{"gene":"XAB2","run_date":"2026-06-11T09:02:06","timeline":{"discoveries":[{"year":2000,"finding":"XAB2 (XPA-binding protein 2) physically interacts with XPA, CSA, CSB, and RNA polymerase II, as demonstrated by immunoprecipitation. Microinjection of anti-XAB2 antibodies into living fibroblasts inhibited transcription-coupled repair (TCR) and transcription but NOT global genome repair, establishing XAB2 as a specific component of the TCR pathway.","method":"Yeast two-hybrid (initial identification), co-immunoprecipitation, antibody microinjection into living fibroblasts with TCR and GGR assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, functional antibody inhibition in living cells, replicated by multiple subsequent studies confirming TCR role","pmids":["10944529"],"is_preprint":false},{"year":2007,"finding":"XAB2 exists as a multimeric protein complex (XAB2 complex) consisting of hAquarius, XAB2, hPRP19, CCDC16, hISY1, and PPIE, all of which are pre-mRNA splicing factors. siRNA knockdown of XAB2 caused UV hypersensitivity and decreased RNA synthesis recovery. Enhanced interaction of XAB2 with RNA polymerase IIo or XPA was observed after DNA damage, indicating a DNA damage-responsive remodeling of the complex.","method":"Biochemical purification (multistep chromatography), mass spectrometry identification of complex components, siRNA knockdown, co-immunoprecipitation after DNA damage","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — biochemical purification with MS identification, functional KD validation, replicated interaction data; multiple orthogonal methods in one study","pmids":["17981804"],"is_preprint":false},{"year":2005,"finding":"Homozygous deletion of XAB2 in mice results in preimplantation lethality: embryos survive to morula stage but fail to develop to blastocyst, demonstrating that XAB2 is essential for early mouse embryogenesis.","method":"Gene targeting/knockout in mice; embryo staging by developmental analysis","journal":"DNA repair","confidence":"High","confidence_rationale":"Tier 2 / Strong — two independent knockout alleles both show the same lethal phenotype in vivo","pmids":["15725628"],"is_preprint":false},{"year":2007,"finding":"XAB2 associates with retinoic acid receptor alpha (RARα) and histone deacetylase 3 (HDAC3) in the nucleus, forming part of a RAR corepressor complex. Overexpression of XAB2 inhibited ATRA-induced cellular differentiation, while siRNA knockdown of XAB2 enhanced ATRA-induced differentiation in HL60 and overcame ATRA resistance in IMR-32 neuroblastoma cells.","method":"Co-immunoprecipitation (nuclear fraction), siRNA knockdown, overexpression, cellular differentiation assays","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — co-IP for complex identification plus functional KD/OE with clear phenotypic readout, single lab","pmids":["17283134"],"is_preprint":false},{"year":2009,"finding":"The yeast ortholog Ntc90 (NTC90/SYF1) interacts with multiple NTC components (Ntc31, Ntc30, Ntc20) through distinct regions but is NOT required for spliceosome activation; instead, Ntc90 is specifically required for recruiting the first-step splicing factor Yju2 after spliceosome activation.","method":"Biochemical pulldown, genetic complementation, spliceosome assembly assays in yeast","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — biochemical and genetic methods in yeast ortholog, defined a specific molecular function with multiple orthogonal approaches","pmids":["19617314"],"is_preprint":false},{"year":2016,"finding":"XAB2 promotes the end resection step of homologous recombination (HR) at chromosomal double-strand breaks. XAB2 depletion impairs: DSB repair via end resection-dependent HR pathways, CtIP hyperphosphorylation, BRCA1 IRIF, RAD51 recruitment to IRIF, and histone acetylation events linked to HR. This function requires complex formation with ISY1 and PRP19. The XAB2–ISY1–PRP19 complex localizes to interchromatin granule-like structures adjacent to (but not coincident with) γH2AX foci.","method":"siRNA knockdown, DSB repair assays (chromosomal), end resection assays, IRIF (RAD51, BRCA1, γH2AX) by immunofluorescence, truncation/domain mutagenesis, co-immunoprecipitation, live cell imaging","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal functional assays (repair, resection, IRIF, histone marks, localization) plus domain mapping in a single study","pmids":["27084940"],"is_preprint":false},{"year":2016,"finding":"XAB2 regulates mitotic cell cycle progression by transcriptionally activating CENPE. XAB2 depletion causes G2/M arrest at prophase/prometaphase, chromosome misalignment, segregation defects, and mitotic catastrophe. XAB2 binds to the CENPE promoter (ChIP assay) and its overexpression increases CENPE promoter-driven luciferase activity. CENPE knockdown phenocopies XAB2 loss, and epistasis shows no additive effect.","method":"siRNA knockdown, live cell imaging, flow cytometry, microarray, luciferase reporter assay, ChIP assay, promoter deletion mapping","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (ChIP, luciferase, live imaging, genetic epistasis) in a single study, single lab","pmids":["27735937"],"is_preprint":false},{"year":2019,"finding":"XAB2 depletion causes intron retention and loss of POLR2A (largest subunit of RNA Pol II) mRNA and protein, impairing global transcription and inducing cellular senescence via p53/p21 upregulation. Re-expression of POLR2A after XAB2 depletion rescues senescence. XAB2 physically associates with spliceosome components required for POLR2A expression, and domain mapping shows that TPR motifs 2–4 and 11 of XAB2 interact with SNW1 and are critical for this function.","method":"siRNA knockdown, RNA-seq, TMT-based quantitative proteomics, co-immunoprecipitation, luciferase/splicing assays, domain truncation mapping, senescence assays (SA-β-gal, p53/p21 western blot), rescue experiments","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (proteomics, IP, domain mapping, rescue) in a single study demonstrating a mechanistic pathway","pmids":["31216022"],"is_preprint":false},{"year":2021,"finding":"XAB2 interacts with the core spliceosome and binds spliceosomal U4 and U6 snRNAs as well as pre-mRNAs in vivo. XAB2 depletion causes aberrant intron retention, R-loop formation, and DNA damage. XAB2 interacts with ERCC1-XPF and XPG endonucleases