{"gene":"KLHL15","run_date":"2026-06-10T02:59:49","timeline":{"discoveries":[{"year":2012,"finding":"KLHL15 acts as a substrate adaptor for Cullin3 (Cul3)-based E3 ubiquitin ligase complexes to specifically target the PP2A regulatory subunit B'β for ubiquitylation and proteasomal degradation. KLHL15 residues critical for homodimerization, Cul3 interaction, and B'β interaction were mapped; the divergent N terminus of B'β (including Tyr-52) was necessary and sufficient for KLHL15-mediated degradation. Although KLHL15 can interact with the PP2A/B'β heterotrimer, it only degrades B'β, promoting exchange with other regulatory subunits.","method":"Unbiased proteomic screens (Co-IP/MS), co-immunoprecipitation, ubiquitylation assays, proteasomal degradation assays, mutagenesis of KLHL15 and B'β","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal methods (proteomic screen, reciprocal Co-IP, in vitro ubiquitylation assay, mutagenesis of both substrate and adaptor) in a single rigorous study","pmids":["23135275"],"is_preprint":false},{"year":2016,"finding":"KLHL15 is a Cullin3 E3 ligase substrate adaptor that binds CtIP via a conserved tripeptide motif (FRY) in CtIP and promotes CtIP ubiquitination and proteasomal turnover. Mutation of the FRY motif blocks KLHL15-dependent CtIP ubiquitination and degradation. Overexpression of KLHL15 strongly attenuates DNA-end resection, while cells expressing FRY-mutant CtIP or lacking KLHL15 show amplified resection, shifting the balance between homologous recombination (HR) and non-homologous end-joining (NHEJ).","method":"Co-immunoprecipitation, ubiquitination assays, site-directed mutagenesis of CtIP FRY motif, KLHL15 overexpression and knockdown, DNA-end resection assays (HR/NHEJ reporter assays)","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — reciprocal Co-IP, in vitro ubiquitination assay, mutagenesis, functional rescue experiments with defined cellular phenotype (resection/HR/NHEJ), single lab but multiple orthogonal methods","pmids":["27561354"],"is_preprint":false},{"year":2020,"finding":"KLHL15 interacts with and ubiquitinates doublecortin (DCX), doublecortin-like kinase 1 (DCLK1), and doublecortin-like kinase 2 (DCLK2) — neuronal microtubule-associated proteins — via a Cul3-based E3 ligase complex, targeting them for proteasomal degradation. The interaction is mapped to 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 markedly stabilizes these proteins and prolongs their half-life. KLHL15 overexpression reduces dendritic complexity of cultured hippocampal neurons in a DCX FRY-motif-dependent manner.","method":"Bioinformatics substrate prediction, co-immunoprecipitation, ubiquitination assays, pulse-chase/half-life assays, mutagenesis of DCX FRY motif, KLHL15 knockdown, dendritic morphology analysis in cultured hippocampal neurons","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal methods (Co-IP, ubiquitination assay, mutagenesis, half-life measurement, functional neuronal phenotype) in a single rigorous study","pmids":["33199366"],"is_preprint":false},{"year":2022,"finding":"PACMP (a lncRNA-encoded micropeptide) prevents CtIP from KLHL15-mediated ubiquitination and degradation by inhibiting the CtIP-KLHL15 association, thereby maintaining CtIP abundance and DNA damage response. PACMP inhibition causes synthetic lethality through combined CtIP and PARP inhibition.","method":"Co-immunoprecipitation showing PACMP-KLHL15 and CtIP-KLHL15 interactions, ubiquitination assays, CtIP stability measurements upon PACMP depletion, synthetic lethality assays","journal":"Molecular cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and functional assays in single lab; mechanistic claim about KLHL15-CtIP axis is corroborated by prior work (PMID 27561354) but PACMP-specific mechanism is from one lab","pmids":["35219381"],"is_preprint":false},{"year":2023,"finding":"Multiplex CRISPR screening identified substrates for the Cul3-KLHL15 E3 ubiquitin ligase and mapped cognate degron motifs through site-saturation mutagenesis, placing KLHL15 within defined E3 ligase-substrate pathways in the ubiquitin-proteasome system.","method":"Multiplex CRISPR screening (~100 pooled CRISPR screens), site-saturation mutagenesis, degron mapping","journal":"Nature cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — large-scale functional screen with mutagenesis, but KLHL15 is one of many E3s profiled and specific substrate identity from this paper alone is not detailed in the abstract","pmids":["37735597"],"is_preprint":false},{"year":2024,"finding":"VGLL3 protects CtIP from KLHL15-mediated ubiquitination and degradation through competitive binding with KLHL15, thereby maintaining CtIP levels and promoting efficient homologous recombination and DNA double-strand break repair.","method":"Co-immunoprecipitation showing VGLL3-KLHL15 and VGLL3-CtIP interactions, competitive