{"gene":"FZR1","run_date":"2026-06-09T23:54:44","timeline":{"discoveries":[{"year":2001,"finding":"FZR1 (Fzr/Cdh1) activates the APC/C to ubiquitinate and degrade human securin/PTTG in vitro. Securin degradation is mediated by both an RXXL destruction box and a KEN box; mutation of both sequences together is required to prevent ubiquitination and degradation.","method":"In vitro APC/C ubiquitination assay; destruction box/KEN box mutagenesis; cell-based expression of non-degradable securin mutant","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution of ubiquitination combined with mutagenesis of degron motifs, replicated with cell-based assays","pmids":["11179223"],"is_preprint":false},{"year":2002,"finding":"Drosophila Fzr/Cdh1 binds microtubules in vitro and associates with spindles in vivo, concentrating at centrosomes throughout the cell cycle. Fzr/Cdh1 is responsible for the second, cytoplasm-wide phase of cyclin B destruction during mitotic exit, distinct from the spindle-localized destruction driven by Fzy/Cdc20.","method":"Microtubule-binding assay in vitro; in vivo live imaging and immunofluorescence; destruction-box mutant cyclin B (CBTPM-GFP) degradation assay in syncytial vs. cellularized embryos","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (in vitro binding, in vivo localization, functional degradation assays with degron mutants)","pmids":["12082076"],"is_preprint":false},{"year":2002,"finding":"APC/C(FZR1)-dependent degradation timing is determined by the specificity of destruction box (RXXL) and KEN box motifs. KEN-box substrates are degraded exclusively by APC/C(Fzr); RXXL substrates can be degraded by both APC/C(Fzy) and APC/C(Fzr), but APC/C(Fzy)-specific RXXL degradation is highly dependent on the location of the RXXL within the substrate. APC/C(Fzr) is activated in early G1.","method":"Swapped destruction box mutant constructs; real-time fluorescence-based degradation assay; in vitro APC/C ubiquitination assay","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution combined with live-cell real-time degradation assays and systematic mutagenesis","pmids":["12198152"],"is_preprint":false},{"year":2002,"finding":"Human Aurora-A kinase is targeted for degradation by APC/C(hCdh1/FZR1) in vivo, dependent on its destruction box, KEN box motifs, and its kinase activity. hCdc20 does not mediate Aurora-A degradation.","method":"Co-expression and immunoprecipitation; in vivo degradation assay with destruction box and KEN box mutants; kinase-dead mutant analysis","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo degradation with mutagenesis of degron motifs, single lab","pmids":["12023018"],"is_preprint":false},{"year":2002,"finding":"C. elegans fzr-1 (Cdh1 homolog) functions redundantly with lin-35/Rb to control cell proliferation. Genetic epistasis places fzr-1 in a pathway regulating cyclin levels and cell cycle progression; simultaneous loss of both fzr-1 and lin-35 produces severe proliferation defects not seen with either single mutant.","method":"Synthetic-lethal genetic screen; double-mutant epistasis analysis in C. elegans","journal":"Genes & development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with defined phenotypic readout, single lab","pmids":["11850412"],"is_preprint":false},{"year":2002,"finding":"Drosophila Fzr (encoded by fzr/rap) is essential during G1 but not for mitotic exit including cyclin B degradation. FZR accumulates predominantly in the cytoplasm in Drosophila cells. Loss of fzr causes lethality corresponding to the rap locus.","method":"Genetic null allele characterization; fzr2 expression analysis; cell fractionation/localization; cyclin B degradation assay in fzr mutants","journal":"Current biology : CB","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with defined phenotypic readout and localization data, single lab","pmids":["12194827"],"is_preprint":false},{"year":2004,"finding":"Mammalian Cdh1/FZR1 mediates its own degradation by activating the APC/C to ubiquitinate itself via two RXXL-type destruction boxes. In G1/G0, Cdh1 is nearly entirely APC/C-associated and present at lower levels. Addition of Cdh1 to Xenopus interphase extracts activates APC/C to degrade Cdh1 itself.","method":"In vitro Xenopus interphase extract degradation assay; destruction box mutagenesis; co-immunoprecipitation of Cdh1 with APC/C; Western blot cell cycle analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution in Xenopus extracts plus mutagenesis plus biochemical fractionation, multiple orthogonal methods","pmids":["15029244"],"is_preprint":false},{"year":2009,"finding":"Loss of FZR1 in human cell lines (RNAi) and mouse embryonic fibroblasts (conditional knockout) shortens G1 phase and prolongs S phase, induces DNA-damage responses, and impairs proliferation independently of p53 status. FZR1 is not required for mitotic exit in mammalian somatic cells.","method":"RNAi knockdown in human cell lines; conditional gene targeting in MEFs; cell cycle analysis; DNA damage response markers","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — two independent model systems (RNAi and conditional KO), multiple cell lines, orthogonal functional readouts","pmids":["19861496"],"is_preprint":false},{"year":2009,"finding":"CDC14B phosphatase prevents meiotic resumption in mouse oocytes through FZR1 (Cdh1). Depletion of FZR1 partially restores normal meiotic timing in oocytes with excess CDC14B, placing FZR1 downstream of CDC14B in controlling APC/C-mediated cyclin B1 proteolysis and prophase I arrest.","method":"mRNA injection for overexpression; morpholino/siRNA depletion of FZR1 and CDC14B in mouse oocytes; epistasis analysis; localization studies","journal":"Biology of reproduction","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis via depletion/overexpression in oocytes, single lab","pmids":["19129509"],"is_preprint":false},{"year":2010,"finding":"APC/C(Fzr/Cdh1) controls peripheral glial migration in post-mitotic Drosophila neurons by regulating the axonal distribution of the cell adhesion molecule Fasciclin2 (Fas2). Fzr/Cdh1 establishes a graded axonal Fas2 distribution, and axonal Fas2 interacts homophilically with a glial isoform to guide glial migration.","method":"Genetic loss-of-function (fzr mutants); immunofluorescence; in vivo imaging of glial migration; epistasis with fas2 alleles","journal":"Nature neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis and in vivo imaging in Drosophila, single lab","pmids":["20890296"],"is_preprint":false},{"year":2011,"finding":"APC/C(FZR1) activity in mouse oocytes is required to repress cyclin B1 levels during prophase I arrest, maintaining meiotic quiescence. In oocyte-specific Fzr1 knockout mice, cyclin B1 levels are ~5-fold elevated, prophase I/GV arrest is compromised, and cyclin B1 knockdown in Fzr1-null oocytes partially rescues the timing of meiotic resumption.","method":"Oocyte-specific conditional knockout; Western blot; cyclin B1 knockdown rescue experiment; in vitro oocyte maturation assay","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with substrate-level rescue experiment, multiple functional readouts, in vivo model","pmids":["21270054"],"is_preprint":false},{"year":2012,"finding":"FZR1 controls the timing of bipolar meiotic spindle assembly in mouse oocytes, thereby regulating when the spindle assembly checkpoint (SAC) is satisfied and APC/C(CDC20) becomes active. Loss of FZR1 accelerates spindle assembly, leading to premature bivalent attachment, poor chromosome congression, and 25% nondisjunction. FZR1 loss does not abrogate SAC functionality.","method":"Oocyte-specific Fzr1 conditional knockout; live imaging; SAC marker (MAD2) localization; spindle assembly timing assay","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with live imaging and mechanistic pathway placement (spindle assembly → SAC satisfaction → APC/C CDC20), multiple orthogonal readouts","pmids":["22918942"],"is_preprint":false},{"year":2012,"finding":"Maternal and zygotic FZR1 is required for syngamy (establishment of a single spindle from two pronuclei) and maintenance of genomic integrity during the first mitotic divisions of mouse embryos. Absence of both maternal and paternal FZR1 leads to formation of two independent spindles after pronuclear fusion, binucleate 2-cell embryos, and embryonic arrest.","method":"Oocyte-specific knockout (maternal FZR1 depleted) crossed to zygotic null; γ-H2AX foci imaging; live imaging of spindle formation","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with defined cellular phenotype and imaging, single lab","pmids":["23097041"],"is_preprint":false},{"year":2015,"finding":"FZR1 is a substrate of CDK4/6-cyclin D kinase. CDK-4/CYD-1 phosphorylates specific residues in the FZR-1 amino terminus (C. elegans), resembling inactivating phosphorylations of human FZR1. Simultaneous knockdown of Rb and FZR1 in human breast cancer cells synergistically bypasses cell division arrest induced by the CDK4/6-specific inhibitor PD-0332991.","method":"Unbiased genetic screen in C. elegans; phosphorylation site mapping; RNAi double knockdown in human breast cancer cells; CDK4/6 inhibitor rescue assay","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — identified in C. elegans screen, validated with human cells using RNAi and pharmacological inhibitor, multiple orthogonal methods across two organisms","pmids":["25562820"],"is_preprint":false},{"year":2016,"finding":"Drosophila Fzr/Cdh1 localizes to centrioles during interphase via direct interaction with the centrosome component Spd2. This centrosomal localization is essential for optimal APC/C activation toward its centrosomal substrate Aurora A. Spd2 is itself a novel APC/C(Fzr) substrate.","method":"Co-immunoprecipitation; Spd2 mutants unable to bind Fzr; in vivo localization (immunofluorescence); APC/C