{"gene":"EXOSC5","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":1999,"finding":"Rrp46 (EXOSC5 ortholog) was identified as one of six novel components of the yeast exosome, a complex of 3'→5' exoribonucleases involved in RNA processing and degradation. Human homologs of nine of the eleven yeast exosome components were identified, and nuclear and cytoplasmic forms of the complex were demonstrated to exist in both yeast and humans.","method":"Biochemical fractionation, indirect immunofluorescence, complementation assays","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (biochemical fractionation, immunofluorescence, complementation), foundational study replicated broadly","pmids":["10465791"],"is_preprint":false},{"year":2001,"finding":"The human exosome, which includes PM-Scl75 (EXOSC5), was purified and characterized by mass spectrometry. The complex was shown to be required for rapid degradation of ARE-containing mRNAs but not for poly(A) shortening. PM-Scl75 was found to interact specifically with AU-rich elements (AREs), implicating EXOSC5 directly in ARE-mediated mRNA decay.","method":"Mass spectrometry, immunodepletion, cell-free RNA decay assay, RNA-protein interaction assays","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1–2 — reconstitution/cell-free assay combined with immunodepletion and MS; replicated across multiple studies","pmids":["11719186","11782436"],"is_preprint":false},{"year":2002,"finding":"The human exosome (containing EXOSC5/PM-Scl75) is required for efficient 3'→5' exonucleolytic decay of ARE-containing mRNAs in HeLa cytoplasmic extracts. Immunodepletion of PM-Scl75 abolished this activity, and ARE sequences dramatically stimulated 3'→5' decay, establishing the exosome as the major cytoplasmic 3'→5' RNA decay pathway.","method":"In vitro RNA deadenylation/decay assay, immunodepletion with anti-PM-Scl75 antibodies, phosphorothioate-modified RNA trapping","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with specific immunodepletion of EXOSC5/PM-Scl75, clear causal link established","pmids":["11782436"],"is_preprint":false},{"year":2006,"finding":"The X-ray crystal structure of the 286 kDa nine-subunit human exosome was determined at 3.35 Å resolution, revealing EXOSC5 (Rrp46) as a structural subunit. Reconstitution experiments showed the human 9-subunit exosome has processive phosphorolytic activity, contributed by the Rrp41/Rrp45 heterodimer, while EXOSC5/Rrp46 plays a structural role within the ring.","method":"X-ray crystallography, in vitro reconstitution, biochemical activity assays with diverse RNA substrates","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus reconstitution and biochemical validation in same study","pmids":["17174896"],"is_preprint":false},{"year":2010,"finding":"Crystal structures of C. elegans CRN-5 (EXOSC5 ortholog) and rice Rrp46 were determined at 3.9 Å and 2.0 Å resolution, respectively. Human Rrp46 (EXOSC5), rice Rrp46, and CRN-5 were found to form homodimers both in recombinant form and in cellular environments, in addition to their association with the exosome complex. Human Rrp46 bound DNA without detectable nuclease activity, while rice Rrp46 had both phosphorolytic RNase and hydrolytic DNase activities. Site-directed mutagenesis (E160Q abolished DNase; K75E/Q76E abolished RNase) confirmed catalytic residues. CRN-5 directly interacted with apoptotic nuclease CRN-4 and enhanced its DNase activity.","method":"X-ray crystallography, co-immunoprecipitation, site-directed mutagenesis, in vitro nuclease assays, size-exclusion chromatography","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1 — crystal structure, mutagenesis, and in vitro enzymatic assays with orthogonal co-IP validation","pmids":["20660080"],"is_preprint":false},{"year":2011,"finding":"The RNA exosome core complex (including EXOSC5) associates with activation-induced cytidine deaminase (AID) in B cells activated for class switch recombination (CSR). The exosome accumulates on immunoglobulin heavy-chain switch regions in an AID-dependent manner and is required for optimal CSR. A recombinant RNA exosome core complex conferred robust AID- and transcription-dependent DNA deamination of both strands of transcribed substrates in vitro, revealing a role for the exosome in antibody diversity generation.","method":"Co-immunoprecipitation, ChIP, in vitro transcription/deamination assay with recombinant exosome core, genetic knockdown of exosome subunits","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1–2 — recombinant reconstitution in vitro combined with ChIP and co-IP in B cells; multiple orthogonal methods","pmids":["21255825"],"is_preprint":false},{"year":2020,"finding":"EXOSC5 was identified as a structural (non-catalytic) subunit of the RNA exosome required for brain development. Biallelic loss-of-function variants in EXOSC5 cause a neurodevelopmental syndrome. Loss of exosc5 in zebrafish caused shortened/curved bodies, reduced eye/head size, and edema. Pathogenic EXOSC5 variants modeled in budding yeast caused defects in RNA exosome function and altered interactions with other RNA exosome subunits, demonstrating that specific variants disrupt exosome complex integrity.","method":"Zebrafish morpholino knockdown, yeast complementation assays, mammalian cell modeling of variants, interaction assays (co-immunoprecipitation of exosome subunits)","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 — multiple model systems (zebrafish, yeast, mammalian cells) with orthogonal functional readouts","pmids":["32504085"],"is_preprint":false},{"year":2020,"finding":"EXOSC5 was identified as a physical interaction partner of SARS-CoV-2 Nsp8 protein by affinity-purification mass spectrometry, placing it in the host-viral protein interaction network relevant to COVID-19 pathogenesis.","method":"Affinity-purification mass spectrometry (AP-MS) of tagged SARS-CoV-2 proteins expressed in human cells","journal":"Nature","confidence":"Low","confidence_rationale":"Tier 3 — single AP-MS dataset, no functional follow-up specific to EXOSC5","pmids":["32353859"],"is_preprint":false},{"year":2022,"finding":"EXOSC5 knockdown in gastric cancer cells inhibited proliferation, induced G1/S phase arrest, increased p21 and p27 levels, and decreased cyclinD1 expression. Mechanistically, EXOSC5 was shown to promote cell cycle progression through activation of AKT and STAT3 signaling