binding assays, CtIP stability assays upon VGLL3 depletion, HR efficiency assays","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and functional HR assay; competitive binding mechanism is consistent with prior KLHL15-CtIP work but VGLL3 competition is from a single lab","pmids":["39383226"],"is_preprint":false},{"year":2021,"finding":"CRISPR screen demonstrated that KLHL15 loss protects cells from DNA damage induced by ATM inhibition, placing KLHL15 loss as a genetic modifier of ATM inhibitor sensitivity in the DNA damage response pathway.","method":"Genome-wide CRISPR loss-of-function screen with ATM inhibitor treatment, cell viability readout","journal":"Nucleic acids research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single screening method, phenotype (resistance to ATMi) established but molecular mechanism of protection not detailed in abstract","pmids":["34320214"],"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 (three KELCH repeats), encoded by a 4-exon gene on the X chromosome, with ubiquitous mRNA expression across tissues and 85–93% amino acid identity to chicken and zebrafish orthologs.","method":"Bioinformatics/in silico analysis, cDNA assembly, domain prediction (Pfam), tissue expression by database analysis","journal":"Oncology reports","confidence":"Low","confidence_rationale":"Tier 4 / Weak — computational/in silico characterization only, no functional experiments performed","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 at Tyr552, which is known to be important for substrate binding, suggesting this residue contributes to the stability of loop regions at the substrate-binding surface.","method":"Comparative protein structural modeling of variant vs wild-type KLHL15 Kelch repeat domain","journal":"European journal of medical genetics","confidence":"Low","confidence_rationale":"Tier 4 / Weak — computational structural modeling only, no experimental validation of substrate binding impact performed","pmids":["37059329"],"is_preprint":false}],"current_model":"KLHL15 functions as a substrate-recognition adaptor for Cullin3-based E3 ubiquitin ligase complexes, targeting substrates containing a conserved FRY degron motif — including CtIP, doublecortin (DCX), DCLK1, DCLK2, and the PP2A regulatory subunit B'β — for ubiquitination and proteasomal degradation, thereby regulating DNA-end resection and the balance between homologous recombination and NHEJ, neuronal dendritogenesis, and cellular dephosphorylation events; its activity toward CtIP can be antagonized by competitive binding of PACMP or VGLL3 to the KLHL15-CtIP interface."},"narrative":{"mechanistic_narrative":"KLHL15 functions as a substrate-recognition adaptor for Cullin3 (Cul3)-based E3 ubiquitin ligase complexes, coupling specific substrates to ubiquitination and proteasomal degradation [PMID:23135275]. It recognizes substrates through a conserved FRY tripeptide degron, a motif first defined on CtIP and subsequently confirmed on the neuronal microtubule-associated proteins DCX, DCLK1, and DCLK2, where mutation of the FRY motif abolishes KLHL15-dependent ubiquitination and turnover [PMID:27561354, PMID:33199366]. Through this activity KLHL15 regulates distinct cellular programs: by degrading CtIP it restrains DNA-end resection and shifts the balance between homologous recombination and non-homologous end-joining [PMID:27561354], while by degrading the doublecortin-family proteins it limits dendritic complexity in hippocampal neurons in a FRY-motif-dependent manner [PMID:33199366]. KLHL15 also targets the PP2A regulatory subunit B'β for degradation via a divergent N-terminal recognition element, selectively removing B'β from the PP2A heterotrimer to promote regulatory-subunit exchange [PMID:23135275]. The KLHL15-CtIP interaction is a regulated node: the micropeptide PACMP and the cofactor VGLL3 each compete for binding to KLHL15, protecting CtIP from degradation and thereby sustaining the DNA damage response and homologous recombination [PMID:35219381, PMID:39383226].","teleology":[{"year":2005,"claim":"Establishing the basic identity of KLHL15 was the prerequisite for any functional study: it was defined as a BTB/POZ- and Kelch-domain protein, the architecture later shown to underlie its adaptor role.","evidence":"in silico cDNA assembly and domain prediction with cross-species sequence comparison","pmids":["15870933"],"confidence":"Low","gaps":["Computational only with no functional assay","No substrate or ligase partner identified","Subcellular localization not determined"]},{"year":2012,"claim":"The first functional question — whether KLHL15 is an active E3 adaptor and what it targets — was answered by showing it bridges Cul3 to the PP2A subunit B'β for degradation, establishing both its mechanism and a role in PP2A subunit exchange.","evidence":"proteomic Co-IP/MS, reciprocal Co-IP, in vitro