year":2020,"claim":"Identified a '4Y' endocytic motif and its phosphatase PTPRK, revealing post-translational control of ZNRF3 internalization independent of R-spondin.","evidence":"Endocytic-signal mutagenesis, Xenopus loss-of-function, Wnt reporter and internalization assays","pmids":["31934854"],"confidence":"High","gaps":["Kinase phosphorylating the motif not yet identified at this stage","In vivo relevance in mammals untested"]},{"year":2021,"claim":"Completed the 4Y-motif regulatory circuit by identifying MET as the kinase opposing PTPRK, linking HGF/MET signaling to Wnt receptor stability.","evidence":"MET–ZNRF3 Co-IP, phosphorylation assays, pharmacological MET inhibition, internalization and Wnt reporter assays","pmids":["34590584"],"confidence":"High","gaps":["Whether MET–ZNRF3 crosstalk operates in tumors in vivo not shown","Quantitative balance of MET vs PTPRK control across tissues unknown"]},{"year":2021,"claim":"Showed USP42 deubiquitinates and stabilizes ZNRF3 at the membrane, adding a deubiquitinase layer that counters R-spondin-induced clearance.","evidence":"Co-IP, in vitro deubiquitination, membrane clearance, Wnt reporter, and organoid assays","pmids":["33786993"],"confidence":"High","gaps":["Regulation of USP42 activity itself not defined","In vivo consequences of USP42–ZNRF3 axis untested"]},{"year":2021,"claim":"Established that ZNRF3 and RNF43 cooperatively restrain Wnt to maintain liver metabolic zonation and limit hepatocyte proliferation and tumorigenesis.","evidence":"Liver-specific conditional single and double KO mice, scRNA-seq, chromatin accessibility, and proliferation/histology readouts","pmids":["34129813"],"confidence":"High","gaps":["Molecular basis of RNF43 compensatory upregulation unknown","Direct receptor substrates driving zonation not pinpointed"]},{"year":2023,"claim":"Refined the receptor cooperativity model, showing LGR4 (but not LGR5) forms a 2:2 complex with ZNRF3/RNF43 to confer high-affinity bivalent R-spondin binding.","evidence":"Whole-cell binding affinity measurements with monovalent and bivalent RSPO ligands and co-expression studies","pmids":["37402772"],"confidence":"Medium","gaps":["Single lab whole-cell assays","Structural basis of LGR4-specific cooperativity not resolved here"]},{"year":2023,"claim":"Provided pharmacological proof-of-concept that engineered ZNRF3-binding peptides can clear ZNRF3 from the surface to activate Wnt, validating ZNRF3 as a druggable node.","evidence":"Disulfide-constrained peptide surface-clearance, ubiquitination, Wnt reporter, organoid, and valency-comparison assays","pmids":["38056465"],"confidence":"Medium","gaps":["Mechanism of valency-dependent clearance not structurally defined","In vivo efficacy/specificity untested"]},{"year":2024,"claim":"Mapped substrate selectivity to the transmembrane domain, showing ZNRF3 and RNF43 prefer distinct FZD subtypes and that TMD swaps redirect specificity.","evidence":"FZD endocytosis assays, TMD-swap mutagenesis, flow cytometry, surface receptor quantification","pmids":["38969364"],"confidence":"High","gaps":["Molecular features within the TMD dictating preference not defined","Physiological significance of subtype preference untested in vivo"]},{"year":2024,"claim":"Extended ZNRF3 substrate range beyond Wnt receptors by identifying EGFR as an ectodomain-engaged target for ubiquitination and degradation.","evidence":"ZNRF3–EGFR Co-IP, ubiquitination assays, overexpression/KO cell growth assays, and proteogenomic correlation","pmids":["41960900"],"confidence":"Medium","gaps":["Single lab","Relative contribution of EGFR vs Wnt-receptor targeting to phenotypes unresolved"]},{"year":2024,"claim":"Linked domain-specific germline ZNRF3 variants to opposite-direction Wnt dysregulation and human neurodevelopmental and adrenal phenotypes.","evidence":"Structural modeling and TCF/LEF reporter assays of RING- and RSPO-binding-domain variants; RT-PCR and reporter assays of ΔEx2-ZNRF3","pmids":["39168120","37878959"],"confidence":"Medium","gaps":["Dominant-negative mechanism inferred from overexpression assays","In vivo validation of variant effects lacking"]},{"year":2024,"claim":"Reassessed disease-variant mechanism at endogenous levels, showing tumor-associated truncating and RSPO-domain variants act as loss-of-function (via ERAD/misfolding) rather than dominant-negative.","evidence":"Endogenous knock-in of variants, β-catenin signaling and protein stability assays, and 27°C temperature rescue","pmids":["39674817"],"confidence":"High","gaps":["Reconciliation with dominant-negative claims from overexpression studies incomplete","Tissue-context dependence of variant behavior not addressed"]},{"year":2025,"claim":"Provided a high-resolution structural mechanism for ZNRF3 inactivation, showing R-spondin/LGR4 assemble a 2:2:2 complex with a central ZNRF3 dimer