{"gene":"IPO9","run_date":"2026-04-28T18:06:54","timeline":{"discoveries":[{"year":2002,"finding":"IPO9 (Imp9a and Imp9b) was identified as a novel importin beta-family member that mediates nuclear import of ribosomal proteins rpS7 and rpL18a, and functions as a cytoplasmic chaperone by covering the basic domains of these substrates to prevent their aggregation with cytoplasmic polyanions such as RNA.","method":"Import assays, co-precipitation, solubility/aggregation assays with recombinant proteins","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — reconstitution of import activity plus chaperone function demonstrated with multiple substrates and orthogonal methods","pmids":["11823430"],"is_preprint":false},{"year":2009,"finding":"IPO9 (Imp9) mediates nuclear import of Sox2 and SRY via their HMG box domain, acting in parallel with Exp4 and the Imp-beta/7 heterodimer; import signals overlap with conserved HMG box residues critical for DNA binding.","method":"Co-immunoprecipitation, in vitro nuclear import assay, RanGTP sensitivity assay","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal binding, functional import assay, multiple parallel pathways tested","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), with binding sensitive to RanGTP; Arx co-precipitates with importin 9 in an NLS2-dependent manner.","method":"In vitro nuclear import assay, co-immunoprecipitation, siRNA knockdown, domain deletion analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including functional import assay and in vivo siRNA validation","pmids":["19494118"],"is_preprint":false},{"year":2013,"finding":"IPO9 forms stimulation-induced heterotrimers with Imp3 and JNK1/2 or p38α/β to mediate Ran-dependent, NLS-independent nuclear translocation of JNK and p38 MAPKs; Imp9 undergoes stimulated post-translational modification that enables MAPK binding, and escorts MAPKs into the nucleus while Imp3 remains at the nuclear envelope.","method":"Co-immunoprecipitation, proximity ligation assay, gel filtration, immunostaining, siRNA knockdown with transcription factor phosphorylation readout","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, knockdown phenotype with defined downstream readout, replicated in follow-up paper","pmids":["24216760"],"is_preprint":false},{"year":2013,"finding":"IPO9 associates with stem-loop structures in the 5'UTR of IFN-ε mRNA (specifically loop 1) and acts as a negative posttranscriptional regulator of IFN-ε expression; IPO9 overexpression decreased and IPO9 silencing increased basal IFN-ε mRNA levels. This regulatory role extends to additional mRNAs containing specific loop structures, including HIF-1α.","method":"RNA affinity pulldown from cell extracts, luciferase reporter assays with UTR constructs, overexpression and siRNA knockdown","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2–3 — RNA pulldown plus functional reporter assays from a single lab","pmids":["23851686"],"is_preprint":false},{"year":2016,"finding":"IPO9 binds two separate elements in the H3 tail (residues 11-27 and an IK-NLS motif at residues 35-40) and similarly binds two basic segments of the H4 tail; acetylation of H3 Lys14 substantially decreases binding to IPO9 and several other importins.","method":"Quantitative binding assays (fluorescence polarization/ITC) with histone tail peptides and deletion/point mutants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — quantitative in vitro binding with systematic mutagenesis across seven importins","pmids":["27528606"],"is_preprint":false},{"year":2019,"finding":"Crystal structure of Importin-9 bound to histones H2A-H2B reveals that IPO9 wraps around the globular core of H2A-H2B through an extensive interface, sequesters H2A-H2B from DNA and H3-H4 interactions (acting as a storage chaperone), and that RanGTP does not dissociate the complex but instead forms a stable RanGTP•Imp9•H2A-H2B ternary complex in which H2A-H2B can be released by DNA to assemble into a nucleosome.","method":"X-ray crystallography, quantitative binding assays (ITC/fluorescence), deletion mutagenesis, DNA competition assay, in vitro nucleosome assembly","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus multiple orthogonal biochemical assays with mutagenesis in a single study","pmids":["30855230"],"is_preprint":false},{"year":2019,"finding":"IPO9 mediates nuclear import of NUAK1 kinase; NUAK1 interacts with IPO9 as identified by mass spectrometry, and knockdown of IPO9 inhibits NUAK1 nuclear import. Oxidative stress induces NUAK1 cytoplasmic accumulation, indicating that this import pathway is stress-regulated.","method":"Mass spectrometry interactome, co-immunoprecipitation confirmation, siRNA knockdown with subcellular localization readout, importazole inhibition","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2–3 — MS identification confirmed by Co-IP and functional knockdown, single lab","pmids":["31090959"],"is_preprint":false},{"year":2019,"finding":"IPO9 is required for optimal flavivirus (YFV, WNV) replication in human cells, as validated by siRNA silencing approaches in a genome-wide gain-of-function screen.","method":"Genome-wide cDNA gain-of-function screen, siRNA silencing validation","journal":"Viruses","confidence":"Low","confidence_rationale":"Tier 3 — functional screen with silencing validation but no molecular mechanism of IPO9 action in viral replication defined","pmids":["30650657"],"is_preprint":false},{"year":2019,"finding":"IPO9 forms stimulation-induced heterotrimers with Imp3 and JNK/p38 MAPKs; binding of JNK1/2 and p38α/β to Imp7 or Imp9 requires stimulated post-translational modification of the importins, confirmed by coimmunoprecipitation and proximity ligation assay.","method":"Coimmunoprecipitation, proximity ligation assay, gel filtration, immunostaining, knockdown","journal":"Cellular physiology and biochemistry","confidence":"High","confidence_rationale":"Tier 2 — replication and extension of earlier findings with multiple orthogonal methods","pmids":["30946556"],"is_preprint":false},{"year":2021,"finding":"In Drosophila, loss of Importin-9 (Ipo9/Ranbp9) causes female and male sterility with chromosome condensation and segregation defects during meiosis, abnormal sperm structure, failure to exchange histones for protamines in males, and disruption of nuclear localization of proteasome components; Ipo9 physically interacts with proteasome proteins.","method":"Genetic knockout, immunofluorescence, FISH, co-immunoprecipitation","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with defined cellular phenotypes and physical interaction demonstrated by Co-IP in Drosophila ortholog","pmids":["33632744"],"is_preprint":false},{"year":2022,"finding":"IPO9, together with cofilin-1 (CFL1), co-mediates nuclear transfer of G-actin in response to dynamic mechanical strain in mesenchymal stem cells; knockdown of IPO9 prevented dynamic strain-mediated nuclear transfer of both actin and β-catenin, indicating that β-catenin nuclear access depends on the actin transport pathway mediated by IPO9.","method":"siRNA knockdown, live-cell imaging, subcellular fractionation, dynamic vs. static strain comparison","journal":"Stem cells","confidence":"Medium","confidence_rationale":"Tier 2–3 — functional knockdown with specific mechanosensing phenotype, single lab","pmids":["35278073"],"is_preprint":false},{"year":2022,"finding":"Silencing components of the nuclear actin import complex IPO9 and CFL1 prevented the cAMP-induced increase in nuclear actin monomer and rescued RelA/p65 levels and NF-κB reporter gene activity, demonstrating that IPO9-mediated nuclear actin import is required for cAMP-induced proteasomal degradation of RelA/p65.","method":"siRNA knockdown, NF-κB reporter assay, western blotting, ubiquitin affinity pulldown","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2–3 — functional knockdown with defined downstream NF-κB pathway readout, single lab","pmids":["35563720"],"is_preprint":false},{"year":2023,"finding":"HDX-MS analysis of the RanGTP•Imp9•H2A-H2B ternary complex shows that RanGTP binding releases H2A-H2B contacts at Imp9 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 Imp9 when H2A-H2B is bound, ensuring release only at high 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 — HDX-MS structural dynamics with multiple binary and ternary complexes compared, plus functional nucleosome assembly assay","pmids":["37379840"],"is_preprint":false},{"year":2016,"finding":"Downregulation of IPO9 in MCF-7 breast cancer cells reduces F-actin content in the nuclear/perinuclear area and is correlated with increased post-translational expression of cofilin-1 (CFL1), and that CFL1 alone does not transport actin into the nucleus but requires functional IPO9 expression for this transport.","method":"siRNA knockdown, western blotting, F-actin fluorescence quantification, flow cytometry for apoptosis","journal":"Oncology reports","confidence":"Medium","confidence_rationale":"Tier 3 — single lab, knockdown with actin localization readout establishing IPO9 requirement for nuclear actin import","pmids":["26934847"],"is_preprint":false},{"year":2025,"finding":"IPO9 directly binds monomeric actin with mid-nanomolar affinity independently of cofilin; cofilin and profilin competitively inhibit IPO9-actin binding (likely via overlapping barbed-face interaction), IPO9 modestly decreases actin filament assembly rate, and RanGTP binds monomeric actin but a tripartite IPO9-actin-RanGTP complex does not form—revising the classical model in which cofilin anchors IPO9 to actin monomers.","method":"In vitro binding assays (competitive binding, fluorescence polarization), actin polymerization kinetics assay, filamentous actin binding assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro binding with systematic competition assays and functional actin polymerization assay","pmids":["41478570"],"is_preprint":false},{"year":2025,"finding":"IPO9 knockdown markedly reduces nuclear F-actin assembly during ferroptosis, indicating that nuclear G-actin import via IPO9 is required for the nuclear F-actin that assembles under conditions of intracellular acidification during ferroptotic cell death.","method":"siRNA knockdown, phalloidin staining, live 3D/time-lapse imaging with nuclear actin chromobody, pH-sensitive reporter","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 2–3 — knockdown with live imaging readout, single lab, mechanistic link to ferroptosis context","pmids":["41450740"],"is_preprint":false},{"year":2026,"finding":"IPO9 directly recognizes the ETS domain (a winged-helix fold) of ETS family transcription factors to mediate their nuclear import; cryo-EM of the EHF:IPO9 complex shows IPO9 wrapping around the ETS domain engaging structural features throughout the fold, with the DNA-binding helix critical for importin recognition. Comparison with the IPO9•H2A-H2B structure reveals distinct interaction hotspots, demonstrating that IPO9 employs unique combinatorial binding surfaces for structurally diverse cargos.","method":"Cryo-electron microscopy, biochemical binding assays, mutagenesis, mammalian cell NLS activity assay","journal":"bioRxiv","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structure with mutagenesis and functional NLS validation","pmids":["41542470"],"is_preprint":true},{"year":2026,"finding":"AKIRIN2 acts as a multivalent scaffold that simultaneously binds the 20S proteasome and importin IPO9 (as well as KPNA2/KPNB1), coordinating assembly of an importin cluster around the proteasome for nuclear import; in the nucleus, RanGTP triggers importin dissociation releasing the proteasome, while AKIRIN2 undergoes ubiquitin-independent degradation.","method":"Protein-wide saturation mutagenesis screens, cryo-EM, biochemical reconstitution, co-immunoprecipitation","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structure combined with saturation mutagenesis and reconstitution","pmids":["41639071"],"is_preprint":false}],"current_model":"IPO9 is a versatile importin-β family nuclear transport receptor that directly recognizes diverse structurally distinct cargoes—including ribosomal proteins, histones H2A-H2B, H3/H4, Sox/ETS transcription factors, MAPKs (JNK/p38), NUAK1, and the proteasome (via AKIRIN2 scaffold)—through extensive contacts with globular domains rather than linear NLS sequences; for H2A-H2B it employs an unusual mechanism where RanGTP forms a ternary complex that partially releases cargo contacts to enable nucleosome assembly, while for actin it directly binds monomeric actin at the barbed face independently of cofilin, and also functions as a cytoplasmic chaperone shielding basic domains from polyanion aggregation, and as a posttranscriptional regulator by binding specific 5'UTR stem-loop structures to suppress mRNA expression."