{"gene":"IPO9","run_date":"2026-06-10T01:55:23","timeline":{"discoveries":[{"year":2002,"finding":"Imp9a and Imp9b (mouse orthologs of human IPO9) mediate nuclear import of ribosomal proteins rpS7 and rpL18a, and act as cytoplasmic chaperones by covering their exposed basic domains to prevent aggregation with cytoplasmic polyanions such as RNA.","method":"In vitro nuclear import assay, chaperone/aggregation prevention assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — direct in vitro import and chaperone assays with multiple substrates, replicated across Imp family members in the same study","pmids":["11823430"],"is_preprint":false},{"year":2009,"finding":"IPO9 mediates nuclear import of Sox2 and SRY transcription factors via their HMG box domain, acting in parallel with Exp4 and the Imp-beta/7 heterodimer; import signals overlap with conserved residues critical for DNA binding.","method":"In vitro nuclear import assay, co-immunoprecipitation, RNAi knockdown","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro import assay plus knockdown, single lab, multiple orthogonal methods","pmids":["19349578"],"is_preprint":false},{"year":2009,"finding":"IPO9 mediates nuclear import of the homeodomain protein Arx via its NLS2 (within the DNA-binding homeodomain); binding to IPO9 is RanGTP-sensitive and NLS2 can be co-precipitated with IPO9.","method":"In vitro nuclear import assay, co-immunoprecipitation, RNAi knockdown, domain deletion analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro import plus co-IP and RNAi, single lab, multiple orthogonal methods","pmids":["19494118"],"is_preprint":false},{"year":2013,"finding":"IPO9 participates in stimulation-induced nuclear translocation of JNK and p38 MAPKs by forming heterotrimeric complexes (Imp3/Imp9/MAPK); JNK1/2 and p38α/β bind Imp9 upon stimulated post-translational modification of Imp9; IPO9 escorts MAPKs into the nucleus while Imp3 remains at the nuclear envelope. Knockdown of IPO9 inhibits MAPK nuclear translocation and downstream transcription factor phosphorylation.","method":"Co-immunoprecipitation, proximity ligation assay, gel filtration, immunostaining, RNAi knockdown","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, PLA, gel filtration, immunostaining, KD), single lab","pmids":["24216760"],"is_preprint":false},{"year":2013,"finding":"IPO9 binds the 5'UTR stem-loop structure 1 of IFN-ε mRNA; IPO9 overexpression decreases and IPO9 silencing increases basal IFN-ε mRNA expression, defining a negative posttranscriptional regulatory role for IPO9. This effect extends to other mRNAs capable of forming similar loop structures (e.g., HIF-1α).","method":"RNA affinity pulldown (agarose-bound RNA with HeLa cell extracts), overexpression, RNAi knockdown, luciferase reporter assay","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — RNA pulldown identification plus functional OE/KD with reporter validation, single lab","pmids":["23851686"],"is_preprint":false},{"year":2016,"finding":"IPO9 binds histone H3 and H4 tails at two separate elements: the segment at residues 11-27 and an isoleucine-lysine NLS (IK-NLS) motif at residues 35-40 of the H3 tail; acetylation of H3 Lys14 substantially decreases binding to IPO9 and several other importins.","method":"Quantitative binding assays (fluorescence anisotropy/ITC), mutagenic analysis of histone tail deletion mutants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — quantitative biochemical binding assays with mutagenesis defining specific binding elements, single lab but rigorous","pmids":["27528606"],"is_preprint":false},{"year":2019,"finding":"Crystal structure of IPO9 bound to the H2A-H2B dimer reveals that IPO9 wraps around the globular core region of H2A-H2B forming an extensive interface; the NLS-like sequences in H2A-H2B tails play a minor role. IPO9 precludes H2A-H2B interactions with DNA and H3-H4 (acting as a chaperone/sequestrant). RanGTP does not dissociate IPO9•H2A-H2B but assembles a stable RanGTP•IPO9•H2A-H2B ternary complex that can facilitate H2A-H2B dissociation by DNA and nucleosome assembly.","method":"X-ray crystallography, quantitative binding assays, nucleosome assembly assay, deletion mutagenesis","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus quantitative binding assays and functional nucleosome assembly, multiple orthogonal methods in single rigorous study","pmids":["30855230"],"is_preprint":false},{"year":2019,"finding":"IPO9 mediates nuclear import of NUAK1 (a serine/threonine AMPK-family kinase) via a bipartite NLS at the N-terminal domain; knockdown of IPO9 (or IPO7) inhibits NUAK1 nuclear import. Oxidative stress induces NUAK1 cytoplasmic accumulation, indicating that oxidative stress affects IPO9-mediated nuclear transport.","method":"Mass spectrometry (interactome), co-immunoprecipitation, RNAi knockdown, subcellular fractionation, importazole inhibition","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — MS identification confirmed by Co-IP and functional KD with localization readout, single lab","pmids":["31090959"],"is_preprint":false},{"year":2019,"finding":"IPO9 (validated by silencing) is required for optimal replication of yellow fever virus (YFV) and West Nile virus (WNV) in human cells, identifying it as a host dependency factor for flavivirus replication.","method":"Genome-wide gain-of-function cDNA screen, RNAi knockdown validation, virological assays","journal":"Viruses","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional validation by knockdown with viral replication readout, single lab","pmids":["30650657"],"is_preprint":false},{"year":2021,"finding":"Drosophila Importin-9 (Ipo9/Ranbp9, ortholog) is required for chromosome condensation and segregation during meiosis, protamine exchange during spermatogenesis, and nuclear localization of proteasome components; Ipo9 physically interacts with proteasome proteins. Loss of Ipo9 causes female and male sterility.","method":"Genetic knockout (Ipo9KO), immunofluorescence, FISH, co-immunoprecipitation","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with multiple cellular phenotype readouts plus physical interaction by Co-IP, single lab","pmids":["33632744"],"is_preprint":false},{"year":2022,"finding":"IPO9 (together with cofilin-1/CFL1) co-mediates nuclear transfer of G-actin; knockdown of IPO9 prevents dynamic strain-mediated nuclear transfer of both actin and β-catenin in mesenchymal stem cells, indicating that β-catenin nuclear entry depends on actin transport via IPO9.","method":"RNAi knockdown of IPO9, nuclear fractionation, fluorescence imaging, mechanical strain application","journal":"Stem