{"gene":"FBXL12","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":2013,"finding":"FBXL12 is the F-box protein subunit of an SCF (Skp1-Cul1-F-box) E3 ubiquitin ligase complex that mediates polyubiquitylation of Ku80 at DNA double-strand breaks, leading to Ku80 removal from DNA and proteasomal degradation. Immunodepletion of Fbxl12 in Xenopus egg extracts prevented Cul1 and Skp1 binding to DSBs and blocked Ku80 ubiquitylation. Uniquely, the F-box domain of Fbxl12 was required for binding both Skp1 and its substrate Ku80.","method":"Xenopus laevis cell-free egg extract system, immunodepletion, F-box protein DSB-binding screen, in vitro ubiquitylation assay","journal":"Cell cycle (Georgetown, Tex.)","confidence":"High","confidence_rationale":"Tier 1-2 — reconstitution in cell-free system, immunodepletion with rescue, substrate identification with multiple orthogonal methods","pmids":["23324393"],"is_preprint":false},{"year":2008,"finding":"FBXL12 (FBL12) forms an SCF(FBL12) E3 ubiquitin ligase complex and directly ubiquitinates p57(KIP2) in a phosphorylation-dependent manner, leading to TGF-beta1-induced proteasomal degradation of p57(KIP2) in osteoblasts. Dominant-negative FBL12ΔF increased steady-state p57(KIP2) levels, and RNAi knockdown of FBL12 suppressed p57(KIP2) degradation.","method":"Co-immunoprecipitation, in vitro ubiquitylation assay, RNAi knockdown, dominant-negative mutant overexpression, osteoblast differentiation assay","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro ubiquitylation reconstitution, loss-of-function with multiple approaches, clear phenotypic readout","pmids":["18660753"],"is_preprint":false},{"year":2013,"finding":"Fbxl12 mediates proteasomal degradation of CaMKI (calcium/calmodulin-dependent kinase I), disrupting cyclin D1/cdk4 complex assembly and causing G1 arrest in lung epithelia. Fbxl12 overexpression attenuated CaMKI-dependent phosphorylation of p27 at Thr157/Thr198 (human) or Thr170/Thr197 (mouse), preventing p27 cytoplasmic relocalization and thus blocking G1 progression.","method":"Overexpression, RNAi knockdown, proteasome inhibitor treatment, cell cycle analysis, phosphorylation site mutagenesis, co-immunoprecipitation","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2-3 — loss- and gain-of-function with defined cellular phenotype, multiple phosphorylation sites validated, single lab","pmids":["23707388"],"is_preprint":false},{"year":2015,"finding":"FBXL12 interacts specifically with ALDH3 family members and mediates their polyubiquitylation via SCF(FBXL12), leading to proteasomal degradation of ALDH3. This degradation is essential for trophoblast stem cell differentiation during placental development; FBXL12-knockout mice showed ALDH3 accumulation in placenta and impaired junctional zone formation.","method":"Co-immunoprecipitation, in vitro ubiquitylation assay, FBXL12 knockout mouse, forced ALDH3 expression, ALDH3 inhibitor rescue experiment","journal":"Stem cells (Dayton, Ohio)","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro ubiquitylation, knockout mouse with rescue experiment, multiple orthogonal methods","pmids":["26124079"],"is_preprint":false},{"year":2016,"finding":"FBXL12-mediated degradation of ALDH3 is required cell-autonomously for DP-to-SP thymocyte maturation in the thymus. FBXL12-null T cells showed a differentiation block at the DP-SP transition with ALDH3 accumulation; this was recapitulated in bone marrow transplant recipients and fetal thymic organ culture, demonstrating cell autonomy.","method":"FBXL12 knockout mouse, bone marrow transplantation, fetal thymic organ culture, flow cytometry","journal":"Genes to cells : devoted to molecular & cellular mechanisms","confidence":"High","confidence_rationale":"Tier 2 — KO mouse with multiple in vivo and ex vivo validation approaches, cell-autonomous mechanism established","pmids":["26999371"],"is_preprint":false},{"year":2019,"finding":"Fbxl12 is transcriptionally induced by pre-TCR signaling during β-selection and, together with Fbxl1 (induced by Notch), forms SCF complexes that polyubiquitinate and proteasomally degrade Cdkn1b (p27), driving cell cycle progression and proliferation of β-selected thymocytes.","method":"Genetic mouse models, flow cytometry, thymocyte proliferation assays, protein degradation assays, epistasis analysis","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis in mouse models, defined substrate (Cdkn1b), clear cellular phenotype replicated with multiple approaches","pmids":["31451788"],"is_preprint":false},{"year":2023,"finding":"CHK1-mediated phosphorylation of FANCD2 creates a phosphodegron recognized by FBXL12, triggering SCF(FBXL12)-dependent proteasomal degradation of FANCD2 at stalled replication forks. FBXL12 depletion caused FANCD2 trapping on chromatin, replication stress, and excessive DNA damage. Phosphodegron mutants of FANCD2 failed to rescue fork progression in FANCD2-deficient fibroblasts.","method":"Co-immunoprecipitation, in vitro ubiquitylation assay, chromatin fractionation, phosphodegron mutagenesis, DNA fiber assay, FBXL12 depletion, reconstitution in FANCD2-deficient fibroblasts","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1-2 — reconstitution with phosphodegron mutants, multiple orthogonal methods, in vitro and in vivo validation","pmids":["37591242"],"is_preprint":false},{"year":2022,"finding":"Depletion of FBXL12, which promotes ubiquitylation and removal of KU70/KU80 from DSBs, leads to more extensive MRE11- and CtIP-dependent DNA end resection in G0 (quiescent) cells, demonstrating that FBXL12-mediated Ku removal limits resection in non-cycling cells.","method":"CRISPR/Cas9 genome-wide screen, FBXL12 depletion, DNA end resection assay, G0 cell synchronization","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 — genome-wide CRISPR screen with functional validation in G0 cells, mechanistic link to Ku removal","pmids":["35575473"],"is_preprint":false},{"year":2024,"finding":"FBXL12 participates in a neddylation-dependent process that actively removes Ku molecules loaded onto DNA ends throughout the cell cycle, limiting Ku accumulation to ~1-2 molecules per DNA end. Loss of this FBXL12-dependent removal leads to excessive Ku chromatin invasion and impaired transcription near DNA ends.","method":"Live-cell imaging, chromatin fractionation, neddylation inhibition, FBXL12 depletion, transcription assays near DSBs","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization and functional consequence experiments, multiple methods, single lab","pmids":["39058590"],"is_preprint":false},{"year":2015,"finding":"An intronic region of Fbxl12 acts as an alternative promoter to produce a short form of Fbl12 lacking the F-box domain (Fbl12ΔF). UV irradiation increases Fbl12ΔF mRNA levels. Fbl12ΔF binds full-length Fbl12 and promotes its relocalization from nucleus to cytoplasm, potentially regulating SCF(Fbl12) activity.","method":"Promoter reporter assay, RT-PCR, UV irradiation, subcellular fractionation, co-immunoprecipitation","journal":"Biochemistry and biophysics reports","confidence":"Low","confidence_rationale":"Tier 3 — single lab, localization data with limited functional follow-up","pmids":["29124172"],"is_preprint":false},{"year":2025,"finding":"FBXL12 promotes K63-linked ubiquitylation of Myosin heavy chain 14 (MYH14) in microglia, driving cytoskeletal reorganization and microglial migration. Overexpression of FBXL12 in microglia maintained a scar-less healing phenotype after spinal cord injury, reducing extracellular matrix deposition.","method":"Multiomics analysis, FBXL12 overexpression in microglia, ubiquitylation assay (K63-linkage specific), cytoskeletal and migration assays, spinal cord injury mouse model","journal":"Signal transduction and targeted therapy","confidence":"Medium","confidence_rationale":"Tier 2-3 — in vivo model with mechanistic substrate identification, K63-ubiquitylation specificity shown, single lab","pmids":["40830106"],"is_preprint":false},{"year":2025,"finding":"FBXL12 mediates ubiquitylation of ALDH1A1 in pancreatic cancer cells. PAX5 transcriptionally induces FBXL12 expression; sorcin sequesters PAX5 in the cytoplasm to suppress this axis. Disruption of sorcin-PAX5 interaction (by celastrol) promotes PAX5 nuclear translocation, FBXL12 upregulation, ALDH1A1 ubiquitylation, and ferroptosis.","method":"Co-immunoprecipitation, ChIP assay, luciferase assay, proteomics, siRNA knockdown, ubiquitylation assay","journal":"Journal of hematology & oncology","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple orthogonal methods (Co-IP, ChIP, luciferase, ubiquitylation assay) in single lab","pmids":["40055736"],"is_preprint":false},{"year":2025,"finding":"CRY1 K151Q/R mutants show enhanced binding to FBXL12 (but not FBXL3) while being more stable than wild-type CRY1, indicating that CRY1-K151 modulates FBXL12 interaction in a ubiquitination-independent manner affecting circadian period length.","method":"Site-directed mutagenesis, circadian rescue assay in Cry1/2-deficient cells, luciferase complementation assay, co-immunoprecipitation","journal":"International journal of molecular sciences","confidence":"Low","confidence_rationale":"Tier 3 — single lab, interaction data without in vitro ubiquitylation confirmation of FBXL12-CRY1 substrate relationship","pmids":["40869282"],"is_preprint":false}],"current_model":"FBXL12 is the substrate-recognition subunit of SCF(FBXL12) E3 ubiquitin ligase complexes that polyubiquitinate and proteasomally degrade multiple substrates—including Ku80 (at DNA double-strand breaks, requiring CHK1-independent DSB recruitment), p57(KIP2) (phosphorylation-dependent, in osteoblasts), Cdkn1b/p27 (in thymocytes downstream of pre-TCR signaling), CaMKI (in lung epithelium causing G1 arrest), ALDH3 family members (controlling stem cell differentiation in placenta and thymus), FANCD2 (via CHK1-phosphorylated phosphodegron at stalled replication forks), ALDH1A1 (in pancreatic cancer), and MYH14 (K63-linked, in microglia)—thereby regulating DNA repair pathway choice, cell cycle progression, stem cell differentiation, and replication stress tolerance."