{"gene":"XRCC6","run_date":"2026-06-11T09:02:06","timeline":{"discoveries":[{"year":1997,"finding":"Ku70 forms a heterodimer with Ku80 that is required for DNA double-strand break (DSB) repair and V(D)J recombination. Loss-of-function (Ku70-/- mice) showed radiation sensitivity, premature senescence, and severe impairment of V(D)J coding and signal sequence joining, establishing Ku70 as an essential component of the NHEJ pathway in vivo.","method":"Ku70 knockout mouse model; cellular IR sensitivity assays; V(D)J recombination assays","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockout model with multiple defined cellular and molecular phenotypes, replicated across multiple subsequent studies","pmids":["9390689"],"is_preprint":false},{"year":1997,"finding":"Ku70 requires heterodimerization with Ku80 and its C-terminal DNA-binding domain (aa 254–609) for DSB repair and DNA end-binding. A core region (aa 439–609) mediates Ku80 heterodimerization. Ku70's roles in DNA-PK activation and IR repair are separable by mutagenesis.","method":"Truncation and chimera mutagenesis of Ku70; complementation of Ku70-/- ES cells; IR sensitivity assay; DNA end-binding assay; DNA-PK activity assay","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro mutagenesis with functional reconstitution and multiple orthogonal assays in a single rigorous study","pmids":["9362500"],"is_preprint":false},{"year":1996,"finding":"The C-terminal 20 kDa of Ku70 and C-terminal 32 kDa of Ku86 mediate subunit–subunit interaction; the C-terminal 40 kDa of Ku70 (aa 254–609) is required for DNA end-binding. Full-length individual subunits are inactive for DNA binding; heterodimer assembly must precede DNA binding.","method":"Genetic and biochemical domain-deletion analysis; DNA end-binding assays with purified proteins","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with systematic domain deletion, multiple binding assays","pmids":["8756676"],"is_preprint":false},{"year":1998,"finding":"Ku70 is required for immunoglobulin heavy chain class switch recombination (CSR). K70T/HL B cells induced with CSR-stimulating agents showed intact germline CH transcription but completely failed to undergo CSR and underwent cell death, placing Ku70 downstream of CSR signaling but essential for the DNA rearrangement step.","method":"Genetic epistasis using Ku70-/- mice carrying rearranged Ig transgenes; in vitro CSR assays; serum Ig measurement","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic epistasis with defined phenotypic readout, multiple lines of evidence","pmids":["9625768"],"is_preprint":false},{"year":2002,"finding":"Inositol hexakisphosphate (IP6) binds specifically to the Ku70/80 heterodimer (not to DNA-PKcs alone), and IP6 binding alters the conformation of Ku70/80 as detected by proteolysis mapping. The yeast Ku70/80 homolog does not bind IP6, indicating this is a mammalian-specific function.","method":"Proteolysis mapping of Ku70/80 with and without IP6; binding competition assays; comparison with yeast Ku homologs","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct biochemical binding assay with conformational read-out, single lab but multiple orthogonal methods","pmids":["11953323"],"is_preprint":false},{"year":2006,"finding":"Full-length 3D structure of human Ku70/Ku80 heterodimer resolved at 25 Å by single-particle electron microscopy, alone and in complex with DNA. C-terminal domains of both subunits were mapped; conformational changes upon DNA and DNA-PKcs binding were defined, providing a structural model for DNA recognition during NHEJ.","method":"Single-particle electron microscopy; 3D reconstruction; structural comparison of Ku70/80 free, DNA-bound, and DNA-PKcs-bound states","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1 / Moderate — structural determination by EM with functional domain mapping and conformational analysis","pmids":["17159921"],"is_preprint":false},{"year":2005,"finding":"Ku70 is a mammalian cell-surface receptor for Rickettsia conorii internalization. Ku70 is recruited to bacterial entry sites; cholesterol-enriched microdomains containing Ku70 are required for invasion. R. conorii infection stimulates Ku70 ubiquitination, and the ubiquitin ligase c-Cbl is recruited to entry foci and mediates Ku70 ubiquitination. The rickettsial surface protein rOmpB was identified as the Ku70 ligand by affinity chromatography.","method":"siRNA knockdown; immunofluorescence/confocal colocalization; affinity chromatography; co-immunoprecipitation; bacterial invasion assay","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (affinity chromatography, siRNA, colocalization, ubiquitination assay) in a single rigorous study","pmids":["16360032"],"is_preprint":false},{"year":2007,"finding":"SIRT1 physically complexes with Ku70, deacetylates it, and thereby enhances DNA repair capacity after radiation. A catalytically inactive SIRT1 dominant-negative mutant failed to deacetylate Ku70 or enhance repair, establishing a writer/eraser relationship between SIRT1 and Ku70 acetylation in DNA repair.","method":"Co-immunoprecipitation; SIRT1 overexpression and siRNA knockdown; DNA strand-break repair assay; dominant-negative SIRT1 mutagenesis","journal":"Experimental & molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP and functional rescue with dominant-negative, single lab","pmids":["17334224"],"is_preprint":false},{"year":2011,"finding":"HDAC6 binds Ku70 and Bax in the cytoplasm of neuroblastoma cells and maintains Ku70 in a deacetylated state. Knockdown of HDAC6 or use of an HDAC6-specific inhibitor triggers Ku70 acetylation, releases Bax from Ku70, and induces Bax-dependent apoptosis, identifying HDAC6 as a key deacetylase (eraser) for cytoplasmic Ku70.","method":"Co-immunoprecipitation; HDAC6 siRNA knockdown; HDAC6-specific inhibitor (Tubacin); apoptosis assays","journal":"Neoplasia","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP, genetic knockdown, and pharmacological inhibition all converging on same mechanism; multiple orthogonal methods","pmids":["21847364"],"is_preprint":false},{"year":2012,"finding":"Ku70 acetylation (mediated by CBP/PCAF) disrupts its interaction with FLIP, triggering FLIP polyubiquitination and proteasomal degradation. HDAC inhibitor (SAHA/Vorinostat) enhances Ku70 acetylation via HDAC6 inhibition to destabilize FLIP and induce caspase-8-dependent apoptosis in colorectal cancer models.","method":"Co-immunoprecipitation; HDAC inhibitor treatment; ubiquitination assays; in vitro and in vivo colorectal cancer models; caspase activation assays","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods including co-IP, ubiquitination assay, in vivo model, and pharmacological inhibition in single rigorous study","pmids":["22322857"],"is_preprint":false},{"year":2005,"finding":"Human Ku70/80 interacts directly with hTR, the RNA component of human telomerase, specifically with a 47 nt region at the 3' end of hTR. This interaction is independent of hTERT, as shown by immunoprecipitation/RT-PCR in hTERT-deficient cell lines, suggesting a conserved role for Ku in telomere maintenance via telomerase RNA interaction.","method":"In vitro binding assay; immunoprecipitation/RT-PCR in hTERT-deficient cell lines; mapping of interaction domain on hTR","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and cellular interaction demonstrated, single lab, two orthogonal methods","pmids":["15824061"],"is_preprint":false},{"year":2000,"finding":"Ku70 interacts with heterochromatin protein 1alpha (HP1alpha) via its Leu-Ser repeat domain (aa 200–385), and HP1alpha's chromo shadow domain mediates the interaction. This was confirmed by GST pull-down with recombinant proteins and co-immunoprecipitation in HeLa cells. The interaction is pH-sensitive and Ku80 does not interact with HP1alpha directly.","method":"Yeast two-hybrid; GST pull-down with recombinant proteins; co-immunoprecipitation in HeLa cells; confocal colocalization","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — GST pull-down (in vitro reconstitution) and co-IP in cells, single lab, two orthogonal methods","pmids":["11112778"],"is_preprint":false},{"year":2010,"finding":"In the Fanconi anemia pathway, FANCD2 (a downstream FA effector) antagonizes Ku70 activity by modifying free DNA ends, thereby diverting DSB repair from NHEJ toward homologous recombination. Disruption of both FANCC and Ku70 suppresses ICL sensitivity, diminishes chromosome breaks, and reverses defective HR, establishing a genetic epistasis where the FA pathway acts upstream of Ku70 to channel repair pathway choice.","method":"Genetic epistasis (FANCC/Ku70 double knockout); ICL sensitivity assays; HR frequency measurement; in vitro biochemical assay with purified FANCD2 and Ku70","journal":"Science","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — genetic epistasis combined with in vitro biochemical reconstitution, multiple orthogonal phenotypic readouts","pmids":["20538911"],"is_preprint":false},{"year":2010,"finding":"Mutant huntingtin (Htt) directly interacts with Ku70 and impairs DNA-PK function in NHEJ, causing accumulation of DSBs in neurons. Exogenous Ku70 expression rescues abnormal behavior and pathological phenotypes in R6/2 HD mice, establishing Ku70 as a critical mediator of DNA repair dysfunction in Huntington's disease pathology.","method":"Co-immunoprecipitation; DNA-PK activity assay; γH2AX foci analysis; R6/2 mouse rescue with Ku70 overexpression; behavioral assays","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — co-IP, enzymatic assay, and in vivo rescue with multiple phenotypic readouts across labs (replicated in Drosophila, PMID 22096569)","pmids":["20439996","22096569"],"is_preprint":false},{"year":2007,"finding":"Ku70/80 modulates ATM-dependent ATR activation during the DSB damage response. In Ku-deficient cells, p53 Ser18 phosphorylation persists via ATM-independent ATR activity at late time points after IR, a pathway not observed in wild-type cells, revealing a novel role for Ku70/80 in suppressing aberrant ATR activation.","method":"ATM/Ku70 double-null cell line generation; p53 phosphorylation analysis; ATM and ATR inhibitors; irradiation experiments","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — double-null cell lines with pharmacological inhibitors, single lab, two orthogonal approaches","pmids":["17272272"],"is_preprint":false},{"year":2000,"finding":"A nuclear CLU/XIP8 protein, induced by low-dose ionizing radiation, co-immunoprecipitates and co-localizes with Ku70/Ku80 in human breast cancer cells. Overexpression of nuclear CLU/XIP8 or its minimal Ku70-binding domain (120 aa C-terminus) reduces cell growth and increases G1 arrest and cell death, identifying clusterin as a Ku70-binding partner that signals cell death.","method":"Yeast two-hybrid; co-immunoprecipitation; confocal colocalization; overexpression of CLU/XIP8 and truncation mutants; colony formation assay","journal":"PNAS","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid confirmed by co-IP and colocalization, functional overexpression, single lab","pmids":["10823943"],"is_preprint":false},{"year":2006,"finding":"Granzyme A cleaves Ku70 after Arg301, disrupting Ku complex binding to DNA, thereby facilitating GzmA-mediated caspase-independent cell death. Silencing Ku70 by RNAi increases GzmA-induced DNA damage and cell death, while Ku70 overexpression has the opposite effect, demonstrating Ku70 has antiapoptotic functions beyond DSBR and Bax sequestration.","method":"In vitro cleavage assay; Ku70 siRNA knockdown; Ku70 overexpression; CTL/perforin cell death assay; DNA damage quantification","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — identified cleavage site biochemically, with genetic knockdown and overexpression rescue experiments converging on same conclusion","pmids":["16440001"],"is_preprint":false},{"year":2002,"finding":"Ku70 can translocate to the nucleus independently of heterodimerization with Ku80, as shown by nuclear localization of Ku70 mutants lacking Ku80-binding ability and by Ku70 expression in Ku80-deficient hamster xrs-6 cells. Ku70 nuclear localization is mediated by its NLS and does not require DNA-PK autophosphorylation