{"gene":"POLDIP3","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2004,"finding":"SKAR (POLDIP3) is a novel and specific binding partner and substrate of S6K1 but not S6K2; serines 383 and 385 of human SKAR are insulin-stimulated, rapamycin-sensitive S6K1 phosphorylation sites, and RNAi-mediated reduction of SKAR decreases cell size.","method":"Co-immunoprecipitation, quantitative mass spectrometry, RNAi knockdown with cell size readout, in vivo phosphorylation assays","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal binding confirmed, phosphorylation sites mapped by MS, functional consequence (cell size) shown by RNAi; replicated in subsequent studies","pmids":["15341740"],"is_preprint":false},{"year":2008,"finding":"SKAR is deposited at the exon junction complex (EJC) during pre-mRNA splicing, and upon mTOR activation, recruits activated S6K1 to newly processed mRNPs to enhance the translation efficiency of spliced mRNAs during the pioneer round of translation.","method":"Co-immunoprecipitation with EJC components, reporter translation assays comparing spliced vs. nonspliced mRNAs, RNAi knockdown of SKAR and S6K1, mTOR/rapamycin pharmacological manipulation","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal biochemical and functional assays in a single rigorous study, mechanistic model supported by spliced vs. nonspliced reporter system and S6K1 recruitment data","pmids":["18423201"],"is_preprint":false},{"year":2006,"finding":"PDIP46/SKAR physically interacts with human Enhancer of Rudimentary (ER) protein; the interaction region maps to residues 274–421 of PDIP46/SKAR, which encompasses the RRM docking site for S6K1 and the S6K1-phosphorylated serines. Both proteins share nuclear co-localization in mammalian cells.","method":"Yeast two-hybrid screen, GST-ER pull-down from nuclear extract with MS identification, nuclear co-localization by microscopy","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — two orthogonal binding methods (Y2H + GST pull-down) and co-localization, single lab, no functional rescue","pmids":["16984396"],"is_preprint":false},{"year":2011,"finding":"TDP-43 regulates alternative splicing of SKAR/POLDIP3 pre-mRNA via its RRM1 domain binding to 5'-GA-3' and 5'-UG-3' repeats; TDP-43 knockdown causes inclusion of an alternatively spliced SKAR isoform that enhances S6K1-dependent signaling, increases translational yield of a splice-dependent reporter, and increases cell size.","method":"Affymetrix exon arrays, RNAi knockdown, minigene splicing reporter, S6K1 signaling assays, cell size measurement","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — exon array plus functional reporter and signaling assays, single lab, multiple orthogonal methods","pmids":["22121224"],"is_preprint":false},{"year":2012,"finding":"TDP-43 RNA binding activity is required for inclusion of POLDIP3 exon 3; loss of TDP-43 leads to increased POLDIP3 variant-2 (lacking exon 3) in cultured cells and in ALS-affected motor cortex and spinal cord tissue.","method":"Exon array analysis, TDP-43 siRNA knockdown, RT-PCR splice variant detection, laser capture microdissection from ALS patient tissue","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — exon array plus molecular validation in cell lines and human tissue, single lab, two orthogonal methods","pmids":["22900096"],"is_preprint":false},{"year":2016,"finding":"PDIP46/POLDIP3 associates with DNA polymerase δ (Pol δ) and PCNA in cell extracts and on chromatin; it contains multiple APIM (AlkB homologue-2 PCNA-Interacting Motif) copies in its N-terminal region that mediate PCNA binding; PDIP46 directly activates Pol δ activity on singly-primed ssM13 DNA templates and facilitates Pol δ synthesis through secondary structures via both PCNA-dependent and PCNA-independent direct Pol δ interaction; mutation of the Pol δ/PCNA binding region abolishes these functions.","method":"Co-immunoprecipitation, protein fractionation, ChIP, in vitro DNA polymerase activity assay on ssM13 templates, primer extension and strand displacement assays, mutagenesis of PCNA/Pol δ binding motifs","journal":"Oncotarget","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstituted polymerase activity assay with mutagenesis, supported by ChIP and co-IP; single lab but multiple orthogonal methods","pmids":["26819372"],"is_preprint":false},{"year":2014,"finding":"IFN-α induces phosphorylation of SKAR by either RSK or S6K1 in a cell-type-specific manner; this phosphorylation promotes SKAR interaction with