{"gene":"FEM1B","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":2024,"finding":"Cryo-EM structures of CRL2FEM1B bound to different C-degrons reveal that FEM1B uses a bipartite mechanism to recognize both the C-terminal proline (Ψ-Pro/C-degron) and an upstream aromatic residue within the substrate; NEDD8-mediated neddylation activates CRL2FEM1B by altering its dimerization state; in vitro ubiquitination and cell-based assays confirm that polyubiquitination and protein turnover depend on both FEM1B-degron interactions and E3 ligase dimerization.","method":"Cryo-EM structure determination, in vitro ubiquitination assay, cell-based degradation assay, mutagenesis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structures with functional validation by in vitro ubiquitination and cell-based assays, multiple orthogonal methods in single study","pmids":["38670995"],"is_preprint":false},{"year":2022,"finding":"A cysteine-reactive covalent ligand EN106 targets C186 of FEM1B and disrupts recognition of the reductive stress substrate FNIP1, establishing FEM1B as the E3 ligase responsible for the cellular reductive stress response; EN106 can serve as a FEM1B recruiter in PROTAC-mediated degradation of BRD4 and BCR-ABL.","method":"Covalent ligand screening, competitive binding assay, PROTAC cellular degradation assay","journal":"Journal of the American Chemical Society","confidence":"High","confidence_rationale":"Tier 1–2 — covalent site identification with functional disruption of substrate binding, replicated in multiple PROTAC contexts; highly cited","pmids":["34994556"],"is_preprint":false},{"year":2021,"finding":"CRL2FEM1B recognizes the C-degron of the SMCR8 isoform (an autophagy regulator); crystal structure of FEM1B bound to SMCR8 C-degron reveals the molecular basis of C-degron recognition by FEM1B.","method":"Crystal structure determination, biochemical binding assay","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — structural determination with biochemical validation","pmids":["33892462"],"is_preprint":false},{"year":2013,"finding":"Fem1b interacts directly with Gli1 (the mammalian homolog of nematode TRA-1), promotes Gli1 ubiquitylation, suppresses Gli1 transcriptional activity, and attenuates an oncogenic Gli1 autoregulatory loop in cancer cells; all effects depend on the VHL-box motif of Fem1b.","method":"Co-immunoprecipitation, GST pull-down, ubiquitylation assay, reporter assay, VHL-box mutant","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1–2 — direct binding confirmed by pulldown, ubiquitylation assay, and mutagenesis with functional readout","pmids":["24076122"],"is_preprint":false},{"year":2009,"finding":"FEM1B associates with chromatin and facilitates chromatin loading of Rad9, acting as an adaptor linking CHK1 and Rad9 to support ATR-mediated checkpoint signaling during replication stress; FEM1B depletion impairs CHK1 Ser345 phosphorylation and CHK1 kinase activity without affecting CHK2.","method":"Yeast two-hybrid, siRNA knockdown, chromatin fractionation, CHK1 kinase assay, phospho-specific western blot","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — clean KD with specific phosphorylation and kinase activity readouts; single lab","pmids":["19330022"],"is_preprint":false},{"year":2009,"finding":"RACK1 co-immunoprecipitates with endogenous Fem1b in metastatic colon cancer cells, stimulates Fem1b ubiquitination, and promotes Fem1b proteasomal degradation; RACK1 overexpression reduces Fem1b levels while RACK1 knockdown increases Fem1b and induces apoptosis in a Fem1b-dependent manner.","method":"Co-immunoprecipitation, ubiquitination assay, siRNA knockdown, proteasome inhibitor treatment, morpholino antisense","journal":"Cancer biology & therapy","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal interaction confirmed, ubiquitination demonstrated, functional epistasis by Fem1b blockade; single lab","pmids":["19855191"],"is_preprint":false},{"year":2011,"finding":"Mouse Fem1b directly binds Ankrd37 (identified by yeast two-hybrid and co-immunoprecipitation) and targets it for ubiquitin-mediated proteasomal degradation in a dose-dependent manner; Ankrd37 facilitates nuclear translocation of Fem1b when co-expressed.","method":"Yeast two-hybrid, co-immunoprecipitation, ubiquitination assay, transfection dose-response, subcellular localization imaging","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2–3 — interaction confirmed by two methods, ubiquitination demonstrated, localization experiment; single lab","pmids":["21723927"],"is_preprint":false},{"year":2008,"finding":"Fem1b interacts with the homeodomain protein Nkx3.1 in GST pull-down and co-immunoprecipitation assays; Fem1b knockout mice display defects in prostate ductal morphogenesis and secretory protein expression similar to Nkx3.1 mutants, suggesting a conserved role in sexual dimorphism.","method":"Yeast two-hybrid, GST pull-down, co-immunoprecipitation, gene-targeted knockout mouse","journal":"Developmental dynamics","confidence":"Medium","confidence_rationale":"Tier 2 — direct interaction confirmed by multiple methods plus KO phenotype; single lab","pmids":["18816836"],"is_preprint":false},{"year":2004,"finding":"FEM1B interacts with the membrane protein PHTF1 via its ANK domain (identified by yeast two-hybrid and confirmed by co-immunoprecipitation); PHTF1 recruits FEM1B to the endoplasmic reticulum membrane.","method":"Yeast two-hybrid, co-immunoprecipitation, domain mapping, subcellular localization by immunofluorescence","journal":"Biology of reproduction","confidence":"Medium","confidence_rationale":"Tier 2–3 — interaction confirmed by two methods with domain mapping and localization consequence; single lab","pmids":["15601915"],"is_preprint":false},{"year":2005,"finding":"Fem1b knockout mice display abnormal glucose tolerance due predominantly to defective glucose-stimulated insulin secretion (and also arginine-stimulated insulin secretion), implicating Fem1b in pancreatic islet function; Fem1b is expressed in both beta and non-beta islet cells.","method":"Gene-targeted knockout mouse, glucose tolerance test, insulin secretion assay","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with specific functional readout; single lab","pmids":["16024793"],"is_preprint":false},{"year":2010,"finding":"Fem1b protein is downregulated by the proteasome in malignant colon cancer cells; proteasome inhibitor treatment upregulates Fem1b and induces apoptosis; blocking Fem1b upregulation with morpholino antisense suppresses this apoptosis, placing Fem1b as a mediator of proteasome inhibitor-induced apoptosis.","method":"Proteasome inhibitor treatment, morpholino antisense knockdown, apoptosis assay","journal":"Molecular carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 — functional epistasis by antisense knockdown with specific apoptosis readout; single