{"gene":"KLHL15","run_date":"2026-04-28T18:30:27","timeline":{"discoveries":[{"year":2012,"finding":"KLHL15 acts as a substrate adaptor for Cullin3 (Cul3)-based E3 ubiquitin ligase complexes, specifically targeting the PP2A regulatory subunit B'β for ubiquitylation and proteasomal degradation. The divergent N terminus of B'β (including Tyr-52) is necessary and sufficient for KLHL15-mediated degradation. KLHL15 residues critical for homodimerization and interaction with Cul3 and B'β were mapped. Although KLHL15 can interact with the PP2A/B'β heterotrimer, it degrades only free B'β, promoting regulatory subunit exchange.","method":"Co-immunoprecipitation, proteomic screens, ubiquitylation assays, proteasomal degradation assays, domain mapping/mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal biochemical methods (Co-IP, ubiquitylation assay, mutagenesis, domain mapping) in a single study with rigorous controls","pmids":["23135275"],"is_preprint":false},{"year":2016,"finding":"KLHL15 functions as a Cullin3 E3 ligase substrate adaptor that promotes CtIP protein turnover via the ubiquitin-proteasome pathway, thereby fine-tuning DNA-end resection and the balance between homologous recombination (HR) and non-homologous end-joining (NHEJ). A conserved FRY tripeptide motif in CtIP is essential for KLHL15 binding; FRY mutation blocks KLHL15-dependent CtIP ubiquitination and degradation. Overexpression of KLHL15 strongly attenuates DNA-end resection, while KLHL15 loss or FRY-mutant CtIP amplifies resection.","method":"Co-immunoprecipitation, ubiquitination assays, site-directed mutagenesis (FRY motif), KLHL15 overexpression and knockout cell lines, DNA-end resection assays, HR/NHEJ reporter assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 — reconstitution of E3 ligase activity, mutagenesis of critical motif, functional epistasis with resection phenotype, multiple orthogonal methods","pmids":["27561354"],"is_preprint":false},{"year":2020,"finding":"KLHL15 targets doublecortin (DCX) and doublecortin-like kinases 1 and 2 (DCLK1, DCLK2) for ubiquitination and proteasomal degradation via a Cullin3-based E3 ligase complex. Interaction is mediated through the tandem DCX domains; a FRY tripeptide at the C-terminal edge of the second DCX domain is necessary for KLHL15-mediated ubiquitination and degradation. Silencing endogenous KLHL15 stabilizes DCX domain-containing proteins and prolongs their half-life. Functionally, KLHL15 overexpression reduces dendritic complexity of hippocampal neurons in a DCX FRY-dependent manner.","method":"Bioinformatics substrate identification, co-immunoprecipitation, ubiquitination assays, domain mapping, site-directed mutagenesis (FRY motif), siRNA knockdown, cycloheximide chase assay, primary neuron morphology analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including mutagenesis, degradation assays, and functional neuronal readout in a single study","pmids":["33199366"],"is_preprint":false},{"year":2022,"finding":"The micropeptide PACMP (encoded by lncRNA CTD-2256P15.2) inhibits CtIP-KLHL15 association, thereby preventing KLHL15-mediated ubiquitination and degradation of CtIP. This represents a regulatory mechanism where PACMP acts as a decoy to block KLHL15 substrate access and maintain CtIP abundance during DNA damage response.","method":"Co-immunoprecipitation, ubiquitination assays, PACMP overexpression/knockdown, CtIP stability assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP and functional ubiquitination assays showing PACMP blocks CtIP-KLHL15 interaction, published in high-impact journal","pmids":["35219381"],"is_preprint":false},{"year":2023,"finding":"Multiplex CRISPR screening identified substrates and cognate degron motifs for Cul3KLHL15, demonstrating that KLHL15 substrate specificity is encoded in defined degron sequences recognizable at scale. The platform confirmed KLHL15 as a Cul3 substrate adaptor with definable substrate degrons.","method":"Multiplex CRISPR screening, site-saturation mutagenesis for degron mapping","journal":"Nature cell biology","confidence":"Medium","confidence_rationale":"Tier 2 — genome-scale functional screen with degron mapping, but KLHL15-specific substrate details are one part of a larger platform