activity assays toward Aurora A substrate","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct interaction identified by co-IP, binding-defective mutants used to demonstrate functional consequence, substrate degradation assay","pmids":["27558644"],"is_preprint":false},{"year":2016,"finding":"APC/C(FZR1) ubiquitinates Topoisomerase IIα (TOPIIα) for degradation. Knockdown of FZR1 in multiple myeloma cells reduces viability and induces growth arrest, with accumulation of TOPIIα as a substrate readout.","method":"siRNA knockdown; Western blot for substrate accumulation (TOPIIα); cell viability assay; APC/C inhibitor (proTAME)","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — substrate accumulation upon FZR1 knockdown with pharmacological validation, single lab","pmids":["27655696"],"is_preprint":false},{"year":2016,"finding":"APC/C(Fzr/Cdh1) negatively regulates Nek2 kinase (a direct substrate targeted for ubiquitination and degradation), which in turn negatively regulates the PCP factor Dishevelled. Loss of APC/C function in Drosophila leads to reduced Dishevelled levels through Nek2 accumulation, establishing a post-mitotic role for APC/C(Fzr) in epithelial planar cell polarity.","method":"Genetic loss-of-function; epistasis analysis; in vivo substrate degradation assay; immunofluorescence","journal":"Developmental cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with defined pathway placement and substrate identification, single lab","pmids":["28041906"],"is_preprint":false},{"year":2017,"finding":"FZR1 inhibits BRAF through two distinct mechanisms: (1) APC/C(FZR1) ubiquitinates BRAF for proteasomal degradation in primary cells; (2) APC/C-free FZR1 suppresses BRAF by disrupting BRAF dimerization. ERK and CYCLIN D1/CDK4 phosphorylate FZR1 to inhibit APC/C(FZR1) activity. CDK4 and/or BRAF/MEK inhibitors restore APC/C(FZR1) activity.","method":"Co-immunoprecipitation; ubiquitination assays; FZR1 phosphorylation site identification; in vivo mouse model (Fzr1 ablation with Pten loss); pharmacological inhibitor treatments","journal":"Cancer discovery","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (ubiquitination assay, Co-IP for dimerization disruption, phosphorylation mapping, in vivo mouse model), mechanistically distinct findings replicated across systems","pmids":["28174173"],"is_preprint":false},{"year":2018,"finding":"PRL-3 phosphatase dephosphorylates FZR1, which activates the APC/C(FZR1) complex, leading to enhanced AURKA ubiquitination and degradation. PRL-3 physically interacts with both AURKA and FZR1.","method":"Co-immunoprecipitation; ubiquitination assay; phosphatase-dead PRL-3 mutant; Western blot for AURKA levels upon PRL-3/FZR1 manipulation","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and functional ubiquitination assay with phosphatase-dead mutant control, single lab","pmids":["30498084"],"is_preprint":false},{"year":2020,"finding":"CDK-mediated phosphorylation of FZR1 is required for entry into meiosis II in mouse male germ cells in vivo. Non-phosphorylatable FZR1 knock-in mice show normal somatic cell cycles but male infertility due to failure to enter meiosis II and form spermatids, associated with dysregulated APC/C activity.","method":"Non-phosphorylatable knock-in mouse model (CDK-site substitution); testis histology; germ cell meiosis progression analysis; Western blot for FZR1 substrates","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo knock-in mouse model with specific CDK phospho-site substitution and defined meiotic phenotype","pmids":["32572094"],"is_preprint":false},{"year":2020,"finding":"Fzr/Cdh1 interacts with chromatin-associated histone H2B to enhance H2B ubiquitination at the Myc promoter, promoting Myc transcription, which in turn drives MCM6 expression to promote DNA replication during endoreplication. This non-APC/C transcriptional cascade is conserved between Drosophila and mammalian cells.","method":"Co-immunoprecipitation; ChIP; promoter reporter assays; genetic knockdown of fzr; conservation validated in mammalian cells","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ChIP, and functional reporter assays in Drosophila with mammalian validation, single lab","pmids":["32182338"],"is_preprint":false},{"year":2021,"finding":"FZR1 ubiquitinates RUNX1 at lysine 125, targeting it for proteasomal degradation. FZR1 insufficiency leads to RUNX1 accumulation, which disrupts HSC quiescence and self-renewal in aplastic anemia.","method":"Ubiquitination assay with K125 mutation; Fzr1 heterozygous knockout mouse models; RUNX1 knockdown rescue in Fzr1+/- HSCs; in vivo repopulation assay","journal":"Leukemia","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ubiquitination site identified by mutagenesis and rescue experiment in vivo, single lab","pmids":["34635784"],"is_preprint":false},{"year":2021,"finding":"FZR1 interacts with pRB via an LxCxD motif; the cysteine residue in this motif is critical for direct binding to pRB's LxCxE-binding pocket. Mutation of this cysteine disrupts pRB interaction but not FZR1 association with core APC/C. FZR1 LxCxD mutant cells show accumulation of SKP2 and PLK1, downregulation of p27Kip1 and p21Cip1, and premature S-phase entry.","method":"Point mutagenesis; in vitro binding assay; competition with HPV E7; co-immunoprecipitation; cell cycle analysis","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis with in vitro and in vivo binding validation plus functional cell cycle readout, single lab","pmids":["33971196"],"is_preprint":false},{"year":2022,"finding":"The reported C-terminal D-box of Aurora A (AURKA) does not function as a degron for APC/C(FZR1)-dependent degradation; instead, it mediates essential structural features of the protein. The N-terminal A-box (containing the QRVL motif, a phospho-regulated D-box) in the intrinsically disordered region of AURKA is sufficient to confer FZR1-dependent mitotic degradation.","method":"In cellulo degradation assays with AURKA deletion/mutation constructs; in silico D-box prediction; cell-based FZR1-dependent degradation assay with N-terminal fragment","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis and deletion analysis in living cells, single lab, reports a negative (C-terminal D-box not functional) and positive (N-terminal A-box sufficient) finding","pmids":["36450448"],"is_preprint":false},{"year":2017,"finding":"APC/C(FZR-1) in C. elegans regulates centrosome duplication by controlling SAS-5 protein levels. FZR-1 directly recognizes the KEN-box motif of SAS-5 to promote its degradation. FZR-1 associates with centrosomes and is enriched at nuclei during mitotic cell division in early embryos.","method":"fzr-1 loss-of-function genetics; immunofluorescence for FZR-1 localization; centrosome duplication assay; KEN-box mutant analysis of SAS-5","journal":"G3 (Bethesda, Md.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with substrate KEN-box mutation and centrosome duplication readout, single lab","pmids":["29030390"],"is_preprint":false},{"year":2025,"finding":"In C. elegans, APC/C(FZR-1) facilitates the degradation of chromatin regulators MES-4 and MES-3 when germline stem cells transition toward oocyte differentiation. Notch signaling from the distal tip cell restricts APC/C(FZR-1) activity to allow MES-3 and MES-4 accumulation in GSCs and maintain stemness.","method":"Genetic loss-of-function of fzr-1 and APC/C subunits; protein level measurements by immunofluorescence; epistasis with Notch pathway mutants","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with defined substrate degradation and functional stemness readout, single lab","pmids":["40446035"],"is_preprint":false},{"year":2025,"finding":"SPD-2 (homolog of human CEP192) is a substrate of APC/C(FZR-1) in C. elegans embryos. SPD-2 physically associates with FZR-1 in vivo. Three distinct D-box motifs in SPD-2 contribute differentially to degradation and centrosomal localization: D-box3 mutation stabilizes centrosomal SPD-2 and restores centrosome duplication in zyg-1 mutants, while D-box1 mutation reduces centrosomal SPD-2 and worsens duplication defects.","method":"Co-immunoprecipitation (FZR-1 and SPD-2 in vivo); D-box site mutagenesis; centrosome duplication rescue assay; immunofluorescence","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and systematic D-box mutagenesis with functional centrosome duplication readout; preprint, single lab","pmids":["41278915"],"is_preprint":true},{"year":2025,"finding":"FZR1/Cdh1 promotes TRAF3 and TRAF6 autoubiquitination independently of the APC/C, attenuates MAVS binding to PFKFB3, promotes MAVS aggregation, and thereby activates IRF3 and NF-κB to drive type I interferon and proinflammatory cytokine production during RNA virus infection. This antiviral function is enhanced by m6A-mediated increase in FZR1 translation upon VSV infection.","method":"Co-immunoprecipitation; ubiquitination assay (TRAF3/6 autoubiquitination); MAVS aggregation assay; FZR1 knockout cells and mice; pharmacological FZR1 inhibition","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple biochemical assays (Co-IP, ubiquitination, aggregation) and in vivo KO validation, but novel non-canonical function reported by single lab","pmids":["41805567"],"is_preprint":false},{"year":2025,"finding":"USP8 deubiquitinase interacts with FZR1 (Fzr) and deubiquitinates it to promote its stabilization, which is required for endoreplication in Drosophila salivary gland and Bombyx silk gland. Hsp70 mediates proper folding of Fzr and increases the Fzr-USP8 interaction, thereby enhancing Fzr deubiquitination.","method":"Co-immunoprecipitation; deubiquitination assay; genetic depletion of USP8 and Hsp70; endoreplication assay","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and deubiquitination assay with functional rescue in two insect