{"gene":"IPO8","run_date":"2026-04-28T18:06:54","timeline":{"discoveries":[{"year":1997,"finding":"IPO8 (RanBP8) was identified as a novel RanGTP-binding protein belonging to the importin-β superfamily. It binds RanGTP directly, prevents RanGAP1-mediated GTPase activation, and inhibits nucleotide exchange on RanGTP. It binds directly to nuclear pore complexes, competing for binding sites with importin-β and transportin, and undergoes Ran-dependent bidirectional transport across the nuclear envelope.","method":"Biochemical binding assays, nuclear pore competition assays, nuclear transport reconstitution","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal in vitro assays with direct functional validation; foundational discovery paper","pmids":["9214382"],"is_preprint":false},{"year":2001,"finding":"IPO8 (importin 8) mediates nuclear import of SRP19 (the 19 kDa subunit of the signal recognition particle) in vitro, establishing SRP19 as the first identified cargo of importin 8. Endogenous SRP19 was shown to reside in the nucleus and nucleolus, consistent with nuclear SRP assembly.","method":"In vitro nuclear import assay, RNA microinjection, cDNA transfection, immunofluorescence localization of endogenous SRP19","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro reconstitution of nuclear import combined with endogenous protein localization","pmids":["11682607"],"is_preprint":false},{"year":2009,"finding":"IPO8 (Imp8) interacts with Argonaute (Ago) proteins and localizes to cytoplasmic P-bodies. Knockdown of Imp8 reduces nuclear Ago2 levels, indicating Imp8 facilitates nuclear localization of Ago2. Imp8 is required for efficient recruitment of Ago protein complexes to a large set of Ago2-associated target mRNAs, thereby enabling cytoplasmic miRNA-guided gene silencing.","method":"Co-immunoprecipitation, siRNA knockdown, fluorescence microscopy (P-body localization), Ago2-mRNA immunoprecipitation followed by microarray analysis","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, KD phenotype with defined molecular readout, and transcriptome-wide target analysis in single high-impact study","pmids":["19167051"],"is_preprint":false},{"year":2013,"finding":"IPO8, together with KPNB1 and XPO7, mediates nuclear translocation of NF-κB/p65. Knockdown of IPO8 reduced nuclear p65 after TNF-α stimulation and lowered NF-κB transcriptional activity. IPO8 imports p65 via an NLS-independent alternative pathway, as NLS-mutated p65 still bound to IPO8 and entered the nucleus.","method":"High-content siRNA screen of 17 importin-β family members, co-immunoprecipitation, nuclear fractionation, NF-κB reporter assay, TNF-α stimulation","journal":"Traffic (Copenhagen, Denmark)","confidence":"Medium","confidence_rationale":"Tier 2 — systematic siRNA screen validated by Co-IP and reporter assay, single study","pmids":["23906023"],"is_preprint":false},{"year":2016,"finding":"RUNX2 transcription factor binds directly to a specific sequence motif (positions −496 to −501 bp) in the IPO8 promoter and is required for maximal IPO8 basal transcription. ChIP confirmed RUNX2 occupancy at this site; RUNX2 knockdown reduced IPO8 mRNA levels, and IPO8 and RUNX2 expression were synchronized during osteoblast differentiation.","method":"ChIP-on-chip, dual luciferase reporter assay with truncation/deletion constructs, ChIP validation, siRNA knockdown of RUNX2","journal":"Molecular medicine reports","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP plus reporter assay with mutagenesis, but single lab and single study","pmids":["27277970"],"is_preprint":false},{"year":2021,"finding":"Bi-allelic loss-of-function variants in IPO8 cause syndromic thoracic aortic aneurysm (TAA). Ipo8 knockout mice recapitulate TAA with elastic fiber disorganization in aortic walls. Loss of IPO8 leads to nuclear accumulation of pSmad2, decreased Smad6/7 expression, and increased Mmp2 and Ccn2 (Ctgf), indicating dysregulated TGF-β signaling. Compliance assays showed augmented passive stiffness of the ascending aorta, linking IPO8-mediated nuclear import to TGF-β pathway homeostasis.","method":"Human genetics (bi-allelic LOF variants), C57BL/6N Ipo8 knockout mouse model, immunohistochemistry (pSmad2 nuclear localization), RT-qPCR, aortic compliance assays, histology","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 — knockout mouse model with multiple orthogonal assays (histology, compliance, IHC, RT-qPCR) corroborated by human genetics","pmids":["34010605"],"is_preprint":false},{"year":2025,"finding":"IPO8 forms a complex with the nuclear lncRNA LINC1467 and NF-κB/p65. LINC1467 interacts with IPO8 to facilitate phosphorylation and nuclear translocation of p65, promoting NF-κB-dependent pro-inflammatory cytokine expression as part of the antiviral innate immune response to enteroviruses.","method":"Co-immunoprecipitation (LINC1467/IPO8/p65 complex), knockdown/overexpression functional assays, reporter assays, mouse viral infection model","journal":"Pathogens (Basel, Switzerland)","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP of ternary complex with functional validation in cell and mouse model, single study","pmids":["41156681"],"is_preprint":false}],"current_model":"IPO8 (importin 8/RanBP8) is a member of the importin-β superfamily that binds RanGTP and mediates nuclear import of diverse cargoes including SRP19, Argonaute proteins, NF-κB/p65, and TGF-β pathway components (SMADs); it also facilitates cytoplasmic miRNA-guided gene silencing by recruiting Ago complexes to target mRNAs, and its transcription is directly regulated by RUNX2 binding to the IPO8 promoter, with loss-of-function causing dysregulated TGF-β/SMAD nuclear signaling and thoracic aortic aneurysm."