study","pmids":["37735597"],"is_preprint":false},{"year":2021,"finding":"KLHL15 loss protects cells from DNA damage induced by ATM inhibition, placing KLHL15 in a genetic interaction network with ATM-dependent DNA damage response, consistent with its role in controlling CtIP levels and DNA-end resection.","method":"CRISPR loss-of-function screen with ATM inhibitor, cell viability assays","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 — unbiased CRISPR screen identifies genetic interaction, but mechanism inferred from prior literature rather than directly characterized in this study","pmids":["34320214"],"is_preprint":false},{"year":2024,"finding":"VGLL3 prevents CtIP from KLHL15-mediated ubiquitination and degradation through competitive binding with KLHL15, thereby stabilizing CtIP and promoting homologous recombination efficiency during DNA damage response.","method":"Co-immunoprecipitation (competitive binding assay), CtIP ubiquitination assays, VGLL3 depletion with HR efficiency measurement","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 — competitive Co-IP and functional ubiquitination assays in a single study with functional HR readout","pmids":["39383226"],"is_preprint":false},{"year":2005,"finding":"KLHL15 was identified as a novel human Kelch-like protein containing an N-terminal BTB/POZ domain and C-terminal Kelch motifs, encoded by a 4-exon gene on chromosome X, with ubiquitous mRNA expression across tissues. The protein shows 85-93% amino acid identity across human, chicken, and zebrafish.","method":"Bioinformatics/in silico analysis, cDNA assembly, domain prediction (Pfam), tissue expression survey","journal":"Oncology reports","confidence":"Low","confidence_rationale":"Tier 4 — computational/bioinformatic identification only, no functional validation","pmids":["15870933"],"is_preprint":false},{"year":2023,"finding":"Structural modeling of the KLHL15 p.(Arg532del) variant predicts altered topology at the substrate-binding surface of the Kelch repeat domain, including perturbation at Tyr552, a residue known to be important for substrate binding, providing a structural rationale for loss of KLHL15 E3 adaptor function.","method":"Comparative structural modelling of variant protein","journal":"European journal of medical genetics","confidence":"Low","confidence_rationale":"Tier 4 — computational modelling only, no experimental biochemical validation of predicted structural effects","pmids":["37059329"],"is_preprint":false}],"current_model":"KLHL15 is a substrate adaptor for Cullin3-based E3 ubiquitin ligase complexes that recruits specific substrates—including CtIP, PP2A B'β subunit, doublecortin (DCX), and doublecortin-like kinases 1/2—via their FRY degron motifs (or analogous N-terminal sequences for B'β) for ubiquitination and proteasomal degradation, thereby regulating DNA-end resection and homologous recombination balance, PP2A holoenzyme composition, and neuronal dendritogenesis; this activity can be antagonized by competing interactors such as PACMP micropeptide and VGLL3 that block substrate access to KLHL15."},"narrative":{"teleology":[{"year":2005,"claim":"Initial identification of KLHL15 as a BTB/Kelch-domain protein established the structural framework predicting it as a candidate Cul3 adaptor, but left its function entirely open.","evidence":"Bioinformatic cDNA assembly, domain prediction, and tissue expression survey","pmids":["15870933"],"confidence":"Low","gaps":["No biochemical or functional validation performed","No substrates or interactors identified","Cul3 binding not tested"]},{"year":2012,"claim":"Demonstration that KLHL15 serves as a Cul3 E3 ligase adaptor targeting the PP2A B'β subunit for ubiquitination and degradation established its molecular function, revealing that KLHL15 selectively degrades free B'β but not the assembled PP2A heterotrimer, thereby regulating PP2A regulatory subunit exchange.","evidence":"Co-immunoprecipitation, in vivo and in vitro ubiquitylation assays, domain mapping and mutagenesis of KLHL15 and B'β","pmids":["23135275"],"confidence":"High","gaps":["Physiological consequence of altered PP2A composition not characterized","Structural basis of B'β N-terminal recognition by KLHL15 Kelch domain unresolved","No in vivo animal model