{"gene":"THOC1","run_date":"2026-04-28T21:42:59","timeline":{"discoveries":[{"year":2000,"finding":"THOC1 (yeast Tho2/Hpr1 ortholog) is a core component of the THO complex, a nuclear oligomeric complex containing Tho2, Hpr1, Mft1, and Thp2 that physically associates and functions as a unit to connect transcription elongation with mitotic recombination in yeast.","method":"Affinity purification (His6-HA-tagged THO2), reciprocal co-immunoprecipitation with anti-Mft1 antibodies, genetic deletion phenotyping","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1-2 — reciprocal Co-IP with multiple subunits, replicated across deletion mutants with defined phenotypes","pmids":["11060033"],"is_preprint":false},{"year":2005,"finding":"Human THOC1 (hHpr1/p84/Thoc1) associates with elongating RNA polymerase II and the RNA splicing/export factor UAP56 in intact cells, and depletion of THOC1 causes transcriptional elongation defects, indicating THOC1 physically links elongating RNA Pol II with RNA processing factors in a human TREX complex.","method":"Co-immunoprecipitation in human cells, siRNA depletion with transcriptional elongation assay and cellular phenotype readout","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP plus functional depletion phenotype, orthogonal methods in one study","pmids":["15870275"],"is_preprint":false},{"year":2006,"finding":"Thoc1 is essential for early mouse embryonic development; homozygous null Thoc1 embryos are arrested around implantation with inner cell mass cells rapidly losing viability upon Thoc1 protein loss, demonstrating a cell-autonomous requirement for THOC1 in mammalian cell viability.","method":"Gene knockout in mice, blastocyst outgrowth assay, immunostaining for Thoc1 protein loss","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined embryonic and cellular phenotype, rigorous genetic model","pmids":["16705185"],"is_preprint":false},{"year":2007,"finding":"Depletion of THOC1 (pThoc1) selectively induces apoptotic cell death in neoplastic (oncogene-transformed) cells coincident with increased DNA damage (phospho-H2AX), while normal isogenic cells are largely unaffected; normal cells lacking Thoc1 cannot be transformed by E1A/Ha-ras.","method":"siRNA depletion, isogenic normal vs. oncogene-transformed cell comparison, apoptosis assay, γ-H2AX immunostaining, transformation assay","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal assays (apoptosis, DNA damage marker, transformation) in isogenic cell pairs","pmids":["17638875"],"is_preprint":false},{"year":2005,"finding":"Yeast Hpr1p (THOC1 ortholog) is poly-ubiquitinated by the HECT ubiquitin ligase Rsp5p (with Ubc4p as conjugating enzyme), leading to proteasomal degradation; Hpr1p degradation is enhanced at high temperature and linked to ongoing RNA Pol II transcription, while other THO subunits are unaffected, suggesting Hpr1p turnover controls THO/TREX complex formation and mRNA export.","method":"In vivo and in vitro ubiquitylation assays, genetic epistasis, proteasome inhibitor experiments, temperature-shift experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro reconstitution of ubiquitylation plus in vivo validation with multiple genetic controls","pmids":["15713680"],"is_preprint":false},{"year":2013,"finding":"Mammalian THOC1 protein is poly-ubiquitinated by the NEDD4-1 E3 ubiquitin ligase and degraded by the proteasome; destabilization of Thoc1 upon transcriptional elongation inhibitor treatment is NEDD4-1-dependent, indicating this regulation is evolutionarily conserved from yeast (Rsp5) to mammals.","method":"In vitro reconstituted ubiquitylation assay, molecularly manipulated cells (NEDD4-1 modulation), proteasome inhibitor treatment, immunoblot","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro biochemical reconstitution plus cell-based validation with transcription inhibitor","pmids":["23460917"],"is_preprint":false},{"year":2007,"finding":"The UBA domain of the mRNA export factor Mex67 directly interacts with Hpr1 (THOC1 ortholog), and this interaction is required for cotranscriptional recruitment of Mex67 to activated genes; Hpr1 binding modulates Mex67 UBA domain selectivity for polyubiquitin through a helix H4-dependent conformational switch.","method":"NMR structure of UBA-Mex67 domain, deletion/point mutagenesis, FRET-based binding assays, ChIP for cotranscriptional recruitment, in vivo mRNA export assay","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1 — NMR structure with functional mutagenesis and multiple orthogonal validation assays","pmids":["17475778"],"is_preprint":false},{"year":2009,"finding":"Hpr1 and FXFG nucleoporin repeats bind to overlapping sites on the Mex67 UBA domain with analogous NMR chemical shift perturbations; Hpr1 binding (unlike FXFG binding) allows the UBA domain to interact with polyubiquitin, demonstrating that substrate identity controls ubiquitin affinity of the UBA domain.","method":"Solution NMR structure of UBA-Mex67/FXFG peptide complex, NMR titration with Hpr1, FRET-based binding assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — atomic-resolution structure with functional binding assays and mutagenesis","pmids":["19401465"],"is_preprint":false},{"year":2014,"finding":"Conditional deletion of Thoc1 in the hematopoietic system reveals a cell-autonomous requirement for THOC1 in granulocyte macrophage progenitor growth and viability, while lymphoid lineages are unaffected under homeostatic conditions, indicating THOC1 is selectively required in rapidly proliferating myeloid progenitors.","method":"Conditional/inducible Thoc1 knockout mice, bone marrow reconstitution, flow cytometry of hematopoietic lineages","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — clean conditional KO with defined cell-type-specific phenotype in vivo","pmids":["24830368"],"is_preprint":false},{"year":2014,"finding":"Conditional Thoc1 deletion in an autochthonous mouse prostate cancer model prevents cancer progression but has little effect on normal prostate tissue; prostate cancer cells deprived of Thoc1 show gene expression defects that compromise cell growth, demonstrating THOC1 is required to support the gene expression demands of aggressive cancer.","method":"Conditional mouse knockout (Cre/lox), autochthonous prostate cancer mouse model, gene expression profiling","journal":"Journal of the National Cancer Institute","confidence":"High","confidence_rationale":"Tier 2 — in vivo conditional KO in autochthonous cancer model with mechanistic gene expression readout","pmids":["25296641"],"is_preprint":false},{"year":2007,"finding":"Mice homozygous for a hypomorphic Thoc1 allele are viable but express reduced pThoc1 and exhibit a dwarf phenotype detectable from mid-gestation, indicating THOC1 is required for normal embryonic and postnatal development.","method":"Generation of hypomorphic