{"gene":"FBXW8","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":2002,"finding":"CUL7 assembles an SCF-ROC1-like E3 ubiquitin ligase complex consisting of SKP1, CUL7, FBXW8 (Fbx29), and ROC1. CUL7 selectively interacts with the SKP1·FBXW8 complex but not with SKP1 alone or with SKP1 bound to other F-box proteins (βTrCP2, Skp2), defining a distinct ubiquitin-dependent proteolysis pathway.","method":"Mass spectrometry identification of CUL7 as ROC1-interacting protein; co-immunoprecipitation; biochemical complex reconstitution","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — reciprocal Co-IP plus reconstitution of the complex, multiple orthogonal biochemical methods in a single rigorous study","pmids":["12481031"],"is_preprint":false},{"year":2006,"finding":"FBXW8 acts as the E3 ligase substrate-recognition subunit that mediates ubiquitination and cytoplasmic degradation of cyclin D1 during S phase. This process requires Thr286 phosphorylation of cyclin D1 driven by the Ras/Raf/MEK/ERK cascade. FBXW8 is predominantly cytoplasmic during G1 and S phase; depletion causes cyclin D1 accumulation and CDK1 cytoplasmic sequestration, severely reducing cancer cell proliferation.","method":"siRNA knockdown, cyclin D1 degradation assay, subcellular fractionation/immunofluorescence, rescue with cyclin D1-T286A mutant, ERK1/2 signaling modulation","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (knockdown, mutagenesis, fractionation, signaling inhibition, rescue) in a focused mechanistic study","pmids":["17205132"],"is_preprint":false},{"year":2006,"finding":"FBXW8 is essential for Cul7–Cul1 heterodimeric complex formation; in Fbxw8-null mouse cells, Cul7 fails to associate with Cul1. Loss of Fbxw8 causes intrauterine growth retardation and abnormal placental development (reduced spongiotrophoblast layer, abnormal labyrinth vessels), phenocopying aspects of Cul7-null mice.","method":"Gene-targeted (knockout) mouse model; co-immunoprecipitation of Cul7 and Cul1 in wild-type vs. Fbxw8-null cells; histological analysis of placenta","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with defined biochemical readout (loss of Cul7-Cul1 interaction) plus phenotypic validation in vivo","pmids":["16880526"],"is_preprint":false},{"year":2007,"finding":"Fbxw8 knockout mice display pre- and postnatal growth retardation. Fbxw8-null embryos and placentas are smaller than wild-type; approximately 70% die in utero. IGFBP1 transcript levels are elevated in Fbxw8-null embryos, and IGFBP2 protein is increased in both Cul7-null and Fbxw8-null fibroblasts, placing FBXW8-CUL7 in a growth-regulatory pathway involving IGF-binding proteins.","method":"Gene-trap mouse model; expression profiling; Western blot for IGFBP2 in fibroblasts; organ size measurement","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — independent KO mouse model with multiple molecular readouts, confirming and extending the parallel Fbxw8-null study","pmids":["17998335"],"is_preprint":false},{"year":2008,"finding":"The CUL7/FBXW8 E3 ubiquitin ligase targets insulin receptor substrate-1 (IRS-1) for ubiquitination and proteasomal degradation, implicating this enzyme in the regulation of insulin signaling downstream of mTORC1/S6K phosphorylation of IRS-1.","method":"Commentary/interpretation of Xu et al. experimental data (Co-IP, ubiquitination assay referenced in the primary paper); mechanistic framework confirmed by cited experiments","journal":"Developmental cell","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — review/commentary citing primary experimental data; functional assignment supported but this paper itself is a secondary interpretation","pmids":["18539111"],"is_preprint":false},{"year":2012,"finding":"mTORC2 stabilizes FBXW8 by phosphorylating it at Ser86 and promotes insulin-stimulated translocation of FBXW8 to the cytosol, where FBXW8 mediates IRS-1 degradation. Disruption of mTORC2 attenuates FBXW8 expression and phosphorylation, causing inactive IRS-1 to accumulate and contributing to insulin resistance.","method":"mTORC2 component knockdown, phospho-specific analysis, subcellular fractionation, IRS-1 ubiquitination and degradation assays, Ser86Ala FBXW8 mutant","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal methods (KD, mutagenesis, fractionation, ubiquitination assay) in a single rigorous study identifying both the PTM and its functional consequence","pmids":["23142081"],"is_preprint":false},{"year":2012,"finding":"FBXW8 co-localizes and co-immunoprecipitates with ATXN2 in vitro and in vivo, and FBXW8 overexpression decreases the level of expanded insoluble ATXN2 protein, indicating FBXW8 participates in degradation of both wild-type and polyQ-expanded ATXN2.","method":"Co-immunoprecipitation (in vitro and in vivo); cell culture overexpression; Western blot for ATXN2 soluble/insoluble fractions; transcriptome profiling of knock-in mouse cerebellum","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP and overexpression data from a single lab, supported by in vivo transcriptome context","pmids":["22956915"],"is_preprint":false},{"year":2013,"finding":"The CUL7/FBXW8 E3 ubiquitin ligase targets hematopoietic progenitor kinase 1 (HPK1) for proteasomal degradation. HPK1 ubiquitination requires its kinase activity and autophosphorylation. Phosphatase PP4 dephosphorylates HPK1 at Thr-355, inhibiting FBXW8-HPK1 interaction and FBXW8-mediated ubiquitination. Fbxw8 knockdown restores HPK1 levels and inhibits pancreatic cancer cell proliferation.","method":"Co-immunoprecipitation; ubiquitination assay; phosphatase-dead PP4 mutant; site-directed mutagenesis (Thr355); siRNA knockdown; proteasome inhibitor treatment","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal methods including mutagenesis, phosphatase mutants, ubiquitination reconstitution, and functional KD in cancer cells","pmids":["24362026"],"is_preprint":false},{"year":2015,"finding":"FBXW8 co-immunoprecipitates with ATXN2 and PARK2 both in vitro and in vivo. Expanded polyQ ATXN2 drives both FBXW8 and PARK2 proteins into insolubility. FBXW8 transcript is selectively upregulated by ATXN2 expansion (confirmed by qPCR in SCA2 patient fibroblasts and blood), whereas PARK2 transcript is not dysregulated.","method":"Co-immunoprecipitation (in vitro and in vivo); solubility fractionation; qPCR in patient-derived cells; co-localization immunofluorescence","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — reciprocal Co-IP plus patient sample qPCR, single lab with two orthogonal methods","pmids":["25790475"],"is_preprint":false},{"year":2017,"finding":"MRFAP1 is an interactor and substrate of FBXW8; the CUL7/FBXW8 ubiquitin ligase ubiquitinates and degrades MRFAP1 during the mitotic anaphase-telophase transition. FBXW8 overexpression increases MRFAP1 polyubiquitination and decreases its stability; FBXW8 knockdown prolongs MRFAP1 half-life. Forced MRFAP1 expression causes genomic instability and mitotic cell death.","method":"Immunoprecipitation-based proteomics screen; co-immunoprecipitation; ubiquitination assay; cycloheximide chase; overexpression