phenotype"]},{"year":2016,"claim":"Identification of CtIP as a KLHL15 substrate through a conserved FRY degron motif revealed that KLHL15 controls DNA-end resection and HR/NHEJ pathway choice, expanding its functional scope from phosphatase regulation to DNA repair.","evidence":"Co-IP, ubiquitination assays, FRY motif mutagenesis, KLHL15 overexpression/knockout, DNA-end resection and HR/NHEJ reporter assays","pmids":["27561354"],"confidence":"High","gaps":["Cell-cycle regulation of KLHL15 activity not determined","How KLHL15 activity is coordinated with other CtIP E3 ligases unclear","No structural data for FRY motif recognition"]},{"year":2020,"claim":"Extension of the FRY degron paradigm to doublecortin-family proteins (DCX, DCLK1, DCLK2) demonstrated that KLHL15 controls neuronal dendritogenesis by degrading microtubule-associated proteins, establishing it as a multi-substrate adaptor with roles beyond DNA repair.","evidence":"Bioinformatic substrate prediction, Co-IP, ubiquitination assays, FRY mutagenesis, siRNA knockdown, cycloheximide chase, primary hippocampal neuron morphology analysis","pmids":["33199366"],"confidence":"High","gaps":["In vivo neuronal phenotype of KLHL15 loss not characterized in animal models","Relative contribution of DCX vs DCLK substrates to dendritic phenotype unknown","Whether KLHL15 regulates neuronal migration through DCX degradation untested"]},{"year":2021,"claim":"A genome-wide CRISPR screen placed KLHL15 in a genetic interaction network with ATM, showing that KLHL15 loss protects cells from ATM inhibitor-induced DNA damage, consistent with its role in CtIP-dependent resection control.","evidence":"CRISPR loss-of-function screen with ATM inhibitor, cell viability assays","pmids":["34320214"],"confidence":"Medium","gaps":["Mechanism inferred from prior CtIP literature rather than directly dissected","Whether protection acts solely through CtIP stabilization not formally tested","Therapeutic relevance of KLHL15 loss in ATMi-treated tumors unexplored"]},{"year":2022,"claim":"Discovery that the micropeptide PACMP competitively blocks the CtIP–KLHL15 interaction revealed a novel regulatory layer in which a non-coding RNA-encoded peptide antagonizes Cul3-KLHL15 substrate access to maintain CtIP abundance during DNA damage.","evidence":"Co-IP, ubiquitination assays, PACMP overexpression/knockdown, CtIP stability assays","pmids":["35219381"],"confidence":"High","gaps":["Structural basis of PACMP–KLHL15 competition unknown","Whether PACMP also blocks other KLHL15 substrates untested","Regulation of PACMP expression during DNA damage incompletely characterized"]},{"year":2023,"claim":"Multiplex CRISPR screening systematically confirmed KLHL15 degron specificity at scale, validating that defined short sequences encode Cul3-KLHL15 substrate recognition.","evidence":"Multiplex CRISPR screening with site-saturation mutagenesis for degron mapping","pmids":["37735597"],"confidence":"Medium","gaps":["Full substrate repertoire beyond known targets not individually validated","Degron affinity hierarchy among substrates not quantified","Screening performed as part of broader platform—KLHL15-specific depth limited"]},{"year":2024,"claim":"Identification of VGLL3 as a second competitive inhibitor of KLHL15-mediated CtIP degradation established that multiple proteins converge to protect CtIP from Cul3-KLHL15 and promote HR, revealing a regulatory hub at the KLHL15–CtIP interface.","evidence":"Competitive Co-IP, CtIP ubiquitination assays, VGLL3 depletion with HR efficiency measurement","pmids":["39383226"],"confidence":"Medium","gaps":["Whether VGLL3 and PACMP act redundantly or in distinct contexts not resolved","Structural mechanism of competitive binding unclear","VGLL3 effects on other KLHL15 substrates not examined"]},{"year":null,"claim":"No high-resolution structure of KLHL15 in complex with any substrate or competitor exists, and the in vivo physiological consequences of KLHL15 loss in animal models remain uncharacterized.","evidence":"","pmids":[],"confidence":"High","gaps":["No crystal or cryo-EM structure of KLHL15 Kelch domain bound to FRY degron or B'β N-terminus","No KLHL15 knockout mouse or zebrafish phenotype reported","Cell-cycle or DNA-damage-dependent regulation of KLHL15 