{"gene":"WDR4","run_date":"2026-06-11T09:02:06","timeline":{"discoveries":[{"year":2023,"finding":"Crystal structure of METTL1-WDR4 and cryo-EM structures of METTL1-WDR4-tRNA revealed that WDR4 serves as a scaffold for METTL1 and the tRNA T-arm; the composite protein surface recognizes the tRNA elbow through shape complementarity. The METTL1 N terminus couples cofactor (SAM) binding with conformational changes in the tRNA, catalytic loop, and WDR4 C terminus, acting as a switch to activate m7G methylation. S27 phosphorylation of the METTL1 N-terminal region inhibits methyltransferase activity by disrupting the catalytic centre.","method":"X-ray crystallography, cryo-EM, biochemical methyltransferase assays, mutagenesis (S27 phosphorylation site), cellular studies","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — two independent Nature papers in 2023 using orthogonal structural methods (crystal + cryo-EM) plus mutagenesis and biochemical validation, both reaching the same mechanistic conclusions","pmids":["36599982","36599985"],"is_preprint":false},{"year":2023,"finding":"WDR4 serves as a scaffold for METTL1 and the tRNA T-arm. The predicted disordered N-terminal region of METTL1 is part of the catalytic pocket and essential for methyltransferase activity. S27 phosphorylation in the METTL1 N-terminal region inhibits methyltransferase activity by locally disrupting the catalytic centre, providing a phosphorylation-mediated regulatory mechanism for METTL1-WDR4.","method":"Cryo-EM structure of METTL1-WDR4-tRNA, crystal structures of METTL1, biochemical methyltransferase assays, phospho-mimetic and phospho-dead mutagenesis, cellular assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution with structural validation and mutagenesis in a single rigorous study, independently corroborated by the companion paper (PMID 36599982)","pmids":["36599985"],"is_preprint":false},{"year":2015,"finding":"WDR4 is the human ortholog of yeast Trm82, an essential non-catalytic component of the Trm8/Trm82 holoenzyme. A missense mutation in WDR4 (and the corresponding yeast mutation) significantly reduces m7G46 methylation of specific tRNA species, establishing WDR4 as required for tRNA m7G46 modification in humans.","method":"Autozygome/exome analysis to identify disease mutation; functional validation by measuring m7G46 methylation of tRNA in patient cells and yeast carrying the corresponding mutation","journal":"Genome biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct tRNA methylation assay in both human patient-derived and yeast models, replicated across two families and organisms","pmids":["26416026"],"is_preprint":false},{"year":2018,"finding":"Mettl1 or Wdr4 knockout in mouse embryonic stem cells (mESCs) reduces m7G tRNA modification at a 'RAGGU' motif in the variable loop of a subset of 22 tRNAs, causes increased ribosome occupancy at corresponding codons (ribosome pausing), impairs mRNA translation globally, and results in defective ESC self-renewal and neural differentiation.","method":"m7G MeRIP-seq (methylated tRNA immunoprecipitation sequencing), TRAC-seq (tRNA reduction and cleavage sequencing), ribosome profiling, CRISPR/Cas9 knockout of Mettl1 and Wdr4, differentiation assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal sequencing methods plus genetic KO with defined cellular phenotypes in a single rigorous study","pmids":["29983320"],"is_preprint":false},{"year":2007,"finding":"The yeast Trm8-Trm82 (ortholog of METTL1-WDR4) complex requires both the D-stem and T-stem structures of tRNA for efficient methyl-transfer to G46. Tertiary base pairs in the D-stem are important but not essential, suggesting they support induced fit of the G46 base into the catalytic pocket.","method":"In vitro methyl-transfer activity assays with truncated and mutant yeast tRNA(Phe) transcripts","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro reconstituted enzyme assay with systematic tRNA mutants, single lab","pmids":["17382321"],"is_preprint":false},{"year":2007,"finding":"Active Trm8-Trm82 (yeast ortholog of METTL1-WDR4) heterodimer is only formed when both subunits are co-translated; mixing individually translated subunits does not produce active enzyme, indicating the association is translationally coupled. Kinetic parameters confirmed comparable activity to other tRNA methyltransferases.","method":"Wheat germ cell-free co-translation, in vitro methyltransferase activity assay, two-dimensional TLC and aniline cleavage to confirm m7G46 production","journal":"Journal of biotechnology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — reconstituted in vitro co-translation and enzymatic assay, single lab","pmids":["18164779"],"is_preprint":false},{"year":2016,"finding":"Drosophila Wuho (WDR4 ortholog) interacts with Flap Endonuclease 1 (FEN1) and localizes to sites of nascent DNA synthesis along with replication proteins FEN1 and PCNA. WH modulates FEN1 endonucleolytic activities in a substrate-dependent manner: it stimulates FEN1 flap endonuclease activity but inhibits gap endonuclease activity. Knockdown of WH in Drosophila, mouse, and human cells causes DNA strand breaks and apoptosis via ATM/Chk2/p53 signaling.","method":"Co-immunoprecipitation to identify FEN1 as binding partner; fluorescence microscopy for co-localization with replication proteins; siRNA knockdown in multiple species; FEN1 endonuclease activity assays with purified proteins; mouse knockout (early embryonic lethal with DNA damage)","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, in vitro enzymatic assay, live-cell localization, and KO phenotype across multiple species in a single study","pmids":["26751069"],"is_preprint":false},{"year":2020,"finding":"Drosophila Wuho (WDR4 ortholog) interacts epistatically with the TRIM-NHL protein Mei-p26 (human TRIM32 ortholog) to maintain ovarian germline stem cell homeostasis. In germline stem cells, Wh and Mei-p26 promote BMP stemness signaling; in GSC progeny they silence nanos translation, downregulate differentiation-related microRNAs, and suppress ribosomal biogenesis via dMyc. Human WDR4 interacts with TRIM32 in human cells.","method":"Genetic epistasis analysis (double mutants), Co-immunoprecipitation (Wh-Mei-p26, WDR4-TRIM32 in human cells), translation reporter assays, signaling pathway readouts","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis combined with Co-IP in both Drosophila and human cells, single lab, multiple phenotypic readouts","pmids":["31941704"],"is_preprint":false},{"year":2006,"finding":"Drosophila Wuho (WDR4 ortholog) is essential for spermatogenesis; wh null mutants arrest spermatogenesis at the elongating spermatid stage. In female wh mutants, cystocytes fail to arrest at the fourth mitotic cycle and do not undergo nurse-cell endoreplication. The WH protein contains five WD40 repeats and a bipartite nuclear localization signal.","method":"P-element mutagenesis, rescue experiments with transgenes (wh vs. top3beta), immunostaining, cytological analysis","journal":"Developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with transgenic rescue, defined cellular phenotype, single lab","pmids":["16762337"],"is_preprint":false},{"year":2023,"finding":"WDR4 acts as a substrate adaptor of the CUL4 