lab","pmids":["19908242"],"is_preprint":false},{"year":2023,"finding":"miR-29a-3p downregulates FEM1B expression, reducing FEM1B-mediated degradation of Gli1, thereby increasing Gli1 levels and conferring oxaliplatin resistance; knockdown of GLI1 reverted chemoresistance, placing FEM1B upstream of Gli1 in this pathway.","method":"miRNA overexpression, western blot, genetic knockdown, oxaliplatin resistance assay, mouse tumor model","journal":"American journal of cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — pathway epistasis established by rescue experiments with specific resistance phenotype; single lab","pmids":["38187042"],"is_preprint":false},{"year":2024,"finding":"FEM1B undergoes stop codon readthrough (SCR) to generate a C-terminally extended, highly unstable isoform; CRISPR deletion of the 81-nt 3'UTR region abolishes SCR, increases FEM1B expression, reduces SLBP levels (an FEM1B-targeted substrate), and causes cell cycle delay; this SCR mechanism is specific to Hominini.","method":"CRISPR editing, stop codon readthrough reporter assay, western blot, cell cycle analysis","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — CRISPR-based functional validation with defined substrate and cell cycle phenotype; single lab","pmids":["39140134"],"is_preprint":false},{"year":2025,"finding":"Mettl3-mediated m6A modification reduces Fem1b mRNA stability, which promotes FEM1B-mediated Gli1 degradation; loss of Mettl3 in skeletal stem cells stabilizes Fem1b mRNA, leading to reduced Gli1 and impaired stem cell quiescence and differentiation.","method":"Conditional Mettl3 knockout mouse, m6A-seq, mRNA stability assay, protein level analysis","journal":"The EMBO journal","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with m6A mapping and mechanistic pathway through FEM1B-Gli1; single lab","pmids":["40016417"],"is_preprint":false},{"year":2025,"finding":"FEM1B enhances TRAIL-induced apoptosis in T lymphocytes (Molt-4, Jurkat) and monocytes (THP-1, U937) via caspase-3 and caspase-8 but not caspase-9 (extrinsic pathway); in T cells FEM1B interacts with TRAF2 and downregulates it to relieve TRAF2's inhibitory effect on caspase-8; in monocytes FEM1B upregulates TRAIL-R2.","method":"FEM1B knockdown/knockout, co-immunoprecipitation, caspase activity assay, TRAIL-induced apoptosis assay, murine KO model","journal":"FEBS open bio","confidence":"Medium","confidence_rationale":"Tier 2–3 — interaction and cell-type-specific mechanisms identified with KO validation; single lab","pmids":["40392678"],"is_preprint":false},{"year":2024,"finding":"A recurrent de novo FEM1B missense variant (Arg126Gln) causes gain-of-function activation; overexpression of FEM1BR126Q but not wild-type FEM1B in mouse brain via in utero electroporation delays neuronal migration; patient cells show oxidative stress and type I interferon signaling induction.","method":"In utero electroporation, patient cell analysis, oxidative stress assay, interferon signaling assay","journal":"Genetics in medicine","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo functional validation with mutant vs. WT comparison; single study","pmids":["38465576"],"is_preprint":false}],"current_model":"FEM1B is a substrate-recognition subunit of the CRL2 (Cullin 2-RING) E3 ubiquitin ligase complex that uses a bipartite mechanism (recognizing a C-terminal proline/Ψ-Pro C-degron and an upstream aromatic residue) and NEDD8-regulated dimerization to polyubiquitinate substrates including FNIP1 (reductive stress sensor), Gli1, SLBP, SMCR8, and Ankrd37 for proteasomal degradation; it additionally functions as a chromatin-associated adaptor linking Rad9 to CHK1 for ATR checkpoint signaling during replication stress, interacts with pro-apoptotic machinery (Fas, TNFR1, TRAF2) to promote extrinsic apoptosis, and its own levels are regulated by RACK1-mediated ubiquitination, miR-29 family members, m6A mRNA modification, and stop codon readthrough."},"narrative":{"teleology":[{"year":2004,"claim":"Identification of PHTF1 as a FEM1B-interacting protein established that FEM1B's ankyrin-repeat domain mediates protein–protein interactions and can be recruited to specific subcellular compartments.","evidence":"Yeast two-hybrid and co-immunoprecipitation with domain mapping and immunofluorescence localization","pmids":["15601915"],"confidence":"Medium","gaps":["Functional consequence of PHTF1–FEM1B interaction on substrate targeting unknown","No independent replication"]},{"year":2005,"claim":"Fem1b knockout mice revealed an unexpected organismal role in glucose homeostasis, demonstrating that FEM1B is required for normal glucose-stimulated insulin secretion from pancreatic islets.","evidence":"Gene-targeted knockout mouse with glucose tolerance and insulin secretion assays","pmids":["16024793"],"confidence":"Medium","gaps":["Molecular mechanism linking FEM1B to insulin secretion machinery unresolved","Whether this reflects substrate degradation or a non-E3-ligase function is unknown"]},{"year":2008,"claim":"Interaction with Nkx3.1 and prostate ductal morphogenesis defects in Fem1b knockout mice connected FEM1B to developmental patterning and sexual dimorphism in mammals, echoing C. elegans Fem1 sex-determination biology.","evidence":"Yeast two-hybrid, GST pull-down, co-immunoprecipitation, and knockout mouse phenotyping","pmids":["18816836"],"confidence":"Medium","gaps":["Whether FEM1B ubiquitinates Nkx3.1 directly was not tested","Single lab observation"]},{"year":2009,"claim":"Two parallel studies established dual functions for FEM1B: as a chromatin-associated adaptor facilitating Rad9–CHK1 coupling in ATR checkpoint signaling, and as a pro-apoptotic protein whose levels are controlled by RACK1-mediated ubiquitination.","evidence":"siRNA knockdown with chromatin fractionation and CHK1 kinase assays (checkpoint); co-immunoprecipitation, ubiquitination assays, and epistasis experiments (RACK1-apoptosis)","pmids":["19330022","19855191"],"confidence":"Medium","gaps":["Whether FEM1B's checkpoint role requires its E3 ligase activity is untested","RACK1-mediated ubiquitination mechanism (direct E3 or scaffold) not resolved","Both findings from single labs"]},{"year":2010,"claim":"Demonstration that proteasome inhibitor-induced apoptosis in colon cancer cells requires FEM1B upregulation placed FEM1B as a functional mediator of apoptosis in malignancy, linking its proteasomal turnover to chemosensitivity.","evidence":"Proteasome inhibitor treatment with morpholino antisense knockdown and apoptosis assay","pmids":["19908242"],"confidence":"Medium","gaps":["Apoptotic substrates of FEM1B in this context not identified","Single lab, single cell type"]},{"year":2011,"claim":"Identification of Ankrd37 as a FEM1B substrate targeted for ubiquitin-mediated degradation expanded the known substrate repertoire, and reciprocally revealed that Ankrd37 promotes FEM1B nuclear translocation.","evidence":"Yeast