protein levels or activity unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,3,4,6]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,2]}],"localization":[],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[1,3,5,6]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,2,4]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[2]}],"complexes":["CUL3-KLHL15 E3 ubiquitin ligase"],"partners":["CUL3","RBBP4","CTIP","PPP2R5B","DCX","DCLK1","DCLK2","VGLL3"],"other_free_text":[]},"mechanistic_narrative":"KLHL15 is a substrate adaptor for Cullin3 (Cul3)-based E3 ubiquitin ligase complexes that targets multiple substrates for ubiquitination and proteasomal degradation, thereby controlling DNA damage repair pathway choice, PP2A holoenzyme composition, and neuronal morphogenesis. KLHL15 recognizes substrates through defined degron motifs—a conserved FRY tripeptide in CtIP and doublecortin-family proteins (DCX, DCLK1, DCLK2), and a divergent N-terminal sequence in the PP2A regulatory subunit B'β—and promotes their polyubiquitination via the Cul3 scaffold [PMID:23135275, PMID:27561354, PMID:33199366]. KLHL15-mediated degradation of CtIP fine-tunes DNA-end resection and the balance between homologous recombination and non-homologous end-joining, while degradation of DCX-domain proteins restricts dendritic arborization in hippocampal neurons [PMID:27561354, PMID:33199366]. Competing interactors including the micropeptide PACMP and VGLL3 antagonize KLHL15 by blocking substrate access, thereby stabilizing CtIP and promoting homologous recombination during the DNA damage response [PMID:35219381, PMID:39383226]."},"prefetch_data":{"uniprot":{"accession":"Q96M94","full_name":"Kelch-like protein 15","aliases":[],"length_aa":604,"mass_kda":69.8,"function":"Substrate-specific adapter for CUL3 E3 ubiquitin-protein ligase complex (PubMed:14528312, PubMed:27561354, PubMed:35219381). Acts as an adapter for CUL3 to target the serine/threonine-protein phosphatase 2A (PP2A) subunit PPP2R5B for ubiquitination and subsequent proteasomal degradation, thus promoting exchange with other regulatory subunits (PubMed:23135275). Acts as an adapter for CUL3 to target the DNA-end resection factor RBBP8/CtIP for ubiquitination and subsequent proteasomal degradation (PubMed:27561354, PubMed:35219381). Through the regulation of RBBP8/CtIP protein turnover, plays a key role in DNA damage response, favoring DNA double-strand repair through error-prone non-homologous end joining (NHEJ) over error-free, RBBP8-mediated homologous recombination (HR) (PubMed:27561354, PubMed:35219381)","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q96M94/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KLHL15","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/KLHL15","total_profiled":1310},"omim":[{"mim_id":"601644","title":"PROTEIN PHOSPHATASE 2, REGULATORY SUBUNIT B (B56), BETA; PPP2R5B","url":"https://www.omim.org/entry/601644"},{"mim_id":"300982","title":"INTELLECTUAL DEVELOPMENTAL DISORDER, X-LINKED 103; XLID103","url":"https://www.omim.org/entry/300982"},{"mim_id":"300980","title":"KELCH-LIKE 15; KLHL15","url":"https://www.omim.org/entry/300980"},{"mim_id":"300334","title":"TRANSIENT RECEPTOR POTENTIAL CATION CHANNEL, SUBFAMILY C, MEMBER 5; TRPC5","url":"https://www.omim.org/entry/300334"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"},{"location":"Aggresome","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"bone marrow","ntpm":53.6}],"url":"https://www.proteinatlas.org/search/KLHL15"},"hgnc":{"alias_symbol":["KIAA1677"],"prev_symbol":[]},"alphafold":{"accession":"Q96M94","domains":[{"cath_id":"3.30.710.10","chopping":"15-127","consensus_level":"high","plddt":93.2273,"start":15,"end":127},{"cath_id":"1.25.40.420","chopping":"159-266","consensus_level":"high","plddt":96.0028,"start":159,"end":266},{"cath_id":"2.120.10.80","chopping":"280-449_465-601","consensus_level":"medium","plddt":91.8426,"start":280,"end":601}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96M94","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96M94-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96M94-F1-predicted_aligned_error_v6.png","plddt_mean":91.