and conditional Thoc1 alleles in mice, Cre-mediated recombination phenotyping, developmental staging","journal":"Genesis (New York, N.Y. : 2000)","confidence":"High","confidence_rationale":"Tier 2 — allelic series in mice with defined developmental phenotypes","pmids":["17211872"],"is_preprint":false},{"year":2016,"finding":"THOC1 is required to support increased E2F protein levels and expression of E2F-regulated apoptotic genes (Apaf1, Bak1) upon Rb1 loss; Thoc1 deficiency reduces apoptosis in the Rb1-null embryonic brain, placing THOC1 downstream of Rb1 in regulating E2F-dependent transcription of apoptotic regulators.","method":"Compound Rb1/Thoc1-hypomorphic mouse mutants, immunostaining for E2F and apoptotic markers, gene expression analysis of E2F targets","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis in mice with defined molecular (E2F, target gene expression) and cellular (apoptosis) readouts","pmids":["27001308"],"is_preprint":false},{"year":2020,"finding":"THOC1 deficiency in zebrafish causes hair cell apoptosis through the p53 signaling pathway; knockdown phenotype (reduced hair cell numbers, absent C-startle response) is rescued by wild-type human THOC1 mRNA but not by the p.L183V disease variant, and is suppressed by p53 depletion or the p53 inhibitor Pifithrin-α.","method":"CRISPR-Cas9 knockout and morpholino knockdown in zebrafish, behavioral testing (C-startle response), transcriptome sequencing, p53 inhibitor rescue, mRNA complementation with wild-type vs. mutant THOC1","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal approaches (KO, KD, rescue, pathway inhibition, transcriptomics) in vertebrate model","pmids":["32776944"],"is_preprint":false},{"year":2013,"finding":"Nitric oxide (NO) produced by activated macrophages suppresses THOC1 expression via Nrf2 binding to the antioxidant response element (ARE) in the THOC1 promoter; THOC1 downregulation is required for subsequent Bcl-2 suppression and cancer cell apoptosis, placing THOC1 in the NO-Nrf2-THOC1-Bcl2 apoptotic axis.","method":"Co-culture of macrophages with cancer cells, iNOS inhibitor rescue, NO donor treatment, promoter-reporter ARE mutation, Nrf2 overexpression/knockdown, immunoblot for Bcl-2","journal":"Biochemical pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple methods in one lab but limited independent replication","pmids":["23688498"],"is_preprint":false},{"year":2006,"finding":"An hpr1-101 point mutation (yeast THOC1 ortholog) impairs transcription and mRNA export without increasing recombination or retarding replication fork progression, and does not cause R-loop accumulation (as shown by AID-induced mutation pattern), demonstrating that THOC1/THO has a transcriptional function separable from R-loop-mediated genome instability.","method":"Site-directed mutagenesis, transcription elongation assays, mRNA export assays, recombination frequency measurement, DNA replication fork assay, AID-induced mutation spectrum analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis combined with multiple functional assays separating mechanistic functions","pmids":["16908536","19451165"],"is_preprint":false},{"year":2020,"finding":"THOC1 knockdown in hepatocellular carcinoma cells leads to R-loop formation and DNA damage, impairs G2/M cell cycle progression, and sensitizes cells to cisplatin; THOC1 promotes HCC proliferation in vivo.","method":"siRNA knockdown, R-loop detection (S9.6 antibody), DNA damage assay (γ-H2AX), cell cycle analysis, xenograft mouse model, colony formation assay","journal":"Journal of experimental & clinical cancer research : CR","confidence":"Medium","confidence_rationale":"Tier 2 — multiple cellular assays plus in vivo model in one lab","pmids":["32669125"],"is_preprint":false},{"year":2024,"finding":"THOC1 interacts with SIN3A (a histone deacetylase complex component), and THOC1 knockdown leads to elevated R-loop levels (particularly at telomeres), reduced histone deacetylation, and shortened telomeres in glioblastoma cells, placing THOC1 in a SIN3A-dependent pathway that prevents telomeric R-loop accumulation.","method":"CRISPR-KO screen, co-immunoprecipitation of THOC1-SIN3A, R-loop detection (S9.6), ChIP for histone deacetylation marks, telomere length assay, RNA-sequencing, in vivo PDX survival model","journal":"Neoplasia (New York, N.Y.)","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP plus functional KD phenotypes in multiple PDX lines, single lab","pmids":["41496272"],"is_preprint":false},{"year":2025,"finding":"THOC1 directly binds U2AF2 (U2 snRNA auxiliary factor 2) at the THOC1-340S interaction site; this interaction regulates U2AF2 expression and suppresses ovarian cancer cell proliferation, migration, and invasion through inhibition of the Wnt/beta-catenin signaling pathway (reduced cyclinD1, c-myc, beta-catenin).","method":"Co-immunoprecipitation, GST pull-down, immunofluorescence, RNA-seq with KEGG pathway analysis, functional cell assays (proliferation, migration, invasion)","journal":"Cancer cell international","confidence":"Medium","confidence_rationale":"Tier 2-3 — reciprocal binding assays (Co-IP + GST pulldown) with defined interaction site plus functional and pathway data, single lab","pmids":["41372894"],"is_preprint":false},{"year":2001,"finding":"High-copy expression of Sub2p (yeast UAP56 homolog) suppresses hpr1Δ-mediated genome instability, and conversely high-copy HPR1 suppresses sub2 mutant instability, establishing a genetic epistatic relationship between THOC1 (Hpr1) and the RNA helicase Sub2/UAP56 in maintaining genome stability.","method":"Genetic suppressor analysis, high-copy suppression, conditional allele experiments in yeast","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — bidirectional genetic suppression establishing pathway relationship, yeast ortholog","pmids":["11463828"],"is_preprint":false},{"year":2009,"finding":"Hpr1 (THOC1 yeast ortholog) loss in cells lacking HPR1 results in increased levels of Nab2, Yra1, and Mex67 in nuclear mRNPs; overexpression of Nab2 or Yra1 suppresses the mRNA export defect of hpr1Δ cells and restores normal Mex67 levels in nuclear mRNPs, indicating THOC1/Hpr1 regulates the composition of nuclear mRNPs to permit efficient mRNA export.","method":"Genetic suppression, mRNP fractionation/immunoblot, mRNA export assay in yeast","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 2 — clean genetic and biochemical evidence but preprint, not yet peer-reviewed","pmids":["bio_10.1101_2025.02.26.640412"],"is_preprint":true},{"year":2022,"finding":"THOC1 promotes triple-negative breast cancer stem cell characteristics and mRNA export of stemness-related genes; THOC1 knockdown reduces mammosphere formation, CSC populations, and lung metastasis in vivo, while THOC1 overexpression promotes TNBC malignancy. NF-κB acts as an upstream transcriptional