eIF4G and recruitment of activated RSK1 to 5' cap mRNA complexes; SKAR is present in CBP80 cap-binding immune complexes via eIF4G; SKAR activity is required for IFN-α-induced expression of ISG15 and p21WAF1/CIP1.","method":"Co-immunoprecipitation with eIF4G and CBP80, phosphorylation assays, RNAi knockdown with downstream gene expression readouts, pharmacological kinase inhibition","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, phosphorylation mapping, functional knockdown with defined downstream targets; single lab","pmids":["25049393"],"is_preprint":false},{"year":2020,"finding":"RTEL1 helicase and POLDIP3 form a complex and are mutually dependent for chromatin binding after replication stress; loss of either protein leads to R-loop accumulation confined to sites of active replication, enhanced endogenous replication stress, and genomic instability; the effects of depleting RTEL1 and POLDIP3 are epistatic, placing them in a shared pathway for DNA replication control under stress conditions.","method":"Proteomics/MS interaction screen, Co-immunoprecipitation, R-loop detection (S9.6 immunofluorescence), chromatin fractionation, gene editing (CRISPR), epistasis analysis by double depletion","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, chromatin fractionation, R-loop imaging, CRISPR KO, and genetic epistasis across complementary human cell models; multiple orthogonal methods","pmids":["32561545"],"is_preprint":false},{"year":2023,"finding":"Coronavirus nsp5 (3C-like protease) cleaves POLDIP3 at glutamine 176 (Q176), reducing POLDIP3 protein levels and abolishing its antiviral activity; POLDIP3 overexpression inhibits PDCoV infection while POLDIP3 knockout promotes it; nsp5 from PEDV, TGEV, and SARS-CoV-2 share this conserved cleavage function on POLDIP3.","method":"iTRAQ proteomics, Western blotting, CRISPR-Cas9 knockout, overexpression assays, in vitro protease cleavage assay mapping Q176 site, in vivo piglet infection model","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro protease cleavage with site-specific mutagenesis (Q176), CRISPR KO and overexpression functional assays, validated in vivo; single lab but multiple orthogonal methods","pmids":["37801439"],"is_preprint":false}],"current_model":"POLDIP3/SKAR/PDIP46 is a nuclear protein that functions at the intersection of RNA and DNA metabolism: it is deposited at the exon junction complex during splicing (with TDP-43 regulating inclusion of its exon 3), recruits activated S6K1 (which phosphorylates it at S383/S385) to newly processed mRNPs to enhance pioneer-round translation efficiency, participates in IFN-α signaling by facilitating eIF4G/RSK1 recruitment to capped mRNAs, directly activates DNA polymerase δ activity via PCNA-binding APIM motifs and direct Pol δ contact, and cooperates with the RTEL1 helicase in an epistatic pathway to suppress R-loop accumulation at replication–transcription conflict sites; additionally, coronavirus nsp5 protease cleaves POLDIP3 at Q176 to disable its antiviral function."},"narrative":{"mechanistic_narrative":"POLDIP3 (SKAR/PDIP46) is a nuclear protein operating at the interface of mRNA biogenesis, translational control, and DNA replication [PMID:15341740, PMID:26819372]. In RNA metabolism, it is deposited at the exon junction complex during pre-mRNA splicing and, upon mTOR activation, recruits S6K1 — which phosphorylates POLDIP3 at S383/S385 — to newly processed mRNPs to enhance the translation efficiency of spliced mRNAs during the pioneer round of translation [PMID:15341740, PMID:18423201]. Its own expression is shaped by TDP-43, whose RRM1-dependent RNA binding promotes inclusion of POLDIP3 exon 3, with loss of TDP-43 shifting the balance toward an isoform that augments S6K1 signaling, translational yield, and cell size [PMID:22121224, PMID:22900096]. In interferon-α signaling, phosphorylation of POLDIP3 by RSK or S6K1 promotes its interaction with eIF4G and recruitment of activated RSK1 to capped mRNA complexes, an activity required for IFN-α-induced ISG15 and p21 expression [PMID:25049393]. In DNA metabolism, POLDIP3 binds PCNA through N-terminal APIM motifs and contacts DNA polymerase δ directly, activating Pol δ and facilitating synthesis through secondary structures [PMID:26819372], and it forms a chromatin-binding complex with the RTEL1 helicase in a shared epistatic pathway that suppresses R-loop accumulation at sites of active replication to limit replication stress and genomic instability [PMID:32561545]. POLDIP3 also has