},"narrative":{"teleology":[{"year":1997,"claim":"The discovery of IPO8 (RanBP8) as a RanGTP-binding member of the importin-β superfamily that competes with importin-β for nuclear pore binding sites established it as a candidate nuclear transport receptor.","evidence":"Biochemical binding assays and nuclear pore competition experiments with recombinant protein","pmids":["9214382"],"confidence":"High","gaps":["No physiological cargo identified at this stage","Transport directionality in vivo not determined"]},{"year":2001,"claim":"Identification of SRP19 as the first cargo of IPO8 demonstrated that it functions as a bona fide nuclear import receptor for specific protein substrates.","evidence":"In vitro nuclear import reconstitution assay with SRP19 and immunofluorescence localization","pmids":["11682607"],"confidence":"High","gaps":["Full cargo repertoire unknown","Structural basis of cargo recognition not determined"]},{"year":2009,"claim":"The finding that IPO8 interacts with Argonaute proteins and is required for Ago2 recruitment to target mRNAs expanded its role beyond nuclear import to cytoplasmic miRNA-mediated silencing.","evidence":"Co-immunoprecipitation, siRNA knockdown of IPO8 with Ago2–mRNA immunoprecipitation and microarray readout","pmids":["19167051"],"confidence":"High","gaps":["Mechanism by which IPO8 facilitates Ago–mRNA engagement in the cytoplasm not resolved","Whether the cytoplasmic silencing role is independent of nuclear import activity remains unclear"]},{"year":2013,"claim":"Demonstrating that IPO8 imports NF-κB/p65 via an NLS-independent pathway revealed a non-canonical import mechanism and implicated IPO8 in inflammatory signaling.","evidence":"Systematic siRNA screen of importin-β family members with nuclear fractionation and NF-κB reporter assays after TNF-α stimulation","pmids":["23906023"],"confidence":"Medium","gaps":["The p65 recognition surface on IPO8 has not been mapped","Relative contribution of IPO8 versus KPNB1 and XPO7 to p65 nuclear accumulation not quantified"]},{"year":2016,"claim":"Showing that RUNX2 directly binds the IPO8 promoter and drives its transcription linked upstream developmental regulation to nuclear import capacity during osteoblast differentiation.","evidence":"ChIP, luciferase reporter with deletion constructs, and RUNX2 siRNA knockdown","pmids":["27277970"],"confidence":"Medium","gaps":["Other transcriptional regulators of IPO8 not surveyed","Functional consequence of reduced IPO8 on osteoblast cargo import not tested"]},{"year":2021,"claim":"Bi-allelic IPO8 loss-of-function variants causing syndromic thoracic aortic aneurysm in humans and mice established IPO8 as essential for TGF-β/SMAD signaling homeostasis and vascular integrity.","evidence":"Human genetic identification of bi-allelic LOF variants; Ipo8 knockout mouse with histology, pSmad2 IHC, RT-qPCR, and aortic compliance assays","pmids":["34010605"],"confidence":"High","gaps":["Which SMAD isoform(s) are direct IPO8 import cargoes versus indirectly affected has not been resolved","Structural basis of IPO8-SMAD interaction unknown"]},{"year":2025,"claim":"Identification of a ternary IPO8–LINC1467–p65 complex that promotes NF-κB nuclear translocation during enterovirus infection revealed lncRNA-mediated regulation of IPO8 import activity in innate immunity.","evidence":"Co-immunoprecipitation of ternary complex, knockdown/overexpression assays, and mouse viral infection model","pmids":["41156681"],"confidence":"Medium","gaps":["Whether LINC1467 binding modulates IPO8 conformation or cargo affinity is unknown","Generalizability of lncRNA-assisted IPO8 import to other cargoes or viral infections not tested"]},{"year":null,"claim":"A comprehensive structural model of IPO8 bound to its diverse cargoes is lacking, and how IPO8 discriminates between nuclear import substrates and participates in cytoplasmic mRNA silencing through a unified mechanism remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution structure of IPO8 in complex with any cargo","Mechanism coupling nuclear import and cytoplasmic Ago-mRNA recruitment not clarified","Full catalogue of IPO8 cargoes not systematically defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,1,2,3,5]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[2]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,1,2,3,5]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[2]},{"term_id":"GO:0005635","term_label":"nuclear