},"narrative":{"teleology":[{"year":2008,"claim":"Identification of the first SCF(FBXL12) substrate established FBXL12 as a functional E3 ligase subunit that targets the CDK inhibitor p57(KIP2) for phosphorylation-dependent ubiquitylation and degradation during osteoblast differentiation.","evidence":"Co-IP, in vitro ubiquitylation, RNAi, and dominant-negative approaches in osteoblast cultures","pmids":["18660753"],"confidence":"High","gaps":["Phosphorylation site on p57 required for FBXL12 recognition not mapped","In vivo relevance in skeletal development not tested"]},{"year":2013,"claim":"Discovery that FBXL12 ubiquitylates Ku80 at DNA double-strand breaks—using an unusual F-box domain for both Skp1 and substrate binding—revealed a direct role in DNA repair pathway choice by removing the NHEJ factor Ku from break sites.","evidence":"Xenopus egg extract immunodepletion, DSB-binding screen, in vitro ubiquitylation reconstitution","pmids":["23324393"],"confidence":"High","gaps":["Structural basis for dual F-box domain interactions unresolved","Mammalian in vivo validation not performed"]},{"year":2013,"claim":"Identification of CaMKI as an FBXL12 substrate linked FBXL12 to cell cycle control in lung epithelium, showing that CaMKI degradation disrupts cyclin D1/cdk4 assembly and blocks G1 progression through impaired p27 phosphorylation.","evidence":"Overexpression and RNAi in lung epithelial cells with proteasome inhibition and phosphosite mutagenesis","pmids":["23707388"],"confidence":"Medium","gaps":["Direct FBXL12–CaMKI binding not demonstrated by in vitro reconstitution","In vivo lung phenotype not examined"]},{"year":2015,"claim":"Knockout mouse studies revealed that FBXL12-mediated ALDH3 degradation is essential for trophoblast stem cell differentiation during placental development, expanding the substrate repertoire to metabolic enzymes controlling stemness.","evidence":"FBXL12 KO mouse, in vitro ubiquitylation, forced ALDH3 expression and inhibitor rescue","pmids":["26124079"],"confidence":"High","gaps":["ALDH3 degron motif uncharacterized","Whether FBXL12 requires ALDH3 post-translational modification for recognition unknown"]},{"year":2016,"claim":"Extension of the ALDH3-degradation axis to the thymus showed that FBXL12 is required cell-autonomously for the DP-to-SP thymocyte transition, demonstrating tissue-specific deployment of the same substrate-targeting mechanism.","evidence":"FBXL12 KO mouse with bone marrow transplantation and fetal thymic organ culture","pmids":["26999371"],"confidence":"High","gaps":["Precise ALDH3-dependent metabolic pathway disrupting thymocyte maturation not identified","Redundancy with other F-box proteins in thymus not tested"]},{"year":2019,"claim":"Genetic epistasis in mouse thymocytes showed that FBXL12 and FBXL1 are transcriptionally induced by pre-TCR and Notch signals, respectively, to cooperatively degrade p27/Cdkn1b and drive proliferative expansion during β-selection.","evidence":"Genetic mouse models with flow cytometry, proliferation assays, and epistasis analysis","pmids":["31451788"],"confidence":"High","gaps":["Whether FBXL12 and FBXL1 target distinct p27 phosphoforms not determined","Direct biochemical reconstitution of cooperative degradation not shown"]},{"year":2022,"claim":"A genome-wide CRISPR screen in quiescent cells demonstrated that FBXL12-mediated Ku removal limits MRE11/CtIP-dependent DNA end resection in G0, establishing FBXL12 as a regulator of resection in non-cycling cells.","evidence":"CRISPR screen with FBXL12 depletion and resection assays in G0-synchronized cells","pmids":["35575473"],"confidence":"Medium","gaps":["Whether Ku80 ubiquitylation is the sole mechanism limiting resection in G0 not confirmed","Contribution in primary quiescent tissues not tested"]},{"year":2023,"claim":"Discovery of the CHK1-phosphorylated phosphodegron on FANCD2 as the FBXL12 recognition signal at stalled forks provided the first fully resolved degron mechanism for SCF(FBXL12) and linked it to replication stress tolerance and the Fanconi anemia pathway.","evidence":"In vitro ubiquitylation, phosphodegron mutagenesis, DNA fiber assays, reconstitution in FANCD2-deficient fibroblasts","pmids":["37591242"],"confidence":"High","gaps":["Crystal structure of FBXL12–phosphodegron complex unavailable","Whether FBXL12 also targets monoubiquitinated FANCD2 not addressed"]},{"year":2024,"claim":"Live-cell imaging and neddylation inhibition studies showed that FBXL12-dependent removal of Ku operates throughout the cell cycle to limit Ku to 1–2 molecules per DNA end, preventing excessive chromatin invasion and transcriptional impairment near breaks.","evidence":"Live-cell imaging, neddylation inhibition, FBXL12 depletion, transcription assays near DSBs","pmids":["39058590"],"confidence":"Medium","gaps":["Whether additional E3 ligases cooperate with FBXL12 for Ku removal not resolved","Quantitative kinetics of Ku turnover at single breaks not fully modeled"]},{"year":2025,"claim":"Identification of K63-linked ubiquitylation of MYH14 in microglia extended FBXL12 function beyond proteasomal degradation to non-degradative signaling, linking it to cytoskeletal reorganization and scar-less healing after spinal cord injury.","evidence":"Multiomics, K63-linkage-specific ubiquitylation assay, microglial migration assays, spinal cord injury mouse