regulator of THOC1 expression.","method":"siRNA knockdown, stable overexpression, mammosphere assay, orthotopic mouse tumor model with lung metastasis readout, mRNA export assay for stemness genes, NF-κB reporter/inhibitor","journal":"Biochemical pharmacology","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple assays in vitro and in vivo, single lab, mechanistic pathway placement via NF-κB","pmids":["36330949"],"is_preprint":false}],"current_model":"THOC1 (hHpr1/p84) is an essential core subunit of the evolutionarily conserved THO/TREX ribonucleoprotein complex that co-transcriptionally associates with elongating RNA polymerase II and physically couples transcriptional elongation with RNA processing and nuclear mRNA export through interactions with UAP56 and the mRNA export receptor Mex67/NXF1; THOC1 loss causes R-loop accumulation, DNA damage, transcription elongation defects, and genome instability, and its protein levels are regulated by ubiquitin-mediated proteasomal degradation (via NEDD4-1 in mammals, Rsp5 in yeast), while its selective requirement in rapidly proliferating and cancer cells makes it a context-dependent survival factor for neoplastic cells."},"narrative":{"teleology":[{"year":2000,"claim":"Identification of THOC1/Hpr1 as an integral subunit of the THO complex established that transcription elongation and mitotic recombination are linked through a discrete multi-protein machine.","evidence":"Affinity purification and reciprocal co-IP of tagged THO subunits in yeast with genetic deletion phenotyping","pmids":["11060033"],"confidence":"High","gaps":["Mammalian THO complex composition not yet defined","Mechanism by which THO suppresses recombination unknown"]},{"year":2001,"claim":"Bidirectional genetic suppression between HPR1 and SUB2 placed THOC1 and the DEAD-box helicase UAP56/Sub2 in a common pathway maintaining genome stability, linking THO function to RNA helicases.","evidence":"High-copy suppressor analysis with conditional alleles in yeast","pmids":["11463828"],"confidence":"Medium","gaps":["Physical interaction between Hpr1 and Sub2 not demonstrated at this stage","Whether suppression reflects direct binding or indirect pathway compensation unclear"]},{"year":2005,"claim":"Demonstration that human THOC1 physically associates with elongating RNA Pol II and UAP56 extended THO/TREX function to mammals and proved that THOC1 directly bridges transcription machinery with RNA processing/export factors.","evidence":"Co-IP in human cells plus siRNA-mediated depletion with transcription elongation assays","pmids":["15870275"],"confidence":"High","gaps":["Stoichiometry of human TREX complex not resolved","Whether THOC1-UAP56 interaction is direct or bridged by other subunits unclear"]},{"year":2005,"claim":"Discovery that Hpr1/THOC1 is selectively poly-ubiquitinated by Rsp5/NEDD4-family E3 ligases and degraded by the proteasome revealed a post-translational mechanism controlling THO complex availability during active transcription.","evidence":"In vitro and in vivo ubiquitylation assays in yeast with proteasome inhibitors and temperature shifts; later confirmed in mammals with NEDD4-1 reconstitution","pmids":["15713680","23460917"],"confidence":"High","gaps":["Ubiquitylation sites on THOC1 not mapped","Physiological signals triggering NEDD4-1-dependent degradation in mammalian cells not identified"]},{"year":2006,"claim":"A separation-of-function hpr1 point mutant showed that THOC1's transcription/export function is genetically separable from R-loop-mediated genome instability, resolving whether these were obligately linked.","evidence":"hpr1-101 mutant analyzed by transcription elongation, mRNA export, recombination, replication fork, and AID mutation assays in yeast","pmids":["16908536","19451165"],"confidence":"High","gaps":["Structural basis for separable functions not resolved","Whether this separation applies to mammalian THOC1 untested"]},{"year":2006,"claim":"Thoc1-null mouse embryos arrested at implantation established THOC1 as essential for mammalian viability and showed the requirement is cell-autonomous in rapidly dividing inner cell mass cells.","evidence":"Gene knockout in mice with blastocyst outgrowth assays and immunostaining","pmids":["16705185"],"confidence":"High","gaps":["Which transcripts are most sensitive to THOC1 loss in early embryos unknown","Mechanism of lethality (transcription vs. export vs. DNA damage) not dissected"]},{"year":2007,"claim":"NMR structure of the Mex67 UBA domain bound to Hpr1 revealed the atomic basis for THOC1-mediated cotranscriptional recruitment of the mRNA export receptor and showed that Hpr1 binding allosterically permits polyubiquitin recognition.","evidence":"NMR solution structure, point mutagenesis, FRET binding assays, ChIP for Mex67 recruitment, and mRNA export assays","pmids":["17475778","19451165"],"confidence":"High","gaps":["Full-length THOC1 structure unavailable","Whether the mammalian NXF1-THOC1 interaction uses the same interface not confirmed"]},{"year":2007,"claim":"Selective apoptosis of oncogene-transformed cells upon THOC1 depletion, with sparing of normal isogenic cells, established THOC1 as a context-dependent survival factor for neoplastic cells.","evidence":"siRNA depletion in isogenic normal vs. E1A/Ras-transformed cells with apoptosis, γ-H2AX, and transformation assays","pmids":["17638875"],"confidence":"High","gaps":["Which oncogenic transcripts depend most on THOC1 not identified","Whether selectivity holds across diverse oncogene drivers not tested"]},{"year":2014,"claim":"Conditional Thoc1 deletion in hematopoietic and prostate cancer models demonstrated lineage-selective essentiality: THOC1 is required for rapidly proliferating myeloid progenitors and cancer progression but dispensable for quiescent normal tissues.","evidence":"Conditional knockout mice with bone marrow reconstitution and autochthonous prostate cancer model with gene expression profiling","pmids":["24830368","25296641"],"confidence":"High","gaps":["Specific gene expression programs dependent on THOC1 in myeloid progenitors not fully characterized","Whether THOC1 loss causes synthetic lethality with specific oncogenic pathways untested"]},{"year":2016,"claim":"Genetic epistasis between Thoc1 and Rb1 in mouse brain showed that THOC1 is required for upregulation of E2F-dependent apoptotic genes upon Rb1 loss, placing THOC1 as a functional enabler of E2F-driven transcription.","evidence":"Compound Rb1/Thoc1-hypomorphic mouse mutants with immunostaining and gene expression analysis","pmids":["27001308"],"confidence":"High","gaps":["Whether THOC1 directly associates with E2F target gene loci not shown","Generalizability to other E2F-dependent contexts unknown"]},{"year":2020,"claim":"THOC1 deficiency in zebrafish causes p53-dependent hair cell apoptosis, and the human THOC1 p.L183V variant