{"gene":"FBXL18","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":2015,"finding":"FBXL18 functions as the substrate-recognition subunit of an SCF (Skp1-Cul1-F-box) E3 ubiquitin ligase complex that mediates K48-linked polyubiquitylation and proteasomal degradation of the pro-apoptotic F-box protein FBXL7. Lys109 of FBXL7 is the essential ubiquitin acceptor site, and an FQ motif in FBXL7 serves as the molecular recognition site for FBXL18 binding. Loss of FBXL18 or mutation of Lys109/FQ motif accentuates FBXL7-induced apoptosis, while ectopic FBXL18 limits it.","method":"Co-immunoprecipitation, in vitro ubiquitination assay, site-directed mutagenesis (Lys109 and FQ motif), siRNA knockdown, apoptosis assays in HeLa cells","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including in vitro ubiquitination, mutagenesis of acceptor site, and functional rescue experiments","pmids":["25654763"],"is_preprint":false},{"year":2016,"finding":"FBXL18 promotes K63-linked ubiquitination of Akt kinase, which is required for Akt activation. Depletion of FBXL18 in glioma cells inhibits Akt activity and downstream phosphorylation of FOXO3a, leading to upregulation of BCL2L11 and increased apoptosis.","method":"siRNA knockdown, ubiquitination assay specifying K63-linkage, Western blotting for Akt pathway components, colony formation and apoptosis assays in glioma cells","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2-3 — K63-linkage specificity demonstrated but mechanistic epistasis relies on single-lab knockdown and downstream marker analysis","pmids":["27926990"],"is_preprint":false},{"year":2016,"finding":"FBXL18 is a component of an SCF (Skp1-Cullin1-F-box) ubiquitin ligase complex that physically associates with LRRK2, selectively targeting phosphorylated LRRK2 for ubiquitination and proteasomal degradation. Dephosphorylation of LRRK2 blocks FBXL18 association. Protein kinase C activation enhances LRRK2 degradation by FBXL18. Fbxl18 overexpression prevents caspase activation and cell death caused by wild-type and PD-linked mutant LRRK2.","method":"Co-immunoprecipitation, siRNA knockdown (stabilizes LRRK2), phosphatase treatment (blocks FBXL18 association), PKC activation assay, caspase activation and cell death assays","journal":"Neurobiology of disease","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, phosphorylation-dependence experiment, genetic knockdown with functional rescue, multiple orthogonal assays in single study","pmids":["27890708"],"is_preprint":false},{"year":2019,"finding":"SCFFBXL18 E3 ligase (comprising Skp1, Cul1, FBXL18, and Rbx1) mediates spironolactone-induced polyubiquitination and proteasomal degradation of XPB (a TFIIH subunit). CDK7 kinase activity is required for this process, and Ser90 of XPB is essential for chemical-induced destabilization, suggesting spironolactone triggers CDK7-mediated phosphorylation of XPB at Ser90, which promotes SCFFBXL18 recognition.","method":"siRNA library screening, Co-IP to confirm SCF complex assembly, ubiquitination assay, CDK7 inhibitor experiments, XPB Ser90 mutagenesis","journal":"Genes to cells","confidence":"High","confidence_rationale":"Tier 1-2 — siRNA screen followed by mutagenesis of substrate phospho-acceptor site and kinase requirement, multiple orthogonal validations","pmids":["30762924"],"is_preprint":false},{"year":2023,"finding":"FBXL18 promotes K63-linked ubiquitination of ribosomal protein RPS15A, enhancing its stability (not degradation), which in turn increases SMAD3 protein levels and promotes SMAD3 nuclear translocation to drive hepatocellular carcinoma cell proliferation. Knockdown of RPS15A or SMAD3 suppresses FBXL18-mediated HCC proliferation.","method":"K63-linked ubiquitination assay, Western blotting for RPS15A/SMAD3 stability, FBXL18 transgenic mouse model, siRNA epistasis knockdown of RPS15A and SMAD3","journal":"Hepatology communications","confidence":"Medium","confidence_rationale":"Tier 2 — K63-ubiquitination specificity demonstrated, epistasis with RPS15A/SMAD3 knockdown, in vivo transgenic model; single lab","pmids":["37378633"],"is_preprint":false},{"year":2024,"finding":"FBXL18 physically interacts with Akt and promotes K63-linked ubiquitination of Akt, leading to Akt activation (increased p-AKT S473) in ovarian cancer cells. AKT inhibitor MK-2206 reverses FBXL18 overexpression-induced proliferation and migration.","method":"Co-immunoprecipitation, K63-linked ubiquitination assay, pharmacological inhibition with MK-2206, siRNA knockdown and overexpression","journal":"American journal of translational research","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP and K63-specific ubiquitination assay with functional rescue by AKT inhibitor; single lab, replicates glioma finding","pmids":["38883375"],"is_preprint":false},{"year":2025,"finding":"FBXL18 mediates K11-type ubiquitination of BST2 on Lys109 and Lys110, stabilizing BST2 (competing with K33-linked degradative