E3 ubiquitin ligase and mediates ubiquitination and proteasomal degradation of PTPN23 (a component of the ESCRT complex). WDR4-mediated PTPN23 degradation suppresses lysosomal trafficking and degradation of EGFR and c-MET, thereby sustaining their signaling in NSCLC. A competing peptide that blocks PTPN23 binding to WDR4 promotes EGFR/c-MET degradation and inhibits EGFR TKI-resistant NSCLC growth.","method":"Unbiased ubiquitylome mass spectrometry, Co-IP, ubiquitination assays, lysosome trafficking assays, peptide competition experiments, in vitro and in vivo proliferation/invasion assays","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 2 / Moderate — ubiquitylome MS plus Co-IP plus functional rescue with competing peptide, multiple orthogonal methods, single lab","pmids":["37821451"],"is_preprint":false},{"year":2023,"finding":"WDR4 promotes cerebellar granule neuron progenitor (GNP) proliferation by inducing ubiquitination and degradation of Arhgap17, thereby activating Rac1 and facilitating cell cycle progression. Wdr4 deficiency in GNPs reduces cerebellar foliation and impairs Purkinje neuron organization, leading to locomotion defects.","method":"Conditional knockout mouse model (Wdr4 in GNPs), ubiquitination assays, Rac1 activity assays, rescue experiments with Arhgap17, immunofluorescence, behavioral locomotion tests","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditional KO with defined phenotype plus mechanistic ubiquitination assay and Rac1 activity measurements, multiple orthogonal methods, single lab","pmids":["36681682"],"is_preprint":false},{"year":2018,"finding":"Wuho (WDR4) deficiency in mouse embryonic fibroblasts (MEFs) induces γH2AX elevation (DNA damage), heterochromatin relaxation, p53 activation, caspase-mediated apoptosis, and p21-mediated G2/M cell cycle arrest.","method":"Tamoxifen-inducible Cre-mediated conditional knockout MEFs (CAGGCre-ER), western blot for γH2AX, p53, p21, caspase markers, flow cytometry for cell cycle","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — genetic KO with defined downstream pathway markers, single lab, no rescue experiment","pmids":["29574139"],"is_preprint":false},{"year":2021,"finding":"METTL1/WDR4-mediated m7G tRNA modification promotes translation of mRNAs enriched in m7G tRNA-decoded codons (codon usage-linked translation regulation); knockdown of METTL1 decreased translation of such mRNAs, impaired lung cancer cell proliferation, invasion, and tumorigenicity in vitro and in vivo.","method":"tRNA methylation profiling, mRNA translation profiling (ribosome footprinting), METTL1 mutagenesis (catalytic mutant), gain- and loss-of-function in lung cancer cell lines, xenograft models","journal":"Molecular therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — tRNA methylation + translation profiling + mutagenesis in a single study, single lab","pmids":["34371184"],"is_preprint":false},{"year":2021,"finding":"WDR4 is transcriptionally activated by c-MYC, and WDR4 promotes CCNB1 mRNA stability and translation in HCC by enhancing binding of EIF2A to CCNB1 mRNA. This defines a MYC/WDR4/CCNB1/PI3K/AKT/P53 signaling axis.","method":"ChIP assay for MYC binding to WDR4 promoter, RNA immunoprecipitation for EIF2A-CCNB1 mRNA interaction, mRNA stability assays, Western blot, luciferase reporter, loss-of-function and gain-of-function in HCC cells, xenograft models","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP and RIP plus mRNA stability assays, multiple orthogonal methods, single lab","pmids":["34244479"],"is_preprint":false},{"year":2023,"finding":"WDR4 promotes nuclear localization of DDX20 and acts as an adaptor to bridge DDX20 and Egr1, thereby inhibiting Egr1-driven transcriptional expression of ARRB2, promoting bladder cancer lymphatic metastasis and progression.","method":"Co-immunoprecipitation (WDR4-DDX20, WDR4-Egr1), nuclear localization assay, luciferase reporter for ARRB2 transcription, loss-of-function assays in bladder cancer cells and in vivo","journal":"Oncogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus transcription reporter plus nuclear localization, multiple methods, single lab","pmids":["37783676"],"is_preprint":false},{"year":2024,"finding":"WDR4 modulates m7G modification at internal sites of tumor-promoting mRNAs by forming a WDR4-METTL1 protein complex (confirmed by Co-IP in Huh7 cells). WDR4 knockdown reduces both mRNA and protein levels of METTL1, indirectly reducing the WDR4-METTL1 complex.","method":"Co-immunoprecipitation (WDR4-METTL1), m7G-MeRIP-seq, RNA-seq, dot blot, CCK-8, colony formation, xenograft tumor models","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP establishing complex formation supported by MeRIP-seq methylation mapping, single lab","pmids":["38493882"],"is_preprint":false},{"year":2025,"finding":"Cytoplasmic WDR4, independently of m7G tRNA modification, directly interacts with eIF4E2 to enhance eIF4E-mediated selective translation of ABCA1, promoting membrane cholesterol efflux and maintaining pro-tumoral macrophage polarization in HCC-associated tumor-associated macrophages (TAMs).","method":"Co-immunoprecipitation (WDR4-eIF4E2), polysome profiling/selective translation assays, cholesterol efflux assays, WDR4 silencing in TAMs via CpG-siRNA delivery, in vivo tumor models","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — Co-IP plus translation profiling plus functional cholesterol efflux rescue, multiple orthogonal methods, published in high-tier journal, single lab","pmids":["41315768"],"is_preprint":false},{"year":2024,"finding":"WDR4 loss-of-function is associated with increased protein synthesis, upregulation of proteasomal activity, and reduction of free ubiquitin precursor pools, leading to impaired ciliogenesis. Inhibition of proteasomal activity or supplementation with free ubiquitin restores normal ciliogenesis and ameliorates microcephaly phenotypes.","method":"Human fibroblasts, zebrafish embryos, patient-derived cells; proteasome activity assays, ubiquitin pool measurement, cilia formation assays, proteasome inhibitor and ubiquitin supplementation rescue experiments","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple model systems with pharmacological and genetic rescue, single lab","pmids":["39251572"],"is_preprint":false},{"year":2025,"finding":"In Drosophila, Wdr4 (WDR4 ortholog) cooperates with Mettl1 to catalyze m7G modification of let-7 miRNA. Loss of Wdr4 or Mettl1 reduces let-7 levels, aberrantly activating TOR-JNK-dMyc signaling, driving elevated ribosome biogenesis, intestinal stem cell overproliferation, and intestinal dysplasia. Expression of human WDR4 and METTL1 (but not catalytic-dead METTL1 mutant) rescues ISC homeostasis.","method":"Drosophila genetic loss-of-function, let-7 miRNA modification assays, TOR/JNK pathway readouts, ribosome biogenesis assays, transgenic human WDR4/METTL1 rescue experiments with catalytic-dead mutant controls","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with orthologous rescue including catalytic-dead mutant control, single lab","pmids":["41663759"],"is_preprint":false},{"year":2025,"finding":"METTL1/WDR4-mediated m7G methylation stabilizes SCLT1 mRNA; knockdown reduces SCLT1 methylation and mRNA stability, while wild-type