cells","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — KD with specific phenotypic readouts for two cargos (actin and β-catenin), single lab","pmids":["35278073"],"is_preprint":false},{"year":2022,"finding":"Silencing IPO9 or CFL1 (components of the nuclear actin import complex) prevents cAMP-induced nuclear actin monomer increase and rescues RelA/p65 levels and NF-κB reporter activity, placing IPO9-mediated nuclear actin import upstream of proteasomal degradation of RelA/p65 in the cAMP anti-inflammatory pathway.","method":"RNAi knockdown, NF-κB reporter assay, western blotting, proteasome inhibitor experiment","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — genetic epistasis by KD with multiple functional readouts, single lab","pmids":["35563720"],"is_preprint":false},{"year":2023,"finding":"HDX-MS analysis of the RanGTP•IPO9•H2A-H2B ternary complex shows that RanGTP releases H2A-H2B contacts at IPO9 HEAT repeats 4-5 but not 18-19, exposing DNA- and histone-binding surfaces of H2A-H2B to facilitate nucleosome assembly. RanGTP has weaker affinity for IPO9 when H2A-H2B is bound, ensuring release only at high nuclear RanGTP concentrations near chromatin.","method":"Hydrogen-deuterium exchange mass spectrometry (HDX-MS), quantitative binding assays, in vitro nucleosome assembly","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 / Moderate — HDX-MS structural dynamics plus quantitative binding and functional nucleosome assembly, single lab but multiple orthogonal methods","pmids":["37379840"],"is_preprint":false},{"year":2025,"finding":"IPO9 directly binds monomeric actin with mid-nanomolar affinity; contrary to the established model, cofilin competitively inhibits (rather than promotes) IPO9-actin complex formation. Profilin similarly competes with IPO9 for actin binding at the barbed face. RanGTP binds monomeric actin but a tripartite IPO9-actin-RanGTP complex does not form. IPO9 modestly decreases the rate of actin filament assembly and exhibits minimal binding to actin filaments.","method":"In vitro binding assays (competitive), actin polymerization kinetics assay, quantitative affinity measurements","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — rigorous in vitro reconstitution with quantitative affinity measurements and multiple competition assays, single lab but multiple orthogonal methods","pmids":["41478570"],"is_preprint":false},{"year":2025,"finding":"IPO9 knockdown markedly reduces nuclear F-actin assembly during ferroptosis in HT-1080 cells, establishing that IPO9-dependent nuclear import of G-actin is required for nuclear F-actin formation during ferroptotic cell death.","method":"RNAi knockdown, phalloidin staining, live imaging with nuclear actin chromobody (nAC-TagGFP2)","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 2-3 / Weak — KD with imaging readout in a single cell line, single lab","pmids":["41450740"],"is_preprint":false},{"year":2026,"finding":"Cryo-EM structure of IPO9 bound to the ETS domain transcription factor EHF reveals that IPO9 wraps around the winged-helix fold (ETS domain) and engages structural features throughout; the DNA-binding helix of the ETS domain is critical for importin recognition and NLS activity. IPO9 uses distinct interaction hotspots compared to its H2A-H2B binding surfaces, demonstrating combinatorial use of binding surfaces for structurally diverse cargos. ETS domains constitute a structure-encoded (globular) NLS class recognized by IPO9 with nanomolar affinity.","method":"Cryo-electron microscopy, biochemical binding assays, mutagenesis, cellular NLS activity assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — cryo-EM structure plus quantitative binding assays and mutagenesis with cellular validation, single lab but multiple orthogonal methods","pmids":["42066049"],"is_preprint":false},{"year":2026,"finding":"AKIRIN2 acts as a multivalent scaffold that simultaneously binds the 20S proteasome and IPO9 (as well as KPNA2/KPNB1), recruiting an importin cluster to mediate nuclear import of the proteasome. In the nucleus, RanGTP triggers IPO9 dissociation to release the proteasome. Identified by saturation mutagenesis screens, cryo-EM, and biochemical reconstitution.","method":"Protein-wide saturation mutagenesis, cryo-EM, biochemical reconstitution, co-immunoprecipitation","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure plus saturation mutagenesis and biochemical reconstitution, multiple orthogonal methods","pmids":["41639071"],"is_preprint":false},{"year":2026,"finding":"Systematic cytoplasmic IP-MS identifies 79 bona fide IPO9-bound cargos (including H2A-H2B, TFIIB, actin, proteasome subunits, and 20 previously validated cargos); IPO9 does not use classical NLS motifs nor any linear peptide motif for cargo recognition. Oxidative footprinting shows both the inner cavity and unstructured loops (H8, H18-19) of IPO9 are protected by bound cargo. Loop perturbation IP-MS shows H8 and H18-19 loops mediate selective cargo recognition; H7, H8, H18-19 loops restrict binding of a secondary set of potential cargos. RanGTP sensitivity for cargo release varies by orders of magnitude across the cargo cohort.","method":"Cytoplasmic immunoprecipitation/mass spectrometry, oxidative protein footprinting, systematic loop-perturbation IP-MS","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (IP-MS, footprinting, loop mutants), single lab, preprint","pmids":["42182196"],"is_preprint":true}],"current_model":"IPO9 is a nuclear import receptor (importin β family) that transports structurally diverse cargos—including histone H2A-H2B (by wrapping around their globular core), ribosomal proteins, actin monomers (by direct barbed-face binding that competes with cofilin and profilin), ETS-domain transcription factors, Sox/homeodomain proteins, MAPKs (JNK/p38 in heterotrimeric complexes with Imp3), NUAK1, and the 20S proteasome (via AKIRIN2 scaffold)—using combinatorial, non-classical binding surfaces (HEAT repeat inner cavity and unstructured loops); it additionally functions as a histone chaperone that sequesters H2A-H2B from inappropriate interactions until RanGTP in the nucleus partially remodels the complex to enable nucleosome assembly, and it also acts as a posttranscriptional repressor of IFN-ε mRNA through binding to 5'UTR stem-loop structures."