in a complex outside nucleotide excision repair, and this trimeric complex binds RNA:DNA hybrids under R-loop-favoring conditions. Transcription-blocking DNA lesions (illudin S treatment; Csb-mutant livers) trigger release of XAB2 from all RNA targets tested.","method":"In vivo biotinylation-tagging/streptavidin pulldown in mice, RNA immunoprecipitation (snRNA and pre-mRNA), co-immunoprecipitation, R-loop detection (DRIP assay), RNA:DNA hybrid binding assay, genetic mouse models (Csbm/m)","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vivo biotinylation pulldown, RNA-IP, biochemical hybrid binding, mouse genetic model; multiple orthogonal methods across organisms","pmids":["34039990"],"is_preprint":false},{"year":2021,"finding":"XAB2 promotes Ku eviction from single-ended DNA double-strand breaks (seDSBs) via a pathway parallel to and independent of the ATM-CtIP-MRE11 axis. XAB2 depletion causes Ku retention at seDSBs induced by temozolomide and camptothecin, unproductive RAD51-ssDNA associations, increased NHEJ in S/G2, and genetic instability. Overexpression of RAD51 or RAD52 rescues XAB2-deficient HR defects, and XAB2 loss is synthetically lethal with RAD52 inhibition.","method":"siRNA knockdown, Ku retention/IRIF assays, RAD51 focus assays, genetic epistasis (ATM inhibition + XAB2 depletion), overexpression rescue, synthetic lethality assay with RAD52 inhibitor","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Strong — epistasis with ATM pathway, multiple repair assays, rescue experiments, and synthetic lethality; multiple orthogonal approaches in one study","pmids":["34500463"],"is_preprint":false},{"year":2022,"finding":"XAB2 is specifically required for Transcription-Coupled Nucleotide Excision Repair (TC-NER) for RNAP2-transcribed genes. Unlike all other studied NER proteins, XAB2 does NOT accumulate at UV-C damage sites but instead becomes MORE mobile after DNA damage, with mobility restored upon repair completion. XAB2 is released from R-loops and from CSA and XPG partners upon DNA damage induction. In the absence of XAB2, RNAP2 is blocked longer on UV lesions. XAB2 also retains RNAP2 on its substrate in the absence of DNA damage.","method":"Live-cell fluorescence recovery after photobleaching (FRAP), local UV-C damage/laser micro-irradiation, co-immunoprecipitation (XAB2 with CSA, XPG, R-loops), TC-NER reporter assays, siRNA knockdown","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — live imaging FRAP, local damage experiments, Co-IP, functional TC-NER assays; multiple orthogonal methods distinguishing XAB2 from all other NER factors","pmids":["35880862"],"is_preprint":false},{"year":2025,"finding":"USP10 deubiquitinates XAB2 at K48-linked polyubiquitination site K593, preventing its proteasomal degradation and thus stabilizing XAB2 protein levels in response to oxaliplatin treatment. Stabilized XAB2 binds the ANXA2 promoter and upregulates ANXA2 transcription, promoting DNA damage repair and oxaliplatin resistance in colorectal cancer cells.","method":"Co-immunoprecipitation, ubiquitination site mass spectrometry, ubiquitin assay, dual-luciferase reporter assay, ChIP-qPCR, ChIP-seq, RNA-seq, site-directed mutagenesis (K593), Western blot","journal":"Journal of experimental & clinical cancer research : CR","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — ubiquitination site mutagenesis, ChIP-seq, deubiquitinase assay, and luciferase reporter; multiple orthogonal methods in single study, single lab","pmids":["40069750"],"is_preprint":false}],"current_model":"XAB2 is a multi-functional tetratricopeptide repeat protein that operates as part of a conserved multimeric complex (with hAquarius/PRP19/ISY1/CCDC16/PPIE) to coordinate pre-mRNA splicing, transcription elongation, and transcription-coupled nucleotide excision repair (TC-NER): it binds spliceosomal U4/U6 snRNAs and pre-mRNAs, is required for correct splicing of key transcripts including POLR2A, is released from R-loops and its partners (CSA, XPG) upon DNA damage to facilitate RNAP2 stalling recognition in TC-NER, promotes Ku eviction and end resection at single-ended DSBs for homologous recombination via an ATM-independent pathway, transcriptionally activates CENPE to support mitotic progression, and is stabilized by USP10-mediated deubiquitination at K593 to drive ANXA2 expression and DNA damage tolerance."},"narrative":{"mechanistic_narrative":"XAB2 is a tetratricopeptide-repeat protein that couples pre-mRNA splicing to genome maintenance and transcription, operating within a conserved multimeric complex comprising hAquarius, PRP19, CCDC16, ISY1, and PPIE [PMID:10944529, PMID:17981804]. First identified through its physical association with XPA, CSA, CSB, and RNA polymerase II, XAB2 is selectively required for transcription-coupled repair and ongoing transcription but not global genome repair [PMID:10944529], a function essential for early development, as its loss causes preimplantation lethality in mice [PMID:15725628]. As a splicing factor, XAB2 binds the core spliceosome and U4/U6 snRNAs and pre-mRNAs in vivo, and its yeast ortholog Ntc90 recruits the first-step factor Yju2 after spliceosome activation [PMID:19617314, PMID:34039990]; loss of XAB2 produces widespread intron retention and, by depleting correctly spliced POLR2A mRNA, collapses global transcription and drives p53/p21-dependent senescence [PMID:31216022, PMID:34039990]. In transcription-coupled nucleotide excision repair XAB2 behaves uniquely among NER factors: rather than accumulating at damage, it becomes more mobile and is released from R-loops and from its CSA and XPG partners upon lesion induction, an event needed for timely resolution of stalled RNAP2 [PMID:35880862]; consistent with this, XAB2 forms a trimeric complex with ERCC1-XPF and XPG that binds RNA:DNA hybrids, and transcription-blocking lesions trigger its release from RNA targets [PMID:34039990]. At double-strand breaks XAB2 promotes end resection and homologous recombination, supporting CtIP phosphorylation, BRCA1 and RAD51 focus formation, and Ku eviction from single-ended breaks through an ATM-independent pathway [PMID:27084940, PMID:34500463]. XAB2 additionally acts as a transcriptional regulator, activating CENPE to enable mitotic progression and, when stabilized by USP10-mediated deubiquitination at K593, driving ANXA2 expression