{"gene":"IER5","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":1999,"finding":"IER5 is an intronless, serum- and growth factor-inducible immediate-early gene encoding a 308-amino-acid proline-rich nuclear protein with a PEST-like sequence (suggesting rapid degradation) and multiple phosphorylation sites; its induction does not require protein kinase C activity.","method":"Genomic cloning, sequence analysis, promoter characterization, kinetic induction assays","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 — original characterization with multiple molecular methods in a single study","pmids":["10049588"],"is_preprint":false},{"year":2009,"finding":"siRNA-mediated knockdown of IER5 in HeLa cells increased cell proliferation, increased radioresistance, potentiated radiation-induced G2/M arrest, and increased the S-phase fraction, establishing IER5 as a regulator of cell cycle checkpoints and radiosensitivity.","method":"siRNA knockdown, cell growth/survival assay, flow cytometry cell cycle analysis","journal":"Radiation and environmental biophysics","confidence":"Medium","confidence_rationale":"Tier 2 — clean KD with defined cellular phenotypes across multiple readouts","pmids":["19238419"],"is_preprint":false},{"year":2011,"finding":"IER5 overexpression induces G2/M arrest and reduces Cdc25B expression in AML cells; IER5 binds directly to the Cdc25B promoter and represses transcription by releasing the coactivators NF-YB and p300.","method":"Overexpression, flow cytometry, ChIP, luciferase reporter assay, co-IP","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP and reporter assays establish direct promoter binding with functional outcome","pmids":["22132193"],"is_preprint":false},{"year":2014,"finding":"HSF1, activated by heat shock, binds the IER5 promoter and drives IER5 expression; IER5 overexpression in turn upregulates chaperone gene expression and improves refolding of heat-denatured proteins, promoting cell recovery from thermal stress.","method":"ChIP, overexpression, protein refolding assay, cell viability assay","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP establishes HSF1 direct binding; functional assays confirm chaperone upregulation","pmids":["25355627"],"is_preprint":false},{"year":2015,"finding":"IER5 interacts with PP2A and its B55 regulatory subunits; co-expression of IER5 and B55 leads to HSF1 dephosphorylation and activation of HSF1 target genes, establishing IER5 as a positive feedback regulator of HSF1 via PP2A/B55.","method":"Co-IP, overexpression, phosphorylation assay, gene expression analysis","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP with functional readout, replicated across multiple papers","pmids":["25816751"],"is_preprint":false},{"year":2015,"finding":"The N-terminal region of IER5 mediates oligomerization and binds the B55 regulatory subunit of PP2A; IER5 physically interacts with S6K and HSF1, and these interactions are essential for PP2A-mediated dephosphorylation of both substrates. Deletion analysis mapped the regions required for cell growth and stress resistance.","method":"Co-IP, deletion analysis, phosphorylation assay","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 — domain mapping with functional consequences on PP2A substrate dephosphorylation","pmids":["26496226"],"is_preprint":false},{"year":2016,"finding":"IER5 forms a ternary complex with HSF1 and PP2A, promoting dephosphorylation of HSF1 at multiple serine and threonine residues to generate a hypo-phosphorylated, transcriptionally active form of HSF1. IER5 is a p53 target gene and its locus is associated with super-enhancers in cancer cell lines.","method":"Co-IP, phosphorylation assay, overexpression, promoter/super-enhancer analysis","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — ternary complex established by Co-IP, dephosphorylation confirmed biochemically, replicated across labs","pmids":["26754925"],"is_preprint":false},{"year":2016,"finding":"IER5 overexpression in HepG2 hepatocellular carcinoma cells reduces phospho-Akt levels, increases cleaved caspase-3 and PARP, causes G2/M arrest, and enhances apoptosis induced by γ-irradiation and cisplatin.","method":"Stable overexpression, Western blot, flow cytometry, MTT assay","journal":"American journal of translational research","confidence":"Medium","confidence_rationale":"Tier 2 — defined molecular readouts (p-Akt, cleaved caspase-3) linking IER5 to apoptosis pathway","pmids":["27186303"],"is_preprint":false},{"year":2016,"finding":"GCF (GC-binding factor) binds two sites in the IER5 promoter and negatively regulates IER5 transcription; radiation reduces GCF–IER5 promoter complex formation in a dose-dependent manner, contributing to radiation-induced IER5 upregulation in HepG2 cells.","method":"Luciferase reporter assay, ChIP, EMSA, site-directed mutagenesis","journal":"Cancer gene therapy","confidence":"Medium","confidence_rationale":"Tier 2 — EMSA and ChIP with mutagenesis establish direct GCF–promoter interaction","pmids":["26915404"],"is_preprint":false},{"year":2017,"finding":"IER5 participates in non-homologous end-joining (NHEJ) DNA repair; IER5 knockdown reduces DSB repair efficiency. IER5 physically interacts with PARP1 and Ku70 (confirmed by co-IP after MS identification), and PARP1 inhibitor Olaparib affects IER5 protein stability.","method":"siRNA knockdown, γH2AX foci assay, mass spectrometry, co-immunoprecipitation","journal":"International journal of medical sciences","confidence":"Medium","confidence_rationale":"Tier 2 — MS identification followed by co-IP confirmation, KD with functional DSB repair readout","pmids":["29104487"],"is_preprint":false},{"year":2019,"finding":"IER5 contains a classical bipartite nuclear localization signal (NLS) at amino acids 217–244 that is conserved across species and mediates complex formation with importin-α and importin-β; an intact NLS is required for HSF1 dephosphorylation and full HSF1 activation by IER5.","method":"Co-IP, NLS mutagenesis, nuclear import