antiviral activity that coronaviruses neutralize: nsp5 protease cleaves it at Q176, reducing protein levels and promoting infection [PMID:37801439].","teleology":[{"year":2004,"claim":"Established POLDIP3/SKAR as a dedicated effector of mTOR/S6K1 signaling by identifying it as a specific S6K1 (not S6K2) substrate with mapped phosphosites and a cell-size phenotype, linking it to growth control.","evidence":"Co-IP, quantitative MS, in vivo phosphorylation mapping (S383/S385), and RNAi with cell-size readout in mammalian cells","pmids":["15341740"],"confidence":"High","gaps":["Did not define the molecular process through which SKAR controls cell size","Subcellular site of S6K1 recruitment unresolved"]},{"year":2006,"claim":"Identified Enhancer of Rudimentary (ER) as a nuclear binding partner mapping to the S6K1-docking/phosphorylation region, situating POLDIP3 in nuclear protein complexes.","evidence":"Yeast two-hybrid, GST pull-down with MS, nuclear co-localization microscopy","pmids":["16984396"],"confidence":"Medium","gaps":["No functional consequence of the ER interaction demonstrated","No rescue or reciprocal in vivo validation"]},{"year":2008,"claim":"Resolved how SKAR couples growth signaling to translation by showing it is EJC-deposited during splicing and recruits activated S6K1 to enhance pioneer-round translation of spliced mRNAs.","evidence":"Co-IP with EJC components, spliced vs. nonspliced reporter translation assays, RNAi of SKAR/S6K1, rapamycin/mTOR manipulation in human cells","pmids":["18423201"],"confidence":"High","gaps":["Which spliced transcripts depend on SKAR in vivo not defined","Stoichiometry of EJC deposition unresolved"]},{"year":2011,"claim":"Showed POLDIP3 is itself an alternative-splicing target of TDP-43, with isoform choice tuning S6K1 signaling and cell size, embedding it in a regulatory feedback on growth.","evidence":"Exon arrays, RNAi, minigene splicing reporter, S6K1 signaling and cell-size assays","pmids":["22121224"],"confidence":"Medium","gaps":["Direct functional difference between isoforms at the protein level not fully characterized","Single-lab data"]},{"year":2012,"claim":"Extended TDP-43 control of POLDIP3 exon 3 inclusion to disease by detecting the variant-2 shift in ALS-affected motor cortex and spinal cord.","evidence":"Exon arrays, TDP-43 siRNA, RT-PCR splice-variant detection, laser capture microdissection of ALS tissue","pmids":["22900096"],"confidence":"Medium","gaps":["Causal contribution of the POLDIP3 isoform shift to ALS pathology not established","Functional consequence in neurons not tested"]},{"year":2014,"claim":"Defined a role in innate immune translation by showing IFN-α-driven phosphorylation of SKAR drives eIF4G binding and RSK1 recruitment to capped mRNAs, required for ISG15 and p21 induction.","evidence":"Co-IP with eIF4G/CBP80, phosphorylation assays, RNAi with downstream gene readouts, kinase inhibition","pmids":["25049393"],"confidence":"Medium","gaps":["Direct mRNA targets selected by SKAR not catalogued","Cell-type determinants of RSK vs. S6K1 phosphorylation unclear"]},{"year":2016,"claim":"Demonstrated a direct DNA-replication function: POLDIP3 binds PCNA via APIM motifs and contacts Pol δ to stimulate its activity through secondary structures, distinct from its RNA/translation roles.","evidence":"Co-IP, ChIP, chromatin fractionation, in vitro Pol δ activity assays on ssM13 templates, mutagenesis of PCNA/Pol δ binding motifs","pmids":["26819372"],"confidence":"High","gaps":["In vivo replication phenotype of binding-motif mutants not established","Relationship between nuclear translation role and Pol δ role unresolved"]},{"year":2020,"claim":"Placed POLDIP3 in a defined genome-stability pathway by showing it forms a chromatin complex with RTEL1 and acts epistatically to suppress R-loops at replication sites under stress.","evidence":"MS interaction screen, reciprocal Co-IP, S9.6 R-loop imaging, chromatin fractionation, CRISPR KO, epistasis by double depletion in human cells","pmids":["32561545"],"confidence":"High","gaps":["Biochemical mechanism by which the complex resolves R-loops not defined","How POLDIP3 Pol δ activation relates to RTEL1 cooperation unclear"]},{"year":2023,"claim":"Identified POLDIP3 as an antiviral factor targeted by coronaviruses, with nsp5 cleaving it at Q176 to abolish its restriction of infection.","evidence":"iTRAQ proteomics, in vitro protease cleavage with Q176 mapping, CRISPR KO and overexpression, in vivo piglet infection