models, single lab","pmids":["40106570"],"is_preprint":false},{"year":2023,"finding":"GEMIN5, an m6A reader protein, binds m6A-modified FZR1 mRNA and recruits the eIF3 translation initiation complex, accelerating FZR1 protein translation. Elevated FZR1 protein maintains G0-G1 quiescence and suppresses gemcitabine sensitivity in pancreatic cancer cells.","method":"m6A profiling; GEMIN5-FZR1 mRNA Co-IP; eIF3 complex co-immunoprecipitation; FZR1 knockdown; cell cycle analysis","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical identification of m6A reader and translation complex recruitment, functional validation with KD, single lab","pmids":["37326469"],"is_preprint":false},{"year":2025,"finding":"FZR1 ubiquitinates ANLN (Anillin) for degradation. CCNE1 (Cyclin E1) competes with FZR1-mediated ANLN ubiquitination by binding ANLN and stabilizing it, promoting TNBC stemness and progression. Mutation of the ANLN ubiquitination site abolishes CCNE1's regulatory effect.","method":"Co-immunoprecipitation; ubiquitination assay; ANLN ubiquitination site mutagenesis; CCNE1 knockdown/overexpression; in vitro and in vivo functional assays","journal":"Cell death discovery","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ubiquitination assay with site-specific mutagenesis and co-IP, single lab","pmids":["40346052"],"is_preprint":false},{"year":2026,"finding":"FZR1 ubiquitinates c-MYC for proteasomal degradation. DSN1 competes with c-MYC for FZR1 binding, thereby attenuating c-MYC ubiquitination and stabilizing c-MYC to promote colorectal cancer metastasis.","method":"Co-immunoprecipitation; ubiquitination assay; cycloheximide chase; proteasome inhibition; rescue experiment with c-MYC overexpression","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ubiquitination assay with competitive binding Co-IP and functional rescue, single lab","pmids":["41713835"],"is_preprint":false}],"current_model":"FZR1 (Cdh1/Fzr) is a WD40-repeat co-activator of the APC/C E3 ubiquitin ligase that recognizes substrates bearing RXXL destruction boxes or KEN boxes and drives their ubiquitination and proteasomal degradation; it is activated during mitotic exit and throughout G1/G0 (after CDC20/Fzy, which acts earlier), requires centrosomal anchoring via Spd2 for local APC/C activity toward Aurora A, and is itself regulated by CDK-mediated phosphorylation (inactivating) and auto-degradation; its canonical substrates include securin, cyclin B, Aurora A, SKP2, PLK1, RUNX1, BRAF, ANLN, c-MYC, and others, and beyond cell-cycle control it functions post-mitotically in axon growth, glial migration, planar cell polarity (via Nek2/Dishevelled), meiotic prophase I quiescence, spindle assembly timing, and antiviral innate immunity (via APC/C-independent TRAF3/6 ubiquitination)."},"narrative":{"mechanistic_narrative":"FZR1 (Cdh1/Fzr) is a substrate-recognition co-activator of the APC/C E3 ubiquitin ligase that drives ubiquitination and proteasomal degradation of cell-cycle regulators bearing RXXL destruction-box and KEN-box degrons [PMID:11179223, PMID:12198152]. By recognizing these motifs it targets securin, Aurora A, and additional substrates, with KEN-box substrates degraded exclusively by APC/C(FZR1) while RXXL substrates can be shared with the CDC20-activated form [PMID:11179223, PMID:12198152, PMID:12023018]. FZR1 acts predominantly during mitotic exit and G1/G0—mediating a cytoplasm-wide phase of cyclin B destruction distinct from the CDC20/Fzy-driven spindle-localized phase—and its loss in mammalian somatic cells shortens G1, prolongs S phase, and triggers DNA-damage responses rather than blocking mitotic exit [PMID:12082076, PMID:19861496]. Its activity is gated by inactivating CDK4/6–cyclin D and ERK phosphorylation and reversed by phosphatases such as PRL-3, and FZR1 also catalyzes its own APC/C-dependent auto-degradation through internal destruction boxes [PMID:15029244, PMID:25562820, PMID:28174173, PMID:30498084]. Centrosomal anchoring via direct binding to Spd2/CEP192 localizes APC/C(FZR1) activity toward centrosomal substrates including Aurora A and SPD-2/CEP192, coupling the ligase to centrosome duplication control [PMID:27558644, PMID:29030390, PMID:41278915]. Beyond canonical cell-cycle control, FZR1 functions in meiotic prophase I quiescence and spindle-assembly timing in oocytes by repressing cyclin B1 [PMID:21270054, PMID:22918942], in post-mitotic neurons and epithelia through substrates such as Fasciclin2 and Nek2/Dishevelled [PMID:20890296, PMID:28041906], and in hematopoietic and cancer contexts by degrading RUNX1, BRAF, ANLN, and c-MYC [PMID:28174173, PMID:34635784, PMID:40346052, PMID:41713835]. FZR1 additionally engages APC/C-independent roles, including suppression of BRAF dimerization, an H2B-ubiquitination/Myc transcriptional cascade driving endoreplication, and promotion of TRAF3/6 autoubiquitination to activate antiviral type I interferon signaling [PMID:28174173, PMID:32182338, PMID:41805567].","teleology":[{"year":2001,"claim":"Established that FZR1 confers substrate specificity on the APC/C through recognition of defined degron motifs, answering how the ligase selects its targets.","evidence":"In vitro APC/C ubiquitination of securin with destruction-box and KEN-box mutagenesis","pmids":["11179223"],"confidence":"High","gaps":["Did not map FZR1 residues contacting the degrons","Limited to one substrate"]},{"year":2002,"claim":"Resolved how APC/C activator choice and degron type set the timing and order of substrate destruction, distinguishing FZR1 from CDC20 function.","evidence":"Swapped degron constructs with real-time degradation assays; Drosophila live imaging of cyclin B destruction phases; Aurora-A degradation assays","pmids":["12198152","12082076","12023018"],"confidence":"High","gaps":["Aurora-A finding from single lab at Medium confidence","Structural basis of differential RXXL recognition not defined"]},{"year":2002,"claim":"Defined FZR1's organismal role as a G1 regulator acting redundantly with the Rb pathway, distinguishing it from a strict mitotic-exit function.","evidence":"C. elegans synthetic-lethal genetics with lin-35/Rb; Drosophila null-allele characterization","pmids":["11850412","12194827"],"confidence":"Medium","gaps":["Molecular substrates underlying proliferation control not identified in these studies","Cross-species generality untested at the time"]},{"year":2004,"claim":"Showed FZR1 catalyzes its own destruction via APC/C, establishing an autoregulatory loop that limits its abundance.","evidence":"Xenopus interphase extract degradation assay with destruction-box mutagenesis and co-IP with APC/C","pmids":["15029244"],"confidence":"High","gaps":["Physiological trigger for auto-degradation timing not defined"]},{"year":2009,"claim":"Demonstrated that in mammalian somatic cells FZR1 governs G1/S timing and genome stability rather than mitotic exit, redefining its mammalian role.","evidence":"RNAi in human cell lines and conditional knockout MEFs with cell-cycle and DNA-damage readouts","pmids":["19861496"],"confidence":"High","gaps":["Specific substrates causing the S-phase/DNA-damage phenotype not pinned down"]},{"year":2009,"claim":"Placed FZR1 in the meiotic-arrest pathway downstream of CDC14B, linking phosphatase regulation to APC/C-mediated cyclin B1 control in oocytes.","evidence":"Overexpression and depletion epistasis in mouse oocytes","pmids":["19129509"],"confidence":"Medium","gaps":["Direct dephosphorylation of FZR1 by CDC14B not shown","Single lab"]},{"year":2010,"claim":"Extended FZR1 function into post-mitotic biology, showing it patterns axonal adhesion molecules to guide glial migration.","evidence":"Drosophila fzr loss-of-function with imaging and fas2 epistasis","pmids":["20890296"],"confidence":"Medium","gaps":["Whether Fas2 distribution is controlled via direct APC/C substrate turnover unclear","Single organism"]},{"year":2011,"claim":"Established that APC/C(FZR1) maintains meiotic prophase I quiescence by repressing cyclin B1 levels in vivo.","evidence":"Oocyte-specific conditional knockout with cyclin B1 knockdown rescue","pmids":["21270054"],"confidence":"High","gaps":["Other meiotic substrates not characterized"]},{"year":2012,"claim":"Showed FZR1 controls meiotic spindle-assembly timing and embryonic syngamy, linking its activity to chromosome segregation fidelity.","evidence":"Oocyte-specific and maternal-zygotic Fzr1 knockouts with live imaging and SAC markers","pmids":["22918942","23097041"],"confidence":"High","gaps":["Mechanism connecting FZR1 to spindle assembly rate undefined","Syngamy study single lab at Medium confidence"]},{"year":2015,"claim":"Identified inactivating CDK4/6–cyclin D phosphorylation of FZR1, linking it to CDK4/6-inhibitor response and revealing a cooperative axis with Rb.","evidence":"C. elegans genetic screen, phospho-site mapping, and RNAi/CDK4-6 inhibitor assays in human breast cancer cells","pmids":["25562820"],"confidence":"High","gaps":["Full repertoire of CDK-regulated FZR1 sites in humans not completely mapped"]},{"year":2016,"claim":"Defined how FZR1 is spatially targeted, showing direct Spd2 binding localizes APC/C(FZR1) to centrosomes for efficient Aurora A degradation.","evidence":"Co-IP, binding-defective Spd2 mutants, and centrosomal APC/C activity assays in Drosophila","pmids":["27558644"],"confidence":"High","gaps":["Conservation of Spd2-mediated anchoring in mammals not addressed here"]},{"year":2016,"claim":"Expanded the FZR1 substrate set in disease, identifying TOPIIα degradation and an FZR1 dependency in multiple myeloma.","evidence":"siRNA, substrate accumulation Westerns, and proTAME treatment in myeloma cells","pmids":["27655696"],"confidence":"Medium","gaps":["Direct ubiquitination of TOPIIα by FZR1 not reconstituted","Single lab"]},{"year":2016,"claim":"Revealed a post-mitotic developmental