model","pmids":["40830106"],"confidence":"Medium","gaps":["Whether K63-linked ubiquitylation is directly catalyzed by SCF(FBXL12) or requires an accessory E2 not established","Generalizability of non-degradative FBXL12 activity to other contexts unknown"]},{"year":2025,"claim":"The PAX5–FBXL12–ALDH1A1 axis in pancreatic cancer revealed transcriptional regulation of FBXL12 as a control layer, with sorcin sequestering PAX5 to suppress FBXL12 expression and protect ALDH1A1 from ubiquitylation.","evidence":"ChIP, luciferase reporter, Co-IP, siRNA, ubiquitylation assays in pancreatic cancer cells","pmids":["40055736"],"confidence":"Medium","gaps":["Direct FBXL12–ALDH1A1 degron characterization lacking","Whether PAX5-dependent FBXL12 regulation operates outside pancreatic cancer unknown"]},{"year":null,"claim":"No structural model of FBXL12 bound to any substrate or degron exists, and the basis for its unusually broad substrate repertoire—spanning Ku80, FANCD2, p57, p27, CaMKI, ALDH3, ALDH1A1, and MYH14—remains mechanistically unexplained.","evidence":"","pmids":[],"confidence":"High","gaps":["No crystal or cryo-EM structure of FBXL12 or any FBXL12–substrate complex","Whether leucine-rich repeats confer distinct degron-binding modes for different substrates unknown","Relative contribution of FBXL12 versus other F-box proteins at shared substrates (e.g., p27) not quantified in vivo"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,3,6,10,11]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,6,9]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[0,6,7,8]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[0,7,8]},{"term_id":"R-HSA-69306","term_label":"DNA Replication","supporting_discovery_ids":[6]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[1,2,5]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,3,6,10,11]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,5]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[3,4]}],"complexes":["SCF(FBXL12)"],"partners":["SKP1","CUL1","XRCC5","FANCD2","CDKN1C","CDKN1B","ALDH3A1","MYH14"],"other_free_text":[]},"mechanistic_narrative":"FBXL12 is the substrate-recognition subunit of SCF(FBXL12) E3 ubiquitin ligase complexes that target diverse substrates for proteasomal degradation, thereby governing DNA repair pathway choice, replication fork integrity, cell cycle progression, and stem cell differentiation. At DNA double-strand breaks, SCF(FBXL12) polyubiquitinates Ku80 to limit Ku accumulation on DNA ends, restricting end resection in quiescent cells and preserving transcription near breaks [PMID:23324393, PMID:35575473, PMID:39058590]. SCF(FBXL12) also degrades FANCD2 at stalled replication forks via a CHK1-generated phosphodegron, preventing FANCD2 trapping on chromatin and replication stress [PMID:37591242], and targets ALDH3 family members to drive trophoblast stem cell differentiation in placenta and DP-to-SP thymocyte maturation in thymus [PMID:26124079, PMID:26999371]. Additional substrates include p57(KIP2) in osteoblasts [PMID:18660753], p27/Cdkn1b downstream of pre-TCR signaling during β-selection [PMID:31451788], CaMKI in lung epithelial G1 arrest [PMID:23707388], and ALDH1A1 in pancreatic cancer cells [PMID:40055736]."},"prefetch_data":{"uniprot":{"accession":"Q9NXK8","full_name":"F-box/LRR-repeat protein 12","aliases":["F-box and leucine-rich repeat protein 12","F-box protein FBL12"],"length_aa":326,"mass_kda":37.0,"function":"Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex. Mediates the polyubiquitination and proteasomal degradation of CAMK1 leading to disruption of cyclin D1/CDK4 complex assembly which results in G1 cell cycle arrest in lung epithelia","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/Q9NXK8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FBXL12","classification":"Not Classified","n_dependent_lines":28,"n_total_lines":1208,"dependency_fraction":0.023178807947019868},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"PSME3","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/FBXL12","total_profiled":1310},"omim":[{"mim_id":"609079","title":"F-BOX AND LEUCINE-RICH REPEAT PROTEIN 12; FBXL12","url":"https://www.omim.org/entry/609079"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Mitochondria","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/FBXL12"},"hgnc":{"alias_symbol":["FLJ20188","Fbl12"],"prev_symbol":[]},"alphafold":{"accession":"Q9NXK8","domains":[{"cath_id":"1.20.1280","chopping":"10-44","consensus_level":"medium","plddt":92.5714,"start":10,"end":44},{"cath_id":"3.80.10.10","chopping":"45-178","consensus_level":"medium","plddt":89.3056,"start":45,"end":178},{"cath_id":"3.40.50","chopping":"204-209_227-318","consensus_level":"medium","plddt":90.4409,"start":204,"end":318}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NXK8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NXK8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NXK8-F1-predicted_aligned_error_v6.png","plddt_mean":89.