model","pmids":["37801439"],"confidence":"High","gaps":["Molecular mechanism of POLDIP3 antiviral activity not defined","Which POLDIP3 function (translation vs. DNA replication) underlies restriction unknown"]},{"year":null,"claim":"How POLDIP3's distinct activities — EJC-coupled translation, Pol δ activation, RTEL1-dependent R-loop suppression, and antiviral restriction — are integrated or partitioned within one protein remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No unifying structural or domain map linking the RNA and DNA functions","No model for how phosphorylation state switches between roles"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[1]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[5]},{"term_id":"GO:0045182","term_label":"translation regulator activity","supporting_discovery_ids":[1,6]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,2]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[5,7]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[1,3]},{"term_id":"R-HSA-69306","term_label":"DNA Replication","supporting_discovery_ids":[5,7]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[6,8]}],"complexes":["exon junction complex","RTEL1-POLDIP3 complex"],"partners":["RPS6KB1","TDP-43","PCNA","POLD1","EIF4G1","RTEL1","ERH","RPS6KA1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9BY77","full_name":"Polymerase delta-interacting protein 3","aliases":["46 kDa DNA polymerase delta interaction protein","p46","S6K1 Aly/REF-like target","SKAR"],"length_aa":421,"mass_kda":46.1,"function":"Is involved in regulation of translation. Is preferentially associated with CBC-bound spliced mRNA-protein complexes during the pioneer round of mRNA translation. Contributes to enhanced translational efficiency of spliced over nonspliced mRNAs. Recruits activated ribosomal protein S6 kinase beta-1 I/RPS6KB1 to newly synthesized mRNA. Involved in nuclear mRNA export; probably mediated by association with the TREX complex","subcellular_location":"Nucleus; Nucleus speckle; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q9BY77/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/POLDIP3","classification":"Not Classified","n_dependent_lines":7,"n_total_lines":1208,"dependency_fraction":0.005794701986754967},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"RBM33","stoichiometry":10.0},{"gene":"PRPF4B","stoichiometry":4.0},{"gene":"DDX39B","stoichiometry":0.2},{"gene":"PSME3","stoichiometry":0.2},{"gene":"RTCB","stoichiometry":0.2},{"gene":"SNRPA","stoichiometry":0.2},{"gene":"SNRPB","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/POLDIP3","total_profiled":1310},"omim":[{"mim_id":"611520","title":"POLYMERASE DELTA-INTERACTING PROTEIN 3; POLDIP3","url":"https://www.omim.org/entry/611520"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nuclear speckles","reliability":"Enhanced"},{"location":"Cytoplasmic bodies","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/POLDIP3"},"hgnc":{"alias_symbol":["PDIP46","KIAA1649","SKAR","PDIP3"],"prev_symbol":[]},"alphafold":{"accession":"Q9BY77","domains":[{"cath_id":"3.30.70.330","chopping":"282-365","consensus_level":"high","plddt":90.5571,"start":282,"end":365}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BY77","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BY77-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BY77-F1-predicted_aligned_error_v6.png","plddt_mean":61.91},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=POLDIP3","jax_strain_url":"https://www.jax.org/strain/search?query=POLDIP3"},"sequence":{"accession":"Q9BY77","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9BY77.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9BY77/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BY77"}},"corpus_meta":[{"pmid":"18423201","id":"PMC_18423201","title":"SKAR links pre-mRNA splicing to mTOR/S6K1-mediated enhanced translation efficiency of spliced mRNAs.","date":"2008","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/18423201","citation_count":251,"is_preprint":false},{"pmid":"15341740","id":"PMC_15341740","title":"SKAR is a specific target of S6 kinase 1 in cell growth control.","date":"2004","source":"Current biology : CB","url":"https://pubmed.ncbi.nlm.nih.gov/15341740","citation_count":156,"is_preprint":false},{"pmid":"22121224","id":"PMC_22121224","title":"TDP-43 regulates global translational yield by splicing of exon junction complex component SKAR.","date":"2011","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/22121224","citation_count":87,"is_preprint":false},{"pmid":"22900096","id":"PMC_22900096","title":"Alteration of POLDIP3 splicing associated with loss of function of TDP-43 in tissues affected with ALS.