sites.","method":"Site-directed mutagenesis of Ku70 NLS and Ku80-binding domains; transfection into Ku80-deficient cells; immunofluorescence localization","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis combined with complementation in Ku80-deficient cells, single lab, two approaches","pmids":["11027597"],"is_preprint":false},{"year":2011,"finding":"Ku70 interacts with FOXO4 via a direct biochemical interaction (Ku70 necessary and sufficient), and sequesters FOXO4 in the nucleus, inhibiting FOXO4-mediated p27(kip1) transcription and cell cycle arrest by >40%. Low oxidative stress increases Ku70-FOXO4 interaction stoichiometry, while higher stress causes dissociation, suggesting a dose-dependent stress-response role for Ku70.","method":"Tandem-affinity purification/mass spectrometry; co-immunoprecipitation; luciferase reporter assay; flow cytometry; Ku70-/- ES cells; immunofluorescence","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — unbiased proteomics identification confirmed by multiple orthogonal functional assays including knockout rescue","pmids":["20570964"],"is_preprint":false},{"year":2011,"finding":"Ku70 interacts directly with HIV-1 integrase (IN) via the N-terminal part of Ku70 (aa 1–430), protecting IN from Lys48-linked polyubiquitination and proteasomal degradation. Ku70 can deubiquitinate IN through their interaction. This interaction is independent of Ku70/80 heterodimerization, and Ku70 is incorporated into progeny virus in an IN-dependent manner; Ku70 knockdown disrupts HIV-1 replication.","method":"Co-immunoprecipitation; mutagenesis mapping; ubiquitination assays; Ku70 siRNA knockdown; HIV infectivity assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro binding domain mapping, ubiquitination/deubiquitination biochemical assay, siRNA knockdown with viral infectivity readout","pmids":["21454661"],"is_preprint":false},{"year":2010,"finding":"MSH6 is a novel Ku70-interacting protein; the Ku70-MSH6 association is enhanced by DSB-inducing agents (NCS, IR). MSH6-deficient cells accumulate persistent DSBs and display impaired NHEJ, which is rescued by MSH6 overexpression, linking the mismatch repair protein MSH6 to NHEJ via Ku70.","method":"Yeast two-hybrid; co-immunoprecipitation; γH2AX foci assay; comet assay; NHEJ assay; clonogenic survival","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid confirmed by co-IP, functional assay with rescue, single lab","pmids":["21075794"],"is_preprint":false},{"year":2007,"finding":"Par3, a cell polarity protein, interacts with Ku70 and Ku80 in the nucleus; this interaction is enhanced by gamma-irradiation. Par3 regulates DNA-PK activity (up- and downregulated by overexpression and knockdown, respectively), and Par3-knockdown cells are defective in NHEJ, random integration, and DSB repair, and are radiosensitive.","method":"In vitro binding assay; LC-MS/MS; co-immunoprecipitation; DNA-PK activity assay; NHEJ reporter assay; IR sensitivity assay","journal":"Cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — unbiased MS identification confirmed by co-IP, functional assays, single lab, multiple methods","pmids":["17287830"],"is_preprint":false},{"year":2008,"finding":"Ku70 and Ku80 interact with full-length RAG1 as demonstrated by co-immunoprecipitation, providing a biochemical link between the RAG cleavage machinery and the NHEJ repair pathway during V(D)J recombination.","method":"Co-immunoprecipitation with full-length RAG1 and Ku70/80","journal":"Nucleic acids research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single co-IP experiment, single lab, no functional follow-up of the specific Ku70-RAG1 interaction","pmids":["18281312"],"is_preprint":false},{"year":2004,"finding":"Ku70/80 and DNA-PKcs modulate RAG-mediated V(D)J cleavage, preferentially inhibiting 12/12 and 23/23 cleavage to increase 12/23 rule specificity. This indicates DNA repair factors are present upstream of cleavage events, not only recruited downstream for repair.","method":"Protein fractionation; biochemical cleavage assays with purified Ku70/80 and DNA-PKcs; 12/23 rule reporter assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — biochemical reconstitution assay with purified factors, single lab","pmids":["15123719"],"is_preprint":false},{"year":2013,"finding":"RECQ1 helicase directly interacts with Ku70/80; depletion of RECQ1 reduces end-joining in cell-free extracts. In vitro, RECQ1 binds and unwinds Ku70/80-bound partial duplex DNA, and linear DNA is co-bound by both RECQ1 and Ku70/80, with DNA binding by Ku70/80 modulated by RECQ1.","method":"Direct protein interaction assays; cell-free end-joining assay; helicase unwinding assay with Ku70/80-bound substrate; co-binding assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro reconstitution biochemistry, single lab, multiple orthogonal assays","pmids":["23650516"],"is_preprint":false},{"year":2005,"finding":"DNA-PK-mediated phosphorylation of Ku70 at serine 6 (and Ku80 at S577, S580, T715) occurs in vitro, but these phosphorylation events are not required for NHEJ in vivo: Ku70/80 with S/T→A mutations at these sites fully complemented radiation sensitivity of Ku-negative cells. In vivo phosphorylation at these sites is regulated by a PP2A-like phosphatase and a staurosporine-sensitive kinase, not DNA-PK.","method":"Mass spectrometry; phosphospecific antibodies; in vitro kinase assays; S/T→A mutagenesis; complementation of Ku-negative cells with mutant Ku70/80; IR sensitivity assay; pharmacological inhibitors","journal":"DNA repair","confidence":"High","confidence_rationale":"Tier 1 / Strong — MS site identification, in vitro kinase assay, alanine mutagenesis with in vivo complementation, negative result rigorously established","pmids":["15941674"],"is_preprint":false},{"year":2012,"finding":"Ku70/80 binds the Apaf1 promoter repressor element and downregulates Apaf1 transcription. This binding is dynamically modulated upon DNA damage: Ku70/80 initially represses Apaf1 after damage, then dissociates allowing Apaf1 upregulation and apoptosis. This defines a transcriptional regulatory function for Ku70/80 at the apoptosome pathway.","method":"Apaf1 promoter mutant analysis; chromatin immunoprecipitation; reporter assays; Ku70/80 knockdown with Apaf1 expression measurement","journal":"Cell death and differentiation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — promoter binding established by ChIP and reporter assays, functional knockdown, single lab","pmids":["20966962"],"is_preprint":false},{"year":2013,"finding":"SET/TAF-Iβ (an INHAT subunit) interacts with Ku70/80, inhibiting CBP- and PCAF-mediated acetylation of Ku70 in an INHAT domain-dependent manner. DNA damage by UV disrupts this interaction, releasing Ku70/80 for recruitment to DSB sites. Overexpressed SET/TAF-Iβ inhibits Ku70/80 recruitment to DNA damage foci.","method":"Co-immunoprecipitation; in vitro acetylation assay with CBP/PCAF; SET/TAF-Iβ overexpression; immunofluorescence of Ku70/80 at damage foci","journal":"Cellular and molecular life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP and in vitro acetylation inhibition assay, functional foci assay, single lab","pmids":["24305947"],"is_preprint":false},{"year":2015,"finding":"Ku70 (XRCC6) directly associates with the HSA/BRK domains of BRG1 (SWI/SNF ATPase). Ku70/86 and components of the TOP2β/PARP1 complex are required for glucocorticoid receptor (GR)-mediated, BRG1-dependent transcriptional activation from endogenous promoters. GR/BRG1-dependent, TOP2β-mediated transient DNA DSBs are required for efficient GR-stimulated transcription.","method":"Co-immunoprecipitation; chromatin immunoprecipitation; transcriptional activation assays; BRG1 mutant analysis; Ku70/86 knockdown","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP with domain mapping, ChIP, functional transcription assay, single lab","pmids":["26055322"],"is_preprint":false},{"year":2017,"finding":"SIRT6 interacts with Ku70 and deacetylates it at lysine K542. Deacetylation of Ku70 by SIRT6 stabilizes its interaction with Bax, preventing Bax mitochondrial translocation and apoptosis. A K542Q acetylation-mimicking mutation abolishes Ku70-Bax association and reverses SIRT6-mediated apoptosis suppression in hepatocellular carcinoma cells.","method":"Co-immunoprecipitation; SIRT6 knockdown; site-directed mutagenesis (K542Q); mitochondrial fractionation; apoptosis assays","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP, site-specific mutagenesis identifying K542, functional apoptosis assays, single lab","pmids":["28238784"],"is_preprint":false},{"year":2023,"finding":"SMYD2 methyltransferase methylates Ku70 at lysines 74, 516, and 539 in response to DNA damage, increasing recruitment of the Ku70/Ku80/DNA-PKcs complex. SMYD2 knockdown or inhibition impairs NHEJ, causes cytosolic DNA accumulation, and activates the cGAS-STING pathway, triggering anti-tumor CD8+ T-cell responses.","method":"Mass spectrometry identification of methylation sites; SMYD2 knockdown/inhibitor (AZ505); ChIP for Ku70 at damage sites; NHEJ assay; cGAS-STING activation measurement; in vivo tumor immunology","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — MS-identified modification sites, biochemical NHEJ assay, in vivo tumor immunology, multiple orthogonal methods in one study","pmids":["37315132"],"is_preprint":false},{"year":2021,"finding":"Cytoplasmic translocation of Ku70 (via nuclear export, inhibited by leptomycin B) is required for cytosolic DNA sensing and induction of IFN-λ1 (but not IFN-α or IFN-β) via a STING-dependent signaling pathway. Enhanced cellular acetylation promotes Ku70 cytoplasmic accumulation and IFN-λ1 induction. HSV-1 infection triggers Ku70 cytoplasmic translocation and IFN-λ1 in a strain-dependent manner.","method":"Nuclear export inhibitor (leptomycin B); IFN-λ1 reporter assay; DNA transfection; HSV-1 infection; subcellular fractionation; kinetic analysis","journal":"Immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological nuclear export block with IFN induction readout, kinetic analysis, viral infection, single lab","pmids":["33548066"],"is_preprint":false},{"year":2017,"finding":"Ku70 senses HTLV-1 reverse transcription intermediate ssDNA90, is induced by HTLV-1 infection, and associates with STING to mediate innate immune responses. Ku70 overexpression inhibited HTLV-1 protein expression while knockdown promoted it. Ku70 interacts with HTLV-1 ssDNA90 and promotes ssDNA-triggered innate immune signaling.","method":"HTLV-1 infection; Ku70 overexpression/knockdown; STING co-association; innate immune cytokine measurement; ssDNA90 binding assay","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain- and loss-of-function with viral readout and innate immune readout, single lab, multiple approaches","pmids":["28821586"],"is_preprint":false},{"year":2011,"finding":"Ku70 accumulates at DSBs immediately after irradiation in living epithelial cells. Three domains—α/β, DNA-binding, and Ku80-binding—but not the SAP domain, are required for early accumulation at DSBs. Leucine 385 in the Ku80-binding domain is required for DSB localization. Accumulation of XRCC4 and XLF at DSBs depends on Ku70 presence, but Artemis accumulation does not.","method":"EGFP-Ku70 domain deletion mutants; live-cell imaging after laser irradiation; domain truncation and point mutagenesis; XRCC4/XLF/Artemis foci analysis in Ku70-depleted cells","journal":"Experimental cell research","confidence":"High","confidence_rationale":"Tier 2 / Strong — live imaging with multiple domain mutants and functional epistasis for downstream NHEJ factors","pmids":["21820429"],"is_preprint":false},{"year":2021,"finding":"Ku suppresses alternative end-joining (A-EJ) in G1-arrested progenitor B cells. In Lig4-deficient G1-arrested progenitor B cells, deletion of Ku70 increases DSB rejoining and translocation, demonstrating Ku70 actively blocks A-EJ of RAG-, Cas9-, and zinc-finger nuclease-generated DSBs in G1 phase.","method":"Genetic epistasis using Lig4-deficient and Ku70/Lig4 double-deficient G1-arrested progenitor B cell lines; translocation assays; V(D)J recombination assays; Cas9 and ZFN-generated DSB rejoining","journal":"PNAS","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic epistasis with multiple endonucleases and multiple phenotypic readouts in defined cell lines","pmids":["34006647"],"is_preprint":false},{"year":2019,"finding":"Ku70 directly interacts with HIV-1 integrase via its C-terminus (IN aa 230–288 binding to Ku70 aa 1–430); this interaction recruits DNA-PK to the site of HIV-1 post-integrational DNA gap repair. Pseudoviruses with Ku70-binding-defective IN are defective in gap repair, and NHEJ pathway disruption by Ku70/Ku80/DNA-PKcs KO or inhibition reduces HIV-1 infectivity in a Ku70-binding-dependent manner.","method":"HIV pseudovirus with mutant IN; CRISPR/Cas9 KO of Ku70/Ku80/DNA-PKcs; qPCR gap-repair assay; HIV infectivity measurement in primary PBMCs and cell lines","journal":"Retrovirology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — CRISPR KO, viral mutagenesis, biochemical gap-repair assay, and primary cell confirmation; multiple orthogonal methods","pmids":["31690330"],"is_preprint":false},{"year":2012,"finding":"CREB-binding protein (CBP) acetylates Ku70 in the nucleus after ionizing radiation in neuroblastoma cells, and this nuclear acetylation plays an inhibitory role in DNA repair. Cytoplasmic Ku70 redistributes to the nucleus following irradiation. Depleting CBP reduces Ku70 acetylation and enhances DNA repair activity.","method":"CBP depletion; IR treatment; Ku70 acetylation measurement; DNA repair assay; nuclear/cytoplasmic fractionation","journal":"Molecular cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — acetylation-repair coupling shown by CBP depletion and functional DNA repair assay, single lab","pmids":["23223795"],"is_preprint":false},{"year":2016,"finding":"LSD1 and SIRT1 competitively bind the core domain of Ku70 on DNA damage foci. The Ku70 SAP/C-terminal motif suppresses LSD1 binding. SIRT1 promotes NHEJ repair and mutation acquisition while LSD1 has the opposite effect; SIRT1 maintains H4K16 acetylation and open chromatin for repair. SAP-deleted Ku70 compromises BCR-ABL mutation acquisition.","method":"Co-immunoprecipitation; chromatin immunoprecipitation at global and locus-specific (ABL) levels; Ku70 domain mutagenesis; BCR-ABL mutation acquisition assay","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP, ChIP, and mutagenesis identifying competing binding domain, single lab","pmids":["27384990"],"is_preprint":false},{"year":2024,"finding":"Ku70 dynamically competes with TEAD4 for binding to YAP, limiting YAP transcriptional activity. Loss of Ku70 enhances YAP-TEAD4 interaction, which drives SMURF2-mediated ubiquitin-proteasome degradation of PARP1, increasing genome instability and tumorigenesis in colon cancer and HCC.","method":"Co-immunoprecipitation; Ku70 depletion; in vivo tumor models; ubiquitination assay; patient HCC sample analysis","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP competition, loss-of-function in vivo, ubiquitination assay, single lab with multiple methods","pmids":["38862269"],"is_preprint":false},{"year":2022,"finding":"Ku70 (XRCC6) directly interacts with the HBoV1 non-structural protein NP1, with a high-affinity KD of ~95 nM. The Ku70 binding domain on NP1 maps to Ku70 aa 266–439. Dominant-negative disruption of Ku70-NP1 interaction impairs HBoV1 DNA replication both in vitro and in HAE-ALI cultures.","method":"Affinity purification; direct binding assay (KD measurement); domain mapping; dominant-negative disruption; viral DNA replication assay in HAE-ALI cultures","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — quantitative affinity measurement, domain mapping, and functional viral replication assay, single lab","pmids":["35653410"],"is_preprint":false},{"year":2021,"finding":"HMGB1 extracellular signaling activates PKCα via TLR4, which phosphorylates Ku70 at Ser77/78. This phosphorylation prevents Ku70-DNA interaction and blocks Ku70 accumulation at DSB foci, impairing DNA repair and causing transcriptional repression-induced atypical cell death (TRIAD) in Alzheimer's disease neurons. Anti-HMGB1 antibody treatment reduces neuronal DSBs and ameliorates cognitive symptoms in AD mice.","method":"Phosphoproteome analysis of AD postmortem brains; site-specific phosphomutant analysis; Ku70-DNA binding assay; foci immunofluorescence; anti-HMGB1 antibody treatment in AD mouse model; behavioral assays","journal":"Communications biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — phosphoproteomics in human tissue, biochemical DNA binding assay, mutagenesis, in vivo rescue with antibody, multiple orthogonal methods","pmids":["34635772"],"is_preprint":false},{"year":2009,"finding":"Ku70 possesses a deubiquitylase (DUB) enzymatic activity on Bax, removing ubiquitin from Bax to prevent its proteasomal degradation. This dual role (sequestration and deubiquitylation of Bax) gives Ku70 both anti-apoptotic (preventing mitochondrial Bax translocation) and pro-apoptotic (blocking Bax degradation) functions.","method":"Deubiquitylation assay with Ku70 and ubiquitinated Bax; co-immunoprecipitation","journal":"Cell cycle","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — enzymatic DUB activity demonstrated in vitro, single lab, single method described in abstract","pmids":["19448404"],"is_preprint":false},{"year":2010,"finding":"The 55 kDa isoform of CDK9 (but not the 42 kDa isoform) specifically associates with Ku70. shRNA depletion of the 55K CDK9 induces apoptosis and DSBs, and rescue with an shRNA-resistant 55K CDK9 reverses these phenotypes, suggesting the 55K CDK9 may function in DSB repair through Ku70.","method":"Co-immunoprecipitation (isoform-specific); shRNA knockdown of 55K CDK9; apoptosis and DSB quantification; rescue experiment","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single co-IP for isoform specificity, functional link to Ku70 is indirect, single lab","pmids":["20493174"],"is_preprint":false},{"year":2014,"finding":"SMAR1 interacts with Ku70 and coordinates with HDAC6 to maintain Ku70 in a deacetylated state. SMAR1 knockdown results in enhanced Ku70 acetylation, impaired chromatin recruitment of Ku70, and increased apoptosis. IR induces SMAR1 redistribution as nuclear foci via ATM-mediated phosphorylation at Ser370. Deacetylated Ku70 (facilitated by SMAR1) maintains its interaction with Bax to prevent mitochondrial translocation.","method":"Co-immunoprecipitation; SMAR1 knockdown; Ku70 acetylation assay; chromatin fractionation; immunofluorescence foci analysis; phosphorylation site mapping","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP, functional knockdown with multiple phenotypic readouts, single lab","pmids":["25299772"],"is_preprint":false},{"year":2016,"finding":"EAF2 (and EAF1) are required for the recruitment and retention of Ku70/Ku80 to DNA damage sites and play a functional role in NHEJ. EAF2 knockdown sensitizes prostate cancer cells and mouse prostate to DNA damage, and blocks androgen repression of DNA damage markers.","method":"EAF2 knockdown; γH2AX marker analysis; Ku70/Ku80 foci recruitment assay; NHEJ reporter assay; EAF2 KO mouse prostate irradiation","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro knockdown with Ku70/80 foci assay, NHEJ assay, and in vivo KO mouse, single lab","pmids":["27721405"],"is_preprint":false},{"year":2012,"finding":"Caveolin-1 is a novel Ku70-binding protein; the scaffolding domain of caveolin-1 (aa 82–101) binds the caveolin-binding domain (CBD) of Ku70 (aa 471–478). Caveolin-1 binding to Ku70 inhibits chemotherapeutic drug-induced Bax release from Ku70 and prevents Bax mitochondrial translocation and apoptosis. A Ku70 mutant unable to bind caveolin-1 (Ku70 Φ→A) does not suppress Ku70/Bax dissociation.","method":"In vitro binding assay (domain mapping); co-immunoprecipitation; Ku70 point mutagenesis; caveolin-1 knockdown; apoptosis/Bax assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro domain mapping, co-IP, and mutagenesis with functional apoptosis readout, single lab","pmids":["22745744"],"is_preprint":false},{"year":2016,"finding":"Ku70 binds double-stranded DNA and hairpin RNA through two distinct binding sites: the C-terminal region including the SAP domain recognizes dsDNA, while a separate site (aa 251–438) mediates hairpin RNA binding. Unlike the Ku heterodimer, monomeric Ku70 can interact with closed circular DNA.","method":"Recombinant Ku70 truncation mutants expressed in E. coli; nucleic acid binding assays with diverse substrates; surface plasmon resonance or equivalent binding assays","journal":"Biochimie","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical assay with systematic truncation mutants identifying two distinct binding sites, single lab","pmids":["27825805"],"is_preprint":false},{"year":2020,"finding":"The Ku70 C-terminal SAP domain is required for stable association of Ku70/80 to DNA ends in the absence of DNA-PKcs, but this requirement is abrogated in the DNA-PK holocomplex. Ku80 C-terminal extension contributes to DNA-PK complex stability but is not absolutely required for its formation. FRET assay with ECFP-Ku70/EYFP-Ku80 confirmed that DNA-PK phosphorylation status influences holocomplex stability.","method":"FRET assay with fluorescently tagged Ku70/80; surface plasmon resonance; SAP domain deletion mutagenesis; Ku80 C-terminal extension deletion; DNA-PK complex formation assays","journal":"International journal of molecular sciences","confidence":"High","confidence_rationale":"Tier 1 / Moderate — FRET quantitative binding assay validated against SPR, domain mutagenesis, single lab with two orthogonal biophysical methods","pmids":["32937838"],"is_preprint":false}],"current_model":"XRCC6/Ku70 is a multifunctional protein that, as a heterodimer with Ku80, binds DNA double-strand break ends via its C-terminal domain (aa 254–609) to initiate classical NHEJ repair by recruiting DNA-PKcs, XRCC4/Ligase IV, and other NHEJ factors; its acetylation status—regulated by acetyltransferases (CBP, PCAF), sirtuins (SIRT1, SIRT6), and HDAC6, and modulated by interactors such as SET/TAF-Iβ and SMAR1—controls both its nuclear DNA repair activity and its cytoplasmic function of sequestering pro-apoptotic Bax (the latter also involving a deubiquitylase activity on Bax); Ku70 additionally acts as a cytosolic DNA sensor that translocates to the cytoplasm upon DNA stimulation to induce IFN-λ1 via STING, serves as an entry receptor for Rickettsia conorii, regulates transcription (including as a BRG1-interacting partner for nuclear receptor activation and as a repressor of Apaf1), modulates ATM/ATR signaling at DSBs, interacts with telomerase RNA (hTR), HIV-1 integrase, RAG1, and FOXO4, and suppresses alternative end-joining in G1-phase cells."