},"narrative":{"teleology":[{"year":2002,"claim":"Establishing IPO9 as a bona fide importin-β family member resolved how ribosomal proteins reach the nucleus and revealed an unexpected cytoplasmic chaperone function that prevents aggregation of basic cargo domains with polyanions.","evidence":"Reconstituted import assays and solubility/aggregation assays with recombinant ribosomal proteins rpS7 and rpL18a","pmids":["11823430"],"confidence":"High","gaps":["Full range of ribosomal protein cargoes not mapped","Structural basis of chaperone function unresolved at this stage","Relationship between chaperone and import functions not dissected"]},{"year":2009,"claim":"Identifying homeodomain (Arx) and HMG-box (Sox2, SRY) transcription factors as IPO9 cargoes demonstrated that IPO9 recognizes DNA-binding folds rather than canonical linear NLS sequences, establishing a pattern of fold-based recognition.","evidence":"In vitro import assays, co-immunoprecipitation, siRNA knockdown, and domain deletion analysis in mammalian cells","pmids":["19349578","19494118"],"confidence":"High","gaps":["Structural basis for HMG-box or homeodomain recognition not determined","Redundancy with other importins (Imp-β/7, Exp4) for these cargoes not quantified in vivo"]},{"year":2013,"claim":"Discovery that IPO9 forms stimulus-induced heterotrimeric complexes with importin-3 and JNK/p38 MAPKs revealed a non-canonical, NLS-independent import mechanism regulated by post-translational modification of the importin itself.","evidence":"Co-immunoprecipitation, proximity ligation assay, gel filtration, siRNA knockdown with transcription factor phosphorylation readout; confirmed in independent follow-up study","pmids":["24216760","30946556"],"confidence":"High","gaps":["Identity of the post-translational modification on IPO9 not determined","Structural basis of the IPO9–Imp3–MAPK heterotrimer unknown","Whether other MAPKs use this pathway not tested"]},{"year":2013,"claim":"Finding that IPO9 binds 5′UTR stem-loops of IFN-ε and HIF-1α mRNAs and suppresses their expression introduced an unexpected post-transcriptional regulatory role distinct from nuclear transport.","evidence":"RNA affinity pulldown, luciferase reporter assays with UTR constructs, overexpression and siRNA knockdown","pmids":["23851686"],"confidence":"Medium","gaps":["Direct RNA-binding site on IPO9 not mapped","Scope of mRNA targets genome-wide unknown","Mechanism of translational or mRNA stability regulation not defined"]},{"year":2016,"claim":"Quantitative binding studies with histone tail peptides revealed that IPO9 recognizes two separate basic segments in the H3 tail and analogous elements in H4, with acetylation of H3K14 reducing binding, linking histone modification state to import efficiency.","evidence":"Fluorescence polarization and ITC with systematic histone tail peptide mutants across seven importins","pmids":["27528606"],"confidence":"High","gaps":["Whether tail recognition contributes to import in vivo vs. chaperone shielding not separated","Interplay with H2A-H2B import not addressed"]},{"year":2016,"claim":"Demonstrating that IPO9 knockdown reduces nuclear/perinuclear F-actin and that cofilin alone cannot transport actin into the nucleus established IPO9 as the essential receptor for nuclear actin import.","evidence":"siRNA knockdown, F-actin fluorescence quantification, western blotting in MCF-7 cells","pmids":["26934847"],"confidence":"Medium","gaps":["Direct IPO9–actin binding not demonstrated at this stage","Mechanism of actin recognition by IPO9 undefined"]},{"year":2019,"claim":"The crystal structure of IPO9 bound to H2A-H2B revealed an extensive interface wrapping around the histone globular core and uncovered a unique cargo-release mechanism: RanGTP forms a stable ternary complex rather than ejecting cargo, allowing DNA-driven histone transfer for nucleosome assembly.","evidence":"X-ray crystallography, ITC, fluorescence binding assays, deletion mutagenesis, DNA competition, in vitro nucleosome assembly","pmids":["30855230"],"confidence":"High","gaps":["In vivo contribution of IPO9 vs. other H2A-H2B chaperones/importins not quantified","Whether ternary complex mechanism applies to other cargoes unknown"]},{"year":2023,"claim":"HDX-MS mapping of the RanGTP•Imp9•H2A-H2B ternary complex resolved how RanGTP selectively releases H2A-H2B contacts at HEAT repeats 4–5 while maintaining contacts at 18–19, explaining the partial release that licenses DNA-mediated nucleosome assembly at chromatin-proximal high-RanGTP concentrations.","evidence":"Hydrogen-deuterium exchange mass spectrometry comparing binary and ternary complexes, quantitative binding assays, nucleosome assembly assay","pmids":["37379840"],"confidence":"High","gaps":["Full kinetic pathway from ternary complex to assembled nucleosome not captured","Whether chromatin remodelers cooperate with the ternary complex in vivo untested"]},{"year":2025,"claim":"Reconstituted binding studies overturned the classical model by showing that IPO9 directly binds monomeric actin at the barbed face with mid-nanomolar affinity independently of cofilin, which instead competitively inhibits IPO9–actin binding, redefining the actin import complex.","evidence":"In vitro competitive binding assays, fluorescence polarization, actin polymerization kinetics","pmids":["41478570"],"confidence":"High","gaps":["In vivo stoichiometry and regulation of IPO9–actin vs. cofilin–actin pools not determined","How RanGTP releases actin in the nucleus (no tripartite complex forms) remains mechanistically unclear"]},{"year":2025,"claim":"IPO9-mediated nuclear actin import was shown to be functionally required for nuclear F-actin assembly during ferroptosis and for cAMP-induced proteasomal degradation of RelA/p65, establishing physiological contexts where nuclear actin import has defined downstream consequences.","evidence":"siRNA knockdown with live 3D imaging of nuclear actin chromobody during ferroptosis; siRNA knockdown with NF-κB reporter assay and ubiquitin pulldown for cAMP signaling","pmids":["41450740","35563720"],"confidence":"Medium","gaps":["Molecular mechanism linking nuclear actin to RelA degradation not fully elucidated","Whether IPO9-dependent nuclear actin import is rate-limiting in these processes in vivo uncertain"]},{"year":2026,"claim":"Cryo-EM of IPO9 bound to the ETS domain of EHF and structural comparison with the H2A-H2B complex revealed that IPO9 uses distinct combinatorial HEAT-repeat surfaces to recognize structurally unrelated globular folds, explaining its cargo versatility; separately, cryo-EM and saturation mutagenesis showed that AKIRIN2 scaffolds an importin cluster (including IPO9) around the 20S proteasome for nuclear import.","evidence":"Cryo-EM structures, saturation mutagenesis screens, biochemical reconstitution, mammalian cell NLS activity assays","pmids":["41542470","41639071"],"confidence":"High","gaps":["ETS-domain cryo-EM is from a preprint and awaits peer review","Whether IPO9 contacts the proteasome directly or solely via AKIRIN2 not fully resolved","Quantitative contribution of IPO9 vs. KPNA2/KPNB1 in proteasome import not determined"]},{"year":null,"claim":"How IPO9 selects among its many structurally diverse cargoes in the crowded cytoplasmic milieu, and whether post-translational modifications or adaptor proteins regulate cargo priority, remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No systematic in vivo cargo prioritization study exists","Post-translational modification of IPO9 identified for MAPK import but identity unknown","Full spectrum of IPO9 cargoes likely incomplete"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,1,2,3,6,7,11,15,18]},{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[0,6]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[4]},{"term_id":"GO:0042393","term_label":"histone binding","supporting_discovery_ids":[5,6,13]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[14,15,16]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,3,15]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1,2,3,6,11]}],"pathway":[{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[0,1,2,3,6,7,11,15,18]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,9,12]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[5,6,13]}],"complexes":["IPO9-Imp3-MAPK heterotrimer","RanGTP-Imp9-H2A-H2B ternary complex","AKIRIN2-IPO9-proteasome import complex"],"partners":["H2AFZ","H2BC1","CFL1","IPO3","AKIRIN2","RAN","NUAK1","ACTB"],"other_free_text":[]},"mechanistic_narrative":"IPO9 (Importin-9) is a versatile importin-β family nuclear transport receptor that imports structurally diverse cargoes—including ribosomal proteins, histones H2A-H2B and H3/H4, homeodomain and HMG-box transcription factors (Sox2, SRY, Arx), ETS-family transcription factors, MAPKs (JNK, p38), NUAK1 kinase, monomeric actin, and the 20S proteasome (via the AKIRIN2 scaffold)—by recognizing globular folds and basic domains rather than classical linear NLS sequences [PMID:11823430, PMID:19349578, PMID:30855230, PMID:41542470, PMID:41639071]. Structural studies reveal that IPO9 wraps its HEAT-repeat solenoid around cargo globular cores using distinct combinatorial binding surfaces for each substrate, and for H2A-H2B it employs an unusual mechanism in which RanGTP forms a ternary complex that partially releases histone contacts at HEAT repeats 4–5, enabling DNA-driven nucleosome assembly rather than simple cargo ejection [PMID:30855230, PMID:37379840]. IPO9 also functions as a cytoplasmic chaperone that shields the basic domains of ribosomal proteins and histones from aggregation with polyanions, directly binds monomeric actin at its barbed face independently of cofilin to mediate nuclear actin import required for mechanosensing and ferroptotic nuclear F-actin assembly, and suppresses expression of specific mRNAs (IFN-ε, HIF-1α) by binding 5′UTR stem-loop structures [PMID:11823430, PMID:41478570, PMID:35278073, PMID:23851686]. Nuclear import of JNK/p38 MAPKs proceeds through stimulus-induced IPO9–importin-3 heterotrimeric complexes requiring post-translational modification of IPO9 [PMID:24216760, PMID:30946556]."