fails to rescue, linking THOC1 mutations to sensorineural phenotypes through p53 signaling.","evidence":"CRISPR-KO and morpholino in zebrafish with behavioral testing, transcriptomics, p53 inhibitor rescue, and variant-specific mRNA complementation","pmids":["32776944"],"confidence":"High","gaps":["Whether p.L183V disrupts THO complex assembly or a specific THOC1 function not determined","Human patient phenotype data limited"]},{"year":2020,"claim":"Direct demonstration that THOC1 knockdown in hepatocellular carcinoma cells causes R-loop accumulation and DNA damage confirmed that THOC1's R-loop suppression function is relevant in human cancer cells and contributes to cisplatin sensitivity.","evidence":"siRNA knockdown with S9.6 antibody R-loop detection, γ-H2AX, cell cycle analysis, and xenograft model","pmids":["32669125"],"confidence":"Medium","gaps":["Genomic loci most prone to R-loop accumulation upon THOC1 loss not mapped","Whether cisplatin sensitization is specific to R-loop-prone tumors unclear"]},{"year":2024,"claim":"Discovery that THOC1 interacts with SIN3A and prevents telomeric R-loop accumulation in glioblastoma cells extended THOC1's genome-protective role to telomere maintenance through histone deacetylation.","evidence":"CRISPR screen, co-IP of THOC1-SIN3A, S9.6 R-loop detection, ChIP for histone marks, telomere length assay in PDX lines","pmids":["41496272"],"confidence":"Medium","gaps":["Whether THOC1-SIN3A interaction is direct or mediated by other subunits untested","Mechanism linking histone deacetylation to telomeric R-loop resolution not defined"]},{"year":null,"claim":"Key unresolved questions include the full-length structure of THOC1 (alone and in the human TREX complex), identification of the specific transcripts most sensitive to THOC1 loss across cell types, the molecular basis of THOC1's selective essentiality in transformed versus normal cells, and whether THOC1 mutations cause defined human Mendelian disease.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of full-length mammalian THOC1","Genome-wide transcript sensitivity to THOC1 loss not systematically mapped","Causative role of THOC1 variants in human hereditary disease not established by family studies"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[0,1,6]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1,6,7]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,1,6]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[1,14,11]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,1,6,20]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[3,15,14]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[4,5]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[3,12]}],"complexes":["THO complex","TREX complex"],"partners":["THOC2","UAP56","NXF1","NEDD4","SIN3A","U2AF2","MFT1","THP2"],"other_free_text":[]},"mechanistic_narrative":"THOC1 (Hpr1/p84) is a core subunit of the evolutionarily conserved THO/TREX complex that co-transcriptionally couples RNA polymerase II elongation with mRNA processing and nuclear export. THOC1 associates with elongating RNA Pol II, recruits the DEAD-box helicase UAP56/Sub2, and facilitates cotranscriptional loading of the mRNA export receptor Mex67/NXF1 via a direct UBA-domain interaction that modulates polyubiquitin recognition [PMID:11060033, PMID:15870275, PMID:17475778]. Loss of THOC1 causes R-loop accumulation, DNA damage, and genome instability; separation-of-function mutations demonstrate that THOC1's transcription-elongation role is mechanistically distinct from its R-loop suppression function [PMID:16908536, PMID:32669125]. THOC1 protein levels are regulated by ubiquitin-mediated proteasomal degradation (Rsp5 in yeast, NEDD4-1 in mammals), and THOC1 is selectively essential in rapidly proliferating and oncogene-transformed cells, where its loss triggers apoptosis and DNA damage without comparably affecting normal quiescent cells [PMID:15713680, PMID:23460917, PMID:17638875, PMID:25296641]."},"prefetch_data":{"uniprot":{"accession":"Q96FV9","full_name":"THO complex subunit 1","aliases":["Nuclear matrix protein p84","p84N5","hTREX84"],"length_aa":657,"mass_kda":75.7,"function":"Component of the THO subcomplex of the TREX complex which is thought to couple mRNA transcription, processing and nuclear export, and which specifically associates with spliced mRNA and not with unspliced pre-mRNA (PubMed:15833825, PubMed:15998806, PubMed:17190602). Required for efficient export of polyadenylated RNA (PubMed:23222130). The THOC1-THOC2-THOC3 core complex alone is sufficient to bind export factor NXF1-NXT1 and promote ATPase activity of DDX39B/UAP56 (PubMed:33191911). TREX is recruited to spliced mRNAs by a transcription-independent mechanism, binds to mRNA upstream of the exon-junction complex (EJC) and is recruited in a splicing- and cap-dependent manner to a region near the 5' end of the mRNA where it functions in mRNA export to the cytoplasm via the TAP/NXF1 pathway (PubMed:15833825, PubMed:15998806, PubMed:17190602). Regulates transcriptional elongation of a subset of genes (PubMed:22144908). Involved in genome stability by preventing co-transcriptional R-loop formation (By similarity). May play a role in hair cell formation, hence may be involved in hearing (By similarity) Participates in an apoptotic pathway which is characterized by activation of caspase-6, increases in the expression of BAK1 and BCL2L1 and activation of NF-kappa-B. This pathway does not require p53/TP53, nor does the presence of p53/TP53 affect the efficiency of cell killing. Activates a G2/M cell cycle checkpoint prior to the onset of apoptosis. Apoptosis is inhibited by association with RB1 (Microbial infection) The TREX complex is essential for the export of Kaposi's sarcoma-associated herpesvirus (KSHV) intronless mRNAs and infectious virus production","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q96FV9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/THOC1","classification":"Common Essential","n_dependent_lines":1171,"n_total_lines":1208,"dependency_fraction":0.9693708609271523},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CPSF6","stoichiometry":0.2},{"gene":"DDX21","stoichiometry":0.2},{"gene":"DDX39B","stoichiometry":0.2},{"gene":"PRPF4B","stoichiometry":0.2},{"gene":"RBM22","stoichiometry":0.2},{"gene":"RBM33","stoichiometry":0.2},{"gene":"RBM39","stoichiometry":0.2},{"gene":"RBM6","stoichiometry":0.2},{"gene":"RBM8A","stoichiometry":0.2},{"gene":"RNF40","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/THOC1","total_profiled":1310},"omim":[{"mim_id":"620280","title":"DEAFNESS, AUTOSOMAL DOMINANT 86; DFNA86","url":"https://www.omim.org/entry/620280"},{"mim_id":"615403","title":"THO COMPLEX, SUBUNIT 6; THOC6","url":"https://www.omim.org/entry/615403"},{"mim_id":"613332","title":"MEMBRANE-ASSOCIATED RING-CH FINGER PROTEIN 