assay, phosphorylation assay","journal":"Experimental cell research","confidence":"High","confidence_rationale":"Tier 1/2 — NLS mapping with mutagenesis, importin binding assay, and functional dephosphorylation readout","pmids":["31669744"],"is_preprint":false},{"year":2020,"finding":"IER5 is a direct Notch target gene in squamous cells required for Notch-induced differentiation; IER5 is epistatic to PPP2R2A (encoding PP2A B55α), and IER5 interacts with PP2A B55α in cells and in purified systems, placing IER5 downstream of Notch and upstream of PP2A in a squamous differentiation pathway.","method":"Genetic epistasis, conditional Notch activation, Co-IP with purified proteins, KO/KD with differentiation readout","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — epistasis + reconstituted interaction + defined cellular differentiation phenotype","pmids":["32936072"],"is_preprint":false},{"year":2020,"finding":"PAF1 inhibits IER5 transcription by promoting RNA Pol II pausing at the IER5 promoter-proximal region; PAF1 binding occurs at IER5 enhancers (confirmed by ChIP and CRISPR/Cas9 enhancer knockout), and PAF1 knockdown increases IER5 expression and radiosensitivity.","method":"ChIP, CRISPR/Cas9 enhancer knockout, siRNA knockdown, qRT-PCR","journal":"Radiation oncology","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP with CRISPR enhancer deletion provides mechanistic link between PAF1 and IER5 transcription","pmids":["32471508"],"is_preprint":false},{"year":2021,"finding":"After irradiation in HeLa cells, IER5 is upregulated and transcriptionally represses Cdc25B by binding its promoter, interacting with NF-YB, and displacing the coactivator p300; both Sp1/Sp3 and NF-YB binding sites mediate irradiation-dependent Cdc25B regulation.","method":"Dual-luciferase reporter assay, ChIP, site-directed mutagenesis, siRNA knockdown","journal":"Toxicology research","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP with mutagenesis identifies specific promoter elements and transcription factor interactions","pmids":["34484679"],"is_preprint":false},{"year":2022,"finding":"IER5 acts as a PP2A adapter that binds both PP2A/B55 and RB/RBL1 (p107), facilitating PP2A-mediated dephosphorylation of RB family proteins; IER5-dependent RB/p107 dephosphorylation represses expression of various cell cycle-related genes.","method":"Co-IP, knockdown, phosphorylation assay, ChIP on RB target promoters, gene expression analysis","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP establishes IER5-RB interaction; KD with phosphorylation and gene expression readouts","pmids":["36047562"],"is_preprint":false},{"year":2024,"finding":"Cryo-EM structure of PP2A/B55α complexed with the N-terminal structured region of IER5 (IER5-N50) reveals that IER5-N50 occludes the substrate recruitment surface of B55α; IER5-N50 inhibits PP2A/B55α-catalyzed dephosphorylation of pTau in vitro; mutations disrupting the interface prevent co-IP of PP2A/B55α. Structural bioinformatics identified homology of IER5-N50 with SERTA domain-containing proteins.","method":"Cryo-EM structure, in vitro biochemical dephosphorylation assay, mutagenesis, co-IP, structural bioinformatics","journal":"bioRxiv (preprint)","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structure with in vitro reconstitution, mutagenesis, and cellular validation","pmids":["37693604"],"is_preprint":true},{"year":2025,"finding":"Cryo-EM structure of PP2A/B55α with IER5-N50 shows that IER5 occludes the B55α substrate recruitment surface; IER5-N50 inhibits PP2A/B55α dephosphorylation of pTau biochemically; interface mutations abolish co-IP; a mini-IER5 (IER5-N50 + NLS) rescues KRT1 expression in IER5 KO keratinocytes. IER5 N-terminal domain shares structural homology with SERTA domain proteins.","method":"Cryo-EM, in vitro dephosphorylation assay, mutagenesis, co-IP, IER5 KO rescue experiment","journal":"Cell chemical biology","confidence":"High","confidence_rationale":"Tier 1 — atomic structure with reconstituted biochemistry, mutagenesis, and KO rescue","pmids":["40209703"],"is_preprint":false},{"year":2025,"finding":"IER5 acts as a positive regulator of p53 by facilitating PP2A/B55-mediated dephosphorylation of MDM2 at Ser166, leading to MDM2 ubiquitination and reduction of nuclear MDM2, thereby inhibiting p53 ubiquitination and increasing p53 stability. This requires nuclear localization of IER5 and its binding to both PP2A/B55 and MDM2.","method":"Co-IP, phosphorylation assay, ubiquitination assay, Nutlin-3 treatment, nuclear fractionation","journal":"Cellular signalling","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Co-IP, phosphorylation, ubiquitination) in a single rigorous study","pmids":["40081547"],"is_preprint":false}],"current_model":"IER5 is a nuclear, immediate-early response protein that functions as a PP2A/B55 adapter and inhibitor: its N-terminal SERTA-like domain occludes the B55α substrate recruitment surface (cryo-EM structure), while simultaneously binding PP2A substrate proteins (HSF1, S6K, RB/p107, MDM2), thereby directing PP2A/B55-catalyzed dephosphorylation toward these targets; downstream consequences include HSF1 activation (promoting chaperone expression), RB/p107 dephosphorylation (repressing cell cycle genes), MDM2 destabilization (stabilizing p53), and transcriptional repression of Cdc25B via NF-YB/p300 displacement—collectively placing IER5 at the intersection of heat shock, DNA damage, Notch, and cell cycle checkpoint signaling."