},"narrative":{"mechanistic_narrative":"XRCC6/Ku70 is the DNA end-binding subunit of the Ku70/Ku80 heterodimer that initiates classical non-homologous end joining (NHEJ) and is essential in vivo for double-strand break (DSB) repair, V(D)J recombination, and immunoglobulin class-switch recombination [PMID:9390689, PMID:9362500, PMID:9625768]. Heterodimerization with Ku80 must precede DNA binding, with the Ku70 C-terminal domain (aa 254–609) mediating DNA end recognition and a core region (aa 439–609) directing Ku80 assembly [PMID:9362500, PMID:8756676]; structural mapping of the heterodimer free, DNA-bound, and DNA-PKcs-bound defines the conformational basis of end recognition [PMID:17159921]. Upon irradiation Ku70 accumulates rapidly at breaks through its α/β, DNA-binding, and Ku80-binding domains, and this recruitment is required for downstream loading of XRCC4 and XLF [PMID:21820429]; the SAP domain stabilizes Ku70/80 on DNA ends in the absence of DNA-PKcs but is dispensable once the DNA-PK holocomplex forms [PMID:32937838]. Ku70 enforces repair-pathway choice by suppressing alternative end-joining in G1-phase cells [PMID:34006647] and is antagonized by the Fanconi anemia effector FANCD2, which diverts breaks toward homologous recombination [PMID:20538911]. NHEJ activity is tuned by post-translational modification: acetylation by CBP/PCAF is inhibitory and is reversed by SIRT1, while methylation of Ku70 by SMYD2 promotes Ku70/Ku80/DNA-PKcs recruitment, with loss of SMYD2 driving cytosolic DNA accumulation and cGAS-STING activation [PMID:17334224, PMID:23223795, PMID:37315132]; recruitment is further gated by acetylation-controlling interactors SET/TAF-Iβ and SMAR1 [PMID:24305947, PMID:25299772]. Beyond repair, Ku70 has cytoplasmic and regulatory functions: it sequesters and deubiquitylates pro-apoptotic Bax in an acetylation-dependent manner controlled by HDAC6 and SIRT6 [PMID:21847364, PMID:19448404, PMID:28238784], acts as a cytosolic DNA/ssDNA sensor that translocates to the cytoplasm to induce STING-dependent IFN-λ1 [PMID:33548066, PMID:28821586], regulates transcription as a BRG1-associated factor for glucocorticoid-receptor activation and as a repressor of Apaf1 [PMID:26055322, PMID:20966962], and is exploited by pathogens as a cell-surface receptor for Rickettsia conorii and a binding partner of HIV-1 integrase and HBoV1 NP1 [PMID:16360032, PMID:21454661, PMID:31690330, PMID:35653410]. Ku70 dysfunction is mechanistically linked to neurodegeneration: mutant huntingtin binds Ku70 and impairs NHEJ, and Ku70 re-expression rescues Huntington's disease phenotypes in mice [PMID:20439996, PMID:22096569], while HMGB1/PKCα-mediated phosphorylation of Ku70 at Ser77/78 blocks its DNA binding and drives neuronal cell death in Alzheimer's models [PMID:34635772].","teleology":[{"year":1997,"claim":"Established that Ku70 is an essential, non-redundant in vivo component of NHEJ and antigen-receptor gene assembly, defining the pathway it serves.","evidence":"Ku70 knockout mice with IR sensitivity and V(D)J recombination assays, plus class-switch recombination epistasis","pmids":["9390689","9625768"],"confidence":"High","gaps":["Did not resolve which molecular step of break sealing requires Ku70","Cytoplasmic and non-repair roles not addressed"]},{"year":1997,"claim":"Defined the domain architecture underlying Ku function, showing heterodimer assembly must precede DNA end binding and mapping the DNA-binding and Ku80-interaction regions.","evidence":"Truncation/chimera mutagenesis, Ku70-/- ES cell complementation, and DNA end-binding assays with purified subunits","pmids":["9362500","8756676"],"confidence":"High","gaps":["Atomic-resolution conformational changes not resolved at this stage","Separability of DNA-PK activation from end-binding only partially mapped"]},{"year":2006,"claim":"Provided a structural model of the Ku70/80 heterodimer recognizing DNA and engaging DNA-PKcs, linking domain maps to physical conformational states.","evidence":"Single-particle EM 3D reconstruction of free, DNA-bound, and DNA-PKcs-bound Ku70/80 (with prior IP6 conformational mapping)","pmids":["17159921","11953323"],"confidence":"High","gaps":["25 Å resolution insufficient for side-chain detail","Functional consequence of IP6-induced conformational change not fully defined"]},{"year":2011,"claim":"Resolved the recruitment hierarchy at breaks, showing Ku70 accumulates first and is required to load downstream NHEJ factors.","evidence":"Live-cell imaging of EGFP-Ku70 domain mutants after laser irradiation with XRCC4/XLF/Artemis foci epistasis","pmids":["21820429"],"confidence":"High","gaps":["Why Artemis recruitment is Ku70-independent unexplained","Role of individual residues beyond Leu385 not exhaustively tested"]},{"year":2020,"claim":"Clarified how the Ku70 SAP domain and DNA-PK assembly state govern stable retention on DNA ends.","evidence":"FRET and SPR with SAP and Ku80 C-terminal deletions in DNA-PK complex formation assays","pmids":["32937838"],"confidence":"High","gaps":["In vivo relevance of holocomplex stability differences not tested","Single biophysical system"]},{"year":2021,"claim":"Showed Ku70 actively enforces repair-pathway choice by suppressing alternative end-joining in G1, distinguishing its barrier function from canonical ligation.","evidence":"Genetic epistasis in Lig4-deficient and Ku70/Lig4 double-deficient G1 progenitor B cells across RAG-, Cas9-, and ZFN-induced breaks","pmids":["34006647"],"confidence":"High","gaps":["Mechanism by which Ku occludes A-EJ factors not defined","Cell-cycle phase specificity not mechanistically explained"]},{"year":2030,"claim":"Mapped how Fanconi anemia signaling counteracts Ku70 to channel breaks toward homologous recombination.","evidence":"FANCC/Ku70 double-knockout epistasis with ICL sensitivity, HR frequency, and in vitro FANCD2/Ku70 biochemistry","pmids":["20538911"],"confidence":"High","gaps":["Molecular nature of FANCD2 end-modification not fully defined","Generalizability beyond ICL-induced breaks unclear"]},{"year":2023,"claim":"Established acetylation, deacetylation, and methylation as the regulatory code controlling Ku70 repair activity and its recruitment to breaks.","evidence":"SIRT1/CBP acetylation-repair coupling, SET/TAF-Iβ and SMAR1 acetylation gating, and SMYD2 methylation site mapping with NHEJ and cGAS-STING readouts","pmids":["17334224","23223795","24305947","25299772","37315132"],"confidence":"Medium","gaps":["Interplay/ordering of competing modifications not resolved","Several modifier relationships rest on single-lab evidence"]},{"year":2017,"claim":"Defined Ku70's cytoplasmic anti-apoptotic function through acetylation-dependent Bax sequestration and deubiquitylation, governed by HDAC6 and SIRT6.","evidence":"HDAC6/SIRT6 co-IP and knockdown, K542 mutagenesis, Bax deubiquitylation assay, and mitochondrial translocation/apoptosis readouts","pmids":["21847364","19448404","28238784","22745744"],"confidence":"Medium","gaps":["Catalytic basis of Ku70 DUB activity on Bax not structurally defined","Balance between Bax sequestration and stabilization context-dependent and unresolved"]},{"year":2021,"claim":"Identified a non-repair role for Ku70 as a cytosolic DNA/ssDNA sensor driving STING-dependent type III interferon induction.","evidence":"Leptomycin B nuclear-export block, IFN-λ1 reporter, ssDNA90 binding, and viral infection (HSV-1, HTLV-1) with STING association","pmids":["33548066","28821586"],"confidence":"Medium","gaps":["Why Ku70 selectively induces IFN-λ1 but not IFN-α/β unexplained","Direct STING-engagement mechanism not biochemically resolved"]},{"year":2024,"claim":"Extended Ku70 into transcriptional and tumor-suppressive control via BRG1-dependent nuclear receptor activation, Apaf1 repression, and YAP-TEAD4 competition.","evidence":"Co-IP/ChIP for BRG1 and Apaf1 promoters, and Ku70-YAP competition with in vivo tumor and ubiquitination assays","pmids":["26055322","20966962","38862269"],"confidence":"Medium","gaps":["Whether these transcriptional roles require DNA-end binding unclear","Single-lab evidence for each axis"]},{"year":2021,"claim":"Connected Ku70 dysfunction to neurodegeneration, showing impaired Ku70-mediated NHEJ contributes to Huntington's and Alzheimer's pathology.","evidence":"Mutant huntingtin co-IP and Ku70 rescue in R6/2 mice; HMGB1/PKCα phosphorylation of Ku70 Ser77/78 with anti-HMGB1 rescue in AD mice","pmids":["20439996","22096569","34635772"],"confidence":"High","gaps":["Causal contribution of Ku70 loss versus broader DSB burden not isolated","No reported XRCC6 Mendelian disease mutation in the corpus"]},{"year":null,"claim":"How the many regulatory inputs (acetylation, methylation, phosphorylation, partner binding) are integrated to switch Ku70 between nuclear repair, cytoplasmic apoptotic control, immune sensing, and transcription remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking modification state to subcellular partitioning","Many partner interactions validated only by single-lab co-IP without reciprocal structural validation"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[1,2,33,46,47]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[10,46]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[19,41]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[26,28]},{"term_id":"GO:0001618","term_label":"virus receptor activity","supporting_discovery_ids":[6]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[31,32]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[8,45]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[17,33,36]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[8,31,36]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[6]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[11,37,43]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[0,1,33,34]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[3,31,32]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[8,26,41]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[26,28]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[13,40]}],"complexes":["Ku70/Ku80 heterodimer","DNA-PK holocomplex"],"partners":["XRCC5","PRKDC","SIRT1","HDAC6","BAX","FOXO4","SMARCA4","FANCD2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P12956","full_name":"DNA repair protein Ku70","aliases":["5'-deoxyribose-5-phosphate lyase Ku70","5'-dRP lyase Ku70","70 kDa subunit of Ku antigen","ATP-dependent DNA helicase 2 subunit 1","ATP-dependent DNA helicase II 70 kDa subunit","CTC box-binding factor 75 kDa subunit","CTC75","CTCBF","DNA repair protein XRCC6","Lupus Ku autoantigen protein p70","Ku70","Thyroid-lupus autoantigen","TLAA","X-ray repair complementing defective repair in Chinese hamster cells 6","X-ray repair cross-complementing protein 6"],"length_aa":609,"mass_kda":69.8,"function":"DNA-binding protein critical for the DNA damage response, specifically in repairing double-strand breaks (DSBs) via the classical non-homologous end joining (NHEJ) pathway. It forms a heterodimer with XRCC5 (Ku80), creating the Ku70:Ku80 heterodimer (Ku complex), which serves as a DNA end-binding complex. It primarily binds DSBs and recruits essential repair factors, assembling the core long-range NHEJ complex to facilitate the alignment and ligation of broken DNA ends (PubMed:11493912, PubMed:20493174, PubMed:33854234, PubMed:34352203, PubMed:9742108). This pathway ensures the rapid repair of cytotoxic and mutagenic DSBs and contributes to the generation of diversity in T-cell receptors and antibodies through mechanisms such as V(D)J recombination (PubMed:9742108). Likely acts as a 5'-deoxyribose-5-phosphate lyase (5'-dRP lyase), catalyzing the beta-elimination of the 5'-deoxyribose-5-phosphate at abasic sites near DSBs. This activity cleans the termini of abasic sites, a common form of nucleotide damage, preparing broken ends for ligation (PubMed:20383123). It may also possess 3'-5' DNA helicase activity, although this has not been confirmed in vivo, and its physiological significance remains unclear (PubMed:7957065). Beyond DNA repair, the protein contributes to telomere maintenance (PubMed:29490055). It is also implicated in transcriptional regulation, acting as a cofactor for various transcription factors (PubMed:12145306, PubMed:8621488). It plays a role in the regulation of DNA virus-mediated innate immune response by assembling into the HDP-RNP complex, a complex that serves as a platform for IRF3 phosphorylation and subsequent innate immune response activation through the cGAS-STING pathway (PubMed:28712728). Can also bind RNAs and recruits PRKDC to a wide range of cellular RNAs, including the U3 small nucleolar RNA, playing a role in the biogenesis of ribosomal RNAs (PubMed:32103174). Additionally, it negatively regulates apoptosis by interacting with BAX, sequestering it from the mitochondria, and may possess deubiquitination activity targeting BAX (PubMed:15023334, PubMed:18362350, PubMed:35545041)","subcellular_location":"Nucleus; Chromosome; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P12956/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/XRCC6","classification":"Common Essential","n_dependent_lines":1207,"n_total_lines":1208,"dependency_fraction":0.9991721854304636},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"PRKDC","stoichiometry":10.0},{"gene":"H2AFZ","stoichiometry":4.0},{"gene":"PSMD6","stoichiometry":4.0},{"gene":"SSRP1","stoichiometry":4.0},{"gene":"TOP1","stoichiometry":4.0},{"gene":"ATG13","stoichiometry":0.2},{"gene":"CAPZB","stoichiometry":0.2},{"gene":"CBX1","stoichiometry":0.2},{"gene":"EMC9","stoichiometry":0.2},{"gene":"HIST2H2BE","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/XRCC6","total_profiled":1310},"omim":[{"mim_id":"621451","title":"SMALL NUCLEOLAR RNA HOST GENE 12; SNHG12","url":"https://www.omim.org/entry/621451"},{"mim_id":"621176","title":"MYC-INDUCIBLE LONG NONCODING RNA INACTIVATING p53; MILIP","url":"https://www.omim.org/entry/621176"},{"mim_id":"620878","title":"INTEGRATOR COMPLEX SUBUNIT 14; INTS14","url":"https://www.omim.org/entry/620878"},{"mim_id":"620563","title":"UBIQUITIN-SPECIFIC PEPTIDASE 50; USP50","url":"https://www.omim.org/entry/620563"},{"mim_id":"619760","title":"ATP23 METALLOPEPTIDASE AND ATP SYNTHASE ASSEMBLY FACTOR HOMOLOG; ATP23","url":"https://www.omim.org/entry/619760"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/XRCC6"},"hgnc":{"alias_symbol":["D22S731","D22S671","KU70","ML8"],"prev_symbol":["G22P1"]},"alphafold":{"accession":"P12956","domains":[{"cath_id":"3.40.50.410","chopping":"31-249","consensus_level":"high","plddt":87.0081,"start":31,"end":249},{"cath_id":"2.40.290.10","chopping":"255-279_341-441","consensus_level":"medium","plddt":93.8578,"start":255,"end":441},{"cath_id":"1.10.1600.10","chopping":"455-527","consensus_level":"high","plddt":90.8626,"start":455,"end":527},{"cath_id":"1.10.720.30","chopping":"560-607","consensus_level":"high","plddt":76.7996,"start":560,"end":607}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P12956","model_url":"https://alphafold.ebi.ac.uk/files/AF-P12956-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P12956-F1-predicted_aligned_error_v6.png","plddt_mean":84.