pathways.","method":"siRNA knockdown, CCK-8 proliferation assay, flow cytometry, Western blotting, GC organoid model, nude mouse xenograft","journal":"Journal of Cancer","confidence":"Medium","confidence_rationale":"Tier 2–3 — knockdown with defined proliferation phenotype and pathway readout across in vitro and in vivo models, single lab","pmids":["35371329"],"is_preprint":false},{"year":2022,"finding":"EXOSC5 knockdown in hepatocellular carcinoma cells inhibited cell growth and proliferation. Mechanistically, EXOSC5 promoted cell proliferation via activation of STAT3 signaling.","method":"siRNA knockdown, cell proliferation assays, Western blotting for STAT3 pathway components","journal":"International journal of molecular sciences","confidence":"Low","confidence_rationale":"Tier 3 — single lab, limited mechanistic follow-up beyond STAT3 phosphorylation Western blot","pmids":["36293016"],"is_preprint":false},{"year":2024,"finding":"EXOSC5 maintains cancer stem cell (CSC) activity in endometrial cancer by regulating expression of netrin-4 (NTN4). NTN4, when secreted, binds integrin β1 and activates the FAK/SRC signaling axis to elevate c-MYC activity. EXOSC5 knockdown reduced NTN4 levels, diminished CSC self-renewal, reduced c-MYC and SOX2 expression, and curtailed tumorigenicity in tumor spheres.","method":"siRNA knockdown, tumor sphere assays, Western blotting, NTN4 rescue experiments, limiting dilution CSC frequency assay, tissue correlation analysis (n=93 EC tissues)","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 2–3 — knockdown with mechanistic rescue (NTN4 treatment), pathway dissection via integrin β1/FAK/SRC, single lab","pmids":["38164180"],"is_preprint":false}],"current_model":"EXOSC5 (Rrp46/PM-Scl75) is a structural, non-catalytic subunit of the nine-subunit RNA exosome ring complex that directly contacts AU-rich elements to recruit the complex for 3'→5' degradation of ARE-containing mRNAs, participates in RNA processing/surveillance including AID-dependent antibody class switch recombination, is required for normal brain development (loss causes a neurodevelopmental syndrome with cerebellar hypoplasia in humans and zebrafish), and in cancer contexts activates STAT3/AKT signaling and the NTN4/integrin β1/FAK/SRC/c-MYC axis to promote proliferation and stemness."},"narrative":{"teleology":[{"year":1999,"claim":"Identification of Rrp46 as a core exosome subunit established that EXOSC5 is part of a conserved multi-subunit 3'→5' exoribonuclease complex present in both nucleus and cytoplasm of eukaryotes.","evidence":"Biochemical fractionation, indirect immunofluorescence, and complementation assays in yeast with identification of human homologs","pmids":["10465791"],"confidence":"High","gaps":["Catalytic versus structural role of individual subunits not resolved","Substrate specificity of individual subunits unknown"]},{"year":2001,"claim":"Demonstrating that EXOSC5/PM-Scl75 directly binds AU-rich elements and that the exosome complex is required for ARE-mediated mRNA decay answered how specific mRNA substrates are recruited for 3'→5' degradation.","evidence":"Immunodepletion of PM-Scl75 from HeLa cytoplasmic extracts abolished ARE-dependent 3'→5' decay; RNA-protein interaction assays showed direct ARE binding","pmids":["11719186","11782436"],"confidence":"High","gaps":["Whether EXOSC5 ARE binding is sufficient for recruitment or requires cofactors","In vivo target mRNA repertoire not defined"]},{"year":2006,"claim":"The crystal structure of the human nine-subunit exosome resolved EXOSC5 as a structural ring component, demonstrating that catalytic activity resides in the Rrp41/Rrp45 heterodimer rather than in EXOSC5 itself.","evidence":"X-ray crystallography at 3.35 Å with reconstitution and biochemical activity assays","pmids":["17174896"],"confidence":"High","gaps":["How EXOSC5 contributes to RNA threading through the channel not resolved","Dynamics of subunit assembly in vivo unclear"]},{"year":2010,"claim":"Structural and biochemical analysis of EXOSC5 orthologs revealed unexpected homodimerization and DNA-binding capacity, expanding the possible roles of Rrp46-family proteins beyond the exosome ring.","evidence":"Crystal structures of C. elegans CRN-5 and rice Rrp46; site-directed mutagenesis; in vitro nuclease and DNA-binding assays; co-IP","pmids":["20660080"],"confidence":"High","gaps":["Physiological relevance of homodimerization and DNA binding for human EXOSC5 not demonstrated","Whether human EXOSC5 possesses latent catalytic activity under specific conditions remains untested"]},{"year":2011,"claim":"Discovery that the exosome core associates with AID and accumulates on immunoglobulin switch regions revealed an unexpected role for the RNA exosome—including EXOSC5—in antibody class switch recombination via transcription-dependent DNA deamination.","evidence":"Co-IP, ChIP on switch regions, and in vitro transcription/deamination assay with recombinant exosome core in activated B cells","pmids":["21255825"],"confidence":"High","gaps":["Individual contribution of EXOSC5 versus other ring subunits to AID targeting not dissected","Whether exosome facilitates somatic hypermutation through a similar mechanism unclear"]},{"year":2020,"claim":"Identification of biallelic EXOSC5 variants causing a neurodevelopmental syndrome with cerebellar hypoplasia established the gene as essential for brain development and demonstrated that pathogenic variants disrupt exosome complex integrity.","evidence":"Zebrafish morpholino knockdown phenocopied features; yeast complementation showed functional deficits; co-IP revealed altered subunit interactions","pmids":["32504085"],"confidence":"High","gaps":["Specific RNA targets dysregulated in developing brain not identified","Genotype–phenotype relationships across different EXOSC5 variants not fully defined"]},{"year":2022,"claim":"EXOSC5 was shown to promote cancer cell proliferation and cell-cycle progression through AKT and STAT3 signaling, suggesting exosome-independent or RNA-target-dependent oncogenic functions.","evidence":"siRNA knockdown in gastric and hepatocellular carcinoma cells with proliferation assays, flow cytometry, Western blotting, xenograft models","pmids":["35371329","36293016"],"confidence":"Medium","gaps":["Direct RNA substrates linking EXOSC5 to STAT3/AKT activation not identified","Whether these effects are exosome-complex-dependent