but not catalytically inactive METTL1 restores stability. METTL1/WDR4-mediated m7G modification of SCLT1 activates the NF-κB signaling pathway to confer gefitinib resistance in NSCLC.","method":"m7G MeRIP-seq, RNA-seq, mRNA stability assays, catalytic mutant rescue experiments, NF-κB pathway assays, xenograft models","journal":"Genomics, proteomics & bioinformatics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — MeRIP-seq plus catalytic mutant rescue plus pathway assays, multiple orthogonal methods, single lab","pmids":["40857569"],"is_preprint":false},{"year":2025,"finding":"WDR4 overexpression reshapes the tRNA m7G methylome in adipocytes, enhancing translation of BMP8B; BMP8B knockdown partially counteracts WDR4-mediated mitophagy and adipocyte browning, placing WDR4-driven tRNA m7G modification upstream of BMP8B translation in the browning pathway.","method":"TRAC-seq, tRNA m7G methylome profiling, BMP8B knockdown rescue, mitophagy markers (LC3, mitochondrial ultrastructure), 3T3-L1 overexpression/knockout experiments","journal":"Adipocyte","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single model (3T3-L1 cells), rescue partially restores phenotype; no structural or reconstitution validation","pmids":["41292047"],"is_preprint":false},{"year":2025,"finding":"WDR4 interacts with GSK3β (identified by Co-IP-LC/MS) and promotes GSK3β phosphorylation, thereby activating the β-catenin pathway to promote CRC proliferation, migration, and invasion.","method":"Co-IP-LC/MS to identify GSK3β binding, western blot for GSK3β phosphorylation, β-catenin pathway readouts, loss-of-function and gain-of-function in CRC cells and xenograft models","journal":"Biochemistry and cell biology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP/MS identification with downstream pathway readout, single lab, no reconstitution","pmids":["40009829"],"is_preprint":false}],"current_model":"WDR4 (Trm82/TRMT82/Wuho) is a non-catalytic WD40-repeat scaffold protein that forms the METTL1-WDR4 heterodimeric methyltransferase complex, in which WDR4 positions both METTL1 and the tRNA T-arm for m7G46 methylation of a subset of tRNAs; structural studies reveal that the METTL1 N-terminus, partly ordered by WDR4 contact, constitutes the catalytic centre and acts as a conformational switch linking SAM-cofactor binding to tRNA methylation, with S27 phosphorylation of METTL1 inhibiting this activity; beyond its role in tRNA modification—which globally shapes mRNA translation through codon usage—WDR4 also functions as a substrate adaptor of the CUL4 E3 ubiquitin ligase (mediating ubiquitination of PTPN23 and Arhgap17 to control EGFR/c-MET trafficking and Rac1 activity, respectively), and in macrophages acts independently of m7G modification by binding eIF4E2 to drive selective ABCA1 translation and cholesterol efflux."},"narrative":{"mechanistic_narrative":"WDR4 is a non-catalytic WD40-repeat scaffold protein best characterized as the obligate partner of METTL1 in the heterodimeric tRNA methyltransferase that installs the m7G46 modification on a defined subset of tRNAs [PMID:36599982, PMID:36599985, PMID:26416026]. Structural studies establish that WDR4 positions both METTL1 and the tRNA T-arm, with the composite protein surface recognizing the tRNA elbow through shape complementarity; the METTL1 N-terminus, partly ordered by WDR4 contact, forms the catalytic centre and acts as a conformational switch coupling SAM binding to methyl transfer, an activity inhibited by S27 phosphorylation [PMID:36599982, PMID:36599985]. Efficient methylation requires both the D-stem and T-stem of the tRNA substrate, and the active heterodimer assembles only through co-translational association of the two subunits [PMID:17382321, PMID:18164779]. Through this modification, METTL1-WDR4 globally shapes mRNA translation in a codon-usage-dependent manner: loss reduces ribosome transit at cognate codons, impairs translation of mRNAs enriched in m7G-decoded codons, and disrupts embryonic stem cell self-renewal and neural differentiation [PMID:29983320, PMID:34371184]. Beyond tRNA, the complex deposits internal m7G marks that stabilize tumor-promoting mRNAs and miRNAs [PMID:38493882, PMID:41663759, PMID:40857569]. WDR4 also operates independently of its methyltransferase role: it serves as a substrate adaptor of the CUL4 E3 ubiquitin ligase, directing ubiquitination and proteasomal degradation of PTPN23 to sustain EGFR/c-MET signaling and of Arhgap17 to activate Rac1 and drive neural progenitor proliferation [PMID:37821451, PMID:36681682]; and in tumor-associated macrophages it binds eIF4E2 to selectively translate ABCA1 and promote cholesterol efflux [PMID:41315768]. A missense mutation in WDR4 that reduces tRNA m7G46 methylation causes a human microcephalic primordial dwarfism, with disease-relevant impairment of ciliogenesis linked to dysregulated protein synthesis and depletion of free ubiquitin pools [PMID:26416026, PMID:39251572].","teleology":[{"year":2006,"claim":"Established that the WDR4 ortholog is required for normal development in a whole organism, framing it as a five-WD40-repeat protein with developmental rather than purely housekeeping functions.","evidence":"P-element mutagenesis and transgenic rescue in Drosophila showing spermatogenesis arrest and female germline cell-cycle defects","pmids":["16762337"],"confidence":"Medium","gaps":["Molecular mechanism not defined","No link to tRNA modification yet established","Phenotype is ortholog-based, not human"]},{"year":2007,"claim":"Defined the biochemical substrate requirements and assembly logic of the methyltransferase, showing the heterodimer requires intact tRNA D- and T-stem structure and forms an active enzyme only via co-translational subunit association.","evidence":"In vitro methyl-transfer assays with truncated/mutant yeast tRNA(Phe) and wheat-germ co-translation reconstitution","pmids":["17382321","18164779"],"confidence":"Medium","gaps":["No structural model of recognition","Performed on yeast orthologs only","Single-lab in vitro reconstitution"]},{"year":2015,"claim":"Linked WDR4 to human disease and confirmed its required role in tRNA m7G46 modification, showing a missense mutation reduces methylation of specific tRNAs.","evidence":"Autozygome/exome analysis of patient families plus tRNA m7G46 assays in patient cells and matched yeast mutants","pmids":["26416026"],"confidence":"High","gaps":["Translational consequences of the hypomorph not measured","How loss of m7G causes the clinical phenotype unresolved"]},{"year":2018,"claim":"Demonstrated the functional output of WDR4-dependent m7G: it prevents ribosome pausing at cognate codons and is required for stem cell self-renewal and differentiation.","evidence":"CRISPR knockout of Wdr4/Mettl1 in mESCs with m7G MeRIP-seq, TRAC-seq, ribosome profiling, and differentiation assays","pmids":["29983320"],"confidence":"High","gaps":["Specific mRNAs driving phenotype not pinpointed","Does not address non-methyltransferase roles"]},{"year":2016,"claim":"Identified a methyltransferase-independent role at replication forks, where the WDR4 ortholog binds FEN1 and modulates its nuclease activity, with loss triggering DNA damage signaling.","evidence":"Reciprocal Co-IP, co-localization with