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=XRCC6","jax_strain_url":"https://www.jax.org/strain/search?query=XRCC6"},"sequence":{"accession":"P12956","fasta_url":"https://rest.uniprot.org/uniprotkb/P12956.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P12956/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P12956"}},"corpus_meta":[{"pmid":"9390689","id":"PMC_9390689","title":"Growth 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Loss-of-function (Ku70-/- mice) showed radiation sensitivity, premature senescence, and severe impairment of V(D)J coding and signal sequence joining, establishing Ku70 as an essential component of the NHEJ pathway in vivo.\",\n      \"method\": \"Ku70 knockout mouse model; cellular IR sensitivity assays; V(D)J recombination assays\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockout model with multiple defined cellular and molecular phenotypes, replicated across multiple subsequent studies\",\n      \"pmids\": [\"9390689\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Ku70 requires heterodimerization with Ku80 and its C-terminal DNA-binding domain (aa 254–609) for DSB repair and DNA end-binding. A core region (aa 439–609) mediates Ku80 heterodimerization. Ku70's roles in DNA-PK activation and IR repair are separable by mutagenesis.\",\n      \"method\": \"Truncation and chimera mutagenesis of Ku70; complementation of Ku70-/- ES cells; IR sensitivity assay; DNA end-binding assay; DNA-PK activity assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro mutagenesis with functional reconstitution and multiple orthogonal assays in a single rigorous study\",\n      \"pmids\": [\"9362500\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"The C-terminal 20 kDa of Ku70 and C-terminal 32 kDa of Ku86 mediate subunit–subunit interaction; the C-terminal 40 kDa of Ku70 (aa 254–609) is required for DNA end-binding. Full-length individual subunits are inactive for DNA binding; heterodimer assembly must precede DNA binding.\",\n      \"method\": \"Genetic and biochemical domain-deletion analysis; DNA end-binding assays with purified proteins\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with systematic domain deletion, multiple binding assays\",\n      \"pmids\": [\"8756676\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Ku70 is required for immunoglobulin heavy chain class switch recombination (CSR). K70T/HL B cells induced with CSR-stimulating agents showed intact germline CH transcription but completely failed to undergo CSR and underwent cell death, placing Ku70 downstream of CSR signaling but essential for the DNA rearrangement step.\",\n      \"method\": \"Genetic epistasis using Ku70-/- mice carrying rearranged Ig transgenes; in vitro CSR assays; serum Ig measurement\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic epistasis with defined phenotypic readout, multiple lines of evidence\",\n      \"pmids\": [\"9625768\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Inositol hexakisphosphate (IP6) binds specifically to the Ku70/80 heterodimer (not to DNA-PKcs alone), and IP6 binding alters the conformation of Ku70/80 as detected by proteolysis mapping. The yeast Ku70/80 homolog does not bind IP6, indicating this is a mammalian-specific function.\",\n      \"method\": \"Proteolysis mapping of Ku70/80 with and without IP6; binding competition assays; comparison with yeast Ku homologs\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct biochemical binding assay with conformational read-out, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"11953323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Full-length 3D structure of human Ku70/Ku80 heterodimer resolved at 25 Å by single-particle electron microscopy, alone and in complex with DNA. C-terminal domains of both subunits were mapped; conformational changes upon DNA and DNA-PKcs binding were defined, providing a structural model for DNA recognition during NHEJ.\",\n      \"method\": \"Single-particle electron microscopy; 3D reconstruction; structural comparison of Ku70/80 free, DNA-bound, and DNA-PKcs-bound states\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — structural determination by EM with functional domain mapping and conformational analysis\",\n      \"pmids\": [\"17159921\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Ku70 is a mammalian cell-surface receptor for Rickettsia conorii internalization. Ku70 is recruited to bacterial entry sites; cholesterol-enriched microdomains containing Ku70 are required for invasion. R. conorii infection stimulates Ku70 ubiquitination, and the ubiquitin ligase c-Cbl is recruited to entry foci and mediates Ku70 ubiquitination. The rickettsial surface protein rOmpB was identified as the Ku70 ligand by affinity chromatography.\",\n      \"method\": \"siRNA knockdown; immunofluorescence/confocal colocalization; affinity chromatography; co-immunoprecipitation; bacterial invasion assay\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (affinity chromatography, siRNA, colocalization, ubiquitination assay) in a single rigorous study\",\n      \"pmids\": [\"16360032\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SIRT1 physically complexes with Ku70, deacetylates it, and thereby enhances DNA repair capacity after radiation. A catalytically inactive SIRT1 dominant-negative mutant failed to deacetylate Ku70 or enhance repair, establishing a writer/eraser relationship between SIRT1 and Ku70 acetylation in DNA repair.\",\n      \"method\": \"Co-immunoprecipitation; SIRT1 overexpression and siRNA knockdown; DNA strand-break repair assay; dominant-negative SIRT1 mutagenesis\",\n      \"journal\": \"Experimental & molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP and functional rescue with dominant-negative, single lab\",\n      \"pmids\": [\"17334224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"HDAC6 binds Ku70 and Bax in the cytoplasm of neuroblastoma cells and maintains Ku70 in a deacetylated state. Knockdown of HDAC6 or use of an HDAC6-specific inhibitor triggers Ku70 acetylation, releases Bax from Ku70, and induces Bax-dependent apoptosis, identifying HDAC6 as a key deacetylase (eraser) for cytoplasmic Ku70.\",\n      \"method\": \"Co-immunoprecipitation; HDAC6 siRNA knockdown; HDAC6-specific inhibitor (Tubacin); apoptosis assays\",\n      \"journal\": \"Neoplasia\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP, genetic knockdown, and pharmacological inhibition all converging on same mechanism; multiple orthogonal methods\",\n      \"pmids\": [\"21847364\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Ku70 acetylation (mediated by CBP/PCAF) disrupts its interaction with FLIP, triggering FLIP polyubiquitination and proteasomal degradation. HDAC inhibitor (SAHA/Vorinostat) enhances Ku70 acetylation via HDAC6 inhibition to destabilize FLIP and induce caspase-8-dependent apoptosis in colorectal cancer models.\",\n      \"method\": \"Co-immunoprecipitation; HDAC inhibitor treatment; ubiquitination assays; in vitro and in vivo colorectal cancer models; caspase activation assays\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods including co-IP, ubiquitination assay, in vivo model, and pharmacological inhibition in single rigorous study\",\n      \"pmids\": [\"22322857\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Human Ku70/80 interacts directly with hTR, the RNA component of human telomerase, specifically with a 47 nt region at the 3' end of hTR. This interaction is independent of hTERT, as shown by immunoprecipitation/RT-PCR in hTERT-deficient cell lines, suggesting a conserved role for Ku in telomere maintenance via telomerase RNA interaction.\",\n      \"method\": \"In vitro binding assay; immunoprecipitation/RT-PCR in hTERT-deficient cell lines; mapping of interaction domain on hTR\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and cellular interaction demonstrated, single lab, two orthogonal methods\",\n      \"pmids\": [\"15824061\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Ku70 interacts with heterochromatin protein 1alpha (HP1alpha) via its Leu-Ser repeat domain (aa 200–385), and HP1alpha's chromo shadow domain mediates the interaction. This was confirmed by GST pull-down with recombinant proteins and co-immunoprecipitation in HeLa cells. The interaction is pH-sensitive and Ku80 does not interact with HP1alpha directly.\",\n      \"method\": \"Yeast two-hybrid; GST pull-down with recombinant proteins; co-immunoprecipitation in HeLa cells; confocal colocalization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — GST pull-down (in vitro reconstitution) and co-IP in cells, single lab, two orthogonal methods\",\n      \"pmids\": [\"11112778\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In the Fanconi anemia pathway, FANCD2 (a downstream FA effector) antagonizes Ku70 activity by modifying free DNA ends, thereby diverting DSB repair from NHEJ toward homologous recombination. Disruption of both FANCC and Ku70 suppresses ICL sensitivity, diminishes chromosome breaks, and reverses defective HR, establishing a genetic epistasis where the FA pathway acts upstream of Ku70 to channel repair pathway choice.\",\n      \"method\": \"Genetic epistasis (FANCC/Ku70 double knockout); ICL sensitivity assays; HR frequency measurement; in vitro biochemical assay with purified FANCD2 and Ku70\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — genetic epistasis combined with in vitro biochemical reconstitution, multiple orthogonal phenotypic readouts\",\n      \"pmids\": [\"20538911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Mutant huntingtin (Htt) directly interacts with Ku70 and impairs DNA-PK function in NHEJ, causing accumulation of DSBs in neurons. Exogenous Ku70 expression rescues abnormal behavior and pathological phenotypes in R6/2 HD mice, establishing Ku70 as a critical mediator of DNA repair dysfunction in Huntington's disease pathology.\",\n      \"method\": \"Co-immunoprecipitation; DNA-PK activity assay; γH2AX foci analysis; R6/2 mouse rescue with Ku70 overexpression; behavioral assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — co-IP, enzymatic assay, and in vivo rescue with multiple phenotypic readouts across labs (replicated in Drosophila, PMID 22096569)\",\n      \"pmids\": [\"20439996\", \"22096569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Ku70/80 modulates ATM-dependent ATR activation during the DSB damage response. In Ku-deficient cells, p53 Ser18 phosphorylation persists via ATM-independent ATR activity at late time points after IR, a pathway not observed in wild-type cells, revealing a novel role for Ku70/80 in suppressing aberrant ATR activation.