{"gene":"DNAJC8","run_date":"2026-06-09T23:54:42","timeline":{"discoveries":[{"year":2009,"finding":"DNAJC8 (Hsp40/DNAJc8) acts as a cochaperone that directly binds SRPK1 and mediates its dynamic interactions with the major molecular chaperones Hsp70 and Hsp90. Inhibition of Hsp90 ATPase or osmotic shock causes dissociation of SRPK1 from these chaperone complexes, leading to SRPK1 translocation from the cytoplasm to the nucleus, differential phosphorylation of SR proteins, and altered splice site selection.","method":"Co-immunoprecipitation, direct binding assays, Hsp90 inhibitor treatment, osmotic shock experiments, SR protein phosphorylation assays, splice site selection assays in mammalian cells","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP and multiple orthogonal functional assays (kinase translocation, phosphorylation, splicing) in a focused mechanistic study; independently informative findings within a single rigorous paper","pmids":["19240134"],"is_preprint":false},{"year":2016,"finding":"DNAJC8 is a nuclear J-protein that suppresses polyglutamine (polyQ) aggregation in a cellular model of SCA3/Machado-Joseph disease. Co-localization with polyQ aggregates in the nucleus was observed. Deletion mutant analysis showed the C-terminal domain is essential for aggregate suppression, while the J-domain is dispensable, indicating a mechanism independent of HSP70-based chaperone machinery. A 22-mer oligopeptide from the C-terminal domain recapitulates suppression.","method":"Overexpression and deletion mutant analysis in SH-SY5Y cells, fluorescence co-localization, apoptosis assays, oligopeptide suppression assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean loss-of-domain experiments with defined phenotypic readout (aggregate suppression) and peptide confirmation, single lab","pmids":["27133716"],"is_preprint":false},{"year":2018,"finding":"TIG1 (tazarotene-induced gene 1) interacts with DNAJC8 in the cytosol. DNAJC8 promotes nuclear translocation of PKM2, which induces GLUT1 expression and glucose uptake. TIG1 binding to DNAJC8 blocks this PKM2 translocation and inhibits glucose uptake. Silencing DNAJC8 or PKM2 abolishes DNAJC8-mediated upregulation of GLUT1 and glucose uptake in cervical cancer cells.","method":"Co-immunoprecipitation (TIG1–DNAJC8 interaction), ectopic overexpression, siRNA knockdown, subcellular fractionation/translocation assay, glucose uptake assay, Western blot","journal":"Molecules and cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus functional knockdown experiments with defined downstream readouts (PKM2 translocation, GLUT1 expression, glucose uptake), single lab","pmids":["29902837"],"is_preprint":false},{"year":2024,"finding":"DNAJC8 is a structural component of the pre-A spliceosomal complex (cross-exon pre-A complex) that specifically stabilizes its conformation along with SF1 and SF3A2 during prespliceosome assembly and branch site proofreading by PRP5, as revealed by atomic cryo-EM structures.","method":"Cryo-EM structure determination of human 17S U2 snRNP and cross-exon pre-A complex; atomic structure resolution with functional interpretation","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — atomic cryo-EM structures directly place DNAJC8 in the pre-A complex with structural validation of its stabilizing role","pmids":["38196034"],"is_preprint":false},{"year":2025,"finding":"DNAJC8 (a spliceosome-associated DNAJC member) retains TDP-43 in the nucleus and promotes its liquid-phase behavior, acting independently of Hsp70 (unlike DNAJBs). Overexpression of DNAJC8 reduces TDP-43 aggregate burden and enhances cell viability under proteotoxic stress in human cells.","method":"Systematic Hsp70 network screen in yeast and human cells, TDP-43 solubility assays, live-cell imaging of TDP-43 phase behavior, viability assays; sequence-activity mapping","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal assays (solubility, localization, phase behavior, viability) in a single preprint study; not yet peer-reviewed","pmids":["40654997"],"is_preprint":true}],"current_model":"DNAJC8 is a nuclear J-domain protein with at least two established mechanistic roles: (1) as a cochaperone bridging SRPK1 to the Hsp70/Hsp90 chaperone system to regulate SR protein phosphorylation and alternative splicing in response to cellular signals, and (2) as a structural stabilizer of the spliceosomal pre-A complex during branch site proofreading; additionally, its C-terminal domain (independently of the J-domain/Hsp70 axis) suppresses polyglutamine aggregation in the nucleus, it promotes PKM2 nuclear translocation and glycolysis until blocked by TIG1, and it retains TDP-43 in the nucleus to maintain its liquid-phase behavior."