and siRNA knockdown; cell death assay","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — proteomics-based interactor identification plus functional ubiquitination assays, single lab","pmids":["29228602"],"is_preprint":false},{"year":2021,"finding":"FBXW8 directs proteasomal degradation of β-TrCP1 in a MAPK pathway-dependent manner, controlling oscillation of β-TrCP1 levels during cell cycle G1 and S phases. Attenuation of β-TrCP1 by FBXW8 is required for Cdc25A-mediated G1-to-S transition and DNA damage-free S phase progression.","method":"Biochemical assays, flow cytometry, immunofluorescence, siRNA knockdown, MAPK pathway inhibition, cell cycle staging","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (biochemistry, flow cytometry, pathway inhibition) in a single lab study","pmids":["33742524"],"is_preprint":false},{"year":2021,"finding":"CUL1 and CUL7 cooperatively and synergistically bind FBXW8 to form a CUL1-SKP1-FBXW8-CUL7 functional ubiquitin ligase complex; absence of either cullin abrogates binding of the other. CUL1 binds the N-terminus of FBXW8 via SKP1 while CUL7 binds the C-terminus directly. This complex maintains basal β-TrCP1 levels and promotes cell migration via β-catenin activation through β-TrCP1 degradation.","method":"Co-immunoprecipitation (in vitro and in vivo); site-directed mutagenesis; computational docking; ubiquitination assay; migration assay; β-catenin reporter","journal":"International journal of biological macromolecules","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, mutagenesis, functional assays) from a single lab","pmids":["34478796"],"is_preprint":false},{"year":2022,"finding":"Cryo-EM and biochemical analysis reveal the structure of CRL7FBXW8: CUL7's selectivity for FBXW8 among all F-box proteins is due to an F-box-independent binding mode. Within CRL7FBXW8, the RBX1 RING domain is constrained in an orientation incompatible with binding E2~NEDD8 or E2~ubiquitin intermediates; purified recombinant CRL7FBXW8 lacks auto-neddylation and ubiquitination activities. Instead, CRL7 functions as a substrate receptor linked via SKP1-FBXW8 to a neddylated CUL1-RBX1 catalytic module that mediates ubiquitination.","method":"Cryo-EM structure determination; in vitro auto-neddylation assay; in vitro ubiquitination assay; biochemical reconstitution; mutagenesis","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure plus in vitro reconstitution and functional assays (neddylation, ubiquitination) with mutagenesis validation in a single rigorous study","pmids":["35982156"],"is_preprint":false},{"year":2024,"finding":"FBXW8 suppresses porcine deltacoronavirus (PDCoV) replication by catalyzing K48-linked polyubiquitination of the viral nucleocapsid (N) protein at a lysine-rich region, but the ubiquitinated N protein is degraded via NDP52-dependent autophagy rather than the proteasome. PDCoV infection increases FBXW8 expression through p65-mediated promoter activation.","method":"Overexpression and knockdown; ubiquitination assay specifying K48 linkage; co-immunoprecipitation of N protein with NDP52; autophagic vs. proteasomal degradation assays; promoter luciferase assay","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional assays (ubiquitination, autophagy, Co-IP with cargo receptor) in a single lab; novel substrate/mechanism finding","pmids":["39624099"],"is_preprint":false},{"year":2025,"finding":"CRL7FBXW8 is the E3 ligase complex responsible for NUMB protein hyper-degradation in breast cancer. Identified by RNAi-based screening; genetic and pharmacological inhibition of CRL7FBXW8 rescues NUMB protein levels and reverses transformation-related phenotypes in breast cancer cell lines and patient-derived xenografts.","method":"RNAi-based E3 ligase screen; genetic knockdown; pharmacological inhibition; PDX models; Western blot for NUMB levels; functional transformation assays","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — unbiased RNAi screen plus genetic and pharmacological validation in multiple models, single lab study","pmids":["40411418"],"is_preprint":false},{"year":2025,"finding":"FBXW8 ubiquitinates and promotes proteasomal degradation of PPT1 (palmitoyl-protein thioesterase 1). FBXW8-mediated PPT1 degradation suppresses EMT by reducing expression of SNAIL and ZEB1 transcription factors, inhibiting HCC cell migration and invasion.","method":"Proteomic analysis; co-immunoprecipitation; ubiquitination assay; FBXW8 overexpression and knockdown; in vitro/in vivo functional assays; Western blot for EMT markers","journal":"Biochimica et biophysica acta. Molecular basis of disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — proteomics-based substrate identification with mechanistic follow-up via ubiquitination assays and functional rescue, single lab","pmids":["40659255"],"is_preprint":false},{"year":2025,"finding":"FBXW8 targets NANOG for ubiquitination and proteasomal degradation in embryonic stem cells. KAP1 competes with FBXW8 for binding to NANOG, thereby blocking FBXW8-mediated NANOG degradation and stabilizing NANOG protein to maintain stem cell pluripotency.","method":"Co-immunoprecipitation; domain-mapping (Kap1 coiled-coil domain); overexpression and siRNA knockdown; ubiquitination assay; cycloheximide chase","journal":"International journal of stem cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP with domain mapping plus ubiquitination and stability assays, single lab, single study","pmids":["40759604"],"is_preprint":false}],"current_model":"FBXW8 is an F-box protein that assembles with SKP1, CUL7, and CUL1-RBX1 into a heterotypic CRL7FBXW8–CRL1 E3 ubiquitin ligase supercomplex (unique among CRLs in requiring a CUL1 catalytic module because CUL7-RBX1 alone cannot support ubiquitination); it recruits substrates—including cyclin D1 (via ERK-mediated Thr286 phosphorylation), IRS-1 (regulated by mTORC2 phosphorylation of FBXW8 at Ser86), HPK1 (regulated by PP4 phosphatase at Thr355), β-TrCP1, MRFAP1, NUMB, PPT1, and NANOG—for ubiquitin-dependent proteasomal (or, for viral N protein, autophagic) degradation, thereby controlling cell cycle progression, insulin/mTOR signaling, placental and embryonic growth, stem cell pluripotency, and cancer-relevant processes including EMT and mammary transformation."