ubiquitination by an unknown E3 ligase). FBXL18-mediated BST2 stabilization leads to hyperphosphorylation of IκBα and excessive NF-κB activation, driving IL-6 production and inflammation in RABV-infected astrocytes. FBXL18 knockdown inhibits IL-6 production, RABV replication, and reduces virulence in mice.","method":"siRNA screen, Co-IP, K11-specific ubiquitination assay with lysine mutagenesis (K109/K110), IκBα phosphorylation Western blot, NF-κB reporter assay, in vivo mouse RABV infection model","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 — mechanistic screen, K11-linkage specificity with acceptor-site mutagenesis, pathway epistasis, in vivo validation; multiple orthogonal methods","pmids":["41390767"],"is_preprint":false},{"year":2025,"finding":"FBXL18 physically interacts with DUSP16 (dual specificity phosphatase 16), promoting its ubiquitination and proteasomal degradation, thereby activating the JNK/c-JUN signaling pathway to facilitate endometrial carcinoma cell proliferation, migration, and invasion. Overexpression of DUSP16 rescues the JNK activation and enhanced cell capacities induced by FBXL18 overexpression.","method":"Co-immunoprecipitation, ubiquitination assay, Western blotting, siRNA knockdown, DUSP16 overexpression rescue experiment, CCK-8/colony formation/Transwell assays","journal":"Cancer cell international","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP, ubiquitination assay, and epistasis rescue; single lab with multiple orthogonal assays","pmids":["40382593"],"is_preprint":false},{"year":2025,"finding":"FBXL18 interacts with Akt and promotes K63-linked polyubiquitination of Akt, activating the AKT/CCND1 signaling pathway to maintain radioresistance in esophageal squamous cell carcinoma cells.","method":"Co-immunoprecipitation, K63-linked polyubiquitination assay by Western blot, siRNA knockdown, CCK-8 radiosensitivity assay","journal":"BMB reports","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP and K63-specific ubiquitination with functional radiosensitivity readout; single lab, corroborates prior Akt-K63 ubiquitination findings","pmids":["41655990"],"is_preprint":false},{"year":2025,"finding":"FBXL18 suppresses FBXL7 protein expression in esophageal squamous cell carcinoma cells, and this mechanism underlies FBXL18's pro-proliferative and radioprotective effects in ESCC.","method":"FBXL18 overexpression/knockdown lentivirus, Western blotting for FBXL7, colony formation, in vivo xenograft, irradiation survival assay","journal":"Strahlentherapie und Onkologie","confidence":"Low","confidence_rationale":"Tier 3 — Western blot for substrate level with functional correlation; no ubiquitination assay or mutagenesis reported, single lab","pmids":["39971770"],"is_preprint":false}],"current_model":"FBXL18 is the substrate-recognition F-box subunit of an SCF (Skp1-Cul1-Rbx1) E3 ubiquitin ligase complex with multiple substrates: it targets FBXL7 (via K48-linked ubiquitination for degradation), LRRK2 (phosphorylation-dependent K48-linked degradation), and XPB (CDK7-phosphorylation-primed degradation), while promoting non-degradative K63-linked ubiquitination of Akt to activate it, K63-linked ubiquitination of RPS15A to stabilize it and activate SMAD3, K11-linked ubiquitination of BST2 to stabilize it and drive NF-κB inflammation, and K48-linked ubiquitination of DUSP16 for degradation to activate JNK signaling."},"narrative":{"teleology":[{"year":2015,"claim":"Establishing that FBXL18 is a functional SCF E3 ligase subunit resolved whether FBXL18 possesses ubiquitin ligase activity and identified its first substrate—the pro-apoptotic F-box protein FBXL7—targeted via K48-linked ubiquitination for proteasomal degradation.","evidence":"In vitro ubiquitination, site-directed mutagenesis of Lys109 and FQ degron, siRNA knockdown with apoptosis rescue in HeLa cells","pmids":["25654763"],"confidence":"High","gaps":["No structural basis for FBXL18–FBXL7 recognition via the FQ motif","Whether other F-box proteins are similarly regulated by FBXL18 is unknown","Physiological tissues where FBXL18–FBXL7 axis operates are not defined"]},{"year":2016,"claim":"Demonstrating that FBXL18 also catalyzes non-degradative K63-linked ubiquitination of Akt for its activation revealed a linkage-type switch capability—K48 for degradation versus K63 for signaling—and connected FBXL18 to pro-survival Akt signaling in glioma.","evidence":"K63-specific ubiquitination assay, siRNA knockdown with Akt pathway Western blotting and apoptosis assays in glioma cells","pmids":["27926990"],"confidence":"Medium","gaps":["The ubiquitin acceptor lysine(s) on Akt were not identified","How FBXL18 selects between K48 and K63 chain assembly on different substrates is unknown","Single-lab finding at the time of publication"]},{"year":2016,"claim":"Showing phosphorylation-dependent recognition of LRRK2 by FBXL18 established that SCF^FBXL18 uses a canonical phosphodegron mechanism and linked this E3 