two-hybrid, co-immunoprecipitation, ubiquitination assay, subcellular localization imaging","pmids":["21723927"],"confidence":"Medium","gaps":["Physiological consequence of Ankrd37 degradation unknown","Single lab, overexpression system"]},{"year":2013,"claim":"Direct binding and ubiquitylation of Gli1 by FEM1B established a conserved link to C. elegans TRA-1 regulation and demonstrated that FEM1B suppresses Hedgehog pathway output in a VHL-box-dependent manner.","evidence":"Co-immunoprecipitation, GST pull-down, ubiquitylation assay, reporter assay, VHL-box mutagenesis","pmids":["24076122"],"confidence":"High","gaps":["Whether endogenous Gli1 turnover depends on FEM1B in vivo not shown in this study","Degron on Gli1 recognized by FEM1B not mapped"]},{"year":2021,"claim":"Crystal structure of FEM1B bound to the SMCR8 C-degron provided the first atomic-resolution view of how FEM1B recognizes C-terminal degradation signals, establishing FEM1B as a bona fide C-degron reader.","evidence":"X-ray crystal structure determination with biochemical binding assay","pmids":["33892462"],"confidence":"High","gaps":["Only one substrate C-degron characterized structurally at this point","Full-length substrate recognition mechanism not addressed"]},{"year":2022,"claim":"Covalent targeting of FEM1B C186 with EN106 disrupted FNIP1 recognition, establishing FEM1B as the E3 ligase responsible for the reductive stress response and demonstrating FEM1B's utility as a PROTAC recruitment handle.","evidence":"Covalent ligand screening, competitive binding assay, PROTAC-mediated degradation of BRD4 and BCR-ABL in cells","pmids":["34994556"],"confidence":"High","gaps":["Structural basis of EN106-mediated disruption not determined","Long-term selectivity of EN106 in vivo untested"]},{"year":2023,"claim":"miR-29a-3p was shown to downregulate FEM1B, relieving Gli1 degradation and conferring oxaliplatin resistance, revealing a microRNA-based regulatory layer controlling the FEM1B–Gli1 axis in chemoresistance.","evidence":"miRNA overexpression, genetic knockdown, oxaliplatin resistance assay, mouse tumor model","pmids":["38187042"],"confidence":"Medium","gaps":["Direct miR-29a-3p binding site on FEM1B 3'UTR not validated by luciferase reporter in this study","Single lab"]},{"year":2024,"claim":"Cryo-EM structures of CRL2-FEM1B with different substrates revealed a bipartite degron recognition mechanism (C-terminal ψ-Pro plus upstream aromatic residue) and showed that NEDD8-dependent dimerization is required for full E3 ligase activity, providing the comprehensive structural framework for substrate polyubiquitination.","evidence":"Cryo-EM structure determination, in vitro ubiquitination assay, cell-based degradation assay, mutagenesis","pmids":["38670995"],"confidence":"High","gaps":["How dimerization is regulated in vivo under different signaling conditions is unknown","Not all known substrates have been mapped to the bipartite degron model"]},{"year":2024,"claim":"Discovery of Hominini-specific stop codon readthrough (SCR) generating an unstable FEM1B isoform revealed an additional post-translational regulatory mechanism; CRISPR deletion of the SCR element increased FEM1B levels, reduced SLBP, and delayed the cell cycle.","evidence":"CRISPR editing, SCR reporter assay, western blot, cell cycle analysis","pmids":["39140134"],"confidence":"Medium","gaps":["Physiological triggers of SCR frequency changes unknown","Single lab"]},{"year":2024,"claim":"A recurrent de novo FEM1B R126Q variant was identified as a gain-of-function cause of a neurodevelopmental disorder, linking FEM1B hyperactivation to impaired neuronal migration, oxidative stress, and interferon pathway induction.","evidence":"In utero electroporation in mouse brain, patient cell analysis, oxidative stress and interferon signaling assays","pmids":["38465576"],"confidence":"Medium","gaps":["Specific substrate(s) hyperactivated by R126Q not identified","Number of families limited; awaits larger cohort replication"]},{"year":2025,"claim":"Mettl3-mediated m6A modification was shown to control Fem1b mRNA stability, connecting epitranscriptomic regulation to the FEM1B–Gli1 degradation axis in skeletal stem cell quiescence and differentiation.","evidence":"Conditional Mettl3 knockout mouse, m6A-seq, mRNA stability assay","pmids":["40016417"],"confidence":"Medium","gaps":["Specific m6A reader mediating Fem1b mRNA decay not identified","Single lab"]},{"year":2025,"claim":"FEM1B was shown to enhance TRAIL-induced extrinsic apoptosis in a cell-type-specific manner: in T cells via TRAF2 interaction and downregulation relieving caspase-8 inhibition, and in monocytes via TRAIL-R2 upregulation.","evidence":"FEM1B knockdown/knockout, co-immunoprecipitation, caspase activity assays, TRAIL-induced apoptosis assay","pmids":["40392678"],"confidence":"Medium","gaps":["Whether FEM1B ubiquitinates TRAF2 directly not demonstrated","Mechanism of TRAIL-R2 upregulation in monocytes unclear"]},{"year":null,"claim":"Key unresolved questions include: the structural and mechanistic basis for FEM1B's non-E3-ligase functions (checkpoint signaling, apoptosis), the identity of hyperactivated substrates in the R126Q neurodevelopmental disorder, and whether all known substrates conform to the bipartite C-degron recognition model.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structure of FEM1B in complex with Rad9 or CHK1","Complete substrate landscape not mapped by unbiased proteomics","In vivo significance of SCR regulation under physiological stress unclear"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,3,6]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4]}],"localization":[{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[4]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[4,6]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,1]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,2,3,6]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[4]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[5,10,14]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,11,13]}],"complexes":["CRL2-FEM1B (Cullin 2-RING E3 ubiquitin ligase)"],"partners":["CUL2","FNIP1","GLI1","SMCR8","RAD9A","TRAF2","RACK1","NKX3-1"],"other_free_text":[]},"mechanistic_narrative":"FEM1B is a substrate-recognition subunit of the CRL2 (Cullin 2-RING) E3 ubiquitin ligase complex that targets diverse substrates for proteasomal degradation through recognition of C-terminal degrons, using a bipartite mechanism that engages both a ψ-Pro C-degron and an upstream aromatic residue, with NEDD8-dependent dimerization activating the ligase [PMID:38670995, PMID:33892462]. Validated substrates include FNIP1 (a reductive stress sensor), Gli1 (a Hedgehog pathway transcription factor), SLBP, SMCR8, and Ankrd37, placing FEM1B at the nexus of stress sensing, developmental signaling, and cell cycle control [PMID:34994556, PMID:24076122, PMID:39140134, PMID:33892462, PMID:21723927]. Beyond its E3 ligase function, FEM1B serves as a chromatin-associated adaptor that links Rad9 to CHK1 for ATR checkpoint signaling during replication stress and promotes extrinsic apoptosis through interaction with TRAF2 and modulation of caspase-8 activation [PMID:19330022, PMID:40392678]. A recurrent de novo FEM1B missense variant (Arg126Gln) causes a gain-of-function neurodevelopmental disorder characterized by impaired neuronal migration, oxidative stress, and type I interferon pathway activation [PMID:38465576]."