2; MARCHF2","url":"https://www.omim.org/entry/613332"},{"mim_id":"612733","title":"THO COMPLEX, SUBUNIT 5; THOC5","url":"https://www.omim.org/entry/612733"},{"mim_id":"611965","title":"THO COMPLEX, SUBUNIT 7; THOC7","url":"https://www.omim.org/entry/611965"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nuclear speckles","reliability":"Enhanced"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in 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phenotyping\",\n \"journal\": \"The EMBO journal\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 1-2 — reciprocal Co-IP with multiple subunits, replicated across deletion mutants with defined phenotypes\",\n \"pmids\": [\"11060033\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2005,\n \"finding\": \"Human THOC1 (hHpr1/p84/Thoc1) associates with elongating RNA polymerase II and the RNA splicing/export factor UAP56 in intact cells, and depletion of THOC1 causes transcriptional elongation defects, indicating THOC1 physically links elongating RNA Pol II with RNA processing factors in a human TREX complex.\",\n \"method\": \"Co-immunoprecipitation in human cells, siRNA depletion with transcriptional elongation assay and cellular phenotype readout\",\n \"journal\": \"Molecular and cellular biology\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus functional depletion phenotype, orthogonal methods in one study\",\n \"pmids\": [\"15870275\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2006,\n \"finding\": \"Thoc1 is essential for early mouse embryonic development; homozygous null Thoc1 embryos are arrested around implantation with inner cell mass cells rapidly losing viability upon Thoc1 protein loss, demonstrating a cell-autonomous requirement for THOC1 in mammalian cell viability.\",\n \"method\": \"Gene knockout in mice, blastocyst outgrowth assay, immunostaining for Thoc1 protein loss\",\n \"journal\": \"Molecular and cellular biology\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 2 — clean KO with defined embryonic and cellular phenotype, rigorous genetic model\",\n \"pmids\": [\"16705185\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2007,\n \"finding\": \"Depletion of THOC1 (pThoc1) selectively induces apoptotic cell death in neoplastic (oncogene-transformed) cells coincident with increased DNA damage (phospho-H2AX), while normal isogenic cells are largely unaffected; normal cells lacking Thoc1 cannot be transformed by E1A/Ha-ras.\",\n \"method\": \"siRNA depletion, isogenic normal vs. oncogene-transformed cell comparison, apoptosis assay, γ-H2AX immunostaining, transformation assay\",\n \"journal\": \"Cancer research\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 2 — multiple orthogonal assays (apoptosis, DNA damage marker, transformation) in isogenic cell pairs\",\n \"pmids\": [\"17638875\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2005,\n \"finding\": \"Yeast Hpr1p (THOC1 ortholog) is poly-ubiquitinated by the HECT ubiquitin ligase Rsp5p (with Ubc4p as conjugating enzyme), leading to proteasomal degradation; Hpr1p degradation is enhanced at high temperature and linked to ongoing RNA Pol II transcription, while other THO subunits are unaffected, suggesting Hpr1p turnover controls THO/TREX complex formation and mRNA export.\",\n \"method\": \"In vivo and in vitro ubiquitylation assays, genetic epistasis, proteasome inhibitor experiments, temperature-shift experiments\",\n \"journal\": \"The Journal of biological chemistry\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution of ubiquitylation plus in vivo validation with multiple genetic controls\",\n \"pmids\": [\"15713680\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2013,\n \"finding\": \"Mammalian THOC1 protein is poly-ubiquitinated by the NEDD4-1 E3 ubiquitin ligase and degraded by the proteasome; destabilization of Thoc1 upon transcriptional elongation inhibitor treatment is NEDD4-1-dependent, indicating this regulation is evolutionarily conserved from yeast (Rsp5) to mammals.\",\n \"method\": \"In vitro reconstituted ubiquitylation assay, molecularly manipulated cells (NEDD4-1 modulation), proteasome inhibitor treatment, immunoblot\",\n \"journal\": \"PloS one\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 1-2 — in vitro biochemical reconstitution plus cell-based validation with transcription inhibitor\",\n \"pmids\": [\"23460917\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2007,\n \"finding\": \"The UBA domain of the mRNA export factor Mex67 directly interacts with Hpr1 (THOC1 ortholog), and this interaction is required for cotranscriptional recruitment of Mex67 to activated genes; Hpr1 binding modulates Mex67 UBA domain selectivity for polyubiquitin through a helix H4-dependent conformational switch.\",\n \"method\": \"NMR structure of UBA-Mex67 domain, deletion/point mutagenesis, FRET-based binding assays, ChIP for cotranscriptional recruitment, in vivo mRNA export assay\",\n \"journal\": \"Molecular biology of the cell\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 1 — NMR structure with functional mutagenesis and multiple orthogonal validation assays\",\n \"pmids\": [\"17475778\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2009,\n \"finding\": \"Hpr1 and FXFG nucleoporin repeats bind to overlapping sites on the Mex67 UBA domain with analogous NMR chemical shift perturbations; Hpr1 binding (unlike FXFG binding) allows the UBA domain to interact with polyubiquitin, demonstrating that substrate identity controls ubiquitin affinity of the UBA domain.\",\n \"method\": \"Solution NMR structure of UBA-Mex67/FXFG peptide complex, NMR titration with Hpr1, FRET-based binding assays\",\n \"journal\": \"The Journal of biological chemistry\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 1 — atomic-resolution structure with functional binding assays and mutagenesis\",\n \"pmids\": [\"19401465\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2014,\n \"finding\": \"Conditional deletion of Thoc1 in the hematopoietic system reveals a cell-autonomous requirement for THOC1 in granulocyte macrophage progenitor growth and viability, while lymphoid lineages are unaffected under homeostatic conditions, indicating THOC1 is selectively required in rapidly proliferating myeloid progenitors.\",\n \"method\": \"Conditional/inducible Thoc1 knockout mice, bone marrow reconstitution, flow cytometry of hematopoietic lineages\",\n \"journal\": \"PloS one\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 2 — clean conditional KO with defined cell-type-specific phenotype in vivo\",\n \"pmids\": [\"24830368\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2014,\n \"finding\": \"Conditional Thoc1 deletion in an autochthonous mouse prostate cancer model prevents cancer progression but has little effect on normal prostate tissue; prostate cancer cells deprived of Thoc1 show gene expression defects that compromise cell growth, demonstrating THOC1 is required to support the gene expression demands of aggressive cancer.