PCNA/FEN1, in vitro FEN1 nuclease assays, and knockdown/KO across Drosophila, mouse, and human cells","pmids":["26751069"],"confidence":"High","gaps":["Relationship to the METTL1 tRNA function unclear","Whether human WDR4 directly modulates FEN1 in vivo not resolved"]},{"year":2020,"claim":"Extended the developmental/translational role by showing WDR4 partners with a TRIM-NHL protein to control germline stem cell homeostasis and ribosome biogenesis.","evidence":"Genetic epistasis with Mei-p26 plus Co-IP of WDR4-TRIM32 in human cells and translation reporter assays","pmids":["31941704"],"confidence":"Medium","gaps":["Direct biochemical mechanism of WDR4-TRIM32 cooperation undefined","Largely ortholog-based"]},{"year":2021,"claim":"Connected the m7G/translation axis to cancer and placed WDR4 downstream of MYC, implicating codon-usage-linked translation and mRNA stability control in tumorigenesis.","evidence":"tRNA/translation profiling with catalytic mutants in lung cancer; ChIP/RIP/mRNA-stability assays defining a MYC/WDR4/CCNB1 axis in HCC","pmids":["34371184","34244479"],"confidence":"Medium","gaps":["EIF2A-CCNB1 mechanism is correlative","Whether translation defects fully account for tumor phenotypes unresolved"]},{"year":2023,"claim":"Resolved the atomic mechanism of the methyltransferase, showing WDR4 scaffolds METTL1 and the tRNA T-arm and that the METTL1 N-terminus is a SAM-coupled conformational switch regulated by S27 phosphorylation.","evidence":"Crystal and cryo-EM structures of METTL1-WDR4(-tRNA) with biochemical and phospho-mimetic mutagenesis (two independent Nature studies)","pmids":["36599982","36599985"],"confidence":"High","gaps":["Upstream kinase for S27 not identified","Structural basis of tRNA subset selectivity not fully mapped"]},{"year":2023,"claim":"Established WDR4 as a CUL4 E3 ligase substrate adaptor, revealing a ubiquitination-based, methyltransferase-independent function controlling receptor trafficking and Rac1 signaling.","evidence":"Ubiquitylome MS, Co-IP, ubiquitination/trafficking assays and peptide competition for PTPN23 (NSCLC); conditional KO plus Arhgap17 rescue and Rac1 assays for cerebellar progenitors","pmids":["37821451","36681682"],"confidence":"High","gaps":["How WDR4 partitions between methyltransferase and ligase-adaptor roles unknown","Direct CUL4-WDR4 architecture not structurally defined"]},{"year":2023,"claim":"Added a nuclear adaptor function, with WDR4 bridging DDX20 and Egr1 to repress ARRB2 transcription in metastatic cancer.","evidence":"Co-IP, nuclear localization and luciferase reporter assays with loss-of-function in bladder cancer cells and in vivo","pmids":["37783676"],"confidence":"Medium","gaps":["Direct vs indirect bridging not biochemically dissected","Single-lab, single-context"]},{"year":2024,"claim":"Linked WDR4 loss to a microcephaly-relevant cellular defect, showing dysregulated protein synthesis and ubiquitin depletion impair ciliogenesis, rescuable by proteasome inhibition or ubiquitin supply.","evidence":"Patient fibroblasts and zebrafish with proteasome/ubiquitin assays, ciliogenesis readouts, and pharmacological/genetic rescue","pmids":["39251572"],"confidence":"Medium","gaps":["Mechanistic chain from m7G loss to ubiquitin depletion not fully defined","Single lab"]},{"year":2025,"claim":"Defined a fully methyltransferase-independent cytoplasmic translational function, with WDR4 binding eIF4E2 to selectively translate ABCA1 and reprogram tumor-associated macrophages.","evidence":"Co-IP, polysome/selective translation profiling, cholesterol efflux assays, and CpG-siRNA WDR4 silencing in TAMs in vivo","pmids":["41315768"],"confidence":"High","gaps":["Structural basis of WDR4-eIF4E2 interaction unknown","Selectivity for ABCA1 mRNA unexplained"]},{"year":2025,"claim":"Broadened the m7G-dependent target repertoire to internal mRNA and miRNA sites controlling stress, growth, and drug-resistance pathways.","evidence":"MeRIP-seq with catalytic-mutant rescue defining m7G of SCLT1 mRNA (NF-kB/gefitinib resistance) and let-7 miRNA (TOR-JNK-dMyc); plus adipocyte browning and GSK3beta/beta-catenin reports","pmids":["40857569","41663759","41292047","40009829"],"confidence":"Low","gaps":["Adipocyte browning and GSK3beta findings are single-lab/single-model and not independently confirmed","Direct vs indirect effects of methylation on each target not always separated"]},{"year":null,"claim":"How WDR4 is partitioned and regulated among its distinct roles — methyltransferase scaffold, CUL4 ligase adaptor, eIF4E2-associated translation factor, and replication/transcription adaptor — and what determines context-specific function remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying regulatory model linking the moonlighting activities","Determinants of subcellular partitioning unknown","Upstream signals controlling each function undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[0,2,3,4]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[9,14,16]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[13,15]},{"term_id":"GO:0045182","term_label":"translation regulator activity","supporting_discovery_ids":[16,12]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[16]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[8,14]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,3]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[3,12,16]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[9]}],"complexes":["METTL1-WDR4 methyltransferase","CUL4 E3 ubiquitin ligase"],"partners":["METTL1","EIF4E2","PTPN23","ARHGAP17","FEN1","TRIM32","DDX20","EIF2A"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P57081","full_name":"tRNA (guanine-N(7)-)-methyltransferase non-catalytic subunit WDR4","aliases":["Protein Wuho homolog","hWH","WD repeat-containing protein 4"],"length_aa":412,"mass_kda":45.5,"function":"Non-catalytic component of the METTL1-WDR4 methyltransferase complex required for the formation of N(7)-methylguanine in a subset of RNA species, such as tRNAs, mRNAs and microRNAs (miRNAs) (PubMed:12403464, PubMed:31031083, PubMed:31031084, PubMed:36599982, PubMed:36599985, PubMed:37369656). In the METTL1-WDR4 methyltransferase complex, WDR4 acts as a scaffold for tRNA-binding (PubMed:36599982, PubMed:36599985, PubMed:37369656). Required for the formation of N(7)-methylguanine at position 46 (m7G46) in a large subset of tRNAs that contain the 5'-RAGGU-3' motif within the variable loop (PubMed:12403464, PubMed:34352206, PubMed:34352207, PubMed:36599982, PubMed:36599985, PubMed:37369656). M7G46 interacts with C13-G22 in the D-loop to stabilize tRNA tertiary structure and protect tRNAs from decay (PubMed:36599982, PubMed:36599985). Also required for the formation of N(7)-methylguanine at internal sites in a subset of mRNAs (PubMed:31031084, PubMed:37379838). Also required for methylation of a specific subset of miRNAs, such as let-7 (PubMed:31031083). Independently of METTL1, also plays a role in genome stability: localizes at the DNA replication site and regulates endonucleolytic activities of FEN1 (PubMed:26751069)","subcellular_location":"Nucleus; Chromosome","url":"https://www.uniprot.org/uniprotkb/P57081/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/WDR4","classification":"Not Classified","n_dependent_lines":441,"n_total_lines":1208,"dependency_fraction":0.3650662251655629},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/WDR4","total_profiled":1310},"omim":[{"mim_id":"618347","title":"GALLOWAY-MOWAT SYNDROME 6; GAMOS6","url":"https://www.omim.org/entry/618347"},{"mim_id":"618346","title":"MICROCEPHALY, GROWTH DEFICIENCY, SEIZURES, AND BRAIN MALFORMATIONS; MIGSB","url":"https://www.omim.org/entry/618346"},{"mim_id":"612032","title":"DPY30 HISTONE METHYLTRANSFERASE COMPLEX REGULATORY SUBUNIT; 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The METTL1 N terminus couples cofactor (SAM) binding with conformational changes in the tRNA, catalytic loop, and WDR4 C terminus, acting as a switch to activate m7G methylation. S27 phosphorylation of the METTL1 N-terminal region inhibits methyltransferase activity by disrupting the catalytic centre.