},"narrative":{"teleology":[{"year":1999,"claim":"Identification of IER5 as an intronless immediate-early gene encoding a nuclear, proline-rich protein with PEST-like sequences established it as a rapidly inducible and likely short-lived signaling effector, but its function was unknown.","evidence":"Genomic cloning, promoter analysis, and induction kinetics in serum-stimulated cells","pmids":["10049588"],"confidence":"Medium","gaps":["No function or binding partners identified","PEST-mediated degradation not directly tested","Expression limited to cell line models"]},{"year":2009,"claim":"Loss-of-function experiments revealed that IER5 suppresses proliferation and sensitizes cells to radiation by modulating G2/M checkpoint control, placing it functionally at the cell cycle–DNA damage interface.","evidence":"siRNA knockdown in HeLa cells with flow cytometry and clonogenic survival assays","pmids":["19238419"],"confidence":"Medium","gaps":["Molecular targets of IER5 in cell cycle regulation unidentified","No direct DNA damage repair mechanism established"]},{"year":2011,"claim":"The mechanism for G2/M arrest was linked to direct transcriptional repression of Cdc25B, where IER5 binds the Cdc25B promoter and evicts the NF-YB/p300 coactivator complex, providing the first mechanistic target for IER5's checkpoint function.","evidence":"ChIP, co-IP, and luciferase reporter assays in AML cells with IER5 overexpression","pmids":["22132193"],"confidence":"Medium","gaps":["Whether IER5 has enzymatic or purely scaffolding activity at promoters was unclear","Physiological relevance beyond overexpression not tested"]},{"year":2015,"claim":"Discovery that IER5 physically interacts with PP2A/B55 and directs dephosphorylation of HSF1 and S6K established IER5 as a phosphatase adapter rather than a conventional transcription factor, fundamentally reframing its mechanism of action.","evidence":"Co-IP of IER5 with PP2A/B55 subunits; deletion mapping of N-terminal B55-binding region; HSF1 and S6K dephosphorylation assays","pmids":["25816751","26496226"],"confidence":"High","gaps":["Structural basis of B55 interaction unknown","Whether IER5 redirects or inhibits PP2A was unresolved"]},{"year":2016,"claim":"A ternary IER5–HSF1–PP2A complex was demonstrated to generate hypo-phosphorylated, transcriptionally active HSF1, closing a positive feedback loop (HSF1 drives IER5 transcription, IER5 activates HSF1), and IER5 was identified as a p53 target gene associated with super-enhancers.","evidence":"Co-IP of ternary complex, phosphorylation mapping, ChIP of HSF1 on IER5 promoter, super-enhancer analysis","pmids":["26754925","25355627"],"confidence":"High","gaps":["Stoichiometry and kinetics of ternary complex not determined","Super-enhancer regulation not mechanistically dissected"]},{"year":2017,"claim":"IER5 was connected to DNA double-strand break repair via NHEJ through physical interaction with PARP1 and Ku70, broadening its role beyond cell cycle control to include direct participation in the DNA damage response.","evidence":"Mass spectrometry identification followed by co-IP validation; γH2AX foci assay after IER5 knockdown","pmids":["29104487"],"confidence":"Medium","gaps":["Mechanism by which IER5 promotes NHEJ not defined","Whether PP2A is involved in the NHEJ function is unknown","Single study without independent replication"]},{"year":2019,"claim":"Mapping of a bipartite NLS (aa 217–244) and demonstration that nuclear import is required for HSF1 dephosphorylation resolved how IER5 accesses its nuclear substrates and confirmed that its phosphatase-adapter function is compartment-dependent.","evidence":"NLS mutagenesis, importin-α/β co-IP, nuclear import and phosphorylation assays","pmids":["31669744"],"confidence":"High","gaps":["Whether cytoplasmic IER5 has any function remained untested","Regulation of IER5 nuclear-cytoplasmic shuttling not explored"]},{"year":2020,"claim":"Genetic epistasis placed IER5 downstream of Notch and upstream of PP2A/B55α in squamous epithelial differentiation, and reconstituted IER5–B55α interaction with purified proteins confirmed a direct binding event independent of other cellular factors.","evidence":"Conditional Notch activation, IER5 KO/KD differentiation assays, co-IP with purified recombinant proteins in keratinocytes","pmids":["32936072"],"confidence":"High","gaps":["PP2A substrates critical for differentiation downstream of IER5 not identified","Whether IER5 functions outside squamous lineage differentiation via Notch is unknown"]},{"year":2022,"claim":"Extension of the PP2A adapter model to RB family proteins showed that IER5 bridges PP2A/B55 to RB and p107, causing their dephosphorylation and repression of cell cycle gene expression, providing a mechanistic explanation for IER5-mediated growth arrest.","evidence":"Co-IP of IER5 with RB/p107, knockdown with phosphorylation analysis, ChIP on RB target promoters","pmids":["36047562"],"confidence":"Medium","gaps":["Relative contributions of Cdc25B repression vs. RB dephosphorylation to G2/M arrest not delineated","In vivo validation lacking"]},{"year":2025,"claim":"Cryo-EM structure of IER5-N50 bound to PP2A/B55α revealed that IER5 occludes the B55α substrate recruitment groove via a SERTA-like domain fold, and a minimal IER5 construct (N50 + NLS) rescues keratinocyte differentiation in IER5 KO cells, defining the minimal functional unit. Concurrently, IER5 was shown to stabilize p53 by directing PP2A/B55-dependent dephosphorylation of MDM2 at Ser166, triggering MDM2 ubiquitination and nuclear depletion.","evidence":"Cryo-EM at near-atomic resolution, in vitro pTau dephosphorylation inhibition, interface mutagenesis, KO rescue in keratinocytes, MDM2 phosphorylation/ubiquitination assays","pmids":["40209703","40081547"],"confidence":"High","gaps":["How IER5 simultaneously occludes B55 substrate surface yet redirects PP2A toward specific substrates is mechanistically paradoxical and unresolved","Full-length IER5 structure remains undetermined","In vivo mouse phenotype of IER5 loss not reported"]},{"year":null,"claim":"The central paradox—how IER5 inhibits general B55 substrate access while simultaneously promoting dephosphorylation of specific substrates—remains structurally unresolved, and whether distinct IER5 pools serve inhibitory versus adapter roles in different signaling contexts is unknown.","evidence":"","pmids":[],"confidence":"Low","gaps":["No full-length IER5 structure with a substrate simultaneously bound","No in vivo genetic model characterizing organismal function","Relative