and DNA damage tolerance [PMID:27735937, PMID:40069750]; it also associates with a RARα/HDAC3 corepressor complex to restrain retinoic-acid-induced differentiation [PMID:17283134].","teleology":[{"year":2000,"claim":"Established XAB2 as a dedicated transcription-coupled repair factor by linking it physically to the NER/TCR machinery and showing its functional requirement in living cells.","evidence":"Yeast two-hybrid, reciprocal Co-IP with XPA/CSA/CSB/RNAP II, and anti-XAB2 antibody microinjection with TCR vs GGR assays in fibroblasts","pmids":["10944529"],"confidence":"High","gaps":["Did not define the biochemical step within TCR at which XAB2 acts","No structural basis for the interactions"]},{"year":2005,"claim":"Demonstrated that XAB2 is indispensable for organismal viability, placing its function at an essential developmental checkpoint.","evidence":"Two independent XAB2 knockout alleles in mice with embryo developmental staging","pmids":["15725628"],"confidence":"High","gaps":["Lethality cause (splicing vs repair vs transcription defect) not resolved","No conditional/tissue-specific analysis"]},{"year":2007,"claim":"Defined XAB2 as a stable subunit of a multimeric splicing-factor complex whose composition is remodeled by DNA damage, unifying its splicing and repair activities.","evidence":"Multistep chromatographic purification with MS identification, siRNA knockdown (UV sensitivity, RNA synthesis recovery), Co-IP after damage","pmids":["17981804"],"confidence":"High","gaps":["Stoichiometry and architecture of the complex unknown","Mechanism of damage-induced remodeling undefined"]},{"year":2007,"claim":"Extended XAB2 function to transcriptional corepression by linking it to a RARα/HDAC3 complex controlling differentiation.","evidence":"Nuclear Co-IP, siRNA knockdown and overexpression with ATRA-induced differentiation assays in HL60 and IMR-32 cells","pmids":["17283134"],"confidence":"Medium","gaps":["Single-lab finding without reciprocal validation of the corepressor complex","Direct vs indirect role in RAR target repression not established"]},{"year":2009,"claim":"Assigned a precise splicing-mechanistic role to the XAB2 ortholog, showing it recruits a first-step factor after spliceosome activation rather than driving activation itself.","evidence":"Biochemical pulldown, genetic complementation, and spliceosome assembly assays of yeast Ntc90/SYF1","pmids":["19617314"],"confidence":"High","gaps":["Conservation of the Yju2-recruitment role in human XAB2 not directly tested","Does not connect splicing step to the repair functions"]},{"year":2016,"claim":"Showed XAB2 promotes the end-resection step of homologous recombination, expanding its genome-maintenance role beyond TCR.","evidence":"siRNA knockdown with DSB repair/resection assays, RAD51/BRCA1/γH2AX IRIF, domain mapping, Co-IP, and live imaging","pmids":["27084940"],"confidence":"High","gaps":["Whether resection role is a direct activity or a splicing-dependent consequence not separated","Molecular target of XAB2 at break sites unidentified"]},{"year":2016,"claim":"Identified XAB2 as a transcriptional activator of CENPE required for mitotic progression, broadening its function to cell-cycle control.","evidence":"ChIP and promoter-deletion mapping, luciferase reporter, live imaging, flow cytometry, and CENPE epistasis","pmids":["27735937"],"confidence":"High","gaps":["Whether CENPE activation reflects direct DNA binding or splicing-mediated regulation unclear","No defined DNA-binding domain for promoter engagement"]},{"year":2019,"claim":"Mechanistically linked XAB2's splicing activity to global transcription by showing it ensures correct POLR2A splicing, with failure driving senescence.","evidence":"RNA-seq, TMT proteomics, Co-IP, SNW1 domain mapping (TPR 2–4, 11), and POLR2A re-expression rescue of senescence","pmids":["31216022"],"confidence":"High","gaps":["Full set of XAB2-dependent transcripts not enumerated","Relationship between POLR2A loss and repair phenotypes not dissected"]},{"year":2021,"claim":"Connected XAB2's RNA-binding/splicing function to R-loop suppression and NER-endonuclease association, providing a substrate-level basis for its genome protection.","evidence":"In vivo biotinylation pulldown, RNA-IP of U4/U6 snRNAs and pre-mRNAs, DRIP, RNA:DNA hybrid binding, and Csb-mutant mouse models","pmids":["34039990"],"confidence":"High","gaps":["Functional consequence of the XAB2–ERCC1-XPF–XPG trimeric complex at R-loops not fully defined","How lesion sensing triggers RNA release unknown"]},{"year":2021,"claim":"Showed XAB2 evicts Ku from single-ended DSBs through an ATM-independent pathway parallel to CtIP-MRE11, refining its HR mechanism.","evidence":"Ku retention/IRIF assays, RAD51 foci, ATM-inhibition epistasis, RAD51/RAD52 overexpression rescue, and synthetic lethality with RAD52 inhibition","pmids":["34500463"],"confidence":"High","gaps":["Direct biochemical activity of XAB2 in Ku displacement not reconstituted","How the ATM-independent branch is regulated unknown"]},{"year":2022,"claim":"Revealed XAB2's distinctive TC-NER mechanism: it is released rather than recruited at damage, with its mobilization required for resolving stalled RNAP2.","evidence":"FRAP live imaging, local UV-C/laser micro-irradiation, Co-IP with CSA/XPG/R-loops, and TC-NER reporter assays","pmids":["35880862"],"confidence":"High","gaps":["Molecular trigger and machinery driving XAB2 release not defined","How released XAB2 promotes downstream repair steps unclear"]},{"year":2025,"claim":"Identified post-translational control of XAB2 stability by USP10 and a downstream ANXA2 transcriptional program promoting chemoresistance.","evidence":"Co-IP, ubiquitination-site MS and K593 mutagenesis, deubiquitinase assay, ChIP-seq/ChIP-qPCR, luciferase, and RNA-seq in colorectal cancer cells","pmids":["40069750"],"confidence":"High","gaps":["Single-lab finding in colorectal cancer context","Generality of USP10–XAB2–ANXA2 axis beyond oxaliplatin resistance untested"]},{"year":null,"claim":"How XAB2's splicing, transcription, R-loop, TC-NER, and HR functions are mechanistically partitioned versus interdependent remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No structure of XAB2 or its complexes","No separation-of-function alleles distinguishing splicing from repair roles","Direct DNA-binding capacity for promoter activation undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[8]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[6,11]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,1]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[3,5]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[0,10,5,9]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[4,7,8]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[6,7]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[6]}],"complexes":["XAB2 complex (hAquarius/XAB2/PRP19/CCDC16/ISY1/PPIE)","XAB2-ERCC1-XPF-XPG trimeric complex","RARα/HDAC3 corepressor complex"],"partners":["XPA","CSA","XPG","PRP19","ISY1","SNW1","ERCC1","USP10"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9HCS7","full_name":"Pre-mRNA-splicing factor SYF1","aliases":["Protein HCNP","XPA-binding protein 2"],"length_aa":855,"mass_kda":100.0,"function":"Involved in pre-mRNA splicing as component of the spliceosome (PubMed:11991638, PubMed:28076346, PubMed:28502770). Involved in transcription-coupled repair (TCR), transcription and pre-mRNA splicing (PubMed:10944529, PubMed:17981804)","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9HCS7/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/XAB2","classification":"Common Essential","n_dependent_lines":1208,"n_total_lines":1208,"dependency_fraction":1.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CPSF6","stoichiometry":0.2},{"gene":"CTNNBL1","stoichiometry":0.2},{"gene":"DNAJC17","stoichiometry":0.2},{"gene":"PRPF19","stoichiometry":0.2},{"gene":"RBM39","stoichiometry":0.2},{"gene":"SF3A1","stoichiometry":0.2},{"gene":"SNRPA","stoichiometry":0.2},{"gene":"SNRPB","stoichiometry":0.2},{"gene":"SNRPC","stoichiometry":0.2},{"gene":"SNRPF","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/XAB2","total_profiled":1310},"omim":[{"mim_id":"610850","title":"XPA-BINDING PROTEIN 2; XAB2","url":"https://www.omim.org/entry/610850"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Vesicles","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/XAB2"},"hgnc":{"alias_symbol":["HCNP","HCRN","SYF1","NTC90"],"prev_symbol":[]},"alphafold":{"accession":"Q9HCS7","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9HCS7","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9HCS7-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9HCS7-F1-predicted_aligned_error_v6.png","plddt_mean":73.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=XAB2","jax_strain_url":"https://www.jax.org/strain/search?query=XAB2"},"sequence":{"accession":"Q9HCS7","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9HCS7.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9HCS7/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9HCS7"}},"corpus_meta":[{"pmid":"10944529","id":"PMC_10944529","title":"XAB2, a novel tetratricopeptide repeat protein involved in transcription-coupled DNA repair and transcription.","date":"2000","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10944529","citation_count":115,"is_preprint":false},{"pmid":"17981804","id":"PMC_17981804","title":"Isolation of XAB2 complex involved in pre-mRNA splicing, transcription, and transcription-coupled repair.","date":"2007","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17981804","citation_count":87,"is_preprint":false},{"pmid":"35442713","id":"PMC_35442713","title":"Phase II Study of Nivolumab and Salvage Nivolumab/Ipilimumab in Treatment-Naive Patients With Advanced Clear Cell Renal Cell Carcinoma (HCRN GU16-260-Cohort A).","date":"2022","source":"Journal of clinical oncology : official journal of the American Society of Clinical Oncology","url":"https://pubmed.ncbi.nlm.nih.gov/35442713","citation_count":82,"is_preprint":false},{"pmid":"27932416","id":"PMC_27932416","title":"A Phase II Trial of Dovitinib in BCG-Unresponsive Urothelial Carcinoma with FGFR3 Mutations or Overexpression: Hoosier Cancer Research Network Trial HCRN 12-157.","date":"2016","source":"Clinical cancer research : an official journal of the American Association for Cancer Research","url":"https://pubmed.ncbi.nlm.nih.gov/27932416","citation_count":61,"is_preprint":false},{"pmid":"34039990","id":"PMC_34039990","title":"The splicing factor XAB2 interacts with ERCC1-XPF and XPG for R-loop processing.","date":"2021","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/34039990","citation_count":47,"is_preprint":false},{"pmid":"15725628","id":"PMC_15725628","title":"Disruption of mouse XAB2 gene involved in pre-mRNA splicing, transcription and transcription-coupled DNA repair results in preimplantation lethality.","date":"2005","source":"DNA repair","url":"https://pubmed.ncbi.nlm.nih.gov/15725628","citation_count":36,"is_preprint":false},{"pmid":"27735937","id":"PMC_27735937","title":"XAB2 functions in mitotic cell cycle progression via transcriptional regulation of CENPE.","date":"2016","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/27735937","citation_count":31,"is_preprint":false},{"pmid":"34160684","id":"PMC_34160684","title":"A multi-center, single-arm, phase Ib study of pembrolizumab (MK-3475) in combination with chemotherapy for patients with advanced colorectal cancer: HCRN GI14-186.","date":"2021","source":"Cancer immunology, immunotherapy : CII","url":"https://pubmed.ncbi.nlm.nih.gov/34160684","citation_count":29,"is_preprint":false},{"pmid":"40069750","id":"PMC_40069750","title":"USP10/XAB2/ANXA2 axis promotes DNA damage repair to enhance chemoresistance to oxaliplatin in colorectal cancer.","date":"2025","source":"Journal of experimental & clinical cancer research : CR","url":"https://pubmed.ncbi.nlm.nih.gov/40069750","citation_count":28,"is_preprint":false},{"pmid":"31669874","id":"PMC_31669874","title":"Enhanced azo dye biodegradation performance and halotolerance of Candida tropicalis SYF-1 by static magnetic field (SMF).","date":"2019","source":"Bioresource technology","url":"https://pubmed.ncbi.nlm.nih.gov/31669874","citation_count":28,"is_preprint":false},{"pmid":"36948504","id":"PMC_36948504","title":"Phase II study of nivolumab and salvage nivolumab/ipilimumab in treatment-naïve patients with advanced non-clear cell renal cell carcinoma (HCRN GU16-260-Cohort B).","date":"2023","source":"Journal for immunotherapy of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/36948504","citation_count":27,"is_preprint":false},{"pmid":"31216022","id":"PMC_31216022","title":"XAB2 