},"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":257,"is_preprint":false,"source_track":"pubmed_title"},{"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,"source_track":"pubmed_title"},{"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":45,"is_preprint":false,"source_track":"pubmed_title"},{"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":43,"is_preprint":false,"source_track":"pubmed_title"},{"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,"source_track":"pubmed_title"},{"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,"source_track":"pubmed_title"},{"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,"source_track":"pubmed_title"},{"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. Clinical applications","url":"https://pubmed.ncbi.nlm.nih.gov/29888431","citation_count":35,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"28585170","id":"PMC_28585170","title":"Rapid and simple identification of carbapenemase genes, bla NDM, bla OXA-48, bla VIM, bla IMP-14 and bla KPC groups, in Gram-negative bacilli by in-house loop-mediated isothermal amplification with hydroxynaphthol blue dye.","date":"2017","source":"World journal of microbiology & biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/28585170","citation_count":35,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"27528606","id":"PMC_27528606","title":"Recognition Elements in the Histone H3 and H4 Tails for Seven Different Importins.","date":"2016","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/27528606","citation_count":34,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"24216760","id":"PMC_24216760","title":"Beta-like importins mediate the nuclear translocation of mitogen-activated protein kinases.","date":"2013","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/24216760","citation_count":32,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"19494118","id":"PMC_19494118","title":"The roles of multiple importins for nuclear import of murine aristaless-related homeobox protein.","date":"2009","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/19494118","citation_count":24,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"30650657","id":"PMC_30650657","title":"Uncovering Flavivirus Host Dependency Factors through a Genome-Wide Gain-of-Function Screen.","date":"2019","source":"Viruses","url":"https://pubmed.ncbi.nlm.nih.gov/30650657","citation_count":21,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"31090959","id":"PMC_31090959","title":"Identification of a nuclear localization signal and importin beta members mediating NUAK1 nuclear import inhibited by oxidative stress.","date":"2019","source":"Journal of cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/31090959","citation_count":18,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"35278073","id":"PMC_35278073","title":"Mechanically Induced Nuclear Shuttling of β-Catenin Requires Co-transfer of Actin.","date":"2022","source":"Stem cells (Dayton, Ohio)","url":"https://pubmed.ncbi.nlm.nih.gov/35278073","citation_count":17,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"33632744","id":"PMC_33632744","title":"Importin-9 regulates chromosome segregation and packaging in Drosophila germ cells.","date":"2021","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/33632744","citation_count":16,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"30946556","id":"PMC_30946556","title":"Beta-Like Importins Mediate the Nuclear Translocation of MAPKs.","date":"2019","source":"Cellular physiology and biochemistry : international journal of experimental cellular physiology, biochemistry, and pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/30946556","citation_count":14,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"23851686","id":"PMC_23851686","title":"Novel role for molecular transporter importin 9 in posttranscriptional regulation of IFN-ε expression.","date":"2013","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/23851686","citation_count":12,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"37379840","id":"PMC_37379840","title":"Molecular basis of RanGTP-activated release of Histones H2A-H2B from Importin-9.","date":"2023","source":"Structure (London, England : 1993)","url":"https://pubmed.ncbi.nlm.nih.gov/37379840","citation_count":8,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"26934847","id":"PMC_26934847","title":"Downregulation of importin-9 protects MCF-7 cells against apoptosis induced by the combination of garlic-derived alliin and paclitaxel.","date":"2016","source":"Oncology reports","url":"https://pubmed.ncbi.nlm.nih.gov/26934847","citation_count":8,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"35246263","id":"PMC_35246263","title":"Enhancer promoter interactome and Mendelian randomization identify network of druggable vascular genes in coronary artery disease.","date":"2022","source":"Human genomics","url":"https://pubmed.ncbi.nlm.nih.gov/35246263","citation_count":8,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"32733881","id":"PMC_32733881","title":"Integrative Genomic Analysis Predicts Regulatory Role of N 6-Methyladenosine-Associated SNPs for Adiposity.","date":"2020","source":"Frontiers in cell and developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/32733881","citation_count":8,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"39263088","id":"PMC_39263088","title":"PGRMC2 influences the onset of postmenopausal osteoporosis through disulfidptosis in monocytes: Evidence from experimental validation and Mendelian randomization.","date":"2024","source":"Heliyon","url":"https://pubmed.ncbi.nlm.nih.gov/39263088","citation_count":4,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"36747879","id":"PMC_36747879","title":"Molecular basis of RanGTP-activated nucleosome assembly with Histones H2A-H2B bound to Importin-9.","date":"2023","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/36747879","citation_count":4,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"35563720","id":"PMC_35563720","title":"Cyclic-AMP Increases Nuclear Actin Monomer Which Promotes Proteasomal Degradation of RelA/p65 Leading to Anti-Inflammatory Effects.","date":"2022","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/35563720","citation_count":4,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"40149595","id":"PMC_40149595","title":"Genomic Characterisation of the Relationship and Causal Links Between Vascular Calcification, Alzheimer's Disease, and Cognitive Traits.","date":"2025","source":"Biomedicines","url":"https://pubmed.ncbi.nlm.nih.gov/40149595","citation_count":2,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"39127651","id":"PMC_39127651","title":"Core biomarkers analysis benefit for diagnosis on human intrahepatic cholestasis of pregnancy.","date":"2024","source":"BMC pregnancy and childbirth","url":"https://pubmed.ncbi.nlm.nih.gov/39127651","citation_count":2,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"41584724","id":"PMC_41584724","title":"IPO9 Promotes Ovarian Cancer Progression by Suppressing HMOX1-Dependent Ferroptosis.","date":"2026","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/41584724","citation_count":1,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"41450740","id":"PMC_41450740","title":"pH-regulated nuclear F-actin assembly during ferroptosis.","date":"2025","source":"Frontiers in cell and developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/41450740","citation_count":1,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"41478570","id":"PMC_41478570","title":"A revised model of nuclear actin import: Importin 9 competes with cofilin, profilin, and RanGTP for actin binding.","date":"2025","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/41478570","citation_count":0,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"41040170","id":"PMC_41040170","title":"A revised model of nuclear actin import: Importin 9 competes with cofilin, profilin, and RanGTP for actin binding.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41040170","citation_count":0,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"41548474","id":"PMC_41548474","title":"RHOJ-induced chemotherapy resistance through epithelial-mesenchymal transition in drug-tolerant persister cells of head and neck cancer.","date":"2026","source":"Translational oncology","url":"https://pubmed.ncbi.nlm.nih.gov/41548474","citation_count":0,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"41542470","id":"PMC_41542470","title":"Importins recognize the winged-helix fold of ETS transcription factors to mediate nuclear import.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41542470","citation_count":0,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"41639071","id":"PMC_41639071","title":"A multivalent adaptor mechanism drives the nuclear import of proteasomes.","date":"2026","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/41639071","citation_count":0,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":null,"id":"bio_10.1101_2025.10.03.680283","title":"Identification of key host genes for influenza A virus in avian cells using a genome-wide CRISPR-Cas9 screen","date":"2025-10-05","source":"bioRxiv","url":"https://doi.org/10.1101/2025.10.03.680283","citation_count":0,"is_preprint":true,"source_track":"pubmed_title"},{"pmid":null,"id":"bio_10.1101_2025.06.18.25329418","title":"Imputation of fluid intelligence scores reduces ascertainment bias and increases power for analyses of common and rare variants","date":"2025-06-20","source":"bioRxiv","url":"https://doi.org/10.1101/2025.06.18.25329418","citation_count":0,"is_preprint":true,"source_track":"pubmed_title"},{"pmid":"12477932","id":"PMC_12477932","title":"Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences.","date":"2002","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/12477932","citation_count":1479,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"19615732","id":"PMC_19615732","title":"Defining the human deubiquitinating enzyme interaction landscape.","date":"2009","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/19615732","citation_count":1282,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"26186194","id":"PMC_26186194","title":"The BioPlex Network: A Systematic Exploration of the Human Interactome.","date":"2015","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/26186194","citation_count":1118,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"28514442","id":"PMC_28514442","title":"Architecture of the human interactome defines protein communities and disease