role in planar cell polarity through the FZR1–Nek2–Dishevelled axis.","evidence":"Drosophila genetics, epistasis, and substrate degradation assays","pmids":["28041906"],"confidence":"Medium","gaps":["Mammalian conservation untested","Single lab"]},{"year":2017,"claim":"Uncovered dual APC/C-dependent and APC/C-independent suppression of BRAF by FZR1 and its inactivation by ERK and CDK4, connecting FZR1 to oncogenic MAPK signaling.","evidence":"Ubiquitination assays, dimerization co-IP, phospho-site mapping, and Fzr1/Pten mouse model with inhibitor treatments","pmids":["28174173"],"confidence":"High","gaps":["Relative contribution of degradation versus dimerization disruption in vivo not quantified"]},{"year":2017,"claim":"Showed FZR1 controls centrosome duplication by degrading SAS-5 via KEN-box recognition, linking the ligase to centriole number control.","evidence":"C. elegans fzr-1 genetics with SAS-5 KEN-box mutagenesis and centrosome assays","pmids":["29030390"],"confidence":"Medium","gaps":["Mammalian SAS-5 orthologs not tested","Single lab"]},{"year":2018,"claim":"Identified PRL-3 as an activating phosphatase that dephosphorylates FZR1 to drive AURKA degradation, complementing the kinase-based inactivation model.","evidence":"Co-IP, ubiquitination assay, and phosphatase-dead PRL-3 mutant","pmids":["30498084"],"confidence":"Medium","gaps":["Specific FZR1 residues dephosphorylated by PRL-3 not mapped","Single lab"]},{"year":2020,"claim":"Established that CDK phosphorylation of FZR1 is required in vivo for the meiotic II transition in male germ cells, defining a germline-specific regulatory requirement.","evidence":"Non-phosphorylatable Fzr1 knock-in mice with testis histology and substrate Westerns","pmids":["32572094"],"confidence":"High","gaps":["Substrates whose mistimed turnover causes the meiosis II failure not fully defined"]},{"year":2020,"claim":"Revealed an APC/C-independent transcriptional role in which FZR1 promotes H2B ubiquitination at the Myc promoter to drive endoreplication.","evidence":"Co-IP, ChIP, and reporter assays in Drosophila with mammalian validation","pmids":["32182338"],"confidence":"Medium","gaps":["Mechanism by which FZR1 stimulates H2B ubiquitination not biochemically reconstituted","Single lab"]},{"year":2021,"claim":"Connected FZR1 to hematopoietic stem cell biology and aplastic anemia through site-specific RUNX1 ubiquitination.","evidence":"Ubiquitination assay with K125 mutant, Fzr1+/- mice, and RUNX1 knockdown rescue in HSCs","pmids":["34635784"],"confidence":"Medium","gaps":["Whether RUNX1 turnover is APC/C-dependent not isolated","Single lab"]},{"year":2021,"claim":"Defined a direct FZR1–pRB interaction via an LxCxD motif separable from core APC/C binding, controlling SKP2/PLK1 and CDK-inhibitor levels and S-phase entry.","evidence":"Point mutagenesis, in vitro binding, HPV E7 competition, and cell-cycle analysis","pmids":["33971196"],"confidence":"Medium","gaps":["Functional significance of pRB binding in normal tissue not established","Single lab"]},{"year":2022,"claim":"Re-mapped the Aurora A degron, showing the N-terminal A-box rather than the C-terminal D-box confers FZR1-dependent degradation.","evidence":"In cellulo degradation assays with AURKA deletion and mutation constructs","pmids":["36450448"],"confidence":"Medium","gaps":["Structural basis of A-box recognition by FZR1 not solved","Single lab"]},{"year":2023,"claim":"Showed FZR1 abundance is set translationally via m6A-dependent GEMIN5/eIF3 recruitment, coupling FZR1 to quiescence and chemoresistance in pancreatic cancer.","evidence":"m6A profiling, GEMIN5–FZR1 mRNA co-IP, eIF3 co-IP, and FZR1 knockdown","pmids":["37326469"],"confidence":"Medium","gaps":["Whether translational upregulation broadly governs FZR1 levels beyond this context unclear","Single lab"]},{"year":2025,"claim":"Expanded oncogenic substrate recognition, showing FZR1 degrades ANLN and c-MYC and that competing factors stabilize these substrates to drive cancer progression.","evidence":"Ubiquitination assays with substrate-site mutagenesis, competitive co-IP, and functional cancer assays","pmids":["40346052","41713835"],"confidence":"Medium","gaps":["APC/C dependence of ANLN and c-MYC degradation not isolated","Each finding single lab"]},{"year":2025,"claim":"Demonstrated germline stem cell roles, with APC/C(FZR-1) degrading chromatin regulators MES-3/MES-4 under Notch control during oocyte differentiation.","evidence":"C. elegans fzr-1 and APC/C genetics with substrate quantification and Notch epistasis","pmids":["40446035"],"confidence":"Medium","gaps":["Direct degron recognition of MES proteins not mapped","Single lab"]},{"year":2025,"claim":"Established stabilizing regulation of FZR1 by USP8 deubiquitination and Hsp70-assisted folding required for endoreplication.","evidence":"Co-IP, deubiquitination assay, and genetic depletion in Drosophila and Bombyx","pmids":["40106570"],"confidence":"Medium","gaps":["Mammalian relevance of USP8/Hsp70 control untested","Single lab"]},{"year":2025,"claim":"Revealed an APC/C-independent antiviral role in which FZR1 promotes TRAF3/6 autoubiquitination and MAVS aggregation to activate type I interferon signaling.","evidence":"Co-IP, autoubiquitination and MAVS aggregation assays, FZR1 knockout cells and mice, and inhibitor treatment","pmids":["41805567"],"confidence":"Medium","gaps":["Direct ligase mechanism on TRAF3/6 versus a scaffolding role not fully separated","Novel function from single lab"]},{"year":2025,"claim":"Provided evidence that SPD-2/CEP192 is an FZR1 substrate with multiple D-boxes differentially controlling centrosomal localization and duplication.","evidence":"In vivo co-IP and systematic D-box mutagenesis with centrosome duplication rescue (preprint)","pmids":["41278915"],"confidence":"Medium","gaps":["Preprint, not peer reviewed","Mammalian CEP192 not tested"]},{"year":null,"claim":"How FZR1 mechanistically partitions between its canonical APC/C co-activator function and its growing set of APC/C-independent activities, and the structural basis for its diverse degron and protein-interaction recognition, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of FZR1 bound to its various degrons","Switch governing APC/C-dependent versus -independent modes not defined","Mammalian conservation of several invertebrate findings untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,3,17,21,30,31]},{"term_id":"GO:0098772","term_label":"molecular function 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Through the regulation of RBBP8/CtIP protein turnover, may play a role in DNA damage response, favoring DNA double-strand repair through error-prone non-homologous end joining (NHEJ) over error-free, RBBP8-mediated homologous recombination (HR) (PubMed:25349192)","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q9UM11/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FZR1","classification":"Not 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HECW2","url":"https://www.omim.org/entry/617245"},{"mim_id":"606946","title":"ANAPHASE-PROMOTING COMPLEX, SUBUNIT 2; ANAPC2","url":"https://www.omim.org/entry/606946"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Nuclear membrane","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in 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management science","url":"https://pubmed.ncbi.nlm.nih.gov/39229824","citation_count":2,"is_preprint":false},{"pmid":"40446035","id":"PMC_40446035","title":"Notch controls APC/CFZR-1 to enable accumulation of chromatin regulators in germline stem cells from Caenorhabditis elegans.","date":"2025","source":"Science advances","url":"https://pubmed.ncbi.nlm.nih.gov/40446035","citation_count":0,"is_preprint":false},{"pmid":"41805567","id":"PMC_41805567","title":"N6-methyladenosine modification of FZR1 mRNA positively regulates antiviral innate immunity by targeting the MAVS-TRAF3/6 axis.","date":"2026","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/41805567","citation_count":0,"is_preprint":false},{"pmid":"41553232","id":"PMC_41553232","title":"Fzr knockdown disrupts cell cycle transition in ovarian follicle cells of Nilaparvata lugens.","date":"2026","source":"Insect science","url":"https://pubmed.ncbi.nlm.nih.gov/41553232","citation_count":0,"is_preprint":false},{"pmid":"28373167","id":"PMC_28373167","title":"Anaphase-Promoting Complex Adaptor FZR1/CDH1 Blocks BRAF Signaling Both by Targeting BRAF for Proteolytic Degradation and by Disrupting BRAF Dimerization.","date":"2017","source":"Cancer discovery","url":"https://pubmed.ncbi.nlm.nih.gov/28373167","citation_count":0,"is_preprint":false},{"pmid":"41278915","id":"PMC_41278915","title":"Distinct D-box Motifs in SPD-2 Mediate APC/CFZR-1-Dependent Degradation and Centrosomal Localization in Caenorhabditis elegans Embryos.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41278915","citation_count":0,"is_preprint":false},{"pmid":"41713835","id":"PMC_41713835","title":"DSN1 promotes colorectal cancer metastasis by Inhibiting FZR1-Mediated ubiquitination of c-MYC.","date":"2026","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/41713835","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.10.14.682142","title":"Distinct D-box Motifs in SPD-2 Mediate APC/C  <sup>FZR-1</sup>  -Dependent Degradation and Centrosomal Localization in  <i>Caenorhabditis elegans</i>  Embryos","date":"2025-10-15","source":"bioRxiv","url":"https://doi.org/10.1101/2025.10.14.682142","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.01.26.634919","title":"Feedback regulation between FOXM1 and APC/C  <sup>Cdh1</sup>  determines the changes in cell cycle dynamics during aging","date":"2025-01-27","source":"bioRxiv","url":"https://doi.org/10.1101/2025.01.26.634919","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":28414,"output_tokens":8229,"usd":0.104339,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":17533,"output_tokens":6843,"usd":0.12937,"stage2_stop_reason":"end_turn"},"total_usd":0.233709,"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\": 2001,\n      \"finding\": \"FZR1 (Fzr/Cdh1) activates the APC/C to ubiquitinate and degrade human securin/PTTG in vitro. Securin degradation is mediated by both an RXXL destruction box and a KEN box; mutation of both sequences together is required to prevent ubiquitination and degradation.