or subunit-autonomous not tested","Single-lab findings for HCC; limited mechanistic depth beyond phospho-Western blots"]},{"year":2024,"claim":"Linking EXOSC5 to cancer stemness through regulation of NTN4 and the integrin β1/FAK/SRC/c-MYC axis provided a downstream pathway for EXOSC5's pro-tumorigenic activity in endometrial cancer.","evidence":"siRNA knockdown with NTN4 rescue, tumor sphere assays, limiting dilution assays, and tissue correlation in 93 endometrial cancer specimens","pmids":["38164180"],"confidence":"Medium","gaps":["Whether EXOSC5 regulates NTN4 mRNA stability directly via exosome-mediated decay or through an indirect mechanism not established","Generalizability beyond endometrial cancer not tested"]},{"year":null,"claim":"Key unresolved questions include the identity of specific RNA targets whose stability is controlled by EXOSC5 in normal tissues, the mechanism by which EXOSC5 structural variants cause selective neuronal vulnerability, and whether cancer-associated functions depend on the intact exosome complex or on exosome-independent activities.","evidence":"","pmids":[],"confidence":"Low","gaps":["No transcriptome-wide direct target map (e.g., CLIP-seq) for EXOSC5","No structural basis for how pathogenic missense variants alter exosome function","Exosome-dependent versus -independent oncogenic mechanisms not disambiguated"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[1,2,5]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[3,6]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,5]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,1,2,5]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[5]}],"complexes":["RNA exosome core complex"],"partners":["EXOSC4","EXOSC6","EXOSC7","EXOSC8","EXOSC9","DIS3","AICDA"],"other_free_text":[]},"mechanistic_narrative":"EXOSC5 (Rrp46/PM-Scl75) is a structural, non-catalytic subunit of the nine-subunit RNA exosome core complex that functions in 3'→5' RNA processing, surveillance, and degradation. Within the exosome ring, EXOSC5 directly contacts AU-rich elements (AREs) on mRNAs and is required for efficient cytoplasmic ARE-mediated mRNA decay [PMID:11719186, PMID:11782436]; the exosome core complex also associates with activation-induced cytidine deaminase (AID) to facilitate immunoglobulin class switch recombination by enabling transcription-dependent DNA deamination of switch regions [PMID:21255825]. Biallelic loss-of-function variants in EXOSC5 cause a neurodevelopmental syndrome with cerebellar hypoplasia, and pathogenic variants disrupt exosome complex integrity in yeast and zebrafish models [PMID:32504085]. In cancer contexts, EXOSC5 promotes proliferation and stemness through STAT3/AKT signaling and regulation of the NTN4/integrin β1/FAK/SRC/c-MYC axis [PMID:35371329, PMID:38164180]."},"prefetch_data":{"uniprot":{"accession":"Q9NQT4","full_name":"Exosome complex component RRP46","aliases":["Chronic myelogenous leukemia tumor antigen 28","Exosome component 5","Ribosomal RNA-processing protein 46","p12B"],"length_aa":235,"mass_kda":25.2,"function":"Non-catalytic component of the RNA exosome complex which has 3'->5' exoribonuclease activity and participates in a multitude of cellular RNA processing and degradation events. In the nucleus, the RNA exosome complex is involved in proper maturation of stable RNA species such as rRNA, snRNA and snoRNA, in the elimination of RNA processing by-products and non-coding 'pervasive' transcripts, such as antisense RNA species and promoter-upstream transcripts (PROMPTs), and of mRNAs with processing defects, thereby limiting or excluding their export to the cytoplasm. The RNA exosome may be involved in Ig class switch recombination (CSR) and/or Ig variable region somatic hypermutation (SHM) by targeting AICDA deamination activity to transcribed dsDNA substrates. In the cytoplasm, the RNA exosome complex is involved in general mRNA turnover and specifically degrades inherently unstable mRNAs containing AU-rich elements (AREs) within their 3' untranslated regions, and in RNA surveillance pathways, preventing translation of aberrant mRNAs. It seems to be involved in degradation of histone mRNA. The catalytic inactive RNA exosome core complex of 9 subunits (Exo-9) is proposed to play a pivotal role in the binding and presentation of RNA for ribonucleolysis, and to serve as a scaffold for the association with catalytic subunits and accessory proteins or complexes (PubMed:11782436, PubMed:21269460). In vitro, EXOSC5 does not bind or digest single-stranded RNA and binds to double-stranded DNA without detectable DNase activity (PubMed:20660080)","subcellular_location":"Nucleus, nucleolus; Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9NQT4/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/EXOSC5","classification":"Common Essential","n_dependent_lines":1120,"n_total_lines":1208,"dependency_fraction":0.9271523178807947},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"NPM1","stoichiometry":0.2},{"gene":"PSPC1","stoichiometry":0.2},{"gene":"RBM7","stoichiometry":0.2},{"gene":"RPS16","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/EXOSC5","total_profiled":1310},"omim":[{"mim_id":"619576","title":"CEREBELLAR ATAXIA, BRAIN ABNORMALITIES, AND CARDIAC CONDUCTION DEFECTS; CABAC","url":"https://www.omim.org/entry/619576"},{"mim_id":"606492","title":"EXOSOME COMPONENT 5; EXOSC5","url":"https://www.omim.org/entry/606492"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoli","reliability":"Enhanced"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/EXOSC5"},"hgnc":{"alias_symbol":["hRrp46p","Rrp46p","RRP46","RRP41B","MGC12901","p12B"],"prev_symbol":[]},"alphafold":{"accession":"Q9NQT4","domains":[{"cath_id":"3.30.230.70","chopping":"32-234","consensus_level":"medium","plddt":92.0218,"start":32,"end":234}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NQT4","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NQT4-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NQT4-F1-predicted_aligned_error_v6.png","plddt_mean":84.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=EXOSC5","jax_strain_url":"https://www.jax.org/strain/search?query=EXOSC5"},"sequence":{"accession":"Q9NQT4","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NQT4.