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FBXL12","jax_strain_url":"https://www.jax.org/strain/search?query=FBXL12"},"sequence":{"accession":"Q9NXK8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NXK8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NXK8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NXK8"}},"corpus_meta":[{"pmid":"30526451","id":"PMC_30526451","title":"Leucine 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Oxidative, Metabolic, and Hormonal Markers Associated with Postpartum Disorder Susceptibility in Barki Sheep (Ovis aries).","date":"2025","source":"Veterinary sciences","url":"https://pubmed.ncbi.nlm.nih.gov/40266925","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11338,"output_tokens":3574,"usd":0.043812},"stage2":{"model":"claude-opus-4-6","input_tokens":6953,"output_tokens":3093,"usd":0.168135},"total_usd":0.211947,"stage1_batch_id":"msgbatch_0118RScg3WGaGkaZRtWZbtce","stage2_batch_id":"msgbatch_01Cpfzvtbj42aqp5oYZ5Te2s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2013,\n      \"finding\": \"FBXL12 is the F-box protein subunit of an SCF (Skp1-Cul1-F-box) E3 ubiquitin ligase complex that mediates polyubiquitylation of Ku80 at DNA double-strand breaks, leading to Ku80 removal from DNA and proteasomal degradation. Immunodepletion of Fbxl12 in Xenopus egg extracts prevented Cul1 and Skp1 binding to DSBs and blocked Ku80 ubiquitylation. Uniquely, the F-box domain of Fbxl12 was required for binding both Skp1 and its substrate Ku80.\",\n      \"method\": \"Xenopus laevis cell-free egg extract system, immunodepletion, F-box protein DSB-binding screen, in vitro ubiquitylation assay\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution in cell-free system, immunodepletion with rescue, substrate identification with multiple orthogonal methods\",\n      \"pmids\": [\"23324393\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"FBXL12 (FBL12) forms an SCF(FBL12) E3 ubiquitin ligase complex and directly ubiquitinates p57(KIP2) in a phosphorylation-dependent manner, leading to TGF-beta1-induced proteasomal degradation of p57(KIP2) in osteoblasts. Dominant-negative FBL12ΔF increased steady-state p57(KIP2) levels, and RNAi knockdown of FBL12 suppressed p57(KIP2) degradation.\",\n      \"method\": \"Co-immunoprecipitation, in vitro ubiquitylation assay, RNAi knockdown, dominant-negative mutant overexpression, osteoblast differentiation assay\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro ubiquitylation reconstitution, loss-of-function with multiple approaches, clear phenotypic readout\",\n      \"pmids\": [\"18660753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Fbxl12 mediates proteasomal degradation of CaMKI (calcium/calmodulin-dependent kinase I), disrupting cyclin D1/cdk4 complex assembly and causing G1 arrest in lung epithelia. Fbxl12 overexpression attenuated CaMKI-dependent phosphorylation of p27 at Thr157/Thr198 (human) or Thr170/Thr197 (mouse), preventing p27 cytoplasmic relocalization and thus blocking G1 progression.\",\n      \"method\": \"Overexpression, RNAi knockdown, proteasome inhibitor treatment, cell cycle analysis, phosphorylation site mutagenesis, co-immunoprecipitation\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — loss- and gain-of-function with defined cellular phenotype, multiple phosphorylation sites validated, single lab\",\n      \"pmids\": [\"23707388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"FBXL12 interacts specifically with ALDH3 family members and mediates their polyubiquitylation via SCF(FBXL12), leading to proteasomal degradation of ALDH3. This degradation is essential for trophoblast stem cell differentiation during placental development; FBXL12-knockout mice showed ALDH3 accumulation in placenta and impaired junctional zone formation.\",\n      \"method\": \"Co-immunoprecipitation, in vitro ubiquitylation assay, FBXL12 knockout mouse, forced ALDH3 expression, ALDH3 inhibitor rescue experiment\",\n      \"journal\": \"Stem cells (Dayton, Ohio)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro ubiquitylation, knockout mouse with rescue experiment, multiple orthogonal methods\",\n      \"pmids\": [\"26124079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"FBXL12-mediated degradation of ALDH3 is required cell-autonomously for DP-to-SP thymocyte maturation in the thymus. FBXL12-null T cells showed a differentiation block at the DP-SP transition with ALDH3 accumulation; this was recapitulated in bone marrow transplant recipients and fetal thymic organ culture, demonstrating cell autonomy.\",\n      \"method\": \"FBXL12 knockout mouse, bone marrow transplantation, fetal thymic organ culture, flow cytometry\",\n      \"journal\": \"Genes to cells : devoted to molecular & cellular mechanisms\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse with multiple in vivo and ex vivo validation approaches, cell-autonomous mechanism established\",\n      \"pmids\": [\"26999371\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Fbxl12 is transcriptionally induced by pre-TCR signaling during β-selection and, together with Fbxl1 (induced by Notch), forms SCF complexes that polyubiquitinate and proteasomally degrade Cdkn1b (p27), driving cell cycle progression and proliferation of β-selected thymocytes.