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22900096","citation_count":76,"is_preprint":false},{"pmid":"32561545","id":"PMC_32561545","title":"Human RTEL1 associates with Poldip3 to facilitate responses to replication stress and R-loop resolution.","date":"2020","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/32561545","citation_count":37,"is_preprint":false},{"pmid":"16984396","id":"PMC_16984396","title":"Human enhancer of rudimentary is a molecular partner of PDIP46/SKAR, a protein interacting with DNA polymerase delta and S6K1 and regulating cell growth.","date":"2006","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/16984396","citation_count":37,"is_preprint":false},{"pmid":"37801439","id":"PMC_37801439","title":"Broad antagonism of coronaviruses nsp5 to evade the host antiviral responses by cleaving POLDIP3.","date":"2023","source":"PLoS pathogens","url":"https://pubmed.ncbi.nlm.nih.gov/37801439","citation_count":21,"is_preprint":false},{"pmid":"28236701","id":"PMC_28236701","title":"An alternative POLDIP3 transcript promotes hepatocellular carcinoma progression.","date":"2017","source":"Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie","url":"https://pubmed.ncbi.nlm.nih.gov/28236701","citation_count":20,"is_preprint":false},{"pmid":"26819372","id":"PMC_26819372","title":"PDIP46 (DNA polymerase δ interacting protein 46) is an activating factor for human DNA polymerase δ.","date":"2016","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/26819372","citation_count":18,"is_preprint":false},{"pmid":"25049393","id":"PMC_25049393","title":"Regulatory effects of SKAR in interferon α signaling and its role in the generation of type I IFN responses.","date":"2014","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/25049393","citation_count":11,"is_preprint":false},{"pmid":"36360158","id":"PMC_36360158","title":"POLDIP3: At the Crossroad of RNA and DNA Metabolism.","date":"2022","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/36360158","citation_count":3,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.02.02.635191","title":"Integrated detection and quantification of aberrant transcripts with novel splicing events","date":"2025-02-07","source":"bioRxiv","url":"https://doi.org/10.1101/2025.02.02.635191","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7965,"output_tokens":2626,"usd":0.031642,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9839,"output_tokens":3357,"usd":0.06656,"stage2_stop_reason":"end_turn"},"total_usd":0.098202,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2004,\n      \"finding\": \"SKAR (POLDIP3) is a novel and specific binding partner and substrate of S6K1 but not S6K2; serines 383 and 385 of human SKAR are insulin-stimulated, rapamycin-sensitive S6K1 phosphorylation sites, and RNAi-mediated reduction of SKAR decreases cell size.\",\n      \"method\": \"Co-immunoprecipitation, quantitative mass spectrometry, RNAi knockdown with cell size readout, in vivo phosphorylation assays\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal binding confirmed, phosphorylation sites mapped by MS, functional consequence (cell size) shown by RNAi; replicated in subsequent studies\",\n      \"pmids\": [\"15341740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SKAR is deposited at the exon junction complex (EJC) during pre-mRNA splicing, and upon mTOR activation, recruits activated S6K1 to newly processed mRNPs to enhance the translation efficiency of spliced mRNAs during the pioneer round of translation.\",\n      \"method\": \"Co-immunoprecipitation with EJC components, reporter translation assays comparing spliced vs. nonspliced mRNAs, RNAi knockdown of SKAR and S6K1, mTOR/rapamycin pharmacological manipulation\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal biochemical and functional assays in a single rigorous study, mechanistic model supported by spliced vs. nonspliced reporter system and S6K1 recruitment data\",\n      \"pmids\": [\"18423201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"PDIP46/SKAR physically interacts with human Enhancer of Rudimentary (ER) protein; the interaction region maps to residues 274–421 of PDIP46/SKAR, which encompasses the RRM docking site for S6K1 and the S6K1-phosphorylated serines. Both proteins share nuclear co-localization in mammalian cells.