whose forced dimerization underlies sequestration and auto-inactivation.","evidence":"Cryo-EM structures of LGR4, LGR4–RSPO2, and LGR4–RSPO2–ZNRF3 complexes","pmids":["41034211"],"confidence":"High","gaps":["Catalytic consequence of dimerization on RING activity not directly demonstrated","Dynamics of complex assembly/disassembly not captured"]},{"year":2025,"claim":"Clarified that ZNRF3 targets Wnt-engaged FZD selectively, with Wnt enhancing FZD–DVL association and DVL recruiting ZNRF3, integrating substrate selection with ligand sensing.","evidence":"FZD endocytosis assays, Co-IP, ZNRF3/RNF43 KO cells, and Wnt stimulation experiments (two concurrent studies)","pmids":["41086253","41070826"],"confidence":"High","gaps":["How Wnt biochemically licenses the FZD–DVL–ZNRF3 handoff not fully resolved","Whether all FZD subtypes follow this Wnt-dependent rule untested"]},{"year":null,"claim":"How the multiple regulatory inputs (R-spondin/LGR sequestration, 4Y phosphorylation, USP42/β-TRCP ubiquitin turnover, DVL recruitment, TMD-encoded substrate choice) are integrated to set tissue-specific Wnt gradients in vivo remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified quantitative model coupling surface ZNRF3 dynamics to β-catenin output across tissues","Catalytic mechanism by which forced dimerization inactivates the RING ligase not directly tested","Relative physiological weight of EGFR versus Wnt-receptor targeting unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,5,16]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,5,16]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,21]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,8,10]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,3,21]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,5,16]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[12,13,11]}],"complexes":["RSPO–LGR4–ZNRF3 ternary (2:2:2) complex"],"partners":["RSPO1","RSPO2","LGR4","DVL","PTPRK","MET","USP42","EGFR"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9ULT6","full_name":"E3 ubiquitin-protein ligase ZNRF3","aliases":["RING finger protein 203","RING-type E3 ubiquitin transferase ZNRF3","Zinc/RING finger protein 3"],"length_aa":936,"mass_kda":100.6,"function":"E3 ubiquitin-protein ligase that acts as a negative regulator of the Wnt signaling pathway by mediating the ubiquitination and subsequent degradation of Wnt receptor complex components Frizzled and LRP6. Acts on both canonical and non-canonical Wnt signaling pathway. Acts as a tumor suppressor in the intestinal stem cell zone by inhibiting the Wnt signaling pathway, thereby restricting the size of the intestinal stem cell zone (PubMed:22575959). 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R-spondin inhibits ZNRF3 by directly binding to its extracellular domain and inducing association between ZNRF3 and LGR4, which results in membrane clearance of ZNRF3.\",\n      \"method\": \"Co-immunoprecipitation, cell surface receptor turnover assays, in vivo Wnt/PCP signaling assays, functional epistasis\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, functional rescue, in vivo assays, replicated across multiple labs\",\n      \"pmids\": [\"22575959\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Crystal structures of the ZNRF3 ectodomain alone and in complex with R-spondin 2 (Rspo2 Fu1-Fu2) and with RNF43 ectodomain reveal that a prominent loop in Rspo Fu1 clamps into a groove on the ZNRF3 ectodomain surface. Rspo binding enhances dimerization of ZNRF3 ectodomain. Signaling potency of Rspo depends on ability to recruit ZNRF3 or RNF43 via Fu1 into a complex with LGR receptors (which bind Rspo via Fu2).\",\n      \"method\": \"X-ray crystallography, biophysical binding assays, cell-based signaling assays, mutagenesis of Rspo chimeras\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures with functional validation and mutagenesis, replicated by multiple structural studies\",\n      \"pmids\": [\"24225776\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Crystal structures of the ZNRF3 ectodomain and its complex with R-spondin 1 (RSPO1) show that ZNRF3 binds RSPO1 via the RSPO1 furin-like 1 (Fu1) domain with micromolar affinity. The ZNRF3-binding site overlaps with trans-interactions seen in 2:2 LGR5-RSPO1 complexes, suggesting that ZNRF3/RNF43 binding disrupts such arrangements.\",\n      \"method\": \"X-ray crystallography, SPR/binding affinity measurements\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with binding measurements, corroborated by multiple independent structural studies\",\n      \"pmids\": [\"24349440\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Both LGR4 and ZNRF3 binding motifs of R-spondin are required for R-spondin-induced LGR4/ZNRF3 interaction, membrane clearance of ZNRF3, and activation of Wnt signaling. A ZNRF3 mutant with reduced affinity to R-spondin cannot be suppressed by R-spondin, supporting a dual receptor model where LGR4/5 is the engagement receptor and ZNRF3/RNF43 is the effector receptor.