\",\n      \"method\": \"Genetic mouse models, flow cytometry, thymocyte proliferation assays, protein degradation assays, epistasis analysis\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in mouse models, defined substrate (Cdkn1b), clear cellular phenotype replicated with multiple approaches\",\n      \"pmids\": [\"31451788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CHK1-mediated phosphorylation of FANCD2 creates a phosphodegron recognized by FBXL12, triggering SCF(FBXL12)-dependent proteasomal degradation of FANCD2 at stalled replication forks. FBXL12 depletion caused FANCD2 trapping on chromatin, replication stress, and excessive DNA damage. Phosphodegron mutants of FANCD2 failed to rescue fork progression in FANCD2-deficient fibroblasts.\",\n      \"method\": \"Co-immunoprecipitation, in vitro ubiquitylation assay, chromatin fractionation, phosphodegron mutagenesis, DNA fiber assay, FBXL12 depletion, reconstitution in FANCD2-deficient fibroblasts\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution with phosphodegron mutants, multiple orthogonal methods, in vitro and in vivo validation\",\n      \"pmids\": [\"37591242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Depletion of FBXL12, which promotes ubiquitylation and removal of KU70/KU80 from DSBs, leads to more extensive MRE11- and CtIP-dependent DNA end resection in G0 (quiescent) cells, demonstrating that FBXL12-mediated Ku removal limits resection in non-cycling cells.\",\n      \"method\": \"CRISPR/Cas9 genome-wide screen, FBXL12 depletion, DNA end resection assay, G0 cell synchronization\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide CRISPR screen with functional validation in G0 cells, mechanistic link to Ku removal\",\n      \"pmids\": [\"35575473\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FBXL12 participates in a neddylation-dependent process that actively removes Ku molecules loaded onto DNA ends throughout the cell cycle, limiting Ku accumulation to ~1-2 molecules per DNA end. Loss of this FBXL12-dependent removal leads to excessive Ku chromatin invasion and impaired transcription near DNA ends.\",\n      \"method\": \"Live-cell imaging, chromatin fractionation, neddylation inhibition, FBXL12 depletion, transcription assays near DSBs\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization and functional consequence experiments, multiple methods, single lab\",\n      \"pmids\": [\"39058590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"An intronic region of Fbxl12 acts as an alternative promoter to produce a short form of Fbl12 lacking the F-box domain (Fbl12ΔF). UV irradiation increases Fbl12ΔF mRNA levels. Fbl12ΔF binds full-length Fbl12 and promotes its relocalization from nucleus to cytoplasm, potentially regulating SCF(Fbl12) activity.\",\n      \"method\": \"Promoter reporter assay, RT-PCR, UV irradiation, subcellular fractionation, co-immunoprecipitation\",\n      \"journal\": \"Biochemistry and biophysics reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, localization data with limited functional follow-up\",\n      \"pmids\": [\"29124172\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FBXL12 promotes K63-linked ubiquitylation of Myosin heavy chain 14 (MYH14) in microglia, driving cytoskeletal reorganization and microglial migration. Overexpression of FBXL12 in microglia maintained a scar-less healing phenotype after spinal cord injury, reducing extracellular matrix deposition.\",\n      \"method\": \"Multiomics analysis, FBXL12 overexpression in microglia, ubiquitylation assay (K63-linkage specific), cytoskeletal and migration assays, spinal cord injury mouse model\",\n      \"journal\": \"Signal transduction and targeted therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — in vivo model with mechanistic substrate identification, K63-ubiquitylation specificity shown, single lab\",\n      \"pmids\": [\"40830106\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FBXL12 mediates ubiquitylation of ALDH1A1 in pancreatic cancer cells. PAX5 transcriptionally induces FBXL12 expression; sorcin sequesters PAX5 in the cytoplasm to suppress this axis. Disruption of sorcin-PAX5 interaction (by celastrol) promotes PAX5 nuclear translocation, FBXL12 upregulation, ALDH1A1 ubiquitylation, and ferroptosis.\",\n      \"method\": \"Co-immunoprecipitation, ChIP assay, luciferase assay, proteomics, siRNA knockdown, ubiquitylation assay\",\n      \"journal\": \"Journal of hematology & oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple orthogonal methods (Co-IP, ChIP, luciferase, ubiquitylation assay) in single lab\",\n      \"pmids\": [\"40055736\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CRY1 K151Q/R mutants show enhanced binding to FBXL12 (but not FBXL3) while being more stable than wild-type CRY1, indicating that CRY1-K151 modulates FBXL12 interaction in a ubiquitination-independent manner affecting circadian period length.