\",\n      \"method\": \"Yeast two-hybrid screen, GST-ER pull-down from nuclear extract with MS identification, nuclear co-localization by microscopy\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — two orthogonal binding methods (Y2H + GST pull-down) and co-localization, single lab, no functional rescue\",\n      \"pmids\": [\"16984396\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"TDP-43 regulates alternative splicing of SKAR/POLDIP3 pre-mRNA via its RRM1 domain binding to 5'-GA-3' and 5'-UG-3' repeats; TDP-43 knockdown causes inclusion of an alternatively spliced SKAR isoform that enhances S6K1-dependent signaling, increases translational yield of a splice-dependent reporter, and increases cell size.\",\n      \"method\": \"Affymetrix exon arrays, RNAi knockdown, minigene splicing reporter, S6K1 signaling assays, cell size measurement\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — exon array plus functional reporter and signaling assays, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"22121224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"TDP-43 RNA binding activity is required for inclusion of POLDIP3 exon 3; loss of TDP-43 leads to increased POLDIP3 variant-2 (lacking exon 3) in cultured cells and in ALS-affected motor cortex and spinal cord tissue.\",\n      \"method\": \"Exon array analysis, TDP-43 siRNA knockdown, RT-PCR splice variant detection, laser capture microdissection from ALS patient tissue\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — exon array plus molecular validation in cell lines and human tissue, single lab, two orthogonal methods\",\n      \"pmids\": [\"22900096\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PDIP46/POLDIP3 associates with DNA polymerase δ (Pol δ) and PCNA in cell extracts and on chromatin; it contains multiple APIM (AlkB homologue-2 PCNA-Interacting Motif) copies in its N-terminal region that mediate PCNA binding; PDIP46 directly activates Pol δ activity on singly-primed ssM13 DNA templates and facilitates Pol δ synthesis through secondary structures via both PCNA-dependent and PCNA-independent direct Pol δ interaction; mutation of the Pol δ/PCNA binding region abolishes these functions.\",\n      \"method\": \"Co-immunoprecipitation, protein fractionation, ChIP, in vitro DNA polymerase activity assay on ssM13 templates, primer extension and strand displacement assays, mutagenesis of PCNA/Pol δ binding motifs\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstituted polymerase activity assay with mutagenesis, supported by ChIP and co-IP; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"26819372\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"IFN-α induces phosphorylation of SKAR by either RSK or S6K1 in a cell-type-specific manner; this phosphorylation promotes SKAR interaction with eIF4G and recruitment of activated RSK1 to 5' cap mRNA complexes; SKAR is present in CBP80 cap-binding immune complexes via eIF4G; SKAR activity is required for IFN-α-induced expression of ISG15 and p21WAF1/CIP1.\",\n      \"method\": \"Co-immunoprecipitation with eIF4G and CBP80, phosphorylation assays, RNAi knockdown with downstream gene expression readouts, pharmacological kinase inhibition\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, phosphorylation mapping, functional knockdown with defined downstream targets; single lab\",\n      \"pmids\": [\"25049393\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"RTEL1 helicase and POLDIP3 form a complex and are mutually dependent for chromatin binding after replication stress; loss of either protein leads to R-loop accumulation confined to sites of active replication, enhanced endogenous replication stress, and genomic instability; the effects of depleting RTEL1 and POLDIP3 are epistatic, placing them in a shared pathway for DNA replication control under stress conditions.\",\n      \"method\": \"Proteomics/MS interaction screen, Co-immunoprecipitation, R-loop detection (S9.6 immunofluorescence), chromatin fractionation, gene editing (CRISPR), epistasis analysis by double depletion\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, chromatin fractionation, R-loop imaging, CRISPR KO, and genetic epistasis across complementary human cell models; multiple orthogonal methods\",\n      \"pmids\": [\"32561545\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Coronavirus nsp5 (3C-like protease) cleaves POLDIP3 at glutamine 176 (Q176), reducing POLDIP3 protein levels and abolishing its antiviral activity; POLDIP3 overexpression inhibits PDCoV infection while POLDIP3 knockout promotes it; nsp5 from PEDV, TGEV, and SARS-CoV-2 share this conserved cleavage function on POLDIP3.