\",\n      \"method\": \"Mutagenesis of R-spondin binding interfaces, co-immunoprecipitation, membrane clearance assays, Wnt signaling reporter assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, mutagenesis, functional assays in multiple cell lines, corroborated by structural studies\",\n      \"pmids\": [\"24165923\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Recombinant ZNRF3 ectodomain and LGR4 LRR1-14 fragment can be reconstituted in vitro from bacterially expressed proteins. ZNRF3 ECD inhibits RSPO-enhanced Wnt3a signaling, and ternary RSPO:LGR4:ZNRF3 complexes were detected for RSPO2 and RSPO3. RSPO proteins bind ZNRF3 weakly compared to LGR4.\",\n      \"method\": \"Bacterial protein reconstitution, TR-FRET binding assay, native gel electrophoretic mobility shift assay, cell-based signaling assay\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with multiple orthogonal biochemical methods, single lab\",\n      \"pmids\": [\"24050775\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Dishevelled (DVL) is required for ZNRF3/RNF43-mediated ubiquitination and degradation of Frizzled. DVL physically interacts with ZNRF3, and this interaction is essential for ZNRF3 Wnt-inhibitory activity. Binding of Frizzled through the DEP domain of DVL is required for DVL-mediated FZD downregulation. Fusion of the DEP domain to ZNRF3 overcomes DVL dependency for FZD downregulation.\",\n      \"method\": \"DVL knockout cells, co-immunoprecipitation, ubiquitination assay, domain fusion rescue experiments, cell surface receptor quantification\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, domain fusion rescue, KO phenotype, multiple orthogonal methods\",\n      \"pmids\": [\"25891077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Crystal structure of the ternary hLGR5-mRspo2Fu1-Fu2-mZNRF3ecto complex at low resolution confirms that Rspo proteins cross-link LGRs and ZNRF3 into a 2:2:2 complex (vs. 1:1:1 complex with RNF43).\",\n      \"method\": \"X-ray crystallography\",\n      \"journal\": \"Journal of structural biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — crystal structure but low resolution, single lab\",\n      \"pmids\": [\"26123262\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SCFβ-TRCP E3 ubiquitin ligase directly interacts with and ubiquitinates ZNRF3, regulating its protein stability via proteasomal degradation. ZNRF3 ubiquitination by β-TRCP is both CKI-phosphorylation- and degron-dependent, analogous to β-catenin degradation.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, proteasome inhibitor treatment, phosphorylation-dependent degron analysis\",\n      \"journal\": \"Protein & cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and ubiquitination assay with degron analysis, single lab, two orthogonal approaches\",\n      \"pmids\": [\"29497989\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PTPRK (protein tyrosine phosphatase receptor-type kappa) promotes ZNRF3 internalization and Wnt receptor degradation by dephosphorylating a '4Y' endocytic tyrosine motif in ZNRF3. Phosphorylation of this motif inhibits ZNRF3 internalization and reduces Wnt receptor turnover; dephosphorylation by PTPRK promotes ZNRF3 internalization. Xenopus Ptprk deficiency increases Wnt signaling with organizer defects.\",\n      \"method\": \"Identification of 4Y endocytic signal by mutagenesis, Xenopus loss-of-function, cell-based Wnt reporter assays, ZNRF3 internalization assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mutagenesis of endocytic signal, in vivo epistasis, multiple orthogonal methods in two systems\",\n      \"pmids\": [\"31934854\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MET proto-oncogene phosphorylates the '4Y' endocytic motif of ZNRF3 in response to HGF stimulation, thereby inhibiting ZNRF3 internalization and reducing Wnt receptor degradation, thus enhancing Wnt/β-catenin signaling. PTPRK dephosphorylates the same motif to promote ZNRF3 internalization. MET inhibition promotes ZNRF3 internalization and Wnt receptor degradation.\",\n      \"method\": \"Co-immunoprecipitation of MET-ZNRF3, phosphorylation assays, pharmacological MET inhibition, ZNRF3 internalization assays, Wnt reporter assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP, phosphorylation assay, pharmacological and genetic perturbation, multiple orthogonal methods\",\n      \"pmids\": [\"34590584\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"USP42 deubiquitinase binds to the Dishevelled-interacting region (DIR) of ZNRF3 and deubiquitinates ZNRF3, protecting it from R-spondin-induced ubiquitin-dependent membrane clearance. USP42 thereby stabilizes ZNRF3 at the plasma membrane, increases FZD/LRP6 turnover, and inhibits Wnt signaling.