envelope","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[0,1,2,3,5]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[3,6]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,5,6]}],"complexes":[],"partners":["AGO2","RELA","SRP19","RAN","RUNX2"],"other_free_text":[]},"mechanistic_narrative":"IPO8 is a member of the importin-β superfamily that functions as a RanGTP-dependent nuclear import receptor, mediating nuclear translocation of diverse cargoes including SRP19, Argonaute proteins, and NF-κB/p65 [PMID:9214382, PMID:11682607, PMID:19167051, PMID:23906023]. Beyond classical nuclear import, IPO8 is required for efficient cytoplasmic miRNA-guided gene silencing by recruiting Ago protein complexes to target mRNAs [PMID:19167051]. IPO8 also participates in TGF-β/SMAD signaling homeostasis, as loss-of-function variants cause dysregulated nuclear pSmad2 accumulation and syndromic thoracic aortic aneurysm in both humans and knockout mice [PMID:34010605]. Transcription of IPO8 is directly regulated by RUNX2 binding to the IPO8 promoter [PMID:27277970]."},"prefetch_data":{"uniprot":{"accession":"O15397","full_name":"Importin-8","aliases":["Ran-binding protein 8","RanBP8"],"length_aa":1037,"mass_kda":119.9,"function":"Involved in nuclear protein import, either by acting as autonomous nuclear transport receptor or as an adapter-like protein in association with the importin-beta subunit KPNB1. Acting autonomously, may serve as receptor for nuclear localization signals (NLS) and promote translocation of import substrates through the nuclear pore complex (NPC) by an energy requiring, Ran-dependent mechanism. At the nucleoplasmic side of the NPC, Ran binds to importin, the importin/substrate complex dissociates and importin is re-exported from the nucleus to the cytoplasm where GTP hydrolysis releases Ran. The directionality of nuclear import is thought to be conferred by an asymmetric distribution of the GTP- and GDP-bound forms of Ran between the cytoplasm and nucleus (PubMed:9214382). In vitro mediates the nuclear import of the signal recognition particle protein SRP19 (PubMed:11682607). May also be involved in cytoplasm-to-nucleus shuttling of a broad spectrum of other cargos, including Argonaute-microRNAs complexes, the JUN protein, RELA/NF-kappa-B p65 subunit, the translation initiation factor EIF4E and a set of receptor-activated mothers against decapentaplegic homolog (SMAD) transcription factors that play a critical role downstream of the large family of transforming growth factor beta and bone morphogenetic protein (BMP) cytokines (Probable)","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/O15397/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/IPO8","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000133704","cell_line_id":"CID001556","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"nucleoplasm","grade":3}],"interactors":[{"gene":"ZBTB10","stoichiometry":10.0},{"gene":"ZNF629","stoichiometry":4.0},{"gene":"CAPZB","stoichiometry":0.2},{"gene":"CDX2","stoichiometry":0.2},{"gene":"ZFP1","stoichiometry":0.2},{"gene":"TRIM28","stoichiometry":0.2},{"gene":"ZNF460","stoichiometry":0.2},{"gene":"RANBP1","stoichiometry":0.2},{"gene":"WEE1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001556","total_profiled":1310},"omim":[{"mim_id":"619472","title":"VISS SYNDROME; VISS","url":"https://www.omim.org/entry/619472"},{"mim_id":"605600","title":"IMPORTIN 8; IPO8","url":"https://www.omim.org/entry/605600"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Vesicles","reliability":"Additional"},{"location":"End piece","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/IPO8"},"hgnc":{"alias_symbol":["IMP8"],"prev_symbol":["RANBP8"]},"alphafold":{"accession":"O15397","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O15397","model_url":"https://alphafold.ebi.ac.uk/files/AF-O15397-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O15397-F1-predicted_aligned_error_v6.png","plddt_mean":87.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=IPO8","jax_strain_url":"https://www.jax.org/strain/search?query=IPO8"},"sequence":{"accession":"O15397","fasta_url":"https://rest.uniprot.org/uniprotkb/O15397.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O15397/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O15397"}},"corpus_meta":[{"pmid":"23906023","id":"PMC_23906023","title":"KPNB1, XPO7 and IPO8 mediate the translocation ofNF-κB/p65 into the nucleus.","date":"2013","source":"Traffic (Copenhagen, Denmark)","url":"https://pubmed.ncbi.nlm.nih.gov/23906023","citation_count":89,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"11451699","id":"PMC_11451699","title":"Identification of a plasmid encoding SHV-12, TEM-1, and a variant of IMP-2 metallo-beta-lactamase, IMP-8, from a clinical isolate of Klebsiella pneumoniae.","date":"2001","source":"Antimicrobial agents and chemotherapy","url":"https://pubmed.ncbi.nlm.nih.gov/11451699","citation_count":81,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"11682607","id":"PMC_11682607","title":"Signal