networks.","date":"2017","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/28514442","citation_count":1085,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"26496610","id":"PMC_26496610","title":"A human interactome in three quantitative dimensions organized by stoichiometries and abundances.","date":"2015","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/26496610","citation_count":1015,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"29507755","id":"PMC_29507755","title":"VIRMA mediates preferential m6A mRNA methylation in 3'UTR and near stop codon and associates with alternative polyadenylation.","date":"2018","source":"Cell discovery","url":"https://pubmed.ncbi.nlm.nih.gov/29507755","citation_count":829,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"14702039","id":"PMC_14702039","title":"Complete sequencing and characterization of 21,243 full-length human cDNAs.","date":"2003","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/14702039","citation_count":754,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"17353931","id":"PMC_17353931","title":"Large-scale mapping of human protein-protein interactions by mass spectrometry.","date":"2007","source":"Molecular systems biology","url":"https://pubmed.ncbi.nlm.nih.gov/17353931","citation_count":733,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"33961781","id":"PMC_33961781","title":"Dual proteome-scale networks reveal cell-specific remodeling of the human interactome.","date":"2021","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/33961781","citation_count":705,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"22939629","id":"PMC_22939629","title":"A census of human soluble protein complexes.","date":"2012","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/22939629","citation_count":689,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"21873635","id":"PMC_21873635","title":"Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium.","date":"2011","source":"Briefings in bioinformatics","url":"https://pubmed.ncbi.nlm.nih.gov/21873635","citation_count":656,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"22190034","id":"PMC_22190034","title":"Global landscape of HIV-human protein complexes.","date":"2011","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/22190034","citation_count":593,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"17110338","id":"PMC_17110338","title":"Hsp90 cochaperone Aha1 downregulation rescues misfolding of CFTR in cystic fibrosis.","date":"2006","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/17110338","citation_count":517,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"15489334","id":"PMC_15489334","title":"The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC).","date":"2004","source":"Genome research","url":"https://pubmed.ncbi.nlm.nih.gov/15489334","citation_count":438,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"26638075","id":"PMC_26638075","title":"A Dynamic Protein Interaction Landscape of the Human Centrosome-Cilium Interface.","date":"2015","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/26638075","citation_count":433,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"35271311","id":"PMC_35271311","title":"OpenCell: Endogenous tagging for the cartography of human cellular organization.","date":"2022","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/35271311","citation_count":432,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"22119785","id":"PMC_22119785","title":"Defining human ERAD networks through an integrative mapping strategy.","date":"2011","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/22119785","citation_count":427,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"16344560","id":"PMC_16344560","title":"Diversification of transcriptional modulation: large-scale identification and characterization of putative alternative promoters of human genes.","date":"2005","source":"Genome research","url":"https://pubmed.ncbi.nlm.nih.gov/16344560","citation_count":409,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"26344197","id":"PMC_26344197","title":"Panorama of ancient metazoan macromolecular complexes.","date":"2015","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/26344197","citation_count":407,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"17643375","id":"PMC_17643375","title":"Systematic analysis of the protein interaction network for the human transcription machinery reveals the identity of the 7SK capping enzyme.","date":"2007","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/17643375","citation_count":367,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"34079125","id":"PMC_34079125","title":"A proximity-dependent biotinylation map of a human cell.","date":"2021","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/34079125","citation_count":339,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"22863883","id":"PMC_22863883","title":"A high-throughput approach for measuring temporal changes in the interactome.","date":"2012","source":"Nature methods","url":"https://pubmed.ncbi.nlm.nih.gov/22863883","citation_count":273,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"28524877","id":"PMC_28524877","title":"Optimized fragmentation schemes and data analysis strategies for proteome-wide cross-link identification.","date":"2017","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/28524877","citation_count":221,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"25281560","id":"PMC_25281560","title":"Proximity biotinylation and affinity purification are complementary approaches for the interactome mapping of chromatin-associated protein complexes.","date":"2014","source":"Journal of proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/25281560","citation_count":215,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"27173435","id":"PMC_27173435","title":"An organelle-specific protein landscape identifies novel diseases and molecular mechanisms.","date":"2016","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/27173435","citation_count":211,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"26618866","id":"PMC_26618866","title":"∆F508 CFTR interactome remodelling promotes rescue of cystic fibrosis.","date":"2015","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/26618866","citation_count":209,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"34048709","id":"PMC_34048709","title":"N6-Methyladenosine on mRNA facilitates a phase-separated nuclear body that suppresses myeloid leukemic differentiation.","date":"2021","source":"Cancer cell","url":"https://pubmed.ncbi.nlm.nih.gov/34048709","citation_count":207,"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"},{"pmid":"11042152","id":"PMC_11042152","title":"Cloning and functional analysis of cDNAs with open reading frames for 300 previously undefined genes expressed in CD34+ hematopoietic stem/progenitor cells.","date":"2000","source":"Genome research","url":"https://pubmed.ncbi.nlm.nih.gov/11042152","citation_count":161,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"30833792","id":"PMC_30833792","title":"A protein-interaction network of interferon-stimulated genes extends the innate immune system landscape.","date":"2019","source":"Nature immunology","url":"https://pubmed.ncbi.nlm.nih.gov/30833792","citation_count":159,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":19539,"output_tokens":3968,"usd":0.059069},"stage2":{"model":"claude-opus-4-6","input_tokens":7452,"output_tokens":3758,"usd":0.196815},"total_usd":0.526867,"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":31325,"output_tokens":4467,"usd":0.08049},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":8259,"output_tokens":3428,"usd":0.190493}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2002,\n      \"finding\": \"Importin-9 (Imp9a and Imp9b) mediates nuclear import of ribosomal proteins rpS7 and rpL18a, and acts as a cytoplasmic chaperone by covering exposed basic domains of these substrates to prevent their aggregation with cytoplasmic polyanions such as RNA.\",\n      \"method\": \"Nuclear import assays, biochemical precipitation/solubility assays with purified proteins\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstituted import assays and chaperone activity demonstrated directly\",\n      \"pmids\": [\"11823430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Importin-9 mediates nuclear import of Sox2 and SRY transcription factors via their HMG box domain, acting in parallel with Exportin-4 and the Imp-beta/7 heterodimer; import signals overlap with conserved DNA-binding residues in the HMG box.\",\n      \"method\": \"Co-immunoprecipitation, in vitro nuclear import assay, RanGTP sensitivity assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP and functional import assays across multiple pathways with parallel validation\",\n      \"pmids\": [\"19349578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Importin-9 (Imp9) forms stimulation-induced heterotrimers with Imp3 and JNK1/2 or p38α/β MAPKs upon stimulated post-translational modification of Imp9, and escorts MAPKs into the nucleus to enable phosphorylation of their transcription factor targets; knockdown of Imp9 inhibits MAPK nuclear translocation.\",\n      \"method\": \"Co-immunoprecipitation, proximity ligation assay, gel filtration, siRNA knockdown, immunostaining\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including co-IP, PLA, gel filtration, and functional knockdown readout\",\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 and acts as a negative posttranscriptional regulator of IFN-ε expression; overexpression of IPO9 decreased, and silencing increased, basal IFN-ε mRNA levels. This regulatory activity extends to other mRNAs with similar loop structures including HIF-1α.\",\n      \"method\": \"RNA pulldown from HeLa cell extracts with agarose-bound RNA, IPO9 overexpression and siRNA knockdown with luciferase/mRNA reporters\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — RNA pulldown plus gain/loss-of-function, but single lab study\",\n      \"pmids\": [\"23851686\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Imp9 and Imp5 bind two separate elements in the histone H3 N-terminal tail: residues 11-27 and an IK-NLS motif at residues 35-40; acetylation of H3 Lys14 substantially decreases binding to several importins including Imp9. Imp9 binds H4 tail with similar but weaker affinity.\",\n      \"method\": \"Quantitative biochemical binding assays (fluorescence anisotropy, ITC), mutagenesis of histone tails\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative binding assays with mutagenesis defining binding elements\",\n      \"pmids\": [\"27528606\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Importin-9 wraps around the globular core region of the H2A-H2B heterodimer to form an extensive interface, acting as both nuclear import receptor and histone chaperone; the interaction precludes H2A-H2B interactions with DNA and H3-H4 as in the nucleosome. Unexpectedly, RanGTP does not dissociate Imp9·H2A-H2B but forms a stable ternary RanGTP·Imp9·H2A-H2B complex; RanGTP modulates Imp9-H2A-H2B interactions to facilitate H2A-H2B release by DNA and assembly into nucleosomes.