},"narrative":{"mechanistic_narrative":"DNAJC8 is a nuclear J-domain (Hsp40-family) protein that operates at the intersection of chaperone biology and RNA splicing [PMID:19240134, PMID:38196034]. As a cochaperone it directly binds the kinase SRPK1 and bridges it to the Hsp70/Hsp90 system; Hsp90 ATPase inhibition or osmotic shock dissociates this complex, driving SRPK1 nuclear translocation, altered SR protein phosphorylation, and changes in splice site selection [PMID:19240134]. Structurally, DNAJC8 is an integral component of the cross-exon pre-A spliceosomal complex, where it stabilizes the assembling prespliceosome together with SF1 and SF3A2 during PRP5-mediated branch site proofreading [PMID:38196034]. Beyond splicing, DNAJC8 has chaperone-related activity against aggregation-prone substrates: its C-terminal domain suppresses polyglutamine aggregation in a cellular SCA3/Machado-Joseph model in a J-domain- and Hsp70-independent manner, with a 22-mer C-terminal peptide recapitulating the effect [PMID:27133716]. DNAJC8 also influences metabolic signaling, promoting nuclear translocation of PKM2 to upregulate GLUT1 and glucose uptake, an activity blocked by the interactor TIG1 [PMID:29902837].","teleology":[{"year":2009,"claim":"Established DNAJC8 as a cochaperone that physically couples the SR-protein kinase SRPK1 to the Hsp70/Hsp90 machinery, providing a signal-responsive mechanism linking chaperone status to splicing regulation.","evidence":"Reciprocal Co-IP, direct binding assays, Hsp90 inhibition and osmotic shock, plus SR phosphorylation and splice-site selection readouts in mammalian cells","pmids":["19240134"],"confidence":"High","gaps":["Did not resolve which DNAJC8 domain mediates SRPK1 binding versus Hsp70/Hsp90 engagement","Nuclear versus cytoplasmic distribution of DNAJC8 itself during the response not defined"]},{"year":2016,"claim":"Showed that DNAJC8 can suppress protein aggregation through a non-canonical route, mapping the anti-aggregation activity to its C-terminal domain rather than the J-domain/Hsp70 axis.","evidence":"Overexpression and deletion-mutant analysis in SH-SY5Y polyQ cells with co-localization, apoptosis, and oligopeptide suppression assays","pmids":["27133716"],"confidence":"Medium","gaps":["Biochemical mechanism by which the C-terminal peptide suppresses polyQ aggregation unresolved","Single-lab cellular overexpression model; endogenous relevance not established"]},{"year":2018,"claim":"Connected DNAJC8 to metabolic control, demonstrating it promotes PKM2 nuclear translocation and glucose uptake and is negatively regulated by the interactor TIG1.","evidence":"Co-IP, ectopic overexpression, siRNA knockdown, subcellular fractionation, and glucose uptake assays in cervical cancer cells","pmids":["29902837"],"confidence":"Medium","gaps":["Whether DNAJC8 acts as a direct chaperone for PKM2 or indirectly is unknown","Mechanism by which TIG1 binding blocks translocation not defined","Single-lab study in one cancer cell context"]},{"year":2024,"claim":"Placed DNAJC8 structurally within the spliceosome, defining it as a stabilizing component of the cross-exon pre-A complex during branch site proofreading.","evidence":"Atomic cryo-EM structures of human 17S U2 snRNP and the cross-exon pre-A complex","pmids":["38196034"],"confidence":"High","gaps":["Functional consequence of DNAJC8 loss on splicing fidelity not tested","Relationship between its spliceosomal role and its SRPK1-cochaperone role unresolved"]},{"year":2025,"claim":"Extended DNAJC8's substrate range to TDP-43, showing it retains TDP-43 in the nucleus and preserves its liquid-phase behavior independently of Hsp70.","evidence":"Hsp70-network screen in yeast and human cells, TDP-43 solubility and live-cell phase assays, and viability assays (preprint)","pmids":["40654997"],"confidence":"Medium","gaps":["Not yet peer-reviewed","Direct binding of DNAJC8 to TDP-43 versus indirect effect not established","Domain requirement for TDP-43 retention not mapped"]},{"year":null,"claim":"How DNAJC8's distinct activities — SRPK1 cochaperone, spliceosomal structural subunit, and Hsp70-independent anti-aggregation/phase regulator — are integrated within one protein remains unresolved.","evidence":"No single study reconciles the J-domain-dependent and J-domain-independent functions","pmids":[],"confidence":"Low","gaps":["No structure-function map separating the chaperone and spliceosomal roles","No knockout phenotype linking the activities in vivo"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[0,1]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,2]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[3]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1,4]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,3]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1]}],"complexes":["pre-A spliceosomal complex","17S U2 snRNP"],"partners":["SRPK1","HSP90","HSPA8","SF1","SF3A2","TIG1","PKM2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O75937","full_name":"DnaJ homolog subfamily C member 8","aliases":["Splicing protein spf31"],"length_aa":253,"mass_kda":29.8,"function":"Suppresses polyglutamine (polyQ) aggregation of ATXN3 in neuronal cells (PubMed:27133716)","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/O75937/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/DNAJC8","classification":"Common Essential","n_dependent_lines":1160,"n_total_lines":1208,"dependency_fraction":0.9602649006622517},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000126698","cell_line_id":"CID000037","localizations":[{"compartment":"nucleoplasm","grade":3}],"interactors":[{"gene":"SF3B4","stoichiometry":4.0},{"gene":"SF3B6","stoichiometry":4.0},{"gene":"SF3B1","stoichiometry":4.0},{"gene":"RBM17","stoichiometry":4.0},{"gene":"U2SURP","stoichiometry":4.0},{"gene":"HSPH1","stoichiometry":0.2},{"gene":"SMEK1","stoichiometry":0.2},{"gene":"HSPA1L","stoichiometry":0.2},{"gene":"GPATCH11","stoichiometry":0.2},{"gene":"DDX42","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000037","total_profiled":1310},"omim":[],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"},{"location":"Cytokinetic bridge","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/DNAJC8"},"hgnc":{"alias_symbol":["SPF31"],"prev_symbol":[]},"alphafold":{"accession":"O75937","domains":[{"cath_id":"1.10.287.110","chopping":"36-111","consensus_level":"medium","plddt":91.8476,"start":36,"end":111}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O75937","model_url":"https://alphafold.ebi.ac.uk/files/AF-O75937-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O75937-F1-predicted_aligned_error_v6.png","plddt_mean":83.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=DNAJC8","jax_strain_url":"https://www.jax.org/strain/search?query=DNAJC8"},"sequence":{"accession":"O75937","fasta_url":"https://rest.uniprot.org/uniprotkb/O75937.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O75937/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O75937"}},"corpus_meta":[{"pmid":"19240134","id":"PMC_19240134","title":"Regulation of SR protein phosphorylation and alternative splicing by modulating kinetic interactions of SRPK1 with molecular chaperones.","date":"2009","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/19240134","citation_count":162,"is_preprint":false},{"pmid":"29760079","id":"PMC_29760079","title":"Selection and environmental adaptation along a path to speciation in the Tibetan frog Nanorana parkeri.","date":"2018","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/29760079","citation_count":59,"is_preprint":false},{"pmid":"38196034","id":"PMC_38196034","title":"Structural insights into branch site proofreading by human spliceosome.","date":"2024","source":"Nature structural & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/38196034","citation_count":36,"is_preprint":false},{"pmid":"27133716","id":"PMC_27133716","title":"A novel nuclear DnaJ protein, DNAJC8, can suppress the formation of spinocerebellar ataxia 3 polyglutamine aggregation in a J-domain independent manner.","date":"2016","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/27133716","citation_count":26,"is_preprint":false},{"pmid":"32059293","id":"PMC_32059293","title":"Analyses of the function of DnaJ family proteins reveal an underlying regulatory mechanism of heat tolerance in honeybee.","date":"2020","source":"The Science of the total environment","url":"https://pubmed.ncbi.nlm.nih.gov/32059293","citation_count":22,"is_preprint":false},{"pmid":"29902837","id":"PMC_29902837","title":"Tazarotene-Induced Gene 1 Interacts with DNAJC8 and