recognition particle protein 19 is imported into the nucleus by importin 8 (RanBP8) and transportin.","date":"2001","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/11682607","citation_count":55,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"19014639","id":"PMC_19014639","title":"Identification of importin 8 (IPO8) as the most accurate reference gene for the clinicopathological analysis of lung specimens.","date":"2008","source":"BMC molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/19014639","citation_count":45,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"21422214","id":"PMC_21422214","title":"First report of Klebsiella oxytoca strain coproducing KPC-2 and IMP-8 carbapenemases.","date":"2011","source":"Antimicrobial agents and chemotherapy","url":"https://pubmed.ncbi.nlm.nih.gov/21422214","citation_count":34,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"22992193","id":"PMC_22992193","title":"Occurrence of IMP-8, IMP-10, and IMP-13 metallo-β-lactamases located on class 1 integrons and other extended-spectrum β-lactamases in bacterial isolates from Tunisian rivers.","date":"2012","source":"Scandinavian journal of infectious diseases","url":"https://pubmed.ncbi.nlm.nih.gov/22992193","citation_count":33,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"26033721","id":"PMC_26033721","title":"Characterization of pKP-M1144, a Novel ColE1-Like Plasmid Encoding IMP-8, GES-5, and BEL-1 β-Lactamases, from a Klebsiella pneumoniae Sequence Type 252 Isolate.","date":"2015","source":"Antimicrobial agents and chemotherapy","url":"https://pubmed.ncbi.nlm.nih.gov/26033721","citation_count":31,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"34010605","id":"PMC_34010605","title":"A human importin-β-related disorder: Syndromic thoracic aortic aneurysm caused by bi-allelic loss-of-function variants in IPO8.","date":"2021","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/34010605","citation_count":14,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"31181270","id":"PMC_31181270","title":"Complete genome sequence of an IMP-8, CTX-M-14, CTX-M-3 and QnrS1 co-producing Enterobacter asburiae isolate from a patient with wound infection.","date":"2019","source":"Journal of global antimicrobial resistance","url":"https://pubmed.ncbi.nlm.nih.gov/31181270","citation_count":13,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"20381610","id":"PMC_20381610","title":"First description of bla IMP-8 in a Pseudomonas mendocina isolated at the Hospital Infante D. 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communications","url":"https://pubmed.ncbi.nlm.nih.gov/28685749","citation_count":176,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"32807901","id":"PMC_32807901","title":"UFMylation maintains tumour suppressor p53 stability by antagonizing its ubiquitination.","date":"2020","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/32807901","citation_count":168,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9230,"output_tokens":1442,"usd":0.02466},"stage2":{"model":"claude-opus-4-6","input_tokens":4725,"output_tokens":1833,"usd":0.104175},"total_usd":0.292284,"stage1_batch_id":"msgbatch_01DzrsgVgYngY1hvM3DU1yF2","stage2_batch_id":"msgbatch_01KA9b7iRzKFdhoBUT7vCvSe","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":21191,"output_tokens":1960,"usd":0.046487},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":5520,"output_tokens":2015,"usd":0.116962}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2001,\n      \"finding\": \"Importin 8 (IPO8/RanBP8) directly mediates nuclear import of SRP19 (the 19 kDa subunit of the signal recognition particle) in vitro, representing the first cargo function assigned to importin 8; this import is RanGTP-dependent and SRP19 localizes to the nucleus and nucleolus.\",\n      \"method\": \"In vitro nuclear import assay, subcellular fractionation, cDNA transfection, RNA microinjection\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstituted import assay with direct functional readout; first cargo assignment for IPO8\",\n      \"pmids\": [\"11682607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"IPO8 mediates nuclear translocation of NF-κB/p65 via an NLS-independent alternative import pathway; knockdown of IPO8 reduces nuclear p65 accumulation after TNF-α stimulation and lowers NF-κB transcriptional activity. IPO8 binds NLS-mutated p65, distinguishing it from the canonical KPNA2/KPNB1 pathway.\",\n      \"method\": \"High-content siRNA screening of 17 importin-β family members, co-immunoprecipitation (binding of IPO8 to NLS-mutated p65), nuclear fractionation, NF-κB reporter assay\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide siRNA screen followed by reciprocal binding and functional reporter assay with mechanistic distinction from canonical pathway\",\n      \"pmids\": [\"23906023\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Bi-allelic loss-of-function of IPO8 disrupts TGF-β signaling in the aortic wall, evidenced by nuclear pSmad2 accumulation, decreased Smad6/7 expression, and increased Mmp2/Ccn2 expression in Ipo8-/- mice, leading to elastic fiber disorganization and thoracic aortic aneurysm. This places IPO8 as a nuclear import receptor for TGF-β signaling components including SMAD proteins.