ubiquitylation and degradation assays, mutagenesis of both adaptor and substrate","pmids":["23135275"],"confidence":"High","gaps":["Recognition element on B'β is divergent, not yet generalized to a shared degron","Physiological consequence of B'β removal on PP2A signaling not measured","No structural data on the adaptor-substrate interface"]},{"year":2016,"claim":"Identification of CtIP as a substrate via a conserved FRY tripeptide defined a generalizable degron and linked KLHL15 to control of DNA-end resection and HR/NHEJ choice.","evidence":"reciprocal Co-IP, in vitro ubiquitination, FRY-motif mutagenesis, KLHL15 gain/loss-of-function, HR/NHEJ resection reporter assays","pmids":["27561354"],"confidence":"High","gaps":["Upstream signals controlling KLHL15-CtIP engagement not defined","No structural model of FRY recognition","Cell-cycle regulation of the interaction unresolved"]},{"year":2020,"claim":"Extending the FRY-degron logic to DCX, DCLK1, and DCLK2 showed KLHL15 governs a neuronal substrate class and influences dendritogenesis, demonstrating the adaptor operates across distinct biological contexts.","evidence":"bioinformatic substrate prediction, Co-IP, ubiquitination and half-life assays, FRY mutagenesis, KLHL15 knockdown, dendritic morphology in hippocampal neurons","pmids":["33199366"],"confidence":"High","gaps":["In vivo requirement for KLHL15 in neuronal development not tested","Which DCX-family member dominates the dendritic phenotype unclear","Regulation of KLHL15 activity in neurons unknown"]},{"year":2021,"claim":"A genetic screen placed KLHL15 in the ATM-inhibitor response, showing its loss protects cells from ATMi-induced damage and implicating it as a modifier of DDR drug sensitivity.","evidence":"genome-wide CRISPR loss-of-function screen under ATM inhibition with viability readout","pmids":["34320214"],"confidence":"Low","gaps":["Molecular mechanism of protection not established","Not linked directly to CtIP degradation in this study","Single screening modality without orthogonal validation"]},{"year":2022,"claim":"Discovery that the micropeptide PACMP competitively blocks the CtIP-KLHL15 interaction revealed the adaptor's substrate engagement is actively regulated, with therapeutic synthetic-lethality implications.","evidence":"Co-IP of PACMP-KLHL15 and CtIP-KLHL15, ubiquitination and CtIP stability assays, synthetic lethality with PARP inhibition","pmids":["35219381"],"confidence":"Medium","gaps":["Single-lab mechanism for PACMP competition","Structural basis of competitive binding unresolved","Whether PACMP affects other KLHL15 substrates untested"]},{"year":2023,"claim":"Systematic screening and degron mapping placed Cul3-KLHL15 within defined E3-substrate pathways, while structural modeling of a disease-associated Kelch-domain variant pinpointed substrate-binding-surface residues including Tyr552.","evidence":"multiplex pooled CRISPR screens with site-saturation degron mutagenesis; comparative structural modeling of the p.(Arg532del) variant","pmids":["37735597","37059329"],"confidence":"Medium","gaps":["Specific substrate identities from the screen not detailed","Variant's predicted binding defect not experimentally validated","Functional consequence of the variant not established"]},{"year":2024,"claim":"Identification of VGLL3 as a second competitive protector of CtIP confirmed that multiple factors converge on the KLHL15-CtIP interface to tune HR capacity.","evidence":"Co-IP of VGLL3-KLHL15 and VGLL3-CtIP, competitive binding assays, CtIP stability and HR efficiency assays","pmids":["39383226"],"confidence":"Medium","gaps":["Single-lab competition mechanism","Relationship between VGLL3 and PACMP regulation not reconciled","No structural definition of the competing interface"]},{"year":null,"claim":"How KLHL15 substrate selection and adaptor activity are regulated across cell-cycle and tissue contexts, and the structural basis of FRY-degron recognition, remain open.","evidence":"","pmids":[],"confidence":"Low","gaps":["No experimental structure of KLHL15 bound to a FRY degron","Signals that activate or inhibit KLHL15 in vivo undefined","Disease relevance of KLHL15 variants not functionally validated"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,1]}],"localization":[],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,2]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[1]}],"complexes":["Cul3-RING E3 ubiquitin ligase (CRL3)"],"partners":["CUL3","RBM6","CTIP","DCX","DCLK1","DCLK2","PACMP","VGLL3"],"other_free_text":[]}},"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":248,"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":77,"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":53,"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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KLHL15 residues critical for homodimerization, Cul3 interaction, and B'β interaction were mapped; the divergent N terminus of B'β (including Tyr-52) was necessary and sufficient for KLHL15-mediated degradation. Although KLHL15 can interact with the PP2A/B'β heterotrimer, it only degrades B'β, promoting exchange with other regulatory subunits.