{"gene":"FBXL20","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":2015,"finding":"FBXL20 is an F-box protein that, as part of the SCF (Skp1-Cullin1-F-box) E3 ubiquitin ligase complex, mediates ubiquitination and proteasomal degradation of Vps34 (the catalytic subunit of class III PI3K). DNA damage activates CDK-mediated phosphorylation of Vps34, which serves as the degradation signal recognized by FBXL20-SCF. This leads to inhibition of autophagy and receptor endocytosis. FBXL20 expression is transcriptionally regulated by p53.","method":"Co-immunoprecipitation, ubiquitination assays, proteasome inhibitor rescue, siRNA knockdown, p53-dependent transcription reporter assays, autophagy and endocytosis functional readouts","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, ubiquitination assays, multiple orthogonal methods (mutagenesis of phosphorylation site, functional autophagy/endocytosis readouts), single focused study with rigorous controls","pmids":["25593308"],"is_preprint":false},{"year":2021,"finding":"FBXL20 directly targets pro-apoptotic proteins PUMA and BAX for ubiquitination and proteasomal degradation in an AKT1 kinase-dependent manner. AKT1-mediated phosphorylation promotes FBXL20 activity toward these substrates. Conversely, inactivation of AKT1 activates GSK3α/β, which facilitates proteasomal degradation of FBXL20 itself via another F-box protein FBXO31.","method":"Co-immunoprecipitation, ubiquitination assays, RNAi-mediated knockdown, flow cytometry (apoptosis), biochemical kinase activity assays, cell proliferation and tumor growth assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, ubiquitination assays, genetic knockdown with defined molecular phenotype, multiple orthogonal methods in one study","pmids":["34587475"],"is_preprint":false},{"year":2021,"finding":"FBXL20, acting as the substrate recognition component of the SCF E3 ubiquitin ligase, promotes ubiquitination and proteasomal degradation of PR55α (a regulatory subunit of PP2A Ser/Thr phosphatase). This represents a mechanism by which the p53/FBXL20 axis negatively regulates PR55α protein stability and downstream c-Myc oncogenic signaling.","method":"siRNA knockdown of p53 and FBXL20, ubiquitination assays, Western blot protein stability measurements, HPV-E6-mediated p53 degradation, p53R175H loss-of-function mutant expression, anchorage-independent growth assays","journal":"Neoplasia (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple genetic perturbations (siRNA, gene deletion, dominant-negative mutant), ubiquitination assays, functional readout, single lab with multiple orthogonal methods","pmids":["34731788"],"is_preprint":false},{"year":2022,"finding":"FBXL20 acts as the E3 ubiquitin ligase that promotes polyubiquitination of 4-1BB (TNFRSF9/CD137), specifically targeting the heavily N-glycosylated mature form at its intracellular domain, leading to its proteasomal degradation.","method":"Proximity-dependent biotin identification (BioID) screening, Co-immunoprecipitation, ubiquitination assays, proteasome inhibitor rescue, domain mapping","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — BioID screen plus biochemical validation (Co-IP, ubiquitination assay), single lab, two orthogonal methods","pmids":["35112462"],"is_preprint":false},{"year":2024,"finding":"FBXL20 promotes ubiquitination and proteasomal degradation of vesicle-associated proteins VGLUT1 and VAMP1 in hippocampal neurons. Elevated FBXL20 in a chronic stress model reduces glutamatergic neurotransmitter release and synaptic transmission; shRNA knockdown of FBXL20 in hippocampus rescues synaptic deficits and depression-like behaviors.","method":"Proteomics analysis, viral stereotaxic injection (shRNA knockdown in vivo), transmission electron microscopy, ubiquitination assays, fluorescent glutamate probe in cultured neurons, biochemical co-immunoprecipitation","journal":"Journal of affective disorders","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo genetic knockdown with synaptic functional readout, ubiquitination assays, multiple methods, single lab","pmids":["38211741"],"is_preprint":false},{"year":2016,"finding":"FBXL20 is expressed in the membrane and cytoplasm of cortical neurons and mediates ubiquitin-dependent degradation of RIM1 (regulating synaptic membrane exocytosis 1), an important factor in synaptic vesicle release. Overexpression of FBXL20 decreases RIM1 protein levels and reduces seizure frequency and duration in a pilocarpine-induced epilepsy model.","method":"Immunofluorescence, immunohistochemistry, Western blot, lentivirus-mediated FBXL20 overexpression in rats, seizure