importance of individual substrate dephosphorylation events in physiological contexts untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4,5,6,14,15,16,17]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[4,5,15,16]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[2,13]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,10,17]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[1,2,7,13,14]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[3,4,6]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[11,17]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[7,17]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[9]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[11]}],"complexes":["PP2A/B55α holoenzyme"],"partners":["PPP2R2A","HSF1","RPS6KB1","RB1","RBL1","MDM2","PARP1","XRCC6"],"other_free_text":[]},"mechanistic_narrative":"IER5 is an immediate-early response gene product that functions as a substrate-specifying adapter for the PP2A/B55α phosphatase, coupling stress and developmental signals to dephosphorylation of key regulatory proteins including HSF1, RB/p107, S6K, and MDM2. Its N-terminal SERTA-like domain binds and occludes the B55α substrate recruitment surface (cryo-EM structure), while simultaneously engaging PP2A substrates to direct their dephosphorylation; a minimal construct comprising this domain plus the bipartite NLS is sufficient to rescue differentiation in IER5-knockout keratinocytes [PMID:40209703, PMID:25816751, PMID:26496226]. Downstream, IER5-dependent dephosphorylation activates HSF1 to drive chaperone expression, hypophosphorylates RB to repress cell-cycle genes, and destabilizes MDM2 to stabilize p53 [PMID:26754925, PMID:36047562, PMID:40081547]. IER5 also directly represses Cdc25B transcription by displacing the NF-YB/p300 coactivator complex from the Cdc25B promoter, enforcing G2/M arrest after irradiation, and is a direct transcriptional target of Notch signaling required for squamous epithelial differentiation [PMID:22132193, PMID:32936072]."},"prefetch_data":{"uniprot":{"accession":"Q5VY09","full_name":"Immediate early response gene 5 protein","aliases":[],"length_aa":327,"mass_kda":33.7,"function":"Plays a role as a transcription factor (PubMed:22132193, PubMed:25355627). Mediates positive transcriptional regulation of several chaperone genes during the heat shock response in a HSF1-dependent manner (PubMed:25355627, PubMed:25816751). Mediates negative transcriptional regulation of CDC25B expression (PubMed:22132193). Plays a role in the dephosphorylation of the heat shock factor HSF1 and ribosomal protein S6 kinase (S6K) by the protein phosphatase PP2A (PubMed:25816751, PubMed:26496226). Involved in the regulation of cell proliferation and resistance to thermal stress (PubMed:22132193, PubMed:25355627, PubMed:26496226). Involved in the cell cycle checkpoint and survival in response to ionizing radiation (PubMed:19238419, PubMed:22132193). Associates with chromatin to the CDC25B promoter (PubMed:22132193)","subcellular_location":"Nucleus; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q5VY09/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/IER5","classification":"Not Classified","n_dependent_lines":5,"n_total_lines":1208,"dependency_fraction":0.0041390728476821195},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/IER5","total_profiled":1310},"omim":[{"mim_id":"607177","title":"IMMEDIATE-EARLY RESPONSE GENE 5; IER5","url":"https://www.omim.org/entry/607177"},{"mim_id":"187040","title":"T-CELL ACUTE LYMPHOCYTIC LEUKEMIA 1; TAL1","url":"https://www.omim.org/entry/187040"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Nucleoli","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/IER5"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q5VY09","domains":[{"cath_id":"1.20.1270","chopping":"2-56_312-327","consensus_level":"medium","plddt":80.387,"start":2,"end":327}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5VY09","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q5VY09-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q5VY09-F1-predicted_aligned_error_v6.png","plddt_mean":53.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=IER5","jax_strain_url":"https://www.jax.org/strain/search?query=IER5"},"sequence":{"accession":"Q5VY09","fasta_url":"https://rest.uniprot.org/uniprotkb/Q5VY09.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q5VY09/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5VY09"}},"corpus_meta":[{"pmid":"26754925","id":"PMC_26754925","title":"IER5 generates a novel hypo-phosphorylated active form of HSF1 and contributes to tumorigenesis.","date":"2016","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/26754925","citation_count":51,"is_preprint":false},{"pmid":"10049588","id":"PMC_10049588","title":"Ier5, a novel member of the slow-kinetics immediate-early genes.","date":"1999","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/10049588","citation_count":41,"is_preprint":false},{"pmid":"19238419","id":"PMC_19238419","title":"Induced expression of the IER5 gene by gamma-ray irradiation and its involvement in cell cycle checkpoint control and survival.","date":"2009","source":"Radiation and environmental biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/19238419","citation_count":41,"is_preprint":false},{"pmid":"22132193","id":"PMC_22132193","title":"Transcriptional repression of Cdc25B by IER5 inhibits the proliferation of leukemic progenitor cells through NF-YB and p300 in acute myeloid leukemia.","date":"2011","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22132193","citation_count":34,"is_preprint":false},{"pmid":"25816751","id":"PMC_25816751","title":"HSF1 transcriptional activity is modulated by IER5 and PP2A/B55.","date":"2015","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/25816751","citation_count":31,"is_preprint":false},{"pmid":"25355627","id":"PMC_25355627","title":"Heat-induced expression of the immediate-early gene IER5 and its involvement in the proliferation of heat-shocked