},"narrative":{"mechanistic_narrative":"IPO9 is an importin-β family nuclear transport receptor that imports a structurally diverse cargo repertoire using non-classical, combinatorial binding surfaces rather than linear NLS motifs [PMID:11823430, PMID:42182196]. It recognizes cargos by wrapping around their globular folds: crystallographic and cryo-EM analyses show IPO9 engaging the H2A-H2B core and the winged-helix ETS domain of EHF through distinct interaction hotspots, with both the HEAT-repeat inner cavity and unstructured loops (H8, H18-19) contributing to selective recognition [PMID:30855230, PMID:42066049, PMID:42182196]. Its validated cargos span ribosomal proteins rpS7/rpL18a [PMID:11823430], HMG-box (Sox2/SRY) and homeodomain (Arx) transcription factors [PMID:19349578, PMID:19494118], the stress-activated MAPKs JNK and p38 (imported in heterotrimeric Imp3/Imp9/MAPK complexes) [PMID:24216760], the kinase NUAK1 [PMID:31090959], monomeric actin [PMID:35278073, PMID:41478570], and the 20S proteasome via the AKIRIN2 scaffold [PMID:41639071]. Beyond transport, IPO9 functions as a histone chaperone that sequesters H2A-H2B from premature contacts with DNA and H3-H4; rather than dissociating the complex, nuclear RanGTP assembles a stable RanGTP·IPO9·H2A-H2B ternary intermediate that selectively releases histone-binding surfaces at HEAT repeats 4-5 to license nucleosome assembly near chromatin [PMID:30855230, PMID:37379840]. For actin, IPO9 binds the monomer barbed face with mid-nanomolar affinity in competition with cofilin and profilin, and this import underlies nuclear actin pools driving β-catenin entry, RelA/p65 regulation, and nuclear F-actin formation during ferroptosis [PMID:35278073, PMID:35563720, PMID:41478570, PMID:41450740]. IPO9 additionally acts as a posttranscriptional repressor by binding the 5'UTR stem-loop of IFN-ε mRNA [PMID:23851686], and is a host dependency factor for flavivirus replication [PMID:30650657].","teleology":[{"year":2002,"claim":"Established IPO9's founding identity as a nuclear import receptor that doubles as a cytoplasmic chaperone, answering how highly basic ribosomal proteins reach the nucleus without aggregating.","evidence":"In vitro nuclear import and aggregation-prevention assays with mouse Imp9 orthologs and rpS7/rpL18a","pmids":["11823430"],"confidence":"High","gaps":["Structural basis of ribosomal-protein recognition not defined","Did not address cargo diversity beyond ribosomal proteins"]},{"year":2009,"claim":"Extended the cargo range to DNA-binding transcription factors, showing IPO9 recognizes the HMG box and homeodomain folds where import determinants overlap DNA-binding residues.","evidence":"In vitro import, co-IP, RNAi and domain deletion for Sox2/SRY and Arx","pmids":["19349578","19494118"],"confidence":"Medium","gaps":["No structure of the importin-cargo complex","Redundancy with parallel receptors (Exp4, Imp-β/7) not fully resolved"]},{"year":2013,"claim":"Revealed a signaling role: IPO9 escorts stimulated JNK/p38 into the nucleus as part of a heterotrimeric Imp3/Imp9/MAPK complex, coupling MAPK activation to nuclear transcription factor phosphorylation.","evidence":"Co-IP, PLA, gel filtration, immunostaining and RNAi in stimulated cells","pmids":["24216760"],"confidence":"Medium","gaps":["The stimulus-induced post-translational modification of Imp9 not molecularly defined","Division of labor between Imp3 and Imp9 at the envelope unresolved"]},{"year":2013,"claim":"Identified a transport-independent function: IPO9 represses IFN-ε mRNA by binding a 5'UTR stem-loop, defining a posttranscriptional RNA-regulatory activity.","evidence":"RNA affinity pulldown, overexpression/silencing and luciferase reporter assays","pmids":["23851686"],"confidence":"Medium","gaps":["Mechanism linking RNA binding to translational/stability repression unknown","Generality across loop-forming mRNAs only partly tested"]},{"year":2016,"claim":"Began mapping the histone-recognition logic, showing IPO9 binds H3/H4 tail elements and that H3K14 acetylation reduces binding, linking histone PTMs to import competence.","evidence":"Fluorescence anisotropy/ITC binding assays with histone tail mutants","pmids":["27528606"],"confidence":"High","gaps":["Did not yet show that the globular core, not tails, dominates H2A-H2B binding","Functional consequence of acetylation-modulated import not tested in cells"]},{"year":2019,"claim":"Solved the H2A-H2B complex structure and redefined IPO9 as a histone chaperone whose RanGTP response builds a remodeling intermediate rather than simple cargo release.","evidence":"X-ray crystallography, binding assays and in vitro nucleosome assembly","pmids":["30855230"],"confidence":"High","gaps":["Dynamics of the RanGTP ternary complex not resolved at residue level","How chaperone hand-off to assembly factors occurs in cells unknown"]},{"year":2019,"claim":"Broadened cargo scope to a stress-regulated kinase and showed import is redox-sensitive, linking IPO9 transport to oxidative stress.","evidence":"Interactome MS, co-IP, RNAi, fractionation and importazole inhibition for NUAK1","pmids":["31090959"],"confidence":"Medium","gaps":["The bipartite NLS recognition mode not structurally defined","Redundancy with IPO7 not dissected"]},{"year":2021,"claim":"Genetic in vivo evidence established essential developmental roles in chromosome segregation, protamine exchange and proteasome nuclear localization, connecting the receptor to fertility.","evidence":"Drosophila Ipo9 knockout with IF, FISH and co-IP","pmids":["33632744"],"confidence":"Medium","gaps":["Which cargo defects drive each phenotype not separable","Mammalian in vivo confirmation absent in corpus"]},{"year":2022,"claim":"Placed IPO9-mediated nuclear actin import upstream of mechanotransduction and inflammatory signaling, showing β-catenin and NF-κB/RelA outputs depend on actin transport.","evidence":"RNAi, nuclear fractionation, imaging, NF-κB reporter and proteasome-inhibitor experiments in MSCs","pmids":["35278073","35563720"],"confidence":"Medium","gaps":["Direct versus indirect coupling of actin import to β-catenin/RelA not biochemically isolated","Stoichiometry with cofilin in cells unknown"]},{"year":2023,"claim":"Resolved the RanGTP-driven release mechanism for histones, showing selective contact release at HEAT repeats 4-5 and affinity tuning that confines release to high-RanGTP chromatin regions.","evidence":"HDX-MS of the RanGTP·IPO9·H2A-H2B complex with binding and nucleosome assembly assays","pmids":["37379840"],"confidence":"High","gaps":["Whether the same partial-release logic applies to other cargos untested at the time","In-cell visualization of the intermediate lacking"]},{"year":2025,"claim":"Quantitative reconstitution overturned the prior actin-import model, showing IPO9 binds the actin barbed face in competition with cofilin and profilin and that no IPO9-actin-RanGTP ternary complex forms.","evidence":"Competitive