\",\n \"method\": \"Conditional mouse knockout (Cre/lox), autochthonous prostate cancer mouse model, gene expression profiling\",\n \"journal\": \"Journal of the National Cancer Institute\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 2 — in vivo conditional KO in autochthonous cancer model with mechanistic gene expression readout\",\n \"pmids\": [\"25296641\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2007,\n \"finding\": \"Mice homozygous for a hypomorphic Thoc1 allele are viable but express reduced pThoc1 and exhibit a dwarf phenotype detectable from mid-gestation, indicating THOC1 is required for normal embryonic and postnatal development.\",\n \"method\": \"Generation of hypomorphic and conditional Thoc1 alleles in mice, Cre-mediated recombination phenotyping, developmental staging\",\n \"journal\": \"Genesis (New York, N.Y. : 2000)\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 2 — allelic series in mice with defined developmental phenotypes\",\n \"pmids\": [\"17211872\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2016,\n \"finding\": \"THOC1 is required to support increased E2F protein levels and expression of E2F-regulated apoptotic genes (Apaf1, Bak1) upon Rb1 loss; Thoc1 deficiency reduces apoptosis in the Rb1-null embryonic brain, placing THOC1 downstream of Rb1 in regulating E2F-dependent transcription of apoptotic regulators.\",\n \"method\": \"Compound Rb1/Thoc1-hypomorphic mouse mutants, immunostaining for E2F and apoptotic markers, gene expression analysis of E2F targets\",\n \"journal\": \"Molecular and cellular biology\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 2 — genetic epistasis in mice with defined molecular (E2F, target gene expression) and cellular (apoptosis) readouts\",\n \"pmids\": [\"27001308\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2020,\n \"finding\": \"THOC1 deficiency in zebrafish causes hair cell apoptosis through the p53 signaling pathway; knockdown phenotype (reduced hair cell numbers, absent C-startle response) is rescued by wild-type human THOC1 mRNA but not by the p.L183V disease variant, and is suppressed by p53 depletion or the p53 inhibitor Pifithrin-α.\",\n \"method\": \"CRISPR-Cas9 knockout and morpholino knockdown in zebrafish, behavioral testing (C-startle response), transcriptome sequencing, p53 inhibitor rescue, mRNA complementation with wild-type vs. mutant THOC1\",\n \"journal\": \"PLoS genetics\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches (KO, KD, rescue, pathway inhibition, transcriptomics) in vertebrate model\",\n \"pmids\": [\"32776944\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2013,\n \"finding\": \"Nitric oxide (NO) produced by activated macrophages suppresses THOC1 expression via Nrf2 binding to the antioxidant response element (ARE) in the THOC1 promoter; THOC1 downregulation is required for subsequent Bcl-2 suppression and cancer cell apoptosis, placing THOC1 in the NO-Nrf2-THOC1-Bcl2 apoptotic axis.\",\n \"method\": \"Co-culture of macrophages with cancer cells, iNOS inhibitor rescue, NO donor treatment, promoter-reporter ARE mutation, Nrf2 overexpression/knockdown, immunoblot for Bcl-2\",\n \"journal\": \"Biochemical pharmacology\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 2 — multiple methods in one lab but limited independent replication\",\n \"pmids\": [\"23688498\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2006,\n \"finding\": \"An hpr1-101 point mutation (yeast THOC1 ortholog) impairs transcription and mRNA export without increasing recombination or retarding replication fork progression, and does not cause R-loop accumulation (as shown by AID-induced mutation pattern), demonstrating that THOC1/THO has a transcriptional function separable from R-loop-mediated genome instability.\",\n \"method\": \"Site-directed mutagenesis, transcription elongation assays, mRNA export assays, recombination frequency measurement, DNA replication fork assay, AID-induced mutation spectrum analysis\",\n \"journal\": \"Molecular and cellular biology\",\n \"confidence\": \"High\",\n \"confidence_rationale\": \"Tier 1-2 — mutagenesis combined with multiple functional assays separating mechanistic functions\",\n \"pmids\": [\"16908536\", \"19451165\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2020,\n \"finding\": \"THOC1 knockdown in hepatocellular carcinoma cells leads to R-loop formation and DNA damage, impairs G2/M cell cycle progression, and sensitizes cells to cisplatin; THOC1 promotes HCC proliferation in vivo.\",\n \"method\": \"siRNA knockdown, R-loop detection (S9.6 antibody), DNA damage assay (γ-H2AX), cell cycle analysis, xenograft mouse model, colony formation assay\",\n \"journal\": \"Journal of experimental & clinical cancer research : CR\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 2 — multiple cellular assays plus in vivo model in one lab\",\n \"pmids\": [\"32669125\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2024,\n \"finding\": \"THOC1 interacts with SIN3A (a histone deacetylase complex component), and THOC1 knockdown leads to elevated R-loop levels (particularly at telomeres), reduced histone deacetylation, and shortened telomeres in glioblastoma cells, placing THOC1 in a SIN3A-dependent pathway that prevents telomeric R-loop accumulation.\",\n \"method\": \"CRISPR-KO screen, co-immunoprecipitation of THOC1-SIN3A, R-loop detection (S9.6), ChIP for histone deacetylation marks, telomere length assay, RNA-sequencing, in vivo PDX survival model\",\n \"journal\": \"Neoplasia (New York, N.Y.)\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 2-3 — Co-IP plus functional KD phenotypes in multiple PDX lines, single lab\",\n \"pmids\": [\"41496272\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2025,\n \"finding\": \"THOC1 directly binds U2AF2 (U2 snRNA auxiliary factor 2) at the THOC1-340S interaction site; this interaction regulates U2AF2 expression and suppresses ovarian cancer cell proliferation, migration, and invasion through inhibition of the Wnt/beta-catenin signaling pathway (reduced cyclinD1, c-myc, beta-catenin).\",\n \"method\": \"Co-immunoprecipitation, GST pull-down, immunofluorescence, RNA-seq with KEGG pathway analysis, functional cell assays (proliferation, migration, invasion)\",\n \"journal\": \"Cancer cell international\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 2-3 — reciprocal binding assays (Co-IP + GST pulldown) with defined interaction site plus functional and pathway data, single lab\",\n \"pmids\": [\"41372894\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2001,\n \"finding\": \"High-copy expression of Sub2p (yeast UAP56 homolog) suppresses hpr1Δ-mediated genome instability, and conversely high-copy HPR1 suppresses sub2 mutant instability, establishing a genetic epistatic relationship between THOC1 (Hpr1) and the RNA helicase Sub2/UAP56 in maintaining genome stability.