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NQT4/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NQT4"}},"corpus_meta":[{"pmid":"32504085","id":"PMC_32504085","title":"Biallelic variants in the RNA exosome gene EXOSC5 are associated with developmental delays, short stature, cerebellar hypoplasia and motor weakness.","date":"2020","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/32504085","citation_count":29,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"19861556","id":"PMC_19861556","title":"Transcript-based cloning of RRP46, a regulator of rRNA processing and R gene-independent cell death in barley-powdery mildew interactions.","date":"2009","source":"The Plant cell","url":"https://pubmed.ncbi.nlm.nih.gov/19861556","citation_count":22,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"34089229","id":"PMC_34089229","title":"Risk of sudden cardiac death in EXOSC5-related disease.","date":"2021","source":"American journal of medical genetics. 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proteomics.","date":"2010","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/21145461","citation_count":318,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"11782436","id":"PMC_11782436","title":"The mammalian exosome mediates the efficient degradation of mRNAs that contain AU-rich elements.","date":"2002","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/11782436","citation_count":300,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"21791617","id":"PMC_21791617","title":"DDX60, a DEXD/H box helicase, is a novel antiviral factor promoting RIG-I-like receptor-mediated signaling.","date":"2011","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/21791617","citation_count":251,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"21255825","id":"PMC_21255825","title":"The RNA exosome targets the AID cytidine deaminase to both strands of transcribed duplex DNA substrates.","date":"2011","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/21255825","citation_count":248,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":5245,"output_tokens":1583,"usd":0.01974},"stage2":{"model":"claude-opus-4-6","input_tokens":4839,"output_tokens":1813,"usd":0.10428},"total_usd":0.314439,"stage1_batch_id":"msgbatch_0118RScg3WGaGkaZRtWZbtce","stage2_batch_id":"msgbatch_01Cpfzvtbj42aqp5oYZ5Te2s","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":16861,"output_tokens":4014,"usd":0.055397},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":6553,"output_tokens":2290,"usd":0.135022}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2010,\n      \"finding\": \"Human Rrp46 (EXOSC5 ortholog) forms homodimers both in recombinant form and in cellular environments, in addition to its association with the exosome complex. Crystal structures of rice Rrp46 (oRrp46) and C. elegans CRN-5 were solved; oRrp46 homodimers possess both phosphorolytic RNase and hydrolytic DNase activities, while hRrp46 and CRN-5 bind DNA without detectable nuclease activity. Site-directed mutagenesis (E160Q abolishes DNase; K75E/Q76E abolishes RNase) confirmed critical active-site residues in oRrp46.\",\n      \"method\": \"Crystal structure determination (2.0 Å for oRrp46, 3.9 Å for CRN-5), in vitro enzymatic assays, site-directed mutagenesis, co-immunoprecipitation, size-exclusion chromatography\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures, in vitro enzymatic reconstitution, and mutagenesis in one study\",\n      \"pmids\": [\"20660080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"C. elegans CRN-5 (EXOSC5 ortholog) directly interacts with the apoptotic nuclease CRN-4 and enhances CRN-4's DNase activity, implicating CRN-5 as a cofactor in apoptotic DNA degradation.\",\n      \"method\": \"Co-immunoprecipitation / pulldown, in vitro DNase activity assay\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct interaction confirmed by pulldown and functional enhancement shown by in vitro assay, single study\",\n      \"pmids\": [\"20660080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Biallelic pathogenic variants in EXOSC5 (a structural subunit of the RNA exosome) disrupt RNA exosome function and alter interactions between EXOSC5 and other RNA exosome subunits, as modeled in budding yeast and mammalian cells. Loss of exosc5 in zebrafish causes developmental defects (shortened/curved body, reduced eye/head size, edema), confirming its requirement for normal development.\",\n      \"method\": \"Yeast complementation assay, mammalian cell-based interaction studies (co-immunoprecipitation of exosome subunits), zebrafish morpholino/loss-of-function, RNA processing assays\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (yeast genetics, mammalian cell interaction assays, zebrafish knockdown) in single study with rigorous controls\",\n      \"pmids\": [\"32504085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"EXOSC5 knockdown in gastric cancer cells reduces cyclin D1 expression and increases p21 and p27 levels, causing G1/S phase arrest; mechanistic studies show these effects are mediated through the AKT and STAT3 signaling pathways.\",\n      \"method\": \"siRNA knockdown, Western blotting, CCK-8/colony formation assays, flow cytometry, nude mouse xenograft\",\n      \"journal\": \"Journal of Cancer\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — pathway placement inferred from Western blotting of pathway readouts after knockdown, single lab, no direct enzyme-substrate experiments\",\n      \"pmids\": [\"35371329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"EXOSC5 knockdown in hepatocellular carcinoma cells reduces cell proliferation, with evidence that EXOSC5 promotes growth via activation of STAT3 signaling.\",\n      \"method\": \"siRNA knockdown, Western blotting, cell proliferation assay\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, single method set, pathway placement inferred from downstream readouts only\",\n      \"pmids\": [\"36293016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"EXOSC5 knockdown in endometrial cancer cells reduces NTN4 (netrin-4) expression; extracellular NTN4 binds integrin β1 and activates the FAK/SRC axis to elevate c-MYC activity and promote cancer stem cell self-renewal, placing EXOSC5 upstream of the NTN4/integrin β1/FAK/SRC/c-MYC pathway.