\",\n      \"method\": \"Co-immunoprecipitation, deubiquitination assay, membrane clearance assay, Wnt signaling reporter, organoid assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP, in vitro deubiquitination assay, multiple cell-based functional assays including organoids\",\n      \"pmids\": [\"33786993\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ZNRF3 deletion in hepatocytes promotes hepatocyte proliferation; RNF43 is upregulated as a compensatory response. Concomitant deletion of both RNF43 and ZNRF3 results in metabolic reprogramming of periportal hepatocytes, clonal expansion, and liver tumor formation, showing that ZNRF3 and RNF43 cooperate to restrict WNT/β-catenin activity and balance metabolic function and proliferation in the liver.\",\n      \"method\": \"Conditional knockout mice (liver-specific), scRNA-seq, chromatin accessibility assays, histology, proliferation assays\",\n      \"journal\": \"Cell stem cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with defined phenotypic readout in multiple genetic combinations, multi-method\",\n      \"pmids\": [\"34129813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ZNRF3 is required for mammalian testis sex determination. XY mice lacking ZNRF3 show gonadal sex reversal associated with ectopic WNT/β-catenin activity and reduced Sox9 expression. Two human ZNRF3 missense variants identified in 46,XY DSD patients disrupt ZNRF3 activity in cell lines and zebrafish embryo assays.\",\n      \"method\": \"Conditional KO mice, exome sequencing, functional assays in human cell lines and zebrafish embryos\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo KO phenotype with pathway epistasis, functional variant validation in two orthogonal model systems\",\n      \"pmids\": [\"29735715\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Adrenocortical-specific loss of ZNRF3 (but not RNF43) results in adrenal hyperplasia dependent on Porcupine-mediated Wnt ligand secretion. ZNRF3 loss triggers moderate-level Wnt/β-catenin activation expanding only the inner cortex, and genetic reduction of β-catenin dosage reverses the ZNRF3-deficient phenotype.\",\n      \"method\": \"Conditional KO mice, Porcupine inhibitor treatment, genetic β-catenin dosage reduction, histology, signaling analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with genetic epistasis, pharmacological validation, multiple orthogonal methods\",\n      \"pmids\": [\"30692207\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"LGR4 (but not LGR5) forms a 2:2 complex with RNF43/ZNRF3 that provides high-affinity bivalent binding of R-spondin. Co-expression of ZNRF3 with LGR4 dramatically increases binding affinity of monovalent RSPO2 furin domain, whereas co-expression of ZNRF3 with LGR5 has no effect, indicating LGR4 and RNF43/ZNRF3 cooperate for high-affinity R-spondin engagement.\",\n      \"method\": \"Whole-cell binding affinity measurements with monovalent and bivalent RSPO ligands, co-expression studies\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional binding assays in whole cells, single lab, two ligand formats tested\",\n      \"pmids\": [\"37402772\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"RNF43 preferentially down-regulates FZD1/FZD5/FZD7 while ZNRF3 preferentially targets FZD6 for endocytosis. The transmembrane domain (TMD) of RNF43 is a key molecular determinant for inducing FZD5 endocytosis; TMD swap between RNF43 and ZNRF3 redirects their FZD substrate preference.\",\n      \"method\": \"FZD endocytosis assays, TMD swap mutagenesis, flow cytometry, cell surface receptor quantification\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain-swap mutagenesis with functional readout, multiple FZD substrates tested, mechanistic insight into TMD specificity\",\n      \"pmids\": [\"38969364\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ZNRF3 and RNF43 interact with EGFR via their extracellular domains, leading to EGFR ubiquitination and subsequent degradation facilitated by the E3 ligase RING domain. ZNRF3 overexpression reduces EGFR levels; ZNRF3/RNF43 knockout increases EGFR signaling and promotes cancer cell growth.\",\n      \"method\": \"Co-immunoprecipitation of ZNRF3-EGFR, ubiquitination assays, ZNRF3 overexpression/KO cell growth assays, proteogenomics correlation\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ubiquitination assay, KO phenotype; single lab, peer-reviewed version\",\n      \"pmids\": [\"41960900\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Deletions of ZNRF3 exon 2 produce a 42-amino-acid deleted protein (ΔEx2-ZNRF3) that impairs R-spondin (RSPO1) binding and attenuates RSPO1-dependent activation of Wnt/β-catenin signaling in cell-based TCF-LEF reporter assays, causing congenital adrenal hypoplasia.