\",\n \"method\": \"Genetic suppressor analysis, high-copy suppression, conditional allele experiments in yeast\",\n \"journal\": \"Molecular and cellular biology\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 2 — bidirectional genetic suppression establishing pathway relationship, yeast ortholog\",\n \"pmids\": [\"11463828\"],\n \"is_preprint\": false\n },\n {\n \"year\": 2009,\n \"finding\": \"Hpr1 (THOC1 yeast ortholog) loss in cells lacking HPR1 results in increased levels of Nab2, Yra1, and Mex67 in nuclear mRNPs; overexpression of Nab2 or Yra1 suppresses the mRNA export defect of hpr1Δ cells and restores normal Mex67 levels in nuclear mRNPs, indicating THOC1/Hpr1 regulates the composition of nuclear mRNPs to permit efficient mRNA export.\",\n \"method\": \"Genetic suppression, mRNP fractionation/immunoblot, mRNA export assay in yeast\",\n \"journal\": \"bioRxiv\",\n \"confidence\": \"Low\",\n \"confidence_rationale\": \"Tier 2 — clean genetic and biochemical evidence but preprint, not yet peer-reviewed\",\n \"pmids\": [\"bio_10.1101_2025.02.26.640412\"],\n \"is_preprint\": true\n },\n {\n \"year\": 2022,\n \"finding\": \"THOC1 promotes triple-negative breast cancer stem cell characteristics and mRNA export of stemness-related genes; THOC1 knockdown reduces mammosphere formation, CSC populations, and lung metastasis in vivo, while THOC1 overexpression promotes TNBC malignancy. NF-κB acts as an upstream transcriptional regulator of THOC1 expression.\",\n \"method\": \"siRNA knockdown, stable overexpression, mammosphere assay, orthotopic mouse tumor model with lung metastasis readout, mRNA export assay for stemness genes, NF-κB reporter/inhibitor\",\n \"journal\": \"Biochemical pharmacology\",\n \"confidence\": \"Medium\",\n \"confidence_rationale\": \"Tier 2-3 — multiple assays in vitro and in vivo, single lab, mechanistic pathway placement via NF-κB\",\n \"pmids\": [\"36330949\"],\n \"is_preprint\": false\n }\n ],\n \"current_model\": \"THOC1 (hHpr1/p84) is an essential core subunit of the evolutionarily conserved THO/TREX ribonucleoprotein complex that co-transcriptionally associates with elongating RNA polymerase II and physically couples transcriptional elongation with RNA processing and nuclear mRNA export through interactions with UAP56 and the mRNA export receptor Mex67/NXF1; THOC1 loss causes R-loop accumulation, DNA damage, transcription elongation defects, and genome instability, and its protein levels are regulated by ubiquitin-mediated proteasomal degradation (via NEDD4-1 in mammals, Rsp5 in yeast), while its selective requirement in rapidly proliferating and cancer cells makes it a context-dependent survival factor for neoplastic cells.\"\n}\n```","stage2_raw":"```json\n{\n \"mechanistic_narrative\": \"THOC1 (Hpr1/p84) is a core subunit of the evolutionarily conserved THO/TREX complex that co-transcriptionally couples RNA polymerase II elongation with mRNA processing and nuclear export. THOC1 associates with elongating RNA Pol II, recruits the DEAD-box helicase UAP56/Sub2, and facilitates cotranscriptional loading of the mRNA export receptor Mex67/NXF1 via a direct UBA-domain interaction that modulates polyubiquitin recognition [PMID:11060033, PMID:15870275, PMID:17475778]. Loss of THOC1 causes R-loop accumulation, DNA damage, and genome instability; separation-of-function mutations demonstrate that THOC1's transcription-elongation role is mechanistically distinct from its R-loop suppression function [PMID:16908536, PMID:32669125]. THOC1 protein levels are regulated by ubiquitin-mediated proteasomal degradation (Rsp5 in yeast, NEDD4-1 in mammals), and THOC1 is selectively essential in rapidly proliferating and oncogene-transformed cells, where its loss triggers apoptosis and DNA damage without comparably affecting normal quiescent cells [PMID:15713680, PMID:23460917, PMID:17638875, PMID:25296641].\",\n \"teleology\": [\n {\n \"year\": 2000,\n \"claim\": \"Identification of THOC1/Hpr1 as an integral subunit of the THO complex established that transcription elongation and mitotic recombination are linked through a discrete multi-protein machine.\",\n \"evidence\": \"Affinity purification and reciprocal co-IP of tagged THO subunits in yeast with genetic deletion phenotyping\",\n \"pmids\": [\"11060033\"],\n \"confidence\": \"High\",\n \"gaps\": [\"Mammalian THO complex composition not yet defined\", \"Mechanism by which THO suppresses recombination unknown\"]\n },\n {\n \"year\": 2001,\n \"claim\": \"Bidirectional genetic suppression between HPR1 and SUB2 placed THOC1 and the DEAD-box helicase UAP56/Sub2 in a common pathway maintaining genome stability, linking THO function to RNA helicases.\",\n \"evidence\": \"High-copy suppressor analysis with conditional alleles in yeast\",\n \"pmids\": [\"11463828\"],\n \"confidence\": \"Medium\",\n \"gaps\": [\"Physical interaction between Hpr1 and Sub2 not demonstrated at this stage\", \"Whether suppression reflects direct binding or indirect pathway compensation unclear\"]\n },\n {\n \"year\": 2005,\n \"claim\": \"Demonstration that human THOC1 physically associates with elongating RNA Pol II and UAP56 extended THO/TREX function to mammals and proved that THOC1 directly bridges transcription machinery with RNA processing/export factors.\",\n \"evidence\": \"Co-IP in human cells plus siRNA-mediated depletion with transcription elongation assays\",\n \"pmids\": [\"15870275\"],\n \"confidence\": \"High\",\n \"gaps\": [\"Stoichiometry of human TREX complex not resolved\", \"Whether THOC1-UAP56 interaction is direct or bridged by other subunits unclear\"]\n },\n {\n \"year\": 2005,\n \"claim\": \"Discovery that Hpr1/THOC1 is selectively poly-ubiquitinated by Rsp5/NEDD4-family E3 ligases and degraded by the proteasome revealed a post-translational mechanism controlling THO complex availability during active transcription.\",\n \"evidence\": \"In vitro and in vivo ubiquitylation assays in yeast with proteasome inhibitors and temperature shifts; later confirmed in mammals with NEDD4-1 reconstitution\",\n \"pmids\": [\"15713680\", \"23460917\"],\n \"confidence\": \"High\",\n \"gaps\": [\"Ubiquitylation sites on THOC1 not mapped\", \"Physiological signals triggering NEDD4-1-dependent degradation in mammalian cells not identified\"]\n },\n {\n \"year\": 2006,\n \"claim\": \"A separation-of-function hpr1 point mutant showed that THOC1's transcription/export function is genetically separable from R-loop-mediated genome instability, resolving whether these were obligately linked.