\",\n      \"method\": \"iTRAQ proteomics, Western blotting, CRISPR-Cas9 knockout, overexpression assays, in vitro protease cleavage assay mapping Q176 site, in vivo piglet infection model\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro protease cleavage with site-specific mutagenesis (Q176), CRISPR KO and overexpression functional assays, validated in vivo; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"37801439\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"POLDIP3/SKAR/PDIP46 is a nuclear protein that functions at the intersection of RNA and DNA metabolism: it is deposited at the exon junction complex during splicing (with TDP-43 regulating inclusion of its exon 3), recruits activated S6K1 (which phosphorylates it at S383/S385) to newly processed mRNPs to enhance pioneer-round translation efficiency, participates in IFN-α signaling by facilitating eIF4G/RSK1 recruitment to capped mRNAs, directly activates DNA polymerase δ activity via PCNA-binding APIM motifs and direct Pol δ contact, and cooperates with the RTEL1 helicase in an epistatic pathway to suppress R-loop accumulation at replication–transcription conflict sites; additionally, coronavirus nsp5 protease cleaves POLDIP3 at Q176 to disable its antiviral function.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"POLDIP3 (SKAR/PDIP46) is a nuclear protein operating at the interface of mRNA biogenesis, translational control, and DNA replication [#0, #5]. In RNA metabolism, it is deposited at the exon junction complex during pre-mRNA splicing and, upon mTOR activation, recruits S6K1 — which phosphorylates POLDIP3 at S383/S385 — to newly processed mRNPs to enhance the translation efficiency of spliced mRNAs during the pioneer round of translation [#0, #1]. Its own expression is shaped by TDP-43, whose RRM1-dependent RNA binding promotes inclusion of POLDIP3 exon 3, with loss of TDP-43 shifting the balance toward an isoform that augments S6K1 signaling, translational yield, and cell size [#3, #4]. In interferon-α signaling, phosphorylation of POLDIP3 by RSK or S6K1 promotes its interaction with eIF4G and recruitment of activated RSK1 to capped mRNA complexes, an activity required for IFN-α-induced ISG15 and p21 expression [#6]. In DNA metabolism, POLDIP3 binds PCNA through N-terminal APIM motifs and contacts DNA polymerase δ directly, activating Pol δ and facilitating synthesis through secondary structures [#5], and it forms a chromatin-binding complex with the RTEL1 helicase in a shared epistatic pathway that suppresses R-loop accumulation at sites of active replication to limit replication stress and genomic instability [#7]. POLDIP3 also has antiviral activity that coronaviruses neutralize: nsp5 protease cleaves it at Q176, reducing protein levels and promoting infection [#8].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Established POLDIP3/SKAR as a dedicated effector of mTOR/S6K1 signaling by identifying it as a specific S6K1 (not S6K2) substrate with mapped phosphosites and a cell-size phenotype, linking it to growth control.\",\n      \"evidence\": \"Co-IP, quantitative MS, in vivo phosphorylation mapping (S383/S385), and RNAi with cell-size readout in mammalian cells\",\n      \"pmids\": [\"15341740\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the molecular process through which SKAR controls cell size\", \"Subcellular site of S6K1 recruitment unresolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identified Enhancer of Rudimentary (ER) as a nuclear binding partner mapping to the S6K1-docking/phosphorylation region, situating POLDIP3 in nuclear protein complexes.\",\n      \"evidence\": \"Yeast two-hybrid, GST pull-down with MS, nuclear co-localization microscopy\",\n      \"pmids\": [\"16984396\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional consequence of the ER interaction demonstrated\", \"No rescue or reciprocal in vivo validation\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Resolved how SKAR couples growth signaling to translation by showing it is EJC-deposited during splicing and recruits activated S6K1 to enhance pioneer-round translation of spliced mRNAs.