},"prefetch_data":{"uniprot":{"accession":"Q9UK73","full_name":"Protein fem-1 homolog B","aliases":["FEM1-beta","Fem-1-like death receptor-binding protein alpha","Fem-1-like in apoptotic pathway protein alpha","F1A-alpha"],"length_aa":627,"mass_kda":70.3,"function":"Substrate-recognition component of a Cul2-RING (CRL2) E3 ubiquitin-protein ligase complex of the DesCEND (destruction via C-end degrons) pathway, which recognizes a C-degron located at the extreme C terminus of target proteins, leading to their ubiquitination and degradation (PubMed:29779948, PubMed:33398168, PubMed:33398170). The C-degron recognized by the DesCEND pathway is usually a motif of less than ten residues and can be present in full-length proteins, truncated proteins or proteolytically cleaved forms (PubMed:29779948, PubMed:33398168, PubMed:33398170). The CRL2(FEM1B) complex specifically recognizes proteins ending with -Gly-Leu-Asp-Arg, such as CDK5R1, leading to their ubiquitination and degradation (PubMed:33398168, PubMed:33398170). Also acts as a regulator of the reductive stress response by mediating ubiquitination of reduced FNIP1: in response to reductive stress, the CRL2(FEM1B) complex specifically recognizes a conserved Cys degron in FNIP1 when this degron is reduced, leading to FNIP1 degradation and subsequent activation of mitochondria to recalibrate reactive oxygen species (ROS) (By similarity). Mechanistically, recognizes and binds reduced FNIP1 through two interface zinc ions, which act as a molecular glue that recruit reduced FNIP1 to FEM1B (By similarity). Promotes ubiquitination of GLI1, suppressing GLI1 transcriptional activator activity (PubMed:24076122). Promotes ubiquitination and degradation of ANKRD37 (By similarity). Promotes ubiquitination and degradation of SLBP (PubMed:28118078). Involved in apoptosis by acting as a death receptor-associated protein that mediates apoptosis (PubMed:10542291). Also involved in glucose homeostasis in pancreatic islet (By similarity). May also act as an adapter/mediator in replication stress-induced signaling that leads to the activation of CHEK1 (PubMed:19330022)","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9UK73/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FEM1B","classification":"Not Classified","n_dependent_lines":30,"n_total_lines":1208,"dependency_fraction":0.024834437086092714},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FEM1B","total_profiled":1310},"omim":[{"mim_id":"621263","title":"NEURODEVELOPMENTAL DISORDER WITH BEHAVIORAL, EAR, AND SKELETAL ABNORMALITIES; NEDBES","url":"https://www.omim.org/entry/621263"},{"mim_id":"613539","title":"FEM1 HOMOLOG B; FEM1B","url":"https://www.omim.org/entry/613539"},{"mim_id":"608767","title":"FEM1 HOMOLOG C; FEM1C","url":"https://www.omim.org/entry/608767"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/FEM1B"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q9UK73","domains":[{"cath_id":"1.25.40.20","chopping":"1-152","consensus_level":"medium","plddt":96.0805,"start":1,"end":152},{"cath_id":"-","chopping":"380-507","consensus_level":"medium","plddt":95.3089,"start":380,"end":507}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UK73","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UK73-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UK73-F1-predicted_aligned_error_v6.png","plddt_mean":94.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FEM1B","jax_strain_url":"https://www.jax.org/strain/search?query=FEM1B"},"sequence":{"accession":"Q9UK73","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UK73.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UK73/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UK73"}},"corpus_meta":[{"pmid":"34994556","id":"PMC_34994556","title":"Discovery of a Covalent FEM1B Recruiter for Targeted Protein Degradation Applications.","date":"2022","source":"Journal of the American Chemical Society","url":"https://pubmed.ncbi.nlm.nih.gov/34994556","citation_count":156,"is_preprint":false},{"pmid":"37521275","id":"PMC_37521275","title":"Glucose-responsive, antioxidative HA-PBA-FA/EN106 hydrogel enhanced diabetic wound healing through modulation of FEM1b-FNIP1 axis and promoting angiogenesis.","date":"2023","source":"Bioactive materials","url":"https://pubmed.ncbi.nlm.nih.gov/37521275","citation_count":55,"is_preprint":false},{"pmid":"19855191","id":"PMC_19855191","title":"RACK1 downregulates levels of the pro-apoptotic protein Fem1b in apoptosis-resistant colon cancer cells.","date":"2009","source":"Cancer biology & therapy","url":"https://pubmed.ncbi.nlm.nih.gov/19855191","citation_count":28,"is_preprint":false},{"pmid":"16024793","id":"PMC_16024793","title":"Abnormal glucose homeostasis and pancreatic islet function in mice with inactivation of the Fem1b gene.","date":"2005","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/16024793","citation_count":24,"is_preprint":false},{"pmid":"10623617","id":"PMC_10623617","title":"Sequence, organization, and expression of the human FEM1B gene.","date":"2000","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/10623617","citation_count":22,"is_preprint":false},{"pmid":"18757445","id":"PMC_18757445","title":"FEM1A and FEM1B: novel candidate genes for polycystic ovary syndrome.","date":"2008","source":"Human reproduction (Oxford, England)","url":"https://pubmed.ncbi.nlm.nih.gov/18757445","citation_count":21,"is_preprint":false},{"pmid":"21723927","id":"PMC_21723927","title":"Mouse Fem1b interacts with and induces ubiquitin-mediated degradation of Ankrd37.","date":"2011","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/21723927","citation_count":20,"is_preprint":false},{"pmid":"19908242","id":"PMC_19908242","title":"Fem1b, a proapoptotic protein, mediates proteasome inhibitor-induced apoptosis of human colon cancer cells.","date":"2010","source":"Molecular carcinogenesis","url":"https://pubmed.ncbi.nlm.nih.gov/19908242","citation_count":20,"is_preprint":false},{"pmid":"38670995","id":"PMC_38670995","title":"Mechanism of Ψ-Pro/C-degron recognition by the CRL2FEM1B ubiquitin ligase.","date":"2024","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/38670995","citation_count":18,"is_preprint":false},{"pmid":"24076122","id":"PMC_24076122","title":"Fem1b promotes ubiquitylation and suppresses transcriptional activity of