\",\n      \"method\": \"RT-PCR, 3D structural modeling, cell-based TCF-LEF reporter assay with RSPO1 stimulation\",\n      \"journal\": \"The Journal of clinical endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional assay with mutant protein, structural modeling, single lab\",\n      \"pmids\": [\"37878959\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ZNRF3 germline missense variants in the RING ligase domain cause macrocephalic NDD through dominant-negative hyperactivation of Wnt/β-catenin signaling (disrupting ubiquitin ligase function/Wnt receptor turnover), while a missense variant in the RSPO-binding domain causes microcephalic NDD by attenuating Wnt/β-catenin signaling through disrupted RSPO binding.\",\n      \"method\": \"Structural modeling, in vitro TCF/LEF transcriptional reporter assays with and without Wnt3a and RSPO stimulation, variant functional testing\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional reporter assays with domain-specific variants, structural modeling, single lab\",\n      \"pmids\": [\"39168120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Tumor-associated ZNRF3 truncating mutations show loss-of-function at endogenous expression levels. Defective R-Spondin domain missense variants undergo ER-associated degradation due to protein misfolding, reducing protein levels and preventing correct membrane localization (partially restorable at 27°C). When representative RING and R-Spondin domain variants are heterozygously introduced at endogenous levels, their effect on β-catenin signaling mirrors heterozygous knockout, with no dominant-negative activity detected.\",\n      \"method\": \"Endogenous knock-in of variants, β-catenin signaling assays, protein stability assays, temperature rescue experiments\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — endogenous knock-in mutagenesis, multiple orthogonal methods, rigorous controls distinguishing LOF from dominant-negative\",\n      \"pmids\": [\"39674817\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cryo-EM structures of human LGR4, LGR4-RSPO2, and LGR4-RSPO2-ZNRF3 ternary complexes show that LGR4, RSPO2, and ZNRF3 assemble into a 2:2:2 complex with the ZNRF3 dimer at the center. Upon RSPO2 binding, LGR4 undergoes no significant conformational change. Forced ZNRF3 dimerization by the ternary complex likely underpins sequestration of ZNRF3 from Wnt receptors and facilitates ZNRF3 auto-inactivation.\",\n      \"method\": \"Cryo-electron microscopy structure determination\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — cryo-EM structure of ternary complex, single lab but high-resolution structural data\",\n      \"pmids\": [\"41034211\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ZNRF3-induced FZD degradation depends on endogenous Wnt stimulation; ZNRF3 selectively degrades Wnt-engaged FZD rather than constitutively degrading all FZD. Wnt enhances FZD-DVL association, and DVL then recruits ZNRF3 to FZD to promote its degradation. ZNRF3/RNF43 selectively target FZD5/8 for degradation upon Wnt stimulation, while DVL promotes ligand-independent FZD endocytosis but is dispensable for Wnt-induced FZD5/8 endocytosis.\",\n      \"method\": \"FZD endocytosis assays, co-immunoprecipitation, ZNRF3/RNF43 knockout cells, Wnt stimulation experiments\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods, KO cells, Co-IP, corroborated by independent concurrent study (eLife 2025)\",\n      \"pmids\": [\"41086253\", \"41070826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Disulfide-constrained peptides (DCPs) that bind ZNRF3 induce ZNRF3 ubiquitination and cell surface clearance, leading to FZD stabilization and Wnt pathway activation. Multimeric DCPs were more effective than monomeric forms at inducing ZNRF3 clearance.\",\n      \"method\": \"Cell surface ZNRF3 clearance assay, ubiquitination assay, Wnt reporter assay, organoid growth assay, peptide valency comparison\",\n      \"journal\": \"Cell chemical biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional assays with mechanistic readout (ubiquitination, surface clearance), single lab\",\n      \"pmids\": [\"38056465\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ZNRF3 is a cell-surface transmembrane RING-domain E3 ubiquitin ligase that constitutes a negative feedback regulator of Wnt signaling by ubiquitinating and promoting lysosomal/endosomal degradation of Frizzled (FZD) and LRP6 Wnt receptors; FZD degradation is selective for Wnt-engaged FZD and requires DVL as an adaptor to recruit ZNRF3 to the FZD-DVL complex; R-spondin proteins inhibit ZNRF3 by cross-linking it via their Fu1 domain with LGR4 into a 2:2:2 ternary complex (visualized by cryo-EM) that sequesters and auto-inactivates ZNRF3 through forced dimerization; ZNRF3 internalization and activity are