in vitro binding, polymerization kinetics and affinity measurements","pmids":["41478570"],"confidence":"High","gaps":["How actin is released in the nucleus if RanGTP does not form a ternary complex is unresolved","Reconciliation with cell-based cofilin-cooperative models needed"]},{"year":2025,"claim":"Linked IPO9-dependent nuclear actin import to a specific cell-death program, showing it is required for nuclear F-actin assembly during ferroptosis.","evidence":"RNAi with phalloidin staining and nuclear actin chromobody imaging in HT-1080 cells","pmids":["41450740"],"confidence":"Medium","gaps":["Functional consequence of nuclear F-actin for ferroptotic death not established","Single cell line, no in vivo validation"]},{"year":2026,"claim":"Structures of ETS-domain and proteasome cargo recognition demonstrated combinatorial use of distinct binding surfaces and a scaffold-based import route, generalizing IPO9's non-classical recognition principle.","evidence":"Cryo-EM, binding assays and mutagenesis for EHF; saturation mutagenesis and reconstitution of the AKIRIN2-proteasome import module","pmids":["42066049","41639071"],"confidence":"High","gaps":["Predictive rules mapping cargo fold to IPO9 surface not yet derived","How RanGTP releases each structurally distinct cargo not uniformly defined"]},{"year":2026,"claim":"Systematic interactome and footprinting defined the full cargo cohort (~79 cargos) and showed recognition uses the inner cavity plus specific loops with no linear motif, plus cargo-specific RanGTP sensitivity.","evidence":"Cytoplasmic IP-MS, oxidative footprinting and loop-perturbation IP-MS (preprint)","pmids":["42182196"],"confidence":"Medium","gaps":["Preprint not yet peer reviewed","Functional import of most newly identified cargos not validated"]},{"year":null,"claim":"A unifying code that predicts which globular folds IPO9 recognizes and how RanGTP release affinity is tuned across structurally unrelated cargos remains undefined.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No general structural rule linking cargo fold to IPO9 binding surface","Mechanism of nuclear release for non-histone cargos lacking a stable ternary intermediate unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[0,1,2,3,7,10,16]},{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[0,6,12]},{"term_id":"GO:0042393","term_label":"histone binding","supporting_discovery_ids":[5,6]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[4]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[10,13]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[16]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,17]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[3,6,10]},{"term_id":"GO:0005635","term_label":"nuclear envelope","supporting_discovery_ids":[3]}],"pathway":[{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[0,6,7,16]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[1,2,15]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,10,11]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[5,6,12]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[14]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[8]}],"complexes":["RanGTP·IPO9·H2A-H2B ternary complex","Imp3/Imp9/MAPK heterotrimer","AKIRIN2-proteasome import module"],"partners":["H2A-H2B","RAN","ACTB","CFL1","AKIRIN2","NUAK1","EHF","IPO7"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96P70","full_name":"Importin-9","aliases":["Ran-binding protein 9","RanBP9"],"length_aa":1041,"mass_kda":116.0,"function":"Nuclear transport receptor that mediates nuclear import of proteins, such as histones, proteasome and actin (PubMed:11823430, PubMed:30855230, PubMed:34711951). Serves as receptor for nuclear localization signals (NLS) in cargo substrates (PubMed:11823430). Is thought to mediate docking of the importin/substrate complex to the nuclear pore complex (NPC) through binding to nucleoporin and the complex is subsequently translocated through the pore by an energy requiring, Ran-dependent mechanism (PubMed:11823430). At the nucleoplasmic side of the NPC, Ran binds to the importin, the importin/substrate complex dissociates and importin is re-exported from the nucleus to the cytoplasm where GTP hydrolysis releases Ran (PubMed:11823430). 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:11823430). Mediates the import of pre-assembled proteasomes into the nucleus; AKIRIN2 acts as a molecular bridge between IPO9 and the proteasome complex (PubMed:11823430, PubMed:34711951). Mediates the nuclear import of histones H2A, H2B, H4 and H4 (PubMed:11823430, PubMed:30855230). In addition to nuclear import, also acts as a chaperone for histones by preventing inappropriate non-nucleosomal interactions (PubMed:30855230). Mediates the nuclear import of actin (By similarity)","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q96P70/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/IPO9","classification":"Common Essential","n_dependent_lines":1005,"n_total_lines":1208,"dependency_fraction":0.831953642384106},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CBX1","stoichiometry":0.2},{"gene":"HIST2H2BE","stoichiometry":0.2},{"gene":"RAN","stoichiometry":0.2},{"gene":"RANBP1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/IPO9","total_profiled":1310},"omim":[{"mim_id":"620893","title":"IMPORTIN 9; IPO9","url":"https://www.omim.org/entry/620893"},{"mim_id":"615223","title":"INTERFERON, EPSILON; IFNE","url":"https://www.omim.org/entry/615223"},{"mim_id":"615165","title":"AKIRIN 2; AKIRIN2","url":"https://www.omim.org/entry/615165"},{"mim_id":"605983","title":"PROTEIN PHOSPHATASE 2, STRUCTURAL/REGULATORY SUBUNIT A, ALPHA; PPP2R1A","url":"https://www.omim.org/entry/605983"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/IPO9"},"hgnc":{"alias_symbol":["Imp9","FLJ10402"],"prev_symbol":[]},"alphafold":{"accession":"Q96P70","domains":[{"cath_id":"-","chopping":"800-887_907-934_988-1041","consensus_level":"medium","plddt":90.6054,"start":800,"end":1041}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96P70","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96P70-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96P70-F1-predicted_aligned_error_v6.png","plddt_mean":88.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=IPO9","jax_strain_url":"https://www.jax.org/strain/search?query=IPO9"},"sequence":{"accession":"Q96P70","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96P70.