cells.","date":"2014","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/25355627","citation_count":24,"is_preprint":false},{"pmid":"26496226","id":"PMC_26496226","title":"Immediate-early response 5 (IER5) interacts with protein phosphatase 2A and regulates the phosphorylation of ribosomal protein S6 kinase and heat shock factor 1.","date":"2015","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/26496226","citation_count":22,"is_preprint":false},{"pmid":"32936072","id":"PMC_32936072","title":"IER5, a DNA damage response gene, is required for Notch-mediated induction of squamous cell differentiation.","date":"2020","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/32936072","citation_count":20,"is_preprint":false},{"pmid":"31669744","id":"PMC_31669744","title":"Nuclear import of IER5 is mediated by a classical bipartite nuclear localization signal and is required for HSF1 full activation.","date":"2019","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/31669744","citation_count":13,"is_preprint":false},{"pmid":"32471508","id":"PMC_32471508","title":"Novel role of PAF1 in attenuating radiosensitivity in cervical cancer by inhibiting IER5 transcription.","date":"2020","source":"Radiation oncology (London, England)","url":"https://pubmed.ncbi.nlm.nih.gov/32471508","citation_count":11,"is_preprint":false},{"pmid":"36047562","id":"PMC_36047562","title":"PP2A-B55 and its adapter proteins IER2 and IER5 regulate the activity of RB family proteins and the expression of cell cycle-related genes.","date":"2022","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/36047562","citation_count":11,"is_preprint":false},{"pmid":"22923252","id":"PMC_22923252","title":"Dose-dependent and gender-related radiation-induced transcription alterations of Gadd45a and Ier5 inhuman lymphocytes exposed to gamma ray emitted by (60)Co.","date":"2012","source":"Radiation protection dosimetry","url":"https://pubmed.ncbi.nlm.nih.gov/22923252","citation_count":10,"is_preprint":false},{"pmid":"27186303","id":"PMC_27186303","title":"IER5 promotes irradiation- and cisplatin-induced apoptosis in human hepatocellular carcinoma cells.","date":"2016","source":"American journal of translational 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is dose-dependent and not associated with the clinical outcomes of radiotherapy in cervical cancer.","date":"2016","source":"Oncology letters","url":"https://pubmed.ncbi.nlm.nih.gov/26893736","citation_count":4,"is_preprint":false},{"pmid":"37693604","id":"PMC_37693604","title":"Molecular Mechanism of PP2A/B55α Phosphatase Inhibition by IER5.","date":"2024","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/37693604","citation_count":4,"is_preprint":false},{"pmid":"40081547","id":"PMC_40081547","title":"PP2A adapter protein IER5 induces dephosphorylation and degradation of MDM2, thereby stabilizing p53.","date":"2025","source":"Cellular signalling","url":"https://pubmed.ncbi.nlm.nih.gov/40081547","citation_count":2,"is_preprint":false},{"pmid":"40002205","id":"PMC_40002205","title":"IER5 Promotes Ovarian Cancer Cell Proliferation and Peritoneal 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assays\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — original characterization with multiple molecular methods in a single study\",\n      \"pmids\": [\"10049588\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"siRNA-mediated knockdown of IER5 in HeLa cells increased cell proliferation, increased radioresistance, potentiated radiation-induced G2/M arrest, and increased the S-phase fraction, establishing IER5 as a regulator of cell cycle checkpoints and radiosensitivity.\",\n      \"method\": \"siRNA knockdown, cell growth/survival assay, flow cytometry cell cycle analysis\",\n      \"journal\": \"Radiation and environmental biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with defined cellular phenotypes across multiple readouts\",\n      \"pmids\": [\"19238419\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"IER5 overexpression induces G2/M arrest and reduces Cdc25B expression in AML cells; IER5 binds directly to the Cdc25B promoter and represses transcription by releasing the coactivators NF-YB and p300.\",\n      \"method\": \"Overexpression, flow cytometry, ChIP, luciferase reporter assay, co-IP\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP and reporter assays establish direct promoter binding with functional outcome\",\n      \"pmids\": [\"22132193\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"HSF1, activated by heat shock, binds the IER5 promoter and drives IER5 expression; IER5 overexpression in turn upregulates chaperone gene expression and improves refolding of heat-denatured proteins, promoting cell recovery from thermal stress.\",\n      \"method\": \"ChIP, overexpression, protein refolding assay, cell viability assay\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP establishes HSF1 direct binding; functional assays confirm chaperone upregulation\",\n      \"pmids\": [\"25355627\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"IER5 interacts with PP2A and its B55 regulatory subunits; co-expression of IER5 and B55 leads to HSF1 dephosphorylation and activation of HSF1 target genes, establishing IER5 as a positive feedback regulator of HSF1 via PP2A/B55.\",\n      \"method\": \"Co-IP, overexpression, phosphorylation assay, gene expression analysis\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with functional readout, replicated across multiple papers\",\n      \"pmids\": [\"25816751\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The N-terminal region of IER5 mediates oligomerization and binds the B55 regulatory subunit of PP2A; IER5 physically interacts with S6K and HSF1, and these interactions are essential for PP2A-mediated dephosphorylation of both substrates. Deletion analysis mapped the regions required for cell growth and stress resistance.