ligase to Parkinson's disease-relevant LRRK2 turnover.","evidence":"Reciprocal Co-IP, phosphatase treatment blocking FBXL18 association, PKC activation enhancing degradation, caspase/cell-death rescue assays","pmids":["27890708"],"confidence":"High","gaps":["Specific phosphorylation site(s) on LRRK2 recognized by FBXL18 were not mapped","In vivo relevance in dopaminergic neurons or animal PD models not tested","Chain linkage type on LRRK2 not explicitly determined"]},{"year":2019,"claim":"Identifying XPB as a spironolactone-induced substrate of SCF^FBXL18, dependent on CDK7-mediated Ser90 phosphorylation, revealed a pharmacologically triggerable phosphodegron and connected FBXL18 to transcription/NER factor turnover.","evidence":"siRNA library screen, Co-IP confirming SCF complex, CDK7 inhibitor epistasis, XPB Ser90 mutagenesis","pmids":["30762924"],"confidence":"High","gaps":["Whether FBXL18 degrades XPB under physiological (non-drug) conditions is unclear","Direct binding interface between FBXL18 LRR domain and phospho-XPB not resolved","Consequences for NER and transcription in vivo not assessed"]},{"year":2023,"claim":"Demonstrating K63-linked ubiquitination of RPS15A by FBXL18 that stabilizes the substrate and activates SMAD3 signaling expanded the non-degradative substrate repertoire and linked FBXL18 to TGF-β/SMAD-driven hepatocellular carcinoma proliferation.","evidence":"K63-ubiquitination assay, FBXL18 transgenic mouse model, siRNA epistasis with RPS15A and SMAD3 in HCC cells","pmids":["37378633"],"confidence":"Medium","gaps":["Mechanism by which K63-ubiquitinated RPS15A stabilizes SMAD3 protein is undefined","Whether this reflects a ribosomal or extra-ribosomal function of RPS15A is unknown","Single-lab observation"]},{"year":2024,"claim":"Independent replication of FBXL18-mediated K63-linked Akt ubiquitination in ovarian cancer, with pharmacological rescue by the Akt inhibitor MK-2206, strengthened confidence in the Akt–K63 ubiquitination axis across tumor types.","evidence":"Co-IP, K63-specific ubiquitination assay, MK-2206 rescue of FBXL18-driven proliferation/migration in ovarian cancer cells","pmids":["38883375"],"confidence":"Medium","gaps":["Akt ubiquitin acceptor sites still unmapped","Whether FBXL18 directly ubiquitinates Akt or acts through an adaptor is not resolved","No in vivo validation in ovarian cancer models"]},{"year":2025,"claim":"Discovery that FBXL18 catalyzes K11-linked ubiquitination of BST2 to stabilize it and drive NF-κB/IL-6 inflammation during rabies virus infection introduced a third chain-linkage type to FBXL18's repertoire and linked it to innate immune/inflammatory signaling.","evidence":"siRNA screen, K11-specific ubiquitination with K109/K110 mutagenesis, NF-κB reporter, in vivo mouse RABV infection model","pmids":["41390767"],"confidence":"High","gaps":["How FBXL18 directs K11 versus K48 versus K63 chain assembly mechanistically is unknown","Whether BST2 stabilization by K11 chains occurs outside viral infection is untested","The E2 conjugating enzyme(s) partnering with FBXL18 for each chain type are not identified"]},{"year":2025,"claim":"Identification of DUSP16 as a degradative substrate whose loss activates JNK/c-JUN signaling extended FBXL18's substrate range to MAP kinase phosphatases and linked it to endometrial carcinoma progression.","evidence":"Co-IP, ubiquitination assay, DUSP16 overexpression rescue of JNK activation, Transwell and colony assays in endometrial carcinoma cells","pmids":["40382593"],"confidence":"Medium","gaps":["Ubiquitin chain type on DUSP16 not specified","Degron or phosphodegron on DUSP16 not mapped","Single-lab finding without in vivo model"]},{"year":2025,"claim":"A third independent study confirmed FBXL18-mediated K63 ubiquitination of Akt, now linked to radioresistance in esophageal squamous cell carcinoma via AKT/CCND1, consolidating Akt as a bona fide non-degradative substrate across multiple cancer types.","evidence":"Co-IP, K63 polyubiquitination assay, siRNA knockdown with radiosensitivity assay in ESCC cells","pmids":["41655990"],"confidence":"Medium","gaps":["Direct in vitro reconstitution of FBXL18-Akt ubiquitination with purified components is lacking","Whether K63-Akt ubiquitination drives radioresistance through membrane recruitment or kinase conformational change is unknown"]},{"year":null,"claim":"A central open question is how a single F-box protein directs three distinct ubiquitin chain types (K48, K63, K11) on different substrates, and whether this reflects E2 switching, substrate-intrinsic determinants, or cofactor-dependent mechanisms.","evidence":"","pmids":[],"confidence":"High","gaps":["No E2 conjugating enzyme partners have been identified for FBXL18","No structural model of the FBXL18 LRR domain or substrate-binding interface exists","Physiological regulation of FBXL18 expression or activity (transcriptional, post-translational) is uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,3,4,5,6,7,8]},{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,2,3,6]}],"localization":[],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,2,3,4,6,7]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,4,5,7,8]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[0,1]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[6]}],"complexes":["SCF (Skp1–Cul1–Rbx1–FBXL18)"],"partners":["FBXL7","AKT1","LRRK2","XPB","RPS15A","BST2","DUSP16","SKP1"],"other_free_text":[]},"mechanistic_narrative":"FBXL18 is the substrate-recognition subunit of an SCF (Skp1–Cul1–Rbx1–FBXL18) E3 ubiquitin ligase that governs cell survival and proliferation by conjugating distinct ubiquitin chain types to different substrates. It mediates K48-linked polyubiquitination and proteasomal degradation of the pro-apoptotic F-box protein FBXL7 (via an FQ degron and Lys109 acceptor), phosphorylated LRRK2 (in a PKC-enhanced, phosphorylation-dependent manner), XPB/TFIIH (primed by CDK7-dependent Ser90 phosphorylation), and DUSP16 (relieving JNK pathway suppression) [PMID:25654763, PMID:27890708, PMID:30762924, PMID:40382593]. In parallel, FBXL18 catalyzes non-degradative K63-linked ubiquitination of Akt to promote its activation and downstream FOXO3a/BCL2L11 or CCND1 signaling, and K63-linked ubiquitination of RPS15A to stabilize it and drive SMAD3 nuclear translocation [PMID:27926990, PMID:38883375, PMID:37378633]. FBXL18 also mediates K11-linked ubiquitination of BST2 at Lys109/Lys110, stabilizing BST2 and hyperactivating NF-κB/IL-6 inflammatory signaling during rabies virus infection [PMID:41390767]."},"prefetch_data":{"uniprot":{"accession":"Q96ME1","full_name":"F-box/LRR-repeat protein 18","aliases":["F-box and leucine-rich repeat protein 18"],"length_aa":718,"mass_kda":78.9,"function":"Substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/Q96ME1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FBXL18","classification":"Not Classified","n_dependent_lines":50,"n_total_lines":1208,"dependency_fraction":0.041390728476821195},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FBXL18","total_profiled":1310},"omim":[{"mim_id":"609084","title":"F-BOX AND LEUCINE-RICH REPEAT PROTEIN 18; FBXL18","url":"https://www.omim.org/entry/609084"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":7.4}],"url":"https://www.proteinatlas.org/search/FBXL18"},"hgnc":{"alias_symbol":["FLJ11467","Fbl18"],"prev_symbol":[]},"alphafold":{"accession":"Q96ME1","domains":[{"cath_id":"3.80.10.10","chopping":"341-429_473-503_511-591","consensus_level":"medium","plddt":89.4124,"start":341,"end":591},{"cath_id":"3.40.50","chopping":"597-687","consensus_level":"medium","plddt":80.4953,"start":597,"end":687}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96ME1","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96ME1-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96ME1-F1-predicted_aligned_error_v6.png","plddt_mean":86.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FBXL18","jax_strain_url":"https://www.jax.org/strain/search?query=FBXL18"},"sequence":{"accession":"Q96ME1","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96ME1.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96ME1/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96ME1"}},"corpus_meta":[{"pmid":"25654763","id":"PMC_25654763","title":"F-box protein Fbxl18 mediates polyubiquitylation and proteasomal degradation of the pro-apoptotic SCF subunit Fbxl7.","date":"2015","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/25654763","citation_count":39,"is_preprint":false},{"pmid":"32922071","id":"PMC_32922071","title":"Circular RNA circRNA_103809 Accelerates Bladder Cancer Progression and Enhances Chemo-Resistance by Activation of miR-516a-5p/FBXL18 Axis.","date":"2020","source":"Cancer management and research","url":"https://pubmed.ncbi.nlm.nih.gov/32922071","citation_count":31,"is_preprint":false},{"pmid":"27926990","id":"PMC_27926990","title":"The F-box protein FBXL18 promotes glioma progression by promoting K63-linked ubiquitination of Akt.","date":"2016","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/27926990","citation_count":30,"is_preprint":false},{"pmid":"30762924","id":"PMC_30762924","title":"Spironolactone-induced XPB degradation depends on CDK7 kinase and SCFFBXL18 E3 ligase.","date":"2019","source":"Genes to cells : devoted to molecular & cellular mechanisms","url":"https://pubmed.ncbi.nlm.nih.gov/30762924","citation_count":20,"is_preprint":false},{"pmid":"27890708","id":"PMC_27890708","title":"Fbxl18 targets LRRK2 for proteasomal degradation and attenuates cell toxicity.","date":"2016","source":"Neurobiology of disease","url":"https://pubmed.ncbi.nlm.nih.gov/27890708","citation_count":14,"is_preprint":false},{"pmid":"37378633","id":"PMC_37378633","title":"Elevated FBXL18 promotes RPS15A ubiquitination and SMAD3 activation to drive HCC.","date":"2023","source":"Hepatology