\",\n      \"method\": \"ATM/Ku70 double-null cell line generation; p53 phosphorylation analysis; ATM and ATR inhibitors; irradiation experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — double-null cell lines with pharmacological inhibitors, single lab, two orthogonal approaches\",\n      \"pmids\": [\"17272272\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"A nuclear CLU/XIP8 protein, induced by low-dose ionizing radiation, co-immunoprecipitates and co-localizes with Ku70/Ku80 in human breast cancer cells. Overexpression of nuclear CLU/XIP8 or its minimal Ku70-binding domain (120 aa C-terminus) reduces cell growth and increases G1 arrest and cell death, identifying clusterin as a Ku70-binding partner that signals cell death.\",\n      \"method\": \"Yeast two-hybrid; co-immunoprecipitation; confocal colocalization; overexpression of CLU/XIP8 and truncation mutants; colony formation assay\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid confirmed by co-IP and colocalization, functional overexpression, single lab\",\n      \"pmids\": [\"10823943\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Granzyme A cleaves Ku70 after Arg301, disrupting Ku complex binding to DNA, thereby facilitating GzmA-mediated caspase-independent cell death. Silencing Ku70 by RNAi increases GzmA-induced DNA damage and cell death, while Ku70 overexpression has the opposite effect, demonstrating Ku70 has antiapoptotic functions beyond DSBR and Bax sequestration.\",\n      \"method\": \"In vitro cleavage assay; Ku70 siRNA knockdown; Ku70 overexpression; CTL/perforin cell death assay; DNA damage quantification\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — identified cleavage site biochemically, with genetic knockdown and overexpression rescue experiments converging on same conclusion\",\n      \"pmids\": [\"16440001\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Ku70 can translocate to the nucleus independently of heterodimerization with Ku80, as shown by nuclear localization of Ku70 mutants lacking Ku80-binding ability and by Ku70 expression in Ku80-deficient hamster xrs-6 cells. Ku70 nuclear localization is mediated by its NLS and does not require DNA-PK autophosphorylation sites.\",\n      \"method\": \"Site-directed mutagenesis of Ku70 NLS and Ku80-binding domains; transfection into Ku80-deficient cells; immunofluorescence localization\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis combined with complementation in Ku80-deficient cells, single lab, two approaches\",\n      \"pmids\": [\"11027597\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Ku70 interacts with FOXO4 via a direct biochemical interaction (Ku70 necessary and sufficient), and sequesters FOXO4 in the nucleus, inhibiting FOXO4-mediated p27(kip1) transcription and cell cycle arrest by >40%. Low oxidative stress increases Ku70-FOXO4 interaction stoichiometry, while higher stress causes dissociation, suggesting a dose-dependent stress-response role for Ku70.\",\n      \"method\": \"Tandem-affinity purification/mass spectrometry; co-immunoprecipitation; luciferase reporter assay; flow cytometry; Ku70-/- ES cells; immunofluorescence\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — unbiased proteomics identification confirmed by multiple orthogonal functional assays including knockout rescue\",\n      \"pmids\": [\"20570964\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Ku70 interacts directly with HIV-1 integrase (IN) via the N-terminal part of Ku70 (aa 1–430), protecting IN from Lys48-linked polyubiquitination and proteasomal degradation. Ku70 can deubiquitinate IN through their interaction. This interaction is independent of Ku70/80 heterodimerization, and Ku70 is incorporated into progeny virus in an IN-dependent manner; Ku70 knockdown disrupts HIV-1 replication.\",\n      \"method\": \"Co-immunoprecipitation; mutagenesis mapping; ubiquitination assays; Ku70 siRNA knockdown; HIV infectivity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro binding domain mapping, ubiquitination/deubiquitination biochemical assay, siRNA knockdown with viral infectivity readout\",\n      \"pmids\": [\"21454661\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"MSH6 is a novel Ku70-interacting protein; the Ku70-MSH6 association is enhanced by DSB-inducing agents (NCS, IR). MSH6-deficient cells accumulate persistent DSBs and display impaired NHEJ, which is rescued by MSH6 overexpression, linking the mismatch repair protein MSH6 to NHEJ via Ku70.\",\n      \"method\": \"Yeast two-hybrid; co-immunoprecipitation; γH2AX foci assay; comet assay; NHEJ assay; clonogenic survival\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid confirmed by co-IP, functional assay with rescue, single lab\",\n      \"pmids\": [\"21075794\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Par3, a cell polarity protein, interacts with Ku70 and Ku80 in the nucleus; this interaction is enhanced by gamma-irradiation. Par3 regulates DNA-PK activity (up- and downregulated by overexpression and knockdown, respectively), and Par3-knockdown cells are defective in NHEJ, random integration, and DSB repair, and are radiosensitive.\",\n      \"method\": \"In vitro binding assay; LC-MS/MS; co-immunoprecipitation; DNA-PK activity assay; NHEJ reporter assay; IR sensitivity assay\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — unbiased MS identification confirmed by co-IP, functional assays, single lab, multiple methods\",\n      \"pmids\": [\"17287830\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Ku70 and Ku80 interact with full-length RAG1 as demonstrated by co-immunoprecipitation, providing a biochemical link between the RAG cleavage machinery and the NHEJ repair pathway during V(D)J recombination.\",\n      \"method\": \"Co-immunoprecipitation with full-length RAG1 and Ku70/80\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single co-IP experiment, single lab, no functional follow-up of the specific Ku70-RAG1 interaction\",\n      \"pmids\": [\"18281312\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Ku70/80 and DNA-PKcs modulate RAG-mediated V(D)J cleavage, preferentially inhibiting 12/12 and 23/23 cleavage to increase 12/23 rule specificity. This indicates DNA repair factors are present upstream of cleavage events, not only recruited downstream for repair.\",\n      \"method\": \"Protein fractionation; biochemical cleavage assays with purified Ku70/80 and DNA-PKcs; 12/23 rule reporter assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — biochemical reconstitution assay with purified factors, single lab\",\n      \"pmids\": [\"15123719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"RECQ1 helicase directly interacts with Ku70/80; depletion of RECQ1 reduces end-joining in cell-free extracts. In vitro, RECQ1 binds and unwinds Ku70/80-bound partial duplex DNA, and linear DNA is co-bound by both RECQ1 and Ku70/80, with DNA binding by Ku70/80 modulated by RECQ1.\",\n      \"method\": \"Direct protein interaction assays; cell-free end-joining assay; helicase unwinding assay with Ku70/80-bound substrate; co-binding assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro reconstitution biochemistry, single lab, multiple orthogonal assays\",\n      \"pmids\": [\"23650516\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"DNA-PK-mediated phosphorylation of Ku70 at serine 6 (and Ku80 at S577, S580, T715) occurs in vitro, but these phosphorylation events are not required for NHEJ in vivo: Ku70/80 with S/T→A mutations at these sites fully complemented radiation sensitivity of Ku-negative cells. In vivo phosphorylation at these sites is regulated by a PP2A-like phosphatase and a staurosporine-sensitive kinase, not DNA-PK.\",\n      \"method\": \"Mass spectrometry; phosphospecific antibodies; in vitro kinase assays; S/T→A mutagenesis; complementation of Ku-negative cells with mutant Ku70/80; IR sensitivity assay; pharmacological inhibitors\",\n      \"journal\": \"DNA repair\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — MS site identification, in vitro kinase assay, alanine mutagenesis with in vivo complementation, negative result rigorously established\",\n      \"pmids\": [\"15941674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Ku70/80 binds the Apaf1 promoter repressor element and downregulates Apaf1 transcription. This binding is dynamically modulated upon DNA damage: Ku70/80 initially represses Apaf1 after damage, then dissociates allowing Apaf1 upregulation and apoptosis. This defines a transcriptional regulatory function for Ku70/80 at the apoptosome pathway.\",\n      \"method\": \"Apaf1 promoter mutant analysis; chromatin immunoprecipitation; reporter assays; Ku70/80 knockdown with Apaf1 expression measurement\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — promoter binding established by ChIP and reporter assays, functional knockdown, single lab\",\n      \"pmids\": [\"20966962\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SET/TAF-Iβ (an INHAT subunit) interacts with Ku70/80, inhibiting CBP- and PCAF-mediated acetylation of Ku70 in an INHAT domain-dependent manner. DNA damage by UV disrupts this interaction, releasing Ku70/80 for recruitment to DSB sites. Overexpressed SET/TAF-Iβ inhibits Ku70/80 recruitment to DNA damage foci.\",\n      \"method\": \"Co-immunoprecipitation; in vitro acetylation assay with CBP/PCAF; SET/TAF-Iβ overexpression; immunofluorescence of Ku70/80 at damage foci\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP and in vitro acetylation inhibition assay, functional foci assay, single lab\",\n      \"pmids\": [\"24305947\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Ku70 (XRCC6) directly associates with the HSA/BRK domains of BRG1 (SWI/SNF ATPase). Ku70/86 and components of the TOP2β/PARP1 complex are required for glucocorticoid receptor (GR)-mediated, BRG1-dependent transcriptional activation from endogenous promoters. GR/BRG1-dependent, TOP2β-mediated transient DNA DSBs are required for efficient GR-stimulated transcription.\",\n      \"method\": \"Co-immunoprecipitation; chromatin immunoprecipitation; transcriptional activation assays; BRG1 mutant analysis; Ku70/86 knockdown\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP with domain mapping, ChIP, functional transcription assay, single lab\",\n      \"pmids\": [\"26055322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SIRT6 interacts with Ku70 and deacetylates it at lysine K542. Deacetylation of Ku70 by SIRT6 stabilizes its interaction with Bax, preventing Bax mitochondrial translocation and apoptosis. A K542Q acetylation-mimicking mutation abolishes Ku70-Bax association and reverses SIRT6-mediated apoptosis suppression in hepatocellular carcinoma cells.\",\n      \"method\": \"Co-immunoprecipitation; SIRT6 knockdown; site-directed mutagenesis (K542Q); mitochondrial fractionation; apoptosis assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP, site-specific mutagenesis identifying K542, functional apoptosis assays, single lab\",\n      \"pmids\": [\"28238784\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SMYD2 methyltransferase methylates Ku70 at lysines 74, 516, and 539 in response to DNA damage, increasing recruitment of the Ku70/Ku80/DNA-PKcs complex. SMYD2 knockdown or inhibition impairs NHEJ, causes cytosolic DNA accumulation, and activates the cGAS-STING pathway, triggering anti-tumor CD8+ T-cell responses.\",\n      \"method\": \"Mass spectrometry identification of methylation sites; SMYD2 knockdown/inhibitor (AZ505); ChIP for Ku70 at damage sites; NHEJ assay; cGAS-STING activation measurement; in vivo tumor immunology\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — MS-identified modification sites, biochemical NHEJ assay, in vivo tumor immunology, multiple orthogonal methods in one study\",\n      \"pmids\": [\"37315132\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cytoplasmic translocation of Ku70 (via nuclear export, inhibited by leptomycin B) is required for cytosolic DNA sensing and induction of IFN-λ1 (but not IFN-α or IFN-β) via a STING-dependent signaling pathway. Enhanced cellular acetylation promotes Ku70 cytoplasmic accumulation and IFN-λ1 induction. HSV-1 infection triggers Ku70 cytoplasmic translocation and IFN-λ1 in a strain-dependent manner.