post-translationally regulated by phosphorylation of a '4Y' endocytic motif—MET kinase phosphorylates this motif (inhibiting internalization) and PTPRK phosphatase dephosphorylates it (promoting internalization)—while the deubiquitinase USP42 stabilizes ZNRF3 at the membrane by antagonizing R-spondin-induced ubiquitination; additionally, SCFβ-TRCP ubiquitinates ZNRF3 itself in a phospho-degron-dependent manner to control its protein stability; beyond Wnt receptors, ZNRF3 also targets EGFR for ubiquitination and degradation via its extracellular domain; in vivo, ZNRF3 controls adrenal cortex homeostasis, liver metabolic zonation and hepatocyte proliferation, and mammalian gonadal sex determination through spatiotemporal regulation of Wnt/β-catenin signaling gradients.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ZNRF3 is a cell-surface transmembrane RING-domain E3 ubiquitin ligase that acts as a negative-feedback regulator of Wnt/β-catenin signaling by ubiquitinating Frizzled (FZD) and LRP6 Wnt receptors and driving their membrane clearance and degradation [#0]. Receptor targeting is selective rather than constitutive: ZNRF3 degrades Wnt-engaged FZD, with Wnt stimulation enhancing the FZD–DVL association and DVL serving as the adaptor that recruits ZNRF3 to FZD; fusing the DVL DEP domain to ZNRF3 bypasses this dependency [#5, #21]. Substrate preference is encoded in part by the transmembrane domain, which directs ZNRF3 toward particular FZD subtypes [#15], and the ligase additionally engages EGFR through its extracellular domain to drive EGFR ubiquitination and degradation [#16]. ZNRF3 is itself the effector arm of the R-spondin/LGR axis: R-spondin binds the ZNRF3 ectodomain via its Fu1 domain and, together with LGR4 (bound through Fu2), cross-links the receptors into a 2:2:2 ternary complex centered on a ZNRF3 dimer, sequestering and auto-inactivating ZNRF3 through forced dimerization and membrane clearance [#0, #1, #3, #20]. ZNRF3 abundance and surface activity are further tuned post-translationally—phosphorylation of a '4Y' endocytic motif by MET inhibits internalization while PTPRK dephosphorylation promotes it [#8, #9], the deubiquitinase USP42 stabilizes ZNRF3 against R-spondin-induced clearance [#10], and SCFβ-TRCP ubiquitinates ZNRF3 in a phospho-degron-dependent manner to control its stability [#7]. In vivo, this regulatory output sets Wnt/β-catenin gradients that govern adrenal cortex homeostasis [#13], hepatocyte proliferation and metabolic zonation [#11], and mammalian testis sex determination [#12]. Germline ZNRF3 variants cause human disease: RING-domain and RSPO-binding-domain variants produce neurodevelopmental disorders with macrocephaly or microcephaly respectively [#18], and exon-2/RSPO-binding-domain lesions cause congenital adrenal hypoplasia [#17], while 46,XY DSD-associated missense variants disrupt ZNRF3 activity [#12].\",\n  \"teleology\": [\n    {\n      \"year\": 2012,\n      \"claim\": \"Established ZNRF3 as the molecular identity of a membrane E3 ligase that limits Wnt signaling and the target of R-spondin, answering how R-spondin potentiates Wnt at the receptor level.\",\n      \"evidence\": \"Co-IP, surface receptor turnover, and in vivo Wnt/PCP assays defining FZD/LRP6 turnover and R-spondin/LGR4-induced ZNRF3 clearance\",\n      \"pmids\": [\"22575959\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of R-spondin/LGR4/ZNRF3 assembly not resolved\", \"Adaptor coupling ZNRF3 to FZD unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Resolved the structural logic of the dual-receptor model, showing R-spondin Fu1 clamps the ZNRF3 ectodomain while Fu2 engages LGR receptors and that binding enhances ZNRF3 ectodomain dimerization.\",\n      \"evidence\": \"X-ray crystallography of ZNRF3 ectodomain alone and bound to Rspo, SPR/binding measurements, Rspo chimera mutagenesis, and in vitro reconstitution of ternary complexes\",\n      \"pmids\": [\"24225776\", \"24349440\", \"24165923\", \"24050775\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of the full ternary complex not definitively established at this stage\", \"How ectodomain dimerization translates to catalytic auto-inactivation unresolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified DVL as the obligate adaptor recruiting ZNRF3 to FZD, explaining how a RING ligase reaches its receptor substrate.\",\n      \"evidence\": \"DVL knockout cells, reciprocal Co-IP, ubiquitination assays, and DEP-domain fusion rescue\",\n      \"pmids\": [\"25891077\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether DVL recruitment selects specific FZD subtypes not addressed\", \"Dependence on Wnt ligand engagement not yet defined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Confirmed that R-spondin cross-links LGR and ZNRF3 into a 2:2:2 assembly (versus 1:1:1 with RNF43), distinguishing the architectures of the two paralogs.