\",\n      \"method\": \"Unbiased proteomic screens (Co-IP/MS), co-immunoprecipitation, ubiquitylation assays, proteasomal degradation assays, mutagenesis of KLHL15 and B'β\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal methods (proteomic screen, reciprocal Co-IP, in vitro ubiquitylation assay, mutagenesis of both substrate and adaptor) in a single rigorous study\",\n      \"pmids\": [\"23135275\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"KLHL15 is a Cullin3 E3 ligase substrate adaptor that binds CtIP via a conserved tripeptide motif (FRY) in CtIP and promotes CtIP ubiquitination and proteasomal turnover. Mutation of the FRY motif blocks KLHL15-dependent CtIP ubiquitination and degradation. Overexpression of KLHL15 strongly attenuates DNA-end resection, while cells expressing FRY-mutant CtIP or lacking KLHL15 show amplified resection, shifting the balance between homologous recombination (HR) and non-homologous end-joining (NHEJ).\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, site-directed mutagenesis of CtIP FRY motif, KLHL15 overexpression and knockdown, DNA-end resection assays (HR/NHEJ reporter assays)\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — reciprocal Co-IP, in vitro ubiquitination assay, mutagenesis, functional rescue experiments with defined cellular phenotype (resection/HR/NHEJ), single lab but multiple orthogonal methods\",\n      \"pmids\": [\"27561354\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"KLHL15 interacts with and ubiquitinates doublecortin (DCX), doublecortin-like kinase 1 (DCLK1), and doublecortin-like kinase 2 (DCLK2) — neuronal microtubule-associated proteins — via a Cul3-based E3 ligase complex, targeting them for proteasomal degradation. The interaction is mapped to 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 markedly stabilizes these proteins and prolongs their half-life. KLHL15 overexpression reduces dendritic complexity of cultured hippocampal neurons in a DCX FRY-motif-dependent manner.\",\n      \"method\": \"Bioinformatics substrate prediction, co-immunoprecipitation, ubiquitination assays, pulse-chase/half-life assays, mutagenesis of DCX FRY motif, KLHL15 knockdown, dendritic morphology analysis in cultured hippocampal neurons\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal methods (Co-IP, ubiquitination assay, mutagenesis, half-life measurement, functional neuronal phenotype) in a single rigorous study\",\n      \"pmids\": [\"33199366\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PACMP (a lncRNA-encoded micropeptide) prevents CtIP from KLHL15-mediated ubiquitination and degradation by inhibiting the CtIP-KLHL15 association, thereby maintaining CtIP abundance and DNA damage response. PACMP inhibition causes synthetic lethality through combined CtIP and PARP inhibition.\",\n      \"method\": \"Co-immunoprecipitation showing PACMP-KLHL15 and CtIP-KLHL15 interactions, ubiquitination assays, CtIP stability measurements upon PACMP depletion, synthetic lethality assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and functional assays in single lab; mechanistic claim about KLHL15-CtIP axis is corroborated by prior work (PMID 27561354) but PACMP-specific mechanism is from one lab\",\n      \"pmids\": [\"35219381\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Multiplex CRISPR screening identified substrates for the Cul3-KLHL15 E3 ubiquitin ligase and mapped cognate degron motifs through site-saturation mutagenesis, placing KLHL15 within defined E3 ligase-substrate pathways in the ubiquitin-proteasome system.\",\n      \"method\": \"Multiplex CRISPR screening (~100 pooled CRISPR screens), site-saturation mutagenesis, degron mapping\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — large-scale functional screen with mutagenesis, but KLHL15 is one of many E3s profiled and specific substrate identity from this paper alone is not detailed in the abstract\",\n      \"pmids\": [\"37735597\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"VGLL3 protects CtIP from KLHL15-mediated ubiquitination and degradation through competitive binding with KLHL15, thereby maintaining CtIP levels and promoting efficient homologous recombination and DNA double-strand break repair.\",\n      \"method\": \"Co-immunoprecipitation showing VGLL3-KLHL15 and VGLL3-CtIP interactions, competitive binding assays, CtIP stability assays upon VGLL3 depletion, HR efficiency assays\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and functional HR assay; competitive binding mechanism is consistent with prior KLHL15-CtIP work but VGLL3 competition is from a single lab\",\n      \"pmids\": [\"39383226\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CRISPR screen demonstrated that KLHL15 loss protects cells from DNA damage induced by ATM inhibition, placing KLHL15 loss as a genetic modifier of ATM inhibitor sensitivity in the DNA damage response pathway.