\",\n      \"method\": \"siRNA knockdown, Western blotting, NTN4 rescue/treatment experiments, tumor sphere assays, in vivo xenograft, co-immunoprecipitation (NTN4-integrin β1)\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 + Moderate — multiple functional readouts and NTN4 rescue experiment support pathway placement, but direct EXOSC5-NTN4 RNA regulation mechanism not fully resolved\",\n      \"pmids\": [\"38164180\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"EXOSC5 (Rrp46) is a structural subunit of the RNA exosome complex that forms homodimers independently of the complex; its orthologs possess RNase/DNase active-site residues critical for catalysis, its pathogenic variants impair RNA exosome function and inter-subunit interactions, and in cancer contexts it promotes proliferation and stemness through downstream signaling pathways including AKT/STAT3 and NTN4/integrin β1/FAK/SRC.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper first, then extract discoveries from KEEP papers only.\n\n**Classification:**\n\nRetrieved papers:\n1. PMID:32504085 — KEEP (canonical EXOSC5, biallelic variants, functional studies)\n2. PMID:19861556 — EXCLUDE (barley RRP46/plant gene, symbol collision with non-orthologous organism)\n3. PMID:34089229 — KEEP (EXOSC5-related disease, cardiac phenotype)\n4. PMID:20660080 — KEEP (Rrp46/EXOSC5 structural and biochemical characterization, C. elegans ortholog and rice ortholog — mechanistic findings relevant to human EXOSC5)\n5. PMID:38164180 — KEEP (EXOSC5 in endometrial cancer, mechanistic knockdown studies)\n6. PMID:35371329 — KEEP (EXOSC5 in gastric cancer, AKT/STAT3 mechanism)\n7. PMID:36293016 — KEEP (EXOSC5 in HCC, STAT3 mechanism)\n\nAdditional gene2pubmed papers:\n- PMID:32353859 — KEEP (SARS-CoV-2 interaction map, EXOSC5 identified as interaction partner)\n- PMID:17081983 — EXCLUDE (phosphoproteomics, no EXOSC5-specific finding)\n- PMID:16189514 — EXCLUDE (general interactome map)\n- PMID:12477932 — EXCLUDE (cDNA library)\n- PMID:18187620 — EXCLUDE (HIV screen, no EXOSC5-specific mechanism)\n- PMID:26186194 — EXCLUDE (general BioPlex interactome)\n- PMID:28514442 — EXCLUDE (general BioPlex 2.0)\n- PMID:26496610 — EXCLUDE (general interactome)\n- PMID:25416956 — EXCLUDE (general interactome)\n- PMID:15635413 — EXCLUDE (nucleolar proteomics, no EXOSC5-specific finding)\n- PMID:32296183 — EXCLUDE (general interactome)\n- PMID:11719186 — KEEP (human exosome purification/characterization, EXOSC5/PM-Scl75 directly studied)\n- PMID:33961781 — EXCLUDE (general BioPlex 3.0)\n- PMID:22939629 — EXCLUDE (general protein complexes)\n- PMID:21873635 — EXCLUDE (GO annotations)\n- PMID:19060904 — EXCLUDE (general interactome framework)\n- PMID:29395067 — EXCLUDE (general mRNA granule mapping)\n- PMID:33060197 — EXCLUDE (coronavirus host factors, no EXOSC5-specific mechanism)\n- PMID:17174896 — KEEP (reconstitution and structure of eukaryotic exosome including human, EXOSC5/Rrp46 is a subunit)\n- PMID:15489334 — EXCLUDE (MGC cDNA)\n- PMID:35271311 — EXCLUDE (general cellular organization)\n- PMID:26344197 — EXCLUDE (general metazoan complexes)\n- PMID:8889548 — EXCLUDE (cDNA library normalization)\n- PMID:10465791 — KEEP (yeast exosome/PM-Scl, Rrp46 identified as exosome component with 3'→5' exonuclease activity)\n- PMID:29656893 — EXCLUDE (DNA repair, no EXOSC5-specific finding)\n- PMID:17643375 — EXCLUDE (transcription machinery, no EXOSC5-specific finding)\n- PMID:21145461 — EXCLUDE (CRL network)\n- PMID:11782436 — KEEP (human exosome mediates ARE-mRNA degradation, PM-Scl75/EXOSC5 antibody used)\n- PMID:21791617 — EXCLUDE (DDX60/SKI2, not EXOSC5)\n- PMID:21255825 — KEEP (RNA exosome targets AID, core complex function)\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1999,\n      \"finding\": \"Rrp46 (EXOSC5 ortholog) was identified as one of six novel components of the yeast exosome, a complex of 3'→5' exoribonucleases involved in RNA processing and degradation. Human homologs of nine of the eleven yeast exosome components were identified, and nuclear and cytoplasmic forms of the complex were demonstrated to exist in both yeast and humans.\",\n      \"method\": \"Biochemical fractionation, indirect immunofluorescence, complementation assays\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (biochemical fractionation, immunofluorescence, complementation), foundational study replicated broadly\",\n      \"pmids\": [\"10465791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The human exosome, which includes PM-Scl75 (EXOSC5), was purified and characterized by mass spectrometry. The complex was shown to be required for rapid degradation of ARE-containing mRNAs but not for poly(A) shortening. PM-Scl75 was found to interact specifically with AU-rich elements (AREs), implicating EXOSC5 directly in ARE-mediated mRNA decay.\",\n      \"method\": \"Mass spectrometry, immunodepletion, cell-free RNA decay assay, RNA-protein interaction assays\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — reconstitution/cell-free assay combined with immunodepletion and MS; replicated across multiple studies\",\n      \"pmids\": [\"11719186\", \"11782436\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The human exosome (containing EXOSC5/PM-Scl75) is required for efficient 3'→5' exonucleolytic decay of ARE-containing mRNAs in HeLa cytoplasmic extracts. Immunodepletion of PM-Scl75 abolished this activity, and ARE sequences dramatically stimulated 3'→5' decay, establishing the exosome as the major cytoplasmic 3'→5' RNA decay pathway.\",\n      \"method\": \"In vitro RNA deadenylation/decay assay, immunodepletion with anti-PM-Scl75 antibodies, phosphorothioate-modified RNA trapping\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with specific immunodepletion of EXOSC5/PM-Scl75, clear causal link established\",\n      \"pmids\": [\"11782436\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The X-ray crystal structure of the 286 kDa nine-subunit human exosome was determined at 3.35 Å resolution, revealing EXOSC5 (Rrp46) as a structural subunit. Reconstitution experiments showed the human 9-subunit exosome has processive phosphorolytic activity, contributed by the Rrp41/Rrp45 heterodimer, while EXOSC5/Rrp46 plays a structural role within the ring.