\",\n      \"evidence\": \"Co-IP with EJC components, spliced vs. nonspliced reporter translation assays, RNAi of SKAR/S6K1, rapamycin/mTOR manipulation in human cells\",\n      \"pmids\": [\"18423201\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which spliced transcripts depend on SKAR in vivo not defined\", \"Stoichiometry of EJC deposition unresolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Showed POLDIP3 is itself an alternative-splicing target of TDP-43, with isoform choice tuning S6K1 signaling and cell size, embedding it in a regulatory feedback on growth.\",\n      \"evidence\": \"Exon arrays, RNAi, minigene splicing reporter, S6K1 signaling and cell-size assays\",\n      \"pmids\": [\"22121224\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct functional difference between isoforms at the protein level not fully characterized\", \"Single-lab data\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Extended TDP-43 control of POLDIP3 exon 3 inclusion to disease by detecting the variant-2 shift in ALS-affected motor cortex and spinal cord.\",\n      \"evidence\": \"Exon arrays, TDP-43 siRNA, RT-PCR splice-variant detection, laser capture microdissection of ALS tissue\",\n      \"pmids\": [\"22900096\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal contribution of the POLDIP3 isoform shift to ALS pathology not established\", \"Functional consequence in neurons not tested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined a role in innate immune translation by showing IFN-α-driven phosphorylation of SKAR drives eIF4G binding and RSK1 recruitment to capped mRNAs, required for ISG15 and p21 induction.\",\n      \"evidence\": \"Co-IP with eIF4G/CBP80, phosphorylation assays, RNAi with downstream gene readouts, kinase inhibition\",\n      \"pmids\": [\"25049393\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct mRNA targets selected by SKAR not catalogued\", \"Cell-type determinants of RSK vs. S6K1 phosphorylation unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrated a direct DNA-replication function: POLDIP3 binds PCNA via APIM motifs and contacts Pol δ to stimulate its activity through secondary structures, distinct from its RNA/translation roles.\",\n      \"evidence\": \"Co-IP, ChIP, chromatin fractionation, in vitro Pol δ activity assays on ssM13 templates, mutagenesis of PCNA/Pol δ binding motifs\",\n      \"pmids\": [\"26819372\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo replication phenotype of binding-motif mutants not established\", \"Relationship between nuclear translation role and Pol δ role unresolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Placed POLDIP3 in a defined genome-stability pathway by showing it forms a chromatin complex with RTEL1 and acts epistatically to suppress R-loops at replication sites under stress.\",\n      \"evidence\": \"MS interaction screen, reciprocal Co-IP, S9.6 R-loop imaging, chromatin fractionation, CRISPR KO, epistasis by double depletion in human cells\",\n      \"pmids\": [\"32561545\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Biochemical mechanism by which the complex resolves R-loops not defined\", \"How POLDIP3 Pol δ activation relates to RTEL1 cooperation unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identified POLDIP3 as an antiviral factor targeted by coronaviruses, with nsp5 cleaving it at Q176 to abolish its restriction of infection.\",\n      \"evidence\": \"iTRAQ proteomics, in vitro protease cleavage with Q176 mapping, CRISPR KO and overexpression, in vivo piglet infection model\",\n      \"pmids\": [\"37801439\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of POLDIP3 antiviral activity not defined\", \"Which POLDIP3 function (translation vs. DNA replication) underlies restriction unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How POLDIP3's distinct activities — EJC-coupled translation, Pol δ activation, RTEL1-dependent R-loop suppression, and antiviral restriction — are integrated or partitioned within one protein remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No unifying structural or domain map linking the RNA and DNA functions\", \"No model for how phosphorylation state switches between roles\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0045182\", \"supporting_discovery_ids\": [1, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [5, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [5, 7]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [6, 8]}\n    ],\n    \"complexes\": [\"exon junction complex\", \"RTEL1-POLDIP3 complex\"],\n    \"partners\": [\"RPS6KB1\", \"TDP-43\", \"PCNA\", \"POLD1\", \"EIF4G1\", \"RTEL1\", \"ERH\", \"RPS6KA1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}