\",\n      \"method\": \"Crystal structure determination, quantitative binding assays with deletion mutants, in vitro nucleosome assembly assay\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus mutagenesis, quantitative binding, and functional nucleosome assembly in a single study\",\n      \"pmids\": [\"30855230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IPO9 mediates nuclear import of the serine/threonine kinase NUAK1; knockdown of IPO9 (or importazole treatment) reduces NUAK1 nuclear localization, and IPO9 co-immunoprecipitates with NUAK1 via its bipartite NLS. Oxidative stress reduces NUAK1 nuclear import.\",\n      \"method\": \"Mass spectrometry identification, co-immunoprecipitation, siRNA knockdown, subcellular fractionation, importazole inhibition\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — MS identification confirmed by co-IP and functional knockdown, single lab\",\n      \"pmids\": [\"31090959\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IPO9 silencing reduces flavivirus (YFV, WNV) replication in human cells, identifying it as a host dependency factor for flavivirus replication.\",\n      \"method\": \"Genome-wide gain-of-function cDNA screen, siRNA silencing validation with viral replication assays\",\n      \"journal\": \"Viruses\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide screen followed by silencing validation, but molecular mechanism not further defined\",\n      \"pmids\": [\"30650657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Drosophila Importin-9 (Ipo9/Ranbp9) is required for chromosome condensation and segregation during meiosis, and for nuclear import of proteasome components necessary for histone-to-protamine exchange during spermatogenesis; Ipo9 physically interacts with proteasome proteins.\",\n      \"method\": \"Genetic knockout, immunofluorescence, FISH, co-immunoprecipitation (Drosophila ortholog)\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular phenotypes and co-IP, but Drosophila ortholog\",\n      \"pmids\": [\"33632744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"IPO9 co-mediates nuclear import of G-actin together with cofilin-1 (CFL1); knockdown of IPO9 prevents dynamic strain-induced nuclear transfer of both G-actin and β-catenin in mesenchymal stem cells, and reduces nuclear actin content and nuclear stiffness.\",\n      \"method\": \"siRNA knockdown of IPO9, nuclear fractionation, fluorescence imaging, mechanical stimulation assay\",\n      \"journal\": \"Stem cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with defined nuclear transport phenotype; consistent with other actin-import studies\",\n      \"pmids\": [\"35278073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"IPO9 and CFL1 together form the nuclear actin import complex; silencing components of this complex (IPO9 and CFL1) prevents cAMP-induced increases in nuclear actin monomer levels, rescuing RelA/p65 levels and NF-κB reporter gene activity.\",\n      \"method\": \"siRNA knockdown of IPO9 and CFL1, NF-κB reporter assay, nuclear actin quantification\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional knockdown with defined pathway consequence; replicated role in nuclear actin import\",\n      \"pmids\": [\"35563720\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Using hydrogen-deuterium exchange coupled with mass spectrometry, RanGTP binding to Imp9 releases H2A-H2B contacts at 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 Imp9 when H2A-H2B is bound, ensuring release only near high RanGTP concentrations adjacent to chromatin.\",\n      \"method\": \"Hydrogen-deuterium exchange mass spectrometry (HDX-MS), in vitro nucleosome assembly assay, binding affinity measurements\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — HDX-MS with reconstituted complexes and functional nucleosome assembly, builds on crystal structure\",\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 accepted model, cofilin competitively inhibits (rather than promotes) IPO9-actin complex formation. Profilin also competes with IPO9 for actin binding. IPO9 engages the barbed face of actin monomers, modestly decreasing actin filament assembly rate, and exhibits minimal binding to F-actin. RanGTP binds monomeric actin but a tripartite IPO9-actin-RanGTP complex does not form.\",\n      \"method\": \"In vitro binding assays (fluorescence anisotropy, competitive binding), actin polymerization kinetics assay, mutagenesis/domain mapping\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — rigorous in vitro reconstitution with quantitative binding assays and 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 RSL3-induced ferroptosis, indicating that nuclear G-actin import via IPO9 is required for nuclear F-actin formation under these conditions.\",\n      \"method\": \"siRNA knockdown of IPO9, live-cell imaging (nuclear actin chromobody), phalloidin staining, SiR-actin\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with fluorescence imaging, single lab study\",\n      \"pmids\": [\"41450740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Cryo-EM analysis of the EHF:IPO9 complex reveals that IPO9 wraps around the ETS domain winged-helix fold, engaging structural features throughout the fold including the DNA-binding helix, which is critical for importin recognition and nuclear import; IPO9 uses distinct interaction surfaces to accommodate ETS domains versus H2A-H2B, demonstrating adaptable cargo recognition.\",\n      \"method\": \"Cryo-EM structure determination, biochemical binding assays, NLS mutagenesis in mammalian cells\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structure with mutagenesis and functional validation in mammalian cells\",\n      \"pmids\": [\"41542470\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"IPO9 acts as part of a multivalent importin cluster coordinated by the scaffold protein AKIRIN2 for nuclear import of the 20S proteasome; AKIRIN2 simultaneously binds the 20S proteasome in multiple copies and interacts with IPO9 and the KPNA2/KPNB1 heterodimer; in the nucleus, RanGTP triggers importin dissociation, releasing the proteasome.\",\n      \"method\": \"Cryo-EM, saturation mutagenesis screens, biochemical reconstitution, co-immunoprecipitation\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM plus biochemical reconstitution and saturation mutagenesis in an integrated approach\",\n      \"pmids\": [\"41639071\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Importin-9 mediates nuclear import of the homeodomain transcription factor Arx via its NLS2 within the DNA-binding homeodomain; binding is RanGTP-sensitive and Arx co-precipitates with importin-9 when NLS2 is present.\",\n      \"method\": \"In vitro nuclear import assay, co-immunoprecipitation, siRNA knockdown, deletion mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro import assay with co-IP and knockdown, single lab study\",\n      \"pmids\": [\"19494118\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Importin-9 (IPO9) is a versatile nuclear import receptor that uses an extensive, wrap-around binding mechanism to recognize structurally diverse cargoes—including histone H2A-H2B (via a crystal-structure-defined interface at HEAT repeats 4-5 and 18-19), ribosomal proteins, Sox/ETS/homeodomain transcription factors, MAPKs (as part of Imp3/Imp9/MAPK heterotrimers), NUAK1, and the 20S proteasome (via the AKIRIN2 scaffold)—and also directly binds monomeric actin at its barbed face with mid-nanomolar affinity to mediate nuclear actin import; for H2A-H2B, RanGTP forms a stable ternary complex that partially remodels the interface to expose histone surfaces for DNA-triggered nucleosome assembly, rather than causing simple cargo release, while IPO9 additionally functions as a cytoplasmic chaperone that shields basic/hydrophobic domains of its cargoes from inappropriate interactions prior to nuclear entry.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2002,\n      \"finding\": \"IPO9 (Imp9a and Imp9b) was identified as a novel importin beta-family member that mediates nuclear import of ribosomal proteins rpS7 and rpL18a, and functions as a cytoplasmic chaperone by covering the basic domains of these substrates to prevent their aggregation with cytoplasmic polyanions such as RNA.\",\n      \"method\": \"Import assays, co-precipitation, solubility/aggregation assays with recombinant proteins\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reconstitution of import activity plus chaperone function demonstrated with multiple substrates and orthogonal methods\",\n      \"pmids\": [\"11823430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"IPO9 (Imp9) mediates nuclear import of Sox2 and SRY via their HMG box domain, acting in parallel with Exp4 and the Imp-beta/7 heterodimer; import signals overlap with conserved HMG box residues critical for DNA binding.\",\n      \"method\": \"Co-immunoprecipitation, in vitro nuclear import assay, RanGTP sensitivity assay\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal binding, functional import assay, multiple parallel pathways tested\",\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), with binding sensitive to RanGTP; Arx co-precipitates with importin 9 in an NLS2-dependent manner.\",\n      \"method\": \"In vitro nuclear import assay, co-immunoprecipitation, siRNA knockdown, domain deletion analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including functional import assay and in vivo siRNA validation\",\n      \"pmids\": [\"19494118\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"IPO9 forms stimulation-induced heterotrimers with Imp3 and JNK1/2 or p38α/β to mediate Ran-dependent, NLS-independent nuclear translocation of JNK and p38 MAPKs; Imp9 undergoes stimulated post-translational modification that enables MAPK binding, and escorts MAPKs into the nucleus while Imp3 remains at the nuclear envelope.\",\n      \"method\": \"Co-immunoprecipitation, proximity ligation assay, gel filtration, immunostaining, siRNA knockdown with transcription factor phosphorylation readout\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, knockdown phenotype with defined downstream readout, replicated in follow-up paper\",\n      \"pmids\": [\"24216760\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"IPO9 associates with stem-loop structures in the 5'UTR of IFN-ε mRNA (specifically loop 1) and acts as a negative posttranscriptional regulator of IFN-ε expression; IPO9 overexpression decreased and IPO9 silencing increased basal IFN-ε mRNA levels. This regulatory role extends to additional mRNAs containing specific loop structures, including HIF-1α.\",\n      \"method\": \"RNA affinity pulldown from cell extracts, luciferase reporter assays with UTR constructs, overexpression and siRNA knockdown\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — RNA pulldown plus functional reporter assays from a single lab\",\n      \"pmids\": [\"23851686\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"IPO9 binds two separate elements in the H3 tail (residues 11-27 and an IK-NLS motif at residues 35-40) and similarly binds two basic segments of the H4 tail; acetylation of H3 Lys14 substantially decreases binding to IPO9 and several other importins.