\",\n      \"method\": \"C57BL/6N Ipo8 knockout mouse model, immunohistology (nuclear pSmad2), compliance assays (aortic stiffness), RT-qPCR (Smad6/7, Mmp2, Ccn2), human genetics (bi-allelic LOF variants in patients)\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse model with multiple orthogonal functional readouts (histology, biomechanics, gene expression) corroborated by human disease genetics\",\n      \"pmids\": [\"34010605\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"RUNX2 transcription factor binds to a specific site (−496 to −501 bp) in the IPO8 promoter and is required for maximal IPO8 basal transcription; RUNX2 knockdown reduces IPO8 mRNA levels, and IPO8 and RUNX2 expression are synchronized during osteoblast differentiation.\",\n      \"method\": \"ChIP-on-chip, ChIP assay, luciferase reporter (truncation and site-specific promoter analysis), RUNX2 knockdown, osteoblast differentiation assay\",\n      \"journal\": \"Molecular medicine reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP and reporter assays with functional KD validation, single lab\",\n      \"pmids\": [\"27277970\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"IPO8 forms a ternary complex with the lncRNA LINC1467 and NF-κB/p65; this LINC1467/IPO8/p65 complex facilitates p65 phosphorylation and nuclear translocation, promoting pro-inflammatory cytokine expression and NF-κB pathway activation as part of the antiviral innate immune response.\",\n      \"method\": \"RNA-protein interaction assay (LINC1467–IPO8 interaction), co-immunoprecipitation (IPO8–p65 complex), functional knockdown/overexpression, NF-κB reporter assay, mouse viral infection model\",\n      \"journal\": \"Pathogens (Basel, Switzerland)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — co-IP and functional assays in cell lines and mouse model, single lab, mechanistic detail on complex formation\",\n      \"pmids\": [\"41156681\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IPO8 is a nuclear import receptor (importin-β family) that translocates cargo proteins into the nucleus in a RanGTP-dependent manner; its characterized cargoes include SRP19 (via direct import), NF-κB/p65 (via an NLS-independent alternative pathway, potentiated by the lncRNA LINC1467), and TGF-β pathway effectors (SMAD proteins), with loss of IPO8 causing dysregulated TGF-β/SMAD signaling and thoracic aortic aneurysm, while its own transcription is controlled by RUNX2.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"IPO8 (RanBP8) was identified as a novel RanGTP-binding protein belonging to the importin-β superfamily. It binds RanGTP directly, prevents RanGAP1-mediated GTPase activation, and inhibits nucleotide exchange on RanGTP. It binds directly to nuclear pore complexes, competing for binding sites with importin-β and transportin, and undergoes Ran-dependent bidirectional transport across the nuclear envelope.\",\n      \"method\": \"Biochemical binding assays, nuclear pore competition assays, nuclear transport reconstitution\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal in vitro assays with direct functional validation; foundational discovery paper\",\n      \"pmids\": [\"9214382\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"IPO8 (importin 8) mediates nuclear import of SRP19 (the 19 kDa subunit of the signal recognition particle) in vitro, establishing SRP19 as the first identified cargo of importin 8. Endogenous SRP19 was shown to reside in the nucleus and nucleolus, consistent with nuclear SRP assembly.\",\n      \"method\": \"In vitro nuclear import assay, RNA microinjection, cDNA transfection, immunofluorescence localization of endogenous SRP19\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution of nuclear import combined with endogenous protein localization\",\n      \"pmids\": [\"11682607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"IPO8 (Imp8) interacts with Argonaute (Ago) proteins and localizes to cytoplasmic P-bodies. Knockdown of Imp8 reduces nuclear Ago2 levels, indicating Imp8 facilitates nuclear localization of Ago2. Imp8 is required for efficient recruitment of Ago protein complexes to a large set of Ago2-associated target mRNAs, thereby enabling cytoplasmic miRNA-guided gene silencing.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, fluorescence microscopy (P-body localization), Ago2-mRNA immunoprecipitation followed by microarray analysis\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, KD phenotype with defined molecular readout, and transcriptome-wide target analysis in single high-impact study\",\n      \"pmids\": [\"19167051\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"IPO8, together with KPNB1 and XPO7, mediates nuclear translocation of NF-κB/p65. Knockdown of IPO8 reduced nuclear p65 after TNF-α stimulation and lowered NF-κB transcriptional activity. IPO8 imports p65 via an NLS-independent alternative pathway, as NLS-mutated p65 still bound to IPO8 and entered the nucleus.