},"narrative":{"mechanistic_narrative":"FBXW8 is the substrate-recognition subunit of a heterotypic cullin-RING E3 ubiquitin ligase that controls protein turnover governing cell cycle progression, growth signaling, and developmental processes [PMID:12481031, PMID:16880526]. It assembles with SKP1 and CUL7 into a CRL7FBXW8 module, but unlike canonical CRLs this module is catalytically inert on its own: cryo-EM and reconstitution show CUL7-RBX1 holds its RING domain in an orientation incompatible with engaging E2~ubiquitin, so CRL7FBXW8 functions as a substrate receptor that must couple via SKP1-FBXW8 to a separate neddylated CUL1-RBX1 catalytic module to achieve ubiquitination [PMID:35982156]. CUL1 binds the FBXW8 N-terminus through SKP1 while CUL7 binds its C-terminus directly, and loss of either cullin abrogates binding of the other, making FBXW8 the obligate bridge of the supercomplex [PMID:16880526, PMID:34478796]. The ligase recognizes substrates marked by upstream phosphorylation and degrades them by the proteasome: ERK-cascade phosphorylation of cyclin D1 at Thr286 directs its cytoplasmic degradation during S phase [PMID:17205132], and FBXW8 attenuates β-TrCP1 in a MAPK-dependent manner to permit the Cdc25A-driven G1-to-S transition [PMID:33742524]. FBXW8 activity is itself regulated by signaling — mTORC2 phosphorylates FBXW8 at Ser86 to stabilize it and promote cytosolic IRS-1 degradation, linking it to insulin signaling and insulin resistance [PMID:23142081]. Additional substrates include HPK1, whose recognition is gated by PP4 dephosphorylation at Thr355 [PMID:24362026], MRFAP1 during the anaphase-telophase transition [PMID:29228602], PPT1 to suppress EMT in hepatocellular carcinoma [PMID:40659255], and NANOG in embryonic stem cells, where KAP1 competes for NANOG to block its degradation and sustain pluripotency [PMID:40759604]. Genetic ablation in mice causes intrauterine and postnatal growth retardation with abnormal placental development, establishing an in vivo role in embryonic and placental growth [PMID:16880526, PMID:17998335].","teleology":[{"year":2002,"claim":"Established that FBXW8 is not a generic SCF F-box protein but the dedicated substrate receptor of a CUL7-based ligase, defining a distinct proteolysis pathway.","evidence":"Mass spectrometry, reciprocal Co-IP, and biochemical reconstitution showing CUL7 binds SKP1·FBXW8 selectively over SKP1 alone or other F-box proteins","pmids":["12481031"],"confidence":"High","gaps":["Substrates of the complex not yet identified","Catalytic architecture and dependence on a second cullin not yet defined"]},{"year":2006,"claim":"Assigned the complex its first substrate and showed phosphodegron-dependent recognition, linking FBXW8 to cell cycle control downstream of Ras/MAPK.","evidence":"siRNA knockdown, cyclin D1 degradation and fractionation assays, ERK modulation, and rescue with the cyclin D1-T286A non-phosphorylatable mutant","pmids":["17205132"],"confidence":"High","gaps":["Direct in vitro ubiquitination of cyclin D1 by reconstituted complex not shown","Did not resolve how cytoplasmic vs nuclear pools are partitioned"]},{"year":2006,"claim":"Demonstrated in vivo that FBXW8 is required for CUL7-CUL1 association and for normal embryonic and placental growth, connecting the biochemistry to physiology.","evidence":"Fbxw8-null mouse model with Co-IP of Cul7/Cul1 in null vs WT cells and placental histology","pmids":["16880526"],"confidence":"High","gaps":["Substrate(s) responsible for growth phenotype not identified","Mechanism of Cul1 requirement at structural level unknown"]},{"year":2007,"claim":"Independent knockout corroborated growth retardation and placed FBXW8-CUL7 in an IGF-binding-protein growth pathway.","evidence":"Gene-trap mouse, expression profiling, and Western blot of IGFBP2 in null fibroblasts","pmids":["17998335"],"confidence":"High","gaps":["IGFBPs shown as correlates, not direct ubiquitination substrates","Causal chain from FBXW8 to IGFBP levels unresolved"]},{"year":2012,"claim":"Identified FBXW8 as a regulated node in insulin signaling, with mTORC2 phosphorylation at Ser86 controlling FBXW8 stability and IRS-1 degradation.","evidence":"mTORC2 knockdown, phospho-specific analysis, fractionation, IRS-1 ubiquitination/degradation assays, and Ser86Ala mutant","pmids":["23142081"],"confidence":"High","gaps":["Whether IRS-1 is a direct CRL7FBXW8 substrate vs indirect not fully resolved","Physiological insulin resistance link tested in cells, not whole animal"]},{"year":2013,"claim":"Extended the phosphodegron logic to HPK1 and showed a phosphatase (PP4) gates substrate recognition, adding a layer of upstream control.","evidence":"Co-IP, ubiquitination assay, phosphatase-dead PP4 mutant, Thr355 mutagenesis, and siRNA knockdown in pancreatic cancer cells","pmids":["24362026"],"confidence":"High","gaps":["Kinase generating the Thr355 phosphodegron not defined","In vivo relevance in tumors not tested"]},{"year":2012,"claim":"Implicated FBXW8 in clearance of ATXN2, suggesting a role in neurodegenerative protein homeostasis.","evidence":"Co-IP in vitro and in vivo, solubility fractionation, overexpression, and SCA2 knock-in transcriptome profiling","pmids":["22956915"],"confidence":"Medium","gaps":["Direct ubiquitination of ATXN2 not demonstrated","Single-lab correlative data; reciprocal validation limited"]},{"year":2015,"claim":"Refined the ATXN2 connection, showing FBXW8 transcript is selectively induced by polyQ expansion and FBXW8/PARK2 are sequestered into insoluble aggregates.","evidence":"Reciprocal Co-IP, solubility fractionation, and qPCR in SCA2 patient cells","pmids":["25790475"],"confidence":"Medium","gaps":["Functional consequence of FBXW8 upregulation in SCA2 unknown","Whether sequestration is cause or consequence unresolved"]},{"year":2017,"claim":"Added MRFAP1 as a mitotic substrate, linking FBXW8 to genomic stability at the anaphase-telophase transition.","evidence":"IP-proteomics, Co-IP, ubiquitination assay, cycloheximide chase, and cell-death assays","pmids":["29228602"],"confidence":"Medium","gaps":["Phosphodegron or recognition signal on MRFAP1 not mapped","Single-lab; no in vivo confirmation"]},{"year":2021,"claim":"Showed FBXW8 controls oscillation of β-TrCP1 levels to enable the Cdc25A-driven G1-to-S transition, integrating it with another ligase axis.","evidence":"Biochemical assays, flow cytometry, immunofluorescence, MAPK inhibition, and siRNA in cell cycle staging","pmids":["33742524"],"confidence":"Medium","gaps":["Direct ubiquitination of β-TrCP1 by reconstituted complex not shown","Single-lab study"]},{"year":2021,"claim":"Defined the architectural requirement that CUL1 and CUL7 synergistically and cooperatively bind FBXW8, with binding to distinct FBXW8 termini, and linked the complex to migration via β-catenin.","evidence":"Co-IP, site-directed mutagenesis, docking, ubiquitination, migration assay, and β-catenin reporter","pmids":["34478796"],"confidence":"Medium","gaps":["Stoichiometry and dynamics of the supercomplex not resolved at this stage","Docking models not validated structurally"]},{"year":2022,"claim":"Resolved the central mechanistic puzzle: cryo-EM revealed CRL7FBXW8 is catalytically inert and acts as a substrate receptor that must couple to a neddylated CUL1-RBX1 module for ubiquitination.","evidence":"Cryo-EM structure, in vitro auto-neddylation and ubiquitination assays, reconstitution, and mutagenesis","pmids":["35982156"],"confidence":"High","gaps":["Structure of the full CUL7-CUL1 supercomplex with substrate engaged not determined","How substrate is transferred between modules unresolved"]},{"year":2024,"claim":"Revealed an unconventional degradation route, showing FBXW8 adds K48 chains to a viral nucleocapsid that are routed to autophagy rather than the proteasome.","evidence":"Overexpression/knockdown, K48-specific ubiquitination assay, Co-IP with NDP52, autophagic vs proteasomal