Gli1.","date":"2013","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/24076122","citation_count":18,"is_preprint":false},{"pmid":"33892462","id":"PMC_33892462","title":"Structural insights into SMCR8 C-degron recognition by FEM1B.","date":"2021","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/33892462","citation_count":14,"is_preprint":false},{"pmid":"15601915","id":"PMC_15601915","title":"Putative homeodomain transcription factor 1 interacts with the feminization factor homolog fem1b in male germ cells.","date":"2004","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/15601915","citation_count":10,"is_preprint":false},{"pmid":"39804678","id":"PMC_39804678","title":"Development of the First-in-Class FEM1B-Recruiting Histone Deacetylase Degraders.","date":"2025","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/39804678","citation_count":9,"is_preprint":false},{"pmid":"18816836","id":"PMC_18816836","title":"Mouse Fem1b interacts with the Nkx3.1 homeoprotein and is required for proper male secondary sexual development.","date":"2008","source":"Developmental dynamics : an official publication of the American Association of Anatomists","url":"https://pubmed.ncbi.nlm.nih.gov/18816836","citation_count":9,"is_preprint":false},{"pmid":"38187042","id":"PMC_38187042","title":"Induction of resistance to oxaliplatin in cancer by a microRNA/Fem1B/Gli1 pathway.","date":"2023","source":"American journal of cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/38187042","citation_count":7,"is_preprint":false},{"pmid":"27323097","id":"PMC_27323097","title":"Molecular cloning and expression analysis of Fem1b from oriental river prawn Macrobrachium nipponense.","date":"2016","source":"Genetics and molecular research : GMR","url":"https://pubmed.ncbi.nlm.nih.gov/27323097","citation_count":6,"is_preprint":false},{"pmid":"19330022","id":"PMC_19330022","title":"Human FEM1B is required for Rad9 recruitment and CHK1 activation in response to replication stress.","date":"2009","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/19330022","citation_count":6,"is_preprint":false},{"pmid":"38465576","id":"PMC_38465576","title":"A recurrent missense variant in the E3 ubiquitin ligase substrate recognition subunit FEM1B causes a rare syndromic neurodevelopmental disorder.","date":"2024","source":"Genetics in medicine : official journal of the American College of Medical Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/38465576","citation_count":4,"is_preprint":false},{"pmid":"10768616","id":"PMC_10768616","title":"Rapid communication: the human FEM1B gene maps to chromosome 15q22 and is excluded as the gene for Bardet-Biedl syndrome, type 4.","date":"2000","source":"The American journal of the medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/10768616","citation_count":3,"is_preprint":false},{"pmid":"36003920","id":"PMC_36003920","title":"miR-29b Regulates Lung Cancer Progression by Downregulating FEM1B and Inhibiting the FOX01/AKT Pathway.","date":"2022","source":"Computational and mathematical methods in medicine","url":"https://pubmed.ncbi.nlm.nih.gov/36003920","citation_count":2,"is_preprint":false},{"pmid":"20952268","id":"PMC_20952268","title":"Fem1b antigen in the stool of ApcMin mice as a biomarker of early Wnt signaling activation in intestinal neoplasia.","date":"2010","source":"Cancer epidemiology","url":"https://pubmed.ncbi.nlm.nih.gov/20952268","citation_count":1,"is_preprint":false},{"pmid":"40016417","id":"PMC_40016417","title":"An epitranscriptomic program maintains skeletal stem cell quiescence via a METTL3-FEM1B-GLI1 axis.","date":"2025","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/40016417","citation_count":0,"is_preprint":false},{"pmid":"39140134","id":"PMC_39140134","title":"Hominini-specific regulation of the cell cycle by stop codon readthrough of FEM1B.","date":"2024","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/39140134","citation_count":0,"is_preprint":false},{"pmid":"40392678","id":"PMC_40392678","title":"FEM1B enhances TRAIL-induced apoptosis in T lymphocytes and monocytes.","date":"2025","source":"FEBS open bio","url":"https://pubmed.ncbi.nlm.nih.gov/40392678","citation_count":0,"is_preprint":false},{"pmid":"37829534","id":"PMC_37829534","title":"Retracted: miR-29b Regulates Lung Cancer Progression by Downregulating FEM1B and Inhibiting the FOX01/AKT Pathway.","date":"2023","source":"Computational and mathematical methods in medicine","url":"https://pubmed.ncbi.nlm.nih.gov/37829534","citation_count":0,"is_preprint":false},{"pmid":"19171189","id":"PMC_19171189","title":"WITHDRAWN: Fem1b interacts with Ankrd37 in mouse testis and induces its degradation by ubiquitin-mediated proteolysis pathway.","date":"2009","source":"Cellular signalling","url":"https://pubmed.ncbi.nlm.nih.gov/19171189","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12575,"output_tokens":3712,"usd":0.046703},"stage2":{"model":"claude-opus-4-6","input_tokens":7139,"output_tokens":3569,"usd":0.18738},"total_usd":0.234083,"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\": 2024,\n      \"finding\": \"Cryo-EM structures of CRL2FEM1B bound to different C-degrons reveal that FEM1B uses a bipartite mechanism to recognize both the C-terminal proline (Ψ-Pro/C-degron) and an upstream aromatic residue within the substrate; NEDD8-mediated neddylation activates CRL2FEM1B by altering its dimerization state; in vitro ubiquitination and cell-based assays confirm that polyubiquitination and protein turnover depend on both FEM1B-degron interactions and E3 ligase dimerization.\",\n      \"method\": \"Cryo-EM structure determination, in vitro ubiquitination assay, cell-based degradation assay, mutagenesis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structures with functional validation by in vitro ubiquitination and cell-based assays, multiple orthogonal methods in single study\",\n      \"pmids\": [\"38670995\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A cysteine-reactive covalent ligand EN106 targets C186 of FEM1B and disrupts recognition of the reductive stress substrate FNIP1, establishing FEM1B as the E3 ligase responsible for the cellular reductive stress response; EN106 can serve as a FEM1B recruiter in PROTAC-mediated degradation of BRD4 and BCR-ABL.\",\n      \"method\": \"Covalent ligand screening, competitive binding assay, PROTAC cellular degradation assay\",\n      \"journal\": \"Journal of the American Chemical Society\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — covalent site identification with functional disruption of substrate binding, replicated in multiple PROTAC contexts; highly cited\",\n      \"pmids\": [\"34994556\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CRL2FEM1B recognizes the C-degron of the SMCR8 isoform (an autophagy regulator); crystal structure of FEM1B bound to SMCR8 C-degron reveals the molecular basis of C-degron recognition by FEM1B.