\",\n      \"method\": \"High-content siRNA screen of 17 importin-β family members, co-immunoprecipitation, nuclear fractionation, NF-κB reporter assay, TNF-α stimulation\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic siRNA screen validated by Co-IP and reporter assay, single study\",\n      \"pmids\": [\"23906023\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"RUNX2 transcription factor binds directly to a specific sequence motif (positions −496 to −501 bp) in the IPO8 promoter and is required for maximal IPO8 basal transcription. ChIP confirmed RUNX2 occupancy at this site; RUNX2 knockdown reduced IPO8 mRNA levels, and IPO8 and RUNX2 expression were synchronized during osteoblast differentiation.\",\n      \"method\": \"ChIP-on-chip, dual luciferase reporter assay with truncation/deletion constructs, ChIP validation, siRNA knockdown of RUNX2\",\n      \"journal\": \"Molecular medicine reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP plus reporter assay with mutagenesis, but single lab and single study\",\n      \"pmids\": [\"27277970\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Bi-allelic loss-of-function variants in IPO8 cause syndromic thoracic aortic aneurysm (TAA). Ipo8 knockout mice recapitulate TAA with elastic fiber disorganization in aortic walls. Loss of IPO8 leads to nuclear accumulation of pSmad2, decreased Smad6/7 expression, and increased Mmp2 and Ccn2 (Ctgf), indicating dysregulated TGF-β signaling. Compliance assays showed augmented passive stiffness of the ascending aorta, linking IPO8-mediated nuclear import to TGF-β pathway homeostasis.\",\n      \"method\": \"Human genetics (bi-allelic LOF variants), C57BL/6N Ipo8 knockout mouse model, immunohistochemistry (pSmad2 nuclear localization), RT-qPCR, aortic compliance assays, histology\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — knockout mouse model with multiple orthogonal assays (histology, compliance, IHC, RT-qPCR) corroborated by human genetics\",\n      \"pmids\": [\"34010605\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"IPO8 forms a complex with the nuclear lncRNA LINC1467 and NF-κB/p65. LINC1467 interacts with IPO8 to facilitate phosphorylation and nuclear translocation of p65, promoting NF-κB-dependent pro-inflammatory cytokine expression as part of the antiviral innate immune response to enteroviruses.\",\n      \"method\": \"Co-immunoprecipitation (LINC1467/IPO8/p65 complex), knockdown/overexpression functional assays, reporter assays, mouse viral infection model\",\n      \"journal\": \"Pathogens (Basel, Switzerland)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP of ternary complex with functional validation in cell and mouse model, single study\",\n      \"pmids\": [\"41156681\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IPO8 (importin 8/RanBP8) is a member of the importin-β superfamily that binds RanGTP and mediates nuclear import of diverse cargoes including SRP19, Argonaute proteins, NF-κB/p65, and TGF-β pathway components (SMADs); it also facilitates cytoplasmic miRNA-guided gene silencing by recruiting Ago complexes to target mRNAs, and its transcription is directly regulated by RUNX2 binding to the IPO8 promoter, with loss-of-function causing dysregulated TGF-β/SMAD nuclear signaling and thoracic aortic aneurysm.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"IPO8 is a RanGTP-dependent nuclear import receptor of the importin-β family that translocates diverse cargo proteins into the nucleus. Its characterized cargoes include SRP19, whose import it mediates directly [PMID:11682607], NF-κB/p65, which it imports via an NLS-independent alternative pathway distinct from the canonical KPNA2/KPNB1 route—an activity potentiated by the lncRNA LINC1467 to drive pro-inflammatory and antiviral gene expression [PMID:23906023, PMID:41156681], and TGF-β/SMAD signaling components, whose nuclear delivery is essential for proper aortic wall homeostasis [PMID:34010605]. Bi-allelic loss-of-function of IPO8 causes dysregulated TGF-β/SMAD signaling, elastic fiber disorganization, and thoracic aortic aneurysm in both mice and humans [PMID:34010605].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"The first cargo for IPO8 was identified, establishing it as a bona fide nuclear import receptor rather than an orphan importin-β family member: IPO8 directly imports SRP19 into the nucleus/nucleolus in a RanGTP-dependent manner.\",\n      \"evidence\": \"In vitro reconstituted nuclear import assay with recombinant proteins and subcellular fractionation in mammalian cells\",\n      \"pmids\": [\"11682607\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Only one cargo identified; full cargo repertoire unknown\",\n        \"Structural basis for IPO8–SRP19 recognition not determined\",\n        \"Physiological consequence of SRP19 import failure not tested\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"IPO8 was shown to operate an NLS-independent alternative import pathway for NF-κB/p65, resolving the question of how p65 reaches the nucleus when the canonical KPNA2/KPNB1 pathway is disrupted.