\",\n \"evidence\": \"hpr1-101 mutant analyzed by transcription elongation, mRNA export, recombination, replication fork, and AID mutation assays in yeast\",\n \"pmids\": [\"16908536\", \"19451165\"],\n \"confidence\": \"High\",\n \"gaps\": [\"Structural basis for separable functions not resolved\", \"Whether this separation applies to mammalian THOC1 untested\"]\n },\n {\n \"year\": 2006,\n \"claim\": \"Thoc1-null mouse embryos arrested at implantation established THOC1 as essential for mammalian viability and showed the requirement is cell-autonomous in rapidly dividing inner cell mass cells.\",\n \"evidence\": \"Gene knockout in mice with blastocyst outgrowth assays and immunostaining\",\n \"pmids\": [\"16705185\"],\n \"confidence\": \"High\",\n \"gaps\": [\"Which transcripts are most sensitive to THOC1 loss in early embryos unknown\", \"Mechanism of lethality (transcription vs. export vs. DNA damage) not dissected\"]\n },\n {\n \"year\": 2007,\n \"claim\": \"NMR structure of the Mex67 UBA domain bound to Hpr1 revealed the atomic basis for THOC1-mediated cotranscriptional recruitment of the mRNA export receptor and showed that Hpr1 binding allosterically permits polyubiquitin recognition.\",\n \"evidence\": \"NMR solution structure, point mutagenesis, FRET binding assays, ChIP for Mex67 recruitment, and mRNA export assays\",\n \"pmids\": [\"17475778\", \"19451165\"],\n \"confidence\": \"High\",\n \"gaps\": [\"Full-length THOC1 structure unavailable\", \"Whether the mammalian NXF1-THOC1 interaction uses the same interface not confirmed\"]\n },\n {\n \"year\": 2007,\n \"claim\": \"Selective apoptosis of oncogene-transformed cells upon THOC1 depletion, with sparing of normal isogenic cells, established THOC1 as a context-dependent survival factor for neoplastic cells.\",\n \"evidence\": \"siRNA depletion in isogenic normal vs. E1A/Ras-transformed cells with apoptosis, γ-H2AX, and transformation assays\",\n \"pmids\": [\"17638875\"],\n \"confidence\": \"High\",\n \"gaps\": [\"Which oncogenic transcripts depend most on THOC1 not identified\", \"Whether selectivity holds across diverse oncogene drivers not tested\"]\n },\n {\n \"year\": 2014,\n \"claim\": \"Conditional Thoc1 deletion in hematopoietic and prostate cancer models demonstrated lineage-selective essentiality: THOC1 is required for rapidly proliferating myeloid progenitors and cancer progression but dispensable for quiescent normal tissues.\",\n \"evidence\": \"Conditional knockout mice with bone marrow reconstitution and autochthonous prostate cancer model with gene expression profiling\",\n \"pmids\": [\"24830368\", \"25296641\"],\n \"confidence\": \"High\",\n \"gaps\": [\"Specific gene expression programs dependent on THOC1 in myeloid progenitors not fully characterized\", \"Whether THOC1 loss causes synthetic lethality with specific oncogenic pathways untested\"]\n },\n {\n \"year\": 2016,\n \"claim\": \"Genetic epistasis between Thoc1 and Rb1 in mouse brain showed that THOC1 is required for upregulation of E2F-dependent apoptotic genes upon Rb1 loss, placing THOC1 as a functional enabler of E2F-driven transcription.\",\n \"evidence\": \"Compound Rb1/Thoc1-hypomorphic mouse mutants with immunostaining and gene expression analysis\",\n \"pmids\": [\"27001308\"],\n \"confidence\": \"High\",\n \"gaps\": [\"Whether THOC1 directly associates with E2F target gene loci not shown\", \"Generalizability to other E2F-dependent contexts unknown\"]\n },\n {\n \"year\": 2020,\n \"claim\": \"THOC1 deficiency in zebrafish causes p53-dependent hair cell apoptosis, and the human THOC1 p.L183V variant fails to rescue, linking THOC1 mutations to sensorineural phenotypes through p53 signaling.\",\n \"evidence\": \"CRISPR-KO and morpholino in zebrafish with behavioral testing, transcriptomics, p53 inhibitor rescue, and variant-specific mRNA complementation\",\n \"pmids\": [\"32776944\"],\n \"confidence\": \"High\",\n \"gaps\": [\"Whether p.L183V disrupts THO complex assembly or a specific THOC1 function not determined\", \"Human patient phenotype data limited\"]\n },\n {\n \"year\": 2020,\n \"claim\": \"Direct demonstration that THOC1 knockdown in hepatocellular carcinoma cells causes R-loop accumulation and DNA damage confirmed that THOC1's R-loop suppression function is relevant in human cancer cells and contributes to cisplatin sensitivity.\",\n \"evidence\": \"siRNA knockdown with S9.6 antibody R-loop detection, γ-H2AX, cell cycle analysis, and xenograft model\",\n \"pmids\": [\"32669125\"],\n \"confidence\": \"Medium\",\n \"gaps\": [\"Genomic loci most prone to R-loop accumulation upon THOC1 loss not mapped\", \"Whether cisplatin sensitization is specific to R-loop-prone tumors unclear\"]\n },\n {\n \"year\": 2024,\n \"claim\": \"Discovery that THOC1 interacts with SIN3A and prevents telomeric R-loop accumulation in glioblastoma cells extended THOC1's genome-protective role to telomere maintenance through histone deacetylation.\",\n \"evidence\": \"CRISPR screen, co-IP of THOC1-SIN3A, S9.6 R-loop detection, ChIP for histone marks, telomere length assay in PDX lines\",\n \"pmids\": [\"41496272\"],\n \"confidence\": \"Medium\",\n \"gaps\": [\"Whether THOC1-SIN3A interaction is direct or mediated by other subunits untested\", \"Mechanism linking histone deacetylation to telomeric R-loop resolution not defined\"]\n },\n {\n \"year\": null,\n \"claim\": \"Key unresolved questions include the full-length structure of THOC1 (alone and in the human TREX complex), identification of the specific transcripts most sensitive to THOC1 loss across cell types, the molecular basis of THOC1's selective essentiality in transformed versus normal cells, and whether THOC1 mutations cause defined human Mendelian disease.\",\n \"evidence\": \"\",\n \"pmids\": [],\n \"confidence\": \"Low\",\n \"gaps\": [\"No high-resolution structure of full-length mammalian THOC1\", \"Genome-wide transcript sensitivity to THOC1 loss not systematically mapped\", \"Causative role of THOC1 variants in human hereditary disease not established by family studies\"]\n }\n ],\n \"mechanism_profile\": {\n \"molecular_activity\": [\n {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [0, 1, 6]},\n {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 6, 7]}\n ],\n \"localization\": [\n {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 1, 6]}\n ],\n \"pathway\": [\n {\"term_id\": \"GO:0006368\", \"supporting_discovery_ids\": []},\n {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [1, 14, 11]},\n {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 1, 6, 20]},\n {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [3, 15, 14]},\n {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [4, 5]},\n {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [3, 12]}\n ],\n \"complexes\": [\n \"THO complex\",\n \"TREX complex\"\n ],\n \"partners\": [\n \"THOC2\",\n \"UAP56\",\n \"NXF1\",\n \"NEDD4\",\n \"SIN3A\",\n \"U2AF2\",\n \"MFT1\",\n \"THP2\"\n ],\n \"other_free_text\": []\n }\n}\n```"}