\",\n      \"method\": \"In vitro APC/C ubiquitination assay; destruction box/KEN box mutagenesis; cell-based expression of non-degradable securin mutant\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution of ubiquitination combined with mutagenesis of degron motifs, replicated with cell-based assays\",\n      \"pmids\": [\"11179223\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Drosophila Fzr/Cdh1 binds microtubules in vitro and associates with spindles in vivo, concentrating at centrosomes throughout the cell cycle. Fzr/Cdh1 is responsible for the second, cytoplasm-wide phase of cyclin B destruction during mitotic exit, distinct from the spindle-localized destruction driven by Fzy/Cdc20.\",\n      \"method\": \"Microtubule-binding assay in vitro; in vivo live imaging and immunofluorescence; destruction-box mutant cyclin B (CBTPM-GFP) degradation assay in syncytial vs. cellularized embryos\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (in vitro binding, in vivo localization, functional degradation assays with degron mutants)\",\n      \"pmids\": [\"12082076\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"APC/C(FZR1)-dependent degradation timing is determined by the specificity of destruction box (RXXL) and KEN box motifs. KEN-box substrates are degraded exclusively by APC/C(Fzr); RXXL substrates can be degraded by both APC/C(Fzy) and APC/C(Fzr), but APC/C(Fzy)-specific RXXL degradation is highly dependent on the location of the RXXL within the substrate. APC/C(Fzr) is activated in early G1.\",\n      \"method\": \"Swapped destruction box mutant constructs; real-time fluorescence-based degradation assay; in vitro APC/C ubiquitination assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution combined with live-cell real-time degradation assays and systematic mutagenesis\",\n      \"pmids\": [\"12198152\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Human Aurora-A kinase is targeted for degradation by APC/C(hCdh1/FZR1) in vivo, dependent on its destruction box, KEN box motifs, and its kinase activity. hCdc20 does not mediate Aurora-A degradation.\",\n      \"method\": \"Co-expression and immunoprecipitation; in vivo degradation assay with destruction box and KEN box mutants; kinase-dead mutant analysis\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo degradation with mutagenesis of degron motifs, single lab\",\n      \"pmids\": [\"12023018\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"C. elegans fzr-1 (Cdh1 homolog) functions redundantly with lin-35/Rb to control cell proliferation. Genetic epistasis places fzr-1 in a pathway regulating cyclin levels and cell cycle progression; simultaneous loss of both fzr-1 and lin-35 produces severe proliferation defects not seen with either single mutant.\",\n      \"method\": \"Synthetic-lethal genetic screen; double-mutant epistasis analysis in C. elegans\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with defined phenotypic readout, single lab\",\n      \"pmids\": [\"11850412\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Drosophila Fzr (encoded by fzr/rap) is essential during G1 but not for mitotic exit including cyclin B degradation. FZR accumulates predominantly in the cytoplasm in Drosophila cells. Loss of fzr causes lethality corresponding to the rap locus.\",\n      \"method\": \"Genetic null allele characterization; fzr2 expression analysis; cell fractionation/localization; cyclin B degradation assay in fzr mutants\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with defined phenotypic readout and localization data, single lab\",\n      \"pmids\": [\"12194827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Mammalian Cdh1/FZR1 mediates its own degradation by activating the APC/C to ubiquitinate itself via two RXXL-type destruction boxes. In G1/G0, Cdh1 is nearly entirely APC/C-associated and present at lower levels. Addition of Cdh1 to Xenopus interphase extracts activates APC/C to degrade Cdh1 itself.\",\n      \"method\": \"In vitro Xenopus interphase extract degradation assay; destruction box mutagenesis; co-immunoprecipitation of Cdh1 with APC/C; Western blot cell cycle analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution in Xenopus extracts plus mutagenesis plus biochemical fractionation, multiple orthogonal methods\",\n      \"pmids\": [\"15029244\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Loss of FZR1 in human cell lines (RNAi) and mouse embryonic fibroblasts (conditional knockout) shortens G1 phase and prolongs S phase, induces DNA-damage responses, and impairs proliferation independently of p53 status. FZR1 is not required for mitotic exit in mammalian somatic cells.\",\n      \"method\": \"RNAi knockdown in human cell lines; conditional gene targeting in MEFs; cell cycle analysis; DNA damage response markers\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — two independent model systems (RNAi and conditional KO), multiple cell lines, orthogonal functional readouts\",\n      \"pmids\": [\"19861496\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CDC14B phosphatase prevents meiotic resumption in mouse oocytes through FZR1 (Cdh1). Depletion of FZR1 partially restores normal meiotic timing in oocytes with excess CDC14B, placing FZR1 downstream of CDC14B in controlling APC/C-mediated cyclin B1 proteolysis and prophase I arrest.\",\n      \"method\": \"mRNA injection for overexpression; morpholino/siRNA depletion of FZR1 and CDC14B in mouse oocytes; epistasis analysis; localization studies\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis via depletion/overexpression in oocytes, single lab\",\n      \"pmids\": [\"19129509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"APC/C(Fzr/Cdh1) controls peripheral glial migration in post-mitotic Drosophila neurons by regulating the axonal distribution of the cell adhesion molecule Fasciclin2 (Fas2). Fzr/Cdh1 establishes a graded axonal Fas2 distribution, and axonal Fas2 interacts homophilically with a glial isoform to guide glial migration.\",\n      \"method\": \"Genetic loss-of-function (fzr mutants); immunofluorescence; in vivo imaging of glial migration; epistasis with fas2 alleles\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis and in vivo imaging in Drosophila, single lab\",\n      \"pmids\": [\"20890296\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"APC/C(FZR1) activity in mouse oocytes is required to repress cyclin B1 levels during prophase I arrest, maintaining meiotic quiescence. In oocyte-specific Fzr1 knockout mice, cyclin B1 levels are ~5-fold elevated, prophase I/GV arrest is compromised, and cyclin B1 knockdown in Fzr1-null oocytes partially rescues the timing of meiotic resumption.\",\n      \"method\": \"Oocyte-specific conditional knockout; Western blot; cyclin B1 knockdown rescue experiment; in vitro oocyte maturation assay\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with substrate-level rescue experiment, multiple functional readouts, in vivo model\",\n      \"pmids\": [\"21270054\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"FZR1 controls the timing of bipolar meiotic spindle assembly in mouse oocytes, thereby regulating when the spindle assembly checkpoint (SAC) is satisfied and APC/C(CDC20) becomes active. Loss of FZR1 accelerates spindle assembly, leading to premature bivalent attachment, poor chromosome congression, and 25% nondisjunction. FZR1 loss does not abrogate SAC functionality.\",\n      \"method\": \"Oocyte-specific Fzr1 conditional knockout; live imaging; SAC marker (MAD2) localization; spindle assembly timing assay\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with live imaging and mechanistic pathway placement (spindle assembly → SAC satisfaction → APC/C CDC20), multiple orthogonal readouts\",\n      \"pmids\": [\"22918942\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Maternal and zygotic FZR1 is required for syngamy (establishment of a single spindle from two pronuclei) and maintenance of genomic integrity during the first mitotic divisions of mouse embryos. Absence of both maternal and paternal FZR1 leads to formation of two independent spindles after pronuclear fusion, binucleate 2-cell embryos, and embryonic arrest.\",\n      \"method\": \"Oocyte-specific knockout (maternal FZR1 depleted) crossed to zygotic null; γ-H2AX foci imaging; live imaging of spindle formation\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with defined cellular phenotype and imaging, single lab\",\n      \"pmids\": [\"23097041\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"FZR1 is a substrate of CDK4/6-cyclin D kinase. CDK-4/CYD-1 phosphorylates specific residues in the FZR-1 amino terminus (C. elegans), resembling inactivating phosphorylations of human FZR1. Simultaneous knockdown of Rb and FZR1 in human breast cancer cells synergistically bypasses cell division arrest induced by the CDK4/6-specific inhibitor PD-0332991.\",\n      \"method\": \"Unbiased genetic screen in C. elegans; phosphorylation site mapping; RNAi double knockdown in human breast cancer cells; CDK4/6 inhibitor rescue assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — identified in C. elegans screen, validated with human cells using RNAi and pharmacological inhibitor, multiple orthogonal methods across two organisms\",\n      \"pmids\": [\"25562820\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Drosophila Fzr/Cdh1 localizes to centrioles during interphase via direct interaction with the centrosome component Spd2. This centrosomal localization is essential for optimal APC/C activation toward its centrosomal substrate Aurora A. Spd2 is itself a novel APC/C(Fzr) substrate.