\",\n      \"evidence\": \"High-content siRNA screen of 17 importin-β members, co-immunoprecipitation of IPO8 with NLS-mutated p65, nuclear fractionation, and NF-κB reporter assay in TNF-α-stimulated cells\",\n      \"pmids\": [\"23906023\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Binding interface between IPO8 and p65 not mapped\",\n        \"Relative contribution of IPO8 vs. canonical pathway under physiological conditions unclear\",\n        \"Whether RanGTP dependence applies to p65 import specifically was not tested\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Transcriptional regulation of IPO8 itself was linked to RUNX2, showing that osteoblast-lineage transcription factors control importin expression during differentiation.\",\n      \"evidence\": \"ChIP, luciferase promoter reporter with site-directed mutations, RUNX2 knockdown, and osteoblast differentiation time-course\",\n      \"pmids\": [\"27277970\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single-lab finding; not independently confirmed\",\n        \"Downstream consequences of RUNX2-driven IPO8 upregulation on nuclear import cargo flux not examined\",\n        \"Other transcription factors regulating IPO8 not surveyed\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Loss of IPO8 was established as the cause of thoracic aortic aneurysm through dysregulated TGF-β/SMAD signaling, identifying SMAD proteins as physiologically critical IPO8 cargoes and linking IPO8 to a Mendelian connective tissue disease.\",\n      \"evidence\": \"Ipo8 knockout mouse with aortic phenotyping (histology, compliance), nuclear pSmad2 immunostaining, RT-qPCR for SMAD target genes, and human bi-allelic loss-of-function variants in patients\",\n      \"pmids\": [\"34010605\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Direct biochemical demonstration of IPO8–SMAD binding not shown\",\n        \"Whether IPO8 imports SMAD2, SMAD3, or both selectively is unresolved\",\n        \"Mechanism by which disrupted SMAD nuclear import leads to paradoxical nuclear pSmad2 accumulation not fully explained\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A ternary complex of lncRNA LINC1467, IPO8, and p65 was identified, revealing that a non-coding RNA can potentiate IPO8-mediated nuclear import to amplify NF-κB-driven innate immune signaling during viral infection.\",\n      \"evidence\": \"RNA-protein interaction assays, co-immunoprecipitation, functional knockdown/overexpression, NF-κB reporter, and mouse viral infection model\",\n      \"pmids\": [\"41156681\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single-lab study; ternary complex stoichiometry and RNA-binding domain on IPO8 not mapped\",\n        \"Whether other lncRNAs similarly modulate IPO8-dependent import is unknown\",\n        \"In vivo relevance tested only for one viral model\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A comprehensive catalog of IPO8 cargoes, the structural basis for cargo recognition (including NLS-independent binding), and the mechanism by which SMAD nuclear import deficiency leads to aortic disease remain to be determined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No structural model of IPO8 with any cargo\",\n        \"Systematic proteomics-based cargo identification not reported\",\n        \"Whether IPO8 has tissue-specific import roles beyond aorta and immune cells is unexplored\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1, 2, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0009607\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [0, 1, 2, 4]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 2, 4]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [1, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"SRP19\",\n      \"RELA\",\n      \"SMAD2\",\n      \"RUNX2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"IPO8 is a member of the importin-β superfamily that functions as a RanGTP-dependent nuclear import receptor, mediating nuclear translocation of diverse cargoes including SRP19, Argonaute proteins, and NF-κB/p65 [PMID:9214382, PMID:11682607, PMID:19167051, PMID:23906023]. Beyond classical nuclear import, IPO8 is required for efficient cytoplasmic miRNA-guided gene silencing by recruiting Ago protein complexes to target mRNAs [PMID:19167051]. IPO8 also participates in TGF-β/SMAD signaling homeostasis, as loss-of-function variants cause dysregulated nuclear pSmad2 accumulation and syndromic thoracic aortic aneurysm in both humans and knockout mice [PMID:34010605]. Transcription of IPO8 is directly regulated by RUNX2 binding to the IPO8 promoter [PMID:27277970].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"The discovery of IPO8 (RanBP8) as a RanGTP-binding member of the importin-β superfamily that competes with importin-β for nuclear pore binding sites established it as a candidate nuclear transport receptor.