\",\n      \"method\": \"Nuclear export inhibitor (leptomycin B); IFN-λ1 reporter assay; DNA transfection; HSV-1 infection; subcellular fractionation; kinetic analysis\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological nuclear export block with IFN induction readout, kinetic analysis, viral infection, single lab\",\n      \"pmids\": [\"33548066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Ku70 senses HTLV-1 reverse transcription intermediate ssDNA90, is induced by HTLV-1 infection, and associates with STING to mediate innate immune responses. Ku70 overexpression inhibited HTLV-1 protein expression while knockdown promoted it. Ku70 interacts with HTLV-1 ssDNA90 and promotes ssDNA-triggered innate immune signaling.\",\n      \"method\": \"HTLV-1 infection; Ku70 overexpression/knockdown; STING co-association; innate immune cytokine measurement; ssDNA90 binding assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain- and loss-of-function with viral readout and innate immune readout, single lab, multiple approaches\",\n      \"pmids\": [\"28821586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Ku70 accumulates at DSBs immediately after irradiation in living epithelial cells. Three domains—α/β, DNA-binding, and Ku80-binding—but not the SAP domain, are required for early accumulation at DSBs. Leucine 385 in the Ku80-binding domain is required for DSB localization. Accumulation of XRCC4 and XLF at DSBs depends on Ku70 presence, but Artemis accumulation does not.\",\n      \"method\": \"EGFP-Ku70 domain deletion mutants; live-cell imaging after laser irradiation; domain truncation and point mutagenesis; XRCC4/XLF/Artemis foci analysis in Ku70-depleted cells\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — live imaging with multiple domain mutants and functional epistasis for downstream NHEJ factors\",\n      \"pmids\": [\"21820429\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Ku suppresses alternative end-joining (A-EJ) in G1-arrested progenitor B cells. In Lig4-deficient G1-arrested progenitor B cells, deletion of Ku70 increases DSB rejoining and translocation, demonstrating Ku70 actively blocks A-EJ of RAG-, Cas9-, and zinc-finger nuclease-generated DSBs in G1 phase.\",\n      \"method\": \"Genetic epistasis using Lig4-deficient and Ku70/Lig4 double-deficient G1-arrested progenitor B cell lines; translocation assays; V(D)J recombination assays; Cas9 and ZFN-generated DSB rejoining\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic epistasis with multiple endonucleases and multiple phenotypic readouts in defined cell lines\",\n      \"pmids\": [\"34006647\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Ku70 directly interacts with HIV-1 integrase via its C-terminus (IN aa 230–288 binding to Ku70 aa 1–430); this interaction recruits DNA-PK to the site of HIV-1 post-integrational DNA gap repair. Pseudoviruses with Ku70-binding-defective IN are defective in gap repair, and NHEJ pathway disruption by Ku70/Ku80/DNA-PKcs KO or inhibition reduces HIV-1 infectivity in a Ku70-binding-dependent manner.\",\n      \"method\": \"HIV pseudovirus with mutant IN; CRISPR/Cas9 KO of Ku70/Ku80/DNA-PKcs; qPCR gap-repair assay; HIV infectivity measurement in primary PBMCs and cell lines\",\n      \"journal\": \"Retrovirology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — CRISPR KO, viral mutagenesis, biochemical gap-repair assay, and primary cell confirmation; multiple orthogonal methods\",\n      \"pmids\": [\"31690330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CREB-binding protein (CBP) acetylates Ku70 in the nucleus after ionizing radiation in neuroblastoma cells, and this nuclear acetylation plays an inhibitory role in DNA repair. Cytoplasmic Ku70 redistributes to the nucleus following irradiation. Depleting CBP reduces Ku70 acetylation and enhances DNA repair activity.\",\n      \"method\": \"CBP depletion; IR treatment; Ku70 acetylation measurement; DNA repair assay; nuclear/cytoplasmic fractionation\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — acetylation-repair coupling shown by CBP depletion and functional DNA repair assay, single lab\",\n      \"pmids\": [\"23223795\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"LSD1 and SIRT1 competitively bind the core domain of Ku70 on DNA damage foci. The Ku70 SAP/C-terminal motif suppresses LSD1 binding. SIRT1 promotes NHEJ repair and mutation acquisition while LSD1 has the opposite effect; SIRT1 maintains H4K16 acetylation and open chromatin for repair. SAP-deleted Ku70 compromises BCR-ABL mutation acquisition.\",\n      \"method\": \"Co-immunoprecipitation; chromatin immunoprecipitation at global and locus-specific (ABL) levels; Ku70 domain mutagenesis; BCR-ABL mutation acquisition assay\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP, ChIP, and mutagenesis identifying competing binding domain, single lab\",\n      \"pmids\": [\"27384990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Ku70 dynamically competes with TEAD4 for binding to YAP, limiting YAP transcriptional activity. Loss of Ku70 enhances YAP-TEAD4 interaction, which drives SMURF2-mediated ubiquitin-proteasome degradation of PARP1, increasing genome instability and tumorigenesis in colon cancer and HCC.\",\n      \"method\": \"Co-immunoprecipitation; Ku70 depletion; in vivo tumor models; ubiquitination assay; patient HCC sample analysis\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP competition, loss-of-function in vivo, ubiquitination assay, single lab with multiple methods\",\n      \"pmids\": [\"38862269\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Ku70 (XRCC6) directly interacts with the HBoV1 non-structural protein NP1, with a high-affinity KD of ~95 nM. The Ku70 binding domain on NP1 maps to Ku70 aa 266–439. Dominant-negative disruption of Ku70-NP1 interaction impairs HBoV1 DNA replication both in vitro and in HAE-ALI cultures.\",\n      \"method\": \"Affinity purification; direct binding assay (KD measurement); domain mapping; dominant-negative disruption; viral DNA replication assay in HAE-ALI cultures\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — quantitative affinity measurement, domain mapping, and functional viral replication assay, single lab\",\n      \"pmids\": [\"35653410\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"HMGB1 extracellular signaling activates PKCα via TLR4, which phosphorylates Ku70 at Ser77/78. This phosphorylation prevents Ku70-DNA interaction and blocks Ku70 accumulation at DSB foci, impairing DNA repair and causing transcriptional repression-induced atypical cell death (TRIAD) in Alzheimer's disease neurons. Anti-HMGB1 antibody treatment reduces neuronal DSBs and ameliorates cognitive symptoms in AD mice.\",\n      \"method\": \"Phosphoproteome analysis of AD postmortem brains; site-specific phosphomutant analysis; Ku70-DNA binding assay; foci immunofluorescence; anti-HMGB1 antibody treatment in AD mouse model; behavioral assays\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — phosphoproteomics in human tissue, biochemical DNA binding assay, mutagenesis, in vivo rescue with antibody, multiple orthogonal methods\",\n      \"pmids\": [\"34635772\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Ku70 possesses a deubiquitylase (DUB) enzymatic activity on Bax, removing ubiquitin from Bax to prevent its proteasomal degradation. This dual role (sequestration and deubiquitylation of Bax) gives Ku70 both anti-apoptotic (preventing mitochondrial Bax translocation) and pro-apoptotic (blocking Bax degradation) functions.\",\n      \"method\": \"Deubiquitylation assay with Ku70 and ubiquitinated Bax; co-immunoprecipitation\",\n      \"journal\": \"Cell cycle\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — enzymatic DUB activity demonstrated in vitro, single lab, single method described in abstract\",\n      \"pmids\": [\"19448404\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The 55 kDa isoform of CDK9 (but not the 42 kDa isoform) specifically associates with Ku70. shRNA depletion of the 55K CDK9 induces apoptosis and DSBs, and rescue with an shRNA-resistant 55K CDK9 reverses these phenotypes, suggesting the 55K CDK9 may function in DSB repair through Ku70.\",\n      \"method\": \"Co-immunoprecipitation (isoform-specific); shRNA knockdown of 55K CDK9; apoptosis and DSB quantification; rescue experiment\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single co-IP for isoform specificity, functional link to Ku70 is indirect, single lab\",\n      \"pmids\": [\"20493174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SMAR1 interacts with Ku70 and coordinates with HDAC6 to maintain Ku70 in a deacetylated state. SMAR1 knockdown results in enhanced Ku70 acetylation, impaired chromatin recruitment of Ku70, and increased apoptosis. IR induces SMAR1 redistribution as nuclear foci via ATM-mediated phosphorylation at Ser370. Deacetylated Ku70 (facilitated by SMAR1) maintains its interaction with Bax to prevent mitochondrial translocation.\",\n      \"method\": \"Co-immunoprecipitation; SMAR1 knockdown; Ku70 acetylation assay; chromatin fractionation; immunofluorescence foci analysis; phosphorylation site mapping\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP, functional knockdown with multiple phenotypic readouts, single lab\",\n      \"pmids\": [\"25299772\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"EAF2 (and EAF1) are required for the recruitment and retention of Ku70/Ku80 to DNA damage sites and play a functional role in NHEJ. EAF2 knockdown sensitizes prostate cancer cells and mouse prostate to DNA damage, and blocks androgen repression of DNA damage markers.\",\n      \"method\": \"EAF2 knockdown; γH2AX marker analysis; Ku70/Ku80 foci recruitment assay; NHEJ reporter assay; EAF2 KO mouse prostate irradiation\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro knockdown with Ku70/80 foci assay, NHEJ assay, and in vivo KO mouse, single lab\",\n      \"pmids\": [\"27721405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Caveolin-1 is a novel Ku70-binding protein; the scaffolding domain of caveolin-1 (aa 82–101) binds the caveolin-binding domain (CBD) of Ku70 (aa 471–478). Caveolin-1 binding to Ku70 inhibits chemotherapeutic drug-induced Bax release from Ku70 and prevents Bax mitochondrial translocation and apoptosis. A Ku70 mutant unable to bind caveolin-1 (Ku70 Φ→A) does not suppress Ku70/Bax dissociation.\",\n      \"method\": \"In vitro binding assay (domain mapping); co-immunoprecipitation; Ku70 point mutagenesis; caveolin-1 knockdown; apoptosis/Bax assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro domain mapping, co-IP, and mutagenesis with functional apoptosis readout, single lab\",\n      \"pmids\": [\"22745744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Ku70 binds double-stranded DNA and hairpin RNA through two distinct binding sites: the C-terminal region including the SAP domain recognizes dsDNA, while a separate site (aa 251–438) mediates hairpin RNA binding. Unlike the Ku heterodimer, monomeric Ku70 can interact with closed circular DNA.\",\n      \"method\": \"Recombinant Ku70 truncation mutants expressed in E. coli; nucleic acid binding assays with diverse substrates; surface plasmon resonance or equivalent binding assays\",\n      \"journal\": \"Biochimie\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical assay with systematic truncation mutants identifying two distinct binding sites, single lab\",\n      \"pmids\": [\"27825805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The Ku70 C-terminal SAP domain is required for stable association of Ku70/80 to DNA ends in the absence of DNA-PKcs, but this requirement is abrogated in the DNA-PK holocomplex. Ku80 C-terminal extension contributes to DNA-PK complex stability but is not absolutely required for its formation. FRET assay with ECFP-Ku70/EYFP-Ku80 confirmed that DNA-PK phosphorylation status influences holocomplex stability.