\",\n      \"method\": \"Co-IP, deletion analysis, phosphorylation assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — domain mapping with functional consequences on PP2A substrate dephosphorylation\",\n      \"pmids\": [\"26496226\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"IER5 forms a ternary complex with HSF1 and PP2A, promoting dephosphorylation of HSF1 at multiple serine and threonine residues to generate a hypo-phosphorylated, transcriptionally active form of HSF1. IER5 is a p53 target gene and its locus is associated with super-enhancers in cancer cell lines.\",\n      \"method\": \"Co-IP, phosphorylation assay, overexpression, promoter/super-enhancer analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ternary complex established by Co-IP, dephosphorylation confirmed biochemically, replicated across labs\",\n      \"pmids\": [\"26754925\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"IER5 overexpression in HepG2 hepatocellular carcinoma cells reduces phospho-Akt levels, increases cleaved caspase-3 and PARP, causes G2/M arrest, and enhances apoptosis induced by γ-irradiation and cisplatin.\",\n      \"method\": \"Stable overexpression, Western blot, flow cytometry, MTT assay\",\n      \"journal\": \"American journal of translational research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined molecular readouts (p-Akt, cleaved caspase-3) linking IER5 to apoptosis pathway\",\n      \"pmids\": [\"27186303\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"GCF (GC-binding factor) binds two sites in the IER5 promoter and negatively regulates IER5 transcription; radiation reduces GCF–IER5 promoter complex formation in a dose-dependent manner, contributing to radiation-induced IER5 upregulation in HepG2 cells.\",\n      \"method\": \"Luciferase reporter assay, ChIP, EMSA, site-directed mutagenesis\",\n      \"journal\": \"Cancer gene therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — EMSA and ChIP with mutagenesis establish direct GCF–promoter interaction\",\n      \"pmids\": [\"26915404\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"IER5 participates in non-homologous end-joining (NHEJ) DNA repair; IER5 knockdown reduces DSB repair efficiency. IER5 physically interacts with PARP1 and Ku70 (confirmed by co-IP after MS identification), and PARP1 inhibitor Olaparib affects IER5 protein stability.\",\n      \"method\": \"siRNA knockdown, γH2AX foci assay, mass spectrometry, co-immunoprecipitation\",\n      \"journal\": \"International journal of medical sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — MS identification followed by co-IP confirmation, KD with functional DSB repair readout\",\n      \"pmids\": [\"29104487\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"IER5 contains a classical bipartite nuclear localization signal (NLS) at amino acids 217–244 that is conserved across species and mediates complex formation with importin-α and importin-β; an intact NLS is required for HSF1 dephosphorylation and full HSF1 activation by IER5.\",\n      \"method\": \"Co-IP, NLS mutagenesis, nuclear import assay, phosphorylation assay\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — NLS mapping with mutagenesis, importin binding assay, and functional dephosphorylation readout\",\n      \"pmids\": [\"31669744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"IER5 is a direct Notch target gene in squamous cells required for Notch-induced differentiation; IER5 is epistatic to PPP2R2A (encoding PP2A B55α), and IER5 interacts with PP2A B55α in cells and in purified systems, placing IER5 downstream of Notch and upstream of PP2A in a squamous differentiation pathway.\",\n      \"method\": \"Genetic epistasis, conditional Notch activation, Co-IP with purified proteins, KO/KD with differentiation readout\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis + reconstituted interaction + defined cellular differentiation phenotype\",\n      \"pmids\": [\"32936072\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PAF1 inhibits IER5 transcription by promoting RNA Pol II pausing at the IER5 promoter-proximal region; PAF1 binding occurs at IER5 enhancers (confirmed by ChIP and CRISPR/Cas9 enhancer knockout), and PAF1 knockdown increases IER5 expression and radiosensitivity.\",\n      \"method\": \"ChIP, CRISPR/Cas9 enhancer knockout, siRNA knockdown, qRT-PCR\",\n      \"journal\": \"Radiation oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP with CRISPR enhancer deletion provides mechanistic link between PAF1 and IER5 transcription\",\n      \"pmids\": [\"32471508\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"After irradiation in HeLa cells, IER5 is upregulated and transcriptionally represses Cdc25B by binding its promoter, interacting with NF-YB, and displacing the coactivator p300; both Sp1/Sp3 and NF-YB binding sites mediate irradiation-dependent Cdc25B regulation.\",\n      \"method\": \"Dual-luciferase reporter assay, ChIP, site-directed mutagenesis, siRNA knockdown\",\n      \"journal\": \"Toxicology research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP with mutagenesis identifies specific promoter elements and transcription factor interactions\",\n      \"pmids\": [\"34484679\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"IER5 acts as a PP2A adapter that binds both PP2A/B55 and RB/RBL1 (p107), facilitating PP2A-mediated dephosphorylation of RB family proteins; IER5-dependent RB/p107 dephosphorylation represses expression of various cell cycle-related genes.\",\n      \"method\": \"Co-IP, knockdown, phosphorylation assay, ChIP on RB target promoters, gene expression analysis\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP establishes IER5-RB interaction; KD with phosphorylation and gene expression readouts\",\n      \"pmids\": [\"36047562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cryo-EM structure of PP2A/B55α complexed with the N-terminal structured region of IER5 (IER5-N50) reveals that IER5-N50 occludes the substrate recruitment surface of B55α; IER5-N50 inhibits PP2A/B55α-catalyzed dephosphorylation of pTau in vitro; mutations disrupting the interface prevent co-IP of PP2A/B55α. Structural bioinformatics identified homology of IER5-N50 with SERTA domain-containing proteins.