\",\n      \"method\": \"Genome-wide CRISPR loss-of-function screen with ATM inhibitor treatment, cell viability readout\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single screening method, phenotype (resistance to ATMi) established but molecular mechanism of protection not detailed in abstract\",\n      \"pmids\": [\"34320214\"],\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 (three KELCH repeats), encoded by a 4-exon gene on the X chromosome, with ubiquitous mRNA expression across tissues and 85–93% amino acid identity to chicken and zebrafish orthologs.\",\n      \"method\": \"Bioinformatics/in silico analysis, cDNA assembly, domain prediction (Pfam), tissue expression by database analysis\",\n      \"journal\": \"Oncology reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — computational/in silico characterization only, no functional experiments performed\",\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 at Tyr552, which is known to be important for substrate binding, suggesting this residue contributes to the stability of loop regions at the substrate-binding surface.\",\n      \"method\": \"Comparative protein structural modeling of variant vs wild-type KLHL15 Kelch repeat domain\",\n      \"journal\": \"European journal of medical genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — computational structural modeling only, no experimental validation of substrate binding impact performed\",\n      \"pmids\": [\"37059329\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"KLHL15 functions as a substrate-recognition adaptor for Cullin3-based E3 ubiquitin ligase complexes, targeting substrates containing a conserved FRY degron motif — including CtIP, doublecortin (DCX), DCLK1, DCLK2, and the PP2A regulatory subunit B'β — for ubiquitination and proteasomal degradation, thereby regulating DNA-end resection and the balance between homologous recombination and NHEJ, neuronal dendritogenesis, and cellular dephosphorylation events; its activity toward CtIP can be antagonized by competitive binding of PACMP or VGLL3 to the KLHL15-CtIP interface.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"KLHL15 functions as a substrate-recognition adaptor for Cullin3 (Cul3)-based E3 ubiquitin ligase complexes, coupling specific substrates to ubiquitination and proteasomal degradation [#0]. It recognizes substrates through a conserved FRY tripeptide degron, a motif first defined on CtIP and subsequently confirmed on the neuronal microtubule-associated proteins DCX, DCLK1, and DCLK2, where mutation of the FRY motif abolishes KLHL15-dependent ubiquitination and turnover [#1, #2]. Through this activity KLHL15 regulates distinct cellular programs: by degrading CtIP it restrains DNA-end resection and shifts the balance between homologous recombination and non-homologous end-joining [#1], while by degrading the doublecortin-family proteins it limits dendritic complexity in hippocampal neurons in a FRY-motif-dependent manner [#2]. KLHL15 also targets the PP2A regulatory subunit B'\\u03b2 for degradation via a divergent N-terminal recognition element, selectively removing B'\\u03b2 from the PP2A heterotrimer to promote regulatory-subunit exchange [#0]. The KLHL15-CtIP interaction is a regulated node: the micropeptide PACMP and the cofactor VGLL3 each compete for binding to KLHL15, protecting CtIP from degradation and thereby sustaining the DNA damage response and homologous recombination [#3, #5].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Establishing the basic identity of KLHL15 was the prerequisite for any functional study: it was defined as a BTB/POZ- and Kelch-domain protein, the architecture later shown to underlie its adaptor role.\",\n      \"evidence\": \"in silico cDNA assembly and domain prediction with cross-species sequence comparison\",\n      \"pmids\": [\"15870933\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Computational only with no functional assay\", \"No substrate or ligase partner identified\", \"Subcellular localization not determined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"The first functional question — whether KLHL15 is an active E3 adaptor and what it targets — was answered by showing it bridges Cul3 to the PP2A subunit B'\\u03b2 for degradation, establishing both its mechanism and a role in PP2A subunit exchange.