depletion induces intron retention in POLR2A to impair global transcription and promote cellular senescence.","date":"2019","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/31216022","citation_count":25,"is_preprint":false},{"pmid":"27084940","id":"PMC_27084940","title":"Tetratricopeptide repeat factor XAB2 mediates the end resection step of homologous recombination.","date":"2016","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/27084940","citation_count":25,"is_preprint":false},{"pmid":"17283134","id":"PMC_17283134","title":"Knockdown of XAB2 enhances all-trans retinoic acid-induced cellular differentiation in all-trans retinoic acid-sensitive and -resistant cancer cells.","date":"2007","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/17283134","citation_count":17,"is_preprint":false},{"pmid":"19617314","id":"PMC_19617314","title":"Ntc90 is required for recruiting first step factor Yju2 but not for spliceosome activation.","date":"2009","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/19617314","citation_count":16,"is_preprint":false},{"pmid":"34500463","id":"PMC_34500463","title":"XAB2 promotes Ku eviction from single-ended DNA double-strand breaks independently of the ATM kinase.","date":"2021","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/34500463","citation_count":13,"is_preprint":false},{"pmid":"26228655","id":"PMC_26228655","title":"XAB2 tagSNPs contribute to non-small cell lung cancer susceptibility in Chinese population.","date":"2015","source":"BMC cancer","url":"https://pubmed.ncbi.nlm.nih.gov/26228655","citation_count":12,"is_preprint":false},{"pmid":"35880862","id":"PMC_35880862","title":"XAB2 dynamics during DNA damage-dependent transcription inhibition.","date":"2022","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/35880862","citation_count":11,"is_preprint":false},{"pmid":"37268519","id":"PMC_37268519","title":"Phase II randomised, double-blind study of mFOLFIRINOX plus ramucirumab versus mFOLFIRINOX plus placebo in advanced pancreatic cancer patients (HCRN GI14-198).","date":"2023","source":"European journal of cancer (Oxford, England : 1990)","url":"https://pubmed.ncbi.nlm.nih.gov/37268519","citation_count":11,"is_preprint":false},{"pmid":"38604810","id":"PMC_38604810","title":"Treatment-free survival outcomes from the phase II study of nivolumab and salvage nivolumab/ipilimumab in advanced clear cell renal cell carcinoma (HCRN GU16-260-Cohort A).","date":"2024","source":"Journal for immunotherapy of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/38604810","citation_count":6,"is_preprint":false},{"pmid":"30038900","id":"PMC_30038900","title":"The Entamoeba histolytica Syf1 Homolog Is Involved in the Splicing of AG-Dependent and AG-Independent Transcripts.","date":"2018","source":"Frontiers in cellular and infection microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/30038900","citation_count":4,"is_preprint":false},{"pmid":"33557438","id":"PMC_33557438","title":"XAB2 TagSNP Is Associated with the Risk of Gastric Cancer in Chinese Population: A Case-Control Study.","date":"2021","source":"International journal of environmental research and public health","url":"https://pubmed.ncbi.nlm.nih.gov/33557438","citation_count":3,"is_preprint":false},{"pmid":"38046376","id":"PMC_38046376","title":"Phase 2 Trial of Nivolumab and Ramucirumab for Relapsed Mesothelioma: HCRN-LUN15-299.","date":"2023","source":"JTO clinical and research reports","url":"https://pubmed.ncbi.nlm.nih.gov/38046376","citation_count":2,"is_preprint":false},{"pmid":"41848795","id":"PMC_41848795","title":"XAB2: a link between RNA metabolism, DNA damage repair, and human health.","date":"2026","source":"Transcription","url":"https://pubmed.ncbi.nlm.nih.gov/41848795","citation_count":0,"is_preprint":false},{"pmid":"42149133","id":"PMC_42149133","title":"Dissecting the Tumor Microenvironment to Identify Biomarkers of Outcome to Anti-PD-1 Therapy in Clear Cell Renal Cell Carcinoma: analyses of the HCRN GU16-260 trial.","date":"2026","source":"Clinical cancer research : an official journal of the American Association for Cancer Research","url":"https://pubmed.ncbi.nlm.nih.gov/42149133","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":16459,"output_tokens":3695,"usd":0.052401,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11309,"output_tokens":4200,"usd":0.080772,"stage2_stop_reason":"end_turn"},"total_usd":0.133173,"stage1_batch_id":"msgbatch_01UT1AahFPCAyn2uVweS7A9z","stage2_batch_id":"msgbatch_01HuKWtKNT4Pqj1bc8eEP5RV","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"XAB2 (XPA-binding protein 2) physically interacts with XPA, CSA, CSB, and RNA polymerase II, as demonstrated by immunoprecipitation. Microinjection of anti-XAB2 antibodies into living fibroblasts inhibited transcription-coupled repair (TCR) and transcription but NOT global genome repair, establishing XAB2 as a specific component of the TCR pathway.\",\n      \"method\": \"Yeast two-hybrid (initial identification), co-immunoprecipitation, antibody microinjection into living fibroblasts with TCR and GGR assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, functional antibody inhibition in living cells, replicated by multiple subsequent studies confirming TCR role\",\n      \"pmids\": [\"10944529\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"XAB2 exists as a multimeric protein complex (XAB2 complex) consisting of hAquarius, XAB2, hPRP19, CCDC16, hISY1, and PPIE, all of which are pre-mRNA splicing factors. siRNA knockdown of XAB2 caused UV hypersensitivity and decreased RNA synthesis recovery. Enhanced interaction of XAB2 with RNA polymerase IIo or XPA was observed after DNA damage, indicating a DNA damage-responsive remodeling of the complex.\",\n      \"method\": \"Biochemical purification (multistep chromatography), mass spectrometry identification of complex components, siRNA knockdown, co-immunoprecipitation after DNA damage\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — biochemical purification with MS identification, functional KD validation, replicated interaction data; multiple orthogonal methods in one study\",\n      \"pmids\": [\"17981804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Homozygous deletion of XAB2 in mice results in preimplantation lethality: embryos survive to morula stage but fail to develop to blastocyst, demonstrating that XAB2 is essential for early mouse embryogenesis.