\",\n      \"method\": \"Site-directed mutagenesis, circadian rescue assay in Cry1/2-deficient cells, luciferase complementation assay, co-immunoprecipitation\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, interaction data without in vitro ubiquitylation confirmation of FBXL12-CRY1 substrate relationship\",\n      \"pmids\": [\"40869282\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FBXL12 is the substrate-recognition subunit of SCF(FBXL12) E3 ubiquitin ligase complexes that polyubiquitinate and proteasomally degrade multiple substrates—including Ku80 (at DNA double-strand breaks, requiring CHK1-independent DSB recruitment), p57(KIP2) (phosphorylation-dependent, in osteoblasts), Cdkn1b/p27 (in thymocytes downstream of pre-TCR signaling), CaMKI (in lung epithelium causing G1 arrest), ALDH3 family members (controlling stem cell differentiation in placenta and thymus), FANCD2 (via CHK1-phosphorylated phosphodegron at stalled replication forks), ALDH1A1 (in pancreatic cancer), and MYH14 (K63-linked, in microglia)—thereby regulating DNA repair pathway choice, cell cycle progression, stem cell differentiation, and replication stress tolerance.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"FBXL12 is the substrate-recognition subunit of SCF(FBXL12) E3 ubiquitin ligase complexes that target diverse substrates for proteasomal degradation, thereby governing DNA repair pathway choice, replication fork integrity, cell cycle progression, and stem cell differentiation. At DNA double-strand breaks, SCF(FBXL12) polyubiquitinates Ku80 to limit Ku accumulation on DNA ends, restricting end resection in quiescent cells and preserving transcription near breaks [PMID:23324393, PMID:35575473, PMID:39058590]. SCF(FBXL12) also degrades FANCD2 at stalled replication forks via a CHK1-generated phosphodegron, preventing FANCD2 trapping on chromatin and replication stress [PMID:37591242], and targets ALDH3 family members to drive trophoblast stem cell differentiation in placenta and DP-to-SP thymocyte maturation in thymus [PMID:26124079, PMID:26999371]. Additional substrates include p57(KIP2) in osteoblasts [PMID:18660753], p27/Cdkn1b downstream of pre-TCR signaling during β-selection [PMID:31451788], CaMKI in lung epithelial G1 arrest [PMID:23707388], and ALDH1A1 in pancreatic cancer cells [PMID:40055736].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Identification of the first SCF(FBXL12) substrate established FBXL12 as a functional E3 ligase subunit that targets the CDK inhibitor p57(KIP2) for phosphorylation-dependent ubiquitylation and degradation during osteoblast differentiation.\",\n      \"evidence\": \"Co-IP, in vitro ubiquitylation, RNAi, and dominant-negative approaches in osteoblast cultures\",\n      \"pmids\": [\"18660753\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphorylation site on p57 required for FBXL12 recognition not mapped\", \"In vivo relevance in skeletal development not tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Discovery that FBXL12 ubiquitylates Ku80 at DNA double-strand breaks—using an unusual F-box domain for both Skp1 and substrate binding—revealed a direct role in DNA repair pathway choice by removing the NHEJ factor Ku from break sites.\",\n      \"evidence\": \"Xenopus egg extract immunodepletion, DSB-binding screen, in vitro ubiquitylation reconstitution\",\n      \"pmids\": [\"23324393\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for dual F-box domain interactions unresolved\", \"Mammalian in vivo validation not performed\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identification of CaMKI as an FBXL12 substrate linked FBXL12 to cell cycle control in lung epithelium, showing that CaMKI degradation disrupts cyclin D1/cdk4 assembly and blocks G1 progression through impaired p27 phosphorylation.\",\n      \"evidence\": \"Overexpression and RNAi in lung epithelial cells with proteasome inhibition and phosphosite mutagenesis\",\n      \"pmids\": [\"23707388\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct FBXL12–CaMKI binding not demonstrated by in vitro reconstitution\", \"In vivo lung phenotype not examined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Knockout mouse studies revealed that FBXL12-mediated ALDH3 degradation is essential for trophoblast stem cell differentiation during placental development, expanding the substrate repertoire to metabolic enzymes controlling stemness.\",\n      \"evidence\": \"FBXL12 KO mouse, in vitro ubiquitylation, forced ALDH3 expression and inhibitor rescue\",\n      \"pmids\": [\"26124079\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"ALDH3 degron motif uncharacterized\", \"Whether FBXL12 requires ALDH3 post-translational modification for recognition unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Extension of the ALDH3-degradation axis to the thymus showed that FBXL12 is required cell-autonomously for the DP-to-SP thymocyte transition, demonstrating tissue-specific deployment of the same substrate-targeting mechanism.\",\n      \"evidence\": \"FBXL12 KO mouse with bone marrow transplantation and fetal thymic organ culture\",\n      \"pmids\": [\"26999371\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise ALDH3-dependent metabolic pathway disrupting thymocyte maturation not identified\", \"Redundancy with other F-box proteins in thymus not tested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Genetic epistasis in mouse thymocytes showed that FBXL12 and FBXL1 are transcriptionally induced by pre-TCR and Notch signals, respectively, to cooperatively degrade p27/Cdkn1b and drive proliferative expansion during β-selection.