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96P70/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96P70"}},"corpus_meta":[{"pmid":"11823430","id":"PMC_11823430","title":"Importins fulfil a dual function as nuclear import receptors and cytoplasmic chaperones for exposed basic domains.","date":"2002","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/11823430","citation_count":260,"is_preprint":false},{"pmid":"19349578","id":"PMC_19349578","title":"Exportin 4 mediates a novel nuclear import pathway for Sox family transcription factors.","date":"2009","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/19349578","citation_count":71,"is_preprint":false},{"pmid":"30855230","id":"PMC_30855230","title":"Importin-9 wraps around the H2A-H2B core to act as nuclear importer and histone chaperone.","date":"2019","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/30855230","citation_count":49,"is_preprint":false},{"pmid":"24211415","id":"PMC_24211415","title":"OprD mutations and inactivation in imipenem-resistant Pseudomonas aeruginosa isolates from China.","date":"2013","source":"Infection, genetics and evolution : journal of molecular epidemiology and evolutionary genetics in infectious diseases","url":"https://pubmed.ncbi.nlm.nih.gov/24211415","citation_count":44,"is_preprint":false},{"pmid":"16377710","id":"PMC_16377710","title":"bla(IMP-9) and its association with large plasmids carried by Pseudomonas aeruginosa isolates from the People's Republic of China.","date":"2006","source":"Antimicrobial agents and chemotherapy","url":"https://pubmed.ncbi.nlm.nih.gov/16377710","citation_count":42,"is_preprint":false},{"pmid":"18160213","id":"PMC_18160213","title":"Characterization of the 12q amplicons by high-resolution, oligonucleotide array CGH and expression analyses of a novel liposarcoma cell line.","date":"2007","source":"Cancer letters","url":"https://pubmed.ncbi.nlm.nih.gov/18160213","citation_count":41,"is_preprint":false},{"pmid":"33620296","id":"PMC_33620296","title":"An IncP-2 plasmid sublineage associated with dissemination of blaIMP-45 among carbapenem-resistant Pseudomonas aeruginosa.","date":"2021","source":"Emerging microbes & infections","url":"https://pubmed.ncbi.nlm.nih.gov/33620296","citation_count":36,"is_preprint":false},{"pmid":"29888431","id":"PMC_29888431","title":"Differential Proteomic Analysis between Small Cell Lung Carcinoma (SCLC) and Pulmonary Carcinoid Tumors Reveals Molecular Signatures for Malignancy in Lung Cancer.","date":"2018","source":"Proteomics. 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prevention assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — direct in vitro import and chaperone assays with multiple substrates, replicated across Imp family members in the same study\",\n      \"pmids\": [\"11823430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"IPO9 mediates nuclear import of Sox2 and SRY transcription factors via their HMG box domain, acting in parallel with Exp4 and the Imp-beta/7 heterodimer; import signals overlap with conserved residues critical for DNA binding.\",\n      \"method\": \"In vitro nuclear import assay, co-immunoprecipitation, RNAi knockdown\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro import assay plus knockdown, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"19349578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"IPO9 mediates nuclear import of the homeodomain protein Arx via its NLS2 (within the DNA-binding homeodomain); binding to IPO9 is RanGTP-sensitive and NLS2 can be co-precipitated with IPO9.\",\n      \"method\": \"In vitro nuclear import assay, co-immunoprecipitation, RNAi knockdown, domain deletion analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro import plus co-IP and RNAi, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"19494118\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"IPO9 participates in stimulation-induced nuclear translocation of JNK and p38 MAPKs by forming heterotrimeric complexes (Imp3/Imp9/MAPK); JNK1/2 and p38α/β bind Imp9 upon stimulated post-translational modification of Imp9; IPO9 escorts MAPKs into the nucleus while Imp3 remains at the nuclear envelope. Knockdown of IPO9 inhibits MAPK nuclear translocation and downstream transcription factor phosphorylation.\",\n      \"method\": \"Co-immunoprecipitation, proximity ligation assay, gel filtration, immunostaining, RNAi knockdown\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, PLA, gel filtration, immunostaining, KD), single lab\",\n      \"pmids\": [\"24216760\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"IPO9 binds the 5'UTR stem-loop structure 1 of IFN-ε mRNA; IPO9 overexpression decreases and IPO9 silencing increases basal IFN-ε mRNA expression, defining a negative posttranscriptional regulatory role for IPO9. This effect extends to other mRNAs capable of forming similar loop structures (e.g., HIF-1α).\",\n      \"method\": \"RNA affinity pulldown (agarose-bound RNA with HeLa cell extracts), overexpression, RNAi knockdown, luciferase reporter assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — RNA pulldown identification plus functional OE/KD with reporter validation, single lab\",\n      \"pmids\": [\"23851686\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"IPO9 binds histone H3 and H4 tails at two separate elements: the segment at residues 11-27 and an isoleucine-lysine NLS (IK-NLS) motif at residues 35-40 of the H3 tail; acetylation of H3 Lys14 substantially decreases binding to IPO9 and several other importins.\",\n      \"method\": \"Quantitative binding assays (fluorescence anisotropy/ITC), mutagenic analysis of histone tail deletion mutants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — quantitative biochemical binding assays with mutagenesis defining specific binding elements, single lab but rigorous\",\n      \"pmids\": [\"27528606\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Crystal structure of IPO9 bound to the H2A-H2B dimer reveals that IPO9 wraps around the globular core region of H2A-H2B forming an extensive interface; the NLS-like sequences in H2A-H2B tails play a minor role. IPO9 precludes H2A-H2B interactions with DNA and H3-H4 (acting as a chaperone/sequestrant). RanGTP does not dissociate IPO9•H2A-H2B but assembles a stable RanGTP•IPO9•H2A-H2B ternary complex that can facilitate H2A-H2B dissociation by DNA and nucleosome assembly.\",\n      \"method\": \"X-ray crystallography, quantitative binding assays, nucleosome assembly assay, deletion mutagenesis\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus quantitative binding assays and functional nucleosome assembly, multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"30855230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IPO9 mediates nuclear import of NUAK1 (a serine/threonine AMPK-family kinase) via a bipartite NLS at the N-terminal domain; knockdown of IPO9 (or IPO7) inhibits NUAK1 nuclear import. Oxidative stress induces NUAK1 cytoplasmic accumulation, indicating that oxidative stress affects IPO9-mediated nuclear transport.