\",\n      \"evidence\": \"Biochemical binding assays and nuclear pore competition experiments with recombinant protein\",\n      \"pmids\": [\"9214382\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No physiological cargo identified at this stage\",\n        \"Transport directionality in vivo not determined\"\n      ]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identification of SRP19 as the first cargo of IPO8 demonstrated that it functions as a bona fide nuclear import receptor for specific protein substrates.\",\n      \"evidence\": \"In vitro nuclear import reconstitution assay with SRP19 and immunofluorescence localization\",\n      \"pmids\": [\"11682607\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Full cargo repertoire unknown\",\n        \"Structural basis of cargo recognition not determined\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"The finding that IPO8 interacts with Argonaute proteins and is required for Ago2 recruitment to target mRNAs expanded its role beyond nuclear import to cytoplasmic miRNA-mediated silencing.\",\n      \"evidence\": \"Co-immunoprecipitation, siRNA knockdown of IPO8 with Ago2–mRNA immunoprecipitation and microarray readout\",\n      \"pmids\": [\"19167051\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism by which IPO8 facilitates Ago–mRNA engagement in the cytoplasm not resolved\",\n        \"Whether the cytoplasmic silencing role is independent of nuclear import activity remains unclear\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrating that IPO8 imports NF-κB/p65 via an NLS-independent pathway revealed a non-canonical import mechanism and implicated IPO8 in inflammatory signaling.\",\n      \"evidence\": \"Systematic siRNA screen of importin-β family members with nuclear fractionation and NF-κB reporter assays after TNF-α stimulation\",\n      \"pmids\": [\"23906023\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The p65 recognition surface on IPO8 has not been mapped\",\n        \"Relative contribution of IPO8 versus KPNB1 and XPO7 to p65 nuclear accumulation not quantified\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showing that RUNX2 directly binds the IPO8 promoter and drives its transcription linked upstream developmental regulation to nuclear import capacity during osteoblast differentiation.\",\n      \"evidence\": \"ChIP, luciferase reporter with deletion constructs, and RUNX2 siRNA knockdown\",\n      \"pmids\": [\"27277970\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Other transcriptional regulators of IPO8 not surveyed\",\n        \"Functional consequence of reduced IPO8 on osteoblast cargo import not tested\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Bi-allelic IPO8 loss-of-function variants causing syndromic thoracic aortic aneurysm in humans and mice established IPO8 as essential for TGF-β/SMAD signaling homeostasis and vascular integrity.\",\n      \"evidence\": \"Human genetic identification of bi-allelic LOF variants; Ipo8 knockout mouse with histology, pSmad2 IHC, RT-qPCR, and aortic compliance assays\",\n      \"pmids\": [\"34010605\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Which SMAD isoform(s) are direct IPO8 import cargoes versus indirectly affected has not been resolved\",\n        \"Structural basis of IPO8-SMAD interaction unknown\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identification of a ternary IPO8–LINC1467–p65 complex that promotes NF-κB nuclear translocation during enterovirus infection revealed lncRNA-mediated regulation of IPO8 import activity in innate immunity.\",\n      \"evidence\": \"Co-immunoprecipitation of ternary complex, knockdown/overexpression assays, and mouse viral infection model\",\n      \"pmids\": [\"41156681\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether LINC1467 binding modulates IPO8 conformation or cargo affinity is unknown\",\n        \"Generalizability of lncRNA-assisted IPO8 import to other cargoes or viral infections not tested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A comprehensive structural model of IPO8 bound to its diverse cargoes is lacking, and how IPO8 discriminates between nuclear import substrates and participates in cytoplasmic mRNA silencing through a unified mechanism remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No high-resolution structure of IPO8 in complex with any cargo\",\n        \"Mechanism coupling nuclear import and cytoplasmic Ago-mRNA recruitment not clarified\",\n        \"Full catalogue of IPO8 cargoes not systematically defined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1, 2, 3, 5]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 1, 2, 3, 5]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005635\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [0, 1, 2, 3, 5]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3, 6]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 5, 6]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"AGO2\",\n      \"RELA\",\n      \"SRP19\",\n      \"RAN\",\n      \"RUNX2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}