\",\n      \"method\": \"Crystal structure determination, biochemical binding assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structural determination with biochemical validation\",\n      \"pmids\": [\"33892462\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Fem1b interacts directly with Gli1 (the mammalian homolog of nematode TRA-1), promotes Gli1 ubiquitylation, suppresses Gli1 transcriptional activity, and attenuates an oncogenic Gli1 autoregulatory loop in cancer cells; all effects depend on the VHL-box motif of Fem1b.\",\n      \"method\": \"Co-immunoprecipitation, GST pull-down, ubiquitylation assay, reporter assay, VHL-box mutant\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct binding confirmed by pulldown, ubiquitylation assay, and mutagenesis with functional readout\",\n      \"pmids\": [\"24076122\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"FEM1B associates with chromatin and facilitates chromatin loading of Rad9, acting as an adaptor linking CHK1 and Rad9 to support ATR-mediated checkpoint signaling during replication stress; FEM1B depletion impairs CHK1 Ser345 phosphorylation and CHK1 kinase activity without affecting CHK2.\",\n      \"method\": \"Yeast two-hybrid, siRNA knockdown, chromatin fractionation, CHK1 kinase assay, phospho-specific western blot\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with specific phosphorylation and kinase activity readouts; single lab\",\n      \"pmids\": [\"19330022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"RACK1 co-immunoprecipitates with endogenous Fem1b in metastatic colon cancer cells, stimulates Fem1b ubiquitination, and promotes Fem1b proteasomal degradation; RACK1 overexpression reduces Fem1b levels while RACK1 knockdown increases Fem1b and induces apoptosis in a Fem1b-dependent manner.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, siRNA knockdown, proteasome inhibitor treatment, morpholino antisense\",\n      \"journal\": \"Cancer biology & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal interaction confirmed, ubiquitination demonstrated, functional epistasis by Fem1b blockade; single lab\",\n      \"pmids\": [\"19855191\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Mouse Fem1b directly binds Ankrd37 (identified by yeast two-hybrid and co-immunoprecipitation) and targets it for ubiquitin-mediated proteasomal degradation in a dose-dependent manner; Ankrd37 facilitates nuclear translocation of Fem1b when co-expressed.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, ubiquitination assay, transfection dose-response, subcellular localization imaging\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — interaction confirmed by two methods, ubiquitination demonstrated, localization experiment; single lab\",\n      \"pmids\": [\"21723927\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Fem1b interacts with the homeodomain protein Nkx3.1 in GST pull-down and co-immunoprecipitation assays; Fem1b knockout mice display defects in prostate ductal morphogenesis and secretory protein expression similar to Nkx3.1 mutants, suggesting a conserved role in sexual dimorphism.\",\n      \"method\": \"Yeast two-hybrid, GST pull-down, co-immunoprecipitation, gene-targeted knockout mouse\",\n      \"journal\": \"Developmental dynamics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct interaction confirmed by multiple methods plus KO phenotype; single lab\",\n      \"pmids\": [\"18816836\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"FEM1B interacts with the membrane protein PHTF1 via its ANK domain (identified by yeast two-hybrid and confirmed by co-immunoprecipitation); PHTF1 recruits FEM1B to the endoplasmic reticulum membrane.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, domain mapping, subcellular localization by immunofluorescence\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — interaction confirmed by two methods with domain mapping and localization consequence; single lab\",\n      \"pmids\": [\"15601915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Fem1b knockout mice display abnormal glucose tolerance due predominantly to defective glucose-stimulated insulin secretion (and also arginine-stimulated insulin secretion), implicating Fem1b in pancreatic islet function; Fem1b is expressed in both beta and non-beta islet cells.\",\n      \"method\": \"Gene-targeted knockout mouse, glucose tolerance test, insulin secretion assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with specific functional readout; single lab\",\n      \"pmids\": [\"16024793\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Fem1b protein is downregulated by the proteasome in malignant colon cancer cells; proteasome inhibitor treatment upregulates Fem1b and induces apoptosis; blocking Fem1b upregulation with morpholino antisense suppresses this apoptosis, placing Fem1b as a mediator of proteasome inhibitor-induced apoptosis.\",\n      \"method\": \"Proteasome inhibitor treatment, morpholino antisense knockdown, apoptosis assay\",\n      \"journal\": \"Molecular carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional epistasis by antisense knockdown with specific apoptosis readout; single lab\",\n      \"pmids\": [\"19908242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"miR-29a-3p downregulates FEM1B expression, reducing FEM1B-mediated degradation of Gli1, thereby increasing Gli1 levels and conferring oxaliplatin resistance; knockdown of GLI1 reverted chemoresistance, placing FEM1B upstream of Gli1 in this pathway.\",\n      \"method\": \"miRNA overexpression, western blot, genetic knockdown, oxaliplatin resistance assay, mouse tumor model\",\n      \"journal\": \"American journal of cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pathway epistasis established by rescue experiments with specific resistance phenotype; single lab\",\n      \"pmids\": [\"38187042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FEM1B undergoes stop codon readthrough (SCR) to generate a C-terminally extended, highly unstable isoform; CRISPR deletion of the 81-nt 3'UTR region abolishes SCR, increases FEM1B expression, reduces SLBP levels (an FEM1B-targeted substrate), and causes cell cycle delay; this SCR mechanism is specific to Hominini.\",\n      \"method\": \"CRISPR editing, stop codon readthrough reporter assay, western blot, cell cycle analysis\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — CRISPR-based functional validation with defined substrate and cell cycle phenotype; single lab\",\n      \"pmids\": [\"39140134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Mettl3-mediated m6A modification reduces Fem1b mRNA stability, which promotes FEM1B-mediated Gli1 degradation; loss of Mettl3 in skeletal stem cells stabilizes Fem1b mRNA, leading to reduced Gli1 and impaired stem cell quiescence and differentiation.