\",\n      \"method\": \"Quantitative binding assays (fluorescence polarization/ITC) with histone tail peptides and deletion/point mutants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative in vitro binding with systematic mutagenesis across seven importins\",\n      \"pmids\": [\"27528606\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Crystal structure of Importin-9 bound to histones H2A-H2B reveals that IPO9 wraps around the globular core of H2A-H2B through an extensive interface, sequesters H2A-H2B from DNA and H3-H4 interactions (acting as a storage chaperone), and that RanGTP does not dissociate the complex but instead forms a stable RanGTP•Imp9•H2A-H2B ternary complex in which H2A-H2B can be released by DNA to assemble into a nucleosome.\",\n      \"method\": \"X-ray crystallography, quantitative binding assays (ITC/fluorescence), deletion mutagenesis, DNA competition assay, in vitro nucleosome assembly\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus multiple orthogonal biochemical assays with mutagenesis in a single study\",\n      \"pmids\": [\"30855230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IPO9 mediates nuclear import of NUAK1 kinase; NUAK1 interacts with IPO9 as identified by mass spectrometry, and knockdown of IPO9 inhibits NUAK1 nuclear import. Oxidative stress induces NUAK1 cytoplasmic accumulation, indicating that this import pathway is stress-regulated.\",\n      \"method\": \"Mass spectrometry interactome, co-immunoprecipitation confirmation, siRNA knockdown with subcellular localization readout, importazole inhibition\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — MS identification confirmed by Co-IP and functional knockdown, single lab\",\n      \"pmids\": [\"31090959\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IPO9 is required for optimal flavivirus (YFV, WNV) replication in human cells, as validated by siRNA silencing approaches in a genome-wide gain-of-function screen.\",\n      \"method\": \"Genome-wide cDNA gain-of-function screen, siRNA silencing validation\",\n      \"journal\": \"Viruses\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — functional screen with silencing validation but no molecular mechanism of IPO9 action in viral replication defined\",\n      \"pmids\": [\"30650657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IPO9 forms stimulation-induced heterotrimers with Imp3 and JNK/p38 MAPKs; binding of JNK1/2 and p38α/β to Imp7 or Imp9 requires stimulated post-translational modification of the importins, confirmed by coimmunoprecipitation and proximity ligation assay.\",\n      \"method\": \"Coimmunoprecipitation, proximity ligation assay, gel filtration, immunostaining, knockdown\",\n      \"journal\": \"Cellular physiology and biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — replication and extension of earlier findings with multiple orthogonal methods\",\n      \"pmids\": [\"30946556\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In Drosophila, loss of Importin-9 (Ipo9/Ranbp9) causes female and male sterility with chromosome condensation and segregation defects during meiosis, abnormal sperm structure, failure to exchange histones for protamines in males, and disruption of nuclear localization of proteasome components; Ipo9 physically interacts with proteasome proteins.\",\n      \"method\": \"Genetic knockout, immunofluorescence, FISH, co-immunoprecipitation\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined cellular phenotypes and physical interaction demonstrated by Co-IP in Drosophila ortholog\",\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 in response to dynamic mechanical strain in mesenchymal stem cells; knockdown of IPO9 prevented dynamic strain-mediated nuclear transfer of both actin and β-catenin, indicating that β-catenin nuclear access depends on the actin transport pathway mediated by IPO9.\",\n      \"method\": \"siRNA knockdown, live-cell imaging, subcellular fractionation, dynamic vs. static strain comparison\",\n      \"journal\": \"Stem cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — functional knockdown with specific mechanosensing phenotype, single lab\",\n      \"pmids\": [\"35278073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Silencing components of the nuclear actin import complex IPO9 and CFL1 prevented the cAMP-induced increase in nuclear actin monomer and rescued RelA/p65 levels and NF-κB reporter gene activity, demonstrating that IPO9-mediated nuclear actin import is required for cAMP-induced proteasomal degradation of RelA/p65.\",\n      \"method\": \"siRNA knockdown, NF-κB reporter assay, western blotting, ubiquitin affinity pulldown\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — functional knockdown with defined downstream NF-κB pathway readout, single lab\",\n      \"pmids\": [\"35563720\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HDX-MS analysis of the RanGTP•Imp9•H2A-H2B ternary complex shows that RanGTP binding releases H2A-H2B contacts at Imp9 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 Imp9 when H2A-H2B is bound, ensuring release only at high 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 — HDX-MS structural dynamics with multiple binary and ternary complexes compared, plus functional nucleosome assembly assay\",\n      \"pmids\": [\"37379840\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Downregulation of IPO9 in MCF-7 breast cancer cells reduces F-actin content in the nuclear/perinuclear area and is correlated with increased post-translational expression of cofilin-1 (CFL1), and that CFL1 alone does not transport actin into the nucleus but requires functional IPO9 expression for this transport.\",\n      \"method\": \"siRNA knockdown, western blotting, F-actin fluorescence quantification, flow cytometry for apoptosis\",\n      \"journal\": \"Oncology reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, knockdown with actin localization readout establishing IPO9 requirement for nuclear actin import\",\n      \"pmids\": [\"26934847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"IPO9 directly binds monomeric actin with mid-nanomolar affinity independently of cofilin; cofilin and profilin competitively inhibit IPO9-actin binding (likely via overlapping barbed-face interaction), IPO9 modestly decreases actin filament assembly rate, and RanGTP binds monomeric actin but a tripartite IPO9-actin-RanGTP complex does not form—revising the classical model in which cofilin anchors IPO9 to actin monomers.\",\n      \"method\": \"In vitro binding assays (competitive binding, fluorescence polarization), actin polymerization kinetics assay, filamentous actin binding assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro binding with systematic competition assays and functional actin polymerization assay\",\n      \"pmids\": [\"41478570\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"IPO9 knockdown markedly reduces nuclear F-actin assembly during ferroptosis, indicating that nuclear G-actin import via IPO9 is required for the nuclear F-actin that assembles under conditions of intracellular acidification during ferroptotic cell death.\",\n      \"method\": \"siRNA knockdown, phalloidin staining, live 3D/time-lapse imaging with nuclear actin chromobody, pH-sensitive reporter\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — knockdown with live imaging readout, single lab, mechanistic link to ferroptosis context\",\n      \"pmids\": [\"41450740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"IPO9 directly recognizes the ETS domain (a winged-helix fold) of ETS family transcription factors to mediate their nuclear import; cryo-EM of the EHF:IPO9 complex shows IPO9 wrapping around the ETS domain engaging structural features throughout the fold, with the DNA-binding helix critical for importin recognition. Comparison with the IPO9•H2A-H2B structure reveals distinct interaction hotspots, demonstrating that IPO9 employs unique combinatorial binding surfaces for structurally diverse cargos.\",\n      \"method\": \"Cryo-electron microscopy, biochemical binding assays, mutagenesis, mammalian cell NLS activity assay\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structure with mutagenesis and functional NLS validation\",\n      \"pmids\": [\"41542470\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"AKIRIN2 acts as a multivalent scaffold that simultaneously binds the 20S proteasome and importin IPO9 (as well as KPNA2/KPNB1), coordinating assembly of an importin cluster around the proteasome for nuclear import; in the nucleus, RanGTP triggers importin dissociation releasing the proteasome, while AKIRIN2 undergoes ubiquitin-independent degradation.\",\n      \"method\": \"Protein-wide saturation mutagenesis screens, cryo-EM, biochemical reconstitution, co-immunoprecipitation\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structure combined with saturation mutagenesis and reconstitution\",\n      \"pmids\": [\"41639071\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IPO9 is a versatile importin-β family nuclear transport receptor that directly recognizes diverse structurally distinct cargoes—including ribosomal proteins, histones H2A-H2B, H3/H4, Sox/ETS transcription factors, MAPKs (JNK/p38), NUAK1, and the proteasome (via AKIRIN2 scaffold)—through extensive contacts with globular domains rather than linear NLS sequences; for H2A-H2B it employs an unusual mechanism where RanGTP forms a ternary complex that partially releases cargo contacts to enable nucleosome assembly, while for actin it directly binds monomeric actin at the barbed face independently of cofilin, and also functions as a cytoplasmic chaperone shielding basic domains from polyanion aggregation, and as a posttranscriptional regulator by binding specific 5'UTR stem-loop structures to suppress mRNA expression.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"Importin-9 (IPO9) is a versatile RanGTP-regulated nuclear import receptor of the importin-β superfamily that transports a remarkably broad range of cargoes—including histones H2A-H2B and H3, ribosomal proteins, actin monomers, MAPKs, the 20S proteasome, and multiple transcription factor families—into the nucleus, while simultaneously functioning as a cytoplasmic chaperone that shields exposed basic and hydrophobic domains of its cargoes from inappropriate interactions [PMID:11823430, PMID:30855230, PMID:41478570]. Structural studies reveal that IPO9 uses an extensive wrap-around HEAT-repeat architecture to recognize structurally diverse cargo folds, engaging the H2A-H2B globular core at HEAT repeats 4–5 and 18–19, and the ETS-domain winged-helix fold via distinct surfaces, with DNA-binding residues of cargoes frequently constituting the import signal [PMID:30855230, PMID:41542470, PMID:19349578]. For H2A-H2B, RanGTP does not simply dissociate the cargo but forms a stable ternary complex that partially remodels the Imp9–histone interface at HEAT repeats 4–5, exposing histone surfaces for DNA-triggered nucleosome assembly near chromatin [PMID:37379840, PMID:30855230]. IPO9 also directly binds monomeric actin at its barbed face with mid-nanomolar affinity to mediate nuclear actin import—a process required for nuclear F-actin dynamics and mechanotransduction—and participates in AKIRIN2-scaffolded importin clusters that collectively import the 20S proteasome [PMID:41478570, PMID:35278073, PMID:41639071].