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KLHL15","jax_strain_url":"https://www.jax.org/strain/search?query=KLHL15"},"sequence":{"accession":"Q96M94","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96M94.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96M94/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96M94"}},"corpus_meta":[{"pmid":"25644381","id":"PMC_25644381","title":"X-exome sequencing of 405 unresolved families identifies seven novel intellectual disability genes.","date":"2015","source":"Molecular psychiatry","url":"https://pubmed.ncbi.nlm.nih.gov/25644381","citation_count":246,"is_preprint":false},{"pmid":"35219381","id":"PMC_35219381","title":"Micropeptide PACMP inhibition elicits synthetic lethal effects by decreasing CtIP and poly(ADP-ribosyl)ation.","date":"2022","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/35219381","citation_count":76,"is_preprint":false},{"pmid":"27561354","id":"PMC_27561354","title":"Cullin3-KLHL15 ubiquitin ligase mediates CtIP protein turnover to fine-tune DNA-end resection.","date":"2016","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/27561354","citation_count":55,"is_preprint":false},{"pmid":"37735597","id":"PMC_37735597","title":"Defining E3 ligase-substrate relationships through multiplex CRISPR screening.","date":"2023","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/37735597","citation_count":49,"is_preprint":false},{"pmid":"23135275","id":"PMC_23135275","title":"Selective proteasomal degradation of the B'β subunit of protein phosphatase 2A by the E3 ubiquitin ligase adaptor Kelch-like 15.","date":"2012","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23135275","citation_count":36,"is_preprint":false},{"pmid":"24817631","id":"PMC_24817631","title":"Intragenic rearrangements in X-linked intellectual deficiency: results of a-CGH in a series of 54 patients and identification of TRPC5 and KLHL15 as potential XLID genes.","date":"2014","source":"American journal of medical genetics. 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The divergent N terminus of B'β (including Tyr-52) is necessary and sufficient for KLHL15-mediated degradation. KLHL15 residues critical for homodimerization and interaction with Cul3 and B'β were mapped. Although KLHL15 can interact with the PP2A/B'β heterotrimer, it degrades only free B'β, promoting regulatory subunit exchange.\",\n      \"method\": \"Co-immunoprecipitation, proteomic screens, ubiquitylation assays, proteasomal degradation assays, domain mapping/mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal biochemical methods (Co-IP, ubiquitylation assay, mutagenesis, domain mapping) in a single study with rigorous controls\",\n      \"pmids\": [\"23135275\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"KLHL15 functions as a Cullin3 E3 ligase substrate adaptor that promotes CtIP protein turnover via the ubiquitin-proteasome pathway, thereby fine-tuning DNA-end resection and the balance between homologous recombination (HR) and non-homologous end-joining (NHEJ). A conserved FRY tripeptide motif in CtIP is essential for KLHL15 binding; FRY mutation blocks KLHL15-dependent CtIP ubiquitination and degradation. Overexpression of KLHL15 strongly attenuates DNA-end resection, while KLHL15 loss or FRY-mutant CtIP amplifies resection.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, site-directed mutagenesis (FRY motif), KLHL15 overexpression and knockout cell lines, DNA-end resection assays, HR/NHEJ reporter assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution of E3 ligase activity, mutagenesis of critical motif, functional epistasis with resection phenotype, multiple orthogonal methods\",\n      \"pmids\": [\"27561354\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"KLHL15 targets doublecortin (DCX) and doublecortin-like kinases 1 and 2 (DCLK1, DCLK2) for ubiquitination and proteasomal degradation via a Cullin3-based E3 ligase complex. Interaction is mediated through the tandem DCX domains; a FRY tripeptide at the C-terminal edge of the second DCX domain is necessary for KLHL15-mediated ubiquitination and degradation. Silencing endogenous KLHL15 stabilizes DCX domain-containing proteins and prolongs their half-life. Functionally, KLHL15 overexpression reduces dendritic complexity of hippocampal neurons in a DCX FRY-dependent manner.