\",\n      \"method\": \"X-ray crystallography, in vitro reconstitution, biochemical activity assays with diverse RNA substrates\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus reconstitution and biochemical validation in same study\",\n      \"pmids\": [\"17174896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Crystal structures of C. elegans CRN-5 (EXOSC5 ortholog) and rice Rrp46 were determined at 3.9 Å and 2.0 Å resolution, respectively. Human Rrp46 (EXOSC5), rice Rrp46, and CRN-5 were found to form homodimers both in recombinant form and in cellular environments, in addition to their association with the exosome complex. Human Rrp46 bound DNA without detectable nuclease activity, while rice Rrp46 had both phosphorolytic RNase and hydrolytic DNase activities. Site-directed mutagenesis (E160Q abolished DNase; K75E/Q76E abolished RNase) confirmed catalytic residues. CRN-5 directly interacted with apoptotic nuclease CRN-4 and enhanced its DNase activity.\",\n      \"method\": \"X-ray crystallography, co-immunoprecipitation, site-directed mutagenesis, in vitro nuclease assays, size-exclusion chromatography\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure, mutagenesis, and in vitro enzymatic assays with orthogonal co-IP validation\",\n      \"pmids\": [\"20660080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The RNA exosome core complex (including EXOSC5) associates with activation-induced cytidine deaminase (AID) in B cells activated for class switch recombination (CSR). The exosome accumulates on immunoglobulin heavy-chain switch regions in an AID-dependent manner and is required for optimal CSR. A recombinant RNA exosome core complex conferred robust AID- and transcription-dependent DNA deamination of both strands of transcribed substrates in vitro, revealing a role for the exosome in antibody diversity generation.\",\n      \"method\": \"Co-immunoprecipitation, ChIP, in vitro transcription/deamination assay with recombinant exosome core, genetic knockdown of exosome subunits\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — recombinant reconstitution in vitro combined with ChIP and co-IP in B cells; multiple orthogonal methods\",\n      \"pmids\": [\"21255825\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"EXOSC5 was identified as a structural (non-catalytic) subunit of the RNA exosome required for brain development. Biallelic loss-of-function variants in EXOSC5 cause a neurodevelopmental syndrome. Loss of exosc5 in zebrafish caused shortened/curved bodies, reduced eye/head size, and edema. Pathogenic EXOSC5 variants modeled in budding yeast caused defects in RNA exosome function and altered interactions with other RNA exosome subunits, demonstrating that specific variants disrupt exosome complex integrity.\",\n      \"method\": \"Zebrafish morpholino knockdown, yeast complementation assays, mammalian cell modeling of variants, interaction assays (co-immunoprecipitation of exosome subunits)\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple model systems (zebrafish, yeast, mammalian cells) with orthogonal functional readouts\",\n      \"pmids\": [\"32504085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"EXOSC5 was identified as a physical interaction partner of SARS-CoV-2 Nsp8 protein by affinity-purification mass spectrometry, placing it in the host-viral protein interaction network relevant to COVID-19 pathogenesis.\",\n      \"method\": \"Affinity-purification mass spectrometry (AP-MS) of tagged SARS-CoV-2 proteins expressed in human cells\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single AP-MS dataset, no functional follow-up specific to EXOSC5\",\n      \"pmids\": [\"32353859\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"EXOSC5 knockdown in gastric cancer cells inhibited proliferation, induced G1/S phase arrest, increased p21 and p27 levels, and decreased cyclinD1 expression. Mechanistically, EXOSC5 was shown to promote cell cycle progression through activation of AKT and STAT3 signaling pathways.\",\n      \"method\": \"siRNA knockdown, CCK-8 proliferation assay, flow cytometry, Western blotting, GC organoid model, nude mouse xenograft\",\n      \"journal\": \"Journal of Cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — knockdown with defined proliferation phenotype and pathway readout across in vitro and in vivo models, single lab\",\n      \"pmids\": [\"35371329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"EXOSC5 knockdown in hepatocellular carcinoma cells inhibited cell growth and proliferation. Mechanistically, EXOSC5 promoted cell proliferation via activation of STAT3 signaling.\",\n      \"method\": \"siRNA knockdown, cell proliferation assays, Western blotting for STAT3 pathway components\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, limited mechanistic follow-up beyond STAT3 phosphorylation Western blot\",\n      \"pmids\": [\"36293016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"EXOSC5 maintains cancer stem cell (CSC) activity in endometrial cancer by regulating expression of netrin-4 (NTN4). NTN4, when secreted, binds integrin β1 and activates the FAK/SRC signaling axis to elevate c-MYC activity. EXOSC5 knockdown reduced NTN4 levels, diminished CSC self-renewal, reduced c-MYC and SOX2 expression, and curtailed tumorigenicity in tumor spheres.\",\n      \"method\": \"siRNA knockdown, tumor sphere assays, Western blotting, NTN4 rescue experiments, limiting dilution CSC frequency assay, tissue correlation analysis (n=93 EC tissues)\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — knockdown with mechanistic rescue (NTN4 treatment), pathway dissection via integrin β1/FAK/SRC, single lab\",\n      \"pmids\": [\"38164180\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"EXOSC5 (Rrp46/PM-Scl75) is a structural, non-catalytic subunit of the nine-subunit RNA exosome ring complex that directly contacts AU-rich elements to recruit the complex for 3'→5' degradation of ARE-containing mRNAs, participates in RNA processing/surveillance including AID-dependent antibody class switch recombination, is required for normal brain development (loss causes a neurodevelopmental syndrome with cerebellar hypoplasia in humans and zebrafish), and in cancer contexts activates STAT3/AKT signaling and the NTN4/integrin β1/FAK/SRC/c-MYC axis to promote proliferation and stemness.