\",\n      \"method\": \"Mass spectrometry (interactome), co-immunoprecipitation, RNAi knockdown, subcellular fractionation, importazole inhibition\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — MS identification confirmed by Co-IP and functional KD with localization readout, single lab\",\n      \"pmids\": [\"31090959\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IPO9 (validated by silencing) is required for optimal replication of yellow fever virus (YFV) and West Nile virus (WNV) in human cells, identifying it as a host dependency factor for flavivirus replication.\",\n      \"method\": \"Genome-wide gain-of-function cDNA screen, RNAi knockdown validation, virological assays\",\n      \"journal\": \"Viruses\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional validation by knockdown with viral replication readout, single lab\",\n      \"pmids\": [\"30650657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Drosophila Importin-9 (Ipo9/Ranbp9, ortholog) is required for chromosome condensation and segregation during meiosis, protamine exchange during spermatogenesis, and nuclear localization of proteasome components; Ipo9 physically interacts with proteasome proteins. Loss of Ipo9 causes female and male sterility.\",\n      \"method\": \"Genetic knockout (Ipo9KO), immunofluorescence, FISH, co-immunoprecipitation\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with multiple cellular phenotype readouts plus physical interaction by Co-IP, single lab\",\n      \"pmids\": [\"33632744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"IPO9 (together with cofilin-1/CFL1) co-mediates nuclear transfer of G-actin; knockdown of IPO9 prevents dynamic strain-mediated nuclear transfer of both actin and β-catenin in mesenchymal stem cells, indicating that β-catenin nuclear entry depends on actin transport via IPO9.\",\n      \"method\": \"RNAi knockdown of IPO9, nuclear fractionation, fluorescence imaging, mechanical strain application\",\n      \"journal\": \"Stem cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — KD with specific phenotypic readouts for two cargos (actin and β-catenin), single lab\",\n      \"pmids\": [\"35278073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Silencing IPO9 or CFL1 (components of the nuclear actin import complex) prevents cAMP-induced nuclear actin monomer increase and rescues RelA/p65 levels and NF-κB reporter activity, placing IPO9-mediated nuclear actin import upstream of proteasomal degradation of RelA/p65 in the cAMP anti-inflammatory pathway.\",\n      \"method\": \"RNAi knockdown, NF-κB reporter assay, western blotting, proteasome inhibitor experiment\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — genetic epistasis by KD with multiple functional readouts, single lab\",\n      \"pmids\": [\"35563720\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HDX-MS analysis of the RanGTP•IPO9•H2A-H2B ternary complex shows that RanGTP releases H2A-H2B contacts at IPO9 HEAT repeats 4-5 but not 18-19, exposing DNA- and histone-binding surfaces of H2A-H2B to facilitate nucleosome assembly. RanGTP has weaker affinity for IPO9 when H2A-H2B is bound, ensuring release only at high nuclear RanGTP concentrations near chromatin.\",\n      \"method\": \"Hydrogen-deuterium exchange mass spectrometry (HDX-MS), quantitative binding assays, in vitro nucleosome assembly\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — HDX-MS structural dynamics plus quantitative binding and functional nucleosome assembly, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"37379840\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"IPO9 directly binds monomeric actin with mid-nanomolar affinity; contrary to the established model, cofilin competitively inhibits (rather than promotes) IPO9-actin complex formation. Profilin similarly competes with IPO9 for actin binding at the barbed face. RanGTP binds monomeric actin but a tripartite IPO9-actin-RanGTP complex does not form. IPO9 modestly decreases the rate of actin filament assembly and exhibits minimal binding to actin filaments.\",\n      \"method\": \"In vitro binding assays (competitive), actin polymerization kinetics assay, quantitative affinity measurements\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — rigorous in vitro reconstitution with quantitative affinity measurements and multiple competition assays, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"41478570\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"IPO9 knockdown markedly reduces nuclear F-actin assembly during ferroptosis in HT-1080 cells, establishing that IPO9-dependent nuclear import of G-actin is required for nuclear F-actin formation during ferroptotic cell death.\",\n      \"method\": \"RNAi knockdown, phalloidin staining, live imaging with nuclear actin chromobody (nAC-TagGFP2)\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Weak — KD with imaging readout in a single cell line, single lab\",\n      \"pmids\": [\"41450740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Cryo-EM structure of IPO9 bound to the ETS domain transcription factor EHF reveals that IPO9 wraps around the winged-helix fold (ETS domain) and engages structural features throughout; the DNA-binding helix of the ETS domain is critical for importin recognition and NLS activity. IPO9 uses distinct interaction hotspots compared to its H2A-H2B binding surfaces, demonstrating combinatorial use of binding surfaces for structurally diverse cargos. ETS domains constitute a structure-encoded (globular) NLS class recognized by IPO9 with nanomolar affinity.\",\n      \"method\": \"Cryo-electron microscopy, biochemical binding assays, mutagenesis, cellular NLS activity assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — cryo-EM structure plus quantitative binding assays and mutagenesis with cellular validation, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"42066049\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"AKIRIN2 acts as a multivalent scaffold that simultaneously binds the 20S proteasome and IPO9 (as well as KPNA2/KPNB1), recruiting an importin cluster to mediate nuclear import of the proteasome. In the nucleus, RanGTP triggers IPO9 dissociation to release the proteasome. Identified by saturation mutagenesis screens, cryo-EM, and biochemical reconstitution.