assays, and promoter luciferase","pmids":["39624099"],"confidence":"Medium","gaps":["Whether the CUL1-CUL7 catalytic logic applies to this substrate not tested","Generality of autophagic routing for FBXW8 substrates unknown"]},{"year":2025,"claim":"Identified NUMB hyper-degradation by CRL7FBXW8 as a driver of breast cancer transformation, providing a therapeutic rationale.","evidence":"RNAi E3-ligase screen, genetic and pharmacological inhibition, and PDX models with NUMB rescue","pmids":["40411418"],"confidence":"Medium","gaps":["Phosphodegron/recognition signal on NUMB not mapped","Pharmacological agent specificity not fully characterized"]},{"year":2025,"claim":"Showed FBXW8 degrades PPT1 to suppress SNAIL/ZEB1-driven EMT and HCC invasion, assigning a tumor-suppressive role in this context.","evidence":"Proteomics, Co-IP, ubiquitination assay, overexpression/knockdown, and in vitro/in vivo EMT-marker functional assays","pmids":["40659255"],"confidence":"Medium","gaps":["Recognition signal on PPT1 not defined","Single-lab study"]},{"year":2025,"claim":"Established FBXW8 as a regulator of pluripotency by degrading NANOG, with KAP1 acting as a competitive stabilizer.","evidence":"Co-IP, KAP1 coiled-coil domain mapping, overexpression/knockdown, ubiquitination assay, and cycloheximide chase","pmids":["40759604"],"confidence":"Medium","gaps":["Phosphodegron on NANOG not characterized","In vivo pluripotency consequence not demonstrated"]},{"year":null,"claim":"How a single FBXW8 ligase selects among its many phospho-regulated substrates in different cellular contexts, and whether all substrates require the CUL1 catalytic module, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified phosphodegron consensus across substrates","Substrate-specific contribution of CUL1 vs CUL7 modules untested for most substrates","Tissue-specific substrate prioritization unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,5,7,9,15,16]},{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,12,13]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,11,12]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[1,5]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[1,9,10]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,12]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5,10,11]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[2,3,16]}],"complexes":["CRL7FBXW8 (SKP1-CUL7-FBXW8-RBX1)","CUL1-SKP1-FBXW8-CUL7 supercomplex"],"partners":["CUL7","CUL1","SKP1","RBX1","ATXN2","KAP1","PARK2","NDP52"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8N3Y1","full_name":"F-box/WD repeat-containing protein 8","aliases":["F-box and WD-40 domain-containing protein 8","F-box only protein 29"],"length_aa":598,"mass_kda":67.4,"function":"Substrate-recognition component of the Cul7-RING(FBXW8) ubiquitin ligase complex, which mediates the ubiquitination and subsequent proteasomal degradation of target proteins (PubMed:17205132, PubMed:18498745, PubMed:21572988, PubMed:24362026, PubMed:35982156). The Cul7-RING(FBXW8) complex mediates ubiquitination and consequent degradation of GORASP1, acting as a component of the ubiquitin ligase pathway that regulates Golgi morphogenesis and dendrite patterning in brain (PubMed:21572988). Mediates ubiquitination and degradation of IRS1 in a mTOR-dependent manner: the Cul7-RING(FBXW8) complex recognizes and binds IRS1 previously phosphorylated by S6 kinase (RPS6KB1 or RPS6KB2) (PubMed:18498745). The Cul7-RING(FBXW8) complex also mediates ubiquitination of MAP4K1/HPK1: recognizes and binds autophosphorylated MAP4K1/HPK1, leading to its degradation, thereby affecting cell proliferation and differentiation (PubMed:24362026). The Cul7-RING(FBXW8) complex also mediates ubiquitination of phosphorylated cyclin-D1 (CCND1) (PubMed:17205132). The Cul7-RING(FBXW8) complex is however not a major regulator of CCND1 stability during the G1/S transition (By similarity). Associated component of the 3M complex, suggesting that it mediates some of 3M complex functions (PubMed:24793695)","subcellular_location":"Cytoplasm, perinuclear region; Golgi apparatus; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q8N3Y1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FBXW8","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FBXW8","total_profiled":1310},"omim":[{"mim_id":"609577","title":"CULLIN 7; CUL7","url":"https://www.omim.org/entry/609577"},{"mim_id":"609073","title":"F-BOX AND WD40 DOMAIN PROTEIN 8; FBXW8","url":"https://www.omim.org/entry/609073"},{"mim_id":"603814","title":"RING-BOX 1; RBX1","url":"https://www.omim.org/entry/603814"},{"mim_id":"601749","title":"GLOMULIN; GLMN","url":"https://www.omim.org/entry/601749"},{"mim_id":"601434","title":"S-PHASE KINASE-ASSOCIATED PROTEIN 1; SKP1","url":"https://www.omim.org/entry/601434"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/FBXW8"},"hgnc":{"alias_symbol":["FBX29","FBW6","FBW8"],"prev_symbol":["FBXO29"]},"alphafold":{"accession":"Q8N3Y1","domains":[{"cath_id":"1.20.1280.50","chopping":"118-198","consensus_level":"medium","plddt":89.7112,"start":118,"end":198}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8N3Y1","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8N3Y1-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8N3Y1-F1-predicted_aligned_error_v6.png","plddt_mean":76.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FBXW8","jax_strain_url":"https://www.jax.org/strain/search?query=FBXW8"},"sequence":{"accession":"Q8N3Y1","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8N3Y1.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8N3Y1/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8N3Y1"}},"corpus_meta":[{"pmid":"17205132","id":"PMC_17205132","title":"A critical role for FBXW8 and MAPK in cyclin D1 degradation and cancer cell proliferation.","date":"2006","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/17205132","citation_count":171,"is_preprint":false},{"pmid":"12481031","id":"PMC_12481031","title":"CUL7: A DOC domain-containing cullin selectively binds Skp1.Fbx29 to form an SCF-like complex.","date":"2002","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/12481031","citation_count":136,"is_preprint":false},{"pmid":"23142081","id":"PMC_23142081","title":"mTOR complex 2 regulates proper turnover of insulin receptor substrate-1 via the ubiquitin ligase subunit Fbw8.","date":"2012","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/23142081","citation_count":91,"is_preprint":false},{"pmid":"22956915","id":"PMC_22956915","title":"ATXN2-CAG42 sequesters PABPC1 into insolubility and induces FBXW8 in cerebellum of old ataxic knock-in 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pharmacotherapie","url":"https://pubmed.ncbi.nlm.nih.gov/29096355","citation_count":40,"is_preprint":false},{"pmid":"24362026","id":"PMC_24362026","title":"The CUL7/F-box and WD repeat domain containing 8 (CUL7/Fbxw8) ubiquitin ligase promotes degradation of hematopoietic progenitor kinase 1.","date":"2013","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/24362026","citation_count":39,"is_preprint":false},{"pmid":"25790475","id":"PMC_25790475","title":"Both