\",\n      \"method\": \"Bioinformatics substrate identification, co-immunoprecipitation, ubiquitination assays, domain mapping, site-directed mutagenesis (FRY motif), siRNA knockdown, cycloheximide chase assay, primary neuron morphology analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including mutagenesis, degradation assays, and functional neuronal readout in a single study\",\n      \"pmids\": [\"33199366\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The micropeptide PACMP (encoded by lncRNA CTD-2256P15.2) inhibits CtIP-KLHL15 association, thereby preventing KLHL15-mediated ubiquitination and degradation of CtIP. This represents a regulatory mechanism where PACMP acts as a decoy to block KLHL15 substrate access and maintain CtIP abundance during DNA damage response.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, PACMP overexpression/knockdown, CtIP stability assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP and functional ubiquitination assays showing PACMP blocks CtIP-KLHL15 interaction, published in high-impact journal\",\n      \"pmids\": [\"35219381\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Multiplex CRISPR screening identified substrates and cognate degron motifs for Cul3KLHL15, demonstrating that KLHL15 substrate specificity is encoded in defined degron sequences recognizable at scale. The platform confirmed KLHL15 as a Cul3 substrate adaptor with definable substrate degrons.\",\n      \"method\": \"Multiplex CRISPR screening, site-saturation mutagenesis for degron mapping\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genome-scale functional screen with degron mapping, but KLHL15-specific substrate details are one part of a larger platform study\",\n      \"pmids\": [\"37735597\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"KLHL15 loss protects cells from DNA damage induced by ATM inhibition, placing KLHL15 in a genetic interaction network with ATM-dependent DNA damage response, consistent with its role in controlling CtIP levels and DNA-end resection.\",\n      \"method\": \"CRISPR loss-of-function screen with ATM inhibitor, cell viability assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — unbiased CRISPR screen identifies genetic interaction, but mechanism inferred from prior literature rather than directly characterized in this study\",\n      \"pmids\": [\"34320214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"VGLL3 prevents CtIP from KLHL15-mediated ubiquitination and degradation through competitive binding with KLHL15, thereby stabilizing CtIP and promoting homologous recombination efficiency during DNA damage response.\",\n      \"method\": \"Co-immunoprecipitation (competitive binding assay), CtIP ubiquitination assays, VGLL3 depletion with HR efficiency measurement\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — competitive Co-IP and functional ubiquitination assays in a single study with functional HR readout\",\n      \"pmids\": [\"39383226\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"KLHL15 was identified as a novel human Kelch-like protein containing an N-terminal BTB/POZ domain and C-terminal Kelch motifs, encoded by a 4-exon gene on chromosome X, with ubiquitous mRNA expression across tissues. The protein shows 85-93% amino acid identity across human, chicken, and zebrafish.\",\n      \"method\": \"Bioinformatics/in silico analysis, cDNA assembly, domain prediction (Pfam), tissue expression survey\",\n      \"journal\": \"Oncology reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational/bioinformatic identification only, no functional validation\",\n      \"pmids\": [\"15870933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Structural modeling of the KLHL15 p.(Arg532del) variant predicts altered topology at the substrate-binding surface of the Kelch repeat domain, including perturbation at Tyr552, a residue known to be important for substrate binding, providing a structural rationale for loss of KLHL15 E3 adaptor function.