\",\n      \"method\": \"Gene targeting/knockout in mice; embryo staging by developmental analysis\",\n      \"journal\": \"DNA repair\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — two independent knockout alleles both show the same lethal phenotype in vivo\",\n      \"pmids\": [\"15725628\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"XAB2 associates with retinoic acid receptor alpha (RARα) and histone deacetylase 3 (HDAC3) in the nucleus, forming part of a RAR corepressor complex. Overexpression of XAB2 inhibited ATRA-induced cellular differentiation, while siRNA knockdown of XAB2 enhanced ATRA-induced differentiation in HL60 and overcame ATRA resistance in IMR-32 neuroblastoma cells.\",\n      \"method\": \"Co-immunoprecipitation (nuclear fraction), siRNA knockdown, overexpression, cellular differentiation assays\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — co-IP for complex identification plus functional KD/OE with clear phenotypic readout, single lab\",\n      \"pmids\": [\"17283134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The yeast ortholog Ntc90 (NTC90/SYF1) interacts with multiple NTC components (Ntc31, Ntc30, Ntc20) through distinct regions but is NOT required for spliceosome activation; instead, Ntc90 is specifically required for recruiting the first-step splicing factor Yju2 after spliceosome activation.\",\n      \"method\": \"Biochemical pulldown, genetic complementation, spliceosome assembly assays in yeast\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — biochemical and genetic methods in yeast ortholog, defined a specific molecular function with multiple orthogonal approaches\",\n      \"pmids\": [\"19617314\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"XAB2 promotes the end resection step of homologous recombination (HR) at chromosomal double-strand breaks. XAB2 depletion impairs: DSB repair via end resection-dependent HR pathways, CtIP hyperphosphorylation, BRCA1 IRIF, RAD51 recruitment to IRIF, and histone acetylation events linked to HR. This function requires complex formation with ISY1 and PRP19. The XAB2–ISY1–PRP19 complex localizes to interchromatin granule-like structures adjacent to (but not coincident with) γH2AX foci.\",\n      \"method\": \"siRNA knockdown, DSB repair assays (chromosomal), end resection assays, IRIF (RAD51, BRCA1, γH2AX) by immunofluorescence, truncation/domain mutagenesis, co-immunoprecipitation, live cell imaging\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal functional assays (repair, resection, IRIF, histone marks, localization) plus domain mapping in a single study\",\n      \"pmids\": [\"27084940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"XAB2 regulates mitotic cell cycle progression by transcriptionally activating CENPE. XAB2 depletion causes G2/M arrest at prophase/prometaphase, chromosome misalignment, segregation defects, and mitotic catastrophe. XAB2 binds to the CENPE promoter (ChIP assay) and its overexpression increases CENPE promoter-driven luciferase activity. CENPE knockdown phenocopies XAB2 loss, and epistasis shows no additive effect.\",\n      \"method\": \"siRNA knockdown, live cell imaging, flow cytometry, microarray, luciferase reporter assay, ChIP assay, promoter deletion mapping\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (ChIP, luciferase, live imaging, genetic epistasis) in a single study, single lab\",\n      \"pmids\": [\"27735937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"XAB2 depletion causes intron retention and loss of POLR2A (largest subunit of RNA Pol II) mRNA and protein, impairing global transcription and inducing cellular senescence via p53/p21 upregulation. Re-expression of POLR2A after XAB2 depletion rescues senescence. XAB2 physically associates with spliceosome components required for POLR2A expression, and domain mapping shows that TPR motifs 2–4 and 11 of XAB2 interact with SNW1 and are critical for this function.\",\n      \"method\": \"siRNA knockdown, RNA-seq, TMT-based quantitative proteomics, co-immunoprecipitation, luciferase/splicing assays, domain truncation mapping, senescence assays (SA-β-gal, p53/p21 western blot), rescue experiments\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (proteomics, IP, domain mapping, rescue) in a single study demonstrating a mechanistic pathway\",\n      \"pmids\": [\"31216022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"XAB2 interacts with the core spliceosome and binds spliceosomal U4 and U6 snRNAs as well as pre-mRNAs in vivo. XAB2 depletion causes aberrant intron retention, R-loop formation, and DNA damage. XAB2 interacts with ERCC1-XPF and XPG endonucleases in a complex outside nucleotide excision repair, and this trimeric complex binds RNA:DNA hybrids under R-loop-favoring conditions. Transcription-blocking DNA lesions (illudin S treatment; Csb-mutant livers) trigger release of XAB2 from all RNA targets tested.\",\n      \"method\": \"In vivo biotinylation-tagging/streptavidin pulldown in mice, RNA immunoprecipitation (snRNA and pre-mRNA), co-immunoprecipitation, R-loop detection (DRIP assay), RNA:DNA hybrid binding assay, genetic mouse models (Csbm/m)\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vivo biotinylation pulldown, RNA-IP, biochemical hybrid binding, mouse genetic model; multiple orthogonal methods across organisms\",\n      \"pmids\": [\"34039990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"XAB2 promotes Ku eviction from single-ended DNA double-strand breaks (seDSBs) via a pathway parallel to and independent of the ATM-CtIP-MRE11 axis. XAB2 depletion causes Ku retention at seDSBs induced by temozolomide and camptothecin, unproductive RAD51-ssDNA associations, increased NHEJ in S/G2, and genetic instability. Overexpression of RAD51 or RAD52 rescues XAB2-deficient HR defects, and XAB2 loss is synthetically lethal with RAD52 inhibition.