communications","url":"https://pubmed.ncbi.nlm.nih.gov/37378633","citation_count":12,"is_preprint":false},{"pmid":"38883375","id":"PMC_38883375","title":"FBXL18 is required for ovarian cancer cell proliferation and migration through activating AKT signaling.","date":"2024","source":"American journal of translational research","url":"https://pubmed.ncbi.nlm.nih.gov/38883375","citation_count":2,"is_preprint":false},{"pmid":"41390767","id":"PMC_41390767","title":"The E3 ubiquitin ligase FBXL18 stabilizes BST2 to promote inflammation in RABV-infected astrocytes.","date":"2025","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/41390767","citation_count":1,"is_preprint":false},{"pmid":"41655990","id":"PMC_41655990","title":"FBXL18 activating AKT/CCND1 signaling pathway mediates radioresistance in esophageal squamous cell carcinoma.","date":"2026","source":"BMB reports","url":"https://pubmed.ncbi.nlm.nih.gov/41655990","citation_count":0,"is_preprint":false},{"pmid":"40382593","id":"PMC_40382593","title":"FBXL18 promotes endometrial carcinoma progression via destabilizing DUSP16 and thus activating JNK signaling pathway.","date":"2025","source":"Cancer cell international","url":"https://pubmed.ncbi.nlm.nih.gov/40382593","citation_count":0,"is_preprint":false},{"pmid":"41676423","id":"PMC_41676423","title":"CircRNA_103809/miR-516a/FBXL18 contributes to stemness and gemcitabine resistance of bladder cancer cells.","date":"2025","source":"Archives of medical science : AMS","url":"https://pubmed.ncbi.nlm.nih.gov/41676423","citation_count":0,"is_preprint":false},{"pmid":"39971770","id":"PMC_39971770","title":"FBXL18 increases cell proliferation and reduces cell radiosensitivity in esophageal squamous cell carcinoma.","date":"2025","source":"Strahlentherapie und Onkologie : Organ der Deutschen Rontgengesellschaft ... [et al]","url":"https://pubmed.ncbi.nlm.nih.gov/39971770","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7338,"output_tokens":2974,"usd":0.033312},"stage2":{"model":"claude-opus-4-6","input_tokens":6307,"output_tokens":3087,"usd":0.163065},"total_usd":0.196377,"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\": 2015,\n      \"finding\": \"FBXL18 functions as the substrate-recognition subunit of an SCF (Skp1-Cul1-F-box) E3 ubiquitin ligase complex that mediates K48-linked polyubiquitylation and proteasomal degradation of the pro-apoptotic F-box protein FBXL7. Lys109 of FBXL7 is the essential ubiquitin acceptor site, and an FQ motif in FBXL7 serves as the molecular recognition site for FBXL18 binding. Loss of FBXL18 or mutation of Lys109/FQ motif accentuates FBXL7-induced apoptosis, while ectopic FBXL18 limits it.\",\n      \"method\": \"Co-immunoprecipitation, in vitro ubiquitination assay, site-directed mutagenesis (Lys109 and FQ motif), siRNA knockdown, apoptosis assays in HeLa cells\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including in vitro ubiquitination, mutagenesis of acceptor site, and functional rescue experiments\",\n      \"pmids\": [\"25654763\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"FBXL18 promotes K63-linked ubiquitination of Akt kinase, which is required for Akt activation. Depletion of FBXL18 in glioma cells inhibits Akt activity and downstream phosphorylation of FOXO3a, leading to upregulation of BCL2L11 and increased apoptosis.\",\n      \"method\": \"siRNA knockdown, ubiquitination assay specifying K63-linkage, Western blotting for Akt pathway components, colony formation and apoptosis assays in glioma cells\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — K63-linkage specificity demonstrated but mechanistic epistasis relies on single-lab knockdown and downstream marker analysis\",\n      \"pmids\": [\"27926990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"FBXL18 is a component of an SCF (Skp1-Cullin1-F-box) ubiquitin ligase complex that physically associates with LRRK2, selectively targeting phosphorylated LRRK2 for ubiquitination and proteasomal degradation. Dephosphorylation of LRRK2 blocks FBXL18 association. Protein kinase C activation enhances LRRK2 degradation by FBXL18. Fbxl18 overexpression prevents caspase activation and cell death caused by wild-type and PD-linked mutant LRRK2.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown (stabilizes LRRK2), phosphatase treatment (blocks FBXL18 association), PKC activation assay, caspase activation and cell death assays\",\n      \"journal\": \"Neurobiology of disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, phosphorylation-dependence experiment, genetic knockdown with functional rescue, multiple orthogonal assays in single study\",\n      \"pmids\": [\"27890708\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SCFFBXL18 E3 ligase (comprising Skp1, Cul1, FBXL18, and Rbx1) mediates spironolactone-induced polyubiquitination and proteasomal degradation of XPB (a TFIIH subunit). CDK7 kinase activity is required for this process, and Ser90 of XPB is essential for chemical-induced destabilization, suggesting spironolactone triggers CDK7-mediated phosphorylation of XPB at Ser90, which promotes SCFFBXL18 recognition.