\",\n      \"evidence\": \"Low-resolution X-ray crystallography of the ternary hLGR5–Rspo2–ZNRF3 complex\",\n      \"pmids\": [\"26123262\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Low resolution limits interface detail\", \"Functional consequence of differing stoichiometry untested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showed ZNRF3 stability is itself regulated by a phospho-degron, placing ZNRF3 protein levels under SCFβ-TRCP control analogous to β-catenin.\",\n      \"evidence\": \"Co-IP, ubiquitination assays, proteasome inhibition, and CKI-phosphorylation/degron analysis\",\n      \"pmids\": [\"29497989\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Physiological/in vivo relevance of β-TRCP-mediated turnover not established\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated ZNRF3 is required for mammalian testis sex determination and linked human ZNRF3 variants to 46,XY DSD via ectopic Wnt/β-catenin activity.\",\n      \"evidence\": \"Conditional KO mice with pathway epistasis, exome sequencing, and variant functional testing in human cells and zebrafish\",\n      \"pmids\": [\"29735715\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell-type-specific substrates in the gonad not defined\", \"Mechanism connecting ZNRF3 loss to Sox9 repression incompletely mapped\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined an in vivo, dosage-sensitive role for ZNRF3 in adrenal cortex homeostasis dependent on Porcupine-secreted Wnt and β-catenin.\",\n      \"evidence\": \"Adrenocortical conditional KO, Porcupine inhibitor treatment, and genetic β-catenin dosage reduction\",\n      \"pmids\": [\"30692207\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why ZNRF3 loss expands only the inner cortex unexplained\", \"Non-redundancy with RNF43 in adrenal context not mechanistically resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identified a '4Y' endocytic motif and its phosphatase PTPRK, revealing post-translational control of ZNRF3 internalization independent of R-spondin.\",\n      \"evidence\": \"Endocytic-signal mutagenesis, Xenopus loss-of-function, Wnt reporter and internalization assays\",\n      \"pmids\": [\"31934854\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase phosphorylating the motif not yet identified at this stage\", \"In vivo relevance in mammals untested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Completed the 4Y-motif regulatory circuit by identifying MET as the kinase opposing PTPRK, linking HGF/MET signaling to Wnt receptor stability.\",\n      \"evidence\": \"MET–ZNRF3 Co-IP, phosphorylation assays, pharmacological MET inhibition, internalization and Wnt reporter assays\",\n      \"pmids\": [\"34590584\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MET–ZNRF3 crosstalk operates in tumors in vivo not shown\", \"Quantitative balance of MET vs PTPRK control across tissues unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed USP42 deubiquitinates and stabilizes ZNRF3 at the membrane, adding a deubiquitinase layer that counters R-spondin-induced clearance.\",\n      \"evidence\": \"Co-IP, in vitro deubiquitination, membrane clearance, Wnt reporter, and organoid assays\",\n      \"pmids\": [\"33786993\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Regulation of USP42 activity itself not defined\", \"In vivo consequences of USP42–ZNRF3 axis untested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established that ZNRF3 and RNF43 cooperatively restrain Wnt to maintain liver metabolic zonation and limit hepatocyte proliferation and tumorigenesis.\",\n      \"evidence\": \"Liver-specific conditional single and double KO mice, scRNA-seq, chromatin accessibility, and proliferation/histology readouts\",\n      \"pmids\": [\"34129813\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of RNF43 compensatory upregulation unknown\", \"Direct receptor substrates driving zonation not pinpointed\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Refined the receptor cooperativity model, showing LGR4 (but not LGR5) forms a 2:2 complex with ZNRF3/RNF43 to confer high-affinity bivalent R-spondin binding.\",\n      \"evidence\": \"Whole-cell binding affinity measurements with monovalent and bivalent RSPO ligands and co-expression studies\",\n      \"pmids\": [\"37402772\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab whole-cell assays\", \"Structural basis of LGR4-specific cooperativity not resolved here\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Provided pharmacological proof-of-concept that engineered ZNRF3-binding peptides can clear ZNRF3 from the surface to activate Wnt, validating ZNRF3 as a druggable node.