\",\n      \"method\": \"Protein-wide saturation mutagenesis, cryo-EM, biochemical reconstitution, co-immunoprecipitation\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure plus saturation mutagenesis and biochemical reconstitution, multiple orthogonal methods\",\n      \"pmids\": [\"41639071\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Systematic cytoplasmic IP-MS identifies 79 bona fide IPO9-bound cargos (including H2A-H2B, TFIIB, actin, proteasome subunits, and 20 previously validated cargos); IPO9 does not use classical NLS motifs nor any linear peptide motif for cargo recognition. Oxidative footprinting shows both the inner cavity and unstructured loops (H8, H18-19) of IPO9 are protected by bound cargo. Loop perturbation IP-MS shows H8 and H18-19 loops mediate selective cargo recognition; H7, H8, H18-19 loops restrict binding of a secondary set of potential cargos. RanGTP sensitivity for cargo release varies by orders of magnitude across the cargo cohort.\",\n      \"method\": \"Cytoplasmic immunoprecipitation/mass spectrometry, oxidative protein footprinting, systematic loop-perturbation IP-MS\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (IP-MS, footprinting, loop mutants), single lab, preprint\",\n      \"pmids\": [\"42182196\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"IPO9 is a nuclear import receptor (importin β family) that transports structurally diverse cargos—including histone H2A-H2B (by wrapping around their globular core), ribosomal proteins, actin monomers (by direct barbed-face binding that competes with cofilin and profilin), ETS-domain transcription factors, Sox/homeodomain proteins, MAPKs (JNK/p38 in heterotrimeric complexes with Imp3), NUAK1, and the 20S proteasome (via AKIRIN2 scaffold)—using combinatorial, non-classical binding surfaces (HEAT repeat inner cavity and unstructured loops); it additionally functions as a histone chaperone that sequesters H2A-H2B from inappropriate interactions until RanGTP in the nucleus partially remodels the complex to enable nucleosome assembly, and it also acts as a posttranscriptional repressor of IFN-ε mRNA through binding to 5'UTR stem-loop structures.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"IPO9 is an importin-β family nuclear transport receptor that imports a structurally diverse cargo repertoire using non-classical, combinatorial binding surfaces rather than linear NLS motifs [#0, #17]. It recognizes cargos by wrapping around their globular folds: crystallographic and cryo-EM analyses show IPO9 engaging the H2A-H2B core and the winged-helix ETS domain of EHF through distinct interaction hotspots, with both the HEAT-repeat inner cavity and unstructured loops (H8, H18-19) contributing to selective recognition [#6, #15, #17]. Its validated cargos span ribosomal proteins rpS7/rpL18a [#0], HMG-box (Sox2/SRY) and homeodomain (Arx) transcription factors [#1, #2], the stress-activated MAPKs JNK and p38 (imported in heterotrimeric Imp3/Imp9/MAPK complexes) [#3], the kinase NUAK1 [#7], monomeric actin [#10, #13], and the 20S proteasome via the AKIRIN2 scaffold [#16]. Beyond transport, IPO9 functions as a histone chaperone that sequesters H2A-H2B from premature contacts with DNA and H3-H4; rather than dissociating the complex, nuclear RanGTP assembles a stable RanGTP·IPO9·H2A-H2B ternary intermediate that selectively releases histone-binding surfaces at HEAT repeats 4-5 to license nucleosome assembly near chromatin [#6, #12]. For actin, IPO9 binds the monomer barbed face with mid-nanomolar affinity in competition with cofilin and profilin, and this import underlies nuclear actin pools driving β-catenin entry, RelA/p65 regulation, and nuclear F-actin formation during ferroptosis [#10, #11, #13, #14]. IPO9 additionally acts as a posttranscriptional repressor by binding the 5'UTR stem-loop of IFN-ε mRNA [#4], and is a host dependency factor for flavivirus replication [#8].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Established IPO9's founding identity as a nuclear import receptor that doubles as a cytoplasmic chaperone, answering how highly basic ribosomal proteins reach the nucleus without aggregating.\",\n      \"evidence\": \"In vitro nuclear import and aggregation-prevention assays with mouse Imp9 orthologs and rpS7/rpL18a\",\n      \"pmids\": [\"11823430\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of ribosomal-protein recognition not defined\", \"Did not address cargo diversity beyond ribosomal proteins\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Extended the cargo range to DNA-binding transcription factors, showing IPO9 recognizes the HMG box and homeodomain folds where import determinants overlap DNA-binding residues.\",\n      \"evidence\": \"In vitro import, co-IP, RNAi and domain deletion for Sox2/SRY and Arx\",\n      \"pmids\": [\"19349578\", \"19494118\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of the importin-cargo complex\", \"Redundancy with parallel receptors (Exp4, Imp-β/7) not fully resolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Revealed a signaling role: IPO9 escorts stimulated JNK/p38 into the nucleus as part of a heterotrimeric Imp3/Imp9/MAPK complex, coupling MAPK activation to nuclear transcription factor phosphorylation.\",\n      \"evidence\": \"Co-IP, PLA, gel filtration, immunostaining and RNAi in stimulated cells\",\n      \"pmids\": [\"24216760\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The stimulus-induced post-translational modification of Imp9 not molecularly defined\", \"Division of labor between Imp3 and Imp9 at the envelope unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified a transport-independent function: IPO9 represses IFN-ε mRNA by binding a 5'UTR stem-loop, defining a posttranscriptional RNA-regulatory activity.\",\n      \"evidence\": \"RNA affinity pulldown, overexpression/silencing and luciferase reporter assays\",\n      \"pmids\": [\"23851686\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking RNA binding to translational/stability repression unknown\", \"Generality across loop-forming mRNAs only partly tested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Began mapping the histone-recognition logic, showing IPO9 binds H3/H4 tail elements and that H3K14 acetylation reduces binding, linking histone PTMs to import competence.\",\n      \"evidence\": \"Fluorescence anisotropy/ITC binding assays with histone tail mutants\",\n      \"pmids\": [\"27528606\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not yet show that the globular core, not tails, dominates H2A-H2B binding\", \"Functional consequence of acetylation-modulated import not tested in cells\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Solved the H2A-H2B complex structure and redefined IPO9 as a histone chaperone whose RanGTP response builds a remodeling intermediate rather than simple cargo release.