\",\n      \"method\": \"FRET assay with fluorescently tagged Ku70/80; surface plasmon resonance; SAP domain deletion mutagenesis; Ku80 C-terminal extension deletion; DNA-PK complex formation assays\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — FRET quantitative binding assay validated against SPR, domain mutagenesis, single lab with two orthogonal biophysical methods\",\n      \"pmids\": [\"32937838\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"XRCC6/Ku70 is a multifunctional protein that, as a heterodimer with Ku80, binds DNA double-strand break ends via its C-terminal domain (aa 254–609) to initiate classical NHEJ repair by recruiting DNA-PKcs, XRCC4/Ligase IV, and other NHEJ factors; its acetylation status—regulated by acetyltransferases (CBP, PCAF), sirtuins (SIRT1, SIRT6), and HDAC6, and modulated by interactors such as SET/TAF-Iβ and SMAR1—controls both its nuclear DNA repair activity and its cytoplasmic function of sequestering pro-apoptotic Bax (the latter also involving a deubiquitylase activity on Bax); Ku70 additionally acts as a cytosolic DNA sensor that translocates to the cytoplasm upon DNA stimulation to induce IFN-λ1 via STING, serves as an entry receptor for Rickettsia conorii, regulates transcription (including as a BRG1-interacting partner for nuclear receptor activation and as a repressor of Apaf1), modulates ATM/ATR signaling at DSBs, interacts with telomerase RNA (hTR), HIV-1 integrase, RAG1, and FOXO4, and suppresses alternative end-joining in G1-phase cells.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"XRCC6/Ku70 is the DNA end-binding subunit of the Ku70/Ku80 heterodimer that initiates classical non-homologous end joining (NHEJ) and is essential in vivo for double-strand break (DSB) repair, V(D)J recombination, and immunoglobulin class-switch recombination [#0, #1, #3]. Heterodimerization with Ku80 must precede DNA binding, with the Ku70 C-terminal domain (aa 254\\u2013609) mediating DNA end recognition and a core region (aa 439\\u2013609) directing Ku80 assembly [#1, #2]; structural mapping of the heterodimer free, DNA-bound, and DNA-PKcs-bound defines the conformational basis of end recognition [#5]. Upon irradiation Ku70 accumulates rapidly at breaks through its \\u03b1/\\u03b2, DNA-binding, and Ku80-binding domains, and this recruitment is required for downstream loading of XRCC4 and XLF [#33]; the SAP domain stabilizes Ku70/80 on DNA ends in the absence of DNA-PKcs but is dispensable once the DNA-PK holocomplex forms [#47]. Ku70 enforces repair-pathway choice by suppressing alternative end-joining in G1-phase cells [#34] and is antagonized by the Fanconi anemia effector FANCD2, which diverts breaks toward homologous recombination [#12]. NHEJ activity is tuned by post-translational modification: acetylation by CBP/PCAF is inhibitory and is reversed by SIRT1, while methylation of Ku70 by SMYD2 promotes Ku70/Ku80/DNA-PKcs recruitment, with loss of SMYD2 driving cytosolic DNA accumulation and cGAS-STING activation [#7, #36, #30]; recruitment is further gated by acetylation-controlling interactors SET/TAF-I\\u03b2 and SMAR1 [#27, #43]. Beyond repair, Ku70 has cytoplasmic and regulatory functions: it sequesters and deubiquitylates pro-apoptotic Bax in an acetylation-dependent manner controlled by HDAC6 and SIRT6 [#8, #41, #29], acts as a cytosolic DNA/ssDNA sensor that translocates to the cytoplasm to induce STING-dependent IFN-\\u03bb1 [#31, #32], regulates transcription as a BRG1-associated factor for glucocorticoid-receptor activation and as a repressor of Apaf1 [#28, #26], and is exploited by pathogens as a cell-surface receptor for Rickettsia conorii and a binding partner of HIV-1 integrase and HBoV1 NP1 [#6, #19, #35, #39]. Ku70 dysfunction is mechanistically linked to neurodegeneration: mutant huntingtin binds Ku70 and impairs NHEJ, and Ku70 re-expression rescues Huntington's disease phenotypes in mice [#13], while HMGB1/PKC\\u03b1-mediated phosphorylation of Ku70 at Ser77/78 blocks its DNA binding and drives neuronal cell death in Alzheimer's models [#40].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Established that Ku70 is an essential, non-redundant in vivo component of NHEJ and antigen-receptor gene assembly, defining the pathway it serves.\",\n      \"evidence\": \"Ku70 knockout mice with IR sensitivity and V(D)J recombination assays, plus class-switch recombination epistasis\",\n      \"pmids\": [\"9390689\", \"9625768\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve which molecular step of break sealing requires Ku70\", \"Cytoplasmic and non-repair roles not addressed\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Defined the domain architecture underlying Ku function, showing heterodimer assembly must precede DNA end binding and mapping the DNA-binding and Ku80-interaction regions.\",\n      \"evidence\": \"Truncation/chimera mutagenesis, Ku70-/- ES cell complementation, and DNA end-binding assays with purified subunits\",\n      \"pmids\": [\"9362500\", \"8756676\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution conformational changes not resolved at this stage\", \"Separability of DNA-PK activation from end-binding only partially mapped\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Provided a structural model of the Ku70/80 heterodimer recognizing DNA and engaging DNA-PKcs, linking domain maps to physical conformational states.\",\n      \"evidence\": \"Single-particle EM 3D reconstruction of free, DNA-bound, and DNA-PKcs-bound Ku70/80 (with prior IP6 conformational mapping)\",\n      \"pmids\": [\"17159921\", \"11953323\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"25 \\u00c5 resolution insufficient for side-chain detail\", \"Functional consequence of IP6-induced conformational change not fully defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Resolved the recruitment hierarchy at breaks, showing Ku70 accumulates first and is required to load downstream NHEJ factors.\",\n      \"evidence\": \"Live-cell imaging of EGFP-Ku70 domain mutants after laser irradiation with XRCC4/XLF/Artemis foci epistasis\",\n      \"pmids\": [\"21820429\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why Artemis recruitment is Ku70-independent unexplained\", \"Role of individual residues beyond Leu385 not exhaustively tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Clarified how the Ku70 SAP domain and DNA-PK assembly state govern stable retention on DNA ends.\",\n      \"evidence\": \"FRET and SPR with SAP and Ku80 C-terminal deletions in DNA-PK complex formation assays\",\n      \"pmids\": [\"32937838\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance of holocomplex stability differences not tested\", \"Single biophysical system\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed Ku70 actively enforces repair-pathway choice by suppressing alternative end-joining in G1, distinguishing its barrier function from canonical ligation.\",\n      \"evidence\": \"Genetic epistasis in Lig4-deficient and Ku70/Lig4 double-deficient G1 progenitor B cells across RAG-, Cas9-, and ZFN-induced breaks\",\n      \"pmids\": [\"34006647\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which Ku occludes A-EJ factors not defined\", \"Cell-cycle phase specificity not mechanistically explained\"]\n    },\n    {\n      \"year\": 2030,\n      \"claim\": \"Mapped how Fanconi anemia signaling counteracts Ku70 to channel breaks toward homologous recombination.\",\n      \"evidence\": \"FANCC/Ku70 double-knockout epistasis with ICL sensitivity, HR frequency, and in vitro FANCD2/Ku70 biochemistry\",\n      \"pmids\": [\"20538911\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular nature of FANCD2 end-modification not fully defined\", \"Generalizability beyond ICL-induced breaks unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Established acetylation, deacetylation, and methylation as the regulatory code controlling Ku70 repair activity and its recruitment to breaks.\",\n      \"evidence\": \"SIRT1/CBP acetylation-repair coupling, SET/TAF-I\\u03b2 and SMAR1 acetylation gating, and SMYD2 methylation site mapping with NHEJ and cGAS-STING readouts\",\n      \"pmids\": [\"17334224\", \"23223795\", \"24305947\", \"25299772\", \"37315132\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Interplay/ordering of competing modifications not resolved\", \"Several modifier relationships rest on single-lab evidence\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined Ku70's cytoplasmic anti-apoptotic function through acetylation-dependent Bax sequestration and deubiquitylation, governed by HDAC6 and SIRT6.\",\n      \"evidence\": \"HDAC6/SIRT6 co-IP and knockdown, K542 mutagenesis, Bax deubiquitylation assay, and mitochondrial translocation/apoptosis readouts\",\n      \"pmids\": [\"21847364\", \"19448404\", \"28238784\", \"22745744\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Catalytic basis of Ku70 DUB activity on Bax not structurally defined\", \"Balance between Bax sequestration and stabilization context-dependent and unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified a non-repair role for Ku70 as a cytosolic DNA/ssDNA sensor driving STING-dependent type III interferon induction.\",\n      \"evidence\": \"Leptomycin B nuclear-export block, IFN-\\u03bb1 reporter, ssDNA90 binding, and viral infection (HSV-1, HTLV-1) with STING association\",\n      \"pmids\": [\"33548066\", \"28821586\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Why Ku70 selectively induces IFN-\\u03bb1 but not IFN-\\u03b1/\\u03b2 unexplained\", \"Direct STING-engagement mechanism not biochemically resolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended Ku70 into transcriptional and tumor-suppressive control via BRG1-dependent nuclear receptor activation, Apaf1 repression, and YAP-TEAD4 competition.\",\n      \"evidence\": \"Co-IP/ChIP for BRG1 and Apaf1 promoters, and Ku70-YAP competition with in vivo tumor and ubiquitination assays\",\n      \"pmids\": [\"26055322\", \"20966962\", \"38862269\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether these transcriptional roles require DNA-end binding unclear\", \"Single-lab evidence for each axis\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Connected Ku70 dysfunction to neurodegeneration, showing impaired Ku70-mediated NHEJ contributes to Huntington's and Alzheimer's pathology.\",\n      \"evidence\": \"Mutant huntingtin co-IP and Ku70 rescue in R6/2 mice; HMGB1/PKC\\u03b1 phosphorylation of Ku70 Ser77/78 with anti-HMGB1 rescue in AD mice\",\n      \"pmids\": [\"20439996\", \"22096569\", \"34635772\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal contribution of Ku70 loss versus broader DSB burden not isolated\", \"No reported XRCC6 Mendelian disease mutation in the corpus\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the many regulatory inputs (acetylation, methylation, phosphorylation, partner binding) are integrated to switch Ku70 between nuclear repair, cytoplasmic apoptotic control, immune sensing, and transcription remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking modification state to subcellular partitioning\", \"Many partner interactions validated only by single-lab co-IP without reciprocal structural validation\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [1, 2, 33, 46, 47]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [10, 46]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [19, 41]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [26, 28]},\n      {\"term_id\": \"GO:0001618\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [31, 32]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [8, 45]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [17, 33, 36]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [8, 31, 36]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [11, 37, 43]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [0, 1, 33, 34]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3, 31, 32]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [8, 26, 41]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [26, 28]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [13, 40]}\n    ],\n    \"complexes\": [\"Ku70/Ku80 heterodimer\", \"DNA-PK holocomplex\"],\n    \"partners\": [\"XRCC5\", \"PRKDC\", \"SIRT1\", \"HDAC6\", \"BAX\", \"FOXO4\", \"SMARCA4\", \"FANCD2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":7,"faith_total":7,"faith_pct":100.0}}