\",\n      \"method\": \"X-ray crystallography, cryo-EM, biochemical methyltransferase assays, mutagenesis (S27 phosphorylation site), cellular studies\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — two independent Nature papers in 2023 using orthogonal structural methods (crystal + cryo-EM) plus mutagenesis and biochemical validation, both reaching the same mechanistic conclusions\",\n      \"pmids\": [\"36599982\", \"36599985\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"WDR4 serves as a scaffold for METTL1 and the tRNA T-arm. The predicted disordered N-terminal region of METTL1 is part of the catalytic pocket and essential for methyltransferase activity. S27 phosphorylation in the METTL1 N-terminal region inhibits methyltransferase activity by locally disrupting the catalytic centre, providing a phosphorylation-mediated regulatory mechanism for METTL1-WDR4.\",\n      \"method\": \"Cryo-EM structure of METTL1-WDR4-tRNA, crystal structures of METTL1, biochemical methyltransferase assays, phospho-mimetic and phospho-dead mutagenesis, cellular assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution with structural validation and mutagenesis in a single rigorous study, independently corroborated by the companion paper (PMID 36599982)\",\n      \"pmids\": [\"36599985\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"WDR4 is the human ortholog of yeast Trm82, an essential non-catalytic component of the Trm8/Trm82 holoenzyme. A missense mutation in WDR4 (and the corresponding yeast mutation) significantly reduces m7G46 methylation of specific tRNA species, establishing WDR4 as required for tRNA m7G46 modification in humans.\",\n      \"method\": \"Autozygome/exome analysis to identify disease mutation; functional validation by measuring m7G46 methylation of tRNA in patient cells and yeast carrying the corresponding mutation\",\n      \"journal\": \"Genome biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct tRNA methylation assay in both human patient-derived and yeast models, replicated across two families and organisms\",\n      \"pmids\": [\"26416026\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Mettl1 or Wdr4 knockout in mouse embryonic stem cells (mESCs) reduces m7G tRNA modification at a 'RAGGU' motif in the variable loop of a subset of 22 tRNAs, causes increased ribosome occupancy at corresponding codons (ribosome pausing), impairs mRNA translation globally, and results in defective ESC self-renewal and neural differentiation.\",\n      \"method\": \"m7G MeRIP-seq (methylated tRNA immunoprecipitation sequencing), TRAC-seq (tRNA reduction and cleavage sequencing), ribosome profiling, CRISPR/Cas9 knockout of Mettl1 and Wdr4, differentiation assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal sequencing methods plus genetic KO with defined cellular phenotypes in a single rigorous study\",\n      \"pmids\": [\"29983320\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The yeast Trm8-Trm82 (ortholog of METTL1-WDR4) complex requires both the D-stem and T-stem structures of tRNA for efficient methyl-transfer to G46. Tertiary base pairs in the D-stem are important but not essential, suggesting they support induced fit of the G46 base into the catalytic pocket.\",\n      \"method\": \"In vitro methyl-transfer activity assays with truncated and mutant yeast tRNA(Phe) transcripts\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro reconstituted enzyme assay with systematic tRNA mutants, single lab\",\n      \"pmids\": [\"17382321\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Active Trm8-Trm82 (yeast ortholog of METTL1-WDR4) heterodimer is only formed when both subunits are co-translated; mixing individually translated subunits does not produce active enzyme, indicating the association is translationally coupled. Kinetic parameters confirmed comparable activity to other tRNA methyltransferases.\",\n      \"method\": \"Wheat germ cell-free co-translation, in vitro methyltransferase activity assay, two-dimensional TLC and aniline cleavage to confirm m7G46 production\",\n      \"journal\": \"Journal of biotechnology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — reconstituted in vitro co-translation and enzymatic assay, single lab\",\n      \"pmids\": [\"18164779\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Drosophila Wuho (WDR4 ortholog) interacts with Flap Endonuclease 1 (FEN1) and localizes to sites of nascent DNA synthesis along with replication proteins FEN1 and PCNA. WH modulates FEN1 endonucleolytic activities in a substrate-dependent manner: it stimulates FEN1 flap endonuclease activity but inhibits gap endonuclease activity. Knockdown of WH in Drosophila, mouse, and human cells causes DNA strand breaks and apoptosis via ATM/Chk2/p53 signaling.\",\n      \"method\": \"Co-immunoprecipitation to identify FEN1 as binding partner; fluorescence microscopy for co-localization with replication proteins; siRNA knockdown in multiple species; FEN1 endonuclease activity assays with purified proteins; mouse knockout (early embryonic lethal with DNA damage)\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, in vitro enzymatic assay, live-cell localization, and KO phenotype across multiple species in a single study\",\n      \"pmids\": [\"26751069\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Drosophila Wuho (WDR4 ortholog) interacts epistatically with the TRIM-NHL protein Mei-p26 (human TRIM32 ortholog) to maintain ovarian germline stem cell homeostasis. In germline stem cells, Wh and Mei-p26 promote BMP stemness signaling; in GSC progeny they silence nanos translation, downregulate differentiation-related microRNAs, and suppress ribosomal biogenesis via dMyc. Human WDR4 interacts with TRIM32 in human cells.\",\n      \"method\": \"Genetic epistasis analysis (double mutants), Co-immunoprecipitation (Wh-Mei-p26, WDR4-TRIM32 in human cells), translation reporter assays, signaling pathway readouts\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis combined with Co-IP in both Drosophila and human cells, single lab, multiple phenotypic readouts\",\n      \"pmids\": [\"31941704\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Drosophila Wuho (WDR4 ortholog) is essential for spermatogenesis; wh null mutants arrest spermatogenesis at the elongating spermatid stage. In female wh mutants, cystocytes fail to arrest at the fourth mitotic cycle and do not undergo nurse-cell endoreplication. The WH protein contains five WD40 repeats and a bipartite nuclear localization signal.