monitoring","journal":"Neurochemical research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — protein level changes by Western blot after overexpression in vivo, no direct ubiquitination assay for RIM1 reported in abstract, single lab","pmids":["27502938"],"is_preprint":false}],"current_model":"FBXL20 is a substrate recognition F-box protein of the SCF (Skp1-Cullin1-F-box) E3 ubiquitin ligase complex, transcriptionally induced by p53, that targets multiple substrates—including Vps34, PUMA, BAX, PR55α (PP2A regulatory subunit), 4-1BB, VGLUT1, and VAMP1—for polyubiquitination and proteasomal degradation, thereby regulating autophagy, receptor endocytosis, apoptosis, PP2A-dependent signaling, immune receptor homeostasis, and synaptic vesicle release; its activity toward apoptotic substrates is modulated by AKT1 kinase, and FBXL20 itself is subject to proteasomal degradation via FBXO31 under GSK3α/β activation."},"narrative":{"mechanistic_narrative":"FBXL20 is the substrate-recognition F-box subunit of an SCF (Skp1-Cullin1-F-box) E3 ubiquitin ligase that controls the abundance of diverse regulatory proteins by targeting them for polyubiquitination and proteasomal degradation, thereby linking the p53 pathway to autophagy, apoptosis, phosphatase signaling, and synaptic vesicle dynamics [PMID:25593308, PMID:34731788]. In the DNA-damage response, p53 transcriptionally induces FBXL20, which then recognizes CDK-phosphorylated Vps34 (the class III PI3K catalytic subunit) and drives its degradation to suppress autophagy and receptor endocytosis [PMID:25593308]. The same p53/FBXL20 axis destabilizes the PP2A regulatory subunit PR55α, restraining downstream c-Myc oncogenic signaling [PMID:34731788]. FBXL20 also governs the apoptotic threshold by degrading the pro-apoptotic proteins PUMA and BAX, an activity stimulated by AKT1-mediated phosphorylation; loss of AKT1 activates GSK3α/β, which in turn promotes FBXL20's own degradation through the F-box protein FBXO31 [PMID:34587475]. Additional substrates include the immune receptor 4-1BB/TNFRSF9, where FBXL20 ubiquitinates the mature N-glycosylated form at its intracellular domain [PMID:35112462], and the synaptic vesicle proteins VGLUT1 and VAMP1, whose FBXL20-driven turnover modulates glutamatergic neurotransmission in hippocampal neurons under chronic stress [PMID:38211741].","teleology":[{"year":2015,"claim":"Established FBXL20 as a p53-inducible SCF substrate receptor that couples DNA damage to autophagy and endocytosis by destroying phospho-Vps34, defining its founding mechanistic role.","evidence":"Co-IP, ubiquitination assays, proteasome inhibitor rescue, siRNA, p53 reporter assays, and autophagy/endocytosis readouts in mammalian cells","pmids":["25593308"],"confidence":"High","gaps":["Degron features beyond CDK-phosphorylated Vps34 not generalized","No structural model of the SCF-FBXL20-substrate complex"]},{"year":2021,"claim":"Showed FBXL20 sets the apoptotic threshold by degrading PUMA and BAX under AKT1 control, and is itself regulated by a GSK3/FBXO31 degradation loop, revealing reciprocal kinase governance of FBXL20 activity and stability.","evidence":"Co-IP, ubiquitination assays, RNAi, kinase activity assays, apoptosis flow cytometry, and tumor growth assays","pmids":["34587475"],"confidence":"High","gaps":["FBXL20 phosphosite(s) targeted by AKT1 not mapped","Mechanism by which GSK3 primes FBXL20 for FBXO31 recognition unresolved"]},{"year":2021,"claim":"Extended the p53/FBXL20 axis to phosphatase signaling by identifying PR55α as a substrate, linking FBXL20 to PP2A regulation and c-Myc-driven transformation.","evidence":"siRNA, ubiquitination assays, protein stability Westerns, HPV-E6 p53 degradation and p53R175H mutant, anchorage-independent growth in cells","pmids":["34731788"],"confidence":"High","gaps":["Degron on PR55α not defined","Direct contribution to PP2A complex remodeling not quantified"]},{"year":2022,"claim":"Identified the immune receptor 4-1BB as an FBXL20 substrate, indicating a role in receptor homeostasis through degradation of the mature glycosylated form.","evidence":"BioID screen, Co-IP, ubiquitination assays, proteasome inhibitor rescue, domain mapping","pmids":["35112462"],"confidence":"Medium","gaps":["Physiological context of 4-1BB regulation by FBXL20 in immune cells not tested","Single lab, two orthogonal methods"]},{"year":2024,"claim":"Connected FBXL20 to synaptic function by showing it degrades VGLUT1 and VAMP1 in hippocampal neurons, with knockdown rescuing chronic-stress synaptic deficits and depression-like behavior.","evidence":"Proteomics, in vivo shRNA via stereotaxic viral injection, TEM, ubiquitination