\",\n      \"method\": \"siRNA library screening, Co-IP to confirm SCF complex assembly, ubiquitination assay, CDK7 inhibitor experiments, XPB Ser90 mutagenesis\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — siRNA screen followed by mutagenesis of substrate phospho-acceptor site and kinase requirement, multiple orthogonal validations\",\n      \"pmids\": [\"30762924\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FBXL18 promotes K63-linked ubiquitination of ribosomal protein RPS15A, enhancing its stability (not degradation), which in turn increases SMAD3 protein levels and promotes SMAD3 nuclear translocation to drive hepatocellular carcinoma cell proliferation. Knockdown of RPS15A or SMAD3 suppresses FBXL18-mediated HCC proliferation.\",\n      \"method\": \"K63-linked ubiquitination assay, Western blotting for RPS15A/SMAD3 stability, FBXL18 transgenic mouse model, siRNA epistasis knockdown of RPS15A and SMAD3\",\n      \"journal\": \"Hepatology communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — K63-ubiquitination specificity demonstrated, epistasis with RPS15A/SMAD3 knockdown, in vivo transgenic model; single lab\",\n      \"pmids\": [\"37378633\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FBXL18 physically interacts with Akt and promotes K63-linked ubiquitination of Akt, leading to Akt activation (increased p-AKT S473) in ovarian cancer cells. AKT inhibitor MK-2206 reverses FBXL18 overexpression-induced proliferation and migration.\",\n      \"method\": \"Co-immunoprecipitation, K63-linked ubiquitination assay, pharmacological inhibition with MK-2206, siRNA knockdown and overexpression\",\n      \"journal\": \"American journal of translational research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP and K63-specific ubiquitination assay with functional rescue by AKT inhibitor; single lab, replicates glioma finding\",\n      \"pmids\": [\"38883375\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FBXL18 mediates K11-type ubiquitination of BST2 on Lys109 and Lys110, stabilizing BST2 (competing with K33-linked degradative ubiquitination by an unknown E3 ligase). FBXL18-mediated BST2 stabilization leads to hyperphosphorylation of IκBα and excessive NF-κB activation, driving IL-6 production and inflammation in RABV-infected astrocytes. FBXL18 knockdown inhibits IL-6 production, RABV replication, and reduces virulence in mice.\",\n      \"method\": \"siRNA screen, Co-IP, K11-specific ubiquitination assay with lysine mutagenesis (K109/K110), IκBα phosphorylation Western blot, NF-κB reporter assay, in vivo mouse RABV infection model\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mechanistic screen, K11-linkage specificity with acceptor-site mutagenesis, pathway epistasis, in vivo validation; multiple orthogonal methods\",\n      \"pmids\": [\"41390767\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FBXL18 physically interacts with DUSP16 (dual specificity phosphatase 16), promoting its ubiquitination and proteasomal degradation, thereby activating the JNK/c-JUN signaling pathway to facilitate endometrial carcinoma cell proliferation, migration, and invasion. Overexpression of DUSP16 rescues the JNK activation and enhanced cell capacities induced by FBXL18 overexpression.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, Western blotting, siRNA knockdown, DUSP16 overexpression rescue experiment, CCK-8/colony formation/Transwell assays\",\n      \"journal\": \"Cancer cell international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP, ubiquitination assay, and epistasis rescue; single lab with multiple orthogonal assays\",\n      \"pmids\": [\"40382593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FBXL18 interacts with Akt and promotes K63-linked polyubiquitination of Akt, activating the AKT/CCND1 signaling pathway to maintain radioresistance in esophageal squamous cell carcinoma cells.\",\n      \"method\": \"Co-immunoprecipitation, K63-linked polyubiquitination assay by Western blot, siRNA knockdown, CCK-8 radiosensitivity assay\",\n      \"journal\": \"BMB reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP and K63-specific ubiquitination with functional radiosensitivity readout; single lab, corroborates prior Akt-K63 ubiquitination findings\",\n      \"pmids\": [\"41655990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FBXL18 suppresses FBXL7 protein expression in esophageal squamous cell carcinoma cells, and this mechanism underlies FBXL18's pro-proliferative and radioprotective effects in ESCC.