\",\n      \"evidence\": \"proteomic Co-IP/MS, reciprocal Co-IP, in vitro ubiquitylation and degradation assays, mutagenesis of both adaptor and substrate\",\n      \"pmids\": [\"23135275\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Recognition element on B'\\u03b2 is divergent, not yet generalized to a shared degron\", \"Physiological consequence of B'\\u03b2 removal on PP2A signaling not measured\", \"No structural data on the adaptor-substrate interface\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identification of CtIP as a substrate via a conserved FRY tripeptide defined a generalizable degron and linked KLHL15 to control of DNA-end resection and HR/NHEJ choice.\",\n      \"evidence\": \"reciprocal Co-IP, in vitro ubiquitination, FRY-motif mutagenesis, KLHL15 gain/loss-of-function, HR/NHEJ resection reporter assays\",\n      \"pmids\": [\"27561354\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream signals controlling KLHL15-CtIP engagement not defined\", \"No structural model of FRY recognition\", \"Cell-cycle regulation of the interaction unresolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extending the FRY-degron logic to DCX, DCLK1, and DCLK2 showed KLHL15 governs a neuronal substrate class and influences dendritogenesis, demonstrating the adaptor operates across distinct biological contexts.\",\n      \"evidence\": \"bioinformatic substrate prediction, Co-IP, ubiquitination and half-life assays, FRY mutagenesis, KLHL15 knockdown, dendritic morphology in hippocampal neurons\",\n      \"pmids\": [\"33199366\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo requirement for KLHL15 in neuronal development not tested\", \"Which DCX-family member dominates the dendritic phenotype unclear\", \"Regulation of KLHL15 activity in neurons unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"A genetic screen placed KLHL15 in the ATM-inhibitor response, showing its loss protects cells from ATMi-induced damage and implicating it as a modifier of DDR drug sensitivity.\",\n      \"evidence\": \"genome-wide CRISPR loss-of-function screen under ATM inhibition with viability readout\",\n      \"pmids\": [\"34320214\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Molecular mechanism of protection not established\", \"Not linked directly to CtIP degradation in this study\", \"Single screening modality without orthogonal validation\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Discovery that the micropeptide PACMP competitively blocks the CtIP-KLHL15 interaction revealed the adaptor's substrate engagement is actively regulated, with therapeutic synthetic-lethality implications.\",\n      \"evidence\": \"Co-IP of PACMP-KLHL15 and CtIP-KLHL15, ubiquitination and CtIP stability assays, synthetic lethality with PARP inhibition\",\n      \"pmids\": [\"35219381\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab mechanism for PACMP competition\", \"Structural basis of competitive binding unresolved\", \"Whether PACMP affects other KLHL15 substrates untested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Systematic screening and degron mapping placed Cul3-KLHL15 within defined E3-substrate pathways, while structural modeling of a disease-associated Kelch-domain variant pinpointed substrate-binding-surface residues including Tyr552.\",\n      \"evidence\": \"multiplex pooled CRISPR screens with site-saturation degron mutagenesis; comparative structural modeling of the p.(Arg532del) variant\",\n      \"pmids\": [\"37735597\", \"37059329\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific substrate identities from the screen not detailed\", \"Variant's predicted binding defect not experimentally validated\", \"Functional consequence of the variant not established\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identification of VGLL3 as a second competitive protector of CtIP confirmed that multiple factors converge on the KLHL15-CtIP interface to tune HR capacity.\",\n      \"evidence\": \"Co-IP of VGLL3-KLHL15 and VGLL3-CtIP, competitive binding assays, CtIP stability and HR efficiency assays\",\n      \"pmids\": [\"39383226\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab competition mechanism\", \"Relationship between VGLL3 and PACMP regulation not reconciled\", \"No structural definition of the competing interface\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How KLHL15 substrate selection and adaptor activity are regulated across cell-cycle and tissue contexts, and the structural basis of FRY-degron recognition, remain open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No experimental structure of KLHL15 bound to a FRY degron\", \"Signals that activate or inhibit KLHL15 in vivo undefined\", \"Disease relevance of KLHL15 variants not functionally validated\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"complexes\": [\"Cul3-RING E3 ubiquitin ligase (CRL3)\"],\n    \"partners\": [\"CUL3\", \"RBM6\", \"CtIP\", \"DCX\", \"DCLK1\", \"DCLK2\", \"PACMP\", \"VGLL3\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}