\",\n      \"evidence\": \"Disulfide-constrained peptide surface-clearance, ubiquitination, Wnt reporter, organoid, and valency-comparison assays\",\n      \"pmids\": [\"38056465\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of valency-dependent clearance not structurally defined\", \"In vivo efficacy/specificity untested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Mapped substrate selectivity to the transmembrane domain, showing ZNRF3 and RNF43 prefer distinct FZD subtypes and that TMD swaps redirect specificity.\",\n      \"evidence\": \"FZD endocytosis assays, TMD-swap mutagenesis, flow cytometry, surface receptor quantification\",\n      \"pmids\": [\"38969364\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular features within the TMD dictating preference not defined\", \"Physiological significance of subtype preference untested in vivo\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended ZNRF3 substrate range beyond Wnt receptors by identifying EGFR as an ectodomain-engaged target for ubiquitination and degradation.\",\n      \"evidence\": \"ZNRF3–EGFR Co-IP, ubiquitination assays, overexpression/KO cell growth assays, and proteogenomic correlation\",\n      \"pmids\": [\"41960900\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Relative contribution of EGFR vs Wnt-receptor targeting to phenotypes unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linked domain-specific germline ZNRF3 variants to opposite-direction Wnt dysregulation and human neurodevelopmental and adrenal phenotypes.\",\n      \"evidence\": \"Structural modeling and TCF/LEF reporter assays of RING- and RSPO-binding-domain variants; RT-PCR and reporter assays of ΔEx2-ZNRF3\",\n      \"pmids\": [\"39168120\", \"37878959\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Dominant-negative mechanism inferred from overexpression assays\", \"In vivo validation of variant effects lacking\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Reassessed disease-variant mechanism at endogenous levels, showing tumor-associated truncating and RSPO-domain variants act as loss-of-function (via ERAD/misfolding) rather than dominant-negative.\",\n      \"evidence\": \"Endogenous knock-in of variants, β-catenin signaling and protein stability assays, and 27°C temperature rescue\",\n      \"pmids\": [\"39674817\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Reconciliation with dominant-negative claims from overexpression studies incomplete\", \"Tissue-context dependence of variant behavior not addressed\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Provided a high-resolution structural mechanism for ZNRF3 inactivation, showing R-spondin/LGR4 assemble a 2:2:2 complex with a central ZNRF3 dimer whose forced dimerization underlies sequestration and auto-inactivation.\",\n      \"evidence\": \"Cryo-EM structures of LGR4, LGR4–RSPO2, and LGR4–RSPO2–ZNRF3 complexes\",\n      \"pmids\": [\"41034211\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic consequence of dimerization on RING activity not directly demonstrated\", \"Dynamics of complex assembly/disassembly not captured\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Clarified that ZNRF3 targets Wnt-engaged FZD selectively, with Wnt enhancing FZD–DVL association and DVL recruiting ZNRF3, integrating substrate selection with ligand sensing.\",\n      \"evidence\": \"FZD endocytosis assays, Co-IP, ZNRF3/RNF43 KO cells, and Wnt stimulation experiments (two concurrent studies)\",\n      \"pmids\": [\"41086253\", \"41070826\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Wnt biochemically licenses the FZD–DVL–ZNRF3 handoff not fully resolved\", \"Whether all FZD subtypes follow this Wnt-dependent rule untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the multiple regulatory inputs (R-spondin/LGR sequestration, 4Y phosphorylation, USP42/β-TRCP ubiquitin turnover, DVL recruitment, TMD-encoded substrate choice) are integrated to set tissue-specific Wnt gradients in vivo remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified quantitative model coupling surface ZNRF3 dynamics to β-catenin output across tissues\", \"Catalytic mechanism by which forced dimerization inactivates the RING ligase not directly tested\", \"Relative physiological weight of EGFR versus Wnt-receptor targeting unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 5, 16]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 5, 16]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 21]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 8, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 3, 21]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 5, 16]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [12, 13, 11]}\n    ],\n    \"complexes\": [\"RSPO–LGR4–ZNRF3 ternary (2:2:2) complex\"],\n    \"partners\": [\"RSPO1\", \"RSPO2\", \"LGR4\", \"DVL\", \"PTPRK\", \"MET\", \"USP42\", \"EGFR\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}