assays, glutamate probe imaging, and Co-IP","pmids":["38211741"],"confidence":"Medium","gaps":["Direct degron recognition on VGLUT1/VAMP1 not mapped","Upstream signal driving FBXL20 elevation under stress unknown"]},{"year":2016,"claim":"Implicated FBXL20 in synaptic vesicle release through RIM1 turnover, with overexpression reducing seizure activity, suggesting a neuronal substrate beyond the later vesicle proteins.","evidence":"Immunofluorescence, IHC, Western blot, lentiviral overexpression in rats, and seizure monitoring in a pilocarpine epilepsy model","pmids":["27502938"],"confidence":"Low","gaps":["No direct ubiquitination assay for RIM1 reported","Causal degradation versus indirect effect not distinguished","Single lab"]},{"year":null,"claim":"How FBXL20 selects among its many substrates across pathways and tissues, and what shared or distinct degrons it recognizes, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying degron consensus established across substrates","Tissue-specific substrate prioritization unknown","No structural basis for substrate recognition"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,3]},{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,2]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[5]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,2,3]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[0]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[1]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[4]}],"complexes":["SCF (Skp1-Cullin1-F-box) E3 ubiquitin ligase"],"partners":["SKP1","CUL1","VPS34","PUMA","BAX","PR55A","TNFRSF9","VAMP1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96IG2","full_name":"F-box/LRR-repeat protein 20","aliases":["F-box and leucine-rich repeat protein 20","F-box/LRR-repeat protein 2-like"],"length_aa":436,"mass_kda":48.4,"function":"Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex. Role in neural transmission (By similarity)","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q96IG2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FBXL20","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CCDC47","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/FBXL20","total_profiled":1310},"omim":[{"mim_id":"609086","title":"F-BOX AND LEUCINE-RICH REPEAT PROTEIN 20; FBXL20","url":"https://www.omim.org/entry/609086"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Microtubules","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/FBXL20"},"hgnc":{"alias_symbol":["MGC15482","Fbl2","Fbl20"],"prev_symbol":[]},"alphafold":{"accession":"Q96IG2","domains":[{"cath_id":"1.20.1280","chopping":"26-64","consensus_level":"medium","plddt":85.3133,"start":26,"end":64}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96IG2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96IG2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96IG2-F1-predicted_aligned_error_v6.png","plddt_mean":90.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FBXL20","jax_strain_url":"https://www.jax.org/strain/search?query=FBXL20"},"sequence":{"accession":"Q96IG2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96IG2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96IG2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96IG2"}},"corpus_meta":[{"pmid":"25593308","id":"PMC_25593308","title":"FBXL20-mediated Vps34 ubiquitination as a p53 controlled checkpoint in regulating autophagy and receptor degradation.","date":"2015","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/25593308","citation_count":68,"is_preprint":false},{"pmid":"23023584","id":"PMC_23023584","title":"Role of FBXL20 in human colorectal adenocarcinoma.","date":"2012","source":"Oncology reports","url":"https://pubmed.ncbi.nlm.nih.gov/23023584","citation_count":22,"is_preprint":false},{"pmid":"24932313","id":"PMC_24932313","title":"FBXL20 acts as an invasion inducer and mediates E-cadherin in colorectal adenocarcinoma.","date":"2014","source":"Oncology letters","url":"https://pubmed.ncbi.nlm.nih.gov/24932313","citation_count":21,"is_preprint":false},{"pmid":"34587475","id":"PMC_34587475","title":"FBXL20 promotes breast cancer malignancy by inhibiting apoptosis through degradation of PUMA and BAX.","date":"2021","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/34587475","citation_count":20,"is_preprint":false},{"pmid":"38211741","id":"PMC_38211741","title":"FBXL20 promotes synaptic impairment in depression disorder via degrading vesicle-associated proteins.","date":"2024","source":"Journal of affective disorders","url":"https://pubmed.ncbi.nlm.nih.gov/38211741","citation_count":13,"is_preprint":false},{"pmid":"33469313","id":"PMC_33469313","title":"LncRNA