Regulates Glycolysis in Cervical Cancer Cells.","date":"2018","source":"Molecules and cells","url":"https://pubmed.ncbi.nlm.nih.gov/29902837","citation_count":18,"is_preprint":false},{"pmid":"35850458","id":"PMC_35850458","title":"Skin immune response to Aeromonas hydrophila infection in crucian carp Carassius auratus revealed by multi-omics analysis.","date":"2022","source":"Fish & shellfish immunology","url":"https://pubmed.ncbi.nlm.nih.gov/35850458","citation_count":18,"is_preprint":false},{"pmid":"30349556","id":"PMC_30349556","title":"Environmental Stress Responses of DnaJA1, DnaJB12 and DnaJC8 in Apis cerana cerana.","date":"2018","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/30349556","citation_count":16,"is_preprint":false},{"pmid":"37989443","id":"PMC_37989443","title":"Specific serum autoantibodies predict the development and progression of Alzheimer's disease with high accuracy.","date":"2023","source":"Brain, behavior, and immunity","url":"https://pubmed.ncbi.nlm.nih.gov/37989443","citation_count":16,"is_preprint":false},{"pmid":"35391795","id":"PMC_35391795","title":"Whole-Genome Analyses Reveal Genomic Characteristics and Selection Signatures of Lincang Humped Cattle at the China-Myanmar Border.","date":"2022","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/35391795","citation_count":13,"is_preprint":false},{"pmid":"35360840","id":"PMC_35360840","title":"LYPD3, a New Biomarker and Therapeutic Target for Acute Myelogenous Leukemia.","date":"2022","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/35360840","citation_count":11,"is_preprint":false},{"pmid":"21223730","id":"PMC_21223730","title":"[Proteomic study of retinoid acid resistant NB4R1 cells apoptosis induced by realgar].","date":"2010","source":"Zhonghua xue ye xue za zhi = Zhonghua xueyexue zazhi","url":"https://pubmed.ncbi.nlm.nih.gov/21223730","citation_count":3,"is_preprint":false},{"pmid":"40654997","id":"PMC_40654997","title":"Scouring the human Hsp70 network uncovers diverse chaperone safeguards buffering TDP-43 toxicity.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/40654997","citation_count":2,"is_preprint":false},{"pmid":"40130083","id":"PMC_40130083","title":"A Chemotherapy Response-Related Gene Signature and DNAJC8 as Key Mediators of Hepatocellular Carcinoma Progression and Drug Resistance.","date":"2025","source":"Journal of hepatocellular carcinoma","url":"https://pubmed.ncbi.nlm.nih.gov/40130083","citation_count":0,"is_preprint":false},{"pmid":"41910470","id":"PMC_41910470","title":"Aerobic exercise intervention in Alzheimer's disease: Proteomic insights into peripheral T cell-mediated immune pathways.","date":"2026","source":"Journal of Alzheimer's disease : JAD","url":"https://pubmed.ncbi.nlm.nih.gov/41910470","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9806,"output_tokens":1566,"usd":0.026454,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8333,"output_tokens":2421,"usd":0.051095,"stage2_stop_reason":"end_turn"},"total_usd":0.077549,"stage1_batch_id":"msgbatch_01AsR7g8dGTEiEw9U83bJeWn","stage2_batch_id":"msgbatch_01YV5ZyxtFNUZEjxRcpd9jzb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2009,\n      \"finding\": \"DNAJC8 (Hsp40/DNAJc8) acts as a cochaperone that directly binds SRPK1 and mediates its dynamic interactions with the major molecular chaperones Hsp70 and Hsp90. Inhibition of Hsp90 ATPase or osmotic shock causes dissociation of SRPK1 from these chaperone complexes, leading to SRPK1 translocation from the cytoplasm to the nucleus, differential phosphorylation of SR proteins, and altered splice site selection.\",\n      \"method\": \"Co-immunoprecipitation, direct binding assays, Hsp90 inhibitor treatment, osmotic shock experiments, SR protein phosphorylation assays, splice site selection assays in mammalian cells\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP and multiple orthogonal functional assays (kinase translocation, phosphorylation, splicing) in a focused mechanistic study; independently informative findings within a single rigorous paper\",\n      \"pmids\": [\"19240134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"DNAJC8 is a nuclear J-protein that suppresses polyglutamine (polyQ) aggregation in a cellular model of SCA3/Machado-Joseph disease. Co-localization with polyQ aggregates in the nucleus was observed. Deletion mutant analysis showed the C-terminal domain is essential for aggregate suppression, while the J-domain is dispensable, indicating a mechanism independent of HSP70-based chaperone machinery. A 22-mer oligopeptide from the C-terminal domain recapitulates suppression.