\",\n      \"method\": \"Co-immunoprecipitation; Spd2 mutants unable to bind Fzr; in vivo localization (immunofluorescence); APC/C activity assays toward Aurora A substrate\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct interaction identified by co-IP, binding-defective mutants used to demonstrate functional consequence, substrate degradation assay\",\n      \"pmids\": [\"27558644\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"APC/C(FZR1) ubiquitinates Topoisomerase IIα (TOPIIα) for degradation. Knockdown of FZR1 in multiple myeloma cells reduces viability and induces growth arrest, with accumulation of TOPIIα as a substrate readout.\",\n      \"method\": \"siRNA knockdown; Western blot for substrate accumulation (TOPIIα); cell viability assay; APC/C inhibitor (proTAME)\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — substrate accumulation upon FZR1 knockdown with pharmacological validation, single lab\",\n      \"pmids\": [\"27655696\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"APC/C(Fzr/Cdh1) negatively regulates Nek2 kinase (a direct substrate targeted for ubiquitination and degradation), which in turn negatively regulates the PCP factor Dishevelled. Loss of APC/C function in Drosophila leads to reduced Dishevelled levels through Nek2 accumulation, establishing a post-mitotic role for APC/C(Fzr) in epithelial planar cell polarity.\",\n      \"method\": \"Genetic loss-of-function; epistasis analysis; in vivo substrate degradation assay; immunofluorescence\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with defined pathway placement and substrate identification, single lab\",\n      \"pmids\": [\"28041906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"FZR1 inhibits BRAF through two distinct mechanisms: (1) APC/C(FZR1) ubiquitinates BRAF for proteasomal degradation in primary cells; (2) APC/C-free FZR1 suppresses BRAF by disrupting BRAF dimerization. ERK and CYCLIN D1/CDK4 phosphorylate FZR1 to inhibit APC/C(FZR1) activity. CDK4 and/or BRAF/MEK inhibitors restore APC/C(FZR1) activity.\",\n      \"method\": \"Co-immunoprecipitation; ubiquitination assays; FZR1 phosphorylation site identification; in vivo mouse model (Fzr1 ablation with Pten loss); pharmacological inhibitor treatments\",\n      \"journal\": \"Cancer discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (ubiquitination assay, Co-IP for dimerization disruption, phosphorylation mapping, in vivo mouse model), mechanistically distinct findings replicated across systems\",\n      \"pmids\": [\"28174173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PRL-3 phosphatase dephosphorylates FZR1, which activates the APC/C(FZR1) complex, leading to enhanced AURKA ubiquitination and degradation. PRL-3 physically interacts with both AURKA and FZR1.\",\n      \"method\": \"Co-immunoprecipitation; ubiquitination assay; phosphatase-dead PRL-3 mutant; Western blot for AURKA levels upon PRL-3/FZR1 manipulation\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and functional ubiquitination assay with phosphatase-dead mutant control, single lab\",\n      \"pmids\": [\"30498084\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CDK-mediated phosphorylation of FZR1 is required for entry into meiosis II in mouse male germ cells in vivo. Non-phosphorylatable FZR1 knock-in mice show normal somatic cell cycles but male infertility due to failure to enter meiosis II and form spermatids, associated with dysregulated APC/C activity.\",\n      \"method\": \"Non-phosphorylatable knock-in mouse model (CDK-site substitution); testis histology; germ cell meiosis progression analysis; Western blot for FZR1 substrates\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo knock-in mouse model with specific CDK phospho-site substitution and defined meiotic phenotype\",\n      \"pmids\": [\"32572094\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Fzr/Cdh1 interacts with chromatin-associated histone H2B to enhance H2B ubiquitination at the Myc promoter, promoting Myc transcription, which in turn drives MCM6 expression to promote DNA replication during endoreplication. This non-APC/C transcriptional cascade is conserved between Drosophila and mammalian cells.\",\n      \"method\": \"Co-immunoprecipitation; ChIP; promoter reporter assays; genetic knockdown of fzr; conservation validated in mammalian cells\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ChIP, and functional reporter assays in Drosophila with mammalian validation, single lab\",\n      \"pmids\": [\"32182338\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FZR1 ubiquitinates RUNX1 at lysine 125, targeting it for proteasomal degradation. FZR1 insufficiency leads to RUNX1 accumulation, which disrupts HSC quiescence and self-renewal in aplastic anemia.\",\n      \"method\": \"Ubiquitination assay with K125 mutation; Fzr1 heterozygous knockout mouse models; RUNX1 knockdown rescue in Fzr1+/- HSCs; in vivo repopulation assay\",\n      \"journal\": \"Leukemia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ubiquitination site identified by mutagenesis and rescue experiment in vivo, single lab\",\n      \"pmids\": [\"34635784\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FZR1 interacts with pRB via an LxCxD motif; the cysteine residue in this motif is critical for direct binding to pRB's LxCxE-binding pocket. Mutation of this cysteine disrupts pRB interaction but not FZR1 association with core APC/C. FZR1 LxCxD mutant cells show accumulation of SKP2 and PLK1, downregulation of p27Kip1 and p21Cip1, and premature S-phase entry.\",\n      \"method\": \"Point mutagenesis; in vitro binding assay; competition with HPV E7; co-immunoprecipitation; cell cycle analysis\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis with in vitro and in vivo binding validation plus functional cell cycle readout, single lab\",\n      \"pmids\": [\"33971196\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The reported C-terminal D-box of Aurora A (AURKA) does not function as a degron for APC/C(FZR1)-dependent degradation; instead, it mediates essential structural features of the protein. The N-terminal A-box (containing the QRVL motif, a phospho-regulated D-box) in the intrinsically disordered region of AURKA is sufficient to confer FZR1-dependent mitotic degradation.\",\n      \"method\": \"In cellulo degradation assays with AURKA deletion/mutation constructs; in silico D-box prediction; cell-based FZR1-dependent degradation assay with N-terminal fragment\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis and deletion analysis in living cells, single lab, reports a negative (C-terminal D-box not functional) and positive (N-terminal A-box sufficient) finding\",\n      \"pmids\": [\"36450448\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"APC/C(FZR-1) in C. elegans regulates centrosome duplication by controlling SAS-5 protein levels. FZR-1 directly recognizes the KEN-box motif of SAS-5 to promote its degradation. FZR-1 associates with centrosomes and is enriched at nuclei during mitotic cell division in early embryos.\",\n      \"method\": \"fzr-1 loss-of-function genetics; immunofluorescence for FZR-1 localization; centrosome duplication assay; KEN-box mutant analysis of SAS-5\",\n      \"journal\": \"G3 (Bethesda, Md.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with substrate KEN-box mutation and centrosome duplication readout, single lab\",\n      \"pmids\": [\"29030390\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In C. elegans, APC/C(FZR-1) facilitates the degradation of chromatin regulators MES-4 and MES-3 when germline stem cells transition toward oocyte differentiation. Notch signaling from the distal tip cell restricts APC/C(FZR-1) activity to allow MES-3 and MES-4 accumulation in GSCs and maintain stemness.\",\n      \"method\": \"Genetic loss-of-function of fzr-1 and APC/C subunits; protein level measurements by immunofluorescence; epistasis with Notch pathway mutants\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with defined substrate degradation and functional stemness readout, single lab\",\n      \"pmids\": [\"40446035\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SPD-2 (homolog of human CEP192) is a substrate of APC/C(FZR-1) in C. elegans embryos. SPD-2 physically associates with FZR-1 in vivo. Three distinct D-box motifs in SPD-2 contribute differentially to degradation and centrosomal localization: D-box3 mutation stabilizes centrosomal SPD-2 and restores centrosome duplication in zyg-1 mutants, while D-box1 mutation reduces centrosomal SPD-2 and worsens duplication defects.\",\n      \"method\": \"Co-immunoprecipitation (FZR-1 and SPD-2 in vivo); D-box site mutagenesis; centrosome duplication rescue assay; immunofluorescence\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and systematic D-box mutagenesis with functional centrosome duplication readout; preprint, single lab\",\n      \"pmids\": [\"41278915\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FZR1/Cdh1 promotes TRAF3 and TRAF6 autoubiquitination independently of the APC/C, attenuates MAVS binding to PFKFB3, promotes MAVS aggregation, and thereby activates IRF3 and NF-κB to drive type I interferon and proinflammatory cytokine production during RNA virus infection. This antiviral function is enhanced by m6A-mediated increase in FZR1 translation upon VSV infection.