\",\n      \"method\": \"P-element mutagenesis, rescue experiments with transgenes (wh vs. top3beta), immunostaining, cytological analysis\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with transgenic rescue, defined cellular phenotype, single lab\",\n      \"pmids\": [\"16762337\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"WDR4 acts as a substrate adaptor of the CUL4 E3 ubiquitin ligase and mediates ubiquitination and proteasomal degradation of PTPN23 (a component of the ESCRT complex). WDR4-mediated PTPN23 degradation suppresses lysosomal trafficking and degradation of EGFR and c-MET, thereby sustaining their signaling in NSCLC. A competing peptide that blocks PTPN23 binding to WDR4 promotes EGFR/c-MET degradation and inhibits EGFR TKI-resistant NSCLC growth.\",\n      \"method\": \"Unbiased ubiquitylome mass spectrometry, Co-IP, ubiquitination assays, lysosome trafficking assays, peptide competition experiments, in vitro and in vivo proliferation/invasion assays\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ubiquitylome MS plus Co-IP plus functional rescue with competing peptide, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"37821451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"WDR4 promotes cerebellar granule neuron progenitor (GNP) proliferation by inducing ubiquitination and degradation of Arhgap17, thereby activating Rac1 and facilitating cell cycle progression. Wdr4 deficiency in GNPs reduces cerebellar foliation and impairs Purkinje neuron organization, leading to locomotion defects.\",\n      \"method\": \"Conditional knockout mouse model (Wdr4 in GNPs), ubiquitination assays, Rac1 activity assays, rescue experiments with Arhgap17, immunofluorescence, behavioral locomotion tests\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with defined phenotype plus mechanistic ubiquitination assay and Rac1 activity measurements, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"36681682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Wuho (WDR4) deficiency in mouse embryonic fibroblasts (MEFs) induces γH2AX elevation (DNA damage), heterochromatin relaxation, p53 activation, caspase-mediated apoptosis, and p21-mediated G2/M cell cycle arrest.\",\n      \"method\": \"Tamoxifen-inducible Cre-mediated conditional knockout MEFs (CAGGCre-ER), western blot for γH2AX, p53, p21, caspase markers, flow cytometry for cell cycle\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — genetic KO with defined downstream pathway markers, single lab, no rescue experiment\",\n      \"pmids\": [\"29574139\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"METTL1/WDR4-mediated m7G tRNA modification promotes translation of mRNAs enriched in m7G tRNA-decoded codons (codon usage-linked translation regulation); knockdown of METTL1 decreased translation of such mRNAs, impaired lung cancer cell proliferation, invasion, and tumorigenicity in vitro and in vivo.\",\n      \"method\": \"tRNA methylation profiling, mRNA translation profiling (ribosome footprinting), METTL1 mutagenesis (catalytic mutant), gain- and loss-of-function in lung cancer cell lines, xenograft models\",\n      \"journal\": \"Molecular therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — tRNA methylation + translation profiling + mutagenesis in a single study, single lab\",\n      \"pmids\": [\"34371184\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"WDR4 is transcriptionally activated by c-MYC, and WDR4 promotes CCNB1 mRNA stability and translation in HCC by enhancing binding of EIF2A to CCNB1 mRNA. This defines a MYC/WDR4/CCNB1/PI3K/AKT/P53 signaling axis.\",\n      \"method\": \"ChIP assay for MYC binding to WDR4 promoter, RNA immunoprecipitation for EIF2A-CCNB1 mRNA interaction, mRNA stability assays, Western blot, luciferase reporter, loss-of-function and gain-of-function in HCC cells, xenograft models\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP and RIP plus mRNA stability assays, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"34244479\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"WDR4 promotes nuclear localization of DDX20 and acts as an adaptor to bridge DDX20 and Egr1, thereby inhibiting Egr1-driven transcriptional expression of ARRB2, promoting bladder cancer lymphatic metastasis and progression.\",\n      \"method\": \"Co-immunoprecipitation (WDR4-DDX20, WDR4-Egr1), nuclear localization assay, luciferase reporter for ARRB2 transcription, loss-of-function assays in bladder cancer cells and in vivo\",\n      \"journal\": \"Oncogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus transcription reporter plus nuclear localization, multiple methods, single lab\",\n      \"pmids\": [\"37783676\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"WDR4 modulates m7G modification at internal sites of tumor-promoting mRNAs by forming a WDR4-METTL1 protein complex (confirmed by Co-IP in Huh7 cells). WDR4 knockdown reduces both mRNA and protein levels of METTL1, indirectly reducing the WDR4-METTL1 complex.\",\n      \"method\": \"Co-immunoprecipitation (WDR4-METTL1), m7G-MeRIP-seq, RNA-seq, dot blot, CCK-8, colony formation, xenograft tumor models\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP establishing complex formation supported by MeRIP-seq methylation mapping, single lab\",\n      \"pmids\": [\"38493882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cytoplasmic WDR4, independently of m7G tRNA modification, directly interacts with eIF4E2 to enhance eIF4E-mediated selective translation of ABCA1, promoting membrane cholesterol efflux and maintaining pro-tumoral macrophage polarization in HCC-associated tumor-associated macrophages (TAMs).\",\n      \"method\": \"Co-immunoprecipitation (WDR4-eIF4E2), polysome profiling/selective translation assays, cholesterol efflux assays, WDR4 silencing in TAMs via CpG-siRNA delivery, in vivo tumor models\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus translation profiling plus functional cholesterol efflux rescue, multiple orthogonal methods, published in high-tier journal, single lab\",\n      \"pmids\": [\"41315768\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"WDR4 loss-of-function is associated with increased protein synthesis, upregulation of proteasomal activity, and reduction of free ubiquitin precursor pools, leading to impaired ciliogenesis. Inhibition of proteasomal activity or supplementation with free ubiquitin restores normal ciliogenesis and ameliorates microcephaly phenotypes.\",\n      \"method\": \"Human fibroblasts, zebrafish embryos, patient-derived cells; proteasome activity assays, ubiquitin pool measurement, cilia formation assays, proteasome inhibitor and ubiquitin supplementation rescue experiments\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple model systems with pharmacological and genetic rescue, single lab\",\n      \"pmids\": [\"39251572\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In Drosophila, Wdr4 (WDR4 ortholog) cooperates with Mettl1 to catalyze m7G modification of let-7 miRNA. Loss of Wdr4 or Mettl1 reduces let-7 levels, aberrantly activating TOR-JNK-dMyc signaling, driving elevated ribosome biogenesis, intestinal stem cell overproliferation, and intestinal dysplasia. Expression of human WDR4 and METTL1 (but not catalytic-dead METTL1 mutant) rescues ISC homeostasis.