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"The initial identification of IPO9 as a nuclear import receptor established that it transports ribosomal proteins (rpS7, rpL18a) and simultaneously acts as a cytoplasmic chaperone by covering their basic domains to prevent aggregation with polyanions—revealing a dual transport/chaperone function.\",\n      \"evidence\": \"In vitro reconstituted nuclear import assays and solubility/precipitation assays with purified proteins\",\n      \"pmids\": [\"11823430\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of chaperone activity not defined\", \"Whether chaperone function extends to other cargo classes was unknown\", \"Range of cargo substrates was unexplored\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Extension of IPO9's cargo repertoire to transcription factors revealed that it imports Sox2/SRY (via HMG box) and Arx (via homeodomain), with import signals overlapping DNA-binding residues—establishing a recurring theme of recognition through DNA-binding domains.\",\n      \"evidence\": \"Co-immunoprecipitation, in vitro nuclear import assays, RanGTP sensitivity assays, deletion mutagenesis for Sox/SRY and Arx\",\n      \"pmids\": [\"19349578\", \"19494118\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural data on how IPO9 recognizes HMG or homeodomain folds\", \"Relative contribution of parallel import pathways unresolved\", \"Whether DNA-binding domain recognition is a general principle was unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Discovery that IPO9 forms stimulus-dependent heterotrimers with Importin-3 and MAPKs (JNK1/2, p38α/β) revealed a regulated, signal-responsive mode of IPO9-mediated import distinct from constitutive cargo transport.\",\n      \"evidence\": \"Co-immunoprecipitation, proximity ligation assay, gel filtration, siRNA knockdown with immunostaining in stimulated cells\",\n      \"pmids\": [\"24216760\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Post-translational modification of IPO9 that triggers heterotrimer formation not molecularly identified\", \"Whether MAPK import via IPO9 is the dominant pathway in all cell types unknown\", \"Structural basis of the Imp3/Imp9/MAPK trimeric complex not determined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Observation that IPO9 binds 5′UTR stem-loop RNA structures and negatively regulates IFN-ε and HIF-1α mRNA levels suggested a non-canonical post-transcriptional regulatory activity beyond nuclear transport.\",\n      \"evidence\": \"RNA pulldown from HeLa extracts, IPO9 overexpression and siRNA knockdown with luciferase/mRNA reporters\",\n      \"pmids\": [\"23851686\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Not independently replicated in a second system\", \"Direct RNA binding not demonstrated with purified IPO9\", \"Mechanism of mRNA level regulation (stability vs. translation) not dissected\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Quantitative biochemical mapping showed that IPO9 binds two separable elements in the histone H3 tail and that acetylation of H3 K14 substantially decreases binding, establishing histone modification as a regulatory input for importin-mediated histone transport.\",\n      \"evidence\": \"Fluorescence anisotropy and ITC binding assays with wild-type and mutant histone tail peptides\",\n      \"pmids\": [\"27528606\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether acetylation-dependent modulation is physiologically relevant in cells not tested\", \"Full-length histone binding vs. tail-peptide binding may differ\", \"Structural basis of H3 tail recognition by IPO9 not solved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"The crystal structure of the Imp9·H2A-H2B complex revealed that IPO9 wraps around the histone globular core at HEAT repeats 4–5 and 18–19, and unexpectedly showed that RanGTP forms a stable ternary complex rather than causing simple cargo release—redefining the canonical import-release model for histones.\",\n      \"evidence\": \"X-ray crystallography, quantitative binding assays with deletion mutants, in vitro nucleosome assembly\",\n      \"pmids\": [\"30855230\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which RanGTP remodels the interface to enable DNA-triggered release was not resolved at residue level\", \"In vivo relevance of the ternary complex not demonstrated\", \"Whether other histone pairs use a similar ternary mechanism unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"IPO9 was shown to import the kinase NUAK1 via a bipartite NLS, broadening the cargo range to include signaling kinases beyond MAPKs.\",\n      \"evidence\": \"Mass spectrometry identification, co-immunoprecipitation, siRNA knockdown, subcellular fractionation\",\n      \"pmids\": [\"31090959\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of NUAK1 recognition not determined\", \"Physiological consequences of blocked NUAK1 import not fully explored\", \"Single lab study\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Genetic knockout of the Drosophila IPO9 ortholog demonstrated requirements for chromosome condensation/segregation during meiosis and for proteasome-dependent histone-to-protamine exchange during spermatogenesis, linking IPO9 to proteasome nuclear import in vivo.\",\n      \"evidence\": \"Drosophila Ipo9 knockout, immunofluorescence, FISH, co-immunoprecipitation with proteasome proteins\",\n      \"pmids\": [\"33632744\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Drosophila ortholog; conservation in mammalian spermatogenesis not confirmed\", \"Whether IPO9 directly imports proteasome subunits or acts indirectly was unclear\", \"Mechanism of chromosome condensation defects not molecularly defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Multiple studies established IPO9 as the principal nuclear import receptor for G-actin (together with cofilin-1), linking it to nuclear actin dynamics, mechanotransduction, and NF-κB signaling regulation.\",\n      \"evidence\": \"siRNA knockdown of IPO9 and CFL1 in mesenchymal stem cells and other cell types, nuclear fractionation, NF-κB reporter assays, mechanical stimulation\",\n      \"pmids\": [\"35278073\", \"35563720\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether cofilin-1 is a co-adaptor or competitor for IPO9-actin binding was unresolved\", \"Structural basis of the IPO9-actin interaction not determined\", \"Relative contribution of IPO9 vs. other import pathways for actin unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"HDX-MS analysis of the RanGTP·Imp9·H2A-H2B ternary complex resolved how RanGTP selectively releases H2A-H2B contacts at HEAT repeats 4–5 while maintaining those at 18–19, explaining how DNA-binding and histone-binding surfaces are exposed for chromatin-proximal nucleosome assembly.\",\n      \"evidence\": \"Hydrogen-deuterium exchange mass spectrometry with reconstituted complexes, binding affinity measurements, nucleosome assembly assay\",\n      \"pmids\": [\"37379840\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo validation of partial-release model near chromatin not performed\", \"Whether analogous partial release occurs for other IPO9 cargoes unknown\", \"Kinetics of DNA-triggered release not measured\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Rigorous in vitro reconstitution demonstrated that IPO9 directly binds monomeric actin at its barbed face with mid-nanomolar affinity and that cofilin competitively inhibits (rather than promotes) this interaction, overturning the prevailing co-import model and establishing IPO9 as a self-sufficient actin import receptor.\",\n      \"evidence\": \"Fluorescence anisotropy, competitive binding assays, actin polymerization kinetics, domain mapping with purified proteins\",\n      \"pmids\": [\"41478570\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How RanGTP triggers actin release in the nucleus if a tripartite complex does not form\", \"In vivo confirmation that cofilin is dispensable for nuclear actin import\", \"Structural model of the IPO9-actin interface not yet available\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"IPO9 knockdown blocked nuclear F-actin assembly during ferroptosis, placing IPO9-mediated actin import upstream of stress-induced nuclear actin reorganization.\",\n      \"evidence\": \"siRNA knockdown of IPO9, live-cell imaging with nuclear actin chromobody during RSL3-induced ferroptosis\",\n      \"pmids\": [\"41450740\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking nuclear actin to ferroptosis response not elucidated\", \"Single cell type and single inducer tested\", \"Whether other importins contribute to actin import under these conditions untested\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Cryo-EM of the IPO9·20S proteasome import complex (via AKIRIN2 scaffold) and IPO9·EHF (ETS factor) complex revealed that IPO9 uses distinct wrap-around surfaces for structurally unrelated cargoes—confirming adaptable cargo recognition as a defining feature.\",\n      \"evidence\": \"Cryo-EM structures, saturation mutagenesis, biochemical reconstitution, NLS mutagenesis in mammalian cells\",\n      \"pmids\": [\"41639071\", \"41542470\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"ETS-domain complex from preprint; awaits peer review\", \"Whether all ETS family members use IPO9 or only a subset is unknown\", \"Stoichiometry and dynamics of the AKIRIN2-IPO9-KPNA2/KPNB1 cluster on the intact 20S proteasome not fully resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include how IPO9 releases actin in the nucleus without forming a canonical tripartite RanGTP·IPO9·actin complex, the in vivo relevance of the partial-release mechanism for H2A-H2B near chromatin, and how post-translational modifications of IPO9 regulate its cargo selectivity and stimulus-dependent heterotrimer formation.