\",\n      \"method\": \"Co-immunoprecipitation; ubiquitination assay (TRAF3/6 autoubiquitination); MAVS aggregation assay; FZR1 knockout cells and mice; pharmacological FZR1 inhibition\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple biochemical assays (Co-IP, ubiquitination, aggregation) and in vivo KO validation, but novel non-canonical function reported by single lab\",\n      \"pmids\": [\"41805567\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"USP8 deubiquitinase interacts with FZR1 (Fzr) and deubiquitinates it to promote its stabilization, which is required for endoreplication in Drosophila salivary gland and Bombyx silk gland. Hsp70 mediates proper folding of Fzr and increases the Fzr-USP8 interaction, thereby enhancing Fzr deubiquitination.\",\n      \"method\": \"Co-immunoprecipitation; deubiquitination assay; genetic depletion of USP8 and Hsp70; endoreplication assay\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and deubiquitination assay with functional rescue in two insect models, single lab\",\n      \"pmids\": [\"40106570\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GEMIN5, an m6A reader protein, binds m6A-modified FZR1 mRNA and recruits the eIF3 translation initiation complex, accelerating FZR1 protein translation. Elevated FZR1 protein maintains G0-G1 quiescence and suppresses gemcitabine sensitivity in pancreatic cancer cells.\",\n      \"method\": \"m6A profiling; GEMIN5-FZR1 mRNA Co-IP; eIF3 complex co-immunoprecipitation; FZR1 knockdown; cell cycle analysis\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical identification of m6A reader and translation complex recruitment, functional validation with KD, single lab\",\n      \"pmids\": [\"37326469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FZR1 ubiquitinates ANLN (Anillin) for degradation. CCNE1 (Cyclin E1) competes with FZR1-mediated ANLN ubiquitination by binding ANLN and stabilizing it, promoting TNBC stemness and progression. Mutation of the ANLN ubiquitination site abolishes CCNE1's regulatory effect.\",\n      \"method\": \"Co-immunoprecipitation; ubiquitination assay; ANLN ubiquitination site mutagenesis; CCNE1 knockdown/overexpression; in vitro and in vivo functional assays\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ubiquitination assay with site-specific mutagenesis and co-IP, single lab\",\n      \"pmids\": [\"40346052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"FZR1 ubiquitinates c-MYC for proteasomal degradation. DSN1 competes with c-MYC for FZR1 binding, thereby attenuating c-MYC ubiquitination and stabilizing c-MYC to promote colorectal cancer metastasis.\",\n      \"method\": \"Co-immunoprecipitation; ubiquitination assay; cycloheximide chase; proteasome inhibition; rescue experiment with c-MYC overexpression\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ubiquitination assay with competitive binding Co-IP and functional rescue, single lab\",\n      \"pmids\": [\"41713835\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FZR1 (Cdh1/Fzr) is a WD40-repeat co-activator of the APC/C E3 ubiquitin ligase that recognizes substrates bearing RXXL destruction boxes or KEN boxes and drives their ubiquitination and proteasomal degradation; it is activated during mitotic exit and throughout G1/G0 (after CDC20/Fzy, which acts earlier), requires centrosomal anchoring via Spd2 for local APC/C activity toward Aurora A, and is itself regulated by CDK-mediated phosphorylation (inactivating) and auto-degradation; its canonical substrates include securin, cyclin B, Aurora A, SKP2, PLK1, RUNX1, BRAF, ANLN, c-MYC, and others, and beyond cell-cycle control it functions post-mitotically in axon growth, glial migration, planar cell polarity (via Nek2/Dishevelled), meiotic prophase I quiescence, spindle assembly timing, and antiviral innate immunity (via APC/C-independent TRAF3/6 ubiquitination).\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"FZR1 (Cdh1/Fzr) is a substrate-recognition co-activator of the APC/C E3 ubiquitin ligase that drives ubiquitination and proteasomal degradation of cell-cycle regulators bearing RXXL destruction-box and KEN-box degrons [#0, #2]. By recognizing these motifs it targets securin, Aurora A, and additional substrates, with KEN-box substrates degraded exclusively by APC/C(FZR1) while RXXL substrates can be shared with the CDC20-activated form [#0, #2, #3]. FZR1 acts predominantly during mitotic exit and G1/G0—mediating a cytoplasm-wide phase of cyclin B destruction distinct from the CDC20/Fzy-driven spindle-localized phase—and its loss in mammalian somatic cells shortens G1, prolongs S phase, and triggers DNA-damage responses rather than blocking mitotic exit [#1, #7]. Its activity is gated by inactivating CDK4/6–cyclin D and ERK phosphorylation and reversed by phosphatases such as PRL-3, and FZR1 also catalyzes its own APC/C-dependent auto-degradation through internal destruction boxes [#6, #13, #17, #18]. Centrosomal anchoring via direct binding to Spd2/CEP192 localizes APC/C(FZR1) activity toward centrosomal substrates including Aurora A and SPD-2/CEP192, coupling the ligase to centrosome duplication control [#14, #24, #26]. Beyond canonical cell-cycle control, FZR1 functions in meiotic prophase I quiescence and spindle-assembly timing in oocytes by repressing cyclin B1 [#10, #11], in post-mitotic neurons and epithelia through substrates such as Fasciclin2 and Nek2/Dishevelled [#9, #16], and in hematopoietic and cancer contexts by degrading RUNX1, BRAF, ANLN, and c-MYC [#17, #21, #30, #31]. FZR1 additionally engages APC/C-independent roles, including suppression of BRAF dimerization, an H2B-ubiquitination/Myc transcriptional cascade driving endoreplication, and promotion of TRAF3/6 autoubiquitination to activate antiviral type I interferon signaling [#17, #20, #27].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established that FZR1 confers substrate specificity on the APC/C through recognition of defined degron motifs, answering how the ligase selects its targets.\",\n      \"evidence\": \"In vitro APC/C ubiquitination of securin with destruction-box and KEN-box mutagenesis\",\n      \"pmids\": [\"11179223\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not map FZR1 residues contacting the degrons\", \"Limited to one substrate\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Resolved how APC/C activator choice and degron type set the timing and order of substrate destruction, distinguishing FZR1 from CDC20 function.\",\n      \"evidence\": \"Swapped degron constructs with real-time degradation assays; Drosophila live imaging of cyclin B destruction phases; Aurora-A degradation assays\",\n      \"pmids\": [\"12198152\", \"12082076\", \"12023018\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Aurora-A finding from single lab at Medium confidence\", \"Structural basis of differential RXXL recognition not defined\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Defined FZR1's organismal role as a G1 regulator acting redundantly with the Rb pathway, distinguishing it from a strict mitotic-exit function.\",\n      \"evidence\": \"C. elegans synthetic-lethal genetics with lin-35/Rb; Drosophila null-allele characterization\",\n      \"pmids\": [\"11850412\", \"12194827\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular substrates underlying proliferation control not identified in these studies\", \"Cross-species generality untested at the time\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Showed FZR1 catalyzes its own destruction via APC/C, establishing an autoregulatory loop that limits its abundance.\",\n      \"evidence\": \"Xenopus interphase extract degradation assay with destruction-box mutagenesis and co-IP with APC/C\",\n      \"pmids\": [\"15029244\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological trigger for auto-degradation timing not defined\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrated that in mammalian somatic cells FZR1 governs G1/S timing and genome stability rather than mitotic exit, redefining its mammalian role.\",\n      \"evidence\": \"RNAi in human cell lines and conditional knockout MEFs with cell-cycle and DNA-damage readouts\",\n      \"pmids\": [\"19861496\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific substrates causing the S-phase/DNA-damage phenotype not pinned down\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Placed FZR1 in the meiotic-arrest pathway downstream of CDC14B, linking phosphatase regulation to APC/C-mediated cyclin B1 control in oocytes.\",\n      \"evidence\": \"Overexpression and depletion epistasis in mouse oocytes\",\n      \"pmids\": [\"19129509\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct dephosphorylation of FZR1 by CDC14B not shown\", \"Single lab\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Extended FZR1 function into post-mitotic biology, showing it patterns axonal adhesion molecules to guide glial migration.\",\n      \"evidence\": \"Drosophila fzr loss-of-function with imaging and fas2 epistasis\",\n      \"pmids\": [\"20890296\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether Fas2 distribution is controlled via direct APC/C substrate turnover unclear\", \"Single organism\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Established that APC/C(FZR1) maintains meiotic prophase I quiescence by repressing cyclin B1 levels in vivo.\",\n      \"evidence\": \"Oocyte-specific conditional knockout with cyclin B1 knockdown rescue\",\n      \"pmids\": [\"21270054\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Other meiotic substrates not characterized\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed FZR1 controls meiotic spindle-assembly timing and embryonic syngamy, linking its activity to chromosome segregation fidelity.