\",\n      \"method\": \"Drosophila genetic loss-of-function, let-7 miRNA modification assays, TOR/JNK pathway readouts, ribosome biogenesis assays, transgenic human WDR4/METTL1 rescue experiments with catalytic-dead mutant controls\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with orthologous rescue including catalytic-dead mutant control, single lab\",\n      \"pmids\": [\"41663759\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"METTL1/WDR4-mediated m7G methylation stabilizes SCLT1 mRNA; knockdown reduces SCLT1 methylation and mRNA stability, while wild-type but not catalytically inactive METTL1 restores stability. METTL1/WDR4-mediated m7G modification of SCLT1 activates the NF-κB signaling pathway to confer gefitinib resistance in NSCLC.\",\n      \"method\": \"m7G MeRIP-seq, RNA-seq, mRNA stability assays, catalytic mutant rescue experiments, NF-κB pathway assays, xenograft models\",\n      \"journal\": \"Genomics, proteomics & bioinformatics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MeRIP-seq plus catalytic mutant rescue plus pathway assays, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"40857569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"WDR4 overexpression reshapes the tRNA m7G methylome in adipocytes, enhancing translation of BMP8B; BMP8B knockdown partially counteracts WDR4-mediated mitophagy and adipocyte browning, placing WDR4-driven tRNA m7G modification upstream of BMP8B translation in the browning pathway.\",\n      \"method\": \"TRAC-seq, tRNA m7G methylome profiling, BMP8B knockdown rescue, mitophagy markers (LC3, mitochondrial ultrastructure), 3T3-L1 overexpression/knockout experiments\",\n      \"journal\": \"Adipocyte\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single model (3T3-L1 cells), rescue partially restores phenotype; no structural or reconstitution validation\",\n      \"pmids\": [\"41292047\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"WDR4 interacts with GSK3β (identified by Co-IP-LC/MS) and promotes GSK3β phosphorylation, thereby activating the β-catenin pathway to promote CRC proliferation, migration, and invasion.\",\n      \"method\": \"Co-IP-LC/MS to identify GSK3β binding, western blot for GSK3β phosphorylation, β-catenin pathway readouts, loss-of-function and gain-of-function in CRC cells and xenograft models\",\n      \"journal\": \"Biochemistry and cell biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP/MS identification with downstream pathway readout, single lab, no reconstitution\",\n      \"pmids\": [\"40009829\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"WDR4 (Trm82/TRMT82/Wuho) is a non-catalytic WD40-repeat scaffold protein that forms the METTL1-WDR4 heterodimeric methyltransferase complex, in which WDR4 positions both METTL1 and the tRNA T-arm for m7G46 methylation of a subset of tRNAs; structural studies reveal that the METTL1 N-terminus, partly ordered by WDR4 contact, constitutes the catalytic centre and acts as a conformational switch linking SAM-cofactor binding to tRNA methylation, with S27 phosphorylation of METTL1 inhibiting this activity; beyond its role in tRNA modification—which globally shapes mRNA translation through codon usage—WDR4 also functions as a substrate adaptor of the CUL4 E3 ubiquitin ligase (mediating ubiquitination of PTPN23 and Arhgap17 to control EGFR/c-MET trafficking and Rac1 activity, respectively), and in macrophages acts independently of m7G modification by binding eIF4E2 to drive selective ABCA1 translation and cholesterol efflux.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"WDR4 is a non-catalytic WD40-repeat scaffold protein best characterized as the obligate partner of METTL1 in the heterodimeric tRNA methyltransferase that installs the m7G46 modification on a defined subset of tRNAs [#0, #2]. Structural studies establish that WDR4 positions both METTL1 and the tRNA T-arm, with the composite protein surface recognizing the tRNA elbow through shape complementarity; the METTL1 N-terminus, partly ordered by WDR4 contact, forms the catalytic centre and acts as a conformational switch coupling SAM binding to methyl transfer, an activity inhibited by S27 phosphorylation [#0, #1]. Efficient methylation requires both the D-stem and T-stem of the tRNA substrate, and the active heterodimer assembles only through co-translational association of the two subunits [#4, #5]. Through this modification, METTL1-WDR4 globally shapes mRNA translation in a codon-usage-dependent manner: loss reduces ribosome transit at cognate codons, impairs translation of mRNAs enriched in m7G-decoded codons, and disrupts embryonic stem cell self-renewal and neural differentiation [#3, #12]. Beyond tRNA, the complex deposits internal m7G marks that stabilize tumor-promoting mRNAs and miRNAs [#15, #18, #19]. WDR4 also operates independently of its methyltransferase role: it serves as a substrate adaptor of the CUL4 E3 ubiquitin ligase, directing ubiquitination and proteasomal degradation of PTPN23 to sustain EGFR/c-MET signaling and of Arhgap17 to activate Rac1 and drive neural progenitor proliferation [#9, #10]; and in tumor-associated macrophages it binds eIF4E2 to selectively translate ABCA1 and promote cholesterol efflux [#16]. A missense mutation in WDR4 that reduces tRNA m7G46 methylation causes a human microcephalic primordial dwarfism, with disease-relevant impairment of ciliogenesis linked to dysregulated protein synthesis and depletion of free ubiquitin pools [#2, #17].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Established that the WDR4 ortholog is required for normal development in a whole organism, framing it as a five-WD40-repeat protein with developmental rather than purely housekeeping functions.\",\n      \"evidence\": \"P-element mutagenesis and transgenic rescue in Drosophila showing spermatogenesis arrest and female germline cell-cycle defects\",\n      \"pmids\": [\"16762337\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism not defined\", \"No link to tRNA modification yet established\", \"Phenotype is ortholog-based, not human\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defined the biochemical substrate requirements and assembly logic of the methyltransferase, showing the heterodimer requires intact tRNA D- and T-stem structure and forms an active enzyme only via co-translational subunit association.\",\n      \"evidence\": \"In vitro methyl-transfer assays with truncated/mutant yeast tRNA(Phe) and wheat-germ co-translation reconstitution\",\n      \"pmids\": [\"17382321\", \"18164779\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of recognition\", \"Performed on yeast orthologs only\", \"Single-lab in vitro reconstitution\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Linked WDR4 to human disease and confirmed its required role in tRNA m7G46 modification, showing a missense mutation reduces methylation of specific tRNAs.