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"EXOSC5 (Rrp46) is a structural subunit of the RNA exosome complex that also forms homodimers independently; its plant ortholog possesses intrinsic phosphorolytic RNase and hydrolytic DNase activities dependent on conserved active-site residues (E160 for DNase, K75/Q76 for RNase), whereas the human protein binds DNA without detectable nuclease activity [PMID:20660080]. Biallelic pathogenic variants in EXOSC5 disrupt inter-subunit interactions within the RNA exosome and impair RNA processing, and loss of function in zebrafish causes severe developmental defects including shortened body axis, microcephaly, and edema, establishing EXOSC5 as essential for vertebrate development [PMID:32504085]. In the C. elegans apoptotic pathway, the ortholog CRN-5 directly interacts with the nuclease CRN-4 and enhances its DNase activity, indicating a conserved role in apoptotic DNA degradation [PMID:20660080].\",\n  \"teleology\": [\n    {\n      \"year\": 2010,\n      \"claim\": \"Establishing that Rrp46/EXOSC5 orthologs can homodimerize and possess intrinsic nuclease activities resolved whether exosome ring subunits are catalytically inert scaffolds or retain enzymatic potential.\",\n      \"evidence\": \"Crystal structures of rice Rrp46 (2.0 Å) and C. elegans CRN-5 (3.9 Å) combined with in vitro RNase/DNase assays and site-directed mutagenesis\",\n      \"pmids\": [\"20660080\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Human Rrp46 binds DNA but lacks detectable nuclease activity; whether it retains latent catalytic function under specific conditions is unresolved\",\n        \"Physiological relevance of homodimerization versus exosome-incorporated function is unclear\",\n        \"No structural data for the human EXOSC5 homodimer\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identifying CRN-5 as a cofactor that enhances the apoptotic nuclease CRN-4 revealed an exosome-subunit function outside the canonical RNA degradation complex.\",\n      \"evidence\": \"Co-immunoprecipitation and in vitro DNase activity enhancement assays in C. elegans\",\n      \"pmids\": [\"20660080\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single study; CRN-5–CRN-4 interaction not validated in a second organism\",\n        \"Whether human EXOSC5 similarly participates in apoptotic DNA degradation is untested\",\n        \"Structural basis of the CRN-5–CRN-4 interaction is unresolved\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrating that patient-derived EXOSC5 variants disrupt exosome subunit interactions and RNA processing, and that zebrafish loss-of-function causes developmental defects, established EXOSC5 as an essential developmental gene and linked it to a novel Mendelian disorder.\",\n      \"evidence\": \"Yeast complementation, mammalian co-immunoprecipitation of exosome subunits, zebrafish morpholino knockdown, RNA processing assays\",\n      \"pmids\": [\"32504085\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Precise RNA substrates misprocessed by EXOSC5 variants are not catalogued\",\n        \"Whether developmental phenotypes arise from loss of exosome-dependent or exosome-independent EXOSC5 functions is unknown\",\n        \"No rescue experiments with wild-type human EXOSC5 in zebrafish reported\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Knockdown studies in gastric and hepatocellular carcinoma cells positioned EXOSC5 as a promoter of cancer cell proliferation acting through AKT and STAT3 signaling, but the direct molecular mechanism linking an RNA exosome subunit to these pathways was not established.\",\n      \"evidence\": \"siRNA knockdown, Western blotting of pathway readouts, cell proliferation and cell cycle assays, xenograft models\",\n      \"pmids\": [\"35371329\", \"36293016\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Pathway placement inferred solely from downstream Western blot readouts without direct enzyme–substrate or RNA target evidence\",\n        \"No identification of specific RNAs whose stabilization or degradation mediates the AKT/STAT3 effects\",\n        \"Findings from single labs without independent replication\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Placing EXOSC5 upstream of NTN4/integrin β1/FAK/SRC/c-MYC in endometrial cancer stemness provided a more defined pathway model, though how EXOSC5 controls NTN4 expression at the RNA level remains unresolved.\",\n      \"evidence\": \"siRNA knockdown, NTN4 rescue experiments, tumor sphere assays, in vivo xenograft, co-immunoprecipitation of NTN4–integrin β1\",\n      \"pmids\": [\"38164180\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct mechanism by which EXOSC5 regulates NTN4 mRNA stability or processing is not shown\",\n        \"Whether this pathway operates through exosome-complex-dependent RNA degradation or an independent function of EXOSC5 is unknown\",\n        \"Generalizability beyond endometrial cancer is untested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The key unresolved question is which specific RNA substrates EXOSC5 controls — both as an exosome subunit and potentially independently — to mediate its developmental and oncogenic roles.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No transcriptome-wide identification of direct EXOSC5-dependent RNA targets (e.g., CLIP or eCLIP data)\",\n        \"No separation-of-function mutants distinguishing exosome-dependent from homodimer/independent activities in vivo\",\n        \"No structural model of human EXOSC5 within the exosome ring at residue-level resolution relevant to disease variants\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"complexes\": [\n      \"RNA exosome\"\n    ],\n    \"partners\": [\n      \"CRN-4\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"EXOSC5 (Rrp46/PM-Scl75) is a structural, non-catalytic subunit of the nine-subunit RNA exosome core complex that functions in 3'→5' RNA processing, surveillance, and degradation. Within the exosome ring, EXOSC5 directly contacts AU-rich elements (AREs) on mRNAs and is required for efficient cytoplasmic ARE-mediated mRNA decay [PMID:11719186, PMID:11782436]; the exosome core complex also associates with activation-induced cytidine deaminase (AID) to facilitate immunoglobulin class switch recombination by enabling transcription-dependent DNA deamination of switch regions [PMID:21255825]. Biallelic loss-of-function variants in EXOSC5 cause a neurodevelopmental syndrome with cerebellar hypoplasia, and pathogenic variants disrupt exosome complex integrity in yeast and zebrafish models [PMID:32504085]. In cancer contexts, EXOSC5 promotes proliferation and stemness through STAT3/AKT signaling and regulation of the NTN4/integrin β1/FAK/SRC/c-MYC axis [PMID:35371329, PMID:38164180].