\",\n      \"method\": \"Overexpression and deletion mutant analysis in SH-SY5Y cells, fluorescence co-localization, apoptosis assays, oligopeptide suppression assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean loss-of-domain experiments with defined phenotypic readout (aggregate suppression) and peptide confirmation, single lab\",\n      \"pmids\": [\"27133716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TIG1 (tazarotene-induced gene 1) interacts with DNAJC8 in the cytosol. DNAJC8 promotes nuclear translocation of PKM2, which induces GLUT1 expression and glucose uptake. TIG1 binding to DNAJC8 blocks this PKM2 translocation and inhibits glucose uptake. Silencing DNAJC8 or PKM2 abolishes DNAJC8-mediated upregulation of GLUT1 and glucose uptake in cervical cancer cells.\",\n      \"method\": \"Co-immunoprecipitation (TIG1–DNAJC8 interaction), ectopic overexpression, siRNA knockdown, subcellular fractionation/translocation assay, glucose uptake assay, Western blot\",\n      \"journal\": \"Molecules and cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus functional knockdown experiments with defined downstream readouts (PKM2 translocation, GLUT1 expression, glucose uptake), single lab\",\n      \"pmids\": [\"29902837\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"DNAJC8 is a structural component of the pre-A spliceosomal complex (cross-exon pre-A complex) that specifically stabilizes its conformation along with SF1 and SF3A2 during prespliceosome assembly and branch site proofreading by PRP5, as revealed by atomic cryo-EM structures.\",\n      \"method\": \"Cryo-EM structure determination of human 17S U2 snRNP and cross-exon pre-A complex; atomic structure resolution with functional interpretation\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — atomic cryo-EM structures directly place DNAJC8 in the pre-A complex with structural validation of its stabilizing role\",\n      \"pmids\": [\"38196034\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"DNAJC8 (a spliceosome-associated DNAJC member) retains TDP-43 in the nucleus and promotes its liquid-phase behavior, acting independently of Hsp70 (unlike DNAJBs). Overexpression of DNAJC8 reduces TDP-43 aggregate burden and enhances cell viability under proteotoxic stress in human cells.\",\n      \"method\": \"Systematic Hsp70 network screen in yeast and human cells, TDP-43 solubility assays, live-cell imaging of TDP-43 phase behavior, viability assays; sequence-activity mapping\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal assays (solubility, localization, phase behavior, viability) in a single preprint study; not yet peer-reviewed\",\n      \"pmids\": [\"40654997\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"DNAJC8 is a nuclear J-domain protein with at least two established mechanistic roles: (1) as a cochaperone bridging SRPK1 to the Hsp70/Hsp90 chaperone system to regulate SR protein phosphorylation and alternative splicing in response to cellular signals, and (2) as a structural stabilizer of the spliceosomal pre-A complex during branch site proofreading; additionally, its C-terminal domain (independently of the J-domain/Hsp70 axis) suppresses polyglutamine aggregation in the nucleus, it promotes PKM2 nuclear translocation and glycolysis until blocked by TIG1, and it retains TDP-43 in the nucleus to maintain its liquid-phase behavior.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"DNAJC8 is a nuclear J-domain (Hsp40-family) protein that operates at the intersection of chaperone biology and RNA splicing [#0, #3]. As a cochaperone it directly binds the kinase SRPK1 and bridges it to the Hsp70/Hsp90 system; Hsp90 ATPase inhibition or osmotic shock dissociates this complex, driving SRPK1 nuclear translocation, altered SR protein phosphorylation, and changes in splice site selection [#0]. Structurally, DNAJC8 is an integral component of the cross-exon pre-A spliceosomal complex, where it stabilizes the assembling prespliceosome together with SF1 and SF3A2 during PRP5-mediated branch site proofreading [#3]. Beyond splicing, DNAJC8 has chaperone-related activity against aggregation-prone substrates: its C-terminal domain suppresses polyglutamine aggregation in a cellular SCA3/Machado-Joseph model in a J-domain- and Hsp70-independent manner, with a 22-mer C-terminal peptide recapitulating the effect [#1]. DNAJC8 also influences metabolic signaling, promoting nuclear translocation of PKM2 to upregulate GLUT1 and glucose uptake, an activity blocked by the interactor TIG1 [#2].