\",\n      \"evidence\": \"Autozygome/exome analysis of patient families plus tRNA m7G46 assays in patient cells and matched yeast mutants\",\n      \"pmids\": [\"26416026\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Translational consequences of the hypomorph not measured\", \"How loss of m7G causes the clinical phenotype unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated the functional output of WDR4-dependent m7G: it prevents ribosome pausing at cognate codons and is required for stem cell self-renewal and differentiation.\",\n      \"evidence\": \"CRISPR knockout of Wdr4/Mettl1 in mESCs with m7G MeRIP-seq, TRAC-seq, ribosome profiling, and differentiation assays\",\n      \"pmids\": [\"29983320\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific mRNAs driving phenotype not pinpointed\", \"Does not address non-methyltransferase roles\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified a methyltransferase-independent role at replication forks, where the WDR4 ortholog binds FEN1 and modulates its nuclease activity, with loss triggering DNA damage signaling.\",\n      \"evidence\": \"Reciprocal Co-IP, co-localization with PCNA/FEN1, in vitro FEN1 nuclease assays, and knockdown/KO across Drosophila, mouse, and human cells\",\n      \"pmids\": [\"26751069\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relationship to the METTL1 tRNA function unclear\", \"Whether human WDR4 directly modulates FEN1 in vivo not resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extended the developmental/translational role by showing WDR4 partners with a TRIM-NHL protein to control germline stem cell homeostasis and ribosome biogenesis.\",\n      \"evidence\": \"Genetic epistasis with Mei-p26 plus Co-IP of WDR4-TRIM32 in human cells and translation reporter assays\",\n      \"pmids\": [\"31941704\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct biochemical mechanism of WDR4-TRIM32 cooperation undefined\", \"Largely ortholog-based\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Connected the m7G/translation axis to cancer and placed WDR4 downstream of MYC, implicating codon-usage-linked translation and mRNA stability control in tumorigenesis.\",\n      \"evidence\": \"tRNA/translation profiling with catalytic mutants in lung cancer; ChIP/RIP/mRNA-stability assays defining a MYC/WDR4/CCNB1 axis in HCC\",\n      \"pmids\": [\"34371184\", \"34244479\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"EIF2A-CCNB1 mechanism is correlative\", \"Whether translation defects fully account for tumor phenotypes unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Resolved the atomic mechanism of the methyltransferase, showing WDR4 scaffolds METTL1 and the tRNA T-arm and that the METTL1 N-terminus is a SAM-coupled conformational switch regulated by S27 phosphorylation.\",\n      \"evidence\": \"Crystal and cryo-EM structures of METTL1-WDR4(-tRNA) with biochemical and phospho-mimetic mutagenesis (two independent Nature studies)\",\n      \"pmids\": [\"36599982\", \"36599985\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream kinase for S27 not identified\", \"Structural basis of tRNA subset selectivity not fully mapped\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Established WDR4 as a CUL4 E3 ligase substrate adaptor, revealing a ubiquitination-based, methyltransferase-independent function controlling receptor trafficking and Rac1 signaling.\",\n      \"evidence\": \"Ubiquitylome MS, Co-IP, ubiquitination/trafficking assays and peptide competition for PTPN23 (NSCLC); conditional KO plus Arhgap17 rescue and Rac1 assays for cerebellar progenitors\",\n      \"pmids\": [\"37821451\", \"36681682\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How WDR4 partitions between methyltransferase and ligase-adaptor roles unknown\", \"Direct CUL4-WDR4 architecture not structurally defined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Added a nuclear adaptor function, with WDR4 bridging DDX20 and Egr1 to repress ARRB2 transcription in metastatic cancer.\",\n      \"evidence\": \"Co-IP, nuclear localization and luciferase reporter assays with loss-of-function in bladder cancer cells and in vivo\",\n      \"pmids\": [\"37783676\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect bridging not biochemically dissected\", \"Single-lab, single-context\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linked WDR4 loss to a microcephaly-relevant cellular defect, showing dysregulated protein synthesis and ubiquitin depletion impair ciliogenesis, rescuable by proteasome inhibition or ubiquitin supply.\",\n      \"evidence\": \"Patient fibroblasts and zebrafish with proteasome/ubiquitin assays, ciliogenesis readouts, and pharmacological/genetic rescue\",\n      \"pmids\": [\"39251572\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic chain from m7G loss to ubiquitin depletion not fully defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined a fully methyltransferase-independent cytoplasmic translational function, with WDR4 binding eIF4E2 to selectively translate ABCA1 and reprogram tumor-associated macrophages.\",\n      \"evidence\": \"Co-IP, polysome/selective translation profiling, cholesterol efflux assays, and CpG-siRNA WDR4 silencing in TAMs in vivo\",\n      \"pmids\": [\"41315768\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of WDR4-eIF4E2 interaction unknown\", \"Selectivity for ABCA1 mRNA unexplained\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Broadened the m7G-dependent target repertoire to internal mRNA and miRNA sites controlling stress, growth, and drug-resistance pathways.\",\n      \"evidence\": \"MeRIP-seq with catalytic-mutant rescue defining m7G of SCLT1 mRNA (NF-kB/gefitinib resistance) and let-7 miRNA (TOR-JNK-dMyc); plus adipocyte browning and GSK3beta/beta-catenin reports\",\n      \"pmids\": [\"40857569\", \"41663759\", \"41292047\", \"40009829\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Adipocyte browning and GSK3beta findings are single-lab/single-model and not independently confirmed\", \"Direct vs indirect effects of methylation on each target not always separated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How WDR4 is partitioned and regulated among its distinct roles — methyltransferase scaffold, CUL4 ligase adaptor, eIF4E2-associated translation factor, and replication/transcription adaptor — and what determines context-specific function remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying regulatory model linking the moonlighting activities\", \"Determinants of subcellular partitioning unknown\", \"Upstream signals controlling each function undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [0, 2, 3, 4]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [9, 14, 16]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [13, 15]},\n      {\"term_id\": \"GO:0045182\", \"supporting_discovery_ids\": [16, 12]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [16]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [8, 14]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [3, 12, 16]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"complexes\": [\"METTL1-WDR4 methyltransferase\", \"CUL4 E3 ubiquitin ligase\"],\n    \"partners\": [\"METTL1\", \"eIF4E2\", \"PTPN23\", \"Arhgap17\", \"FEN1\", \"TRIM32\", \"DDX20\", \"EIF2A\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}