\",\n      \"method\": \"FBXL18 overexpression/knockdown lentivirus, Western blotting for FBXL7, colony formation, in vivo xenograft, irradiation survival assay\",\n      \"journal\": \"Strahlentherapie und Onkologie\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — Western blot for substrate level with functional correlation; no ubiquitination assay or mutagenesis reported, single lab\",\n      \"pmids\": [\"39971770\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FBXL18 is the substrate-recognition F-box subunit of an SCF (Skp1-Cul1-Rbx1) E3 ubiquitin ligase complex with multiple substrates: it targets FBXL7 (via K48-linked ubiquitination for degradation), LRRK2 (phosphorylation-dependent K48-linked degradation), and XPB (CDK7-phosphorylation-primed degradation), while promoting non-degradative K63-linked ubiquitination of Akt to activate it, K63-linked ubiquitination of RPS15A to stabilize it and activate SMAD3, K11-linked ubiquitination of BST2 to stabilize it and drive NF-κB inflammation, and K48-linked ubiquitination of DUSP16 for degradation to activate JNK signaling.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"FBXL18 is the substrate-recognition subunit of an SCF (Skp1–Cul1–Rbx1–FBXL18) E3 ubiquitin ligase that governs cell survival and proliferation by conjugating distinct ubiquitin chain types to different substrates. It mediates K48-linked polyubiquitination and proteasomal degradation of the pro-apoptotic F-box protein FBXL7 (via an FQ degron and Lys109 acceptor), phosphorylated LRRK2 (in a PKC-enhanced, phosphorylation-dependent manner), XPB/TFIIH (primed by CDK7-dependent Ser90 phosphorylation), and DUSP16 (relieving JNK pathway suppression) [PMID:25654763, PMID:27890708, PMID:30762924, PMID:40382593]. In parallel, FBXL18 catalyzes non-degradative K63-linked ubiquitination of Akt to promote its activation and downstream FOXO3a/BCL2L11 or CCND1 signaling, and K63-linked ubiquitination of RPS15A to stabilize it and drive SMAD3 nuclear translocation [PMID:27926990, PMID:38883375, PMID:37378633]. FBXL18 also mediates K11-linked ubiquitination of BST2 at Lys109/Lys110, stabilizing BST2 and hyperactivating NF-κB/IL-6 inflammatory signaling during rabies virus infection [PMID:41390767].\",\n  \"teleology\": [\n    {\n      \"year\": 2015,\n      \"claim\": \"Establishing that FBXL18 is a functional SCF E3 ligase subunit resolved whether FBXL18 possesses ubiquitin ligase activity and identified its first substrate—the pro-apoptotic F-box protein FBXL7—targeted via K48-linked ubiquitination for proteasomal degradation.\",\n      \"evidence\": \"In vitro ubiquitination, site-directed mutagenesis of Lys109 and FQ degron, siRNA knockdown with apoptosis rescue in HeLa cells\",\n      \"pmids\": [\"25654763\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No structural basis for FBXL18–FBXL7 recognition via the FQ motif\",\n        \"Whether other F-box proteins are similarly regulated by FBXL18 is unknown\",\n        \"Physiological tissues where FBXL18–FBXL7 axis operates are not defined\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrating that FBXL18 also catalyzes non-degradative K63-linked ubiquitination of Akt for its activation revealed a linkage-type switch capability—K48 for degradation versus K63 for signaling—and connected FBXL18 to pro-survival Akt signaling in glioma.\",\n      \"evidence\": \"K63-specific ubiquitination assay, siRNA knockdown with Akt pathway Western blotting and apoptosis assays in glioma cells\",\n      \"pmids\": [\"27926990\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The ubiquitin acceptor lysine(s) on Akt were not identified\",\n        \"How FBXL18 selects between K48 and K63 chain assembly on different substrates is unknown\",\n        \"Single-lab finding at the time of publication\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showing phosphorylation-dependent recognition of LRRK2 by FBXL18 established that SCF^FBXL18 uses a canonical phosphodegron mechanism and linked this E3 ligase to Parkinson's disease-relevant LRRK2 turnover.\",\n      \"evidence\": \"Reciprocal Co-IP, phosphatase treatment blocking FBXL18 association, PKC activation enhancing degradation, caspase/cell-death rescue assays\",\n      \"pmids\": [\"27890708\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Specific phosphorylation site(s) on LRRK2 recognized by FBXL18 were not mapped\",\n        \"In vivo relevance in dopaminergic neurons or animal PD models not tested\",\n        \"Chain linkage type on LRRK2 not explicitly determined\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identifying XPB as a spironolactone-induced substrate of SCF^FBXL18, dependent on CDK7-mediated Ser90 phosphorylation, revealed a pharmacologically triggerable phosphodegron and connected FBXL18 to transcription/NER factor turnover.\",\n      \"evidence\": \"siRNA library screen, Co-IP confirming SCF complex, CDK7 inhibitor epistasis, XPB Ser90 mutagenesis\",\n      \"pmids\": [\"30762924\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether FBXL18 degrades XPB under physiological (non-drug) conditions is unclear\",\n        \"Direct binding interface between FBXL18 LRR domain and phospho-XPB not resolved\",\n        \"Consequences for NER and transcription in vivo not assessed\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Demonstrating K63-linked ubiquitination of RPS15A by FBXL18 that stabilizes the substrate and activates SMAD3 signaling expanded the non-degradative substrate repertoire and linked FBXL18 to TGF-β/SMAD-driven hepatocellular carcinoma proliferation.