EWSAT1 Promotes Colorectal Cancer Progression Through Sponging miR-326 to Modulate FBXL20 Expression.","date":"2021","source":"OncoTargets and therapy","url":"https://pubmed.ncbi.nlm.nih.gov/33469313","citation_count":13,"is_preprint":false},{"pmid":"36374774","id":"PMC_36374774","title":"SP1-induced PROX1-AS1 contributes to tumor progression by regulating miR-326/FBXL20 axis in colorectal cancer.","date":"2022","source":"Cellular signalling","url":"https://pubmed.ncbi.nlm.nih.gov/36374774","citation_count":8,"is_preprint":false},{"pmid":"34731788","id":"PMC_34731788","title":"p53/FBXL20 axis negatively regulates the protein stability of PR55α, a regulatory subunit of PP2A Ser/Thr phosphatase.","date":"2021","source":"Neoplasia (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/34731788","citation_count":5,"is_preprint":false},{"pmid":"34338995","id":"PMC_34338995","title":"F-Box and Leucine-Rich Repeat Protein 20 (FBXL20), Negatively Regulated by microRNA (miR)-195-5p, Accelerates the Malignant Progression of Ovarian Cancer.","date":"2021","source":"Molecular biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/34338995","citation_count":5,"is_preprint":false},{"pmid":"27502938","id":"PMC_27502938","title":"Abnormal Expression of FBXL20 in Refractory Epilepsy Patients and a Pilocarpine-Induced Rat Model.","date":"2016","source":"Neurochemical research","url":"https://pubmed.ncbi.nlm.nih.gov/27502938","citation_count":4,"is_preprint":false},{"pmid":"31889792","id":"PMC_31889792","title":"Expression and association of IL-21, FBXL20 and tumour suppressor gene PTEN in laryngeal cancer.","date":"2019","source":"Saudi journal of biological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/31889792","citation_count":4,"is_preprint":false},{"pmid":"35112462","id":"PMC_35112462","title":"FBXL20-mediated ubiquitination triggers the proteasomal degradation of 4-1BB.","date":"2022","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/35112462","citation_count":3,"is_preprint":false},{"pmid":"37881684","id":"PMC_37881684","title":"LncRNA EWSAT1 Promotes Colorectal Cancer Progression Through Sponging miR-326 to Modulate FBXL20 Expression [Retraction].","date":"2023","source":"OncoTargets and therapy","url":"https://pubmed.ncbi.nlm.nih.gov/37881684","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8743,"output_tokens":1904,"usd":0.027394,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8782,"output_tokens":2693,"usd":0.055618,"stage2_stop_reason":"end_turn"},"total_usd":0.083012,"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\": 2015,\n      \"finding\": \"FBXL20 is an F-box protein that, as part of the SCF (Skp1-Cullin1-F-box) E3 ubiquitin ligase complex, mediates ubiquitination and proteasomal degradation of Vps34 (the catalytic subunit of class III PI3K). DNA damage activates CDK-mediated phosphorylation of Vps34, which serves as the degradation signal recognized by FBXL20-SCF. This leads to inhibition of autophagy and receptor endocytosis. FBXL20 expression is transcriptionally regulated by p53.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, proteasome inhibitor rescue, siRNA knockdown, p53-dependent transcription reporter assays, autophagy and endocytosis functional readouts\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, ubiquitination assays, multiple orthogonal methods (mutagenesis of phosphorylation site, functional autophagy/endocytosis readouts), single focused study with rigorous controls\",\n      \"pmids\": [\"25593308\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FBXL20 directly targets pro-apoptotic proteins PUMA and BAX for ubiquitination and proteasomal degradation in an AKT1 kinase-dependent manner. AKT1-mediated phosphorylation promotes FBXL20 activity toward these substrates. Conversely, inactivation of AKT1 activates GSK3α/β, which facilitates proteasomal degradation of FBXL20 itself via another F-box protein FBXO31.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, RNAi-mediated knockdown, flow cytometry (apoptosis), biochemical kinase activity assays, cell proliferation and tumor growth assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, ubiquitination assays, genetic knockdown with defined molecular phenotype, multiple orthogonal methods in one study\",\n      \"pmids\": [\"34587475\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FBXL20, acting as the substrate recognition component of the SCF E3 ubiquitin ligase, promotes ubiquitination and proteasomal degradation of PR55α (a regulatory subunit of PP2A Ser/Thr phosphatase). This represents a mechanism by which the p53/FBXL20 axis negatively regulates PR55α protein stability and downstream c-Myc oncogenic signaling.