\",\n      \"method\": \"Conditional Mettl3 knockout mouse, m6A-seq, mRNA stability assay, protein level analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with m6A mapping and mechanistic pathway through FEM1B-Gli1; single lab\",\n      \"pmids\": [\"40016417\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FEM1B enhances TRAIL-induced apoptosis in T lymphocytes (Molt-4, Jurkat) and monocytes (THP-1, U937) via caspase-3 and caspase-8 but not caspase-9 (extrinsic pathway); in T cells FEM1B interacts with TRAF2 and downregulates it to relieve TRAF2's inhibitory effect on caspase-8; in monocytes FEM1B upregulates TRAIL-R2.\",\n      \"method\": \"FEM1B knockdown/knockout, co-immunoprecipitation, caspase activity assay, TRAIL-induced apoptosis assay, murine KO model\",\n      \"journal\": \"FEBS open bio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — interaction and cell-type-specific mechanisms identified with KO validation; single lab\",\n      \"pmids\": [\"40392678\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"A recurrent de novo FEM1B missense variant (Arg126Gln) causes gain-of-function activation; overexpression of FEM1BR126Q but not wild-type FEM1B in mouse brain via in utero electroporation delays neuronal migration; patient cells show oxidative stress and type I interferon signaling induction.\",\n      \"method\": \"In utero electroporation, patient cell analysis, oxidative stress assay, interferon signaling assay\",\n      \"journal\": \"Genetics in medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo functional validation with mutant vs. WT comparison; single study\",\n      \"pmids\": [\"38465576\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FEM1B is a substrate-recognition subunit of the CRL2 (Cullin 2-RING) E3 ubiquitin ligase complex that uses a bipartite mechanism (recognizing a C-terminal proline/Ψ-Pro C-degron and an upstream aromatic residue) and NEDD8-regulated dimerization to polyubiquitinate substrates including FNIP1 (reductive stress sensor), Gli1, SLBP, SMCR8, and Ankrd37 for proteasomal degradation; it additionally functions as a chromatin-associated adaptor linking Rad9 to CHK1 for ATR checkpoint signaling during replication stress, interacts with pro-apoptotic machinery (Fas, TNFR1, TRAF2) to promote extrinsic apoptosis, and its own levels are regulated by RACK1-mediated ubiquitination, miR-29 family members, m6A mRNA modification, and stop codon readthrough.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"FEM1B is a substrate-recognition subunit of the CRL2 (Cullin 2-RING) E3 ubiquitin ligase complex that targets diverse substrates for proteasomal degradation through recognition of C-terminal degrons, using a bipartite mechanism that engages both a ψ-Pro C-degron and an upstream aromatic residue, with NEDD8-dependent dimerization activating the ligase [PMID:38670995, PMID:33892462]. Validated substrates include FNIP1 (a reductive stress sensor), Gli1 (a Hedgehog pathway transcription factor), SLBP, SMCR8, and Ankrd37, placing FEM1B at the nexus of stress sensing, developmental signaling, and cell cycle control [PMID:34994556, PMID:24076122, PMID:39140134, PMID:33892462, PMID:21723927]. Beyond its E3 ligase function, FEM1B serves as a chromatin-associated adaptor that links Rad9 to CHK1 for ATR checkpoint signaling during replication stress and promotes extrinsic apoptosis through interaction with TRAF2 and modulation of caspase-8 activation [PMID:19330022, PMID:40392678]. A recurrent de novo FEM1B missense variant (Arg126Gln) causes a gain-of-function neurodevelopmental disorder characterized by impaired neuronal migration, oxidative stress, and type I interferon pathway activation [PMID:38465576].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Identification of PHTF1 as a FEM1B-interacting protein established that FEM1B's ankyrin-repeat domain mediates protein–protein interactions and can be recruited to specific subcellular compartments.\",\n      \"evidence\": \"Yeast two-hybrid and co-immunoprecipitation with domain mapping and immunofluorescence localization\",\n      \"pmids\": [\"15601915\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of PHTF1–FEM1B interaction on substrate targeting unknown\", \"No independent replication\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Fem1b knockout mice revealed an unexpected organismal role in glucose homeostasis, demonstrating that FEM1B is required for normal glucose-stimulated insulin secretion from pancreatic islets.\",\n      \"evidence\": \"Gene-targeted knockout mouse with glucose tolerance and insulin secretion assays\",\n      \"pmids\": [\"16024793\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism linking FEM1B to insulin secretion machinery unresolved\", \"Whether this reflects substrate degradation or a non-E3-ligase function is unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Interaction with Nkx3.1 and prostate ductal morphogenesis defects in Fem1b knockout mice connected FEM1B to developmental patterning and sexual dimorphism in mammals, echoing C. elegans Fem1 sex-determination biology.\",\n      \"evidence\": \"Yeast two-hybrid, GST pull-down, co-immunoprecipitation, and knockout mouse phenotyping\",\n      \"pmids\": [\"18816836\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether FEM1B ubiquitinates Nkx3.1 directly was not tested\", \"Single lab observation\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Two parallel studies established dual functions for FEM1B: as a chromatin-associated adaptor facilitating Rad9–CHK1 coupling in ATR checkpoint signaling, and as a pro-apoptotic protein whose levels are controlled by RACK1-mediated ubiquitination.\",\n      \"evidence\": \"siRNA knockdown with chromatin fractionation and CHK1 kinase assays (checkpoint); co-immunoprecipitation, ubiquitination assays, and epistasis experiments (RACK1-apoptosis)\",\n      \"pmids\": [\"19330022\", \"19855191\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether FEM1B's checkpoint role requires its E3 ligase activity is untested\", \"RACK1-mediated ubiquitination mechanism (direct E3 or scaffold) not resolved\", \"Both findings from single labs\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstration that proteasome inhibitor-induced apoptosis in colon cancer cells requires FEM1B upregulation placed FEM1B as a functional mediator of apoptosis in malignancy, linking its proteasomal turnover to chemosensitivity.\",\n      \"evidence\": \"Proteasome inhibitor treatment with morpholino antisense knockdown and apoptosis assay\",\n      \"pmids\": [\"19908242\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Apoptotic substrates of FEM1B in this context not identified\", \"Single lab, single cell type\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identification of Ankrd37 as a FEM1B substrate targeted for ubiquitin-mediated degradation expanded the known substrate repertoire, and reciprocally revealed that Ankrd37 promotes FEM1B nuclear translocation.