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"Established DNAJC8 as a cochaperone that physically couples the SR-protein kinase SRPK1 to the Hsp70/Hsp90 machinery, providing a signal-responsive mechanism linking chaperone status to splicing regulation.\",\n      \"evidence\": \"Reciprocal Co-IP, direct binding assays, Hsp90 inhibition and osmotic shock, plus SR phosphorylation and splice-site selection readouts in mammalian cells\",\n      \"pmids\": [\"19240134\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Did not resolve which DNAJC8 domain mediates SRPK1 binding versus Hsp70/Hsp90 engagement\",\n        \"Nuclear versus cytoplasmic distribution of DNAJC8 itself during the response not defined\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed that DNAJC8 can suppress protein aggregation through a non-canonical route, mapping the anti-aggregation activity to its C-terminal domain rather than the J-domain/Hsp70 axis.\",\n      \"evidence\": \"Overexpression and deletion-mutant analysis in SH-SY5Y polyQ cells with co-localization, apoptosis, and oligopeptide suppression assays\",\n      \"pmids\": [\"27133716\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Biochemical mechanism by which the C-terminal peptide suppresses polyQ aggregation unresolved\",\n        \"Single-lab cellular overexpression model; endogenous relevance not established\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Connected DNAJC8 to metabolic control, demonstrating it promotes PKM2 nuclear translocation and glucose uptake and is negatively regulated by the interactor TIG1.\",\n      \"evidence\": \"Co-IP, ectopic overexpression, siRNA knockdown, subcellular fractionation, and glucose uptake assays in cervical cancer cells\",\n      \"pmids\": [\"29902837\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether DNAJC8 acts as a direct chaperone for PKM2 or indirectly is unknown\",\n        \"Mechanism by which TIG1 binding blocks translocation not defined\",\n        \"Single-lab study in one cancer cell context\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Placed DNAJC8 structurally within the spliceosome, defining it as a stabilizing component of the cross-exon pre-A complex during branch site proofreading.\",\n      \"evidence\": \"Atomic cryo-EM structures of human 17S U2 snRNP and the cross-exon pre-A complex\",\n      \"pmids\": [\"38196034\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Functional consequence of DNAJC8 loss on splicing fidelity not tested\",\n        \"Relationship between its spliceosomal role and its SRPK1-cochaperone role unresolved\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended DNAJC8's substrate range to TDP-43, showing it retains TDP-43 in the nucleus and preserves its liquid-phase behavior independently of Hsp70.\",\n      \"evidence\": \"Hsp70-network screen in yeast and human cells, TDP-43 solubility and live-cell phase assays, and viability assays (preprint)\",\n      \"pmids\": [\"40654997\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Not yet peer-reviewed\",\n        \"Direct binding of DNAJC8 to TDP-43 versus indirect effect not established\",\n        \"Domain requirement for TDP-43 retention not mapped\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How DNAJC8's distinct activities — SRPK1 cochaperone, spliceosomal structural subunit, and Hsp70-independent anti-aggregation/phase regulator — are integrated within one protein remains unresolved.\",\n      \"evidence\": \"No single study reconciles the J-domain-dependent and J-domain-independent functions\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No structure-function map separating the chaperone and spliceosomal roles\",\n        \"No knockout phenotype linking the activities in vivo\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 4]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"complexes\": [\n      \"pre-A spliceosomal complex\",\n      \"17S U2 snRNP\"\n    ],\n    \"partners\": [\n      \"SRPK1\",\n      \"HSP90\",\n      \"HSPA8\",\n      \"SF1\",\n      \"SF3A2\",\n      \"TIG1\",\n      \"PKM2\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":5,"faith_pct":80.0}}