\",\n      \"method\": \"siRNA knockdown of p53 and FBXL20, ubiquitination assays, Western blot protein stability measurements, HPV-E6-mediated p53 degradation, p53R175H loss-of-function mutant expression, anchorage-independent growth assays\",\n      \"journal\": \"Neoplasia (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple genetic perturbations (siRNA, gene deletion, dominant-negative mutant), ubiquitination assays, functional readout, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"34731788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FBXL20 acts as the E3 ubiquitin ligase that promotes polyubiquitination of 4-1BB (TNFRSF9/CD137), specifically targeting the heavily N-glycosylated mature form at its intracellular domain, leading to its proteasomal degradation.\",\n      \"method\": \"Proximity-dependent biotin identification (BioID) screening, Co-immunoprecipitation, ubiquitination assays, proteasome inhibitor rescue, domain mapping\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — BioID screen plus biochemical validation (Co-IP, ubiquitination assay), single lab, two orthogonal methods\",\n      \"pmids\": [\"35112462\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FBXL20 promotes ubiquitination and proteasomal degradation of vesicle-associated proteins VGLUT1 and VAMP1 in hippocampal neurons. Elevated FBXL20 in a chronic stress model reduces glutamatergic neurotransmitter release and synaptic transmission; shRNA knockdown of FBXL20 in hippocampus rescues synaptic deficits and depression-like behaviors.\",\n      \"method\": \"Proteomics analysis, viral stereotaxic injection (shRNA knockdown in vivo), transmission electron microscopy, ubiquitination assays, fluorescent glutamate probe in cultured neurons, biochemical co-immunoprecipitation\",\n      \"journal\": \"Journal of affective disorders\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo genetic knockdown with synaptic functional readout, ubiquitination assays, multiple methods, single lab\",\n      \"pmids\": [\"38211741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"FBXL20 is expressed in the membrane and cytoplasm of cortical neurons and mediates ubiquitin-dependent degradation of RIM1 (regulating synaptic membrane exocytosis 1), an important factor in synaptic vesicle release. Overexpression of FBXL20 decreases RIM1 protein levels and reduces seizure frequency and duration in a pilocarpine-induced epilepsy model.\",\n      \"method\": \"Immunofluorescence, immunohistochemistry, Western blot, lentivirus-mediated FBXL20 overexpression in rats, seizure monitoring\",\n      \"journal\": \"Neurochemical research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — protein level changes by Western blot after overexpression in vivo, no direct ubiquitination assay for RIM1 reported in abstract, single lab\",\n      \"pmids\": [\"27502938\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FBXL20 is a substrate recognition F-box protein of the SCF (Skp1-Cullin1-F-box) E3 ubiquitin ligase complex, transcriptionally induced by p53, that targets multiple substrates—including Vps34, PUMA, BAX, PR55α (PP2A regulatory subunit), 4-1BB, VGLUT1, and VAMP1—for polyubiquitination and proteasomal degradation, thereby regulating autophagy, receptor endocytosis, apoptosis, PP2A-dependent signaling, immune receptor homeostasis, and synaptic vesicle release; its activity toward apoptotic substrates is modulated by AKT1 kinase, and FBXL20 itself is subject to proteasomal degradation via FBXO31 under GSK3α/β activation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"FBXL20 is the substrate-recognition F-box subunit of an SCF (Skp1-Cullin1-F-box) E3 ubiquitin ligase that controls the abundance of diverse regulatory proteins by targeting them for polyubiquitination and proteasomal degradation, thereby linking the p53 pathway to autophagy, apoptosis, phosphatase signaling, and synaptic vesicle dynamics [#0, #2]. In the DNA-damage response, p53 transcriptionally induces FBXL20, which then recognizes CDK-phosphorylated Vps34 (the class III PI3K catalytic subunit) and drives its degradation to suppress autophagy and receptor endocytosis [#0]. The same p53/FBXL20 axis destabilizes the PP2A regulatory subunit PR55\\u03b1, restraining downstream c-Myc oncogenic signaling [#2]. FBXL20 also governs the apoptotic threshold by degrading the pro-apoptotic proteins PUMA and BAX, an activity stimulated by AKT1-mediated phosphorylation; loss of AKT1 activates GSK3\\u03b1/\\u03b2, which in turn promotes FBXL20's own degradation through the F-box protein FBXO31 [#1]. Additional substrates include the immune receptor 4-1BB/TNFRSF9, where FBXL20 ubiquitinates the mature N-glycosylated form at its intracellular domain [#3], and the synaptic vesicle proteins VGLUT1 and VAMP1, whose FBXL20-driven turnover modulates glutamatergic neurotransmission in hippocampal neurons under chronic stress [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 2015,\n      \"claim\": \"Established FBXL20 as a p53-inducible SCF substrate receptor that couples DNA damage to autophagy and endocytosis by destroying phospho-Vps34, defining its founding mechanistic role.