\",\n      \"evidence\": \"Genetic mouse models with flow cytometry, proliferation assays, and epistasis analysis\",\n      \"pmids\": [\"31451788\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether FBXL12 and FBXL1 target distinct p27 phosphoforms not determined\", \"Direct biochemical reconstitution of cooperative degradation not shown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"A genome-wide CRISPR screen in quiescent cells demonstrated that FBXL12-mediated Ku removal limits MRE11/CtIP-dependent DNA end resection in G0, establishing FBXL12 as a regulator of resection in non-cycling cells.\",\n      \"evidence\": \"CRISPR screen with FBXL12 depletion and resection assays in G0-synchronized cells\",\n      \"pmids\": [\"35575473\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether Ku80 ubiquitylation is the sole mechanism limiting resection in G0 not confirmed\", \"Contribution in primary quiescent tissues not tested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Discovery of the CHK1-phosphorylated phosphodegron on FANCD2 as the FBXL12 recognition signal at stalled forks provided the first fully resolved degron mechanism for SCF(FBXL12) and linked it to replication stress tolerance and the Fanconi anemia pathway.\",\n      \"evidence\": \"In vitro ubiquitylation, phosphodegron mutagenesis, DNA fiber assays, reconstitution in FANCD2-deficient fibroblasts\",\n      \"pmids\": [\"37591242\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Crystal structure of FBXL12–phosphodegron complex unavailable\", \"Whether FBXL12 also targets monoubiquitinated FANCD2 not addressed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Live-cell imaging and neddylation inhibition studies showed that FBXL12-dependent removal of Ku operates throughout the cell cycle to limit Ku to 1–2 molecules per DNA end, preventing excessive chromatin invasion and transcriptional impairment near breaks.\",\n      \"evidence\": \"Live-cell imaging, neddylation inhibition, FBXL12 depletion, transcription assays near DSBs\",\n      \"pmids\": [\"39058590\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether additional E3 ligases cooperate with FBXL12 for Ku removal not resolved\", \"Quantitative kinetics of Ku turnover at single breaks not fully modeled\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identification of K63-linked ubiquitylation of MYH14 in microglia extended FBXL12 function beyond proteasomal degradation to non-degradative signaling, linking it to cytoskeletal reorganization and scar-less healing after spinal cord injury.\",\n      \"evidence\": \"Multiomics, K63-linkage-specific ubiquitylation assay, microglial migration assays, spinal cord injury mouse model\",\n      \"pmids\": [\"40830106\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether K63-linked ubiquitylation is directly catalyzed by SCF(FBXL12) or requires an accessory E2 not established\", \"Generalizability of non-degradative FBXL12 activity to other contexts unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"The PAX5–FBXL12–ALDH1A1 axis in pancreatic cancer revealed transcriptional regulation of FBXL12 as a control layer, with sorcin sequestering PAX5 to suppress FBXL12 expression and protect ALDH1A1 from ubiquitylation.\",\n      \"evidence\": \"ChIP, luciferase reporter, Co-IP, siRNA, ubiquitylation assays in pancreatic cancer cells\",\n      \"pmids\": [\"40055736\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct FBXL12–ALDH1A1 degron characterization lacking\", \"Whether PAX5-dependent FBXL12 regulation operates outside pancreatic cancer unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"No structural model of FBXL12 bound to any substrate or degron exists, and the basis for its unusually broad substrate repertoire—spanning Ku80, FANCD2, p57, p27, CaMKI, ALDH3, ALDH1A1, and MYH14—remains mechanistically unexplained.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal or cryo-EM structure of FBXL12 or any FBXL12–substrate complex\", \"Whether leucine-rich repeats confer distinct degron-binding modes for different substrates unknown\", \"Relative contribution of FBXL12 versus other F-box proteins at shared substrates (e.g., p27) not quantified in vivo\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 3, 6, 10, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 6, 9]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [0, 6, 7, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [0, 7, 8]},\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [1, 2, 5]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 3, 6, 10, 11]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 5]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [3, 4]}\n    ],\n    \"complexes\": [\n      \"SCF(FBXL12)\"\n    ],\n    \"partners\": [\n      \"SKP1\",\n      \"CUL1\",\n      \"XRCC5\",\n      \"FANCD2\",\n      \"CDKN1C\",\n      \"CDKN1B\",\n      \"ALDH3A1\",\n      \"MYH14\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}