ubiquitin ligases FBXW8 and PARK2 are sequestrated into insolubility by ATXN2 PolyQ expansions, but only FBXW8 expression is dysregulated.","date":"2015","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/25790475","citation_count":25,"is_preprint":false},{"pmid":"35982156","id":"PMC_35982156","title":"Structure of CRL7FBXW8 reveals coupling with CUL1-RBX1/ROC1 for multi-cullin-RING E3-catalyzed ubiquitin ligation.","date":"2022","source":"Nature structural & molecular 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death.","date":"2017","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/29228602","citation_count":9,"is_preprint":false},{"pmid":"39624099","id":"PMC_39624099","title":"FBXW8 suppresses PDCoV proliferation via the NPD52-dependent autophagic degradation of a viral nucleocapsid protein.","date":"2024","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/39624099","citation_count":6,"is_preprint":false},{"pmid":"40411418","id":"PMC_40411418","title":"The CRL7FBXW8 Complex Controls the Mammary Stem Cell Compartment through Regulation of NUMB Levels.","date":"2025","source":"Advanced science (Weinheim, Baden-Wurttemberg, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/40411418","citation_count":5,"is_preprint":false},{"pmid":"18539111","id":"PMC_18539111","title":"Shooting the messenger: CULLIN' insulin signaling with Fbw8.","date":"2008","source":"Developmental 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Molecular basis of disease","url":"https://pubmed.ncbi.nlm.nih.gov/40659255","citation_count":2,"is_preprint":false},{"pmid":"36322340","id":"PMC_36322340","title":"Structure-based drug design of potential inhibitors of FBXW8, the substrate recognition component of Cullin-RING ligase 7.","date":"2022","source":"Molecular diversity","url":"https://pubmed.ncbi.nlm.nih.gov/36322340","citation_count":2,"is_preprint":false},{"pmid":"29310837","id":"PMC_29310837","title":"Assessment of a FBXW8 frameshift mutation, c.1312_1313delGT, in breast cancer patients and controls from Central Europe.","date":"2017","source":"Cancer genetics","url":"https://pubmed.ncbi.nlm.nih.gov/29310837","citation_count":1,"is_preprint":false},{"pmid":"40759604","id":"PMC_40759604","title":"Kap1 Regulates Protein Stability of Nanog by Interfering with Fbxw8-Dependent Ubiquitination.","date":"2025","source":"International journal of stem cells","url":"https://pubmed.ncbi.nlm.nih.gov/40759604","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.02.27.640530","title":"The CRL7  <sup>FBXW8</sup>  Complex Controls the Mammary Stem Cell Compartment Through Regulation of NUMB Levels","date":"2025-03-03","source":"bioRxiv","url":"https://doi.org/10.1101/2025.02.27.640530","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13355,"output_tokens":4941,"usd":0.05709,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12954,"output_tokens":5042,"usd":0.09541,"stage2_stop_reason":"end_turn"},"total_usd":0.1525,"stage1_batch_id":"msgbatch_01AsR7g8dGTEiEw9U83bJeWn","stage2_batch_id":"msgbatch_01YV5ZyxtFNUZEjxRcpd9jzb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2002,\n      \"finding\": \"CUL7 assembles an SCF-ROC1-like E3 ubiquitin ligase complex consisting of SKP1, CUL7, FBXW8 (Fbx29), and ROC1. CUL7 selectively interacts with the SKP1·FBXW8 complex but not with SKP1 alone or with SKP1 bound to other F-box proteins (βTrCP2, Skp2), defining a distinct ubiquitin-dependent proteolysis pathway.\",\n      \"method\": \"Mass spectrometry identification of CUL7 as ROC1-interacting protein; co-immunoprecipitation; biochemical complex reconstitution\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — reciprocal Co-IP plus reconstitution of the complex, multiple orthogonal biochemical methods in a single rigorous study\",\n      \"pmids\": [\"12481031\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"FBXW8 acts as the E3 ligase substrate-recognition subunit that mediates ubiquitination and cytoplasmic degradation of cyclin D1 during S phase. This process requires Thr286 phosphorylation of cyclin D1 driven by the Ras/Raf/MEK/ERK cascade. FBXW8 is predominantly cytoplasmic during G1 and S phase; depletion causes cyclin D1 accumulation and CDK1 cytoplasmic sequestration, severely reducing cancer cell proliferation.\",\n      \"method\": \"siRNA knockdown, cyclin D1 degradation assay, subcellular fractionation/immunofluorescence, rescue with cyclin D1-T286A mutant, ERK1/2 signaling modulation\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (knockdown, mutagenesis, fractionation, signaling inhibition, rescue) in a focused mechanistic study\",\n      \"pmids\": [\"17205132\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"FBXW8 is essential for Cul7–Cul1 heterodimeric complex formation; in Fbxw8-null mouse cells, Cul7 fails to associate with Cul1. Loss of Fbxw8 causes intrauterine growth retardation and abnormal placental development (reduced spongiotrophoblast layer, abnormal labyrinth vessels), phenocopying aspects of Cul7-null mice.\",\n      \"method\": \"Gene-targeted (knockout) mouse model; co-immunoprecipitation of Cul7 and Cul1 in wild-type vs. Fbxw8-null cells; histological analysis of placenta\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with defined biochemical readout (loss of Cul7-Cul1 interaction) plus phenotypic validation in vivo\",\n      \"pmids\": [\"16880526\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Fbxw8 knockout mice display pre- and postnatal growth retardation. Fbxw8-null embryos and placentas are smaller than wild-type; approximately 70% die in utero. IGFBP1 transcript levels are elevated in Fbxw8-null embryos, and IGFBP2 protein is increased in both Cul7-null and Fbxw8-null fibroblasts, placing FBXW8-CUL7 in a growth-regulatory pathway involving IGF-binding proteins.\",\n      \"method\": \"Gene-trap mouse model; expression profiling; Western blot for IGFBP2 in fibroblasts; organ size measurement\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — independent KO mouse model with multiple molecular readouts, confirming and extending the parallel Fbxw8-null study\",\n      \"pmids\": [\"17998335\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The CUL7/FBXW8 E3 ubiquitin ligase targets insulin receptor substrate-1 (IRS-1) for ubiquitination and proteasomal degradation, implicating this enzyme in the regulation of insulin signaling downstream of mTORC1/S6K phosphorylation of IRS-1.\",\n      \"method\": \"Commentary/interpretation of Xu et al. experimental data (Co-IP, ubiquitination assay referenced in the primary paper); mechanistic framework confirmed by cited experiments\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — review/commentary citing primary experimental data; functional assignment supported but this paper itself is a secondary interpretation\",\n      \"pmids\": [\"18539111\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"mTORC2 stabilizes FBXW8 by phosphorylating it at Ser86 and promotes insulin-stimulated translocation of FBXW8 to the cytosol, where FBXW8 mediates IRS-1 degradation. Disruption of mTORC2 attenuates FBXW8 expression and phosphorylation, causing inactive IRS-1 to accumulate and contributing to insulin resistance.