\",\n      \"evidence\": \"Co-IP, ubiquitination assays, proteasome inhibitor rescue, siRNA, p53 reporter assays, and autophagy/endocytosis readouts in mammalian cells\",\n      \"pmids\": [\"25593308\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Degron features beyond CDK-phosphorylated Vps34 not generalized\", \"No structural model of the SCF-FBXL20-substrate complex\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed FBXL20 sets the apoptotic threshold by degrading PUMA and BAX under AKT1 control, and is itself regulated by a GSK3/FBXO31 degradation loop, revealing reciprocal kinase governance of FBXL20 activity and stability.\",\n      \"evidence\": \"Co-IP, ubiquitination assays, RNAi, kinase activity assays, apoptosis flow cytometry, and tumor growth assays\",\n      \"pmids\": [\"34587475\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"FBXL20 phosphosite(s) targeted by AKT1 not mapped\", \"Mechanism by which GSK3 primes FBXL20 for FBXO31 recognition unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Extended the p53/FBXL20 axis to phosphatase signaling by identifying PR55\\u03b1 as a substrate, linking FBXL20 to PP2A regulation and c-Myc-driven transformation.\",\n      \"evidence\": \"siRNA, ubiquitination assays, protein stability Westerns, HPV-E6 p53 degradation and p53R175H mutant, anchorage-independent growth in cells\",\n      \"pmids\": [\"34731788\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Degron on PR55\\u03b1 not defined\", \"Direct contribution to PP2A complex remodeling not quantified\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified the immune receptor 4-1BB as an FBXL20 substrate, indicating a role in receptor homeostasis through degradation of the mature glycosylated form.\",\n      \"evidence\": \"BioID screen, Co-IP, ubiquitination assays, proteasome inhibitor rescue, domain mapping\",\n      \"pmids\": [\"35112462\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological context of 4-1BB regulation by FBXL20 in immune cells not tested\", \"Single lab, two orthogonal methods\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Connected FBXL20 to synaptic function by showing it degrades VGLUT1 and VAMP1 in hippocampal neurons, with knockdown rescuing chronic-stress synaptic deficits and depression-like behavior.\",\n      \"evidence\": \"Proteomics, in vivo shRNA via stereotaxic viral injection, TEM, ubiquitination assays, glutamate probe imaging, and Co-IP\",\n      \"pmids\": [\"38211741\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct degron recognition on VGLUT1/VAMP1 not mapped\", \"Upstream signal driving FBXL20 elevation under stress unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Implicated FBXL20 in synaptic vesicle release through RIM1 turnover, with overexpression reducing seizure activity, suggesting a neuronal substrate beyond the later vesicle proteins.\",\n      \"evidence\": \"Immunofluorescence, IHC, Western blot, lentiviral overexpression in rats, and seizure monitoring in a pilocarpine epilepsy model\",\n      \"pmids\": [\"27502938\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No direct ubiquitination assay for RIM1 reported\", \"Causal degradation versus indirect effect not distinguished\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How FBXL20 selects among its many substrates across pathways and tissues, and what shared or distinct degrons it recognizes, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying degron consensus established across substrates\", \"Tissue-specific substrate prioritization unknown\", \"No structural basis for substrate recognition\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 3]},\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 2, 3]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"complexes\": [\"SCF (Skp1-Cullin1-F-box) E3 ubiquitin ligase\"],\n    \"partners\": [\"SKP1\", \"CUL1\", \"VPS34\", \"PUMA\", \"BAX\", \"PR55A\", \"TNFRSF9\", \"VAMP1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}