\",\n      \"method\": \"Cryo-EM structure, in vitro biochemical dephosphorylation assay, mutagenesis, co-IP, structural bioinformatics\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structure with in vitro reconstitution, mutagenesis, and cellular validation\",\n      \"pmids\": [\"37693604\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cryo-EM structure of PP2A/B55α with IER5-N50 shows that IER5 occludes the B55α substrate recruitment surface; IER5-N50 inhibits PP2A/B55α dephosphorylation of pTau biochemically; interface mutations abolish co-IP; a mini-IER5 (IER5-N50 + NLS) rescues KRT1 expression in IER5 KO keratinocytes. IER5 N-terminal domain shares structural homology with SERTA domain proteins.\",\n      \"method\": \"Cryo-EM, in vitro dephosphorylation assay, mutagenesis, co-IP, IER5 KO rescue experiment\",\n      \"journal\": \"Cell chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — atomic structure with reconstituted biochemistry, mutagenesis, and KO rescue\",\n      \"pmids\": [\"40209703\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"IER5 acts as a positive regulator of p53 by facilitating PP2A/B55-mediated dephosphorylation of MDM2 at Ser166, leading to MDM2 ubiquitination and reduction of nuclear MDM2, thereby inhibiting p53 ubiquitination and increasing p53 stability. This requires nuclear localization of IER5 and its binding to both PP2A/B55 and MDM2.\",\n      \"method\": \"Co-IP, phosphorylation assay, ubiquitination assay, Nutlin-3 treatment, nuclear fractionation\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Co-IP, phosphorylation, ubiquitination) in a single rigorous study\",\n      \"pmids\": [\"40081547\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IER5 is a nuclear, immediate-early response protein that functions as a PP2A/B55 adapter and inhibitor: its N-terminal SERTA-like domain occludes the B55α substrate recruitment surface (cryo-EM structure), while simultaneously binding PP2A substrate proteins (HSF1, S6K, RB/p107, MDM2), thereby directing PP2A/B55-catalyzed dephosphorylation toward these targets; downstream consequences include HSF1 activation (promoting chaperone expression), RB/p107 dephosphorylation (repressing cell cycle genes), MDM2 destabilization (stabilizing p53), and transcriptional repression of Cdc25B via NF-YB/p300 displacement—collectively placing IER5 at the intersection of heat shock, DNA damage, Notch, and cell cycle checkpoint signaling.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"IER5 is an immediate-early response gene product that functions as a substrate-specifying adapter for the PP2A/B55α phosphatase, coupling stress and developmental signals to dephosphorylation of key regulatory proteins including HSF1, RB/p107, S6K, and MDM2. Its N-terminal SERTA-like domain binds and occludes the B55α substrate recruitment surface (cryo-EM structure), while simultaneously engaging PP2A substrates to direct their dephosphorylation; a minimal construct comprising this domain plus the bipartite NLS is sufficient to rescue differentiation in IER5-knockout keratinocytes [PMID:40209703, PMID:25816751, PMID:26496226]. Downstream, IER5-dependent dephosphorylation activates HSF1 to drive chaperone expression, hypophosphorylates RB to repress cell-cycle genes, and destabilizes MDM2 to stabilize p53 [PMID:26754925, PMID:36047562, PMID:40081547]. IER5 also directly represses Cdc25B transcription by displacing the NF-YB/p300 coactivator complex from the Cdc25B promoter, enforcing G2/M arrest after irradiation, and is a direct transcriptional target of Notch signaling required for squamous epithelial differentiation [PMID:22132193, PMID:32936072].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of IER5 as an intronless immediate-early gene encoding a nuclear, proline-rich protein with PEST-like sequences established it as a rapidly inducible and likely short-lived signaling effector, but its function was unknown.\",\n      \"evidence\": \"Genomic cloning, promoter analysis, and induction kinetics in serum-stimulated cells\",\n      \"pmids\": [\"10049588\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No function or binding partners identified\", \"PEST-mediated degradation not directly tested\", \"Expression limited to cell line models\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Loss-of-function experiments revealed that IER5 suppresses proliferation and sensitizes cells to radiation by modulating G2/M checkpoint control, placing it functionally at the cell cycle–DNA damage interface.\",\n      \"evidence\": \"siRNA knockdown in HeLa cells with flow cytometry and clonogenic survival assays\",\n      \"pmids\": [\"19238419\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular targets of IER5 in cell cycle regulation unidentified\", \"No direct DNA damage repair mechanism established\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"The mechanism for G2/M arrest was linked to direct transcriptional repression of Cdc25B, where IER5 binds the Cdc25B promoter and evicts the NF-YB/p300 coactivator complex, providing the first mechanistic target for IER5's checkpoint function.\",\n      \"evidence\": \"ChIP, co-IP, and luciferase reporter assays in AML cells with IER5 overexpression\",\n      \"pmids\": [\"22132193\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether IER5 has enzymatic or purely scaffolding activity at promoters was unclear\", \"Physiological relevance beyond overexpression not tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Discovery that IER5 physically interacts with PP2A/B55 and directs dephosphorylation of HSF1 and S6K established IER5 as a phosphatase adapter rather than a conventional transcription factor, fundamentally reframing its mechanism of action.