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of Rrp46 as a core exosome subunit established that EXOSC5 is part of a conserved multi-subunit 3'→5' exoribonuclease complex present in both nucleus and cytoplasm of eukaryotes.\",\n      \"evidence\": \"Biochemical fractionation, indirect immunofluorescence, and complementation assays in yeast with identification of human homologs\",\n      \"pmids\": [\"10465791\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic versus structural role of individual subunits not resolved\", \"Substrate specificity of individual subunits unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Demonstrating that EXOSC5/PM-Scl75 directly binds AU-rich elements and that the exosome complex is required for ARE-mediated mRNA decay answered how specific mRNA substrates are recruited for 3'→5' degradation.\",\n      \"evidence\": \"Immunodepletion of PM-Scl75 from HeLa cytoplasmic extracts abolished ARE-dependent 3'→5' decay; RNA-protein interaction assays showed direct ARE binding\",\n      \"pmids\": [\"11719186\", \"11782436\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether EXOSC5 ARE binding is sufficient for recruitment or requires cofactors\", \"In vivo target mRNA repertoire not defined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"The crystal structure of the human nine-subunit exosome resolved EXOSC5 as a structural ring component, demonstrating that catalytic activity resides in the Rrp41/Rrp45 heterodimer rather than in EXOSC5 itself.\",\n      \"evidence\": \"X-ray crystallography at 3.35 Å with reconstitution and biochemical activity assays\",\n      \"pmids\": [\"17174896\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How EXOSC5 contributes to RNA threading through the channel not resolved\", \"Dynamics of subunit assembly in vivo unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Structural and biochemical analysis of EXOSC5 orthologs revealed unexpected homodimerization and DNA-binding capacity, expanding the possible roles of Rrp46-family proteins beyond the exosome ring.\",\n      \"evidence\": \"Crystal structures of C. elegans CRN-5 and rice Rrp46; site-directed mutagenesis; in vitro nuclease and DNA-binding assays; co-IP\",\n      \"pmids\": [\"20660080\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological relevance of homodimerization and DNA binding for human EXOSC5 not demonstrated\", \"Whether human EXOSC5 possesses latent catalytic activity under specific conditions remains untested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Discovery that the exosome core associates with AID and accumulates on immunoglobulin switch regions revealed an unexpected role for the RNA exosome—including EXOSC5—in antibody class switch recombination via transcription-dependent DNA deamination.\",\n      \"evidence\": \"Co-IP, ChIP on switch regions, and in vitro transcription/deamination assay with recombinant exosome core in activated B cells\",\n      \"pmids\": [\"21255825\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Individual contribution of EXOSC5 versus other ring subunits to AID targeting not dissected\", \"Whether exosome facilitates somatic hypermutation through a similar mechanism unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identification of biallelic EXOSC5 variants causing a neurodevelopmental syndrome with cerebellar hypoplasia established the gene as essential for brain development and demonstrated that pathogenic variants disrupt exosome complex integrity.\",\n      \"evidence\": \"Zebrafish morpholino knockdown phenocopied features; yeast complementation showed functional deficits; co-IP revealed altered subunit interactions\",\n      \"pmids\": [\"32504085\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific RNA targets dysregulated in developing brain not identified\", \"Genotype–phenotype relationships across different EXOSC5 variants not fully defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"EXOSC5 was shown to promote cancer cell proliferation and cell-cycle progression through AKT and STAT3 signaling, suggesting exosome-independent or RNA-target-dependent oncogenic functions.\",\n      \"evidence\": \"siRNA knockdown in gastric and hepatocellular carcinoma cells with proliferation assays, flow cytometry, Western blotting, xenograft models\",\n      \"pmids\": [\"35371329\", \"36293016\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct RNA substrates linking EXOSC5 to STAT3/AKT activation not identified\", \"Whether these effects are exosome-complex-dependent or subunit-autonomous not tested\", \"Single-lab findings for HCC; limited mechanistic depth beyond phospho-Western blots\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linking EXOSC5 to cancer stemness through regulation of NTN4 and the integrin β1/FAK/SRC/c-MYC axis provided a downstream pathway for EXOSC5's pro-tumorigenic activity in endometrial cancer.\",\n      \"evidence\": \"siRNA knockdown with NTN4 rescue, tumor sphere assays, limiting dilution assays, and tissue correlation in 93 endometrial cancer specimens\",\n      \"pmids\": [\"38164180\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether EXOSC5 regulates NTN4 mRNA stability directly via exosome-mediated decay or through an indirect mechanism not established\", \"Generalizability beyond endometrial cancer not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the identity of specific RNA targets whose stability is controlled by EXOSC5 in normal tissues, the mechanism by which EXOSC5 structural variants cause selective neuronal vulnerability, and whether cancer-associated functions depend on the intact exosome complex or on exosome-independent activities.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No transcriptome-wide direct target map (e.g., CLIP-seq) for EXOSC5\", \"No structural basis for how pathogenic missense variants alter exosome function\", \"Exosome-dependent versus -independent oncogenic mechanisms not disambiguated\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [1, 2, 5]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [3, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 1, 2, 5]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"complexes\": [\"RNA exosome core complex\"],\n    \"partners\": [\"EXOSC4\", \"EXOSC6\", \"EXOSC7\", \"EXOSC8\", \"EXOSC9\", \"DIS3\", \"AICDA\"],\n    \"other_free_text\": []\n  }\n}\n```"}