\",\n      \"evidence\": \"K63-ubiquitination assay, FBXL18 transgenic mouse model, siRNA epistasis with RPS15A and SMAD3 in HCC cells\",\n      \"pmids\": [\"37378633\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which K63-ubiquitinated RPS15A stabilizes SMAD3 protein is undefined\",\n        \"Whether this reflects a ribosomal or extra-ribosomal function of RPS15A is unknown\",\n        \"Single-lab observation\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Independent replication of FBXL18-mediated K63-linked Akt ubiquitination in ovarian cancer, with pharmacological rescue by the Akt inhibitor MK-2206, strengthened confidence in the Akt–K63 ubiquitination axis across tumor types.\",\n      \"evidence\": \"Co-IP, K63-specific ubiquitination assay, MK-2206 rescue of FBXL18-driven proliferation/migration in ovarian cancer cells\",\n      \"pmids\": [\"38883375\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Akt ubiquitin acceptor sites still unmapped\",\n        \"Whether FBXL18 directly ubiquitinates Akt or acts through an adaptor is not resolved\",\n        \"No in vivo validation in ovarian cancer models\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Discovery that FBXL18 catalyzes K11-linked ubiquitination of BST2 to stabilize it and drive NF-κB/IL-6 inflammation during rabies virus infection introduced a third chain-linkage type to FBXL18's repertoire and linked it to innate immune/inflammatory signaling.\",\n      \"evidence\": \"siRNA screen, K11-specific ubiquitination with K109/K110 mutagenesis, NF-κB reporter, in vivo mouse RABV infection model\",\n      \"pmids\": [\"41390767\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"How FBXL18 directs K11 versus K48 versus K63 chain assembly mechanistically is unknown\",\n        \"Whether BST2 stabilization by K11 chains occurs outside viral infection is untested\",\n        \"The E2 conjugating enzyme(s) partnering with FBXL18 for each chain type are not identified\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identification of DUSP16 as a degradative substrate whose loss activates JNK/c-JUN signaling extended FBXL18's substrate range to MAP kinase phosphatases and linked it to endometrial carcinoma progression.\",\n      \"evidence\": \"Co-IP, ubiquitination assay, DUSP16 overexpression rescue of JNK activation, Transwell and colony assays in endometrial carcinoma cells\",\n      \"pmids\": [\"40382593\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Ubiquitin chain type on DUSP16 not specified\",\n        \"Degron or phosphodegron on DUSP16 not mapped\",\n        \"Single-lab finding without in vivo model\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A third independent study confirmed FBXL18-mediated K63 ubiquitination of Akt, now linked to radioresistance in esophageal squamous cell carcinoma via AKT/CCND1, consolidating Akt as a bona fide non-degradative substrate across multiple cancer types.\",\n      \"evidence\": \"Co-IP, K63 polyubiquitination assay, siRNA knockdown with radiosensitivity assay in ESCC cells\",\n      \"pmids\": [\"41655990\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct in vitro reconstitution of FBXL18-Akt ubiquitination with purified components is lacking\",\n        \"Whether K63-Akt ubiquitination drives radioresistance through membrane recruitment or kinase conformational change is unknown\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A central open question is how a single F-box protein directs three distinct ubiquitin chain types (K48, K63, K11) on different substrates, and whether this reflects E2 switching, substrate-intrinsic determinants, or cofactor-dependent mechanisms.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No E2 conjugating enzyme partners have been identified for FBXL18\",\n        \"No structural model of the FBXL18 LRR domain or substrate-binding interface exists\",\n        \"Physiological regulation of FBXL18 expression or activity (transcriptional, post-translational) is uncharacterized\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 5, 6, 7, 8]},\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 2, 3, 6]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 2, 3, 4, 6, 7]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 4, 5, 7, 8]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"complexes\": [\n      \"SCF (Skp1–Cul1–Rbx1–FBXL18)\"\n    ],\n    \"partners\": [\n      \"FBXL7\",\n      \"AKT1\",\n      \"LRRK2\",\n      \"XPB\",\n      \"RPS15A\",\n      \"BST2\",\n      \"DUSP16\",\n      \"SKP1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}