\",\n      \"method\": \"Comparative structural modelling of variant protein\",\n      \"journal\": \"European journal of medical genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational modelling only, no experimental biochemical validation of predicted structural effects\",\n      \"pmids\": [\"37059329\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"KLHL15 is a substrate adaptor for Cullin3-based E3 ubiquitin ligase complexes that recruits specific substrates—including CtIP, PP2A B'β subunit, doublecortin (DCX), and doublecortin-like kinases 1/2—via their FRY degron motifs (or analogous N-terminal sequences for B'β) for ubiquitination and proteasomal degradation, thereby regulating DNA-end resection and homologous recombination balance, PP2A holoenzyme composition, and neuronal dendritogenesis; this activity can be antagonized by competing interactors such as PACMP micropeptide and VGLL3 that block substrate access to KLHL15.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"KLHL15 is a substrate adaptor for Cullin3 (Cul3)-based E3 ubiquitin ligase complexes that targets multiple substrates for ubiquitination and proteasomal degradation, thereby controlling DNA damage repair pathway choice, PP2A holoenzyme composition, and neuronal morphogenesis. KLHL15 recognizes substrates through defined degron motifs—a conserved FRY tripeptide in CtIP and doublecortin-family proteins (DCX, DCLK1, DCLK2), and a divergent N-terminal sequence in the PP2A regulatory subunit B'β—and promotes their polyubiquitination via the Cul3 scaffold [PMID:23135275, PMID:27561354, PMID:33199366]. KLHL15-mediated degradation of CtIP fine-tunes DNA-end resection and the balance between homologous recombination and non-homologous end-joining, while degradation of DCX-domain proteins restricts dendritic arborization in hippocampal neurons [PMID:27561354, PMID:33199366]. Competing interactors including the micropeptide PACMP and VGLL3 antagonize KLHL15 by blocking substrate access, thereby stabilizing CtIP and promoting homologous recombination during the DNA damage response [PMID:35219381, PMID:39383226].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Initial identification of KLHL15 as a BTB/Kelch-domain protein established the structural framework predicting it as a candidate Cul3 adaptor, but left its function entirely open.\",\n      \"evidence\": \"Bioinformatic cDNA assembly, domain prediction, and tissue expression survey\",\n      \"pmids\": [\"15870933\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No biochemical or functional validation performed\", \"No substrates or interactors identified\", \"Cul3 binding not tested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Demonstration that KLHL15 serves as a Cul3 E3 ligase adaptor targeting the PP2A B'β subunit for ubiquitination and degradation established its molecular function, revealing that KLHL15 selectively degrades free B'β but not the assembled PP2A heterotrimer, thereby regulating PP2A regulatory subunit exchange.\",\n      \"evidence\": \"Co-immunoprecipitation, in vivo and in vitro ubiquitylation assays, domain mapping and mutagenesis of KLHL15 and B'β\",\n      \"pmids\": [\"23135275\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological consequence of altered PP2A composition not characterized\", \"Structural basis of B'β N-terminal recognition by KLHL15 Kelch domain unresolved\", \"No in vivo animal model phenotype\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identification of CtIP as a KLHL15 substrate through a conserved FRY degron motif revealed that KLHL15 controls DNA-end resection and HR/NHEJ pathway choice, expanding its functional scope from phosphatase regulation to DNA repair.\",\n      \"evidence\": \"Co-IP, ubiquitination assays, FRY motif mutagenesis, KLHL15 overexpression/knockout, DNA-end resection and HR/NHEJ reporter assays\",\n      \"pmids\": [\"27561354\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell-cycle regulation of KLHL15 activity not determined\", \"How KLHL15 activity is coordinated with other CtIP E3 ligases unclear\", \"No structural data for FRY motif recognition\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extension of the FRY degron paradigm to doublecortin-family proteins (DCX, DCLK1, DCLK2) demonstrated that KLHL15 controls neuronal dendritogenesis by degrading microtubule-associated proteins, establishing it as a multi-substrate adaptor with roles beyond DNA repair.