\",\n      \"evidence\": \"Co-IP of IER5 with PP2A/B55 subunits; deletion mapping of N-terminal B55-binding region; HSF1 and S6K dephosphorylation assays\",\n      \"pmids\": [\"25816751\", \"26496226\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of B55 interaction unknown\", \"Whether IER5 redirects or inhibits PP2A was unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"A ternary IER5–HSF1–PP2A complex was demonstrated to generate hypo-phosphorylated, transcriptionally active HSF1, closing a positive feedback loop (HSF1 drives IER5 transcription, IER5 activates HSF1), and IER5 was identified as a p53 target gene associated with super-enhancers.\",\n      \"evidence\": \"Co-IP of ternary complex, phosphorylation mapping, ChIP of HSF1 on IER5 promoter, super-enhancer analysis\",\n      \"pmids\": [\"26754925\", \"25355627\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and kinetics of ternary complex not determined\", \"Super-enhancer regulation not mechanistically dissected\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"IER5 was connected to DNA double-strand break repair via NHEJ through physical interaction with PARP1 and Ku70, broadening its role beyond cell cycle control to include direct participation in the DNA damage response.\",\n      \"evidence\": \"Mass spectrometry identification followed by co-IP validation; γH2AX foci assay after IER5 knockdown\",\n      \"pmids\": [\"29104487\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which IER5 promotes NHEJ not defined\", \"Whether PP2A is involved in the NHEJ function is unknown\", \"Single study without independent replication\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Mapping of a bipartite NLS (aa 217–244) and demonstration that nuclear import is required for HSF1 dephosphorylation resolved how IER5 accesses its nuclear substrates and confirmed that its phosphatase-adapter function is compartment-dependent.\",\n      \"evidence\": \"NLS mutagenesis, importin-α/β co-IP, nuclear import and phosphorylation assays\",\n      \"pmids\": [\"31669744\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether cytoplasmic IER5 has any function remained untested\", \"Regulation of IER5 nuclear-cytoplasmic shuttling not explored\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Genetic epistasis placed IER5 downstream of Notch and upstream of PP2A/B55α in squamous epithelial differentiation, and reconstituted IER5–B55α interaction with purified proteins confirmed a direct binding event independent of other cellular factors.\",\n      \"evidence\": \"Conditional Notch activation, IER5 KO/KD differentiation assays, co-IP with purified recombinant proteins in keratinocytes\",\n      \"pmids\": [\"32936072\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"PP2A substrates critical for differentiation downstream of IER5 not identified\", \"Whether IER5 functions outside squamous lineage differentiation via Notch is unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Extension of the PP2A adapter model to RB family proteins showed that IER5 bridges PP2A/B55 to RB and p107, causing their dephosphorylation and repression of cell cycle gene expression, providing a mechanistic explanation for IER5-mediated growth arrest.\",\n      \"evidence\": \"Co-IP of IER5 with RB/p107, knockdown with phosphorylation analysis, ChIP on RB target promoters\",\n      \"pmids\": [\"36047562\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contributions of Cdc25B repression vs. RB dephosphorylation to G2/M arrest not delineated\", \"In vivo validation lacking\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Cryo-EM structure of IER5-N50 bound to PP2A/B55α revealed that IER5 occludes the B55α substrate recruitment groove via a SERTA-like domain fold, and a minimal IER5 construct (N50 + NLS) rescues keratinocyte differentiation in IER5 KO cells, defining the minimal functional unit. Concurrently, IER5 was shown to stabilize p53 by directing PP2A/B55-dependent dephosphorylation of MDM2 at Ser166, triggering MDM2 ubiquitination and nuclear depletion.\",\n      \"evidence\": \"Cryo-EM at near-atomic resolution, in vitro pTau dephosphorylation inhibition, interface mutagenesis, KO rescue in keratinocytes, MDM2 phosphorylation/ubiquitination assays\",\n      \"pmids\": [\"40209703\", \"40081547\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How IER5 simultaneously occludes B55 substrate surface yet redirects PP2A toward specific substrates is mechanistically paradoxical and unresolved\", \"Full-length IER5 structure remains undetermined\", \"In vivo mouse phenotype of IER5 loss not reported\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The central paradox—how IER5 inhibits general B55 substrate access while simultaneously promoting dephosphorylation of specific substrates—remains structurally unresolved, and whether distinct IER5 pools serve inhibitory versus adapter roles in different signaling contexts is unknown.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No full-length IER5 structure with a substrate simultaneously bound\", \"No in vivo genetic model characterizing organismal function\", \"Relative importance of individual substrate dephosphorylation events in physiological contexts untested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4, 5, 6, 14, 15, 16, 17]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [4, 5, 15, 16]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [2, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 10, 17]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [1, 2, 7, 13, 14]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [3, 4, 6]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [11, 17]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [7, 17]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"complexes\": [\n      \"PP2A/B55α holoenzyme\"\n    ],\n    \"partners\": [\n      \"PPP2R2A\",\n      \"HSF1\",\n      \"RPS6KB1\",\n      \"RB1\",\n      \"RBL1\",\n      \"MDM2\",\n      \"PARP1\",\n      \"XRCC6\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}