\",\n      \"method\": \"mTORC2 component knockdown, phospho-specific analysis, subcellular fractionation, IRS-1 ubiquitination and degradation assays, Ser86Ala FBXW8 mutant\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal methods (KD, mutagenesis, fractionation, ubiquitination assay) in a single rigorous study identifying both the PTM and its functional consequence\",\n      \"pmids\": [\"23142081\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"FBXW8 co-localizes and co-immunoprecipitates with ATXN2 in vitro and in vivo, and FBXW8 overexpression decreases the level of expanded insoluble ATXN2 protein, indicating FBXW8 participates in degradation of both wild-type and polyQ-expanded ATXN2.\",\n      \"method\": \"Co-immunoprecipitation (in vitro and in vivo); cell culture overexpression; Western blot for ATXN2 soluble/insoluble fractions; transcriptome profiling of knock-in mouse cerebellum\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP and overexpression data from a single lab, supported by in vivo transcriptome context\",\n      \"pmids\": [\"22956915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The CUL7/FBXW8 E3 ubiquitin ligase targets hematopoietic progenitor kinase 1 (HPK1) for proteasomal degradation. HPK1 ubiquitination requires its kinase activity and autophosphorylation. Phosphatase PP4 dephosphorylates HPK1 at Thr-355, inhibiting FBXW8-HPK1 interaction and FBXW8-mediated ubiquitination. Fbxw8 knockdown restores HPK1 levels and inhibits pancreatic cancer cell proliferation.\",\n      \"method\": \"Co-immunoprecipitation; ubiquitination assay; phosphatase-dead PP4 mutant; site-directed mutagenesis (Thr355); siRNA knockdown; proteasome inhibitor treatment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal methods including mutagenesis, phosphatase mutants, ubiquitination reconstitution, and functional KD in cancer cells\",\n      \"pmids\": [\"24362026\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"FBXW8 co-immunoprecipitates with ATXN2 and PARK2 both in vitro and in vivo. Expanded polyQ ATXN2 drives both FBXW8 and PARK2 proteins into insolubility. FBXW8 transcript is selectively upregulated by ATXN2 expansion (confirmed by qPCR in SCA2 patient fibroblasts and blood), whereas PARK2 transcript is not dysregulated.\",\n      \"method\": \"Co-immunoprecipitation (in vitro and in vivo); solubility fractionation; qPCR in patient-derived cells; co-localization immunofluorescence\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — reciprocal Co-IP plus patient sample qPCR, single lab with two orthogonal methods\",\n      \"pmids\": [\"25790475\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"MRFAP1 is an interactor and substrate of FBXW8; the CUL7/FBXW8 ubiquitin ligase ubiquitinates and degrades MRFAP1 during the mitotic anaphase-telophase transition. FBXW8 overexpression increases MRFAP1 polyubiquitination and decreases its stability; FBXW8 knockdown prolongs MRFAP1 half-life. Forced MRFAP1 expression causes genomic instability and mitotic cell death.\",\n      \"method\": \"Immunoprecipitation-based proteomics screen; co-immunoprecipitation; ubiquitination assay; cycloheximide chase; overexpression and siRNA knockdown; cell death assay\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — proteomics-based interactor identification plus functional ubiquitination assays, single lab\",\n      \"pmids\": [\"29228602\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FBXW8 directs proteasomal degradation of β-TrCP1 in a MAPK pathway-dependent manner, controlling oscillation of β-TrCP1 levels during cell cycle G1 and S phases. Attenuation of β-TrCP1 by FBXW8 is required for Cdc25A-mediated G1-to-S transition and DNA damage-free S phase progression.\",\n      \"method\": \"Biochemical assays, flow cytometry, immunofluorescence, siRNA knockdown, MAPK pathway inhibition, cell cycle staging\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (biochemistry, flow cytometry, pathway inhibition) in a single lab study\",\n      \"pmids\": [\"33742524\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CUL1 and CUL7 cooperatively and synergistically bind FBXW8 to form a CUL1-SKP1-FBXW8-CUL7 functional ubiquitin ligase complex; absence of either cullin abrogates binding of the other. CUL1 binds the N-terminus of FBXW8 via SKP1 while CUL7 binds the C-terminus directly. This complex maintains basal β-TrCP1 levels and promotes cell migration via β-catenin activation through β-TrCP1 degradation.\",\n      \"method\": \"Co-immunoprecipitation (in vitro and in vivo); site-directed mutagenesis; computational docking; ubiquitination assay; migration assay; β-catenin reporter\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, mutagenesis, functional assays) from a single lab\",\n      \"pmids\": [\"34478796\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cryo-EM and biochemical analysis reveal the structure of CRL7FBXW8: CUL7's selectivity for FBXW8 among all F-box proteins is due to an F-box-independent binding mode. Within CRL7FBXW8, the RBX1 RING domain is constrained in an orientation incompatible with binding E2~NEDD8 or E2~ubiquitin intermediates; purified recombinant CRL7FBXW8 lacks auto-neddylation and ubiquitination activities. Instead, CRL7 functions as a substrate receptor linked via SKP1-FBXW8 to a neddylated CUL1-RBX1 catalytic module that mediates ubiquitination.\",\n      \"method\": \"Cryo-EM structure determination; in vitro auto-neddylation assay; in vitro ubiquitination assay; biochemical reconstitution; mutagenesis\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure plus in vitro reconstitution and functional assays (neddylation, ubiquitination) with mutagenesis validation in a single rigorous study\",\n      \"pmids\": [\"35982156\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FBXW8 suppresses porcine deltacoronavirus (PDCoV) replication by catalyzing K48-linked polyubiquitination of the viral nucleocapsid (N) protein at a lysine-rich region, but the ubiquitinated N protein is degraded via NDP52-dependent autophagy rather than the proteasome. PDCoV infection increases FBXW8 expression through p65-mediated promoter activation.\",\n      \"method\": \"Overexpression and knockdown; ubiquitination assay specifying K48 linkage; co-immunoprecipitation of N protein with NDP52; autophagic vs. proteasomal degradation assays; promoter luciferase assay\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional assays (ubiquitination, autophagy, Co-IP with cargo receptor) in a single lab; novel substrate/mechanism finding\",\n      \"pmids\": [\"39624099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CRL7FBXW8 is the E3 ligase complex responsible for NUMB protein hyper-degradation in breast cancer. Identified by RNAi-based screening; genetic and pharmacological inhibition of CRL7FBXW8 rescues NUMB protein levels and reverses transformation-related phenotypes in breast cancer cell lines and patient-derived xenografts.