\",\n      \"method\": \"siRNA knockdown, Ku retention/IRIF assays, RAD51 focus assays, genetic epistasis (ATM inhibition + XAB2 depletion), overexpression rescue, synthetic lethality assay with RAD52 inhibitor\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — epistasis with ATM pathway, multiple repair assays, rescue experiments, and synthetic lethality; multiple orthogonal approaches in one study\",\n      \"pmids\": [\"34500463\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"XAB2 is specifically required for Transcription-Coupled Nucleotide Excision Repair (TC-NER) for RNAP2-transcribed genes. Unlike all other studied NER proteins, XAB2 does NOT accumulate at UV-C damage sites but instead becomes MORE mobile after DNA damage, with mobility restored upon repair completion. XAB2 is released from R-loops and from CSA and XPG partners upon DNA damage induction. In the absence of XAB2, RNAP2 is blocked longer on UV lesions. XAB2 also retains RNAP2 on its substrate in the absence of DNA damage.\",\n      \"method\": \"Live-cell fluorescence recovery after photobleaching (FRAP), local UV-C damage/laser micro-irradiation, co-immunoprecipitation (XAB2 with CSA, XPG, R-loops), TC-NER reporter assays, siRNA knockdown\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — live imaging FRAP, local damage experiments, Co-IP, functional TC-NER assays; multiple orthogonal methods distinguishing XAB2 from all other NER factors\",\n      \"pmids\": [\"35880862\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"USP10 deubiquitinates XAB2 at K48-linked polyubiquitination site K593, preventing its proteasomal degradation and thus stabilizing XAB2 protein levels in response to oxaliplatin treatment. Stabilized XAB2 binds the ANXA2 promoter and upregulates ANXA2 transcription, promoting DNA damage repair and oxaliplatin resistance in colorectal cancer cells.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination site mass spectrometry, ubiquitin assay, dual-luciferase reporter assay, ChIP-qPCR, ChIP-seq, RNA-seq, site-directed mutagenesis (K593), Western blot\",\n      \"journal\": \"Journal of experimental & clinical cancer research : CR\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — ubiquitination site mutagenesis, ChIP-seq, deubiquitinase assay, and luciferase reporter; multiple orthogonal methods in single study, single lab\",\n      \"pmids\": [\"40069750\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"XAB2 is a multi-functional tetratricopeptide repeat protein that operates as part of a conserved multimeric complex (with hAquarius/PRP19/ISY1/CCDC16/PPIE) to coordinate pre-mRNA splicing, transcription elongation, and transcription-coupled nucleotide excision repair (TC-NER): it binds spliceosomal U4/U6 snRNAs and pre-mRNAs, is required for correct splicing of key transcripts including POLR2A, is released from R-loops and its partners (CSA, XPG) upon DNA damage to facilitate RNAP2 stalling recognition in TC-NER, promotes Ku eviction and end resection at single-ended DSBs for homologous recombination via an ATM-independent pathway, transcriptionally activates CENPE to support mitotic progression, and is stabilized by USP10-mediated deubiquitination at K593 to drive ANXA2 expression and DNA damage tolerance.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"XAB2 is a tetratricopeptide-repeat protein that couples pre-mRNA splicing to genome maintenance and transcription, operating within a conserved multimeric complex comprising hAquarius, PRP19, CCDC16, ISY1, and PPIE [#0, #1]. First identified through its physical association with XPA, CSA, CSB, and RNA polymerase II, XAB2 is selectively required for transcription-coupled repair and ongoing transcription but not global genome repair [#0], a function essential for early development, as its loss causes preimplantation lethality in mice [#2]. As a splicing factor, XAB2 binds the core spliceosome and U4/U6 snRNAs and pre-mRNAs in vivo, and its yeast ortholog Ntc90 recruits the first-step factor Yju2 after spliceosome activation [#4, #8]; loss of XAB2 produces widespread intron retention and, by depleting correctly spliced POLR2A mRNA, collapses global transcription and drives p53/p21-dependent senescence [#7, #8]. In transcription-coupled nucleotide excision repair XAB2 behaves uniquely among NER factors: rather than accumulating at damage, it becomes more mobile and is released from R-loops and from its CSA and XPG partners upon lesion induction, an event needed for timely resolution of stalled RNAP2 [#10]; consistent with this, XAB2 forms a trimeric complex with ERCC1-XPF and XPG that binds RNA:DNA hybrids, and transcription-blocking lesions trigger its release from RNA targets [#8]. At double-strand breaks XAB2 promotes end resection and homologous recombination, supporting CtIP phosphorylation, BRCA1 and RAD51 focus formation, and Ku eviction from single-ended breaks through an ATM-independent pathway [#5, #9]. XAB2 additionally acts as a transcriptional regulator, activating CENPE to enable mitotic progression and, when stabilized by USP10-mediated deubiquitination at K593, driving ANXA2 expression and DNA damage tolerance [#6, #11]; it also associates with a RARα/HDAC3 corepressor complex to restrain retinoic-acid-induced differentiation [#3].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established XAB2 as a dedicated transcription-coupled repair factor by linking it physically to the NER/TCR machinery and showing its functional requirement in living cells.\",\n      \"evidence\": \"Yeast two-hybrid, reciprocal Co-IP with XPA/CSA/CSB/RNAP II, and anti-XAB2 antibody microinjection with TCR vs GGR assays in fibroblasts\",\n      \"pmids\": [\"10944529\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the biochemical step within TCR at which XAB2 acts\", \"No structural basis for the interactions\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstrated that XAB2 is indispensable for organismal viability, placing its function at an essential developmental checkpoint.\",\n      \"evidence\": \"Two independent XAB2 knockout alleles in mice with embryo developmental staging\",\n      \"pmids\": [\"15725628\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Lethality cause (splicing vs repair vs transcription defect) not resolved\", \"No conditional/tissue-specific analysis\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defined XAB2 as a stable subunit of a multimeric splicing-factor complex whose composition is remodeled by DNA damage, unifying its splicing and repair activities.