\",\n      \"evidence\": \"X-ray crystallography, binding assays and in vitro nucleosome assembly\",\n      \"pmids\": [\"30855230\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Dynamics of the RanGTP ternary complex not resolved at residue level\", \"How chaperone hand-off to assembly factors occurs in cells unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Broadened cargo scope to a stress-regulated kinase and showed import is redox-sensitive, linking IPO9 transport to oxidative stress.\",\n      \"evidence\": \"Interactome MS, co-IP, RNAi, fractionation and importazole inhibition for NUAK1\",\n      \"pmids\": [\"31090959\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The bipartite NLS recognition mode not structurally defined\", \"Redundancy with IPO7 not dissected\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Genetic in vivo evidence established essential developmental roles in chromosome segregation, protamine exchange and proteasome nuclear localization, connecting the receptor to fertility.\",\n      \"evidence\": \"Drosophila Ipo9 knockout with IF, FISH and co-IP\",\n      \"pmids\": [\"33632744\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Which cargo defects drive each phenotype not separable\", \"Mammalian in vivo confirmation absent in corpus\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Placed IPO9-mediated nuclear actin import upstream of mechanotransduction and inflammatory signaling, showing β-catenin and NF-κB/RelA outputs depend on actin transport.\",\n      \"evidence\": \"RNAi, nuclear fractionation, imaging, NF-κB reporter and proteasome-inhibitor experiments in MSCs\",\n      \"pmids\": [\"35278073\", \"35563720\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus indirect coupling of actin import to β-catenin/RelA not biochemically isolated\", \"Stoichiometry with cofilin in cells unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Resolved the RanGTP-driven release mechanism for histones, showing selective contact release at HEAT repeats 4-5 and affinity tuning that confines release to high-RanGTP chromatin regions.\",\n      \"evidence\": \"HDX-MS of the RanGTP·IPO9·H2A-H2B complex with binding and nucleosome assembly assays\",\n      \"pmids\": [\"37379840\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the same partial-release logic applies to other cargos untested at the time\", \"In-cell visualization of the intermediate lacking\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Quantitative reconstitution overturned the prior actin-import model, showing IPO9 binds the actin barbed face in competition with cofilin and profilin and that no IPO9-actin-RanGTP ternary complex forms.\",\n      \"evidence\": \"Competitive in vitro binding, polymerization kinetics and affinity measurements\",\n      \"pmids\": [\"41478570\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How actin is released in the nucleus if RanGTP does not form a ternary complex is unresolved\", \"Reconciliation with cell-based cofilin-cooperative models needed\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Linked IPO9-dependent nuclear actin import to a specific cell-death program, showing it is required for nuclear F-actin assembly during ferroptosis.\",\n      \"evidence\": \"RNAi with phalloidin staining and nuclear actin chromobody imaging in HT-1080 cells\",\n      \"pmids\": [\"41450740\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of nuclear F-actin for ferroptotic death not established\", \"Single cell line, no in vivo validation\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Structures of ETS-domain and proteasome cargo recognition demonstrated combinatorial use of distinct binding surfaces and a scaffold-based import route, generalizing IPO9's non-classical recognition principle.\",\n      \"evidence\": \"Cryo-EM, binding assays and mutagenesis for EHF; saturation mutagenesis and reconstitution of the AKIRIN2-proteasome import module\",\n      \"pmids\": [\"42066049\", \"41639071\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Predictive rules mapping cargo fold to IPO9 surface not yet derived\", \"How RanGTP releases each structurally distinct cargo not uniformly defined\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Systematic interactome and footprinting defined the full cargo cohort (~79 cargos) and showed recognition uses the inner cavity plus specific loops with no linear motif, plus cargo-specific RanGTP sensitivity.\",\n      \"evidence\": \"Cytoplasmic IP-MS, oxidative footprinting and loop-perturbation IP-MS (preprint)\",\n      \"pmids\": [\"42182196\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint not yet peer reviewed\", \"Functional import of most newly identified cargos not validated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A unifying code that predicts which globular folds IPO9 recognizes and how RanGTP release affinity is tuned across structurally unrelated cargos remains undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No general structural rule linking cargo fold to IPO9 binding surface\", \"Mechanism of nuclear release for non-histone cargos lacking a stable ternary intermediate unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [0, 1, 2, 3, 7, 10, 16]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [0, 6, 12]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [5, 6]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [10, 13]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [16]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 17]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 6, 10]},\n      {\"term_id\": \"GO:0005635\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [0, 6, 7, 16]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [1, 2, 15]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 10, 11]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [5, 6, 12]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [14]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"complexes\": [\n      \"RanGTP·IPO9·H2A-H2B ternary complex\",\n      \"Imp3/Imp9/MAPK heterotrimer\",\n      \"AKIRIN2-proteasome import module\"\n    ],\n    \"partners\": [\n      \"H2A-H2B\",\n      \"RAN\",\n      \"ACTB\",\n      \"CFL1\",\n      \"AKIRIN2\",\n      \"NUAK1\",\n      \"EHF\",\n      \"IPO7\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}