\",\n      \"method\": \"RNAi-based E3 ligase screen; genetic knockdown; pharmacological inhibition; PDX models; Western blot for NUMB levels; functional transformation assays\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — unbiased RNAi screen plus genetic and pharmacological validation in multiple models, single lab study\",\n      \"pmids\": [\"40411418\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FBXW8 ubiquitinates and promotes proteasomal degradation of PPT1 (palmitoyl-protein thioesterase 1). FBXW8-mediated PPT1 degradation suppresses EMT by reducing expression of SNAIL and ZEB1 transcription factors, inhibiting HCC cell migration and invasion.\",\n      \"method\": \"Proteomic analysis; co-immunoprecipitation; ubiquitination assay; FBXW8 overexpression and knockdown; in vitro/in vivo functional assays; Western blot for EMT markers\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular basis of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — proteomics-based substrate identification with mechanistic follow-up via ubiquitination assays and functional rescue, single lab\",\n      \"pmids\": [\"40659255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FBXW8 targets NANOG for ubiquitination and proteasomal degradation in embryonic stem cells. KAP1 competes with FBXW8 for binding to NANOG, thereby blocking FBXW8-mediated NANOG degradation and stabilizing NANOG protein to maintain stem cell pluripotency.\",\n      \"method\": \"Co-immunoprecipitation; domain-mapping (Kap1 coiled-coil domain); overexpression and siRNA knockdown; ubiquitination assay; cycloheximide chase\",\n      \"journal\": \"International journal of stem cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP with domain mapping plus ubiquitination and stability assays, single lab, single study\",\n      \"pmids\": [\"40759604\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FBXW8 is an F-box protein that assembles with SKP1, CUL7, and CUL1-RBX1 into a heterotypic CRL7FBXW8–CRL1 E3 ubiquitin ligase supercomplex (unique among CRLs in requiring a CUL1 catalytic module because CUL7-RBX1 alone cannot support ubiquitination); it recruits substrates—including cyclin D1 (via ERK-mediated Thr286 phosphorylation), IRS-1 (regulated by mTORC2 phosphorylation of FBXW8 at Ser86), HPK1 (regulated by PP4 phosphatase at Thr355), β-TrCP1, MRFAP1, NUMB, PPT1, and NANOG—for ubiquitin-dependent proteasomal (or, for viral N protein, autophagic) degradation, thereby controlling cell cycle progression, insulin/mTOR signaling, placental and embryonic growth, stem cell pluripotency, and cancer-relevant processes including EMT and mammary transformation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"FBXW8 is the substrate-recognition subunit of a heterotypic cullin-RING E3 ubiquitin ligase that controls protein turnover governing cell cycle progression, growth signaling, and developmental processes [#0, #2]. It assembles with SKP1 and CUL7 into a CRL7FBXW8 module, but unlike canonical CRLs this module is catalytically inert on its own: cryo-EM and reconstitution show CUL7-RBX1 holds its RING domain in an orientation incompatible with engaging E2~ubiquitin, so CRL7FBXW8 functions as a substrate receptor that must couple via SKP1-FBXW8 to a separate neddylated CUL1-RBX1 catalytic module to achieve ubiquitination [#12]. CUL1 binds the FBXW8 N-terminus through SKP1 while CUL7 binds its C-terminus directly, and loss of either cullin abrogates binding of the other, making FBXW8 the obligate bridge of the supercomplex [#2, #11]. The ligase recognizes substrates marked by upstream phosphorylation and degrades them by the proteasome: ERK-cascade phosphorylation of cyclin D1 at Thr286 directs its cytoplasmic degradation during S phase [#1], and FBXW8 attenuates \\u03b2-TrCP1 in a MAPK-dependent manner to permit the Cdc25A-driven G1-to-S transition [#10]. FBXW8 activity is itself regulated by signaling \\u2014 mTORC2 phosphorylates FBXW8 at Ser86 to stabilize it and promote cytosolic IRS-1 degradation, linking it to insulin signaling and insulin resistance [#5]. Additional substrates include HPK1, whose recognition is gated by PP4 dephosphorylation at Thr355 [#7], MRFAP1 during the anaphase-telophase transition [#9], PPT1 to suppress EMT in hepatocellular carcinoma [#15], and NANOG in embryonic stem cells, where KAP1 competes for NANOG to block its degradation and sustain pluripotency [#16]. Genetic ablation in mice causes intrauterine and postnatal growth retardation with abnormal placental development, establishing an in vivo role in embryonic and placental growth [#2, #3].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Established that FBXW8 is not a generic SCF F-box protein but the dedicated substrate receptor of a CUL7-based ligase, defining a distinct proteolysis pathway.\",\n      \"evidence\": \"Mass spectrometry, reciprocal Co-IP, and biochemical reconstitution showing CUL7 binds SKP1\\u00b7FBXW8 selectively over SKP1 alone or other F-box proteins\",\n      \"pmids\": [\"12481031\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrates of the complex not yet identified\", \"Catalytic architecture and dependence on a second cullin not yet defined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Assigned the complex its first substrate and showed phosphodegron-dependent recognition, linking FBXW8 to cell cycle control downstream of Ras/MAPK.\",\n      \"evidence\": \"siRNA knockdown, cyclin D1 degradation and fractionation assays, ERK modulation, and rescue with the cyclin D1-T286A non-phosphorylatable mutant\",\n      \"pmids\": [\"17205132\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct in vitro ubiquitination of cyclin D1 by reconstituted complex not shown\", \"Did not resolve how cytoplasmic vs nuclear pools are partitioned\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrated in vivo that FBXW8 is required for CUL7-CUL1 association and for normal embryonic and placental growth, connecting the biochemistry to physiology.\",\n      \"evidence\": \"Fbxw8-null mouse model with Co-IP of Cul7/Cul1 in null vs WT cells and placental histology\",\n      \"pmids\": [\"16880526\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrate(s) responsible for growth phenotype not identified\", \"Mechanism of Cul1 requirement at structural level unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Independent knockout corroborated growth retardation and placed FBXW8-CUL7 in an IGF-binding-protein growth pathway.\",\n      \"evidence\": \"Gene-trap mouse, expression profiling, and Western blot of IGFBP2 in null fibroblasts\",\n      \"pmids\": [\"17998335\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"IGFBPs shown as correlates, not direct ubiquitination substrates\", \"Causal chain from FBXW8 to IGFBP levels unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identified FBXW8 as a regulated node in insulin signaling, with mTORC2 phosphorylation at Ser86 controlling FBXW8 stability and IRS-1 degradation.