\",\n      \"evidence\": \"Yeast two-hybrid, co-immunoprecipitation, ubiquitination assay, subcellular localization imaging\",\n      \"pmids\": [\"21723927\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological consequence of Ankrd37 degradation unknown\", \"Single lab, overexpression system\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Direct binding and ubiquitylation of Gli1 by FEM1B established a conserved link to C. elegans TRA-1 regulation and demonstrated that FEM1B suppresses Hedgehog pathway output in a VHL-box-dependent manner.\",\n      \"evidence\": \"Co-immunoprecipitation, GST pull-down, ubiquitylation assay, reporter assay, VHL-box mutagenesis\",\n      \"pmids\": [\"24076122\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether endogenous Gli1 turnover depends on FEM1B in vivo not shown in this study\", \"Degron on Gli1 recognized by FEM1B not mapped\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Crystal structure of FEM1B bound to the SMCR8 C-degron provided the first atomic-resolution view of how FEM1B recognizes C-terminal degradation signals, establishing FEM1B as a bona fide C-degron reader.\",\n      \"evidence\": \"X-ray crystal structure determination with biochemical binding assay\",\n      \"pmids\": [\"33892462\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Only one substrate C-degron characterized structurally at this point\", \"Full-length substrate recognition mechanism not addressed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Covalent targeting of FEM1B C186 with EN106 disrupted FNIP1 recognition, establishing FEM1B as the E3 ligase responsible for the reductive stress response and demonstrating FEM1B's utility as a PROTAC recruitment handle.\",\n      \"evidence\": \"Covalent ligand screening, competitive binding assay, PROTAC-mediated degradation of BRD4 and BCR-ABL in cells\",\n      \"pmids\": [\"34994556\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of EN106-mediated disruption not determined\", \"Long-term selectivity of EN106 in vivo untested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"miR-29a-3p was shown to downregulate FEM1B, relieving Gli1 degradation and conferring oxaliplatin resistance, revealing a microRNA-based regulatory layer controlling the FEM1B–Gli1 axis in chemoresistance.\",\n      \"evidence\": \"miRNA overexpression, genetic knockdown, oxaliplatin resistance assay, mouse tumor model\",\n      \"pmids\": [\"38187042\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct miR-29a-3p binding site on FEM1B 3'UTR not validated by luciferase reporter in this study\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Cryo-EM structures of CRL2-FEM1B with different substrates revealed a bipartite degron recognition mechanism (C-terminal ψ-Pro plus upstream aromatic residue) and showed that NEDD8-dependent dimerization is required for full E3 ligase activity, providing the comprehensive structural framework for substrate polyubiquitination.\",\n      \"evidence\": \"Cryo-EM structure determination, in vitro ubiquitination assay, cell-based degradation assay, mutagenesis\",\n      \"pmids\": [\"38670995\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How dimerization is regulated in vivo under different signaling conditions is unknown\", \"Not all known substrates have been mapped to the bipartite degron model\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Discovery of Hominini-specific stop codon readthrough (SCR) generating an unstable FEM1B isoform revealed an additional post-translational regulatory mechanism; CRISPR deletion of the SCR element increased FEM1B levels, reduced SLBP, and delayed the cell cycle.\",\n      \"evidence\": \"CRISPR editing, SCR reporter assay, western blot, cell cycle analysis\",\n      \"pmids\": [\"39140134\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological triggers of SCR frequency changes unknown\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"A recurrent de novo FEM1B R126Q variant was identified as a gain-of-function cause of a neurodevelopmental disorder, linking FEM1B hyperactivation to impaired neuronal migration, oxidative stress, and interferon pathway induction.\",\n      \"evidence\": \"In utero electroporation in mouse brain, patient cell analysis, oxidative stress and interferon signaling assays\",\n      \"pmids\": [\"38465576\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific substrate(s) hyperactivated by R126Q not identified\", \"Number of families limited; awaits larger cohort replication\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Mettl3-mediated m6A modification was shown to control Fem1b mRNA stability, connecting epitranscriptomic regulation to the FEM1B–Gli1 degradation axis in skeletal stem cell quiescence and differentiation.\",\n      \"evidence\": \"Conditional Mettl3 knockout mouse, m6A-seq, mRNA stability assay\",\n      \"pmids\": [\"40016417\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific m6A reader mediating Fem1b mRNA decay not identified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"FEM1B was shown to enhance TRAIL-induced extrinsic apoptosis in a cell-type-specific manner: in T cells via TRAF2 interaction and downregulation relieving caspase-8 inhibition, and in monocytes via TRAIL-R2 upregulation.\",\n      \"evidence\": \"FEM1B knockdown/knockout, co-immunoprecipitation, caspase activity assays, TRAIL-induced apoptosis assay\",\n      \"pmids\": [\"40392678\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether FEM1B ubiquitinates TRAF2 directly not demonstrated\", \"Mechanism of TRAIL-R2 upregulation in monocytes unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the structural and mechanistic basis for FEM1B's non-E3-ligase functions (checkpoint signaling, apoptosis), the identity of hyperactivated substrates in the R126Q neurodevelopmental disorder, and whether all known substrates conform to the bipartite C-degron recognition model.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structure of FEM1B in complex with Rad9 or CHK1\", \"Complete substrate landscape not mapped by unbiased proteomics\", \"In vivo significance of SCR regulation under physiological stress unclear\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 3, 6]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [4, 6]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 2, 3, 6]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [5, 10, 14]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 11, 13]}\n    ],\n    \"complexes\": [\n      \"CRL2-FEM1B (Cullin 2-RING E3 ubiquitin ligase)\"\n    ],\n    \"partners\": [\n      \"CUL2\",\n      \"FNIP1\",\n      \"GLI1\",\n      \"SMCR8\",\n      \"RAD9A\",\n      \"TRAF2\",\n      \"RACK1\",\n      \"NKX3-1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}