\",\n      \"evidence\": \"Multistep chromatographic purification with MS identification, siRNA knockdown (UV sensitivity, RNA synthesis recovery), Co-IP after damage\",\n      \"pmids\": [\"17981804\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and architecture of the complex unknown\", \"Mechanism of damage-induced remodeling undefined\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Extended XAB2 function to transcriptional corepression by linking it to a RARα/HDAC3 complex controlling differentiation.\",\n      \"evidence\": \"Nuclear Co-IP, siRNA knockdown and overexpression with ATRA-induced differentiation assays in HL60 and IMR-32 cells\",\n      \"pmids\": [\"17283134\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab finding without reciprocal validation of the corepressor complex\", \"Direct vs indirect role in RAR target repression not established\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Assigned a precise splicing-mechanistic role to the XAB2 ortholog, showing it recruits a first-step factor after spliceosome activation rather than driving activation itself.\",\n      \"evidence\": \"Biochemical pulldown, genetic complementation, and spliceosome assembly assays of yeast Ntc90/SYF1\",\n      \"pmids\": [\"19617314\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conservation of the Yju2-recruitment role in human XAB2 not directly tested\", \"Does not connect splicing step to the repair functions\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed XAB2 promotes the end-resection step of homologous recombination, expanding its genome-maintenance role beyond TCR.\",\n      \"evidence\": \"siRNA knockdown with DSB repair/resection assays, RAD51/BRCA1/γH2AX IRIF, domain mapping, Co-IP, and live imaging\",\n      \"pmids\": [\"27084940\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether resection role is a direct activity or a splicing-dependent consequence not separated\", \"Molecular target of XAB2 at break sites unidentified\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified XAB2 as a transcriptional activator of CENPE required for mitotic progression, broadening its function to cell-cycle control.\",\n      \"evidence\": \"ChIP and promoter-deletion mapping, luciferase reporter, live imaging, flow cytometry, and CENPE epistasis\",\n      \"pmids\": [\"27735937\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CENPE activation reflects direct DNA binding or splicing-mediated regulation unclear\", \"No defined DNA-binding domain for promoter engagement\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Mechanistically linked XAB2's splicing activity to global transcription by showing it ensures correct POLR2A splicing, with failure driving senescence.\",\n      \"evidence\": \"RNA-seq, TMT proteomics, Co-IP, SNW1 domain mapping (TPR 2–4, 11), and POLR2A re-expression rescue of senescence\",\n      \"pmids\": [\"31216022\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full set of XAB2-dependent transcripts not enumerated\", \"Relationship between POLR2A loss and repair phenotypes not dissected\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Connected XAB2's RNA-binding/splicing function to R-loop suppression and NER-endonuclease association, providing a substrate-level basis for its genome protection.\",\n      \"evidence\": \"In vivo biotinylation pulldown, RNA-IP of U4/U6 snRNAs and pre-mRNAs, DRIP, RNA:DNA hybrid binding, and Csb-mutant mouse models\",\n      \"pmids\": [\"34039990\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of the XAB2–ERCC1-XPF–XPG trimeric complex at R-loops not fully defined\", \"How lesion sensing triggers RNA release unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed XAB2 evicts Ku from single-ended DSBs through an ATM-independent pathway parallel to CtIP-MRE11, refining its HR mechanism.\",\n      \"evidence\": \"Ku retention/IRIF assays, RAD51 foci, ATM-inhibition epistasis, RAD51/RAD52 overexpression rescue, and synthetic lethality with RAD52 inhibition\",\n      \"pmids\": [\"34500463\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biochemical activity of XAB2 in Ku displacement not reconstituted\", \"How the ATM-independent branch is regulated unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Revealed XAB2's distinctive TC-NER mechanism: it is released rather than recruited at damage, with its mobilization required for resolving stalled RNAP2.\",\n      \"evidence\": \"FRAP live imaging, local UV-C/laser micro-irradiation, Co-IP with CSA/XPG/R-loops, and TC-NER reporter assays\",\n      \"pmids\": [\"35880862\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular trigger and machinery driving XAB2 release not defined\", \"How released XAB2 promotes downstream repair steps unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified post-translational control of XAB2 stability by USP10 and a downstream ANXA2 transcriptional program promoting chemoresistance.\",\n      \"evidence\": \"Co-IP, ubiquitination-site MS and K593 mutagenesis, deubiquitinase assay, ChIP-seq/ChIP-qPCR, luciferase, and RNA-seq in colorectal cancer cells\",\n      \"pmids\": [\"40069750\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Single-lab finding in colorectal cancer context\", \"Generality of USP10–XAB2–ANXA2 axis beyond oxaliplatin resistance untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How XAB2's splicing, transcription, R-loop, TC-NER, and HR functions are mechanistically partitioned versus interdependent remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure of XAB2 or its complexes\", \"No separation-of-function alleles distinguishing splicing from repair roles\", \"Direct DNA-binding capacity for promoter activation undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [6, 11]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 5]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [0, 10, 5, 9]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [4, 7, 8]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [6, 7]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"complexes\": [\n      \"XAB2 complex (hAquarius/XAB2/PRP19/CCDC16/ISY1/PPIE)\",\n      \"XAB2-ERCC1-XPF-XPG trimeric complex\",\n      \"RARα/HDAC3 corepressor complex\"\n    ],\n    \"partners\": [\n      \"XPA\",\n      \"CSA\",\n      \"XPG\",\n      \"PRP19\",\n      \"ISY1\",\n      \"SNW1\",\n      \"ERCC1\",\n      \"USP10\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":6,"faith_total":6,"faith_pct":100.0}}