\",\n      \"evidence\": \"mTORC2 knockdown, phospho-specific analysis, fractionation, IRS-1 ubiquitination/degradation assays, and Ser86Ala mutant\",\n      \"pmids\": [\"23142081\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether IRS-1 is a direct CRL7FBXW8 substrate vs indirect not fully resolved\", \"Physiological insulin resistance link tested in cells, not whole animal\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Extended the phosphodegron logic to HPK1 and showed a phosphatase (PP4) gates substrate recognition, adding a layer of upstream control.\",\n      \"evidence\": \"Co-IP, ubiquitination assay, phosphatase-dead PP4 mutant, Thr355 mutagenesis, and siRNA knockdown in pancreatic cancer cells\",\n      \"pmids\": [\"24362026\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase generating the Thr355 phosphodegron not defined\", \"In vivo relevance in tumors not tested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Implicated FBXW8 in clearance of ATXN2, suggesting a role in neurodegenerative protein homeostasis.\",\n      \"evidence\": \"Co-IP in vitro and in vivo, solubility fractionation, overexpression, and SCA2 knock-in transcriptome profiling\",\n      \"pmids\": [\"22956915\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ubiquitination of ATXN2 not demonstrated\", \"Single-lab correlative data; reciprocal validation limited\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Refined the ATXN2 connection, showing FBXW8 transcript is selectively induced by polyQ expansion and FBXW8/PARK2 are sequestered into insoluble aggregates.\",\n      \"evidence\": \"Reciprocal Co-IP, solubility fractionation, and qPCR in SCA2 patient cells\",\n      \"pmids\": [\"25790475\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of FBXW8 upregulation in SCA2 unknown\", \"Whether sequestration is cause or consequence unresolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Added MRFAP1 as a mitotic substrate, linking FBXW8 to genomic stability at the anaphase-telophase transition.\",\n      \"evidence\": \"IP-proteomics, Co-IP, ubiquitination assay, cycloheximide chase, and cell-death assays\",\n      \"pmids\": [\"29228602\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Phosphodegron or recognition signal on MRFAP1 not mapped\", \"Single-lab; no in vivo confirmation\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed FBXW8 controls oscillation of \\u03b2-TrCP1 levels to enable the Cdc25A-driven G1-to-S transition, integrating it with another ligase axis.\",\n      \"evidence\": \"Biochemical assays, flow cytometry, immunofluorescence, MAPK inhibition, and siRNA in cell cycle staging\",\n      \"pmids\": [\"33742524\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ubiquitination of \\u03b2-TrCP1 by reconstituted complex not shown\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined the architectural requirement that CUL1 and CUL7 synergistically and cooperatively bind FBXW8, with binding to distinct FBXW8 termini, and linked the complex to migration via \\u03b2-catenin.\",\n      \"evidence\": \"Co-IP, site-directed mutagenesis, docking, ubiquitination, migration assay, and \\u03b2-catenin reporter\",\n      \"pmids\": [\"34478796\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry and dynamics of the supercomplex not resolved at this stage\", \"Docking models not validated structurally\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Resolved the central mechanistic puzzle: cryo-EM revealed CRL7FBXW8 is catalytically inert and acts as a substrate receptor that must couple to a neddylated CUL1-RBX1 module for ubiquitination.\",\n      \"evidence\": \"Cryo-EM structure, in vitro auto-neddylation and ubiquitination assays, reconstitution, and mutagenesis\",\n      \"pmids\": [\"35982156\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of the full CUL7-CUL1 supercomplex with substrate engaged not determined\", \"How substrate is transferred between modules unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Revealed an unconventional degradation route, showing FBXW8 adds K48 chains to a viral nucleocapsid that are routed to autophagy rather than the proteasome.\",\n      \"evidence\": \"Overexpression/knockdown, K48-specific ubiquitination assay, Co-IP with NDP52, autophagic vs proteasomal assays, and promoter luciferase\",\n      \"pmids\": [\"39624099\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether the CUL1-CUL7 catalytic logic applies to this substrate not tested\", \"Generality of autophagic routing for FBXW8 substrates unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified NUMB hyper-degradation by CRL7FBXW8 as a driver of breast cancer transformation, providing a therapeutic rationale.\",\n      \"evidence\": \"RNAi E3-ligase screen, genetic and pharmacological inhibition, and PDX models with NUMB rescue\",\n      \"pmids\": [\"40411418\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Phosphodegron/recognition signal on NUMB not mapped\", \"Pharmacological agent specificity not fully characterized\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Showed FBXW8 degrades PPT1 to suppress SNAIL/ZEB1-driven EMT and HCC invasion, assigning a tumor-suppressive role in this context.\",\n      \"evidence\": \"Proteomics, Co-IP, ubiquitination assay, overexpression/knockdown, and in vitro/in vivo EMT-marker functional assays\",\n      \"pmids\": [\"40659255\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Recognition signal on PPT1 not defined\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established FBXW8 as a regulator of pluripotency by degrading NANOG, with KAP1 acting as a competitive stabilizer.\",\n      \"evidence\": \"Co-IP, KAP1 coiled-coil domain mapping, overexpression/knockdown, ubiquitination assay, and cycloheximide chase\",\n      \"pmids\": [\"40759604\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Phosphodegron on NANOG not characterized\", \"In vivo pluripotency consequence not demonstrated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single FBXW8 ligase selects among its many phospho-regulated substrates in different cellular contexts, and whether all substrates require the CUL1 catalytic module, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified phosphodegron consensus across substrates\", \"Substrate-specific contribution of CUL1 vs CUL7 modules untested for most substrates\", \"Tissue-specific substrate prioritization unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 5, 7, 9, 15, 16]},\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 12, 13]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 11, 12]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [1, 9, 10]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 12]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 10, 11]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [2, 3, 16]}\n    ],\n    \"complexes\": [\"CRL7FBXW8 (SKP1-CUL7-FBXW8-RBX1)\", \"CUL1-SKP1-FBXW8-CUL7 supercomplex\"],\n    \"partners\": [\"CUL7\", \"CUL1\", \"SKP1\", \"RBX1\", \"ATXN2\", \"KAP1\", \"PARK2\", \"NDP52\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}