\",\n      \"evidence\": \"Bioinformatic substrate prediction, Co-IP, ubiquitination assays, FRY mutagenesis, siRNA knockdown, cycloheximide chase, primary hippocampal neuron morphology analysis\",\n      \"pmids\": [\"33199366\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo neuronal phenotype of KLHL15 loss not characterized in animal models\", \"Relative contribution of DCX vs DCLK substrates to dendritic phenotype unknown\", \"Whether KLHL15 regulates neuronal migration through DCX degradation untested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"A genome-wide CRISPR screen placed KLHL15 in a genetic interaction network with ATM, showing that KLHL15 loss protects cells from ATM inhibitor-induced DNA damage, consistent with its role in CtIP-dependent resection control.\",\n      \"evidence\": \"CRISPR loss-of-function screen with ATM inhibitor, cell viability assays\",\n      \"pmids\": [\"34320214\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism inferred from prior CtIP literature rather than directly dissected\", \"Whether protection acts solely through CtIP stabilization not formally tested\", \"Therapeutic relevance of KLHL15 loss in ATMi-treated tumors unexplored\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Discovery that the micropeptide PACMP competitively blocks the CtIP–KLHL15 interaction revealed a novel regulatory layer in which a non-coding RNA-encoded peptide antagonizes Cul3-KLHL15 substrate access to maintain CtIP abundance during DNA damage.\",\n      \"evidence\": \"Co-IP, ubiquitination assays, PACMP overexpression/knockdown, CtIP stability assays\",\n      \"pmids\": [\"35219381\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of PACMP–KLHL15 competition unknown\", \"Whether PACMP also blocks other KLHL15 substrates untested\", \"Regulation of PACMP expression during DNA damage incompletely characterized\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Multiplex CRISPR screening systematically confirmed KLHL15 degron specificity at scale, validating that defined short sequences encode Cul3-KLHL15 substrate recognition.\",\n      \"evidence\": \"Multiplex CRISPR screening with site-saturation mutagenesis for degron mapping\",\n      \"pmids\": [\"37735597\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Full substrate repertoire beyond known targets not individually validated\", \"Degron affinity hierarchy among substrates not quantified\", \"Screening performed as part of broader platform—KLHL15-specific depth limited\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identification of VGLL3 as a second competitive inhibitor of KLHL15-mediated CtIP degradation established that multiple proteins converge to protect CtIP from Cul3-KLHL15 and promote HR, revealing a regulatory hub at the KLHL15–CtIP interface.\",\n      \"evidence\": \"Competitive Co-IP, CtIP ubiquitination assays, VGLL3 depletion with HR efficiency measurement\",\n      \"pmids\": [\"39383226\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether VGLL3 and PACMP act redundantly or in distinct contexts not resolved\", \"Structural mechanism of competitive binding unclear\", \"VGLL3 effects on other KLHL15 substrates not examined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"No high-resolution structure of KLHL15 in complex with any substrate or competitor exists, and the in vivo physiological consequences of KLHL15 loss in animal models remain uncharacterized.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal or cryo-EM structure of KLHL15 Kelch domain bound to FRY degron or B'β N-terminus\", \"No KLHL15 knockout mouse or zebrafish phenotype reported\", \"Cell-cycle or DNA-damage-dependent regulation of KLHL15 protein levels or activity unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 6]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 2]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [1, 3, 5, 6]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 2, 4]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"complexes\": [\n      \"CUL3-KLHL15 E3 ubiquitin ligase\"\n    ],\n    \"partners\": [\n      \"CUL3\",\n      \"RBBP4\",\n      \"CTIP\",\n      \"PPP2R5B\",\n      \"DCX\",\n      \"DCLK1\",\n      \"DCLK2\",\n      \"VGLL3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}