\",\n      \"evidence\": \"Oocyte-specific and maternal-zygotic Fzr1 knockouts with live imaging and SAC markers\",\n      \"pmids\": [\"22918942\", \"23097041\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism connecting FZR1 to spindle assembly rate undefined\", \"Syngamy study single lab at Medium confidence\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified inactivating CDK4/6–cyclin D phosphorylation of FZR1, linking it to CDK4/6-inhibitor response and revealing a cooperative axis with Rb.\",\n      \"evidence\": \"C. elegans genetic screen, phospho-site mapping, and RNAi/CDK4-6 inhibitor assays in human breast cancer cells\",\n      \"pmids\": [\"25562820\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full repertoire of CDK-regulated FZR1 sites in humans not completely mapped\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Defined how FZR1 is spatially targeted, showing direct Spd2 binding localizes APC/C(FZR1) to centrosomes for efficient Aurora A degradation.\",\n      \"evidence\": \"Co-IP, binding-defective Spd2 mutants, and centrosomal APC/C activity assays in Drosophila\",\n      \"pmids\": [\"27558644\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conservation of Spd2-mediated anchoring in mammals not addressed here\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Expanded the FZR1 substrate set in disease, identifying TOPIIα degradation and an FZR1 dependency in multiple myeloma.\",\n      \"evidence\": \"siRNA, substrate accumulation Westerns, and proTAME treatment in myeloma cells\",\n      \"pmids\": [\"27655696\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ubiquitination of TOPIIα by FZR1 not reconstituted\", \"Single lab\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Revealed a post-mitotic developmental role in planar cell polarity through the FZR1–Nek2–Dishevelled axis.\",\n      \"evidence\": \"Drosophila genetics, epistasis, and substrate degradation assays\",\n      \"pmids\": [\"28041906\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mammalian conservation untested\", \"Single lab\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Uncovered dual APC/C-dependent and APC/C-independent suppression of BRAF by FZR1 and its inactivation by ERK and CDK4, connecting FZR1 to oncogenic MAPK signaling.\",\n      \"evidence\": \"Ubiquitination assays, dimerization co-IP, phospho-site mapping, and Fzr1/Pten mouse model with inhibitor treatments\",\n      \"pmids\": [\"28174173\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of degradation versus dimerization disruption in vivo not quantified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showed FZR1 controls centrosome duplication by degrading SAS-5 via KEN-box recognition, linking the ligase to centriole number control.\",\n      \"evidence\": \"C. elegans fzr-1 genetics with SAS-5 KEN-box mutagenesis and centrosome assays\",\n      \"pmids\": [\"29030390\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mammalian SAS-5 orthologs not tested\", \"Single lab\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified PRL-3 as an activating phosphatase that dephosphorylates FZR1 to drive AURKA degradation, complementing the kinase-based inactivation model.\",\n      \"evidence\": \"Co-IP, ubiquitination assay, and phosphatase-dead PRL-3 mutant\",\n      \"pmids\": [\"30498084\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific FZR1 residues dephosphorylated by PRL-3 not mapped\", \"Single lab\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Established that CDK phosphorylation of FZR1 is required in vivo for the meiotic II transition in male germ cells, defining a germline-specific regulatory requirement.\",\n      \"evidence\": \"Non-phosphorylatable Fzr1 knock-in mice with testis histology and substrate Westerns\",\n      \"pmids\": [\"32572094\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrates whose mistimed turnover causes the meiosis II failure not fully defined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Revealed an APC/C-independent transcriptional role in which FZR1 promotes H2B ubiquitination at the Myc promoter to drive endoreplication.\",\n      \"evidence\": \"Co-IP, ChIP, and reporter assays in Drosophila with mammalian validation\",\n      \"pmids\": [\"32182338\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which FZR1 stimulates H2B ubiquitination not biochemically reconstituted\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Connected FZR1 to hematopoietic stem cell biology and aplastic anemia through site-specific RUNX1 ubiquitination.\",\n      \"evidence\": \"Ubiquitination assay with K125 mutant, Fzr1+/- mice, and RUNX1 knockdown rescue in HSCs\",\n      \"pmids\": [\"34635784\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether RUNX1 turnover is APC/C-dependent not isolated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined a direct FZR1–pRB interaction via an LxCxD motif separable from core APC/C binding, controlling SKP2/PLK1 and CDK-inhibitor levels and S-phase entry.\",\n      \"evidence\": \"Point mutagenesis, in vitro binding, HPV E7 competition, and cell-cycle analysis\",\n      \"pmids\": [\"33971196\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional significance of pRB binding in normal tissue not established\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Re-mapped the Aurora A degron, showing the N-terminal A-box rather than the C-terminal D-box confers FZR1-dependent degradation.\",\n      \"evidence\": \"In cellulo degradation assays with AURKA deletion and mutation constructs\",\n      \"pmids\": [\"36450448\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of A-box recognition by FZR1 not solved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed FZR1 abundance is set translationally via m6A-dependent GEMIN5/eIF3 recruitment, coupling FZR1 to quiescence and chemoresistance in pancreatic cancer.\",\n      \"evidence\": \"m6A profiling, GEMIN5–FZR1 mRNA co-IP, eIF3 co-IP, and FZR1 knockdown\",\n      \"pmids\": [\"37326469\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether translational upregulation broadly governs FZR1 levels beyond this context unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Expanded oncogenic substrate recognition, showing FZR1 degrades ANLN and c-MYC and that competing factors stabilize these substrates to drive cancer progression.\",\n      \"evidence\": \"Ubiquitination assays with substrate-site mutagenesis, competitive co-IP, and functional cancer assays\",\n      \"pmids\": [\"40346052\", \"41713835\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"APC/C dependence of ANLN and c-MYC degradation not isolated\", \"Each finding single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstrated germline stem cell roles, with APC/C(FZR-1) degrading chromatin regulators MES-3/MES-4 under Notch control during oocyte differentiation.\",\n      \"evidence\": \"C. elegans fzr-1 and APC/C genetics with substrate quantification and Notch epistasis\",\n      \"pmids\": [\"40446035\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct degron recognition of MES proteins not mapped\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established stabilizing regulation of FZR1 by USP8 deubiquitination and Hsp70-assisted folding required for endoreplication.\",\n      \"evidence\": \"Co-IP, deubiquitination assay, and genetic depletion in Drosophila and Bombyx\",\n      \"pmids\": [\"40106570\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mammalian relevance of USP8/Hsp70 control untested\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Revealed an APC/C-independent antiviral role in which FZR1 promotes TRAF3/6 autoubiquitination and MAVS aggregation to activate type I interferon signaling.\",\n      \"evidence\": \"Co-IP, autoubiquitination and MAVS aggregation assays, FZR1 knockout cells and mice, and inhibitor treatment\",\n      \"pmids\": [\"41805567\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ligase mechanism on TRAF3/6 versus a scaffolding role not fully separated\", \"Novel function from single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Provided evidence that SPD-2/CEP192 is an FZR1 substrate with multiple D-boxes differentially controlling centrosomal localization and duplication.\",\n      \"evidence\": \"In vivo co-IP and systematic D-box mutagenesis with centrosome duplication rescue (preprint)\",\n      \"pmids\": [\"41278915\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not peer reviewed\", \"Mammalian CEP192 not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How FZR1 mechanistically partitions between its canonical APC/C co-activator function and its growing set of APC/C-independent activities, and the structural basis for its diverse degron and protein-interaction recognition, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of FZR1 bound to its various degrons\", \"Switch governing APC/C-dependent versus -independent modes not defined\", \"Mammalian conservation of several invertebrate findings untested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 3, 17, 21, 30, 31]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 2, 6, 14]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0016567\", \"supporting_discovery_ids\": []}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [1, 14, 24, 26]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1, 5]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [20, 24]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [0, 2, 6, 7]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 3, 17, 21]},\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [10, 11, 12, 19]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [27]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [17, 21, 30, 31]}\n    ],\n    \"complexes\": [\"APC/C\"],\n    \"partners\": [\"Spd2/CEP192\", \"RB1\", \"PRL-3\", \"USP8\", \"GEMIN5\", \"TRAF3\", \"TRAF6\", \"Nek2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}