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Mechanism of nuclear actin release by IPO9 unresolved\", \"Post-translational regulation of IPO9 cargo selectivity molecularly undefined\", \"No disease-associated mutations in IPO9 characterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1, 2, 5, 6, 9, 12, 15, 16]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [4, 5, 11]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [12, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 2, 12]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 5, 9, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [0, 1, 2, 5, 6, 9, 12, 15, 16]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [5, 11]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 10]}\n    ],\n    \"complexes\": [\n      \"Imp3/Imp9/MAPK heterotrimer\",\n      \"AKIRIN2-IPO9-KPNA2/KPNB1 importin cluster\"\n    ],\n    \"partners\": [\n      \"KPNA2\",\n      \"KPNB1\",\n      \"AKIRIN2\",\n      \"IPO5\",\n      \"CFL1\",\n      \"H2AFZ\",\n      \"RAN\",\n      \"MAPK8\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"IPO9 (Importin-9) is a versatile importin-β family nuclear transport receptor that imports structurally diverse cargoes—including ribosomal proteins, histones H2A-H2B and H3/H4, homeodomain and HMG-box transcription factors (Sox2, SRY, Arx), ETS-family transcription factors, MAPKs (JNK, p38), NUAK1 kinase, monomeric actin, and the 20S proteasome (via the AKIRIN2 scaffold)—by recognizing globular folds and basic domains rather than classical linear NLS sequences [PMID:11823430, PMID:19349578, PMID:30855230, PMID:41542470, PMID:41639071]. Structural studies reveal that IPO9 wraps its HEAT-repeat solenoid around cargo globular cores using distinct combinatorial binding surfaces for each substrate, and for H2A-H2B it employs an unusual mechanism in which RanGTP forms a ternary complex that partially releases histone contacts at HEAT repeats 4–5, enabling DNA-driven nucleosome assembly rather than simple cargo ejection [PMID:30855230, PMID:37379840]. IPO9 also functions as a cytoplasmic chaperone that shields the basic domains of ribosomal proteins and histones from aggregation with polyanions, directly binds monomeric actin at its barbed face independently of cofilin to mediate nuclear actin import required for mechanosensing and ferroptotic nuclear F-actin assembly, and suppresses expression of specific mRNAs (IFN-ε, HIF-1α) by binding 5′UTR stem-loop structures [PMID:11823430, PMID:41478570, PMID:35278073, PMID:23851686]. Nuclear import of JNK/p38 MAPKs proceeds through stimulus-induced IPO9–importin-3 heterotrimeric complexes requiring post-translational modification of IPO9 [PMID:24216760, PMID:30946556].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Establishing IPO9 as a bona fide importin-β family member resolved how ribosomal proteins reach the nucleus and revealed an unexpected cytoplasmic chaperone function that prevents aggregation of basic cargo domains with polyanions.\",\n      \"evidence\": \"Reconstituted import assays and solubility/aggregation assays with recombinant ribosomal proteins rpS7 and rpL18a\",\n      \"pmids\": [\"11823430\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full range of ribosomal protein cargoes not mapped\", \"Structural basis of chaperone function unresolved at this stage\", \"Relationship between chaperone and import functions not dissected\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identifying homeodomain (Arx) and HMG-box (Sox2, SRY) transcription factors as IPO9 cargoes demonstrated that IPO9 recognizes DNA-binding folds rather than canonical linear NLS sequences, establishing a pattern of fold-based recognition.\",\n      \"evidence\": \"In vitro import assays, co-immunoprecipitation, siRNA knockdown, and domain deletion analysis in mammalian cells\",\n      \"pmids\": [\"19349578\", \"19494118\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for HMG-box or homeodomain recognition not determined\", \"Redundancy with other importins (Imp-β/7, Exp4) for these cargoes not quantified in vivo\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Discovery that IPO9 forms stimulus-induced heterotrimeric complexes with importin-3 and JNK/p38 MAPKs revealed a non-canonical, NLS-independent import mechanism regulated by post-translational modification of the importin itself.\",\n      \"evidence\": \"Co-immunoprecipitation, proximity ligation assay, gel filtration, siRNA knockdown with transcription factor phosphorylation readout; confirmed in independent follow-up study\",\n      \"pmids\": [\"24216760\", \"30946556\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the post-translational modification on IPO9 not determined\", \"Structural basis of the IPO9–Imp3–MAPK heterotrimer unknown\", \"Whether other MAPKs use this pathway not tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Finding that IPO9 binds 5′UTR stem-loops of IFN-ε and HIF-1α mRNAs and suppresses their expression introduced an unexpected post-transcriptional regulatory role distinct from nuclear transport.\",\n      \"evidence\": \"RNA affinity pulldown, luciferase reporter assays with UTR constructs, overexpression and siRNA knockdown\",\n      \"pmids\": [\"23851686\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct RNA-binding site on IPO9 not mapped\", \"Scope of mRNA targets genome-wide unknown\", \"Mechanism of translational or mRNA stability regulation not defined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Quantitative binding studies with histone tail peptides revealed that IPO9 recognizes two separate basic segments in the H3 tail and analogous elements in H4, with acetylation of H3K14 reducing binding, linking histone modification state to import efficiency.\",\n      \"evidence\": \"Fluorescence polarization and ITC with systematic histone tail peptide mutants across seven importins\",\n      \"pmids\": [\"27528606\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether tail recognition contributes to import in vivo vs. chaperone shielding not separated\", \"Interplay with H2A-H2B import not addressed\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrating that IPO9 knockdown reduces nuclear/perinuclear F-actin and that cofilin alone cannot transport actin into the nucleus established IPO9 as the essential receptor for nuclear actin import.\",\n      \"evidence\": \"siRNA knockdown, F-actin fluorescence quantification, western blotting in MCF-7 cells\",\n      \"pmids\": [\"26934847\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct IPO9–actin binding not demonstrated at this stage\", \"Mechanism of actin recognition by IPO9 undefined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"The crystal structure of IPO9 bound to H2A-H2B revealed an extensive interface wrapping around the histone globular core and uncovered a unique cargo-release mechanism: RanGTP forms a stable ternary complex rather than ejecting cargo, allowing DNA-driven histone transfer for nucleosome assembly.\",\n      \"evidence\": \"X-ray crystallography, ITC, fluorescence binding assays, deletion mutagenesis, DNA competition, in vitro nucleosome assembly\",\n      \"pmids\": [\"30855230\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo contribution of IPO9 vs. other H2A-H2B chaperones/importins not quantified\", \"Whether ternary complex mechanism applies to other cargoes unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"HDX-MS mapping of the RanGTP•Imp9•H2A-H2B ternary complex resolved how RanGTP selectively releases H2A-H2B contacts at HEAT repeats 4–5 while maintaining contacts at 18–19, explaining the partial release that licenses DNA-mediated nucleosome assembly at chromatin-proximal high-RanGTP concentrations.\",\n      \"evidence\": \"Hydrogen-deuterium exchange mass spectrometry comparing binary and ternary complexes, quantitative binding assays, nucleosome assembly assay\",\n      \"pmids\": [\"37379840\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full kinetic pathway from ternary complex to assembled nucleosome not captured\", \"Whether chromatin remodelers cooperate with the ternary complex in vivo untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Reconstituted binding studies overturned the classical model by showing that IPO9 directly binds monomeric actin at the barbed face with mid-nanomolar affinity independently of cofilin, which instead competitively inhibits IPO9–actin binding, redefining the actin import complex.\",\n      \"evidence\": \"In vitro competitive binding assays, fluorescence polarization, actin polymerization kinetics\",\n      \"pmids\": [\"41478570\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo stoichiometry and regulation of IPO9–actin vs. cofilin–actin pools not determined\", \"How RanGTP releases actin in the nucleus (no tripartite complex forms) remains mechanistically unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"IPO9-mediated nuclear actin import was shown to be functionally required for nuclear F-actin assembly during ferroptosis and for cAMP-induced proteasomal degradation of RelA/p65, establishing physiological contexts where nuclear actin import has defined downstream consequences.\",\n      \"evidence\": \"siRNA knockdown with live 3D imaging of nuclear actin chromobody during ferroptosis; siRNA knockdown with NF-κB reporter assay and ubiquitin pulldown for cAMP signaling\",\n      \"pmids\": [\"41450740\", \"35563720\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism linking nuclear actin to RelA degradation not fully elucidated\", \"Whether IPO9-dependent nuclear actin import is rate-limiting in these processes in vivo uncertain\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Cryo-EM of IPO9 bound to the ETS domain of EHF and structural comparison with the H2A-H2B complex revealed that IPO9 uses distinct combinatorial HEAT-repeat surfaces to recognize structurally unrelated globular folds, explaining its cargo versatility; separately, cryo-EM and saturation mutagenesis showed that AKIRIN2 scaffolds an importin cluster (including IPO9) around the 20S proteasome for nuclear import.\",\n      \"evidence\": \"Cryo-EM structures, saturation mutagenesis screens, biochemical reconstitution, mammalian cell NLS activity assays\",\n      \"pmids\": [\"41542470\", \"41639071\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"ETS-domain cryo-EM is from a preprint and awaits peer review\", \"Whether IPO9 contacts the proteasome directly or solely via AKIRIN2 not fully resolved\", \"Quantitative contribution of IPO9 vs. KPNA2/KPNB1 in proteasome import not determined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How IPO9 selects among its many structurally diverse cargoes in the crowded cytoplasmic milieu, and whether post-translational modifications or adaptor proteins regulate cargo priority, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No systematic in vivo cargo prioritization study exists\", \"Post-translational modification of IPO9 identified for MAPK import but identity unknown\", \"Full spectrum of IPO9 cargoes likely incomplete\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1, 2, 3, 6, 7, 11, 15, 18]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [5, 6, 13]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [14, 15, 16]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 3, 15]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 2, 3, 6, 11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0009607\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [0, 1, 2, 3, 6, 7, 11, 15, 18]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 9, 12]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [5, 6, 13]}\n    ],\n    \"complexes\": [\n      \"IPO9-Imp3-MAPK heterotrimer\",\n      \"RanGTP-Imp9-H2A-H2B ternary complex\",\n      \"AKIRIN2-IPO9-proteasome import complex\"\n    ],\n    \"partners\": [\n      \"H2AFZ\",\n      \"H2BC1\",\n      \"CFL1\",\n      \"IPO3\",\n      \"AKIRIN2\",\n      \"RAN\",\n      \"NUAK1\",\n      \"ACTB\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}